Catalytic Polymerization of Cycloolefins (Studies in Surface Science and Catalysis, 131)

Studies in Surface Science and Catalysis 131 CATALYTIC POLYMERIZATION OF CYCLOOLEFINS Ionic, Ziegler-Nwtta and ring-opening met~he~s polymerization

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Studies in Surface Science and Catalysis Advisory E d i t o r s :

B. D e l m o n

a n d J.T. Y a t e s

Vol. 131

CATALYTIC POLYMERIZATION OF CYCLOOLEFINS Ionic, Ziegler-Natta and ring-opening metathesis polymerization

Valerian Dragutan

Institute of Organic Chemistry of the Romanian Academy, Bucharest, Romania

Roland

Streck

H~ils AG, Marl, Germany

20O0

ELSEVIER Amsterdam

- - L a u s a n n e - - N e w York - - O x f o r d - - S h a n n o n J

Singapore -- Tokyo

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V

To the outstanding community of prominent scientists and researchers, who devoted their efforts and ingenuity to the development of this facinating field of polymer chemistry and greatly inspired us in our work.

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vii

PREFACE

Ring-opening metathesis polymerization (ROMP) of cycloolefins is one of the most remarkable findings in polymer chemistry since the discovery of Ziegler-Natta polymerization of olefins. The unprecedented development of the new catalytic process originates in the high levels of achievement in olefin metathesis as well as in the abundant data accumulated on Ziegler-Natta polymerization. The impressive development of both ROMP and Ziegler-Natta polymerization inspired us to also take a broader view backwards to the existing research conducted on the cationic polymerization of cycloolefins and on its anionic counterpart, in order to outline the apparent connections between these earlier catalytic processes and the new discovery. As a natural consequence of this spectacular evolution, an array of new cycloolefin derived products have made their way to industrial sc~e manufacture. Moreover, a larger range of licensed products with excellent chemical, electrical, mechanical, optical and thermal properties expect their turn to be commercialized. Research in the area of catalytic polymerization of cycloolefins is intensely continuing in various academic and industrial teams, and many practical applications are emerging and, at the same time, further thermodynamic, kinetic, mechanistic and stereochemical aspects of these reactions are being elucidated. It is significant to follow the strong increase of the number of patents and publications, especially on ring-opening metathesis polymerization (ROMP) and Ziegler-Natta copolymerization, during the last four decades, which have promoted a range of new commercial products and opened the way to potential other applications in the near future. The obvious interest in this area is manifested by the many outstanding contributions presented at various international conferences and symposia on catalysis, organometallics and polymer chemistry. The book "Catalytic Polymerization of Cycloolefins: Ionic, ZieglerNatta and Ring-Opening Metathesis Polymerization" highlights the major trends appeared in the field of cycloolefin polymerization over the last four decades. The book critically evaluates the two main pathways that cycloolefins can follow under the action of specific catalytic systems,

VIII namely vinyl and ring-opening metathesis polymerization, both allowing the manufacture of numerous products with wide applicability in modem technologies. Furthermore, related emerging synthetic procedures are also elaborately outlined emphasizing the unlimited possibilities of these catalytic reactions under a variety of conditions. The wealth of information is systematically and logically compiled according to the basic catalytic processes involved, the types of monomers and catalysts, the structure and properties of the produced polymers. A distinctive feature is an exhaustive literature survey, till the end of 1999, with special accent on published patents and industrial applications. In the first introductory chapter, the short presentation of some general aspects of cycloolefin polymerization is followed by essential definitions and a description of reaction types, the scope and limitations of these catalytic reactions are further presented. The next three chapters largely illustrate a wide range of monomers, catalytic systems and reaction conditions. Special attention is devoted to the versatility of cycloolefin monomers and minute synthesis of substituted monomers, to the recently developed, selective chiral metallocene catalysts, to well-defined, living metathesis catalytic systems, to catalysts tolerant toward functionlities or water soluble catalytic systems as well as to the main reaction parameters. Chapters 5 through 10 cover the broad area of the studied cationic, anionic, Ziegler-Natta and ring-opening metathesis polymerization reactions of cycloolefins. Treatment of these processes is essentially organized on monocyclic, bicyclic and polycyclic olefins. Functionalized or heteroatomcontaining monomers are also included. The next chapter deals with the vast field of cycloolefin copolymerization. Herein, the multiple reaction types are briefly presented, then the three oopolymerization modes (cationic, Ziegler-Natta and ringopening metathesis) are fully illustrated. Of special significance from a theoretical and practical point of view is Chapter 12 focusing on the structure and properties of poly(cycloolefin)s, as determined from solution and solid state investigations. Despite the fact that the difficult task of structure elucidation makes use of most sophisticated spectroscopic methods, sometimes particular properties of polymers, such as insolubility in common solvents or infusibility in normal conditions, can render them practically not r Chapters 13 through 16 thoroughly discuss the thermodynamics, kinetics, mechanisms and stereochemistry of catalytic cycloolefin polymerization. The fundamental thermodynamic and kinetic aspects of

IX vinyl and ring-opening metathesis polymerization are separately dealt with and conclusions on the reaction mechanisms are drawn therefrom. Stereochernistry topics are interpreted on the basis of the presently accepted reaction mechanisms. The most important related processes, such as Ziegler-Natta polymerization of olefins and dienes, olefin metathesis, ring-opening metathesis (ROM), ring closing metathesis (RCM), acyclic diene metathesis (ADMET) and polymerization of acetylenes are surveyed in the following chapter. The last chapter of the book offers the reader the ultimate result of decades of outstanding research in these areas - industrial applications of cycloolefin polymers, with some emerging strategies for new products. Herein, pertinent data about synthesis procedures, physical-mechanical and chemical properties, as well as economical aspects are made available. The monograph, a well-constructed and stimulating guide to the ever-growing area of catalytic polymerization of cycloolefins, is intended mainly for the specialist research audience but will be of great use to post graduates and teaching staff with an interest in current developments in this field. Since the book includes reference to more general aspects and related fundamental reviews, it addresses itself also to chemical engineers, researchers and advanced students working in catalysis, organicYorganometaUic chemistry, petrochemistry and macromolecular chemistry. At the same time, it is hoped that some parts of the work will be useful to specialists from areas applying specialty polymers, e.g. computer technology, telecommunications, optics, microelectronics, fine mechanics, medicine, transportation, construction, sports and agriculture. The authors take a great pleasure in gratefully acknowledging the generous assistance of many colleagues and collaborators and are especially indebted to Drs. H. Eleuterio (DuPont), N. Calderon (Goodyear Tire & Rubber Co.) and G.D. Benedikt (BFGoodrich Co.) and Professors A.J. Amass (University of Aston, Birmingham, UK), J.M. Basset (Villeurbanne, Fr), H.-H. Brintzinger (University of Konstanz), T.C. Chung (PennState University), M. Farona (UNC, Greensboro), W.J. Feast (Durham University, UK), R.H. Gmbbs (Caltech, Pasadena), H HOcker (RWTH, Aachen), K. Hummel (TU, Graz), W. Kaminsky (University of Hamburg), T.J. Katz (Columbia University), R.R. Schrock (MIT, Cambridge), F. Stelzer (TU, Graz), E. Thom-Csanyi (University of Hamburg) and K. Weiss (Bayreuth University) for kindly providing manuscripts or reprints of their extensive work. We are much obliged to Drs. K.-M. Diedrich (Htils AG), A.E. Martin (Hercules Co), H.-T. Land (Hoechst A.G.) for providing

X valuable information on properties and technological applications of commercial cycloolefin polymers. One of the authors (R.S.) thanks his former employers at Hials AG for permission to use their information facilities. The other author (V.D.) deeply thanks his wife, Dr. lleana Dragutan, for helpful discussions and relevant suggestions during the manuscript elaboration and his son, Matei Dragutan, for his generously offered expertise in producing the graphical material included in this work. Very special thanks are due to Elesevier Science, and particularly to Drs. A. van der Avoird and H. Manten-Werker, for their kind and stimulating support for the publication of this book.

Bucharest, Romania Marl, Germany March, 2000

Valerian Dragutan Roland Streak

X1

CONTENTS

PREFACE ......................................................................... Chapter 1. I.I. 1.2. 1.3. 1.4.

VII

INTRODUCTION .................................................... ~ e r a l Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Definitions and Reaction Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Scope and Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 l 2 11 12

Chapter 2. C Y C L O O L E F I N M O N O M E R S . TYPES AND S Y N T H E S E S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2. I. Monomers for Cationic Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.2. Monomers for Anionic Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 2.3. Monomers for Ziegler-Natta Polymerization . . . . . . . . . . . . . . . . . . . . 19 2.4. Monomers for Ring-Opening Metathesis Polymerization ...... 21 2.4.1. Monocyclic Olefins for Ring-Opening Metathesis Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 l 2.4.2. Bicyclic and Polycyclic Olefins for Ring-Opening Metathesis Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.4.3. Monomers with Functional Groups . . . . . . . . . . . . . . . . . . . . . . . 27 2.4.4. Hetero~yclic Monomers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 2.5. Synthesis of Cycloolefin Monomers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 2.5. I. Synthesis of Monocyclic Olefins . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 2.5.2. Synthesis of Bicyclic and Polycyclic Olefins . . . . . . . . . . . . . . 5 l 2.5.3. Synthesis o f Functionalized Cycloolefins . . . . . . . . . . . . . . . . . 69 2.5.3.1. Halogen-Containing Monomers . . . . . . . . . . . . . . . . . . 69 2.5.3.2. Oxygen-Containing Monomers . . . . . . . . . . . . . . . . . . 77 2.5.3.3. Sulphur-Containing Monomers . . . . . . . . . . . . . . . . . . 8 l 2.5.3.4. Nitrogen-Containing Monomers . . . . . . . . . . . . . . . . . 82 2.5.3.5. Boron-Containing Monomers . . . . . . . . . . . . . . . . . . . . 83 2.5.3.6. Silicon-Containing Monomers . . . . . . . . . . . . . . . . . . . . 84 2.5.3.7. Metal-Containing Monomers . . . . . . . . . . . . . . . . . . . . . 85 2.5.3.8. Monomers for Side-Chain Liquid Crystalline Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 2.5.3.9. Synthesis of Heterocyclic Monomers ........... 90

XII 2.5.3.10. Synthesis of Macromonomers . . . . . . . . . . . . . . . . . . 99 2.6. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Chapter 3. CATALYTIC S Y S T E M S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 3.1. Cationic Catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 3.1.1. BrOnsted Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 3.1.2. Lewis Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 3.1.2.1. One-Component Lewis Acid Catalysts ........ 117 3.1.2.2. Two-Component Lewis Acid Catalysts ........ 118 3.2. Anionic Catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 3.3. Ziegler-Natta Catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 3.3.1. One-Component Ziegler-Natta Catalysts . . . . . . . . . . . . . . . . 120 3.3.2. Two-Component Coordination Catalysts . . . . . . . . . . . . . . . 121 3.4. Ring-Opening Metathesis Polymerization (ROMP) Catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 3.4.1. One-Component ROMP Catalysts . . . . . . . . . . . . . . . . . . . . . . . 128 3.4.2. Two-Component ROMP Catalysts . . . . . . . . . . . . . . . . . . . . . . . 140 3.4.3. Multicomponent ROMP Catalysts . . . . . . . . . . . . . . . . . . . . . . . . 146 3.4.4. Catalysts for R O M P in Water Systems . . . . . . . . . . . . . . . . . . 150 3.5. Synthesis of Catalysts for Cycloolefin Polymerization ........ 152 3.5.1. Synthesis of Cationic Catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 3.5.2. Synthesis of Anionic Catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 3.5.3. Synthesis of Two-Component Ziegler-Natta Catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 3.5.4. Synthesis of Ring-Opening Metathesis Polymerization Catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 3.5.4.1. One-Component Metathesis Catalysts ......... 162 3.5.4.2. Two-Component Metathesis Catalysts ........ 165 3.5.4.3. Three-Component Metathesis Catalysts ....... 165 3.5.4.4. WeU-Defined Metathesis Catalysts . . . . . . . . . . . . . 165 3.6. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 Chapter 4. REACTION C O N D I T I O N S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 4.1. Monomer Concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 4.2. Catalyst Concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202 4.3. Ratio of Reactants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 4.4. Premixing Time of Reaction Components. 9 ... 206 4.5. Addition of Reaction Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208 4.6. Reaction Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210

XlII

4.7. Reaction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216 4.8. Reaction Medium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8.1. Solvents for Homogeneous Catalysis . . . . . . . . . . . . . . . . . . . . 4.8.2. Solvents for Heterogeneous Catalysts . . . . . . . . . . . . . . . . . . . 4.9. Inhibitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.10. Activators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.11. Reaction Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.12. Effect of Agitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.13. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

220 220 224 225 226 230 232 233

Chapter 5. CATIONIC P O L Y M E R I Z A T I O N OF C Y C L O O L E F I N S . . . 2 3 7 5.1. Cationic Polymerization of Monocyclic Olefins . . . . . . . . . . . . 237 5. I. I. Four-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . 237 5.1.2. Five-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . 239 5. 1.3. Six-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . . . 253 5.1.4. Seven-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . 260 5.1.5. Eight-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . 26 l 5.2. Cationic Polymerization of Bicyclic Olefins . . . . . . . . . . . . . . . . 264 5.3. Cationic Polymerization of Polycyclic Olefins . . . . . . . . . . . . . . 303 5.4. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313 Chapter 6. ANIONIC P O L Y M E R I Z A T I O N OF C Y C L O O L E F I N S ..... 319 6.1. General Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319 6.2. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325 Chapter 7. Z I E G L E R - N A T T A P O L Y M E R I Z A T I O N OF C Y C L O O L E F I N S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327 7.1. Polymerization o f Monocyclic Olefins . . . . . . . . . . . . . . . . . . . . . . 327 7.1.1. Four-Membered Rings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327 7.1.2. Five-Membered Rings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331 7.1.3. Six-Membered Rings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338 7.1.4. Seven-Membered Rings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339 7.1.5. Eight-Membered Rings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340 7.2. Polymerization ofBicyclic Olefins . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343 7.3. Polymerization of Polycyclic Olr . . . . . . . . . . . . . . . . . . . . . . . . . . 355 7.4. Polymerization o f Functionalized Cycloolefins . . . . . . . . . . . . . . 363 7.5. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372

XIV Chapter 8. RING-OPENING METATHESIS POLYMERIZATION OF CYCLOOLEFINS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 75 8. I. Ring-Opening Polymerization of Monocyclic Olefins .... 375 8.1.1. Four-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . 375 8.1.2. Five-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . . 383 8.1.3. Six-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . . . 394 8.1.4. Seven-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . 395 8. 1.5. Eight-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . 397 8.1.6. Nine-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . 413 8.1.7. Ten-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . . 414 8.1.8. Twelve- and High-Membered Ring Monomers ..... 416 8.2. Ring-Opening Polymerization of Bicyclic Olefins ......... 421 8.3. Ring-Opening Polymerization of Polycyclic Monomers... 455 8.4. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492 Chapter 9. POLYMERIZATION OF FUNCTIONALIZED CYCLOOLEFINS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513 9.1. General Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513 9.2. Four-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . . . . . . . 513 9.3. Five-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 520 9.4. Six-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 521 9.5. Eight-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . . . . . . 523 9.6. Higher Monocyclic Olefins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 530 9.7. Functionalized Bicyclic Olefins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532 9.8. Functionalized Polycyclic Olefins . . . . . . . . . . . . . . . . . . . . . . . . . . . . 631 9.9. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 639 Chapter 10. POLYMERIZATION OF HETEROCYCLIC OLEFINS... 651 l 0. I. Four-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . . . . . 651 10.2. Five-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . . . . . . 65 l 10.3. Heteroatom-Containing Norbomenes and Norbomadienes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 656 l 0.4. Seven-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . . . . 683 10.5. High-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . . . . . 683 l 0.6. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 684 Chapter 11. COPOLYMERIZATION REACTIONS OF CYCLOOLEFINS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 687 11.1. Introduction. Reaction Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 687

XV 11.2. Cationic Copolymerization of Cycloolefins . . . . . . . . . . . . . 690 11.2.1. Monocyclic Monomers . . . . . . . . . . . . . . . . . . . . . . . . . . . 690 11.2.2. Bicyclic and Polycyclic Monomers . . . . . . . . . . . . . . 698 11.3. Ziegler-Natta Copolymerization of Cycloolefins ....... 707 11.3.1. Monocyclic Monomers . . . . . . . . . . . . . . . . . . . . . . . . . . . 707 11.3.2. Bicyclic and Polycyclic Monomers . . . . . . . . . . . . . . 715 11.4. Ring-Opening Metathesis Copolymerization of Cycloolefins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 774 11.4. I. Monocyclic Monomers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 774 11.4.2. Bicyclic and Polycyclic Monomers . . . . . . . . . . . . . . . 782 11.4.3. Copolymers by ROMP of Functionalized Cycloolefins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 801 I 1.4.4. Synthesis of Star Copolymers . . . . . . . . . . . . . . . . . . . . . 836 11.4.5. Synthesis of Graft Copolymers . . . . . . . . . . . . . . . . . . . . 842 11.4.6. Copolymers from Macromonomers . . . . . . . . . . . . . . 844 11.4.7. Copolymers from Cycloolefins and Unsaturated Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 846 11.4.8. Copolymers from Unsaturated Polymers ......... 849 11.4.9. Copolymers from Cycloolefins and Acetylenes..850 11.4.10. Copolymers from Heterocyclic Olefins .......... 854 11.4.11. Copolymers by Different Polymerization Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 857 11.5. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 862 Chapter 12. STRUCTURE AND PROPERTIES OF POY(CYCLOOLEFIN)S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.1. Structure of Poly(cycloolefin)s . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12. I. I. Cationic Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.1.2. Anionic Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.1.3. Ziegler-Natta Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.1.4. ROMP Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.2. Solution Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.3. Solid State Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.4. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

875 875 875 888 890 90 l 923 924 93 5

Chapter 13.THERMODYNAMIC ASPECTS OF C Y C L O O L E F I N P O L Y M E R I Z A T I O N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 943 13.1. Thermodynamic Stability of Cycloolefin Monomers .... 943 13.2. Thermodynamic Parameters of Cycloolefin

XVI Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 945 13.3. Thermodynamic Equilibrium in Ring-Opening Metathesis Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 949 13.4. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 964 Chapter 14. REACTION KINETICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 967 14.1. Kinetics of Cationic Polymerization . . . . . . . . . . . . . . . . . . . . . . 967 14.2. Kinetics of Ziegler-Natta Polymerization . . . . . . . . . . . . . . . . 973 14.3. Kinetics of Ring-Opening Metathesis Polymerization..980 14.3.1. Kinetics of Initiation and Propagation. Living Metathesis Polymerization . . . . . . . . . . . . . . . . 980 14.3.2. Kinetic Models for Mctathesis Polymerization.981 14.4. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 992 Chapter 15. ASPECTS OF REACTION MECHANISM . . . . . . . . . . . . . . . . . . . 995 15.1. Mechanism of Cationic Polymerization of Cycloolefins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 995 15.1. I. Initiation Systems for Cationic Polymerization.996 15.1.2. Nature of Cationic Propagation Reactions ...... 997 15.1.3. Termination Reactions of Cationic Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1005 15.2. Mechanism of Anionic Polymerization of Cycloolefins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1006 15.2.1. Initiation and Propagation. Living Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1007 15.2.2. Molecular Structure of Anionic Initiators ...... 1009 15.3. Mechanism of Ziegler-Natta Polymerization of Cycloolefins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . l 010 15.3. I. Structure of Active Species . . . . . . . . . . . . . . . . . . . . . . 101 l 15.3.2. Mechanism of Insertion Reactions .............. 1013 15.4. Mechanism of Ring-Opening Metathesis Polymerization of Cycloolefu~ . . . . . . . . . . . . . . . . . . . . . . . . . . . l 015 15.4. I. Survey of Proposed Mechanisms . . . . . . . . . . . . . . . . l 016 15.4.2. Features of Metallacarbene/ Metallacyclobutane Mechanism ................. 1020 15.4.2. I. Mechanism of Initiation Reaction .... 1020 15.4.2. I. 1. Initiation with WCI6/ Organoaluminium Compounds ..... 1023 15.4.2.1.2. Initiation with WCI6/

XVII Organotin Compounds ............... 1026 15.4.2.1.3. Initiation with WClgqNater .......... 1027 15.4.2.1.4. Initiation with Metallacarbene Complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1028 15.4.2.1.5. Evidence for Initiating Metallacarbene Complexes .......... 1029 15.4.2.2. Mechanism of Propagation Reaction. 1031 15.4.2.2.1. Features of Metallacarbene/ Metallacyclobutane Mechanism .... 1031 15.4.2.2.2. Detection of Reduced Paramagnetic Species in WCk Systems . . . . . . . . . . . . . . . . . . . . . 1038 15.4.2.2.3. Evidence for MetallacarbeneOlefin Complexes .................... 1040 15.4.2.2.4. Evidence for Propagating Metallacarbene Complexes .......... 1041 15.4.2.2.5. Evidence for Propagating MetaUacyclobutane Complexes ..... 1042 15.4.2.3. Mechanism of Termination Reaction.. 1043 15.5. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1044 Chapter 16. STEREOCHEMISTRY OF CYCLOOLEFIN POLYMERIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1051 16.1. Steric Efffects in Cationic Polymerization .............. 1051 16.2. Steric Configuration of Vinyl Polymers ................ 1053 16.3. Stereoselectivity in Ziegler-Natta Polymerization ..... 1055 16.4. Steric Configuration of Polyalkenamers ................ 1057 16.5. Stereoselectivity in Ring-Opening Metathesis Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1059 16.6. Tacticity of Polyalkenamers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1079 16.7. The Nature of Steric Interactions in ROMP ........... 1088 16.8. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1097 Chapter 17. RELATED PROCESSES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1103 17.1. Catalytic Polymerization of Olefins and Dienes ....... 1103 17. I. I. Cationic Polymerization of Olefins and Dienes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1103

XVIIl 17.1.2. Anionic Polymerization of Olefins and Dienes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1104 17.1.3. Ziegler-Natta Polymerization of Olefins and Dienes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1105 17.2. Atom Transfer Radical Polymerization of Vinyl Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1108 17.3. Metathesis Reactions of Olefins and Acetylenes ....... 1109 17.3.1. Ring-Opening Metathesis (ROM) .............. 1111 17.3.2. Ring-Closin Metathesis (RCM) ................. 1112 17.3.2.1. Synthesis of Carbocycles ............. 1113 17.3.2.2. Synthesis of Unsaturated Heterocycles . . . . . . . . . . . . . . . . . . . . . . . . . . . 1115 17.3.2.3. Synthesis of Crown Ethers .......... 1117 17.3.2.4. Synthesis of Polycyclic Polymers... 1118 17.4. Acyclic Diene Metathesis (ADMET) and Acyclic Diyne Metathesis (ADIMET) Polymerization ......... 1118 17.5. Carbonyl Olefination Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . 1120 17.5.1. Synthesis of Olefins and Cycloolefins .......... 1121 17.5.2. Carbonyl-Olefin Exchange Polymerization... 1122 17.6. Metathesis Degradation of Unsaturated Polymers .... 1123 17.6.1. Intramolecular Degradation ..................... 1123 17.6.2. Intermolecular Degradation .................... 1124 17.6.3. Acyclic Diene Metathesis (ADMET) Depolymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1124 17.7. Catalytic Polymerization of Acetylenes ................ 1125 17.7.1. Cationic Polymerization of Acetylenes ........ 1125 17.7.2. Anionic Polymerization of Acetylenes ........ 1125 17.7.3. Ziegler-Natta Polymerization of Acetylenes.. 1126 17.7.4. Metathesis Polymerization of Acetylenes ..... 1126 17.8. Ring-Opening Polymerization of Heterocycles ......... 1128 17.8.1. Cationic Ring-Opening Polymerization of Heterocycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1128 17.8.2. Anionic Ring-Opening Polymerization of Heterocycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1129 17.9. Miscellaneous Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1129 17.9.1. Metathesis of Alkanes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1130 17.9.2. Catalytic Isomerization of Olefins .............. 1130 17.9.2.1. Cationic Isomerization of Olefins .... 1131 17.9.2.2. Anionic Isomerization of Olefins .... 1131

XIX 17.9.2.3. Ziegler-Natta Isomefization of Olefins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17.9.2.4. Metathefieal Isomerization of Olefins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17.9.3. Cyclopropanation of Olefins . . . . . . . . . . . . . . . . . . . . 17.9.4. Friedel-Crafis Alkylation Reactions ........... 17.10. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1132 1132 1134 1134

Chapter 18. P R A C T I C A L APPLICATIONS AND F U T U R E OUTLOOK ........................................................ 18.1. Commercial Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18.1. I .Hydrocarbon Resins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18.1.2. Polyalkenamers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18.1.2.1. trans-Polyoctenamer . . . . . . . . . . . . . . . . .

1141 1141 1141 1153 1153

1131

18.1.2.2. Polynorbornene . . . . . . . . . . . . . . . . . . . . . . . 1161 18.1.2.3. Poly(dicyclopentadiene) . . . . . . . . . . . . . . 1173 18.1.3. Cycloolefin Copolymers . . . . . . . . . . . . . . . . . . . . . . . . . 1179 18.1.3.1. Topas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1179 18.2. Products of Interest for Industry . . . . . . . . . . . . . . . . . . . . . . . 1181 18.2.1. trans-Polypentenamer . . . . . . . . . . . . . . . . . . . . . . . . . . 1181 18.2.2. cis-Polypentenamer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1200 18.2.3. cis-Polyoctenamer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1203 18.2.4. Cyclorene Rubber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1206 18.3. Potential Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1207 18.3.1. Synthesis of Monodispersed Polyethylene... 1207 18.3.2. Synthesis of 1,4-Polybutadiene . . . . . . . . . . . . . . . . 1207 18.3.3. Synthesis of 1,4-Polyisoprenr . . . . . . . . . . . . . . . . . 1208 18.3.4. Alternating Copolymers . . . . . . . . . . . . . . . . . . . . . . . . 1209 18.3.5. Block Copolymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1210 18.3.6. Comb and Star Copolymers . . . . . . . . . . . . . . . . . . . . 1214 18.3.7. Amphiphilic Star Block Copolymers ......... 1215 18.3.8. Macrocyclic Compounds . . . . . . . . . . . . . . . . . . . . . . . 1215 18.3.9. Conducting Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . 1216 18.3.10. Semiconductors and Metal Clusters ......... 1221 18.3.11 .Functionalized Polymers . . . . . . . . . . . . . . . . . . . . . . . 1227 18.3.12.Polymers from Heterocyclic Olefins ......... 1231 18.3.13.Telechelic Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1232 18.3.14.Liquid Crystalline Polymers . . . . . . . . . . . . . . . . . . . 1233

XX 18.3.15. Optically Active P o l y m e r s . . . . . . . . . . . . . . . . . . . . 1235 18.3.16. M i s c e l l a n e o u s Applications . . . . . . . . . . . . . . . . . . 1236 18.4. F u t u r e O u t l o o k . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 8 18.5. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1239

SUBJECT INDEX ..............................................................

1249

Chapter I

INTRODUCTION

1.1. General Aspects In the presence of some specific catalytic systems, the cycloolefms (cycloalkenes) undergo vinyl and ring-opening metathesis polymerization yielding poly(cycloalkene)s in the former and polyalkenamers in the latter case (Eq 1.1).

CI

(1.1)

The polyalkenamers produced by ring-opening metathesis polymerization are also named poly(1-alkenylene)s At present, the two types of polymerization reactions of cycloolefins are well documented for a large number of monomers and catalytic systems. ~'~ Generally, the vinyl polymerization of cycloolefins is initiated by cationic, anionic and Ziegler-Natta coordination catalysts while the ringopening polymerization is promoted by metathesis (ROMP) catalysts. Extensive kinetic and thermodynamic work as well as stereochemical and mechanistic studies are published by numerous research groups. ~,-z0 While vinyl polymerization has found various applications in the manufacture of hydrocarbon resinsz~ and recently in the production of copolymers of cycloolefins, zz ring-opening metathesis polymerization has become a versatile method for the synthesis of a large class of polymers having desired physical and chemical properties, particularly good mechanical, electrical and optical characteristics as well as a superior weathering and heat resistant behavior. ~

1.2. Definitions and Reaction Types

In the course of vinyl polymerization, the cycloolefin wig open the carbon-carbon double bond with formation of polymers containing cyclic moieties in their recurring units (F~. 1.2).

The carbon-carbon double bond will open formally by a 1,2-addition reaction involving a carbocationic, cmbanionic or Ziegler-Natta insertiontype mechanism, depending primarily on the nature of the catalyst employed. In the first case, the initiating and propagating species will consist of free or associated carbocations, in the second of free or associated carbanions and in the third one will possess single m e t a l - ~ n bonds as the active sites. Of these reaction pathways, the most encountered are the carbocationic and Ziegler-Natta type mechanisms which are commonly present in the reactions of a large number of monomers. By vinyl polymerization, the c a r b o n ~ o n double bond can be opened via a trans mode, resulting in threo polymers of diisotactic, disyndiotactic or atactic structure (F-xl. 1.3).

GI

trent

-9

(1.3)

or via a cis mode, to yield erythro polymers of diisotactic, disyncfiotactic or atactic configuration (Eq. 1.4).

(3'

ds

(1.4)

:

Depending on the structure of the monomer and reaction conditions, in ~ o e a t i o n i c polymerization the 1,2-~ldition of ~ n - c a r b o n double bond may be accompanied by some side addition reactions or skeleton rearrangements. For instance, in the case of cyclodienes, the 1,2-addition reaction will be currently accompanied by 1,4-addition reactions (Eq. 1.5).

r

(1.5) r

11,

Alternatively, the polycyclic olefins will give also polymers having 1,2recurring units beside rearranged units with a more complicated structure (Eq. 1.6).

(1.6)

When the recurring unit in the polymer chain has one or more unsaturated bonds, cross-linked structures may arise as result of some secondary intemmlecular reactions under the action of the catalytic system (Eq. 1.7).

n

L.

Vinyl copolymers can be obtained by the reaction of two or more different cycloolefins, working under adequate reaction conditions (Eq.

].8).

I

!1

!

(1.8)

These copolymers may have a random, alternating or block distribution of the monomer units, depending essentially on the monomer reactivity and the reaction conditions (Eq. 1.9-1.11).

/~

~

_ 1

ca2~~ --

II

II

II

1 (1.9)

| [ ((cHz~I '~~(( z~r (1"10) i

I

i

[

l

(1.11)

Starting from monocyclic or polycyclic diolefins or polyolefins, graft copolymers can be obtained by a rigorous control of the monomer selection and using appropriate catalytic systems and operating conditions (F~. 1.12).

n

~

=

(1.12)

m

By the ring-opening metathesis polymerization, the cycloolefin will open the ring at the carbon-carbon double bond with formation of unsaturated polymers in which the u~turation degree is preserved throughout the polymer chmn (F~. 1.13).

In this process, the polymer chain is growing by an insertion-type mechanism involving a metallacar~ne propagating species. Depending primarily on the reaction conditions and monomer structure, the ring-opening metathesis polymerization can result in the formation of trans or cis stereoconfigurations of the double bonds in the polymer chain (Eq. 1.14).

I

(1.14)

In the case of polycyclic olefins, the cycle incorporated into the polymer chain will give rise to structures in which the successive rings stand in isotactic (m) or syndiotactic (r) configurational relationship (Eq. 1.15).

=

0.1S)

Furthermore, when the cycloolefin has substimcnts in certain positions or is chiral, polymers with head-head (HH), head-tail (HT) or tailtail (TT) structures may arise, each one having m or r configurational relationships and containing cis or trans double bonds along the polymer chain (Eq. 1.16).

=

(1.1e) \

~ \

i

Cross-linked polymers can also form when the monomer has two or more orders of unsaturation (Eq. 1.17).

(1.17)

..--.------lit,.

1,

By ring-opening polymerization of cycloolefins, cyclic oligomers or macrocycles can form along with linear polymers, depending on the monomer nature, catalyticsystem and reaction parameters (Eq. I.18).

,=

OI

(1.18)

C:__IIIIIIIIIIIIIIIIIII-D

Formation of cyclic oligomers, ranging from simple dimers, trimers etc. to macr~-'Tclic structures, ~.~urs by several parallel prc~,esses, under the action of the catalytic systen~ when a more severe thermodynamic control exists. Formally, by metathesis oligomerizatio~, the cycl~lefm will lead to cyclic dimers or higher cyclic oligomers with a macrocyclic structure, having an advanced degree of' un~turation (F~. 1.19).

,0,. C:_D --

-C:IIIIIIIIIIIIIIIIIII-__D

,'.'~,

The macrocycles thus obtained can be cleaved by intramolecular metathesis reactions with forn~tion of lower macr~"~jcles and eyclooletns (Eq. 1.20).

C]iill

iiiiiiiiiiiii_=D

C: ...................~,-,0 :*~176

-

~,.~o)

****** * * ' " * " * 1

By a similar way, unsaturated linear polymers can be ring-closed through an intramolecular metathesis reaction leading to new macrocycles with structures dependent on the starting material employed (Eq. 1.21).

C-IIIIIIIIIIIIIII ....---

~'-= .................. i=l.

"~._.--.

..................

I

17

(121)

Such processes are currently encountered in the metathesis desradation reactions of polyalkenamers or of other unsaturated polymers If, during the oligomerization reaction of cycloolcfins via metathesis, the macrocyclic ring is twisted, it will lead to catenanes or knots, depending on the number of half-twists that the chain will perform Thus, the catenanes are formed when the macrocycles undergo n=2 hafttwists (Eq. 1.22).

and the knots when the macrocycles undergo n=3 half-twists (F-~I. 1.23).

(1.23)

When the number of half twists is zero (n=O), the macrocycle will cleave into two cycloolefins (Eq. 1.24).

In the same way, a degenerate metathesis reaction occurs for one half-twist, when the same starting macrocycle is formed (Eq. 1.25).

il

I

II

Catenanes and knots of higher order can arise through further intramolecular metathesis reactions of initially formed structures. By a similar process, metathesis reactions between unsaturated catenanes and knots will lead to more complex compounds having structures of polycatenanes, catenanes,-knots and polyknots. Metathesis reaction of unsaturated catenanes or other interlocked tings makes possible the synthesis of a new type of compounds from the class of rotaxanes. For instance, by the reaction of a catenane having the interlocking order 1 with a linear disubstimted olefin, a rotaxane of the order 1 will arise (Eq. 1.26).

By the same process, catenanes having a higher interlocking number will lead to rotaxanes of higher orders.

10 Copolymefizafion reactiom of two or more different cycloolefim in the presence of metathesis catalysts will give copolymers along with c,~ligomers by a metathesis pathway (F-Xl. 1.27 and 1.25).

