Polyethers E d w i n J. Vandenberg, Editor
A symposiu Division of Polymer Chemistry at the 167th Meeting of the America...
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Polyethers E d w i n J. Vandenberg, Editor
A symposiu Division of Polymer Chemistry at the 167th Meeting of the American Chemical Society, Los Angeles, Calif., A p r i l 2, 1974.
ACS SYMPOSIUM SERIES 6
AMERICAN
CHEMICAL
SOCIETY
WASHINGTON, D. C. 1975
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
Library of Congress
Data
Polyethers. ( A C S symposium series; 6 ) Includes bibliographical references and index. 1. Polymers and polymerization—Congresses. 2. Ethers—Congresses. I. Vandenberg, Edwin J., 1 9 1 8 - ed. II. American Chemical Society. Division of Polymer Chemistry. III. Series: American Chemical Society. A C S symposium series; 6. QD380.P63 I S B N 0-8412-0228-1
547'.84 74-30327 A C S M C 8 6 1-207 ( 1 9 7 5 )
Copyright © 1975 American Chemical Society A l l Rights Reserved P R I N T E D IN THE U N I T E D S T A T E S O F A M E R I C A
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
ACS Symposium Series Robert F. Gould, Series Editor
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
FOREWORD The A C S S Y M P O S I U M SERIES was founded i n 1974
to provide
a medium for publishing symposia quickly i n book form. The format of the SERIES parallels that of its predecessor, A D V A N C E S I N C H E M I S T R Y SERIES, except that i n order to save time the papers are not typese mitted by the authors in camera-ready form. As a further means of saving time, the papers are not edited or reviewed except by the symposium chairman, who becomes editor of the book. Papers published i n the A C S S Y M P O S I U M SERIES are original contributions not published elsewhere i n whole or major part and include reports of research as well as reviews since symposia may embrace both types of presentation.
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
PREFACE >Tphis book is based largely on the papers presented at a "Polyether" Symposium i n honor of D r . Charles C . Price, Benjamin Franklin Professor of Chemistry at the University of Pennsylvania, on the occasion of his receiving the Creative Invention A w a r d of the American Chemical Society for his pioneering U.S. Patent 2,866,774 on elastomeric polyether urethanes. One of the symposiu and C . C . Price has already been published i n /. Polymer Set., Polym. Phys. E d . (1974) 12, 1395. In addition, two papers are included from P. Dreyfuss and T. Saegusa with S. Kobayashi, outstanding polyether researchers who were not able to participate i n the symposium. The Price Award patent covers elastomeric polyurethanes made from the reaction of diisocyanates with the propylene oxide adducts of polyols. These polyether urethanes have proved to be of great commercial value as foamed rubber products, which have contributed greatly to the comfort and well-being of mankind. Approximately 1 billion lbs of these superior foamed products are used each year i n the United States, particularly i n cushioning for furniture and cars. In addition to the Award patent, D r . Charles C . Price has played a broad, pioneering role i n the polyether field. I n organizing the symposium, the editor sought new contributions on polyethers which generally related to D r . Price's work which is described i n part i n his Award address at the beginning of this book. The editor thanks D r . Charles C . Price and the other contributors for their outstanding papers and for their cooperation i n organizing, presenting, and publishing this symposium. EDWIN J. VANDENBERG
November 11, 1974 Wilmington, Del.
vii In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
1 Polyethers CHARLES C. PRICE Department of Chemistry, University of Pennsylvania, Philadelphia,Penn.19174
A.
Introduction
Several inherent c h a r a c t e r i s t i c s of the ether l i n k a g e have stimulated extensive research and development o f l i n e a r polymers with ether l i n k s i n the polymer backbone (1,2). The ether l i n k age has low p o l a r i t y and low vander Waals i n t e r a c t i o n character istics (ΔΗ = 87.5 cal/g f o r pentane vs. 83.9 cal/g f o r d i e t h y l e t h e r ) . The carbon-oxygen bond has a lower b a r r i e r to r o t a t i o n than the carbon-carbon bond (2.7 kc/m f o r dimethyl ether vs. 3.3 f o r propane) and thus provides a lower b a r r i e r to coiling and u n c o i l i n g of chains. The ether oxygen has an even lower ex cluded volume than a methylene group (vander Waals radii of 1.4 Å v s . 2.1 Å) and thus, o f all backbone u n i t s , has the s m a l l e s t "excluded volume". This a l s o is a f a c t o r which permits greater chain flexibility. The carbon-oxygen bond has as great a bond energy (85 kc/m) as a carbon-carbon bond (82 kc/m) and much g r e a t e r h y d r o l y t i c r e s i s t a n c e than e s t e r , a c e t a l or amide l i n k s . vap
These u s e f u l c h a r a c t e r i s t i c s have, in the past two decades, led to extensive commercial development and use of a v a r i e t y of p o l y e t h e r s . Poly(propylene oxide) has become the b a s i s of the l a r g e s c a l e , world-wide development of "one-shot" polyurethan foam rubber, f o r mattresses, f u r n i t u r e , cushions, padding, e t c . P o l y ( t e t r a h y d r o f u r a n ) has been an important component of Corfam s y n t h e t i c l e a t h e r s u b s t i t u t e and of elastic f i b r e s . Linear poly(2,6-xylenol) i s made on a large s c a l e as an engineering plastic with an important combination of p r o p e r t i e s , such as high g l a s s t r a n s i t i o n temperature, good thermal stability, good electrical p r o p e r t i e s , e x c e l l e n t adhesion and ready s o l u b i l i t y in common organic s o l v e n t s . In each o f these p o l y e t h e r s , the ether l i n k is p a r t of the "backbone" of the polymer chain. In each, the ether linkage makes an important c o n t r i b u t i o n to the p h y s i c a l p r o p e r t i e s and chemical stability on which the utility i s based. Since the chemistry of the generation of polyethers has been d i f f e r e n t from that of the classical v i n y l p o l y m e r i z a t i o n 1
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
POLYETHERS
2
processes, many academic i n v e s t i g a t o r s have a l s o been i n v o l v e d i n studying the mechanism, stereochemistry and other aspects o f polyether formation. I t i s our purpose here to present some of the r e s u l t s o f these s t u d i e s f o r those polyether systems i n which we have been p a r t i c u l a r l y i n t e r e s t e d , the polyepoxides, the poly(£-phenylene ethers) and the a l t e r n a t i n g poly(£-phenylenemethylene e t h e r s ) . B.
Polyepoxides
Epoxide p o l y m e r i z a t i o n can be described i n terms of three d i f f e r e n t mechanisms; (1) a n i o n i c (base-catalyzed), (2) c a t i o n i c ( a c i d - c a t a l y z e d ) , and (3) coordinate. The t h i r d a c t u a l l y com bines features of the f i r s t two extremes, since i t involves c o o r d i n a t i o n o f the monomer oxygen a t a Lewis a c i d c a t a l y s t s i t e ( L ) , followed by a l k o x i d e already boun
ο
θ
+
C ^ ι ,ο
C
^ C ». ^ 0
φ \
(1)
0
G
0 ^ L
~>
L '
-
0
G
>
L
(3)
°
C
G
0
The ring-opening step i n each case i s a n u c l e o p h i l i c sub s t i t u t i o n and, i n every case where the stereochemistry has been e s t a b l i s h e d , has been shown to occur with i n v e r s i o n of c o n f i g u r a t i o n at the carbon atom undergoing n u c l e o p h i l i c attack (.3,4). The e t h e r - l i k e oxygen i n the s t r a i n e d three-membered r i n g thus behaves l i k e a good " l e a v i n g group. In the monomer i t s e l f , a strong n u c l e o p h i l e such as alkoxide i o n i s r e q u i r e d f o r S^2 11
a t t a c k . However, when the epoxide i s converted to an oxonium s t a t e , as i n the c a t i o n i c process, i t becomes such a good " l e a v i n g " group that even the weakly n u c l e o p h i l i c oxygen of the monomer i s able to attack e f f e c t i v e l y . The c h a r a c t e r i z a t i o n o f the epoxide oxygen as a good " l e a v i n g " group i s supported by the f a c t that i t not only can undergo S 2 displacement but E e l i m i n a t i o n . For example, t e t r a M
9
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
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methylethylene oxide, on treatment with a c a t a l y t i c amount of a base such as potassium t^-butoxide, undergoes " e l i m i n a t i o n " almost q u a n t i t a t i v e l y (5^.
Θ 0 t-BuO
+
H6H C •
0 ν
C
2
CH
t-BuOH C H
3
(
I
+
3
CH =Ç - Ç — CH CH 2
CH
3
)
OH II
+
CH
0
ZZ C —
I
2
I I
C —CH
CH
0
3
CH
B ( l ) . A n i o n i c . Because of the i n t e r v e n t i o n of the E2 process, only ethylene oxide i s r e a d i l y converted to highpolymer by b a s e - c a t a l y s i s . The p o l y m e r i z a t i o n can be c a r r i e d out so that one polymer molecule forms f o r each c a t a l y s t molec u l e added (5). With propylene oxide, however, the E2 r e a c t i o n intervenes and serves, i n e f f e c t , as a c h a i n - t r a n s f e r process. The a l k y l o x i d e i o n formed by e l i m i n a t i o n i s , of course, capable of i n i t i a t i n g a new chain, now capped at one-end by an a l l y l ether group (6).
CH 0CH CH0© 3
2
******* Q0
OH +CH =CHCH 0© 2
2
The maximum molecular weight of base-catalyzed propylene o x i d e polymer i s l i m i t e d by the r a t i o of the r a t e s of propagation (k ) to t r a n s f e r ( k ) ; s i n c e at operable temperatures k ^ / k ^ i t r
100,
t h i s i s 6000 awu. I t was t h i s molecular-weight l i m i t i n g chain t r a n s f e r which led us to seek s y n t h e t i c approaches to b u i l d i n g a c r o s s l i n k e d rubber s t r u c t u r e from poly(propylene oxide) chains. T h i s was s u c c e s s f u l l y accomplished i n 1949 by b u i l d i n g branched chain
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
POLYETHERS
4
l i q u i d polymer, followed by conversion i n t o a rubber network s t r u c t u r e by r e a c t i o n with d i i s o c y a n a t e s (7).
CH CH-CH V 0 3
2
+
Base (CH OH) - = 2 »
C
2
4
C[CH 0(CH CHO)„H] CH 2
f
4
3
+ HO(CH^HO)„H CH,
The a l l y l ether end group i s preserved only under m i l d c o n d i t i o n s of p o l y m e r i z a t i o n . Studies on i t s disappearance under more vigorous c o n d i t i o n s l e d to discovery of the basec a t a l y z e d rearrangement of a l l y l to c i s - p r o p e n y l ethers (8,9,10, 11) and p o s t u l a t i o n of a t r a n s i t i o n complex i n v o l v i n g oxygenpotassium c o o r d i n a t i o n to e x p l a i n the c i s - s t e r e o s p e c i f i c i t y .
ROCH CH=CH 2
2
*
»»
CH=CH
This rearrangement was a l s o found to extend to a l l y l although without c i s - s t e r e o s p e c i f i c i t y (12).
R NCH,CH=CH, 2
-
amines,
R NCH=CHCH, 2
t>Butylethylene oxide was s t u d i e d i n the hope that a s t r u c t u r e not p e r m i t t i n g E2 e l i m i n a t i o n to an a l l y l oxide would lead to high molecular weight polymer (5). However, the S 2 d i s placement i s also much slower i n t h i s monomer, presumably due to s t e r i c hindrance. Under the more vigorous c o n d i t i o n s necessary f o r p o l y m e r i z a t i o n , another c h a i n t r a n s f e r process must occur, although i t s exact nature has not yet been e s t a b l i s h e d . In any event, the l i m i t i n g molecular weight f o r poly (t.-butyl ethylene oxide) i s about 2000.
t-Bu 0CH CH0© ?
C
H
3
/ (S) ,
3
3
Θ + 0 Η (S)
\
CH
\
I CH
(S)
3
Γ vST 3
CH
3
(S)
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
Η
1. PRICE
Polyethers
9
oxonium intermediate d e r i v e d from S-VIII, as i l l u s t r a t e d , with the two three-membered r i n g s i n a f a v o r a b l e r i g h t angled o r i e n t a t i o n , an H i n V I I I confronts a methyl i n the oxonium r i n g and v i c e v e r s a . I f the approaching monomer were R-VIII, then there would be two h i g h l y unfavorable methyl-methyl c o n f r o n t a t i o n s . Thus the stereochemistry of the growing chain end d i c t a t e s the stereochemistry of the incoming monomer. Β(3). Coordination P o l y m e r i z a t i o n . S t e r e o s e l e c t i v e polym e r i z a t i o n s of epoxides have played an important r o l e i n d e v e l oping the mechanistic concepts f o r t h i s major development i n polymer chemistry. The f i r s t r e p o r t by Natta o f i s o t a c t i c p o l y propylene (24) appeared a few months before the P r u i t t and Baggett patent i s s u e d on the p r e p a r a t i o n of i s o t a c t i c p o l y propylene oxide (25). Undoubtedly the work of P r u i t t and Baggett antedated that o f Natta f i r s t paper before ou Baggett polymer was indeed i s o t a c t i c (26). The c h i r a l i t y (asymmetry) of the methine carbon i n propylene oxide and i n i t s polymer has provided many e x t r a experimental parameters to use i n s t u d i e s o f the mechanism o f s t e r e o s e l e c t i v e p o l y m e r i z a t i o n by c o o r d i n a t i o n c a t a l y s t s . The f i r s t proposal of the c o o r d i n a t i o n p o l y m e r i z a t i o n scheme t o e x p l a i n s t e r e o s e l e c t i v e o/-olefin and o l e f i n oxide p o l y m e r i z a t i o n arose from the propylene oxide s t u d i e s (26,27). There are many e f f e c t i v e c a t a l y s t systems, such as FeCl^propylene oxide, d i e t h y l z i n c - w a t e r and trialkylaluminum-water acetylacetone r e a c t i o n products. For none i s the exact s t r u c t u r e of the c a t a l y s t s i t e e s t a b l i s h e d . For a l l , the number of polymer molecules formed i s small compared to the metal atoms used to make the c a t a l y s t . T h i s suggests that the f r a c t i o n o f metal atoms at c a t a l y s t s i t e s must be at l e a s t as s m a l l . While the d e t a i l e d s t r u c t u r e of a c a t a l y s t s i t e remains to be e l u c i d a t e d , s e v e r a l important f e a t u r e s of these c a t a l y s t s are now known. Perhaps the most important feature was e s t a b l i s h e d by Tsuruta (28) who proved that the s t e r e o s e l e c t i v i t y was not a f e a t u r e of the c h i r a l i t y o f the growing end but was b u i l t i n t o the c a t a l y s t s i t e i t s e l f ( " c a t a l y s t - s i t e " c o n t r o l ) . The normal c a t a l y s t p r e p a r a t i o n gives an equal number of R- and S - c h i r a l c a t a l y s t s i t e s which s e l e c t i v e l y coordinate with R- and S-monomer, r e s p e c t i v e l y . This was demonstrated by s t a r t i n g with 75% Rand 25% S-monomer. A f t e r extensive p o l y m e r i z a t i o n , the recovered monomer was o f unchanged o p t i c a l p u r i t y . I f the c h i r a l i t y o f the c a t a l y s t s i t e were due to the c h i r a l i t y of the growing chain ("chain end" c o n t r o l ) one would expect that the growing chains would assume a 75 to 25 r a t i o . The p r e f e r e n t i a l r e a c t i v i t y f o r R-monomer would then be 9 to 1 ( r a t h e r than the experimentally observed 3 to 1) and the recovered monomer should tend toward a 50:50 mixture with i n c r e a s i n g conversion. The c h i r a l i t y of the c a t a l y s t s i t e s can be i n f l u e n c e d i n
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
10
POLYETHERS
some cases. For example, Tsuruta (29) has shown that the c a t a l y s t made from R-borneol and d i e t h y l z i n c i s s t e r e o e l e c t i v e , i . e . , i t w i l l polymerize RS-propylene oxide g i v i n g i s o t a c t i c polymer with an excess of R-monomer u n i t s and l e a v i n g the unreacted monomer r i c h i n the S-isomer. This behavior can be accounted f o r by assuming that R-borneol produces the two c h i r a l c a t a l y s t s i t e s i n unequal numbers. A number of other c h i r a l a l c o h o l s and R-monomer f a i l e d to give s t e r e o e l e c t i v e c a t a l y s t , i . e . , they gave c a t a l y s t which behaved as though i t had equal numbers of R- and S - s i t e s (29,30). One p o s s i b l e explanation which has been o f f e r e d (31) i s that the more hindered bornyl group prevents i t from m i g r a t i n g from the c a t a l y s t s i t e L i n the propagation step ( r e a c t i o n ( 3 ) ) . Other simpler groups are known to migrate, becoming end groups i n the polymer (29,32). Another e f f e c t i v e s t e r e o e l e c t i v e c a t a l y s t f o r both epoxide and e p i s u l f i d e p o l y m e r i z a t i o S-) J:-butylethylene g l y c o One of the key f e a t u r e s of the s t e r e o s e l e c t i v e c o o r d i n a t i o n c a t a l y s t s f o r propylene oxide p o l y m e r i z a t i o n i s that, while they can give i s o t a c t i c polymer with a very high r a t i o of i s o t a c t i c to s y n d i o t a c t i c sequences (e.g. > 370) (34), i n the same r e a c t i o n mixture a l a r g e p a r t of the polymer i s amorphous. Even when Rpropylene oxide i s used as s t a r t i n g m a t e r i a l , much of the product i s amorphous polymer of low o p t i c a l r o t a t i o n c o n t a i n i n g many Spropylene oxide u n i t s (30). T h i s amorphous polymer has been shown to c o n t a i n head-tohead u n i t s as the imperfections i n s t r u c t u r e . T h i s was shown by degradation and i s o l a t i o n of the dimer g l y c o l s (35,36).
1. -/OCHCH V I ^ CH 3
0
H O
( f
3
=—• 2. LAH
H0CHCH 0CHCH 0H I I CH CH ix 9
3
9
+
C H
2> ° 2
CHL χ J
3
^HOCH CH) O 2
XI
2
GH
3
The diprimary (XI) and disecondary (X) dimer g l y c o l s w i l l a r i s e only from head-to-head u n i t s i n the polymer. F o r t u n a t e l y , the three isomeric g l y c o l s can be separated by g l c . For i s o t a c t i c polymer or amorphous polymer made by base c a t a l y s i s of RS-monomer, l i t t l e i f any X and XI were found. The amorphous polymer separated from i s o t a c t i c polymer prepared f o r a v a r i e t y of c o o r d i n a t i o n c a t a l y s t s gave 25 to 40% of X and XI. F u r t h e r more, the c o r r e l a t i o n of the head-to-head content from such degradative s t u d i e s with the o p t i c a l a c t i v i t y of the amorphous f r a c t i o n u s i n g R-monomer with the same c a t a l y s t shows that f o r every head-to-head u n i t there i s one R-monomer converted to an S-polymer u n i t . T h i s proves that, at the c o o r d i n a t i o n s i t e
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
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g i v i n g amorphous polymer, the abnormal r i n g opening which occurs at the secondary carbon, to give the head-to-head u n i t , has done so with i n v e r s i o n of c o n f i g u r a t i o n . A more recent s i m i l a r study of amorphous polymer accompanying i s o t a c t i c polymer i n the polymerization of RS-jt-butylethylene oxide by c o o r d i n a t i o n c a t a l y s t s has shown that i t a l s o contains head-to-head u n i t s (14). In t h i s case, the 1°, 2°dimer g l y c o l , which was only 30 t o 40% of the dimer mixture, could be separated i n t o i t s erythro and threo isomers by g l c . The i s o t a c t i c polymer gave, as expected, almost e x c l u s i v e l y the erythro-isomer, while the amorphous f r a c t i o n s gave only 40-45% e r y t h r o and 55-60% threo. These data combined i n d i c a t e that a t y p i c a l c o o r d i n a t i o n c a t a l y s t , such as Et^Zn-H^O, contains i s o t a c t i c c a t a l y s t s i t e s and amorphous c a t a l y s t s i t e s The i s o t a c t i c s i t e s are h i g h l y selective i n coordinatin t i o n (3), step 1) and opening only at the primary carbon of the epoxide r i n g (react i o n (3), step 2). The amorphous c a t a l y s t s i t e can coordinate e q u a l l y w e l l with R- or S-monomer i n step 1, and has very l i t t l e preference f o r attack at the primary o r secondary carbon i n the r i n g opening propagation step. Not much q u a n t i t a t i v e information i s a v a i l a b l e on the r e l a t i v e r e a c t i v i t i e s of epoxides i n copolymerization. With base i n DMSO, phenyl g l y c i d y l ether i s 7 times more r e a c t i v e than p r o p y l ene oxide, presumably due to the i n d u c t i v e electron-withdrawing e f f e c t o f the phenoxy group (37). A £-chloro-substituent enhances the r e a c t i v i t y o f PGE while a £-methoxy group diminishes it. That c o o r d i n a t i o n c a t a l y s t s e x h i b i t p r o p e r t i e s c l o s e r to c a t i o n i c than a n i o n i c c a t a l y s t s i s i n d i c a t e d by the opposite i n f l u e n c e o f £-chloro and £-methoxy groups i n PGE, the l a t t e r now being the more r e a c t i v e (38). Furthermore, propylene oxide i s 50% more r e a c t i v e than phenyl g l y c i d y l ether and e p i c h l o r o h y d r i n 33% l e s s r e a c t i v e u s i n g Et^At-H^O as a c a t a l y s t . C.
Polyphenylene Oxides
The thermal and chemical s t a b i l i t y o f diphenyl ether has long been recognized as suggesting i n t e r e s t i n g and u s e f u l prope r t i e s f o r high polymers IbuiÎÊ with t h i s s t r u c t u r a l u n i t (2). The development o f s u c c e s s f u l methods f o r preparing such s t r u c tures has been a challenge to the s y n t h e t i c chemist. The r e markable chemistry o f the processes discovered has a l s o l e d t o s i g n i f i c a n t new f a c t s and hypotheses about the behavior o f phenoxy r a d i c a l s . The i n v e s t i g a t i o n s i n our l a b o r a t o r y were o r i g i n a l l y i n s p i r e d by the work o f Hunter and h i s students (39). They concluded that the amorphous products formed from t r i h a l o p h e n o l s on treatment with v a r i o u s o x i d i z i n g agents were low-molecular weight polymers formed by l o s s o f a halogen atom i n e i t h e r the 2- or 4-
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
12
POLYETHERS
p o s i t i o n . We decided to i n v e s t i g a t e t h i s r e a c t i o n f u r t h e r , but w i t h 4~halo-2,6-xylenols as monomers. T h i s proved s u c c e s s f u l when c a t a l y s t s were used which Cook (40,41) found u s e f u l i n converting 2 , 4 , 6 - t r i - t - b u t y l p h e n o l to i t s s t a b l e blue f r e e r a d i c a l . Under these c o n d i t i o n s , 4-bromo-2,6x y l e n o l can be converted to a high-molecular weight polymer i n seconds, l i b e r a t i n g the bromine as bromide i o n . In the absence of oxidant c a t a l y s t , no bromide i o n i s l i b e r a t e d even a f t e r months. The p o l y m e r i z a t i o n i s thus obviously not a n u c l e o p h i l i c displacement. Furthermore, i t has the c h a r a c t e r i s t i c s of a chain r e a c t i o n , s i n c e polymer formed even at only 5% conversion i s of high molecular weight (42). While the polymer has a very low b r i t t l e temperature (-150°), i t s high g l a s s - t r a n s i t i o n tempera ture (> 200°) makes i t very hard to c r y s t a l l i z e . The polymer i s
L
CH
3
J
normally amorphous and s o l u b l e i n the usual organic s o l v e n t s , such as benzene. By h e a t i n g a s o l u t i o n i n α-pinene overnight, i t separates as c r y s t a l l i n e polymer, mp 275° (43). The commercial synthesis of p o l y x y l e n o l (sometimes r e f e r r e d to as PPO, £ply(uhenylene oxide)) i s c a r r i e d out by the oxida t i v e c o u p l i n g of 2,6-xylenol. This remarkable r e a c t i o n was d i s covered by Hay and h i s coworkers (44). One i n t r i g u i n g f e a t u r e of t h i s p o l y m e r i z a t i o n i s that i t i s a stepwise condensation. The product at 50% conversion i s a low-molecular weight o i l . The dimer (XIII) and trimer i n t h i s m a t e r i a l are as e a s i l y polymeri z a b l e as the monomer. The accepted mechanism i n v o l v e s coupling of aryloxy intermediates to give quinone k e t a l s (45,46,47). The Dutch workers i n p a r t i c u l a r s t u d i e d many simple models
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
1.
PRICE
Polyethers
to determine what s t r u c t u r a l f a c t o r s and c o n d i t i o n s favored con v e r s i o n of XIV to XV by d i r e c t rearrangement (a) or through d i s s o c i a t i o n and recombination (b). One of the i n t r i g u i n g features of the o x i d a t i v e coupling i s the question of the features d i c t a t i n g C-0 coupling to give dimer X I I I vs_. C-C coupling to give the diphenoquinone XVI. For
o x i d a t i o n by Ag20 (48) or MnO^ (47), excess oxidant gives polyx y l e n o l , while excess x y l e n o l gives XVI. Even under the Hay con d i t i o n s , replacement of one methyl by t^-butyl or both by _i-Pr l e d to the diphenoquinone as the main product. The r a t e of phenol o x i d a t i o n under the Hay c o n d i t i o n s i s f i r s t order i n c a t a l y s t , f i r s t order i n 0^ pressure and zero order i n phenol, although the magnitude of the r a t e i s q u i t e s e n s i t i v e to s u b s t i t u t i o n s i n the phenol r i n g , being favored by e l e c t r o n - r e l e a s i n g groups (49). We have suggested the scheme on the next page to account f o r these observations. The dimer X I I I could a r i s e e i t h e r by coupling of two f r e e f r e e r a d i c a l s or by attack of a r a d i c a l , l i b e r a t e d i n the transformation from Β to C i n Scheme I to remove ArO* from D. Decreased base c o o r d i n a t i o n on Cu (by l i g a n d concentration, l i g a n d hindrance or ortho hindrance i n the phenol) favors C-G coupling (50). We have proposed the modified Scheme I I to exl a i n t h i s behavior. The e s s e n t i a l f e a t u r e i s that decreased ase c o o r d i n a t i o n at Cu increases the a f f i n i t y of the Cu f o r the
f
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
14
POLYETHERS
Scheme I
ArO^
y \
(pyrV
\(
,(pyr>2
(Pyr)
2
(pyr)2
gAr
CI
Β + 2ArOH, -2ArO-
ArO.
yPL Cu°
, 1 , 2 - d i m e t h o x y e t h a n e , b y w e i g h t ,
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
POLYETHERS
22
i n a W e b e e l l C o n t i n u o u s D i a l y z e r - M o d e l B, e q u i p p e d w i t h c e l l o phane membranes. D i a l y s i s was d i s c o n t i n u e d a f t e r l 6 h o u r s . The c o m p l e x was r e c o v e r e d b y c e n t r i f u g a t i o n s u s p e n d e d i n d r y n-hexane, t h e n c o l l e c t e d b y vacuum f i l t r a t i o n a n d d r i e d a t room tempe r a t u r e u n d e r vacuum. S i n c e t h e h e x a c y a n o m e t a l a t e complexes c a n be o f v a r i a b l e c o m p o s i t i o n , i t i s i m p o r t a n t t o have some means o f d e t e r m i n i n g w h e t h e r a c o m p l e x w i l l have s u f f i c i e n t a c t i v i t y i n a n e p o x i d e polymerization. This i s p o s s i b l e by examining the i n f r a r e d a b s o r p t i o n s p e c t r a (2) o f N u j o l m u l l s o f t h e s e c o m p l e x e s . F o r l i q u i d 1,2-dimethoxyethane (glyme), t h e strong absorption a t 851 cm"" h a s b e e n a s s i g n e d ( 1 0 ) t o t h e m e t h y l e n i c r o c k i n g mode. In a h i g h l y a c t i v e c a t a l y s t c o n s i s t i n g o f z i n c hexacyanocobaltate, glyme, z i n c c h l o r i d e and water, t h i s a b s o r p t i o n i s s h i f t e d t o 838 cm"" , w h e r e a s i n a c a t a l y s t o f l o w a c t i v i t y , t h e a b s o r p t i o n o c c u r s a t 857 cm"" . K i n e t i l e n e e t h e r ) d i o l was p r e p a r e c o b a l t a t e ( i l l ) c o m p l e x c a t a l y s t were c a r r i e d o u t i n c a p p e d b o t t l e s u n d e r a n i t r o g e n a t m o s p h e r e . The e x t e n t o f r e a c t i o n was c a l c u l a t e d f r o m a measurement o f t o t a l s o l i d s a f t e r t h e p r o p y l e n e o x i d e was removed b y e v a p o r a t i o n . Rate s t u d i e s on "seeded" p o l y m e r i z a t i o n s were c a r r i e d o u t b y c h a r g i n g r e a c t a n t s i n a n a l l g l a s s r e a c t o r a t 10~ T o r r , a n d f o l l o w i n g t h e c o u r s e o f t h e r e action dilatometrically. S p e c i a l g l a s s e q u i p m e n t was c o n s t r u c t e d f o r t h e s e m a n i p u l a t i o n s , a s shown i n F i g u r e 1. I n c r e m e n t a l monomer a d d i t i o n s t u d i e s , b e a r i n g o n t h e mechani s m o f i n i t i a t i o n a n d t e r m i n a t i o n , w e r e done u n d e r a n i t r o g e n atmosphere i n b o t t l e s . The b o t t l e s were f i t t e d w i t h a p e r f o r a t e d cap h a v i n g a b u t y l g a s k e t w h i c h was e x t r a c t e d u s i n g a m i x t u r e o f e t h a n o l w i t h 32$> b y w e i g h t o f t o l u e n e . These p o l y m e r i z a t i o n s w e r e c a r r i e d o u t a t a n i n i t i a l c a t a l y s t c o n c e n t r a t i o n o f 0.OhQ w e i g h t p e r c e n t a n d a t 50°C. 5
1
1
1
6
M o l e c u l a r W e i g h t C h a r a c t e r i z a t i o n . G e l p e r m e a t i o n chromat o g r a p h y was c a r r i e d o u t u s i n g a W a t e r s A s s o c i a t e s i n s t r u m e n t . P o l y m e r s f r o m i n c r e m e n t a l monomer a d d i t i o n s w e r e a n a l y z e d i n t e t r a h y d r o f u r a n a t room t e m p e r a t u r e u s i n g a 1 0 , 1 0 , a n d 10 A d e s i g n a t e d column s e t packed w i t h S t y r a g e l . A l l o t h e r p o l y m e r s w e r e a n a l y z e d i n b e n z e n e s o l u t i o n . One p e r c e n t s o l u t i o n s o f p o l y m e r were i n j e c t e d f o r one m i n u t e w i t h t h e i n s t r u m e n t o p e r a t i n g at a f l o w r a t e o f 1 ml/min. Number-average m o l e c u l a r w e i g h t s w e r e d e t e r m i n e d i n b e n z e n e , u s i n g a M e c h r o l a b V a p o r P r e s s u r e Osmometer(VPO). 6
4
3
F u n c t i o n a l i t y Determination. H y d r o x y l c o n t e n t s were d e t e r m i n e d u s i n g t h e p h t h a l i c a n h y d r i d e method a n d u n s a t u r a t i o n was m e a s u r e d b y a m e t h o x y m e r c u r a t i o n m e t h o d , b o t h a c c o r d i n g t o ASTM D28U9 (11). C a r b o n y l c o n t e n t s were o b t a i n e d u s i n g h y d r o x y l a m i n e h y d r o c h l o r i d e , a c c o r d i n g t o S. S i g g i a (12).
