Thermal Oxidation of Polymer Blends: The Role of Structure

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THERMAL OXIDATION OF POLYMER BLENDS. THE ROLE OF STRUCTURE.

Lyudmila S. Shibryaeva Anatoly A. Popov Gennady Ye. Zaikov Institute of Biochemical Physics, Russian Academy of Sciences, e-mail: [email protected] (Lyudmila S. Shibryaeva) Translated by E.Yu. Kharitonova

CONTENTS

CHAPTER 1. 1.1. 1.2. 1.2.1. 1.2.2. 1.2.2.1. 1.2.2.2. 1.2.2.3. 1.2.2.4. 1.2.2.5. 1.2.2.6. 1.2.2.7. 1.2.2.8. CHAPTER 2. 2.1. 2.1.1.

2.1.1.1. 2.1.1.2. 2.1.1.3. 2.1.1.4. 2.1.2.

2.1.2.1. 2.1.2.2. 2.1.2.3. 2.2. CHAPTER 3. 3.1. 3.2. 3.3. 3.4.

PREFACE

5

LIST OF ABBREVIATIONS

7

INTRODUCTION

8

The particularities of structures of polymers blends Thermal oxidation of model micro-heterogeneous systems The particularities of oxidation of liquid phase blends Kinetics of copolymers oxidation The role of chemical nature of comonomer units in thermal oxidation The influence of copolymer chain structure on thermal oxidation The role of physical structure of copolymers The particularities of kinetics of copolymers oxidation Origination of kinetic chains Continuation of kinetic chains Termination of kinetic chains The stage of branching of kinetic chains

8 14 14 17 17 21 22 25 26 28 29 30

STRUCTURE EFFECTS IN THERMAL OXIDATION OF POLYOLEFINES

35

Structure effects accompanying oxidation of isotropic polypropylene samples The regularities of change of structural parameters during oxidation process of micro-spherulite samples and PP with various molecular structure Structural parameters of non-oxidized polymers Change of polymers structure during oxidation process Kinetics of accumulation of nonvolatile products of oxidation Kinetics of oxygen absorption The regularities of change of structure during oxidation process of isotropic samples of polypropylene with various morphology (largespherulite and small-spherulite samples) Structural parameters of non-oxidized samples Changes of structure during oxidation of large- and small-spherulite samples of polypropylene Kinetics of oxidation of isotropic samples of polypropylene with various morphology Structural-physical processes in oxidation of oriented samples of polypropylene MODEL SYSTEMS. ISOTACTIC POLYPROPYLENE MODIFIED BY ESTERS The structure of modified polypropylene The particularities of crystallization of modified polypropylene Kinetics of oxygen absorption by modified polypropylene Physical-mechanical parameters of oxidized modified polypropylene

36 36 36 41 45 47 49 49 52 53 57 63 63 67 75 80 2

3.5. 3.6. 3.7. CHAPTER 4.

4.1. 4.2. 4.3. 4.4. CHAPTER 5.

5.1. 5.1.1. 5.1.2. 5.2. 5.2.1. 5.2.2. 5.2.3. 5.3.

CHAPTER 6.

6.1. 6.1.1. 6.1.2. 6.1.3. 6.1.4. 6.1.5. 6.1.6.

Products of oxidation of modified polypropylene Structural parameters of oxidized modified polypropylene On question about the mechanism of oxidation of polypropylene modified by esters

86

BLENDS OF CRYSTALLIZING BIOPOLYMER AND POLYOLEFINE: POLY-3-OXYBUTIRATE AND POLYETHYLENE OF LOW DENSITY

90

The structure of poly-3-oxybutiratepolyethylene of low density blends Kinetics of absorption of oxygen by poly-3oxybutiratepolyethylene of low density blends On the question about the mechanism of oxidation of poly-3oxybutiratepolyethylene of low density blends The role of inter-phase phenomena in kinetics of thermal oxidation of poly-3-oxybutiratepolyethylene of low density blends THE BLENDS OF CRYSTALLIZING POLYMERS: ISOTACTIC POLYPROPYLENE AND POLYETHYLENE OF HIGH DENSITY Mechanical blends of isotactic polypropylene and polyethylene of high density Kinetics of oxygen absorption by samples of polypropylenepolyethylene of high density blends Nonvolatile products of oxidation of polypropylenepolyethylene of high density blends The blends of isopolypropylenepolyethylene of high density with equal compositions but of various blending techniques The structure of initial samples of blends Kinetics of oxygen absorption Kinetics of accumulation of non-volatile products of oxidation On question about the mechanism of oxidation of polypropylenepolyethylene of high density blends THE BLENDS OF CRYSTALLIZING POLYOLEFIN AND AMORPHOUS RUBBER: ISOTACTIC POLYPROPYLENE AND TRIPLE ETHYLENEPROPYLENEDIENE COPOLYMER The isopropylenesynthetic ethylene-propylene triple rubber blends (E-50) Kinetics of oxygen absorption The structure of crystal regions of iso-propylenesynthetic ethylenepropylene triple rubber blends The particularities of crystallization of mechanical isopropylenesynthetic ethylene-propylene triple rubberE-50 blends Structure of amorphous regions of polypropylenesynthetic ethylenepropylene triple rubber blends Analysis of non-volatile products of oxidation of propylenesynthetic ethylene-propylene triple rubberE-50 blends Investigation of structure of oxidized propylenesynthetic ethylene-

82 83

90 93 95 98

103 103 103 109 111 111 118 121 122

128

128 129 133 139 153 155 161 3

6.2.

CHAPTER 7. 7.1. 7.2. 7.3. 7.3.1. 7.3.2. 7.3.3. 7.3.4. 7.3.5. 7.3.6.

propylene triple rubber blends On the mechanism of oxidation of propylenesynthetic ethylenepropylene triple rubber blends

165

THE OBJECTS AND THE METHODS OF INVESTIGATION

167

The characteristics of samples Preparation of polymer compositions The methods of investigation Kinetics of oxidation Investigations of films with the help of differential scanning calorimetry Investigation of structure of films by the method of X-ray analysis Investigation of molecular structure of polymers samples and oxidation products by IR-spectroscopy method Determination of segmental mobility Determination of physical-mechanical characteristics

167 168 168 168

REFERENCES

171

168 168 169 169 170

4

Preface Thermal oxidation is one of the most common and important processes in which polymer materials participate. It accompanies the production and processing of polymers and polymer compositions, exploitation of their products and it usually leads to deterioration of material properties. The main problem posed for chemistsexperimenters and producers engaged in polymer materials creation is the problem of maintenance of high quality of output, prolongation of its service life at conditions of thermal oxidation influence and thermal-oxidative destruction. Wide use of polymer compositions replacing expensive materials makes this problem very important all over the world. For solution of this problem it is necessary to know the regularities of thermal oxidation of heterogeneous and hetero-phase systems, to know what factors influence on kinetics of their oxidation. At that it is also necessary to take into account structurally-physical processes developing in the course of oxidation of separate components and the blend in the whole. In the case of polymers their structure significantly influences on chain oxidation. Heterogeneity of polymers structures, the presence of regions differing in amplitudes of molecular motions, decrease of segment mobility, reduction of oxygen diffusion coefficient underlie this effect. These factors change process kinetics and change reactions' mechanisms. It is obvious that there will be the ones and the same principles in the base of influence of blend's components and homopolymers structures able to form in polymer blends. Polymers blends may be mono-phase and multi-phase, compatible, partially compatible and incompatible, they may have inter-phase layers or phase interfaces. Each of mentioned structure elements will make its own contribution into thermal oxidation kinetics and at that it will reveal the particularities of morphology of the blend in the whole, phase and molecular structure of each of the components. In accordance with the theory of oxidation of liquid-phase blends on the base of formally-kinetic approach to process one may propose three kinetic models which may describe the regularities of oxidation of heterogeneous and hetero-phase systems. In accordance with the first one the oxidation of components in polymer blends proceeds separately and independently; accordingly to the second one conception the oxidation is developed in the most active component of blend and hinders oxidation of another components; and according to the third one conception oxidation of blend proceeds by the law of conjugated oxidation mutually influencing on process rate. In the last case the determinative role in kinetics of radical processes is played by cross reactions between macromolecules of various components that may relate also to solid polymers blends. The contact of opposite macromolecules necessary for realizing of cross reactions of exchange by free valency may be realized in the volume of compatible blends or in incompatible blends in interphase layer (anisotropic melt) and also on phase boundary. The consideration of initial structure of polymer blends only is insufficient for estimation of every contribution of each blend's structural component into oxidation kinetics. The establishment of correlation between oxidation kinetics and initial structure of polymer blend is the only one side of the problem. Thermal oxidation is a complex process including chain oxidation of hydrocarbon radicals, destruction of macro-chains and structurization (cross-linking, cyclization). Under the action of high temperature and due to listed processes thermal oxidation is accompanied by the change of structure of amorphous and crystal regions of components. The mechanism of structural changes or reconstructions depends on polymer morphology and in its turn influences on kinetics of oxidation. Structural reconstructions may change the structure of inter-phase layer (boundary). The presence of various in activity reactionary RH bonds in blend's components will inevitably lead to localization of oxidation in phases, zones, etc. and as a result to the increase of contribution of secondary reactions and low-molecular radicals. Structural reconstructions in blends of polymers may change the character of process localization, kinetics of the main and competitive reactions characteristic for homopolymers and consequently the mechanism of radical process of blends oxidation. In this 5

connection the question about the influence of initial structure of polymers blends on the mechanism of structure reconstructions accompanying thermal oxidation of blend's components and their correlation with process kinetics is appeared. Due to the number of particularities of the technology of polymer blends production thermal oxidation may play positive role. Functionalization of polymers is widely used with the aim of improvement of compatibility of polymers under mixing and for regulating of structure of resulted compositions recently. Low-molecular substances of maleic anhydride type, etc. are usually used now. In this connection thermal oxidation of polymers up to definite process depth may also be considered as the method of their functionalization. Such application of oxidation is possible if key factors controlling the kinetics of oxidation of heterogeneous and hetero-phase systems are well known. Establishment of correlations between structure and kinetic parameters gives the possibility to realize the approach to polymers oxidation as to positive process. Thus for revealing of particularities of kinetics of polymer blends oxidation, for determination of key elements, for creation of model able to describe regularities of thermal oxidation of polymers blends one should determine the correlation between the structure of polymer blned, structural reconstructions accompanying oxidation and process' kinetics. The problem that is posed for the authors is to cover complex problem of correlation between structure and regularities of oxidation of heterogeneous and hetero-phase polymer blends. Material presented in given book is devoted to both particularities of oxidation kinetics and particularities of structure of polymer systems. In given book the analysis of key factors able to influence principally on regularities of polymer blends thermal oxidation is made, the role of phase morphology, components and inter-phase layer (boudary) structure in kinetics of heter-phase systems oxidation is determined by the example of polyolefines blends. Together with kinetics of oxidation of hetero-phase systems the questions concerning the studying of their structural parameters in oxidized state are considered. With the same aim the material presented in the book covers the regularities of oxidation of both polymer blends and homopolymers of various morphology and model systems.

6

Abbreviations AA BA DAF DCPD DOS DSC DTA G HCVT HP IA IMF IR-spectroscopy LPHD M MA MM MMA MMD PA PAN PA-12 PC PE PEAP PEHD PELD PO POB PP PVC r/c SEPR SEPTR SEVA SIER SIPR SIR s/c SRN T TPE TPR X-ray SA Mn w

Acrylic acid Butylacrylate Di-n-alkyl ester of orto-phthalic acid and alcohol fractions 79 Dicyclopentadiene Di-2-ethylhexyl ester of sebacic acid Differential scanning calorimetry Differentail thermal analysis Gauche-conformer High critical vitrification temperature Hydroperoxide Itaconic acid Index of melt fluidity Infrared spectroscopy Linear polyethylene of high density Monomer Methylacrylate Molecular mass Methylmethacrylate Molecular-mass distribution Polyamide Polyacrylonitrile Polydodecane amide Polycarbonate Polyethylene Polyethylene of average pressure Polyethylene of high density Polyethylene of low density Polyolefine Poly-3-oxybutyrate Polypropylene Polyvinyl chloride Rapidly cooled Synthetic ethylene-propylene double rubber Synthetic ethylene-propylene triple or ethylene-propylene-diene rubber Synthetic ethylene-vinyl acetate rubber (copolymer of ethylene with vinyl acetate) Synthetic isoprene-ethylene rubber (copolymer of isoprene with ethylene) Synthetic isoprene-propylene rubber (copolymer of isoprene with propylene) Synthetic isoprene rubber Slowly cooled Synthetic nitrile rubber (butadienenitrile rubber) Trans-conformer Thermoplastic elastomer (thermoelastic plastic) Thermoplastic rubber X-ray structure analysis Number-average molecular weight Mass-average molecular weight 7

Chapter 1. Introduction 1.1. The particularities of structures of polymers blends

The laws of thermodynamics and colloidal chemistry underlie the mechanism of formation of polymers blends structures, great role is also played by inter-phase phenomena revealing on phases interface [1-25]. Two- or multi-phase structure is characteristic for them in dependence on the number of components. Two-phase structure may represents disperse system where disperse phase is distributed in disperse medium in the shape of colloidal particles or may contain two continuous phase networks of dispersed polymer in polymer matrix by type "network in network". In dependence on the ratio of components in polymers blends the inversion of phases occurs  transition of disperse phase into continuous matrix and interphase layer is also formed [610, 12 ,13, 14]. Appearance of phase structure of blend depends on compatibility of mixed components. The great role is played by thermodynamic compatibility determining possibility of components to spontaneous mixing with each other and to form true solution [1620]. The main thermodynamic condition of polymers compatibility is the negative value of Gibbs' energy: 'G = 'H  T'S, where 'H  free enthalpy; 'S  entropy At 'G < 0 the spontaneous mixing occurs; if 'G > 0 the system is incompatible. The sign of 'G is determined by competition between values of change of enthalpy and entropy of mixing. For 'G < 0 |'H| > |'S|. Thus, the main thermodynamic requirement of compatibility conditions is 'S < 0 that means that macromolecules in blendss are situated in more ordered way than among macromolecules analogues to them, i.e. they formed combined ordered polymer structures. The enthalpy of polymers mixing 'H < 0 is possible in the case when interaction energy between heterogeneous molecules is higher than between homogeneous ones [16, 17, 20]. In the presence of strong interactions between macromolecules of mixed polymers and at their favorable spatial configurations and conformations providing formation of stable ordered combined structures the negative values of enthalpies and entropies of mixing in every phase are observed, and |'h| > |T's| and 'g < 0, (where 'h, 's are the enthalpy and the entropy of phase), i.e. polymers are compatible in the whole region of compositions. If the polymer components in the one region of compositions are combined ('g < 0) and in the other one not combined ('g > 0), then in the region of compatibility 'h > 0 's > 0, T's > 'h, and in the region of incompatibility 'h < 0, 's < 0, |T's| > |'h|. This fact means that transition from compatibility to incompatibility always occurs at definite ratio of components for each system polymerpolymer [20]. At that the ratio between 'h and T's is changed. Complex character of change reflects the presence of superposition of several processes proceeding under mutual mixing of polymers including destruction of components' structures and formation of novel structures and lays the foundation of particularities of blend's morphology. Molecular weight of polymers, their nature, chemical structure, the form of mixed macromolecules, identity of cross sizes of macromolecules, their segment mobility significantly influences on polymers compatibility [1523]. Compatibility of polymers is determined as ability to form common permolecular structures. In the case of mixing of crystallized polymers one may observe the effect of appearance of common crystallographic lattice (co-crystallization process) [21, 23]. Compatibility depends on the temperature and regimes of mixing. At usual temperatures the components are restrictedly combined and their thermodynamic compatibility is improved under heating or under the action of external mechanical fields [17, 18, 24]. Mechanical stirring promotes molecular distribution of one polymer in the other one [2529]. Diffusion phenomena of gradual transition of macromolecules are realized with temperature rise under the influence of heat motion. 8

These processes may lead either to intersolution of components, or to the increase of macroheterogeneity of material. The direction of this process is determined by thermodynamic changes and the rate  by kinetic factors. There is kinetic compatibility in these cases. The deformation of shear or stretching significantly influences on compatibility [2932]. Under the effect of mechanical fields the transition from two-phase solution or melt of polymers to one-phase or vice versa may occur. While changing conditions of mixing, intensity of mechanical effects one may obtain materials differing not only by permolecular structure but also by crystal morphology. For example if under usual mixing PP and PE form individual crystal lattices then under external effects and in dependence on conditions of cooling blends reveal ability to form common primary permolecular structures, common crystallographic lattice. However under applying of shear deformation the interaction between components may deteriorate that is revealed in the rise of crystallization and melting temperatures [2932]. Kinetic compatibility depends on production conditions, on conditions at which resulted blend is stayed. For example at prolonged storage blends are delaminated into macroscopic phases. According to modern conceptions [33] the segregation process of thermodynamically incompatible units doesn't stop on formation of macroscopic phases, and micro-phase lamination with formation of thermodynamically equilibrium domain structure occurs. Meso-scopic more or less delimiting domains of various structures turn out to be the most thermodynamically profitable. Sizes of domains are large in comparison with the thickness of transition layer between them. The kinetics of micro-phase lamination depends on morphology and chemical structure of polymer systems [33]. Thermodynamic compatibility of polymers may be improved by formation of combined structures or by increase of energetic interaction between macromolecules. Incompatible systems may become partially compatible or compatible under the change of chemical structure of macromolecules of components by introduction of functional groups leading to strong chemical interaction, under modifying of one of mixing polymers by change of monomer units by copolymerization or oxidation [3436]. Phase lamination and consequent coagulation of phases' particles lead to formation of various morphologic structures in blends. In blends of dispersed polymers the five main types of phase structures were established: usual dispersion of polymer in polymer, fiber structures, layered structures, micro-emulsion of matrix's polymer in particles of disperse phase, matrix structure [8]. The type of the structure is determined by rheology of system and technological regimes of mixing. Deformational effect under polymers mixing is of great importance. For example, for blends on the base of PO, for example in system of viscoelastic polymers such as PP and SKEPT the process of dispersion and formation of phase structures may be described from position of dynamic theory of RaleyTeylorTomotiki via stages of deformation of primary particles into fibers (liquid cylinders) and destruction of these fibers into drops with their further coalescence. This process is described by the equation: V˜M M / K˜JJ -(4 / S)˜W˜M M˜U r = (12 / S)˜W˜V where U  the energy of destruction of disperse phase; V  interfacial tension; M  inclusion volume fraction of disperse phase; K  effective viscosity of blend; J  rate of shear; W  probability of collisions leading to aggregation. Thus, formation of stability of dispersion of particles with radius "r" in PO is determined by the value of shear interaction, viscoelastic properties of components, by the ratio of their viscosities and inclusion volume fractions of disperse phase. Probability of inversion of phases into PO also depends on viscous elasticity of components and mixing conditions (on stress and rate of shear, temperature), and effectiveness of action of the last ones is determined by viscous elasticity. Under the action of specific surface forces directed on molecules situated on the phase interface and also under the action of heat motion of particles forming the system the eroding of interface and disruption of its geometric accuracy occur. As a result the surface interphase layer of defi9

nite thickness G depending on properties of contacting phases is formed. There are several models of interphase layer and correspondingly various conceptions about their structure. Among them there are models obtained in the framework of thermodynamic theories of phase distribution in systems polymerpolymer and structural models based on analysis of distribution of density in interphase layer. Theories by Gibbs, Guggengeim, Khelfand, Kammer developed for polymer blends and by KanKhillard for low-molecular systems underlie the first ones [3741]. On the base of analysis of their models the models of inter-phase layer were suggested by Lipatov, Kuleznev, Langer, Jennes, Park, Pol and Newmen [610, 4244]. Thermodynamic models in multicomponent polymer systems are based on conceptions about interphase layers of finite thickness between micro-regions of various structures and density within the limits of which the structure and density are smoothly changed from one component to another approaching to them asymptotically. The type of distribution of components densities in interphase layer is evident from suggestions about the character of components interaction and role of thermodynamic parameters. X-ray analysis of experimental deviations in distribution of density in two-phase system from Porod's model [45, 46] with sharp interphase boundaries underlies structure models of transition layer for polymers blends. These models postulate the presence of smooth distribution of electron density on phases interface and types of distribution Uc() are various. In accordance with conceptions developed by Kuleznev [5, 8, 47, 48] the nature of interphase layer appearance in blends of incompatible polymers is caused by solubility of segments and part of macromolecules diffused from the layer of one polymer into the layer of another one. The motive force of mutual diffusion of segments and segmental solubility is the change of thermodynamic parameters of surface layer of contacting polymers. And if the thickness of layer is lower than radius of curvature of interface then its state together with energetic parameters are determined by phase interface: Psidnsi dUs = TsdSs + Vds + ¦P where U  internal energy; S  entropy; T  temperature; P  chemical potential; n  number of components; V  surface tension; s  specific surface (index s relates given value to surface layer). The equation of state for volumetric phase D: dUD = TDdSD  DdVD + ¦PDidnDi where instead of specific surface the volume of phase V is appeared. The internal energy of system is equal to the sum of UD and Us. Thus, the thickness of layer is determined by the surface tension of system. The increase of surface tension (reduction of thermodynamic affinity of phases) leads to the decrease of thickness of surface layer. In the systems with developed interphase layer low interphase tension is observed. Dependence of layer thickness G on interphase tension V may be obtained on the base of Gibbs conceptions about surface layer: G = (V2V V12)˜Vs20 / (RTr2/r1Ms1) 1 2 where r and r  polymerization degrees of each polymer; Vs20  molar volume of segment; V2  surface tension of one of the polymers; V12  interphase tension; Ms1  inclusion volume fraction of component 1 in interphase layer. The lower the V, the higher the G. The thickness of layer may be estimated by measuring of interphase tension on interface polymerpolymer. Interphase tension is determined with the help of expression: 10

V12 = V1 + V2 – 2d – 2p where V12  interphase tension between phases 1 and 2; V1 and V2  surface tension of phases 1 and 2 correspondingly; d and p  express the contribution of disperse and dipoledipole interaction on phases interface. The expression for d and p was also proposed: d = V1dV2d / V1d + V2d d d where V1 and V2  the components of surface tension of each phase caused by dispersion and dipoledipole interaction. From this the following expression for V12 is evident: V12 = V1 + V2  (4V1d˜V2d / V1d + V2d) – (4V1p˜V V 2 p / V 1 p + V 2 p) The given equation shows that the closer the values of phases polarity, the lower the interphase tension. Theory of interphase layer developed by Kammer [40] proposed that for appearance of interphase layer the presence of gradient of density and free energy is necessary. In accordance with this theory thickness of interphase layer E may be determined with the use of FloryKhaggins' expression: E = (2 / 3˜—3) / {[b˜(T / To)1/2] / [—F F12 (1-1,33T / To)]}, where b  effective length of monomer unit; F12  the parameter of components interaction; T0  characteristic temperature. Calculations of E value were made for blends of homopolymers. The value E determined by this formula is 70-100 Å. According to Khelfand [3739] theory in the case of incompatible polymers in interphase region the interosculation of macromolecules occurs. The main statements of this theory are based on low values of F12, equal densities of monomer units U, high polymerization degrees of components z1, z2. The distribution of density of the first component along the normal line to plane of the layer for polymer systems in the framework of Khelfand theory is described by the following expression: Uc(x) = tgh˜(Sx / —12V). If we assume that the thickness of interphase layer E is the distance between two points of intersection of tangent of density gradient to the point of inflection with levels of densities of components U1 and U2, then: E = (U1 + U2)˜(dUc(x) / dx)-1 = 2—(U1b12 + U2b22) / —6F12 where b1, b2  statistical segments for components 1 and 2. Since the values of F12 are in the limits 0,01 and 0,1, then E is comparable with the sizes of components segments and approaches to several dozens of Angstroem units. The mentioned models reflect the characteristics of interphase layer in systems polymerpolymer, for example POPO. Formation of interphase layer in polymers blends sharply differing in rigidity, for example elastomer and plastic PPSEPTR is described by the Lipatov's theory [6, 9, 12]. For mentioned systems Lipatov proposed adsorption mechanism of formation of boundary layers and theory of formation of interphase region of two types. The first type represents two boundary layers separated by boundary surface and possessing morphologic differences from volumetric part of polymer and constant chemical structure. Formation of transition layer of this type is determined by thermodynamic mechanism. The second type of transition layer represents spontaneously forming emulsion of one polymer in the other one and is characterized by variable structure. This model proposed the presence of one transition layer limited from two sides. Formation of transition layer of such type is determined by colloidal-chemical mechanism. Among structural models obtained with the help of X-ray analysis of distribution of electron density in interphase layer [45, 46, 49-62] the linearly-gradient models are the most applicable: sigmoid model of Stein and Ruland [61, 62] and equilibrium model of Roe [63, 64] as the most for sure describing the structure of interphase layer in systems polymerpolymer. 11

Mentioned models allow estimating the correlation between characteristics of polymer systems and thicknesses of interphase layers. The last ones depend on degree of components segregation D, parameter of components interaction F12 and diffusion coefficient D. The presence of transition layer of terminal thickness between regions with various density leads to the decrease of average squared fluctuation of electron density in accordance with the expression: 'U 2c = (U1  U2)2 (M1M2  ES / 6V), where S / V  specific internal surface of micro-regions. For the systems with lamellar structure there is analogous formula: 'U 2c = (U1  U2)2 (M1M2 – M3 / 6), c 2 where (U1  U2) – the squared difference of densities of phases 1 and 2; M1, M2 and M3  volumetric parts of phases 1 and 2 and transition layer correspondingly. The values of squared fluctuations of electron density 'U 2c are used under determination of degree of components segregation D which characterizes completeness of processes of micro-phase separation of components: D = 'U2‘exp. / 'U 2, 2‘ where 'U exp.  experimentally determined; 'U 2  the value of fluctuation of electron density calculated from components densities, inclusion volume fractions of phases and transition layers. This expression is applicable for systems with sharp interphase boundaries and in the case of developed interphase layers. On the base of estimations of interphase layer by method of Stein or Roe [61, 62] one may determine the parameter of components interaction in binary polymer systems F1,2 knowing the effective lengths of monomers of separate components: F1,2 | 48—(U1b12 + U2b22) / S2(2. Diffusion coefficient of components D may be determined with the help of kinetics of formation of two-phase structure under transition of system from the region of one-phase into two-phase states, from dependence of interphase layer thickness decrease on the time of being in the region of two-phase states. The value of D is connected with the change of thickness of interphase layer in time 2(t) by the ratio: D = 2(t)  2V2o / 4t where parameter Vo is initial thickness of interphase layer. According to the X-ray analysis data the thicknesses of interphase layers in polymerpolymer systems are from several dozens of Angstroem units but in any cases don't exceed 50-100Å. At the same time in accordance with electron microscopy and IR-spectroscopy data the thicknesses of interphase layers reach several microns. The difference in obtained by various methods results is caused by the fact that X-ray techniques estimate interphase layer connected with density gradient and electron microscopy estimates morphologic changes, and IR-spectroscopy  conformational differences of macromolecules [65]. Two last methods may correspond not only to phase interface but also to their volume. The methods based on establishment of a number of temperatures, relaxation (glass transition) or phase (fro example melting) transitions in blends are widely used methods of studying of polymers compatibility and consequently of revealing of interphase layer [6676]. They are DSC, DTA, radiothermoluminescence, dynamic mechanical method, etc.. At that glass transition temperature may be used as the criterion of compatibility [66]. The existence of Tc of each of the components the values of which are characteristic for homopolymers indicates on the absence of polymer compatibility. In the case of partial compatibility in the presence of interphase layer in amorphous polymers, amorphous with crystallizing or in two crystallizing polymers as a result of solubility of their amorphous regions except Tc the glass transition temperature also appears for blend that is intermediate between homopolymers glass transition. In these cases two-phase blend of polymers has three glass transition temperatures 1, 2 and 3 that is intermediate between the first two. 12

1, 2 are the temperatures of components' phases glass transition, 3 is the temperature of glass transition of one polymer solution in the other or of interphase layer. For example in the blends PPPEHD, PP-PELD, PP-SEPR on the curve of radiothermoluminescence the appearance of the third maximum of highlighting corresponding to glass transition of common homogeneous amorphous phase, i.e. interphase layer is observed [6770]. The position of glass transition temperature in it Tc1 may be obtained with the use of Fox's equation [69]: 1 / T1 = (1  M2 / T 1) + (M2 / T 2), where T1  glass transition temperature of soluble component; T 1 and T 2  glass transition temperatures of soluble and insoluble components in blend; M2  inclusion volume fraction of soluble polymer in blend. The sign of thermodynamic incompatibility in two-phase PO systems is the presence of two various endothermic peaks on thermogram of melting of DSC or DTA with melting temperatures of initial homopolymers [71, 72]. The main signs of the presence of interphase layer are reduction of temperature of each of blend's components in comparison with Tmelt. of initial polymers, the decrease of crystallinity degree, the ability to formation of common primary permolecular structures, appearance of common crystallographic lattice. At that the phenomena of cocrystallization or polymorphism are possible [71]. The appearance of common crystallographic lattice was found under analysis of thermograms of blends of linear and branched PE [72, 73]. In the case of partial covering of phases of PP and SEPR or PP with SEPTR, when rubber interacts with PP on molecular level the morphology of polymer crystallites may be changed [69, 70, 74, 75]. Very often compatible binary systems containing crystallizing polymers after crystallization of both components have the structure of two interpenetrative carcasses or networks (IPC) [8, 13]. Formation of interphase layer leads to nonadditive change of free volume with the change of blend structure. For blends of linear polymers they found that with the rise of content of the second component the part of transition region was reduced and due to excessive association of components the retained volume might become lower than additive one [76]. At the same time in some cases for blends of linear polymers as a result of the same excessive association in the interphase region the excessive free volume localized on phases interface between components appears [77, 78]. In the case of IPC, at low contents of network of component 2 in the network 1 the retained volume becomes higher than additive that indicates on appearance of more flocculent structure of interphase transition layer in comparison with the structures composing the networks [7779]. Excessive free volume promotes acceleration of proceeding of relaxation processes in blends as a result of which the activation energies of some processes relating to some component of blend becomes lower than for the same component separately [80]. With the increase of part of network 2 the tendency to decrease of activation energy is observed that is connected with friability of transition layer and localization of free volume on interphase boundary. For example, for blends of PE and PP under transition from compatible systems to incompatible ones the sign of (de – d / de) is changed to the opposite that is the proof of concentrational boundary of compatibility (here de and da are experimental and additive values of blend density accordingly) [74]. The most reliable data about interphase interaction are obtained when using the complex of methods. More often it is the combination of the diffraction of X-ray beams at small and large angles, DSC, IR-spectroscopy. Obtained in this case data allow establishing the morphology of polymer blend and structure of interphase layer. In connection with complexity of structural organization of polymers blends the complex of factors which are reflected on regularities of blends' thermal oxidation and determine the role of structure in this process is appeared. The models describing dependence of physical-mechanical properties on blends structure allow analyzing the influence of blends morphology on their properties, revealing key structure factors in this influence [29, 7592]. The aim of application of these models is in theoretical description of the influence of following factors on quantitative level: 1. properties of separate components: particles geometry, size of dispersed particles, distribution by sizes, their orientation, volume of dispersed fraction, distance between phase particles, physical state of dispersion; 13

2.

characteristics of matrix: physical-chemical state, polymerization degree, crystallinity degree, degree of cross-linking; 3. the main factors characterizing bonds between matrix and phase (Van der Waals forces, forces of intermolecular interaction, chemical bonds, etc.), transferring stresses from matrix to phase particles, on physical-mechanical parameters of heterophase system in the whole. The number of models is based on "meso-phase" conception of blends structure in accordance with which distributed phase stabilizes composition at the expense of adsorption interaction [82, 83]. They consider that meso-phase is the zone surrounding inclusions and consists of homogeneous and isotropic material of limited thickness. In the case of completed adhesion the interphase layer may reach the thickness from several dozens up to 100 Angstroem units. In accordance with these models the main parameters able to influence on properties of polymers blends are phase morphology and structure of interphase layer. 1.2. Thermal oxidation of model micro-heterogeneous systems

Morphologic effects in heterogeneous systems of polymers are complicated by various chemical activities of blend's components. The investigation of model systems allows separating of the role of structure from various chemical activities of components in kinetics of oxidation of solid polymer blends [93, 94-131, 132-220]. It is convenient to use liquid phase blends as such systems. 1.2.1. The particularities of oxidation of liquid phase blends

The investigation of kinetics of oxidation of hydrocarbons binary blends [94102], systems with oxygen-containing derivatives of hydrocarbons [103, 104], oxygen-containing compounds with polyatomic alcohols or esters [105], binary systems containing aldehydes [106115], etc. with various contents of components showed that oxidation process of liquid phase blends was described by kinetic scheme corresponding to the mechanism of chain oxidation with degenerated branching of kinetic chains. Dependences of oxidation rate on composition structure very often have complex character and addition of one oxidable substance to the other one may accelerate the oxidation of the last one or to hinder it in dependence on the ratio of their reaction abilities and blend composition. Various types of dependences of w on structure were obtained in works [94102]: a. additive; b. with positive deviation from additive dependence; c. with negative deviation from additive dependence; d. with several extremums. Analysis of obtained data allowed authors of mentioned works to conclude that specificity of kinetics of blends oxidation was the presence of "cross" reactions. The scheme of components oxidation is as follows: x Initiation of kinetic chain of oxidation: R1H o R1* R2H o R2* x Continuation of kinetic chain: k1 R1* + O2 o R1 O2 * (1) k2 (2) R2* + O2 o R2 O2 * kp11 R1O2* + R1H o R1OOH + R1* (3) kp22 R2O2* + R2H o R2OOH + R2* (4) x Cross reactions of chain continuation: 14

kp12 R1O2* + R2H o R1OOH + R2* (5) kp21 (6) R2O2* + R1H o R2OOH + R1* x The stage of branching of kinetic chains: kd11 R1OOH + R1H o R1O* + R1* + H2O (7) kd22 R2OOH + R2H o R2O* + R2* + H2O (8) x Cross reactions: kd12 R1OOH + R2H o R1O* + R2* + H2O (9) kd21 R2OOH + R1H o R2O* + R1* + H2O (10) x Chain termination (there is quadratic termination on peroxide radicals at high pressure of oxygen): kt11 (11) R1O2* + R1O2* o products kt22 R2O2* + R2O2* o products (12) x Cross reaction of termination: kt12 R1O2* + R2O2* o products (13) The second particularity of liquid phase oxidation of binary blend of hydrocarbons is reaction of chain transfer  interaction of alkyl radical with hydrocarbon competitive to its reaction with oxygen (1): k3 R1* + R2H o R2* + R1H (14) Such competition may lead to critical transition from auto-accelerated regime to complete stopping or slowing of oxidation of one of blend's components that was observed under autooxidation of liquid phase blend of paraffin and alkylaromatic hydrocarbons [94, 96]. This reaction may be realized if k1[O2] 0 and criterion of inhibition is (kt12 kp21 /kp12kt11) – (kp21/kp11) > 0. the value of specific rate of oxidation of components doesn’t depend on their concentration. In the case when Z1 is decreased the inhibiting effect is observed, and when it is increased  the initiation one. In the absence of cross reactions under the addition of one substance to another the rate of component oxidation in the blend is changed only at the expense of dilution effect. At that the specific rate of oxidation under the change of composition remains constant. There are reactions of degenerated branching of oxidation kinetic curves under auto-oxidation of liquid phase systems at 100140qC. At that decomposition of hydroperoxides R1OOH and R2OOH except bimolecular reactions (79) is realized by monomolecular reactions proceeding in each component separately: R1OOH o R1O* + *OH (18) (19) R2OOH o R2O* + *OH The presence of the reactions of degenerated branching (710, 18, 19) leads to the change of regularities of oxidation of multi-component systems and to complication of dependence of oxidation rate on blend composition. Chemical structure and the mechanism of hydroperoxides decomposition are of great importance. Cross reactions may change the both the first factor and the second one. Thus, on the base of analysis of kinetics of liquid-phase oxidation of hydrocarbons blends we may formulate the number of regularities of multi-components systems oxidation and these regularities are conditioned by differences in components' chemical activities:  the particularity of process of multi-components systems oxidation is the presence of cross reactions between components;  under oxidation of multi-component systems there is competition between reactions of alkyl radical woth oxugen molecule and RHbond of neighboring component;  under auto-oxidation of multi-component systems significant contribution in to process is made by cross reactions of hydroperoxides decomposition reaction that may change process kinetics at moderate temperatures;  the presence of cross reactions and competition between reactions of connection to RH-bond of oxygen and alkyl radical may lead to inhibiting or initiating effects, i.e. hindering or acceleration of oxidation of one component by another one. The first or the second variant is determined by the ratio of constants of elementary stages rates in reactions of oxidation of individual substances or cross reactions. 1.2.2. Kinetics of copolymers oxidation

The other system modelling heterogeneous systems are copolymers [93, 132220]. The description of particularities of thermal oxidation of copolymers allows revealing complex influence of chemical heterogeneity, macromolecular nature of substance and solid-phase state. With the help of given model system one may estimate the influence of not only chemical, but also structure factors on oxidation of solid polymers blends. 1.2.2.1. The role of chemical nature of comonomer units in thermal oxidation

The role of chemical nature of comonomers is evident from the analysis of works [132155]. In accordance with the results presented in these works the process of thermal oxidation of copolymers is a complex process and is accompanied by structurization (cross-linking and cyclization), destruction of chain and depolymerization. The reactions characteristic for homopolymers which monomer units entering the copolymer underlie these reactions. Thermal oxidation of polyolefines and polydienes proceeds by radical-chain mechanism with degenerated branching of kinetic chains and is accompanied by destruction of macromolecules 17

[132134, 159163]. The main product of oxidation is hydroperoxide functioning as branching agent initiating oxidation and destruction of chains [132134, 159163]. Under rubbers oxidation the formation of cross-links is characteristic [132141, 143147]. Under thermal oxidation of polymers of polystyrene and poly-D-methylstyrene type thermal oxidation initiates thermal destruction proceeding by two-stage mechanism [156158, 164, 165]: with decomposition via weak bonds obeying the incident law with formation of chain's fragments which sizes are biger than for monomer, and with depolymerization accompanying by monomer isolation. These processes prevail over accumulation of hydroperoxide groups. Thermal oxidation of polymethyl methacrylate and polyacrylate proceeds via oxidation of hydrocarbon radicals with formation of hydroperoxide [142, 167169]. However the main reactions are depolymerization and cyclization [140, 168, 169]. Thus, the mechanism and kinetics of reactions proceeding under thermal oxidation of copolymers may be changed in dependence on the type of alien monomer unit accelerating or hindering thermal oxidation of polymer. For example, as they showed in works [149, 150] the process of thermal oxidation of copolymers of ethylene with allenic groups (>C = CH2) [149], ethylene with propylene, vinyl chloride, nbutene units [150], block-copolymers of ethylene oxide and propylene oxide [170] proceeded by radical-chain mechanism with degenerated branching of kinetic chains. The rate of oxygen absorption depends on hydroperoxide concentration that branches out the kinetics chains of oxidation, rate of hydroperoxide decomposition and effectiveness of its initiation. At that introduction into PE chain of allenic, propylene and vinyl chloride monomers mainly accelerates the process of its oxidation [149, 150]. More bulk n-butene (C2H5) comonomer units insignificantly influence on PE oxidation rate [150]. The other picture is observed if one introduces into PE chain the comonomer units of acrylate, methacrylate [171, 172], styrene [173, 174], siloxane [133, 136, 173, 175], ethers of vinylphosphonic acid [166], dicyclopentadiene [176], etc., for which homopolymers the process of depolymerization or cross-linking is characteristic. In this case oxidation of PE is significantly hindered [136, 166, 171175] as a result of substitution of process mechanism. Destruction of PE chain accompanying thermal oxidation of copolymer is substituted by reactions of cross-linking or cyclization. The change of character of radical reactions in chain process is observed under introduction into homopolymers of monomer units wit double bonds in the main chain, for example isoprene, butadiene, etc.. As Bevington, Melvil and Teylor [158] established thermal oxidation of copolymers with polydienes comonomers (cis-1,4-polyisoprene, ethylene-propylene-diene comonomer, butadienenitrile rubber, butyl rubber, etc.) proceeded with participation of double bonds. At that the continuation of kinetic chains of oxidation is realized by reaction of intra-molecular connection of peroxide radical by double bond with formation of cyclic peroxide and by reaction of detachment of hydrogen atom of D-methylene group with formation of hydroperoxide. Thermal oxidative destruction of macro-chains of such copolymers is also mainly realized as a result of reactions with participation of hydroperoxide groups and radicals conjugated with double bond [132134, 173]. As a result, the rates of mentioned processes in copolymers in comparison with homopolymers are decreased. Phanton et. al. [177] came to analogous conclusion when studied thermal oxidation of polyethylene of low density with vinyl and vinyliden unsaturation (ethylene-1-butene and ethylene1-propene). Comonomer units differing by chemical nature and participating in various radical reactions under thermal oxidation are in close contact with each other. Radical reactions proceeding in every comonomer mutually influence on each other. Kinetic parameters characterizing copolymers oxidation are not additive functions of analogous parameters of comonomers. From this fact the number of distinctive features of copolymers thermal oxidation from oxidation of hydrocarbons mixtures is evident. The "effect of neighbor" and inter-chains effects relate to such particularities. These effects were found in works by Plate et. al. [178, 179] and Shlyapnikov et. al. [150, 180, 181]. 18

The "effect of neighbor" is described in monograph by Plate et. al. [178] in details, where authors brought out clearly that reaction ability of concrete functional group in copolymer chain, for example monomer A with reagent C depended on chemical nature of neighbor groups B. Thus, reaction ability of consecution 121 may be higher than in consecutions 111 or 222. However, it is obvious that during thermal oxidation of copolymers this effect will reveal in more complex way. The "effect of neighbor" leading to acceleration of reactions in copolymers is revealed in a number of works [139, 149155, 166, 167, 182186]. For example in work [139] they showed that appearance of double bond near the reaction group led to sharp rise of elimination rate. Introduction of ether group into copolymer chain promotes significant destabilization effect [139]. Presence of ether units close to block of vinyl chloride sharply increases the rate of detachment of HCl in the case of methylacrylate (MA) and butylacrylate (BA). In non-oxidized copolymers "the effect of neighbor" may lead to acceleration of radicals origination and consequently initiation of radical reactions. However the type of radical reactions which may be developed after formation of free valency will depend on the nature of comonomer unit. In their turn the rates of development of kinetic chains of oxidation, destruction, depolymerization, cross-linking or cyclization depend on reaction ability of R-Hbonds in monomer units and structure parameters. As a result in one case the effect of neighbor leads to initiation of kinetic chain and acceleration of copolymer oxidation in comparison with homopolymers. In the other case the processes are accelerated which compete with development of kinetic chains (cross-linking, cyclization), as a result of which kinetic chains are blocked, their lengths are reduced and free valency is terminated and oxidation process is hindered. The "blocking effect" is revealed in relation to oxidation process of hydrocarbon radicals and thermal-oxidative destruction. The example of "blocking effect" is presented in the work by McNeill [138]. Introduction of alien comonomer units of various nature (acetylene phenyl, methyl, ethyl, n-propyl and n-butyl acrylates and styrene) in PMMA has a blocking effect on depolymerization process. As a result of this fact in the interval 200-300qC depolymerization initiated by end radicals formed during synthesis is substituted by chain destruction and in such way increases thermal stability of PMMA. Effectiveness and the mechanism of depolymerization blocking by comonomer units depend on their nature and are connected with the ability of comonomer unit to create conditions at which the process of chain braking by bonds between opposite monomers will compete with process of depolymerization initiation of methylmethacrylate [138]. Thus, in dependence on the nature of contacting comonomers "the effect of neighbor" may lead to initiation or inhibition of copolymer oxidation. It is obvious, that the ratio between parameters of acceleration or blocking of oxidation process or the effectiveness of oxidation initiation in copolymer reflects the properties of reaction medium. That is why the effectiveness of initiation of inhibition depends on the nature f comonomer units, reaction ability of RH-bondsof monomer units and also on structure of copolymer chains. Under thermal oxidation of solid copolymers the inter-molecular and inter-chain effects are of essential importance. In the works by Shlyapnikov et.al. [150, 180, 181] on the example of reaction between quinone and ethylenepropylene copolymer authors showed dependence of reaction ability of copolymer on the order in relative disposition of macromolecules and monomer units. Thus, after thermal oxidation of SEPR there is competition between reactions of cross-linking and destruction of copolymers chains. At that the polymer in the course of reaction will be cross-linked with formation of simple ether bonds if RH-bonds of hydrocarbon fragments are fragments of two neighbor macromolecules. According to [150, 180] the rate of cross-linking reaction is determined from the ratio: W = [Q]nZkpqr[MpMqMr], where n  the order of reaction by Q; p, q, r  the consecution of three monomer units and q reacts with quinone Q directly; , q, r = 1 or 2. 19