-

~=c,..,J~~,..,~~

(-)

( }

( } ! C''O Scheme 2.8

Substitution of monocyelic olefins with linear or branched alkyl and aryl groups provides useful monomers for the ring-opened polymers with particular structures and properties. It is essential that the substituents have to be attached at distant position with respect to the ear.n-carbon double bond in order to diminish the steric hindrance during the initiation and propagation processes of the ring-opening polymerization. Interesting examples are 3-methylcyclobutene, 4-methylcyclopentene, 4isopropylcyclopentene and several other alkyl- and aryl-substituted cycloolefins that have been polymefz~ in the presence of specific ringopening metathesis catalysts to the respective ring-opened polymers 2~'3~ (Scheme 2.9). In these monomers the distant substituent will not interfere with the active site in such a way as to hinder the initiation or propagation reaction. Importantly, if these substituents are attached directly at or in the vicinity of the carbon-ca~on double bond of the monomer, the polymerization reaction is strongly inhibited.

23 Rx

!11

III

/

R

1

!1 I

R

/ R

il I\ R

O

~

/ Alkyl

Ph

Scheme 29 2.4.2. Bicyclic and Polycyclic Old'ms for Ring-Opening Metathesis Polymerization Due to their high reactivity in this type of reaction, norbomene and substituted norbornenes represent a large group of bicyclic olefi~ that have been extensively applied in ring-opening metathesis polynmrizalJon. 31"3s Different alkyl radicals, e.g., methyl, ethyl, propyl, butyl, etc., have been attached in various positions of the norbomene skeleton leading to polymers with different structures and properties, depending on the substituent (Scheme 2.10). The re,activity of the substituted norbomene will change substantially as a function of the nature and position of the substituent. ~u~ In the same way, norbomadiene and substituted norbomadienes 3~9 offer another group of monomers for ring-opening polymerization providing related polymers of a higher unsaturation

24 degree which can be further processed and transformed into new products having totally different physical properties (Scheme 2.10).

Scheme 2.10

Many monomers of interest are derived from a large series of bicyclic, tricyclic or polycyclic hydrocarbons such as bicycloheptene, bicycloheptadiene, bicyclooctene, bicydooctadiene, 4~ indene," bicyclononadiene, benzvalene, ~s deltacyclene, ~ barrelene, benzobarrelene, ~ paracyclophene, 47 fullerene and their derivatives a (Scheme 2.11). It is worth mentioning that one of these monomers, indene, ~ which was widely employed as a cationic substrate, will produce by ring-opening polymerization products with interesting electrical properties. Benzvalene (5 and cyclophene 47 will also produce by ring-opening polymerization good precursors for highly unsaturated polymers with special electrical properties. Several benzo derivatives of various bicyclic and polycyclic monomers will lead to polymers with benzene moieties in the

25

reoming units, what will afford special properties, e.g. heat resistance, to the products obtained. +9 Finally, a norbornene derivative of fidlerene" will be able to introduce this particular stmcaue as a recurring unit in the polynorbomene chain by ring-opening polymerization reaction."

Q

Scheme 2. l I

26 Dicyclopentadiene has been extensively employed as an attractive monomer for ring-opening metathesis p o l y m ~ o n to produce highly appreciated linear and cross-linked products s~ (Scheme 2.12). Important industrial procedures for manufacture of poly(dicyclopentadiene) have been developed starting from this monomerss. Dihydrodicyclopentadiene is also a suitable monomer for the ring-opening polymerization reaction to linear polymers. Due to the absence of unsaturation in the condensed cycle, cross, linking is not possible and linearity of the polymer chain can thus be conveniently controlled. The next higher oligomer of the series, tricyclopentadiene, presents also unsaturated functionality similar to dicyclopentadiene leading by ring-opening to poly(tricyclopentadiene), able to cross-link.

Scheme 2.12 A great number of norbomene-like monomers available for ring-opening metathesis polymerization can be obtained by Diels-Alder method from norbomadiene and various substituted or unsubstituted dienes. ~s Using this class of monomers, a wide range of special ring-opened polymers with excellent mechanical and optical properties have been prepared . ' ~

27 2.4.3. Monomers with Functional Groups

Functional groups, when present in the cycloolefins, provide new sites of a t ~ t y towards the catalysts so that under these circumstances only a limited number of c,s~ysts will allow the polymerization p r ~ to ocxa~. In early explorations of the ring-opening p o l y m ~ t i o n , the reaction has been successfully applied to many monomers bearing specific fiu~onal groups like esters, nitrile, halogen etc. Recently, the re,action has been extended to monomers bearing a wide range of functionalities 2 (Scheme 2.13).

COOR

CO

OOR

/ CO

[~COOR QOH

/ N-CH2Ph CO

[~Y--COOR OCOOR

~~

CO

.CI

~

t OR CN

,/BR2

OCN

O ~~

CH~C,

BEt2 ICF3 CONH2

,,o oo.

~ ~

--CN

CH2CN

sicl,

Scheme 2.13

~

Si(OCH3)3

28

Thus, norbomene monomers, substituted with ester groups, cyan or halogens in the 5- or 7-position, have been frequently used in the ringopening metathesis polymerization in the presence of various catalytic systems. At the same time, as it has been observed in monocyclic olefu~ containing fimctional groups in the distant positions with respect to the carbon-carbon double bond, these functionality wig not hinder the accx=ss of the polymerizable double bond at tl~ active center. In this way, monomers like cyclopentene, cyclooctene, cyclononene, cyclodecene and c y c l o d o d ~ e substituted with ester, nitrile, halogen groups in remote positions have been s u ~ f u l l y polymerized under the action of the catalysts that tolerate such fimctional groups. Polycyclic olefins bearing functional groups constitute a special class of monomers for ring-opening metathesis polymerization. The majority of this group of cycloolefi~ have a norbomene-like structure and, unless the presence of the functional group will affect the carbon-carbon double bond and the catalytic center, the polymerizability is rather high due to strain relief and relatively diminished steric hindrance. Thus, a wide series of fluorine substituted norbomenes and related cyclic olefins have been employed as monomers in the ring-opening polymerization reaotion 61'62 (Schemes 2.14 - 2.15).

F

C5F11

~CF3

C~CF F3

F3

C~F3 F

~ C

F 2F5

Cl~

F3 F3 CeFs

CF3 F3 Schen~ 2.14

C4F9

CF3 CF3

29 Fluorinated polymers with.good mechanical and physical properties can be obtained conveniently ,by this route and find interesting pra~cal applications. It is worth mentioning that the fluorine atom may be introduced directly in the bicyclic skeleton or in the attached substituent as can be seen from Scheme 15. Some rich fluorine containing monomers have the fluorine atoms in both positions. Of a special interest are the fluorine containing monomers for polyng~ precursors of polyacetylene prepared by the Durham route ~2 (Scheme 2.15).

i~

F F.F

F F F

F

F3C~

F3C~ F

Scheme 2.15 Chlorine substituted cycloolefins of various types have been used as monomers in many ring-opening polymerization reactions~3 (Scheme 2.16).

,,,C,c,

••••-C

I

k,~ ~Cl

()-c' ~~-CI Cl

I~ qlo

#'-.Z_/.-c. #J~o-'c o Scheme 2.16

c' Cl

c ~ ] ~ c ~lo

Cl

.S--'c0

30 As Scheme 2.16 illustrates the chlorine atoms are situated in a remote position with respoct to the reactive carbon-carbon double bond in order to maintain the monomer reactivity. A very wide range of oxygen-containing monomers have also been employed in the ring-opening polymerization reactions~ ~ (Scheme 2.17).

r ~ o"

~--OR

/~~f

f_i.cooa

i-[ -~

\~

~COs

,OM

i_[. c-(:x:~ ~COOI~

/~~~,ocOCOOR _1~ CO\

oo. f,L ,7-00 o,,O

R

~ , cCH2OCOCH3 H2OCOCH3

OMe OMe I

x---OMe Scheme 2.17

Among the sulphur-containing monomers, ~ alkylthiocyclooctenes and a number of norbornene derivatives appear to be well tolerated by specific metathesis catalysts (Scheme 2.18).

(y"

SI~

SMe

~ O C S _OCS--SI~ _ SIV~

Scheme 2.18 In the case of alkylthiocyclooctenes, the reactivity showed to be crucially influenced by the steric crowding at the heteroatom ( R = c-Hex, n-Hex, tert-Bu, n-Bu, Et).

31 Of a great interest are the nitrogen-c~ntaining monomers that have been fi'uiffuUy employed in a number of ring-opening metathesis polymerization reactions. ~ u This type of monomers can tolerate a wide range of met~e~is polymerization catalysts and provide polymers with good physical and mechanic~ properties. The products can be further transformed by appropriate chemical reactions to new polymers with desired properties. Some examples are illustrated in Scheme 2.19.

CON 0

'CH2--

~~CH3 0

0

0

0

0

0

0

Scheme 2.19

Monong~ containing boron, e.g., (5-cyclooctenyl)diethylborane and 5-norbomenyl-9-borabicyclononane (Scheme 2.20), have been s u ~ f u l l y used in the ring.~ning polymerization reason to produce functionalized polyalkenamers. ~

Schomo 2.20

32 The alkylborane group has been easily removed from the polyalkenamer by oxidation with alkaline H202 to the corresponding hydroxy polymer. Many silicon-containing monomers have been employed in the ringopening metathesis reactions to produce interesting polymers, having particular physical-chemic~ properties 7s'n (Scheme 2.21). slch

~OSIMe 3 ~SiMe

~Si(OMe)3 ~Si(OEt)3

~

3

~li--'-(CH2)n'

iMe2tBu

0 S i(tBu)M

-N

e 2

Scheme 2.21 Of a great potential is the use of metal-containing monomers to prepare metallated polyalkenamers by ring-opening polymerization reaction. A first series is that of cyclic monomers containing organotin moieties (Scheme 2.22). 79