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
2.
LiviGNi E T A L .
F*oly{Propylene Ether) Polyols
23
F u n c t i o n a l i t y determinations, using the Williams Plastometer ( 1 3 ) , w e r e c a r r i e d o u t o n a one gram sample a t a f o r c e o f 5000 + 5 grams. The p o l y u r e t h a n e s were p r e p a r e d "by r e a c t i n g t h e p o l y (propylene ether) d i o l s w i t h 2,^-tolylene diisoeyanate, i n the p r e s e n c e o f 0.0h% s t a n n o u s o c t a n o a t e a s a c a t a l y s t , f o r k-0 h o u r s a t 120°C. A p l u g t a k e n f r o m t h e c e n t e r o f t h e r u b b e r h a v i n g a d i a m e t e r o f 13 mm a n d w e i g h t o f one gram was u s e d i n t h e m e a s u r e ment. The W i l l i a m s p l a s t i c i t y was e x p r e s s e d i n m i l s a n d t a k e n as t h e h e i g h t o f t h e s p e c i m e n a f t e r a t h r e e m i n u t e p e r i o d u n d e r the l o a d s p e c i f i e d . R e s u l t s and D i s c u s s i o n Kinetic studies. The r a t e o f f o r m a t i o n o f p o l y ( p r o p y l e n e e t h e r ) d i o l u s i n g 1 , 5 - p e n t a n e d i o l as an i n i t i a t o r and t h e z i n c h e x a c y a n o c o b a l t a t e comple The r e a c t i o n r a t e c u r v e monomer p o l y m e r i z a t i o n s t u d y , a s w e l l a s a p o l y m e r i z a t i o n c a r r i e d out i n n-pentane (10.7 m o l / l ) . Each o f t h e e x p e r i m e n t a l p o i n t s r e p r e s e n t s a s e p a r a t e r u n i n w h i c h t h e p o l y m e r i z a t i o n was t e r m i n a t e d a t t h e s p e c i f i e d t i m e a n d r e s i d u a l monomer a n d s o l v e n t r e moved. The g e n e r a l f e a t u r e s o f t h e s e p o l y m e r i z a t i o n s a r e t h e i n i t i a l l y s l o w c o n s u m p t i o n o f monomer e x t e n d i n g o v e r t h r e e t o f o u r h o u r s f o l l o w e d b y t h e r a p i d d i s a p p e a r a n c e o f monomer t o i t s t o t a l consumption. The c a t a l y s t , i n i t i a l l y i n s o l u b l e i n e i t h e r o f t h e r e a c t i o n m e d i a , i s o b s e r v e d t o become a l m o s t t o t a l l y d i s p e r s e d when t h e r e a c t i o n r a t e b e g i n s t o show r a p i d a c c e l e r a t i o n . The s o l u t i o n s , a t t h i s t i m e , show o n l y a s l i g h t t u r b i d i t y . F o l l o w i n g t h e i n i t i a l slow disappearance o f propylene o x i d e , t h e monomer i s consumed a c c o r d i n g t o f i r s t - o r d e r k i n e t i c s , a s shown by t h e s t r a i g h t l i n e p l o t s o f l o g [ M ] / [ M ] versus time, g i v e n i n F i g u r e 3. G e l p e r m e a t i o n chromatograms w e r e o b t a i n e d o n t h e e n t i r e r e a c t i o n mixture r e s u l t i n g from t h e p o l y m e r i z a t i o n as a f u n c t i o n o f t h e e x t e n t o f c o n v e r s i o n (lh) a n d t h e s e a r e shown i n F i g u r e k. The p e a k p o s i t i o n a t t h e l a r g e s t e l u t i o n volume c o r r e s p o n d s t o the l o w e s t m o l e c u l a r weight s p e c i e p r e s e n t i n t h e r e a c t i o n mixt u r e , which i s the 1,5-pentanediol. T h i s component i s consumed d u r i n g t h e i n i t i a l stage o f t h e r e a c t i o n p r o d u c i n g a h i g h molecul a r weight substance o f n e a r l y constant molecular weight. A t 23.2$ c o n v e r s i o n , t h e g e l p e r m e a t i o n c h r o m a t o g r a m g a v e n o i n d i c a t i o n o f the presence o f 1,5-pentanediol. A s d i s c u s s e d above, there i s a rapid increase i n the rate o fpolymerization o f the p r o p y l e n e o x i d e a t 10^ t o 15^ c o n v e r s i o n . We a t t r i b u t e t h e i n i t i a l l y slow r a t e o f p o l y m e r i z a t i o n t o b o t h t h e consumption o f the 1,5-pentanediol t o form a propylene oxide a d d i t i o n product, as w e l l a s t h e d i s p e r s i o n o f t h e i n i t i a l l y i n s o l u b l e z i n c hexac y a n o c o b a l t a t e complex c a t a l y s t . The m o l e c u l a r w e i g h t o f t h e polymer i s observed t o i n c r e a s e , as noted b y t h e s h i f t o f t h e peak p o s i t i o n towards s m a l l e r e l u t i o n volumes, as t h e r e a c t i o n 0
t
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
POLYETHERS
PROPYLENE OXIDE-
n-PENTANE
*
2
PROPYLENE Q Π OXIDE
Q
REACTOR FOR POLYETHER "SEED"
-SEED REACTOR EQUIPPED WITH
ù
POLYETHER SEED SPLIT-DOWN Figure 1.
Special glass equipment for "seeded? polymerizations
l.O0.9-
= 13.6 MOL./L. CATALYST = 0.4 G./L. [DIOL] = 0.4 MOL./L.
-O-[M]
0
0
0.8
-•-[M] = 10.7 MOL./L. CATALYST = 0.3 G./L. [DIOL] = 0.3 MOL./L. 0
0.7-
0
0.6-
(n-PENTANE)
0.5'
Q
0.40.30.20.13
4
5
TIME (HRS.)
Figure 2. Formation rate of poly(propylene ether) diol in bulk and n-pentane at 50°C
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
LiviGNi ET AL.
Poly(Propylene Ether) Poly ois
100
0
90 •
Ι
βοτο-
- O - [ M ] = 13.6 M0L./L. CATALYST = 0.4 G./L. [DIOLJo = 0.4 M0L./L.
-D-[M] = 10.7 MOL./L. CATALYST = 0.3 G./L. [DI0L] = 0.3 MOL./L
60-
0
0
(n-PENTANE)
oc
LU g
50-
o υ ^
403020103
4
5
TIME (HRS.) Figure 3.
Figure 4.
First-order rate plots for poly(propylene ether) diol formation at 50°C
Gel permeation chromatograms of reaction mixture at different extents of polymerization
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
POLYETHERS
26
proceeds. The p o l y m e r f o r m e d h a s a n a r r o w m o l e c u l a r w e i g h t d i s t r i b u t i o n w i t h some t a i l i n g t o w a r d s t h e h i g h m o l e c u l a r w e i g h t values. The n a r r o w m o l e c u l a r w e i g h t d i s t r i b u t i o n o f t h e s e p o l y (propylene ether) d i o l s i s s i m i l a r t o that obtained i n t h e soc a l l e d " l i v i n g p o l y m e r i z a t i o n s " , t h a t i s , those proceeding i n t h e absence o f a c h a i n t e r m i n a t i o n r e a c t i o n . The f a c t o r s w h i c h a r e necessary t o produce polymers having a narrow m o l e c u l a r weight d i s t r i b u t i o n h a v e b e e n d e l i n e a t e d b y F l o r y (15). These a r e : (l) c h a i n p r o p a g a t i o n o f e a c h p o l y m e r m o l e c u l e must p r o c e e d e x c l u s i v e l y b y a d d i t i o n o f monomers t o a n a c t i v e c e n t e r , (2) a l l c h a i n s must have a n e q u a l p r o b a b i l i t y o f u n d e r g o i n g g r o w t h t h r o u g h o u t t h e c o u r s e o f t h e r e a c t i o n , a n d (3) a l l c h a i n s must b e i n i t i a t e d a t thebeginning o f the reaction. Since the p o l y (propylene ether) d i o l s prepared w i t h the zinc hexacyanocobaltate complex c a t a l y s t have a s t u d y was c a r r i e d o u t v i d u a l s t e p s i n t h i s p o l y m e r i z a t i o n c o r r e s p o n d t o t h e above c r i teria. P r o p y l e n e o x i d e was p o l y m e r i z e d u s i n g 1 , 5 - p e n t a n e d i o l a s an i n i t i a t o r a n d z i n c h e x a c y a n o c o b a l t a t e complex as t h e c a t a l y s t . A f t e r p o l y m e r i z a t i o n was c o m p l e t e , a sample was w i t h d r a w n a n d i t s number-average m o l e c u l a r weight determined u s i n g vapor p r e s s u r e osmometry. A n a d d i t i o n a l q u a n t i t y o f p r o p y l e n e o x i d e was a d d e d t o t h e s y s t e m a n d p o l y m e r i z a t i o n o f t h i s i n c r e m e n t was a l l o w e d t o go t o c o m p l e t i o n . A sample was o n c e a g a i n removed, i t s number-average m o l e c u l a r weight d e t e r m i n e d a n d a d d i t i o n a l monomer added. T h i s f i n a l i n c r e m e n t o f p r o p y l e n e o x i d e was p o l y m e r i z e d and t h e number-average m o l e c u l a r w e i g h t o f t h e f i n a l product determined. The r e s u l t s o f t h i s s t u d y a r e g i v e n i n Table I . TABLE I Comparison o f C a l c u l a t e d and Measured M o l e c u l a r Weight o f Poly(Propylene Ether) D i o l s Prepared by Sequential A d d i t i o n o f Propylene
Oxide
ÏL η
Polymer From i n i t i a l p o l y m e r i z a t i o n F r o m f i r s t monomer i n c r e m e n t F r o m s e c o n d monomer i n c r e m e n t ^ Weight o f Polymer Moles o f 1,5-Pentanediol
( M e a s u r e d b v VPO) 169Ο 2350 3130
M
n
η
(C^lc) I783* 2209 30^+9
=
n
Charged
The m o l e c u l a r w e i g h t o f t h e f i r s t sample was c a l c u l a t e d f r o m t h e weight o f polymer o b t a i n e d d i v i d e d b y t h e moles o f 1,5-pentanediol
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
2.
LrviGNi E T A L .
27
Ρ oly (Propylene Ether) Poly ois
charged. The g o o d agreement i n t h e c a l c u l a t e d v e r s u s m e a s u r e d m o l e c u l a r w e i g h t d e m o n s t r a t e s t h a t an i n s i g n i f i c a n t number o f chains r e s u l t d i r e c t l y from t h i s c a t a l y s t , under these c o n d i t i o n s . I n d e e d , i f one c a l c u l a t e s t h e maximum a v a i l a b l e number o f p o t e n t i a l c a t a l y s t g r o w t h s i t e s , assuming f o u r s i t e s p e r z i n c atom p r e s e n t , one f i n d s t h a t t h e r e a r e a t l e a s t 10 t i m e s more c h a i n ends p e r a v a i l a b l e c o o r d i n a t i n g s i t e . T h i s demands t h a t a s p e c i f i c c a t a l y s t s i t e must a c t i v a t e many d i f f e r e n t c h a i n ends d u r i n g polymerization. Comparing the c a l c u l a t e d v e r s u s d e t e r m i n e d molecular weights of the poly(propylene ether) d i o l prepared from t h e i n c r e m e n t a l monomer a d d i t i o n s , i t i s c o n c l u d e d t h a t t h e r e a r e no new p o l y m e r c h a i n s t h a t a r e i n t r o d u c e d d u r i n g t h e s e p o l y m e r i z a t i o n s , e i t h e r f r o m an i n i t i a t i o n r e a c t i o n o r b y a c h a i n t r a n s f e r p r o c e s s w i t h monomer. G e l p e r m e a t i o n chromatograms w e r e o b t a i n e d on a l l t h r e e o f t h e p o l y ( p r o p y l e n e e t h e r ) d i o l s p r e p a r e d i n t h i s s t u d y and a r e show w e i g h t d i s t r i b u t i o n was t a i l i n g towards the h i g h m o l e c u l a r w e i g h t r e g i o n . As i s a l s o a p p a r e n t , the i n c r e a s e i n the number-average m o l e c u l a r w e i g h t w i t h t h e p o l y m e r i z a t i o n o f s u c c e s s i v e monomer i n c r e m e n t s i s d e m o n s t r a t e d b y a s h i f t i n t h e p e a k p o s i t i o n o f t h e chromatograms towards lower e l u t i o n volumes. From these d a t a , i t i s concluded t h a t a l l c h a i n s h a v e e s s e n t i a l l y t h e same p r o b a b i l i t y o f u n d e r g o i n g c h a i n p r o p a g a t i o n a n d t h i s p o l y m e r i z a t i o n must t a k e p l a c e i n the v i r t u a l absence o f a c h a i n t e r m i n a t i o n r e a c t i o n . The hydroxyl f u n c t i o n a l i t y of these poly(propylene ether) d i o l s i s c l o s e t o t h e t h e o r e t i c a l v a l u e o f two, a s i s shown b y t h e v a l u e s c a l c u l a t e d f r o m t h e m e a s u r e d h y d r o x y l number and n u m b e r - a v e r a g e m o l e c u l a r w e i g h t f o r t h e l a s t two p o l y m e r s ; n a m e l y , I . 9 8 + 0.2 and 2.10 + 0.2, r e s p e c t i v e l y . Having e s t a b l i s h e d t h a t the p o l y m e r i z a t i o n o f propylene o x i d e by the z i n c h e x a c y a n o c o b a l t a t e complex c a t a l y s t proceeds i n t h e a b s e n c e o f a c h a i n t e r m i n a t i o n r e a c t i o n , i t was o f i n t e r e s t to study s e p a r a t e l y the chain propagation r e a c t i o n . A non-termi n a t e d p o l y m e r " s e e d " was p r e p a r e d and i t s r a t e o f r e a c t i o n w i t h p r o p y l e n e o x i d e was s t u d i e d . The r e s u l t s o f a s e r i e s o f t h e s e s e e d e d p o l y m e r i z a t i o n s c a r r i e d o u t a t 30°, ^0° and 50° a r e g i v e n i n F i g u r e 6, where l o g [ M ] / [ M ] i s p l o t t e d a g a i n s t t i m e . S t r a i g h t l i n e s a r e o b t a i n e d i n t h i s p l o t e x c e p t i n g f o r an o b s e r v able increase i n the r e a c t i o n r a t e i n the i n i t i a l p a r t o f the p o l y m e r i z a t i o n s c a r r i e d o u t a t t h e two l o w e r t e m p e r a t u r e s . It i s concluded from these r e s u l t s t h a t the chain propagation r e a c t i o n i s f i r s t - o r d e r i n monomer c o n c e n t r a t i o n . A n a p p a r e n t a c t i v a t i o n e n e r g y o f 13.7 + 0.8 k c a l / m o l e was c a l c u l a t e d f o r the chain propagation r e a c t i o n i n v o l v i n g the formation of p o l y (propylene ether) d i o l . T h i s v a l u e compares v e r y w e l l w i t h t h a t o f 1^4·. 7 k c a l / m o l e r e p o r t e d b y S h i g e m a t s u and c o w o r k e r s (16) for the sodium h y d r o x i d e c a t a l y z e d a d d i t i o n o f propylene o x i d e t o isopropyl alcohol. The r a t e s o f c h a i n p r o p a g a t i o n o f p r o p y l e n e o x i d e w e r e a l s o 2
0
t
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
POLYETHERS
-J
1
50 6 Volume of Eluate After Injection, ml Figure 5. Gel permeation chromât ο grams of poly propylene ether) diols prepared by incremental monomer addition
0.5 h
TIME (HRS.) Figure 6. Effect of temperature on propagation rate during poly(propylene ether) diol formation
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
2.
LiviGNi E T A L .
Ρoly(Propylene
Ether) Polyols
29
measured f o r the seed, prepared u s i n g the z i n c hexacyanocobaltate c o m p l e x c a t a l y s t , a t two d i f f e r e n t t e m p e r a t u r e s i n n-hexane and tetrahydrofuran. The r e s u l t s f o r t h e s e p o l y m e r i z a t i o n s a r e g i v e n i n F i g u r e 7, where l o g [M] /[M] i s p l o t t e d v e r s u s t i m e . The r e s u l t s a r e u n e x p e c t e d i n t h a t t h e r a t e i s f a s t e r , a t b o t h temp e r a t u r e s , i n n-hexane t h a n i n t e t r a h y d r o f u r a n . F o r a t y p i c a l i o n i c p o l y m e r i z a t i o n , one m i g h t e x p e c t t h e o p p o s i t e r e s u l t . However, i f t h e s o l v e n t c o u l d compete w i t h t h e monomer f o r c o o r d i n a t i o n s i t e s , t h i s c o u l d c a u s e a d e c r e a s e i n t h e number o f a c t i v e c e n t e r s g r o w i n g a t any t i m e and r e s u l t i n a d e c r e a s e i n t h e r a t e o f p o l y m e r i z a t i o n . Thus, t h e s l o w e r r a t e o f p o l y m e r i z a t i o n i n t e t r a h y d r o f u r a n , compared t o n-hexane, m i g h t be due t o the e f f e c t caused by c o o r d i n a t i o n o f the e t h e r c o m p e t i t i v e l y w i t h t h e monomer, p r o p y l e n e o x i d e , b e i n g more s i g n i f i c a n t t h a n i t s a c c e l e r a t i n g the r a t e o f r e a c t i o n by s o l v a t i o n o f the i o n p a i r s . 0
t
F u n c t i o n a l i t y Measurements c h a r a c t e r i z e the hydroxyl f u n c t i o n a l i t y of poly(propylene ether) d i o l s p r e p a r e d w i t h the z i n c h e x a c y a n o c o b a l t a t e complex c a t a l y s t was t o compare t h e e q u i v a l e n t s o f -OH g r o u p s p r e s e n t r e l a t i v e t o a l l o t h e r f u n c t i o n a l groups which might comprise polymer c h a i n e n d s . The g r o u p s w h i c h w e r e c o n s i d e r e d , i n a d d i t i o n t o -OH, w e r e ~C=C— a r i s i n g f r o m a c h a i n t r a n s f e r r e a c t i o n w i t h p r o p y l e n e o x i d e , and ^~C=0 i n t r o d u c e d e i t h e r by i s o m e r i z a t i o n o f propy l e n e o x i d e f o l l o w e d b y an a l d o l c o n d e n s a t i o n , b y c h a i n o x i d a t i o n , o r b y t h e p r e s e n c e o f i m p u r i t i e s i n t h e monomer (8). A further a s s u m p t i o n i n t h i s a n a l y s i s was t h a t t h e r e a r e o n l y two c h a i n ends p e r c h a i n . U s i n g t h e s e a s s u m p t i o n s , t h e number a v e r a g e m o l e c u l a r w e i g h t o f t h e p o l y m e r was c a l c u l a t e d a n d compared w i t h t h e f r a c t i o n a l amount o f t h i s t e r m i n a l f u n c t i o n a l i t y w h i c h c o n s i s t s o f h y d r o x y l groups. The number a,verage m o l e c u l a r w e i g h t c a l c u l a t e d i n t h i s manner i s i n g o o d a g r e e m e n t w i t h v a l u e s ob t a i n e d b y v a p o r p r e s s u r e osmometry, g i v i n g v a l i d i t y t o t h i s a p p r o a c h . The change i n t h e h y d r o x y l f u n c t i o n a l i t y as t h e molecular weight of the polymer i s i n c r e a s e d , c a l c u l a t e d i n the manner d e s c r i b e d , i s g i v e n i n F i g u r e 8 f o r d i o l s p r e p a r e d e x p e r i m e n t a l l y and t h o s e a v a i l a b l e c o m m e r c i a l l y . The a b s c i s s a i n t h i s p l o t r e p r e s e n t s t h e c a l c u l a t e d m o l e c u l a r w e i g h t and t h e o r d i n a t e i s the h y d r o x y l f u n c t i o n a l i t y c a l c u l a t e d from the e q u i v a l e n t s o f f u n c t i o n a l groups present. I t i s o b s e r v e d t h a t t h e r e i s a much more g r a d u a l d e c r e a s e i n t h e h y d r o x y l f u n c t i o n a l i t y w i t h i n c r e a s i n g molecular weight f o r the polymer prepared w i t h the z i n c h e x a c y a n o c o b a l t a t e complex c a t a l y s t than f o r t h e c o m m e r c i a l l y a v a i l a b l e poly(propylene ether) d i o l s , presumably prepared using an a l k a l i m e t a l h y d r o x i d e c a t a l y s t . F o r example, a t a m o l e c u l a r w e i g h t o f 3000, 97$ o f t h e c h a i n ends a r e h y d r o x y l f o r t h e d i o l s p r e p a r e d w i t h the z i n c h e x a c y a n o c o b a l t a t e complex c a t a l y s t , w h e r e a s o n l y a b o u t 90$ o f t h e c h a i n ends a r e h y d r o x y l i n t h e commercially a v a i l a b l e d i o l s . Poly(propylene
ether) d i o l s are u s u a l l y chain extended
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
30
POLYETHERS
0.7 0.6
50 C n-HEXANE
0.5 5 0 X TETRAHYDROFURAN
0.4 ο
3
0.3 0.2 0.1
//S
Y f/jS^fi^WZ 2
ο 40°C n-HEXANE
TETRAHYDROFURAN 3 4 5 6 TIME (HRS.)
Figure 7. Effect of solvent on propagation rate during poïy(propylene ether) diol formation
2.0, -•-GENERAL TIRE DIOLS
ο 11 ο
-•-COMMERCIAL DIOLS
11.91
1°
>-
1.8
1.71
1
2 3 4 5 6 7 8 9 MOLECULAR WEIGHT (OH + C=C + C=0) x 10
10 3
Figure 8. Change in hydroxyl functionality with molec ular weight for poly(propylene ether) diols
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
2. LiviGNi E T A L .
Poly(Propylene Ether) Polyols
31
by r e a c t i o n w i t h diisocyanates. The p o l y u r e t h a n e s r e s u l t i n g f r o m t h i s r e a c t i o n w e r e a l s o u s e d t o compare t h e f u n c t i o n a l i t y o f t h e d i o l s p r e p a r e d w i t h t h e z i n c hexacyano c o b a l t ate complex w i t h those a v a i l a b l e commercially. Of course, t h e extent o f r e a c t i o n reached, and l i m i t a t i o n s o f measuring r e a c t a n t s , as w e l l as t h e f u n c t i o n a l i t y w i l l determine t h ep r o p e r t i e s o f t h e f i n a l product. E x p e r i m e n t a l d i o l s were c h a i n extended w i t h 2 , 4 - t o l y l e n e d i i s o c y a nate and t h e W i l l i a m s p l a s t i c i t y determined f o r t h e r e s u l t i n g r u b b e r s . F i g u r e 9 shows t h e p l a s t i c i t y v a l u e s a s a v a r i a t i o n of the2,4-tolylene diisocyanate equivalents f o r d i o l s o f approxim a t e l y 3500 m o l e c u l a r w e i g h t . The h e i g h t o f t h e maxima i n t h i s figure i s a relative indication of thefunctionality of diols of comparable m o l e c u l a r weight. The W i l l i a m s p l a s t i c i t y depends on t h e m o l e c u l a r w e i g h t o f t h e p o l y ( p r o p y l e n e e t h e r ) d i o l ( i t g o v e r n s t h e amount o f p o l a r g r o u p s p r e s e n t ) , a s w e l l a s t h e o t h e r f a c t o r s a l r e a d y mentioned d i o l s prepared using th a higher p l a s t i c i t y , a t equivalent molecular weights, than t h e commercial d i o l s , again demonstrating t h e r e l a t i v e l y h i g h e r f u n c t i o n a l i t y o f the experimental d i o l s . We have s o f a r b e e n c o m p a r i n g t h e p o l y ( p r o p y l e n e e t h e r ) d i o l s w h i c h r e s u l t f r o m "KOH c a t a l y s i s " a n d t h e z i n c h e x a c y a n o c o b a l t a t e complex c a t a l y s i s w i t h r e s p e c t t o f u n c t i o n a l i t y . I t i s o f value t o compare t h e m o l e c u l a r w e i g h t d i s t r i b u t i o n o f d i o l s p r e p a r e d b y t h e s e two p r o c e s s e s , u s i n g t h e g e l p e r m e a t i o n chromatograms g i v e n i n F i g u r e 10. G e n e r a l l y , t h e l o w m o l e c u l a r weight polymers from b o t h p r o c e s s e s have a narrow m o l e c u l a r w e i g h t d i s t r i b u t i o n . However, the molecular weight d i s t r i b u t i o n o f t h e d i o l s prepared w i t h KOH t a i l t o w a r d s t h e l o w m o l e c u l a r w e i g h t r e g i o n , w h e r e a s t h o s e p r e p a r e d u s i n g t h e z i n c h e x a c y a n o c o b a l t a t e complex t a i l towards the h i g h m o l e c u l a r weight r e g i o n . As a consequence o f t h i s , t h e d i o l s p r e p a r e d w i t h t h e z i n c h e x a c y a n o c o b a l t a t e complex have a h i g h e r b u l k v i s c o s i t y t h a n t h e d i o l s p r e p a r e d w i t h KOH, a t t h e same n u m b e r - a v e r a g e m o l e c u l a r w e i g h t . The g e l p e r m e a t i o n chromat o g r a m o f a d i o l o f m o l e c u l a r w e i g h t o f 12,000, p r e p a r e d w i t h t h e z i n c h e x a c y a n o c o b a l t a t e c o m p l e x i s g i v e n i n F i g u r e 10 a n d demonstrates t h e i n c r e a s e d breadth i n the molecular weight d i s t r i b u t i o n r e s u l t i n g a t higher molecular weights. M e c h a n i s m . The f o l l o w i n g scheme i s o f f e r e d t o a c c o u n t f o r t h e d a t a p r e s e n t e d above. P o l y m e r i z a t i o n p r o b a b l y o c c u r s w i t h t h e g r o w i n g c h a i n c o o r d i n a t e d t o a z i n c atom. The c o o r d i n a t i o n s i t e s a r e i n i t i a l l y made a v a i l a b l e b y d i s p l a c e m e n t o f t h e 1,2dimethoxyethane from the c a t a l y s t , e i t h e r b y propylene o x i d e o r the i n i t i a t o r , 1,5-pentanediol. The 1 , 5 - p e n t a n e d i o l d i s a p p e a r s e a r l y i n t h e r e a c t i o n b e c a u s e o f i t s more a c i d i c n a t u r e a n d g r e a t e r ease o f c o o r d i n a t i o n t h a n t h e secondary h y d r o x y l o f t h e poly(propylene ether). C o o r d i n a t i o n o f a growing c h a i n would decrease t h e f r e e - i o n character o f t h epropagating center, compared t o c a t a l y s i s w i t h a l k a l i m e t a l h y d r o x i d e s . A s a r e s u l t ,
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
POLYETHERS
I
ι
»
I
3300 3400 350 GRAMS DIOL PER MOL 2 4-TDI f
Figure 9. propylene
Williams plasticity of polyurethanes prepared from poly ether) diols at different ratios of 2,4-tolylene diisocyanate
I 125
"
• ^ 150 175 VOLUME OF ELUATE AFTER INJECTION (ML)
Figure 10. Gel permeation chromatogram of com mercial polypropylene ether) diol and diols pre pared using zinc hexacyanocobaltate complex catalyst
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
2.
LiviGNi E T A L .
Ρoly(Propylene
33
Ether) Polyoh
c h a i n t r a n s f e r t o p r o p y l e n e o x i d e s h o u l d n o t o c c u r as r e a d i l y i n polymerizations catalyzed with the zinc hexacyanocobaltate complex. T h i s l e a d s t o p o l y ( p r o p y l e n e e t h e r ) p o l y o l s w h i c h con t a i n a g r e a t e r number o f t e r m i n a l h y d r o x y l g r o u p s . Of a d d i t i o n a l importance i s t h a t the z i n c hexacyanocobaltate catalyst gives more r a p i d p o l y m e r i z a t i o n r a t e s , t h e r e f o r e , l o w e r p o l y m e r i z a t i o n t e m p e r a t u r e s c a n b e u s e d . T h i s s h o u l d a l s o r e d u c e t h e amount o f c h a i n t r a n s f e r t o monomer. S i n c e t h e r e a r e a n i n s u f f i c i e n t number o f c a t a l y s t s i t e s t o be a s s o c i a t e d w i t h e v e r y c h a i n e n d o f t h e d i o l a n d y e t t h e p o l y m e r s have a n a r r o w m o l e c u l a r w e i g h t d i s t r i b u t i o n , a p a r t i c u l a r c a t a l y s t s i t e must a c t i v a t e d i f f e r e n t c h a i n ends d u r i n g t h e c o u r s e o f t h e r e a c t i o n . T h u s , a l l c h a i n ends must h a v e a p p r o x i m a t e l y t h e same p r o b a b i l i t y o f g r o w t h , a l t h o u g h o n l y a f r a c t i o n o f c h a i n ends u n d e r g o c h a i n p r o p a g a t i o n a t a n y t i m e d u r i n g t h e reaction. T h i s may be
CHAIN
PROPAGATION:
/
NACH ÇH-0—-Zn 5
α
H
+ CHfÇH—•
2 +
CH3 CHAIN
H
^CHj-CH-O-CHj-CH-U—Zn
CH3
2 +
CH3
CH3
+
^P CHyCH-0'---Zn
ACTIVATION:
^P CH ÇH-0---Zn n
/
?