Accelerating inter-chains effects are also considered in the work by Plate et. al. [179]. In accordance with the theory of inter-chain effect they propose that moment reaction ability of M1 and M2 depends on micro-environment with which they may interact directly. Acceleration of interchain reaction between M1 and M2 is possible if M1 is in the environment of the same monomers belonging to one macromolecule and the neighbor to it M2 belongs to the neighbor chain. In other words it is the same effect of neighbor revealing in relation to neighbor macro-chains. It is obvious that even at revealing of inter-chain effects during copolymers thermal oxidation process the dual role of alien units will be revealed: initiation of radical oxidation process and their blocking. We should note, that the result of the effect of neighbor and inter-chain effects under copolymers oxidation is that the cross reactions analogous to those ones under liquid phase oxidation of mixtures of low-molecular hydrocarbons are of great importance in chain oxidation of hydrocarbons radicals. One more particularity of copolymers thermal oxidation is essential contribution of secondary reactions. Adjacency of oxidable opposite monomer units containing various in nature and activity RH-bonds or functional groups with primary products of oxidation leads to realization of the effect of neighbor and inter-chain effects between them and accelerates secondary reactions. Very often these reactions are the reactions between hydroperoxide groups and double bonds [187] or ROOH and alkyl radicals [162] changing the mechanism and kinetics of their decomposition and consequently the stage of branching of kinetic chains of oxidation. The whole number of reactions is also possible which leads to the change of composition or stationary concentration of radicals [162, 134, 173, 188] and consequently the rate of process in the whole. The third particularity is catalytic action of products of comonomers oxidation. The effect of neighbor revealing in oxidized macro-chains of copolymers that is realized between various functional groups  products of oxidation or functional groups and non-oxidized RH-bond of comonomer leads to catalytic effect directed on acceleration of cross-linking, cyclization, elimination [132, 134, 173]. It is reasonable that this phenomenon for a number of copolymers leads to "blocking effect" and consequently to the reduction of rate of thermal oxidation. Usually in copolymers cyclization is realized via interaction between donors and acceptors of hydrogen atom that leads to formation of covalent cross-links [156, 172]. For example in the work [156] they showed that oxidation of SEVA led to formation of >= bonds contacting with OCH3 in MA and accumulation of alcohol groups, and also carbon acids in PE. Cyclic compound is formed at the expense of interaction between donor of H atom  alcohol group and acceptor of H atom  ether. At that the acids of ethylene comonomer are catalysts of covalent cross-links [156]. Cross-linking via ether groups in ethylenepropylene copolymer [150] or cyclization via ether groups in ethylene copolymer with methylmethacrylate [187] are realized due to reaction of recombination of alkyl radicals or reactions between alkyl radicals and aromatic cycles of comonomers. It is obvious that various revealing of "the effect of neighbor", inter-chain effects, catalytic action, contribution of secondary reactions changing the mechanism and kinetics of thermal oxidation depends not only on nature and activity of comonomer units, but also on their content in copolymers. The analysis of data obtained in the works [147-155, 166, 167, 182-185, 189] shows that in the majority of cases in copolymers the dependences of rates of thermal oxidation process on their structure have complex extreme character. For example Tenchev [189] when studied thermal oxidative stability of chlorinated polyethylene obtained at various conditions established that the samples with chlorine content about 10-20% and more than 60-70% possess the highest stability. Authors of [190] when oxidized ethylene with vinyl acetate obtained the data testifying to the fact that rate of accumulation of acetic acid deep oxidation product was maximum for the sample with 50% of -2-(OCOCH3)- units and concentration of hydroperoxide groups accumulated for 60 minutes at 200qC was decreased with the rise of concentration of vinyl acetate units. In work [154] authors showed on the example of copolymers of vinyl chloride and E,E'dichlorethyl or E,E'-di(2-thiobenzthiazolyl)-ethyl ester of vinyl phosphoric acid that introduction of 20

insignificant amounts (up to 0,83 mole %) of phosphonic units into PVC chain hindered thermal oxidative destruction (the temperature of the beginning of weight loss and maximum temperature of decomposition were increased and the rate of volatile products formation was reduced). However the further increase of phosphonic units content led to the decrease of thermal oxidative stability of copolymer. It is obvious that the main reason of complex character of dependences of rate of thermal oxidation and destruction of copolymers on their composition is the competition between processes of initiation and blocking of oxidation. The driving forces of this competition are not only chemical nature of comonomers units but also the structures of copolymer chains. 1.2.2.2. The influence of copolymer chain structure on thermal oxidation

As it is known that the structure of copolymer chain depends on the way of connection of comonomers with each other and on their content. At that if we change conditions of synthesis then we obtain statistical, block-copolymers, graft copolymers, polyallomer. Thus, copolymers with equal chemical composition may be different in the character of distribution of heterogeneous monomer units and their blocks in chain. When we divide copolymer chain into blocks alien units determine the length of blocks and change the environment of reactive sites that is reflected on the mechanism and kinetics of thermal oxidation. This fact is clearly revealed under studying of regularities of oxidation of statistical, alternating and block copolymers. McNeill demonstrated the role of chain structure [138]. He established that block degree of copolymer chain, lengths of blocks consisting of monomer units of MMA determined what process would prevail: depolymerization with isolation of methylmethacrylate or decomposition of copolymer chain by incident law. Comparison of copolymers of methylacrylate and methylmethacrylate showed that shortening of the consecution of MMA units at the expense of introduction of MA units decreased the length of kinetic chain of depolymerization and the higher was the content of MA and the shorter was the consecution of MMA units this phenomenon was more significant. Decomposition of chains between weak bonds of MMA and MA occurred in such samples instead of depolymerization. The larger the number of joints, the larger the number of radical pairs as a result of chain destruction. If the cell effect is not revealed then forming free radicals may terminate kinetic chains of depolymerization initiating by end radicals. And destruction of radicals in copolymers MMA / MA proceeds by reaction of disproportionation. The other striking example of the role of chain's structure is the change of thermal destruction of PMMA after introduction into its chain of styrene comonomer. Copolymer of methylmethacrylate with styrene is differed by significantly higher stability in comparison with PMMA. When styrene content in PMMA chain is increased from 1/4 to 1/1 the MMA consecutions depolymerization is sharply decreased or completely absent. Shortening of methylmethacrylate units consecutions changes the mechanism of radical reactions. Reactions initiated by chains ends are inhibited. However the mechanism of blocking effect by styrene units is the other in comparison with MMA copolymer with acrylates. In this copolymer the end radicals formed from unsaturated bonds of MMA and able to initiate kinetic chains of depolymerization, they are destructed only in recombination reactions. The initiating reaction of copolymer chain decomposition according to the work [138] is the opening of bonds between pairs of MMA units but not of bonds MMAC. In copolymer with ratio MMA / C = 1 / 1 radical pairs able t initiate thermal destruction belong to styrene. However due to low segment mobility these radical pairs don't leave the "cell" (cellular effect is revealed) and are destructed via recombination or disproportionation. On the example of given copolymer we may see the role of cellular effect. Thus, it is obvious from the example of work [138] that shortening of consecution of monomer units should promote the blocking effect of reaction proceeding in more active comonomer. However more active copolymer may initiate kinetic chains of one or another process in less active one, if the radical carrying out kinetic chains of process will not be destructed via quadratic termination. 21

As a consequence of blocking effect revealing alternating copolymers may possess higher stability than statistical ones, however initiating effect on joint of pair of alien units may lead to acceleration of process in them. Joesten and Johnston [191] studying thermal decomposition of copolymers of vinyl chloride and acrylonitrile showed that alternating copolymers were more stable than accidental ones. Analogous data were obtained by other authors on the examples of copolymers of styrene with butylacrylate [192, 193]. The presence of blocking effect in copolymers of block structure leads to localization of thermal oxidation in blocks of more active comonomers. For example in the work [170] Topchieva showed that auto-oxidation of block-copolymers of ethylene oxide and propylene oxide was localized in more active polypropyleneoxide block. Process of oxidation localization and consequently the mechanism of oxidation and contribution of secondary reactions will depend on comonomers nature entering into blocks, on comonomers blocks structure and their mutual disposition. The regularity of initial chain determines the character of destruction of macromolecules and the higher the regularity of ethylene comonomer and the higher the length of its block, the lower the number of brakes in this block [194]. Memetea et. al. [195] when studying the oxidative destruction of copolymer system acrylonitrilebutadienestyrene by method of chemiluminescence of oxidized samples established that the type of processes accompanying oxidation was differed in dependence on chemical nature of blocks. Oxidation is localized mainly in butylenes comonomer and is generated by tertiary carbon atoms analogously to PP. In blocks of butylenes comonomer the accumulation of peroxide radicals proceeds which originate the hydroperoxide. At the same time thermal oxidation of polyacrylonitrile is accompanied by methyleneimine cyclization and oxidation in which tertiary carbon atoms participate. Oxidation also proceeds on styrene blocks and on tertiary carbon atoms free radicals are formed originating hydroperoxide. As a result the acrylonitrilebutadienestyrene copolymer has several types of hydroperoxides differing in structure and decomposition kinetics, and both facts are determined by the structure of comonomers blocks. Among butylene blocks they observed the appearance of set of various types of ROOH that was the result of presence of 1,4-cis- and 1,4-transisomers forms in blocks. Oxidable blocks ABC interact with each other. At that hydroperoxide groups initiate the cyclization process in acrylonitrile blocks. Initiating effect of thermal oxidation process on inter-blocks bonds in block-copolymers of polycarbonate with polysiloxane was demonstrated in work by Gorelik [148]. Joints of opposite units initiate kinetic chains of oxidation and lead to acceleration of thermal oxidative destruction of polymer. Increase of concentration of inter-block bonds lead to the rise of block-copolymer destruction rate. At that the oxidation process is developed in PC block. Thus, structure of copolymer chain influences on the ratio between rates of competitive processes accompanying oxidation. 1.2.2.3. The role of physical structure of copolymers

Heterogeneities of structure in copolymer caused by chemical heterogeneity and various distributions of units along the chain influences on physical-dynamic parameters and consequently on the mechanism and kinetics of oxidation. Alien units at their essential content change not only the structure of polymer but also the gross-process of oxidation, combined oxidation of comonomers with various reaction activities proceeds in the presence of their interaction. For example introduction of small amount of propylene [150] or vinyl chloride into PE [190] in the narrow concentrations interval (0,10,5%) leads to the sharp rise of density of copolymer amorphous regions and as a result the thermal oxidative stability of polymer is increased. At higher content of comonomers, when both comonomers participate in the process in the first case the decrease of PE stability is observed, and in the second it is increased in accordance with particularities of oxidation mechanism in dependence on distribution of comonomers units in copolymer chain [150, 190].

22

The regularities of influence of structure on mechanism and kinetics of thermal oxidation depend on morphologic forms formed in copolymer. At one and the same total content of comonomers the topping role of one or another structural element in copolymer revealing under oxidation of crystal regions or structure of separate macromolecule may be changed. For example in crystallizing block copolymers the mechanism of oxidation will clearly depend on structure of intercrystal chains, in block and graft-copolymers differing by micro-phase separation of comonomers oxidation will strongly depend on inter-phase interaction and structure of inter-phase regions. The role of copolymer structure is come to the fact that chain oxidation will be localized in zones presented by more reactive comonomer or less compact and more defective in structure sections of chain. Physical structure of copolymer may promote strengthening or weakening of effects connected with chemical nature of comonomers and chemical structure of copolymer chains including "the effect of neighbor" and "inter-chain effects", and also will determine the contribution of secondary reactions. So localization of oxidation inside of flexible chain block of comonomers caused by structural particularities of copolymer chain may inhibit "the effect of neighbor" in primary oxidation. However this effect may be strengthened during reaction between secondary products of oxidation accumulated inside of this block. Such effect for example is observed in copolymer on the base of flexible PE chain and rigid chain of PMMA in Dole's work [172] when accumulation of OH-groups in PE block lead to reaction between hydroxides and ether groups of methylmethacrylate. In given case structural parameters promote localization of oxidation and proceeding of secondary reactions. The main factors determining the character of influence of structure on thermal oxidative stability of copolymers re analogous to those ones for polymers. The question of reaction ability of copolymers is closely connected with diffusion and solubility of oxygen and low-molecular substances in copolymer and also with molecular dynamics. For copolymers the general character of formation of transport properties, diffusion and selfdiffusion coefficients is observed [196199]. Crystal phase and also rigid (ordered) blocks in amorphous phase (in amorphous copolymers) have high density, low free volume and due to these facts they are inaccessible for oxygen and low-molecular substances. High order of chains or blocks of rigid chain macromolecules provides low segment mobility. At the same time soft blocks and interphase regions with defective structure have friable package, large free volume, high segment mobility [198203]. Investigation of the influence of structure on transport properties of copolymers [198, 199, 202206] on the example of block-copolymers consisting of rigid chain and flexible chain blocks of polycarbonate and polysiloxane showed that values of coefficients of gas permeability by O2 and N2 and also diffusion properties were naturally higher for systems with larger length of siloxane (soft) block and in systems with continues polycarbonate phase and they were monotonously increased with the rise of PC block length. And in the region of continues siloxane phase (more than 40 mass %) distribution by lengths of rigid PC blocks doesn’t essentially influence on presented parameters. When studying diblock-copolymers of styrene and butadiene Krisyuk et. al. [201] came to the conclusion that solubility of oxygen in diblock-copolymers to a greater extent was determined by elastomer component and except soft rubber blocks in copolymers the interphase regions were the regions of high solubility and gas permeability. In alternate and statistic copolymers diffusion coefficients and oxygen solubility depend on structure of copolymer chain, on the length of comonomer consecutions. The shorter the microblocks the structure is less ordered and the solubility is higher in this copolymer [198, 199, 201]. We should note that although the diffusion of oxygen and low-molecular substances in copolymer is realized mainly through amorphous regions and soft blocks and namely these regions determine free volume and consequently diffusion properties of copolymers [203] the crystal phase significantly influences on transport and diffusion properties. Rigid blocks in the aggregate with crystallites decrease inclusion volume fraction of accessible space and increase sinuosity of the way [200, 204, 205]. Besides crystallites in copolymer blocks when creating stresses on inter-crystallite and inter-domain chains control their structure order [200]. Kinning et. al. in the work [206] when studied the influence of block-copolymer of styrene with butadiene on transfer of CO2 established 23

the correlation of diffusion coefficients with the interface of volume fractions of comonomer blocks and structure of inter-microphase chains. Diffusion limitations connected with heterogeneity of copolymers structure may lead to redistribution of diluted oxygen between structure regions with various densities. As a result in more compact regions of amorphous phase the reactions competitive with oxidation will be developed and in friable regions of oxidation localization it may lead to proceeding of secondary reactions. The role of permolecular structure of copolymers in process of their thermal oxidation is demonstrated in work [207] by Leplyanin et. al.. On the example of oxidation of crystallizing polyvinylenes they showed that thermal oxidative stability was determined by density of sample caused by degree of structure order of both amorphous and crystal regions. In accordance with the data of work [207] the presence of crystallites promotes reduction of oxidation and thermolysis rates due to revealing of oxygen diffusion limitations. The presence of crystal unoxidized regions may increase the degree of oxidation localization in inter-crystal zones of copolymer. At that the probability of secondary reactions will be increased. Actually, in work [208] they showed that change of part of amorphous phase in copolymers on the base of polyacrylonitrile (PAN) and acid comonomers: itaconic acid (IA), methacrylic acid (MAA) and acrylic acid (AA) led to the change of contribution of reaction of secondary oxidation. The rise of part of amorphous phase in the raw IA > MAA > AA is caused by the presence of unconnected comonomer units destructing package of chains and this effect is revealed to a greater extent if the introduced comonomer is bulky. Amorphousable copolymer is oxidized with higher rate and has higher degree of transformation in oxidation reaction and the contribution of dehydration reaction and cyclization is reduced. The order of chains packing in PAN is higher than in AA and MAA. Moreover small content of alien comonomer may promote freer package of polymer chains of amorphous regions. Lower density of amorphous zones will provide possibility for oxygen to contact with groups presenting in these zones. Decrease of oxygen concentration in polydimethylvinyl siloxane also changes the mechanism of thermal oxidation, hinders oxidation of organic radicals [136]. And instead of this phenomenon the structurization with participation of double bonds of vinyl groups with formation of rigid network or decomposition of SiO bond occur [136]. For reaction the presence of definite mobility of molecular environment is necessary. The scope of molecular mobility and the value of free volume of copolymer matrix depend on the nature of comonomer units. Diffusion limits don't influence on rubber micro-blocks in diblock-copolymers PCPB [198, 199, 201]. In the case when one of comonomers is rubber localization of process will be realized namely in rubber phase since friable phase is practically always saturated by oxygen. At that the rate of oxidation reaction of rubber phase is determined by molecular dynamics. In Krisyuk's work [201] on the example of oxidative reaction of block-copolymers PCPB with ozone the decisive role of molecular mobility is demonstrated. Obviously the decrease of segment mobility of copolymer chains may lead to reduction of rate of interaction between reactive RH-bonds and oxygen molecule, to cellular effect and in such way it may change the mechanism of elementary stages of oxidation. Analogous effects were observed in the work by Kalinina [150]. The influence of chain structure on thermal oxidation of copolymer may come to determination of rate of mutual diffusion of active sites and reactive RH-bonds in copolymer chain. However for copolymer the mutual diffusion influences not only on kinetics of elementary stages of chain oxidation but also on reactions accompanying and competing with this process. Moreover the structure of copolymer chain determines the character of oxidation localization in the zones which may be presented by soft blocks and comonomer with higher reactivity and as a result it controls the mechanism and kinetics of secondary reactions. At that the possibility of effects revealing connected with chemical nature of comonomers (the effect of neighbor and inter-chain effects) will also depend on copolymer topology. The particularity of copolymers is also the fact that relaxation processes in polymer matrixes determining mobility of polymer chains, limiting progressive and rotational diffusion of diluted in 24

polymers low-molecular compounds are responsible for processes of formation and decomposition of inter-molecular interactions between opposite comonomer blocks and consequently for change of structure during oxidation process. Freezing of small-scale motions of chains corresponding to conformational transitions significantly influences on diffusion of small molecules introduced into copolymer. Diffusion coefficient depends on sizes of associating molecules and micro-phases. The spectrum of relaxation times is especially broad due to heterogeneity of microstructure and chemical structure of copolymers in defective regions. Due to the same reason the role of structure in reactions realizing with participation of low-molecular radicals is increased and this participation in oxidative process in copolymer is increased in comparison with homopolymer. Under oxidation in kinetic regime when diffusion of oxygen doesn't influence on process in copolymer the problem of chain construction and their localization inside of opposite micro-phases and between them, of the ratio of length to width of polymer crystal in the direction of chain (the measure of morphology) and also the orientation of anisotropic regions is appeared. It is obvious that these factors will determine the mechanism of transfer of free valency, the possibility of its transition along entrance chain from one micro-phase into other one or transition of macro-radical as intra-molecularly along the chain, so inter-molecularly from one molecule to another but inside of one micro-phase. 1.2.2.4. The particularities of kinetics of copolymers oxidation

Oxidation of hydrocarbons radicals in copolymers is developed by the same mechanism of chain process with degenerated branching of kinetic chains that in usual liquid phase oxidation of hydrocarbons and polymer materials. However copolymer is stiff system and in contrast to hydrocarbons blends it contains alien units with various reaction ability inside one macromolecule. These differences make essential corrections in the mechanism of oxidation and radical reactions of copolymers [93, 147149]. The question devoted to the mechanism of initiation of kinetic chains of oxidation in polymers is considered in a number of monographs and articles [161163, 209211]. Origination of kinetic chains in copolymer may be realized analogously to the polymer in bi- or tri-molecular reaction between RH-bonds and oxygen [161163, 209211]. However such reactions in copolymer may proceed on two various types of reactive sites M1 and M2 according to the scheme: M1H + O2 o[M1* + HO2*]oM1* + HO2 (3) (4) M2H + O2 o[M2* + HO2*]oM2* + HO2 2M1H + O2 o[M1* + M1*] + 2 HO2*o 2M1* + HO2* (5) 2M2H + O2 o[M2* + M2*]+ 2 HO2* o 2M2* + HO2* (6) Obviously on this stage the particularities of copolymer structure should be revealed. Mentioned reactions between M1 and O2 and M2 and O2 will be realized independently only in the case of separate phases: in block-copolymers or polyallomers. In the majority of cases in statistic or alternating copolymers where the effect of neighbor is revealed the initiation of kinetic chains will be realized predominantly on the joints of alien monomer units or blocks according to the following reaction: ki (7) M1M2+O2oM1*+M2OO* ki or M1M2 + O2oM2* + M1OO* (8) where M1 and M2 are opposite monomer units of macromolecules. At that the rate of initiation will be determined by the following expression: Wi = ki[M1-M2][O2], (9) where ki is the constant of rate of opening of the bond between monomer units M1 and M2; [M1M2]  the concentration of joints between M1 and M2. 25

In other words the rate of initiation should be described by linear dependence by concentration of joints between alien units or blocks. Proceeding of initiation reaction on inter-block bonds of polycarbonatepolysiloxane copolymers was found in work [148] by Gorelik et. al. and the dependence of rate of thermal oxidative destruction on concentration of joints was described linear dependence. In the case of phase or micro-phase separation of comonomers in copolymer when reaction abilities of comonomers are significantly differed or in the case of cell effect revealing in comonomers with various rigidity of chain the initiation of kinetic chains of oxidation of one of comonomers may significantly delay in comparison with the other one. In this case oxidation will develop locally in blocks of more active comonomer that was reported in works [138, 149151, 170]. Thus, initiation of kinetic chains of oxidation of less active in relation to oxygen comonomer is possible in reaction being the stage of continuation of kinetic chains of oxidation of more active comonomer, for example by the following reaction: (10) M1* + M2H oM1H + M2* and also: M2* + M1H oM2H + M1* (11) Initiation on the stage of kinetic chain continuation in copolymer also may occur as a result of intermolecular transfer of free valency from monomer M1 of one macromolecule to comonomer M2 of the other macromolecule. It is obvious that probability of such transfer will depend on the flexibility of copolymer chain. As they showed in works [138, 173] origination of free radicals under thermolysis of copolymers is realized by decomposition of weak CC bonds in macro-chain skeleton. Such bonds may be the end unsaturated bonds [167, 172, 184], overstrained CC bonds which may appear analogously to polymers due to conformation reasons inside of comonomer consecutions [163, 186] or on joint of opposite monomer units, strained inter-block bonds [143]. 1.2.2.5. Origination of kinetic chains

Origination of free valency will be realized by reaction of decomposition of CC bonds inside of monomer block: kdi1 M1M1 o2M1* (12) kdi2 M2M2 o2M2* (13) or by inter-block or comonomer joints: kdi12 M1M2 oM1 + M2 (14) In this case rates of initiation are equal: Wi1 = kdi1 [M1]2, Wi2 = kdi2 [M2]2, and also (15) Wi12 = kdi12 [M1-M2], where kdi1, kdi2, kdi12  constants of CC bond dissociation between monomer units ~11~, ~22~ and in joints of units ~1-2~ correspondingly. It is obvious that the contribution of each reaction into initiation of free radicals under thermolysis of copolymer depends on the nature of weak bonds. Actually, detailed investigation of processes of destruction of a wide set of polymers and rubbers carried out in works [134, 173, 187] showed the dependence of destruction processes on chemical structure of the polymer. Formed radical pairs under thermal destruction or under oxidation may leave "cell" and initiate radical processes or may die in recombination or disproportionation reaction [161163, 212, 213] not originating chains in dependence on chain rigidity. In other words for reaction of radical initiation in copolymers the "cellular effect" is characteristic and this reaction is structurally sensitive. Spatial distribution of radical pairs in the shape of two initiating radicals proceed by diffusion way [161163, 212, 213]. As a result initiation reaction is diffusion-controlled at the stage of leaving of cell by initiating radical. Decomposition of bond between alien monomer units in copolymer chain may be 26

considered in analogous way. Effectiveness of initiation by radicals formed in the joints of monomer units depends on the degree of chain rigidity. It is also obvious that structure parameters determining relaxation properties of copolymer chains (chemical structure, stereoregularity, chain conformation) will influence on cell leaving and consequently on the value of effectiveness of initiation hindering or facilitating relaxation of "cell walls". One more mechanism of origination of free valency in copolymers is connected with participation of low-molecular radicals r* [214]. If in one of oxidable comonomers blocks in copolymer chain the oxidation or destruction products are accumulated in the shape of low-molecular radicals the initiation of kinetics chains of oxidation will occur in the reaction of this r*-radical with any accessible RH-bond of monomer unit, for example by the reaction: kc (16) r*+ M1H o M1* + rH k1 c  r*+ M2H o M2* + rH (17) Reaction (16) or (17) will make more significant contribution into oxidation process in dependence on parameters of physical structure [161, 163, 214]. For realization of initiation of kinetic chains of oxidation in copolymer with the help of r* the time of radical disappearance in the reaction of substitution (16 or 17) should be longer or comparable with the time of its diffusion from oxidable block or zone to bond 1H or 2H. If radical r will disappear in reaction (16) then time necessary for consumption of radical is equal to: t1 = (kc[1H])-1 [141], and in the case of reaction (17): t2 = (k1c[2H])-1. From the other hand the time necessary for diffusion transfer of lowmolecular radical r* (tr) may be expressed from the formula for diffusion coefficient [161]: Do= O2 (6tr)-1. In given case O is the distance on which r* radical should transfer from comonomer M1 to reach the bond M2H and initiate free valency M2*, or from monomer M2 to reach the bond 1 and initiate free valency M1 . It is obvious that initiating of free valency will proceed in the case when: O12 (6D1)-1 > (kc[1H])-1 or O22 (6D2)-1 > (k1c [2H])-1 Thus, initiating ability of low-molecular radical in reaction with any of comonomers will depend on the ratio between transport properties of copolymer and parameters of chemical reaction including effective constants kc, k1c of rates of reactions between low-molecular radical and 1H, M2H-bonds and also concentration of monomer units. The parameters of physical diffusion in their turn depend on segment mobility and free volume in comonomer micro-blocks or associates. Parameters of chemical reaction depend on the nature of comonomers, on their distribution along the chain (chemical structure and chemical composition), and also in conformation of macromolecule and its dynamics. For prevailing of one of the reactions it is necessary the rate of diffusion of low-molecular radical r* originated in the block of more active comonomer for example ~11~ to be higher than rate of reaction between 1H and r* [93]. In this case the distance on which r* radical may be transferred to reach M2H bond and originate free valency 2* should be lower: O1 = Do11/2 (6k c[M2H])-1/2. The probability of origination of kinetic chains of oxidation will be determined by the ratio between O1 and O2 which is equal to [93]: O1 Do1/2(k1c[M2H])1/2 O2 Dco1/2 (k c[M1H]) 1/2 We should note the particularities of origination of kinetic chains in crystallizing copolymers. The presence of crystallites may lead to reduction of diffusion coefficient of macro- and lowmolecular radical and increase of diffusion way, strengthening of "cellular effect". The particularities of chain structure of copolymers, heterogeneity of chemical structure and composition, and the presence of non equal in reaction ability monomer units will reflect also on the stage of origination of free valency of copolymers. Heterogeneity in copolymer leads to heterogeneity in kinetics of radical reactions originating in it. 27

1.2.2.6. Continuation of kinetic chains

In copolymer continuation of kinetic chains of oxidation is realized by connection of oxygen by radicals as a result of which hydroperoxide radicals are formed: (18) M1* + O2 o M1OO* M2* + O2 o M2OO* (19) And their further interaction with monomer units leads to formation of hydroperoxides: (20) M1OO*, M2OO* + RH o M1OOH, M2OOH + R*, Accumulation of hydroperoxides under thermal oxidation of copolymers was found in all copolymers where hydrocarbon groups presented [136, 149, 150]. There is the "cellular effect" and the yield of radicals V is less than one at the stage of chain transfer as well as at initiation stage [162]. The necessary condition for transfer of free valency on RH-bond of one or other comonomer units is that macro-radical with this bond should fall into one "cell" providing necessary for chemical act turning and reorientation of particles [145, 212]. The last ones depend on segment mobility of chains and free fluctuation volume [161, 163]. Chemical and physical heterogeneity in copolymers [215, 216] lead to localization of oxidation in zones, blocks, etc. [132, 138, 148, 170]. As a consequence of localization of oxidation in blocks of copolymers intra-molecular reactions of continuation of oxidation kinetic chains will play essential role [93, 163, 217, 218]. kp11 M1OO* + M1Ho M1OOH + M1* (21) kp22 M2OO* + M2Ho M2OOH + M2* (22) Revealing of "the effect of neighbor" and inter-chain effects in copolymers should lead to considerable contribution of cross reactions. In such case transfer of free valency may be realized intra-molecularly: kp12 M1OO* + M2H o M1OOH + M2* (23) kp21 (24) M2OO* + M1H o M2OOH + M1* or inter-molecularly: kcp11 M1OO* + Mc1H o M1OOH +Mc1* (25) kcp12 M1OO* + Mc2H o M1OOH + Mc2* (26) kcp21 M2OO* + Mc1H o M2OOH + Mc1* (27) kcp22 M2OO* + Mc2H o M2OOH + Mc2* (28) In solid polymer reactions of alkyl radicals with neighbor RH-bond: RH+R'*oR*.+R'H compete with interaction of alkyl radicals with oxygen (18, 19) [93, 161, 209, 210, 218]. This reaction that transfers free valency along the macro-chain without formation of ROOH in rubbers is also observed [132, 134]. Obviously given reactions are also possible in copolymer for example by the following scheme: M1* + Mc1H o Mc1* + M1H (29) M2* + Mc2H o Mc2* + M2H (30) (31) or: M1*+ M2H o M2* + M1H M2* + M1H o M1* + M2H (32)

28

Reactions (29, 30) may proceed in block-copolymers or polyallomers in separate microphases or phases, and reactions (31, 32) in alternating and statistical copolymer and obviously the effect of neighbor will promote namely the two last reactions. It is important that in copolymer the reactions (31, 32) may lead to initiating and inhibiting effect. If the activity of one of radicals for example M1 is higher than of the second one for example M2, then reaction (29) will lead to reduction of M1H and consequently to M1* death, but at that the oxidation process will be initiated in less active comonomer M2 (inhibiting action in relation to M1 and initiating in relation to M2). These reactions are of great importance also since they promote facilitation of cell leaving by radicals. Except chemical relay-race the transfer of free valency in polymer and rubbers is realized by physical diffusion of low-molecular radical [93, 134]. As it is known, the process of copolymers oxidation is accompanied by accumulation of low-molecular radicals; consequently transfer of free valency in copolymers may be realized by physical diffusion of low-molecular radicals by reactions (16, 17). The combined mechanism is known at which connecting of particles occurs by alternation of elementary acts of physical diffusion and chemical relay-race [93, 161, 209, 210, 218]. Obviously for copolymers the combination of two mechanisms of free valency transfer will be relevant since it is caused by difference of chemical nature of comonomer units. It is also important to note that in accordance with the theory of Plate et. al. [179] about interchain effects in copolymers chains interacting with oxygen the mutual diffusion of various segments is possible. This fact may also influence on radicals yield and formation of ROOH. It is known, that coefficient of physical diffusion of low-molecular radical and also the rate of chemical relay-race depend on segment mobility of macro-chains and free volume [161, 163, 179, 200, 201, 219]. It is also known that the change of ratios of rates of various competing reactions depends on the ratios of diffusion and kinetic regimes. Limiting stages are often changed and physical meaning of kinetic constants corresponding to these stages is also changed. Kinetic non-equivalence of active sites is also possible [161-163, 178, 179, 188]. The reasons of kinetic non-equivalence are differences in conformational states of particles, in structure of their environment, in spatial disposition of reacting particles, in molecular mobility. 1.2.2.7. Termination of kinetic chains

Termination of kinetic chains in copolymer may be realized by classical reactions of quadratic termination, for example: kt11 2M1OO*oinactive products (33) kt22 22OO*o inactive products (34) and in cross reaction: kt21 (35) 2OO*+1OO* oinactive products Free valency appeared in comonomer and leaved the "cell" may initiate radical reactions of chain continuation. However in dependence on nature of comonomers the formed radicals may participate in processes competing with oxidation of hydrocarbons radicals, for example in depolymerization and destruction of copolymer chains [136139]. At that the chain process of hydrocarbons oxidation may be blocked. Practically free valency leaves oxidation process. Analogously, in copolymers the reactions of cyclization and cross-linking proceeding by radical mechanism are accompanied by consumption of free valency which may participate in oxidation of hydrocarbons radicals. Obviously, the mentioned reactions lead to termination of kinetic chains of oxidation namely to linear termination. For example, if free valency of monomer M1 is transferred to monomer M2 and participates in structurization reactions then it may be presented as follows: k12 29

(36) 1OO* (M1*)+M2H oinactive products k2 2OO* (M2*)+M1H oinactive products (37) k12 or M1OO*+M2H o[M2*+ M1OOH]oM2-O-M1 (38) in the case of depolymerization: k1,k2 1OO*,2OO* o M1, M2 + R*z RO2*. Linear termination of kinetic chain with participation of radical M1 or M2 will be observed in both cases. The rate of termination will be equal to: Wter = k12 [1OO*] (39) Wter = k21 [2OO*] (40) Moreover in copolymer as a result of exchange by free valency between M1 and M2 the radical may transfer from flexible chain comonomer to rigid chain one, where the "cell effect" is more clearly expressed, then the radical may be temporarily stabilized or died in recombination reaction. In the case of transfer of free valency (kinetic chain of oxidation) for example from comonomer M1 to comonomer M2 which is subjected to depolymerization or cyclization, i.e. to the reactions terminating kinetic chains of oxidation or to rigid chain fragment of chain ~M2M2M2~, comonomer M2 will fulfill inhibiting or blocking role in relation to M1 [93]. In this case the length of kinetic chain of oxidation of copolymer is [93]: (41) Under oxidation in block: Q = 1+ ª kp1[M1H] º ¬ kp2[M2H] ¼ and under oxidation in statistical or alternating copolymer where cross reaction predominate [177]: Q = 1+ ª (kp12[M1O2 *][M2H]+kp21[M2O2 *][M1H]) º (42) ¬ kt12[M1O2*][M2O2*] ¼ Obviously the lengths of kinetic chains of oxidation will be determined by lengths of consecutions of comonomer units. Actually, in works [138, 149] they observed such dependence and with the decrease of length of block the length of kinetic chain was decreased. With the rise of blocking effect the length of kinetic chain of oxidation is also decreased. 1.2.2.8. The stage of branching of kinetic chains

The first valence-unsaturated product of copolymers oxidation as well as for polymer and rubbers is hydroperoxide. ROOH in copolymer is found in a lot of works devoted thermal oxidation [148150, 170]. As it is known, if at the stage of interaction of peroxide radical with comonomer units the intra-molecular reaction prevails, then usual block hydroperoxides are formed [161163]. Under inter-molecular interaction of hydroperoxide radicals with monomer units the single hydroperoxides predominate [161163]. The ratio between contents of block and single ROOH and also the length of hydroperoxide block in copolymer depend on the structure of its macro-chain. The nature of comonomer, its content, block structure of copolymer chains influence on physical-dynamics parameters of copolymer [219], consequently on the mechanism of formation and properties of hydroperoxide. The character of transfer of free valency of copolymer depends on mobility of its chains or segments [161, 163] and also on comonomer unit nature. For example introduction of propylene [150] and allene units having tertiary carbon atoms in the main chains into polyethylene chain with the rise of their content leads to localization of oxidation in these blocks and consequently to increase of part of block hydroperoxides. Segment mobility of copolymer chains influences on such parameter as yield of hydroperoxide per absorbed oxygen [162, 163, 204, 219]. Its reduction leads to the decrease of D and in solid polymer this value is lower than one. In block copolymers the competition of structurization and oxidation processes is of great importance that leads to localization of oxidation in blocks, more active in relation to oxygen comonomer that increases lock character of hydroperoxide with the rise of 30

length of such comonomer consecution. In its turn the structure of hydroperoxides determines kinetics of decomposition and consequently the effectiveness of the stage of degenerated branching of kinetic chains. In thermal oxidation of multi-component systems the cross reactions of degenerated branching of kinetic chains play significant role [80, 93, 220]. kd11 1OOH + 1H o1O* + 1* + H2O o 1* (48) kd22 2OOH + 2H o2O* + 2* + H2O o 2* (49) kd21 (50) 2OOH + 1H o2O* + 1* + H2O o 1* kd12 1OOH + 2H o1O* + 2* + H2O o 2* (51) Except bimolecular decomposition of ROOH (reactions 4851) the essential contribution into thermal oxidation of copolymers may be made by monomolecular decomposition by the following reactions: kd1 1OOH o 1O* +*OH (52) kd2 2OOH o 2O* + *OH (53) There is dependence of hydroperoxide yield and their stability on structure of copolymer and their composition. For example for ethylene copolymers with propylene and ethylene with vinyl chloride in work [150] they obtained kinetic curves of decomposition of polyethylene hydroperoxides and copolymers of ethylene with propylene and ethylene with vinyl chloride. The values of constants of rates of mentioned hydroperoxides decomposition obtained by authors demonstrate higher stability to thermal destruction of copolymers hydroperoxides in comparison with PE hydroperoxide [150]. However in PE copolymers with allene [149] the opposite effect is observed. With the rise of content of the last one the constants of decomposition rate, initiation of ROOH and the kinetic parameter of oxidation k2[RH](k6)-1/2 are increased in comparison with homopolymer PE. According to modern conceptions [162, 214] the rate of oxidation of PO is determined by hydroperoxide concentration: Wo2 = [ROOH]1/2+b[ROOH], (54) where = kp (Gkd/kt)1/2, b = V kd [RH]; Kd  the constant of ROOH decomposition rate; G  the probability of degenerated branching of kinetic chains; G = DV, V  the yield of radicals from cell; D  the yield of hydroperoxide per mole of absorbed oxygen. Thus the rate of polymers and copolymers oxidation also depends on concentration and constant of ROOH destruction. In its turn concentration of ROOH depends on HP yield per mole of absorbed oxygen. For determination of hydroperoxides yield (D) in work [150] the formula was used considering thermal destruction of hydroperoxide of polymer during oxidation: D = kd[ROOH]max (55) (Wo2)max where kd  effective constant of hydroperoxide decomposition rate; [ROOH]max  its maximum concentration; (Wo2)max  the rate of sample oxidation at the moment pf reaching of maximum concentration. Parameters of formation and destruction of hydroperoxides of PE, copolymers of ethylene with propylene (CEP) and ethylene with vinyl chloride (CEVC) (2 = 300 millimeters of mercury, 130 ): kd,[ROOH]max, (Wo2)max and values of "D" obtained with the use of expression (55) allow 31

authors of [150] making conclusion about determinative role of hydroperoxide yield in the change of reaction ability of copolymers in comparison with pure PE. They showed that the value "D" is significantly lower than one, however under oxidation of copolymers of ethylene with propylene "D" is increased with the rise of propylene units, and under oxidation of ethylene copolymers with vinyl chloride it is decreased with the rise of vinyl chloride units content. As a reason of low yield of hydroperoxides under oxidation of polymer they proposed [150] that during the oxidation radical RO2* attacked one of neighbor monomer units forming hydroperoxide group and radical R*: O-O H OOH _ _ _ ~CH - + -CH-o - CH + -HC* The radical R* (-HC*-) is close to just formed hydroperoxide group and may either attack this group by scheme: OOH O* OH _ _ _ ~CH- + -HC*- -o -HC- + -HCor to react with oxygen or neighbor monomer groups. At that the reaction site moves off the group OOH that leads to its stabilization. Oxidized polymer represent the set of hydroperoxide groups OOH and groups CO and OH formed under their decomposition distributed in definite way along polymer substance [162]. Change of polymer composition influences not only on composition near OOH groups, but also on their mutual disposition. Due to this reason introduction into polymer of various (as more, so less reactive) units leads in given case to the rise of stability of hydroperoxides (to decrease of kd). This fact was explained by increase of average distance between groups OOH under introduction into polymer of alien units with the help of reaction R*+RH. Increase of this distance hinders chain decomposition of hydroperoxide groups which makes significant contribution into sum reaction of hydroperoxide decomposition. In other words the chemical nature of comonomer units is revealed, to be more correct their activity in relation to oxygen. That is why under substitution of one of CH2 groups neighbor to radical CH* by more reactive group  (3) the probability of reaction R* + RH is increased and under substitution by less reactive group –l* it is decreased. So, in the first case the part of R* radicals participating in chain decomposition of hydroperoxides will be decreased and in the second  increased. The value "D" representing the ratio of a number of groups OOH formed by reaction RO2* with RH to the number of groups remaining after removal from it of reaction site in the first case will be increased, and in the second  decreased. In this connection we should note the essential importance of secondary reactions between oxidation products. The important factor is significantly larger contribution of secondary reactions in copolymer in comparison with homopolymers [93]. It is promoted by localization of oxidation for example in blocks [132, 138, 148, 150, 170] due to blocking effect by neighbor comonomers or in separate more "soft" structure units due to blocking by rigid segments of copolymer. It is obvious that the first variant will influence to a greater extent on block copolymers, the second  on statistical. Both cases may lead to reaction between ROOH and other oxidation products. For example thermal oxidation of copolymers may be accompanied by reactions of cross-linking and cyclization which are realized via oxygen bridges or ether bonds with participation of alcoxyradicals and functional groups. So, in the ethylene-propylene copolymer [150]: ~CH2-CH-CH2~ ° O ° O ° ~CH2-CH-CH2~ 32

In the copolymer of polyethylene with methylmethacrylate the cross-linking via ether groups occurs: ~CH2-CH-CH2~ ° O ° C=O ° ~CH2-CH-CH2~ and cyclization ~COOCH3  \ O C=O ° ° O OCH3 \ H Transfer of free valency from one comonomer to another in copolymer may lead to the change of mechanism of radical reaction. In copolymer the processes of radical decomposition and cross-linking reactions compete with formation of hydroperoxide [187, 194]. Competing processes may not only change the mechanism of radical reactions and reduce the yield of ROOH but also to change its structure and consequently properties. Realization of these processes will depend on chemical nature of comonomer units and structure of copolymer chain in amorphous polymers and also on permolecular structure in crystallizing copolymers. One of competing reactions of ROOH formation is decomposition of peroxide radical. As they showed in works [161, 162] the decomposition of peroxide radical in copolymer might occur with formation of alkyl radical and lowmolecular substances, for example by the reaction: OO* ° ~CH2-CH2-CHX-CH2 -C- CHX-CH2~ o ~CHX-CH2* + CHXO + CHOCHX~ Under interaction of peroxide radical with double bond the polymerization with formation of dialkylperoxide group and alkyl radical occurred: ~CHOO* + - CH = CH - o ~CH-O-O-CH ° *CH~ In the case when one of comonomers is unsaturated compound the oxidation of copolymer will be accompanied by reactions of direct consumption of ROOH groups [132]. These are reactions of cross-linking and cyclization of chain molecules which may be realized between hydroperoxide group and double bond with formation of epoxide bond and hydroperoxide deactivation: O / \ ROOH + - CH=CH- o- HC - CH - + ROH The changes in ratios of rates of various competing reactions also depend on ratios of diffusion and kinetic regimes. When limiting stage is change the physical nature of kinetic constants is also often changed. In copolymer it influences on mechanism and kinetics of thermal oxidation and first of all on the contribution of competing with it processes.

33

It is obvious that regularities of influence of structure factors on oxidation may be general for copolymers with systems having the contact between various components, i.e. with compatible blends or in the region of meso-phase (in the inter-phase layer) of partially compatible blends. The exclusions may be effects caused by permolecular structure and diffusion properties. All of them may essentially influence on incompatible blends. In the last ones the role of structure factors in oxidation process may be changed in comparison with compatible systems. In such systems the structure of components will have more significant meaning. Thus, kinetic and mechanism of processes in heterogeneous and heterophase systems depend on the following factors:  competition of radcial reactions of oxidation with processes of structurization (cross-linking or cyclization), destruction and depolymerization in dependence on componentns nature and their reaction ability;  contribution of cross reactions proceeding between components of various nature, on migration of free valency along polymer chains or between macro-chains;  on the mechanism of hydroperoxides decomposition;  on competition of reactions of alkyl radicals with peroxide radicals and decomposition of the last ones;  on the contribution of secondary reactions and processes proceeding with participation of double bond;  on revealing of catalytic effect. Structure parameters of systems will:  determine localization of oxidation in zones having friable structure, high segment mobility and lead to secondary reactions;  control diffusion processes and in such way promote the change of ratios between constants of rates of competing reactions;  determine the role of low-molecular radicals in oxidation process including every elementary stage. The contribution of every of mentioned above factors will depend on compatibility of components and their chemical activity in relation to oxygen.