sou,

~

,~.~--Sn~

SnBu, (

~~~ ,

Scheme 2.22

~

C

H

~

C

H

2

-

-

S

n

B

~

33 The monomer and the metal can be varied in a wide range to obtain polymers with good physicS-chemical properties, suitable for many applicationss~ (Scheme 2.23-2.24). /tl~

iMe~

~N? \l'b

\t~

N/

/tBu R N ~r \

Scheme 2.23

Scheme 2.24 The metals induce specific properties to the polymers which can not be attained with the conventional substituents. These speciality polymers could be applied in various electric and electronic devices. Monomers containing a nematic side group attached at the monocyclic and bicyclic olefim, e.g., cyclooctene and norbomene, have been successfully employed to prepare side-chain liquid crystalline polymers by the ring-opening metathesis polymerization re.action,wg~

34 With the discovery of quite tolerable metathesis catalysts, the side group can be widely varied and the nematic properties conveniently tuned. Several examples are offered by monosubstituted cyclooctene and norbomene with nitrile and ether containing mesogenic groups u4s (Scheme 2.25).

O0.CH2.,,O~-->l\-~_c,

~C ~~C~~OMe ~~~,CO2(C H2)~OMe

~cm + CI2 ~

~-CI

+ HCI

(2.119)

Chlorinated cyclobutene can be manufactured by similar methods from cyclobutene by the selective chlorination in the allylic position or from dichlorocyclobutane by mild dehydrochlorination (Eq. 2. 120-2.121). /CI

§

oh

il !

+

NO,

(2 2o)

74 /CI

! !

\

"~

[

I

J

CI

+

HCI

(2.121)

cI

Using the above procedures, l-cldorocyclopentene can be obtained from 1,2-dichlorocyclopentane through dehydrochlorination while 3chlorocyclopentene from cyclopentene via direct chlorination of cyclopentene (F4.2.122-2.123). Cl

+

HCI

(2.122)

Cl

On the other hand, chlorinated bicyclic and polycyclic olefins can be prepared by several more specific methods. Thus, reaction of norbomadiene with dichlorocarbene, generated from chloroform under the action of aqueous alkali solution in the presence of a phase transfer catalyst, provides exo-3,4-dichlorobicyclo[3.2.1]octa-2,6-diene as the main product m76 (Eq. 2.124). (2.124) CI

Reaction of this compound with lithium aluminium hydride in dry ethyl ether produced 3-chlorobicyclo[3.2.1]octa-2,6-diene in high yield (Eq. 2.125).

C~CI LiAIH_._

(2.125)

I Tetrachlorocyclopropene, prepared from trichloroethylene and dichlorocarbene with subsequent dehydrochlorination, ~" reacts readily I

75 with excess cyclopentadiene at room temperature to form 2,3,4,4tetrachlorobicyclo[3.2.1 ]octa-2,6~ene ~76(Eq. 2.126).

+

C

I

25oc

c,

cs

(2.126)

C Reaction of tetrachlorocyclopropene with 6,6-dimethylfidvene under more severe conditions (reflux temperature for 24 hr) gives rise to 2,3,4,4tetrachloro-8-isopropylidenebicyclo[3.2, l]octa-2,6-diene~*S (Eq. 2.127). C +

c

CI I

CI

24h cch

-

CI cI

(2 127) "

Diels-Alder reaction of cis-3,4-dichlorocyclobutenem with dicyclopentadiene yields as the main product endo-cmti-3,4dicNorotricyclo[4.2.1.0~]non-7-ene of the fmH" possible isomers, endo, anti-, a~o, syn-, exo, anti-exo, syn-isomers 1~6(Eq. 2.128).

~ +

~

I

CI

endo-enli

"~CI cl$

exo-syn

CI endo4yn

(2.128)

exo4ntl

Chlorinated cyclopentadiene reacts with a wide range of dienophiles to produce chlorinated norbomene derivatives of high interest as monomers for ring-opening p o l y m ~ o n reactions. Thus, the Diels-Alder adduct of 5,5-dichlorocyclopentadiene with acetylene will readily produce 7,7dichloronorbomadiene (Eq. 2.129).

76 C

cl

CI

+ III

=

(2.129)

Reaction of dichlorocyclopentadiene with cyclooctadiene will form the corresponding chlorinated tricyclic and tetracyclic hydrocarbons (Eq. 2.130-2.131). C

I

+

( )

CI

~

(2.130)

8O

c c, (2.131)

Similar reactions of hexachlorocyclopentadiene (obtained by the exhaustive chlorination of cyclopentadiene) with various cyclodienes, including cyclooctadiene and norbomadiene, give rise to potential monomers for flame retardant polymers. With an excess of cyclooctadiene, the 11 Diels-Alder adduct of perchlorocyclopentadiene with cyclooctadiene was prepared in high yield~79(Eq. 2.132).

cK~Cl

CI

CI

(2.132)

i,...._

CI

C

This monomer is a crystalline product and is recovered by precipitation rather than by distillation. Elastomers derived from this compound have been explored in some detail. Analogously, the Diels-Alder reaction of perchlorocyclopentadiene with norbomadiene will form the 1"1 adduct, Aldrin, a potential monomer for flame retardant polymers ~s~(Eq. 2.133).

77 CI Cl

CI CI Cl

O

cK/cl C l ~ ~

+

(2 133)

Other cycloolefins can react in a similar way with chlorinated cyclopentadienes to produce a variety of chlorinated bicyclic and polycyclic monomers of interest for specialty polymers production. Isodrin~S~ obtained from cyclopentadiene and 1,2,3,7,7pentachloronorbomadiene, is another attractive monomer for highly chlorinated polymers (Eq. 2.134).

Os 3§ > gu 3+. It is worth noting that the osmiumbased system yielded a polyalkenamer with a high content of cis stereoconfiguration while the iridium-based system afforded a polyalkenamer with a high trans stereoconfiguration. Several complexes of cycloolefins with mthenimn, osmiun and iridium salts are active and selective in ring-opening polymerization. These complexes are formed from a cycloolefin with one or two double bonds like cyclooctene, 1,3-cyclooctadiene, 1,5-cyclooctadiene, norbomadiene and a halide of the above transition metal. For this purpose, Porri and coworkers" employed di-I~-chlorochlorobis(cyclooctene)iridium for the polymerization of norbornene in high yield to polynorbomene. Various one-component catalysts consisting of ~ complexes of transition metals were used by Kormer et al. ~ to polymetize a large number of cycloolefins such as cyclobutene, cyclopentene cyclooctene, cyclooctadiene, cyclododecatriene and norbomene. These catalysts proved to be particularly active leading in very high yield either to poyalkenamers or to a mixture of polyalkenamers with vinyl polymers. It is noteworthy that 7t-allyl complexes of tungsten and molybdenum formed totally polyalkenamers by ring-opening while x-allyl complexes of chromium and zirconium led to both the ring-opened and vinyl polymers (Table 3.8). A quite active catalyst for ring-opening p o l y m ~ o n of cycloolefins showed to be an arylmngsten compound, phenyltungstentrichloride (CfflsWCl3) in the absence of cocatalyst. On employing this compound alone, Grahlert et a/ss reported appreciable polypentenamer yields in the polymerization of cyclopentene. Titanacyclobutanes and tantalacyclobutanes showed to promote

130 Table 3.8 Polymerization of cytloolofms with o n ~ e m ~=all~ic r Catalytic System

Vinyl polymer % 70 70 0

(~-allyl)4Zr

(~-allyl)3Cr (~-allyl)oMo

, -aUyg,W,

0 i

i

Ring-evened polymer % 30 30 100 100

i i

"Data from reference ~4 the ring-opening metathesis polymerization of strained cyclic olefins like norbornene and its derivatives. Gilliom and Grubbs ~s have demonstrated that titanacycles derived from Tebbe reagent and norbomene or 3,3-dimethylcyclopropene upon reaction with norbornene give monodisperse polynorbomene (PDI=I. 1) with virtually no chain transfer or termination.

33

34

35

The catalysts are active at higher temperatures (>65 ~ and upon cooling to room temperature the living polymer was stable for several days. If stored at room temperature under an inert atmosphere, these systems retain some activity even after several months. Rapid decomposition was observed, however, at the polymerization temperature in the absence of monomer. Block copolymers of norbomene with benzonorbomene, 6methylbenzonorbomadiene and eta/o- and exo~cyclopentadiene were prepared by Cannizzo and Grubbs 57 using the titanacycles derived from di(cycl~ complex and isobutene or 3,3dimethylcyclopropene. The living polymers were end-capped by Wittig-type si/-.

CP2Ti

CpzT 36

37

131 reaction with acetone. Low polydispersity indices were recorded in all cases. On the other hand, Schrock and coworkers s= employed two

tantalacyclobutanes derived from Ta(CH'Bu)(OR)3(THF) complexes (OR 2,6-diisopropylphenoxide or 2,6-dimethylphenoxide) for the living polymerization of norbornene. =

-4-

38

39

These catalysts mimic ring-opening polymerization of norbomene by the riving titanacycles discovered by Gmbbs. A significant class of well-defined one-component catalysts for the ring-opening polymerization of cycloolefins derives from metallacarbene complexes. As soon as the carbene mechanism has become more and more popular for the initiation and propagation steps of the olefm metathesis and ring-opening polymefiz~on of cycloolefins, metaflacarbenes proved as a new potential class of catalysts for this process.

(C O)sW

40

.

/,OMe ~'~1:~h

( c o ) s w

,

Ph ~Ph

-~/

41

In fact, Katz was the first to employ diphenyl-pentacarbonylmngstencarbene, (CsHs)2C=W(CO)s, as a very active and stereo selective onecomponent catalyst in the polymerization of l-methylcyclobutene, cycloheptene and norbomene, affording in high yield the corresponding polyalkenamers with considerable stereochemical purity, s9 Later on, the number of metallacarbenes as ring-opening metathesis catalysts increased substantially spreading out to a large number of transition metals and covering a wide range of activity and stereo selectivity in the polymet~tion reaction of numerous cycloolefins. This class of ring-opening polymerization catalysts became quite attractive due to the particular features they possess in contrast to the classical metathesis catalysts such

132

as: well-controlled metathesis activity and stereosclcctivity, good tolerance toward functionality, "living" character affording narrow and monomodal molecular weight distribution of polyalkenamers and the possibility to

produce block copolymers as well as easinessand simplicity in handling and application in polymerization processes. In their early work on aryloxide complexes of tungsten, Basset and coworkerss~ reported the synthesis and catalytic properties of two families of chloro-aryloxide carbene complexes (VI) (42-43). CI

CI

ArO I H ArO/~/~/==~ (OR2)

ArO,, I H ArO/7==~ (OR2) CI

CH2CMe 3 43

42

The complexes of type 43 proved to be active without any cocatalyst for metathesis of various kinds of cyclic and acyclic olefins with or without functional groups. Also, depending on the nature of the aryloxide ligand and the coordinated ether, they exhibit various degrees of activity and stereoselectivity with respect to a given olefin. Very active tungsten carbene catalysts, particularly when they are associated with gallium halides (GaX3, X = CI, Br), prepared Krcss and O s b o m 61 (44-46).

RO./

Br -

Br 44

/~'

Br

RO. I RO

Br 45

/~,

Br RO. I

RO

/-"X

Br 46

Using this class of initiators, Kress and Osl~m were the first to detect by means of elegant NMR measurements the occurrence of intermediate tungstene-carbene and tungsten-cyclobutane complexes during the polymerization reactions of norbomene and its derivatives. 62 The tungstencyclopentylidene complex, W[cyclopentylidene](OCHzCMe3)2Brz, was used in association with GaBr3 to initiate the metathesis polymerization of synand a~ti-7-methylbicydo[2.2.1]hept-2-ene to produce homolxdymers as well as block and tapered block copolymers of the two stereoisomers. 63 In this ease, the intermediate met~lacyclobutane could be detected during the

133 reaction of ant/-7-methylnorbomene, but not for that of syn-7methylnorbomene. Tungsten-e,arbene complexes of the type W(=CRR'XOR")2Xz, where CRR' = cyclohexylidene, cyclopentylidene, CH'Bu or CIT'Bu, have also been used by Kress as catalysts to initiate ringopening metathesis p o l y m ~ o n of cyclopentene, cycloheptene and cyclooctene to living polyalkenamers. Their CmBr3 adducts react similarly but much more rapidly. A wide range of well-defined pseudotetrahedral imido alkylidene complexes of the type M(=CHR)(=NAr)(OR')2 ( M = Mo, W, R = C(CH3)3, C(CH3)2Ph, Ar = 2,6-dimethylphenyl, 2,6-diisopropylphenyl, OR' = OC(CH3)3, OCMe-2(CF3), OCMe(CF3)2, OC(CF3)2(CF2CF2CF3X47),

R'O_ @N-Ar \M R'O/ %CHR 47

suitable for ring-opening polymerization of cycloole~ were prepared by Schrock and coworkers~ from an "universal precursor" M(::~HRX=NArXtriflate)-XI,2-dimethoxyethane) (48). TfO

\

~0 --M~

N-Ar

CO/I \~Ol'f CHR 48

Several examples of effective molybdenum alkylidene complexes are given below

(49-54).

N

CH(CH3)2

(CH3)3CO\ Moo// 3)2 / (CH3)3CO '~CHC(CH3)~ 49

CH(CH3)2 (CH3)3CO\IMo/N_,~H(CH3)2 (CH3)3CO ~CHC(CH3)2Ph 50

134

CH(CH3h

CH(CH3h

(CF3XCH3)2CO\ Mo/N~dH(cH3)2 (CF3XCH3)2CO~oJf NcNh / CHC(CH3)2Ph (CF3XCH3)2CO/~CHC(CH~h (CF3XCH3)2CO 51

52

CH(CH92

1CF3)2(CH3)CO~o/'N CHC(C~h 53

CH(CH3h

(CF3)2(CH3)COk.,/N-~ ~

(CF3)2(CH3)C O

CH(C~h

X

CHC(CH3hPh

54

The molybdenum neophylidcnr complexes Mo(=CHCMe2Ph)(=NAr)(O'Bu) and Mo(=CHCMe2Ph)(=NAr)(OC(CH3XCF3hh as well as their precursor Mo(=CHCMe2Ph)(=NAr)(TfO)2(DME) are all now commercially available from Strem Chemicals, Inc. Selected ~H and ~3C NMR data for molybdenum and tungsten alkylidene complexes are given in Table 3.9. Table 3.9. tH and ~3CNMR Data for Molybdenum (and Tungsten) Alkylidene Complexes~b Mo Alkylidme Complex

~(ca ppm 312.2(283.8) 326.2 288.2(253.9) 276.8(244.9) 265.8(236.5) 289.8(242.8)

Jc.

Hz ppm 115 12.91(9.97) Mo(=CH'BuX=NAr)(DME)CI2 124 14.10 [Mo(=CHtBuX=NAs)Clz], 11~ 12.06(8.87) Mo(=CHtBuX=NAr)[OCMe(CF3h]z 11~ 11.61(8.41) Mo(---CH'BuX=NAr)[OCMez(CF3)]z 11~ 11.23(8.05) Mo(--~H'Bu)(=NArXOCMe3)z 11": 13.86(9.97) Mo(--CHSiMe3X=NAr)[OCMe(CF3)z]z Mo(=CHFX~=NAr)[OCMo(CF3)2]z _ 12.44(9.22) 9Data from reference6~; s Values for the correspcmdmg tungsten complexes are shown in parentheses

135 The activity of tungsten complexes of the type W(=CI-I'BuX=NArXORh ( A r - 2,6-diisopropylphenyl; OR = O'Bu, OCMe2(CF3), OCMe(CF3)2, OC(CF3)2(CF2CF2CF3)) in the metathesis of olefins depends critically upon the nature of the OR group. For instance, the complex in which OR = OCMe(CF3)2 is an active catalyst for the metathesis of ordinary olefins at rates that may be as high as 103 turnovers per minute at 25~ in a hydrocarbon solvent, while analogous W(=CI-~Bu)(=NAr)(OtBuh complexes do not react readily with internal olefms but react with more reactive cyclic monomers such as norbomene, benzvalene, 7,8-bis(trifluoromethyl)tricyclo[4.2.2.0z'S]deca-3,7,9-triene, and acetylene, a circumstance that allows one to prepare essentially monodisperse living polymers and block copolymers. Analogous molybdenum alkylidene catalysts of the type Mo(=CHRX=NArXOtBuh (Ar=-2,6-Cd-13~Pr2; R= q3u, CMe2Ph) have been used to initiate living ringopening p o l y m ~ t i o n of funetionalized norbomenes, norbomadienes, and 7,8-bis(trifluoromethyl)trieyclo[4.2.2.02"S]deea-3,7,9-triene to give polymers with narrow molecular weight distributions (polydispersity of 1.05-1.10). In some eases, e.g. with 2,3-bis(trifluoromethyl)norbomadiene and 2,3-bis(c,arbomethoxy)norbornadiene), the resulting polymer was virtually all-trans and possibly also tactic. The tolerance of the M(=CI-I'BuX=NArXOR)z(M=W, Mo) catalysts for fim~onalities allowed them to be used to ring-open norbomene that contains metals like Pb, Sn, Zn, etc. Recently, Grubbs and eoworkers 67 described the living ring-opening polymerization of norbornene catalyzed by the discrete ruthenium earbene complex (55). Ph3/H

~

Cl"~u=CXRcl /

PPh3

Other highly r

55 cyclic oleos such as cyelobut~e and ~ ~ -

cyclooetene were also readily polymefized by this ruthenium earbene complex in a living fashion, however it was inactive for the polymerization of less-strained cyclic olefins and aeyelie metathesis. Modification of this complex by the exchange of the triphenylphosphine (PPh3) ligands with tricyclohexylphosphines (PCy3) or tricyclopentylphosphines(PCyp3)resulted in more active catalysts. ~s

136 Cl....~ cy3 H

P.CyP3 u Cl..,. l u = c / ' '

C I"'~u=C~ R PCY3

Cl'" I

56

"R PCyP3

57

New active and selective benzylidene and vinylidene ruthenium complexes are represented by compounds 58-61. IPh3 / Ph C~.....PR I

U

CI,., !Cy3 / Ph

-

"~ U

CI/pph3

-

CI//cy 3

58

59

C L....I~Ph3 / Ph Ru / - - - \ I Ph C~'PPh3

Ck.. P CY3 Ru ~/f I Cid, PCy 3

/ Ph \p h

61

6O

The new ruthenium carbene complexes were active for the polymerization of cyclopentene, cyclooctcne and 1,5-cyclooctadiene as well as the metathesis of acyclic olefins.69 In addition, the copolymedzation of both high- and low-strain cyclic olefins employing these ruthenium complexes as catalysts was performed. The effect of the ligand as well as the nature of the carbene on the copolym~tion reaction was particularly pointed out by the above authors. Water-soluble ruthenium complexes containing preformed aJkylidene fragments that initiate rapidly and quantitatively cycloolefin polymerization were also reported by Grubbs and coworkcrs 7~ Me... Me ~. N CI

~N(Me)3

9 C IE) C k...l .....Ph ~ , ~ C P"~ U ~ A H

C I,... ...,P h C I~FIu'~~ H c,

62

/eK CI Me Me

63

137 In the presence of a BrOnsted acid, these complexes showed to initiate the living polymerization of water-soluble monomers in the absence of surfactants or organic solvents. Synthesis of five-coordinate tungsten(Vl) alkylidene complexes containing a bidentate C,N-bonded arylamine ligand or a monoanionic O,Nchelating ligand has been reported by Van Koten and coworkers (6466).'I,~

~ CH~iMea

/'-~

1-12SiMea C1-12SiMe.s ~ / C O-W.~ II"~"CHSiMe3 N N

0

64

65

66

Such complexes are inert toward linear olefi~ but can polymerize strained cyclic olefins e.g. norbomene in a ring-opening metathesis reaction. The reactivity of some of these complexes toward norbomene will differ considerably (Table 3.10). Table 3.10 Polymerization of norbornene with amgstm-alkylidenes W(--CHSiMe3)(CHaSiMe3)(=NI~)(L)~ '

Ligand(L)

'

8-qumolmola~

oc~(2-Py)

OCH(CMB3X2-Py) 'Dam from ~ c e

n

T~-t ~ 25 25 70 25 70

Reaction Rate 99 % cis and >99 % tactic. The synthesis of these chiral molybdenum alkylidene catalysts proceeded readily in high yield from the appropriate alkoxide and the universal precursor Mo(=CH'Bu)(=NArXtriflate)-z(1,2-dimethoxyethane) (67-70). Me.

R R OTf6

O X~ ,tN~Ar

R~

O or-C

OTf6

67 StMezPh

on.

I~O,,MIo.....N_Ar SIMe2Ph 68

SlMezPh

t,~

o on.

X~o=l~b..Ar

SIMe2Ph 69

's"r"Y

tBu

OT,.

W~/I-O,l~--Ar

tB

tBu

70

More recently, using new chelating chiral diol ligands, Grubbs and coworkersTM synthesized chiral metal alkylidene complexes for ring-opening polymerization of both strained and less strained cycloolefins. When (lS,2S)and (lR,2R)- 1,2-bis-(2-hydroxy-2,2bis(trifluoromethyl)c~yl)cyclo~tane (L), 71, has been employed as a chiral ligand, the chiral molybdenum alkylidene complex Mo(=CHCMc2PhX=NArXL), 72, active in polymerization of 1,5cyclooctadiene, has been produced.

139 AF

I N

F3cCF3 H

F3C_CF3 II

...,,,X-O//H /

"OF 3

"Z

F3

71

72

Stable chiral tungsten oxo vinylalkylidene complexes and tungsten amide vinylalkylidene complexes have been also obtained from the above chiral d i o l ligands and W(clLPh~clopropene)Cl2(O)[P(OMe)~]2, and W(=CHCHCOCH2CH2CH2OXO)CIz[P(OMe)3] W(=CHCHCPh2X=NAr)CI2[P(OMe)3]2, which are effective in the polymerization of norbomene, cyclooctene, 1,5-cyclooctadiene and substituted cyclooctatetraenes (73..75). h" I 0 N 0 Orb

F~.7 3 II ~ P ( ~

-

91

"CF3 74

73

75

Asymmetric tungsten-aJkylidene complexes containing either one or two l,l'-bi-2-naphtholate (RzBINO) ligands prepared Heppert and coworkers7s (76-77).

R

R

o

I o11

OtB u

76

,R

77

140 Both (RzBINO)('BuO)2W(=CHPh) and (Mc~BINOhW(=CHPh) act as ring-opening metathesis catalysts for norbomene polymerization, although there are startling differences in their reactivity. While neither catalyst produces a quantitative conversion of norbomene in 15 min, (Me2BINO)2W(=CHPh) exhibits extremely low activity, generating only 35 % yields of polymer. The addition of GaBr3 as a Lewis acid cocatalyst markedly increased the activity of (~BINOX'BuO)2W(=CHPh), generating virtually instantaneous quantitative yields of polynorbornene at O~ This increased activity probably stems from the abstraction of a terminal 'BuO ligand by the Lewis acid gallium reagent, generating a highly active four-ea3ordinate polymerization catalyst [(R2BINO)(tBuO)W(~HPh)] *, rehted to Osbom's structurally characterized [(RO),~Br3~W(=CHR')+I[GaBr4"] complex. 76

3.4.2. Two-Component ROMP Catalysts Soon after the discovery of ring-opening polymefz~tion reaction of cycloolefins by Eleuterio ~ with heterogeneous molybdena-type catalysts, the process attracted an increased number of research groups due to the great potential offered by the new reaction. A first objective was to create new catalytic systems and apply them to a wide range of cycloolfins in order to obtain products with highly performant characteristics. This trend generated a large variety of now termed "classic~" catalysts that have been used extensively to study various aspects of ring-opening polymerization of cycloolefins such as reaction kinetics and thermodynamics, reaction mechanism and stereochemistry as well as the ways of industrial valorification. These catalytic systems are mainly two-component catalysts that contain a transition metal derivative of group IV-VII of the periodic table associated with a coc,alalyst. The latter may be an organometallic compound (Ziegler-Natta type catalysts), Lewis acid (Friedel-Crafls type catalysts), x-complex or carbene complex. Their activity is generally high depending on the nature of the transition metal, the number and nature of ligands attached at the transition metal, the nature of the coc,atalyst, the solvent and other reaction conditions. The reaction selectivity is quite variable depending primarily on the nature of the transition metal, ligands and coc~talyst but also on the structure and conformation of the monomer. They display low tolerance relative to the functional groups and their activity may be substantially diminished by a strong complexation of the active sites.

141

The first two-component cattalyst to ring-open polymerize norbomene reported by Truer et eL/.33 OOl~sted of TiCh and tetraheptyllithiumaluminium. These authors investigated the influence of the molar ratio AI:Ti on the two types of p o l y m ~ t i o n , vinyl and ringopened. It is noteworthy their finding that at molar ratio AI:TiI the reaction occurred through ring-opening polymerization. Soon afterwards, Natta and coworkers 34"36 used numerous binary catalytic systems in the ring-opening p o l y m ~ o n and copolymerization of a wide range of cyeloolefins. Depending essentially on the nature of the transition metal compound, some of these catalysts led to both vinyl and ring-opened polymerization reactions while others gave preferentially ringopened polyalkenamers. The activity and stereoselectivity of these catalytic systems were also strongly dependent on the nature of the transition metal, cocatalyst, cycloolefin and reaction conditions. In eyelobutene polymerization, Natta and eoworkers 35 studied various binary ~ y f i c systems consisting of transition metal salts from the groups IV-VII of the periodic table and organoaluminium compounds (Table 3.11). Table 3. I I

Polymerization of cyclobutene with two-component ROMP catalysts'

CatalyticSystem TiCh/EhAI VCh/EhAl MoCI~3AI MoCI~3AI MoOz(acac)7]Et2AICI WCId~AI

Cotlv.

% 100 100 3 5 55 100

pcB ,

% 5 99 10 30 10 40 ,

cis-PB %

trans-PB %

30

65

,

0

l

60

30 30

40 45

45

40 30 "Data frvm refermce" PC-Poly(cyclobutyiename0, PB=Polybmman~r

They found that titanium-, vanadium- and tungsten-based systems were the most active while those based on molybdenum the least active. Moreover, vanadium-based catalysts formed preponderently poly(cyclobutylenamer) while titanium-, molybdenum- and t u n g s t e n - b ~ catalysts led to polybutenamer or poly(1-butylenamer).

142 A greater number of two-component ROMP catalysts, both heterogeneous and homogeneous systems, have been investigated by several research groups in cyclopentene polymerization due to the ready accessibility of this monomer and the increased interest in its polyalkenamers. Early studies of Natta and coworkers ~s showed that the binary catalysts based on molybdenum pentachloride and tungsten hexachloride associated with EhAI or Et2AICI were the most active and selective in ring-opening polymerization whereas those derived from titanium tetrachloride in conjunction with the above organoaluminium compounds led to both types of polymers, vinyl and ring-opened. It is significant that molybdenum-based catalysts formed preferentially cispolypentenamer and tungsten-based catalysts ~ave trans-polypentenamer. Extensive studies of Cmnther et a/. 3 used a large range of twocomponent catalysts consisting of tungsten halides and organometallic compounds in cyclopentene polymerization. Though initially the activity of some of these catalysts was low or moderate, later on their activity and stability have been substantially improved on using adequate activators and additives in ternary systems (see below). It is noteworthy that the stereospecificity of several catalysts of this group is rather high being of interest for their industrial application into trans- or cis-polypentenamer production. Thus, catalysts derived from WCI~ and ~Bu3AI or HSnEh gave polypentenamers with more than 90% trans stereoconfiguration, the use of Table 3.12 Cyclopemene polymerization with two-conq~ent tungstm catalysts' Yield % Catalytic System 35 WC~Bu~d 34 WF6/Et3AI2C]3 5 WCl~a3~h5 8 WCI6/(HSiOCH3)4 II WCls/(HSiOCH3), 4 WCI~i3WF~ 6 WCls/(x-allyl)sCr 18 WCId(x-allyl),W~ 35 WCl~SnEh 62 WCIJPh3Cr 'Data from referelloe37 i

i

trans- Polypmtmmrm., 90.4 17.2 24.4 65.1 55

cts-Polypmtmmner" 9.6 82.8

75.6 34.9 45

88.2

11.8

27.4 60.3 90.2 45

72.6 39.7 9.8

55

143 tungsten hexafluoride in the catmlytic systems WF~hAI2CI3 or WFdEtaAICI produced polypentenamers with more than 82% cis stereoconfiguration. Binary ROMP catalysts of this type were extended also to other tungsten derivatives and to other transition metals. With catalytic systems consisting of W(PhO)4Cb and MeAICI2 it was possible to obtain polypentenamer in 69% yield containing 84% trans stereo~ntiguration at the carbon-carbon double bond. On studying the effect of r on the activity and selectivity of the binary WCts-ba.q~ ROMP catalysts in cyclopentene polymerization, Dimonie and Dragutan " ~ showed that the catalytic systems containing isobutylaluminoxane and tetraphenyltin as cocatalysts were highly cis stereoselective, especially at lower temperatures (Table 3.13). Table 3.13 Catalytic System WCIJBu2AIOAIiBu2 WCIJBu2AIOAItBuz WCloq~e2AllyizSi WCI~,Sn WCIs/Ph4Sn WCldMe~n WCIs/Et4Sn WCld13u4Sn 'Data from reference

WCl~-ba.uxl Temp trans-Pol~ntmamer c i s - P o ~ r ~ % % - 10

9.1

0

11.2

-20 -20 +10 -20 -20 -10

38.0 11.7 45.3 80.0 28.9 24.2

'

90.9

88.8 62.0 88.3 54.7 20.0 71.1 75.8

It was observed, however, that the effect of temperature on the catalyst activity and polymer stereo selectivity was considerable, parfic~arly for the catalyst WCI~.Ph4Sn. In the two-component catalytic systems the tungsten halide has been replaced by MoCIs, ReCI5 and TaCls thereby changing drasti~y the catalyst activity and stereo selectivity . On using MoCIs associated with ~Bu3AI inste~ of WCI6 in cyclopentene polymerization, Natta and coworkers st varied the polypentenamer stereostructure from over 90% warts to over 90% cis. Similarly, Gtmther et al. rz's3 employing a catalyst consisting of ReCl5 and 'Bu3AI obtained a polypentenamer containing 96% cis stereoconfiguration with special properties of natural rubber. A different class of two-component catalytic systems has been obtained by replacing

144 the organometaUic compound from the above Ziegler-Natta ROMP systems with a Lewis acid. This new catalysts of Friedel-Crat~ type proved to be highly active in the ring-opening polymerization of cycloolefins. Thus, DaU'Asta and Carella s~ used two-component tungsten-based catalysts consisting of WCI6, WOCI4, WCIz or WBrs in conjunction with AICI3 or AIBr3 in the polymerization of cyclopentene and higher cycloolefins to obtain polyalkenamer with high tra~ stereoconfiguration at the carboncarbon double bonds. Furthermore, Marshall and Ridgewell ss carried out the polymerization of several cycloolefms such as cyclopentene, cycloheptene, cyclooctene, c y c l o d o d ~ e , 1,5-r and 1,5,9cyclododecatriene with catalysts consisting of WCI6 or MoCIs and AIBr3. It was observed that when using AIBr3 instead of AICI3 in these catalysts the efficiency of the process increased. A large variety of heterogeneous two-component catalytic systems formed from inorganic compounds of tungsten, for instance, tungsten trioxide, tungstic acid, isopolyacids, heteropolyacids or salts of these acids associated with AICI3 or AIBr3 were used by Herisson and Chauvin ~s to polymerize cyclopentene. On employing chlorobenzene as a reaction medium, they obtained high yields in polymers though the structures of the products were not completely elucidated. Significant results in cyclopentene polymerization obtained NiRzel et al. g7 with a series of two-component catalysts formed from organic compounds of transition metals of groups IV-VI of the Periodic Table and several Lewis acids. They used mainly aryl derivatives of tungsten, molybdenum, chromium or vanadium and halides of boron, aluminium, tin, tungsten or molybdenum (Table 3.14). It can be seen that these twocomponent FriedeI-Crafls systems displayed a substantial activity and stereoselectivity in cyclopentene polymerization comparable to the above presented binary Ziegler-Natta systems. For instance, catalysts like Li3WPh6.BCI3 gave a high yield of polymer (52%) and a considerable content of trans polypentenamer (92%). Similarly, Judyu employed several two-component catalysts based on tungsten or molybdenum compounds and ~ s acids in polymerization and c o p o l y m ~ t i o n reactions of cyclopentene, cyclooctene, cyclooctadiene and cyclododecatriene. These catalytic systems were very active affording high yields in polyalkenamers and copolyalkenamers. With such a system consisting of KWCI6 and AICI3 or AIBr3 Judy obtained a polyoctenamer in 82% yield. Furthermore, on employing tungsten carbonyl compounds associated with Lewis acids, e.g., W(CO)~(o-phenanthroline)

145

and AIBr3, this author was able to attain a 86.3% yield of polyoctenamer Table 3.14 Cyclopmtene polymerization with two-compcment ROMP catalysts of FriedeI-CratLs type' Catalytic System

Yield % 45

tram-

cis-

Pol.ypm_tetmmer, % 80

Polypmtmanm, % 20

Li3VVPhJBCI3

52

92

8

Li~MoPhdBF3

43 20 62 32

62 92 45 32

38

WCt,/AIO3

Pr4W/SnCI4

Ph3Cr~Cl6 LizVPhdMoCls 'Data from

8

55 68

Remarkably, two-component catalysts, consisting of tungsten compounds in conjunction with alkali metals or alkaline earth metals, showed to be very active and stereoselective in cyclopentene polymerization. Such binary systems, containing Li or Ca associated with tungsten halides, used Cmnther e t al. t9 to obtain high yields of trcms polypentenamer(Table 3.15). Table 3.15 Cyclopentene polymerizationwith two-c,ong~ent tungsten-based catalysts'

Polymer yield Catalytic % System 38 WCldLi 21 WCldCa 66 WCIsOX/Ca 30 WBr~/Ca 19 'Data from reference

trans-

~$-

80 90 80 89

Polypmtammer % 2O 10 20 11

Polypemmmnor %

Tungsten and molybdenum ~-complexes, in combination with aluminium and gallium halidcs, formed very active two-~mponent ROMP catalysts. Thus, GOnther9~ and Ntitze191 carried out the p o l y m ~ t i o n of cyclopentene using binary catalysts consisting of WCI6 and 0t-allyl)3Cr or

146 (~-allyl)4Wz. They obtained both cls- and trans-polypentenamers but the yields were relatively low. Furthermore, Yufa et al. ~ performed the ringopening polymerization of 1,5-r with the system 0tallylhW/GaBr3 to obtain 1,4-polybutadiene in high yields. It is noteworthy that the resulting polybutadiene contained 60% cis and 40% trans stereoisomer. However, when the catalyst (~-r was used in polymerization of trans, trans, cis-l,5,9-cyclododecatriene, Yufa et al. ~z obtained polybutadiene with 40% cis and 60% trans content of stereoisomer. Interesting binary catalytic systems for the ring-opening polymerization of cycloolefins, consisting of metal-carbene complexes and organoaluminium compounds or Lewis acids, reported Chauvin et al. s~ Such systems are formed from RR'C=M(CO)s (where R = CffIsO or CH30; R' = CH3 or Cd-15; M = W or Mo) and EtAICI2 or AICI3. Using such a system in cyclopentene polymerization, they obtained in 70~ yield polypentenamer. Related catalysts were also prepared starting from CIAPh3P)Pd--C(OCH3)NHC~s and AICI3 or EtAICIz. It is noteworthy also that Commereuc et al. sa employed the tungsten-carbene (CO)sW=C(OCffls)R, associated with TiCh in the two-c~mponent catalytic systems for cycloolefm polymerization. A range of asymmetric alkylidene and oxo complexes of tungsten (VI) were prepared by Heppert and coworkers95 by incorporating Czsynunetric l,l'-bi-2-naphtholate and other chelating bisaryloxides ligands onto tungsten oxo and tungsten arylimido complexes. Using these asymmetric complexes as procatalysts in association with EhAICI, norbomene and 5,5'-dimethylnorbornene were polymerized to the corresponding ring-opened polymers. The microstrucu~es of the resulting polymers were correlated with the structure of the procatalyst and the nature of the Cz-synunetric naphtholate ligand.

3.4.3. Multicomponent ROMP Catalysts Starting from the binary ROMP catalysts, ternary, quaternary and multicomponent catalytic systems have been prepared by adding a special component to the parent systems which may act as an activator, promoter, stabilizer or inhibitor of side reactions. These substances are usually organic compounds containing oxygen, nitrogen, sulphur, phosphorus, halogen or other heteroatom, in some cases they may be also inorganic compounds

147 containmg these heteroatoms or having a particular role in ROMP catalysis. The first catalytic system employed by Eleuterio *s in the discovery of ring-opening metathesis polymerization was a heterogeneous ternary catalyst consisting of an oxide of chromium, molybdenmn, tungsten or uranium deposited on alumina, titania or zirconia associated with a third component such as alkali metal, alkaline earth metal, boron or aluminium hydride. This ~ y s t allowed unsaturated polymers with cis and trans configuration to be obtained from cyclopentene, cyclobutene, norbornene and dicyclopentadiene working under inert atmosphere in hydrocarbons as reaction medium. L~er on, DalrAsta and Carella9~ obtained a series of homogeneous ternary catalytic systems consisting of tungsten or molybdenum salts, organometallic compounds and oxygen-c~ntaining substances such as organic peroxides, hydroperoxides, alcohols, phenols, molecular oxygen or water. The transition metal salts employed were WCIs, WOCh or MoCls, the organometallic compounds were EhAICI, EhAI, 'Bu3AL Hexyl3Al or EtzBe, and the oxygen-c~ntaining compounds benzoyl peroxide, tertbutylperoxide, cumyl hydroperoxide, hydrogen peroxide, ethanol, phenol, molecular oxygen or water. The optimum molar ratios between the catalytic components were in the range W" AI" O of 1 90.5-100" 0.5-1. With such systems Dall'Asta et al. 9~ prepared highly trans polyalkenamers in the polymerization and copolymerization reactions of cyclopentene, cycloheptene, cyclooctene or cyclopentadiene. Soon aider reporting the olefin metathesis with the ternary catalyst WCIdEtOH/EtAICI2 in homogeneous phase, Calderon and coworkers sa carried out successfully the ring-opening polymerization of a large range of cycloole~ with this catalytic system. They obtained mainly trcmspolyalkenamers in high yields in the reactions of cyclooctene, 3methylcyclooctene, 3-phenylcyclooctene, 1,5-r and 1,5,9cyclododecatriene. Subsequently, instead of ethanol, Calderon and Judyss employed also methanol, aUyl alcohol, cumyl alcohol, glycol, phenol, thiophenol and cumyl hydroperoxide. In addition, Judy ~~176 reported very active and stereo selective catalysts consisting of WCI~ AICl3 and powdered aluminium for the polymerization of cyclopentene, cyclooctene, cyclooctadiene and cyclododecatriene. For example, with such a catalyst this author obtained a polyoctenamer in 74.5% yield. Instead of WCk, Judy employed also WF6, MoCls, MoF6, MoF4, WOF4, WCh and MoOCh. Particularly active ternary catalytic systems for the polymerization of cycloolefins to polyalkenamers obtained Ofstead ~~ by using tungsten or

148

molybdenum carbonyl complexes. Such catalytic systems consisting of (CO)~(1,5-COD)W or (CO),(NBD)Mo, EtAICI2 and oxygen, bromine, iodine or cyanogen bromide gave high yields of polyoctenamer by cyclooctene polymerization. Furthermore, Ofste~ ~~ prepared new ternary catalytic systems derived from WCh,, EtAICIz and a hydroxynitrile (cyanohydrin) such as HOCHzCH2CN or chlorosilane of the type CICHzCHzOSiMe very active in cyclopentene polymerization. A large number of ternary catalytic systems based on tungsten salts prepared Ganther et al. ~o3 to be employed particularly in cyclopentene polymerization to trans-polypentenamer. In these systems, they used mainly oxygen-containing compounds such as alcohols, epoxides, peroxides, hydroperoxides, acetates, phenols or ethers, nitrogen-containing compounds such as amides, amines or nitroderivatives, various halogenated compounds as well as inorganic peroxides such as sodium or barium peroxides. In addition, Pampus et a l ~~ employed chloroethane or epichlorohydrin in catalysts derived from WCI~ and EhAICI or ~Bu3AI. With such catalyticsystems, they obtained high yields of trtms-polypentenamer and copolymers of cyclopentene with butadiene as well as graft copolymers with good elastomericproperties. It is noteworthy that 2-cyclopentenehydroperoxide increased the activity of the binary catalytic systems consisting of WCts and 'Bu3AI or tungsten salts and ~ s acids. Using such a ternary catalyst, N0tzel et a l ~~ obtained h i g h yields in trans-polypentenamer by cyclopentene polymerization. The catalyst proved to be very stable and reproducible. Similar results were reported also for nitroaromatic compounds and inorganic peroxides such as Na202 and BaOz.~~ Interesting tungsten-based ternary catalytic systems prepared W'me et a l ~~ using halogenated alcohols or halogenatod phenols as the third component. On using these compounds, the above authors s u ~ e d to improve the stability of the catalytic systems derived from WCI6 and ~u3Al or Et2AICI. Examples of such halogenated alcohols are 2-chloroethanol, 2bromoethanol, 1,3-dichloro-2-isopropanol, 2-chlorocyclohexanol and 2iodocyclohexanol and as halogenated phenol is o-chlorophenol. With a catalytic systems consisting of WCI6, CICH2OH and 'Bu3AI, Witte et al. ~o6 obtained high yields of polypentenamer having around 94% trans stereoconfiguration at the carbon-carbon double bonds. Moreover, acetals such as CHz(OCH3)2, CH2(OCH2CH2CI)2, CHsCH(OC2Hs)2, CI3CCH(OCH3h or Cd-lsCH(OC2Hsh have also been employed by Sch6n et al. ~~ as good stabilizersfor the binary catalysts formed from WCI6