CH
2 +
+
^CHyÇH-OH
CH3
3
^P
n
CHjÇH-OH CH
3
2+
m
CH
3
This d e s c r i p t i o n i s quite s i m i l a r t o that given f o r the polymeriz a t i o n o f e t h y l e n e o x i d e i n i t i a t e d b y sodium methoxide i n dioxane and m e t h a n o l , p r o v i d e d b y Gee, H i g g i n s o n a n d M e r r a l l (17). I f the r a t e o f c h a i n end a c t i v a t i o n proceeded a t a v e r y r a p i d r a t e r e l a t i v e t o chain growth, a narrow, symmetrical d i s t r i b u t i o n would be o b t a i n e d . I f t h i s a c t i v a t i o n p r o c e s s was v e r y much s l o w e r t h a n t h e r a t e o f monomer a d d i t i o n , a b r o a d d i s t r i b u t i o n would r e s u l t . I n t h e case o f t h e p o l y ( p r o p y l e n e ether) d i o l s
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
POLYETHERS
34
prepared w i t h the z i n c hexacyanocobaltate complex, the r a t e o f c h a i n end a c t i v a t i o n must be s u f f i c i e n t l y d i f f e r e n t t o t h a t o f c h a i n g r o w t h t o g i v e some b r o a d e n i n g i n t h e m o l e c u l a r w e i g h t distribution. Alternatively, catalyst sites of different a c t i v i t y may be p r e s e n t . I f s u c h a m e c h a n i s m as d e s c r i b e d above was o p e r a t i n g , i t w o u l d be e x p e c t e d t h a t a more n a r r o w m o l e c u l a r w e i g h t d i s t r i b u t i o n c o u l d be o b t a i n e d b y: ( l ) a d d i n g monomer s l o w l y t o the p o l y m e r i z a t i o n , thus i n c r e a s i n g the degree o f a c t i v a t i o n of d i f f e r e n t c h a i n ends p r i o r t o c h a i n p r o p a g a t i o n ; and (2) i n c r e a s ing the c a t a l y s t c o n c e n t r a t i o n , thus i n c r e a s i n g the f r a c t i o n o f c h a i n s t h a t can u n d e r g o g r o w t h s i m u l t a n e o u s l y . P a r t i a l confirm a t i o n o f t h e s e e f f e c t s has b e e n o b t a i n e d f o r t h e p r e p a r a t i o n o f p o l y (propylene ether) t r i o l s . The g e l p e r m e a t i o n chromatograms f o r s u c h p o l y m e r s , p r e p a r e d d u r i n g c o n d i t i o n s where a l l o f t h e p r o p y l e n e o x i d e was a d d e d i n i t i a l l y , and w h e r e t h e p r o p y l e n e o x i d e i s added s l o w l y F i g u r e 11. The i n i t i a t o p r o p a n e . I t i s a p p a r e n t t h a t a c o n s i d e r a b l y more n a r r o w m o l e c u l a r weight d i s t r i b u t i o n i s obtained f o r the polymer prepared u s i n g s l o w I n c r e m e n t a l monomer a d d i t i o n s u b s t a n t i a t i n g t h e m e c h a n i s m proposed. Acknowledgment The a u t h o r s a c k n o w l e d g e t h e v a l u a b l e e x p e r i m e n t a l a s s i s t a n c e o f Mr. J . A. W i l s o n i n t h e k i n e t i c s and m e c h a n i s m s t u d i e s , Mr. J . L. C o w e l l i n s p e c i a l s a m p l e p r e p a r a t i o n s f o r c h a r a c t e r i z a t i o n and Mr. J . S. Duncan i n f u n c t i o n a l i t y d e t e r m i n a t i o n s b y c h a i n e x t e n s i o n . We a l s o w i s h t o t h a n k D r s . R. A. B r i g g s and Ε. E. G r u b e r f o r h e l p f u l d i s c u s s i o n s d u r i n g t h e c o u r s e o f t h i s study. A s p e c i a l note of g r a t i t u d e i s extended to Professor C. C. P r i c e who, a s a c o n s u l t a n t t o o u r l a b o r a t o r y , made many h e l p f u l suggestions. Summary C e r t a i n complexes o f z i n c hexacyanocobaltate are e f f e c t i v e c a t a l y s t s i n the p r e p a r a t i o n o f p o l y (propylene ether) p o l y o l s f r o m l o w m o l e c u l a r w e i g h t h y d r o x y l compounds and p r o p y l e n e o x i d e . The Z n [ C o ( G N ) ] 2 . i | - ( l , 2 - d i m e t h o x y e t h a n e ) 0.85 Z n C l k.k BQO catalyzed polymerization of propylene oxide w i t h 1,5-pentanediol was s t u d i e d . A n i n i t i a l l y s l o w r a t e o f p o l y m e r i z a t i o n i s f o l l o w e d b y a r a p i d r a t e . The n u m b e r - a v e r a g e m o l e c u l a r w e i g h t o f the p o l y (propylene ether) d i o l i s governed e n t i r e l y by the w e i g h t o f the p o l y m e r formed and moles o f 1 , 5 - p e n t a n e d i o l c h a r g e d . U s i n g g e l p e r m e a t i o n c h r o m a t o g r a p h y , i t was e s t a b l i s h e d t h a t t h e p o l y m e r has a n a r r o w m o l e c u l a r w e i g h t d i s t r i b u t i o n . The amount o f c a t a l y s t u s e d i n t h e p o l y m e r i z a t i o n i s i n s u f f i c i e n t t o h a v e a l l c h a i n ends g r o w i n g s i m u l t a n e o u s l y . A mechanism i s proposed which involves a c a t a l y s t s i t e a c t i v a t i n g d i f f e r e n t 3
6
2
s
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
2. LiviGNi E T A L .
Ρoly(Propylene
Ether) Polyols
ALL P.O P.O. ADDED SLOWLY
—
VOLUME OF ELUATE AFTER INJECTION (ML.) Figure 11. Effect of monomer addition method on gel permeation chromatogram for polypropylene ether) triols prepared using zinc hexacyanocobaltate complex catalyst
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
36
POLYETHERS
c h a i n s throughout t h e r e a c t i o n , g i v i n g each a n e q u a l chance f o r growth. The p o l y o l s p r e p a r e d w i t h t h e z i n c h e x a c y a n o c o b a l t a t e c a t a l y s t were found t o have b e t t e r f u n c t i o n a l i t y t h a n p o l y ( p r o p y l e n e e t h e r ) p o l y o l s p r e p a r e d b y c o n v e n t i o n a l methods. Literature Cited 1. B e l n e r , R. J., Herold, R. J., M i l g r o m , J., U.S. Patents 3,427,256; 3,427,334; a n d 3,427,335 to General Tire & R u b b e r Company (1969). 2.
H e r o l d , R. J., Livigni, R. A., A d v a n c e s in Chemistry Series, Polymerization Kinetics and T e c h n o l o g y , Number 128, (1973)
208.
3.
P a r k e r , R. Ε., Isaacs,
4. St. Pierre, L. Ε., Price, C. C., J. Am. Chem. S o c . (1956)
78, 5.
3432.
Dege, G. J., Harris, R. L., M a c K e n z i e , J. S., J. Am. Chem.
Soc., (1959) 81, 3374. H.
6. G e e , G., Higginson, W. C. Ε., Taylor, K. J. a n d T r e n h o l m e , W., J. Chem. Soc. (1961) 4298. 7.
S n y d e r , W. H., Taylor, K. J., Chu, Ν. S. a n d Price, C. C., T r a n s . Ν. Y. Acad. of Science Ser. II (1962) 24, (#4) 341.
8.
S i m o n s , D. Μ., Verbanc, J. J., J. P o l y m . Sci. (1960) 44,
303. 9. Siggia, S., Hanna, J. G., A n a l y . Chem. 10. 11.
Iwamoto, R., S p e c t r o c h i m
Acta
(1961) 3 3 , 896.
(1971) 27A, 2385.
"1973 A n n u a l Book of ASTM S t a n d a r d s " , P a r t 26, p . 888, American Society for Testing and Materials, Philadelphia, Pennsylvania 19103.
12.
Siggia, S., "Quantitative Organic G r o u p s " , 3rd Edition, 73-75, J o h n
13.
"1973 A n n u a l Book of ASTM S t a n d a r d s " , American Society for Testing and Pennsylvania 19103.
Analysis Via Functional Wiley & Sons (1963) Part 28, p . 438 Materials, Philadelphia,
14. Pavelich, W. Α., Livigni, R. Α., J. P o l y m . Sci. (1968)
C-21,
215.
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
2.
LIVIGNI E T A L .
Ρ*oly'(Propylene Ether) Poly oh
15. Flory, P. J., J. Am. Chem. S o c . (1940) 6 2 ,
37 1561.
16.
S h i g e m a t s u , H., Miura, Y. a n d Ishii, Υ., Kogyo K a g a k u Zasshi (1962) 6 5 , 360. S e e , for e x a m p l e : Frisch, K. C. ed., " R i n g Opening Polymerization", p. 25, Marcel D e k k e r , N.Y. and L o n d o n (1969)
17.
Gee, G., Higginson, W. C. E. and Merrail, J. Chem. S o c .
(1959) 1345.
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
3 Propylene Oxide Polymers of Varying Stereosequence Distribution S. L. A G G A R W A L and L. F. M A R K E R Research and Development Division, The General Tire and Rubber Co., Akron, Ohio 44329
Introduction In 1956, C. C. P r i c e (1) demonstrated that when l-isomer of propylene oxide i s polymerized w i t h potassium hydroxide c a t a l y s t , a s t e r e o s p e c i f i c and c r y s t a l l i n e polymer i s produced. Yet, the racemic monomer polymerized w i t h the same c a t a l y s t gave an amorphous product. A ferric c h l o r i d e c a t a l y s t on the other hand produced, from e i t h e r racemic or o p t i c a l l y a c t i v e monomer, a crystalline high molecular weight f r a c t i o n having i d e n t i c a l c r y s t a l s t r u c t u r e . These studies demonstrated that long s t e r e o r e g u l a r sequences having e i t h e r d or l c o n f i g u r a t i o n , necessary f o r crystallization, can be produced by one c a t a l y s t , w h i l e another c a t a l y s t may lead to amorphous polymers, which may have only short s t e r e o r e g u l a r sequences of a p a r t i c u l a r c o n f i g u r a t i o n . Poly(propylene oxide) was unique among s t e r e o s p e c i f i c p o l y mers developed up to that time. The monomer has an o p t i c a l cent e r which, under a p p r o p r i a t e synthesis c o n d i t i o n s , can be preserved i n the polymer so that d or l forms could be i d e n t i f i e d at each asymmetric carbon atom. Examination of the c r y s t a l s t r u c ture of i s o t a c t i c poly(propylene oxide) (2) shows that it crystallizes in a helical form and that the c r y s t a l s can accommodate only the h e l i c e s of one o p t i c a l form and are t h e r e f o r e o p t i c a l l y active. A number of c a t a l y s t systems have been developed (3,4,5) which r e s u l t i n propylene oxide polymers of d i f f e r e n t s t e r e o s e quence d i s t r i b u t i o n . In the f o l l o w i n g , we review some of our work on the c h a r a c t e r i z a t i o n of stereosequence length i n propylene oxide polymers prepared w i t h d i f f e r e n t c a t a l y s t s , and more import a n t l y , studies on the e f f e c t of the d i f f e r e n c e s i n stereosesequence length on the crystallization behavior and mechanical p r o p e r t i e s of the polymers. D e s c r i p t i o n of Stereosequence
Distribution
As i n other polymeric systems, both head-to-head
and
38
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
3. AGGARWAL A N D M A R K E R
Propylene Oxide Polymers
39
h e a d - t o - t a i l arrangements of consecutive monomer u n i t s have been i d e n t i f i e d i n poly(propylene oxide (6). These arrangements can be detected by chemical means and have important e f f e c t s i n modi f y i n g the c r y s t a l l i z a t i o n behavior of the polymer (6 7)· Another s t r u c t u r a l feature that may a f f e c t c r y s t a l l i z a t i o n behavior i s that, f o r a given c o n f i g u r a t i o n (d or 1_) of the repeating u n i t i n the i s o t a c t i c s t e r e o r e g u l a r polymer chain, two d i s t i n c t chains s t r u c t u r e s are p o s s i b l e depending upon the r e l a t i v e p o s i t i o n s of the oxygen and the asymmetric carbon. These may be designated as up and down chain s t r u c t u r e f o r each of the ci and _1 c o n f i g u r a t i o n of the i s o t a c t i c polymer c h a i n . They are superimposable by turning the polymer chain end-over-end ( 8 ) . We recognize such complications as above i n the c r y s t a l l i z a t i o n of s t e r e o r e g u l a r poly(propylene o x i d e ) . The main i n t e r e s t of our s t u d i e s , how ever, has been i n the stereosequence d i s t r i b u t i o n i n propylene oxide polymers prepare e f f e c t of stereosequenc polymers. The simplest s t a t i s t i c a l model which has s u f f i c i e n t gener a l i t y to represent the sequence d i s t r i b u t i o n i n poly(propylene oxide) i s one i n which the c o n f i g u r a t i o n of the l a s t three mono mer u n i t s i n the growing chain determine the c o n f i g u r a t i o n of the next u n i t coming onto the chain. The c o n f i g u r a t i o n of the t r i a d of successive u n i t s may take on e i g h t p o s s i b l e arrange ments as l i s t e d i n Table I below. Recent studies have jhown that s e v e r a l types of such t r i a d s may be d i s t i n g u i s h e d from H and carbon-13 NMR spectra (9,10,11). We have adopted a shorthand n o t a t i o n of representing by + the case when two successive u n i t s have the same c o n f i g u r a t i o n , and by - when they have opposite configurations. Triads are r e f e r r e d to as i s o t a c t i c , t r i a d s as s y n d i o t a c t i c , and E„ and E^ as h e t e r o t a c t i c . The A and Β t r i a d s i n a polymer made from a racemic monomer cannot be d i s t i n g u i s h e d from each other by any p h y s i c a l method, and equal pop u l a t i o n s , i n any case, of the corresponding A and Β t r i a d s may be assumed. Thus, the number of p o s s i b l e t r i a d s t a t e s of i n t e r est i n a model f o r analyzing stereosequence d i s t r i b u t i o n reduces to f o u r . f
φ)α-οο3φ)
2
5
( R 2 f
. 24)
( 4 )
Here φ i s the contact angle between the f i l l e r particle and the polymer, with f (φ) increasing as the wetting angle increases. In particular, when
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
62
POLYETHERS
Φ +
0°,
φ
90°,
f (φ) f (φ)
0
+
i
As the interfacial energy between the polymeric liquid and the f i l l e r decreases, the wetting decreases, and so φ increases, or, as f(φ) increases the interfacial energy decreases. Thus from equations ( 3 ) and ( 4 ) i t i s apparent that the free energy for nucleus formation in the heterogeneous case will always be smaller than that for homogeneous nucleation. It i s reasonable to assume that, in order for a crystal lisation exotherm to be detectable by D.S.C., there must exist a critical nucleation rate S . Accordingly, comparison of the •temperatures at which these isotherms appear i s in effect a measurement of the relative rates of nuclei formation in the varioxas samples. Thu with smaller free energie nuclei necessary for observation are present at higher temper atures relative to the pure sample. In the pure sample the nucleation i s probably heterogeneous, but the number of nucleat ing species present is relatively small. Furthermore, with increasing f i l l e r content, the number of filler-polymer contacts increases with a resultant increase in the number of nuclei, and an upward shift in the exotherm temperature. In addition to changing the quantity of silica present, i t i s also possible to change the nature of the inter face present between the f i l l e r and the iPPO. The trimethylsilyl coated f i l l e r has a lower epoxide-silica interfacial energy than that between epoxides and pure silica. Thus the wetting of this sample will be less, and the differences between AGh* and ÙGq* will be diminished (equations ( 3 ) and ( 4 ) ) . At lower loadings this results in smaller shifts from the pure iPPO behaviour? ΔΤ = 9°C for 1 0 parts pure silica, while ΔΤ = 5 . 5 ° C for 1 0 parts trimethylsilyl coated silica. However, as the f i l l e r content i s increased, the number of silica particles present becomes so large that there is effective cros si inking of polymer segments by adsorption on the silica; this increases the transport term, E Q , in equation ( 2 ) , and thus the effective number of nuclei is lessened, resulting in a lowering of T p. Also the decrease in the number of effective nuclei at higher loadings i s greater for the composites contain ing pure silica than for the treated silica. This is expected because, as shown by Howard and McConnell, for poly (ethylene oxide) ( 2 6 ) , an epoxide polymer adsorbs more strongly on the hydroxyl group-covered surface than on the trimethylsilylated surface. R
Q
2 . Dilatometry. The kinetics of the isothermal crystal lisation of pure and f i l l e d iPPO samples from the melt were studied between 4 5 . 0 0 and 5 5 . 0 0 ° C . The composites contained 1 0
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
4.
COLE
A N D SX-PIERRE
Isotactic Έ*oly'(Propylene Oxide)
Crystallization
63
parts of filler/100 parts of iPPO. The increase in density was taken as a measure of the increase in overall crystallinity. In Fig. 2, (1 - X-t/Xoo) i s plotted against log (time) for the pure polymer; X t i s the weight fraction of polymer crystallised at time t and Xoo i s the weight fraction of polymer crystallised at infinite time. The sigmoidal isotherms usually found in polymer crystal lisation are observed; these represent primary crystallisation i.e. the nucleation and growth of crystalline regions until mutual impingement stops further growth. The second part of curves 2 and 3 as shown in Fig. 3, where the crystallinity increases logarithmically with time, corresponds to secondary crystallisation: this i s usually considered to be the crystal lisation of any remaining melt, and rearrangement of parts of the crystal regions grown in the primary phase (27). In Fig. 3 the crystallisatio silica composite i s 90 crystallised. A similar but lesser effect is shown in the low energy surface silica composite. Another parameter characterising the nucleation of the crystallisation i s the apparent induction time; this i s the time during which there i s no apparent change in the height of the mercury column in the dilatometer, when the change in polymer density i s too small to be observed. As shown in Fig. 4 there is an appreciable lengthening of the induction period with i n creasing temperature. At the same crystallisation temperature the induction times vary in the order: Pure iPPO > iPPO + low energy surface silica > iPPO + high energy surface silica. Indeed, at 45.00°C the high energy surface silica composite began to crystallise before the sample reached thermal equilibrium (this was usually reached after 3 minutes). At the same temper ature the pure iPPO did not begin to crystallise until 11 minutes had elapsed. The half-time of primary crystallisation, t i , shows a similar dependence on temperature and polymer- f i l l e r interaction energy (see Fig. 5). To find t i , i t was assumed that the contribution of the slow secondary crystallisation process to the primary portion of the overall crystallisation curve was negligible. Thus t i was half the value of the time at the intersection point (see curve 3, Fig. 3), using the extra polation method of Vidotto et a l (28) for the crystallisation of isotactic poly butene-1, and used by Groeninckx et a l (11) for the crystallisation of poly (ethylene terephthalate). These results show that, since the primary crystallisation is composed of two processes, primary nucleation and subsequent crystal growth, and as the crystal growth is independent of the origin of the primary nucleus, the silicas act as heterogeneous nucleating agents for iPPO. Also the high energy surface silica is markedly more effective than the low energy surface silica. A semi-quantitative analysis of the time dependence of the
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
64
POLYETHËRS
Time (mins) Figure 2.
Crystallization isotherms for pure iPPO at crystallization temperatures of 2,45.00°C; 2,47.50°C; 3,50.00°C; 4,52.50°C; and 5,55.00°C
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
4.
COLE
A N D ST-PIERRE
Isotactic Ρoly(Propylene
Oxide)
Crystallization
T i m e (min) Figure 3. Crystallization isotherms of 1, pure iPPO; 2, iPPO + MeSiCl treated silica; and 3, iPPO + untreated silica. Crystallization temperature = 50.00°C.
0
50 Induction Time (mins)
100
Figure 4. Plots of induction time against crystallization tem perature. • = pure iPPO. φ = iPPO + Me SiCl treated silica. Ο = iPPO + untreated silica. 3
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
65
POLYETHERS
66
primary crystallisation process was made using the Avrami relationship (29-31): 11
θ = expi-kjt )
(5)
where θ = (dp-d )/(dp-d ), with dp being the polymer density at the end of the primary crystallisation i.e. at the intersection point as drawn on curve 3 in Fig. 3, and do i s the density of the amorphous polymer; d-j- i s the density of the polymer at time t. ki i s the Avrami constant, and η i s the Avrami exponent; η depends on both the type of primary nucleation and the mode of growth of the crystallising polymer. Plots of log(-log6) against log (time) were drawn for a l l samples examined, and typical examples are shown in Fig. 6. From the slopes of these lines, the Avrami exponent η i s obtained. The average η value fo the treated and untreate temperatures except for the untreated silica sample at 45.00°C, which gave an anomalous η value of 2.50. The η values of 3.0, according to the simple Avrami theory suggest either instantaneous nucleation and three-dimensional crystal growth, or a first order nucleation rate and twodimensional crystal growth. However, as Mandelkern has shown (25), a more general Avrami equation can give non-integral values for n, as was found in the crystallisation of pure iPPO; thus i t i s difficult to attach a quantitative interpretation to a value of n. Qualitatively i t may be noted that the constant values of η for both types of silica f i l l e r s at a l l experimental temperature (with the one exception) indicates a similar crystallisation mechanism by both the high and low energy surface silica composites. For thé pure polymer, there operates a different mechanism, showing either a change in heterogeneous nucleation time dependence or in growth morphology. t
0
Summary The effectiveness of chemically different, but physically similar, silica f i l l e r s as nucleating agents in the crystallisation of isotactic poly (propylene oxide) was studied using differential scanning calorimetry and dilatometry. It was found that varying the epoxide-silica interfacial energy by treating a silica surface with trimethylchlorosilane caused a change in i t s nucleating ability; the greater the interfacial energy, the more efficiently the silica nucleates. This effect i s interpreted in terms of the Fisher-Turnbull equation for nucleation, with change in interfacial energy causing a change in the free energy of heterogeneous nucleation. Increase in f i l l e r content of the composites up to a certain loading increased nucleation; additional f i l l e r caused effective
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
Isotactic Poly(Propylene
C O L E A N D ST-PIERRE
4500
47-50
Oxide) Crystallization
50 0 0
Crystallisation
52-50
Temperature
5500 (°C)
Figure 5. Plots of half-time of primary crystallization (ti/2) against crystallization temperature. • = pure iPPO. m = iPPO + Me SiCl treated silica. Ο = iFPO -f- untreated silica. ( 3
+ 20 b b
Log(-log0) -2-0
-40
-60 2-0
3-0 Log
40
50
t(min)
Figure 6. Avrami plots of log(—logO) against log t. • = pure iPPO. φ = iPPO + MeSiCl treated silica. Ο = iPPO + untreated silica at different temperatures, a, a\ a" = 52.50° C. b, b\ b" = 47.50°C.
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
«S
POLYETHERS
cross-linking of polymer segments, thus increasing the free energy of activation for transport across the liquid polymerf i l l e r interface and so decreasing the nucleation rate. Acknowledgement Acknowledgement i s given to the National Research Council of Canada for financial support which permitted this work to be undertaken. I also acknowledge a debt of gratitude to Professor C.C. Price, a great chemist, a great man and a friend of decades. He has been an inspiration to me and to a host of other former students (L.E.St-P.). Literature Cited 1. Beck, H.N and Ledbetter 9, 2131. 2. Beck,H.N.,J. Appl. Poly. Sci., (1967), 11, 673. 3. Rybnikar, F., J. Appl. Poly. Sci., (1969), 13, 827. 4. Binsbergen, F.L., Polymer, (1970), 11, 253. 5. Binsbergen F.L. and de Lange, B.G.M., Polymer, (1970), 11, 309. 6. Kargin, V.A., Sogolova, T.I., Rapoport-Molodtsova, N.Ya., Dokl. Akad. Nauk. S.S.S.R., (1964), 156, 1406. 7. Cormia, R.L., Price, F.P. and Turnbull, D., J. Chem. Phys., (1962), 37, 1333. 8. Koutsky, J.A., Walton, A.G. and Baer, Ε., Polymer Letters, (1967), 5, 185. 9. Mauritz, K.A., Baer, E. and Hopfinger, A.J., J. Poly. Sci., A2, (1973), 11, 2185. 10. Van Antwerpen, F. and van Krevelin, D.W., J. Poly. Sci., A2, (1972), 10, 2423. 11. Groeninckx, G., Berghmans, Η., Overbergh, N. and Smets, G., J. Poly. Sci., A2, (1974), 12, 303. 12. Hobbs, S.Y., Nature, Physical Science, (1971), 234, (44), 12. 13. Hobbs, S.Y., Nature, Physical Science, (1972), 239, (89), 28. 14. Chahal, R.S., Ph.D. Ihesis, McGill university, (1968). 15. Chahal, R.S. and St-Pierre, L.E., Macromolecules, (1968), 1, 152. 16. Yim, A. and St-Pierre, L.E., Polymer Letters, (1970), 8, 241. 17. Yim, Α., Ph.D. Thesis, McGill University, (1971). 18. Turnbull, D. and Fisher, J.C., J. Chem. Phys., (1949), 17, 71. 19. Price, C.C. and Osgan, M., J. Am. Chem. Soc., (1956), 78, 4787. 20. Aggarwal, S.L., Marker, L., Kollar, W.L. and Geroch, R., J. Poly. Sci., A2, (1966), 4, 715. 21. Allen, G., Booth, C. and Jones, M.N., Polymer, (1964), 5, 195.
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22. 23. 24. 25. 26. 27. 28. 29. 30. 31.
A N D ST-PIERRE
Isotactic Ρoly(Propylene
Oxide)
Crystallization
69
Slonimskii, G.L. and Godovskii, Yu.K.,Vysokomol.Soyed., (1967), 9, 863. Teilel'baum, B.Ya and Anoshina, N.P., vysokomol. Soyed., (1965), 7, 2117. Turnbull, D., Solid State Physics, (1956), 3, 277. Mandelkern, L., "Crystallisation of Polymers", McGraw-Hill Book Co., Inc., New York, 1964. Howard, G.J. and McConnell, P., J. Phys. Chem., (1967), 71, 2974. Keith, H.D., Koll.-Z.Z. Polym., (1969), 231, 421. Vidotto, G., andKovacs,A.J., Koll.-Z.Z. Polym., (1967), 220, 2. Avrami, M., J. Chem. Phys., (1939), 7, 1103. Avrami, M., J. Chem. Phys., (1940),8,212. Avrami, M., J. Chem Phys. (1941) 9 177
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
5 Applied Crystallization Kinetics. III. Comparison of Polyepichlorohydrins of Different Stereoregularity P. D R E Y F U S S B. F. Goodrich Research and Development Center, Brecksville, Ohio 44141
Introduction In the course of some of our work on polyethers, we encountered a series of crystalline polyepichlorohydrins which differed quite markedly in their processing characteristics but otherwise seemed quite s i m i l a r . Differences revealed by the infrared and nuclear magnetic resonance techniques then available were too insignificant to be helpful in their characterization. A l l polymers were shown to be crystalline and isotactic by X - r a y analysis. Small differences in optical activity were measurable. However, these differences were too small to be useful for correlation with physical properties. We found that an examination of their crystallization behavior and rates of crystallization was an extremely sensitive and revealing way of characterizing them. Experimental Microscopy. Thin films (1-2 mils) were pressed at 1 5 0 ° C using a Pasedena press fitted with West SCR controllers. T y p i cally, a small sample was placed between Teflon coated a l u m i num foil sheets, preheated for 30 sec, and held at 25, 000 lb. gauge load for 5 min. Samples were then rapidly transferred to a cooling press and held at 25, 000 lb. gauge load for 5 min. Some of the lower melting samples were pressed at 1 0 0 ° C . Portions of these films were placed on a glass slide and covered with a cover glass. Samples were melted in an air oven at the desired temperature, usually 1 5 0 ° C for the desired time, usually 15 min and then rapidly transferred to a hot stage at Current address: Institute of Polymer Science, University of Akron, A k r o n , Ohio 44325. 70 In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
5.
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Polyepichlorohydrins
71
constant temperature. The hot stage temperature was controlled by circulating liquid f r o m a Haake NBS bath through the stage. Temperatures, measured by means of a thermocouple in the stage near the sample, were constant to 0. 1 ° C or less. The growth of the spherulites that formed was observed using a Unitron polarizing microscope with crossed polaroids. Photographs were taken with the aid of an A m e r i c a n Optical Co. Photomicrographic camera with a Polaroid Land camera back. Melting was followed using a heating rate of 0. 5 to 1° per min. The slower rate was used in the vicinity of the melting temperature. Dilatometry. Volume-temperature measurements, and c r y s tallization rate measurement dilatometers made f r o lary tubing with mercury as the confining liquid. The procedure followed was very s i m i l a r to that described by Bekkedahl (JJ. Well-fused pellets of appropriate dimensions were pressed at 5 Ram force/lb. Hydraulic Pressure on the gauge and 25 to 120°C (usually 9 0 ° G ) . The pellets were cooled to 4 5 - 5 0 ° C at full pressure before removing f r o m the moid. The sealed dilatometers containing the pellets were evacuated to about 10"* 5 m m Hg while heating at 1 2 5 - 3 5 ° C for about 3 hrs prior to filling with mercury. F o r the rate studies, the prepared dilatometers were placed in a 1 5 0 ° C bath for about 30 min before transferring rapidly to a second bath at the crystallization temperature. Crystallization temperatures were controlled to + 0. 01 °C with the aid of a Dynapac-15 temperature controller. Higher temperatures of the melting bath and longer melting times were tried occasionally. These did not change the observed rates for any of the samples studied. A l l rates are reported in terms of the time, ti., for half the total change in height to occur. Whenever the value of t i was less than about 10 min, we were not able to determine an exact value because crystallization began before thermal equilibrium was achieved. Melting temperatures after isothermal crystallization were obtained in the same bath using heating rates of 0. 3 ° C per min and observing the change in height with temperature which was measured with a calibrated mercury thermometer. Melting temperatures were taken as the temperature where the last traces of crystallinity disappeared.