34

Chapter 2. Structure effects in thermal oxidation of polyolefines The correlation of homopolymers' morphology with their reactivity in relation to oxygen may be presented by the following scheme [159, 161-163, 221-224]: MORPHOLOGY OF POLYMER

PERMOLECULAR STRUCTURE

DISTRIBUTION OF REAGENTS Cloc. > Caver.

Structurallyorientational correspondence

MOLECULAR MOBILITY

Diffusion of reagents

CONFORMATIONAL SET

Probability of intramolecular reactions

The direct correlation between initial structure of polymer and kinetics of oxygen absorption is consequent from this scheme. However thermal oxidation is complex process including chain oxidation of hydrocarbon radicals, destruction of macro-chains and structure formation (cross-linking, cyclization) [153, 154, 160-162, 164, 166, 167, 210, 220-224]. Thermal oxidation is accompanied by structural-physical processes leading to structure change (structural reconstructions) under the action of high temperature [221]. The mechanism of these processes will depend on polymer's morphology and in its turn will influence on oxidation kinetics. It is important that in polymer blends they may change the structure not only of components but of mixture in the whole, influence on structure of interface (or bounder) and as a result they may lead to the change of kinetics of competing reactions characteristic for homopolymers, change the mechanism of oxidation. The presence of various in activity reaction RH-bonds in mixture components will influence on the character of structural reconstructions proceeding in them under thermal oxidation. Structural effects mentioned above may be strengthened or weakened in blends in comparison with homopolymers in the presence of inter-phase interactions. Thus, comparing of differences in revealing of structural effects for homopolymers and components of polymers blends is one of the ways of establishing of character of influence of blend's components structures and inter-phase layer on oxidation process. Comparing of structural reconstructions accompanying blend oxidation with the composition of products also allows getting the most exact conception about the role of blend's morphology. The number of works is devoted to annealing of polymer crystallites in vacuum and on air [160, 221-226]. They showed in these works that the effect of high temperature may lead to perfection of crystallites structure, rise of temperature and melting heat, at the same time at long high temperature effect the destruction of chains occurs and crystallites are decomposed [225]. There are the data demonstrating the influence of annealing temperature on relaxation parameters in polymer which allow concluding that there is significant change of structure of amorphous regions [227, 228]. However there are practically no data characterizing reconstructions occurring in amorphous regions of polymer under the action of thermal oxidation. At that the amorphous regions to a greater 35

extent determine the particularities of oxidation radical reactions kinetics developing in them. That is why the given Chapter is devoted to investigation of regularities of structure changes under oxidation of pure polymers being the components of blends, studying of mechanisms of structure reconstructions accompanying thermal oxidation, their dependence on morphology of polymer. With the aim of revealing of the role of structure (conformational set) of polymer macro-chains we also studied structure reconstructions, accompanying oxidation of oriented samples of PP with various extract degree. 2.1. Structure effects accompanying oxidation of isotropic polypropylene samples 2.1.1. The regularities of change of structural parameters during oxidation process of small-spherulite samples and polypropylene with various molecular structure

The number of film samples of isotactic PP with various molecular-mass characteristics obtained by pressing at hardening conditions was studied. Among total number of hardened polymers the samples PP1 and PP2 are mostly differed by the character of structural changes. Their analysis allows marking out the main structural effects which may be observed under PP oxidation. 2.1.1.1. Structural parameters of non-oxidized polymers

Small-spherulite samples PP1 and PP2 (results of optical microscopy are presented in Figure2.1) have various permolecular structures. In PP1 with higher Mw the crystallites in Dmodification are formed [229], in PP2  in "quenched" or mesomorphic modification [230, 231] (diffraction pictures in large and small angles for PP1 and PP2 are presented in Figures 2.2 and 2.3 accordingly; the data obtained from them are presented in Table 2.1).

Figure 2.1. The microphotographs of surfaces of films of PP1 (rapidly cooled) (a) and PP2 (rapidly cooled) (b) (microscope "Polam P112" in polarized light).

36

Figure 2.2. Large-angle difractograms of PP1 (a) and PP2 (b) samples initial ones (1) and oxidized for 30 (2) and 160 (3) minutes at 130qC and PO2 = 150 millimeters of mercury.

37

Intensity of small angle reflex, f (standard units)

28 80 56 48

17 94 57 68

Sample

Initial Annealing for 30 min Oxidation for 30 min Oxidation for 160 min

Initial Annealing for 30 min Oxidation for 30 min Oxidation for 160 min

11,7 17,5 17,5 18,4

13,3 15,5 15,5 16,3

Large period, nm

Size of crystallites, nm

58 63 63 63

55 66 66 66

Index of crystallinity, % (X-ray analysis)

PP "Moplen" 6,0 7,3 5,2 10,3 5,2 10,3 5,6 10,7 PP of Russian production 4,9 6,8 6,5 11,0 6,5 11,0 6,8 11,6

Size of amorphous interlayer, nm

50-54 60-62 58-61 53-64

45-58 61 59 63

Degree of crystallinity, % (DSC)

2,9-3,1 5,0 -

1,6-1,8 4,0-4,6 -

D840 D1300

4,9-5,4 4,5 -

2,1-2,5 3,8-4,2 -

D975 D1300

Content of straightened conformers

0,9-1,3 1,5 -

1,7-2,0 0,9-1,4 -

D1155 D1300

Content of coagulated conformers

Data of IR-spectroscopy

Table 2.1. Structural parameters of initial, annealed in vacuum and oxidized samples of PP1 and PP2.

38

More perfect and large crystallites of PP1 in comparison with PP2 are characterized by higher melting temperature (higher melting temperature in the maximum of melting peak on DSC thermogram (Table 2.2)). Table 2.2. Thermophysical parameters of oxidized samples of PP1 and PP2. Conditions: Tox. = 130°C, 2 = 150 millimeters of mercury. DSC data Sample

Duration of oxidation

0 5 23 30 PP1 40 85 120 160 0 25 30 45 PP2 60 100 120

' mel.1 ' mel.2 (J/g) 79,1 80,9 71,4 77,4 89,0 73,0 106,3 78,5 105,6 75,5 97,3 74,9 81,0 64,4 94,8 78,8 74,4 70,7 85,6 86,0 65,0 68,0 74,5 78,8 77,8 65,2 69,7 68,8 70,0 71,0

160

75,5

cr.1

cr.2 ( ) 106,8 108,4 107,4 107,2 106,0 106,0 107,4 107,4 107,2 107,0 106,8 106,8 104,2 104,0 104,0 104,5 109,4 109,2 105,8 106,0 103,0 103,0 103,2 104,2 102,4 102,0 -

'Qcr.1 'Qcr.2 (J/g) 77,0 87,1 81,4 89,4 83,5 84,5 82,5 73,6 82,5 80,0 94,7 87,2 95,6 98,8 96,0 84,7 85,8 90,0 90,0 97,9 92,0 93,0 82,2 66,8 77,2 68,9 -

102,3

68,5

Cryst. D(') % 58,2 59,5 52,5 57,0 65,5 53,7 78,2 57,8 77,7 55,5 71,6 55,1 59,6 47,4 69,8 57,9 54,7 52,0 63,0 63,3 47,8 50,0 54,8 58,0 57,2 48,0 51,3 50,6 51,5 52,2 55,6

Cryst. D('Q) % 56,7 64,1 60,0 65,8 61,4 62,2 60,7 54,2 60,7 58,9 69,7 64,2 70,3 72,7 70,6 62,3 63,0 66,2 66,2 72,0 67,7 68,0 60,5 49,2 56,8 50,7 50,4

Notes: '+mel and 'mel. , cr. , cr. are primary and secondary heats and temperatures after recrystallization in the maximum of peaks of melting accordingly. 'Qcr.1 and 'Q cr.2 are the heats of primary and secondary crystallization; D(') and D('Q) are the degrees of crystallinity determined by heat of melting and heat of crystallization correspondingly. 1

2

1

2

PP1 and PP2 having close indexes of crystallinity are significantly differed in structure of amorphous regions, conformational composition of through-pass chains (the last one was determined by IR-spectroscopy method, the data were presented in Table 2.1). Inter-crystallite throughpass chains of PP1 are characterized by high content of coagulated conformers. Analogous chains of PP2 are enriched by straightened conformers.

39

Difractograms of X-ray SA of both samples demonstrate strong central small angle scattering (s | 0,025nm-1) caused by heterogeneities of electron density [232] (Figure 2.3).

Figure 2.3. Small-angle difractograms of PP1 (a) and PP2 (b) samples initial ones (1) and annealed in vacuum at 130qC for 30 min (2), oxidized for 30 (3) and 160 (4) min at 130qC and PO2 = 150 millimeters of mercury.

Approximation of the initial part of curve of scattering by Ginue formula allows estimating the radius of inertia of these heterogeneities, Rg basing on sphere form R2g = 3/5R2 [232]. Radius of heterogeneities was ~ 15-18nm. Comparing of crystallinity index from X-ray SA (it determines volume of crystallites inside of large period) with crystallinity degree obtained by DSC method (Table 2.1) showed that the part of amorphous regions might be formed by trough-pass macrochains connecting neighbor spherulites (namely these regions may contain fluctuations of density with size ~15-18nm revealing on small angle difractogram). The part of such amorphous regions in both polymers is from 4 up to 10%. 40

2.1.1.2. Change of polymers structure during oxidation process

In PP1 and PP2 during the first 30 minutes the annealing occurs leading to perfection of crystallites structure. In the case of PP1 crystal reflexes become narrower and more clear, the intensity of amorphous halo is decreased (Figure 2.2a). Mesomorphic form of crystallites of PP2 transforms into D-modification (Figure 2.2b). For both polymers thickness of crystallites is increased and the degree of crystallinity is increased, however for PP1 this fact is less clearly expressed than in the case of PP2 (this fact is followed from analysis of position of small angle reflexes on angle scale (Figure 2.3a, b; Table 2.1)). The structure of amorphous regions and conformational composition of trough-pass chains are changed. During the first 30 minutes oxidation leads to partial decrease of intensity of the first small angle reflex (at s | 0,025 1/nm) for PP1 (Figure 2.3a) and to it complete disappearance for PP2 (Figure 2.3b) that indicates on corresponding partial or complete destruction of trough-pass chains in inter-spherulite amorphous regions. At that intensities of the second small angle reflex (s t 0,05 1/nm) are increased (in the case of PP2 more essential than for PP1). With the rise of oxidation duration in the case of PP2 the upward trend of reflex intensity is observed, and for PP1 the downward trend is observed, whereas sizes of crystallites and amorphous interlayers are practically not changed. Since the intensity of this reflex depends on difference between densities of crystallites and inter-crystallites amorphous interlayers 'U2 = (Ucr-Uam)2, the rise of reflex at the initial stage of oxidation may be caused by the rise of quantity and density of crystallites. However comparison of intensities of mentioned reflexes of slightly and deeply oxidized PP1 and PP2 and also of their crystallite parameters which are not changed with the depth of oxidation shows that under polymers oxidation the change of intensity of small angle reflexes is caused by the rise of densities of amorphous regions for PP1 and by decrease for PP2. This phenomenon occurs as a result of change of molecular structure of interlamelar interlayers. Kinetic curves of chain content change in limit straightened conformation during oxidation process of both polymers are presented in Figure 2.4a, b (the data were obtained by IR-spectroscopy). It is obvious from Figures that with the rise of oxidation duration for PP1 the concentration of straightened trough-pass chains in interlamelar interlayers is increased (the intensities of IR bands at 975 and 460 cm-1 are increased) (Figure 2.4a), and for PP2 it is decreased (intensitied of mentioned bands are decreased) (Figure 2.4b). Structural reconstructions may be caused by the influence of high temperature and oxidation process. Comparison of data of X-ray SA of oxidized samples of PP1 and PP2 and of samples annealed in vacuum at the same temperature showed that changes of crystallites structures were connected with both annealing and oxidation process. This process significantly influences also on the structure of amorphous interlayers (Figure 2.3, Table 2.1). Annealing of PP1 and PP2 in vacuum leads to the increase of crystallinity degree, sizes of crystallites and of large period. However on the small angle X-ray photograph the intensities of the first reflex relating to inter-spherulite amorphous interlayers are not changed. Intensities of the second small angle reflex of annealed samples are essentially higher than for oxidized ones since annealing increases density of crystallite and decreases it for amorphous regions.

41

D D130

D D130

a

0

b

0

ox, min

Figure 2.4. The change of content of limit straightened trough-pass chains in crystal (band at 840cm-1) and amorphous (intensities at 975 and 460cm-1) regions during oxidation of: PP1 (r/c) (a) and PP2 (r/c) (b). Tox = 130qC, PO2 = 150 millimeters of mercury.

Thus, the mechanism of structural reconstructions in polymers under their oxidation essentially depends on the interaction of RH-bonds of macro-chains with oxygen. As a result of oxidation of PP1 and PP2 the DSC thermograms are changed in different ways. In the case of PP1 already after 20 minutes of oxidation instead of one peak of melting the lowmelting shoulder is revealed and the second peak shifted to the high temperature region is expressed (Figure 2.5). Repeated melting of oxidized PP1 after recrystallization leads to disappearance of both low temperature shoulder and high temperature peak (Figure 2.5a). The value of melting enthalpy is significantly decreased after remelt (Table 2.2), and Tmel in the maximum of peak of oxidized sample is shifted to the low temperature region in comparison with non-oxidized one (Figure 2.5a). Deep oxidation of PP1 leads to essential shift of peak's maximum of repeated melting to the low temperature region. Endotherms of melting of both non-oxidized and oxidized PP2 are characterized by one peak, temperature in its maximum is increased to the point of 100 minutes of oxidation and then begins to decrease (Figure 2.5b). Oxidation during 40 minutes leads to appearance of low melting shoulder but of less intensity than for PP1. This shoulder disappears after remelt and '+ is practically not changed (Table 2.2).

42

Figure 2.5. The endotherms of melting of samples. (a) initial PP1 (r/c) (1, 1') and oxidized for 5(2, 2'), 30 (3, 3'), 60 (4, 4'), 85 (5, 5') and 160 (6, 6', 6'') min; 15  primary melting, 1'6'  secondary melting after recrystallization, 6''  the third melting, 7  annealing in vacuum for 30 minutes. (b) initial PP2 (r/c) (1, 1') and oxidized for 5(2, 2'), 30 (3, 3'), 60 (4, 4'), 85 (5, 5') and 160 (6, 6', 6'') min; 15  primary melting, 1'5'  secondary melting after recrystallization, 5''  the third melting, 6  annealing in vacuum for 30 minutes. Tox = 130 , P2 = 150 millimeters of mercury.

Initial rise with further fall of Tmel and crystallinity degree observing with developing of PP1 and PP2 oxidation (DSC and X-ray SA data are presented in Tables 2.1 and 2.2) indicate on annealing and decomposition of crystallites correspondingly. Appearance of low temperature maximums on endotherms of melting of slightly oxidized PP1 may point out the presence of crystallites of low temperature modification or the decrease of their sizes as a result of oxidation. However this fact conflicts with X-ray SA data accordingly to which the modifications of crystallites are not changed, and sizes of crystallites are increased. It is known that annealing of crystals leading to the thickening of their solder pads includes the process of additional entering of straightened sections of chains with non-ordered inter-crystal regions into crystallites [233236]. The change of forms of endothermic peaks after oxidation may be connected with the change of crystallites structure, with the change of thermodynamics parameters, or may be caused by conformation transitions in troughpass interlamelar chains [237] which are the precursors of crystallites melting or accompany their intra-chain cooperative melting. In accordance with generally accepted scheme [238] interlamelar interlayers of PP have the structure presented in Figure 2.6.

43

Figure 2.6. The scheme of inter-lamellar inter-layer of isotropic (a) and oriented (b) PP. 1  crystal centers of solder pads, 2  regular folders with depressed mobility, 3  long non-regular loops, 4  coagulated through-pass chains, 5  long ends of molecules, 6  poorly curved trough-pass chains, 7  folders in which the motion is limited by crystallites, 8  completely strengthened trough-pss chains which ends are "fixed" in solder pads, 9  inter-fibrillar trough-pass chains.

Between crystal cores of solder pads (1) and regular folds with inhibited mobility (2) there are macromolecular elements with various conformational mobility lower than Tmelt: long irregular loops (3), coagulated trough-pass chains (4) and long ends of molecules (5) outgoing from crystals; slightly curved trough-pass chains (6) and folds (7) in which the movement is limited by crystals to a greater extent the lower the degree of their coagulation (y = l/h, where h is distance between molecules ends and l is their contour length); straightened trough-pass chains (8) which ends are clamped in solder pads. It is obvious that relaxation processes in long irregular loops and coagulated through-pass chains are realized lower than Tmel of crystallites and can't influence of their melting. Unfreezing of movement in strengthened trough-pass chains fixed by crystals is realized at the expense of change of rotary-isomer composition of these chains via ToGtransirions [233235]. It may occurs with the beginning of melting of the smallest solder pads and will determine relaxation at temperatures lower than Tmel by 1015qC. The most probable reason of appearance of lowtemperature shoulder on DSC curve of oxidized PP1 is coagulation of trough-pass interlamellar chains with the lowest degree of coagulation under unfreezing of their mobility at front surfaces of crystallites. Such chains in oxidized polymers may be formed as a result of slipping of interlamellar chains at crystallites thickening during their annealing at high temperature. Estimation of activation energy of endothermic processes in oxidized samples (ox = 60 min) 44

PP1 and PP2 was carried out with the use of dependence of temperature in maximums of melting peaks on rate of heating of sample by formula [235, 237]: E = (RT1T2 / T2 - T1) ln (v2 / v1), where R is gas constant equal to 8,31 J/mole˜K; T1, T2 – temperatures in maximum of peak at rates of heating v1 and v2 accordingly. For example for scanning rates v1 = 8 and v2 = 32 degree/min on endotherms of PP1 melting they obtained at the first (low-temperature) peak 1 = 415,5 and 2 = 376,4 , at the second peak 1 = 433,4 and 2 = 428,4. Ea were 46kJ/mole for lowtemperature and 428 kJ/mole for moderate peak of melting. In the case of PP2 at v1 = 8 and v2 = 32 degree/min analogous values are 1 = 433,5 and 2 = 429,4 and Ea of melting is 523 kJ/mole. We should note that the value = 46 kJ/mole is characteristic for relaxation conformational transitions proceeding in PP and PE [233236]. Whereas = 428 and 523 kJ/mole by the order of magnitude are equal to the energy of activation of crystallites melting [233236]. And the difference in these values for PP1 and PP2 is obviously caused by various initial structures of crystallites. High-temperature peak of PP1 melting from the one hand may be connected with relaxation processes in extremely strengthened chains of interlamellar regions able to form tension bars analogous to those ones revealing in oriented samples of polyolefines [235, 238240]. From the other hand this peak may belong to high-melting fraction of crystallites appeared as a consequence of crystallization acceleration under the action of oxidative destruction of extremely strengthened interlamellar trough-pass chains. For PP2 conformational transitions are revealed less clearly. The rise of intensity of low-melting shoulder with the rise of oxidation duration of PP1 obviously means the rise of content of strengthened trough-pass chains in inter-crystallites chains. So, due to higher content of coagulated chains they have a possibility to reveal more clearly in PP1 than in PP2. It is obvious from kinetic curves of change of content of extremely strengthened conformers (at 975cm-1) and trough-pass chains in strengthened conformation (460cm-1) during oxidation of PP1 and PP2 (Figure 2.4a, b) that for the first the rise of content of such chains in interlamellar regions passes ahead of the increase of their content in crystal regions. (The rise of intensity of bands at 975cm-1 and 460cm-1 begins earlier than the rise of intensity of crystal band at 840cm-1 (Figure 2.4a).) At the same time for PP2 with the rise of regular chains concentration of crystal regions the decrease of content of strengthened trough-pass chains in amorphous interlayers is observed (Figure 2.4b). This may be connected with including of trough-pass chains from amorphous phase into crystallites with braking of trough-pass chains and realization of ToG-transitions. It is obvious from the totality of DSC, X-ray and IR-spectroscopy data that annealing of PP at temperature close to Tmel leads to appearance of intensive heat movements in polymer macromolecules, and this fact increases the length of molecules folds in crystal regions and consequently the longitudinal sizes of crystallites and creates stresses on trough-pass interlamellar chains. Authors of works [161, 163, 236, 241] observed analogous phenomena during annealing of polyolefines. Heat motions appearing in macro-chains under the action of high temperature create stresses which at first promote conformation GoT-transitions in curved interlamellar chains of PP1 and increase the part of extremely strengthened chains and then promote thickening of crystallites. In PP2 heat motion of macro-chains leads to transformation of "quenchet" form of crystallites into more perfect structure, into D-modification. At that instead of conformation transitions on trough-pass initially strengthened chains of PP2 the local overstresses leading to their destruction may appear. It is obvious that this process is facilitated in acid medium. From this possible increase of density of amorphous interlayers at the expense of rise of content of strengthened chains under the action of high temperature in deeply oxidized PP1 and decrease of density of these interlayers at the expense of oxidative destruction of PP2 follow. However the alternative explanation of observing effect is various rate of accumulation of solid products of oxidation and the rise of their contribution into change of density of amorphous regions. 2.1.1.3. Kinetics of accumulation of nonvolatile products of oxidation

Analysis of nonvolatile products of oxidation of PP1 and PP2 demonstrated quantitative dif45

ferences in contents and rates of accumulation of various functional groups (IR-spectra of oxidized samples are presented in Figure 2.7).

Figure 2.7. IR-spectra in region of OH-groups (14) and >C=O groups (1c4c) of initial (1, 1c) and oxi-

dized for 30 (2, 2c), 45 (3, 3c) and 60 minutes (4, 4c) samples of PP1 (r/c) (a) and PP2 (r/c) (b). Conditions: Tox = 130qC, PO2 = 150 millimeters of mercury. For the first 30 minutes of PP2 oxidation the accumulation of aldehydes and ketones at very low concentration of hydroxyls and hydroperoxides (Table 2.3) is observed, and aldehydes predominate over ketones. During further oxidation the monotonous rise of carbonyl- and hydroxylcontaining groups and sharp decrease between contents of the first and the second ones are observed. In contrast to PP2 for PP1the monotonous rise of both caribonyl and hydroxyl groups concentrations and the ratio between them is observed. In this polymer contents of aldehydes and ketones are close (Table 2.3). After oxidation for 30 minutes for PP1 the rates of accumulation of all products are decreased right up to 100 minutes of oxidation, and then the acceleration of process is observed. We should note the absence of significant differences between moderate concentrations of functional groups of both polymers.

46

Table 2.3. Non-volatile products of oxidation of samples PP1 and PP2 Conditions: Tox. = 130°C, 2 = 150 millimeters of mercury. Sample

PP1

PP2

Duration of oxidation, min 0 5 23 30 40 85 120 160 0 5 25 30 45 60 100 120 160

Data of IR-spectroscopy D1710 D1300 0 0,12 0,13 0,13 0,15-0,17 0,20 0,34 0,54 0 0,1-0,17 0,50 0,5 0,16 0,13 0,31 0,46 0,64

D1740 D1300 0 0,05-0,1 0,05 0,07 0,10-0,15 0,15 0,25 0,37 0 0,17 0,67 0,60 0,1 0,05 0,14 0,28 0,55

D3420 D1300 0 0,1-0,17 0,15 0,15 0,17 0,15 0,18-0,24 0,40 0 0,05 0,10 0,10-0,15 0,10 0,10 0,21 0,28 0,60

D1740 D1710 0 0,4-0,8 0,4 0,5 0,6-1,0 0,8 0,7 0,7 0 1,0-1,7 1,3 1,2 0,6 0,4 0,5 0,6 0,9

D1710 D3420 0 0,7-1,2 0,9 0,9 0,9-1,0 1,3 1,4-1,9 1,4 0 2-3,4 5,0 3,3-5,0 1,6 1,3 1,5 1,6 1,1

It is known that aldehydes groups arise in polymer matrix as end groups formed during chains braking [161, 163]. Together with them ketones are formed in the zone of brake which are the middle products of oxidation of relaxed trough-pass chains [161, 163]. It is known that overstresses appearing on chains during deformation accelerate chains braking and increase the aldehydes concentration [163]. Obviously, high content of aldehydes without hydroperoxides in the beginning of PP2 oxidation indicates on appearance of overstressed bonds in trough-pass inter-crystallites chains subjected to destruction under temperature effect. Comparison of small angle difractograms of initial and oxidized PP2 with the data of IRspectroscopy (kinetic of change of chains conformational composition and products of oxidation) allows assuming that oxidation of this polymer begins from destruction of inter-spherulite troughpass chains possessing extremely strengthened conformation as a result of which we observe disappearance of central reflex on difractogram. Probably these breaks may initiate further oxidation of polymer. There is smaller amount of such chains in PP1 and their influence is expressed less clearly. However, except destruction of inter-spherulite chains the destruction of interlamellar ones is possible. Deformation of the last ones under the action of high temperature is obviously confirmed by the rise of thickness of amorphous interlayer (Table 2.1). The change of conformational composition of trough-pass interlamellar chains is of great importance for development of oxidation in PP1. Their enrichment by strengthened conformers leads to deceleration of accumulation of oxidation products. 2.1.1.4. Kinetics of oxygen absorption

The difference in mechanism of structural reconstructions accompanying oxidation of PP1 and PP2 corresponds to various kinetics of oxygen absorption. Comparison of kinetic curves of oxygen absorption by PP1 and PP2 (Figure 2.8) at common S-shaped from characteristic for chain oxidation with degenerated branching of kinetic chains of oxidation shows essential differences in values of induction periods W and stationery rates of oxygen absorption. The values of W for PP1 and PP2 (duration of the initial stage of oxidation at which noticeable acceleration of reaction doesn't occur) is determined as section of axes of time obtained by 47

cutting off the linear anamorphosis by kinetic curve in parabola coordinates ('1R)1/2 – tox. At 130qC and PO2 = 600 millimeters of mercury the values are W = 70 and 44 min for PP1 and PP2 accordingly. Stationary rates of oxygen absorption (W(stat)R = 1,6˜10-4 and 2,2˜10-4 for PP1 and PP2) and also the values of slopes of linear anamorphosises ("b" = 1,4˜10-4 and 1,8˜10-4 (mole)0,5/kg˜s for PP1 and PP2) characterizing reactivity of polymer testify that PP1 is oxidized slower than PP2.

Figure 2.8. Initial sections of kinetic curves of oxygen absorption by samples of PP1 and PP2 at

Tox = 130qC, PO2 = 150 millimeters of mercury. Parameter "b" is connected with ratio of constants of rates of separate stages of oxidation process by the following expression [161]: '120,5 = (DVk22k4 [RH]3)0,5 L / (8k6) 0,5, 0,5 where '12  change of amount of absorbed oxygen at initial stage of oxidation process when oxidation rate is determined by the rate of accumulation of hydroperoxide and concentration of monomer units remains constant; L  segment that is cut off by linear anamorphosis on axis of time; k2, k6  constants of rate of continuation and quadratic termination of kinetic chains of oxidation; k4  constant of hydroperoxide decomposition rate; D  yield of hydroperoxide per 1 mole of absorbed oxygen; V  probability of degenerated branching of kinetic chains of oxidation. Differences in kinetic parameters of oxidation of studied isotropic samples of iPP may be caused by differences in values of parameter k2/—k6 (reaction ability) or by difference in he mechanism of oxidation due to particularities of their molecular structure. As the analysis of literature data shows [161-163, 242] samples of PP even with various structure and including oriented ones at equal conditions of oxidation have one and the same kinetic parameter of oxidation. At that differences in molecular structure of polymer causing changes in induction periods are conditioned by difference in mechanisms of their oxidation. Difference in rates of oxidation of PP1 and PP2 may be explained from position of "zone" model of oxidation [162, 242]. The chains in coagulated conformation localized in inter-crystal region and between extremely strengthened trough-pass chains may be considered as a "zone" in which oxidation may be developed, as it was made in work [242] 48

(Figure 2.6). In accordance with "zone" model of oxidation the volume of zone is in inverse proportion to time of transfer of free valency from one zone to another ș and consequently to oxidation development [242]. Form the one hand the enrichment of trough-pass interlamellar PP1 chains by strengthened conformers decreases the volume of such zone. Form the other hand this fact leads to deceleration of segment mobility of interlamellar chains and consequently hinders transfer of free valency from zone to zone. In the case of PP2 we observe the opposite picture. Decrease of content of strengthened trough-pass chains as a result of their decomposition leads to increase of zone volume in which oxidation is developed and to the rise of chain segment mobility. As a result oxidation of PP1 proceeds slower in comparison with PP2. Thus, the obtained results allow concluding that there is significant influence of structure of trough-pass chains on processes mechanism causing changes of structure during polymer oxidation. 2.1.2. The regularities of change of structure during oxidation process of isotropic samples of PP with various morphology (large-spherulite and small-spherulite samples) 2.1.2.1. Structural parameters of non-oxidized samples

The use of regimes of rapid (~1000 degree/min) (r/c) and slow (~10 degree/min) (s/c) cooling after pressing of polymers films (PP2 and PP3) differing in parameters of molecular structure allows variation of polymer's morphology, sizes of structure elements and concluding that there is the influence of morphology and permolecular structure on the character of structural reconstructions proceeding during thermal oxidation process. Large (PP2 (s/c), PP3 (s/c)) and small-spherulite (PP2 (r/c), PP3 (r/c)) samples form crystallites with various morphology, the first ones  D-modeification, and the last ones  D-modification in combination with meso-form ("quenched") [229231] (Figure 2.9). More large crystallites of slowly cooled samples PP2 (s/c) and PP3 (s/c) have higher temperatures in maximums of endotherms of melting Tmel in comparison with smaller crystallites of annealed samples of PP2 (r/c) and PP3 (r/c). Crystal regions of small-spherulite samples PP2 (r/c) and PP3 (r/c) have lower in values heats of melting '+mel and crystallization Qcr (Table 2.4) that corresponds to lower degree of crystallinity.

49

Figure 2.9. Large-angle (1, 2) and small-angle (3, 4) difractograms of samples PP3 obtained by rapid (2, 4) and slow (1, 3) cooling after pressing.

50

~10

~10

PP3(s/c)

PP2(r/c)

~1000

~1000

PP1(r/c)

PP3(r/c)

~1000

Sample

PP2(s/c)

Conditions of preparation, rate of cooling, degree/min

11,0 (10,0)

6,3 (4,2)

10,0 (4,9)

10,3 (5,2)

7,5 (5,4)

Size of crystallites, nm (amorphous interlayers, nm)

55-60

53

58

57

58

Crystallinity degree, % (X-ray analysis)

50-54

50-54

59

50-54

54-59

Crystallinity degree, % (DSC)

164,0

162,0

161,6

160,0

159,7

1mel., 

87

72

89

71-79

75

'+mel, J/g

108,1

108,4

108,8

109,4

109,0

cr, 

95,0

72,0

92,0

86,0

86,0

'Qcr, J/g

4,8-5,3

3,4-3,8

3,5-4,0

2,9-3,1

1.6-1.8

D840 D1300

4,0-4,7

4,0-4,4

4,6-5,6

4,9-5,4

2.1-2,5

D975 D1300

Content of straightened conformers

Data of IR-spectroscopy

51

1,5-1,6

2,0

1,4

0,9-1,3

1,7-2,0

D1155 D1300

Content of coagulated conformers

Table 2.4. Structural parameters of initial rapidly (r/c) and slowly cooled (s/c) samples PP1, PP2 and PP3with various molecular-mass characteristics.

Higher concentration of crystal chains in strengthened conformation of spiral 31 corresponds to more perfect structure of crystallites of PP2 (s/c) and PP3 (s/c) in comparison with PP2 (r/c) and PP3 (r/c), and for PP2 this spiral is somewhat smaller than for PP3 (s/c) (intensities of IR-bands at 840 and 998cm-1 indicate to this fact (Table 2.4)). For small-spherulite samples the amorphous regions are enriched by coagulated conformers in comparison with large-spherulite. Inter-crystallite interlayers of PP3 (s/c) have more ordered structure than for PP2 (s/c), its chains to a greater extent are enriched by strengthened conformers (this fact is a consequence of ratio of optical densities of bands D975/D1155 (Table 2.4)). 2.1.2.2. Changes of structure during oxidation of large- and small-spherulite samples of polypropylene

Analysis of DSC and IR-spectroscopy data on structure of oxidized large- and smallspherulite samples of PP and character of change of their structure in the course of oxidation shows that mechanism of structural reconstructions including crystallites annealing and change of conformational composition of trough-pass chains found in small-spherulite samples doesn't change.

Figure 2.10. (a) Change of content of strengthened chains in the course of oxidation of PP3 (s/c) at

Tox = 130qC, PO2 = 150 millimeters of mercury (the depth of oxidation correlates with the rise of intensity of diffuse phone of band at 1275cm-1). Content of strengthened chains was determined by D840/D810 (2) and D975/D1155 (3). (b) Change of content of strengthened trough-pass chains (D975/D1300) in the course of oxidation of PP1(r/c) (1), PP2 (r/c) (2), PP2 (s/c) (3), PP3 (r/c) (4), PP3 (s/c) (5) at Tox = 130qC, PO2 = 150 millimeters of mercury. However for large-spherulite samples of PP in contrast to small-spherulite these processes are significantly decelerated (Figure 2.10a, b). Only at deep stage of developed oxidation the rate of chains decomposition (decrease of content of strengthened conformers) is close to the rate of chains decomposition for small-spherulite samples. At that difference in the change of structure of trough52

pass chains for various large-spherulite samples is not so clear as in the case of small-spherulite. Obviously this fact is caused by more equilibrium structure of polymer, by another structure of trough-pass chains. 2.1.2.3. Kinetics of oxidation of isotropic samples of polypropylene with various morphology

Kinetic curves of oxygen absorption by PP samples with various morphology (r/c) and (s/c) are presented in Figure 2.11. Curves of accumulation of non-volatile products of oxidation are presented in Figures 2.12, 2.13 and 2.14. [O2],

a

Duration of oxidation, min

[O2], b

Duration of oxidation, min

Figure 2.11. (a): Kinetic curves of oxygen absorption by samples PP2 (s/c) (1) and PP2 (r/c) (2) at Tox=130qC, PO2=150 millimeters of mercury. (b): Kinetic curves of oxygen absorption by samples PP3 (s/c) (1) and PP3 (r/c) (2) at Tox=130qC, PO2=150 millimeters of mercury.

53

Figure 2.12. Kinetics of accumulation of functional groups in PP (s/c). Conditions: Tox=130qC, PO2=150 millimeters of mercury.

Figure 2.13. Kinetics of accumulation of non-volatile products of oxidation of PP (r/c) (Buplen). Conditions: Tox=130qC, PO2=150 millimeters of mercury.

54

Duration of oxidation, min

Figure 2.14. Kinetics of accumulation of carbonyl-containing products of oxidation of PP3 (s/c) (1) and PP3 (r/c) (2). Conditions: Tox=130qC, PO2=150 millimeters of mercury.

As it is obvious at the initial stage of oxidation the large-spherulite samples of PP are oxidized slower than small-spherulite, have large induction periods (low initial rates of oxygen absorption). However at the stage of developed oxidation the rate of oxidation of large-spherulite samples is increased in comparison with small-spherulite. Analogous regularities are observed during process of accumulation of non-volatile products of oxidation. Initial rate of accumulation of non-volatile products of oxidation (hydroxyl-containing and carboxyl-containing groups) for large-spherulite samples is lower and at the stage of developed oxidation it is higher than for small-spherulite samples (Figures 2.12, 2.13, 2.14). Analysis of structure of carbonyl- and hydroxyl-containing products of oxidation of samples of small- and large-spherulite PP demonstrates noticeable differences. The content of ketones and acids is higher in the case of products of oxidation of large-spherulite samples (PP2 (s/c) and PP3 (s/c)) in comparison with small-spherulite (PP2 (r/c) and PP3 (r/c)) (Table 2.5). The ratio between optical densities of bands D1715/D3420 relating to ketones / acids and hydroperoxide OH-groups for PP2 (s/c) and PP3 (s/c) is significantly higher that for PP2 (r/c) and PP3 (r/c). At the initial stage of oxidation during the first 15 minutes of oxidation for large-spherulite samples of PP the alcohol OH-groups and unsaturated ketones / acids were also found. This fact is not observed for small-spherulite samples. At the same time at longer oxidation for large-spherulite samples the sharp rise of concentration of oxidation products (carbonyl, and also hydroperoxide and alcohol OH-groups) is observed. For small-spherulite samples the concentrations of carbonyl and hydroxyl groups are monotonously increased during oxidation process. As a result at the stage of deep oxidation (more than 1,5 mole/kg of absorbed oxygen) the average concentration of oxidation products for PP2 (s/c) and PP3 (s/c) is higher than for PP2 (r/c) and PP3 (r/c).

55

Table 2.5. Composition of products of oxidation of PP with various morphology. Conditions: Tox. = 130°C, 2 = 150 millimeters of mercury. Sample

Duration of oxidation, min

D1680/D1300

D1710/D1300

D1740/D1710

D3370/D3420

D1715/D3420

PP1(r/c)

15 30 60 160

0,1 0,1 0,1 0,3

0,1 0,1 0,2 0,5

0,05-0,07 0,1 0,15 0,5

0,9 1,0 1,0 1,1

0,9 0,9 1,0 1,4

25 60 160 25 60 160 15 30 60 15 35 60

0,4 0,2 0,2 0,07 0,1 0,4 0,05 0,1 0,1 0,15 0,2 0,3

0,25 0,1 0,6 0,1 0,05 1,7 0,15 0,15 0,2 0,1 0,2 0,15

1,3 0,3 0,6 0 0,2 1,0 0,1 0,15 0,2 0,05 0,1 0,2

1,4 1,1 1,2 1,1 1,6 1,0 1,0 1,0 0,9 1,0 1,0 1,0

2,1 1,1-1,3 1,1 0,5 2,1 3,7 1,2 1,0 1,0-1,3 1,0 1,5-2,4 2,5-3,5

PP2(r/c)

PP2(s/c)

PP3(r/c)

PP3(s/c)

Higher value of ratio between contents of >C=O and OH groups for large-spherulite samples in comparison with small-spherulite may be conditioned by the following facts:  firstly by shorter kinetic chains of oxidation due to participation of crystallites in radical reaction of termination of oxidation kinetic chains [242];  secondly due to the change of mechanism of transfer of free valency  the rise of contribution of inter-molecular and decrease of contribution of intra-molecular transfer of kinetic chains of oxidation [161163];  thirdly by the difference in character of oxidation localization as a result of which forming hydroperoxides have various chemical structure and possess various initiation ability under thermal decomposition [243];  fourthly, larger crystallites and higher concentration of chains in extremely strengthened conformation may increase diffusion limitations and transport way of oxygen thereby hindering the development of oxidation process [161, 162];  fifthly, in accordance with the data obtained in our work [244], differences in both structure of oxidation products and kinetics of oxygen absorption may be caused by contribution of additional initiation of kinetic chains of oxidation at the expense of decomposition of overstressed trough-pass chains forming in the course of oxidation. For large-spherulite samples such chains are appeared slower than in the case of small-spherulite, so, contribution of their destruction into oxidative process may be revealed at deeper stage of process. Comparison of decrease of content of strengthened chains with accumulation of oxidation products and their structures for large-spherulite samples of PP shows that breakage of overstressed bonds appearing on interlamellar chains under the action of high temperature significantly influences on kinetics of oxidation of these samples. Decomposition of overstressed chains is accelerated in the presence of oxygen catalyzing the process. This fact leads to the rise of maximum WO2. At that the concentration of carbonyl-containing products is increased and end carbonyl groups are appeared. For specification of role of over-stressed chains in oxidation process of PP the correlations between oxidation kinetics, accumulation of non-volatile products and structural-physical process in macro-chains of oriented samples of PP with various degree of extraction were established. 56

2.2. Structural-physical processes in oxidation of oriented samples of polypropylene

Investigation of oriented samples allows more unambiguously considering of the role of structure of polymer chains and over-stressed bonds during oxidation process, considering of character of change of chains structure accompanying oxidation of polymer and establishing of the correlation between structure of oxidized samples, kinetics of oxidation and structure of oxidation products. Orientational extraction leads to orientation of crystals without changing of their morphology (the data of X-ray SA are presented in Table 2.6). Table 2.6. Structural parameters of non-oxidized and oxidized samples of isotropic and oriented PP films Sample i-PP o-PP

Extract degree, O

State

Large period dr5%

0 0 6 6 9 9

non-oxidized oxidized non-oxidized oxidized non-oxidized oxidized

180 185 178 178 187 187

Index of crystallinity ,% 64 62 60 60 60 60

The shape of large angle reflex rings rings strokes points strokes points

Orientation of crystallites and amorphous regions is increased with the rise of extraction degree O (relative elongation = (l-l0) / l0) (Table 2.7) [163, 234, 238, 241, 245]. Table 2.7. Change f intensities of IR-bands in the spectra of isotropic and oriented PP samples processed by boiling concentrated nitric acid Sample

O

i-PP

0

i-PP

0

o-PP

9

o-PP

9

o-PP

9

Conditions before processing after the second processing before processing after the first processing after the second processing

D840 D900

D840 D2727

D840 D1360

D998 D900

D998 D2727

D998 D1360

D1360 D900

D1380 D2727

D1460 D1360

D1460 D2720

3,1

2,7

0,7

3,6

3,1

0,9

4,2

8,8

9,4

6,2

4,5

4,5

1,3

3,7

3,7

1,0

3,6

4,2

5,6

5,6

3,4

2,8

0,8

4,1

3,4

1,0

4,1

17,0

16,4

13,7

3,3

2,9

0,7

3,6

3,2

0,8

4,6

14,7

16,7

14,6

0,54

1,4

1,3

0,7

1,8

0,6

1,3

2,0

3,5

8,9

Endotherms of melting of oPP consist of two covering peaks. At secondary melting after recrystallization the low-melting shoulder disappears, and '+mel and mel of the rest peak are decreased (Figure 2.15).

57

Figure 2.15. Endotherms of melting (1, 1c, 2, 2c) and exotherms of crystallization (1cc3cc) of initial (1, 1c, 1cc) and oxidized at Tox=130qC and PO2=150 millimeters of mercury (2, 2c, 2cc, 3cc) samples of oPP (O = 9). 1, 2  primary melting; 1c, 2c  melting after recrystallization; 3cc – peak of crystallization of oPP after its secondary melting.

This moment testifies to the fact that melting of low-melting shoulder on the primary endotherm of oPP melting is connected with melting of linear systems in amorphous regions of intrafibrillar and inter-fibrillar trough-pass chains (Figure 2.6b) in extremely strengthened conformation characteristic for crystallites of PP. In contrast to the last ones linear systems don't have threedimensional order [234, 237, 238]. Appearance of low-melting shoulder is caused by ToG transitions in intra- and inter-fibrillar trough-pass chains. During the oPP oxidation process lower than crystallites melting temperature the values of large period and degree of crystallinity of polymer are changed insignificantly. Orientation of crystallites is changed noticeable (data of X-ray SA, Table 2.6). Oxidation of oPP leads to the change of structure of polymer chains (according to the IR-spectroscopy data). We should note the particularities of IR-spectra of oPP. Decrease of intensity of bands after processing of oPP by concentrated nitric acid shows that both bands of regularity at 840 and 998cm1 relate to macro-chains of amorphous regions (Figure 2.16a).

58

Figure 2.16. (a) the part of transversely polarized IR-spectrum of oPP in the region of local stresses of trough-pass chains; (b) changes of relative intensities of IR-bands at 998 (1, 5), 840 (2, 6), 962 (3, 7), 955 (4, 8), 1155 (11, 12) cm-1 and content of carbonyl groups (9, 10) during oxidation of oPP with O = 9 at Tox=130qC and PO2=150 millimeters of mercury in isometric (l = const) regime (1-4, 9, 11) and at conditions of free shrinkage (5-8, 10, 12).