149 and EtzAICI for cyclopentene polymerization. It is worth mentioning that epoxides such as ethyleneoxide or l-butyleneoxide have been employed by the same authors to improve the activity and stability of the binary catalysts derived from WCI~ and 'Bu3AI. On using a catalyst consisting of equimolar amounts of WCls, Czl~O and 'Bu3Al, they prepared in 82% yield a polypentenamer containing 90.5% trans stereoconfiguration at the carboncarbon double bonds. Halogenated hydrocarbons such as vinyl chloride have been employed by OberkJrch et al. ~os for cyclopentene polymerization with the catalytic systems formed from WCIs or TaCls and organoaluminium compounds. It was observed that these halogenated hydrocarbons increase substantially the activity of the catalyst but, at the same time, they modify the molecular weight of the polyalkenamer. Thus, on employing the ternary system WCI6, 'Bu3AI, CH2--CHCI, these authors obtained in 78% yield a high trans-polypentenamer having an intrinsic viscosity [11] of 3.27 dl/g (toluene). A wide range of ternary ROMP catalysts consisting of WCI6, organoaluminium compounds and halogen-, oxygen- and nitrogencontaining comtx~nds reported Dimonie, Coca and Dragutan ~~ for cyclopentene polymerization. These catalysts proved to be substantially trans-stereoselective. As Table 3.16 illustrates, polypentenamers with trans contents varying from 72 to 83% are readily obtaining using various organic compounds. In some cases the added compound may slightly increase (e.g. epichlorohydrin) or decrease (e.g. chloranil) the trans content but no drastic change in the steric configuration was observed for the range of additives employed. On using oxygen-containing compounds as a third component in ROMP catalysts derived from WCts and EtAICIz, Streck and coworkers tt~ obtained very active and stereoselective ternary systems for cycloolefin polymerization. Such systems with organic acids or their salts have been employed in cyclooctene polymerization. In one example, cyclooctene gave polyoctenamer with 63% cis configuration at the c,arbon-carbon double bond in the presence of the catalyst WCk/CH3COOH/C2HsAICI2. Heterogeneous three-component catalytic systems derived from 7tallyltungsten complexes and aluminosilicates containing trichloroaex~c acid as a third component have been prepared by Oreshkin et al. ~ to polymerize trans, trans, cis- l ,5 ,9-cyclododecatriene to polybutadiene. Though the catalysts had a high degree of activity their stereospecificity was limited to the cis:trans ratio from the initial cycloolefin.

150 Table 3.16 Polymerization of cyclcTamtme with WCl6-based ternary catalytic systems"b

trans'-Poly-

Catalytic System

|

cis-Poly~ r , % pmtmamr r t % WC rSu P o 85.5 14.5 WCh,/'Bu3/CA 0 72.0 28.0 WC~3AI/EP 0 81.6 18.4 0 WCIe.Et3AI2CI3/EP 81.9 18.1 0 WCI6/Et2A]CI/EP 78.4 21.6 -15 WCI6/'Bu3AI/DBQ 83.0 17.0 WCId'Bu3AI/MANH 0 72.O 28.0 0 WCI~Bu3AI/SALD 80.4 19.6 0 WCIJBu3AI/CYAC 74.2 25.8 0 WCI~Bu3AI/CYCL 73.0 27.0 'Data from rofwmoet~; bEP = epichlorohydrm, CA = chloranil, DBQ = dibenzoquinone, MANH --maleicanhydride, SALD = salicyiicaldehyde, CYAC = cyanuric acid, CYCL = cyanuric chloride. ~

3.4.4. Catalysts for ROMP in Water Systems

Early publications reponod the use of iridium salts and complexes as initiators for the polymerization of exo-bicyclo[2.2.1]hept-5-ene-2carboxylic acid in aqueous and alcoholic solvents. ~2 Noteworthy, investigations by Ivin and Rooney ~3 revealed that the trichlorides of ruthenium, iridium and osmium were also effective as initiators for the ringopening metathesis polymerization of both exo- and endobicyclo[2.2.1 ]hept-5-ene derivatives in ethanolic medium. ~13 The applic~ility of ruthenium salts in the polymerization of certain heteropolycyclic alkenes in poorly aqueous media has also been demonstrated by Novak and Grubbs. ~~4 Detailed studies on the polymerization of exo, exo-5,6ruthc~mn, bis(methoxymethyl)-7-oxabicyclo[2.2.1 ]hept-2-ene using iridium and osmium chlorides as the precursors of the active ring-opening metathesis polymerization initiators were carried out by Feast and Harrison. t~s In general, the polymerization was performed by adding aqueous solutions of the metal halide to stirred emulsions of the monomer in either pure water or mixtures of water and a chain transfer agent such as cis-but-2-ene-l,4-diol or its dimethyl ether. The reactions tcx~k place at

151 55~ under normal atmosphere and were run for two days. The product polymers were white solids; exposure to air resulted in slow degradation as evidenced by a yellow/green coloration. Typical experimental conditions and polymer yields with RuCI3.3H20, IrCI3.3HzO and OsCI3.3H20 in water are illustrated in Table 3.17. Table 3.17 Polymerization of exo, exo-5,6-bis(methoxymethyl)-7-oxabicyclo[2.2.1 ]hept-2-me initiated by RuCI3.3HzO, IrCl3.3HzO and OsCIs.3HzO in watzr ' Parameter Monomer, g Catalyst, g Water, ml Temperature, ~ Yield, % M., K tram-Double bonds, %

RuCI.3.3H20 1.0 0.07 7.5 55 95 155

IxCi3.3H20 1.0 0.07 7.5 55 2.0 20

OsCl3'.3HzO 1.0 0.07 7.5 55 95 5

60

90

75 |

i

9Data from r ~ r m o e ~'.

data indicated that the polymerization of exo, exo-5,6bis(methoxymethyl)-7-oxabicyclo[2.2.1 ]hept-2-ene initiated by RuCIs.3H~3and OsCls.3H~3 in water cwocurred in high yields, the molecular weight of the polymers being varied between 155 K and 5 K. In all ca.~s the microstructure of the polymer was altered only by the catalyst and was not dependent on the molecular weight or solvent composition. A new class of well-defined ruthenium carbene complexes, e.g. (Cy3P)2CIzRu=CHCH=CPh2, (Cy3P)2CIzRu=CHPh, (Cy--cyclohexyl) were used by Cmabbs and ooworkers ll6'll' for living ring-opening metathesis polymerisation of functionalized norbomene and 7-oxanorbomene in aqueous media. Monomers were dispersed in water using a cationic surfactant, and polymerization was initiated by injection of a catalyst solution to yield a polymer latex. The polymerization of hydrophilic 7oxanorbornene and a hydrophobic norbomene monomer displayed similar behavior in aqueous media, with the resultant polymers having lower molecular weights relative to polymerization in anhydrous organic solution on a similar time sc~e. The polydispersity indices of polymers prepared form the hydrophilic monomer using the catalyst

152 (CysPhCI2Ru=CHCH=CPh2 in the presence of water (PDI=I.20) were narrower than those obtained by solution polymerization (PDI=2.11) while polydispersity for polymers prepared using the catalyst (Cy3PhCI2Ru~HPh remained low in both the presence of water and in anhydrous solution (PDI=I. 13). The linear relationship between molecular weight and monomer/catalyst ratios and the absence of chain transfer and termination processes indicated that these systems are living. This technique was shown to be an efficient method for the preparation of well-defined block copolymers.

3.5. Synthesis of Catalysts for Cydoolef'm Polymerization 3.5.1. Synthesis of Cationic Catalysts Aluminium chloride, AICh. Due to its importance in the petroleum industry as a cracking and a refining agent and in the chemical industry as an alkylating and polymerizing catalyst, much work has been done on the commercial manufacture of aluminium chloride from bauxite or other aluminiferous ores. 6 The common commercial process developed by Gulf Refining Company (Texas) involves reaction of chlorine with bauxite under specific conditions. 6 In the laboratory, aluminium chloride is most readily prepared by passage of chlorine or hydrogen chloride over heated aluminium filings tts (Eq. 3.1). AI + 3HCI = AICI3 + 3/2 H2

(3.1)

Besides aluminium and aluminiferous ores, various compounds of aluminium, such as aluminium sulphate, aluminium phosphate, aluminium nitride, or aluminium carbide, have been used for the synthesis of aluminium chloride. Chlorination has been effected with chlorine, hydrogen chloride, metal chlorides, or other chlorine compounds. Several commercial processes with information on the cost of raw materials and economic feasibility have been described in the literature. 6'~9 Hydrogen fluoride, IIF. Hydrogen fluoride is currently obtained ~z~ from fluorite (CaF2) or even better, from cryolite (Na3AIF6) by reaction with 97.5% As-free H2SO4. (Eq. 3.2-3.3). CaF2 + H2SO4 = 2HF + CaSO(

(3.2)

153 2Na3AIF6 + 6HzSO4 = 12HF + 3NazSO4 + AI2(SO4)3

(3.3)

For further purification, it is distilled from a NaF-c~ntaining Pt retort into a Pt re~ver, leaving behind the SO42 and SiFe2" ions. A little PbCO3 is added to remove the CI'; this yields PbCIF, which is insoluble in concentrated HF. An excess of PbCO3 does not harm, even in the presence of H2S04. Organic material is removed only when KMnO~ is added. Boron fluoride, BF3. Several proc~ures for the preparation of BF3 in high yield are known starting from B203 and alkali fluoroborates (Eq. 3.4-3.5) KBF4 + 2B203 = BF3 + KF.B406 6NaBF4 + B203 + 6H2SO4 = 8BF3 + 6NaHSO4 + 3H20

(3.4)

(3.5)

or from H~BO3and fluorosulphonie acid (Eq. 3.6). H3BO3 + 3HSO3F = BF3 + 3H2SO4

(3.6)

The older method for preparing BF3 from CaF2 is not recommended, since the yields are low and the product is contaminated with SiF4. BF3 is conveniently stored in glass containers over Hg or in steel cylinders. Boron fluoride.etherate BF3.EhO. The etherate of BF3 is easily obtained by the reaction of BF3 with ethyl ether (Eq. 3.7). BF3 + O(C2Hs)2 = BF3.O(C2Hs)2

(3.7)

The product distils readily at 38~ (6 mm) and can be used as such or in ether solution. Aluminium bromide, AIBr3. Very pure AIBr3 may be prepared from aluminium turnings and dry bromine at a temperature sufficient for refluxing (Eq. 3.8). AI + 3/2 Br2 = AIBr3

(3.8)

The product is readily soluble in many organic solvents, hydrolyzes in moist air and reacts violently with water. Gallium bromide, GaBr3. Gallium bromide is readily prepared from metallic Ga by bromination (Eq. 3.9).

154 Ga + 3/2 Br2 = CraBr3

(3.9)

Very pure GaBr3 can be produced by vacuum sublimation in quarz equipment. Titanium tetrachloride, TiCh. Titanium tetrachloride is prepared by chlorinating titanium dioxide (mille) in the presence of charcoal or carbon black (Eq. 3.10). TiO2 + 2C + 2C12 = TiCh + 2CO (3.10) The crude product is decolorized and contaminants such as FeCI3, VOCI3, etc., are removed by means of Cu powder, Na amalgam or Hg. Zirconium tetrachloride, ZrCh. Zirconium tetrachloride is prepared similarly to titanium chloride by chlorinating zirconium dioxide in the presence of carbon black or charcoal (Eq. 3.11). Zr02 + 2C + 2C12 = ZrCl4 + 2C0

(3.11)

Preferably, zirconium dioxide with no admixtures is chlorinated in a CI2CCh gas mixture produced by passing CI2 through CCLs. The industrial chlorination of ZrC prepared from ZrSiO4 is described by KroU e t al. ~zo Iron trichloride, FeO~. Iron trichloride is prepared by reaction of dry chlorine with pure iron wire at 250-400~ (Eq. 3.12). 2Fe + 3C12 = 2FeCI3

(3.12)

An excess of chlorine should always be present. In another process the reaction occurs between chlorine and Fe(Ol~. The product is very readily soluble in water, ethyl alcohol, ethyl ether and acetone. Tin tetrachloride, SnCI4. Tin tetracloride is readily prepared in quantitative yield by direct chlorination of pure tin metal (Eq. 3.13). Sn + 2C12 = SnCh

(3.13)

The product is fuming in air, taking up moisture and forming various hydrates. It is stable only when kept in hermetically closed vessels. Zinc dichloride, ZnCIz. Very pure, anhydrous zinc chloride is prepared by treating Zn with dry HCI at 700~ in a quartz boat placed in a tube of highmelting glass (Eq. 3.14). Zn + 2HCI = ZnCIz + He (3.14)

155 At this temperature, the formation and sublimation of zinc chloride p r ~ at sufficiently high rates. The sublimed chloride is collected in a section of the tube which is kept cool for this purpose. For additional purification, the chloride may be resublimed in a stream of HCI. An efficient method for preparing ZnClz is by electrolysis of an acetonitrile solution of CuCI at room temperature with a Pt cathode and a Zn anode (Eq. 3.15). Zn + 2CuCI = ZnCI~ + 2Cu

(3.15)

The product is highly hygroscopic, soluble in methanol, ethanol, ether, acetone and other organic solvents. Triethylaluminium, Et~Al. Several proc~ures for the synthesis of triethylaluminium are known. ~'~2~ Pure triethylaluminium is readily produced from diethylaluminium bromide and sodium (Eq. 3.16). AI(C2Hs)zBr + Na = AI(C2Hsh + NaBr + AI

(3.16)

The product is spontaneously flammable in air and immediately hydrolyzed by moisture to AI(OH~ and C~-I~. Pressure processes for aluminium dkyls starting with Al, hydrogen and olefms are described by Ziegler and coworkerslZZ (Eq. 3.17). Al + 3CHz--CH2 + 3/2Hz = AI(C2Hsh

(3.17)

Diethylaluminium chloride, (CzHshAICL The ether complex of diethylaluminium chloride is prepared by the reaction of AICI3 with AI(CzHs)3.O(C2Hs~h (Eq. 3.18). AICI3 + AI(CzHsh.O(C2Hsh = (CzHshAICI.O(CzHs)2

(3.18)

3.5.2. Synthesis of Anionic Catalysts Organolithium compounds, RLL The most widely employed anionic catslyst, n-butyllithium, is readily prepared by reaction of lithium with nbutyl chloride in ether or pentane in an inert atmosphere, z3 Since the concentration of n-butyllithium solution in ether drops to half its original value in about a week at 25~ it is advantageous to store the solution in ice or in a refrigerator. Ethyllithium is best obtained by the slow addition of ethyl bromide to a well-stirred mixture of lithium and pentane or pentene

156 (mixture of isomers). Good yields result only when the ethyl bromide is added steadily and slowly. The first product is a precipitate consisting of lithium bromide and ethyllithium, the latter being only moderately soluble. Since ethyllithium is about ten times as soluble in benzene as in pentane at room temperature, it is conveniently separated from lithium bromide by solution in benzene, removal of pentane or pentene by distillation followed by crystallization of the ethyUithium from benzene. When the isolation of the organolithium compound is desired, the preparation is more difficult than when the product is intended for more or less immediate use for synthetic purposes. In this ease the method of choice is the reaction between lithium and an organomercury compound. An excess of lithium is desirable, to drive the reaction to completion and thus to avoid the presence of any soluble material except the desired product. An inert solvent is necessary and this may be light petroleum or benzene; ether is sometimes used but the product must then be worked up without delay. Solid compounds, e.g., ethyllithium, phenyllithium, are crystallized from the reaction mixture after filtration from insoluble matter, while liquid products, e.g., n-propyllithium, must be obtained by evaporation of the solvent in vacuum and cannot readily be purified. Organosodium compounds, RNa. Amylsodium and phenytsodium are conveniently prepared by reaction of amyl chloride and ehorobenzene with fine dispersions of sodium in hydrocarbon solvents under stirring at low temperatures. ~ Thus, if amyl eldodde is added slowly to a well-stirred sodium dispersion in a hydrocarbon solvent at room temperature, reaction generally starts within about two minutes (a little amyl alcohol helps to start the reaction if it does not begin on its own within several minutes). When the reaction has started, and not before, the reaction vessel is cooled, and amyl chloride (diluted with a h y d r ~ o n solvent) slowly added at such a rate as to maintain a reaction temperature about 25-30~ By the same procedure, phenylsodium can be prepared from ehlorobenzene in hydrocarbon solvent at temperatures of 30-35~ When the organosodium compound must be isolated, the exchange reaction between an alkali metal and the appropriate mercury compound, g2Hg, is the only satisfactory method. The reaction is carried out in light petroleum, in an atmosphere of pure nitrogen. Phenyl derivatives are best prepared by stirring the alkali metal with a benzene solution of dimbutylmercury. Grignard compounds, RMgX. Grignard compounds are normally prepared by the reaction of an alkyl or aryl halides with magnesium in dry

157 ether. 23 Since the reagents are very sensitive to air and moisture it is desirable that air should be excluded and that both reactants and installation should be carefully dried. The induction period at the beginning of the synthesis is in part due to thepresence of moisture, and in fact it increases rapidly with water content. Addition of a small crystal of iodine without stirring until reaction is well started, or the use of some magnesium which has previously been heated in the presence of iodine, are favored method for starting reaction. A similar effect may be achieved by the use of a little methyl iodide, ethyl bromide or ethylene dibromide. The formation of the Grignard reagent is generally a strongly exothermic process and, though slow to begin with common halides, accelerates very markedly when an appreciable amount of reagent has been formed. Care is necessary to avoid adding too much halide before it has been established that the reaction is well started. Halide is then added at such a rate as to maintain steady boiling of the ether.

3.5.3. Synthesis of Two-Component Ziegler-Natta Catalysts Two component catalysts for Ziegler-Natta polymerization of cycloolefins containing a metal halide such as TiCI4, ZrCI4, HIEh, VCI5 and organometallic compounds e.g. organoaluminium or organotin compounds are generally prepared in situ by adding a solution of the metal halide to a solution of the organometallic compounds in the presence or absence of the monomer. Examples for such catalyst preparation, including the systems EhAI/TiCI4, 'Bu3AIfFiCI4, NaAmfFiCI4, EhAI/ZrCI4 and Et3AI/VCIs, can be found elsewhere. ~23-~25 Metal(acetylacetonate), catalysts. Binary catalysts were prepared from V(acac)3, Cr(acac)3, Ni(acac)2, Mn(acach, MoOz(acac)2 and organoaluminium compounds or methylaluminoxane for polymerization and copolymerization of several cycloolefins such as cyclobutene, cyclopentene, norbomene and norbomene-like monomers. 126,127 Metallocene catalysts. Several metallocene catalysts employed for cycloolefin polymerization have been prepared by reacting CpTiCI3, Cp2TiCl2, CpzZrCl2, Cp2HfUIz, CpzVCIz, CpNi(Tt-allyl) or CpzCr with organoaluminium compounds or methylaluminoxane. ~z8'~29 Chiral metallocene catalysts. Various prochiral and chiral ligands have been designed and attached to the transition metal to form chiral precatalysts which in conjunction with aluminoxane as cocatalyst afforded chiral catalysts with a high activity and stereoselectivity in acyclic and cyclic

158 olefin polymerization. ~3~ Thus, ansa-zirconocene complexes, 1,2ethylenebi s(q Lind enyl)zirconiu m dichloride and 1,2-ethylenebi s(rl s_ tetrahydroindenyl)zirconium dichloride were prepared by the reaction of sodium or lithium derivatives of the C2 symmetric ligands 1,2ethylenebis(inden-l-yl) or 1,2-ethylenebis(4,5,6,7-tetrahydroinden-l-yl) with zirconium tetrachloride (Eq. 3.19-3.20).

§

K)~

_---

,,CI

*Z~~

Zr

(3.19)

(3.20)

. ~~

When dimethyl-, diphenyl- and dibenzylbis(l-indenyl)silane or dimethyl-, diphenyl- and dibenzylbis(4,5,6,7-tetrahydroinden-l-yl)silane have been used as C2 symmetric ligands in reaction with zirconium tetrachloride, dialkyl-, diaryl- and diaralkylsilyl-bridged zirconocene dichloride were prepared 133(Eq. 3.21-3.22).

K)~

*Z~I4

R"

i

R,..%R

Na(K)~

R. S

,Z~I4

R,.~.j R',

...

Nc,

(3.21)

(3.22)

These chiral zirconocene complexes in association with methylaluminoxane produced very active and stereoselective catalysts for the cycloolefin Ziegler-Natta polymerization and copolymerization.

159 The activity and stereoselectivity of these chiral zirconocene catalysts were further improved by introducing substituents such as alkyl, phenyl, naphthyl, benzo, substituted benzo, etc. into either the five- or sixmembered ring of the indene or tetrahydroindene moiety (Eq. 3.23- 3.26).

*ZrCI4

i~

+ZrC

R..

(3.23)

R" ~R Na(K)Na(K)

=

(3.24)

R" ~'R R I~

(3.25)

R (3.26)

o

When cyclopentadienyl or other aromatic anions are used as building units of the C2 symmetric ligand, various complexes can be prepared (78-80).

160

M ~~,

~

78

P

79

80

By replacing the dialkyl-, diaryl- and diaralkylsilyl bridge with a dialkyl-, diaryl- and diaralkylcarbyl bridge, a new class of active and stereoselective chiral zirconoc~e precatalysts bearing C2 symmetric ligands have been obtained (Eq. 3.27-3.28).

+Z~I4

;,,cI

~

I~

~'~a

(3.27)

R (3.28)

R

R

Chiral zirconocene complexes bearing C,-synunetric ligands containing different aromatic entities have been prepared by reacting a dialkyl- or diarylc,arbyl bridged cyclopentadiene and fluorene ligand with zirconuim tetrachloride (Eq. 3.29).

lnBuLi

2.Zrci4

d

(3.29)

161 A wide range of candidates for metallocene precatalysts in olefin polymerization that retain the C2 symmetry and highly stereodifferentiated reactive sites of ethylenebis(inden-l-yl)- and ethylenebis(4,5,6,7tetrahydroinden-l-yl)zirconium complexes have been designed and prepared recently having various stereogenic spacers while preserving the bis(cyclopentadienyl) framework. TM A first series was prepared using biphenyl and binaphthyl groups attached directly to the cyclopentadiene ligands in bis(cyclopentadieneyl) and bis(inden-l-yl) complexes of Ti and Zr. (81-83).

,o

81

o

c,

82

83

Another series of complexes contain more rigid alicyclic moieties of cyclopentane-l,3-diyl and cyclohexane-l,4-diyl bridges in r dichlorides TM (Eq. 3.30-3.32)

1.nBuLi ~.~

(3.30)

a.HC~ir

-p

(3.31)

a. lnBLd_i 3HCI/air

(3.32)

162 and various double bridges between the coordinated cyclopentadienyl ligands, e.g. two ethanediyl bridges or two dialkyl- or diaryl-silyl bridges ~3s (Eq. 3.33-3.36).

nBLLi.. zrc

r

h

reut.

ch

TiCl3/'i'H~

Me 2

Me2

,•

Ph2Si SiPh2

nBulLi ZI~Us

.._

Me2S~

nBLs Ph2S~~I2

ZrCl4 ~

(3.33)

(3.34)

(3.35)

(3.36)

3.5.4. Synthesis of Ring-Opening Metathesis Polymerization Catalysts 3.5.4.1. One-Component Metathesis Catalysts Tungsten hexachloride,WCl~ The most convenient ways to prepare tungsten hexachloride are the direct chlorination of tungsten with chlorine gas and indirect chlorination of tungsten trioxide with carbon tetrachloride. ~36 According to the first procedure W powder is contacted with chlorine in a special Vycor tube at elevated temperatures (ca. 600~ to produce highly pure oxychloride-free almost black crystalline tungsten

163 hexachloride (F,q. 3.37). W

+ 3C12 = W C l 6

(3.37)

In the second procaxlure tungsten trioxide is reacted with excess caubon tetrachloride under anhydrous conditions to thorough completion of the reaction (Eq. 3.38). WO3 + 3CCLs = WCts + 3COCb (3.38) If these conditions are not observed, yellow-red by-product WOCh forms readily (Eq. 3.39). WC[6 + H 2 0 = WOC[4 + 2HCI

(3.39)

Moreover, the WOCh has the undesirable property of catalyzing the hydrolysis of WCI6 in most air. Under these conditions, the process advances to formation of yellow WOzCIz by further hydrolysis of WOCLs (Eq. 3.40). WOCh + H20 = WOOl2 + 2HCI (3.40) The proper method yields an almost black crystalline tungsten hexachloride with no red or yellow impurities of tungsten oxychlorides. The product is very readily soluble in alcohol (with yellow color), CHCI3, CCh (with red and dark-brown color, respectively), CS2, ether, benzene, ligroin and acetone. Molybdenum pentachloride, MoCIs. The common procedure for preparing molybdenum pentachloride consists of chlorination of molybdenum in a special apparatus ~36(Eq. 3.41). 2Mo

+ 5C12 =

2MOC15

(3.41)

The blue-black, extremely hygroscopic c r y ~ e product, dark-green if oxychloride is present, is soluble in water and alcohol with solvolysis. The pure product is soluble without decomposition in organic solvents such as ether, CHCI3, CCh and CS2. Rhenium pentachloride, ReOs. Rhenium pentachloride is prepared by chlorination of rhenium metal at 500~ in a proper installation in a stream ofCl2 (Eq. 3.42). Re + 5/202 = ReCI5

(3.42)

164 A deep, black-brown product, sensitive to air is formed. It hydrolyzes with water forming various products. Rhenium pentachloride is soluble in hydrochloric acid (green solution) with liberation of CIz. Ruthenium trichloride, RuCI3. Ruthenium trichloride is prepared by chlorination of ruthenium metal at 700-800~ in a special Vyoor tube m36 (Eq. 3.43). Ru + 3/2Ciz = RuCI3

(3.43)

Good crystals in the form of shiny black platelets, insoluble in water, are obtained. RuCla.HzO. A pure product corresponding to the formula RuCI3.HzO can be obtained from hydrochloric acid solutions of RuCI3 (which is not free of Ru(IV)) by electrolytic reduction. 136 The process is adjusted to produce red colored solutions of Ru(Ill), a blue color indicating the formation of the undesirable R(II) product. Iridium trichloride, IrCl~. Iridium trichloride can be prepared by various procedures depending on the starting materials. ~s The most convenient way is by chlorination of iridium metal at 600~ in a special combustion tube

(Eq. 3.44).

Ir + 3/2CI2 = IrCI3

(3.44)

Alternatively, IrO2.2H20 may be heated to 240~ in a stream of C12 and illuminated with sunlight or a burning magnesium ribbon (Eq. 3.45).

IrOz.2HzO + 7/202 - IrCl3 + 4HCIO

(3.45)

Finally, (Nl'hhlrClz may be decomposed in a stream of CIz at 440-550~ for several hours (Eq. 3.46).

(NI-hhlrCl6 = IrCI3 + 2NH4CI + 1/2CI2

(3.46)

A dark olive-green powder, stable up to 760~ under a CIz pressure, is obtained. At 700~ the color changes to bright yellow.

165 x-Allyl complexes. There are various methods for preparin~ ~-allyl complexes of group V-VII transition metals published elsewhere ~3

3.5.4.2. Two-Component Metathesis Catalysts Synthesis of two-c~mponent metathesis catalysts ~ r s m s/tu by contacting the catalyst components in solution of the monomer or by precomplexafion the reacting components before adding the monomer. Variants for such catalysts as WCI6/Et3AI, WCIjMe4Sn and MoCIs/Et3AI are found in the open or patent literature. ~3s

3.5.4.3. Three-Component Metathesis Catalysts In addition to the catalyst and coc~talyst components, a great number of metathesis catalytic systems contain a third component introduc~ to adjust the catalyst activity, selectivity and stability. Depending on the nature of the catalyst, the third component can be an electron donor or acceptor compound, with specific electronic and steric effect on the catalyst active species. 139

3.5.4.4. Well-Defined Metathe~is Catalysts Ttianacyclobutanes. A wide range of titanacyclobutanes have been synthesized and characterized by Grubbs and coworkers 14~starting from the Tebbe reagent, olefins and a Lewis base. For example, reaction of Tebbe reagent with 1 equiv of norbomene gave the corresponding titanacyclobutane (Eq. 3.47).

CP2"I]=CH2+ ~

~

CP2T~

(3.47)

Similarly, reaction of Tebbe reagent with 3 , 3 - d ~ y l c y c l o p r o p e n e and isobutene formed the respective titanacyclobutanes (Eq. 3.48-3.49).

CP2Ti=CH2 + ~:~

~ CP2T{~

(3.48)

166

Such titanacyclobutanes have been used in the first living polymerization systems for the ring-opening polymerisation of cyclic olefins. Tantalaeydobutanes. Two Tantalacyclobutanes prepared Wallace and Schrock TM by the reaction of tantalum-neopentylidene complexes, Ta(=~I-I~uXOKh(TItT) (OR = 2,6-diisopropylphenoxide or 2,6dimethylphenoxide) with 1 equiv of norbornene (Eq. 3.50-3.51).

(3.50)

(3.51)

The Ta neopentylidene complexes were obtained from TaCls and Zn(CH2'Bu) as described below. Tantalum- and niobium-alkylidene complexes. Ta(=CH'BuXOR)3(THF) (OR = 2,6-diisopropylphenoxide or 2,6-dimethylphenoxide) were prepared by Schrock and coworkers 14z from TaCI5 and Zn(CHztBu)z in three highyield steps (F-~I. 3.52-3.54).

TaCI 5 +

Zn(CH2tBu )2 -ZnCI2~ ' ~ Ta(CH2tBu )2CI3 (3 52)

Ta(CH2tBu)2CI3 + 3ROLi (RO)3Ta(CH2tBuh

-3LiCI

-CH3tBUTHF"=

-

(RO)3Ta(CH2tBu)2 ( R O ) 3 " ~ a ~H

(3.53)

(3.54)

THF Tuntalum- and niobium-neopentylidet~ complexes were also prepared by Schrock and coworkers 143 from the corresponding trialkyl metal dichloride by subsequent alkylation and elimination reactions (Eq. 3.5 5-3.57).

167

M(CH2CMo3hCI2 M(CH2CMe3)4CI

LiCH2CMe 3 .= - I_JCI

(3.55)

[(MeaCCH2~CIM=CHCMe 3]

- CMe4 .

[~CCH2hCN=CHCMe-.j

M(CH2CMe3hCI

13.56)

UCHzCM~ - UC~ = M(CHzCMe:~(CHCM~)

0.57)

where M is Ta or Nb. The key step showed to be the decomposition of the initially formed monochloride by loosing neopentane as result of ahydrogen abstraction to give mb~uently an u n . ~ l e complex which reacts further with LiCHzCMe3 to give the final metal-alkylidene product.

Tungsten-alkylidene

complexes.

A

series of tungsten-alkylidene

complexes of the type W(=CHCMe3XOAr)2CI2(OR'2) and W(=CHCMe3XCH2CMe3)(OAr)z(OR'2) were prepared by Basset and coworkers6~ by means of the reaction of W(OAr~hCh with 1 equiv and 1.5 equiv of Mg(neopentyl)~dioxane), respectively (Eq. 3.58-3.59).

IAX

cloxane) - - - , -

(ArOhWCh* 1.5 Mg(Cl'12CMe3h(dtoxane) ~

(ArOhCl(

H (3.59)

Very active ring-opening metathesis catalysts, W(=CHR)(OR')zBr2, particularly when they were associated with GaBr3, prepared Kress and O s l ~ m 61'145 by reaction of WO(OCHz'Bu)~CH2'Buh with AIX3 (Eq. 3.60).

H Four-coordinate, Lewis acid-flee complexes of the type W(=CHCMe3X=NArXORh prepared Schrock and coworkers ~ by the route shown in Eq. 3.61-3.63.

168

x^ CI ,.,, -Me3SiC=I .u,, I / ~ ' [O..~/,^ .. + ArNH(SiMe3) CI ~mu ~0

9

~ INHAr

~o'~V\%ctBu CI 9

CI

.0.. [ ~NA r

(~I.NHAr vu (~ICtBu

~3

(3.61)

CI

NEt3

~-O..[ ~ NAr

Et20

,U ~, CHtBu

(3.62)

AF

+ 2 MOR

- 2MCI ~

m '~ RO""'V~/==K,

(3.63)

I-~uc, M=Li or K and OR=OCMr OCMez(CF3), OCMc(CF3h, OR/'. The key step is the catalysis of a proton transfer in W(-=CCMe3)(NHAr)(DME)CI2 by triethylamine in diethyl ether at -40~ to give orange W(=CHCMe3)(=NAr)(DME)CI2. Addition of two r of LiOR to W(=CHCMc3X=NAr)(DME)CIz gives four-cx~ordinate dialkoxy alkylidene complexes, since a six-coordinate complex is too crowded to retain a relatively weakly bonding DME ligand. A more convment route to W(=CHCMe~X=NAr)(ORh complexes starts from WOCh when 2 equiv of the ncopcntyl Grignard rcagem are required t47(Eq. 3.64-3.67).

WOCI4 + ArNCO

Octane.=. .~

CI4W==NAr+ 2 LiOtBu THF/Et20

CI2(OtBu)2CrHF)W=NAr

C12(tBuO)2(ll"f)~r + 2 (tBuCHz)MgCl ~

(tBuO)2(tBuCl'~)2~r + PCls

CI4W_-NAr

DME

=

(3.64) (3.85)

(tBuO)2(lSuCH~~r (3.66) 9 CI NAr .O.~

[.,

(3.e7)

169 The proposed intermediate, W(=NArXCH2'Bu)2CI2 is unstable with respect to a-elimination, at least in the presence of a donor solvent such as dimethoxyethane. The simplest synthesis of a "versatile precursor" to a variety of tungsten alkylidene complexes, W(=CHR)(=NAr)(OT0z(DME), uses WO2C12 as a raw materialla(F~. 3.68-3.69). WO2Cl2 +2AtNH2-- ~)2Cl2(DME)*2RCH2MgCI= W(NAr)2(CH2R)2 (3.68) ~O ~OTf VV(NAr)2(CPhRh,

+ DME

,.

= - ArNPhOTf _RCH 3

( . ,,~NAr

LJIW' "R 4U OTf H

(3.69)

The intermediate in the last step is believed to be the unstable compound W(=NArXCH2R)2(OTfh formed readily from W(=NArh(CHzR~h. The success of this reaction is attributed to the fact that the product W(=CHRX=NArXOTfh(DME) is relatively stable to triflic acid, presumably because the DME is bound tightly and the metal is relatively ionic. The neophyl ligand (R=CMe2Ph) is much less expensive than the neopentyl ligand (R=CMe3). A wide variety of W(=CWBuX=NAr)Xz complexes could be prepared from W(=CHK)(=NAr)CI~ME) or W(=CHRX=NArXOTf)2(DME) where X = alkoxide, primarily with examples of X = thiolate, amide, or alkyl. In all cases the X groups must be bulky in order to stabilize the four-cx~rdinate species toward bimolecular decomposition, especially when the alkylidene ligand is small. In addition, a variety of alkylidene complexes can be prepared from CWBu complexes by metathetical reactions involving an internal or terminal olefin. A new five-coordinate tungsten-alkylidene complex in which a bidentate arylamine ligand is present was prepared by van Koten and oowork~l"$ 72'149 by t r a n s l a t i o n between the lithium salt of 2[(dimethylamino)methyl]phenyl and tris[(trimethylsilyl)methylphenylimidotungsten chloride (Me3SiCH2)3W(=NPh)CI (F_x].3.70-3.71). ~ W

~

~_ ?Li

NMe2

+ W(CH2SiMe3)3CI(=NPh).~,--p,

~Me2

~CH2SiMe3 ~'~'CHSiMe3

(5

(3.70)

170

NM~ OU + V~CH~~,j~C(-NPh)---,,.

CH~~

(3.71)

The analogous transmetallation reaction of natrium 8-quinolinolate with tris[(trimethylsilyl)methylphenylimidotungsten chloride produced readily the tungsten(VI) alkylidene complex containing O,N chelating ligand, 8-

quinolinolate (Eq. 3.72). N

+ V~CH2SiMe3)3CI(=NPh ) ~

CH2SiMe3

O- II ~CHSiU~ 3,,~ N

(3.72)

{3

ONa

This complex was very active and stereoselective in the ring-opening metathesis polymerization of norbomene. Reaction of Li salts of 2-pyridylmeth~ol derivatives R~RZC(OI~2 Py) with tris[(trimethylsilyl)methylphenylimidotungsten chloride afforded

similar O,N-chelated tungsten(Vl) alkylidene complexes active in ringopening metathesis polymerization. Thus, reaction of Li[OCPh2(2-Py)] with (Me3SiCH2)3W(=NPh)CI in THF gave W(=CHSiMe~)(CH2SiMe~X=NPh)[OCPh2(2-Py)] (Eq. 3.73).

U[OCPh~(2-Py)] * V~CI"I2SiMe3)3CK=NPh)

r~

~N. p C-O-

Ph...L , ~

N

/

.CH2Si~ (3.73)

171 The 'H NMR spectrum of W(=CHSiMe3XCHzSiMe3X=NPh)[OCPhz(2Py)] in benzcno-d~ showed to be a mixture of two rotamers, in an anti:syn ratio of approximately 1"10. In an analogous m ~ e r , reaction of Li[OCH(CMe3)(2-Py)] with (Me3SiCH2)3W(=NPh)CI provided W(=CHSiMe3)(CH2SiMe3X=NPh)[OCH(CMe3X2-Py)] (Eq. 3.74).

U[OCH(CMe3X2-Py)]

9VV(CH2SiMe3)3CI(=NPh )

"n-IF

. H..•

~. *~

/

.CH2SiMe3

,c-o-W*cHsi

Me3C

(3.74)

N

Both O,N-chelated tungsten alkylidenr complexes of 2-pyridylmethanol derivatives showed to be active in the ring-opening metathesis polymerization of norbomene.

Molybdenum-alkylidene complexes, Mo(=CHCR'3X=NArXOR")2 A wide range of four-coordinate molybdenum-alkylidene complexes of the type Mo(=CHCRIR2RSX=NAr)(OR4)2 prepared Schrock and coworkers 15~ in high yield from amn~nium dimolybdate. The first series of neopentylidene complexes, Mo(=CI-~BuX=NArXOR)2 (Ar=2,6 diisopropylphenyl; OR = O~Bu, OCMe2(CF3), OCMe(CF3)2, etc.), can be prepared from a "universal precursor", Mo(=CH'Bu)(=NAr)(triflate)ADME) which is obtained in three steps from ammonium dimolybdate (Eq. 3.75-3.76).

[NH412M0207 ---~ Mo(NAr)2CI2(DME)__.~ Mo(NAr)2(CH2tBu)2 (3.75) (I)

TfO NAr (I) '-ArNH30-TfCH3~Bu/~d t~.,HtBu - 2 l.iOTf I OTf

ROI~-Ar ''CHtBu

The second series of neophylidene complexes, Mo(=CHCMe~h)(=NAr)(ORh (~---2,6-diisopropylphenyl; OR = O'Bu, OCMe-z(CF3), OCMe(CF3)z, etc.), can be prepared from another

172 "universal precursor", Mo(=CHCMe2Ph)(=NAr)(triflate)z(DME), which is obtained analogously in three high-yield steps from ammonium dimolybdate tsl (Eq. 3.77-3.78).

[NH412M0207~

Mo(NAr)2CI2(DME)--~Mo(NAr)2(CH2CMe2Ph)2 (3.77)

(u) § 3 TTOH/DME

T~~NAr ,~)_

(II) -ArNH3OTf-CH3CMe2Ph%6

+2L.iOR

R.O ?-Ar

HCMe2Ph-zLiOTI7

HCMezPh

These complexes serve as initiators for the ring-opening metathesis polymerization of norbomene and substituted norbornene as well as for related olefin metathesis reaction. Some of the neophylidene molybdenum complexes, Mo(=CHCMe2Ph)(=NAr)(ORh, and their precursor, Mo(=CHCMezPhX=NArXtriflate)-z(DME), are available commercially. An universal catalyst precursor ~sz that contains a benzylidene ligand could be prepared directly in four steps from ammonium dimolylxlate, one of which involves an co-hydrogen-abstraction reaction in a dibenzyl complex. Mo(=NA(hCIffDME) reacts cleanly with 2 equiv of KCHzPh to give Mo(=NAr)z(CHzPhh. Treatment of this compound with 3 equiv of triflie acid afforded Mo(=CHPhX=NArXOTfh(DME), which is isolated as a mixture of isomers according to NMR spectra (Eq. 3.79-3.81).

Ar I Mo(NAr)2(CH2Ph)2 -ArNH3OTf -CH3Ph

Ar s

c.6 o

.o~Mo.. / v

(3.80)

Ar I

=

"W,M,o-" L

"

(3.81)

173 Five-coordinate molybdenum (VI) alkylidene hexafluoro-tertbutoxide complexes that are stabilized by internal Lewis base coordination were prepared by Schroc~ and coworkers ~" starting from tetrac,oordinate molybdenum (VI) alkylidene complexes. For instance, reaction of 4methoxy- 1-hexene with Mo(=CHCMerPhX=NArXOI~h or Mo(=CHCMe3X=NArXOI~)~ in pentane (O1~ = OCMe(CF3)2) afforded crystalline, red-orange Mo[CHCHzCH(OMe)CHzCH3 ](=NArXOILssh in good yield (Eq. 3.82). Ar

Ar

I

RfeO".Mo//N

I R~O.... NI

+

Rf6C)~AM~ (3.82)

_CHz=CHCMezPh =

~

A related difimctional Mo alkylidene complex could be prepared in a similar manner from Mo(=CHCMe2Ph)(=NAr)(OR~h and the appropriate r diene (Eq. 3.83). ,sat-- N

R~)~.. |

I~

N-At

~ ~

-

Ar--~"O1~ M R spectra of these complexes indicated that no plane of symmetry was present in either complex and the Jcrk, value (158 Hz) suggested that the alkylidene was the anti rotamer in each case. Six-coordinate molybdenum (VI) alkylidene hexafluoro-tertbutoxide complexes that are stabilized by external Lewis base coordination were also prepared by Schrock and coworkers ~" starting from tetracoordinate molybdenum (VI) alkylidene complexes. Thus, st~cn@ or reacts cleanly with Mo(=CHCMe2Ph)(=NAr)(OR~)2 orange Mo(=CHCMe3)(=NArXOR~h in DME to afford Mo(=CHPh)(=NAr)(OI~)2(DME) in good yield (Eq. 3.84).

N~Ar RI'eQ,II ;[r

.O" "C H C M e a

/~ + (~ ?

[

+ DME

At

~

- I'hC=CHCMe3

RfoQ --.~ x.II / ("~'~ X...O ORf6

i

0 (3.84)

174 4-(Dimethylamino)styrene and 2,4,6-trimethoxystyrene react also with Mo(=CHCM~PhX=NArXOI~h or Mo(=CHCMe3X=NArXORch to yield dark red Mo[CH-4-GH4-NM~](=NArXOI~s).z(DME) and red Mo[CH2,4,6-CtH2(OMe)~](=NArXOR~s)z(DME), respectively (Eq. 3.85-3.86). NMe2

afoO,

+ Me2N~ RfsO/I~cHCMe,

RfeO / f ':.M0 .

R~O

=_ ~.,.~\..11 -H2C=CHCMe2Ph ~ ~ O R f s

(3.85)

|

1 ,DME ..n .~ Mo----/~"~ + MeO--~~ j '~ r - zP':'C=CHCMe=--h l'h ~,,.O-" -\r~of OMe ~CHCMezPh xC)Me ' v"~e

/-~

13.86)

On the basis of the relatively low value for Jca~ in the first two sixcoordinate complexes, they are believed to be the syn rotamers with the structures shown in Eq. 3.85-3.86. In contrast, the alkylidene ligand in the last Mo complex is in the anti orientation in solution (Jca~ = 159 Hz), consistent with internal coordination of an o-methoxy group to the metal, probably in a five-coordinate species (Eq. 3.87).

AIr = ~ ~ O M e ~1

-O9 2Mo ( ~ q %Rfe

OMe

Ar

NI

-DME

~Q

|

+DME

RfsO~-M Me"

OMo

(3.87)

OMe

Dimethoxyethane could not be removed m vacuo from solid samples of this Mo complex, however, so it was presumed that DME was extemaUy coordinated to form a six-coordinate compound in the solid state. The metathesis reaction between Mo(--CHCMe2PhX=NArXORas:h or Mo(=CHCMe3)(=NAr)(OI~)~ and 0.5 equiv of octatctracne in DME afforded the difunctional Mo complex [(DME)(Rf~O)-z(=NAr)Mo]z(CH~

3.88).

175

Ar

Rf6q-~~-O~

9

(3.88)

It was observed that the solution changed from yellow to deep red as the reaction went to completion, consistent with formation of a conjugated alkylidene complex. The six-coordinate structure of the difi~ctional complex was proposed on the basis of the observed stoichiometry, the stability of the compound in solution and in the solid state, and the values from the ~H NMR spectra. However, it was inferred that the six-coordinate complex must be in equilibrium in solution with fie, DME and a fourcoordinate alkylidene complex, on the basis of the reactivity of the complex toward norbomene and norbomadiene, as well as the fact that the DME ligand could be replaced easily by diethyl ether or T t ~ to form