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
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Results D e s c r i p t i o n of P o l y m e r s . A wide v a r i e t y of c r y s t a l l i n e p o l y e p i c h l o r o h y d r i n s w e r e e x a m i n e d i n this study. S o m e t y p i c a l e x a m p l e s a r e g i v e n i n T a b l e 1. A l l the p o l y m e r s w e r e p r e p a r e d f r o m r a c e m i c m o n o m e r , but s o m e of t h e m w e r e p r e p a r e d u s i n g i n i t i a t o r s of the type p r e v i o u s l y r e p o r t e d to give p a r t i a l l y o p t i c a l l y a c t i v e p o l y m e r s (2-6). T h e p o l y m e r s w e r e shown to be i s o t a c t i c by c o m p a r i s o n of the o b s e r v e d d - s p a c i n g s with those r e p o r t e d i n the l i t e r a t u r e f o r c r y s t a l l i n e i s o t a c t i c p o l y e p i c h l o r o h y d r i n (8,9). A l s o i n c l u d e d i n T a b l e 1 f o r c o m p a r i s o n a r e s o m e data on p o l y p r o p y l e n e o x i d e s p r e p a r e d with d i f f e r e n t i n i t i a t o r s . Spherulite Morphology readily f o r m s spherulit i n F i g u r e 1, we have o b s e r v e d two k i n d s of s p h e r u l i t e s .
b Figure 1. Polyepichlorohydrin spherulites. Left: Type I spherulites from 329C after melting at 170°C and crystallizing at 50°C for 185 min. (128%). Right: Type II spherulites from 39A after melting at 150°C and crystallizing at 50°C for 222 min. (128x).
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
Ferric chloride
Polymer from ^ - p r o p y l ene oxide
b
17+5
b
C
c
b c Crystalline, 8.0 , -9.3 c Semicrystalline, 6. 1^, -8 Amorphous, 4 . 9 , + l 25 + 5^, -16 4- 5
0 0 -2. 36 -2.80 -9.75 -10.1
in M - P y r o l at 2 3 ° C
'
7
7
Ref
c
a
D e t e r m i n e d in benzene at 2 0 ° C .
Determined in chloroform at 2 0 ° C .
A is a typical initiator for the preparation of non-optically active but crystalline polymers fr racemic monomer. Β are typical initiators for the preparation of optically active polymer f i racemic monomer.
Potassium hydroxide
Polymer f r o m J - p r o p y l ene oxide
a
Diethyl zincd-borneol
A A Β Β Β Β
Initiate-r
Polymer f r o m racemic propylene oxide
Sample 329C 100Z 162A 2437 2413 2431
Table 1 T y p i c a l Crystalline Polyepichlorohydrins
POLYETHERS
74
B o t h have f i b r i l l a r s t r u c t u r e s but the s t r u c t u r e of T y p e I is c o a r s e r than that of T y p e II. O c c a s i o n a l l y r i n g s a r e o b s e r v e d in T y p e II s p h e r u l i t e s . S o m e t i m e s as shown i n F i g u r e 2 both types of texture a r e o b s e r v e d i n a s i n g l e s p h e r u l i t e . W h e n the s p h e r u l i t e s w e r e o b s e r v e d between c r o s s e d p o l a r o i d s u s i n g a 1st o r d e r r e d plate i n the u s u a l 45° o r i e n t a t i o n , it was found that both types of s p h e r u l i t e s a r e n e g a t i v e l y biréfringent. T h i s is not s u r p r i s i n g s i n c e negative s p h e r u l i t e s have a l s o been o b s e r v e d i n p o l y p r o p y l e n e o x i d e f i l m s (10). N e v e r t h e l e s s , the s p h e r u l i t e s a r e not i d e n t i c a l when v i e w e d with the 1st o r d e r r e d plate. T y p e I is blue i n the s e c o n d and f o u r t h q u a d r a n t s and o r a n g e i n the f i r s t and t h i r d . T y p e II i s s i m i l a r but the q u a d rants a r e s e p a r a t e d by a r e d c r o s s .
Figure 2. Type I and II spherulites both seen in the same spherulite, from 164A melted at 150'C and crystallized at 50°C for 168 min. (128x)
T h e type of s p h e r u l i t e that f o r m s does not s e e m to be a f f e c t e d by the t e m p e r a t u r e at w h i c h the s a m p l e i s m e l t e d o r by the t e m p e r a t u r e of c r y s t a l l i z a t i o n . We have o b s e r v e d the g r o w t h of s p h e r u l i t e s of both types at 30, 50, and 6 0 ° C a f t e r m e l t i n g at 1 5 0 ° C . S i m i l a r m o r p h o l o g y was obtained f r o m the s a m e s a m p l e at a l l t e m p e r a t u r e s . H o w e v e r , as expected, the g r o w t h rate and
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
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Polyepichlorohydrins
perfection of the spherulites are dependent on the temperature of crystallization. Rates are slower and perfection is greater at temperatures nearer to the polymer melting temperature. We have been able to grow very large spherulites by crystallizing for several days at 5 0 ° C . The morphology does not seem to be affected by the temperature at which the sample is melted prior to crystallization. We have crystallized at 50°C after melting at 130, 150, and 1 7 0 ° C . The morphology obtained f r o m the same sample was similar in all cases. The main difference was that more small spherulites, unresolvable at our usual magnification of 150x, formed after melting at 1 3 0 ° C . Melting Temperatures. The melting temperatures we observe microscopically ar thoseobserved dilatometrically. Some typical results are given in Table 2 and in Figures 3-5. This is not an unexpected result, since polymer melting temperatures are very sensitive to the rate of heating unless extremely slow heating rates, such as 0. 5 ° C per day, are used. A l s o , the heat transfer in a dilatometer and on a hot stage may be quite different. In addition, Table 2 Microscopic and Dilatometric Melting Temperatures of Crystalline Polyepichlorohydrin Polymer 329C 39A 164A 2413 2431 100Z
Microscopic T
m
115-16 119-20 114 and 117
(°C)
Dilatometric T
m
(°C)
113 115 108.5 and 113 115-17 117.5 111
sample preparation and previous heat history can affect the exact melting temperature observed ( j _ l ) . The important point here is that two different melting temperatures have been observe d_boJhjrujcj^^ the same sample and in different samples. In some of the later experiments, samples were held at temperatures between the higher and lower melting temperatures for several hours to verify that the higher melting polymer was not just slower to melt. Thus, there are two families of crystalline polyepichlorohydrins. A s
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
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Figure 3.
Melting of 329C and 39A after simultaneously melting at 150°C crystallizing at 50°C on the same slide
and
Figure 4. Melting of spherulites of 164A. At 80°C both Type I and Type II spherulites are visible. By 115°C Type I spherulites are melted. Type II spherulites disappear by 117°C (83%).
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
DREYFUSS
Figure 5.
Polyepichlorohydrins
Dilatometric melting curve of 164A. Two inflections suggest two different melting temperatures.
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
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will be discussed below these two families can be related to the stereoregularity of the polymers. Crystallization Rates. We determined growth rates of the spherulites microscopically, but only examined the rates of nucleation qualitatively for reasons that will emerge below. Overall rates of crystallization were determined dilatometrical-
iy. Nucleation of Spherulites. We have examined the rates of crystallization of the two kinds of spherulites microscopically in order to obtain further evidence to aid in understanding the differences observed. We found that different kinds of nucleation apparently occurred in different samples. Some samples gave spherulites of uniform geneous nucleation. Other samples gave spherulites of variable size such as would be expected f r o m sparodic, homogeneous nucleation. Only these latter samples were used in the comparison made below in determinations of overall rates of c r y s t a l l i zation. The number of nuclei that appear in the field of view also varies considerably f r o m sample to sample and even f r o m area to area in the same sample. Nevertheless, throughout our studies it appears that spherulites form more readily f r o m Type II spherulites, that is, f r o m more optically active polymer. Growth Rates of Spherulites. A s shown in Figure 6, both types of spherulites grow in the typical fashion observed many times for spherulites: namely, linearly with time. In the particular examples illustrated it was not possible to follow the growth of 39A for as long as 329C was studied because impingement occurred sooner. The fact that a single straight line can be drawn for both types is fortuitous in as much as the particular spherulites examined happened to have the same diameter at the same initial time. But it is significant that the growth rates determined f r o m the slope of the line do not appear to be different. Both are of the order of 1.5 microns per minute. If either type grows faster, the data in Figure 6 suggests that Type II spherulites grow faster. Overall Rates of Crystallization. We divided our studies of overall rates of crystallization into two areas: reproducibility studies and determination of the temperature of maximum rate of crystallization.
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
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1. R e p r o d u c i b i l i t y . A s stated above, o b s e r v a t i o n s of the o v e r a l l rate of c r y s t a l l i z a t i o n of c r y s t a l l i n e p o l y e p i c h l o r o h y d r i n s t u r n e d out to be a p a r t i c u l a r l y s e n s i t i v e was of c h a r a c t e r i z i n g polyepichlorohydrins. T h u s , we have taken s p e c i a l c a r e to c h e c k the r e p r o d u c i b i l i t y of o u r d i l a t o m e t r i c o b s e r v a t i o n s of o v e r a l l r a t e s . We have c a r r i e d out three d i f f e r e n t kinds of a n a l y s i s to c h e c k r e p r o d u c i b i l i t y . F i r s t , we s h o w e d that the data f r o m a n y given d i i a t o m e t e r w e r e s u p e r i m p o s a b l e o v e r the whole range on r e p e a t e d runs at the s a m e t e m p e r a t u r e . T h i s was t r u e f o r both " s l o w " a n d " f a s t " c r y s t a l l i z i n g p o l y m e r s . Second, we d e m o n s t r a t e d that two d i f f e r e n t s a m p l e s of the s a m e p o l y m e r i n two d i f f e r e n t d i l a t o m e t e r s gave r e p r o d u c i b i l i t y of t i m e a s u r e ments o v e r the whole t e m p e r a t u r e range studied. F i n a l l y , we showed that good s u p e r p o s i t i o obtained a t d i f f e r e n t c r y s t a l l i z a t i o d u c i b i l i t y is t y p i c a l of d i l a t o m e t r i c r e s u l t s on c r y s t a l l i n e p o l y m e r s i n g e n e r a l (11). F r o m these studies we conclude that c r y s t a l l i n e polyepichlorohydrin c r y s t a l l i z e s in a n o r m a l r e p r o d u c i b l e m a n n e r . T h e v a r i a t i o n s r e p o r t e d below a r e due to d i f f e r e n c e s i n the p o l y m e r s * 28,
3
Figure 6. Comparison of spherulite growth rates at 50°C after melting at 150°C. Ο = Type I spherulites from 329C. • = Type II spher ulites from 39A.
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
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2. D e t e r m i n a t i o n of the m a x i m u m rate of c r y s t a l l i z a t i o n . T h e rate of c r y s t a l l i z a t i o n of any g i v e n p o l y m e r i s v e r y s e n s i t i v e to the t e m p e r a t u r e a t w h i c h the m e a s u r e m e n t i s c a r r i e d out (11). It goes t h r o u g h a m a x i m u m at a f a i r l y w e l l - d e f i n e d t e m p e r a t u r e . A b o v e that t e m p e r a t u r e , as the m e l t i n g t e m p e r a t u r e i s a p p r o a c h ed, the rate of n u c l e a t i o n i s l o w e r a n d l o w e r a n d the o v e r a l l rate d e c r e a s e s . B e l o w that t e m p e r a t u r e as the g l a s s t r a n s i t i o n tempe r a t u r e i s a p p r o a c h e d , the m e l t b e c o m e s i n c r e a s i n g l y v i s c o u s , the rate of d i f f u s i o n of the p o l y m e r chains d e c r e a s e s , and a slowe r o v e r a l l c r y s t a l l i z a t i o n rate is obtained. Therefore, in order to m a k e m e a n i n g f u l c o m p a r i s o n s of p o l y m e r s p r e p a r e d u n d e r d i f f e r e n t conditions i t was n e c e s s a r y to d e t e r m i n e the e f f e c t of t e m p e r a t u r e on the c r y s t a l l i z a t i o n rate of e p i c h l o r o h y d r i n . We have e x a m i n e d the rat ent p o l y e p i c h l o r o h y d r i n S o m e of o u r m o r e t h o r o u g h studies a r e i l l u s t r a t e d i n F i g u r e 7. A s the f i g u r e i l l u s t r a t e s , the m a x i m u m rate of c r y s t a l l i z a t i o n
Figure 7. Effect of temperature on the crystallization rate of polyepichlorohydrin
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
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(lowest t i ) o c c u r s at about 5 0 ° C . T h e r e a r e s e v e r a l i n t e r e s t i n g a n d u n u s u a l f e a t u r e s about c r y s t a l l i z a t i o n r a t e s of p o l y e p i c h l o r o h y d r i n i l l u s t r a t e d i n F i g u r e 7. E v i d e n t l y , t h e r e a r e not one o r even two p o l y e p i c h l o r o h y d r i n s . Instead t h e r e i s a whole f a m i l y of c r y s t a l l i n e p o l y e p i c h l o r o h y d r i n s . T h e r e a r e the s l o w l y c r y s t a l l i z i n g " m e m b e r s of the f a m i l y l i k e 8 E . T h e s e p o l y m e r s have a r e l a t i v e ly s h a r p m a x i m u m and a n i n t e r m e d i a t e m e l t i n g t e m p e r a t u r e . T h e y c r y s t a l l i z e too s l o w l y and have too n a r r o w a p r o c e s s i n g range to be u s e f u l f o r , say, m o l d e d a r t i c l e s . T h e r e a r e the m e m b e r s with a n " i n t e r m e d i a t e " r a t e of c r y s t a l l i z a t i o n l i k e 100Z. T h e s e p o l y m e r s s u r p r i s i n g l y have a s o m e w h a t l o w e r melting temperature. T h e y too have a r a t h e r s h a r p m a x i m u m in the rate v e r s u s t e m p e r a t u r to p r o c e s s w e l l o v e r a " f a s t c r y s t a l l i z i n g " m e m b e r s , i l l u s t r a t e d by 2413 and 2431. T h e s e p o l y m e r s have the h i g h e s t m e l t i n g t e m p e r a t u r e s we have o b s e r v e d so f a r and a b r o a d m a x i m u m i n rate v e r s u s t e m p e r a t u r e c u r v e that suggests a b r o a d p r o c e s s i n g range. T h e " f a s t c r y s t a l l i z i n g " p o l y m e r s a l s o have the h i g h e s t o p t i c a l r o t a t i o n s that we o b s e r v e d . T h e y c r y s t a l l i z e i n the f o r m of T y p e II s p h e r u l i t e s . We have studied m a n y e x a m p l e s of e a c h type of polymer. F r o m the c u r v e s and the i n t r i n s i c v i s c o s i t i e s g i v e n f o r the p o l y m e r s , i t a p p e a r s that i n the range studied, i n t r i n s i c v i s c o s ity does not have a n i m p o r t a n t effect on c r y s t a l l i z a t i o n rate. A n a p p a r e n t a n o m a l y i l l u s t r a t e d by the data i n F i g u r e 7 i s the r e l a t i o n s h i p o r r a t h e r l a c k of r e l a t i o n s h i p between the o b s e r v e d rate and the m e l t i n g t e m p e r a t u r e . U s u a l l y a l o w e r m e l t i n g t e m p e r a t u r e c o r r e s p o n d s to g r e a t e r s t r u c t u r a l i r r e g u l a r i t y a n d s l o w e r c r y s t a l l i z a t i o n rate (11). In this c a s e 329C has a l o w e r m e l t i n g t e m p e r a t u r e than 8 E and yet c r y s t a l l i z e s m u c h m o r e r a p i d l y . T h e s e o b s e r v a t i o n s a r e d i s c u s s e d below and an e x p l a n ation is g i v e n . ff
3. O v e r a l l c r y s t a l l i z a t i o n rate of blends of " f a s t " a n d " s l o w " c r y s t a l l i z i n g p o l y m e r s . We obtained f u r t h e r e v i d e n c e that the g r e a t e r ease of n u c l e a t i o n of o p t i c a l l y a c t i v e p o l y m e r into T y p e II s p h e r u l i t e s is r e s p o n s i b l e f o r the o b s e r v e d i n c r e a s e i n c r y s t a l l i z a t i o n rate by s t u d y i n g s o l u t i o n blends of 2413 and a nonopti c a l l y a c t i v e p o l y e p i c h l o r o h y d r i n . We found that a d d i t i o n of only 6% of 2413 r e d u c e d the t i a t 5 0 ° C of the 'slow" p o l y m e r f r o m 32 m i n to l e s s than 10 m i n .
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D i s c u s s i o n and Conclusions P o l y m e r i z a t i o n of m o n o m e r s l i k e e p i c h l o r o h y d r i n , O C H — ( C H C l ) , l e a d s to p o l y m e r s w h i c h t h e o r e t i c a l l y c a n have m a n y d i f f e r e n t i s o m e r s . A s a r e s u l t of the v e r y elegant w o r k of P r i c e and c o w o r k e r s (12) a n d of V a n d e n b e r g (13) i n t h e i r m e c h a n i s t i c s t u d i e s of the r i n g opening p o l y m e r i z a t i o n of epoxides, the task of a n a l y z i n g these p o l y m e r s i s s o m e w h a t s i m p l i f i e d . F o r exa m p l e , head-to-head, t a i i - t o - t a i l , and h e a d - t o - t a i l p o l y m e r s a r e a l l t h e o r e t i c a l l y p o s s i b l e , but only h e a d - t o - t a i l need to be c o n s i d e r e d f o r the f o l l o w i n g r e a s o n s . We know that p o l y m e r i z a t i o n o c c u r s by r i n g opening i n w h i c h the bond between o x y g e n a n d the c a r b o n l a b e l l e d w i t h a n a s t e r i s k (the a s y m m e t r i c c a r b o n atom) is b r o k e n . F u r t h e r m o r e kno f r o studie with o p t i c a l l active propyleneoxide the a s y m m e t r i c c a r b o n and that no r a c e m i z a t i o n o c c u r s on p o l y m e r i z a t i o n . We a l s o know that e v e n when o p t i c a l l y a c t i v e monom e r i s used, s o m e a m o r p h o u s p o l y m e r i s p r o d u c e d . P r i c e a n d c o w o r k e r s (7) have found that these i r r e g u l a r i t i e s a r e l a r g e l y , i f not e n t i r e l y units of head-to-head, t a i l - t o - t a i l s t r u c t u r e f o r m e d as a r e s u l t of s o m e r e a c t i o n i n v o l v i n g c l e a v a g e of the bond c o r r e s p o n d i n g to the C H -O bond i n e p i c h l o r o h y d r i n . In a d d i t i o n we know that a l l c r y s t a l l i n e p o l y e p o x i d e s known to date a r e i s o t a c t i c . S y n d i o t a c t i c p o i y e t h e r s r e m a i n a p r o d u c t of the f u t u r e . 3
2
2
A l t h o u g h s i m i l a r s t u d i e s have not been r e p o r t e d f o r p o l y e p i c h l o r o h y d r i n , there i s no r e a s o n to e x p e c t any d i f f e r e n c e s i n m e c h a n i s m of p o l y m e r i z a t i o n f o r this epoxide. It c a n be a s s u m ed that p o l y m e r i z a t i o n l e a d i n g to c r y s t a l l i n e p o l y m e r o c c u r s p r e d o m i n a n t l y by i n v e r s i o n a t the a s y m m e t r i c c a r b o n a t o m a n d r e s u l t s i n h e a d - t o - t a i l p l a c e m e n t of the m o n o m e r . M a i n l y i s o t a c t i c p o l y m e r w i l l be f o r m e d . O u r s t u d i e s a n d p r e v i o u s w o r k have b o r n this out (8, 9, 14, 15). T h e r e s u l t s of this study f u r t h e r r e v e a l that the c r y s t a l l i n e p o l y e p i c h l o r o h y d r i n we have s t u d i e d c o n s i s t s of i s o t a c t i c s e q u e n c e s that c a n c r y s t a l l i z e i n the f o r m of two d i f f e r e n t kinds of s p h e r u l i t e s . We have shown that the two kinds of s p h e r u l i t e s c a n c o c r y s t a i l i z e . A t p r e s e n t o u r e d u c a t e d guess is that a l l the p o l y m e r s we have e x a m i n e d c o n t a i n e i t h e r T y p e I o r a m i x t u r e of T y p e I a n d T y p e II s p h e r u l i t e s in v a r y i n g p r o p o r t i o n s . The p o l y m e r s that c r y s t a l l i z e m o s t r a p i d l y a n d that have the h i g h e s t m e l t i n g t e m p e r a t u r e s have s o m e o p t i c a l a c t i v i t y a n d t h e i r f i l m s c o n t a i n p r e d o m i n a n t l y T y p e II s p h e r u l i t e s . We c o n c l u d e that the T y p e II s p h e r u l i t e s a r e obtained f r o m o p t i c a l l y a c t i v e p o l y m e r s e q u e n c e s . We do not m e a n to i m p l y that a l l s e q u e n c e s i n these
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
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p o l y m e r s have the s a m e c o n f o r m a t i o n . We m e r e l y w i s h to s u g g e s t that enough of an e x c e s s of one e n a n t i o m e r has p o l y m e r i z e d to give a m e a s u r a b l e r o t a t i o n and that the o v e r a l l s t r u c t u r e of these p o l y m e r s is m o r e r e g u l a r . We s u g g e s t that T y p e I s p h e r u l i t e s a r e obtained f r o m r a c e m i c p o l y m e r that shows l i t t l e o r no o p t i c a l r o t a t i o n . It is unfortunate f r o m a t h e o r e t i c a l point of v i e w that o u r c o n c l u s i o n s cannot be d e f i n i t e l y r e l a t e d to the d e g r e e of o p t i c a l a c t i v i t y i n the p o l y m e r . T o a c c o m p l i s h this we would need to p r e p a r e p o l y m e r of known and v a r i a b l e a m o u n t s of o p t i c a l r o t a tion, p r e f e r a b l y f r o m o p t i c a l l y a c t i v e m o n o m e r . T h i s we have not done. H o w e v e r , we b e l i e v e that o u r r e s u l t s a r e s u f f i c i e n t l y c o n c l u s i v e e v e n without this c o m p a r i s o n . P o l y m e r s of l o w e r m e l t i n g t e m p e r a t u r e ca having a higher meltin a l l y and m o r p h o l o g i c a l l y d i f f e r e n t . R a c e m i c p o l y m e r c r y s t a l l i z e s i n the f o r m of T y p e I s p h e r u l i t e s . A s long as the p o l y m e r has a s u f f i c i e n t l y low c o n c e n t r a t i o n of a t a c t i c s e q u e n c e s , f a i r l y r a p i d c r y s t a l l i z a t i o n c a n o c c u r . H o w e v e r , the r a t e w i l l be s l o w e r than that of p o l y m e r s that l e a d to T y p e II s p h e r u l i t e s . The f r e e e n e r g y b a r r i e r to n u c l e a t i o n of T y p e II s p h e r u l i t e s s e e m s to be l o w e r . P o l y m e r c o n t a i n i n g s o m e o p t i c a l l y a c t i v e s e q u e n c e s c r y s t a l l i z e m o s t r a p i d l y p r i m a r i l y b e c a u s e the rate of n u c l e a t i o n is g r e a t e r . A n i n c r e a s e d r a t e of n u c l e a t i o n c o m b i n e d w i t h the d e m o n s t r a t e d p o t e n t i a l of c o c r y s t a l l i z a t i o n of T y p e I and T y p e II s p h e r u l i t e s a l s o p r o v i d e s an e x p l a n a t i o n f o r the u s e f u l n e s s of f a s t c r y s t a l l i z i n g p o l y e p i c h l o r o h y d r i n i n i n c r e a s i n g the rate of c r y s t a l l i z a t i o n of s i o w c r y s t a l l i z i n g p o l y e p i c h l o r o h y d r i n . In fact, t h e r e is a d i r e c t p a r a l l e l to s o m e of o u r f i n d i n g s r e p o r t e d i n the c a s e of c r y s t a l l i n e p o l y p r o p y l e n e o x i d e , which is s t r u c t u r a l l y the s a m e as p o l y e p i c h l o r o h y d r i n excep t that the c h l o r i n e a t o m on the pendant m e t h y l e n e substituent is r e p l a c e d by a h y d r o g e n atom. Two kinds of s p h e r u l i t e s have b e e n o b s e r v e d in c r y s t a l l i n e p o l y p r o p y l e n e o x i d e (14 ). The two w e r e not shown to c o c r y s t a l l i z e . f T
M
n
n
A ck now ledge me nt I a m e s p e c i a l l y indebted to M. P. D r e y f u s s, M. L . D a n n i s , and R. W. S m i t h f o r h e l p f u l d i s c u s s i o n s at c r i t i c a l points i n this study. I a m g r a t e f u l to P. S. N e a l f o r a s s i s t a n c e with s o m e of the e x p e r i m e n t a l work. I w i s h to thank H. A. T u c k e r and C. A. M a r s h a l l f o r p r o v i d i n g the p o l y m e r s u s e d i n this study and M. H. L e h r f o r s h a r i n g the r e s u l t s of h i s study of the m e c h a n i c a l p r o p e r t i e s of the p o l y m e r s .
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
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Summary The purposes of this study were to determine what chemical and physical structures are present in polyepichlorohydrin and to correlate these structures with the crystallization rates ob served microscopically and dilatometrically. Crystallization rates were shown to be an extremely sensitive way of character izing these polymers. F o r example, the study revealed that the crystalline polyepichlorohydrins examined consisted of isotactic sequences that can crystallize as two different kinds of spheru lites, arbitrarily called Type I and Type II. The two types can cocrystallize. The polymers that crystallize most rapidly and that have the highest melting temperature have some optical activity. Their films contain predominantly Type II spherulites. Polymers that contain little or no optical activity. These polymers are racemic mixtures. Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.
Bekkedahl, N., J. Research Nat'l. B u r . Standards, (1949), 43, 145. Tsuruta, Τ., Inoue, S., Yoshida, Ν., and Furukawa, J., Makromol. C h e m . , (1962), 53, 215. Tsuruta, Τ., Inoue, S. Yoshida, Ν., and Furukawa, J., (1962), 55, 230. Inoue, S., Tsuruta, T., and Yoshida, Ν., Makromol. Chem., (1964), 79, 34. Tsuruta, Τ., Inoue, S., Ishimori, Μ., and Yoshida, Ν., J . Polym. Sci., C. (1963), (No. 4), 267. Tsuruta, Τ., Macromolecular Reviews, J . Polym. Sci., D, (1972), 179. P r i c e , C. C., and Osgan, M., J. A m . Chem. Soc., (1956), 78, 4787. Kambara, S. and Takahashi, A., Makromol. C h e m . , (1963), 63, 89. Richards, J. R., P h . D . Thesis, University of Pennsylvania, 1961, P a r t III, University M i c r o f i l m s , 61-3547. Magill, J. Η., Makromol. C h e m . , (1965), 86, 283. Mandelkern, L., "Crystallization of Polymers," McGraw - H i l l Book Co., New York, Ν. Υ., 1964. P r i c e , C. C., and Spector, R., J. A m . Chem. Soc., (1965) 87, 2069. Vandenberg, E. J., J. Polym. Sci., A-1, (1969), 7, 525.
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14. Perego, G., and C e s a r i , Μ., Makromol. Chem., (1970), 133, 133. 15. Hughes, L. J., Dangieri, T. J., Watros, R. G., and A i l i n g , J., Polymer Preprints, (1968), 9, 1126.