Application of these bands allows estimating the change of content of strengthened conformers in inter-crystallites regions of oPP. In a number of works they used not only the band at 1155cm1 , but also at 528 and 460cm-1 for determination of content of coagulated conformers. They also used bands at 945, 955 and 962cm-1 which were the low-frequency shoulders of the band at 975cm-1 (Figure 2.16b). They are sensitive to stresses and relaxation of stresses on trough-pass intra-fibrillar chains [163]. In Wool's work [247] they showed that their intensities were the measure of accumulation of local stresses in trough-pass chains. Analysis of kinetic curves characterizing the change of intensities of above mentioned bands in IR-spectra of samples of oPP with various O during the oxidation process confirmed the dependence of character of physical processes accompanying oxidation on the initial structure of oPP and conditions of oxidation [239, 246]. The change of conformational structures of chains occurring in the process of thermal oxida59

tion of oPP with O = 9 at isometric conditions (l = const) and in the regime of free shrinkage are presented in Table 2.8. Table 2.8. Change of structure (conformational set) and orientation of oriented PP chains (O = 9) under its oxidation in isothermal regime and at conditions of free shrinkage. Conditions: Tox. = 130°C, 2 = 150 millimeters of mercury. Duration Do998 Do840 of oxidaDo900 Do900 tion, min Isothermal regime 3,1 2,5 0 3,1 2,5 30 3,4 2,9 58 3,3 2,9 118 3,0 2,7 188 3,9 2,6 268 Regime of free shrinkage 0 3,7 4,4 15 2,7 3,3 42 3,0 3,9 177 2,8 3,1

Do945 Do900

Do955 Do900

R840

R998

Do1715 Do900

Do3410 Do900

0,6 0,5 0,5 0,3 0,3 0,4

0,5 0,5 0,5 0,2 0,3 0,3

34 34 34 30 26 43

18 18 19 17 18 22

0,1 0,1 0,1 0,4 0,4 0,4

0,1 0,1 0,1 0,3 0,3 0,3

0,6 0,3 0,3 0,7

0,8 0,2 0,1 0,5

37 20 19 22

15 12 12 14

0,1 0,5 0,8 0,3

0,1 0,2 0,4 1,5

As it is obvious from presented data oxidation of oPP in isometric regime at the initial stage leads to the change of rotary-isomeric structures of chains: to the rise of content of strengthened and decrease of content of coagulated conformers, to increase of local stresses appearing on trough-pass chains. The rise of intensities of bands at 998, 840cm-1, decrease of intensity of band at 1155cm-1 indicate to the first fact, and the rise of intensities of bands at 945, 955 and 962cm-1 indicates to the second fact. As far as oxidation is developed the relaxation of stresses occurs and intensities of bands at 945, 955 and 962cm-1 are decreased. Decrease of intensities of mentioned bands coincide with appearance of end groups >C=O. Obviously relaxation of stresses is caused by decomposition of overstressed chains under thermal oxidation. The further isometric oxidation of sample doesn't lead to noticeable change of rotary-isomeric structure of chains. Only at long oxidation one may find the tendency to rise of their regularity. At that the essential concentrations of carbonylcontaining groups are not accumulated. The other picture is observed under oxidation at conditions of shrinkage. Even during the first 20 minutes of oxidation the contents of regular conformers is sharply decreased and of coagulated ones is increased, simultaneously the stresses on trough-pass chains are reduced (the intensity of bans at 945, 955 and 962cm-1 are decreased). The rise of concentration of carbonyl-containing oxidation products corresponds to structural reconstructions. Accumulation of essential concentration of oxidation products in oPP once again leads to appearance of local stresses on trough-pass chains. And as during oxidation in isometric regime, so at free shrinkage conditions (Tables 2.8 and 2.9) their concentration is the higher the higher is concentration of [>C=O]. In other words appearance of stresses is caused by oxidation process. Analysis of change of conformational set and local stresses in sample of oPP with O = 9,5 under thermal oxidation in inert medium and under thermal oxidation in equal regimes (Table 2.9) showed independence of character of structure reconstructions on conditions of annealing at the beginning of process.

60

0,4 0,6 0,6 0,5 0,5

4,6 4,2 4,2 3,8 3,9

3,3 3,8 3,3 3,1 3,2

0 18 43 73 178

0,85 1,4 1,0

1.06

0 130 0 137 0 112

0 140

0 1,0 0 O=6 (II) 1,0 0 O=9 (IV) 1,0 Regime of free shrinkage 0 O=9 (III) 1,0 0,6

0,8 0,9 0,7

Parameters of oxidation Do1710 Do3410 o D 900 Do900

ox, min

O=6 (I)

f840

Isothermal regime 0,95 53 0,95 55 0,96 69 0,95 50 0,95 60 Regime of free shrinkage 32 0,9 34 0,9 0,9 33 0,9 32 0,9 30

R840

0,7 0,8 0,7 0,8 0,7

6,0 6,6 5,0 6,0 5,0

1,0 0,6 0,7 0,5 0,7

19,0 4,0 5,0 3,6 5,0

1,8

2,5

Do1710 Do3410 o D 3410 Do3560 Isothermal regime 1,1 4,5 1,6 3,0 1,4 3,0 3,0 1,3

2,3 3,2 2,1 2,8 3,2 2,5

Do840 Do900

3,9 1,9

2,9 4,0 2,7 3,0 3,6 2,8

Do998 Do900

4,4 2,9

3,8 4,1 3,4 3,5 4,2 3,2

0,96 0,85

0,96 0,94 0,96 0,95 0,96 0,95

Structural parameters Do975 f 840 Do900

f998

1,0 1,0

0,99 0,80 0,99 1,0 1,0 1,0

0,76 0,76 0,76 0,80 0,79

f975

6,6 6,5 6,4 7,5 7,2

R975

1,0 1,0 1,0 1,0 0,96

f998

25,5 24,0 20,0 20,0 15,0

R998

Table 2.10. The correlation between structural characteristics and parameters of oxidation of samples of oriented PP. Conditions: Tox. = 130°C, 2 = 150 millimeters of mercury.

No2, mole/kg

Sample

0,3 0,4 0,2 0,4 0,4

3,2 3,9 3,8 3,7 3,9

2,8 3,4 3,5 3,5 3,7

2,2 2,9 2,8 3,1 3,0

0 18 43 73 178

4,1 5,9 5,2 5,5 5,1

Do945 Do900

Do975 Do900

Do998 Do900

Do840 Do900

Duration of annealing, min

-

0,70 0,80 0,70 0,80 -

f975

0,1 0,3 0,2 0,3 0,2

0,3 0,2 0,1 0,04 0,02

R945

61

Table 2.9. Change of structure (conformational set) and orientation of oriented PP macro-chains (O = 9) during annealing in inert sphere in isothermal regime and at conditions of free shrinkage. Conditions: Tox. = 130°C, 2 = 150 millimeters of mercury.

At isometric conditions and at free shrinkage the rise of chains orientation in crystallites (R840), the rise of content of strengthened and decrease of coagulated conformers are observed. At that local stresses on trough-pass chains even at conditions of free shrinkage remain for a long time (Table 2.9). The initial sections of curves of change of polymer chains structures under oxidation reflect relaxation conformational transitions and accumulation of stresses in trough-pass chains caused by high temperature effect. Relaxation of local stresses on trough-pass chains and decrease of contents of strengthened and rise of coagulated conformers are observed under longer oxidation and are the consequents of oxidative destruction. Acceleration of structural reconstructions correlates with the rise of rate of oPP oxidation. In its turn the initial rate of accumulation of >C=O- groups correlates with the rate of stresses relaxation in trough-pass chains: the higher is the first one the high the last one. However concentration of products in oriented polymer depends on the rate of chains coagulation (ToG transitions) and is increased with decrease of content of strengthened conformers, and coagulated conformers are spent during oxidation process. At deeper stages of oxidation at accumulation of noticeable amount of carbonyls the change of polymer chain structure occurs and the influence of chemical composition of macro-molecules on its conformational structure, its orientation and the presence of stresses on trough-pass chains is revealed. With the rise of [>C=O] the orientation of chains is increased and over-stresses are again revealed. The rise of IR-dichroism and factors of orientation of bands at 998, 975 and 840cm-1and also intensities of bands at 945, 955 and 962cm-1 (Table 2.8) is observed. The clearly expressed correlation between the structures of chains of various samples of oPP, their relaxation characteristics and kinetic parameters of oxidation is consequent from analysis of data of Table 2.10. As it is obvious relaxation processes determine the rate of formation and structure of products of oxidation. The rates of oxidation and accumulation of non-volatile products and also their structures for oPP samples with definite extraction degree but possessing various structure of chains or oxidized in various regimes are significantly differed. In dependence on initial structure of chains and oxidation conditions relaxation processes occur in various chains and with various rates. This fact influences on kinetics of separate stages of oxidation, on contribution of inter-molecular and intra-molecular transfer of kinetic chain of oxidation. The ratios between content of carbonyl- and hydroxyl-containing groups and also between block and single hydroperoxides testify to this fact (Table 2.10). On the base of values of mentioned ratios the studied samples of oPP may be disposed to the raw PP (I) < PP (II) < PP (III) < PP (IV). In this raw the part of inter-molecular transfer of kinetic chains of oxidation is increased and the rise of ratio between content of carbonyl- and hydroxyl-containing products and the rise of single groups OH in their total content indicate on this fact. The first in this raw is the sample of oPP (I) with O = 6 in which relaxation of inter-fibrillar chains occurs and significant decrease of factor of orientation of band at 998 and rise of band at 975cm-1 indicate on this. In sample of oPP (II) with O = 6 these chains don't relax; oPP (III) with O = 9 oxidized in isometric regime when relaxation of all chains is hindered and finally PP (IV) with O = 9 is the sample oxidized at conditions of free shrinkage. Thus, the main mechanisms of structure reconstruction accompanying oxidation are crystallites annealing, relaxation conformation transitions in inter-crystallites trough-pass chains, appearance and relaxation of over-stresses on trough-pass chains. These reconstructions are catalyzed by oxygen medium and correlate with the rate of thermal oxidative destruction of trough-pass chains. Differences between large- and small-spherulite samples to a greater extent determining difference in kinetics of polypropylene oxidation come to difference in sizes of crystallites and structure of trough-pass chains entering the inter-crystallite regions. The last one is connected with the width of distribution by lengths of trough-pass chains, i.e. with variety of their lengths. The contribution of change of structure of trough-pass chains during annealing process depends on various lengths of chains. In its turn the change of chains structures influences on oxidation mechanism.

62

Chapter 3. Model systems. Isotactic polypropylene modified by esters. The given Section is devoted to regularities of thermal oxidation and to structural reconstructions in the course of oxidation of model heterogeneous systems. The samples of PP filled by esters were chosen as such systems. Introduction of low-molecular substances into polymer may lead to both acceleration [263, 264] and deceleration [265268] of its thermal oxidative destruction. It depends on polymer nature, reactivity of additive, on the reaction in which this additive participates: in termination of kinetic chains of oxidation [265, 266] or in reaction of transfer of kinetic chain of co-oxidation [267, 268]. The second factor determining regularities of oxidation of filled polymers is compativility of additive with polymer which determines the mechanism of its influence on structure of polymer matrix [269279]. Compatible additive leads to the change of molecular structure of matrix, dynamics of molecular movements, rate of relaxation processes [270278]. In the case of incompatible additive the phase separation of low-molecular substance and polymer is observed. Such additive causes the change of permolecular structure of polymer matrix and under the action of forces of inter-phase tension may increase the order of amorphous regions enriching macro-chains by regular conformers on the interface [270]. Variation of nature of additive in polymer allows obtaining of system modelling compatible and incompatible blends of polymers that allows revealing of structure effects during the process of thermal oxidation of heterogeneous systems. The following modifiers of PP were used as fillers: x dibutyl ester of polypropylenglycol adipinate (PPA-4), chemical formula of the primary composition: C4H9OOC(CH2)4CO[O-CH(CH3)-CH2OOC(C4H9)4CO]3OC4H9; x di-2-ethylhexyl ester of sebacic acid (DOS), chemical formula of the primary composition: C2H5-CH(CH3)-CH2-CH2-CH2-CH2OOC(CH2)8COOCH2-CH2-CH2-CH2CH(CH3)-C2H5; x di-n-alkyl ester of orto-phthalic acid and alcohol fractions 79 (DAF): C8H4O4R2. Introduction of additives was realized by their mixing with powder polymer in laboratory onescrew extruder at temperature 210qC. Polymer samples were studied in the form of films which were obtained by pressing at the same temperature and pressure 70MPa with further slow cooling (a10 degrees/min) down to room temperature. Investigation of microstructure was carried out by the method of optical microscopy in polarized light on microscope "Polan-P112". The estimation of physical-mechanical properties was carried out in accordance with all-Union State Standard 11262-80. 3.1. The structure of modified polypropylene

With the help of interference micro-method of wedge they showed that DAF and DOS were restrictedly compatible with PP at 25qC and had the high critical vitrification temperatures (HCVT) equal to 165 and 145qC accordingly [279]. PPA-4 is practically incompatible with PP in the interval 25200qC (Figure 3.1). As a consequence of this fact during the process of cooling of films of modified PP after pressing at 180qC the partial delamination in systems PPDOS, PPDAF at simultaneous crystallization of PP occurs and delamination begins lower than 110qC. Introduction of PPA-4 independently on concentration leads to slight decrease of sizes of PP spherulites. Introduction of DAF and DOS significantly decreases the sizes of permolecular structures of polymer and this decrease is the most significant the higher the concentration of additive (microphotographs of initial and modified PP are presented in Figure 3.2).

63

Figure 3.1. Diagram of phase state of systems: 1  PP+PPA-4, 2  PP+DAF, 3  PP+DOS.

PP+5% DAF PP+1% PPA-4

PP initial

PP+10% DAF

Figure 3.2. Micro-photographs of surfaces of films PP+oligoester. Microscope "Polam P112" in polarized light.

The sizes of spherulites of PP, PP + 1% PPA-4, PP + 5% DAF, PP + 5% DOS are 373, 382, 77 and 80mcm accordingly.

64

Additives to PP don't change morphology of crystallites but influence on structure of its crystal and amorphous regions. And the character of influence depends on chemical nature of modifier. The data of X-ray structural analysis in small angles are presented in Figure 3.3. I, rel. units

S, nm-1 Figure 3.3. Small-angle difractograms of samples of pure PP (1) and PP modified by 10% of DAF (2) and 1% of PPA-4 (3).

Diffraction pictures of samples of PP and PP filled by DAF and DOS are significantly differed from those ones with PP and PPA-4. Difractograms of the first two samples demonstrate central small-angle scattering (s | 0,025nm-1) caused by heterogeneities of electron density [29] (Figure 3.3). Approximation of initial section of curve of scattering by Ginue formula allows estimating of radius of inertia of these heterogeneities Rg which is equal to ~17nm. For heterogeneities of density of ball-shaped form when R2g = 3/5R2 [29] we may obtain the value of radius of heterogeneities R near 20nm. The obtained sizes allow assigning of heterogeneities to the regions formed by troughpass macro-chains connecting neighbor spherulites, i.e. inter-spherulite amorphous regions. There is no central scattering on difractogram of PP enriched by PPA-4. Obviously, this fact is explained by that circumstance that incompatible with PP ester PPA-4 is localized in inter-spherulite regions leveling in them the difference of electron densities. The character of localization is another in the case of compatible additives. Except diffusion scattering for all samples the clearly expressed small-angle reflex conditioned by periodically alternation of amorphous and crystal inter-layers in spherulites is observed (large period) (Figure 3.3). As it is consequent from analysis of small-angle reflexes the introduction of additives into PP doesn’t lead to essential changes of crystallites thickness (Table 3.1).

65

PP2 (s/c) PP2(s/c) + + 1% PPA-4 PP2(s/c) + + 5% DAF PP2(s/c) + + 5% DOS

Sample

18,2

20,2

18,2

18,0

7,2

3,1

-

Large period, nm

7,0

Intensity of small angle reflex, f (standard unis)

9,0

8,8

8,5

8,8

Size of amorphous interlayers, nm

9,0

9,4

11,7

9,4

Size of crystallites, nm

50

52

58

52

Index of crystallinity, % (Xray SA)

45-49

59

59

66

Degree of crystallinity, % (DSC)

1,9

3,3-4,1

4,3

3,6-3,7

D840 D900

3,1

2,4-3,5

3,0-3,2

2,9-3,4

D998 D900

0,04

0,4-0,7

0,9

3,0

2,0-2,4

2,6-2,7

2,5

66

D1155 D900(1-D)

D975-D998 D900(1-D) 0,7-1,0

Coagulated conformers

Straightened conformers

Amorphous regions

Data of IR-spectroscopy Content of straightened conformers

Table 3.1. Structural parameters of pure and modified by oligoethers PP.

Decrease of intensity of small-angle reflex for PP samples filled by compatible additives may be explained by predominant localization of these additives in inter-crystallite amorphous interlayers. Introduction of compatible with PP DAF and DOS leads to amorphization of polymer and decrease of regularity of chains in amorphous phase and for the first one it reveals to a lesser degree (Table 3.1). For PP with incompatible additive PPPPA-4 the formation of more homogeneous crystal structure occurs and regularity of chains of amorphous phase is slightly changed. It is obvious from IR-spectra of modified PP, by the character of change of intensities of bands at 840, 975 and 998cm-1 and from the ratio between optical densities of two last bands by formula [245]: [D975D998] / (1D D)Det where D  the part of crystal phase in polymer (Table 3.1). The analogous conclusion is evident form data of analysis of DSC endotherms of melting (Table 3.2). In incompatible system PP + PPA4 at constant temperatures and heats of melting the half-width of peak of melting is decreased that testifies to formation of more homogeneous crystal structure. Table 3.2. Thermophysical parameters of samples of PP modified by oligoethers. Sample PP PP + + 5% DAF PP + + 5% DOS

(1)

mel, 

cr, 

161,6

161,2

108,8

81,1

83,5

'h1/2 mel, degrees 10,2

162,6

161,2

110,0

71,3

69,0

12,0

159,0

159,0

105,6

62,0

60,3

12,5

78,8

80,0

8,0

mel, 

(2)

(1)

PP + 164,4 164,0 111,2 + 1% PPA-4 1 '+mel  the enthalpy of the first melting; 2 '+mel – the enthalpy of repeated melting after recrystallization.

'+mel, J/g

(2)

(1)

'+mel, J/g

Change of polymer chains structure leads to the rise of segment mobility in amorphous regions of PP and decrease of its vitrification temperature indicates on it (Table 3.3). Table 3.3. Glass-transition temperature of samples of PP modified by oligoethers

Sample

PP

PP + DAF

PP + DOS

PP + PP -4

Tg , 

-7

-13

-20

-15

3.2. The particularities of crystallization of modified polypropylene

As it is known, regularities of crystallization are determined by structure of non-crystallizing part of polymer [248255]. That is why change of crystallization rate in PP modified by esters should depend on compatibility of PP with esters and correlate with the data of diagram of phase state of systems PPDAF, PPDOS and PPPPA-4. This fact means that for estimation of phase state of hetero-phase systems one may use isothermal crystallization of crystallizable component. Kinetics of isothermal crystallization of samples of modified by esters PP was studied by DSC method. For obtaining of isotherms of crystallization the sample was heated up to 200qC, stayed for 5 minutes at this temperature and then cooled with rate 64 degrees/min down to temperature of crystallization. On the base of obtained isotherms the degree of crystallization of PP from melt was calculated by formula [249]: ’

67

D = '+t / '+, t

where D  the degree of crystallization or transformation of melt into crystal phase; ’

'+t, '+  heats of crystallization evolved for the time t and the whole time of process t

correspondingly. For description of kinetics of isothermal crystallization of polymer samples two equations were used: mainly the widely used Avrami-Kolmogorov's equation [249]: X(t) = 1-exp (-Ktn) (1) where K  rate constant; n  the index, characterizing geometry of propagating crystal. The isotherms of crystallization of pure and modified PP in coordinates of mentioned equation are presented in Figure 3.4. the effect of additives is revealed more clearly at high temperature of crystallization Tcr (Table 3.4) that obviously corresponds to higher solubility of additive in polymer.

l g [ - l nD()1] 1

1

0

2

-1 4

3

-2

2 ,4

2 ,8

3 ,2

lg t, [c ]

Figure 3.4. Kinetic curves of isothermal crystallization at Tcr = 130qC in coordinates of Avrami equation for PP (1) and PP modified by 1% of PPA-4 (2), 5% of DAF (3), 5% DOS (4).

The dependence of half-period of crystallization W1/2 of studied compositions on temperature also indicates on it (Figure 3.5).

68

Table 3.4. Kinetic parameters of isothermal crystallization of pure and modified PP. Sample PP

PP + + 1%PP -4

PP + + 5%DAF PP + + 10%DAF PP + + 5%DOS

cr,  115 120 125 130 135 115 120 125 130 135 115 120 125 130 115 120 125 130 115 120 125 130

mel,  162 163 165 167 168 161 162 164 166 170 160 161 163 165 159 160 161 164 160 161 162 165

'7,  61 56 51 46 41 61 56 51 46 41 61 56 51 46 61 56 51 46 61 56 51 46

n 4,0 3,7 3,3 4,6 4,0 3,8 3,8 4,0 3,9 4,0 4,4 3,9 3,6 3,9 3,4 3,6 3,2 3,3 4,0 3,7 3,9 3,9

K 2,3.10-7 1,4.10-7 9,1.10-8 2,5.10-13 1,6.10-14 7,9.10-7 6,3.10-8 1,0.10-9 9,6.10-12 1,4.10-14 7,0.10-8 2,8.10-8 2,0.10-9 2,6.10-12 7,8.10-7 1,5.10-8 2,0.10-9 1,8.10-11 2,0.10-7 4,5.10-8 3,2.10-10 2,8.10-12

W1/2, s 42 63 122 506 2572 37 71 162 609 2646 39 79 221 848 56 134 416 1619 43 87 248 838

Figure 3.5. Temperature dependence of semi-crystallization for PP (1), PP+1% of PPA-4 (2), PP+%5 DAF (3), PP+10% DAF (4), PP+5% DOS (5).

69

At low Tcr additives practically don't influence on crystallization rate. Temperature rise leads to decrease of crystallization rate. It is especially noticeable under the rise of system compatibility, rise of content of ester (Table 3.4). In the system PPester, as well as in pure PP not only primary but also secondary crystallization occurs (Figure 3.4). The value of Avrami parameter n for PP is changed in the limits 34 that corresponds to three-dimensional rise of spherulites on thermal nucleus of crystallization [248]. For modified PP values of n are close to indexes of pure polymer, only for sample with 10% of DAF these values are significantly lower (Table 3.4). The rise of crystallization temperature leads to monotonous rise of temperature of melting of modified PP (Figure 3.6). At that temperature dependences of crystallization heat demonstrate the change of mechanism of isothermal crystallization under temperature rise (Figure 3.7).

TTmel , 0qC .,  1

2

168

3 164

4

160

115

125

135

Tcr , qC ., 0 

Figure 3.6. Dependence of melting temperature on temperature of crystallization for PP (1) and PP modified by esters: PP+1% PPA-4 (2), PP+5% DAF (3), PP+5% DOS (4).

70

H / Hmel , J/g ., 1

80

2

3 70

4

60

115

125

135

., 0 T

, qC cr

Figure 3.7. Temperature dependence of heat of melting for PP (1) and PP modified by esters: PP+PPA-4 (2), PP+5% DAF (3), PP+5% DOS (4).

Temperature at which enthalpy is sharply increased is the characteristic of crystallizing polymers. This temperature is called "equilibrium", however it is far from equilibrium. Heat of melting and consequently degree of crystallinity at high Tcr is monotonously decreased with the rise of compatibility of PP with additive. With the rise of temperature the degree of PP crystallinity is increased almost by 20%. For incompatible system PP + PPA-4 this rise is somewhat higher than 10%, for compatible systems PP + DAF it is lower than 5%, PP + DOS  the degree of crystallinity is not increased. Estimation of influence of esters differing in compatibility with polypropylene on thermodynamic parameters of its crystallization was carried out with the use of temperature dependence of rate of spherulites growth. G = G0˜exp (-'G* / RT-'GK / RT), (1) where G0  pre-exponential factor not depending on temperature; 'G*  free energy of crystallization during formation of critical nucleus; 'GK  free energy of activation of process of diffusion of crystallizing element through phases boundary to small distance; k, R  Boltzmann and gas constants; T  temperature. For description of temperature dependence of diffusion member of equation 'GK they used equation of Williams-Landel-Ferry (WLF) which described temperature dependence of polymers viscosity [248, 249]: 'GK / RT = 1˜ / (2 + T-Tv)RT, In relation to PP this equation is as follows: 71

'GK / RT = 17238˜ / (51,6+T-Tv)RT, where Tv  vitrification temperature of polymer. The dependence of 'GK on temperature of crystallization is presented in Figure 3.8a. Since vitrification temperature of PP under addition of modifiers is decreased, the value of 'GK is also decreased. a 'GK

12,0

1 2 4

11,6

3 5 11,2

10,8

115

125

135

T, 0C

b

a, mcm ,  9

1 2 3

8

4 5 7

6

115

125

135

T, 0

72

c

l, mcm

l,  5

140

4 1 3

2

120

100

115

125

135

T, 0

Figure 3.8. Temperature dependences of: (a) free enthalpy of diffusion process of crystallizing element trough interface; (b) side surface of crystallization nucleus and (c) front surface of crystallization nucleus for PP (1), PP+1% PPA-4 (2), PP+5% DAF (3), PP+10% DAF (4), PP+5% DOS (5).

The values of 'GK of modified PP are somewhat lower than activation energy of viscous flow but they all have similar order. It is obvious from Table 3.5 that activation energy of viscous flow of PP is decreased independently on additive's nature. Table 3.5. Activation energy of viscous flow of compositions on the base of PP. Composition PP PP + 1% PP -4 PP + 2% PP -4 PP + 3% DOS PP + 5% DOS PP + 10% DOS

Activation energy of viscous flow, kJ/mole 31,7 28,7 26,9 29,4 27,9 22,0

Decrease of value of 'GK should lead to acceleration of crystallization process at the expense of increase of mobility of polymer chains. Decrease of crystallization rate in modified PP (Table 3.4) is probably connected with screening of propagating spherulites and in compatible systems  with hindering action of diluted in polymer additive. Since half-period of crystallization is in inverse proportion to rate of crystallization expression (1) may be presented with the use of WLF equation in the following way: 1/(t1/2) = A0 exp [-17238˜/RT(51,6+T-Tv)-'G*/RT] or ln[1/(t1/2)]-lnA0+ [17238/R(51,6+T-Tv)]= -'G*/RT. The right part of equation may be presented as follows: 73

-'G*/RT=-WT0mel/(˜' '7), where W  constant including energetic characteristics; T0mel  equilibrium temperature of melting; A0  constant. The dependences: lg[1/(t1/2)]+ [17238 /2,3 R (51,6+T-Tv)]= f [T0 /( '7)]. for all modified samples of PP are approximated by straight lines with negative gradients equal to W, where W is the value of activation barrier of nucleation. In its turn: 7U, (-'G*) = 4iVVeb0T0mel/RT'+mel'7 W=4VVeb0/2,3 R'+mel (2) where V  side free surface energy of crystallite; Ve – free surface energy of front surfaces of crystallite; Tm – equilibrium temperature of melting; '7  overcooling; '+  specific heat of melting; U  density of crystal phase; b0  thickness of polymer chain; i  the multiplier taking on the values equal to one in the case of one-nucleus regime (weak or very strong overcooling, regimes I and III) or 0,5 at multi-nucleus regime (moderate overcooling, regime II [249]). For calculation of values of V the empiric ratio is used [248, 249]: V = Eb0'Hfmel (3) where E  the constant taking on the value 0,1 for polymers; 'Hfmel – heat of melting of 100% crystallites expressed in J/m3. By equations (2) and (3) the values of V and Ve were calculated. The results are presented in Table 3.6. Table 3.6. Energetic parameters of nucleation (temperature of crystallization Tcr = 130°C). Composition PP PP + 3% DOS PP + 5% DOS PP + 7% DOS PP + 10% DOS

V u 103, J/m2 6,48 6,45 6,75 6,78 6,81

V u 103, J/m2 76,8 76,6 77,4 76,4 76,0

Change of values of V and Ve may influence on linear sizes of critical nucleus of crystallization. That is why side "a" and front "l" sizes of nucleus were calculated in dependence on temperature of crystallization by formulas: a = 2V0mel / 'Hmel' l = 2Ve0mel / 'Hmel' Obtained data are also presented in Figure 3.8a, b. Ve, sizes of critical Thus, introduction of esters changes front energy of nucleation Ve and V˜V nucleus and also the ratio between sizes of nucleus of crystallization of PP with DAF and DOS and PP with PPA-4. For compatible system PP + DAF, PP + DOS sizes of critical nucleus are increased, for incompatible PP + PPA-4 they are decreased. Comparison of values by which front energy, sizes of critical nucleus and periods of semicrystallization are changed shows that the observing decrease of crystallization rate of PP in samples modified by esters can not be explained by thermodynamic factors. In accordance with modern concepts of thermal kinetics [250-255] the entropy factor influences on crystallization rate. Accordingly to these conceptions the phenomenon analogous to entan74

gling of chains ends or increase of part of non-crystallizing fraction of polymer decreases the rate of process of crystallites formation. In our case as such phenomenon we may consider intermolecular interaction of PP with molecules of esters diluted in PP. In the incompatible system PPPPA-4 the rate of crystallites formation in comparison with pure PP is changed insignificantly. This fact correlates with the character of localization of compatible and incompatible additives in PP matrix: the first ones in inter-crystal regions, and the second ones in inter-spherulites regions. 3.3. Kinetics of oxygen absorption by modified polypropylene

Oligo-esters significantly influence on kinetics of oxygen absorption by PP. kinetic curves (obtained in kinetic regime) for pure and modified PP are presented in Figure 3.9.

No2, mole/kg 7,5

2

3 5,0

1

4 1/2

2,5

(No2) , (mole/kg) ,

2 3

,

1

1/2

,

4

1

,

5 6 0

100

200

300

400

500

600

tox, min

Figure 3.9. Kinetic curves of oxygen absorption during oxidation of PP (1), PP+5% DAF (2), PP+5% DOS (3) and PP+1% PPA-4 (4), pure DAF (5) and PPA-4 (6), and also linear anamorphism of kinetic curves for PP (1), PP+5% DAF (2), PP+5% DOS (3) and PP+1% PPA-4 (4) in coordinates (NO2)1/2=f(t). ox = 130q and PO2 = 150 millimeters of mercury.

At the same Figure the kinetic curves of oxygen absorption by pure oligoesters are presented. It follows from Figure that all curves have S-shaped form characteristic for chain oxidation with degenerated branching of kinetic chains. On kinetic chains there are three clear parts corresponding to decelerated initial stage  induction period, stationary process and deceleration of oxidation at deep stage. As it is obvious from the values of induction periods (which are determined as sections on the axis of time cutting off by linear anamorphism of kinetic curves in coordinates '121/2WWx (Figure 3.9)) at the initial stage of auto-oxidation the incompatible (PPA-4) and compatible (DAF, DOS) additives oppositely influence on process kinetics. PPA-4 decelerate, and DAF and DOS accelerate especially the initial stage of oxidation of polymer sample; PPA-4 increases and DAF and 75

DOS decrease Wind of pure PP. Analogous conclusion is consequent from comparison of kinetic parameters "b" characterizing reactivity of initial and modified PP estimated from inclinations of linear anamorphism of kinetic curves of oxygen absorption at stage of oxidation up to 1 mole/kg of O2 (Figure 3.9, Table 3.7) in coordinates '121/2WWx. The parameter b is connected with ratio of constants of rates of separate stages of oxidation process stages in the following way [161, 162]: '120,5 = (DVk22k4 [RH]3)0,5 L / (8k6)0,5, 0,5 where '12  change of amount of absorbed oxygen at the initial stage of oxidation process when rate of oxidation is determined by the rate of accumulation of hydroperoxide and concentration of monomer units is constant; L-Wind, k2, k6  the constants of rate of continuation and quadratic termination of kinetic chains of oxidation; k4  the constant of rate of hydroperoxide decomposition; D  the yield of hydroperoxide per 1 mole of absorbed oxygen; V  the probability of degenerated branching of kinetic chains of oxidation. Table 3.7. Kinetic parameters of oxidation of PP modified by esters. Conditions: Tox. = 130°C, 2 = 150 millimeters of mercury.

Sample PP PP + + 5% DAF PP + + 5% DOS PP + + 1% PP -4

106-120

Maximum rate of oxidation Wo2 u 104, mole/kg˜s 4,5-5,0

80-90

5,5-6,3

30,4

0,7-0,8

90

4,5-4,7

23,3

0,8

152-170

3,3

17,0

1,3-1,5

Induction period W, min

Parameter b u 105 , mole1/2/kg1/.2˜s

WindPP+ester WindPP

18,7

1,0

Acceleration of oxidation in samples of PP filled by compatible additives and deceleration in sample with incompatible additive are consequent from analysis of curves of change of rate in the course of samples oxidation (Figure 3.10) obtained by method of differentiation of curves of oxygen absorption.

76

d (No2) / dt, mole/kg.min 0,04

2 0,03

3 0,02

1 0,01

4 200

400

600

tox, min

Figure 3.10. The change of rate during oxidation of PP (1), PP+5% DAF (2), PP+5% DOS (3) and PP+1% PPA-4 (4) at ox = 130q and PO2 = 150 millimeters of mercury.

Change of rate of PP oxidation in modified samples may be the result of change of structure of PP matrix under the action of modifiers or participation of the last ones in oxidation process. At that one may propose that oligoesters participate in combined radical reactions with PP matrix and play role of initiators (in the case of DAF and DOS) or inhibitors (in the case of PPA-4) of oxidation. As the data of Figure 3.9 show the initial acceleration of oxidation process of PP modified by DAF and DOS is not connected with absorption of oxygen by low-molecular additives without participation in polymer oxidation. Low rates of oxidation of pure DAF and DOS contradict to the last fact. In opposite case the reaction ability of esters diluted in polymer should significantly exceed reaction ability of pure samples. With the aim of reveling of contribution of change of structure factors (degree of crystallinity and structure of chains of amorphous regions) into PP oxidation the kinetic curves of oxygen absorption by samples of initial and modified polymer were transformed in coordinates of equation (1): No2 / (1-x)˜b = f(t), and also in coordinates of equation (2): No2 / (1-x)˜b˜[RHPP]G / Go = f(t), where b and [RHPP]  concentration of PP and its monomer units accordingly; (1-)  the part of amorphous phase of PP; 77

G, Go  concentration of coagulated conformers in amorphous regions of pure and modified PP. If oxidation of PP in modified samples is determined by changes of structural parameters, then calculated kinetic curves and determined from these curves parameters should be close to parameters of pure polymer. Expression (1) allows considering the absorption of oxygen by amorphous regions of PP. At that the content of amorphous phase was determined by the value of crystallinity degree of polymer at oxidation temperature. As calculated curves obtained from expression (1) (Figure 3.11) and (2) (Figure 3.12) show the initial rates of oxidation (Wind) of pure PP and PP modified by DAF and DOS are close, the current rates of oxygen absorption up to the stage of developed oxidation are also close. At deeper stage the rate of oxidation of PP sample modified by compatible with PP additives is higher than in the case of pure PP. At that the maximum concentration of reactive RH-bonds is increased (Figure 3.11, 3.12). In contrast to PP modified by compatible additives DAF and DOS, for PP modified by incompatible additive PPA-4 the value of Wind is significantly higher and rates of oxidation are essentially lower than for pure PP.

Figure 3.11. Kinetic curves of oxygen absorption by samples of PP (1), PP + 5% DAF (2), PP + 5% DOS (3) and PP+1% PPA-4 (4) in calculation per amorphous regions of PP and also kinetic curves of oxygen absorption by pure DAF (5), DOS (6) and PPA-4 (7). ox = 130q and PO2 = 150 millimeters of mercury.

78

Figure 3.12. Kinetic curves considering oxygen absorption preliminary by RH-bonds of PP chains in coagulated conformation for samples PP (1), PP + 5% DAF (2), PP + 5% DOS (3) and PP+1% PPA-4 (4) ox = 130q and PO2 = 150 millimeters of mercury.

One may propose that observing particularities of process kinetics for samples of modofoed PP are conditioned by co-oxidation of polymer matrix and modifier. In other words oligoesters "take part" in oxidation of polymer samples. Thus, acceleration of oxidation of PP with DAF and PP with DOS may be the result of initiation of kinetic chains of oxidation of oligoester by macro- or micro-radicals of oxidable polymer matrix. In the case of incompatible system of PP modified by PPA-4 the inverse effect is observed  inhibition of oxidation of polymer matrix by oligoester and the different mechanism of additives influence on polymer matrix promotes it. Initial acceleration of PP oxidation process in the presence of compatible additives is caused by the rise of part of chains in coagulated conformation possessing higher segment mobility. Deceleration of PP oxidation in the presence of PPA-4 may be connected with higher homogeneity of polymer crystal structure. Moreover, the important factor influencing on co-oxidation reaction of polymer and additive is localization of additives in polymer promoting the contact between PP macromolecules and molecules of esters.

79

3.4. Physical-mechanical parameters of oxidized modified polypropylene

Physical-mechanical parameters of oxidized samples of pure and modified PP were compared with the aim of establishment of effect of modifiers on thermal oxidation of polymer matrix. Curves of dependences of strength limit and lengthening under the breakage of modified PP on duration of oxidation are presented in Figure 3.13a, b. Dependences of the same parameters on modifier content for initial and oxidized samples of PP modified by DAF and DOS are presented in Figures 3.14, 3.15. a VVR 1,0

3

0,8

2 0,6

1 4 40

80

120

tox, min

b HHR 1,00

0,75

0,50

0,25 3 5 4

1

2 50

100

150

200

250

tox, min

Figure 3.13. (a) Change of relative strength of PP (1), PP + 5% DAF (2), PP + 5% DOS (3) and PP+1% PPA-4 (4) in the course of oxidation at ox = 130q and PO2 = 150 millimeters of mercury. (b) Change of relative elongation in the course of oxidation of PP (1), PP+5% DAF (2), PP+5% DOS (3), PP+PPA-4 (4), inhibited PP (5). ox = 130q and PO2 = 150 millimeters of mercury samples.

80

V MPa

1 3

35

2

30

4

25

0

3

6

9

Content of ester, %

Figure 3.14. Change of strength in dependence on concentration of additive into PP in the case of systems PP+DAF (1, 2), PP+DOS (3, 4), initial samples (1, 3) and oxidized (2, 4) for 5 hours at ox = 130q and PO2 = 150 millimeters of mercury.

H 3

800

1

700

600

2

500

4 400

300

200 0

2

4

6

8

10

[C], mass %.

Figure 3.15. Dependence of lengthening on DAF (1, 2) and DOS (3, 4) concentrations in PP in the case of initial (1, 3) and oxidized (2, 4) for 5 hours at ox = 130q and PO2 = 150 millimeters of mercury samples.

81

As it is obvious from Figures under oxidation of all studied samples of PP significant reduction of strength and elongation at rupture is observed. The decrease of part of trough-pass chains in strengthened conformation able to bearing may be the reason of decrease of strength of PP chains in the presence of DAF and DOS. However in this case the lengthening should be increased. As the shape of dependence of strength and elongation at rupture on additive's concentration shows the rise of part of coagulated chains can not lead to sharp decrease of both parameters in oxidized samples. It is obvious that decrease of physical-mechanical parameters is caused by destruction of chains. In other words the oxidation process of modified PP is accompanied by thermal oxidative destruction of polymer chains. And destruction of chains in the case of modified polymer is started earlier than in the case of pure one. This fact demonstrates that modifiers compatible with PP accelerate destruction of chains and incompatible with PP ones decelerating oxidation of polymer don't hinder it. 3.5. Products of oxidation of modified polypropylene

The data obtained with the help of IR-spectroscopy (Table 3.8) show that there are no visible changes in structure of hydroxyl-containing groups of modified samples in comparison with pure PP. In all samples only a small amount of single OH-groups is formed. The rate of accumulation of block OH-groups at one and the same concentration of absorbed oxygen at the initial stage of oxidation for PP modified by DAF and DOS is somewhat lower than for pure PP (Table 3.8). The lower rate of accumulation of block OH-groups in the course of oxidation of sample of PP+PPA-4 may be explained by lower rate of its oxidation. Table 3.8. Products of oxidation of PP modified by esters. Conditions: Tox. = 130°C, 2 = 150 millimeters of mercury. Products of oxidation Carbonyl-containing products (lower than * there are ester groups Hydroxel-containing products additives + oxidation products) D3420 D1725 D1735 D1760 D3370 D900 D900 D900 D900 D900

Sample

Duration of oxidation, min

PP

0 30 60 120 160

0,1 0,12 0,10 0,18 0,29

0,08 0,10 0,08 0,14 0,32

0,5 0 0,38 0,64 1,2

0,5 0,7 0,38 0,78 1,2

0 30 60 120 160 240 0 30 60 120 160 0 30 60 120 160 240

0,13 0,13 0,13 0,12 0,13 0,13 0,1 0,08 0,09 0,22 0,35 0,075 0,11 0,13 0,11 0,08 0,19

0,10 0,13 0,10 0,10 0,11 0,13 0,08 0,08 0,09 0,25 0,33 0,11 0,09 0,09 0,11 0,08 0,22

*

PP + + 1%PP -4

PP + + 5% DAF

PP + + 5%DOS

1,2 0,5 0,64 0,50 0,50 0,77 1,64 1,77 1,5 1,76 1,27 4,5 6,15 4,0 4,0 2,7 3,0

1,2 0,68 0,64 0,50 0,50 0,73 2,3 1,65 1,4 1,76 1,04 4,5 6,15 4,0 4,0 2,7 2,7

0,07 0,03 0,14 0,23 *0,05 0,06 0,07 0,05 0,08 0,10 0,13 0,11 0,05 0,16 0,18 0,20 0,18 0,13 0,21 0,17 0,20

82

Since in IR-spectra of samples characteristic bands of ester groups of additives and carbonylcontaining products of oxidation are found in one region at 1700-1800cm-1 covering each other, the changes of intensities of mentioned bands for oxidized polymer samples may be the result of superposition of two processes: accumulation of carbonyl-containing products and decrease of concentration of additives in the course of oxidation (Table 3.8). For samples of pure PP during the oxidation of which >C=O groups are accumulated, the rise of intensities of bands at 1725, 1735 and 1760 m1 is observed, fir the samples of modified PP intensities of the first two bands are decreased and intensity of the last one is practically not changed. If esters participate in oxidation then they should be spent in the course of process. Obviously this fact is the reason of decrease of intensity of bands at 1725 and 1735cm-1 at the beginning of oxidation. 3.6. Structural parameters of oxidized modified polypropylene

Comparison of DSC endotherms of melting of initial and oxidized samples of modified PP shows essential influence of oxidation on the structure of polymer matrix. In all cases near the endothermal peak of PP crystallites melting in oxidized samples the low-temperature shoulder is revealed (Table 3.9). At that the decrease of temperature in the maximum of peak of melting of all modified samples is observed (Table 3.9). Table 3.9. Thermophysical parameters of initial and oxidized samples of pure and modified PP. Conditions: Tox. = 130°C, 2 = 150 millimeters of mercury. Sample

Duration of oxidation, min 0 60 0 60

(1)

mel, 

(2)

mel, 

cr, 

'+mel, J/g

(1)

'+mel, J/g

(2)

161,6 161,2 108,8 81,1 83,5 159,2 159,0 107,8 80,2 80,8 162,6 161,2 110,0 71,3 69,0 PP + 159,5+ 157,5+ 106,0 78,5 70,7 + 5% DAF shoulder 142,0 shoulder 147,5 PP + 0 159,0 159,0 105,6 62,0 60,3 + 5% DOS 60 157,5 155,5 103,0 56,0 59,0 PP + 0 164,4 164,0 111,2 78,8 80,0 + 1% PP -4 60 159,5 158,0 104,0 76,6 62,0 Notes: Symbols (1) and (2) relate to the parameters of primary melting and the repeated melting after recrystallization accordingly. PP (s/c)

Repeated remelting doesn't lead to the change of heat of melting of oxidized samples of PP+DAF and PP+DOS, small decrease of '+mel is observed for sample of PP+PPA-4. Obviously, mentioned changes in endotherm of melting of crystallites of oxidized samples of modified PP are caused by decomposition of crystal regions of polymer. Analysis of change of structural parameters in the course of oxidation of modified PP with the help of IR-spectroscopy shows (Table 3.10) that for modified as well as for pure PP the initial stage of oxidation is accompanied by crystallites annealing and increase of intensity of regular crystal bands testifies to this fact; it is also accompanied by the rise of regularity of chains of amorphous inter-crystal interlayers, by decrease of concentration of coagulated conformers (Table 3.10). With the increase of oxidation depth the decrease of concentration of strengthened conformers occurs. At that the listed processes proceed in various ways for pure PP and PP with compatible and incompatible additives. So, for PP with DAF and DOS structural parameters are changed to a lesser degree than for pure PP. Obviously this fact is connected either with high content of trough-pass

83

chains in coagulated conformation that hinders relaxation GoT transitions, or with high rate of destruction of trough-pass chains. With increase of oxidation depth in he case of PP+PPA-4 decrease of regular chains is started earlier than for PP modified by DAF and DOS, and monotonous and sharp (sharper than in the case of pure PP) decrease of content of strengthened conformers is observed (Table 3.10) that confirms the conclusion about the rise of rate of destruction of trough-pass chains of PP matrix.