monoadducts (Eq. 3.89).

/--[Mo~(DME) S

(DME._. _~]tMoR5/'~

/~~/--[Mo]f~S)

'2DME-~ ( S ) [ M o ~ - '

(3.89)

S = Et20,THF

[Mo~ = MoKNkrXOR~h

The monoadduct with ether could be prepared directly from Mo(=CHCMe2Ph)(=NAr)(OP~)2 or Mo(=CHCMe3)(=NAr)(OR,s)2 and octatetraene in ether in 66 % yield while the monoadduct with THF could not be prepared directly in THF, because the initial metathesis step is too low under these circumstances. A l l these difimctional Mo complexes are isolable, crystalline species that are stable at 25~ in solution and in solid state. The value for Jca,, for DME complex (132 Hz) and ether complex (127 Hz) indicated them as syn rotamers while the value of Jc~ for THF complex (152 Hz) was more consistent with its being anti rotamer. Reaction of the DME adduct with 4 equiv of LiOtBu and 2 equiv of quinuclidine (quin) afforded the difunctional complex (quinX'BuOh(=NAr)Mo(CH)sMo(=NArXO'Bu)~(quin) (Eq. 3.90).

J

(DMEXMo~~ [Mo~ = Mo(NArXORfeh

[M~

2quin 9 ..~

/[MoXquin)

,4 LiO~u ( q u i n t ] - " [Mo] = Mo(NArXO~uh

(3.go)

176 This complex is less stable than its precursor in the solid state. Presumably, the quinuclidine ligand is not bound strongly because of the more electrondonating nature of the alkoxide ligands. 1,4-Divinylbenzene reacted with Mo(=CHCMe2PhX=NArXOR~)2 or Mo(=CHCMe~X=NArXOR~h to produce another difunctional alkylidene complex, 1,4-[(DME)0~F60)2(ArN=)MoCH]zCasH4 (Eq. 3.91). Ar

Rf8

_ ~1~-O,.

.o.,.,:v_.

+

HCMe3

A,

L,,,.O'OR/8

This complex could be isolated as a crystalline, bright orange solid which was soluble in DME and THF but was nearly insoluble in other common solvents. Proton and carbon NMR data suggested that the structure of the complex was analogous to that proposed for the six-coordinate benzylidene complex. The value for Jct~ (125 Hz) was consistent with a syn orientation of the alkylidene ligand with respect to the imido ligand. An isolable THF adduct could be prepared from 1 , 4 - [ ( D M E ) ( R F 6 0 ) 2 ( A r N = ) M o C H ] 2 ~ simply by dissolving this complex in THF (F-4.3.92). Ar i

9 N

0 ~

'M'o ORf8

Ar

I .~'_

i

M

L;

N-ORI~

(3.92)

B'6o ORb Mo(=CHCMe2PhX=NArXOR~)2 or of However, metathesis Mo=(CHCMe3X=NArXOR~h with divinylbenzene in THF proceeds to slowly to prepare 1,4-[(TtW)(RF60)2(ArN=)MoCH]2Cdh directly by this reaction. Tungsten oxo alkylidene c o m p l e x e s . The first successful synthesis of a tungsten oxo alkylidene complex of the type w(oX=CHCMe3)(PEt3)2CI2 was reported by Schrock and coworkers ~s4'~ss starting from a tantalum alkylidene complex (Eq. 3.93). Ta(CHCMe3XPEh)2CI3

* w~oXOCMe3)4

PEh ..._ C k , ~ O

"- cr. i .CHCMea

- Ta(OC Me3)4cl

PEt3

(3.93)

177 Analogous benzylidene, ethylidene, propylidene and methylene complexes were prepared by treating W(O)(=CHCMe3)(PEt3)2CI2 with RCH~2H2 (R = Ph, Me, Et, H) in the presence of AICI3(Eq. 3.94).

PEh PEh Ck.~~3 + H2C=CHR Ck IW~-_ CI,"I~'CHCMe3 -H2C=CHClVl% 3 CI" I"CHR PEt3 PEh

(3.94)

Furthermore, the five-ca3ordinate, tungsten oxo alkylidene complex W(O)(=CHCMe3)(PEh)CIz was prepared by adding transition metal complexes which will scavenge phosphine ligands (Eq. 3.95).

Ck.l~ + Pd(Pt~N)2CI2 =- Et31:x.'.~.V~HCMe3 CF I'CHCMe3 -Pd(PEh)2CI2 ~ ~1 PEt3

(3.95)

Interestingly, this five-ca3ordinate tungsten oxo complex can metathesize terminal and internal olefins in chlorobenzene in the absence of AICl3 at an initial rate which is at least equal to that of the hexaooordinate tungsten oxo complex W(O)(=CHCMe3)(PEh)2CIz plus AICI3. The oxo alkylidene complex syn-W(=CHtBu)(O)(OAr)2(PMe3) (Ar=-2,6-Ph2C6H3) was prepared by Schrock and coworkers Is6 by the reaction between W(=Cl-r'Bu)(O)(PMe~)zClz and 2 equiv of KO..2,6PhzC6H3 (Eq. 3.96).

PEt3 Ck..i ~.O

CI~~~CHCMe3 PEt3

+ 2 KOAr - 2 KCI-PMe3=-

PMo3 ArO, l O

AK~'VV~cHCMe3

(3.96)

The alkylidene I~ resonance was found at l 0.13 ppm and the C= resonance at 287.4 ppm. A Jcn value of 120 Hz suggested that the alkylidene has the syn orientation. 3~p M R data (0.35 p p ~ ~Jpw=333 Hz) suggested that the PMe3 ligand was bound to tungsten on the M R time sc~e. A strong absorbance a t - 960 cmm has been assigned to the metal-oxo stretch. An analogous PPh2Me complex, syn-W(~H~uXOXOAr)z(PPheMe) could be prepared by adding 2 equiv of KOAr to W(=CHfBu)(O)(PPheMe)~Br2 (x=l,2) (Eq. 3.97).

178

P,Ph2Me

Br,. I ~

+

P,Ph2Me

2 KOAr

ArO. l O

B~'I'*~CHCMe3Wr- 2KCl_pph2Me~ PPh2Me

ArO~'~CHCMe3

(3.97)

Only a single broad 31p NMR resonancewas observed at 11.6 ppm at 22~ but a sharp resonance was found upon cooling the sample (Jpw=305 Hz). The alkylidene Ha (10.37 ppm) and C= (287.2 ppm) resonances also did not show coupling to 3~p at room temperature. A Jca value of 118 Hz was consistent again with the syn rotamer being present. A neophylidene complex, W(=CHCMe2Ph)(OXOAr)~pPh2Me), was also prepared (Eq. 3.98).

PPh2Me Br,,.I ~

,PPh2Me

ArO... V~I,~O Br"!'CHCMe2Ph-2KCI-PPh2M~ ArO/ ~CHCMe2Ph PPh2Me +2 KOAr

(3.98)

All these tungsten oxo alkylidene complexes react readily with 2,3dicarbomethoxynorbomadiene and 2,3-bis-(trifluoromethyl)norbomadiene in dichloromethane or toluene to give polyng~s that are >95% cis and >95% isotactic. Tungsten oxo vinylalkylidene complexes. Synthesis of tungsten oxo vinylalkylidene complexes ~" involved two main steps starting from tungsten oxo precursors WCI2(OXPX3)3 (PX3=P(OMe)3, PMePh2); first, formation of rl2-cyclopropene complexes, W(q2-diphenylcyclopropene)Cl2(O)(PX3)2, by reaction with 3,3-diphenylcyclopropene and second, conversion of these complexes into tungsten oxo v i n y l alkylidene complexes, W(=CHCHCPhzXO)(ORI~)z(PX3), by reaction with LiOC(CH3)(CF3h (LiORf6) in benzene or toluene at 55-60~ (Eq. 3.99-3.100).

X3R.,0 ,px 3 Ph . .,, ph2Mep~ O ~ P h Cff,~l,PMePh2

Ph

2 LiORfs 6~C, 12h Benzene

..=

=-

X3R.'ii'..J~ Ph

Rfs(~

(3.99)

~Ph

Ph Rfs~ PMePh2

(3.100)

179 The products were isolated as a mixture of the two rotaries, syn and an#, based on the values of the Jan coupling constants observed in the 'H NMR $po~i~m. Reaction of W(=CH=CHCPh2)(O)(OAr)2(POMe)3 with an excess of Tt~ led to the corresponding THF adduct W(=CH=CHCPh2XOXOAr)2(THF) (F_,q. 3. l01).

_o, LPh

Rf60"~V~v xPh Rf60 P(OMe)3

THF-da

O -Ph RfsO,j ~ ~ V ~ p h Rf60 THF

I

Benzenede

(3.101)

The complex appeared as a mixture of syn and anti rotamers, in 1"1 ratio, probably due to the low ligand steric bulk. In this case, the ~H NMR spectrum presented two doublets for the resonances of the H~ and H0 in each rotamer, at/~=l 1.86 and 9.32 for the anti rotamer and at 8=10.25 and 9.28 for the syn rotamer. These complexes were active in the ring-opening metathesis polymerization of norbomene as well as for cyclic olefins such as cyclooctene, 1,5-cyclooctadiene and cyclooctatetraene derivatives. Ruthenium-alkylidene complexes, Ru(CHR)LL A series of RuCI2(CHR)(PPh3h complexes (R= Me, Et, At) were prepared by Grubbs and coworkers rossfrom RuCI2(PPI~)3 via alkylidene transfer reactions from diazoalkanes. When RuCI2(PPh3)3 was reacted with diazoetlmne, diazopropane and variously para-substituted aryldiazoalkanes, pC6tGXCI-iN2, a spontaneous Nz evolution at-78 ~ indicated formation of RuCI2(=CHR)(PPh3)3 (R=Me, Et) and RuCI2(=CH-p-Cd-hX)(PPh3h (X=H, NMez, OMe, Me, F, CI, NO2) complexes (Eq. 3.102-3.103). PP~ H P,PlM H ,

Cl'Ru-PPh3pPh3 + N2--"C,R |Ph3 P

Ck u._pp .

~

Cl/-I" 'PR113 P

(3.1

CL..,PPh3 ,.,-H

H

= cp.&=,.,

PPh3

X

02)

(3.103)

X

The m~um-alkylidene complexes were isolated in 80-900,6 yield as green air-stable compounds. The awl complexes polymefized

180 norbomene in methylene chloride at room temperature to give polynorbomene in quantitative yields. Ruthenium-vinylalkylideae complexes, RuCIz(CHCHCR'2). Several ruthenium vinylalkylidene complexes of the type RuCIz(=CH=CHCPh2)(PR3h (g=Ph, Cy, Cyp) were prepared by Cnubbs and coworkers ~59 by the reaction of RuClz(PPh3)3 with 3,3diphenylcyclopropene and fiulher substitution by the appropriate phosphine

ligand (Eq. 3.104). PPI~ p c ~ U - Ph3

Ck~

PPh3

PPh3 Ckl~~p

Ph

PPh3

,Ph h

Ph

pR3 / = , , ~ P h .~ C l ~ ~ Ph

(3.104)

PR3 R = Ph, Cy, Cyp

compounds showed a remarkable activity in ring-opening metathesis reactions and good stability toward functional groups and protic media. However, the multistep synthesis of the cyclopropene and the low initiation rates of the resultant diphenylvinyl alkylidenes are present limitations of these complexes. Chiral alkylidene complexes. A number of ehiral molybdenum complexes have been synthesized by Schrock and coworkers ~6~ using C2-symmetric chiral diolate ligands which were active in ring-opening metathesis polymerization of 2,3-bis(trifluoromethyl)norbomadiene and 2,3diearbomethoxynorbornadiene. Synthesis of Mo(=CHCMe2PhX=NAr)[(+) Ph4tart](S) was carried out by the reaction of (+)-Pl~tartH2 with Mo(=C HCMe2PhX=NArXOTf):4"I)ME) (DME=dimethoxyethane) in diethyl ether in the presence of triethylamine (Eq. 3.105) M M

~~hh

P,l~h

~ O'TT8..Ar

+ L~ (~"~o I~l~I 2

I ~-~-Ph o~

Ph Ph O'l'fA Ar Ph Ph OTrr

where S was a mixture of NEt3 and DME. In an analogous manner were synthesized Mo(=CHCMe2Ph)(=NAr)[(-)-Ph4tart](S) and Mo(=CHCMezPh)(=NAr)[(+)-Naph4tart](S) (Eq. 3.106).

181

O RR ~~X~

\ OTf, . r'~"~'~ ~~]

M

9

I~N..Ar ~o~

Me. O 1 ~

RR Olfe R~

Mo(=CH'Bu)(=NAr)[(:I:)-BINO(SiMezPh)2](THF) was obtainr in 70~ yield from Mo(=CH*Bu)(=NAr)(OTf)2(DME) by reaction with (+)BINO(SiM~Ph)K2 in tetr~ydrofuran as a solvent (F~. 3.107). SiMe2Ph OT~,

SiMe2Ph [~OH

\O OTfe ,,_

~SiMe2Ph /

KOH

~,,~~o.~,~N-~

(3.107)

SIMe2Ph

O'r~

Similarly, Mo(=CHCMe2Ph)(=NAr')[(+)-BINO(SiMe~h)x](THF) (Ar'=2,6-GH3Mr was prepared from (:I:)-BINO(SiM~Ph)K2 and Mo(--CHCMezPh)(=NArXOTOADME) (Eq. 3.108). SiMe2Ph OH \.. OTfs Ar

[~[~ OH

+

SiMe2Ph

/

SiMe2Ph

OT~, .o~N_A~

KOH

OTfe

(3.108)

SiMe2Ph

Chiral Mo(~WBu)(=NAr)[Bipheno(tBu)4] was obtained by adding Bipheno('Bu),K2 to Mo(=CH'Bu)(=NAr)(OTOADME)in tetrahydrofuran

(~. 3.]09). ,,,,.O.. I ~ N ~ , "

KOH

O.

tBu

tBu OTfe

Ar

(3.1o9)

182 Starting from a new chelating chiral diol (IS,2S)- and (IR,2R)-1,2bis(2-hydroxy-2,2-bis(trifluoromethyl)ethyl)cyclopentane (TBEC-H2), the chiral alkylidene complex Mo(=CHCMezPhX=NAr)(TBEC) was prepared by Gmbbs and coworkers ~ by reaction of the dilithium alkoxide of TBEC with Mo(--CHCMe2PhX=NArXOTf~(DME) (Eq. 3.110). Ar i TftQ,. ~ -..),

Fac-CF3 H ~ H "

F3 -CF3

LiOH

"/O'/M~--'ph 9

~...O

OTfe

~

Ar i N Fac-CFa 'I "J' /'L O.'/M~' = " "p h I~~,CFa t ~ / ~ ' - "CF3

(3.110)

The chiral alkylidene molybdenum complex could be isolated as a brown yellow solid in 85% yield and used in ring-opening metathesis polymerization of strained and less strained cycloolefins. In an analogous manner, chiral tungsten oxo vinylalkylidene and tungsten amide

vinylalkylidcne complexes have been prepared by the reaction of the dilithium alkoxide of TBEC with W(rl2diphenylcyclopropene)Clz(O)[P(OMr W(=CH=CHCOCH2CHzCHzOXO)CIz[P(OMeh] and W(--CH--CHCPh2X=NAr)CI2[P(OMeh]2 (Ar=-2,6.-('Pr)~Cd-I3) (F-xi. 3.1113.113).

F3c.CFaH

.~d H

~

CF3

-CFa

F3C.~3F3H

~

(MeO)~pi~.~:~~hh L i % i %P(OMeh CK'CI 0 .,P(OMe)3

C"F, "(~.o~P~, -CF3

FaGcFaO...P(OMeh ,~IL,~..W~-,,.j~ ~Ph : u I ~ ~'Ph CF3 CF3

o.

o~

(3.111)

F3C CF3 0 ,,P(OMe)3

~% ~ c ~ ,

t.../-- "CF3

o.j

(~"~)

k F3C....?F3H ~J

-CF3

Ar NI P(OMeh U/" "" CF-W=~ .,~ .Ph 9 / \ " ~ " ~' CH3-CH2 > CH(CH3h. Allylcydopentadiene. Aso and Ohara 3~ carried out the cationic polymerization of mixtures of allylcyclopentadiene isomers to produce

251

polymers consisting of equal amounts of 1,4- and 3,4-enchainments (Eq.

5.2s).

The reaction was first undertaken by these authors in the presence of BF3.EhO, AIBr3, TiCh and SnCI4 in toluene and methylene chloride at 0~ and -78~ when soluble polymers were prepared with intrinsic viscosity [11] of 0.1 to 0.3. It is worth mentioning that the propagation proceeded essentially by the cyclopentadiene ring and the much less reactive allyl group remained unchanged. The microstruc~e of the polymer was investigated by IR and NMR spectroscopy to confirm the above indicated 1,4- and 3,4-enchainments of the monomer units in the polyng'r chain. Later on, Mitchell et al. 3z carried out allylcyclopentadiene polymerization induced by BF3.EtzO, in chloroform at room temperature, to obtain polymers with intrinsicviscosity[11] of 0.19, whose mierostmcture indicted -53% 1,4a n d - 47% 1,2-enchainment of the repeat units. In this way the latter investigators confirmed the earlier findings of Aso and Ohara c o ~ n g the nonreactivity of the allyl group in contrast to the substituted cyclopentadiene moiety. Methallylcydopentadiene. Mitchell et al. 32 synthesized and subsequently p o l ~ a mixture of methallylcyclopentadiene isomers in the presence of BF3.Et20 to obtain poly(methallylcyclopentadiene) with 1,2- and 1,4enchainment of the repeat units in the polymer chain (Eq. 5.29).

(5.29) The reaction has been effected in chloroform at room temperature. Microstructure of the poly(methallylcyclopemadiene) has been examined by NMR spectroscopy to result i n - 35% 1,2- and --65% 1,4-enchaimn~t. Allylmethylcydopentadiene. Allylmethylcyclopentadiene was f i ~ synthesized by Mitchell and c o w o r k ~ ' $ 32 al~ employed in cationic polymerization to produce polymers with 1,2- and 1,4-enchainment of the repeat units (Eq. 5.30).

252

The reaction was carried out using an unresolved mixture of isomers in chloroform with BF3.EhO at room temperature. The NMR spectroscopy indicated a polymer having- 31% 1,2 linkages and -69% 1,4 linkages. Substituted fulvenes. Several substituted fulvenes have been polymerized with cationic initiators. The high reactivity and specific structure of these monomers will lead readily to products having particular structures and interesting properties. 6,6-Dimethylfulvene. Cationic polymerization of 6,6- 90%, large intrinsic viscosities, [11] = 0.36-0.47 and high molecular weights, M, = 56000-90000 of poly(3-methylacenaphthylene) (Eq. 5.111).

[ n

----~

]n (5.111)

Interestingly, they observed that to reach the highest molecular weights of the polymer large amounts of SnCI4 were necessary, practically equimol~ SnCl4:monomer ratio. In their studies, they examined the influence of temperature on the molecular weight to find that, as expected, the molecular weight increased with decreasing temperature. 5-Methylacenaphthylene. The cationic polymerization of 5methylacenaphthylene, of interest due to the new position of the methyl group with respect to the reactive double bond, has also been investigated by Bellied and M~eehal Iz3(FN. 5.112).

=

(5.112)

In the presence of the catalytic complex BF3.EtzO in methylene chloride at 72~ they prepared in 57% yield polymers having intrinsic viscosity [11] = 0.55. Preparation of light-colored resins by cationic polymerization of multicyclic olefins has been reported in a patented process by Nippon Oil Co. t2s Starting from non-conjugated dienes or polyenes of the norbomene type, the monomer is first selectively hydrogenated in the presence of Ziegler catalysts then the partially hydrogenated product is submitted to the action of cationic catalyst to form high molecular weight addition polymers (Eq. 5.113-5.114).

313

+H2

AlCl 3

n :

(5.114)

Examples are given for dicyclopentadiene hydrogenated with titanocene dichloride and triethylaluminium and subsequently polymerized with aluminium chloride. Interestingly, when Pd/C was used as the hydrogenation catalyst, the product could hardly be polymerized. 5.4. References

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319

Chapter 6 ANIONIC POLYMERIZATION OF CYCLOOLEFINS 6.1. General Aspects The literature referring to the anionic polymerization of cycloolefins is limited so that this topic will be briefly reviewed in the present chapter. It is reasonable to assume that simple cycloolefins in the presence of anionic initiators have a reduced polymerizability because under these conditions stable vinyl anions may readily arise by a proton transfer from the most reactive allylic positions of the cycloolefin (Eq. 6.1).

(6.1)

=

However, under favorable conditions, i.e., when some strong electronegative groups are attached to the cycloolefin like nitrile, carboxyl, c,arboalkoxy, etc., the 1,2-addition polymerization of cycloolefins with anionic initiators might occur with formation of the corresponding saturated vinyl polymers (Eq. 6.2).

There exists several publications on the anionic polymerization of cyclic dienes. As it will be shown later, more data available are reported on the anionic ring-opening polymerization of substituted silacycloalkenes. It is of interest that the anionic polymerization of a cyclic diene, methylenecyclobutene, with alkyllithium, reported by Wu and Lenz,~ gives rise to a 1,2-addition product by opening the endocyclic double bond (Eq. 6.3).

n

f

1-1

[1 ] In f

(6.3)

320 It is not ruled out that some 1,4-addition units may oexmr along 1,2-repeat units in the polymer chain but their presence has not been proved yet (F_,q. 6.4).

n~

~

!1 l ]n

[__/

(6.4)

Since a dramatic improvement of the thermal stability, chemical properties and mechanical strength is expected for the obtained polymers with directly connected alicyclic structures in the main chain, the polymerization of a series of cyclic conjugated dienes, e.g., 1,3cyclopentadiene, 1,3-cyclohexadiene and 1,3-cyclooctadiene has been carried out using the classical anionic initiator alkyllithium, z'~2 However, the obtained polymers were of low molecular weight, undefined microstructure and in a low yield. In the presence of anionic initiators, cyclopentadiene will form a poly(cyclopentadiene) having two recurring units in the polymer chain (Eq.

6.5).

(6.5) The contribution of these two structures will depend on the reaction conditions. Details on these types of structures from classic~ studies are scarce. Anionic polymerization of' 1,3-cyclohexadiene w i l l form poly(cyclohexadiene) with 1,2 and 1,4 recurring units in variable amounts, depending also on the reaction conditions (Eq. 6.6).

n(

~

~

+

(6.6)

For instance, low molecular weight poly(cyclohexadiene) was obtained in substantial yield in the polymerization of 1,3-cyclohexadiene initiated by butyllithium ("BuLi)using benzene, tetrahydrofuran, dioxane, diethyl ether, n-heptane and cyclohexane as solvent. 2"s By contrast, in the polymerization of 1,3-cyclohexadiene initiated by Li-naphthalene,

321 Na-naphthalene and K-naphthalene, higher polymers with a broad molecular weight distribution were obtained in low yield.4'+ It has been reported that the anionic polymerization of 1,3cyclohexadiene in the presence of alkyllithium and alkylsodium (e.g., nbutyllithium, Na-naphthalene, polystryryllithium) in nonpolar solvents (e.g., n-hexane, cyclohexane, benzene) at room temperature, leads to low molecular weight products, in low yields and broad molecular weight distributions of polymers due to the deactivation of the living ends. 2"~'8'9 Furthermore, in the polymerization of 1,3-cyclohexadiene initiated by alkyllithium, the formation of 1,4-cyclohexadiene and benzene was observed, due to the abstraction of the allylic hydrogen from 1,3cyclohexadiene by organolithium species competing with the propagation reaction (Eq. 6.7-6.8).

~

L~

---

Lie* G

(6.7)

~

~

(6.8)

+ LiH

The first successful example of the living anionic polymerization of 1,3-cyclohexadiene with the "BuLi/TMEDA (N,N,N',N'tetramethylethylenediamine) system was reported by Natori ~2 leading to homopolymer, poly(l,3-cyclohexadiene), as well as to block copolymers. In addition, these authors, reported the relative reactivity of 1,3cyclohexadiene in the copolymefization with styrene and isoprene and the relative reactivity of the propagating species of living poly(l,3cyclohexadiene) and living polystyrene. ~3 The relationships between the microstructure and properties of homopolymers, block copolymers and their hydrogenated derivatives are also reported. ~4 Detailed studies on the polymerization of 1,3-cyclohexadiene with various alkyllithium (RLi)/amine systems have been carried out by Natori and Inoue. ~ Conversion-time relationships of the polymerization of 1,3cyclohexadiene with some ~BuLi/TMEDA systems in cyclohexane at 40~ are illustrated in Figure 6. !.

322 Yield,% 100 O0 60 40 20

0

lO0

200

300

400

5OO

Time, min Figure 6.1. Conversion-time curves for 1,3-cyclohexadiene polymerization with "BuLifFMEDA catalytic systems in cyclohexane at 40~ ([ 1,3-CHD]J[Li]o = 250, I-"BuLi/TMEDA = 4/5; 2-"BuLi/TMEDA = 4/2; 3-"BuLiFrMEDA = 4/0.5; 4-~BuLi)(Adapted from Ref. ~s) Of several catalytic systems employed (RLi -- MeLi, "BuLi, "BuLi, 'BuLi, PhLi), they observed that the "BuLi~gtEDA catalyst (molar ratio TMEDA/'BuLi higher than 4/4) induced polymerization of this monomer in a "living" manner to polymers having narrow molecular weight distributions with well controlled chain lengths. The rate of polymerization and polymer yield increased with increasing the ratio of TMEDA to "BuLi (Table 6.1). Table 6.1 Polymerization of !,3-cycl.ohexadiane .with.:BuLl frMED A mm.a!mg ~ ' Initiator Yield M,,/M. 1 , 2 - u n i t 1,4-unit % % % 98 2 2.2"I 33 nBuLi 79 21 2.42 77 "BuLifFMEDA(4/0.5) 67 43 1.52 72 "BuLifrMEDA(4/2) 52 48 1.12 100 "BuLifrMEDA(4/3) 49 51 1.07 100 "BuLifFMEDA(4/4) 48 52 1.06 100 "BuLi;YMEDA(4/5) 46 54 1.08 100 "BuLifYMEDA(4/6) "BuLi/TM ED A(4/8) 100 1.07 54 46 'Data from reference~ ~ffMEDA = NiN,N',N'4etram~hylethylenodiamme.

323 As it can be seen from Table 6.1, the molecular weight distribution of poly(l,3-cyclohexadiene) became narrower with the ratio TMEDA/~uLi. The microstructure of the polymer, determined by 2D-NMR, indicated a higher content of 1,4-units in the polymerizations initiated with higher "BuLi/TMEDA ratios. It is interesting that higher contents of 1,4-units have been also obtained in the polymerization of 1,3-cyclohexene using ~ u L i associated with other amines as compared with tetramethylethylenediamine (Table 6.2).

Table 6.2 Polymerizauon of 1,3-cyclohexene with ~BuLi/amme initiating systems'

Initiator ~

Yield %

M,,~.

"BuLifFMEDA(4/5) "BuLifFMMDA(4/5) "BuLifFMPDA(4/5) "BuLi/TMHDA(4/5) "BuLi/TEEDA(4/5) "BuLi/DABCO(4/5)

100 70 33 67 16 100

1.06 1.75

1,2-unit %

1,4-unit

52 24

48

%

76

2.16 91

1.95

1.14 1.69

21

79

'Data from re.fence ~s', brMEDA = N,N,N',N'4etramethylethylenediamine, TMMDA = N,N,N',N'-tetramethylmethylenediamme, PMPDA = N,N,N',N'tetramethyl- 1,3-propanodiamine, TMHDA = N,N,N',N'-tetramethyl- 1,6hexanecliamme, TEEDA = N,N,N',N'-4etraethylethylenediamme, DABCO=-I,4diazabicyclo[2.2.2]octane

It has been also found that the polymerization of 1,3-cyclohexadiene with polystyryllithium/amine systems can give in some cases poly(1,3cyclohexadiene) with narrow molecular weight, having a high content of 1,2-units in the polymer chain (Table 6.3). The highest content of 1,4-units has been obtained using n-butyllithium associated with N,N,N',N'tetramethyl- 1,6-hexanediamine and 1,4-diazabicyclo[2.2.2]octane. However, even though these initiating systems were quite active and selective, the molecular weight distribution was not narrower than that obtained with the ~BuLiFFMEDA system.

324 Table 6.3 Polymenzation of 1,3-cyclohexene with polystyryllithium/amme mitiating., Initiatorb Yield Mw/M. 1,2-unit % % l . e m ~

PStLi PStLi/TMEDA(4/5) PStLifFMMDA(4/5) PStLifFMPDA(4/5) PStLi/TMHDA(4/5) PStLi/DABCO(4/5) PStLi~Et3(4/5)

15 100 39 84 98 100 23

It

1,4-und:

%

21 64 26 32 18 25 14

1.60 1.29

1.55 1.55 1.27

1.14 1.45

79 34 74 68 82 75 86

*Data from reference*~; ~PStLi = Polystyryllithimn, TMEDA = N,N,N',N'tetra~ylethylenediamine, TMMDA = N,N,N,,N,_tetramethylmethylenediamme, PMPDA = N,N,N',N'-tetramethyl-l,3-propanediamme, TMHDA = N,N,N',N'~methyl-l,6-hexanediamine, TEEDA - N,N,N',N'-tetraethylethylenodiamme, DABCO= 1,4-diazabicyclo[2.2.2]octane Anionic polymerization of cyclooctatetraene carried out by Ushakov and Solomon ~6 in the presence of Na initiator led to a high molecular weight polymer which was insoluble in methanol and acetone. Plausibly, the highly unsaturated 1,2-addition polymer formed from eyclooctatetraene under anionic conditions underwent further cross-linking reactions to a branched polymer (Eq. 6.9).

n

~

~

(6.9)

t

Jp

Polymerization of l-isopropylidene-3a,4,7,7a-tetrahydroindene with anionic initiators gave oligomers, probably by competitive 1,2- and 1,4addition reactions of the endocyclic and conjugated double bonds of the monomer ~7(Eq. 6.10).

n

~

I

m

§ [(

IF< ~]P

(e.lo)

325 The actual nature of the products obtained in this reaction has not been accurately determined. l-lsopropylidenedicyelopentadiene, a monomer easily polymerizable by cationic initiators, has produced in the presence of anionic initiators poly(l-isopropylidenedicyclopentadiene), probably by 1,2- and 1,4-addition reactions Is (Eq. 6.11). [ n

,

I

]

m

+

(6.11) (

Details about the mierostructure of these polymers, however, have not been reported. 6.2. References

C.C.Wu and R.W. Lenz, Polymer Preprlnts (Amer. Chem. Soc., Div. Polym. Chem.), 12, 209 (1971 ). G. Lefebvre and F. Dawans, J. Polym. Sci., Part A, 2 3277 (1964). 3. P.E. Cassidy and C.S. Marvel, J. Polym. Sci., Part A, 3 1533 (I 965). 4. H. Lussi and J. Barman, Helv. Chim. Acta, 50 1233 (!967). 5. L.A. Mango and R.W. Lenz, Polymer Preprints (Am. Chem. Soc., Div. Polym. Chem.), 12 402 (I 971 ). L.A. Mango and R.W. Lenz, Makromol. Chem., 163 13 (1973). 7. Z. Sharaby, J. Jagur-Grodzinsky, M. Maritan and D. Vofsi, J. Polym. Sci., Polym. Chem. Fwl., 20 901 (1982). X.F. Zhong and B. Francois, Makromol. Chem., 191 2735 (1990). 9. B. Francois and X.F. Zhong, Makromol. Chem., 191 2743 (1990). 10. Y. Imanishi, K. Matsuzaki, T. Yamane, S. Kohjiya and S. Okamura, J. Macromol. Sci., Chem. A3 249 (1969). 11. B.A. Dolgoplosk, S.I. Beilin, Yu. V. Korshak, G.M. Chernenko, L.M. Vardanyan and M.P. Teterina, Fur. Polym. J., 9 895 (1973). 12. I. Natori, Macromolecules, 30 3696 (1997). 13. I. Natori and S. Inoue, Macromolecules, 31 982 (1998). 14. I. Natori, K. Imaizumi, H. Yamagishi and M. Kazunori, J. Poym. Sci., Polym. Phys. Ed, cited after reference 13. .

.

~

326 15. I. Natori and S. Inoue, Macromolecules, 31 4687 (1998). 16. S.N. Ushakov and O.F. Solomon, USSR Patent 104,198 (1956). 17. S. Cesca, A. Roggero, N. PaUadino, and A. DeChirico, Makromol. Chem., 136 23 (1970). 18. S. Cesca, A. Priola, A. DeChirico, and G. Santi, Makromol. Chem., 143 211 (1971).

327

Chapter 7

ZIEGLER-NATTA POLYMERIZATION OF CYCLOOLEFINS

Taking advantage of the abundant results published on the ZieglerNatta polymerization of linear olefins and dienes, polymerization of cycloolefins with this type of catalysts has been successfully performed in order to manufacture polymers with new structures and properties. For this purpose, all the traditional catalysts as well as new ones have been employed to polymerize monocyclic and polycyclic olefins, uncovering unexpected details of this challenging process.

7.1. Polymerization of Monocyclic Olefins A substantial number of substituted and unsubstituted monocyclic olefins have been reacted under the conditions of Ziegler-Natta catalysis to form polymers with interesting properties.

7.1.1 Four-Membered Rings Vinyl polymerization of cyclobutene and substituted cyclobutene has been effected with various types of Ziegler-Natta. The product selectivity depended essentially on the type of catalyst and reaction conditions. Cyclobutene. The vinyl polymerization of cyclobutene leads to a saturated polymer, poly(l,2-cyclobutene)or poly(cyclobutylenamer), by opening of the carbon-carbon double bond of the monomer (Eq. 7.1).

n ~-]

~

[I

[ in

(7.1)

The reaction occurs under the influence of a variety of coordination catalytic systems derived from transition metal compounds with or without organometallic derivatives as the cocatalysts. Often, the addition

328 polymerization is accompanied by ring-opening polymerization forming along with saturated vinyl polymers, unsaturated polymers, known as polyalkenamers or poly(l-alkenylene)s (Eq. 7.2).

[I lira

or-il

(7.2)

Cyclobutene polymerization has been extensively studied by Natta and coworkers ~'2 using a wide variety of binary or ternary catalysts based on group IV-VI transition metal compounds. In the majority of these studies, the two type of polymers, addition and ring-opened, have been obtained. Typical examples are outlined in Table 7.1. Table 7.1.

Cyclobutene polymerization with transition metal based catalytic systems' Temp ~

Catalytic System

3TiCI3/AICI~3AI TiCIVEhAI VCI4/EhAI VCI4~ex3AI VCI3/Et3AI VOCI3/Et3AI

+45 -10 -20 -20 +45 -20

V(acac)3/Et2AICl

-50

Cr(acac)dEt2AICl CrO2CI2/Et2AICI MoO2(acac)z/Et2AICl MoCI~zt3AI WCI6/Et3AI 'Data from reference~

m

u

-20 -20 - 10 -20 -20

Conversion Poly(cyclobutylenamer) % % 40 100 5 100 99 100 99 100 80 100 90 100 I00 100 I00 100 I00 100 I0 55 30 5 40 100

Polybutenamer

% 60 95 1 traces

20 10 0 0 0 90 70 60

As can be seen from Table 7.1, vanadium- and chromium-based catalysts were very active and promoted preferentially the addition polymerization ofcyclobutene to form poly(cyclobutylenamer). It is quite

329 interesting that the other catalysts based on titanium, molybdenum and tungsten, some of them very active, direct cyclobutene polymerization by the two pathways, addition and ring-opening reaction to produce both types of polymers, vinyl and ring-opened, that is poly(cyclobutylenamer) and polybutenamer, respectively, in various amounts. Several other catalysts have been used to transform selectively cyclobutene to saturated poly(cyclobutene) for instance the following x-complexes of nickel xC3HsNiBr, (~-CffIT)Ni 0t-CffITNiCI)2 provided entirely the addition polymer poly(cyclobutylenamer). 3"s More recently, addition polymerization of cyclobutene has been investigated by Kaminsky and coworkers 6 using two-component catalysts consisting of chiral metallocenes and methylaluminoxane. The activity of cyclobutene polymerization in the presence of ethylenebis(vlsindenyl)zirconiumdichloride/methylaluminoxane in toluene was high and dependent on the reaction temperature (Table 7.2). Table 7.2 Polymerization of cyclobutene (M) reduced by ethylenebis(rl'-mdenyl)zirconiumdichloride/methylalummoxane' Reaction Tc~g~rature ~

Catalyst Activity

Melting Point in Vacuum ~

0

149

-10

50

485 485

.

_

kg Polymer

'Data from reference ~ Under these conditions, highly melting point poly(cyclobutene) (Me 485~ in vacuum) has been prepared; the decomposition temperature was in the same range. The monomer conversion in cyclobutene polymerization at 0 and -10~ v s time is represented in Figure 7.1. As this figure illustrates, following a rapid start, the rate of eyelobutene polymerization decreases to become linear after a few hours for a long period. At the same temperature, it was found that the activity for cyclobutene polymerization induced by the ethylenebis(rlS-indenyl)zirconiumdichloride/ methylaluminoxane catalyst was about five times that of cyclo~tene reaction in the presence of the same catalyst.

330 Yield, %

50

( A ) ~ 0~ (B) - -10~

40 :30 20 10

o

~

z

3

4

5

~o

~5

20

2s

Time, hr

Figure 7.1. Monomer conversion in cyclobutenepolymerization reduced by ethylenebis(qS-indenyl)zirconiumdichloride/methylalummoxanecatalyst (Adapted from Ref.6) Substituted cydobutene. Several alkyl substituted cyclobutenes have been explored in Ziegler-Natta polymerization with various catalytic systems. Of these monomers, 1- and 3-methylcyclobutene provided the most interesting results. l-Methylcyclobutene By addition polymerization in the presence of the binary Ziegler-Natta catalysts l-methylcyclobutene will form readily the vinyl product, poly(l-methylcyclobutene) (Eq. 7.3).

n [--

-"-

[I

1

I In

(7.3)

This reaction has been investigated by Dall'Asta and Manetti 7 in the presence of a wide variety of transition metal based catalysts. On using catalysts derived from titanium, vanadium, chromium and molybdenum salts and organometallic compounds they found the activity was very low and the product was mainly a saturated polymer probably of a vinyl structure as in Eq.7.3. Alternatively, when catalysts based on tungsten hexachloride and organoaluminium compounds have been employed, saturated polymers having polyisoprene skeleton were formed, probably involving in a first step ring-opening polymerization and further intramolecular cyelization. (See later in section 7.3)

331 3-Methylcyclobutene. Addition polymerization of 3-methylcyclobutene in the presence of some binary transition metal catalysts gives the saturated polymer, poly(3-methylcyclobutene) (Eq. 7.4). n

i-I

l In

\

(7.4)

\

A series of binary Ziegler-Natta systems consisting of vanadium tetrachloride and organometallic compounds have been investigated by Dall'Asta s in 3-methylcyclobutene polymerization (Table 7.3). Table 7.3. Polymerization of 3-methylcyclobutene in the presence of binary Ziegler-Natta c,atalysts" Catalytic System

Conversion % 37 25 17 14

VC~3AI VC~3Ga VC~zBe VCI4/EttMg "Data from reference *

vm4 Polymer % 90 90 85 94

Polyalkenamer % 10 10 15 6

As Table 7.3 illustrates, the catalysts containing Et3AI and Et3Ga were the most active and produced vinyl polymer in 90*,6 proportion. The other catalytic systems obtained from Et2Be and Et2Mg, though displayed a moderate activity, afforded at a high selectivity vinyl polymer. 7.1.2. Five-Membered Rings Of the five-membered ring monomer, cyclopentene has been

examined with several types of Ziegler-Natta catalysts affording interesting data on the product selectivity and reaction mechanism. Cydopentene. By vinyl polymerization cyclopentene gives rise to a saturated product, poly(1,2-cyclopentylene), as result of the opening of carbon-carbon double bond (Eq. 7.5).

n

[~,v~]n

(7.5)

332 The opening of the carbon-carbon double bond can take place in a cis or trans fashion, giving rise to two type of isomeric polymers, erythro and threo poly(l,2-r The erythro polymers formed by cis opening of the double bond from cyclopentene may have di-isotactic or disyndiotactic stereocontiguration (I and II, Eq. 7.6).

cis

(7.6)

The threo polymers produced by trans opening of the double bond from cyclopentene may also possess di-isotactic or di-syndiotactic stereoconfiguration (I and II, Eq. 7.7).

0

trans

(7.7)

In addition, the threo di-syndiotactic poly(1,2-cyclopentylene) is expected to show optical activity. Boor et al. 9'!~ have carried out a systematic study on the polymerization of cyclopentene in the presence of Ti- and V-based ZieglerNatta catalysts. This cycloolefin was polymerized very slowly by TiCI3/Me3AI, TiCIdEt3AI, VCIdMe3AI and VCIdMe2AICI to give a poly(cyclopentene) with ring-retention along with cis-/transpolypentenamer. More recently, cyclopentene was found to polymerize via the double bond opening by Farona and Tsonis ~t~3 under the action of the catalytic system Re(CO)~CI~tAICI2. The microstructure of the product indicated that the cyclic ring was prevailingly retained in the polymer chain and the final polymers were made up of repeating 1,2-unit, or a combination of 1,2 and isomerized structures. In contrast to Re(CO)sCI/EtAICI2 catalyst, when Mo(CO)sPy/EtAICI2/Bu4NCI has been employed, cyclopentene

333 polyme~ predominantly with ring-opening but also ring-retained poly(cyclopentene) has been obtained (Table 7.4). Table 7.4 Polymerization of cyclopentme in the presence of Mo(CO)sPy/FaAICIz/Bu4NCI~b Solvent

Temp. ~

Heptane Chlorobenzene

30 26

Yiel~ %

O:Aa

0.5 14.7

I "3.6 1:4.8

Vinyl Product %

ROMP" Product %

7

93

18

82

'Data from reference~2; bThe polymerizations have born carriod out' for 20-22 hours; Wield of methanol insoluble polymer; aO:A=olefm to aliphatic proton ratio in NMR spectrum; "ROMP=ring-opening metathesis polymerization product. As Table 7.4 illustrates, both the polymer )ield and polymer structure have been significantly influenced by the reaction conditions. Polymerization of cyclopentene has been investigated by Kaminsky and coworkers" in the presence of several metallocene complexes. Some data obtained, using the binary systems zirconocene/methylaluminoxane in toluene at various reaction temperatures, are presented in Table 7.5. Table 7.5 Addition polymerization of cyclopmtme (M) reduced by zirconocene(1)/methylaluminoxane(MAO) catalysts~b Catalyst

Temp. ~

Reaction Time~ hr

Cp2ZrCI2 F_,t(Ind)2ZrCl2 Et0ndhZrCl2

30 10 25 22

20 90 72 10

Et(IndH,hZrC]z

Yield g Polymer m

13.6 20.0 24.5

'Data fzom reference 14; bPamction conditions: [M] = lOOml, [I] = 104 molo/L,

MAO = 200 mg. As Table 7.5 shows, there was no activity when cyclopentadienylzkconium dichloride was used as a catalyst component. However, the chiral catalysts

334 derived from ethylenebis(~ 5-indenyl)zirconium dichloride and ethylenebis(TIS-tetrahydroindenyl)zirconium dichloride were quite active. Similar results were found with other cyclic olefins. The poly(cyclopentylene) produced under these conditions was highly crystalline and insoluble in common hydrocarbons. Examination by ~3C NMR spectroscopy indicated that no ring-opening of the monomer occurred. Particularly active in cyclopentene polymerization showed to be the catalyst consisting of ethylenebis(TI~-indenyl)zirconium dichloride and methylaluminoxane. However, the activity of this catalyst was strongly dependent on the reaction temperature (Table 7.6). Table 7.6 Polymeriza~on of cyclopentene reduced by ethy!enebis(q'-mdenyl)zirconium dichloride/methylalummoxane catalyst Lb Reaction Temperature, Catalyst Activity, Melting Point in ~ k~ Polymer Vacuum~ ~ 22 195 395 0 32 395 'Data from references ~14;bReaction solvent=Toluene i

The monomer conversion v s time in cyclopentene polymerization with this catalytic system at the two temperatures is plotted in Figure 7.2 Yield, % (A)

I---(A)- 22~---I

50

/

40 30 20 J 10

-

/

~)

f o

~

2

3

4

5

~o

~5

zo

Time, hr

Figure 7.2. Monomer conversion in cyclopentene polymerization reduced by ethylenebis(Q~-indenyl)zirconiumdichloride/methylalummoxane catalyst (Adapted from Ref.6)

335

As it can be observed, following a rapid start of cyclopentene reaction, the rate decreased to become linear for a long period. Interestingly, at the same temperature, the activity of this catalyst in cyclopentene polymerization was about five times lower than that of cyclobutene reaction. The melting point of poly(1,2-cyclopentylene), determined under vacuum to avoid oxidation, was found to be rather high, i.e., 395~ The decomposition temperature was in the same range. Since the vinyl homopolymers of cyclopentene were insoluble in common solvents, it was difficult to study accurately their structure. To circumvent this difficulty, lower oligomers, soluble in hydrocarbons, were prepared by changing the reaction conditions. Higher reaction temperatures, higher zirconocene concentration and lower monomer concentration allowed soluble oligomers of cyclopentene to be prepared. By comparing the ~3C NMR spectra of soluble oligomers of cyclopentene with the solid state spectrum of insoluble poly(cyclopentene), all peaks could be identified. Two different kinds of end groups in the polymer could also be observed (Eq. 7.8). n j~~.. _