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6 X-ray Structural Analysis of Crystalline Polymers RICHARD J. CELLA* and ROBERT E. HUGHES Department of Chemistry, Cornell University, Ithaca, Ν. Y. 14853
The d e t e r m i n a t i o talline polymers by wide a n g l e X - r a y diffraction tech n i q u e s p r e s e n t s f o r m i d a b l e problems w h i c h cannot c o n v e n i e n t l y be t r e a t e d by the c o n v e n t i o n a l methods of structure analysis. Consequently, existing methods need t o be m o d i f i e d and new approaches t o the p r o b l e m d e v e l o p e d t o e x t r a c t the maximum amount of s t r u c t u r a l i n f o r m a t i o n f r o m the a v a i l a b l e e x p e r i m e n t a l d a t a . The n a t u r e of the problems e n c o u n t e r e d will be d i s c u s s e d i n this p a p e r , t o g e t h e r w i t h a description of methods t h a t have been utilized t o overcome them. A subsequent p a p e r will d e a l w i t h the a p p l i c a t i o n s o f t h e s e methods to the d e t e r m i n a t i o n of the m o l e c u l a r s t r u c t u r e of several crystalline polyethers. Characteristically, c r y s t a l s composed of l o n g c h a i n m o l e c u l e s p r o v i d e much l e s s diffraction d a t a than do s i n g l e c r y s t a l s of low m o l e c u l a r weight s u b s t a n c e s , and o f t e n t h i s d a t a i s of v e r y p o o r quality. This i s a d i r e c t consequence of the limited l o n g range o r d e r e x h i b i t e d by crystalline polymers; small crystallite size, imperfect crystallite orientation, structural d e f e c t s , and the p r e s e n c e of a non-crystalline compo nent in the sample all c o n t r i b u t e t o the r a p i d a t t e n u a tion of the a v a i l a b l e d a t a . The first of these deficiencies, the l i m i t e d l o n g range t h r e e d i m e n s i o n a l o r d e r , i s the s i n g l e most i m p o r t a n t f a c t o r i n v o l v e d in c r e a t i n g the difficulties e n c o u n t e r e d i n the structural a n a l y s i s of macromolecular m a t e r i a l s . The g r e a t l e n g t h of the polymer c h a i n s and the concomitant possibilities f o r chain entangle ments prohibit the m o l e c u l e s from o r d e r i n g themselves *E. I . du Pont de Nemours and Company, ton, Delaware 19898
Inc.,
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86 In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
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over an extended region w i t h a h i g h degree o f r e g u l a r i t y . Furthermore, the i n d i v i d u a l molecules themselves are not p e r f e c t l y r e g u l a r , and often c o n t a i n i n t r i n s i c s t r u c t u r a l defects such a s s t e r i c inversions o f asym metric sites, c h a i n branches, and c r o s s l i n k s . Such d e f e c t s d on o t n e c e s s a r i l y p r e v e n t t h e c h a i n f r o m becoming i n c o r p o r a t e d into a c r y s t a l l i n e domain; often times a molecule c o n t a i n i n g a minor s t r u c t u r a l imper f e c t i o n w i l l manage t opack reasonably w e l l into the s t r u c t u r e , thereby e n l a r g i n g the c r y s t a l l i n e domain but at the same time d e s t r o y i n g the p e r f e c t r e g u l a r i t y o f the assemblage. Another type o fp a c k i n g defect occurs when a "multi-state s t r u c t u r e i s p o s s i b l e . This happens when each successive c h a i n may enter the c r y s t a l l i t e i n any of several s p a t i a l l a c h a i n may b eaccommodate e i t h e r a n ' u p " o ra " d o w n " p o s i t i o n a t w o - s t a t e s t r u c ture w i l l r e s u l t ; i fa side group may assume any o f t h r e e d i f f e r e n t a n g u l a r p o s i t i o n s i nt h e s o l i d phase, then a three-state s t r u c t u r e i sp o s s i b l e . These defects may occur s p o r a d i c a l l y w i t h low p r o b a b i l i t y o r they may occur randomly each time the o p p o r t u n i t y p r e s ents i t s e l f . I nt h e l a t t e r c a s e i ti sl i k e l y t h a t a s t a t i s t i c a l d i s t r i b u t i o n o f several d i f f e r e n t models w i l l h a v e t o b e i n v o k e d i no r d e r t o o b t a i n s a t i s f a c t o r y agreement t othe experimental data. Each o fthe s t r u c t u r a l defects described w i l l tend to attenuate the i n t e n s i t y o f the d i f f r a c t e d beam a t higher s c a t t e r i n g angles, and a s i t u a t i o n i s soon r e a c h e d i n w h i c h t h e s c a t t e r e d b e a m i s o fl o w e r i n t e n s i t y than the background s c a t t e r i n g . This f a l l - o f f o f the d a t a a t h i g h e r s c a t t e r i n g a n g l e s i ss i m i l a r t o t h a t c a u s e d b yt h e r m a l m o t i o n a n d a t o m i c s c a t t e r i n g , but these phenomena also occur i n non-polymeric systems and can b ec o r r e c t e d f o r rather e a s i l y . The c y l i n d r i c a l l y symmetric d i s t r i b u t i o n o f c r y s t a l l i t e s about the f i b e r axis also leads t oa decrease i n the q u a n t i t y o fdata obtainable, although for a n e n t i r e l y d i f f e r e n t reason. The r o t a t i o n a l character o f the d i f f r a c t i o n p a t t e r n causes a l l l a t t i c e plans whose r e c i p r o c a l l a t t i c e points have the same ξ and ζ c o o r d i n a t e s t o d i f f r a c t i n t o t h e s a m e p o i n t i ns p a c e , i r r e s p e c t i v e o ft h e v a l u e o ft h e i r a n g u l a r r e c i p r o c a l l a t t i c e c o o r d i n a t e (l). T h i s l e a d s t o a no v e r l a p p i n g o f r e f l e c t i o n s which would otherwise b e d i s t i n g u i s h a b l e were i tnot f o r the c y l i n d r i c a l symmetry o f the p o l y meric f i b e r . Thus, i n many instances two or more independent r e f l e c t i o n s produce o n l y one observable d i f f r a c t i o n maximum. 1
1
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
88
POLYETKERS
I s o t a c t i c poly(propylene oxide), PPO, provides a n u m e r i c a l example of the above c o n s i d e r a t i o n s . U s i n g copper r a d i a t i o n , this polymer should i n p r i n c i p l e g e n e r a t e a p p r o x i m a t e l y 400 u n i q u e r e f l e c t i o n s (regard l e s s of whether or not t h e i r i n t e n s i t i e s are large enough to be measurable above background scattering) o u t t o a r e s o l u t i o n o f Ο.77 A. In p r a c t i c e ^ an a c t u a l f i b e r o f P P O y i e l d e d d a t a o u t t o o n l y Ο.97 A, thereby r e d u c i n g t h e p o t e n t i a l n u m b e r o f d a t a t o I78 r e f l e c tions; for this purpose, each allowable r e f l e c t i o n con t r i b u t i n g to an o v e r l a p p i n g group of r e f l e c t i o n s is counted separately, and a r e f l e c t i o n is counted whether or not i t is of s u f f i c i e n t i n t e n s i t y to be detectable. When the r o t a t i o n a l symmetry of the f i b e r specimen is taken into c o n s i d e r a t i o n and o v e r l a p p i n g r e f l e c t i o n s are counted as one o b s e r v a t i o n o n l y observations are to be expected. O i n t e n s i t y to be experimentally measurable above the background s c a t t e r i n g . This example d r a m a t i c a l l y i l l u s t r a t e s t h a t a t b e s t l e s s t h a n 25$ of the t h e o r e t i c a l l y a l l o w a b l e data may be observed, and of these less than two-thirds a c t u a l l y are observed. Furthermore, i t should be emphasized that i s o t a c t i c PPO is a polymer w h i c h y i e l d s a r e l a t i v e l y large amount of data, and many examples could be quoted i n which an even smaller f r a c t i o n of the data is a c t u a l l y obtained. The poor q u a l i t y of the data obtained is a conse quence of the imperfect alignment of the c r y s t a l l i n e domains w i t h respect to the f i b e r axis of the sample. The c r y s t a l l i t e s are not p e r f e c t l y u n i a x l a l l y oriented, and this m i s o r i e n t a t i o n causes the r e f l e c t i o n s from polymeric substances to appear as elongated arcs rather than as sharp, w e l l defined spots. Measuring the total, or integrated, i n t e n s i t y of these arcs proves to be extremely d i f f i c u l t , and even the simpler task of determining the peak i n t e n s i t y is subject to large e r r o r (2). F u r t h e r m o r e , a l l c r y s t a l l i n e p o l y m e r s c o n t a i n a c e r t a i n amount of n o n - c r y s t a l l i n e m a t e r i a l which produces only diffuse s c a t t e r i n g and has the e f f e c t of i n c r e a s i n g the background l e v e l , thereby r e n d e r i n g even more d i f f i c u l t the process of measuring i n t e n s i t i e s . These two f a c t o r s t a k e n t o g e t h e r , therefore, are r e sponsible f o r the poor q u a l i t y of the data when com pared w i t h the accuracy achieved i n single c r y s t a l analyses. The c h a r a c t e r i s t i c features of polymer structures d e s c r i b e d above were d i s c u s s e d at some l e n g t h because they are almost wholly responsible f o r the d i f f i c u l t i e s encountered i n the s t r u c t u r a l analysis of these m a t e r i a l s . Many of the powerful methods existent f o r single
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
6.
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t a l studies are inadequate when d e a l i n g w i t h such m i t e d amount o fdata, and the poor q u a l i t y o f the merely serves t o i n t e n s i f y the problem. Thus, niques such a s d i r e c t methods, P a t t e r s o n synthesis, somorphous replacement are not a p p l i c a b l e t o p o l y c r y s t a l s t r u c t u r e analyses, and r e s o r t must b e made r i a l a n d e r r o r m e t h o d s t os e l e c t a r e a s o n a b l e t i n g s t r u c t u r e w h i c h must subsequently b e r e f i n e d . The standard technique for r e f i n i n g a proposed s t r u c t u r e i sa l e a s t s q u a r e s a n a l y s i s i n w h i c h the s t r u c t u r a l parameters are s y s t e m a t i c a l l y v a r i e d s o a s to produce the best agreement between the c a l c u l a t e d d i f f r a c t i o n p a t t e r n and the experimental data. When a p p l i e d t o the determination o fpolymer s t r u c t u r e s , however, t h i s method s u f f e r s f r o m two d e f i c i e n c i e s . T h e f i r s t o ft h e s e i s t h a t a l e a s t s q u a r e s refinement w i l l c o n v e r g e t ot h dimensional parameter space, and unless the proposed s t a r t i n g m o d e l i sq u i t e c l o s e t o t h e c o r r e c t s t r u c t u r e this w i l l not b e the g l o b a l minimum. Thus, the l e a s t squares approach w i l l often converge t oan i n c o r r e c t s t r u c t u r e . T h e s e c o n d s h o r t c o m i n g o ft h e l e a s t s q u a r e s method l i e s i nt h e p o o r d a t a t o p a r a m e t e r r a t i o g e n e r a l l y encountered i n polymer s t r u c t u r e s . T y p i c a l l y , the number o fparameters t ob er e f i n e d i n a polymeric s t r u c t u r e i so f t h e same o r d e r o f m a g n i t u d e a s t h a t f o u n d i ns m a l l m o l e c u l e s t r u c t u r e s , y e t t h e r e i s m u c h l e s s data w i t h w h i c h t owork. Consequently, i f one independently refines the atomic p o s i t i o n a l coordinates i n a d d i t i o n t o scale factors and thermal parameters the results w i l l b es t a t i s t i c a l l y meaningless. Thus, f o r these types o f s t r u c t u r e s i twould b eb e n e f i c i a l t o p o s s e s s c o m p u t a t i o n a l m e t h o d s w h i c h d on o t a l l o w a l l o f the atomic coordinates t ovary independently, but r a t h e r which couples them i n a meaningful way t o reduce the number o fparameters i n v o l v e d . The p r e c e d i n g d i s c u s s i o n has d e s c r i b e d the inadequacy o f standard c r y s t a l l o g r a p h i c methods when a p p l i e d to the determination o fpolymer s t r u c t u r e s . The l a c k of an a n a l y t i c a l method o fphase d e t e r m i n a t i o n makes t h e s o l u t i o n o ft h e s e s t r u c t u r e s a m a t t e r o ft r i a l and e r r o r ; t h e r e i sn oa l t e r n a t i v e b u t t o p o s t u l a t e various models and compare the t h e o r e t i c a l l y c a l c u l a t e d i n t e n s i t i e s t ot h o s e a c t u a l l y o b s e r v e d . I tw o u l d b e u s e f u l , therefore, t odevelop computational techniques whereby p h y s i c a l l y r e a l i s t i c models may b es y s t e m a t i c a l l y generated and evaluated i n a s t r a i g h t f o r w a r d , e f f i c i e n t manner. The problem d i v i d e s i t s e l f n a t u r a l l y into two d i s t i n c t parts: (1) t h e c a l c u l a t i o n o f g e o m e t r i c a l l y
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
POLYETHERS
90
a n d e n e r g e t i c a l l y a l l o w a b l e s t r u c t u r e s , a n d (2) the refinement of these s t r u c t u r e s to produce the b e s t agreement to the a v a i l a b l e X - r a y d a t a . Geometric
C o n s i d e r a t i o n s
It is not p o s s i b l e to r e l y s o l e l y on geometric arguments to determine a polymer s t r u c t u r e ; u l t i m a t e l y , recourse must be made to v a r i a t i o n a l methods. Geomet r i c c o n s t r a i n t s , however, are extremely u s e f u l i n e l i m i n a t i n g from c o n s i d e r a t i o n v a s t numbers of p h y s i c a l l y unreasonable s t r u c t u r e s , thereby r e d u c i n g the number of t r i a l models w h i c h need to be i n v e s t i g a t e d . A survey of the many substances whose m o l e c u l a r s t r u c tures have been e s t a b l i s h e d i n d i c a t e s that c e r t a i n s t r u c t u r a l features, namely bond lengths and bond angles, assume value any series of r e l a t e d compounds. On the other extreme, the i n t e r n a l r o t a t i o n angles about single bonds are free to assume a wide range of values, and i n most cases i t is not p o s s i b l e a p r i o r i to a s s i g n values to these parameters w i t h any degree of c e r t a i n t y (the r e l a t i v e i n v a r i a n c e of some m o l e c u l a r parameters i n r e l a t i o n to others is of course a d i r e c t consequence of the energetics i n v o l v e d i n e f f e c t i n g changes i n t h e i r v a lu es , but the problem is b e s t t r e a t e d from a p u r e l y geometric p o i n t of view). Thus, to a good approxima t i o n , i t is p o s s i b l e to assume values f o r the bond lengths and bond angles and to use these values i n the g e o m e t r i c a l d e t e r m i n a t i o n of the i n t e r n a l r o t a t i o n angles. Because of the s m a l l amount of d i f f r a c t i o n data a v a i l a b l e this p r a c t i c e is u n i v e r s a l l y followed i n polymer s t u d i e s , and i t is necessary i n order to reduce the a n a l y s i s to manageable p r o p o r t i o n s . If the data allows, i t w i l l be p o s s i b l e to v a r y these values s l i g h t l y at a l a t e r stage i n the s t r u c t u r a l d e t e r m i n a t i o n . Consider a l i n e a r polymer molecule whose s k e l e t a l a t o m s a r e n u m b e r e d 0 , 1, N, and represented by C , Gi, Cjp s u c c e s s i v e l y f r o m one end of the c h a i n to the other. Let r^ represent the v e c t o r from C i _ to C^ a n d l e t 0j_ r e p r e s e n t t h e s u p p l e m e n t o f t h e angle between r. and "?^ · The angle between the two planes determined by r ^ _ and r^, and r ^ and Γ^ , r e s p e c t i v e l y , is measured from the cis p o s i t i o n i n the d i r e c t i o n of clockwise r o t a t i o n of f a c i n g i n the d i r e c t i o n of r ^ . The c h a i n skeleton of a h e l i x w i t h two backbone atoms i n the r e p e a t i n g u n i t may be completely d e s c r i b e d by s p e c i f y i n g the two types of bond lengths, b = Q
1
+
1
1
+ 1
x
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
6.
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= ] Ï 3 - | = . . . = \r \ = ... and b = | r | = |r | = ... = | r j _ | = . .., the two t y p e s o f b o n d a n g l e s 0 i = 0 3 = . . . = 0 j _ = ... and 0 2 = 0 4 = ... = 0 i + i ···* ^ t h e t w o t y p e s o f d i h e d r a l a n g l e s τ.χ = τ = · . . . = τ ι = ... a n d τ = τ = ... T j _ = .... A l t e r n a t i v e l y , the h e l i c a l conformation i s u n i q u e l y determined b y s p e c i f y ing the bond lengths, the bond angles, the r o t a t i o n a l angle about the h e l i x axis, θ (unit twist), and the t r a n s l a t i o n a l distance along the h e l i x axis per repeat u n i t , d ( u n i t t r a n s l a t i o n ) ; t h e r e i so n l y one set o f d i h e d r a l a n g l e s , τχ and τ , c o m p a t i b l e w i t h t h e s e six q u a n t i t i e s . S i m i l a r l y , the s k e l e t a l conformation o fa three a t o m h e l i x i s u n i q u e l y d e t e r m i n e d b ys p e c i f y i n g the f o l l o w i n g q u a n t i t i e s : b i= | r i | = . . |rj_| = 2
±
2
4
+ 1
=
a n
-Ό(^Γ-*«ο(ξ)' w ε a e t t
here r i s the e q u i l i b r i u m i n t e r n u c l e a r distance and i s the i n t e r a c t i o n energy a tr . The values o f e nd r t obe u s e d f o r a g i v e n a t o m p a i r a r e determined m p i r i c a l l y by studying e s t a b l i s h e d s t r u c t u r e s and f i t i n g the e n e r g e t i c a l l u a l s t r u c t u r e by v a r y i n P o l a r i n t e r a c t i o n s may be i n c l u d e d e i t h e r by using a monopole approximation, which replaces p o l a r bonds b y p o i n t charges on the bonded atoms and then uses a Coulombic p o t e n t i a l , or b y the more i n v o l v e d treatment o f d e l R e (15-16). T h e l a t t e r m e t h o d u s e s a s e m i e m p i r i c a l quantum mechanical approach t o d i s t r i b u t e p a r t i a l charges throughout the molecule; i tthen uses a Coulombic p o t e n t i a l t oc a l c u l a t e the energies o f various charge p a i r s . When a p p l i e d t othe d e t e r m i n a t i o n o f c r y s t a l s t r u c t u r e s the program f i r s t generates the coordinates of the e n t i r e s t r u c t u r a l a r r a y i n accordance w i t h the given space group. I t then c a l c u l a t e s the p a c k i n g energy by i n c l u d i n g a l l p a i r w i s e i n t e r a c t i o n s (both p o l a r and non-bonded), i n c l u d i n g any d e s i r e d c o n t r i b u tions from s p e c i f i c terms such a st o r s i o n a l b a r r i e r s . The s t r u c t u r e i schanged by v a r y i n g any predetermined m o l e c u l a r o rs t r u c t u r a l p a r a m e t e r s a n d t h e e n e r g y i s r e c a l c u l a t e d . By proceeding i n this manner the program s e l e c t s the s t r u c t u r e w h i c h i s o fl o w e s t energy using the g i v e n degrees o ff r e e d o m . Even though the absolute e n e r g i e s c a l c u l a t e d may n o t b ee x a c t , the r e l a t i v e energies are extremely useful i n determining favorable s t r u c t u r e s . B y a p p l y i n g energy c a l c u l a t i o n s t othose s t r u c tures which are g e o m e t r i c a l l y allowable i ti s possible t o r e d u c e t h e n u m b e r o fp r o b a b l e s t r u c t u r e s t o m a n a g e able p r o p o r t i o n s . In g e n e r a l , two or more s t r u c t u r e s w i l l remain which are both e n e r g e t i c a l l y and geometric a l l y reasonable and the d i s t i n c t i o n among them must b e made on the b a s i s o fthe X - r a y d a t a . I f s u c c e s s f u l , however, the u t i l i z a t i o n o fgeometric and energetic c o n s t r a i n t s w i l l generate t r i a l s t r u c t u r e s which are Q
0
Q
ç
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
Q
6.
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quite close t othe a c t u a l structure, thereby the e f f i c i e n c y o fthe s t r u c t u r a l refinement S t r u c t u r a l
i n s u r i n g process.
Refinement
An extremely v e r s a t i l e computer program, POLYMIN, which i s designed s p e c i f i c a l l y f o r the s t r u c t u r a l refinement o fc r y s t a l l i n e polymers has been developed. It incorporates several features not found i n standard refinement programs and thereby eliminates many o f the d i f f i c u l t i e s encountered i n t h e i r use. The main advantages o fthe program are that i t : (a) uses l i n e search rather than l e a s t squares m i n i m i z a t i o n (b) maintains geometric and stereochemical constraint (c) u t i l i z e s overlapping and unobserved data in the refinement process. By using a line search minimizer rather than least squares the program does not require that t h e s t r u c t u r e t ob er e f i n e d b ec l o s e t o the c o r r e c t s t r u c ture i norder t oinsure convergence. U n l i k e a least squares treatment, the line search refinement w i l l not of necessity converge t othe nearest minimum, and thus i t has a higher p r o b a b i l i t y o ff i n d i n g the global minimum. The quantity being minimized, however, i s t h e same a sthat b e i n g minimized i nthe l e a s t squares approach: w
m
[
I
o (
m
)
-
I
c(
f f i
)
] 2 =
â
V * I ( m ) ]
2
w i t h w™
= s t a t i s t i c a l
m "fc I ( m )= c o r obs I (m) = c a l Q
c
=
s
dard recte ervat c u l a t
a n
weight
o fthe
m ^
1
observation
=
d e v i a t i o n o fthe m observation d observed i n t e n s i t y o fthe m^ ion e d i n t e n s i t y o fthe m observation 1
The main advantage o fusing this program, however, i s t h a t i t e n a b l e s a r e f i n e m e n t t ob e c a r r i e d o u t subj e c t t ogeometric c o n s t r a i n t s . B yv a r y i n g atomic coordinates a l e a s t squares procedure simultaneously changes bond lengths, bond angles, and d i h e d r a l angles. As stated p r e v i o u s l y , the minimal amount o f data obtainable from polymeric structures makes i t desirable to f i x the bond lengths and bond angles during the course o fa s t r u c t u r a l d e t e r m i n a t i o n i na d d i t i o n t o the h e l i c a l parameters θ and d . Consequently, while a l e a s t squares refinement TTreats the atomic p o s i t i o n s a s
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
96
POLYETHERS
independent parameters, t h e l i n e search refinement program couples the movement o fthe atoms, thereby p r e s e r v i n g the geometrical nature o fthe problem. POLYMIN has the a b i l i t y t orefine a s t r u c t u r e using any or a l l o fthe f o l l o w i n g parameters: fa) scale factors bo) r i g i d b o d y r o t a t i o n s a n d t r a n s l a t i o n s (c) i s o t r o p i c thermal parameters ( i n d i v i d u a l o r o v e r a l l ) id) bond lengths fe) bond angles If) d i h e d r a l angles (g) atomic m u l t i p l y i n g factors D u r i n g the course o fa refinement the parameters ( a ) , (b), (c), and ( f ) would n o r m a l l y b e v a r i e d ; i f t h e d a t a / p a r a m e t e r r a t i o i s f a v o r a b l e i tw o u l d b e p o s s i b l e to refine using ( d The atomic m u l t i p l y i n g factors, ( g ) ,a r e u s e f u l f o r studying m u l t i - s t a t e systems, where i t i s desirable t o d e t e r m i n e t h er e l a t i v e a b u n d a n c e s o f e a c h o f s e v e r a l d i f f e r e n t models. The program i sextremely w e l l suited for the d e t e r m i n a t i o n o fp o l y m e r s t r u c t u r e s i n i t st r e a t m e n t o f unobserved and o v e r l a p p i n g data. Standard l e a s t squares treatments assume that o n l y one r e f l e c t i o n con t r i b u t e s t oa n y g i v e n o b s e r v a t i o n ; due t othe c y l i n d r i c a l symmetry o ff i b e r d i f f r a c t i o n patterns a great many of t h e observations are a c t u a l l y s u p e r p o s i t i o n s o f two or more r e f l e c t i o n s . Under these circumstances t h e observed i n t e n s i t y must b ecompared t othe sum o f t h e c o n t r i b u t i n g c a l c u l a t e d i n t e n s i t i e s . Thus, i f £ i n d e pendent r e f l e c t i o n s contribute t othe nr* observation, then 1
A l ( m ) = I (m) - Σ I * (m) Q
11
where iS'(m) i s the c a l c u l a t e d i n t e n s i t y of the q* v t h r e f l e c t i o n c o n t r i b u t i n g t othe m observation. The treatment o funobserved data i s o f necessity d i f f e r e n t from that g i v e n t oobserved data. For these data there i s only a t h r e s h o l d i n t e n s i t y w i t h which t o compare the c a l c u l a t e d v a l u e , and i tbecomes necessary to define a number, f , such that fI (m) i s the most probable value o fthe observed i n t e n s i t y , where I (m) i s now t h e m i n i m u m i n t e n s i t y w h i c h the m** observation w o u l d h a v e t o d i s p l a y i n o r d e r t ob e d e t e c t a b l e above background s c a t t e r i n g ( i thas been shown that f=0.33 Q
0
1
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
6.
CELLA
Crystalline Polymers
A N D HUGHES
97
f o r a centrosymmetric space group). i n t e n s i t y i s lower than the t h r e s h o l d a g r e e m e n t i sc o n s i d e r e d t ob e p e r f e c t t i o n t othe l e a s t squares residue, § zero. I f ,h o w e v e r , the c a l c u l a t e d i n than the t h r e s h o l d value then § i sin a m o u n t w [I (m) - f I ( m ) ] . Thus, i n are l a r g e r Ohan the observable thresh used i n d r i v i n g the refinement t othe It has become customary i n X - r a y to describe the agreement between the c a l c u l a t e d s t r u c t u r e f a c t o r s b yu s i n g index, Rp, defined b y m
2
Q
ç
I fthe c a l c u l a t e d value then the and the c o n t r i b u , i st a k e n t o b e t e n s i t y i s l a r g e r cremented b y the t e n s i t i e s which old values are c o r r e c t structure. c r y s t a l l o g r a p h y observed and the r e s i d u a l
Σ| | F ( n ) l - | F ( n ) | | o
c
where η i sthe t o t a l number o fr e f l e c t i o n s (not the number o fobservations .). For purposes o fcomputing R ^ P O L Y M I N d i v i d e s I (m) u p i n t o £ p a r t s i n t h e r a t i o o f the c o n t r i b u t i n g c a l c u l a t e d i n t e n s i t i e s . By t a k i n g the s q u a r e r o o t o ft h e s e " o b s e r v e d and c a l c u l a t e d i n t e n s i t i e s |Fg(n)| and |Fp(n)| r e s p e c t i v e l y are obtained a n d u s e d m t h e c a l c u l a t i o n o fRp,. The terms c o n t r i b u t i n g t o t h e n u m e r a t o r a n d d e n o m i n a t o r o ft h e r e s i d u a l index are a s follows: (1) For observed r e f l e c t i o n s ||F (n)|-|F (n)| | i s a d d e d t o t h e n u m e r a t o r a n d | F ( n ) | i sa d d e d t o t h e denominator. (2) F o r unobservable r e f l e c t i o n s for which | F ( n ) | ^ | F ( n ) | t h e a g r e e m e n t i s t a k e n t ob e e x a c t and n o t h i n g i sa d d e d t o e i t h e r t h e n u m e r a t o r o rt h e denomi nator o fRp. These r e f l e c t i o n s are omitted from the c a l c u l a t i o n because t h e i r i n c l u s i o n could r e s u l t i n a m i s l e a d i n g l y l o w v a l u e f o r R-p. (3) For unobservable r e f l e c t i o n s for which |F (n)| < |F |n)| the numerator i sincremented b y I IF (n)| - !*8|F (n)|| and the denominator i s i n c r e m e n t e d b yf sI F ( n ) | . T h e c a l c u l a t i o n o f R i nt h i s f a s h i o n , while s l i g h t l y a r t i f i c i a l , leads t ovalues f o r the r e s i d u a l i n d e x w h i c h c a n b em e a n i n g f u l l y compared t o those v a l u e s f o u n d i nt h e l i t e r a t u r e . When used i n conjunc t i o n w i t h the large body o fc r y s t a l l o g r a p h i c knowledge a v a i l a b l e this number provides a useful c r i t e r i o n w i t h w h i c h t oa s s e s s the c o r r e c t n e s s o f the s t r u c t u r e . B y c o n v e n t i o n , R™ i s n o r m a l l y c a l c u l a t e d u s i n g only o b s e r v a b l e r e f l e c t i o n s a n d i ts h o u l d b e p o i n t e d out that adherence t oitems (2) a n d (3) a b o v e w i l l produce a v a l u e o fR w h i c h w i l l b ea tb e s t e q u a l t o t h a t 1
0
1 1
Q
c
0
0
c
0
c
c
0
p
F
F
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
=
Unobservable Reflections
if
m
0
SljJ(m)>I (m)
0
0
w [l (m)-ffilj(m)]
m
w [l (m)-|lj(m)]«
0
= 0 i f Zlj|(m)£l (m)
=
Observable Reflections
to $
0
c
c
o
0
c
0
c
0
= 0 i f |F (n)|*|F (n)|
Q
f*|F (n)|
= 0 i f |F (n)|i|F (n)|
=
i f |F (n)|>|F (n)|
o
Q
= |F (n)|
Denominator
Index
i f |F (n)|>|F (n)|
c
c
||F (n)|-|P (n)||
= ||F (n)|-f*|F (n)||
=
Numerator
Contribution to
to the Least Squares Residue and Residual
Contribution
Contributions
TABLE I
6.
CELLA
A N D HUGHES
Crystalline Polymers
99
c a l c u l a t e d i nt h e u s u a l w a y a n d w i l l m o s t l i k e l y b e s l i g h t l y l a r g e r . I tw a s f e l t , h o w e v e r , that the unob s e r v e d r e f l e c t i o n s a r e o fs u f f i c i e n t i m p o r t a n c e t o d e m a n d t h e i r i n c l u s i o n i n t o R-m w h e n t h e c a l c u l a t e d s t r u c t u r e factors are l a r g e r t h a n the threshold values. In other words, any s t r u c t u r a l model w h i c h p r e d i c t s i n t e n s i t y values above the threshold i n t e n s i t y f o r very m a n y o ft h e u n o b s e r v e d d a t a m u s t o fn e c e s s i t y b e i n c o r rect.. I ns i n g l e c r y s t a l w o r k , where t h o u s a n d s o f r e f l e c t i o n s are measurable, this c r i t e r i o n i s unneces sary, since any s t r u c t u r e which p r e d i c t s the observable data w i l l very l i k e l y also p r e d i c t the unobservable data. I na n a l y s i s i n v o l v i n g o n l y a l i m i t e d n u m b e r o f data, however, this may not b e the case and such miss ing data can then give p o s i t i v e s t r u c t u r a l i n f o r m a t i o n . C o n c l u s i o n This paper has described i n very general terms the u n i q u e p r o b l e m s e n c o u n t e r e d i nt h e d e t e r m i n a t i o n o f t h e molecular p a c k i n g i n polymeric c r y s t a l s . Standard c r y s t a l l o g r a p h i c procedures lose t h e i r u t i l i t y when d e a l i n g w i t h such problems, and a d d i t i o n a l information, such a s stereochemical c o n s t r a i n t s and p a c k i n g energies, s h o u l d b e b r o u g h t t o b e a r i nt h e p r o b l e m . F i n a l l y , a method o fs t r u c t u r a l r e f i n e m e n t w h i c h i s e s p e c i a l l y s u i t e d t op o l y m e r i c s t r u c t u r e s s h o u l d b eemployed i n p l a c e o fc l a s s i c a l l e a s t s q u a r e s m e t h o d s . A subsequent paper w i l l deal w i t h the a p p l i c a t i o n o fthese p r i n c i p l e s a n d t e c h n i q u e s t ot h e d e t e r m i n a t i o n o ft h e c r y s t a l structures o f s e v e r a l c r y s t a l l i n e p o l y e t h e r s . Acknowledgment The authors g r a t e f u l l y acknowledge the c o n t r i b u t i o n s o fP . W a r d a n d R . F l e t t e r i c k t o t h e development of the computer programs DIKED and POLYMIN. W e are a l s o p l e a s e d t oa c k n o w l e d g e f i n a n c i a l s u p p o r t through NIH Grant GM-148J2-02 and a d d i t i o n a l support through the M a t e r i a l s S c i e n c e C e n t e r a tC o r n e l l U n i v e r s i t y . Literature Cited 1. Buerger, M., "X-Ray Crystallography," John Wiley and Sons, Inc., New York, N.Y. (1962). 2. Cella, R. J., Lee, B., and Hughes, R. Ε., Acta Cryst., (1970), A26, (6). 3. Miyazawa, T., J. Polym. Sci., (1961), 55, 215. 4. Hughes, R. Ε. and Lauer, J. L., J. Chem. Phys., (1959), 30 (5), 1 1 6 5 . 5. McCullough, R., Polymer
Letters,
(1965),
3,
509.