84

PP + + 5% DOS

PP + + 5%DAF

PP + + 1%PP -4

PP2 (s/c)

Composition

D900

0,55 0,36 0,33 0,35 0,32 0,27 1,8 1,2 0,9 1,2 0,47 0,35 0,35 0,14 0,19 0,10 0,12

0 30 60 120 160 0 30 60 120 160 240 0 30 60 120 160 0 30 60 120 160 240

D1265

Duration of oxidation, min

D1725 D 900 1,18 0,51 0,65 0,49 0,52 0,76 1,6 1,8 1,5 1,7 1,27 4,5 3,2 4,0 4,0 2,7 3,0

D1737 D900 1,24 0,68 0,65 0,49 0,52 0,73 2,3 1,6 1,4 1,7 1,04 4,5 3,2 4,3 4,0 2,7 2,7

Content of oligoethers D750 D900 0,10 0,09 0,10 0,05 0,07 0,08 0,56 0,30 0,22 0,36 0,13 0,6 0,3 0,4 0,5 0,35 0,52

D840 D1300 2,9 3,3 2,7 5,9 1,9 2,5 3,5 2,7 2,9 2,7 2,8 1,4 1,5 3,9 1,4 1,7 3,6 3,9 5,9 5,5 3,7 3,5

D975 D1300 2,8 3,3 2,6 5,9 1,9 2,4 3,3 3,0 2,8 2,7 2,8 1,2 1,4 3,6 1,3 1,7 3,9 3,4 4,7 5,6 3,3 3,2

85

Structure of macromolecules of modified PP Crystal regions Amorphous regions D998 D998 D840 D810 D975 D1155 D460 D975 D900 D900 D900 D900 D900 D900 0,34 1,2 2,0 1,7 2,0 2,0 1,0 0,4 1,3 2,5 1,5 2,5 2,5 1,0 0,4 1,2 1,8 1,2 1,9 1,8 1,0 0,32 1,6 4,0 1,3 4,0 3,5 0,9 0,34 1,2 1,7 1,13 1,6 1,5 0,9 0,37 1,33 2,4 1,3 2,5 1,0 2,4 0,41 1,33 3,2 1,3 3,4 1,0 3,2 0,40 1,26 2,3 1,3 2,1 1,0 2,3 0,38 1,23 2,4 1,3 2,4 1,0 2,4 0,40 1,14 2,0 1,3 2,1 1,0 2,0 0,39 1,39 2,0 1,3 2,1 2,0 1,0 0,34 2,3 1,8 1,3 2,5 2,24 0,98 0,33 1,25 1,1 2,4 2,5 2,4 0,99 0,28 1,4 1,08 4,5 4,9 4,0 0,90 0,36 1,64 1,26 1,6 1,7 1,56 0,98 0,31 1,3 1,04 1,9 1,9 1,9 0,97 0,38 1,6 3,1 2,9 2,9 1,13 0,94 0,33 1,6 2,4 2,3 2,9 1,14 0,94 0,37 1,6 3,5 2,8 3,6 1,09 0,81 0,33 1,6 3,5 1,1 0,81 2,8 3,5 0,33 1,4 2,5 1,17 1,0 2,5 3,7 0,42 1,5 2,6 1,23 0,95 2,5 2,9

Table 3.10. Change of oligoethers concentration and structure of PP chains in the course of oxidation of non-inhibited samples of modified PP. Conditions: Tox. = 130°C, 2 = 150 millimeters of mercury; the data were obtained by IR-spectroscopy.

3.7. On question about the mechanism of oxidation of polypropylene modified by esters

If the rise of oxidation rate in samples of PP modified by DAF and DOS and the decrease of rate in PP modified by PPA-4 as well as the rise of rate of destruction of modified PP were caused only by the rise of reactivity of polymer matrix as a consequence of its enrichment by coagulated conformers, then the rate of hydroperoxides accumulation should be increased, that was not observed on practice. The change of destruction rate of PP chains in the presence of modifier may be explained by the change of mechanism of polymer oxidation. Increase of segment mobility of chain leads to increase of contribution of inter-molecular transfer of kinetic chains of oxidation. As a result of this kinetic chains of oxidation become shorter and the number of breakages in macromolecules is increased. But in the case of destruction process acceleration at the stage of kinetic chains continuation at the expense of prevailing of inter-molecular transfer in composition of hydroxyl-containing products the single OH-groups will prevail. However analysis of products composition didn't reveal prevailing of single OH-groups over block ones. Increase of chains mobility is observed not only in the case of PP with compatible additives, but also for PP+PPA-4, nevertheless the rate of PP oxidation in its presence is reduced. The most probable reason of oxidation process acceleration in samples of PP+DAF and PP+DOS, of the rise of PP chains destruction rate is joint oxidation (co-oxidation) of polymer and additives. If esters participate in oxidation, then they should be spent in the course of the process. Analysis of kinetics of esters spending obtained by IR-spectroscopy method (by the change of intensities of bands at 720 and 1270cm-1 (Table 3.10)) showed that the highest rate of oligoester concentration decrease was observed for DAF, this rate was significantly decreased for DOS and spending of PPA-4 was sharply decelerated. One may propose that decrease of oligoesters concentration is connected with their bleeding and volatilization from PP in the course of oxidation. Then volatility of additives should be increased in the raw DAF > DOS > PPA-4. Actually, in the work [279] mentioned ratio is fulfilled, however oligoesters lost from polymer at studied concentration even after processing at significantly higher temperature (>200°C) in comparison with temperature of oxidation doesn't exceed 20% from initial concentration, whereas under oxidation the concentration of esters was decreased in several times. Lost of compatible additive in polymer is in good agree with the rise of rate of sample oxidation and decrease of elongation at rupture; the highest rates of additive spending, polymer oxidation decrease of elongation at rupture are characteristic for the sample modified by DAF. Obviously localization of compatible additive in inter-crystallite amorphous regions promotes conjugated oxidation of PP and ester and accelerates oxidation of polymer matrix. Since activity of pure esters in relation to oxygen is lower than for PP oxidable polymer may initiates kinetic chains of oxidation in low-molecular additive by reaction: RmelO2 + MH o RmelOOH + M M + O2 o MO2

MO2 + MH o MOOH + M At that oxidable modifiers may inhibit oxidation of PP participating in reactions of termination and continuation of kinetic chains of oxidation. If radicals of modifiers participated in termination of kinetic chains of oxidation by reaction: MO2 + RmelO2 o inactive products + O2, the rate of destruction of PP matrix should decrease. Consequently, radicals MO2 participate in kinetic chains continuation. Probably products of oxidation of esters may interact with hydroperoxides decreasing their concentration. The fact that sum rate of oxidation of system of modified PP is not additive function of rates of oxidation reactions of pure PP and esters and also of character of changes of structural parame86

ters of PP under the action of DAF and DOS allows suggesting that inhibiting action of additive in the case of compatible systems is leveled. Amorphism of crystal phase and acceleration of oxidation in PP+DAF and PP+DOS may be the consequence of particularities of small-spherulite morphology of PP and also are connected with the fact that samples have high content of coagulated conformers and small crystallites also. From the other hand the presence of inter-molecular contacts between PP and DAF, DOS in amorphous inter-crystallite regions of PP may promote acceleration of oxidation process of PP and as a result initiating action of PP hinders inhibiting action of esters. Deceleration of oxidation of PP in the presence of PPA-4, inhibiting action of modifier may be strengthened by higher homogeneity and order of structure of crystallites in modified polymer matrix. The character of structural reconstructions accompanying oxidation of PP+PPA-4 is differed from PP+DOS and PP+DAF. Basing on the fact that degree of crystallinity of PP and also Tmel in the maximum of endotherm of melting of oxidized samples of PP with PPA-4 are changed slightly (in DAF and DOS Tmel is decreased), but at that the content of strengthened conformers is decreased shows that oxidation of PP+PPA-4 is accompanied by destruction of trough-pass intercrystal chains and for PP modified by DAF and DOS crystallites are destructed. It is important to note that yield of breakages in macromolecule of PP modified by PPA-4 in calculation per mole of absorbed oxygen is higher than in PP modified by DAF and DOS. Probably the over-stresses on trough-pass chains of polymer matrix appearing as a result of inter-phase interactions in incompatible system favour this fact [9]. But destruction of polymer crystallites in PP with DAF and DOS may be explained by higher rate of oxidation of PP in the presence of compatible additives. For specification of particularities of mechanism of thermal oxidative destruction accompanying oxidation of PP modified by esters the thermal oxidation of these samples in the presence of inhibitor was studied. Introduction of inhibitor into modified PP may lead to the change of destruction rate is chains are destructed in the course of chain process at the stage of continuation or termination of kinetic chains. At initiation stage inhibitor may influence at the expense of destruction of over-stressed bonds significantly weaker. Actually, introduction of inhibitor into investigated sample of PP significantly decreases initial rate of oxygen absorption of pure polymer and PP modified by DAF and DOS (Table 3.11). At that the rate of DAF spending is decreased and destruction of through-pass chains in the course of inhibited oxidation is decelerated. In the sample of PP+PPA-4 the rate of spending of ester practically doesn't depend on the presence of inhibitor. The fact that inhibitor introduced in to sample PP+PPA-4 can't decelerate the destruction of trough-pass chains in PP+PPA-4 sample significantly obviously indicates on destruction of overstressed trough-pass chains as on mechanism of destruction of macro-chains of PP in the presence of incompatible additive. The presence of inter-molecular contacts of polymer and low-molecular substances may promote acceleration of PP oxidation process in mixtures of PP with DAF and PP with DOS. In this connection the systems PP+DAF and PP+DOS may be considered as models of compatible blends of polymers or models of interface. Thermal oxidation of such systems is characterized by the presence of exchange reactions which may lead to initiating effect at the initial stage of oxidation which at deeper stage of process may be transformed into inhibiting effect.

87

PP + + 5% DOS inhibited

PP + + 5%DAF non-inhibited

PP + + 5% DAF inhibited

PP + + 1%PP -4 non-inhibited

PP + + 1% PP -4 inhibited

Composition

Duration of oxidation, min 0 45 120 180 240 300 0 30 60 120 160 240 45 120 180 240 300 0 30 60 120 160 0 45 120 180 240 300 D1737 D900 1,0 0,5 1,48 0,8 1,5 1,5 1,24 0,68 0,65 0,49 0,52 0,73 2,5 1,8 1,9 2,0 1,8 2,3 1,6 1,4 1,7 1,04 2,7 2,7 2,5 2,4 2,0 2,8

D1725 D 900

0,96 0,42 1,9 0,7 1,5 1,5 1,18 0,51 0,65 0,49 0,52 0,76 2,3 1,5 1,9 2,0 0,57 1,6 1,8 1,5 1,7 1,27 2,7 2,7 2,5 2,4 2,0 2,9

D1265 D900

0,44 0 0,48 0,1 0,4 0,3 0,55 0,36 0,33 0,35 0,32 0,27 1,7 0,8 1,0 0,8 0,55 1,8 1,2 0,9 1,2 0,47 0,25 0,01 0,13 0,04 0,13 0,30

Content of oligoethers D998 D900 2,7 3,4 3,8 3,4 3,5 3,6 2,4 3,2 2,3 2,4 2,0 2,0 3,7 3,8 3,6 3,5 3,7 2,24 2,4 4,0 1,56 1,9 2,6 2,7 2,5 2,3 2,6 3,0

D998 D975 1,0 0,9 0,9 0,95 0,94 1,0 1,0 1,0 1,0 1,0 1,0 1,0 0,92 0,90 0,90 0,90 0,87 0,98 0,99 0,90 0,98 0,97 1,0 1,0 1,0 1,0 1,0 1,0

D975 D1300 3,2 3,7 4,7 4,3 4,1 4,2 2,4 3,3 3,0 2,8 2,7 2,8 3,4 3,9 3,9 4,0 4,1 1,2 1,4 3,6 1,3 1,7 3,2 3,3 2,2 2,2 2,6 3,1

D840 D1300 3,3 4,5 5,3 5,3 4,5 4,5 2,5 3,5 2,7 2,9 2,7 2,8 4,6 5,5 5,0 5,3 5,4 1,4 1,5 3,9 1,4 1,7 3,3 3,4 2,3 2,3 2,7 3,2

D750 D900 0,4 0 0,14 0,06 0,1 0,1 0,10 0,09 0,10 0,05 0,07 0,08 0,44 0,16 0,26 0,19 0,16 0,56 0,30 0,22 0,36 0,13 0,07 0,06 0,07 0,07 0,04 0,1

2,8 4,1 4,9 4,4 4,2 4,0 2,5 3,4 2,1 2,4 2,1 2,1 5,6 5,9 5,4 5,3 5,6 2,5 2,5 4,9 1,7 1,9 2,7 2,8 2,6 2,4 2,7 3,2

D840 D900

0,40 0,47 0,46 0,43 0,44 0,45 0,37 0,41 0,40 0,38 0,40 0,39 0,53 0,46 0,47 0,45 0,47 0,34 0,33 0,28 0,36 0,31 0,6 0,5 0,48 0,47 0,48 0,50 1,4 1,5 1,4 1,3 1,2 1,3 1,33 1,33 1,26 1,23 1,14 1,39 1,4 1,4 1,2 1,0 1,4 1,8 1,25 1,4 1,64 1,3 1,5 1,3 1,3 1,3 1,2 1,4 2,7 3,4 4,3 3,6 3,8 3,7 2,4 3,2 2,3 2,4 2,0 2,0 4,1 4,2 4,1 3,9 4,3 2,3 2,4 4,5 1,6 1,9 2,7 2,7 2,5 2,3 2,6 3,1 1,3 1,4 1,4 1,4 1,4 1,4 1,3 1,3 1,3 1,3 1,3 1,3 1,3 1,6 1,3 1,25 1,5 1,3 1,1 1,08 1,26 1,04 1,7 1,7 1,7 1,6 1,6 1,6

88

D460 D900

D1155 D900

D975 D900

D810 D900

Structure of macromolecules of modified PP Crystal regions Amorphous regions

Table 3.11. Confrontation of oligoethers concentration change and structure of PP chains during the oxidation of inhibited and non-inhibited samples of modified polymer. Conditions: Tox. = 130°C, 2 = 150 millimeters of mercury; the data were obtained by IR-spectroscopy.

PP + + 5% DOS non-inhibited

0 30 60 120 160 240

0,35 0,35 0,14 0,19 0,10 0,12

4,5 3,2 4,0 4,0 2,7 3,0

4,5 3,2 4,3 4,0 2,7 2,7

0,6 0,3 0,4 0,5 0,35 0,52

3,6 3,9 5,9 5,5 3,7 3,5

3,9 3,4 4,7 5,6 3,3 3,2

0,94 0,94 0,81 0,81 1,0 0,95

2,9 2,3 2,8 2,8 2,5 2,5

2,9 2,9 3,6 3,5 3,7 2,9

1,13 1,14 1,09 1,1 1,17 1,23

3,1 2,4 3,5 3,5 2,5 2,6

1,6 1,6 1,6 1,6 1,4 1,5

89

0,38 0,33 0,37 0,33 0,33 0,42

Chapter 4. Blends of crystallizing biopolymer and polyolefine: poly-3-oxybutirate and polyethylene of low density Compositions on the base of polyolefines and bio-degradable polymers one of which is poly3-oxybutirate (POB) are usually thermodynamically incompatible. Such systems are characterized by polydisperse structure with developed boundary surface [3-9, 13, 37, 47, 48, 91, 280, 281]. Polymer chains of biodegradable polymer under the temperature influence may destruct with formation of low-molecular radicals. One may assume that the determinative factor which will influence on kinetics of oxidation of blend POBPELD is the ability of low-molecular radicals of POB to initiate kinetic chains of oxidation in PE. It is obvious that this ability will depend on POB morphology and structure of interface. Thus, investigation of regularities of thermal oxidation of blend POBPE allows establishing of the role of structure in thermal oxidation of hetero-phase polymer systems. In this work we used compositions containing from 2 up to 32 mass % of POB in PELD. POB was of brand "Lot 0997" of "Biomer" firm (Germany) as fine powder with density equal to 1,25g/cm3. Blending of polymers was realized on laboratory heated micro-roll mills VK-6 at 150°C. Films with the thickness 60mcm were formed from these blends. 4.1. The structure of poly-3-oxybutiratepolyethylene of low density blends

The fact of incompatibility of components in mixture POBPELD is consequent from microphotographs of samples obtained with the help of electron microscopy. These microphotographs demonstrate clear interfaces between phases (Figure 4.1).

90

Figure 4.1. Microphotographs of chips of films of PELDPOB containing (a) 32 mass %, (b) 16 mass %, (c) 8 mass % of POB along and across the direction of extrusion obtained with the help of electron microscopy.

91

Moreover, the endotherms of mixtures POBPELD containing from 2 up to 32% of POB in polyethylene have only two peaks in temperature intervals belonging to melting of PELD and POB (Figure 4.2).

Figure 4.2. The endotherms of melting of POB (a) and of blends PELDPOB (b).

Insignificant change of thermophysical parameters namely of Tmel of both components in blend POBPELD in comparison with pure polymers also demonstrate that blends form two phases and confirm the heterogeneity of blend (Table 4.1). Table 4.1. Thermophysical properties of initial samples of blend POBPELD. PELD : POB mass % 100:0 98:2 96:4 92:8 84:16 68:32

mel,  PELD POB 107 172 106 172 106 171 106 173 106 173 106

'+mel, J/g PELD POB 102,0 37,8 87,0 40,9 71,7 42,2 74,7 44,1 67,4 49,5 58,6

Dcr, % PELD 35 30 24 26 23 20

POB 42 45 47 49 55

cr,  PELD 89 90 89 90 90 90

Nevertheless the blends POBPE are characterized by interaction of chains of components on interface. The result of such interaction is strong deceleration of POB crystallization in blend in comparison with pure polymer and appearance of chains orientation. The presence of orientation of molecular chains of components was found by the method of polarization IR-spectroscopy. Degree of PE orientation in samples of films of blends is decreased in comparison with the films of pure PE (Figure 4.3). The degree and direction of orientation of crystal regions of POB phase in blends with PE are changed with change of composition of blend and are differed from indexes for initial POB (Figure 4.3). Thus, the degree and direction of chains orientation of components may serve as qualitative characteristics of inter-molecular interaction on interface.

92

Figure 4.3. The dependence of PE chains orientation (by IR-dichroism (R) of band at 729cm-1) and the dependence of POB chains orientation (by IR-dichroism (1/R) of band at 1228cm-1) in blends POBPE on concentration of POB.

4.2. Kinetics of absorption of oxygen by poly-3-oxybutiratepolyethylene of low density blends

Kinetic curves of oxygen absorption by samples of POB, PELD and their blends containing from 2 up to 32 mass % of POB are presented in Figure 4.4.

93

Figure 4.4. (a) Kinetic curves of oxygen absorption by pure POB, PELD and their blends of various composition. Tox = 90°C, PO2 = 600 millimeters of mercury. (b) The initial parts of the same curves.

At conditions of experiment carrying out POB possesses high thermal oxidative stability. Kinetic curves for all studied samples of blends are characterized by the presence of two parts. The first part of kinetic curves corresponds to the induction period of oxidation of POB and on this part the oxidation of polymer matrix occurs. At the second stage POB participates in oxidation process. The first part of kinetic curve of oxygen absorption has complex character of dependence on blends

94

composition. The second part demonstrates monotonous dependence o oxidation rate on POB content. It is obvious that complex character of dependence of oxidation rate on composition of blend POBPELD at the initial stage of process is caused by the changed structure of PE matrix. POB introduced into PE modifies structure of this component [282, 283]. While modifying PE matrix POB changes permolecular and molecular structure of this polymer. If the analysis of character of change of structural parameters of PE as components of blends under introduction of POB into it allows concluding that the first part of kinetic curves corresponds to the change of PE matrix structure, so the second part of kinetic curves couldn't be described by these changes. 4.3. On the question about the mechanism of oxidation of poly-3-oxybutiratepolyethylene of low density blends

In spite of the fact that at conditions of oxidation POB possesses high thermal oxidative stability it may be destructed with formation of low-molecular radicals [284]. The data of study of destruction process of POB by DSC and IR-spectroscopy methods and also the kinetics of gas evolution under POB destruction in inert medium indicate on this fact. The thermophysical properties of samples oxidized during the time oncoming to POB decomposition were studied. Analysis of parameters of blends' samples melting presented in Table 4.2 shows that temperature of POB melting is decreased by more than 10°C that indicates on decomposition of crystallites of this polymer which is caused by destruction of polymer chains. We should also mention the decrease of POB crystallinity degree (cr) by 3-5% that also testifies to the beginning of destruction processes in it. It is important that PE in blends with POB reacts to high temperature influence in other way. Beginning from the composition PE : POB = 96 : 4 (Table 4.2) the heat of melting and degree of crystallinity are increased. Crystallization temperature is also increased in 2-3°C that testifies to the rise of rate of nucleation during formation of crystals due to the rise of order of crystal PE chains as a result of annealing. The last fact is confirmed by IR-spectroscopy data. Table 4.2. Thermophysical properties of initial and oxidized for 500 hours samples of blend POBPELD*. PELD : POB, mel,  cr,  '+mel, J/g Dcr, % mass % PELD POB PELD POB PELD POB PELD 89/ 93 - / 35/ 27 - / 102,0/ 80 - / 107/ 107 100:0 90/ 93 42/30/ 26 37,8/ 87,0/ 76,1 172/ 106/ 107 98:2 89/ 93 45/24/ 25 40,9/ 71,7/ 75,8 172/ 106/ 106 96:4 90/ 92 47/44 26/ 28 74,7/ 73,1 42,2/ 40,2 171/ 161 106/ 106 92:8 90/ 92 49/47 23/ 29 67,4/ 89,1 44,1/ 42,3 173/ 159 107/ 106 84:16 90/ 91 55/50 20/ 30 58,6/ 90,3 49,5/ 45,2 173/ 157 106/ 106 68:32 Notes: *  in the numerator there are values for initial samples, and in denominator  for the oxidized ones.

The dependence of change of degree of regularity of PE crystal chains in the course of blends oxidation is presented in Figure 4.5. Obviously in blends with various compositions oxidation of PE is accompanied by the rise of content of chains in strengthened conformation of trans-zigzag. It is confirmed by the rise of intensity of band at 730cm-1. It is important that at general character of change of crystallinity degree and regularity of chains of PE component in mixtures the quantitative changes don't depend on its structure. It is obvious when comparing samples containing 16 and 32% of POB that structural reconstructions conditioned by annealing in crystallites of more perfect structure are facilitated under oxidation. Obviously the process of PE annealing is directly connected with blend oxidation. It is promoted by destruction of inter-crystal trough-pass chains initiated by POB. The dependence of intensity of IR-band at 1360cm-1 responsible for content of trough-pass inter-crystal coagulated chains is presented in Figure 4.5. The rise of value of D1360 indicates on the

95

increase of content of GTGconformers of PE [234, 235, 238] as a result of relaxation and coagulation of destructed stressed trough-pass chains in amorphous regions of polymer.

Figure 4.5. The change of regularity degree of crystal chains of PE (a) and content of inter-crystal troughpass chains in coagulated conformation of PE (b) in samples PELD : POB = 84 : 16 (1) and 68 : 32 mass % (2).

It is obvious from the analysis of accumulation of carbonyl groups in the course of thermal oxidation of studied compositions that with the rise of content of POB in mixture the rate of accumulation of carbonyl groups, i.e. products of oxidation characteristic for PE is increased (Figure 4.6).

Figure 4.6. Kinetic curves of accumulation of carbonyl-containing products of oxidation of PELD (1) and blends PELDPOB of the following compositions: 98 : 2 (2), 96 : 4 (3), 92 : 8 (4), 84 : 16 (5) and 68 : 32 (6) mass %. Tox = 90°C, PO2 = 150 millimeters of mecury.

96

The data on accumulation of single and block OH groups (by the values of optical densities of bands at 3620 and 3420cm-1 accordingly) are presented in Table 4.3. Table 4.3. The ratio between concentrations of single hydroxyl-containing groups and groups connected by hydrogen bonds (D3620/D3420). Duration of oxidation, hours 0 150 500

100:0 2,9 1,4 1,1

D3620 / D3420 for blends PELD : POB, mass % 98:2 96:4 92:8 84:16 0,7 1,2 2,2 2,1 0,6 0,7 1,0 1,1 0,3 0,5 0,7 0,8

68:32 0,5 0,4 0,2

It follows from the ratio D3620/D3420 that for more elastic PE the intermolecular transfer of kinetic chains of oxidation is characteristic, as well as for samples containing 2 and 4 mass % of POB, chains become more rigid since POB contains heteroatom oxygen in the main chain; viscosity of the system is increased [237, 238, 285] and changes in the mechanism of free valency transfer are observed: the contribution of intra-molecular chain transfer is increased. It is obvious from Table 4.3 that the ratio of single to block OH groups is sharply decreased with the rise of POB content in the system and with the rise of oxidation depth. Thus at given stage of oxidation POB changes the morphology of polyethylene matrix and thereby influences on the mechanism and kinetics of oxidation process. Thus, low-molecular radicals resulted from destruction of POB may diffuse into PE matrix initiating there kinetic chains of oxidation by the following reaction: r* + RPE o RPE + rH Obviously this is the reason of observing at the second part of kinetic curves of oxygen absorption by samples of blends POBPELD directly proportional dependence between rate of process and content of POB in mixture. Since the rate of decomposition of POB is equal to: Wd = kd[POB], where kd – the constant of rate of POB process, then initiating ability of this polymer will be equal to: Wi = fi kd[POB], where fi – effectiveness if initiation, the coefficient depending on structure of POB phase. In this case the role of structure factors will come to influence of morphology of POB component and structure of interface on diffusion of low-molecular radical (transfer of free valency) from phase of POB to PE. Reaction of low-molecular radical r* with RH-bond in matrix of PE, i.e. initiation of kinetic chains of PE oxidation will proceed if the rate of this radical deactivation for example in reaction with RH-bond of POB, i.e. in exchange reaction of r* by stable macro-radical R* is lower than the rate of its diffusion into PE-component. Let's estimate the probability of kinetic chains origination in PE with the help of radicals diffused from POB. With this aim we shall determine the time of r* radical transition W2* from POB into PE component with the help of expression: O = (6DoWr*)0,5 [161], where D0  coefficient of radical diffusion. According to the data of works [162, 214] D0 is ~10-7 cm2/sec; O  is the distance depending on diameter of particle of disperse phase lying in the interval 10-6 up to 10-4cm. Then the time of diffusion (in seconds) of low-molecular radical r* from phase of POB into PE phase is: Wr* = O2/6Do  (10-1210-8)/6  10-7  10-610-2. If radical r* disappears in termination reaction with formation of stable radical of POB: r* + RPOBH — rH + RPOB* then the time necessary for spending of r*radical is equal to: Wr*' = l/k[RPOBH]. 97

Maximum value of [RH] in POB polymer composition is changed in the limits from 2 up to 32 mole/kg taking into account the destruction of amorphous regions. Then the magnitude Wr*' 101 10-3sec, i.e. the time of reaction of substitution by radical r* of hydrogen atom in RH-bonds of POB is larger than time of radical diffusion from POB into PE-phase in the case when particles have spacious interface between phases. Thus, the form of POB particles or extension of boundary of contact between POB and PE should cause the influence on rate of oxidation kinetic chains initiation in PE and consequently determine the rate of oxidation. For examination of this hypothesis the thermal oxidation of blends POBPELD of one composition prepared by various methods of mixing was studied. Various techniques of mixing allow obtaining various degrees of particles fining, i.e. various sizes of phases and length of interface. 4.4.

The role of inter-phase phenomena in oxybutiratepolyethylene of low density blends

kinetics

of

thermal

oxidation

of

poly-3-

For the solution of posed problem the following compositions were prepared: PE 92 mass % + POB 8 mass % in various regimes of blending. With the help of ball drum the granulated PE was mixed mechanically with POB powder and PE powder was mixed with POB powder. With the help of one-screw laboratory granulator the granules of blends were obtained from which the film sleeve was formed with the help of extruder. The dispersion degree of POB in samples of blends was determined by method of raster electron microscopy on longitudinal and cross (in relation to extrusion direction) chips at magnification 10010000 with the help of electron microscope "BS-301" (TESLA USA). By obtained microphotographs using the principle of KavalieryAkker the average sizes of POB phase were calculated and differential curves of distribution by sizes of particles of POB phase in PE matrix were plotted (they are presented in Figure 4.7).

Figure 4.7. Differential curves of distribution of POB particles diameters in blends films in dependence on initial aggregate state of particles of mixed PELD and POB: (a) granules of PE + powder of POB, (b) powder of PE + powder of POB.

98

It is obvious from presented estimations that average size of POB phase in films obtained from systems "granulespowder" is about 1mcm. In films obtained from system "powderpowder" the average size of POB phase is about v0,30,6mcm. Since POB concentration in compositions is not changed then films obtained by mixing of two powders have more developed specific boundary surface. Since there is no developed interface, so obviously all particularities of kinetics of oxidation of PEPOB blends are connected with the value of interface (boundary surface). The sizes of particles of disperse phase and length of interface will have the determinative importance. More fine structure is formed under mixing of equal by sizes particles in contrast to system with essentially different in sizes particles (in dozens of times) due to unequal behavior of various by mass particles in the field of gravitation forces. For estimation of effect of boundary surface on structure of POBPELD films their structural parameters were determined. Analysis of structural and physical-mechanical parameters of compositional films shows that: Firstly, in accordance with the data of investigations of blends with the help of DSC the melting temperatures of components are practically don't depend on polydispersity degree and are not differed from characteristic values for films obtained from initial pure polymers. This fact testifies to the absence of inter-molecular interaction between PELD and POB leading to appearance of clearly expressed interface; Secondly, the crystallinity degree of blends components is decreased in comparison with its value for initial homopolymers. Amorphism of crystal phase of polymers in blends in comparison with homopolymers is confirmed by data of IR-spectroscopy (Table 4.4). Obviously this fact is connected with inter-molecular interactions of components interfaces, i.e. with the influence of boundary surface on structure formation processes. Thirdly, by method of polarization IR-spectroscopy the presence of orientation of molecular chains of components was found. All these facts indicate on the interaction of components of blends on interface and may serve as its qualitative characteristic. It is obvious from Table 4.4 that degree of PE orientation in blends samples is decreased in comparison with films of pure PE but practically doesn't depend on the value of boundary surface. The change of value of orientation of crystal regions in PE matrix is obviously conditioned by the change of rate of relaxation processes due to inter-molecular interaction in resulted boundary layer (adhesion layer) in blends with POB. The degree and direction of orientation of crystal region of POB phase in blends with PE significantly depend on boundary surface value and are differed from those values for initial POB. We may conclude that the change of spatial orientation of macromolecules in POB crystallites and rate of crystallization process more likely are the functions of composites dispersion degree. In other words the smaller the average size of dispersion phase particles, the stronger the influence of boundary surface value and connected with it value of adhesion layer on mentioned size. In support of this statement there is the fact that decrease of value of average sizes of diameters of particles of POB phase in 2 times corresponds to the difference between degrees of orientation of POB crystal phase also in 2 times. Comparing the values of orientation degrees of PE and POB in blends films with various lengths of boundary surfaces one may notice the unconformity of numerical values of parameters of orientation (R) of these phases obviously connected with various rates of relaxation processes proceeding in PE matrix and POB phase during films formation. This fact may indirectly testifies to the absence of through-pass (inter-phase) layer in blends and existence of thin adsorption layer smaller than 5-10nm [810]. This layer as a sonsequence of small thickness (in comparison with the thickness of boundary layer adjacent to the interface) doesn't reveal properties of independent phase.

99

Granules of PE + + powder of POB Powder of PE + + powder of POB PELD POB

Sample

Degree of crystallinity, %

PELD

POB 21,8 31,4 19,1 51,4 35,0 70,0

mel, 

PELD

POB 105 171,2 106,0 172 107,0 175,4 5,52 11,6 2,38 0,013

15,6 20,0 40,0

2

cm ˜h˜mm of mercury

___g˜cm_____

Water permeability (18 )

18,0

MPa

Tension strength (along the extrusion)

1,50 -

1,42

1,46

Relative units

Intensity of IR-band at 729cm-1

5,86

1,52

1,42

Relative units

Intensity of IR-band at 1228cm-1

1,75 -

1,07

0,94

Relative units

R of band at 729cm-1

Table 4.4. Structural parameters of films of blends of PELD with POB prepared at various conditions of mixing.

100

2,500

0,72

1,4

Relative units

1/R of band at 1228 cm-1

Fourthly, the films of blends PEPOB have somewhat understated in comparison with PE values of strength and increased permeability. And the lowest strength and the highest permeability are characteristic for films with large square of boundary surface. This moment is explained by the fact that there is no interface; at that the structure of polymers near to boundary surface is as a rule less compact than in the volume and elements themselves may form microscopic canals on interface which are formed as a result of extraction (and bulge) of film sleeve. As it is obvious from data of Table 4.4 the crystallinity of PE in blends is practically not changed in dependence on value of boundary surface. Most likely that PE matrix possesses low sensitivity to the change of crystallinity in boundary surface due to comparatively low content of POB. On the contrary, degree of crystallinity of POB phase is changed with the change of boundary surface value. In the blends with larger lengthening of boundary surface POB phase has higher crystallinity. This effect may be explained by unequal proceeding of process of structure formation on molecular level under the flow of blends melts and formation of film samples. Basing on all said above we may assume that dispersion degree of bio-degradable polymer POB in matrix of PE will influence on kinetics of oxidation process of compositional films. Actually we see it from the data presented in Figure 4.8. As it is obvious, kinetics of oxygen absorption by blends samples is significantly differed from oxidation kinetics of pure polymers and are differed between each other. At deep oxidation levels (more than 0,5mole/kg) the sample with large boundary surface is oxidized practically with the same rate that the sample with smaller boundary surface. But both of them are oxidized faster than initial PE. At the initial stage of oxidation (less than 0,5mole/kg) samples with higher value of bounder surface are oxidized faster than sample of pure PE and sample with smaller boundary surface, and the sample of pure POB is not oxidized in the given interval of temperatures. The value of induction period of oxidation and the change of oxygen absorption in the course of process indicate on last facts. It is obvious from comparison of induction period and rate of oxygen absorption with the value of boundary surface that the highest rate of oxidation will observe in the case of sample with more developed boundary surface. From the one hand it is connected with the fact that POB at high temperatures undergoes destruction and becomes the origin of low-molecular radicals which may initiate oxidation in PE matrix at the expense of phases contact on interface by transferring of kinetic chain of oxidation into the volume of PE phase. The larger the specific boundary surface, the larger the square of contact of POB phase with PE matrix and the higher the stresses of macromolecules adjoining to boundary surfaces in polymer layers. As it is obvious from data of Table 4.4 the degree of PE phase orientation in the case of large boundary surface is higher than in the case of smaller one. The rise of orientation degree of PE macromolecules leads to decrease of their stability to oxidation. High rate of oxidation in the case of lengthier boundary surface is explained by this fact. At low degrees of oxidation (at the initial stage of oxidation) kinetics of process for various blends is differed. In blends with small value of boundary surface the rate of oxidation is lower. And initial POB is not oxidized. Such different behavior of blends under oxidation is a consequence of conformational changes in PE matrix on molecular level under POB phase effect. Obviously at deep oxidation degrees (duration of oxidation more than 700 hours) POB is oxidized and destructed forming low-molecular radicals which accelerate oxidation process of polymer matrix. The slip on the curve of oxidation of pure POB testifies to this fact. This may indicate on independence of oxidation process of blends on the value of boundary surface dispersion, since the numbers of radicals resulted from POB phase in both blends are equal due to equal content of POB in compositions. Thus, thermal oxidation of blends POBPELD is the process of oxidation of PE matrix initiated by POB. Kinetics of the process at the initial stage of oxidation is determined by structure of PE at deep stage, i.e. by structure of POB component and length of interface.

101

Figure 4.8. (a) Kinetic dependences of oxygen absorption on oxidation duration for the films of: (1)  PELD, (2)  POB, (3)  blend "PE granules + POB powder", (4)  blend "PE powder + POB powder." (b) Kinetics of oxidation of films samples at the initial stage of process. The rest as in (a).

102

Chapter 5. The blends of crystallizing polymers: isotactic polypropylene and polyethylene of high density Blends PPPEHD are the blends of two incompatible polymers with crystallizing components and are characterized by heterogeneity at various permolecular levels [8, 11, 22, 23, 26, 28-32, 8385]. The structure of such blend is formed at the stage of blending of components in melt or solution. Structure of its crystal regions is developed at the stage of melt cooling or dilution of blend. Processes of crystallites formation of both components depend on ratios of phase lamination and process of components crystallization. In dependence on rate of cooling of melt or solution of PP and PE one of the components may play role of crystallization nucleus for another one or they may decelerate rate of propagation of each other and change morphology of blend. Thus, while changing conditions of blending, intensity of mechanical effects, composition of blend, conditions of crystallization one may obtain materials differing not only by morphology of blend, but also by permolecular and molecular structures of components. For example, during crystallization of blends of PE with PP in ratio 1 : 1 the last one forms three-dimensional structure filled by PE melt. After PE crystallization morphology of blend represents two interpenetrative to each other structures of the type "net in net" [8]. For polymer blends PPPE with insignificantly differed in polarity components the conception of segmental solubility is applicable [8] and they may form not only the interface but also interphases layers by thermodynamic mechanism. Thickness of layer may be changed from 10 up to 100Å in dependence on blend composition [69]. In inter-phases regions under the mutual influence of blend components the change of conformations of macromolecules occurs on the inter-phases surface in comparison with their conformations in block polymers [69, 79]. The presented chapter is devoted to establishing of the role of structure parameters in kinetics of auto-oxidation of blends on the base of PP and PEHD which structure was varied by changing of blends composition and way of blending. The following blends were studied: a) blends of components of various composition obtained by mechanical blending; b) blends of one composition obtained by various methods of preparation. 5.1. Mechanical blends of isotactic polypropylene and polyethylene of high density

We used non-inhibited polymers: polyethylene of high density (w = 4,2˜104, Mn = 2,7˜104, density d = 0,960g/cm3) and isotactic polypropylene (Mw = 2,86˜105, Mn = 6,2˜104, d = 0,906g/cm3). Blending was carried out in micro-extruder (Tbl = 180qC) with preliminary mixing of polymer powders in ball drum (for 60 minutes). Conditions of blending provided homogeneity of mixing and absence of polymers destruction. Content of components in blends was controlled with the help of IR-spectroscopy, by this method the structure of components chains was also determined. For determination of crystallinity degree of components we used DSC. 5.1.1. Kinetics of oxygen absorption by samples of polypropylenepolyethylene of high density blends

Kinetic curves of oxygen absorption by samples of PP, PE and their blends with various contents of components were obtained at conditions when both polymers were in solid phase. The shape of these blends is differed from analogous curves of homopolymers by the presence of more or less clearly expressed inflections connected with sharp acceleration of oxygen absorption at deep stages of oxidation (Figure 5.1).

103

Figure 5.1. Kinetic curves of oxygen absorption by samples of PP (1), PE (2) and their blends containing 10 (3), 40 (4), 50 (5), 80 (2) mass % of PP at Tox = 110qC, PO2 = 600 millimeters of mercury.

Analysis of these curves shows that introduction of PP into PE leads to acceleration of oxidation process and in dependence on composition the blends may be oxidized faster not only in comparison with pure PE, but in comparison with PP also. The values of induction period Wind and maximum rate of oxidation Wmax at the initial part of kinetic curve depend on blend composition in various ways, but both dependences are not its additive functions (Figure 5.2).

104

Figure 5.2. The dependences of induction period (1, 3) and maximum rate of oxidation (2, 4) of blends PPPEHD on their composition. Curves 1, 2are experimental and 3, 4 are calculated.

Dependence of Wind on contents of components is described by curve with minimum. Sharp decrease of Wind of blend in comparison with PE is observed already at small concentrations of PP. The minimum corresponds to 50 mass % of PP and by value of Wind of this blend it is significantly lower than for pure PP. With the rise of PP content from 50% Wind of blend is increased but in value remains lower than induction period of PP. Maximum rate of oxidation of polymer compositions is exponentially increased with the rise of PP content in them. Parameters of blend oxidation are determined by chemical structure of oxidizing material (reaction ability of components) and structure of blend. Absence of additivity of mentioned above dependences testifies to the change of mechanism of radical reactions, and/or to significant influence of structural parameters of polymer blends on kinetics of their oxidation. With the rise of PP content reaction ability of blend is increased and for blends with high content of PP it approaches to pure PP remaining lower than for it. Reaction ability of blend with low content of PP is higher than for pure PE. (The values of inclination of linear anamorphosis of kinetic curves of oxygen absorption for samples of homopolymers of PP and PE were correspondingly 6,7˜10-5 and 6,3˜10-6 (mole05/kg05sec), for samples of blends containing 10, 40, 50 and 80 mass % of PP they were correspondingly 1,1˜10-5, 3,0˜10-5, 4,7˜10-5, 6,0 (mole0,5/kg0,5sec)). The presented data allow concluding that at the initial stage of blend oxidation the important role if played by active PP-component. Since PP and PE are separate phases (in dependence on composition of blend they may represent either the disperse phase, or dispersing medium) they may participate in auto-oxidation process independently from each other. In this case rate of oxidation of blend will be formed by the rates of oxidation of its components. One may expect that due to the difference in reactivity of secondary and tertiary carbon atoms at the initial stage the oxidation of more active component PP will be observed. PE may "take part" in process in accordance with the value of kinetic parameter of oxida105

tion k2/—k6 at the stage when PP is significantly oxidized. Kinetic parameter used in the work for determination of reactivity of blend at the initial stage of oxidation should be considered as corresponding to the oxidation of PP component. Then the inclinations of anamorphosis of kinetic curves obtained by transformation of experimental data with consideration of PP-component oxidation should be equal for blends of all compositions. Under transformation the crystallinity degrees of PP in each sample were taken into account and kinetic curves of oxygen absorption by homopolymers and blends samples were recalculated per 1 mole of monomer units of amorphous regions of PP. Obtained in such way kinetic curves and their anamorphosis are presented in Figure 5.3.

Figure 5.3. Kinetic curves of oxygen absorption obtained from the experimental ones, recalculated per oxygen absorption by monomer units of amorphous phase of PP-component ([RH]) (16), their linear anamorphosis (1'6') for samples of PP (1, 1'), PE (2, 2') and their blends of the following compositions: 10 (3, 3'), 40 (4, 4'), 50 (5, 5'), 80 (6, 6') mass % of PP. Tox = 110qC, PO2 = 600 millimeters of mercury.

It follows from the Figure that values of induction periods of blends oxidation are differed. And at each linear anamorphosis there are two parts differing in values of inclinations (b05). At the first part the values of b05 are practically equal to each other and are as follows 1,7˜10-5, 1,6˜10-5, 1,8˜10-5, 1,5˜10-5 (mole of 2)0,5 / ((mole of RH)0,5˜sec) for the blends containing 10, 40, 50, 80 106

mass % of PP accordingly and approach to inclination of analogous anamorphosis of pure PP but remain somewhat lower (b05PP = 3,4˜10-5 (mole of 2)0,5 / ((mole of RH)0,5sec). in other words reaction ability of PP in blend is lower than for homopolymers. Inclinations of the second parts are significantly lower than first ones and are equal to 7,0˜10-6, 5,8˜10-6, 6,4˜10-6 and 5,8˜10-6 (mole of 2)0,5/((mole of RH)0,5˜sec) for the samples of the same compositions. The listed values testify to the sharp decrease of reactivity of PP, but nevertheless this decrease doesn’t reach the value of bPE. It is important that the times corresponding to inflections of anamorphosis are essentially lower than induction period of homopolymer PE oxidation. The first ones don't reach 10 hours, whereas induction period of oxidation of PE is equal to 29 hours. The levels of oxidation corresponding to the inflections are equal to 0,2; 0,9; 0,7 and 1,4 mole/kg of samples in blends containing 10, 40, 50 and 80 mass % of PP correspondingly, i.e. they are increased with the rise of content of PP component in blend. It is obvious that the change of inclination of linear anamorphosis indicates on the decrease of sum reactivity of RH-bonds participating in oxidation. The given fact from the one hand may testify to structural effects, from the other it may indicate on entering of less active PE component into oxidation process and to the fact that initial rate of its oxidation in blend is higher than in the case of homopolymer. It is possible in the case of interaction between oxidized components of blends when they may influence on the rates of oxidation of each other. Let's assume that inflection of anamorphosis is not connected with participation of PE component in oxidation and the last one is oxidized with the same rate as homopolymer. Then the law of additivity is fulfilled and the ratio for determination of concentration of absorbed oxygen by blends samples (with consideration of particularities of components structure and data of conformational analysis (Table 5.1)) may be presented as follows: No2bl(W) = {Nqo2PE˜[(1-iPE)/(1-XqPE)]GiPE + Nqo2bl˜[(1-iPE)/(1-XqPE)](1-GiPE)˜GiPP/GqPP}Wa/Wi where Nqo2PE, Nqo2PP  concentration of oxygen absorbed by initial PE and PP at the moment W, GiPE  part of PE component in blend, PE, PP  the parts of crystal phases of components, GPP  concentration of coagulated conformers of PP, i  indexes relating to initial homopolymers and components of blends accordingly, Wa  the time of correlation calculated from additive scheme: W = WqPEGiPE + WqPP(1-GiPE). (All the used parameters were calculated for temperature at which oxidation was carried out.) With the use of presented above expressions we obtained calculated kinetic curves of oxygen absorption by samples of blends of various compositions. The values of induction periods and maximum rates of oxidation characterizing given curves are presented in Figure 5.2 in comparison with experimentally obtained dependences. It follows from the Figure that calculated values of Wind and rates of oxidation are significantly higher than experimental ones. Moreover, the character of dependences of calculated values of Wind and WO2 on blend composition is significantly differed from the character of experimentally obtained dependences. The totality of obtained data indicates on the fact that initial rate of oxidation of samples of blends PPPE is determined by the rate of oxidation of PP component and the rate of oxidation of this component is somewhat lower than for homopolymer whereas PE component is oxidized with higher rate than homopolymer. With the aim of examination of data obtained from analysis of kinetic curves we investigated nonvolatile products of blends oxidation.