~

n12

n/2

C

sH9

(7.8)

Similar investigations on cyclopentene polymerization were carried out by Okamoto et al. mSwithtransition metal complexes/methylaluminoxane catalysts. On using complexes of Zr, Hf and Ni in conjunction with methylaluminoxane in toluene at 25~ they obtained poly(cyclopentene) of low molecular weight. In all cases the structure of the polymer was of vinyl type. More recently, Collins et al. ~6"~7 examined the polymerization of cyclopentene induced by metallocene catalysts and provided new, interesting data on the reaction mechanism and poly(cyclopentene) structure. Using rac-ethylenebis(rlS-indenyl)zirconium dichloride in conjunction with methylaluminoxane in the polymerization of cyclopentene, poly(cis-l,3-cyclopentylene) has been produced in high yield ~6 (Table 7.7). The polymer microstructure of poly(cis-l,3-cyclopentylene), in which the individual monomer units are incorporated by cis-l,3-enchainment in an isotactic manner, was evidenced through independent synthesis of the single, stereoisomeric tetramer produced under hydro-oligomerization conditions ~6(Eq. 7.9). -

n

[~

= m

C~

§ p

' "

c~r

~

(7.9)

336 Table 7.7 Polymerization of cyclopentene(M) using the catalytic system rac-ethylenebis(v ILmdenyl)zirconium dichloride (1)/methylalummoxane(MAO) ~b [I], mM 0.36 0.33

[MAO], mM 96 105

[M], Yield~, Cis d, M|~ M g % O 3.79 2.7 i~ i 2.02 7.4 96.0 39O 'Data from reference~6; bReaction conditions: Solvent=Toluene, Temperature=250C, Reaction time=24 hr; Wield of unffactionated polymer; dDetermmed from ~3C NMR spectrum; 'Not determined due to insolubility of the polymer. On the other hand, polymerization and hydro-oligomerization of cyclopentene in the presence of rac- and (S)-ethylenebis(rlstetrahydroindenyl)zirconium dichloride associated with methylaluminoxane led to the production of poly(cyclopentene) in which the monomer was incorporated in both cis- and trans-l,3-manner ~7 (Eq. 7.10). n O

~

9p

I-I9 * P

~

(7.10)

The polymer yield and molecular weight were strongly dependent on the reaction conditions(Table 7.8). Table 7.8 Polymerization of cyclopentene(M) using the catalytic system r a c-eth y lene b i s ( vl ~-t et rah yd rom den y l) zi rcon iu m

dichloride ~/methylalummoxane ~IAO) ~b [MAO] [M] ~ Temp [ giel~ Cis d M, [I] % o C M mM mM s 1.46 I 25 I 0.80 60.5 1400 0.043 94 1.46 I 25 I 0.74 59.6 1200 0.043 31 1.46 ! 25 I 2.03 60.6 920 0.17 94 0.91 1.46 I 25 [ 60.4 810 0.17 31 1.13 [ 0 [ 1.74 68.0 900 0.20 100 1.13 I 25 I 2.73 62.0 600 0.20 100 1.13 / 50 I 1.8s" 50.0 350 0.20 100 3.73 l 25 1 6.1 63.0 390 0.47 74 bReaction conditions: Solvent = Toluene, Timr = 'Data from reference 24hr;~'ield of unfraetionated polymer; dDetermmed from the ~3C NMR spectrum; "The reduced yield of polymer at higher ten~ratures is due to the formation of large amounts of oligomers (i.e., dimer, trimer, tetramer, etc.).

337 In contrast to poly(cyclopentene) produced using the catalytic system racethylenebis(rl Lindenyl)zireonium diehloride/methylaluminoxane, the majority of the polymers prepared with the catalytic system racethylenebis(rls-tetrahydroindenyl)zirconium dichloride /methylaluminoxane were soluble in hot toluene or 1,2,4-trichlorobenzene. The cis content of the polymer was found to be unaffected by the catalyst or eocatalyst concentration but was higher at lower temperatures. It is noteworthy that the cis content in the poly(1,3-cyclopentylene) prepared with this catalytic system was somewhat lower than that found for the trimers or even the tetramers. The number-average molecular weight of these unfraetionated polymers was low and dependent on the polymerization temperature. These authors observed that the occurrence of competitive "trans insertion" in cyclopentene polymerization with rac-ethylenebis(rl s_ tetrahydroindenyl)zirconium dichloride led to the production of poly(cyclopentene) with significantly lower erystaUinity than that observed for polymers prepared using rac-ethylenebis(rlLindenyl)zirconium dichloride (Table 7.9). Table 7.9 Melting temperature range and crystallmity of poly(cyclopmtene) prepared with rac-ethylmebis(rl~-mdmyl)zircoaium dichloride00 and rac-eth yleneb is(rl Lt~ trahydromdenyl)zireomum Zirconocene Cis, M. T.~ C~llmit% % % ~ I! 140-350 i 60 i 9 6 d 34 d 390 d 50-160 d 11 68 900 160-285 25 62 600 125-250 19 12 50 70-190 350 4 12 63" 40-80~ 390" 2" 12 'Data fixan reference 17; ~-,eaetJon conditions: Solvent = toluene, Time = 24 hr; "Not determined due to insolubility of the polymer; eData reported are for the fraction soluble in toluene; "Data reported are for a fraction msoluble m acetone r

r

,m

but soluble m hexane.

As it is obvious from Table 7.9, the r and melting temperatures decrease with decreasing cis content and molecular weight. For similar degrees of polymerization, it is the cis content that most dramatically influenced the product crystallinity.

338 Cyclopentene polymerization has also been investigated by Natta and coworkers ~s2~ under the influence of several catalytic systems, in numerous cases the vinyl polymerization is accompanied by ring-opening metathesis polymerization when polypentenamer is formed beside poly(cyclopentenylene) (Eq. 7.11).

0

%1

(7.11)

7.1.3. Six-Membered Rings Cyclohexene and several substituted cyclohexenes have been polymerized with various Ziegler-Natta catalysts, the product selectivity being greatly dependent on the nature of monomer and catalyst. Cyr Although attempts to polymerize cyclohexene in the presence of TiCl~te3Al,, TiCIJEhAI, VCLjMe3AI and VCI~te2AICI have been made by Boor et al. 9'!~ they have not observed the monomer to polymerize under these conditions. The reason for this failure has been attributed to the high ring-stability of cyclohexene. More recently, Tsonis and Farona, 12 however, discovered that Re(CO)sCI/EtAICI2 system promoted the homopolymerization of cyclohexene via the double bond opening process (Eq. 7.12). n

0

=

n

(7.12)

The weight average molecular weight of poly(cyclohexene) was about and ~3C ~ on the 2500. Physical measurements by IlL ~H ~ poly(cyclohexene) thus prepared indicated that the cycle was retained in the polymer chain and that the final product was made up of repeating 1,2or a combination of 1,2- and isomerized single-bond units. Further support for ring retention was provided by pyrolysis and gas chromatographic studies of poly(cyclohexene). 4-Methylcydohexene. Tsonis and Farona ~2 noted that the methyl group attached to cyclohexene in position 4 with respect to double bond will not impede the polymerization of the corresponding monomer, 4methylcyclohexene, by opening of the double bond. On this line, the above

339 authors s u ~ e d to polymerize 4-methylcyclohexene under the influence of Re(CO)sCl~tAIClz to manufacture the saturated polymer, poly(4methylcyclohexene), by ring-retention (Eq. 7.13).

n ~/~\

=

[~]n

(7.13)

4,4-Dimethylcydohexenr Remarkably, introduction of two methyl groups in the remote position of cyclohexene with respect to the double bond allowed to polymerize this monomer via 1,2-~ldition reaction. In their studies on the polymerizability of cyclohexene tings under various conditions, Tsonis and Farona ~z found that 4,4-dimethylcyclohexene polymerize in the presence of the Re(CO)sCI/EtAICI2 system by opening of the double bond to produce poly(4,4..dimethylcyclohexene) with ringretention(Eq. 7.14).

7.1.4. Seven-Membered Rings Of the scven-membcred tings, cycloheptene has bccn carefully examined in the presence of Ziegler-Natta catalysts. Cydoheptene. On extending their investigations of cychxdefin polymerization under the action of Re(CO)sCl~tAIClz catalyst to higher cycloolefins, Tsonis and Farona ~z'~3 disclosed that cycloheptene can be polymerized by opening of the double bond with this catalyst to obtain poly(cycloheptene) or poly(cycloheptylene) with ring-retention (Eq. 7.15).

(7.15) The reaction has been effected at 110~ using a molar ratio Re:AI of 12. The product was analyzed by IIL ~H- and ~3C-NMR and displayed saturated cyclic structures in the polymer chain.

340

7.1.5. Eight-Membered Rings The easy availability of eight-membered ring monomers offered an appealing field of research for Ziegler-Natta polymerization with this class of monomers. Cyclooctene. Of a great interest is the polymerization of cyclooctene to produce a vinyl polymer, poly(cyclooctene) or poly(cyclooctylene), in the presence of appropriate catalysts (Eq. 7.16). n

~

(7.16)

This reaction has been reported by Tsonis and Farona t2"~3tO proceed under the action of the Re(CO)~CI/EtAICI2 system, with a molar ratio ge:Al of 1:2 at I I0~ Structural measurements by IlL ~H NMR and t3C NMR spectroscopy on the poly(cyclooctene) prepared in these conditions indicated that the ring was retained in the polymer and the final product was made up of repeating 1,2-units, or a combination of 1,2- and isomerized units. 1,5-Cyclooctadiene. Polymerization of 1,5-cyclooctadiene has been effected by Bokaris et al. z~ using several metallocene catalysts associated with alkylaluminium compounds. The monomer conversion and polymer Table 7.10 Polymerization of 1,5-cyclooctadiene (M) with bmary catalysts Cp2MtCI2/alkylalummiumcompounds in c h l o r ~ y l e n e at 25 *C~b Polymer Catalytic System Monet Yield, % Conwrsion~ % 73 100 Cp2TiCI2/Et3AI2CI3 64 75 Cp2TiCI~2AICI 36 50 Cp2TiCI~3AI 69 90 CpzZrCI2~3A]2CI3 32 50 Cp2ZrCIz/F_,t2AICI 10 Cp2ZrCI2/Et3AI 37 52 Cp2HfCI2/~3AI2CI3 25 42 Cp2HfCI2/Et2AICI _r 8 Cp2H~I2~3AI "Data from reference 21. bReaction conditions: [CpzMtCI2]=10"z Mole, [Mt]/[AI]= 1/6, [Mt]/[M]=1/200; ~No polymerization was observed. r

m

y

341 yield with a series of binary catalysts derived from m e t a l l ~ e s , Cp2MtCIz (Mt=Ti, Zr, H0 and Et3AI2CI3, EtzAICI or EhAI are presented in Table 7.10. The order of activityof these catalysts dependedon the metal and the r and was found to be Ti>Zr>Hf and Et3AI2CI3>Et2AICI>Et3AI. The molecular weights of the resulting oligomers were in the range of 8001800. The values of molecular weights, intrinsic viscosity and polydispersity for poly(l,5-cyclooctadiene) prepared under these conditions are given in Table 7.11. Table 7.11 Molecular weights, intrinsic viscosity and polydispersity for poly(l,5-cyclooo~diene) prepared with metallocene r Catalytic System

M.~ I M,~ !

M.'

M,/M,

s'b

[n]', ml/g 0.22 0.52 O.77 0.26 0.45

760 1.18 860 728 Cp2TiCIz/Et3AI2CI3 1.21 950 1068 884 CpzTiCI~2AICI 1.35 1350 1758 129[ Cp2TiCI~3AI 1.17 830 905 775 Cp2ZrCI2/Et3AI2CI3 1.24 870 1007 813 Cp2ZrCI2/EtzAICI Cp2ZrCl~3Al f 0.40 1.75 670 1106 630 CpIHt~I~3AIzCI3 0.58 1.64 920 1352 826 CpzHICI2/~IAICI C~2HfC|2/Et3AIf ~ from reference 2,: 'Reaction conditions as m Table 7.10; =By GPC in toluene at 25~ ~By vapour phase osmomctry; "In toluene at 25~ fNo polymerizauon was observed The main structure of this polymer, as concluded from l~ and ~H NMR spectra, seemed to contain saturated transannular recurring units formed by a cationic process (Eq. 7.17).

n~

"~ ~ n

(7.17)

The products obtained were soluble in benzene, chloroform, dichloromethane and other chlorinated compounds. Based on these results, vinyl polymers formed by 1,2-addition reaction of one of the two double bonds of the monomer (Eq. 7.18)

342

n~

~

~ )|m__

(7.18)

while cross-linked polymers arisen by subsequent cross-linking reaction of the remaining double bond (Eq. 7.19) were ruled out. p

(;,.19) t

]p

A more detailed study of the effect of the reaction conditions on monomer conversion in 1,5-cyclooctadiene polymerization with the binary catalyst Cp2TiCl2/EtzAICl was effected by Bokaris et al. z~. Thus, on employing various solvents such as toluene, chlorobenzene and dichloromethane at temperatures of-10~ and 25~ they observed that the best results can be obtained when working in dichloromethane at 25~ On varying the ratio catalyst/l,5-cyclooctadiene from 1/50 to 1/400, the highest monomer conversions were found at a catalyst/monomer ratio of 1/200 (Figure 7.3).

Cony.% , 80-

f

I

A

60-

40

20

v

f /

! i I

2

t'"

.-'-" 111.-

3

S /I 9

~/1t

t

11

7" Time, hr Figure 7.3. The effect of molar ratio catalyst/monomer on monomer conversion in 1,5-cyclooctadiene polymerization with the catalytic system CpzTiCIz/~2AICI: 11/50, 2-1/100, 3-1/200, 4-1/400 (Reaction conditions:[Ti] = 10ZMole, [Ti]/[AI] = I/6,T = 25~ Solv~nt=Dichloromethane) (Adapted from Ref.z*)

343 Of a particular interest is the effect of molar ratio eatalyst/eoeatalyst of the binary system Cp2TiCIdEtzAICI on the monomer conversion and polymer structure in 1 , 5 - e y e l ~ i e n e polymerization. On carrying out the reaction in toluene at 25~ they observed that the best efficiency for this binary catalyst is obtained working at molar ratios Ti/AI of 1/6 (Figure 7.4). Cony., % 15 4

10 / /

I

-,

/

~

5 i

0

!

8

2

Time, hr Figure 7.4. The effect of molar ra~o c a t a l y s t / ~ l y s t (Ti/AI) on monomer conversion in 1,5-cyclocx~diene polymerization with the catalytic system CpzTiCl~_,tzAICl: Ti/AI=I/I(1), I/3(2), I/4(3), I/6(4), 1/10(5)and 1/15(6) (Reaction conditions: rri] = 10"2Mole, [Ti]/[AI] = 1/6, T = 25~ Solvent = Toluene) (Adapted from Ref.z~) As shown in Figures 7.3 and 7.4, the monomer conversion increased considerably in the first stages of the reaction and then decreased. The incomplete conversion of the monomer was attributed to the reduction of the catalyst (Ti ~v to Tim). Related studies on the catalyst structure of the system Cp2TiCI~/Et2AICI in toluene as a solvent were performed by ESR spectroscopy but the results have not been discussed.

7.2. Polymerization of Bicyclic Olefins Due to their particular structure and reactivity, a great number of bicyclic olefins have been tested in Ziegler-Natta polymerization using various catalytic systems.

344

Bicyclo[2.2.1 ]hept-2-ene(Norbornene) Polymerization of bicyclo[2.2, l]hept-2-ene (norbomene)inducexl by coordination catalysts of the Ziegler-Natta type will normally p r o ~ by opening of the carboncarbon double bond and subsequent 1,2-addition to form poly(bicyclo[2.2. I ]hept-2-ene), containing 2,3-enchainments of the recurring units (Eq. 7.20). (7.20) This reaction has been extensively investigated by many research groups in the presence of a large variety of catalytic systems derived from transition metal salts and organometallic compounds. Under various reaction conditions, poly(bicyclo[2.2.1]hept-2-ene) having different structures and physical-chemical properties has been prepared, depending essentially on the nature of the catalytic system employed. In their early report, Anderson and Merckling z2 polymerized bicyclo[2.2, l]hept-2-ene under the action of coordination catalysts derived from titanium tetrachloride and a reducing agent such as Gfignard compounds, metal alkyls and aryls, metal hydrides and even alkali metals or earth alkaline metals. The activity and stability of the catalytic systems employed were relatively low and impurities like water, carbon dioxide or oxygen led to a rapid deactivation of the process. Interesting work on the polymerization of bicyclo[2.2.1]hept-2-ene reported later Truett et al. z3 in the presence of catalysts derived from LiAIILs and TiCI4. On using binary systems consisting of LiAl(Heptyl)4 and TiCI4, these authors proved that the polymerization ofbicyclo[2.2, l]hept-2ene takes place either by vinyl addition at the double yielding saturated polymers, poly(2,3-bicyclo[2.2.1 ]hept-2-ene) or via ring-opening yielding unsaturated polymers, poly( 1,3-cyciopentylenevinylene), containing cyclopentylene tings linked in a c i s - l , 3 fashion with trans double bonds (Eq. 7.21).

Jm (7.21) -P

345 An important observation was that the vinyl polymerization at the double bonds was favored by molar ratios AI:Ti < 1, whereas ratios AI:Ti > 1 led, via ring-opening reaction, preferentially to unsaturated polymers. Furthermore, the ring-opening polymerization occurred with high stereospecificity and provided polymer with high crystallinity and good elastomeric properties. Crystalline polymers of poly(bicyclo[2.2.1]hept-2-ene) containing exclusively recurring units formed by opening of the double bonds prepared Sartori et al. 24 with catalysts derived from aluminium alkyls and titanium tetrachloride. Structural examination by IR and NMR methods of the polymer thus produced showed no unsaturation in the polymer chain. Substitution of molybdenum pentachloride for titanium tetrachloride in these catalytic systems provided effectively stereoselective catalysts for ring-opening polymerization of bicyclo[2.2.1]hept-2-ene to highly cispoly(l,3-cyclopentylenevinylene). Similarly, binary catalysts derived from aluminium alkyls or lithium-aluminium alkyls and titanium tetrachloride have been employed by Saegusa et al. ~ to polymerize bicyclo[2.2.1 ]hept-2ene to poly(bicyclo[2.2.1]hept-2-ene) containing predominantly saturated or unsaturated recurring units, depending on the nature of the catalytic components and the ratio metal alkyl : transition metal compound. Interestingly, on employing some Lewis bases such as tertiary amines, dioxane, dibutyl sulphide or pyridines associated with these catalysts, ternary catalytic systems leading exclusively to unsaturated polymers with trans or cis double bonds have been produced. Farona and coworkers 26 carried out relevant studies on the bicyclo[2.2.1]hept-2-ene polymerization in the presence of Re- and Mobased catalysts. Generally, the polymers obtained at higher reaction temperatures were of ring-retained type whereas those formed at lower temperatures of ring-opened type. At intermediate temperatures, polymers which showed both ring-retained and ring-opened structures in the same chain were obtained. Thus, when Re(CO)sCI/CzHsAICI2 was used as the catalyst, bicyclo[2.2.1]hept-2-ene produced a polymer in 26.8% yield in chlorobenzene, at 100~ for 24 hr. The molecular weight of the polymer, as determined by gel permeation chromatography in THF and by osmometry in toluene, was M~--433,00, M,,=154,000 and the polydispersity 2.14. The olymer softens at 220~ and melts completely at 260~ Examination by NMR spectroscopy (by integration of olefinic to aliphatic proton signals) of the polymer microstructure indicated that poly(bicyclo[2.2.1]-hept-2erie) prepared under the above conditions contained 10 monomers units

346 with ring-retention for every monomer unit with ring-opening in the same polymer chain (Eq. 7.22).

Further studies on the polymerization of bicyclo[2.2.1 ]hept-2-ene at various temperatures in the presence of the systems Re(CO)sCI/EtAICI2 and Mo(CO)sPy/EtAICIz/~NCI evidenced the occurrence of the two types of monomer insertion in the polymer chain, by ring-retention and ringopening. 26 The extent of ring-retention and ring-opening was strongly influenced by the nature of the catalyst and reaction temperature (Table 7.12). Table 7.12 Polymerization of bicyclo[2.2, l]hept-2-cne reduced by Re- and Mo-basod catalysts at various temperatures' O:A b

Ring-reteation/ Rmg-oponmg %

1:4.07

0.7:99.3

Catalytic System

Reaction Temp. ~C

Polymer Yield %

Re(C)~CI/EtAICI2 Re(C)5CFEtAICIz Re(C)~CI/EtAICI2 Re(C)~CI/EtAICI2 Mo(CO),Py/EtAICIj

100 110 120 132 26

77.2 41.4 25.4 100

1:97.5 1:175 0:100 1:4.0

90.3:9.7 94.5:5.5 I00:0 0:I00

100

89.7

1:6

17:83

110

84.6

1"15

52:48

I0

(C4Hg)qCI Mo(CO)sPy/EtAICIz/ (C4H9)4NCI Mo(CO)~Py/EtAICIz/

(C,H9),NCI

;Data from reference u; tO:A=olefmic to aliphatic proton ratio in tH NMR spectrum. These results suggested that propagation in bicyclo[2.2.1]hept-2-ene polymerization, under the action of the Re(C)sCI/EtAICIz and Mo(CO)sPy/EtAICIz/(C4H9)4NCI catalysts, occurred by a 1,2 insertion

347 process with an ocx,asional ring-opening step in the same chain. Evidence for this behavior came from NMR measuremems, where DEPT spectra of the polymer showed the disappearance of some olefinie carbons that do not have hydrogen atoms attached to them. Ozonolysis of poly(bicyelo[2.2.1 ]hept-2-ene) supported the NMR findings. Selective catalysts for vinyl polymerization of bicyelo[2.2.1 ]hept-2ene derived from various transition metal compounds and methylaluminoxane reported recently Okamoto et al. ~s. Depending on the transition metal compounds, variable monomer conversions and polymer yields have been reported (Table 7.13). Table 7.13 Polymerization of bicyclo[2.2. I ]hept-2-ene (M) transition metal compounds 0) and methylalummoxane~ Transition Metal

Corr~ound

Monon~r

Polymer Yield,

Conversions%

g

0.02 0.08 1.7 0.10 2.0 1.21 25.7 2.41 51.3 2.60 55.3 bReaction conditions" [M]=50 mml, [I] Al:Metal=200, Temperature=25~ Reaction time=4 hr V(acac)3 Cr(acach Mn(acach CpNi(allyl) Ni(aeach Pd(~COD~)CIi~

MW~

103 3.0 402 188

194 = 2.5 nml,

As it can be seen from Table 7.13, Ni and Mn containing catalysts provided high molecular weight poly(bicyclo[2.2.1 ]heptene). A new class of coordination catalysts based on Pd(II) for vinyl polymerization of norbornene and norbornene derivatives have been described by several Schulz 27, Gaylord ~, Kinnemann ~ and Sen. 3~ The poor solubility of the polymer hindered, however, its full characterization. Union Carbide Corp. 3~ prepared a series of very active palladium catalysts for norbornene polymerization containing at least one Pd-C bond and at least one Pd-halogen bond. These catalysts were obtained by reaction of a preformed complex having zerovalent Pd and stabili~g the monodentate or bidentate ligands of the phosphine, phosphite or arsine type with an organic compound containing at least one halogen-carbon bond and an alkyl, aryl, aralkyl, cyeloalkyl, acyl or alkenyl group.

348 Such catalysts with methyl, phenyl, acetyl, methallyl, cyano and ethyl formate groups and I, CI or Br ligands were obtained from tetrakis (trihydrocarbylphosphine)Pd(0) or bis(trihydrocarbylphosphine)Pd(0) and phenyl iodide, methyl iodide, acetyl chloride, methaUyl chloride, cyanogen bromide or ethyl chloroformate. Starting from tetrakis(triphenylphosphine)palladium, [(C6Hs)3P],Pd, and methyl iodide, bis(triphenylphosphine)methylpalladium iodide, [(C6Hs)sP]2CH3Pdl, was prepared in high yield by this proc~ure (Eq. 7.23).

[(C6Hs)3P],

+

CH31

=

[(C6H,)3PI2(CH3)Pdl

(7.23)

These catalytic systems were also used in vinyl polymerization of substituted norbornene. Hojabri et al. 32 reported on the polymerization of norbornene under the influence of palladium/~-complexes to produce selectively poly(norbornene) at high reaction temperatures (Eq. 7.24).

n~

~

[~]n

(7.24)

Relevant studies on the addition polymerization of bicyclo[2.2.1]hept-2-ene in the presence of cationic Pd(ll) complexes with the structure [Pd(RCN)4I[BF4]2 (where R=CH3, C2H5 and (CH3hC) were camed out by Risse et al. "'36. The resulting polymer, poly(2,3bicyclo[2.2.1]hept-2-ene), was insoluble in most other common organic solvents like THF, toluene, chloroform, dichloromethane. The product was, however, soluble in a few unsaturated halogenated hydrocarbons such as trichloroethylene, tetrachloroethylene, chlorobenzenr 1,2-dichlorobenzene and bromobenzene. This allowed polymer characterization by gelpermeation chromatography, vapour phase osmometry, and solution viscosimetry. With [Pd(CH3CNh][BF4]2 as a catalyst, higher molecular weight polymers were formed when the ratio of norbornene to Pd 2+compound was increased. (Table 7.14).

349

Table 7.14 Polymerization of bicyclo[2.2, l]hept-2-ene (M) with the [Pd(CH3CN)4][BF4]z (1) catalyst' [M]'[I]

n ~ ,b

MIIr

M,,q~o

dL.g"l 20 100 200 333 1000

0.07 0.22 0.31 0.45 1.10

qsd

24000 38000 70000 d

d

1.41 1.45 1.36 d

'Data frofll i~rellc.e33; bIIlherellt visoosity l'lialt in chlorobenzene(25~ ~Numberaverage molecular weight determined by GPC in chlorobethzene (vs. polystyrene standards); ~Not determined.

The relationship between the molecular weight and initial mole ratio of monomer to initiator was approximately linear while polydispersities were distributed in the range from 1.3 to 1.5. Furthermore, chain growth was found to continue after renewed monomer addition. These results indicated relatively fast initiation of polymerization and rare chain transfer and termination. Noteworthy, the addition of free nitrile to the polymerization mixture caused limitation of the molecular weight by chain transfer reaction. The inherent viscosity dropped from 0.22 dL/g down to 0,09 dL/g when 20 equivalents of acetonitrile (respective to Pd z§ were used. No polymerization occurred when the reaction was carried out in pure acetonitrile. On the other hand, addition of 1 equivalent of triphenylphosphine resulted in a molecular weight increase, corresponding to deactivation of a half of the [Pd(CH3CN)4][BF~]2 used for polymerization. Poly(2,3-bicyclo[2.2.1]hept-2-ene) with a polydispersity, M , ~ ~ . as low as 1.07 was obtained when [Pd(CH3CH2CN)4][BF4]2 was used as the catalyst35 and the polymerization was carried out at a temperature of 0~ The relationship between the molecular weight and monomer conversion was approximately linear for molar ratios of monomer to Pd-c,atalyst ([M]:[I]) up to 500:1 (Table 7.15).

350

Table 7.15 Polymerization of bicyclo[2.2.1 ]hept-2-ene (M) with the [Pd(CH3CH2CN)4][BF4]20) catalyst' Monomer Conversion

M.(GPC)

M,.~.

35

11200 21400 29400

1.07 1.12 1.34

54

100 |

9Data from reference3~ However, the reaction medium has to be carefully selected as the polymer was soluble only in a few unsaturated halogenated solvents. In a solvent mixture of chlorobenzene with nitrobenzene (volume ratio 2:1) the reaction medium remained nearly homogeneous up to high monomer conversions. In addition, the product was soluble in dichloromethane, nitromethane and nitrobenzene as long as a sufficiently high concentration of unreacted norbomene was present. This also allowed the preparation of poly(2,3bicyclo[2.2.1]hept-2-ene) having M,,/M~ below 1.2 by the use of high concentrations of bicyclo[2.2, l]hept-2-ene (higher than 4 mole/L) in the above mentioned solvents. Materials with molecular weights below 10000 were obtained from reaction mixtures containing molar ratios [M]:[I] smaller than 100:1. Higher molecular weight polymers were prepared from larger mole ratios of monomer to initiator (Table 7.16). Table 7.16 Molecular weights of poly(2,3-bicyclo[2.2.1]hept-2-ene) otgamed with the [Pd(CH3CH2CN)4][BF4]2catalyst' [M]'[I]b

Mo(GPC)~

M.(GPC) r

M,,(LS)d

M.(GPC)/ M.~S)

200 600

32900 79500

35200 112300

22000 77500

1.6 1.5

"Data from reference3S;blnitial molar ratio of monomer to Pd-catalyst; ~.elative number and weight average molecular weights determined by GPC in chlorobenzene calibrated with polystyrene standards; dAbsolute weight average molecular weights determined by light scarring (LS) in trichloroe~ylene.

351 Absolute weight average molecular weights MalLS) smaller than relative MdGPC) indicated that poly(2,3-bicyclo[2.2.1]hept-2-ene) has a more rigid molecular structure than polystyrene. The values for absolute M,,(LS) was by a factor of 1.5 to 1.6 smaller than that of relative M~GPC) for the two samples presented in Table 7.16. A radius of gyration l/2 of 130A found for the polymer with a M~LS)=77500 suggested the presence of slightly expanded Gaussian coils. In these studies, Risse e t al. 36 observed that the palladium-carbon bond of the end group remained intact after the isolation of the polymer by precipitation. Subsequent reaction with NaBI-h resulted in cleavage of the Pd-C bond and precipitation of Pd(0). This finding evidenced that an insertion type mechanism into Pd-C bond was responsible for chain propagation. The Pal-catalyzed polymerization of bicyclo[2.2.1]hept-2-ene was unexpectedly insensitive toward water present in the monomer solution. For instance, polymerization of norbornene still ~ r r e d when 1000 equivalents of water (molar ratio of H20 to Pd(II) = 1000:1) was added to a monomer solution containing 200 equivalents of norbomene ([M]:[I] = 200) (Table 7.17).

[M]:[I]b 2OO 200 200 200 3000

Table 7.17 The influence of water on the Pd(ll)-catalyzed (I) l]hept-2-ene (M)' pol~anerization of bi~clo[ M~~ d Yield~ % [H20]:[Pd]r M,(GPC)d ,is

10 100 1000 200

33000 11100 7000 4100 62000

1.24

90

2.06 2.44 2.57 2.00

80

70 70 60

"Data from reference~;blnitial' molar ratio of bicyclo[2.2.1]hept-2-ene to Pd(ll)catalyst, ~Molar ratio of water to monomer in the reaction mixture; aM.(GPC) relative molecular weights by GPC, calibration with polystyrene standards, M,,/M, = polydispersity index determined by G PC. The polymer yield of 70% was relatively little affected at such a high water:Pd ratio employed in this reaction. However, the molecular weight of poly(2,3-bicyclo[2.2, l]hept-2-ene) was drastically reduced from M~(GPC) = 33000 to 1~ (GPC) = 4100 (M,,/M~ = 2.6) indicating that water acts as

352 a chain transfer agent. The chain transfer property could be specifically used for the synthesis of reduced molecular weight poly(2,3- bicyclo[2.2, l]hept2-ene) using very small amounts of the Pd-catalyst. Examination by X-ray spectroscopy of the poly(2,3bicyclo[2.2.1]hept-2-ene) prepared with Pd(II)-tetrakisnitrile catalysts revealed that this polymer is predominantly amorphous. Thermomechanical analysis (TMA) studies on polymers with M,(GPC) = 33000 indicated a softening temperature of 330-335~ However, at this temperature also the onset of thermal decomposition occurred. According to thermogravimetric analysis (TGA) under nitrogen, the polymer of bicyclo[2.2.1]hept-2-ene was reasonably stable up to 300~ to 320~ A weight loss of 5% was recorded at a temperature between 370~ and 380~ The glass transition temperatures determined by two indirect methods indicated T s of 320~ for a low molecular weight polymer and of 330~ for a high molecular weight polymer. Bicyclo[2.2.1 ]hepta-2,5-diene (Norbornadiene). In their extensive studies on the polymerization on the norbomene-like systems with palladium chloride, Schulz27 reported on the polymerization of norbomadiene induced by PdCI2 complexes. Using this type of compounds, products of low molecular weight were obtained in which one of the double bond of the monomer was retained (Eq. 7.25).

n

]n

(7.25)

The polymer was a solid product and had quite a high decomposition temperature. Hojabri e t al. 32 investigated the polymerization of norbomadiene induced by palladiumht-complexes under various reaction conditions. Working at 300~ these authors observed that in the presence of the above catalysts poly(norbornadiene) was formed having only one c a r b o n - ~ o n double bond of the diene system opened (Eq. 7.26).

(7.26)

353 Nickel complexes in association with alkylaluminium halides showed to be very active in norbornadiene polymerization. Such catalytic systems have been reported by Sun Oil Co. 37 to be produced starting from nickelacetylacetonate-bis(tri-n-butylphosphine) or niekeldiehoride-bis(tri-nbutylphosphine) and diethylaluminium chloride or ethylaluminium dichloride at AI:Ni molar ratios between 0.5-100. Norbomadiene polymerization was performed in bulk or solution at temperatures ranging from -40~ to 120~ to form poly(norbornadiene) usable as energy rich solid fuel. Efficient binary catalysts for v i n y l polymerization of bicyclo[2.2.1]hepta-2,5-diene prepared Okamoto e t al. ~5 from various transition metal compounds and methylaluminoxane. On working in toluene at 25~ high monomer conversions and polymer yields have been obtained, depending essentially on the nature of transition metal compound (Table 7.18). Table 7.18 Polymerization of bicyclo[2.2.1 ]hepta-2,5-diene (M) reduced b), transition metal compounds ~ and methylalummoxane~b Transition Metal Monomer PolymerYield, M,,

(xlo")

Conversion,

Compound

% 66 2 47 95 66 69

CpTiCI3 CpzVCI2

V(acac)3 Cr(acac)3 Cp2C3 Mn(acach

1.52

3.0

0.05 1.08

3.8

2.20 1.52

1.60

5.7

'Data from referencelS;b Reaction condition" [M]=25 mmole, [I]=5 mmole Al:catalyst=200, Temperature 25~ Reaction time=4 hr Significantly, among the transition metal compounds employed in these systems, Cr(acac)3 exhibited the highest activity leading to 95~ comonomer conversion. It is noteworthy that the structures of the polymers obtained with Ti, V, Cr and Mn compounds consist of both the vinyl and transannular recurring units (Eq. 7.27).

n . \

/

.

=

(7.27)

354 The ratio of the two structures was found to depend primarily on the nature of the transition metal compound. It is noteworthy that when Mn compound was used associated with methylaluminoxane, the proportion of the transannular structure was 97%. Palladium salts such as PdCI2 was reported by Schulz 27 to polymerize bicyclo[2.2, l]hepta-2,5-diene to vinyl polymers in which one of the double bonds was retained (Eq. 7.28). n

O

=

(7.28)

The products were of low molecular weight and had quite a high decomposition temperature. Addition polymerization of bicyclo[2.2, l]hepta-2,5-diene has also been investigated more recently by Risse et al. 35 using the Pd(II) coordination complex [Pd(CH3CH2CN)~][BF4]2. Under the influence of this catalyst, bicyclo[2.2.1]hepta-2,5-diene gave a soluble unsaturated polymer which consisted predominantly of the 1,2-addition repeating units. Subsequent thermal treatment of poly(bicyclo[2.2, l]hepta-2,5-diene) at 240~ resulted in the formation of polyacetylene accompanied by elimination of cyclopentadiene (Eq. 7.29). [~2~ n

=

in

=

[\--/]n +

o()

(7.29)

These authors observed that it is important to keep the monomer conversion in the synthesis of poly(bicyclo[2.2.1]hepta-2,5-diene) low to avoid gelation by cross-linking reaction. After 3 hr reaction time at 20~ a polymer yield of 20% was obtained from an initial molar ratio monomer to catalyst [M][I] = 100:1. Interestingly, the molecular weight distribution of the addition polymer was very broad, with M~(GPC) = 3700 and M,,(GPC) = 11800. Examination by ~H NMR spectroscopy of the poly(bicyclo[2.2.1 ]hepta-2,5-diene) thus prepared showed that the polymer was not perfectly free of defects. It contained slightly less than one olefin bond in each repeating unit, i.e., approximately 85 to 90% according to the

355 signal at/5 = 6 ppm. This result indicated the presence of a small amount of branches and nortricyclene units in poly(bicyclo[2.2.1]hepta-2,5-diene) prepared under the above conditions. Alternatively, at higher monomer conversions, i.e., 90% after 30 hr reaction time at a temperature of 20~ a highly cross-linked product was obtained. Bicyclo[4.3.0t'6]nona-l,3,5,7-tetraene (Indene). Vinyl polymerization of indene under the action of Ziegler-Natta catalysts will form by the 1,2addition reaction of the nonaromatic double bond a saturated polymer bearing side aromatic moieties attached along the chain (Eq. 7.30).

n

~--

(I'o

(7.30)

This reaction has been investigated by Farona and coworkers 3s using the catalytic system Mo(CO)sPy/EtAICI2/Bu4NCI. Working in chlorobenzene at 30~ for 20-22 hours, a polyindene in 92% yield has been obtained. Structure determinations by m3C ~ spectroscopy indicated that polyindene thus prepared contained 34% repeating units formed by double bond opening, i.e., 7,8-indenylene units, and 66 % repeating units formed by ring-opening i.e., 1,4-phenylene-l',3'-propenylene.

7.3. Polymerization of Polycyclic Olefins Up to now, a substantial number of polycyclic olefins have been polymerized with Ziegler-Natta catalysts giving rise to polymers with outstanding physical and mechanical properties. Dicyclopentadiene. Relevant results on the polymerization of exo- and endo-dicyclopentadiene under the action of Re- and Mo-based catalysts reported Farona and coworkers 3s in connection with their investigations on norbornene and related cycloolefins. On using Mo(CO)sPy/EtAICI2 as a catalyst, they found that the polymer yield and the ratio of ring-retention to ring-opening was essentially dependent on the reaction temperature and nature of the solvent (Table 7.19).

356

Table 7.19 Polymerization of dicyclopentadiene(M) with Mo(CO)sPy/EtAICl2 as a catalyst"b O/A d Temp. Yiel~ % ~ exo-M 100 Heptane 1:2.7 100 exo-M 1:4.0 Chlorobenzene 54.7 25 Chlorobenzene 44.7 1:3.8 50 exo-M 1:5.8 exo-M 100 100 Chlorobenzene 1:7.3 endo-M 46.8 26 Heptane 1:3.7 endo-M 26 Chlorobenzene 31.7 1:8.6 I00 45.5 endo-M Chlorobenzene 'Data from reference 31, hAl I polymerizations were carried out for 20-22 h~rs;Wield of methanol m~luble poly(dicyclopemadime); aOlefin to aliphatic proton ratio from NMR spectrum. Dicyclopentadiene

|

|

Solvent

,

=,

The major product from the polymerization of exo- and endodicyclopentadiene was an insoluble material, a gel from the former and a white powder from the latter. The molecular weights and polydispersities are given in Table 7.20. Table 7.20 Molecular weights and polydispersities of poly(dicyclopmtadiene) prepared with Mo(CO)~Py/EtAICI~as a catalyst~b Dicyclopentadiene

Solvent

Temp., ~C

MwCy 103

PDI

2.4 1.1 50 chlorc~zene 2.8 189 100 chlorobenzene 2.2 2.4 26 heptane 2.0 1.9 26 chlorobenzene 1.6 121 100 chlorobenzene 'Data fron~ reference 3t; bReaction condition as in Table 7.19; CMolecular w'eights of the soluble fraction of poly(dicyclopemadiene). exo-M exo-M endo-M endo-M endo-M

As Table 7.20 illustrates, the nature of the solvent and reaction temperature exert a significant influence on the molecular weight and polydispersity

357 of poly(dicyclopentadiene) prepared under these conditions. Vinyl polymerization of dicyclopentadiene to poly(dicyclopentadiene) was reported by Mitsui Toatsu Chemical Co. 39 to proceed in the presr162 of catalytic systems consisting of a transition metal compound from Group IVB, VB or VIB of the Periodic Table and aluminoxanes. The transition metal compound was that of titanium, zirconium, hafnium, vanadium or chromium (e. g. bis[ cyclopentadienyl] diethyltitanium, bis[ cyclopentadienyl]titanium difluorid e, bis[ cyclopentadienyl ]d imethylzirconiu m, bis[cyclopentadienyl]diethyl~rconium, bis[cyclopentadienyl]zirconium difluoride or dichloride) and the aluminoxane was derived from an organoaluminium compound (Eq. 7.31) 13 n

,.~

(7.31)

where R = hydrocarbon group, preferably methyl, ethyl, propyl or butyl. The polymerization was conducted in a h y d r ~ o n solvents such as butane, pentane, cyclohexane, benzene, toluene or xylene at temperatures ranging from -30~ to 200~ In one example, poly(dicyclo~tadiene) was prepared in toluene at 20~ for 6 hr with bis(cyclopentadienyl)titanium dichloride and methylaluminoxane as the catalyst. The poly(dicyclopentadiene) thus produced was useful for paint, adhesive and thermoplastic resins. During their studies on the polymerization of e x o - and e n d o dicyclopentadiene induced by the Pd(II) coordination complex [Pd(CH3CN)4][BF4]z, Rissr et al. 35~ observed a significant differetw,r on the reactivity of the two stereoisomers in the presence of this catalytic system. Under these conditions, the exo monomer produced the addition polymer, poly(exo-dicyclopentadiene), with l~(GPC) = 8300 in 80% yield after 30 rain reaction time at a temperature of 25~ (Eq. 7.32).