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
100
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6. Shimanouski, T. and Mizushima, S., J. Chem. Phys., (1955), 23 (4), 707. 7. Sugeta, H. and Miyazawa, T., Biopolymers, (1967), 5, 673. 8. Kijima, H., Sato, T., Tsuboi, M., and Wada, Α., Bull. Chem. Soc. Jap., (1967), 40, 2544. 9. Nagai, K. and Kobayashi, M., J. Chem. Phys., (1962), 36 (5), 1268. 10. Nemethy, G. and Scheraga, H., Biopolymers, (1965), 3, 155. 11. Scott, R. A. and Scheraga, H., J. Chem. Phys., (1966), 45, 2091. 12. Ooi, T., Scott, R., Vanderkooi, G., and Scheraga, H., J. Chem. Phys., (1967), 46, 4410. 13· DeSantis, P., Giglio, E., Liquori, Α., and Ripamonti, Α., J. Polym. Sci., (1963), 14. Liquori, Α., J. Polym. 12, 209. 15. Del Re, G., Theor. Chim. Acta, (1963), 1, 188. 16. Del Re, G., Rev. Mod.
Sci., Phys.,
(1966), (1965),
Part 34,
C, 604.
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
No.
7 Coordination Polymerization of Trimethylene Oxide E.
J.
VANDENBERG
and
A.
E.
ROBINSON*
Research Center, Hercules Inc., Wilmington, Del. 19899
INTRODUCTION General The p o l y m e r i z a t i o n o f oxetanes with c a t i o n i c c a t a l y s t s has been s t u d i e d by many i n v e s t i g a t o r s . (1) (2) Rose(3) i n p a r t i c u l a r , first reported the homopolymerization o f the parent compound, trimethylene oxide (TMO), with a Lewis a c i d c a t a l y s t , boron trifluoride. The use o f c o o r d i n a t i o n c a t a l y s t s to polymerize oxetanes has been reported i n the patent l i t e r a t u r e by Vandenberg. (4) In t h i s work, Vandenberg polymerized oxetanes with the aluminum trialkyl-water-acetylacetone c o o r d i n a t i o n c a t a l y s t ( r e f e r r e d t o as chelate c a t a l y s t ) that he discovered f o r epoxide polymerization(5). This paper d e s c r i b e s the homo- and co-polymerization o f TMO with these c o o r d i n a t i o n c a t a l y s t s . S p e c i f i c TMO copolymers, p a r t i c u l a r l y with unsaturated epoxides such as allyl g l y c i d y l ether (AGE), are shown t o provide the b a s i s f o r a new f a m i l y o f p o l y e t h e r elastomers. These new elastomers are compared with the r e l a t e d propylene o x i d e - a l l y l g l y c i d y l ether (PO-AGE) copolymer elastomers. The historical development and general characteristics o f p o l y e t h e r elastomers and, in particular, the propylene oxide elastomers, are reviewed below. E a r l y Polyether Elastomer Studies Charles C. P r i c e played a p i o n e e r i n g r o l e i n the p o l y e t h e r elastomer f i e l d ( 6 ) . In 1948, as reported in his 1961 Chemist article, P r i c e recognized t h a t an oxygen chain atom would c o n t r i bute g r e a t l y t o chain flexibility and thus enhance elastomeric behavior, p a r t i c u l a r l y s i n c e such polyethers should have low Hercules Research Center C o n t r i b u t i o n No. 1645 * Current address: Hercules Incorporated, Bacchus Works, Magna, Utah 84044
101
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
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cohesive energy between chains. At t h a t time, he suggested t h a t poly(propylene oxide) should be a s u p e r i o r elastomer but unfor t u n a t e l y soon found that the known methods o f p o l y m e r i z i n g pro pylene oxide gave o n l y low polymers, not the d e s i r e d high polymer. However, he q u i c k l y devised a simple way around t h i s impasse, i . e . , the polyurethane approach, which c o n s i s t e d o f making a pro pylene oxide adduct o f a p o l y o l and then r e a c t i n g t h i s polyfunct i o n a l p o l y e t h e r with a d i i s o c y a n a t e t o give a p o l y e t h e r urethane network. T h i s approach t o p o l y e t h e r elastomers was p r o t e c t e d by a U.S. p a t e n t ^ which r e c e n t l y r e c e i v e d the C r e a t i v e Invention Award o f the American Chemical S o c i e t y . Although these p o l y e t h e r urethane elastomers proved t o be o f tremendous value i n foam rubber, the more conventional p o l y e t h e r elastomer based on a c r o s s - l i n k a b l e high polymer remained u n a v a i l a b l e . The l a t t e r r e q u i r e d the development o f new c a t a l y s t systems f o r polymerizing propylene oxide. The f i r s t improve polymer was the i r o n c a t a l y s t o f P r u i t t and B a g g e t t ® , i . e . , the simple r e a c t i o n product o f f e r r i c c h l o r i d e and propylene oxide. P r i c e and O s g a n ® recognized that t h i s i r o n c a t a l y s t i n v o l v e d a new p o l y m e r i z a t i o n mechanism—coordination p o l y m e r i z a t i o n - - i n which the propylene oxide coordinates with the i r o n atom before i n s e r t i o n i n t o the propagating polymer chain. P r i c e and Osgan a l s o discovered a new c o o r d i n a t i o n c a t a l y s t f o r polymerizing propylene oxide t o high polymer, i . e . , the aluminum isopropoxidez i n c c h l o r i d e c a t a l y s t systemOH?. In subsequent work with t h i s c o o r d i n a t i o n c a t a l y s t , P r i c e d e s c r i b e d the copolymerization o f PO with an unsaturated epoxide, such as butadiene monoxide(JLL). In the same time p e r i o d o f P r i c e ' s work, H i l l , B a i l e y and F i t z p a t r i c k o f Union Carbide Corporation developed some improved c a t a l y s t s f o r polymerizing ethylene oxide t o high p o l y m e r U ) . These new c a t a l y s t s i n c l u d e d improvements on the very e a r l y sys tems o f Staudinger, i . e . , strontium, calcium, and z i n c oxides and carbonates t i l ) , as w e l l as some new, even b e t t e r , systems based on calcium alkoxides (14) and a m i d e s ( 1 6 ) B a i l e y used the l a t t e r systems i n 1958 t o make water-soluble ethylene oxide-unsaturated epoxide copolymers (iD. V u l c a n i z a t e s o f these copolymers were very water s e n s i t i v e and thus not very u s e f u l i n the conventional elastomer area. In 1957, Vandenberg d i s c o v e r e d some e s p e c i a l l y e f f e c t i v e c o o r d i n a t i o n c a t a l y s t s f o r polymerizing epoxides t o high p o l y mers. Some o f these new c a t a l y s t s were the r e a c t i o n products o f organo-compounds o f aluminum, z i n c , and magnesium with w a t e r · An e s p e c i a l l y v e r s a t i l e system was the combination o f organoaluminums with water and a c e t y l acetone. These new c a t a l y s t s were much b e t t e r than e a r l i e r epoxide c a t a l y s t s , g i v i n g g e n e r a l l y higher r a t e s a t lower temperatures, h i g h e r molecular weight, and broader u t i l i t y . As a r e s u l t o f f i n d i n g these s u p e r i o r new c a t a l y s t s , Vandenberg was able t o make many new high polymers from epox2
β
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
7.
VANDENBERG
A N D ROBINSON
103
Trimethylene Oxide
ides (§) CjJ), i n c l u d i n g a wide spectrum o f new p o l y e t h e r e l a s t o mers. Some o f these new p o l y e t h e r elastomers have been commerc i a l i z e d , such as the e p i c h l o r o h y d r i n elastomers a v a i l a b l e from Hercules Incorporated under the trademark HERCLOi^and from B. F. Goodrich Chemical Co. a l i c e n s e e o f Hercules Incorporated, under the trademark HYDRIN. Very e a r l y i n t h i s work, Vandenberg a l s o made high molecular weight, l a r g e l y amorphous propylene oxideunsaturated epoxide copolymers and recognized i n unpublished s t u d i e s with A. E. Robinson t h e i r p o t e n t i a l value as improved elastomers. Subsequently, Gruber et a l . (12), f General T i r e , p u b l i s h e d d e t a i l e d p r o p e r t i e s o f s i m i l a r propylene oxide-unsaturated epoxide copolymer elastomers. Vandenberg a l s o f i l e d two patent a p p l i c a t i o n s on these copolymers. As a r e s u l t o f patent i n t e r f e r e n c e s i n v o l v i n g the Hercules a p p l i c a t i o n s , a Carbide patent, and a General T i r e a p p l i c a t i o n the l a s t a P r i c e a p p l i c a t i o n , and extensive subsequen p r i o r i t y . Two patents copolymers as new compositions o f m a t t e r ( _ ) (21) T h i s new type o f p o l y e t h e r elastomer i s commercially a v a i l a b l e from Hercules Incorporated under the trademark PARE I®. PAREL elastomer i s a s u l f u r - c u r a b l e copolymer o f propylene oxide and a l l y l g l y c i d y l ether. Some o f the key p r o p e r t i e s o f PAREL elastomer v u l c a n i z a t e s are summarized i n Table I. They have e x c e l l e n t low temperature p r o p e r t i e s ; e x c e l l e n t dynamic p r o p e r t i e s , which are much l i k e those o f n a t u r a l rubber; good ozone r e s i s t a n c e ; and good heataging r e s i s t a n c e . T h i s i n t e r e s t i n g combination o f p r o p e r t i e s i s leading to s u b s t a n t i a l s p e c i a l t y markets i n such a p p l i c a t i o n s as automotive engine mounts. V u l c a n i z a t i o n and s t a b i l i z a t i o n s t u d i e s on PAREL elastomer, as w e l l as a d d i t i o n a l s p e c i f i c p r o p e r t i e s o f PAREL elastomer, are reported i n t h i s book by Boss. The work described above f o r PO copolymers has been extended to the homo- and co-polymers o f oxetanes, p a r t i c u l a r l y TMO, and are reported i n t h i s paper. 0
m
Table I KEY PROPERTIES OF PAREL ELASTOMER VULCANIZATES - E x c e l l e n t low temperature p r o p e r t i e s - E x c e l l e n t dynamic p r o p e r t i e s ( l i k e n a t u r a l
rubber)
- Good ozone r e s i s t a n c e - Good heat aging r e s i s t a n c e EXPERIMENTAL Polymerization Studies General.
Reagents and general procedures f o r making
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
POLYETHERS
104
c a t a l y s t s , f o r running polymerizations and f o r c h a r a c t e r i z i n g polymers were the same as d e s c r i b e d p r e v i o u s l y ( 5 ) unless other wise noted. The c h e l a t e c a t a l y s t s were prepared by the general procedure p r e v i o u s l y given f o r t h i s c a t a l y s t ® . The unmodified EtgAl-O.S H2O c a t a l y s t was made by t h i s same procedure, i n the solvent noted i n Table I I I , by o m i t t i n g the a c e t y l acetone. Monomers. Commercial, p o l y m e r i z a t i o n grade monomers were used as r e c e i v e d . The sources were: ethylene oxide (E0), propy lene oxide (PO), and e p i c h l o r o h y d r i n (ECH) from Union Carbide Corp.; a l l y l g l y c i d y l ether (AGE) from S h e l l Chemical Corp.; butadiene monoxide (BMO) from PPG I n d u s t r i e s , Inc. (no longer commercially a v a i l a b l e ) ; and 3,3-bis(chloromethyl) oxetane (BCMO) from Hercules Incorporated (no longer commercially a v a i l a b l e ) . The other monomers d e s c r i b e d below were f i n a l l y p u r i f i e d by f r a c t i o n a t i o n i n a 25-50 p l a t e column at a 25:1 r e f l u x r a t i o . Trimethylene oxid Labs, was f r e e d o f wate ether and then f r a c t i o n a t e d (b.p. 4 8 ° C , η£ 1.3870). 3,3-Bis(allyloxymethyl) oxetane (BAMO) was prepared by adding BCMO (31.0 g., 0 . 2 mole) over 2 h r s . t o a mixture o f a l l y l a l c o h o l (23.2 g., 0.40 mole) and NaOH ( 1 6 . 0 g., 0.4 mole) i n dimethyl s u l f o x i d e (100 ml.) a t 50°C. A f t e r the mixture was heated f o r an a d d i t i o n a l 2 h r s . at 5 0 ° C , water was added, and the w a t e r - i n s o l uble f r a c t i o n recovered, d r i e d , and f r a c t i o n a t e d (b.p. 118°/10 mm., nj50 1.4538). 3,3-Dimethyloxetane was prepared from n e o p e n t y l g l y c o l by the procedure o f Schmoyer and C a s e ( 2 2 ) The f r a c t i o n a t e d product had: b.p. 8 1 ° C , nj* 1.3921. 9
0
Polymer I s o l a t i o n . The procedures used f o r the runs i n Tables II and I I I are given below. Unless otherwise noted, products were d r i e d a t 80°C. i n vacuo (0.4 mm.). Procedure A. Ether was added and then the product was washed twice with 3% HC1 (15 min. t o 1 h r . s t i r p e r wash), and then with water u n t i l n e u t r a l . The e t h e r - i n s o l u b l e ( i f any) was c o l l e c t e d , washed twice with ether and once with 0.05% Santonox i n ether and d r i e d as the e t h e r - i n s o l u b l e f r a c t i o n . The ethers o l u b l e was s t a b i l i z e d with 0.5% Santonox (based on t o t a l s o l i d s ) , the ether s t r i p p e d o f f , and the polymer d r i e d . In Run 7, Table I I I , the e t h e r - s o l u b l e was s t a b i l i z e d with 1% phenyl 3-naphthyl amine. Procedure B. Excess n-heptane (4-6 v o l s . ) was added and the heptane-insoluble polymer was c o l l e c t e d , washed once with heptane, washed once with 0.5% HC1 i n CH3OH, washed n e u t r a l with CH^OH, washed with 0.1% Santonox i n CH3OH, and then d r i e d . Run 5, which was used i n the v u l c a n i z a t i o n s t u d i e s , was s t a b i l i z e d with 1% phenyl 3-naphthyl amine.
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
7.
VANDENBERG
AND
Trimethylene
ROBINSON
Oxide
105
Procedure C. Product p r e c i p i t a t e d with 4 v o l s , o f τιheptane (ether i n Run 3, Table I I ) . The i n s o l u b l e was c o l l e c t e d , washed with η-heptane (or ether, i f used i n i t i a l l y ) , washed with 1% HC1 i n anhydrous ethanol, washed n e u t r a l with CH3OH, washed with 0.4% Santonox i n CH3OH and d r i e d . In Run 2, Table I I , the heptane-insoluble was not HC1 washed but i n s t e a d washed with 0.1% Santonox i n heptane and d r i e d . This product was then f u r t h e r sep arated by tumbling 1-gram i n 40 ml. o f H 0 overnight and then c o l l e c t i n g the w a t e r - i n s o l u b l e , washing with H2O, and d r y i n g . The water-soluble was recovered by s t r i p p i n g o f f the water and d r y i n g . 2
Procedure D. Excess ether was added, the e t h e r - i n s o l uble f r a c t i o n was c o l l e c t e d , washed with ether, washed with 0.5% HC1 i n 80-20 ether-methanol, washed n e u t r a l with 80-20 ethermethanol, washed with 0.4% Santonox i n ether and then d r i e d i n vacuo a t 50°C. Polymer C h a r a c t e r i z a t i o n . Inherent v i s c o s i t y was determined under the f o l l o w i n g c o n d i t i o n s : TMO-ECH copolymer, 0.1%, achloronaphthalene, 1 0 0 ° C ; other TMO and DM0 homo and copolymers 0.1%, CHC1 , 2 5 ° C ; TMO-P0-AGE terpolymer and PO-BCMO copolymer, 0.1%, benzene, 2 5 ° C ; BCMO homopolymer, 1.0%, cyclohexanone, 50°C. Unsaturated copolymers were analyzed f o r the unsaturated comonomer by Kemp Bromine No. ( i n CHCI3) (21) after correcting f o r the Bromine No. o f the a n t i o x i d a n t (Santonox, 125 and phenyl 3naphthyl amine, 143). C h l o r i n e - c o n t a i n i n g comonomers were deter mined by a c h l o r i n e a n a l y s i s . The composition o f the TMO-EO co polymers was determined by C and H a n a l y s i s . The PO content o f the TMO-PO-AGE terpolymer was determined by i n f r a r e d a n a l y s i s . The r e l a t i v e r e a c t i v i t y o f monomers i n copolymerization was c a l c u l a t e d from the f o l l o w i n g equation based on i d e a l copolymer ization. In [[ MM ii ll lο ri = 3
In [M ] t 2
where r ^ 2, [M^Jo monomers t i o n s at
i s the r e a c t i v i t y r a t i o o f monomer 1 r e l a t i v e t o monomer and [ M ] are i n i t i a l monomer concentrations o f 1 and 2, and [M-Jt and [ Μ ] ^ are the monomer concentra time t during the copolymerization. t
2
n
e
0
2
V u l c a n i z a t i o n Studies V u l z a n i z a t e s were prepared by conventional m i l l i n g and com pounding a t 100°F. followed by press c u r i n g according t o the f o r mula i n Table IV unless otherwise noted. The HAF carbon b l a c k was P h i l b l a c k 0 (N-330) o f P h i l l i p s Petroleum Co. A cure r a t e study i s given i n Figure 1. G e l / s w e l l data (wt. %) were deter-
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
106
POLYETHERS
mined i n cyclohexanone a f t e r 4 hours a t 80°C. Tests used t o evaluate v u l c a n i z a t e s were as f o l l o w s : ASTO Test Tensile D412 (miniature, 2 Die C dumbbell) Tear D624 (miniature Die C) Hardness D676 Bashore r e s i l i e n c e D2632 Yerzley oscillograph D945 Torsional r i g i d i t y D1043 Heat Build-up D623 Oven aging D573 Solvent Resistance D1460 ff
Table IV
Elastomer HAF Black ZnO Stearic Acid Sulfur Benzothiazyl d i s u l f i d e Tetramethyl thiuram d i s u l f i d e
10 50 5 1 2 1 2
Cured 30 min. a t 310°F.
CURE TIME - MINUTES AT
Figure
1.
310°F.
Effect of cure time on properties of elastomer
TMO-AGE
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
7.
VANDENBERG
RESULTS AND
AND
ROBINSON
Trimethylene Oxide
107
DISCUSSION
Polymerization S t u d i e s . TMO homopolymerization. The E t 3 A l - 0 . 5 H O - l . 0 acetylacetone c a t a l y s t polymerized TMO at 65°C. i n heptane d i l u e n t to a high conversion o f a very high molecular weight polymer ( n i h = 12), which was tough, rubbery, and c r y s t a l l i n e , with a 40°C. melting p o i n t (Table I I ) . The polymer was i n s o l u b l e i n η-heptane and methanol but s o l u b l e i n benzene and chloroform. T h i s homopolymer i s apparently s i m i l a r to t h a t prepared by R o s e ® with BF3 c a t a l y s t except t h a t the present product i s o f much higher molecu l a r weight and a l i t t l e h i g h e r m e l t i n g . Rose obtained an n i h o f 1.3 at 50°C. and 2.9 at -80°C. with a melting p o i n t o f 35°C. The p o l y m e r i z a t i o n o f TMO i s to be compared with that o f PO s i n c e the monomers an 2
n
n
(-CH CH CH -0-) 2
2
2
n
Eq. 1
TMO
Eq. 2 •0' PO On the b a s i s o f our p r i o r work on PO p o l y m e r i z a t i o n , with t h i s same c h e l a t e c a t a l y s t ® , TMO polymerizes about 10 times more slowly than PO does under the same c o n d i t i o n s . A l s o , the TMO homopolymer i s much l e s s s o l u b l e than poly(propylene o x i d e ) , s i n c e the l a t t e r polymer i s s o l u b l e i n heptane and methanol, both nonsolvents f o r p o l y f t r i m e t h y l e n e o x i d e ) . The TMO homopolymer i s , o f course, c r y s t a l l i n e because o f i t s very r e g u l a r s t r u c t u r e . On the other hand, the poly(propylene oxide) prepared with the c h e l a t e c a t a l y s t i s l a r g e l y amorphous because o f t a c t i c i t y and head-tot a i l v a r i a t i o n s i n s t r u c t u r e which are not p o s s i b l e i n p o l y ( t r i methylene o x i d e ) . T h i s TMO p o l y m e r i z a t i o n with the c h e l a t e c a t a l y s t no doubt i n v o l v e s coordinate propagation and i s the f i r s t such case o f coordinate propagation o f an oxetane. Heretofore, oxetanes have been c a t i o n i c a l l y polymerized. There are s e v e r a l reasons f o r concluding t h a t t h i s c h e l a t e c a t a l y s t system i s a c o o r d i n a t i o n p o l y m e r i z a t i o n . F i r s t , the very h i g h molecular weight obtained at e l e v a t e d temperature with a low r a t e i s c h a r a c t e r i s t i c o f c o o r d i n a t i o n p o l y m e r i z a t i o n r a t h e r than o f c a t i o n i c polymeriza t i o n . A l s o , Vandenberg's work on the c i s - and trans-2,3-epoxy-
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
PO AGE
BMO
AGE
45(g) 5(g)
9.4
5.6(f)
n-heptane
n-heptane
n-heptane
AGE
3
Toluene
n-heptane Toluene
92
82
82
92
42
92 92
Diluent Name ml.
ECH
EO
0 20
Comonomer Name
1.0
1.0
1.0
1.0
1.0 0.5 8 4
Catalyst A c e t y l Acetone mmoles per A l (Al Basis)
10
14
.7
7.5
19 12
Time hrs.
e
65
65
65
65
65
65 30
Temp. °C.
27
85 13
Total % Conv.
2
Heptane-insol.(h) Heptane-sol.(i)
Heptane ξ CHjOHinsol.(e)
Ether-insol.(d)
Ether-insol.(d) Ether-sol., Heptane-insol.(e)
Ether-insol.(b) Water-insol.(c) Water-sol. (c)
I s o l a t e d Polymer Procedure Fraction
28 20
89
71
23
5.6 10
67 1.4 12
% Conv.
5.3 4.1
13.5
15.4
8.1
3.3 1.0
12 11.0 6.5
Hjnh
PO AGE 58 10.0 60 9.3
6.5
4.4
12.6
12 55
44 8
% Co-m
(a) Based on 10 g. t o t a l monomer. See Experimental f o r i s o l a t i o n procedure. TMO » t r i m e t h y l e n e o x i d e , EO « ethylene o x i d e , ECH • e p i c h l o r o h y d r i n , AGE = a l l y l g l y c i d y l e t h e r , BMO = butadiene monoxide, and PO * propylene o x i d e . (b) Very s t r o n g , tough, o r i e n t a b l e rubber. C r y s t a l l i n e by x-ray (m.p. • 4 0 C ) . I n s o l u b l e i n H 0, n-heptane and CH3OH. S o l u b l e i n benzene and chloroform. (c) I s o l a t e d from i n i t i a l heptane and methanol-insoluble product. (d) Largely amorphous and rubbery. (e) Amorphous and rubbery. ( f ) 20% o f t o t a l comonomer added i n i t i a l l y , remainder added i n 6 equal p o r t i o n s a t 2-hr. i n t e r v a l s . (g) Added i n 5 equal p o r t i o n s a t 2-hr. i n t e r v a l s . (h) Tough, amorphous rubber ( i ) Tack/ rubber.
No.
T
P o l y m e r i z a t i o n o f TMO w i t h E t A l - 0 . 5 H?Q-Acetyl Acetone C a t a l y s t (a)
Table I I
ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
3
2
2.7
0.29
3.3
27
94
60
Heptane-and CHjOH-insol. Heptane- and CH*0H-insol.
Β
C
1.5
5.3 65
(a) Based on 10-g. t o t a l monomer. See Experimental f o r i s o l a t i o n d e t a i l s . TMO • t r i m e t h y l e n e o x i d e ; DMO «* 3,3-dimethyl oxetane; BAMO (allyl oxymethy1)oxetane. (b) Unless otherwise noted, c a t a l y s t prepared i n n-heptane w i t h 3 moles o f d i e t h y l e t h e r per aluminum. (c) Ether omitted frow c a t a l y s t p r e p a r a t i o n . (d) Most o f p o l y m e r i z a t i o n occurred i n a few minutes. (e) I n i t i a l l y a t a c k y rubber a f t e r d r y i n g a t 80 C. which s l o w l y c r y s t a l l i z e d t o Λ hard s o l i d o f c a . 50 C. m.p.; heptane-soluble. ( f ) Low c r y s t a l l i n i t y [poly(3,3-dimethyl oxetane) p a t t e r n ] ; heptane-soluble, (gj E t A l - u . S H 0-0.5 a c e t y l acetone c a t a l y s t . e
5.2 27 T o t a l polymer A
27
30
5
4 (g)
40
80
PO BGM0
8
1.3 92
T o t a l polymer (*)
A
92
0
0.08
4
32
n-heptane
90 10
DMO BAMO
7
A
100(d)
0
42
4
48
n-heptane
100
DMO
6
99
T o t a l polymer (e)
C
60
30
19
2 (c)
50
100
BCMO
5
50
6
2
42
Toluene
100
BCMO
4
51
30
2
4
83
Toluene
94 6
TMO BAMO
3
Β
29 47 78
30
0.5 2.0 23
5.5
4
66
48
Toluene
100
TMO
2
Heptane and CtUOH-insol.
Β
49 78
65
Hint*
0.25 2.3
I s o l a t e d Polymer % Conv.
4
48
Toluene
100
TMO
1
Fraction
Procedure
e
Total % Conv.
Catalyst(b) mmoles
Temp. C.
mU
Monomer 1 Name
No.
Time hrs.
Diluent Name
P o l y m e r i z a t i o n o f Oxetanes w i t h Et^Al-0.5 H?0 C a t a l y s t (a)
Table I I I
POLYETHERS
110
butanes c l e a r l y e s t a b l i s h e d t h a t the c h e l a t e c a t a l y s t operates by a c o o r d i n a t i o n mechanism and does not give c a t i o n i c polymerization I t i s perhaps s u r p r i s i n g t h a t TMO polymerizes ten times more slowly than PO, s i n c e i t i s a stronger base than PO by about 4 orders o f magnitude (24)
and thus i t should coordinate much more r e a d i l y with a metal. One explanation f o r the more f a c i l e p o l y m e r i z a t i o n o f PO i s that the g r e a t e r r i n g s t r a i n i n PO, compared with t h a t i n TMO, g r e a t l y f a c i l i t a t e s the r i n g opening propagation step with PO and more than compensates f o r i t s lower c o o r d i n a t i o n tendency because o f i t s lower base s t r e n g t h . TMO polymerizes much f a s t e r (about t e n - f o l d ) with the Et-jAlO.5H2O c a t a l y s t (Table I I I ) and s t i l l gives f a i r l y high molecular weight homopolymer. In t h i s case, based on Vandenberg's p r i o r work with the 2,3-epoxybutanes c a t i o n i c or c o o r d i n a t i o n expected t o be f a s t e r . A l s o , the lower s t e r i c hindrance a t propagation s i t e s with the unmodified organoaluminum-i^O should a l s o permit more f a c i l e c o o r d i n a t i o n and thus f a s t e r c o o r d i n a t i o n p o l y m e r i z a t i o n . The i n c r e a s e d Lewis a c i d c h a r a c t e r o f propagation s i t e s with the unmodified c a t a l y s t could a l s o enhance the coordina t i o n step and thus propagation. TMO Copolymerization With Saturated Epoxides. Copolymerizing TMO with ethylene oxide (EO) i n an 80:20 weight r a t i o with the c h e l a t e c a t a l y s t gave a water-soluble product (90% o f the t o t a l ) which contained only 8% TMO (Run 2, Table I I ) . On the b a s i s o f an i d e a l copolymerization, the EO i s estimated t o enter the copolymer i n t h i s f r a c t i o n approximately 70 times more r e a d i l y than does the TMO. T h i s r e s u l t confirms that a l k y l e n e oxides polymerize much more r e a d i l y than oxetanes with the c h e l a t e c a t a l y s t . A small amount (10% o f the T o t a l ) o f a w a t e r - i n s o l u b l e copolymer c o n t a i n i n g 44% TMO was obtained. T h i s r e s u l t i n d i c a t e s that the c h e l a t e c a t a l y s t contains some s i t e s which give more f a v o r a b l e copolymeri z a t i o n . One p o s s i b l e explanation i s t h a t the unfavorable copolym e r i z a t i o n o f TMO a t the major s i t e s i s due t o s t e r i c hindrance which reduces the a b i l i t y o f TMO t o coordinate a t t h i s s i t e . Based on t h i s hypothesis, l e s s hindered s i t e s would be more f a v o r able f o r copolymerization. An a l t e r n a t e but u n l i k e l y p o s s i b i l i t y i s that there are a l i m i t e d number o f c a t i o n i c s i t e s i n the chelate c a t a l y s t and t h a t these give some copolymer by a more f a v o r a b l e c a t i o n i c propagation mechanism. The copolymerization o f TMO and e p i c h l o r o h y d r i n (ECH) with the c h e l a t e c a t a l y s t and a 50:50 weight r a t i o charge i s more favorable (Run 3, Table I I ) ; again, two f r a c t i o n s , both rubbery i n nature, were obtained which d i f f e r e d i n s o l u b i l i t y and composition. Thus, the c h e l a t e c a t a l y s t again appears t o c o n t a i n a t l e a s t two d i f f e r e n t copolymerization s i t e s . I t i s s i g n i f i c a n t that these two monomers, which probably have s i m i l a r s t e r i c r e quirements, do copolymerize b e t t e r , thus adding credence t o the e a r l i e r proposal that s t e r i c r e s t r i c t i o n s at c e r t a i n s i t e s a f f e c t
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
7.