107

0,20 0,40 0,40 0,70 0,70 0,90 0,90 1,00 1,00 1,10

100% PE

37,0 40,0 40,7 37,0 43,5 46,3 38,9 47,7 64,0

XPP, %

50,0 50,1 49,6 46,8 48,2 41,3 40,8 32,5 42,4 -

XPE, % 5,3 5,0 6,0 7,3 10,5 17,0

Correlation time, W˜1010, s

Notes: XPP, XPE – degrees of crystallinity of PP and PE accordingly.

100% PP

80% PP

50% PP

40% PP

10% PP

D1375 D1460

Composition of blend 1,5 1,4 5,0 4,9 6,7 6,4 11,7 10,0 8,6

[RH]mel 18,0 16,0 16,0 12,7 13,5 10,5 10,6 4,8 4,1 -

[RH]PE

[RH] in amorphous phase

0,63 0,67 0,74 0,70 0,94 0,99 0,87 0,97 -

D1155 D1170(1-NPP)

Table 5.1. Structural parameters of samples of PPPEHD blends.

1,60 1,66 1,70 1,60 1,50 1,45 1,77 2,00 -

D975 D1170(1-NPP) 1,94 2,00 2,10 2,04 2,03 1,93 2,04 2,00 -

108

D720 D730(1-NPE)

5.1.2. Nonvolatile products of oxidation of polypropylenepolyethylene of high density blends

Significant difference between compositions of non-volatile products of oxidation of PP and PE allows estimating the contribution of each of the components of PPPE blend into oxidation process in dependence on its structure if we assume that mechanisms of radical reactions of oxidation of blend's components and homopolymers are identical. The difference in the structures of homopolymers oxidation products is in the fact that, firstly, carbonyl-containing groups of PE predominate over hydroxyl-containing ones; secondly, the content of OH groups in PE connected by hydrogen bonds is low in comparison with single ones, in PP connected OH groups prevail and the content of single ones is low. The ratios between contents of separate functional groups in samples of studied polymer blends oxidized for different levels were analyzed. It follows from the data presented in Figure 5.4 that at equal amount of absorbed oxygen the structures of products in blends PPPE and homopolymers are essentially differed. In the samples of blends of all compositions the ratio between content of groups and OH connected by hydrogen bonds is lower than in pure PE; simultaneously this ratio in samples of blends is higher than in PP.

Figure 5.4. The dependences between ratios of carbonyl- and hydroxyl-containing groups and concentrations of absorbed oxygen for samples PP (1), PE (2) and their blends containing 10 (3), 40 (4), 50 (5), 80 (6) mass % at Tox = 110qC, PO2 = 600 millimeters of mercury.

The observed differences between products of oxidation of blends and homopolymers are hard to explain from the point of view of changes in the mechanism of radical reactions due to localization of oxidation in PP phase. In the last case the structure of products of oxidation of blends should correspond to the structure of products of deep oxidation [162]. However we observe higher than in the last case ratio between CO content and content of bonded OH groups. So, we may assume that ratios between mentioned groups characterize the contribution into the structure of products of oxidation of blend of products of one or another component. The values of this ratio are exponentially decreased with the rise of PP content in blend at equal levels of samples oxidation. And 109

in the course of oxidation the composition of products is transformed in dependence on composition characterizing the oxidation of PP component into the composition characterizing oxidation of PE component (Figure 5.4). In the samples of blends with the rise of oxidation depth the increase of ratio between contents of groups CO and OH is observed and it is more noticeable the higher the content of PE in blend. It is important to note that the differences between compositions of products of oxidation of blends and homopolymers are revealed already at early stages of oxidation of blends ('12=1 /) and testify to the contribution of products of PE component oxidation into the total composition of non-volatile products. This fact confirms that initial rate of PE component oxidation is significantly higher than initial rate of oxidation of PE-homopolymer. The analogous conclusion is followed from the analysis of kinetic curves of CO groups accumulation (Figure 5.5a) and change of ratios between CO and OH, and also between single and bonded OH groups in samples of homopolymers and blend containing 10% of PP (Figure 5.5b).

Figure 5.5. (a) Kinetic curves of accumulation of carbonyl-containing groups of products of oxidation of samples of PP (1), PE (2) and their blend with 10% of PP (3). (b) Kinetic curves f change in ratios between concentrations of single and bonded by hydrogen bonds hydroxyl-containing groups (1', 2'), carbonyl- and hydroxyl-containing groups (1", 2") in the course of oxidation of samples of PP (1, 1") and blend PPPE with 10% of PP (2, 2"). Conditions are Tox = 110qC, PO2 = 600 millimeters of mercury.

It is obvious from presented Figures that rate of accumulation of oxidation products in blend is higher than in pure PE (Figure 5.5a). The dependences reflecting changes of ratios between sepa110

rate functional groups in samples of PP, PE and their blend with 10% of PP in the course of their oxidation show that increase of rate of oxidation of blend is connected not only with the oxidation of PP component (Figure 5.5b). As it is obvious from data presented in this Figure the compositions of products of blend and PP oxidation at the beginning of the process are equal, but in several hours the significant inclination of composition of products of blend oxidation from the composition of products of PP oxidation and approaching to the structure of PE oxidation products are observed (Figure 5.5b). Thus, the analysis of kinetic curves of oxygen absorption and composition of products of oxidation of samples of PPPEHD blends indicates on the fact that rate of oxidation of less active in relation to oxygen polymer PEHD in blend with more active PP is increased in comparison with pure polymer, i.e. PP initiates oxidation of PE. Since the structure of PP component is the determinative factor at the initial stage of oxidation its change should influence on kinetics of polymer blend oxidation, the character of this change allows specifying the role of morphology of components in oxidation process. The morphology of blends may be varied by the change of blending regime. That is why the samples of blends PPPEHD of equal composition by prepared in various ways were studied in the work. 5.2. The blends of isopolypropylenepolyethylene of high density with equal compositions but of various blending techniques

The blends of iPP with PEHD were prepared from common solution of polymers in methaxylene (in inert medium) by coprecipitation by cold ethanol out of: 1. boiling solution (the regime of rapid cooling); 2. by precipitation from the same solution after its cooling (the regime of slow cooling); 3. by mechanical blending in ball drum for 60 minutes with further passing through the microextruder at 180qC (the conditions of blending provided the homogeneity of composition of blend and the absence of components destruction process). All samples have 10 mass % of PP and 90 mass % of PEHD. We studied the films of thickness equal to 10-60mcm which were pressed at 180qC in inert atmosphere under the pressure 10MPa with further hardening at room temperature. 5.2.1. The structure of initial samples of blends

The microphotographs of surfaces of low-temperature chips of films of blends No.13 are presented in Figure 5.6. It is obvious from the Figure that permolecular organization of all samples is characterized by the totality of similar elements: lamellar solder pads of PE phase, ellipse-like particles  nucleus of spherulites and ball-shaped forms  spherulites of PP. The differences between samples are come to the sizes of separate elements. In the case of rapidly cooled samples these sizes are lower than in the case of slowly cooled ones (PE phase of sample (r/c) consists of solder pads with sizes 100-200nm each of them, aggregated in to associates with sizes 1-2mcm). The region of the polymer filled by such associates is 4-8mcm. At the rest regions there is unstructured surface against which the nucleus of spherulites of PP phase with sizes 10 mcm are observed. Permolecular organization of sample No.2 (s/c) is presented by plates of PE by 1-2mcm concentrating in the region with 10-20mcm as ellipse-like particles of 100-200nm and spherulites of PP by 36mcm). In the case of sample No.3 obtained by mechanical blending against the aggregated plate structures of PE with sizes 4-6mcm there are also spherulites of 4-6mcm and ellipse-like particles of 200-400nm belonging to PP phase.

111

(a)

(b)

(c)

Figure 5.6. Micro-photographs of surface of low-temperature chips of films of samples of blends with composition 10 mass % of PP : 90 mass % of PEHD obtained from solution No.1 by rapid cooling (a), No.2  by slow cooling (b), No.3  from the melt of polymers by extrusion (c).

Sharp cooling of polymers solution (sample No.1) leads to both formation of small particles of PE matrix and imperfect spherulites of PP and to freezing of some part of solution of PP in PE due to incomplete phase delaminating. In the case of sample obtained by slow cooling of polymer solution (No.2) phase delaminating occurs to a greater extent but also incompletely that is why the PE plates in it are larger and PP phase has more perfect structure (there are not only nucleus but also the spherulites, nevertheless even the sample No.2 is characterized by the presence of unstruc112

tured surface relating to "frozen" solution of PP in PE). It is obvious that solution of PP in PE is practically the meso-phase. For the first sample the regions of meso-phase is significantly more extensive than for the second one. By the sizes of structural elements the sample No.3 obtained from the melt is close to sample No.2 but it has clear interfaces between separate particles of PP and between PP and PE phases, i.e. this sample practically doesn't have meso-phase. Differences in blends morphologies are reflected on the structure and composition of chains of their components. Structural parameters were determined by DSC method and IR-spectroscopy. Parameters of components were compared with polymers' ones treated in analogous regimes to reveal how blending of PP with PE changed the structures of one and another polymer. Endotherms of melting of PP, PE and blends No.13 are presented in Figure 5.7.

Figure 5.7. DSC thermograms of melting of samples PP (1), PE (2) and blends with 10 mass % of PP No.1 (r/c) (3), No.2 (s/c) (4), No.3 (extr.) (5).

As it is obvious each of endotherms f pure polymers has one peak. There are two regions of melting on thermograms of all blends relating to melting of PEHD and PP that indicates on twophase blends and if in the case of sample No.1 there is single peak of melting of PP component, so for the samples No.2 and 3 there are two peaks  intensive low-temperature and low-intensive hightemperature for sample No.2, low-intensive low-temperature and intensive high-temperature for sample No.3 (Figure 5.7). Temperatures of melting of PE component for all studied samples are slightly differed from Tmel of pure polymer. A the same time Tmel of PP component for sample No.1 and low-temperature paeks for samples No.2 and 3 are close to Tmel of pure polymer. Tmel of high-temperature peak of PP component of blends No. 2 and 3 are more than by 10K higher than Tmel of pure PP. Comparing of thermalphysic parameters of initial polymers and components of blends shows that blending of polymers leads to amorphyzation of both components (Table 5.2) and degrees of amorphyzation are various. Sample No.2 obtained by slow cooling of solution has the highest crystallinity degree of PE among others blends and the lowest crystallinity degree of PP component. Sample No.3 obtained by mechanical blending has the lowest XPE and the highest XPP. 113

Table 5.2. Thermophysical parameters of components of samples of blends obtained from the solution (No.1, 2) by extrusion mixture (No.3). Sample 100% PEHD average

100% PP average

10%PP 90%PEHD (r/c) No.1 average

10%PP 90%PEHD (s/c) No.2 average

10%PP 90%PEHD (ex.) No.3 average

melPE,  124,4 126,7 126,8 127,8 126,4 125,8 127,2 126,8 125,4 125,2 126,1 128,8 126,6 129,0 127,6 125,6 127,5 126,6 126,5 126,4 125,3 127,0 126,4

PE, % 54,3 57,0 53,8 51,8 54,0 48,8 39,5 47,6 45,7 40,6 44,4 45,5 53,1 48,2 42,4 47,3 47,3 46,0 38,4 37,4 41,4 38,4 40,3

melPP,  158,3 158,0 158,0 158,3 158,2 159,4 161,4 162,5 161,4 161 161,1 162,0 160,8+174,0 160,6+173,2 159,8+174,0 161,2+174,0 160,8+174 157,6+167,2 157,6+168 157,6+165,6 155,2+166,3 157,0+166,8 157,0+166,8

PP, % 47,4 40,3 45,4 43,5 44,4 24,5 37,1 37,3 28,6 38,7 33,2 31,0 15,2 28,8 20,6 32,2 25,5 39,2 35,0 40,0 37,2 36,0 37,5

The analogous data were obtained by IR-spectroscopy method (Table 5.3). The ratio between total content of chains of PE and PP in regular conformations (trans-zigzag and spiral 3i) characterizing crystallites for all studied samples remain the same as the ratios between their crystallinity degrees obtained by DSC method are (this fact follows from the ratio between the values of intensities of bands at 730cm-1 in PE and at 998cm-1 in PP). It is obvious that appearance of P crystallites with high melting temperature insamples No. 2 and 3 and their absence in sample No.1 and also the character of components amorphyzation in blends are determined by particularities of process of crystallization caused, firstly, by the ratio between rates of components phase lamination and their crystallization, and secondly, by the difference of degrees of overcooling of PP and PE crystallites. The structure of polymer chains in amorphous phases of PP and PE components of blends is also differed from the structure of chains in pure polymers and in samples between each other and depends on conditions of preparation regime. As it is obvious from Table 5.3 blending of PP and PE leads to the increase of chains regularity of both components in comparison with pure polymers. Among all investigated samples the sample No.2 has the most regular structure of chains of amorphous regions of PP and PE components (the lowest content of coagulated and the highest content of strengthened chains in amorphous regions of PP and PE (Table 5.4)). The most disordered structure of chains of both components is characteristic for sample No.1 (amorphous regions of both components are characterized by the highest degree of coagulation of polymer chains). Obviously the last fact is the result of intermolecular interaction between PP and PE in mesophase.

114

Table 5.3. Structure of polymer chains of components in blends PPPEHD obtained by various methods (crystal regions). The data were obtained by IR-spectroscopy. Sample

PP PEHD 10% PP 1 (r/c) average 10% PP 2 (s/c) average 10% PP 3 (ex) average

Degree of crystallinity*

Degree of crystallinity**

0,81 0,70 0,70 0,60 0,63 0,64 0,65 0,37 0,40 0,45 0,40 0,40 0,40 0,55

Structure of chains in crystal regions

66,7 60,0 60,0 47,0 53,0 54,0 54,8 33,0 35,0 39,0 35,0 35,0 36,0

D730 EPE˜D4320 4,7 3,6 4,0 3,08 3,08 3,08 3,8 4,1 4,6 4,5 4,4 3,8 4,3

D998 GPP˜D4320 5,4 3,0 3,0 2,0 3,0 3,0 2,8 2,0 2,0 2,1 2,0 2,0 2,0

D4250 D4320 0,76 0,40 0,45 0,46 0,46 0,46 0,45 0,46 0,44 0,45 0,45 0,45 0,45 0,45

2,15

46,7

3,5

3,0

0,45

1,17

D730 D998 -

1,36

Notes: *  degree of crystallinity was determined by the method of IR-spectroscopy by ratio D840/D1170 (method of Kheinen); **  degree of crystallinity was determined by DSC; EPE, GPP  mass parts of PE and PP accordingly.

Figure 5.8. Curves of de-excitation of samples PP (1), PEHD (2) and their blends containing 10% of PP: No.1 (r/c) (3), No.2 (s/c) (4), No.3 (extr.) (5).

115

5,8 7,0

3,2

1,2

2,8

0,68

0,38

0,49

7,0

D1155_____ D4320GPP(1-FPP)

0,44 0,70

D1155 D975 0,60

1,17

1,30

1,10

1,20 1,10

1,10

D975 D998

0,40

0,50

0,30

0,50 0,21

0,24

D975 - D 998__ D4320GPP(1-FPP)

0,10

0,14

0,10

0,08 0,05

0,05

D1055____ D4320EPE(1-FPE)

0,15

0,14

0,13

0 0,05

0,10

D1085______ D4320EPE(1-FPE)

Notes: GPP, EPE  are the mass parts of PP and PE accordingly, (1F FPP), (1F FPE) – !#: G, E$ -  &? @    Z  ^&^^&## , (1-F), (1-F$) – @   `#? ^€   ##^ &.

100%PP (s/c) 100%PP (ex.) 10%PP 1 (r/c) 10%PP 2 (s/c) 10%PP (ex.)

100% PP (r/c)

Sample

0,50

0,50

0,85

0,80 0,90

0,95

D1305_____ D4320EPE(1-FPE)

Table 5.4. Structure of polymer chains in amorphous regions of components of samples of blends PPPEHD, No.1, 2, 3.

0,92

1,00

0,62

0,60 0,40

0,40

116

D720-D730_ D4320EPE(1-Fpe)

It is known that the change in polymers' chains structures is reflected on molecular dynamics [202, 233238, 286]. We estimated the molecular dynamics in studied samples by the character of relaxation transitions observing with the help of radiothermo-luminescence (RTL). RTL curves of PP, PEHD and their blends No.13 are presented in Figure 5.8. One should expect the changes of segment mobility of PP and PE chains for blends No.13 in comparison with pure polymers connected with their inter-molecular interactions and also with the structure, sizes and forms of components' phases and with structure of their chains. In this connection the observed differences between blends are the result of particularities of phase separation and crystallization of PP and PE components. Comparison of de-excitation curves of pure polymers and blends shows that the last ones have relaxation transitions of the same type (J-relaxations or transition I and E-relaxation or transition II [237, 287]) as the first ones but the shape of their curve and its position on temperature scale are differed. RTL curves of samples No.2 and 3 in accordance with the shape of de-excitation curve are close to PE. Their low-temperature peak I as well as in PE consists of two covering maximums, but these maximums are shifted to the high-temperature region and are differed in the ratio of intensities. For blend No.2 relaxation transition II is practically degenerated and transform into hightemperature wing. At the same time for blend No.3 the intensity of peak II is increased in comparison with pure PE. For sample No.1 relaxation transition I is the most intensive and is shifted to the region of high temperatures as by the ratio to PE peak, so to PP peak. Relaxation transition II is analogues to that one for sample No.2. Relaxation transition I corresponds to the act of segment relaxation in polymer melt, may realize in solid polymer at the place of less compact packing, localization of structure defects, elements of free volume at the places of high mobility of strongly coagulated through-pass chains, long irregular loops and macromolecules ends [238]. It is accompanied by overwhelming of intermolecular barriers conditioned by TG transitions [233238]. Relaxation transition II (E-relaxation) is related to the vitrification process [287] and in works [237, 288] to the segment motions limited by the presence of crystallites, to the motions of short folders or strengthened chains which ends are fixed in solder pads. This process is caused by intermolecular-cooperative motion in polymer chain and has direct correlation with relaxation transition I. Analysis of the curve of de-excitation of sample No.3 allows concluding that there is more complete in comparison with other samples inter-phase lamination of PP and PE components. Close to PE shape of de-excitation curve indicates on weak inter-phase interaction. Introduction of PP into PE doesn't lead to essential change of temperature of maximum of relaxation transition II. In other words, introduction of PP into PE in given sample doesn't lead to the lost of cooperative segment motion of PE matrix. Changes of the form of relaxation peak I in given case may be considered as a result of PP phase addition (this phase is enriched by chains in coagulated conformation (Table 5.4)) and also as a result of change of conformational set of chains of PE component in comparison with pure PE (Table 5.3). High degree of coagulation of PP phase chains at its low content may provide the observing rise of intensity of peak at 170K at the expense of small-scale conformational motions [287]. At the same time PE phase is enriched by chains in regular conformation, depleted by coagulated conformers, that obviously results in the decrease of contribution of transition I of conformational motions into intensity and in decrease of segment mobility of chains. At that the intensity of maximum 1 of peak of relaxation transition I is decreased and it is shifted to hightemperature region by 15K. The other picture of inter-phase interaction characterizes sample No.1 obtained by polymers blending in solution in hardening regime. Appearance of intensive peak at 175K in the region between relaxation transitions of PE, degenerating of relaxation transition II in given sample of blend couldn't be explained by the change of conformational composition of polymer chains of components, otherwise we should observe the picture analogous to that one as for previous sample. Appearance of relaxation peak I between two relaxation transitions in polymer at degenerating of relaxation peak II is conditioned by transformation of relaxation transition II into transition I [237, 288]. This transformation is connected with the change of character of segments motion with 117

the lost of corporative motion and increase of role of small-corporative, kinetically independent processes which are intermediate between transitions I and II [287]. Obviously observed by us particularities of de-excitation curve of sample No.1 are conditioned by the decrease of segment mobility of PE and PP chains due to strengthening of inter-molecular interaction that is connected with contacting of PP and PE segments as a result of interpenetration of components, their molecular mixing [30, 31, 287-289], formation of meso-phase. For sample No.2 RTL curve is as it was intermediate between previous samples. It has as in the cases of samples No.3 and PE the double peak of relaxation I and relaxation peak II is close to degenerating analogously to sample No.1. Broadening of peak II, decrease of its intensity and shift of maximum to 160K may partially connected with the decrease of segment mobility of PE and PP chains due to their inter-molecular interaction in meso-phase. Presence of unstructured region in blend testifies to it. Moreover, the observing particularities of the shape of de-excitation curve for given sample may be connected with conformational structure of polymer chains of blend components. As a consequence of PP phase chains enrichment by strengthened conformers the intensity of peak I may be decreased and broadened to the side of higher temperatures. However, the fact that changes of conformational composition of PP chains in sample No.2 don't cause changes of intensity of peak of relaxation transition II allows asserting that the shift of peak I to the hightemperature region testifies to the presence of some amount of meso-phase (solid solution of PP in PE). Thus, the totality of data obtained in the work by various methods allows asserting that blends prepared from solutions and melts of polymers have various structures of components, and in the first two blends the inter-phase layer with various thickness is formed. The blend prepared in the regime of rapid cooling possesses the most extensive meso-phase. Sample No.2 has significantly smaller meso-phase by the volume of amorphous regions. And finally, for the sample obtained by mechanical blending of polymer melts only inter-phase boundary is formed. 5.2.2. Kinetics of oxygen absorption

With the aim of studying of role of structure in the process of auto-oxidation of blends PPPEHD the kinetics of oxygen absorption by samples of PP, PE and blends No.13 was investigated. The experiments were carried out at conditions when components of blends were solid. Kinetic curves of oxygen absorption are presented in Figure 5.9. As it is obvious from Figure all studied blends are oxidized in accordance with auto-catalytic law. It follows from analysis of kinetic curves that blending of PP and PE changes initial and maximum rates of oxidation. Induction periods of oxidation of all blends are bigger than for PP and smaller than for PE. Comparing of values of ind allows placing PP, PE and blends No.13 to the following raw (in this raw the initial rate of oxidation is decreased and ind is increased): indPP < indNo.1 < indNo.3 < indNo.2 < indPE

118

mole/kg

ox, hours Figure 5.9. Kinetic curves of oxygen absorption by samples of PP (1), PEHD (2) and their blends with 10% of PP and 90% of PEHD: r/c solution No.1 (3), s/c solution No.2 (4), extrusion blend No.3 (5). Tox = 110°C, PO2 = 600 millimeters of mercury.

Thus, the most active sample of blends in relation to oxygen is the blend No.1, and the less active is No.2. Since ind of samples of blends is lower than for PE one may assume that at the initial stage the oxidation of more active PP component is observed. At that differences in ind for samples of blends may be caused, firstly, by differences in structural parameters of PP component (degree of crystallinity and regularity of structure of polymer chains), secondly, by morphology of particles of PP component. With the aim of revealing of role of PP and its structure at the initial stage of oxidation of blends it is necessary to eliminate the influence of its structural parameters on kinetics of oxygen absorption. For this we transform the obtained curves of gross-process into curves in which concentration of absorbed oxygen is related to concentration of RH-units in amorphous phase of blend sample and part of chains of PP in coagulated conformation (G/G0, where G and G0 are the contents of coagulated conformers in PP component of blend and pure polymer). [RHnn] in amorphous regions were 13,4; 1,60; 1,79 and 1,5 mole/kg for PP and samples No.1, 2, 3 correspondingly. G/G0 were 0,46; 0,20 and 0,40 for samples No.1, 2 and 3 accordingly. As a result of curves transformation in coordinates: ('12 / [RHPP am.ph.] G / Go)1/2– f (tox) we obtain rectification of the initial parts of kinetic curves (curves 14) that allows comparative estimating of PP component in all studied blends and pure polymer by reactivity (Figure 5.10). Comparing of parameters "b" characterizing activity of polymer in relation to oxygen obtained from the values of inclinations of initial parts of calculated curves showed that values of this parameter have close values for all blends and pure PP. Values of "b" are 6,1˜10-5; 10,2˜10-5; 7,8˜10-5 and 7,4˜10-5 (mole1/22 / mole1/2RH˜sec) in PP, blends No.1, 2, 3 correspondingly. The obtained data allow concluding that beginning of oxidation of blends No. 2 and 3 is mainly determined by oxidation of PP

119

component and doesn't depend on its structure. We should note significantly higher value of parameter "b" and also lower value of Wind for sample No.1 in comparison with PP (Figure 5.10).

Figure 5.10. Kinetic curves of oxygen absorption by samples of PP (1, 1') and by samples of blends No.1 (2, 2'), No.2 (3, 3'), No.3 (4, 4') transformed in coordinates: NO2/[RH]PP am.ph.˜G/G0 = f(t) (curves 14) and also their linear anamorphosis in coordinates [NO2/[RH]PP am.ph.˜G/G0]0,5 = f(t) (curves 1'4').

The second important conclusion followed from obtained results is that kinetics of blend oxidation at deeper stages ('12 > 0,5 mole/kg) is determined by oxidation of PE matrix. The given conclusion is followed from the analysis of curves of change of samples oxidation rates in the course of process. Existing curves obtained by the method of graphic differentiation of curves of oxygen absorption by samples of PP, PE and by blends are presented in Figure 5.11. As it is obvious from Figure the profile of curve of change of oxygen absorption by samples of blends is close to the profile of analogues curve of PEHD and is radically differed from PP. Comparing of current values of oxidation rates of PP, PEHD and samples of blends shows, firstly, that at the initial stage of oxidation rate of sample is determined by the rate of PP component oxidation; secondly, already at not deep levels of oxidation of blend ('12 > 0,5 mole/kg) kinetics of process is determined by rate of PE matrix oxidation; thirdly, oxidation of PE component begins earlier in comparison with pure PE. It follows from the analysis of form of differential curves (Figure 5.11) that the rates of PE entering into the oxidation process of samples No.1, 2, 3 are various: in the case of No.1 PE component enters the oxidation process at early stages, i.e. PE and PP are oxidized practically simultaneously, for samples No.2 and 3 the lateness of oxygen absorption by PE in comparison with PP component is observed and for the first this lateness is more significant.

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Figure 5.11. Curves of change of rate of oxygen absorption in the course of oxidation of samples of PP (1), PEHD (2) and their blends with 10 mass % of PP: No.1 (r/c) (3), No.2 (s/c) (4), No.3 (extr.) (5). Curves are obtained by differentiation of kinetic curves of oxygen absorption by samples presented in Figure 5.9.

Thus, it follows from the analysis of kinetic curves of oxygen absorption that PP component plays role of initiator of oxidation process of PE (at the stage of kinetic chains transfer). Current rate of oxidation (d'No2/dt) of studied polymer blends depends on the rate of PE matrix entering into the process that in its turn depends on morphology of blend. Consequently, the rate of initiation of kinetic chains of PE oxidation by polypropylene component should depend on structure (or volume) of meso-phase. 5.2.3. Kinetics of accumulation of non-volatile products of oxidation

The analysis of structure of non-volatile products of oxidation, ratios between contents of carbonyl- and hydroxyl-containing products, between contents of OH-groups single and bonded by hydrogen bond, and of kinetics of change of all listed factors in dependence on concentration of absorbed oxygen allows estimating the contribution into oxidation of PE component or PE molecules in meso-phase (inter-phase layer). As it is obvious at the initial stage of blends samples oxidation already (by the time of oxidation it corresponds to Wind. PE) the composition of non-volatile products approaching to composition characteristic for PE matrix that may testify to initiation of kinetic chains of PE oxidation by polypropylene. At that for sample No.1 (the sample with extensive interphase layer) at small depths of oxidation the values of ratios between functional groups >=0, sing., bond. are higher that for samples of blends No.2 and 3 (Table 5.5).

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Table 5.5. Composition of non-volatile products of oxidation of samples of PP, PEHD, blends No.1 (r/c), No.2 (s/c), No.3 (ex.). Conditions: Tox. = 110qC, PO2 = 600 millimeters of mecury. Sample PP 100%

PEHD 100% Sample 1 (r/c) Sample 2 (s/c) Sample 3 (ex.)

'No2, mole/kg 0,5 0,7 1,1 1,3 0,5 0,7 1,0 0,5 1,5 0,5 1,5 0,5 1,5

Wox, h 8,0 8,5 9,5 10,0 45,0 53,0 65,0 19,0 52,0 34,0 75,0 21,0 60,0

D1720/D4320

D1720/D3420

D3610/D3420

6,7 7,7 8,9 12,0 1,0 1,6 3,4 1,5 4,6 0,6 5,9 1,2 2,7

2,0 2,5 3,5 3,5 38,0 50,0 56,0 7,7 36,0 3,5 56,0 6,67 39,0

0,1 0,1 0,1 0,1 2,5 2,5 2,8 0,9 1,4 1,0 2,5 1,1 2,0

However the picture is changed to the opposite one at deep oxidation and the values of mentioned ratios in the last samples become higher than in the case of the first one. This fact in combination with the fact that one and the same depths of oxidation of sample No.1 are reached for shorter time than for samples No. 2 and 3, and also higher value of parameter "b" and Wind.No.1 < Wind.PP obtained from transformed kinetic curves of oxygen absorption (in Figure 5.10) indicate on practically simultaneous oxidation of PP and PE components. 5.3. On question about the mechanism of oxidation of polypropylenepolyethylene of high density blends

The analysis of composition of products of oxidation of PPPE blends of various structures and various preparation methods confirms that rate of oxidation of PE component is higher than for homopolymer. The rise if initial rate of PE component oxidation is possible in the case if oxidable PP component will initiate kinetic chains of PE oxidation in the blend. Initiation of kinetic chains of PE component oxidation may be realized by two ways. The first one is realized with the help of lowmolecular radicals r* of the type 3*, 37* and others accumulated in PP component as a result of decomposition of hydroperoxide or alkoxyl radicals. These radicals possess high diffusion coefficient and may diffuse from PP phase into PE phase initiating there kinetic chains of oxidation by reaction: (1) * + RPE o RPE + rH Secondly, initiation of kinetic chains of PE oxidation is possible by transfer of free valency from macro-chain of PP to macro-chain of PE by chemical relay-race by the following reactions: RPPO2 + RPEH o RPPOO + RPE (2) RPE + O2 o RPEO2 (3) It is obvious that mechanism of initiation of kinetic chains of PE oxidation, i.e. contribution of reactions (1) or (2), (3) into this stage will depend on intermolecular interaction of components macro-chains or, in other words on structure of inter-phase (inter-components) layer. In the samples of blends PPPEHD enriched by PE the last one is continues plastic matrix in which particles of PP phase of spherical form with diameter from 2 up to 12 mcm are situated. In these blends there are practically no bonds between particles of disperse phase and disperse phase and dispersing medium, i.e. there is no inter-phase layer. In the samples enriched by PP the particles of disperse phase of PE are entered into dispersing medium. Strong interaction is observed between them. Particles of PE occlude the part of matrix polymer and thereby increase the both the surface of contact between components and the volume of inter-phase boundary layers. Developed inter122

phase layer consists of cohesions of heterogeneous macromolecules of components. the samples of blend with 50% of PP are characterized by phases inversion [7, 8, 28, 84, 291, 292]. Let's estimate the possibility of realization of mentioned above mechanisms of initiation of kinetic chains of oxidation of PE component in samples of studied blends PPPE. Reaction of lowmolecular radical r* with RH-bond (equation 1) may proceed in both components. For realization of initiation of kinetic chains of PE oxidation it is necessary the time of radical disappearance in substitution reaction (r* + RH) in PP to be higher or comparable with the time of its diffusion into PE component. Then we estimate the probability of initiation of kinetic chains in PE with the help of radicals diffused from PP phase. With this aim we determine the time of transition Wr* of 25* radical from PP into PE component with the help of the following expression: O = (6DoWr*) [161-163] where D0  the coefficient of radical diffusion (in accordance with the data of [290] D0 is ~10-7 cm2/sec); O  the distance changing in the limits from diameter of particle of disperse phase up to the thickness of interface and lying in the interval from 10-6 up to 10-4cm [291]. Then the time of diffusion (in seconds) of low-molecular radical r* from PP phase into PE phase is: Wr* = O2/6D0  (10-12  10-8) / 6˜˜10-7  10-6  10-2. If radical r* disappears in reaction of substitution: r* + RPPH ——o rH + RPP* then the time necessary for spending of this radical is equal to Wr*' = l/k[RPPH]. the maximum value of [RH] in pp-phase of polymer composition is changed in the limits from 1,5 up to 12 mole/kg. then the value of Wr*' is 10-110-3 sec, i.e. the time of reaction of substitution of hydrogen atom by radical r* in RH-bond of PP is higher than the time of radical diffusion from PP into PE-phase in the case when the inter-phase layer is absent or its thickness is not big. In the case of extensive inter-phase layer the transition of radical from PP phase may occur into its definite thickness. At that radical r* won't reach PE phase, but may interact with RH-bonds of PE in inter-phase layer analogously to the RH-bonds of PP. Thus, in the samples of blends enriched by PP low-molecular radicals from PP phase may initiate kinetic chains of oxidation of both components in inter-phase layer. The necessary condition for transition of free valency from macro-chain of PP on macro-chain of PE is ingress of PP macro-radical and RH-bond of PE into one element of space providing necessary for chemical act turn and re-orientation of particles. Obviously it may realize in inter-phase layer if there are intermolecular interactions, i.e. in samples of blends PPPE enriched by PP. It is important to note that inter-phase layer is the part of amorphous phase in which [163] structural defects may be localized  macro-chains enriched by coagulated conformers possessing high segment mobility and large free volume [163]. It may facilitate transfer of free valency from PP to PE by chemical relay-race. Exchange of RO2* radicals of PP component at tertiary carbon atom by secondary radicals of PE component in the course of mentioned above reactions proceeding leads to deactivation of kinetic chains of oxidation of PP and as a result to the decrease of xodiation rate of PP component (the inhibiting effect of polypropylene by polyethylene). Obviously this fact is observed in given work as a consequence of which the inclinations of linear anamorphosis of kinetic curves of oxygen absorption by samples of blends are lower than for PP homopolymer (Figure 5.3). Thus, while determining the mechanism of initiation of kinetic chains of oxidation of PE component by polypropylene the structure of inter-phase layer will determine the mechanism of interaction between oxidizing components of blend (initiation of kinetic chains of PE oxidation by polypropylene and inhibiting of PP oxidation by polyethylene). Permolecular structure [162], conformational composition of macro-chains of polymer [162, 290] significantly influence on the value of diffusion coefficient of low-molecular radical. D0 may be decreased in several times under the rise of both degree of crystallinity and degree of regularity of polymer macro-chains [162, 290]. It is obvious that analogues effects will be observed in blends PPPE also. We may assume that in samples enriched by PE the diffusion of radicals will significantly influence on the initial rate of oxidation. As it is known, the higher the content of coagulated 123

chains in amorphous phase of PP, the4 higher the rate of its oxidation [163], and consequently the higher the stationary concentration of radical r* in PP and the higher that rate of its diffusion from PP into PE phase [290]. At that, the higher will be the content of coagulated chains of PE, the higher will be the rate of initiation if its kinetic chains of oxidation [290] and the higher the rate of oxidation of blend in the whole. Obviously in such samples one should expect from the one hand significant influence of physical structure of components on kinetic of blend oxidation, anf from the other hand the prevailing of effect of initiation of PE oxidation by polypropylene. In the samples enriched by PP the rise of part of chains in coagulated conformation means the rise of their local segmental mobility [163] and increase of probability of transfer of free valency from PP macro-chain to PE macro-chain [163]. In dependence on microstructure of PE and PP chains in inter-phase layer, their mutual orientation kinetic chains of PP oxidation may be either terminated to PE component, or may be continued as kinetic chains of PE oxidation. We may expect that increase of defectiveness of blends components of given composition (especially in inter-phase layer) will lead to the increase of rate of PP radicals exchange by less active radicals of PE and consequently to inhibition of PP oxidation by polyethylene, i.e. increase of structure defectiveness of blends components may promote inhibiting effect. Thus we may expect that one and the same structural parameters of components will influence on kinetics of oxidation samples of blends enriched by PP and samples of blends enriched by PE component in various ways. Let's consider the question about the influence of structural parameters of components on kinetics of oxygen absorption by studied samples of blends PPPE. Analysis of structure of components in blend shows that introduction of PP components into the blend is accompanied by amorphyzation of both components, and the decrease of crystallinity degree in comparison with homopolymers indicates on it (Table 5.1). Analogous data were obtained by authors of [291, 292]. As investigated in the work samples of blends were enriched by PP component the degree of crystallinity of PE component was monotonously decreased, of PP component it at first was sharply decreased (for samples of composition 10% of PP and 40% of PP) then it was somewhat increased (for samples of composition 50% of PP and 80% of PP), but at that it remained the lower value than for homopolymer. Amorphyzation of blend components is accompanied by the change of conformational composition of their macro-chains (Table 5.1). With the rise of PP component content in blend from 10 up to 50% its amorphous phase is enriched by macro-chains in coagulated conformation and is depleted by chains in regular conformation. The rise of intensity of band at 1155cm-1 and decrease of intensity of band at 975cm-1 assigned to PP content indicate on this fact. The further enrichment of blend by PP component leads to the decrease of content of coagulated and increase of regular chains. At that conformational set of polymer chains of PE is practically not changed. The ratios between intensities of bands at 720 and 730cm-1 assigned to PE content in amorphous phase have close values for all samples. We should note that increase of PP content in blend leads to monotonous decrease of segment mobility of polymer chains (Table 5.1.). We also may propose that extreme dependence of value of Wind on composition of blend PPPEHD is conditioned by the influence of permolecular structure and microstructure of polymer chains of blend's components on kinetic of oxidation. Actually, the correlation between mentioned above parameters is observed. However the ratios between values of Wind and crystallinity degree, Wind and conformational composition of components macro-chains can't be described by simple dependences. Dependence of Wind on content of coagulated chains of PP in amorphous phase of this component is presented in Figure 5.12.

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ind, hours

D1155/D1170(1-kPP)

D1155/D1170(1-kPP) Figure 5.12. Dependence of Wind (1) and lgWind (2) on the content of coagulated conformers in amorphous regions of PP component for samples of blends PPPEHD.

As it is obvious two parts may be selected on the curve. These sections are clearly observed on mentioned dependence in semi-logarithmic coordinates (Figure 5.12, curve 2). The one part is related to samples with high content of PE, the other one – to samples with high content of PP. For the first ones under enrichment of amorphous regions of PP component by chains in coagulated conformation the sharp decrease of Wind is observed, for the seconds ones Wind slightly depends on mentioned parameter. Induction period of polymers oxidation to a greater extent is determined by the stage of origination of kinetic chains of oxidation (under the decomposition of hydroperoxide) [63]. The obtained change on the dependence of Wind on blend composition more likely testifies t the change of mechanism of oxidation kinetic chains initiation, in other words to the transfer of free valency from one component to the other under the change of structure of inter-component boundary. We showed above that namely in given case one and the same structural parameters of components might influence on Wind in various ways in the case of samples enriched by PE and samples enriched by PP. The rate of oxidation of blend PPPE is formed by the rate of PE component oxidation initiated by PP and the rate of oxidation of PP component inhibited by PE. If one presents the contribution of PE and PP components into oxidation process as the ratio between content of CO and bonded OH groups in samples of various compositions possessing various microstructure of components oxidized to equal depths the correlation between maximum rate of oxidation and mentioned ratio will be described by curve presented in Figure 5.13.

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Figure 5.13. Dependence of the maximum rate of oxidation on ratio between concentrations of groups >C=O and OH in samples of blends PPPEHD of various composition oxidized for depth 'NO2 = 1,0 mole/kg at Tox = 110qC and PO2 = 600 millimeters of mercury. Different points correspond to blends of various compositions.

As it is obvious this curve consists of three sections. At the first one oxidation rate is sgarply decreased when the value of ratio between CO and OH groups' contents is increased. This section corresponds to composition of blends enriched by PP component and possessing extensive interphase layer. At such composition of blend the rate of its oxidation is decreased with the rise of PE component contribution evolved into oxidation process (the increase of ration between [CO] and [OH]). At the second section the character of correlation between oxidation rate and ratio of functional groups is not changed but decrease of oxidation rate is expressed less clearly. The second section corresponds to blends composition (40 and 50% of PP) characterizing by phase transformation. The third part corresponds to blends composition enriched by PE component. On the section the rise of oxidation rate correlates with the rise of ratio []/[] or the part of component "evolved" into oxidation. It is obvious that changeable character of correlation between oxidation rate and ratio []/[] is caused by differences in mechanism of blends oxidation with various structure of interphase layer. At that the first section of mentioned correlation reflects predominance of process of inhibiting of PP oxidation by polyethylene component, whereas at the second part the ratio between initiating and inhibiting effects of components is changed in the favour of the first one. The third section is characterized by prevailing of initiation effect of kinetic chains of PE oxidation by polypropylene. The fact that inter-molecular interactions in the interphase layer accelerate transfer of kinetic chains of oxidation from PP to PE which is realized by transfer of free valency by mechanism of "chemical relay-race" and is determined by structure of PP component follows from the data on kinetics of oxidation of blends PPPEHD of similar composition (10% of PP) prepared by various techniques. Low crystallinity degree of components and also high concentration of coagulated conformers in polymer chains of amorphous regions of PP component promote mentioned process. The last factor decreases Wind No.1 in comparison with Wind No.2 and Wind No.3. For these samples ratio [>=0]/[] at the initial stage of oxidation (up to 0,5 mole of O2/kg) is lower than in sample No.1 126

and pure PE. At deeper stage the mentioned ratio is sharply increased and approaches pure PE (Table 5.5). It reveals more clearly in sample No.2. The observing in samples No.2 and 3 particularities of products accumulation are obviously conditioned by later in comparison with sample No.1 entering into oxidation process of PE matrix and separate oxidation of components at the meginning of process due to absence of extensive interphase layer providing contact of PP and PE macromolecules. Obviously, as a consequence of mentioned particularities of structure of samples of blends No.2 and 3 the decrease of oxidation process initial rate is observed due to decrease of rate of initiation of kinetic chains of oxidation of PE component. The probable reason of decrease of Win of PE in sample No.2 and 3 in comparison with No.1 is substitution of mechanism of transfer of free valency from PP to PE by "chemical relay-race" by physical diffusion [161163, 218, 290]. We may conclude so on the base of analysis of kinetic curve of change of rate of oxygen absorption by samples No. 2 and 3. From the standpoint of the influence of PP component structure on kinetics of oxidation process of blends PPPE we should note that samples No. 2 and 3 have similar morphology but are differed in structures of polymer chains of PP and PE (Table 5.3). And the sample No.2 possessing more ordered structure of polymer chains of PP component has the highest Wind. The absence of extensive inter-phase layer reduces the rate of entering into oxidation process of PE component on which the structure of oxidation products and profile of differential kinetic curve of sample oxidation rate change indicate (two peaks separated from each other). Thus, microstructure of components and structure of inter-phase layer determine kinetics of oxidation of polymer blends on the base of PPPE. Structure of inter-phase layer of blends PPPE determines the mechanism of transfer of free valency from the one component to another (components exchange by free valences). Microstructure of PP component determines rates of initial stage of blend oxidation. Microstructures of both components determine the rate of exchange by free valences, i.e. of initiating and inhibiting action of PP and PEHD components on each other. It follows from the obtained data that oxidation process of polymer blends PPPEHD represents the process of polyethylene oxidation initiated by PP and process of oxidation of polypropylene inhibited by PE. The both processes are realized at the stage of continuation of kinetic chains of oxidation. Kinetics of oxygen absorption by blends samples is determined by the rates of PP oxidation, initiation of kinetic chains of PE component oxidation by polypropylene, inhibiting of kinetic chains of polypropylene oxidation by PE and depends on the structure of inter-phase layer or boundary, permolecular structure of components and microstructure of their polymer chains. The mechanism of initiation of kinetic chains of oxidation of PE phase by polypropylene is determined by the structure and thickness of inter-phase layer. The presence of inter-phase boundary instead of inter-phase layer leads to predominance of transfer of free valency from PP to PE by physical diffusion of low-molecular radical, in the presence of inter-phase layer  by chemical relay-race by the following reaction: R*PP + RPEH ! RPE* + RPPH, in oxygen atmosphere or by the following reaction: RO2*PP + RPEH ! RPE* + RPPOOH. The initial rates of oxidation (Wind) of samples of PPPE blends depend on permolecular structure and microstructure of PP component.