n~

=

(7.32)

358 By contrast, the endo monomer gave only a 13% yield of addition polymer with M,(GPC) = 700 after 24 hr reaction time at a temperature of 25~ (Eq. 7.33).

n

=

(7.33)

-,,,/ By means of ~H M R spectroscopy these authors found that the polymers thus prepared contained two unreacted olefinic protons, indicating that the double bond of the less strained five-membered ring of both dicyclopentadiene monomers remained intact. The presence of the additional double bond in exo-dicyclopentadiene resulted in a smaller reaction rate as compared with exo-l,2-dihydrodicyclopentadiene. No structural rearrangements were observed for poly(dicyclopentadiene) which is a further indication that these Pd(II)-catalyzed reactions proceed by an insertion mechanism. 6,7-Dihydro-exo-dicyclopentadiene. Addition polymerization of exo-6,7dihydrodicyclopentadiene to poly(exo-l,2-dihydrodicyclopentadiene) has been conducted by Risse et al.36 using Pd z§ coordination complexes such as [Pd(CH3CN)4] [BF4]2(Eq. 7.34).

~

n

(7.34)

When a molar ratio monomer to initiator of 100:1 was employed, saturated vinyl polymers having a molecular weight M,(GPC) = 22000 and polydispersity M,,/M~ = 1.3 were obtained. Most of the monomer (75%) was consumed within 15 min at a reaction temperature of 25~ 1,4,5,8-Dimethano-l,2,3,4,4a,5,8,8a-octahydronaphthalene. The steric effect of the endo geometry was substantial in the addition polymerization of endo, exo- 1,4,5,8-dimethano- 1,2,3,4,4a,5,8,Sa-octahydronaphthalene carried out by Risse et al. 36 in the presence of [Pd(CH3CN)4][BF4]z as a catalyst (Eq. 7.3 5).

359

~ [ ~ n

[

in

=

(7.35)

In this process, poly(erMo,exo-l,4,5,8-dimethano-l,2,3,4,4a,5,8,Saoctahydronaphthalene) with molecular weight M~(GPC) = 2000 in a 23% yield was formed after 24 hr reaction time at a temperature of 25~ Starting with a molar ratio monomer to catalyst [M]:[I] = 100:1, they observed that this reaction was a "non-living" polymerization which led to a broad molecular weight distribution. 1,4,5,8-. Dim eth a n o--1,4,4a,5,8,$a-h exa hyd rona phthalen e. The vinyl polymerization of 1,4,5,8-dimethano-l,4,4a,5,8,Sa-hexahydronaphthalene (endo,exo-isomer:er~,endo-isomer = 85" 15) has been effected by Rissr et a/=.~ using the Pd(ll) complex [Pd(CH3CHzC~4][BF4]z to produce poly(1,4,5,8-dimethano- 1,4,4a,5,8,8a-hexahydronaphthalene) (Eq. 7.36).

n

=

~.

in

(7.36)

Working in CHaCI2 at a molar ratio [M]'[I] of 100:1, reaction temperature of 20~ and reaction time of 10 min, a soluble polymer having a molecular weight M,,(GPC) = 9100 and M,,(GPC) = 59000 was obtained for a monomer conversion of 35%. This polycyclic monomer with two double bonds, one being part of an exo-subsfituted bicyclic system, the second belonging to an endo-substituted bicyr unit, was expected to be less likely to cross-link under these conditions, due to the difference in reactivity between the two olefin units. However, the polymer was actually found to become cross-linked when longer reaction times were employed. For instance, when the polymerization was conducted for 100 min at 20~ a cross-linked polymer in 85% yield was produced. Substituted 1,4,5,8-d im eth a n o- 1,2,3,4,4 a,5,8,8 aoctahydronaphthalene. Vinyl p o l y m ~ t i o n of norbornene-like monomers of the types I and II was reported by Mitsubishi Petrochemical Co. 4~ to proceed in the presence of Ziegler-Natta catalysts consisting of vanadium compounds and organoaluminium compounds

360 e.g., trialkylaluminium, dialkylaluminium halide (Eq. 7.37-7.38).

n

~

[

R'

]n

(7.37)

R"

(D

R '/

\R" in

n

(7.38)

~ )l

(ID

(''3

(OH2)

4,9,5,8-Dimethano-3a,4,4a,5,8,8a,9,9a-octahydro-

1H-benzoindene.

Polymers of 4,9, 5,8-dimethano-3 a,4,4a, 5,8,8a,9,9a-octahydro- 1Hbenzoindene were manufactured by Nippon Zeon Co. 4~ in the presence of Ziegler catalysts comprising transition metal compounds and organoaluminium compounds in hydrocarbon solvents (Eq. 7.39).

In

(7.39)

Thus, working in hexane or benzene at temperatures from -30~ to 200~ under a pressure of 0-20 kg/cm 2, polymers soluble in organic solvents with excellent heat resistance and transparency, good chemical and ageing behavior as well as excellent dielectric and mechanical properties were produced. The polymer was useful for the manufacture of mouldings, e.g., optical lens, photo discs, optical fibers and circuit base boards for high frequency.

361

1,4,5,8-Dimethano-l,2,3,4,4a,4b,5,8,8a,9-decahydro-9H-fluorene. New addition polymers were obtained by Nippon Zeon Co. '2 from 1,4,5,8dimet~o-l,2,3,4,4~,4b,5,8,8~9..dec~ydm-9H-fluorene by Ziegler-Natta polymerization in hydrocarbon solvents (Eq. 7.40). n

(7.40)

The reaction occurred in various solvents e.g., hexane, benzene, toluene, in the presence of catalytic systems derived from Ti or other transition metal compounds and reducing agents e.g., organoaluminJum compounds at temperatures between-30~ and 200~ and pressures of 0-20 kg/cm 2. The poly(1,4, 5,8-dimethano- 1,2,3,4,4a,4b,5,8,8a,9-decahydro-9H-fluorene) was soluble in common solvents and had good chemical stability, good solvent

resistance, high glass transition temperature, excellent heat resistance, excellent transparency, improved dielectric and mechanical properties. The product could be used for manufacture of optical lens, photo discs, base boards for crystalline liquids, printing base boards, electronic and electric devices (Eq. 7.41-7.42).

n

(7.41)

n

L v

m

(7.42)

362 Hexacyclo [9.2.1.02"to.03'8.04'6.0x9] tetradec- 12-enes (exo, exoand endo,endo-dinorbomadiene). Investigations ~ e d out on the polymerization of exo,exo- and endo, endo~inorbomadiene, carried out by Alonso and Farona 43, in the presence of the Re(CO)sCI/EtAICI2 system, are of a great practical and theoretical interest due to the particular structure of these highly strained polycydic olefins (Eq. 7.43).

(7.43) (0

(lO

Reaction of exo, exo-dinorbomadiene has been performed in chlorobenzene at I I0~ for 24 hours to produce in 47.6 % yield a vinyl polymer, poly(exo, exo-dinorbomadiene) (Eq. 7.44). n

(7.44)

n

Analysis of the ~H NMR spectrum of poly(exo, exo-dinorbomadiene) with an olefin to aliphatic proton ratio of 1:32 indicated a minor contribution of unsaturated ring-opened structures along with the saturated vinyl units in the polymer chain. The molecular weights and polydispersity, as determined by GPC in THF and by osmometry in toluene, were M,=462,300 and M,=lg0,000, respectively, and PDI=2.57. The polymer softened at 200~ and melted above 300~ Reaction of endo, endo-dinorbomadiene, under the same conditions as the exo,exo-isomer, gave also a vinyl polymer, poly(endo, endo-dinorbomadiene), in 60~ yield by a preponderant opening of the double bond with ring-retention (Eq. 7.45).

n

=

--"

-

(7.45)

363 Although the homopolymer was of the ring-retained type, a minor olefinic signal appeared also in the mHNMR spectrum. The product had molecular weight M~--55600 and M,=37300, respectively, and polydispersity, PDI=1.49.

7.4. Polymerization of Functionalized Cydoolefins During their early studies on the vinyl polymerization of norbomene-like systems with palladium chloride, PdCI2, Schulz et al. z7 disclosed that this catalyst was quite tolerant to hydroxyl groups attached to the norbornene derivatives. Thus, 2-hydroxymethylbicyclo[2.2.1 ]hept-5-ene was readily polymerized under the action of PdCIz in acetone at 25~ for 6 hr. The polymer obtained in 20% yield was insoluble in chloroform and benzene and dissolved in dimethylformamide, dimethylsulphoxide and ethanol. The product had a low molecular weight, M~=2130, and decomposed at temperatures of 320-330~ The transition metal catalysts derived from the Pd(ll) cooordination complexes, [Pd(RCH2CN)4CI2][BF4]2, were found by Risse et al. 35 to tolerate the ester functionalities attached to norbomene moieties. However the rate of polymerization was reduced in comparison to the polymerization of norbomene. It is important to note that polymers with appropriate substituents, synthesized by this way, were found to possess a better solubility in organic solvents and a lower glass transition temperature than the parent, unsubstituted polynorbomene. Aliphatic esters of bicyclo[2.2, l]hept-5-ene-2-methanol with methyl, n-butyl, n-heptyl, n-nonyl and n-undecyl groups were polymerized by Risse et al. 44 using [Pd(CH3CN)4][BF4]z in nitromethane at 25~ resulting in the corresponding vinyl addition polymers (Eq. 7.46).

n ~CH20R

=

[~]n \

CH2OR

(7.46)

The polymer yields were moderate, i.e., in the range of 22-32%, when norbomene derivatives with a low e x o / e n d o ratio of 20:80 were used for polymerization (Table 7.21).

364 Table 7.21 Polymerization of aliphatic esters of bicyclo[2.2.1 ]hept-5-ene-2-methanol (~endo/exo : 80/20) with the Pd~CH3CN~,][ BF4]z (1~)in nitromethane at 250C~b Ma c R [M]:[I] Mwr Yieldt % CH3 100: I 3900 6600 22 200: l 8200 15000 24 nC4H9 100:1 5900 11000 24 350:1 17000 32000 24 900:1 32000 78000 25 7200 "C7HI 5 100:1 12000 25 550:1 33000 66000 26 nC9HI9 100:1 6800 12000 22 170:1 8400 16000 25 700:1 25000 53000 24 7100 12000 28 "Ct IHz3 100:1 1000:1 42000 92000 32 'Data from reference44; bReaction conditions: 16 hr at 20~ " M., M,, = number and weight-average molecular weight, respectively, determined by gel permeation chromatography (calibrated with polystyrene). 9

|

The exo-isomer of the above mixture underwent predominantly the polymerization under the above conditions. An increase in the molecular weight was observed when higher ratios of monomer to Pd(ll) catalyst were used for polymer synthesis: e.g., the molecular weight M, of the polymer prepared from n-butyl ester increased from 5900 to 32000, upon increasing monomer to catalyst ratio from 100:1 to 900 1, whereas of the polymer prepared from n-nonyl ester increased from 6800 to 25000, upon increasing the monomer to catalyst ratio from 100:1 to 700:1. However, the molecular weight distributions M,JM, (in the range of 1.6 to 2.5) were considerably broader than those of the unsubstituted poly(2,3bicyclo[2.2.1 ]hept-2-ene) prepared under similar reaction conditions. Similarly, aromatic esters of bicyclo[2.2, l]hept-5-ene-2-methanol with phenyl, 4-chlorophenyl and 3-nitrophenyl groups were polymerized by Risse et al.44 using [Pd(CHaCN)4][BF4]z in nitromethane at 20~ resulting in the corresponding vinyl addition polymers (Eq. 7.47).

n ~CH20R

..~

[~v~]n \

cNor

(7.47)

365 The polymer yields were also moderate, i.e., in the range of 24-28 %, when norbomene derivatives with a low exo:endo ratio of 20:80 were used for polymerization (Table 7.22). Table 7.22 Polymerization of aromatic esters of bicyclo[2.2.1]hept-5-ene-2-methaaol (M) (endo/exo:80/20) with the [Pd(~CH3CN)d[BFd20) in nitromethane at 20~ Lb [Ml:[x] Yielr % MW Mi R 24 8800 4200 100:1 C~l~ 26 19000 7700 150:1 28 3800 1400 100:1 4.-CI-.C~h 27 4300 1600 100:1 3-NO2-CffI4 28 5700 2300 250:1 M., M,, = number 'Data from reference**; ~.eaction conditions: l6 hr at 20~ and weight-average molecular weight, respectively, determined by gel penneauon chronmtography (calibrated with polystyrene). Again, predominantly the exo isomer underwent the polymerization reaction. An increase in the molecular weight was also observed when higher mole ratios of monomer to catalyst were used for the polymer synthesis. The molecular weight distributions M j M , in the range of 1.6 to 2.5 were further considerably broader than those of unsubstituted poly(2,3bicyclo[2.2.1 ]hept-2-ene) prepared under the same reaction conditions. The thermal properties of aliphatic and aromatic poly(5,6bicyclo[2.2, l]hept-5-ene) derivatives were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) (Table 7.23). As it can be observed, a weight loss of 5 % (under N2) was recorded at temperatures of 340~ to 350~ for the aliphatic ester derivatives and at 285~ to 339~ for the aromatic ester derivatives. The glass transition temperatures, T s, of these poly(5,6-bicyclo[2.2.1 ]hept-5-ene) derivatives were in the range of-40~ to 268~ For comparison, T 8 of the parent polymer, poly(2,3-bicyclo[2.2, l]hept-2-ene), could not be recorded clue to the onset of thermal decomposition above 320~ It was found that linear long-chain substituents such as "CTHmsC(O)O-CH2- and nCgHIgC(O)-O-CH2-drastically reduced T s to values of-25~ and -40~ respectively. Polymers of bicyclo[2.2, l]hept-2-ene ester derivatives thus prepared were soluble in a wide range of organic solvents, e.g., chloroform, dichloromethane, tetrahydrofuran, toluene and chlorobenzene.

366 Table 7.23 Thermal properties of aliphatic and aronmtic poly(5,6-bicyclo[2.2.1 ]hept-2-ene) derivatives' R

T~(5 %)/~ 349 343 344 346 339 331 285

Ta/'C ~ CH3 268 124 "C4H9 "C7H1~ -25 -40 "C9HI9 Cd'l~ 193 172 4-CI-C~-14 144 3-NOz-CrH4 'Data fxom reference"; bTon-~mmrr corrospoadmg to 5 % weight loss, determined by thermogravimetry (TGA) under Nz; "Class transition ten~erature, determined by differential scanning calorimetry (DSC).

In contrast to the polymerization of endo/exo..nf~ures of bicyclo[2.2.1]hept-2-ene derivatives, yields in the range of 70-85% were obtained for the polymerization of the pure exo~monomers with Pd(ll)compounds (Table 7.24). Table 7.24 Polymerization of esters of exo-bicyclo[2.2. I ]hept-5-ene-2-methanol (M) with the [Pd(CH3CN)4][BF4]z (I) in n i t r ~ a n e at 20~ '

R

[M]-[I] b

M8

CH3

I00:I 170:1 I000:I I00:I 200:1 I000:I I00:I 200:1 I000:I

II000 19000 138000 14000 30000 163000 14000 24000 142000

nC4H9

C~,

MW

Yield, %

14000 30000 310000

79 85 81 79 85 82 70 72 70

18000

46000 359000 18000

41000 345000

'Data from reference*~; bReaction 'conditions: 16~hr at 20~ ~ M., M, - number and weight-avorage molecular weight, resp~vely, determined by gel permeation chromatography (calibrated with polystyrene).

367 A nearly linear dependence of molecular weight on the initial mole ratio of monomer to Pd(lI) catalyst ([M]'[I]) was found, even though the polydispersity, MJM~, was quite high for the high-molecular-weight polymers. For instance, the molecular weight M, (GPC) of the addition polymer resulted from exo methyl ester increased from 11000 to 138000, when mole ratios [M]/[I] of 100:1 and 1000:1, respectively, were used. Approximately linear relationships of molecular weight to monomer conversions were found for the polymerization of esters of exa-substituted bicyclo[2.2.1]hept-2-enes (Table 7.25). Table 7.25 Molecular weight to monomer conversion in polymerization of esters of exo-bicyclo[2.2, l]hept-5-ene-2-methanol (M) with the [Pd(CH3CN)4][BF4]2 (I) in nitromethane at 20~ ~b R

Time, hr

CH3

0.5 1

nC4H9

3 0.5

C~,

4 10 0.5

1

1

4 10

Conv., ~

39 51 70 22 28 48 70 15 29 58 68

M. d

Mw 4

5800 7100 8800 4100 5100 9100 13600 3000 5800 9700 12600

7600 9200 11600 5100 5900 10400 16300 3700 8000 14500 20200

'Data from reference~; b~lole ratio monomer to P(II)-complex = I00:I m nitromethane at 20~ ~ conversion corresponds to polymer yield (cxmfirmed by GC); aM, (GPC) and M, (GPC) = number- and weight-average molecular weight, respectively, detennmed by GPC (calibrated with polystyrene). These results indicated that chain transfer and chain termination reactions were rare in pd2"-catalyzed polymerization of esters of exo-substituted norbomene derivatives. Furthermore, the ester substituents of bicyclo[2.2.1]hept-5-ene-2-methanol induced a drastically reduced rate of polymerization compared to the rate of polymerization of unsubstituted

368 bicyclo[2.2, l]hept-2-ene (50 % monomer conversion within 1-2 min under similar reaction conditions). Aliphatic esters of bicyclo[2.2.1 ]hept-5-ene-2-methanol were polymerized by Risse and coworkers 45'~ using more active (1'13allyl)palladium catalysts, (rl3-allyl)Pd(BF4) and (rl3-allyl)Pd(SbF6). Results obtained for bicyclo[2.2, l]hept-5-en-2-ylmethyl decanoate with these two catalysts are given in Table 7.26. Table 7.26 Polymerization of bicyclo[2.2.1 ]he~-5-en-2-ylmethyl decanoate (M) with the catalysts (rl3-all~r )Pd(BF4) ; nd (rlLallyl) 'd(SbF~)~ Yield M,,/M, M. Time Catalyst [M]/[Pd] % ~GPC) hr [Pd(CH3CN)4][BF4]b (rlLallyl)Pd(BF4)r (l'lLaIlyl)Pd(B F4)r (rlLallyl)Pd(BF4)~ (q3-allyl)Pd(BF4)~ (q3-allyl)Pd(gbF6)~

50/1 50/1 50/1 50/1 150/1 50/1

16 6 18 48 48 18

3900 17800 9700 9600 8800

25000

1.56 1.68

2.18 2.40 2.46 2.19

22

39 74 97 100 99

"Data from reference ~S;bSolvent: nitromethane; "Solvent: chlorobenzene The difference in activity between the (rl3-allyl)palladium catalysts was attributed to a more intimate association of the (rlLallyl)palladium unit with the smaller tetrafluoroborate anion. The presence of the solvent (nitrometh~e or chlorobenzene) was important for the stability of the (1"13al!yl)palladium complexes. Both catalysts were stable in solution at 20~ for approximately one hour; the decomposition was only slightly accelerated in the presence of air. More recently, Safir and Novak 4~ expanded the scope of this reaction by incorporating functional groups in the monomers to yield highly reactive precursor polymers. To this end, they synthesized and examined the polymerizability of diethyl bicyclo[2.2.1 ]hepta-2,5--diene-2,3dicarboxylate and diethyl 7-oxabicyr ]hepta-2, 5-diene-2,3diearboxylate. During some preliminary tests they found that Pd(CH3CN)4(BF4)z, normally a highly reactive insertion catalyst, failed to polymerize these two monomers under all conditions. They found, however, that in rigorously anhydrous organic solvents Pd(OAc)~ catalyzed

369 the slow oligomerization of diethyl 7-oxabicyclo[2.2.1 ]hepta-2,5-diene-2,3d i ~ x y l a t e over the course of several days. Surprisingly, addition of water to the reaction mixture led to a subsequent increase in the activity of the catalyst, i.e., 4-5 fold increase in the polymer yield at comparable times. The exact role of water remained unknown; the possibilities included nucleophilic aRack by water on a Pd-bound monomer to yield a Pd-alkyl species similar to the Wacker process a or the water-induc~ break-up of the inactive palladium aggregates. 49 Because excess water did not act as an inhibitor, the most convenient reaction conditions involved a simple aqueous emulsion polymerization of diethyl bicyclo[2.2.1 ]hepta-2,5-diene2,3..di~xylate or diethyl 7.-o~icyclo [2.2. l]hepta-2,5-diene-2,3dicarboxylate initiated by PdCl2 (Eq. 7.48-7.49).

. . [ ~ .COOEt ~ . i ~ C OOEt _(~ .COOEt n/~~ /~COOEt

.~._

[~]n

/ EtOOC

=

x COOEt

[~]n

EtOOC COOEt

(7.48)

(7.49)

Both poly(diethyl bicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate) and poly(diethyl 7-oxabicyclo[2.2. l]hepta-2,5-diene-2,3-dicarboxylate) were readily soluble in a variety of organic solvents. A typical p o l y m ~ o n with Pd(OAc)2, using a monomer to initiator ratio of 200:1, gave a polymer in 75% yield with a molecular weight (GPC, relative to polystyrene) of 28000 and a polydispersity of 1.8. The structures of poly(diethyl bicyclo[2.2, l]hepta-2,5-diene-2,3-dicmboxylate) and poly(diethyl 7oxabicyclo[2.2.1 ]hepta-2,5-diene-2,3-dicarboxylate) were confirmed by IR, IH NMR, and {IH} 13C NMR spectroscopic methods as well as by elemental analysis. Both the ~H NMR and ~3C NMR spectra of poly(diethyl bicyclo[2.2, l]hepta-2,5-&ene-2,3-dicarboxylate) and poly(diethyl 7oxabicyclo[2.2.1 ]hepta-2,5-diene-2,3-dicarboxylate) showed evidence of a particular microstmcture, the nature of which was to be elucidated. Interestingly, kinetic studies of the homogeneous polymerization of diethyl 7-oxabicyclo [2.2.1 ]hepta-2,5-diene-2,3-~carboxylate in wet chloroform-d

370 revealed a zero-order rate dependence on monomer, a first-order rate dependence on catalyst, and a ko~ of 4.2 x 10-4 s"l (i.e., -d[monomer]/dt = k~Pd2+]). This rate behavior suggested that propagation involved a monomer-independent, rate-determining insertion p r ~ . Poly(diethyl 7-oxabicyclo[2.2. l]hepta-2,5-diene-2,3.

/

ol II (1)

Interesting remits in the polymerization of l-methylcyclobutene obtained Katz and coworkers ~4 using a series of catalysts active in metathesis of acyclic olefins (Table 8.2). Table 8.2 R m g ~ m g polymerization of l-n~ylcyclobutene catalysts" in presence of transition metal ~ e s i s Polyisoprenic Conversion, CatalyticSystem % product, % 20

MoC 12(NO)z(Ph~)2/Me3AIzCI3 WCI6/Ph3SnEt

67 74

WCld~uLi Ph2C=W(CO)~

83

75

91

94

58

'Data horn referencet4 A first catalyst that these authors employed in this reaction was prepared from MoCI2(NO)'z(Ph3P)2 and Me3A]2CI3, a well-known catalyst, active in olefin metathesis. As Table 8.2 shows, the monomer conversion and the isoprenic compound were low in this case.

380 On using highly active metathesis catalysts derived from WCI6 and organometaUic compounds, both the monomer conversion and the polyisoprenic content of the product were increased. The best catalytic system for this reaction, however, was the tungsten carbene complex Ph2C=W(CO)5. Using this catalyst, Katz and coworkers obtained form lmethylcyclobutene 94% polyisoprenic product having 84-87% cis and 1316% trans stereoconfiguration. It is noteworthy that the polymer had, along with 2-methyl-butene structural units, also 2-butene and 2,3-dimethyl-2butene units. It is probable that the latter units result by subsequent migration of the methyl groups in the polymer chain under the influence of the catalytic system after the ring-opening polymerization of lmethylcyclobutene occurred. Recent studies by Thorn and coworkers ~2 on the ring-chain equilibrium in I-methylcyclobutene ring-opening metathesis polymerization and polyisoprene degradation with the well-defined molybdenum carbene initiator Mo(=CHR)(=NAr)(OR')2 indicated that, under rigorous thermodynamic control, cyclic oligomers with ttt-trimer prevailing (m - 0), along with the polymer, are formed (Eq. 8.6).

n I~/"

._._~ ~

_.., ~

(8.6)

The same products arise also in the metathesis degradation of polyisoprene under similar conditions, using the above catalytic system. 3-Methylcyr The ring-opening polymerization of 3methylcyclobutene was effected first by Natta~ Dall'Asta and Porri~ with one-component catalyst RuCI3 in polar media and then by Dall'Asta ~s using two-component catalytic systems based on vanadium chloride and organometallic compounds. In all cases, the ring-opened product was a substituted polybutenamer bearing one methyl group in the monomer unit. It is noteworthy that no methyl group migration in the chain was observed (Eq. 8.7). n

! II

n

381 It is interesting to .note that when RuCI3 in polar media was used as a catalyst, the structure of the polyalkenamer was substantially influenced by the nature of the solvent. Thus, similarly to the reaction of unsubstituted cyclobutene, ethanol as a solvent led to an increase of the trans stereoconfiguration in the polyalkenamer whereas water to an increase of the cis stereoconfiguration. The polymer resulted had an amorphous structure which was assigned to a lack of stereoregularity due to the tertiary carbon atom in the chain. Significant studies on the activity and regioselectivity in the ringopening polymerization of 3-methylcyclobutene have been effected by Dall'Asta using a series of two-component catalytic systems based on VCI4 and organometallic compounds (Table 8.3). Table 8.3 Rmg-~ening polymerization of 3-methylcyclobutene wnh two~mponemca~l:c .s~ ' n a s .~ transcisCatalytic System Conversion, Vinyl Polyalken% Polymer, Polyalken% amer~% amer,% VC LI/Et3A ]

VC~3Ga VCI4/Et2Be VC~zMg VCI4./"BuLi

37 25 17 14 3

90 90 85 94 0

0 4

3 0 45

10 6 12 6 55

'Data from reference~ As Table 8.3 illustrates, the most active systems proved to be those consisting of VCL~ and EhAl but in this case the polyalkenamer was formed in a lower amount. By contrast, the least active system, VCL,/"BuLi, showed to be the most regioselective directing the reaction exclusively toward the ring-opening pathway. It is interesting that in this case, the stereoconfiguration of the polyalkenamer was 45% cis and 55% trans. Significantly, with Mo(-CHCMe3)(=NAr)(OCMe3h as initiator, the polymer obtained had 84% cis double bonds and the methyl substituents were randomly oriented with respect to both cis and trans double bonds, t6 3,3-Dimethyleyelobutene. In the presence the of molybdenum carbene initiator, Mo(=CHCMe3)(=NAr)(OCMe3h, 3,3-dimethylcyclobutene gives

382 an all-tram, alI-HT polymer ~6 (Eq.

8.8).

I! ~

~~n

OsCl3 > RuCl3. They observed that, although the catalytic systems were homogeneous at the beginning of the reaction, the system gradually turned heterogeneous, suddenly altering the catalyst activity and changing the reaction kinetics. Depending on the catalyst employed, polymers with totally different physical properties were produced, working under identical conditions. Representative conversions of norbornene and the softening range of the polymers obtained with these catalytic systems are given in Table 8.16.

Table 8.16 Polymerization of norbomene with transition metal salts m polar media' Catalyst

OsCI3 RuCI3 IrCl3

Time

Conversion %

SoRenmg Range oC

4 hr 6.5 hr 7min

55 60 73

58-90 72-90 90-I 15

Reaction

'Data from reference ~7~

Monomer

425 In these experiments the above authors observed that the polynorbomene obtained with osmium catalysts had the lowest softening range and the highest content of cis stereoconfiguration while the polymer formed with iridium catalyst displayed the highest softening range and content of trans stereoconfiguration. Similar catalytic systems based on iridium and osmium salts were employed by Rinehart and Smith m~6for norbornene polymerization in polar media. Working under specific conditions, they obtained polymers having a higher degree of saturation which did not possess an uniform structure. On the other hand, in the presence of ruthenium complexes with phosphine ligands, Hirald and coworkers ~" prepared both types of polymers from norbomene, polyalkenamers and vinyl polymers. It was found that RuCI3.3H20 in hexane as a solvent is only effective in ring-opening polymerization of norbomene if ethanol is present as a coc~talyst (EtOH 9RuCI3 ratio = 3 9 1). In alcoholic solvents, the reaction rate increases in the order EtOH < n-BuOH < t-BuOH. By contrast, addition of trace amounts of cyclopentadiene to the reacting system brings it to a dead stop within a few minutes. Furthermore, small amounts of Ph3P enhance the reaction rate, with maximum effect at a molar ratio RuCI3 : Ph3P = 1 : 1, when the molar ratio reaches 1 : 10, the polymerization rate is very slow. All these effects were rationalized by Tanielian ~78 in terms of different strengths of coordination of the additives to the metal center, leading to a change in the rate of initiation and/or a modified rate of propagation. Porri ~9'ms~examined the activity of several catalysts derived from iridium and ruthenium complexes such as [(Cuql4hlr(CO)Cl]2, [(CsH ~4)21r(OCOCF3)]2, H21rCI6.6H20, [IrC1(C~II4)212 and {Ru[C~-II0(CH3)2]X}2 (CsHl4 = cyclooctene, X = Cl or OCOCF3) in norbornene polymerization. The presence of cross-metathesis products of norbornene with but-2-ene, 2-methylpropene, pent-l-ene and pent-2-ene was evidenced. Other catalysts that were active in norbornene polymerization included (Ph3P)~RuH2, (Ph3P)3RuHCI, (Ph3P)3RuH(OCOCF3), (Ph3P)3Ru(OCOCF3h, [(C6H6hRuCI2]2, [(1,5CsHI2)RuC12]n, and (C~Hs)RuCI2, where CTHs = bicyclo[2.2, l]hepta-2,5diene. Linear polyalkenamers with high molecular weight and uniform structure have been obtained by Oshika et al. ~s~ by norbomene polymerization in the presence of one-component catalysts working in a variety of chlorinated solvents. For instance, good conversions were

426 attained using molybdenum pentachloride in carbon tetrachloride, monchlorobenzene and o-dichlorobenzene at normal temperature. Interestingly, they found that in oxygenated compounds such as dioxan and tetrahydrofuran or in saturated hydrocarbons such as n-heptane, no polymers were formed under the influence of the same catalytic system. However, low conversions of the monomer were reached under the same conditions working in toluene as a solvent. In all cases, the polynorbornene produced had a prevailing trans stereoconfiguration at the double bond. It is noteworthy that the authors observed a gelification phenomenon which could not be explained. During their investigation on the norbornene polymerization with transition metal halides, Oshika and Tabuchi ~82 found that tungsten, molybdenum and rhenium chlorides in solvents such as carbon tetrachloride and carbon disulphide were very active catalysts. Moreover, in most cases a high degree of stereospecificity was observed. Thus, molybdenum pentachloride yielded a polymer having predominantly trans stereostructure at the carbon-carbon double bond, rhenium pentachloride a polymer with a cis stereostructure while tungsten hexachloride produced a polymer with both cis and trans stereoconfigurations. It is of interest that on raising the temperature, both the monomer conversion and polymer yield increaseA. Moreover, the addition of tertiary amines such as triethylamine and tributylamine during the course of polymerization also increased the polymer yield. Remarkably, traces of water caused a substantial decrease of catalyst activity but did not affect the polymer microstructure. Furthermore, elemental analyzes pointed out chlorine atoms to be attached at the polymer chain obtained in the presence of molybdenum pentachloride as a catalyst. Several other molybdenum-based catalysts have been successfully used for norbornene polymerization consisting of 0r-allyl)~lo, ~83

MoCI2(PPh3)2(NO)2,184

Mo(CO)6,185'1s6

Mo(CO)5(Py), 187

(Bu4N)2(Mo6Ot9), 188 [Mo2(CH3CN)8](BF4)2 and related complexes, !s9 usually associated with a cocatalyst. A great number of very active tungsten catalysts have been used in norbornene polymerization. ~9~ A first group consists of unicomponent tungsten carbonyl complexes, TM tungsten aryloxy derivatives ~92 sometimes with a cocatalyst.~93 unicomponent tungsten c,arbene complexes W(=CPh2)(CO)~ and W(=C(COMe)Ph)(CO)5 with or without a r TM tungsten carbene complexes with monodentate ligands of which two are alkoxy o r al~loxy, 195"200 with bidentate ligands, 2~176 or with one tridentate ligand. ~ Another group widely applied for norbornene

427 polymerization consists of WCI6 associated with a variety of organometallic compounds as cocatalysts. 2~176 As mentioned earlier, homogeneous rhenium catalysts consist mainly of ReCI5 and give polymers of high cis content. ~s2"2~'2~3 The heterogeneous rhenium catalyst Re2OT/AI203 leads also to an all-cis polymer, but when pretreated with Me~Sn gives a polymer with comparable content of cis and trans configuration. 2~4 Detailed studies on the norbornene polymerization carded out Ivin and coworkers 2~'2~s using a series of catalysts derived from WCI6, MoCIs, ReCIs, IrCl3 and RuCI3. The microstructure of poly(l,3cyclopentylenevinylene) thus obtained was more accurately evaluated from ~3C NMR spectra and indicated a fraction of cis double bonds (or from 1,0 to 0,14, depending on the catalyst employed. MoCI5 in conjunction with EtAICI2 (molar ratio from 10:1 to 1:10) in chlorobenzene at -46~ to 50~ gave polymers having 35-47% cis content. TM Addition of substantial amounts of Michael acceptors such as ethyl acrylate, diethyl maleate, or diethyl fumarate in the reaction mixture increased the cis content of the polymer to 65% or even higher. It was assumed that these additives might coordinate to the metal site providing a more crowded environment for the approach of the monomer, thereby favoring the formation of cis double bonds. On using ReCls in benzene at high monomer concentration, Ivin and coworkers 2~ were able to obtain for the first time all-cis poly(1,3cyclopetylenevinylene) by norbomene ring-opening polymerization. Iridium-based catalysts provided polymers with cis content in the range 2145% with a random distribution of cis and trans double bonds. Remarkable work on norbornene polymerization reported Farona and coworkers 2~6 using soluble catalysts prepared from Mo(CO)Py and Re(CO)sCI associated with EtAICI2. Interestingly, microstructure investigation by NMR spectroscopy of polynorbomene thus obtained indicated that, depending on the catalyst employed and reaction temperature, vinyl and ring-opened units were present in the same polymer chain (Eq. 8.68).

For instance, under cenain reaction conditions, using Re(CO)sO catalyst system, norbomene was converted to high molecular weight

428 polynorbornene (M, = 154200; Mw = 443000; polydispersity = 2,9) and the composition of the polymer was determined to have, by integration of olefinic to aliphatic proton signals in the ~H M R spectrum, 10 vinyl units for every ring-opened monomer unit. Tungsten-based catalytic systems yield polynorbornene with cis stereoconfiguration ranging from 35% to nearly 100%. WCI6 alone will induce norbornene polymerizationS9~ but its activity is much enhanced in the presence of a coc~talyst such as BuLi, EtAICIz, (~-allyl)4Sn, Ph4Sn. In addition to these cocatalysts, several other organometallic compounds or metallic hydrides such as Et2AICI, 'Bu2AICI, 'Bu3AI, Bu4Sn or LiAlt-h, respectively, showed to be effective. 2~2 It was observed that in some cases, e.g., WCI6/PIhSn, the molar ratio of catalyst to cocatalyst has little effect on the proportion of cis content (or but in other cases, e.g., WCIdBuLi, there is a marked variation of the cis content with the catalyst composition. Additives such as ethyl acrylate, diethyl fumarate and diethyl maleate increased also the cis content of the polymer. TM Polynorbornene with high molecular weight was prepared by Katz and coworkers ~94 using one-component tungsten-carbene complexes PhzC=W(CO)5, Ph(MeO)C=W(CO)5 and PhzC=W(CO)4(Ph3P) in benzene, toluene or heptane at 20~ and 50~ Microstructure examination by t3C spectroscopic method indicated cis content ranging from 75% to over 90%. Kormer et al. ~83 employed a series of n-complexes of various transition metals to manufacture polynorbornene under various conditions. Thus, on using (~:-CJ-17)4Mo in benzene at 30~ they attained 18% monomer conversion in 16 hr, the polymer formed having 86% cis stereocontiguration. With the catalytic systems (n-C41-17)~lo/TiCh and (nCJ't7)4W/TiCI4 a much faster reaction has been recorded but a somewhat lower cis content in the polymer (64% and 51%, respectively) has been obtained. Of the other catalysts, WCId(n-C3Hs)3Cr, WCId(n-C3Hs)4Zr, though rather active, produced polynorbomene of moderate stereospecificity. Recently, a variety of well-defined transition metal complexes have been used as efficient initiators for the living ring-opening polymerization of norbornene. 2~7 Thus, a number of titanacyclobutane complexes have been prepared and used for the living polymerization of norbornene 2~8'2~9 and synthesis of block copolymers~ or star shaped polymers2z~. The living process initiated with these complexes allowed the synthesis of

429 polynorbornene with various end-functional groups ~ ~ Tantalum carbene complexesZ24 Ta(-CH'Bu)(OCc,I-13'Prz-2,6)3(THF) and Ta(=CHtBu)(SC6Hz~r3-2,4,6h(Py) proved to be effective under conditions which allow monomer coordination to metal center. A ditantalacyclobutadiene complex, (Me~SiCH2hTa2(~t-CSiMe3)2, was found to induce ring-opening polymerization of norbomene in the presence of an equivalent amount of oxygen. ~ Several molytxlenum carbene complexes of the type Mo(=CHR)(=NAR)(OCtBu)2 (R = tBu or CMe2Ph) have been prepared and used for living ring-opening polymerization of norbomene ~'227 and production of block copolymers and star shaped polymers from norbomene. 228"~ Moreover, polynorbomene with a variety of functionalized end-groups have been prepared with substituted benzaldehydes as terminating agents. 23~The molybdenum carbene complex bearing a tridentate ligand [tris(pyrazolyl)borate] proved to be effective in the polymerization of norbomene only when AICI3 has been added. TM A related rhenium carbene complex has been also reported to be active in norbomene polymerization. 23z Ruthenium carbene complexes, Ru(=CHR)(CI)2(PPh3)2 (R = Me, Et, Ph)233 and Ru(=CHCH=CPhz)(CI)2(PR3h (R = Ph, Cyclohexyl), TM showed to be very active and efficient in ring-opening polymerization of norbomene. The latter ruthenium complex was also active when supported on polystyrene. TM In addition, a binuclear ruthenium carbene complex, (RuCICp)2(--CHCH=CPh2), showed to be less active as compared to the other ruthenium complexes. TM Substituted bieyclo[2.2.1lhept-2-ene.Numerous mono- and disubstituted norbomene derivatives have been polymerized under the action of ringopening metathesis catalysts yielding a wide variety of substituted polynorbomene. The ready accessibility of these compounds by the DielsAlder reaction, the high reactivity of norbomene moiety bearing substituents and the special architecture, stereochemistry and properties of the resulting substituted polynorbomenes opened a challenging research area in the polymer chemistry. Monosubstituted bicyclo[2.2.1]hept-2-,ne Norbomene monosubstituted with alkyl or aryl groups and beating functional groups in various positions as well as monosubstituted heteroatom- or metal-containing norbomenes have been extensively investigated in the ring-opening polymerization reaction. Aikyl-, alkylidene- and arylnorbornene. Several alkyl-, alkylidene- and phenylsubstituted norbornenes have been employed as monomers

430 in the polymerization reaction under the influence of ring-opening metathesis catalysts to manufacture substituted polynorbomene. Methylnod~menes. The l-methyl, 2-methyl, exo-5-methyl, e~do-5methyl, syn-7-methyl and anti-7-methylnorbomene have been reacted under the action of various transition metal catalysts to produce unsaturated polynorbomene bearing the methyl substituent in the corresponding position. The tacticity and stereoconfiguration of the resulted substituted polynorbomene is essentially dependent on the initial position of the methyl group and catalytic system employed. l-Methylnorbornene Ring-opening polymerization of 1methylnorbomene has, except when prepared with certain catalysts, a strong head-tail bias~7'23s (F.q. 8.69).

n~

"~r

(8.69)

Interesting work has been reported by Hamilton et al. z~7 using a wide variety of transition metal-based catalysts. Polymer stereoconfiguration and tacticity have been minutely examined by m3C NMR spectroscopy and the data obtained were interpreted in terms of trans-trtms, trans-cis, cis-trtms, cis-cis geometries and tail-head, tail-tail, heM-head, head-tail sequences. Significant studies on the stere~selectivity and regioselectivity of polymerization reaction of 1-methylnorbomene with titanacyclobutane catalyst published Gilliom and Grubbs. 2ts They found that the olefinic linkages in the polymer were primarily trans (90-95%) and the regiochemistry of addition favored head-tail diads. These data allowed the most probable titanacyclobutane intermediate of the propagation reaction to be postulated. 2-Methylnorbornene, Polymerization of 2-methylnorbomene in the presence of a variety of transition metal-based catalysts gives rise preferentially to all-head-tail polymers (Eq. 8.70).

n

=