VANDENBERG
A N D ROBINSON
Trimethylene Oxide
111
copolymerization. Of course, t h i s r e s u l t i s a l s o evidence f o r a coordination polymerization. TMO Copolymerization With Unsaturated Epoxides and Oxetanes. The low conversion copolymerization o f TMO and a l l y l g l y c i d y l ether (AGE) with the c h e l a t e c a t a l y s t and a 97:3 weight r a t i o charge gave a rubbery, l a r g e l y amorphous, high molecular weight copolymer product which contained about 13% AGE (Run 4, Table I I ) . On the b a s i s o f an i d e a l copolymerization, the AGE enters the copolymer about 14 times more r e a d i l y than TMO does. This r e s u l t i s to be c o n t r a s t e d with the i d e a l PO-AGE copolymerization, with t h i s same c a t a l y s t , i n which the copolymer has the same composit i o n as the i n i t i a l monomer charge. To compare the elastomer behavior o f t h i s TMO elastomer with a comparable PO-AGE elastomer, a procedure was developed f o r making l a r g e r samples o f r e l a t i v e l y uniform TMO-AGE copolymer II). Thus, the copolymerizatio the i n i t i a l charge along with 20% o f the t o t a l AGE used. As the p o l y m e r i z a t i o n proceeded, a d d i t i o n a l AGE was added as i n d i c a t e d i n Table I I . In t h i s way, a high conversion to heptane- and methanol-insoluble, amorphous copolymer c o n t a i n i n g 4.4% AGE was obtained. On the b a s i s o f the s u l f u r v u l c a n i z a t e data that i s presented i n the v u l c a n i z a t e property data s e c t i o n , t h i s product appears to be r e l a t i v e l y uniform. However, t h i s procedure and perhaps even the c a t a l y s t may not be optimal and some degree o f nonuniformity may s t i l l p e r s i s t . A copolymer o f TMO with butadiene monoxide (BMO) was a l s o made by u s i n g the same procedure as i n the l a r g e sample method for TMO-AGE (Run 6, Table I I ) . Since BMO gives i d e a l copolymeri z a t i o n with PO, as does AGE, with the c h e l a t e c a t a l y s t , i t was assumed that the system which worked with TMO-AGE would work with TMO-BMO. A terpolymer o f TMO-PO-AGE was a l s o made by the same general procedure used i n the l a r g e s c a l e TMO-AGE work (Run 7, Table I I ) . The terpolymer was i s o l a t e d i n two f r a c t i o n s o f s i m i l a r composit i o n (ca. 60% PO and 10% AGE), but d i f f e r e n t s o l u b i l i t y , and d i f f e r e n t molecular weight. The highest molecular weight f r a c t i o n was heptane-insoluble, confirming that TMO u n i t s c o n t r i b u t e substantial heptane-insolubility. TMO was a l s o copolymerized with an unsaturated oxetane, 3,3b i s ( a l l y l o x y m e t h y l ) o x e t a n e (BAMO) (Run 3, Table I I I ) . This work was done with the Et3Al-0.5H20 c a t a l y s t . This copolymerization appears to be a n e a r l y p e r f e c t one. Polymerization o f Other Oxetanes. The c a t i o n i c polymerizat i o n o f 3 , 3 - d i s u b s t i t u t e d oxetanes, e s p e c i a l l y 3 . 3 - b i s ( c h l o r o methyl)oxetane (BCMO), has been widely studied(±/t£?. A few experiments with t h i s type o f oxetane u s i n g the Et Al-0.5H2O c a t a l y s t are given i n Table I I I . BCMO polymerizes r e a d i l y with t h i s c a t a l y s t to give high molecular weight polymer, n i h 3.0, at 3
n
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
POLYETHERS
112
3 0 ° C , provided there i s no ether i n the c a t a l y s t system (Run 5, Table I I I ) . However, with ether present (Run 4, Table I I I ) , the molecular weight i s g r e a t l y reduced as i n d i c a t e d by the 0.3 inherent v i s c o s i t y . The l a r g e e f f e c t o f ether i n d i c a t e s that the E t 3 A l 0.5H O c a t a l y s t i s behaving here as a c a t i o n i c c a t a l y s t with ether a c t i n g as a chain t r a n s f e r agent. The molecular weight without ether i s , however, very high f o r an o r d i n a r y c a t i o n i c c a t a l y s t with BCMO a t these temperatures. U s u a l l y lower temperatures are r e q u i r e d t o o b t a i n high molecular weight polymer from BCMO with Lewis a c i d type c a t a l y s t s Some experiments on the p o l y m e r i z a t i o n o f BCMO with the chelate c a t a l y s t are recorded i n the patent literature(£). In t h i s work, high molecular weight polymer ( n i h P 4.3) obtained a t very high temperatures (200-250°C.) i n a continuous, bulk p o l y m e r i z a t i o n method These data i n d i c a t e that the c h e l a t e c a t a l y s t polymerizes BCM ably the very high temperatur t i v e l y low b a s i c i t y o f BCMot^£). The copolymerization o f PO with BCMO u s i n g the c h e l a t e c a t a l y s t (Run 8, Table I I I ) a t 30°C. i n d i c a t e s that the PO enters the copolymers about t h i r t y f o l d more r e a d i l y than does BCMO, based on i d e a l copolymerization. This r e s u l t i s s i m i l a r t o our f i n d i n g s on the copolymerization o f TMO with ethylene oxide. S i m i l a r explanations no doubt apply. 3,3-Dimethyloxetane (DMO) polymerizes very r a p i d l y a t 0°C. with Et3Al-0.5 H 0 c a t a l y s t t o a high molecular weight, ( n ^ h * 1.6), low m e l t i n g (ca. 5 0 ° C ) , c r y s t a l l i n e polymer (Run 6, Table I I I ) . This p o l y m e r i z a t i o n i s apparently c a t i o n i c , on the b a s i s o f the v e r y r a p i d p o l y m e r i z a t i o n . The small amount o f ether i n the c a t a l y s t does not have a large chain t r a n s f e r e f f e c t , as with BCMO, presumably because o f the much higher base strength o f DMO compared with BCMO and ether. DMO was copolymerized with BAMO (Run 7, Table I I I ) . Because of the very r a p i d p o l y m e r i z a t i o n , i t was d i f f i c u l t t o o b t a i n a low conversion and t o assess the copolymerization behavior o f t h i s monomer p a i r . However, v u l c a n i z a t e p r o p e r t i e s on t h i s product (Table III) were good, i n d i c a t i n g a r e l a t i v e l y uniform copolymer and thus a f a v o r a b l e copolymerization. 2
U
t
0
w
a
s
n
2
V u l c a n i z a t e Studies The various unsaturated copolymers were v u l c a n i z e d with the s u l f u r - a c c e l a t o r system given i n Table IV. TMO-AGE Elastomers. The s u l f u r v u l c a n i z a t e o f the 96-4 TMO-AGE copolymer had high t e n s i l e , modulus, and t e a r strength a t 23°C. a t a good e l o n g a t i o n l e v e l (Table V). The hot t e n s i l e p r o p e r t i e s a t 100°C. are somewhat lower but s t i l l good. C r y s t a l l i n i t y and/or c r y s t a l l i z a t i o n on s t r e t c h i n g could enhance t e n s i l e p r o p e r t i e s a t 2 3 ° C ; apparently t h i s i s not the case, s i n c e the hot t e n s i l e r e s u l t s , which could not i n v o l v e c r y s t a l l i n i t y
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
7.
VANDENBERG
AND
ROBINSON
THmethylene Oxide
113
e f f e c t s , are i n l i n e with the usual e f f e c t o f increased temper ature on t e n s i l e p r o p e r t i e s . The p r o p e r t i e s obtained i n these studies are a f f e c t e d only s l i g h t l y by i n c r e a s i n g the cure time f o u r f o l d over the optimum used ( F i g . 1 ) . Table V VULCANIZATE PROPERTIES OF TMO-AGE ELASTOMER
Tensile strength, p s i . 300% modulus, p s i . Elongation a t break, % Break s e t , % Hardness, A2 Tear Strength, p . / i R e s i l i e n c e , Bashore Y e r z l e y Dynamic Data Modulus, p s i . Resilience, % Frequency, Hz K i n e t i c Energy, i n . - l b . / c u . i n . Heat Build-up, °F. Tg., °c. V o l . % Swell (5 days a t 60°C.) Toluene H 0 2
23°C. 3190 2590 400 20 82
100°C. 1800 1515 225 0 82
6555 67 7.5 31.7 27 -75
315 0
The TMO-AGE copolymer v u l c a n i z a t e a l s o has e x c e l l e n t r e s i l ience, low heat b u i l d - u p , and a low Tg o f -75°C. (Table V ) . Volume % s w e l l i n toluene i s high but water-swell i s low. A l though not measured, we would expect, based on the heptanei n s o l u b i l i t y o f the amorphous 96-4 TMO-AGE copolymer, that o i l r e s i s t a n c e o f TMO-AGE copolymer would be f a i r l y good. The m e t h a n o l - i n s o l u b i l i t y o f the amorphous TMO-AGE copolymer a l s o suggests that i t should have r e s i s t a n c e t o p o l a r s o l v e n t s . The gum v u l c a n i z a t i o n p r o p e r t i e s o f the TMO-AGE copolymer (Table VI) are low. These data are f u r t h e r evidence that the e x c e l l e n t t e n s i l e p r o p e r t i e s observed f o r the b l a c k - f i l l e d TMOAGE v u l c a n i z a t e s i s not due t o c r y s t a l u n i t y o r c r y s t a l 1 1 z a b i l i t y . The 91% g e l r e s u l t does support our conclusion that the TMO-AGE copolymer i s reasonably uniform. A i r aging f o r 48 hours a t 100°C. does not g r e a t l y a f f e c t the room temperature p r o p e r t i e s o f the TMO-AGE v u l c a n i z a t e (Table V I I ) . These c o n d i t i o n s would s e r i o u s l y degrade the p r o p e r t i e s o f n a t u r a l rubber and thus c l e a r l y show that TMO elastomers, l i k e PO elastomers, are s u p e r i o r i n heat aging t o n a t u r a l rubber. Unfort u n a t e l y we d i d not make an extended a i r aging study on the TMO v u l c a n i z a t e t o determine i t s long term o x i d a t i o n r e s i s t a n c e . One
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
114
POLYETHERS
would expect, however, that the lack o f t e r t i a r y hydrogens i n the TMO chain u n i t would be a favorable f a c t o r . Table VI GUM VULCANIZATE PROPERTIES OF TMO-AGE ELASTOMER Tensile strength, p s i . 300% Modulus, p s i . E l o n g a t i o n at break, % Break s e t , % Hardness, A2 Tear s t r e n g t h , p / i G e l / s w e l l , %/%
515 260 515 10 48 80 91/520
EFFECT OF AIR AGING ON TMO-AGE VULCANIZATE(a) h r s . at 100°C. 0 48 Tensile strength, p s i . 200% Modulus, p s i . Elongation at break Break s e t , % Hardness, A2
3190 2590 400 20 82
3380 2630 290 10 70
(a) S t a b i l i z e d with 1% phenyl 3-naphthylamine. T o r s i o n a l r i g i d i t y versus temperature data f o r the TMO-AGE v u l c a n i z a t e and a comparable PO-AGE v u l c a n i z a t e are given i n Figure 2. The increase i n modulus f o r the TMO v u l c a n i z a t e from 0 to -60° o b v i o u s l y i s due to a low temperature c r y s t a l l i z a t i o n o f t h i s copolymer. Other samples d i d not e x h i b i t t h i s c r y s t a l l i z a t i o n problem. The data do i n d i c a t e that the TMO and PO e l a s tomers have about the same Tg at about -75°C. The low temperature c r y s t a l l i z a t i o n problem o f the TMO e l a s tomer can no doubt be e l i m i n a t e d i n a v a r i e t y o f ways, such as preparing a more uniform copolymer, adding a p l a s t i c i z e r such as an aromatic o i l , and/or a l t e r i n g the composition o f the copolymer. An approach t o a l t e r i n g the TMO-AGE copolymer composition would be to make a terpolymer c o n t a i n i n g PO as described prev i o u s l y . V u l c a n i z a t e data are given on the PO-TMO-AGE elastomers i n Table V I I I . The p r o p e r t i e s are f a i r but i n d i c a t e that the v u l c a n i z a t e s are overcured. The AGE l e v e l was e v i d e n t l y too high f o r the cure system used. The r e s u l t s do confirm the p r e p a r a t i o n o f the d e s i r e d terpolymer and i n d i c a t e that t h i s approach i s feasible.
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
7.
VANDENBERG
A N D ROBINSON
Figure 2.
Trimethtflene Oxide
115
Torsional rigidity vs. temperature for TMO and PO elastomers
Other Qxetane Elastomers. The TMO-butadiene monoxide (BMO) copolymer elastomer (Run 6, Table II) c o n t a i n i n g 6.5% BMO gave i n f e r i o r p r o p e r t i e s (Table VIII) t o the TMO-AGE elastomer with 4.4% AGE d e s c r i b e d i n the previous s e c t i o n . A c t u a l l y the propert i e s were even s l i g h t l y i n f e r i o r t o a 98-2 TMO-AGE copolymer v u l canizate (Table V I I I ) . Thus AGE appears about three times more e f f e c t i v e (on a weight b a s i s ) i n c o n f e r r i n g s u l f u r v u l c a n i z a b i l i t y than BMO. On a molar b a s i s , the d i f f e r e n c e i s even g r e a t e r , i . e . , AGE i s f i v e times more e f f e c t i v e . T h i s same d i f f e r e n c e between BMO and AGE was p r e v i o u s l y observed on comparing PO-BMO elastomer with PO-AGE elastomer. Bis(3,3-allyloxymethyl)oxetane (BAMO), on the other hand, appears t o have about the same order o f e f f e c t i v e n e s s f o r conf e r r i n g s u l f u r c u r a b i l i t y t o a TMO elastomer as does AGE (on an equal double-bond content b a s i s ) . The 88:12 DMO:BAMO elastomer gave only f a i r p r o p e r t i e s s i n c e i t was s u b s t a n t i a l l y overcured with the high l e v e l o f BAMO used (Table V I I I ) . The low heat-build-up does i n d i c a t e that t h i s e l a s tomer i s i n h e r e n t l y a good one. CONCLUSIONS The f i r s t p o l y m e r i z a t i o n o f an oxetane, trimethylene oxide, by c o o r d i n a t i o n p o l y m e r i z a t i o n has been d e s c r i b e d . Copolymers o f TMO with epoxides were r e a d i l y made. Such copolymers provide an i n t e r e s t i n g f a m i l y o f new elastomers. One such elastomer, the TMO-AGE copolymer, was i n v e s t i g a t e d i n some d e t a i l and found t o have a d e s i r a b l e combination o f p r o p e r t i e s . Such TMO elastomers,
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
(a)
88-12
93.5-6.5 98-2 (b) 93.3-6.7
58-32-10 60-31-9
Composition
99 390
625 820 270
-
94 93 100
% Swell
% Gel
1985
2090 3010 3280
2040 2030
Tensile psi.
g
char^
d
b
n
/
inh (c) 100% modulus.
P
a
= 1
S
6
6
? !f · '
0
c
e
d
u
r
e
-
1155 1035 3250
695 (c) 930 (c)
300% Modulus psi.
210
535 770 305
225 200
Elongation
a s c r i b e d i n Run 5, Table I I , u s i n g 2.6% t o t a l AGE i n t h e
(a) Products d e s c r i b e d i n Tables I I andI I I u n l e s s otherwise noted.
DMO-BAMO
TMO-BMO TMO-AGE TMO-BAMO
PO-TMO-AGE, h e p t a n e - i n s o l . " " " " -sol.
Elastomer Name
V u l c a n i z a t e P r o p e r t i e s o f V a r i o u s Oxetane Elastomers
Table V I I I
14
Heat Build-up @ 212°F.
7.
VANDENBERG
AND
ROBINSON
THmethylene Oxide
117
l i k e the PO elastomers, are e x c e l l e n t rubbers with low Tg and high r e s i l i e n c e . A l s o , the TMO elastomers give good t e n s i l e and t e a r p r o p e r t i e s and should have at l e a s t f a i r o i l r e s i s t a n c e . Although abrasion r e s i s t a n c e data has not been obtained, we would expect the good t e n s i l e and t e a r p r o p e r t i e s o f the TMO v u l c a n i z a t e s to favor good abrasion r e s i s t a n c e . There appear to be two main d i s advantages o f the TMO elastomers; f i r s t , the low temperature c r y s t a l l i z a t i o n problem which can no doubt be e a s i l y c o r r e c t e d . Second, and more important, there i s no c u r r e n t economic source of TMO. For example, trimethylene g l y c o l , a p o s s i b l e p r e c u r s o r , s e l l s f o r about $4/lb. i n volume. Thus the development o f t h i s i n t e r e s t i n g f a m i l y o f elastomers based on TMO must await the development o f a low cost route to t h i s monomer. Acknow1edgment The a s s i s t a n c e o f t h i s work i s g r a t e f u l l y acknowledged, p a r t i c u l a r l y Dr. T. J . Prosser f o r the s y n t h e s i s o f 3,3-bis(allyloxymethyl)oxetane, Dr. F. E. Williams f o r the s y n t h e s i s o f 3,3-dimethyloxetane, and S. F. Dieckmann f o r the continuous bulk p o l y m e r i z a t i o n o f 3,3-bis(chloromethyl)oxetane c i t e d . Summary The f i r s t c o o r d i n a t i o n p o l y m e r i z a t i o n o f an oxetane, t r i methylene oxide (TMO), occurs r e a d i l y , much l i k e propylene oxide (PO) , with the Et3Al-H20-acetyl acetone c a t a l y s t at 6 5 ° C , to give high molecular weight polymer ( n ^ ^ up to 12) . TMO copolymerizes with epoxides with t h i s c o o r d i n a t i o n c a t a l y s t . For example, TMO copolymerized w e l l with a l l y l g l y c i d y l ether (AGE) which was about seven times more r e a c t i v e than TMO, i n c o n t r a s t to the PO-AGE copolymerization i n which both monomers are o f equal r e a c t i v i t y . A 96-4 TMO-AGE copolymer prepared under c o n d i t i o n s to make i t r e a sonably uniform gave an i n t e r e s t i n g s u l f u r - c u r a b l e elastomer. P r e l i m i n a r y v u l c a n i z a t e data on t h i s elastomer show good t e n s i l e and t e a r p r o p e r t i e s , a low Tg (-75°C.), high r e s i l i e n c e , and good heat r e s i s t a n c e . Further development of t h i s f a m i l y o f i n t e r e s t ing elastomers r e q u i r e s a lower cost route to TMO. Copolymerizations o f TMO with other epoxides and oxetanes as w e l l as the polymerization o f other oxetanes are a l s o d e s c r i b e d . Literature Cited 1. Boardman, Η., E n c y l . o f Chem. Tech., 2nd Supplement, 655.
(1960),
2. Dreyfuss, P. and Dreyfuss, M. P., "Polymerization o f 1,3 Epoxides" i n "Ring Opening P o l y m e r i z a t i o n " (K. C. F r i s c h and S. L. Reegen, eds.), Marcel Dekker, Inc., New York, 1969, Chap. 2-2.
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
118
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3. Rose, J. Β., J. Chem. Soc. 1956, 542, 546. 4. Vandenberg, E. J. (to Hercules Incorporated), U.S. Pat. 3,205,183 (1965). 5. Vandenberg, E. J., J. Polym. Sci., A1, (1969), 7, 525. 6. P r i c e , C. C., Chemist
(1961), 38, 131.
7. P r i c e , C. C., (assigned t o U n i v e r s i t y Pat. 2,866,774 (1958).
o f Notre Dame), U.S.
8. P r u i t t , M. E. and Baggett, J. M., (to Dow Chemical Co.), U.S. Pat. 2,706,181 (1955). 9. P r i c e , C. C. and 78, 4787. 10. Osgan, M. and P r i c e , C. C., J. Polym. Sci., (1959), 34, 153. 11. P r i c e , C. C., (to General T i r e and Rubber Co.), Br. Pat. 893,275 (1962). 12. Hill, F. N., Bailey, Jr., F. E., and F i t z p a t r i c k , J. T., Ind. Eng. Chem., (1958), 50, 5. 13. Staudinger, H. and Lohmann, Η., Ann. Chem. (1933), 505, 41. 14. B a i l e y , Jr., F. Ε., Hill, F. N., and F i t z p a t r i c k , J. T., (to Union Carbide Corp.) U.S. Pat. 3,100,750 (1963). 15. B a i l e y , Jr., F. E., Hill, F. N., and F i t z p a t r i c k , J. T., (to Union Carbide Corp.) U.S. Pat. 2,969,402 (1961). 16. B a i l e y , Jr., F. E., Hill, F. N., and F i t z p a t r i c k , J. T., (to Union Carbide Corp.) U.S. Pat. 3,062,755 (1962). 17. B a i l e y , Jr., F. E., (to Union Carbide Corp.) U.S. Pat. 3,031,439 (1962). 18. Vandenberg, E. J., J. Polym. Sci. (1960), 47, 486. 19. Gruber, Ε. E., Meyer, D. Α., Swart, G. H., and Weinstock, Κ. U., Ind. Eng. Chem. Prod. Res. Develop. (1964), 3 ( 3 ) , 194. 20. Vandenberg, E. J. ( t o Hercules Incorporated), U.S. Pat. 3,728,320 (1973). 21. Vandenberg, E. J. (to Hercules Incorporated), U.S. Pat. 3,728,321 (1973).
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
7.
VANDENBERG
A N D ROBINSON
Trimethylene Oxide
22. Schmoyer, L. F. and Case, L. C., Nature (1960), 187, 592. 23. Kemp, A. R. and M u e l l e r , G. S., Ind. Eng. Chem. Anal. Ed. (1934), 6, 52. 24. Yamashita, Y., Tsuda, T., Okada, M., and Iwatsuki, S., J. Polym. Sci., A1, (1966), 4, 2121.
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
119
8 Vulcanization and Stabilization Studies on Propylene Oxide Rubber C. R. BOSS Research Center, Hercules Inc., Wilmington, Del. 19899
®
Parel elastomer i with a small amount o f allyl g l y c i d y l ether. T y p i c a l samples have reduced s p e c i f i c v i s c o s i t i e s (RSV) between 4 and 12, i n d i c a t i n g molecular weights o f the order o f a million. The unsatura t i o n c o n t r i b u t e d by the allyl glycidyl ether monomer u n i t s provides s i t e s f o r s u l f u r c r o s s - l i n k i n g . V u l c a n i z a t i o n can be e f f e c t e d with combinations o f s u l f u r and s u l f u r donors as used f o r other unsaturated rubbers. A t y p i c a l v u l c a n i z a t i o n formulat i o n i s given i n Table 1. Peroxides are i n e f f e c t i v e f o r c u r i n g t h i s elastomer s i n c e they tend t o degrade r a t h e r than c r o s s - l i n k it. When P a r e l elastomer i s cured with the formulation shown, f o r the recommended 30 minutes at 160°C., the p r o p e r t i e s given in Table 2 are obtained. T h i s paper will summarize some o f the s t u d i e s l e a d i n g t o s e l e c t i o n o f a number o f the components o f t h i s v u l c a n i z a t i o n formulation and t o determination o f the advantageous p r o p e r t i e s o f the v u l c a n i z e d products. Vulcanization S u l f u r cure systems are w e l l known t o be complex in t h e i r r e a c t i o n s and i n the types o f c r o s s - l i n k s they produce(1) (2). There is general agreement that i f s u l f u r alone is used to v u l canize a rubber, most o f the c r o s s - l i n k s will have more than two s u l f u r atoms i n them(1). These p o l y s u l f i d e s are l e s s s t a b l e than monosulfides or d i s u l f i d e s . T h i s phenomenon has been examined i n some v u l c a n i z e d elastomers by u s i n g chemical probes, which modify or break only c e r t a i n kinds o f cross-1inks(3) (4) (5). P a r e l e l a s tomer is more difficult to study i n t h i s f a s h i o n than styrenebutadiene rubber (SBR) or n a t u r a l rubber because many o f these chemical reagents a l s o r e a c t with the C-O bonds o f the p o l y e t h e r . © R e g i s t e r e d trademark o f Hercules Incorporated Hercules Research Center C o n t r i b u t i o n No.
1648
120
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
8.
BOSS
121
Propylene Oxide Rubber
However, triphenylphosphine i s a reagent which can be u t i l i z e d advantageously. I t reduces p o l y s u l f i d e s t o disulfides(§), but does not break the polymer chains i n P a r e l elastomer. To determine the types o f c r o s s - l i n k s which are produced i n representat i v e cure systems, two samples o f v u l c a n i z e d P a r e l elastomer were prepared. One was cured with s u l f u r alone, and the other with the formulation shown i n Table 1. The samples were then t r e a t e d with triphenylphosphine i n benzene. The r e s u l t s o f continuous s t r e s s r e l a x a t i o n measurements run on the products at 150°C. are shown i n Figure 1. The s t a b i l i z e r s were e x t r a c t e d by the benzene used i n the triphenylphosphine treatment so subsequent t e s t s i n a i r could not be compared with previous t e s t r e s u l t s . Therefore, a l l o f these s t r e s s r e l a x a t i o n measurements were made i n n i t r o g e n .
1.0-
• 3Î.
J
I
2
4
0
I 6
I 8
I
I 10
12
1 14
TIME (HRS) RUN IN N AT 150°C UNTREATED; — REACTED 24 HOURS WITH TRIPHENYLPHOSPHINE IN BENZENE. 2
Figure 1.
Effect of polysulfides on the stress relaxation of vulcanized Parel elastomer
Both o f the unextracted samples s u f f e r from a r a p i d i n i t i a l l o s s o f modulus, but the sample cured with s u l f u r has a considerably more severe l o s s . A f t e r the c r o s s - l i n k s were converted from
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
POLYETHERS
TABLE 1 TYPICAL VULCANIZATION FORMULATION
100 50
FOR PAREL ELASTOMER
PAREL ELASTOMER HAF BLACK
1.0
STEARIC ACID
1.5
NICKEL DIBUTYLDITHIOCARBAMATE
5.0
ZNI
1.5
TETRAETHYLTHIURAM
1.5 1.25
MONOSULFIDE
MERCAPTOBENZOTHIAZOLE SULFUR
TABLE 2 TYPICAL PHYSICAL PROPERTIES OF VULCANIZED PAREL ELASTOMER
100$ MODULUS
465 P . S . I .
300% MODULUS
1740 P . S . I .
TENSILE STRENGTH
2075 P . S . I .
ELONGATION
375 %
HARDNESS (SHORE A)
68
BAYSHORE RESILIENCE
48 %
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
8.
BOSS
123
Propylene Oxide Rubber
p o l y s u l f i d e s to d i s u l f i d e s , both samples had a much s m a l l e r l o s s o f modulus i n the f i r s t few hours o f t e s t . These s t r e s s r e l a x a t i o n r e s u l t s show that p o l y s u l f i d e s are weaker than d i s u l f i d e s . L a i has shown t h a t r e d u c t i o n o f p o l y s u l f i d e s to d i s u l f i d e s 4oes not i n t e r f e r e with the t e n s i l e p r o p e r t i e s o f n a t u r a l rubber^Z.). We d i d not determine whether t h i s was true f o r the P a r e l e l a s t o mer. The s u l f u r content o f these samples was determined a f t e r treatment with benzene alone and a f t e r treatment with t r i p h e n y l phosphine i n benzene. The samples l o s t about 1/3 o f t h e i r s u l f u r i n the benzene. About h a l f o f t h i s l o s s (about 1/6 o f the t o t a l amount o f s u l f u r ) could be a t t r i b u t e d to l o s s o f n i c k e l d i b u t y l d i t h i o c a r b o n a t e (NBC), the s t a b i l i z e r . When these samples were t r e a t e d with triphenylphosphine i n benzene, the sample cured with an a c c e l e r a t o r l o s t about 50% o f i t s o r i g i n a l s u l f u r The one cured with s u l f u r alon have f u r t h e r evidence tha c r o s s - l i n k s , but they represent a s m a l l e r percentage o f the t o t a l when an a c c e l e r a t o r i s used. S t a b i l i z a t i o n and Hydroperoxide
Decomposers
When p r o p e r l y compounded, v u l c a n i z e d P a r e l elastomer i s q u i t e s t a b l e i n hot a i r . N i c k e l d i b u t y l d i t h i o c a r b a m a t e (NBC) has been found to be a very e f f e c t i v e s t a b i l i z e r f o r t h i s rubber. Results o f aging a standard formulation i n a 150°C. a i r oven are shown i n Table 3. The hardness r e s u l t s are given as a change ( i n p o i n t s ) from the o r i g i n a l value, while the percentage o f the o r i g i n a l value i s given f o r the other p r o p e r t i e s . During the f i r s t three days o f aging, the 100% modulus and hardness were higher than the o r i g i n a l v a l u e s , while the e l o n g a t i o n was lower. These changes are probably due to a d d i t i o n a l c r o s s - l i n k i n g . Then the rubber g r a d u a l l y softened and l o s t s t r e n g t h . A f t e r a week, the v u l c a n i z e d elastomer l o s t only about 10% o f i t s 100% modulus, l e s s than o n e - t h i r d o f i t s t e n s i l e s t r e n g t h , and softened very l i t t l e ; the rubber was s t i l l q u i t e s e r v i c e a b l e . A f t e r 10 days under these t e s t c o n d i t i o n s , the elastomer d e t e r i o r a t e d considerably. These heat aging t e s t s show t h a t p r o p e r l y compounded P a r e l elastomer v u l c a n i z a t e s are outstanding i n high temperature oxidation resistance. TABLE 3 CHANGE OF PROPERTIES OF PAREL ELASTOMER AGED IN AIR AT 150°C. DAYS
100£
% OF ORIGINAL ELÔNÊ. MOD. T.S.
CHANGE IN HARDNESS
1
130
95
65
+4
3
145
75
60
+3
7
90
70
65
-2
10
60
30
55
-7
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
124
POLYETHERS
Figure 2 compares the e f f e c t i v e n e s s o f two s t a b i l i z e r s i n P a r e l elastomer. Since the elastomer contains an in-process a n t i o x i d a n t , o n l y a hydroperoxide decomposer was added. The s u p e r i o r i t y o f NBC i n maintaining the p h y s i c a l p r o p e r t i e s o f P a r e l elastomer i s obvious.