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Chapter 6. The blends of crystallizing polyolefin and amorphous rubber: isotactic polypropylene and triple ethylenepropylenediene copolymer The blends PPSEPR, PPSEPTR, PPSIR, etc. are the representatives of class of thermoplastic elastomers. This class of materials has a very wide application in motor-car industry. The problem of thermal oxidative stability of machine elements produced on the base of TPE and in particular of PPSEPTR blends is one of the most important one on solution of which the high quality maintenance of domestic motor-cars depends. Polymer chains of SEPTR may be presented as macro-chains of polyethylene with included in them propylene and diene monomer units. Thus, transition from PPPE blend to PPSEPTR blend is the transition from simpler to more complex but allied system. So, investigations of regularities of oxidation and structure of PPSEPTR blend are directed on the solution of more complex problem of establishing of the correlation between structure and kinetics of thermal oxidation of heterophase systems of one chemical nature with components differing in structure of polymer chains. PP and SEPTR are thermodynamically incompatible polymers. The structures of PPSEPTR blends are determined by kinetic compatibility which depends on composition, structure of components and conditions of blending. The particularity of structure of these blends is in the fact that one of its components is partially crystal polymer, and the other is amorphous elastomer. In accordance with existing in literature conceptions [293295] under the cooling of melt of PPSEPTR blend the one part of polypropylene transforms into crystal state, and the other one due to closeness of surface energies of blending polymer and rubber capturing the part of rubber macromolecules forms the inter-phase layer including both polymers. Inter-molecular interactions may lead to the formation of inter-phase layer – solid solution of PPSEPTR, but this solution will not be stable and under the change of blending conditions the delamination of components with further coagulation of phase particles may occur [9, 293, 296, 297]. The systems of combined phases stable to external effects may appear in that case when chemical bonds are formed: (cross-links) between PP molecules and diene comonomers in rubber. Formation of cross-links means formation of net structure analogous to that one which is realized in SRNPVC blends and other polar rubbers [8, 298]. In PPSEPTR, PESEPTR blends rubber's particles may play role of PP crystals nucleus [299, 300], create molecular cohesions between crystallites chains of polymer and rubber and in that way form physical net. Stability of system to delamination will depend on density of chemical or physical net and also on intensity of intermolecular interactions which may appear in amorphous regions in interphase layer. It is obvious that thermal oxidative ability of such system will be determined by components structure and structure of interphase-layer. The question about what structure element is the key one is a very important question. The presented Chapter is devoted to the solution of this problem. 6.1. The isopropylenesynthetic ethylene-propylene triple rubber blends (E-50)

The samples of isotactic PP, SEPTR and their blends containing 37,5, 50,0 and 61,5 mass % of PP were studied in this work. We used polymers of home manufacture. The characteristics of PP are: molding index of melt 1,9 g / 10 min, density d = 0,906 g/cm3, degree of isotacticity 96%. The sample of SEPTR of E-50 brand contains 4 mole % of ethylidennorbornene, 32 mass % of propylene. The Mooney viscosity was 65 conditioned units at 100qC. The blends were obtained in closed blender of "Brabender" type at 180qC for 8 minutes. The conditions of blending provided homogeneity of blends composition. The samples of polymers and blends represented films with thickness 40-80mcm obtained by pressing at 453K in inert atmosphere at pressure 20MPa with further hardening. Contents of components in blends were controlled by IR-spectroscopy method by the ratio between optical densities of two pairs of bands: at 1380 and 1460cm-1, and also at 2720 and 4320cm-1. Temperature and heat of melting were determined by DSC method. Structures of 128

crystallites were studied by RSA method. Structures of chains, compositions of products of oxidation were analyzed by IR-spectroscopy data in accordance with the same technique that was used for homopolymers. Except mechanical blends we studied dynamic vulcanizates preparaed with the help of resinous vulcanizing system. 6.1.1. Kinetics of oxygen absorption

Kinetic curves of oxygen absorption with their linear anamorphosis in coordinates '120,5 = f(t) for samples of polymers PP and SEPTR, and their blends of various compositions are presented in Figure 6.1a. The curves obtained by graphic differentiation of kinetic curves of oxygen absorption which characterize the change of O2 absorption rate in the course of the process are presented in Figure 6.1b.

Figure 6.1. (a) Kinetic curves of oxygen absorption (15) and their linear anamorphosis in coordinates '120,5 = f(tox) (1'5') of samples of pure PP (1, 1'), SEPTR (2, 2') and their blends containing 37,5 mass % of PP (3, 3'), 50 mass of PP (4, 4'), 61,5 mass % of PP (5, 5'). (b) The curves of change oxygen absorption rate in the course of the oxidation of samples of pure PP (1''), SEPTR (2'') and their blends containing 37,5 mass % of PP (3''), 50 mass of PP (4''), 61,5 mass % of PP (5'') obtained by graphic differentiation of curves (15). Tox = 110qC, PO2 = 600 millimeters of mercury. 129

As it obvious from Figure, at the initial stage of oxidation (including induction period) its significant decelerating is observed (the value of Wind is increased) for blends PPSEPTR in comparison with PP, and for the sample containing 61,5 mass % of PP this phenomenon is observed also in comparison with rubber. At the stage of deeper oxidation (higher than 0,5 mole of O2 / kg of polymer blend) the difference between rates of oxidation of blends of various compositions is leveled, although the dependence of wmax on composition is described by the curve with extremum, the sample containing 50 mass % of PP has the highest value of wmax (Figure 6.1b). Dependence of kinetic parameter of oxidation bbl characterizing reactivity of blend in relation to oxygen (*) on its composition has the same character. The values of b obtained for samples oxidized at 110qC and PO2 = 600 millimeters of mercury for PP and SEPTR were 5˜10-5 and 1,4˜10-6 mole0,5/kg0,5˜sec, bbl for samples containing 37,5, 50 and 61,5 % of PP were equal to 8,6˜10-6, 1,4˜10-5 and 6,1˜10-6 mole0,5/kg0,5˜sec accordingly. One may expect that introduction of PP into SEPTR, i.e. of more active in relation to oxygen polymer into less active one will lead to monotonous rise of reactivity of blend with the rise of PP concentration. However we didn't observe it in practice. Obviously, the established in work particularities of oxidation of blends PPSEPTR including the differences in character of oxidation rate dependence on composition at various stages of process are conditioned by the influence of both chemical and structural factors on blends oxidation. There may be several reasons of observed particularities of oxidation of PPSEPTR blends. Among them there is the change in oxidation mechanism connected with interaction of oxidable components differing in their nature, with spatial localization of process, with the change of rates of separate elementary stages as a result of change of components structures. The oxidation process in considered blends may be localized either in the phase of more active PP component, or in inter-phase layer, or in the regions of components with more defective structure of macro-chains. That is why the observed regularities of oxidation of blends and the change of reactivity of polymer material in relation to oxygen in comparison with pure polymers may be caused by both particularities of phase structure and structure of inter-phase layer. We should note, that differences in the character of dependences of oxidation rate on the composition of PPSEPTR blend at the initial and stationary stages of process are caused by various influence of structural and kinetic factors on oxidation kinetics. For example the analysis of literature data devoted to oxidation of polymers shows that the rate at the initial stage of oxidation (the value of induction period) to a greater extent is determined by physical-dynamic parameters and transport properties of polymer matrix than at the stage of deep oxidation. Let's analyze the number of kinetic models of oxidation of PPSEPTR blends. First of all we assume that oxidation is localized in amorphous regions of PP component and kinetic of process is determined by its structure. Oxidation of SEPTR doesn't proceed due to low reaction ability. In this case initial parts of kinetic curves of oxygen absorption by samples of blends transformed in coordinates considering oxygen absorption by tertiary RH bonds in monomer units of PP amorphous regions of samples in accordance with the expression: '1o2 / [RHPP] G (1-DPP) = f(Wox), (1) where [RHPP] – concentration of monomer PP units in 1kg of polymer; G  the part of PP component in blend; (1-DPP)  the part of amorphous regions of PP component, should coincide with kinetic curve of oxygen absorption by monomer units in amorphous phase of pure PP. the curves obtained as a result of carried out transformation are presented in Figure 6.2.

130

Figure 6.2. Kinetic curves of oxygen absorption (15) (transformation of curves from Figure 6.1a in the coordinates of equation 'NO2 / G[RH]PP(1-D)=f(tox)) (a) and their linear anamorphosis in coordinates {'NO2 / G[RH]PP(1-D)}0,5=f(tox) (1'5') (b) for pure PP (1, 1'), SEPTR (2, 2') and their blends containing 37,5 (3, 3'), 50 (4, 4'), 61,5 (5, 5') mass % of PP. Tox = 110qC, PO2 = 600 millimeters of mercury.

As it is obvious, curves for sample of pure PP and blend with 37,5% of PP are close to each other. However the other picture is observed for samples with higher contents of PP. On each curve there are three clear parts. The first one is the beginning of oxygen absorption, on this part the depth of oxidation reaches ~ 0,1 mole of O2/kg; it described the process in induction period. The second part on which deceleration of process is observed reaches the oxidation levels 0,2 and 0,4 mole of O2/kg for samples with 50 and 61,5 mass % of PP correspondingly. The third part (up to ~ 1 mole of O2/kg) is characterized by sharp acceleration of oxidation process. Comparing of inclinations of linear anamorphosis of initial parts of kinetic curves in coordinates ['12 / [RHPP]G(1DPP)]0,5 = f(Wx) (i.e. comparing of "b1" values) for sample of pure PP, blends PPSEPTR (Figure 6.2a) and SEPTR (Figure 6.2b) shows that the beginning of blends' samples oxidation is truly de131

termined by oxidation of PP component. The values of b1 are changed in the limits of one order, however in blends they are turned to be lower (they are 11˜10-6, 8˜10-5, 6˜10-6 and 4˜10-6 (mole0,52 / mole0,5[RPP]˜sec) for PP and blends with 37,5, 50 and 61,5 mass % of PP correspondingly). At that the value b1 is in order lower for SEPTR. After passing the induction period for samples with PP contents 50 and 61,5 mass % the value of b1 is sharply decreased (down to 5˜10-7 and 7˜10-7 (mole0,5 2/mole0,5[RHPP]˜sec) in the first and the second sample correspondingly), i.e. reactivity of PP component is reduced. The reduce of reactivity of PP component can't be explained by the change of structural parameters of this component. The change of dynamic parameters is in slope opposition to the change of reaction ability: blend with 37,5% of PP with the lowest segment mobility of polypropylene macro-chains (Tg = 290K) possesses the highest reactivity and vise versa, the sample with 50% of PP with high segment ability of PP chains (Tg = 257K) has low reactivity that contradicts with literature data. As it is known [95, 96] the rate of solid phase reactions is decreased with the reduce of segment mobility of chains. One may suggest that observing decrease of incline of kinetic curves caused by the decrease of reactivity of blends is connected with "entering" of SEPTR into oxidation process. And "entering" of SEPTR obviously first of all means the beginning of oxidation not of copolymer phase (rubber) but of its macromolecules in that place where the contact between PP and rubber is realized and the first one may initiate kinetic chains of oxidation of the last one. The fact that decrease of value b1 is the highest for the sample with low content of SEPTR and vise versa the lowest decrease is observed for the sample with high content of SEPTR confirms this supposition. "Entering" of SEPTR into reaction is possible in inter-phase layer. Let's consider the other model. This model supposes separate and independent oxidation of phases of PP and SEPTR. In this case the activity of blend in relation to oxygen will be determined by the values of kinetic parameters of oxidation characteristic for each of the components bPP and bSEPTR. The value of bbl may be determined by the law of additivity with the help of values bPP and bSEPTR by the expression: bbl = E bPP + (1E E)˜bSEPTR, where E  the part of PP, (1E E)  the part of SEPTR in blend. The obtained in such way values of bbl were 2˜10-5, 2,5˜10-5 and 3,1˜10-5 mole/kg˜sec for blends with 37,5, 50 and 61,5% of PP correspondingly. In other words, in the case of independent oxidation of components the rise of reactivity of blend in relation to oxygen is in direct proportion to PP content. Comparison of calculated and experimental values of parameters bbl of blends of various compositions showed that for reception of observing in the work extreme dependence of bbl on PP content it was necessary the values of bPP and bSEPTR of components of blend to be changed in comparison with analogous parameters of pure polymers. At that the value of bPP should be decreased not less than in 2,3; 1,8 and 5,1 times for samples with 37,5, 50 and 61,5% of PP correspondingly or the value of bSEPTR should be increased more than in order. As in the first case the change of parameter bbl may be explained by acceleration of oxidation of rubber component as a result of exchange by free valency between oxidizing macromolecules of PP and SEPTR in interphase layer. The third model supposes localization of oxidation in inter-phase layer and the presence of cross reactions between polypropylene and rubber components of blend. In accordance with this model the observing change of parameter bbl, i.e. reaction ability of blend is caused by initiation of kinetic chains of oxidation of SEPTR by oxidable polypropylene at the stage of transfer of kinetic chains of oxidation. The following reactions are realized: RPPH + O2 o RPP* + HO2 RPP* + RSEPTRH o RSEPTR* + RPPH Change of bSEPTR and bPP and consequently of bbl is possible as a result of change of kinetic constants of separate elementary stages of components oxidation in cross reactions (for PP  decrease of k2, k4, increase of k6, for SEPTR quite the contrary). 132

It is important to note the fact that macromolecules of rubber are complex in chemical structure, they include ethylene, propylene and diene comonomers. Each of comonomers of SEPTR may participate in radical reactions of oxidation process in dependence on reaction ability of RH-bonds in relation to oxygen. That is why the change of reaction ability of rubber component in comparison with pure SEPTR may be caused by the substitution of participating in oxidation reaction sites of one nature by other ones. The necessary condition for this is the change of local chemical structure of rubber chains adjoining to active sites. This condition may be realized either as a result of significant change of rubber component chain topology, or in reactions of exchange by free valency between SEPTR and PP in the process of oxidation kinetic chain transfer. The last one with higher probability may be realized in inter-phase layer. If as a result of oxidation kinetic chain transfer from PP to SEPTR the initiation of kinetic chains of rubber oxidation occurs, then leaving of free valency from PP phase into SEPTR may be considered as additional linear termination of kinetic chains of PP oxidation which will lead to the decrease of parameter b. However free radical formed in SEPTR by reaction: RPP* + RSEPTRH mo RSEPTR* + RPPH, may once again return to PP by inverse reaction, or may be stabilized if transfer of kinetic chain is realized to ethylene or diene comonomer. In the last case the deactivation of free valency of PP in cross-linking reaction of diene comonomer is possible. Thus, the analysis of the third model allows concluding that as a result of exchange reactions between PP and SEPTR the initiation of oxidation kinetic chains of rubber by polypropylene and hindering (inhibition) of PP oxidation by rubber occur. Deceleration of oxidation of PP and blend in the whole will depend on microstructure of polymer chains of SEPTR and conformation of PP chain, i.e. it will be determined mainly by the composition and structure of inter-phase layer. For establishing of the most reliable model of oxidation of blends PPSEPTR, i.e. for revealing of role of structure factors in kinetics of thermal oxidation of blends PPSEPTR their structures were studied. 6.1.2. The structure of crystal regions of iso-propylenesynthetic ethylene-propylene triple rubber blends

The data of X-ray diffraction (Figure 6.3a) and also of differential scanning calorimetry (Figure 6.3b) showed that blending of PP and ethylenepropylenediene rubber led to the change of crystallites morphology. If in pure PP the crystallites of D-modification are formed, then in blend PPSEPTR together with this form of crystallites the crystallites of J-modification are also appeared. (There are four intensive reflexes in the field of PP scattering characteristic for D-moficiation of PP crystallites). On the curves of scattering by samples of compositions PPSEPTR against crystal maximums of Dmodification the reflexes are appeared partially covering mentioned maximums by position on angle scale relating to J-form of crystallites [229, 230, 301] (Table 6.1).

133

Composition of blend PPSEPTR 100/0 37,5/62,5 50/50 61,5/38,5

51-57 36-41 35-39 51-58

, %

6,22 6,09 6,66 6,307

d110,Å

14q12c 14q30c 14q12c 14q

2 5,20 5,08 5,20 5,20

D040,Å 17q 17q24c 17q 17q

2

D-modification of crystallites of PP

]

4,76 4,66 4,73 4,76

d130,Å 18q36c 19q 18q42c 18q36c

2

J-modification of crystallites of PP The part of Jd,Å 2 modification 0 4,58 ~0,2 19q18c 4,49 ~0,3 19q42c 4,61 ~0,4 19q12c

Table 6.1. Structural parameters of crystal regions of PP and blends PPSEPTR. The data were obtained by X-ray analysis.

134

Figure 6.3. (a) Broad-angle difractograms of X-ray analysis of PP (1), SEPTR (2) and their blends with 37,5 (3), 50 (4) and 61,5 (5) mass % of PP. On curve 5 the division of reflexes of D- and J-modifications of PP crystallites is shown. The estimation of the part of PP crystallites fraction in J-form was carried out with the help of ratio HJ/HJ+HD. (b) DSC curves in the region of PP melting at the first (15) and the second (4') scanning for PP (1), SEPTR (2), blends PPSEPTR with 37,5 (3), 50 (4, 4') and 61,5 (5) mass % of PP, sample of vulcanizate with 37,5 mass % (3''), and also of the blend with 61,5 mass % of PP after annealing at 200qC (5''').

It is important to note that on diffraction curve of X-ray SA of SEPTR sample the diffuse halo is observed, the position of which corresponds to diffuse maximums of intensity relating to amorphous phases of PE and PP [229] and there are no crystal reflexes. The temperature in maximum of endo-thermal peak of melting of pure PP also corresponds to melting temperature of PP crystallites in D-modification (160qC) (Figure 6.3b). At the same time for blends of PP with SEPTR the appearance of low-temperature shoulder of melting peak in the region of 147qC corresponding to melting of crystallites in J-modification is observed [230]. On the endotherm of SEPTR melting clearly expressed peaks of PE and PP melting were not found.

135

160,8-161,2

161,2-162,8

162-162,8

161,2-162,8

100/0

61,5,5/38,5

50/50

37,5/62,5

162,8

161,2-162,2

(161,8+147,6)(159,0+150,0)

162,2-160,0

(2)mel, q

105,0

107,2109,2 105,4108,4 104,8105,6

cr, q

134,8-135,0

127-129

134,0-136,6

140-142

(1)beg.mel, q 9,6(156,4-166,0) 11,2(155,8-167,0) 9,6(155,8-165,4) 10,2(154,6-164,8) 14,0(152,0-166,0) 14,2(150,8-165,0) 10,0(155,8-165,8) 11,2(155,6-166,8)

'h1/2,qC 90,7-93,8 (=61,7-64%) 81,5-88,8 (=55-60,4%) 79,0-79,5 (=54%) 54,8-71,8 (=37-52,8%)

'+(1)melPP, J/g

61,1

71,8

88,0

93,8

'+(2)melPP, J/g

103,0

65,5-78,0

97,1

105,8

'QcrPP, J/g

136

Notes: (1)mel, (2)mel,  temperatures of first an second melting after recrystallization of samples accordingly; '+(1)mel, '+(2)mel – hetas of first an second melting after recrystallization of samples accordingly; (1)beg. mel.  initial temperature of peak of the first melting; 'h1/2,  half-width of peak of the first (the upper value) and of the second (down value) melting; in the brackets there is the interval of temperatures corresponding to the half-width of peak; X  degree of crystallinity calculated on the base of the first peak of melting; 'QcrPP  heat of crystallization of PP after the first melting. All parameters are presented in calculation per 100% of PP in mixture.

(1)mel, q

Composition of blend PPSEPTR

Table 6.2. Thermophysical parameters of samples of PP and blends PPSEPTR

Estimation of the part of J-phase in blends of various composition by Terner method [301] (by the ratio of intensities of reflex of J-phase (2T = 19012/) and reflex of D-phase (2T = 16°36')) (Figure 6.3a, Table 6.1) showed that the part of J-phase was increased from ~0,2 in the sample with PP content 37,5% up to 0,3 and up to 0,4 in samples with PP content 50,0 and 61,5%. In other words in studied samples the ratios between content of two crystal modifications depend on the ratios of blend components. The change of crystallites structures in polymer blends is accompanied by amorphyzation of PP (it follows from X-ray SA and DSC data, Table 6.2). The highest amorphyzation of polymer is observed for the sample with lowest content of PP (37,5% of PP). Obviously the appearance of J-modification of PP crystallites in studied blends is the result of interaction between rubber and PP and may a consequence of change of PP component chains structure or rubber crystallization [302]. In accordance with literature data [75, 301, 303, 304] formation of PP crystallites in J-form may occur as a result of crystallization of short sections of macro-chains in conformation of spiral 31 consisting of alternating trans-gauche-conformers. The change of rotary-isomer composition of PP chain in blend with SEPTR accompanying by the increase of content of short sections in spiral conformation is actually observed by IR-spectroscopy method. This fact follows from the decrease of intensities of bands at 998 and 840cm-1 and increase of intensity of band at 975cm-1 (Table 6.3). This change correlates with the rise of PP concentration in blend and consequently the part of Jform of crystallites. We should note that the rubber applied in work contains significantly more ethylene comonomer in comparison with propylene. Its copolymer chains are enriched by ethylene consecutions in regular conformation of trans-zigzag (Table 6.3) which under crystallization of pure copolymer may form PE macro-crystallites [302]. Investigation of samples of blends by IRspectroscopy method showed that blending of SEPTR with PP leads to the rise of part of long and to the decrease of part of short ethylene blocks in rubber component, and increase of intensity of band at 723cm-1 and decrease of intensities of bands at 729 and 740cm-1 testify to this fact (Table 6.3). However in the diffraction picture of blends there were no reflexes of PE and PP crystallites. Furthermore, the change of content of regular conformers in rubber chains doesn't correspond to monotonous increase of content of crystallites in J-form with the rise of PP, and is described by extreme dependence on components content and consequently is connected with the change of molecular structure of rubber which however doesn't lead to crystallization of rubber in the volume of its phase. Appearance of short sections of PP chain may occur at the expense of decrease of the part of long ones as a result of disruption of regularity in polypropylene isotactic consecution [75, 301, 303]. The simplest reason of increase of part of short sections of PP chains in spiral conformation may be the decrease of sizes of particles of its phase under blending with rubber. However the highest content of crystallites in J-modification of sample with high content of PP, i.e. when PP is matrix contradicts with this fact. It is obvious that in our case desintegration of PP phase leads to amorphyzation of PP crystallites, decrease of their sizes without the change of modification and consequently to the decrease of Tmel of D-form of PP crystallites that to a greater extent is observed in samples with 37,5 and 50% of PP. Disruption of regularity of PP chain in studied blends leading to the change of crystallites modification may be caused by intermolecular interactions of PP chains with alien monomer unit, i.e. with ethylene unit from methylene consecution in rubber macromolecular or under entering of ethylene unit into PP chain for example as a result of chemical cross-linking [301, 303, 304] formed under interaction of radicals mechanically initiated in the process of polymers blending [280, 305]. Such disruptions may shorten the length of crystallizing PP consecutions and effect on polymer crystallization.

137

0,6 0,9 1,03 1,2 1,4

D1380 D1460

0,33 0,69 1,6 1,8 1,9

D2727 D4320

3,2-3,4 4,7-4,9 4,1-4,4 4,4-4,7 0

D723 D4320

3,8-4,2 2,0-3,3 2,8-3,3 2,7-3,0 0

D729 D4320 2,2-2,9 1,2-1,5 2,0-2,1 1,4-1,8 0

D740 D4320 D729 0,8-0,9 1,5-2,4 2,0-2,1 1,4-1,8 0

D723

Structure of SEPTR samples

1,2-1,5 3,1-4,0 2,0-2,1 2,6-3,1 0

D723 D740

Notes: *  the data are presented in relation to the content of component SEPTR, mole %; **  the data are presented in relation to the content of component PP, mole %.

0 37,5 50 61,5 100

Content of PP, %

Composition of sample

0 10,4-10,9 8,9-9,5 9,7-10,9 -

D840

D4320 0 12,2-12,9 10,5-11,8 9,9-12,0 -

D998

D4320 0 2,8-3,8 2,6-3,2 3,2 3,4-3,9

D840 D900 0 3,4-4,0 3,0-3,9 3,7 3,7-4,3

D998 D900

Structure of PP samples

Table 6.3. Molecular structure of chains of PP, SEPTR and blends PPSEPTR.

0 5,5 4,5 4,5 2,9

'D1155

D4320

138

3,2 2,3 2,4 1,9

D1155 D900

We also can't exclude the possibility of formation of co-crystallites of PP and SEPTR having intermediate parameters between PP and PE and thereby of creation of physical net of cohesions between macromolecules of polymers. Analogous phenomenon (co-crystallization) was observed earlier in compatible and partially compatible blends of crystallizing polymers [304]. It is important that the necessary condition of appearance of J-modification of crystallites in PPSEPTR blend in both cases is the intermolecular interactions, consequently the necessary condition is compatibility of components on molecular level, i.e. the presence of inter-phase layer. From the other hand this fact shows that J-modification may be localized at the phases interface. 6.1.3. The particularities of crystallization of mechanical iso-propylenesynthetic ethylene-propylene triple rubberE-50 blends

With the aim of specifying of reasons causing the appearance of new modification of PP crystallites and consequently the character of interaction between components in studied blends the kinetics of isothermal crystallization of PP and PPSEPTR samples in temperatures interval 90135qC was studied. Analysis of endotherms of crystallites melting obtained in isothermal regime (we considered dependences of temperatures and heats of melting, half-width of peaks of melting on Tcr (Figure 6.4a, b, c)) and X-ray SA data showed, firstly that in selected interval of temperatures in PPSEPTR blends the set of PP crystallites fractions is formed differed in structure. Among them there are low-melting and high-melting crystallites of D-modification, and also of Jmodification. The ratio between their content is changed in dependence on blend composition and crystallization temperature Tcr. Secondly, with the rise of Tcr from 90 up to 120qC the part of crystallites in D-form in more perfect structure with high Tmel is increased (endo-thermal peaks of melting are converged, Tmel is increased and half-width of peak of melting 'h1/2 conditionally presenting the degree of polydispersity is decreased). At Tmel higher than 120qC the low-melting D-form either is not realized, or its insignificant amount is formed and J-form is formed in samples in proportion to he content of PP component independently on Tcr right up to 127qC. Thirdly, crystallization of Jform of crystallites decelerates crystallization of D-form (as it appears the values of '+mel, mel and h1/2 are decreased). It is especially clearly expressed in blend with 61,5% of PP (Figure 6.4).

139

Figure 6.4. Dependences of melting temperature Tmel (a), heat of crystallization Qcr (b), and half-width of peak of melting 'h1/2 (c) on crystallization temperature for PP (1) and its blends with SEPTR containing 61,5 (2), 50 (3) and 37,5 (4) mass % of PP.

Comparison of isotherms of crystallization of PP and samples of blends at one degree of overcooling ('7 = 7mel  7cr) or Tcr demonstrates clear deceleration of gross-process of PP crystallization in blends (Figure 6.5a, b, c). And this deceleration depends not only on blend composition, but also on crystallites part having J-modification (Figure 6.5b, c).

140

Figure 6.5. (a) The curve of isothermal crystallization of samples of PP (1), blends PPSEPTR containing 61,5 (2), 50 (3) and 37,5 (4) mass % of PP at Tcr = 120qC. (b) The isotherm of crystallization in coordinates Pi/Pf(Wcr) of samples of PP (1), blends PPSEPTR containing 61,5 (2), 50 (3) and 37,5 (4) mass % of PP 141

with similar contents of crystallites in J-modification. (c) The isotherm of crystallization in coordinates Pi/Pf(Wcr) of samples of PP (1), blends PPSEPTR containing 61,5 (2), 50 (3) and 37,5 (4) mass % of PP with similar contents of crystallites in J-modification. PP (1, 2), PP after annealing (3), blend with 37,5% (47).

Kinetic curves of isothermal crystallization of PP and blends with low content of PP are straightened in coordinates of Avrami equation [104] up to conversion degree ~0,8, higher which the inflection is observed due to sharp reduce of line inclination that is connected with secondary crystallization. For blends with 61,5% of PP having high content of crystallites of J-form except the inflection corresponding to secondary crystallization one more inflection at conversion degrees close to 0,5 is observed (Figure 6.6). Parameters of crystallization of studied systems obtained at initial sections of curves at equal degrees of over-cooling presenting in Table 6.4 confirm that the presence of SEPTR changes kinetics of PP crystallization.

Figure 6.6. Kinetic curves of crystallization of blend with 61,5% of PP at Tcr=127 (1, 2), 120 (25) and 115qC (6).

First of all the value n of pure PP is ~ 3, that corresponds to three-dimensional growth of spherulites on athermic nucleus of crystallization [104]. In blends with 37,5 and 50% of PP and on the first section of blend with 61,5% of PP the value of n is decreased approaching 2. This decrease becomes more essential with the rise of rubber concentration. It is known that n = 2 is observed in the case of formation of lamellar crystallites or lamellar structures in the limits of spherulites [248]. Moreover, the deceleration of crystallization rate with the rise of rubber content follows from comparison of periods of semi-crystallization W1/2 of samples of pure PP and blends (Table 6.4). It is obvious that observing differences in kinetics of isothermal crystallization between blends with low

142

50% PP

61,5% PP

100% PP

Composition of sample

' = = cr, q

76 66 61 56 51 46 44 86 86 71 66 66 61 56 56 56 56 56 51 49 86 71 66 61 56 56 56 51

mel, q

158,4 159,6 160,6 162,0 163,0 164,0 165,0 161,8+148 158,0 162,0+148 161,6+148 158,0 162,0+148 158,2 159+147 162,4+149 161,6+148 159,4+148 162,8+148 161,0+148 161,6 161,4 161,0 160,9 161,8+148 161,8+149 161,4+148 162,8+149

cr, q

100 110 115 120 125 130 132 90 90 105 110 110 115 120 120 120 120 120 125 127 90 105 110 115 120 120 120 125

3,0 3,0 3,0 3,06 3,0 3,0 3,0 2,0 2,5 2,4 2,5 3,0 2,95 2,90 3,40 4,75 3,1 4,9 3,22 1,7 1,7 2,1 2,3 2,4 2,82 2,57 3,28 2,95

n -4

1,0.10 3,0.10-5 4,0.10-6 3,2.10-7 1,1.10-8 2,0.10-10 7,0.10-11 7,9.10-4 4,6.10-4 1,1.10-4 5,0.10-5 8,3.10-6 1,8.10-6 3,3.10-7 6,3.10-9 1,6.10-11 6,3.10-8 1,8.10-12 1,7.10-9 1,2.10-5 1,2.10-3 1,9.10-4 5,0.10-5 5,2.10-6 5,0.10-7 1,26.10-6 1,0.10-8 2,95.10-9

k 15 22 37 110 322,5 1605 2000 23 19 31 36 41 62 150 232 173 187 240 420 635 22,5 24 31 64 150 170 240 660

W1/2 ex. 19 28 56 118 398 1513 2147 30 18 38 45 44 78 151 220 173 187 223 472 632 42 50 63 137 151 171 246 680

W1/2 cal

Period of semicrystallization, sec

Kolmogorov-Avrami Induction period, sec Wi 0 11 18 31 53 180 300 3 7 10 15 22 30 45 45 60 47 40 175 255 0 5 12 30 47 60 60 175

Parameters of crystallization by equation of

0 0 0 0 0 0 0 0,36 0,25 0,30 0,29 0,34 0,29 0,10 0,21 0,38 0,33 0,39 0,30 0,28 0,2 0,3 0,3 0,32 0,28 0,20 0,31 0,30

IJ / ID

48,9 51,7 50,2 49,0 47,5 48,2 55,7 90,6 60,7 81,3 81,7 61,2 90,0 60,7 65,4 83,5 54,5 62,9 67,5 87,5 57,6 60,1 59,8 53,2 75,9 56,7 57,0 70,4

'+mel, J/g

9,5(154,5-164) 9,2(155-164,2) 9,0(154,8-163,8) 6,6(158,2-164,8) 7,2(158,2-165,4) 11,6(155-166) 12,2(155,2-167,4) 13,2(152,8-166) 14,4(148-162,4) 12,4(153,6-166) 11,4(154,6-166) 13,0(150,0-163,0) 10,0(155,4-165,4) 8,2(152,8-161) 9,0(153,8-162,8) 8,4(157-165,4) 9,6(155,2-164,8) 10,2(152-162,2) 10,0(155,4-165,4) 10,0(157-167) 12,2(153,6-165,8) 13,0(152,8-165,8) 11,3(153,8-165,1) 11,4(154-165,4) 9,4(155,4-164,8) 10,8(154,2-165) 11,0(153-164) 13,2(153-166,2)

'h1/2mel,qC

Table 6.4. Parameters of isothermal crystallization of PP and blends PPSEPTR. Cooling of the melt was carried out from 200°C.

and high content of PP more likely are conditioned by the fact that kinetic curves are the superposition of crystallization curves of crystallites of D and J-modifications differing in process parameters.

143

37,5% PP

90 105 110 115 120 120 120 120 120 125 135

160,6 160,4 160,0 160,0 162,0+148 161,1+148 161,0+148 160,6+147 161,4+149 163,6+150 169+164+148

86 71 66 61 56 56 56 56 56 51 41

3,0 2,6 2,5 2,6 2,5 2,35 2,6 4,0 3,25 2,34 2,38

4,6.10-5 2,8.10-5 1,0.10-4 1,3.10-5 2,0.10-6 4,5.10-6 1,8.10-6 1,6.10-10 1,8.10-8 1,9.10-7 1,0.10-9 15-20 30 35-42 57 165 156 150 247 210 636 5015

24 49 34 65 165 161 141 257 217 637 5000

0 10 16 22 45 45 37 45 38 120 500 0,18 0,18 0,21 0,18 0,14 0,10 0,14 0,30 0,25 0,34 0,20 59,8 63-67 70-66 70,3 79,0 77,0 69,6 61,6 64,7 81,7 99,5

11,6(153-164,6) 10,4(153,6-164) 10,0(154-164) 9,0(154,6-163,6) 9,8(155,8-165,6) 8,6(155,9-164,5) 7,4(156,4-163,8) 9,4(154-163,4) 9,0(155,4-164,4) 11,0(154,2-165,2) 20,0(152-172)

144

To separate the regularities of formation of D and J-modifications we carried out fractional crystallization of samples of blends with high content of the last one (with 50 and 61,5% of PP), at low '7 (at 120qC), i.e. in the absence of low-melting D-form. Isotherms of crystallization obtained in the course of processes of various durations and corresponding to them peaks of crystallites melting formed for these times are presented in Figure 6.7. As it is obvious from melting endotherms for the first 100 seconds of crystallization the high-melting fraction of D-crystallites is formed and Avrami index for these crystallites is increased in comparison with pure PP (it is equal to five), and the values of rates of crystallization are decreased (Table 6.5).

Figure 6.7. Kinetic curves of isothermic crystallization of blend PPSEPTR with 61,5% of PP (fractional experiment) at 120qC, durations of crystallization were: 420sec (1), 118sec (2), 180sec (3), 735 sec (4); for comparison the kinetic curve of pure PP is presented (5). The to the Figure presents endotherms of melting of crystallites formed for corresponding times of the process.

At longer crystallization formation of the J-modification begins and correspondingly the peak of melting of formed crystallites is changed (Figure 6.7). Appearance of J-crystallites leads to the decrease of value of n and deceleration of grosscrystallization. As the process is developed up to final stage when high-melting D- and Jmodifications of crystallites are formed and the part of the last one is changed from 0 up to 0,4 at the initial section of kinetic curve the decrease of "n" value down to ~ 2 is observed. It is obvious from the results obtained from fractional and gross-kinetics crystallization that decrease of Avrami index in blends accompanying by deceleration of gross-crystallization is the consequence of competition between the growth of lamellar structures and spherulites, and as crystallization processes are developed the first ones may hinder the growth of the last ones. From the 145

120

After 48 hours of annealing at 60°C

840

-

0 0,17 0,27 0,38

119 180 420 735

120

0

570

120

0

IJ/ID

310

Wcr, sec

120

cr, q

61,5% PP initial

100% PP initial After 48 hours of annealing at 60°C

Composition of sample

159,0

159 159+148 160,6+148 160+148

161,2

162

mel, q

56,2

21,9 66,1 73,8 84,0

45,0

49,0

'+mel, J/g

-

5,0 5,0 5,0 5,0

3,2

3,06

D-form

N

2,75

3,3 2,9 2,25

-

-

J- + Dforms

1,0.10-8 3,2.10-7 5,0.10-6

3,2.10-11 3,3.10-11 3,1.10-11 3,0.10-11 6,3.10-8

-

5,0.10-8

-

-

J- + Dforms

3,16.10-7

D-form

K

-

120 116 117 118

170

118

360

150 155 193

-

-

Calculated period of half-crystallization, W1/2c, sec J- + DD-form forms

Parameters of crystallization by equation of KolmogorovAvrami

Table 6.5. Parameters of fractional kinetics of crystallization of blends PPSEPTR. Cooling of melt was carried out from 200°C.

80

40 42 38 45

60

50

Induction period, sec Wi

other hand, if crystallites of J-form are formed as a result of interaction of ethylene units of SEPTR and PP chains being localized at boundary surface of interface they may hinder the growth of large D-crystallites in the volume of PP phase decelerating chain moving to crystallization nucleus analogously to net points or hinder moving of spherulites growth front [248, 306].

146

37,5% PP

50% PP

61,5% PP

Composition of sample

mel,q

159,2 160,0 158 159,2+150 160,2+148 159,6

cr,q

115 120 120 115 120 115

61 56 56 61 56 61

' = = cr, q

3,1 5,4 3,0 2,5 4,9 3,5

N 4,5.10-6 6,3. 10-12 5,0.10-8 2,5.10-5 2,5.10-11 1,0.10-7

K

Period of halfcrystallization, W1/2c, sec W1/2cal. W1/2ex. 48 47 135 111 240 240 56 60 146 135 70 78

KolmogorovAvrami Induction period, sec Wi 30 37 43 30 37 37

Parameters of crystallization by equation of

0 0 0,39 0,17 0,20 0

IJ/ID

68,8 69,8 56,3 66,1 67,0 63,9

'+mel, J/g

'h1/2mel, qC (T1-T2)

7,6(155,2-162,8) 5,8(156,8-162,6) 11,4(149,2-160,6) 8,0(154,6-162,6) 6,6(156,1-162,7) 8,0(155-163)

Table 6.6. Parameters of isothermal crystallization of PP and blends PPSEPTR. Cooling of melt was carried out from 175°C.

147

It is known that crystallites morphology is determined by the nature of crystallization nucleus [248]. In our case such nucleus may be the nucleus of D-modification localized in PP phase and nucleus of J-modification which may be the short PP consecutions localized at the surface of phases interface of polymer and rubber, or rubber's particles. Consequently various mechanisms of nucleation of D- and J-forms of crystallites are possible. As it is known, temperature of melt previous to crystallization influences on process rate for example accelerates homogeneous nucleation and doesn't influence on heterogeneous one. Comparison of parameters of PP crystallization from melts of blends of various compositions cooled from 200 down to 175qC (Table 6.6) showed that the influence of pre-history of melt on kinetics of crystallization to a greater extent was determined by blend composition. In the blend with 61,5% of PP (high content of crystallites of J-form) it practically doesn't influence on the initial rate of gross-process which may be determined by the value of induction period (Wi) [307], however it decreases the Avrami index. It may be the consequence of the rise of rate of J-modification formation against D-form. However for the blends with 37,5 and 50% of PP index n may be increased. Obviously, in the case of predominance in blend of PP crystallites of D-form formation of the last one is accelerated. The both effects show that nucleation of both forms of crystallites is more likely homogeneous, however kinetic factors significantly influence on crystallization process of PP in blend with rubber. And if thermodynamic parameters of crystallization of blends are conditioned by the nature and energetic parameters of nucleation, then kinetic ones are conditioned by the structure of inter-phase layer. The contribution of the first ones may be estimeated with the use of temperature dependence of rate of spherulites growth. Since formation of spherulites begins earlier than of lamellar structures for estimation of thermodynamic parameters of crystallization of D-form we used temperature dependences of induction period of crystallization Wi. these dependences allow estimating kinetic parameters of crystallization of D-modification in blends PPSEPTR when we may neglect by the crystallization of Jform. At the same time temperature dependence of W1/2 allows characterizing the process of formation of J- against D-modification. In this work temperature dependence of rate of spherulites growth was transformed with reference to Wi and W1/2. At that for description of temperature dependence of diffusion member of equation 'GK we used Williams-Landel-Ferry (WLF) equation presented in the following way: 1/t1/2 = A0 exp[-17238uT/RT(51,6+T-Tvit)]-G /RT 1/ti = A0 exp[-17238uT/RT(51,6+T-Tvit)]-G /RT

0 where G /RT= WT mel /(T'T). Or: ln[1/(t1/2)]-lnA0+ [17238/R(51,6+T-Tvit)]= -'G*/RT ln[1/(ti)]-lnA0+ [17238/R(51,6+T-Tvit)]= -'G*/RT where -'G*/RT=-WT0mel/( '7), W – the constant including energetic characteristics; T0mel  equilibrium temperature o melting; A0  contant. The following dependences: lg[1/(t1/2)]+ [17238/2,3 R (51,6+T-T )]= f [Tqmel /( '7)]. lg[1/(ti)]+ [17238/2,3 R (51,6+T-T )]= f [Tqmel /( '7)]. are approximated by lines with negative inclination equal to W1 and W2, where W is the value of activation barrier of nucleation. The obtained values of W1 and W2 for PP and blends samples are presented in Table 6.7. they demonstrate a little influence of SEPTR on the energy of PP nucleation in blends.

148

'+f˜10-6 J/m3

W, 

V.103, J/m2

Vl˜103, J/m2

V.Vl˜104, J2/m4 a 66,3 69,6 75,1 74,6

L

Sizes of critical nucleus, Å (cr = 120ºC)

100% PP 151 320 9,6 62,4 6,0 10 61,5% PP 151 336 9,6 65,5 6,3 10 50,0% PP 159 368 9,7 71,7 7,0 10,3 37,5%PP 151 360 9,6 70,2 6,7 10 '+f, J/m3  volumetric heat of melting of 100% crystallites of PP in blend and pure polymer; V1 = 2,3kW/0,4b02; b0 = 6,38.10-10m; V = 0,1'+f˜b0˜V -23 0 k = 1,38˜10 ˜l = 2V1˜T m / '+f˜'T; a = 2VTomel / '+f˜'T; l = 2V1Tomel / '+˜'T; V1˜b0˜T0m / k'+f K = 4V˜V

Composition of sample

Determination of parameters with the use of WLF equation

2,0 2,2 2,1 2,5

9,6 9,6 9,7 9,6

38 42 40 47

10 10 10,3 10

40,2 44,3 41,8 50,3

Determination of parameters by induction period of crystallization, Wi Sizes of critical nucleus, Å . . 3 3 V 10 , V 10 , 1 K˜105 (cr = 120ºC) 2 2 J/m J/m a l

Table 6.7. Energetic parameters of nucleation in blends PPSEPTR.

149

Under transition from pure PP to blends the tendency to the increase of parameter W is only revealed. By the equations (2) and (3) that values of V and Ve were calculated (Table 6.7). Linear sizes of critical nucleus of crystallization, side "a" and front "l" sizes of nucleus were determined by formulas: a = 2V0mel/'Hmel' l = 2Ve0mel/'Hmel' The obtained data are also presented in Table 6.8. Table 6.8. Temperature dependences of sizes of critical nucleus of crystallization in blends PPSEPTR. The dependences were determined with the use of WLF model and induction period Wi. Sizes of critical nucleus Composition of blend

100% PP 61,5 % PP

50,0% PP

37,5% PP

Tcr, ºC

'7, °C

120 115 110 120 115 110 125 120 115 110 125 120 115 110

56 61 66 56 61 66 51 56 61 66 51 56 61 66

Determination by WLF

Determination by Wi

a

l

a

l

10,2 9,3 8,7 10,2 9,3 8,7 11,3 10,3 9,5 8,7 11,2 10,3 9,5 8,7

66,3 60,8 56,2 69,5 63,8 59,0 83,6 76,1 69,9 64,6 82,0 74,6 68,4 63,3

10,2 9,3 8,7 10,2 9,3 8,7 11,3 10,3 9,5 8,7 11,2 10,3 9,5 8,7

40,4 37,0 34,2 44,6 40,9 37,8 46,6 42,5 39,0 36,0 54,8 49,9 45,8 42,3

As it is obvious introduction of SEPTR increases the front energy of nucleation Ve and V˜V Ve, the sizes of critical nucleus, and changes the ratio between sizes of nucleus of crystallization for crystallites in D-modification. Temperature rise leads to the rise of sizes of critical nucleus of crystallization (Table 6.8). However comparison of values by which the front energy is changed, the sizes of critical nucleus with values of Wi and W1/2 shows that observing decrease of crystallization rate of PP in all studied samples of blends can’t be explained only by thermodynamic parameters. The conclusion about essential influence of kinetic factors, i.e. inter-molecular cohesions in interphase layer follows from obtained parameters of crystallization. For establishment of the role of inter-phase layer in crystallization of blends PPSEPTR the samples were underwent additional annealing at low temperature (60qC for several hours). It is known that annealing at low temperature increases interpenetration of macromolecules of polymer and rubber [31]. The obtained data showed that the process of isothermic gross-crystallization of annealed samples of blends was significantly decelerated (Figure 6.8, Table 6.9).