Figure 2.
Effect of stabilizer on vulcanized Parel elastomer aged at 150°C
A model system has been used t o e x p l a i n the e f f e c t i v e n e s s o f dithiocarbamates as hydroperoxide decomposers. Table 4 summarizes r e s u l t s o f decomposing t - b u t y l hydroperoxide (TBHP) with d i t h i o carbamates o r d i l a u r y l t h i o d i p r o p i o n a t e (LTDP). The d i t h i o c a r b a mates were t e s t e d at room temperature and at 6 0 ° C , while the experiment with LTDP was run at 100°C. LTDP i s an e f f e c t i v e hydroperoxide decomposer and i s o f t e n used f o r t h i s purpose i n polypropylene and other polymers. It decomposes hydroperoxides c a t a l y t i c a l l y and q u i c k l y at 100-150°C, but not at room temperature Each mole o f NBC r e a c t s with about 6 moles o f hydroperoxide i n 15 minutes at 25°C. The z i n c compound r e q u i r e s s e v e r a l hours at 25° or about 20 minutes at 60°C. to e f f e c t i v e l y decompose TBHP. Undoubtedly more important than the r a t e o f decomposition o f hydroperoxides i s the type o f product obtained. Table 5 l i s t s the major products obtained by completely decomposing TBHP with v a r i o u s s u l f u r compounds. With n i c k e l and z i n c dithiocarbamates
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
8.
BOSS
125
Propylene Oxide Rubber
TABLE 4 DECOMPOSITION OF TBHP BY SULFUR COMPOUNDS
NBC (25°)
TIME (MIN)
TBHP CONCENTRATION NBC ZEC (60°) (25°)
(MOLAR) ZEC (60°)
LTDP (100°)
0
0.205
0.203
0.201
0.201
0.188
15
0.060
-
0.020
0.188
0.162
30
0.030
0.198-
0.016
0.075
0.108
60
0.029
0.195
0.014
0.026
0.014
0.179
-
-
-
0.019
180 ALL
SOLUTIONS
NBC= n i c k e l d i b u t y l d i t h i o c a r b a m a t e ZEC= z i n c d i e t h y l d i t h i o c a r b a m a t e LTDP= d i l a u r y l t h i o d i p r o p i o n a t e TBHP= t - b u t y l h y d r o p e r o x i d e
TABLE 5 PRODUCTS OF TBHP DECOMPOSITION
ΓΤΒΗΡΙ
STABILIZER NBC
L > s
% TBHP TO TBA DTBP
5
70
5
ZBC
4
80
5
LTDP
5
0
40
(C^HgS)2
5
0
40
10
0
90
so TBA=
2
t-butanol
DTBP- di-t-butylperoxide
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
126
POLYETHERS
most o f the hydroperoxide went t o the a l c o h o l , and only a small amount t o the peroxide; LTDP formed the peroxide from TBHP, but not the a l c o h o l . About h a l f o f the TBHP was unaccounted f o r , but n e i t h e r methanol n o r acetone was detected. The products formed from TBHP may e x p l a i n why LTDP does not work w e l l i n P a r e l elastomer. The peroxides formed i n p o l y e t h e r s would not be s t a b l e , so t h e i r decomposition would cause continua t i o n o f the o x i d a t i v e chain r e a c t i o n . Heat Aging Comparison with Other Elastomers P a r e l elastomer, n a t u r a l rubber, and neoprene, compounded with standard recommended formulas f o r each, were heat aged i n a 125°C. f o r c e d d r a f t oven. Figure 3 i s a p l o t o f the change i n t e n s i l e strength and hardness o f the v u l c a n i z e d P a r e l and neoprene elastomers. Neoprene maintaine a f t e r a week a t 1 2 5 ° C with n a t u r a l rubber are not i n c l u d e d i n the f i g u r e because i t f a i l e d so q u i c k l y a t 125°C. I t was s e r i o u s l y d e t e r i o r a t e d i n about 3 days a t 100°C.
1050
65
700
60
350
55
10 DAYS
Figure 3.
50
10 DAYS
Physical properties of Parel and neoprene elastomers aged at 125°C
Compression s e t i s the i n a b i l i t y o f rubber t o r e t u r n t o i t s o r i g i n a l s i z e a f t e r being squeezed. Standard t e s t s u s u a l l y compress the v u l c a n i z e d rubber t o 75% o f i t s o r i g i n a l s i z e f o r 1 o r
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
8.
BOSS
Propylene Oxide Rubber
127
3 days a t 70°, 100°, o r 125°C. Figure 4 i s a p l o t o f the compress i o n set o f v u l c a n i z e d P a r e l elastomer t e s t e d f o r up t o 7 days a t temperatures from 70° t o 150°C. While r a t h e r h i g h compression s e t was a t t a i n e d i n i t i a l l y there was not much change as the time and temperature increased. F o r example, there was n e a r l y 50% s e t a f t e r 1 day a t 100°, but s t i l l l e s s than 70% a f t e r a week a t 150°C. The r e s u l t s obtained a t 125° and 150°C. are w i t h i n e x p e r i mental e r r o r o f each other.
100r-
90 -
80[-
DAYS Figure 4. Effect of time and temperature on the compression set of vulcanized Parel elastomer
Figures 5 and 6 compare the compression s e t o f v u l c a n i z e d P a r e l , n a t u r a l rubber, and neoprene elastomers a t 100° and 1 5 0 ° C , r e s p e c t i v e l y . At 1 0 0 ° C , the compression s e t o f P a r e l elastomer i s w i t h i n experimental e r r o r o f that o f n a t u r a l rubber; neoprene i s c l e a r l y s u p e r i o r . When the compression s e t t e s t was run f o r a long time at 150°C. (Figure 7), P a r e l elastomer was the best o f these three rubbers. Natural rubber had 100% compression s e t
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
128
POLYETHERS
100
90
80
70
S oc
50
40
30
20 10
0 0
1
2
3
4
5
6
_ 7
-
DAYS
Figure 5.
Compression set at
100°C
w i t h i n three days, probably as a r e s u l t o f o x i d a t i v e degradation. Neoprene had a lower compression set than the P a r e l elastomer v u l c a n i z a t e f o r about f i v e days, but then i t became worse. S t r e s s r e l a x a t i o n measurements were made on cured Parel and neoprene elastomers. The samples were h e l d at 25% e l o n g a t i o n i n our t e s t s . T h i s technique measures chain o r c r o s s - l i n k s c i s s i o n , but does not show the e f f e c t o f any recombination or a d d i t i o n a l c u r i n g that occurs. Such new bonds would be load-bearing i f the sample were p u l l e d f u r t h e r as happens i n an i n t e r m i t t e n t run where the sample i s extended f o r a few seconds, then returned t o i t s o r i g i n a l length f o r about 10 minutes. Since the sample spends about 95% o f i t s time i n the r e l a x e d s t a t e , new bonds are loadbearing the next time the sample i s elongated. Many rubbers undergo a r a p i d l o s s o f modulus i n continuous experiments, but not i n i n t e r m i t t e n t runs. At 70°C. n a t u r a l rubber underwent l e s s r a p i d i n i t i a l l o s s than P a r e l elastomer or neoprene. Since oxidat i v e degradation i s not s i g n i f i c a n t i n 10-20 hours at 7 0 ° C , n a t u r a l rubber was s u p e r i o r to P a r e l elastomer or neoprene i n t h i s t e s t . At 1 0 0 ° C , however, the o x i d a t i v e chain s c i s s i o n or n a t u r a l
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
8.
BOSS
Propylene Oxide Rubber
129
10
01 5
I 1
I
I
2
3
I 4
I
1
L
5
6
7
DAYS
Figure 6.
Compression set at
150°C
rubber was much more r a p i d than that o f e i t h e r o f the s y n t h e t i c rubbers. Therefore, i t s modulus dropped r a p i d l y a f t e r a few hours. Figure 7 shows s t r e s s r e l a x a t i o n r e s u l t s with P a r e l e l a s tomer and neoprene at 1 2 5 ° C ; t h e i r r a t e s o f chain s c i s s i o n are similar. In t h i s t e s t , neoprene maintained a l a r g e r f r a c t i o n o f i t s i n i t i a l modulus than the v u l c a n i z e d Parel elastomer. However, Figure 8 shows s t r e s s r e l a x a t i o n r e s u l t s with these two rubbers at 150°C. Under these c o n d i t i o n s , the g r e a t e r o x i d a t i v e s t a b i l i t y o f the P a r e l elastomer i s more s i g n i f i c a n t than i t s somewhat greater l o s s o f modulus i n the f i r s t few hours o f t e s t . Dynamic
Properties
The dynamic p r o p e r t i e s o f t y p i c a l formulations o f P a r e l elastomer, neoprene, n i t r i l e , and n a t u r a l rubber were measured from -55°C. t o +80°C. u s i n g a v i b r a t i n g reed apparatus. These
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
POLYETHERS
I
•31 0
PAREL ELASTOMER
I 2
ι 4
I 6
I 8
I
I
1 0 1 2
1 14
TIME (HRS)
Figure 7.
Stress relaxation at
125°C
measurements were made a t a frequency o f about 500 h e r t z a t temperatures below the g l a s s t r a n s i t i o n , and a t about 30 h e r t z a t higher temperatures. The dynamic modulus o f the four rubbers i s p l o t t e d against temperature i n Figure 9. Although the samples were s t r a i n e d l e s s than 0.5%, dynamic modulus r e s u l t s are c a l c u l a t e d by e x t r a p o l a t i n g t o 100% s t r a i n . Therefore, dynamic t e s t s gave h i g h e r modulus values than s t a t i c t e s t s . The g l a s s t r a n s i t i o n temperatures are very obvious, as shown by the r a p i d changes i n modulus. They v a r i e d from about -55°C. f o r P a r e l elastomer t o about 0°C. f o r neoprene. In many a p p l i c a t i o n s , the region o f importance i s from about -25° t o +40°C. The dynamic modulus o f these f o u r rubbers changed l i t t l e as the temperature was increased above 30°C. A t w e l l below room temperature, the dynamic modulus o f P a r e l elastomer and n a t u r a l rubber remained d e s i r a b l y constant. The other two rubbers are so c l o s e t o t h e i r glass t r a n s i t i o n temperatures that the p r o p e r t i e s o f a r t i c l e s prepared from them
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
8.
BOSS
Propylene Oxide Rubber
.31
0
1
I
2
4
131
I
»
I
6
8
10
t
12
ι
14
TIME (HRS) Figure 8.
Stress relaxation at
150°C
would vary c o n s i d e r a b l y a t temperatures encountered i n the winter. Decreasing the l e v e l o f carbon b l a c k o r adding p l a s t i c i z e r s h i f t e d these curves t o lower modulus v a l u e s , and adding p l a s t i c i z e r s lowered the Tg. However, p l a s t i c i z e r s can be l o s t by e x t r a c t i o n or v o l a t i l i t y , and so should be s e l e c t e d t o avoid such l o s s . In a rubber, there i s a time l a g between an a p p l i e d s t r e s s and the r e s u l t i n g s t r a i n . In a dynamic t e s t , the s t r e s s i s ap p l i e d i n a s i n u s o i d a l f a s h i o n so t h i s delay can be t r e a t e d as a phase angle - d e l t a . Dynamic r e s u l t s are o f t e n given as the tangent o f d e l t a . Tan β i s a measure o f the r a t i o o f energy absorbed t o energy put i n p e r c y c l e . Heat b u i l d u p i n a f l e x i n g rubber i s dependent upon the energy r e q u i r e d t o s t r a i n the sample (the dynamic modulus), and on tan δ, which i s a measure o f the f r a c t i o n o f t h i s energy r e t a i n e d by the sample as heat. Small values are d e s i r a b l e where heat b u i l d u p may be a problem, while l a r g e r values mean the m a t e r i a l w i l l absorb a l a r g e r f r a c t i o n o f v i b r a t i o n a l energy. Tan 2
4
n
Scheme 1 propagating species and with the unreacted i n i t i a t o r should q u a n t i t a t i v e l y produce the polymer phenyl ether and phenetole, r e s p e c t i v e l y . The quant i t a t ivenes s of the r e a c t i o n between sodium phenoxide and the propagating c y c l i c oxonium has been e s t a b l i s h e d i n the previous s t u d i e s by using Lewis a c i d c a t a l y s t s (17,18). Therefore, the r e a c t i o n s of sodium phonoxide with superacid e s t e r s of EtOS0 F and E t O S 0 C l were examined (Table I ) . From the r e s u l t s shown i n Table I Reaction 1 has been regarded 2
2
as q u a n t i t a t i v e (3). This i n d i c a t e s that the phenoxyl endcapping method can be used f o r the k i n e t i c a n a l y s i s of the THF p o l y m e r i z a t i o n by superacid e s t e r i n i t i a t o r s as i n the case of Et 0+BF^~ i n i t i a t o r system (19). The i n i t i a t i o n r e a c t i o n can be formulated as 3
EtOS0 X 2
+
(2)
On the b a s i s of an S 2 i s given by N
mechanism the r a t e equation of
initiation
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
POLYETHERS
152 Table I . Reactions of EtOSOJC (X=F and CI) with Sodium Phenoxide a t Room Temperature a
EtOS0 X ^ 2
NaOC H
X
6
b) 5
Reaction Time
Yield
(min)
(%)
(mmol)
(mmol) 0.99
F
4.0
10
96
0.59
F
2.9
30
95
1.15
Cl
3.5
5
93
b) S o l u t i o n i n 6 ml of THF.
a) S o l u t i o n i n 3 ml of THF. c) Based on EtOS0 X. 2
c )
Determined by UV a n a l y s i s .
d[I] dt
Μ [I] [M]
(3)
I n t e g r a t i o n of Equation 3 gave
[ I ]n[I] L 1 J
η
r = ki I [M]dt T
(4)
Λ
t
where
i s the r a t e constant of i n i t i a t i o n . I t has already been e s t a b l i s h e d that the propagation of the c a t i o n i c p o l y m e r i z a t i o n of THF i s expressed by
^y^Tl
> 0 ( C H ) - ( Q · A"
· A"
2
4
(5)
According to a bimolecular mechanism the r a t e equation of propagation i s given by
d[M] dt
= k [P*] f[M] - [H]ej D
(6)
where [M] and [M]e represent the instantaneous and e q u i l i b r i u m monomer c o n c e n t r a t i o n s , r e s p e c t i v e l y , and kp i s the r a t e constant of propagation. I n t e g r a t i o n of Equation 6 leads to
F i g u r e 1 shows the [P*] - time (curve A) and monomer conversion - time (curve B) r e l a t i o n s h i p s i n the THF polymerizat-
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
10.
SAEGUSA
AND
KOBAYASHi
153
Cyclic Ethers
i o n i n i t i a t e d by EtOSO F i n C I ^ C l a t 0°C. A f t e r 20 hr, [P*] reached to 63% of the feed c o n c e n t r a t i o n of the i n i t i a t o r . The presence of the i n d u c t i o n p e r i o d (curve B) i n d i c a t e s a slow i n i t i a t i o n followed by a f a s t propagation. P l o t s of Equations 4 and 7 were made on the b a s i s of the data of curves A and B, respectively. In both cases s t r a i g h t l i n e s passing through the o r i g i n were obtained, the slopes of which gave values of k i = 0.33 Χ ΙΟ"- 1/mol-sec and kp = 0.66x10-3 1/mol-sec, r e s p e c t i v e l y . Table I I l i s t s the k i n e t i c data of three superacid ester i n i t i a t o r s as w e l l as of an oxonium species of EtgO+'BF^*". 5
Table I I .
K i n e t i c Data of the THF P o l y m e r i z a t i o n with Ester I n i t i a t o r s i n CH C1 S o l u t i o n 2
Superacid
2
+
a)
Initiation kiXlO
5
at 0°C
0.33
0.38
0.80
6.1
b
)
(l/mol» sec) Δ Η * (kcal/mol)
13.5
12.8
10.5
16.4
AS* (e.u.)
-34
-37
-44
-16
Propagation kpxlO
3
a t 0°C
0.66
1.4
1.7
3.7
(l/mol- sec) Δ Hp^(kcal/mol)
13.0
11.8
11.6
12
A S * (e.u.)
-26
-28
-29
-26
p
a) Taken from (15, 16, 19, 20). b) Data at 2.5°C (20).
B u l l . Chem. Soc. Japan (3).
The i n i t i a t i o n i s a d i p o l e - d i p o l e r e a c t i o n to produce an oxonium i o n (Equation 2 ) . The k^ values of superacid e s t e r s a r e 1/20 - 1/10 of that of Et30+BF~ and a t l e a s t 2 Χ 1 0 times smaller than the kp values i n the superacid e s t e r systems. The a c t i v a t i o n parameters e x h i b i t e d r e l a t i v e l y low Δ Η * ( f a v o r a b l e ) and Δ s£ (unfavorable) v a l u e s . This tendency has o f t e n been observed i n d i p o l e - d i p o l e S^2 r e a c t i o n s producing i o n i c s p e c i e s , e.g., the Menschutkin r e a c t i o n (21) and the oxonium formation r e a c t i o n from superacid e s t e r s and tetrahydropyran (Reaction 8) ( 2 2 ) . 2
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
POLYETHERS
154
R0S0 X 2
+
"0(3
=
R
'
0
S
° 2
X
"
(
8
)
The kp v a l u e of EtOSC^F i s extremely s m a l l , e.g., about 1/6 of that of Et30BF^T i n i t i a t o r . The kp values of EtOSC^Cl and EtOS0 CF3 are between those of EtOSC^F and Et30 BF4~. Since the a c t i v a t i o n parameters of the propagation are very c l o s e to those of Et30 BF4~", i t i s reasonable to conclude that the propagation i n i t i a t e d by EtOSC^X proceeds mainly v i a an oxonium mechanism (Equation 5 ) . +
2
+
K i n e t i c s of the EtOS02CF3-Initiated P o l y m e r i z a t i o n of THF by and i ^ F Nmr Spectroscopy. I t has been pointed out i n s e v e r a l s t u d i e s (3> Jb 12* 23) that i n the THF polymerization.by a supera c i d e s t e r i n i t i a t o r , e.g., EtOSÛ2CF3, the propagating chain end may be i n the e q u i l i b r i u (Equation 9). Our previou Κ 0S0 CF " 2
I
3
=
0(CH ) 0S0 CF 2
4
2
(9)
3
II
p o l y m e r i z a t i o n i n i t i a t e d with superacid e s t e r s could be c a r r i e d out by % nmr spectroscopy alone ( 3 ) . However, i t was very d i f f i c u l t to v e r i f y d i r e c t l y the e q u i l i b r i u m of Equation 9 due to the l i m i t a t i o n of the s e n s i t i b i t y and r e s o l u t i o n of *H nmr spectroscopy. We d i s c l o s e d that l ^ F spectroscopy i s very powerful to abserve d i r e c t r y both the oxonium counteranion OSO2CF3- (I) and e s t e r species CH2OSO2CF3 ( I I ) . 19
F
nmr spectroscopy (11). F i g u r e 2 shows the ^F nmr spectrum of the THF p o l y m e r i z a t i o n system i n i t i a t e d by EtOS0 CF i n CCI4 a f t e r 48 min a t 13°C. The molar r a t i o of THF to i n i t i a t o r was 5 : 1 . Peak A at S -2.52 ( i n ppm r e l a t i v e to the e x t e r n a l standard of CF3CO2H c a p i l l a r y ) i s assigned to the i n i t i a t o r EtOS02CF3. Peak Β at 8 +0.46 i s due to the oxonium counteranion of I (OSO2CF3-) of the propagating s p e c i e s . F i n a l l y , peak C a t S -2.80is reasonably a s c r i b e d to the e s t e r species of I I (~~-CH OS02CF3). No other peaks were detected during a k i n e t i c run. Thus, the l ^ F spectroscopy provides w i t h a new method f o r the d i r e c t determination of the instantaneous concentrations of i n i t i a t o r and the oxonium and e s t e r species of propagation. F i g u r e 3 shows the v a r i a t i o n s of ([0+] + [E]) (curve A) and [ 0 ] (curve B) as a f u n c t i o n of time under the p o l y m e r i z a t i o n c o n d i t i o n s of F i g u r e 2, where [0+] and [E] denote the concentra t i o n s of the oxonium (I) and e s t e r (II) s p e c i e s , r e s p e c t i v e l y . At the end of the k i n e t i c run ( a f t e r 76 min) 28% of the charged i n i t i a t o r has been r e a c t e d . The molar r a t i o of [0+] to [E] reached to a constant v a l u e of 46 : 54 a t a l a t t e r stage of 2
2
Μ
+
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
3
10.
SAEGUSA
AND
155
Cyclic Ethers
KOBAYASHi
p o l y m e r i z a t i o n ( a f t e r about 30 min). This i n d i c a t e s that the e q u i l i b r i u m of Equation 9 i s a c t u a l l y present i n the THF p o l y m e r i z a t i o n i n i t i a t e d with Et0S0 CF3. S i m i l a r l y the THF polymerization was monitored by 19 nmr spectroscopy i n other four s o l v e n t s . In CHC1«, C ^ C ^ * and benzene s o l v e n t s the f r a c t i o n s of [ 0 ] were 85, 89, and 75% a t 0°C, r e s p e c t i v e l y , a f t e r the e q u i l i b r i u m was reached. In n i t r o benzene, however, the [E] f r a c t i o n was very small, e.g., below 2% a t 0°C throughout the p o l y m e r i z a t i o n . Kinetics. Based on the above nmr r e s u l t s the f o l l w i n g r e a c t i o n s w i l l e x p l a i n the course of the THF p o l y m e r i z a t i o n i n i t i a t e d with E t O S 0 C F (EtOTf). Initiation 2
F
+
2
EtOTf
oQ
+
3
—J
Et-0^_J- OTf" =
Et0(CH ) 0Tf
(10)
Propagation
+ ^^0Q-0Tf-
k
+
oQ
P(i)
+ /-^0(CH ) -0Q · 2
4
OtCH^-^OTf
OTf (11)
and
-0(CH ) 0Tf 2
4
+
W)
oQ
—0(CH ) -0Q · 2
4
0(CH ) ^0Tf 2
IXL
- [Ml
[M]
- [M]
l n
2 t
L
rt
=
k
[ p P
e
U
P
)
J
*
(12)
4
The i n t e g r a t e d form of the r a t e equation of propagation expressed as
OTf"
is
] d t
( 1 3 )
0
where kp^ p) i s the apparent r a t e constant of propagation and [P*] represents the t o t a l c o n c e n t r a t i o n of the propagating s p e c i e s , a
e
8
' "
[P*] = [0 ] +
+
[E]
(14)
The e s t e r species (II) i s not dead, but i s thought to be i n h e r e n t l y capable of propagation (Equation 12), s i n c e the e s t e r species EtOTf i n i t i a t e s the THF p o l y m e r i z a t i o n . [P*] was equal to the amount of the reacted i n i t i a t o r . Therefore, the f o l l o w i n g r e l a t i o n s h i p i s derived
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
156
POLY ETHERS
Time ( hr· * Bulletin of the Chemical Society of Japan Figure 1. Polymerization of THF by EtOSO F at 0°C. [P*]-time (curve A) and monomer conversion-time = 4. 8 X CH Cl soluiion (3). x
2
2
A
c -3
II
1 -2
-1
B
I
0(ppmf
1
Macromolecules Figure 2. F nmr spectrum of the THF po lymerization mixture by EtOSO^CFs initiator in CCl after 48 min at 13°C (11) 19
h
Time(min)
Macromolecules Figure 3. Polymerization of THF with EtOSO CF monitored by F nmr spectroscopy in CCl at 13°C. Rehtionships of ([0 ] + [E])-time (curve A) and of [0*)-time (curve B): [ M ] o = 5.30 mol/U U] ο = 1.05 mol/l. (11). r
S
19
k
+
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
10.
SAEGUSA
AND
k
157
Cyclic Ethers
KOBAYASHi
p(ap) = p ( i )
* i
k
x
+
k
p(e)
· *
( )
x
15
where k p ( i ) and k p ( ) are the r a t e constants of propagation due r e s p e c t i v e l y to the oxonium i o n (I) a n d e s t e r (II) s p e c i e s , and X i and Xe a r e the molar f r a c t i o n s of [0 ] and [Ε], r e s p e c t i v e l y , i . e . , X i + Xe = 1. I t i s reasonable to assume that the magnitude of k p ( ) i s a t l e a s t smaller than that of k-^ which was about 140-280 times smaller than that of k ( i ) (Tables I I I and IV), i . e . , k p ( i ) » k p ( ) . Furthermore, Xe was not so l a r g e , i . e . , below 0.55 i n a l l cases (Tables I I I and I V ) . Therefore, Equation 15 becomes e
+
e
p
e
kp(ap) Consequently,
~
k p ( i ) · Xi
06)
Equation 13 i s converted to
In
[ML -
2
Ê [M] - [M] t
P V
e
U
0
+
The i n t e g r a t e d values of [P*] i n Equation 13 and [ 0 ] i n Equation 17 were obtained by g r a p h i c a l i n t e g r a t i o n on curves A and Β i n F i g u r e 3, r e s p e c t i v e l y . The monomer conversion was followed by % nmr spectroscopy (3) under the same r e a c t i o n c o n d i t i o n s as F i g u r e 3. Thus, p l o t s of Equations 13 and 17 could be made as shown i n F i g u r e 4 (A) and (Β), whose slopes gave values of kp(ap) = I . 6 X I O - and k p ^ ) = 3 . 6 *10"* 1/mol-sec at 13°C i n C C l ^ . S i m i l a r l y the k^(ap) *d k p ( i ) values were determined at 0 and 25°C (Table I I I ) . I t i s i n t e r e s t i n g to note that the [0 ] f r a c t i o n was not changed a t the r e a c t i o n temperatures 3
3
ai
+
+
Table I I I .
Rate Constants, A c t i v a t i o n Parameters, and the [ 0 ] F r a c t i o n i n the THF P o l y m e r i z a t i o n by E t 0 S 0 C F I n i t i a t o r i n CCI, ) 4 2
3
a
Temp
k
±
X 10
5
k
p(
a
p
)
Χ 10
3
k
p(
i
)
χ 10
3
[0+] Γ &
(°C)
(1/mol-sec)
(1/mol-sec)
(1/mol-sec)
0
0.80
0.84
2.2
45
13
2.1
1.6
3.6
46
25
3.9
3.0
5.7
47
16
13
-12
-24
ΔΗ* 20 (kcal/mol) AS^e.u.) a) b)
_5
(%)°
b
)
η
[M] = 5.30 mol/1, [I] = 1.05 mol/1. ο ο A f t e r the e q u i l i b r i u m was reached. Macromolecules (11).
In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
158
POLYETHERS
of 0, 13, and 25°C, a f t e r the e q u i l i b r i u m of Equation 9 has been reached. The r e s u l t s of s i m i l a r k i n e t i c s i n other four solvents a r e shown i n Table IV. The k^ values were increased with an i n c r e a s e
+
β
ο
ϋ
Ο
•Η U c0 Ν •Η
ch co oo σ> A
co
CO «4-1
lyme
M
ο
υ
rH
Φ
u 4-1 CJ CM
χ•Η ?Ο
ο CO
Γ*·*
Ο
CM
Η
•Η 4-»
Â
00
Ρ-τΗ
Φ
Ν-/
/-s ϋ
+
o
>
_
β
«—' TH
ω
μ
ο
43 4-1 4-1 CO
m
ΓΗ
β
«H
ω
H
β
c0 4J
α
m
te
u ω CM C Ο ο CO
ο 4οJ Φ w 4J
.
Ο
Ο
·
M
33 H
Φ
43
rH
50 β •Η
Ν-/
Φ Ο 43 Φ 4-1 V4
β
o
«4-4 4-1 Ο Χ
CO 4-J CO
co oo
co
CM
Ο
g
43 CM
00
CO ON
CM
co
β
ο
CO CO CO
o
43
CO
ϋ
T3
m
•Η U
φ
Ο
c0
II
υ φ
Ο rH
Γ-.
Φ
eu
42
U
43 •H Φ
CM
4J
β
CO
Φ
co H
II
CO co
Ο
ο oo
ω
4J
c0 4-»
Ο
χ-5 •πι
nd *H
Φ
•Η
Φ
ο
ιΗ
•Η
CO Ο
•H — · . Pu
Φ 43
ϋ
Ο CO
CO U
CO
β
co Ο /"Ν ιΗ Ο ν Φ ω
Ο
φ
.5
3.7
+
Et30 BF4~
4.I
b
4.6
d
7.8
d
3
BF -ECH ) 3
c
C
b
BF -ECH )
3, 11
e, f
0.70
a
e
e
13
g
19
g
18
g
18
g
18
b
SnCl4-ECH ) AlEtCl a) b) c) d) f)
2
Ethyl 2,4,6-trinitrobenzenesulfonate. ECH : e p i e h l o r o h y d r i n as a promotor. S o l u t i o n p o l y m e r i z a t i o n i n CH^C^. Bulk p o l y m e r i z a t i o n . e) By % nmr spectroscopy. By l ^ F nmr spectroscopy, g) By phenoxyl end-capping method.
CH C1
CH G1
0
EtOCH CCH OS0 CF 2
2
CH C1 2
IV
CH C1
9
l 2
2
3
9
, 2
ι i
EttOCHgGCHg^jOCHgÇCHgOSOgCFg CH C1
CH C1
2
V
2
(rè"2)
nitrobenzene s o l v e n t . C h a r a c t e r i s t i c peaks a t e ( S 4.80) and A ( S 4.83), which a r e assigned to o(-methylene protons (2H) o f -OSC^CF^ group i n e s t e r type species IV and V, r e s p e c t i v e l y . Other peaks assignments may be found i n F i g u r e 5. These r e s u l t s i n d i c a t e that the propagating species of the BCMD p o l y m e r i z a t i o n i s e s t e r type species given by IV and V. An a u t h e n t i c compound o f IV was prepared by the r e a c t i o n of EtOSOoCF^ with BCMO and i s o l a t e d by d i s t i l l a t i o n i n vacuo, bp, 45-46*0 10.04 mmHg). The chemical s h i f t of the methylene protons