150

37,5% PP annealing

50,5% PP annealing

annealing

PP annealing cooling from 200°C Initial 61,5% PP cooling of melt from 200°C

Composition of sample

161,2 162,0 163,2 163,6

158 158 159,4

157,5+150 159+150 161,2+150 156,7+147 159+150 158,9 159 158+146 158+146 159,2+146 160,8+146

90 110 120

115 120 125 115 120 125 125 115 115 120 125

mel, q

120 123 125 127

cr, q

61 56 51 61 56 61 61 61 61 56 51

86 66 56

56 53 51 49

', q

2,4 2,8 2,2 2,5 2,5 3,15 2,8 1,8 1,7 2,4 2,15

2,5 3,0 4,93

3,2 2,8 3,4 2,7

n1

1,5 2,22 2,03 1,3

2,47

-

n2 3,16.10-7 2,0.10-5 4,6.10-8 8,3.10-8 3,02.10-5

4,6.10-4 8,3.10-6 1,8.10-12 5,6.10-6 7,9.10-8 3,0.10-7 2,8.10-7 5,5.10-8 1,6.10-10 9,1.10-10 8,3.10-5 5,5.10-5 2,0.10-7 1,8.10-7

k2

4,4.10-8 1,6.10-8 7,9.10-9 2,0.10-8

k1

141 1164

123 288 708

19 41 240

175 350 426 660

132 301 780 360 692 1149 1485 151 276 531 1156

18,7 44 223

177 352 444 650

2132

1065 1836 2566

-

372

-

Period of halfcrystallization, sec W(1)1/2 W(2)1/2 W1/2 ex. cal. cal.

-

7 22 40

30 45 90 45

Induction period, sec Wi

Parameters of crystallization by equation of KolmogorovAvrami

0,4 0,36 0,4 0,3 0,32 0,30 0,32 0,24 0,27 0,24 0,3

~0,25 ~0,34 0,39

0 0 0 0

IJ/ID

Table 6.9. Parameters of isothermal crystallization of PP and blends PPSEPTR after annealing at 60°C.

61,5 56,2 69,4 49,0 53,0 54,7 55,0 78,2 55,3 54,0 82,5

60,7 61,2 63,0

45,0 45,2 41,2 48,6

'+mel J/g

-

151

14,4(148-162,4) 13(150-163) 10(151,8-61,8)

8,0(156-164) 6,0(157,8-163,8) 6,2(158-164,2) 6,4(159,2-165,6)

'h1/2mel qC (T1-T2)

Figure 6.8. The isotherms of crystallization of PPSEPTR blends annealed in inert medium and oxidized on air at 130qC.

The rise of values of Wi and W1/2 in annealed samples of blends is significantly higher than in pure PP annealed at the same conditions. Maximum deceleration of crystallization is observed for the sample with 50% of PP. This fact shows that the higher the degree of PP and SEPTR cohesions in inter-phase layer, the harder the phase separation and crystallization of PP in blend. In annealed samples Avrami index decreases from 5 down to 2,75 that also indicates on the fact that increase of volume of inter-phase layer decelerate PP crystallization (Table 6.9). It is important to note that observing deceleration of crystallites formation relates to crystallites in Dmodification. Annealing doesn’t change the content of crystallites in J-from. Obviously, content of this form of crystallites depends on composition of blend and conditions of blending. In this connection crystallites of J-modification represent "the points of chemical net". As it was said above, in accordance with modern conceptions of thermo-kinetics [107, 108] the increase of inter-molecular interactions in inter-phase layer decelerated gross-crystallization of PP as a result of mixing up of chains ends or increase of part of non-crystallizing fraction of polymer. Annealing of blends leads to the rise of physical cohesions, to the decrease of PP crystallization rate. Thus, obtained data allow concluding firstly that studied blends PPSEPTR are partially compatible systems in which inter-phase layer is formed. Kinetics of crystallization of PP crystallites D-from in blends with SEPTR to a greater extent is determined by structure of inter-phase layer. The process of phase lamination will be the limitative stage of crystallization. Maximum deceleration of crystallization is observed for the sample of blend with 50% of PP. 152

Secondly, part of polypropylene transforms into crystal state forming D-modification, its other part forms crystallites of J-modification, the last ones are formed due to entering of rubber ethylene units into propylene chains at the surface of interface and may play the role of physical net between components. Thirdly, PP crystallites in J-modification capturing the part of macromolecules of rubber localizing at the surface of interface will isolate phases of PP and SEPTR influencing on oxidation kinetics, changing the diffusion of oxygen and low-molecular radicals, influencing on free valency transfer by the mechanism of chemical relay race. We should note that contribution of these structural factors into oxidation is increased with the rise of the part pf crystallites in J-modification, i.e. in the raw of samples: 37,5% PP < 50% PP < 61,5 % PP. 6.1.4. Structure of amorphous regions of polypropylenesynthetic ethylene-propylene triple rubber blends

Investigation of structure of amorphous phase in blends of PP with SEPTR with the help of curves of RTL highlighting of samples of PP, SEPTR and their blends confirm the presence of inter-phase or inter-components layers.

Figure 6.9. Curves of radio luminescence of samples of PP (1), SEPTR (2) and their blends with 37,5 (3), 50 (4) and 61,5 (5) mass % of PP, and also of vulcanizate of blend PPSEPTR with 37,5% of PP obtained by dynamic vulcanization by resin vulcanizing system (3').

As it is obvious from Figure 6.9 for pure polymers there are in two maximums characteristic for J- and E-relaxation transitions [237, 287], for samples of blends appearance of intensive new relaxation transition is observed in common temperature interval of vitrification of PP and SEPTR. At that the intensities of peaks of J- and E-relaxation are decreased. It is known that third peak on the curves of polymers blends samples RTL highlighting appears as a result of combining of amorphous regions of components on the level of molecular segments and indicates on formation of inter-phase layer [30, 31]. It is obvious that in our case appearance of the third maximum of new relaxation transition is conditioned by segmental solubility of rubber and polymer in amorphous regions of blends, i.e. by appearance of inter-phase layer. Analysis of structures of amorphous regions by IR-spectroscopy method showed that as a result of introduction of SEPTR into PP the degree of regularity of ethylene blocks in copolymer 153

chain is increased, but degree of regularity of PP chains is decreased and its amorphous regions are enriched by coagulated conformers (Table 6.3). (In IR-spectrum of blends the part of long (n>5) methylene consecutions in conformation of trans-zigzag is increased and the part of shorter (n=4 and 3) ones is decreased, optical density of the band at 723cm-1 is increased and at 740cm-1 it is decreased, the value of ratios between intensities of bands at 723 and 729cm-1, at 723 and 740cm-1 are increased, and also the intensity of PP band at 1155cm-1 is increased (Table 6.3)). Thus, the existence of inter-phase layer is confirmed by significant change of crystallinity degree, structure and morphology of PP crystallites, by the influence on crystallization kinetics, structure of polymer chains of both components in blend and also by decrease of segment mobility of PP [233-237]. The last fact follows from the shear of maximum of PP vitrification on RTL curves of blends to the high-temperature region. Non-monotonous of dependence of temperature of maximum of new relaxation transition TEc and vitrification of PP component TE on structure of blend against obvious correlation between TEc and TE of PP, i.e. between segment mobility of PP in phase and of macro-chains in inter-phase layer indicate on difference in structure of inter-phase layer for blends of various compositions. It is known from the works devoted to the investigation of structure of thermo-elastoplastics [293, 294, 308-310] that boundary layer consists of equilibrium part conditioned by mutual segment solubility of PP and SEPTR and non-equilibrium part arisen as a result of contacts of macroparticles of disperse phase with disperse medium and incomplete process of phases lamination. In given work we selected compositions of blends PPSEPTR including the region of phases inversion. It is obvious that in this case in dependence on the fact the polymer or SEPTR is the disperse phase morphology and structure of blend components and also chemical composition and structure of inter-components layer will be changed. Reliability of conclusions about changing chemical composition of inter-phase or inter-component layer may be estimated on the base of conceptions about inter-phase layer as about homogeneous solution. In this case its composition may be calculated using the Fox's equation for compatible blends. 1/TEc = 1  w/ TESEPTR + w / TEPP, where TEc  temperature of homogeneous solution is 240, 216 and 225K for samples of blends with PP content 37,5, 50 and 61,5% correspondingly; TESEPTR = 210, TEPP = 260; w  mass part of PP in blend. Estimations show that composition of inter-phase layer doesn’t correspond to homogeneous solution of one composition for various samples. At that for sample enriched by copolymer the inter-phase layer is enriched by PP and for sample enriched by PP the inter-phase layer is enriched by SEPTR. If we assume that intensity of highlighting in the region of J-maximum is determined by concentration of luminescence sites localized in components phase, then observing monotonous increase of intensity of peak of J-relaxation may testify to the increase of content of PP-component in amorphous regions as separate phase and the higher the content of PP in blend it will be observed to a greater extent. However as it is obvious from the obtained data (Table 6.2), with the rise of PP content in blend the degree of its crystallinity and consequently the content of this component in amorphous regions are changed in such way that concentrations of monomer units of PP ([RHPP]) in these regions are 5,4, 5,6, 6,0 and 8,6 mole/kg in blends with 37,5, 50, 61,5% of PP and pure PP accordingly. It follows from this fact that under enrichment of blend by PP-component it is separated as phase and depleted by its content the inter-phase layer. In our estimations we neglect the decrease of intensity of J-peak due to superposable on it of J-peak of SEPTR since the intensity of J-peak of SEPTR is lower than of PP. Thus, inter-phase layer formed in investigated blends changes its composition in dependence on components content. It is obvious that driving force leading to the change of chemical composition of blends' amorphous regions are the particularities of PP component crystallization in blends in the presence of inter-phase layer. Under crystallization the non-crystallizing macromolecules of amorphous phase are ejected out of crystal net and localized on the boundaries of growing crystals. The growth 154

of the crystal depends on macromolecules diffusion to growing crystal bound and also on the rate of impurities removal from crystallization front. Introduction of SEPTR into PP leads to the change of melt viscosity, hindering of phase lamination and consequently the rate of macromolecules diffusion to crystallization nuclear. In this case intergrowth of crystallite becomes preferable since bounders surrounding by impurity molecules of SEPTR grow slower, and rubber is ejected into amorphous regions of polymer. Thus, it follows from the obtained data that the reason of change of reactivity of blend PPSEPTR in dependence on its structure may be caused firstly by the change of blend components structure in comparison with homopolymers (consequently of the densities of amorphous regions, structurally-dynamic parameters, etc.); and secondly by the presence on inter-phase layer, its chemical composition and structure. The analysis of the structure of studied samples of blend PPSEPTR of various compositions allows concluding that neither the first, nor the second models suggested for the description of their oxidation couldn't explain in full measure the observing in this work influence of PP structure on process kinetics. Obviously the presence of inter-phase layer in blend will promote proceedingof cross radical reactions between PP and SEPTR. The character of PP component structure change, appearance of crystallites of J-modification, their localization at the surface of phases interface between components may explain the observing monotonous increase of induction period of blends oxidation with the rise of PP content. Obviously with the rise of the part of such crystallites that corresponds to the rise of PP content in blend, the diffusion of oxygen into the sample may be hindered decelerating the initial rate of oxidation. However the decrease of reaction ability of mixture, value b couldn't be explained by the change of structural parameters only of this component. As we said above, the change of dynamic parameters of PP in samples was in slope opposition to the change of blend reactivity. The other explanation of the observing deceleration of oxidation initial rate of blends PPSEPTR may be the change in the mechanism and kinetics of oxidation reactions as in interphase layer, so in components phases. For example, the crystallites of J-modification localized at the surface of interface may play the role of traps of free valency of PP and SEPTR. In this case deceleration of oxidation of blends PPSEPTR will be determined by the number of such traps or by concentration of crystallites in J-modification. 6.1.5. Analysis of non-volatile products of oxidation of propylenesynthetic ethylene-propylene triple rubberE-50 blends

one should expect that changes in the rates of separate stages of oxidation process of PP and SEPTR components and in mechanism of oxidation of blends PPSEPTR will be reflected on the composition and kinetics of non-volatile oxidation products accumulation. That is why we studied the composition of the products of PPSEPTR blends oxidation. Comparison of the data on accumulation of oxidation products of PP, SEPTR and their blends obtained with the help of IR-spectroscopy showed that rates of accumulation of functional groups in blends samples correlate with the initial rates of oxidation and are decreased in the raw: 37,5% PP > 50% PP > 61,5% PP. Analysis of composition of non-volatile products of oxidation established with the use of identification of bands of carbonyl- and hydroxyl-containing groups in IR-sepctra of oxidized samples showed significant differences between compositions of products of pure PP and SEPTR and their blends PPSEPTR (Figure 6.10, Table 6.10).

155

a

c

b

d

e

initial

initial

f

j

Q, cm-1

Figure 6.10. IR-spectra of oxidized samples of PP (a), SEPTR (b) and blends PPSEPTR with 37,5(c), 50 (d) and 61,5 (e) % of PP at Tox = 130qC, PO2 = 150 millimeters of mercury, Wox = 0 (1), 260 (2), 620 (3) and 2200 (4) min, and also the spectra of oxidized samples of blends PPSEPTR with 37,5% of PP after thermal treatment (f) and treatment by KOH in isopropyl alcohol (j).

156

100% PP

61,5% PP + + 38,5 % SEPTR

50% PP + + 50% SEPTR

37,5% PP + + 62,5% SEPTR

100% SEPTR

Sample

Duration of oxidation, min 60 100 280 360 440 560 680 800 60 260 310 360 410 560 60 260 360 560 60 2195 2295 2350 5 25 40 85 120 160

[>C=O]˜102 (1720cm-1), mole/kg 0,4 1,4 1,0 1,0 2,0 1,4-2,0 2,6 3,0 1,4 0,8 3,0 5,0 3,0 5,0 0,9 2,0 3,0 2,6 1,6-2,4 0,7-1,0 1,3 1,4 0,5 1,5 1,0-2,0 1,5-1,7 3,0-3,3 5,0-8,0

[>C=O]˜102 (1750cm-1), mole/kg 4,5 4,2 1,7-2,6 2,2-2,4 3,2 2,5-3,5 3,8 6,4 2,2 1,0 9,4 13,0 15,0 19,0 1,4 14,0 15,0 18,0 1,6-2,4 2,5-2,7 2,3 1,4 0,7 0,5 1,3-1,4 0,9-1,0 2,1-2,7 2,3-4,2

[-OH]block˜102 (3370cm-1), mole/kg 3,0 2,0 2,0 2,4 5,4 3,7-5,1 3,6 4,4 2,6 2,6 3,0 3,0 4,0 9,4 0,14 2,6 2,7 2,0 3,0 1,4-2,1 3,0 4,0 4,0 5,0 1,6-3,6 4,3-4,7 6,1 8,0-10,0

[-OH]block˜102 (3420cm-1), mole/kg 3,4 2,6 2,6 3,4 4,6 3,5 3,0 4,0 2,4 2,6 2,6-4,0 4,0 4,0 11,0 0,1 2,5 4,0 3,0 2,6 1,7-2,1 1,4 2,7 2,1 3,0 3,0-4,6 4,3-4,6 5,4 9,3-12,0

[-OH]singl˜102 (3650cm-1), mole/kg 4,6 5,9 2,3 2,1 3,9 2,3 3,1 4,3 1,0 1,3 1,4 2,9 3,4 3,7 0 0,7 0,7 4,6 1,4 1,0-1,7 2,6 2,9-3,6 0 0 0 0 0 0

Table 6.10. Non-volatile products of oxidation of blends PPSEPTR. Conditions: Tox. = 130°C, 2 = 150 millimeters of mercury.

0,6-1,6 1,4-3,0 1,1 1,9 4,2 2,0 1,5-4,6 2,9-2,5 1,8-1,6 1,9-2,4

0,1 1,2 1,3

8,5 2,0 2,4 3,4 2,3 2,1-2,9 1,2 1,3 1,8 3,3 0,9-1,3 0,8 1,3 2,2

[-OH]3420 [>C=O]1720

157

If hydroxyl-containing products prevail in the composition of PP oxidation products and among carbonyl-containing ones  saturated ketones and acids that corresponds to literature data obtained earlier [162], then in composition of SEPTR oxidation products unsaturated carbonyl compounds prevail (absorption bands in the regions of 1580, 1620, 1640, 1690 and 1700 m-1 testify to these facts (Figure 6.10)). OH-groups are observed in low concentrations and at deeper (>0,5mole/kg) stages of oxidation (Table 6.10). In contrast to pure polymers for samples of blends already at early stage of the process the IRspectra contain two groups of bands: in the regions of 1690-1720 and 1750-1770 m-1. Changes in IR-spectra of oxidized films of blends caused by treatment by NaOH solution in isopropyl alcohol (Figure 6.10j), and also by treatment in vacuum at 130°C (Figure 6.10f) showed the presence of acid and ester in products. As a result of treatment the peak at 1750-1770cm-1 disappeared and the broad absorption in the region of 1580cm-1 corresponding to asymmetric vibrations of CO2-group appeared (Figure 6.10j). After thermal treatment this peak also disappeared (Figure 6.10f). The peak at 1700-1720 -1 partially saved after the treatment of blend by alkali indicates on its belonging to saturated and unsaturated ketones. In oxidized samples of blends there too little amount of OH-groups analogously to SEPTR, they were found only at deeper (>0,5mole/kg) stages of oxidation. The increase of content of single OH-groups is observed in the structure of hydroxyl-containing groups, at that if in the case if blend with 37,5% of PP these groups are revealed at frequency characteristic for OH- at tertiary carbon atoms (the band at 1560cm-1 relates to single OH-groups in oxidized PP and is observed in diluted solutions of low-molecular tertiary alcohols and hydroperoxides), then for the samples with 5- and 61,5% OH-groups are revealed connected with secondary carbon atoms (the band at 3610cm-1 characteristic for hydroxyl-containing products of PEHD oxidation and also for solutions of secondary alcohols indicates on it) (Table 6.10). Comparison of structure of products of PP, SEPTR and their blends oxidation with the help of intensities of characteristic IR-bands and ratios between them shows that the structure of oxidation products of blends is changed in the course of the process. Analysis of the character of this change allows concluding the following: firstly, at the beginning of the oxidation and up to the depth of oxidation corresponding to 1mole/kg of absorbed oxygen in the composition of oxidation products of blends the functional groups are found characteristic for SEPTR, and at deeper oxidation there are the products characteristic for PP (Table 6.10). Secondly, in the composition of products of blends oxidation especially those ones with high content of PP component the functional groups of SEPTR prevail already at the beginning of oxidation (Table 6.10). Obviously it testify to inclusion macromolecules of rubber into oxidation of blends already at early stage of process that is possible in inter-phase layer. Nevertheless the differences in composition of blends oxidation products from the products of oxidation of pure SEPTR and PP demonstrate changes in kinetics of radical reactions. These changes may be both the consequence of inclusion of SEPTR macromolecules into oxidation process and the consequence of change of components oxidation mechanism. Let's consider this question in details. Firstly, low content of hydroperoxides in blends may be connected with higher in comparison with pure polymers constant of rate of their thermal decomposition. However the annealing of oxidized sample of blend PPSEPTR in vacuum at 130°C didn't lead to the decrease of intensity of hydroxyl peak in its IR-spectrum (Figure 6.10f). It means that the constant of rate of thermal decomposition of ROOH in blends is at least higher than in homopolymers. Secondly, the decrease of segment mobility of chains in solid polymers may lead to induced decomposition of hydroperoxide without the rise of the number of radicals [162]. Then among the samples of blends for the blend with 37,5% of PP as for blend possessing the lowest segment mobility the contribution of induced decomposition should be revealed to a greater extent. In this case in composition of oxidation products of this sample the alcohol groups should prevail. However tha 158

ratio between the content of alcohol and hydroperoxide OH-groups for samples of blends of various compositions are close. Thirdly, the presence of unsaturated bonds in copolymer (as end ones, so the bonds of diene comonomer) contacting with PP chains may increase the probability of reactions betweeb unsaturated compounds and hydroperoxide groups, that usually leads to destruction of ROOH and formation of cross-links between neighbor segments or macro-chains. Transverse cross-links may appear as a result of cross reactions. High localization of diene comonomers in inter-phase layer will promote it. In this case pero-acid may be formed from aldehydes appeared during oxidation in branches of both secondary carbon atoms and transverse bonds. Fourthly, peroxy-acids may be the products of secondary reactions, the consequence of recombination of alcoxy-radicals. Recombination of these radicals leads to formation of aldehydes and ketones, and further oxidation of aldehydes creates peroxy-acids. Ester and ketones also may the products of secondary reactions. It is obvious that in blends PPSEPTR as a result of oxidation localization in inter-phase layer the probability of proceeding of secondary reactions may be increased. It is promoted by close contact between oxidizing RH-bonds of PP and ethylene, propylene and diene comonomer units of SEPTR able to participate in cross reactions of oxidation kinetic chain transfer. Secondary reactions will promote thermal oxidative destruction of macro-chains of oxidizing components that obviously is observed in the experiment (Table 6.11). Fifthly, participation of double bonds of diene comonomer in oxidation process also may lead to the change of radicals composition carrying on the kinetic chains of oxidation, to appearance of allyl radicals fast decomposing with formation of ketones with conjugated double bonds, and to the decrease of stationary concentration of peroxide radicals. With the rise of PP content in blends the increase of the part of unsaturated ketones in the total mass of products obtained at the initial stage of oxidation is observed. This fact correlates from the one hand with enrichment of inter-phase layer by SEPTR, from the other hand with the value of induction period. Increase of the content of rubber in inter-phase layer of blends PPSEPTR leads to the increase of local concentration of diene comonomer and consequently to the rise of its contribution into kinetics of cross reactions. Actually the probability of cross-linking of macro-chains in blends samples is increased with the rise of SEPTR content in inter-phase layer, i.e. from the sample containing 37,5% of PP to the sample with 61,5% of PP. It follows from the high cokeformation during burning pf the sample with 61,5% of PP in comparison with the sample with 37,5% of PP (Table 6.12) [311]. Sixthly, appearance in the composition of products of blends oxidation with high content of PP of single hydroperoxides connected with secondary carbon atoms in contrast to the sample with 37,5% of PP in which the analogous groups are appeared at tertiary carbon atom indicates on the rise of contribution of SEPTR into oxidation of first blends of ethylene comonomer. Essential influence of change of active sites nature on kinetics of rubber oxidation was found under investigation of double ethylenepropylene copolymers with various structures of macromolecules [303]. Copolymer enriched by ethylene comonomer are oxidized significantly slower in comparison with SEPR enriched by propylene comonomer (Table 6.13) [303]. Obviously the appearance of crystallites of J-modification in blends PPSEPTRE-50 conditioned by the interaction of PP chains with ethylene blocks (consecutions) leads to the rise of localization of the last ones in inter-phase layer. This fact increases the probability of oxidation kinetic chain transfer from PP to less active in oxidation process ethylene comonomer and in such way reduces the rate of process. Since the content of crystallites of this modification in polymer is significantly increased from the sample with 37,5% of PP tp the sample with 61,5% of PP, than the contribution of ethylene comonomer into SEPTR oxidation in inter-phase layer will be also monotonous increased with the rise of PP content in blend.

159

0 350

37,5% PP 'No2 = 1,1mole/kg

mel, q

161,0 152,8+155,2

158,4-160,0 157,6

161,2 158,6+shoulder 143

162,0 154,8

(1)

mel, q

160,8 153,0

156,8 152,6

161,8 156,2

160,8 154,8

(2)

(2)

(1)

mel, (1)'mel  temperature and heat of primary melting; mel, (2)'mel  temperature and heat of secondary melting after recrystallization; (1) 'Qcr  heat of crystallization after primary melting.

0 350

50,0% PP 'No2 = 0,6mole/kg

0 350

0 350

100% PP 'No2 = 2mole/kg

61,5% PP 'No2 = 0,2mole/kg

Duration of oxidation, min

Composition of sample

106,0 103,4

106,0 104,8

107,0 104,8

108,0 101,8

cr, q

55,0-61,0 113,6

79,5 85,8

82,0-88,0 84,6

91,0-94,0 87,0

'mel, J/g

(1)

Table 6.11. Thermophysical parameters of oxidized samples of PP and blends PPSEPTR. Conditions: Tox. = 130°C, ‚ 2 = 150 millimeters of mercury.

61,2 93,9

77,4 87,5

92,8 103,7

'mel, J/g 94,8 95,3

(2)

65,0 118,8

83,0 85,5

90,0 94,5

94,0 83,6

'Qcr, J/g

(1)

160

Table 6.12. The values of oxygen index and coke number of blends PPSEPTR Composition of sample 100 % PP 61,5 % PP 37,5 % PP 100 % SEPTR

Oxygen index, % 17,0 21,0 19,5 18,5

Coke number, mass % 0 3,4 1,5 0,5

Table 6.13. Concentration of products of oxidation of double ethylene-propylene copolymers (SEPR). Conditions: Tox. = 130°C, 2 = 150 millimeters of mercury.

Composition of sample

Stationary rate of oxidation, Wo2, mole/kg˜sec

SEPR of "CO-034" brand contains 78,8 mole % of ethylene comonomer

5,2˜10-5

SEPR of "CO-059" brand contains 67,4 mole % of ethylene comonomer

2,9˜10-4

Duration of oxidation, min

[>C=O]1760 u102 , mole/kg

[-OH]3420 u102 , mole/kg

[-OH]3420 [>C=O]1760

10 25 90 715 1140 10 25 65 159 235 325 715 1140

0,9-1,4 0,9-1,3 0,7 0,3 0,1 0,5 0,5-1,1 0,9 2,4 0,7 0,6 0,6 0,3

2,4-3,0 3,0-4,6 7,4 3,7 4,6 1,4 1,5-2,2 4,4 5,4 5,9 7,0 0,1 0,1

2,1-2,6 3,3-3,5 8,3-12,0 12,5-33,3 46,0 2,8 2,0-3,0 4,8-5,0 2,2 8,5 11,8 16,7 33,3

In accordance with the obtained data we may say that initial rate of oxidation depends on local concentration of double bonds and ethylene comonomer in inter-phase layer: the higher are these two concentrations, the lower is the initial rate of blend oxidation. In other words the inhibiting role of double bonds and less active comonomer in SEPTR in oxidation of blends is clearly observed. Obviously the role of double bonds is come to decrease of stationary concentration of peroxide radicals and deceleration of ROOH accumulation from the one hand, and to secondary reactions leading to decomposition of ROOH from the other. The role of ethylene comonomer is changing of constants of rates of tertiary carbon atoms oxidation by the constants of rates of oxidation of the secondary ones. Destruction of inter-phase layer leads to development pf oxidation reaction in phases of PP and SEPTR. It is obvious that rate of oxidation of localized in phases component will be determined by structural-physical characteristics of blend components. The change of monotonous deceleration of oxidation of PPSEPTR blend with the rise of content of PP by extreme deceleration follows from the last fact. 6.1.6. Investigation of structure of oxidized propylenesynthetic ethylene-propylene triple rubber blends

The particularities of structure of each of the components of blend and the presence of interphase layer will be inevitably reflected on both kinetics of oxygen absorption and oxidation products accumulation, and also on kinetics of structurally-physical processes accompanying blend oxidation.

161

100% PP

61,5% PP

50% PP

PP

7,5%

SEPTR

00%

amples

3

1

S

0 310

260 310 360 410 0 260 360 455 0 360 2195 2293 2346 2500

310 1155 1550

min

0

oxidation,

ration of

Du

0,2 1,9 3,4 5,4-7,6 0,2-0,25 0,2 3,8 4,6 0-0,4 0,3 0,5-0,6 0,7-0,9 0,21 0,8-0,6 (at 1750m-1) 0 0,5

0,4 0,85 5,4

D1760 D4320

0,7-0,8 0,6 1,6 1,4 1,4-1,7 0,5-0,7 0,4 0,4-0,5 0,7 0,2-0,7 0,3 0,4 0,7 0,7 0,3 -

-

-

1,7 2,7 1,9

D750 D4320

2,0-2,2 2,2 2,3 2,5 2,0-2,6 1,7-2,0 2,4 1,2-1,5 1,3 1,4-2,0 2,0 1,8 1,7 1,4 1,1

3,3 3,6 4,0

D730 D4320

2,6-3,2 2,6 2,1 1,7 0,8-1,0 2,4-3,3 1,5-2,1 1,2-1,4 2,2 1,8-2,4 2,4 2,2 1,7 0,8 1,6

3,5-3,7 4,9 5,3

D723 D4320

0,8-1,0 1,1 0,3 1,0 1,2 1,2-3,5 1,6-2,3 0,8-1,0 1,4 1,8-2,9 2,0 1,4 1,8 1,0 1,5 -

1,0-1,2 1,2 0,7 1,9 2,1 2,0-3,6 1,8-2,6 1,5-1,8 1,3 2,2-3,0 2,5 1,0 1,9 1,3 2,3 0,4 0,6 -

(937) 0,9-1,0 (937) 1,0 (937) 1,2

D723

D723 (975) 1,4 (975) 1,3 (975) 1,1

D840

D998

0,3 0,6 0,6 0,5 0,3 0,4 0,5 1,5 0-0,3 0,2 0,2 0,2

0,5 0,9 0,5

D4320

D723 0,6 0,5 0,4

D540

D750

0,25 0,23 0,8 0,4 1,7 0,2-0,8 0,2-0,3 0,4 0,3 0,1-0,2 0,2 0,2 0,4 0,9 0,2

0,4 0,7 0,7

D730 D723

0,7-0,8 0,9 1,1 1,5 2,6 2,3 1,1-1,6 0,9-1,3 0,6 0,9-1,3 0,9 0,8 1,0 1,7 0,7

Structure of SPETR chains

162

The ratio between content of PP chains in spiral conformation and long ethylene blocks of rubber

Table 6.14. Change of structure of polymer chains of components of blend PPSEPTR in the course of oxidation. Conditions: Tox. = 130°C, 2 = 150 millimeters of mercury.

The rate of change of structural parameters of each of the components should correspond to the depth of oxidation or concentration of absorbed oxygen by this component. Thus, the character and kinetics of change of structural parameters of components in the course of oxidation of blend may indicate on localization of process. That is why investigation of correlation between oxidation kinetics and change of structural parameters allows more accurate establishing of the role of structural elements into thermal oxidation of polymer blend PPSEPTR.

Analysis of oxidized samples of PPSEPTR blends of various compositions by IR-spectroscopy and DSC methods showed that oxidation was accompanied by destruction of polymer chains of both components (Table 6.14, Figure 6.11) and by decomposition of PP crystallites that follows from the decrease of Tmel in the maximum and appearance of broad low-temperature shoulder at PP crystallites melting peak (Table 6.11). The most essential decomposition of crystallites for one and the same time of initial stage of oxidation is observed for the sample with 37,5% of PP, the lowest decomposition is observed for the sample with 61,5% of PP.

Duration of oxidation, min

Figure 6.11. The change of structure of polymer chains in the course of oxidation of blends PPSEPTR (E50). Tox = 130°C, PO2 = 150 millimeters of mercury.

It follows from IR-spectroscopy data that the highest initial rate of destruction of trough-pass chains of PP and chains of SEPTR is observed for blends with 50 and 37,5% of PP and the lowest one is for the blend with 61,5% of PP. At the stage of deep oxidation the rate of PP chains destruction fro the sample with 61,5% of PP is sharply increased in comparison with samples with 37,5 and 50% of PP (Figure 6.11). Thus, the rise of the rate of destruction processes of PP component at the initial stage of process corresponds to the rise of oxidation rate rise observing in the raw of samples 37,5% PP >50% PP >61,5 % PP.

163

cr, q

mel,q

', q n1

61,5% PP 'N 2 = 0,2 mole/kg

2,1 86 158+145 90 2,85 76 158+146 100 3,4 61 158 115 2,0 56 160 120 1,75 51 162 125 90 153,5 86 2,64 50% PP 100 153,5 76 3,1 110 152+140 66 2,4 'N 2 = 0,64 115 153,4+144 61 2,25 mole/kg 120 155 56 2,3 2,6 86 155,5 90 37,5% PP 2,57 76 155,0 100 2,28 61 155,6 115 'N 2 = 1,11 2,14 56 157 120 mole/kg 3,1 46 157,7 130 W1/2 ex.  experimental period of half-crystallization; W1/2 cal.  period of half-crystallization calculated by Avrami's equation.

Composition of sample 1,0.10-3 2,5.10-5 7,9.10-8 7,1.10-6 6,3.10-6 7,5910-5 7,9410-6 3,510-5 1,010-5 9,110-7 110-4 6,310-5 1,1510-5 4,010-6 7,110-13

k1

Period of halfcrystallization, sec W1/2 ex. W1/2 cal. 22,5 22,5 36 34 110 113 313 330 759 770 33 32 38 39 63 61 138 142 354 360 30 28 37 37 125 129 281 288 7378 7260

gorovAvrami Induction period, sec Wi 3 15 60 90 145 0 15 30 45 45 7,5 18 67 120 540

Parameters of crystallization by equation of Kolmo-

64,6 54,6 61,3 56,3 74,0 59,3 50,1 47,5 57,1 49,2 70,5 70 63,7 80,8 84,0

'+mel J/g

Table 6.15. Parameters of isothermal crystallization of oxidized samples of PP and blends PPSEPTR. Conditions: Tox. = 130°C, ‚ 2 = 150 millimeters of mercury, Wox = 259min.

12,6(150,4-163) 12,4(150-162,4) 8,8(153,2-162) 8,8(154-162,8) 15,0(150,2-165,2) 18,0(141-159) 16,0(143-159) 19,0(139-158) 15,0(142,8-157,8) 15,4(143-158,4) 14,8(146-160,8) 15(146-161) 11(148,4-159,4) 15,8(144,4-160,2) 15,5(148-163,5)

'h1/2mel, qC (T1-T2)

164

Destruction of ethylene comonomer, ethylene chains in extremely straightened conformation prevails in rubber component in blends. And at the initial stage of oxidation the decomposition of long ethylene (methylene) consecutions and accumulation of shorter ones occur. The decrease of intensity of the band at 723cm-1 and intensity rise of bands at 729 and 750cm-1 tesitfy to the last fact (Table 6.14). With the rise of depth of oxidation process the short ethylene consecutions are decomposed (Table 6.14). At the same time under oxidation of pure SEPTR decomposition of propylene consecutions and accumulation of single units occur (intensity of band at 968cm-1 is decreased and intensity of band at 937cm-1 is increased), and the length of ethylene blocks is practically not changed (Table 6.14). The change of mechanism of destruction of rubber component correlates with the change of composition of non-volatile products of blends oxidation, that obviously indicates on the change of nature of SEPTR reaction sites participating in cross radical reactions with PP component in inter-phase layer. Analysis of regularities of PP crystallization in oxidized state allows studying of particularities of change of structure of polymer chains during oxidation of PPSEPTR blends. In particular, the kinetics of isothermic PP crystallization in oxidized blends will depend on particularities of oxidation and structural reconstructions in polymer and will be differed in the case of localization of oxidation in components or inter-phase layer of blend. Comparison of isotherms of crystallization of initial, annealed and oxidized samples of blends with 37,5, 50 and 61,5 % of PP at cr = 120  ()Table 6.15) demonstrated significant acceleration of PP crystallization in oxidized samples (the deeper is the degree of oxidation, the higher is the rate of crystallization (Table 6.15) in comparison with the samples annealed at conditions of oxidation). The conclusion about acceleration of destructive processes is followed from the decrease of value of energetic barrier of nucleation calculated from temperature dependence of parameters of isothermic crystallization (Table 6.15). Oxidation of polymer due to accumulation of functional groups in trough-pass macro-chains of amorphous regions may lead to deceleration of its crystallization analogously to the formation of inter-molecular cross-links, however in the case of blends PPSEPTR oxidation leads to accumulation of PP crystallization. Such significant acceleration of process of crystallites formation may mean destruction of chains localized in amorphous phase and hindering crystallization of PP component, i.e. destruction of chains of inter-phase layer. The increase of destruction rate may be caused by the increase of rate of oxidation kinetic chain transfer, by the increase of contribution of inter-molecular mechanism of chain transfer, increase of rate of destruction of over-stressed bonds appearing in trough-pass chains under the action of high temperature and oxygen. The reaction of transfer of free valency should lead to the rise of rate of accumulation of hydroperoxides if it is localized in one PP component. However transfer of oxidation kinetic chain may be realized by transfer of free valency from macro-chain of one component to another one and back, i.e. from PP tp SEPTR and from SEPTR to PP. Such exchange by radicals may be realized due to intermolecular contacts in inter-phase layer. Since there is such a layer in studied blends, then obviously namely the transfer of valency by such mechanism may lead to the rise of process of chains destruction of both components first of all in the inter-phase layer. 6.2. On the mechanism of oxidation of propylenesynthetic ethylene-propylene triple rubber blends

As the comparison of kinetic parameters, compositions of non-volatile products of oxidation, changes of structural parameters in the course of oxidation of blends PPSEPTR of various compositions showed the presence of inter-phase layer in blends of crystallizing polypropylene with ethylene-propylene rubber provided essential decrease of oxidation rate of blends in comparison with homopolymers. In other words the presence of exchange reactions between oxidizing PP and SEPTR in contrast to blends PPPE leads to both deceleration of oxidation of more active PP and of the second component. If in the case of oxidation of blends with low content of PP the observing 165

changes in kinetics of oxidation may be explained by "inclusion" of less active rubber into oxidation, then in the case of blend with high content of PP the change of process mechanism is also obvious. Nevertheless the presented explanations in full measure may relate to the blends which oxidation rates are lower than for PP but higher than for SEPTR. Obviously for explanation of deceleration of oxidation of blend with 61,5% of PP in comparison with pure rubber the attraction of additional factors is necessary. Table 6.16. Parameters of PPSEPTR blends oxidation. Ratio Wbl / WPP

Sample

37,5% of PP 50% of PP 61,5% of PP

110  600 millimeters of mercury 1,3 12 25

130  150 millimeters of mercury -

Ratio Wbl / WSEPTR 110  130  600 milli150 millimeters of meters of mercury mercury 0,125 0,1 1 2,5 6,0

[PP], mole/kg in amorphous phase of blend

Content of crystallites in J-modification

5,4 5,6 6,0

0,2 0,3 0,4

The decrease of initial rate of oxidation of blend with 61,5% of PP in comparison with pure SEPTR is about 2,5 times. If we consider that such change of WO2 (under oxidation at 110°C) is conditioned by the rise of local concentration of SEPTR in inter-phase layer, then SEPTR concentration should be increased in inter-phase layer and decreased in phase not less than in 2,5 times. In this case RTL curves should be significantly decreased from the blends with 37,5 and 50% of PP. It is also important to note that the form of the initial section of curve of oxygen absorption is differed from parabolic law and has the form of linear dependence of oxygen absorption rate on time. The mechanism of crystallites formation (as the analysis of blends crystallization kinetics showed), appearance of physical cohesions (cross-links) between PP chains and ethylene blocks (crystallites in J-modification) lead to localization of ethylene comonomer at phases interface. Localization of double bonds of diene comonomer and ethylene blocks of SEPTR in interphase layer provides changes in the mechanism of radical reactions. Reactions between unsaturated bonds of diene comonomer and hydroperoxide groups of PP may lead to ROOH destruction and formation of cross-links between neighbor segments or macro-chains. The contact between oxidizing RH-bonds of PP and ethylene, propylene and diene comonomer units of SEPTR able to participate in cross reactions of oxidation kinetic chains transfer may promote the proceeding of secondary reactions and thermal oxidative destruction of macro-chains of oxidizing components. The increase of local concentration of diene comonomer in inter-phase layer leads to the rise of its contribution into kinetics of cross reactions and probability of cross-linking of macro-chains in blends samples. The rise of contribution of ethylene and diene comonomers of SEPTR into oxidation of blends inhibits the oxidation of PP component. Localization of both components in inter-phase layer leads to deceleration of initial stage of oxidation of PPSEPTR blend in comparison with both pure PP and SEPTR. The mechanism of inhibition of kinetic chains of oxidation by polypropylene rubber is determined by the structure of SEPTR chains localized in inter-phase layer and by the mechanism and kinetics of radical reactions characteristic for diene propylene and ethylene comonomers.

166

Chapter 7. The objects and the methods of investigation 7.1. The characteristics of samples Polypropylene

Non-inhibited isotactic PP of "Montedison" firm production was applied without additional purification (the powder of polymerizate, d = 0,92˜103 kg/m3, Dcr = 60%, [K] = 1,83 in decalin at 135 , Mw = 330000, Mn = 40000). Isotactic PP of Bulgarian production of "Buplen" brand d = 0,93˜103kg/m3, Dcr = 62%, ITE = 4,0g / 10min, (230 , 2,16kg); ƒ = 1330P, V = 25,0MPa, H = 625%. Isotactic PP of native production, non-inhibited powder of polymerizate with the following characteristics d = 0,906˜103kg/m3, Mw = 2,86˜105, Mn = 6,23˜104, Mw / Mn = 4,6. The polymer was purified by standard technique: inhibitor remains were extracted, low-molecular and atactic fractions were extracted in apparatus consecutively by diethyl ether (for 5 hours) and by heptane (for 10 hours), then it was washed out from inorganic impurities by treatment by boiling solution of oxalic acid in ethanol (0,5 hour), washed out by distilled water, ethanol and reprecipitated from m-xylene in ethanol; reprecipitated polymer was washed by ethanol and dried in vacuum. All operations were carried out in the current of inert gas. Polyethylene

Non-inhibited linear PEHD of "Montedison" firm production (powder, d = 0,960 103kg/m3, w = 4,2˜104, Mn = 2,7˜104, Dcr = 75%). PELD of native production of 15803-020 brand with the following characteristics: ITE, g/10 min Molecular mass average-viscosity Density, g/cm3 Breaking stress at tension, MPa Relative lengthening at rupture, % Structural formula of elementary unit

1,2-1,4 a200 000 0,92 20-22 400-450 -[CH2-CH2]n-

all-Union State Standard 11645-73 ( = 185q, load 2,16kg) all-Union State Standard 901-56 all-Union State Standard 12020-72 all-Union State Standard 11262-80 all-Union State Standard 11262-80

Triple ethylene-propylene copolymer (rubber)

The polymer was purified from anti-oxidant in apparatus consecutively by heptane, benzene, mixture of benzene with ethanol in nitrogen current, washed by heptane and dried in vacuum. Completeness of removal of anti-oxidants was controlled with the help of UV-spectrometer by the absence of corresponding peaks in hexane and alcohol extracts. Poly-3-oxybutirate

The poly-3-oxybitirate of “BIOMER” Germany production, Lot -0997, it was a powder. POB was prodiced by two-stage microbiological synthesis with the help of definite types of bacteria which nutrient medium was various polysaccharides with further washing out and drying. ITE, g/10 min Molecular mass average-viscosity Density, g/cm3

3,2-3,6 a250 000 1,25

all-Union State Standard 11645-73 ( = 185q, load 2,16kg) all-Union State Standard 901-56 all-Union State Standard 12020-72 167

Breaking stress at tension, MPa Relative lengthening at rupture, % Structural formula of elementary unit

35-40 5-7 --[-C()-CH2CH(3)-O-]n-H

all-Union State Standard 11262-80 all-Union State Standard 11262-80

7.2. Preparation of polymer compositions

Blending of polymers was carried out in micro-extruder of "Brabender" type (Tbl = 180qC) with preliminary blending of polymer powders in ball drum (for 60 minutes). Conditions of blending provide homogeneity of mixing. Destruction processes of polymers were controlled. The films were pressed under the pressure 20MPa: PP at 190qC; from PE at 140qC; from POB at 180qC, the samples of blends POBPELD, PPPE, PPSEPTR were also prepared as films which were pressed at 190qC. Cooling of polymer films after pressing was carried out in two regimes: fast cooling in water (~1000 degrees/min) and slow cooling in press (