~~~~"n

(8.70)

For instance, on using the carbene complex Ph2C=W(CO)5, Katz and coworkers 239 prepared in 91% yield poly(2-methylnorbomene) having both cis and trans geometries at the double bonds.

431

5-Methylnorbornene. Ring-opening polymerization of

exo- and endo-5-

methylnorbomene in the presence of a wide range of metathesis catalysts has been investigated in detail by Ivin and coworkers 24~ It is significant that under these circumstances, starting from exo-5-methylnorbomene, polymers having cis double bond contents of 11-100~ while from endo-5methylnorbomene, polymers with cis double bond contents of 22-100~ have been produced (Eq. 8.71).

(8.71) / On studying the polymer microstructure by ~3C NMR spectroscopy, Ivin provided also a full interpretation of these results in terms of tail-head(TH), tail-tail(TT), head-head(HH), head-tail(HT) and trans-trans(tt), transcis(tc), cis-trans(ct) and cis-cis(cc) sequences. In the case of the exo monomer, the all-cis polymer prepared with ReCI5 had a fully syndiotactic ring sequence as revealed by the TT, HH structure, identified by the olefinic carbon resonances in the ~3C NMR spectrum. TM By contrast, polymers prepared with RuCl3-cycloocadiene complex had a high-trans atactic structure in which TT, HH, TH and HT occur to equal extents. In the case of the endo monomer, the fine structure of the olefinic region indicated that the cis/trans double bond distribution was blocky when the cis contents were more than 50%. However, with most catalysts based on Ru, It, W and Re used in the polymerization of exo- and endo-5-methylnorbomene, Ivin et aLZ4~ obtained polymers with randomly oriented methyl groups along the chain. Interestingly, in a related work, Takada, Otsu and Imoto 242 prepared an unsaturated polymer containing primarily trans configuration at the double bond from 5-methylnorbomene in the presence of TiCLt and Et3AI (molar ratio AI Ti = 2.5). 7-Methylnorbornene. Ring-opening polymerization of syn- and anti-7methylnorbomene to poly(l,3(2-methyl)cyclopentylenevinylene) (Eq. 8.72) has been studied by several groups, z43z~

(8.72)

432 On employing conventional ring-opening metathesis polymerization catalysts, such as those derived from RuCI3, WCI6/Me4Sn and ReCls, Hamilton, Ivin and Rooneyz43 showed that anti-7-methylnorbomene polymerized selectively from a mixture of the syn and anti isomers. Analysis of the ~3C ~ spectra of the polymers thus obtained, gave detailed information about their tacticity. Noteworthy, of the catalysts originally tested only that derived from (mes)W(CO)~/EtAICl2/norbomene epoxide polymerized syn-7-methylnorbornene. In a more recent work, Kress et al. TM evidenced that the metalcarbene W[C(CHz)3CHz](OCH2CMe3)2Br2 selectively polymerizes anti-7methylnorbornene from a mixture of syn and anti isomers, but the complex W[C(CH2)~CHz](OCHzCMe3hBr]'GaBrs is more reactive and yields a tapered block copolymer of the two isomers. It is of interest that by using the above metal-carbene to polymerize the anti isomer and then producing the complex on adding GaBr3 to the initial metal-c~:~e, it was possible to induce the formation of a true block copolymer of the anti and syn isomers. Block copolymers of the two isomers prepared also Feast et al. 24s by ringopening polymerization of syn- and anti-7-methylnorbomene under the influence of the well-defined molybdenum complex Mo(--CHCMe3)(=NC~3-2,6-'Pr2)(OCMe3)2. These authors found that the anti monomer polymerizes first, followed much more slowly by the syn monomer. The reaction was considerably faster in CD2CI2 where it proceeded to completion, than in C6D~. Significantly, in C6D6 kc,/ki, = 9, as determined from the proportion of residual initiator. In addition, the double bonds formed were mainly tra~s (80-90%) in both blc~ks and the diads embracing the trans double bonds in the cmti blocks have an isotactic bias, (a,n)~ = 0.69 in Cd~6, independent of monomer concentration; the di~s in the syn blocks have a slight tactic bias, probably isotactic. Further studies on the ring-~pening polymerization of 7-methylnorbomene induced by several Schrock-type complexes [Mo(--CHRIX=NC6H3-2,62Pr2XOR2h] [R~=rBu, CMe2Ph; OR2=OCMe~, OCMe(CF3h] revealed a zero-order dependence on the monomer concentration in some cases; syn-ami alkylidene conversion of the initiator was proposed as the rate-limiting step. Polymerization of the anti-7-methylnorbomene from the mixture of the two isomers were also reported by ~lliom and Grubbsz~s under the influence of a titanacyclobutane catalyst. In these circumstances, a 80:20 trans:cis ratio of double bonds in the chin and a 31 ratio of racemic (r) to meso (m) junctions at the trans double bonds have been observed. Interestingly, in the polymer produced by reaction of ant/-7-methvlnorbomene with the

433 titanacyclobutane catalyst, the trans double bonds were primarily associated with r diads, while the cis double bonds with m diads, in contrast to that observed by Hamilton et al. z43 using classical metathesis catalysts. 5-Methylenenorbornene. While cationic polymerization of 5methylenenorbornene leads to a saturated polymer having nortricyclic recurring units (A), ring-opening polymerization of this monomer forms an unsaturated polymer (B) (Eq. 8.73).

\,

(A)

Jn (8.73)

(B) The reaction has been effected in the presence of several catalytic systems, 24~ e.g., WCI6/Et3AI, WCIdMe4Sn, MoCIdEt3AI or IrCl3. The structure of he polymer is essentially dependent on the catalyst employed. For instance, in the presence of WCIdEt3AI 5-methylenenorbornene yielded the expected ring-opened polymer (B) characterized by its t3C NMR spectrum corresponding to TH, TT, HH and TT carbons in cis and trans double bonds. However, when WCI6/Me4Sn was used as the catalyst, the polymer was totally devoid of double bonds and its ~3C NMR spectrum was consistent with the rearranged structure (A). The formation of this polymer is attributed to a cationic mechanism. 5-1sopropylnorbornene. 5-1sopropylnorbomene has been reacted by Tenney et al. TM in the presence of MoCIdEt2AII to obtain substituted polynorbornene with isopropyl groups randomly distributed in the polymer chain (Eq. 8.74).

(8.74)

c"

434 As it can be observed, the isopropyl groups maintained their initial structure and their position in the resulted polymer. 5-Isopropylidenenorbornene. By ring-opening polymerization 5isopropylidenenorbomene gives the corresponding polyalkenamer having the isopropylidene moiety attached at the cyclopentane unit 24s (Eq. 8.75).

n

(8.75)

r

The reaction has been effected by Tenney eta/. 245 in the presence of MoCIs/Et2AII producing the expected unsaturated polyalkenamer. 5-(4-Butenyl)-norbornene. Dekking 249 observed that norbomene substituted in position 5 with butenyl groups yielded in the presence of the catalytic system consisting of TiCI4 and LiAI(C~0Hz3)4 a mixture of substituted polynorbomene with vinyl polymer (Eq. 8.76).

n~

(A) I

(8.76) I"

1

By spectroscopic measurements it was found that the products contained 41% polyalkenamer and 59~ vinyl polymer. Details about the exact structure of the saturated polymer were not available, probably, both saturated units were present in the vinyl polymer (B). Interestingly, the polymer had a softening temperature of 150~ and did not contain gel.

435 5-Octyl- and higher alkylnorbornene. In the course of their studies on the polymerization reactions of substituted norbomenes, Tenney et al. TM investigated the behavior of 5-substituted norbomene with octyl and higher C ~ , § groups (n = 9-12) in the presence of MoCI~/EtzAII. Under these conditions, they prepared unsaturated polymers beating the alkyl substituent in the corresponding position of the recurring unit (Eq. 8.77).

(8.77) R

where g = n-octyl and C.H2.+mgroups (n = 9-12). 5-Phenylnorbornene. Ring-opening polymerization of 5-phenylnorbornene gives rise usually to poly(5-phenylnorbomene) by a normal ring-opening reaction of the norbornyl moiety (Eq. 8.78).

n

...~_~ ~ n

(8.78)

\

Ph The reaction has been effected by Rinehart, TM Tanaka25z and Komatsu ~3 using catalytic systems based on W, Ru and Ir. Di- and Polysubstituted bieydo[2.2.1]hept-2-~ne. The interesting results obtained in the norbornene polymerization with metathesis catalysts allowed a rapid extension of this reaction to di- and polysubstituted norbomenes. Dialkylnorbornene Ring-opening polymerization of norbornene carrying two alkyl groups will form substituted polynorbomene or poly(1,3cyclopentylenevinylene) having usually the two alkyl groups in the initial position of the cyclopentylene recurring unit (Eq. 8.79).

436 The two alkyl groups may be situated in gemminal positions, e.g., 5,5- or 7,7-dialkylnorbomene, in vicinal positions, e.g., 1,2-, 1,6-, 1,7-, 2,3-, 5,6dialkylnorbomene or at distant positions e.g., 1,3-, 1,4-, 1,5-, 2,5-, 2,7-, 5,7-dialkylnorbornene. Of the dialkylnorbornenes, the dimethylnorbornenes are the most studied disubstituted compounds of this class in the ringopening metathesis polymerization. Depending on the position of the two methyl groups, the reactivity of the monomers is totally different and the structure and properties of the resulted polyalkenamers are strongly dependent on the substituents. 5,S-Dimethylnorbornene Ring-opened polymers of optically active 5,5dimethylnorbomene, having cis double bond contents of 0-100~ were prepared by Ivin and coworkers TM using various catalytic systems based on Mo, W, Re, Os, Ru and Ir compounds. The polymer microstructure and ring diad tacticity varied considerably as a function of the catalyst employed and reaction parameters (Eq. 8.80).

(8.80)

n

I The ring diad tacticities in these polymers, with respect to both cis and t r ~ s double bonds, were determined from ~3C NMR spectra. They found that cis double bonds were always associated with 50-100% r diads (syndiotacticity (o,)~ - 0.5-1.0), while trans double bonds were always associated with 50-100% m diads (isotacticity (o~)t = 0.5-1.0). According to their tacticity, the polymers obtained were divided into four groups: (1) those of high tacticity, with (o,)r -- (om)~ -- 1.0, (ii) those of intermediate tacticity, with (o,)~ - (o~h - 0.6-0.9, (iii) those with (o,)~ > (om)~ (o,)~ >(om~h and (iv) those of low tacticity, with (o,)~ - (o~)t ---0.5. They observed that there was no correlation between tacticity and cis content, but all-cis polymers were generally highly syndiotactic and all-trans polymers slightly isotactir when prepared from 3 M monomer at 20~ Interestingly, the tacticity falls with increasing preparation temperature but not always with decreasing monomer concentration. Taking these results into account, a complete mechanism for the ring-opening metathesis polymerization was developed in order to explain the general features of the reaction stereospeeificity and selectivity. Relevant results concerning the values of cis content, cis-trans blockiness, ring-diad tacticity and head-tail bias in 5,5-

437 dimethylnorbomene polymerization with tungsten-carbene complexes as determined from ~3C NMR spectra reported Kress 19s and Greene. TM 5,6-Dimethylnorbomene. In order to evaluate the microstructure of poly(5,6~imethylnorbomene), the ring-opening polymerization of endo, endo-5,6-~imethyl- and exo,exo-5,6-dimethylnorbomene has been investigated by Kress ~95in the presence of tungsten carbene complexes and by Greene TM with conventional metathesis catalysts. At the same time, ringopening polymerization of endo,exo-5,6~imethylnorbomene has been examined by Greene ~99 using a series of conventional initiators and by Schrock and coworkers zss in the presence of well-defined molytxienumcarbene complexes. Thus, ring-opened polymers of (+)-endo,exo-5,6.~imethyl- and (+)endo, exo-5,6-dimethylnorbornene having cis double bonds contents between 5 and 85% were prepared by Schrock 2" using Mo(=CH ~Bu)(=NArXORh (At = Cd-13-t'r-2,3, OR = OCMe3, OCMe2(CF3), OCMe(CF3h) complexes as initiators (Eq. 8.81). (8.81) f

/

\

The cis content of the polymer was correlated with the electronwithdrawing ability of the alkoxy ligands, maximizing for the most electronwithdrawing hexafluoro-tert-butoxide group of the initiator. Some of relevant data are given in Table 8.17. Table 8.17 Polymerization of (+)- and (+)-endo.exo-5,64unethylnorbomene (M) usm~ nmlybdmum-carbene congdexes as initiators" M [ Catalyst [Yield [ o,r [ M,,/ i T. % I I M, I ~ (+) (+) (+) (+) (+)

Mo(--CH~u)(=NAr)(OC Mesh Mo(=CH~u)(=NArXOCMe3)2 Mo(=CHtBuX=NAr)(OCMe2(CF3h Mo(--CH~u)(=NAr)(OCMe2(CF3)2 Mo(--CH~uX=NArXOCMe(CF3)2)2 Mo(--CHtBuX=NAr)(OCMe (CF3h)2

'Data from reference "~

94 91 96 93 97 95

0.05 0.05 0.58 0.44 0.85 0.85

1.03 1.03 I. 15 1.13 1.20 1.19

55 55 75 71 85 79

438 The microstructure of these polymers has been thoroughly evaluated from ~3C NMR spectra in terms of the various possible diad relationship. They found that lfigh-cis polymer made from 98% (+)-endo, exo-5,6dimethylnorbomene contained 78% m diads (isotactic bias, (Om)~ = 0.78) and displayed more than twice the optical rotatory power and a higher glass transition temperature (T s = 85~ than the Ifigh-trans polymer which contained 48% m diads (atactic, (om)~ ---0.48) and had glass transition temperature T 8 = 55~ 5,6- Oi met h ylen en o rbo rn en r Polymerization of 5,6dimethylenenorbomene has been carried out by Shahada and Feast 2s6 with the catalyst WCldMe4Sn. The polymer obtained was insoluble but its solidstate ~3C NMR spectrum indicated that the reaction occurred by ringopening (Eq. 8.82).

n

~

(8.82)

//

"%

Spiro[cyclopropane-7,1']norbornene, It is remarkable that ring-opening polymerization of spiro[cyclopropane-7,1']norbomene under the influence of metathesis catalysts proceeds readily at the monomer double bond, without affecting essentially the cyclopropane ring (Eq. 8.83).

(8.83) This reaction has been examined by Makovetsky et al. 257 using heterogeneous rhenium-based and homogeneous ruthenium- and tungstenbased catalysts. The best results were obtained with the homogeneous WCldphenylacetylene system which afforded a quantitative yield of poly(spiro[cyclopropane-7,1']norbornene) within a short reaction time (Table 8.18). According to IR and ~H NMR spectroscopic measurements, the main chain structure of poly(spiro[cyclopropane-7,1']norbomene) was usually formed via ring-opening. Significantly, in the IR spectrum of these polymers an intense absorption band at 1010 cm~ and two moderate bands at 840 and 3080 cm~ characteristic of cyclopropane ring were observed.

439 Table 8.18 Polymerization of spiro[cyclopropane-7,1 ']norbomene under the mfluence of maathesis catalysts' Catalytic System

Mollofllcr:

Catalyst, mole

Reaction Time, hr

Polymer Yield, %

[n] dlg-I

0.2 I0 7 0.7 20 53 40 4.0 1000 20 mm I00 WCk/PhC=CH d 'Data from reference'7; ~3 wt.% ~Bu4Sn, toluene, 45~ ~C6HsCI:EtOH 1"1, 60~ dWCl6:Phenylacctylene 1 1, toluene, 20~ Re2OdAlzO3/"Bu4Snb RuCI3.3H20'

350

Likewise, ~H NMR spectra of the polymers indicated the presence of cyclopropane protons (d 0.2-0.45 ppm) along the chain. On the other hand, IR data showed that the microstructure of poly(spiro[cyclopropane7,1']norbomene) thus prepared ranged from all-trans in the case of Rubased catalyst to ca. 85% cis with Re-based systems. Parallel studies on the polymerization of spiro[cyclopropane7,1']norbomene carried out Seehof and Risse25s with the WCIjPh4Sn and RuCI3 as catalysts. The polymers thus obtained had a predominant trans stereoconfiguration for the two catalysts The first catalyst resulted in a o~ = 0.15 and a diad configuration of m / r = 44/56 for trans centered diads of the polymer and the second in a or = 0.05 and a diad configuration of m/r = 38/62 for trans centered diads. It should be mentioned that the polymers obtained from spiro[cyclopropane-7,1']norbornene were completely soluble in hydrocarbon solvents. This fact indicated that the reactive spirocyclopropane group remained intact during the ring-opening polymerization of norbomene moieties and did not participate in the intermolecular cross-linking reactions. Polysubstituted norbornene. A substantial number of polysubstituted norbornene derivatives have been examined in ring-opening polymerization reactions with various catalytic systems. The majority of them bear alkyl or aryl substituents in different positions of the norbomene skeleton. 1,7,7-Trimethylnorbornene. By ring-opening metathesis polymerization of 1,7,7-trimethylnorbomene, a trisubstituted polynorbomene bearing the three methyl groups in the recurring units can arise (F-xl. 8.84).

440

n

n

=

(8.84)

The kinetics of this reaction has been followed by Feast and coworkers 259 by ~3C NMR technique under the influence of the complex Mo(=CHCMe2Ph)(=NC6H3-'Pr2-2,6)(OCMe(CF3)2) in CD2C12 at 20~ (Table 8.19). Table 8.19 R i n g ~ m g polymerization of 1,7,74fimethylnorbomene reduced by Mo(=CHCMeqPh)(=NCtJ-132Prz-2,6)(OCMe(CF3)2)~ Catalyst Concentration

kdl0 -~ s-~

10 [ll,

Monomer:Catalyst [M]./[I].

1.9 2.85 2.6 2.85

5.2 14 23 34

1.02 2.84 3.51 4.12 6.1

'Data from reference 259 Under these circumstances, Feast et al. observed that the reaction of 1,7,7trimethylnorbomene was very slow, a first-order decay of the initiator over 4 half-lives was found while monomer concentration remained almost constant in each experiment. It initially produced the first insertion metallacarbene intermediate and eventually an all-trans, all-head-tail polymer which was isotactic when made from (-)-monomer and atactic when made from (+)-monomer. Bicyclo[2.2.1 ]hepta-2,5-diene (Norbornadiene). Ring-opening polymerization of norbomadiene occurs readily under appropriate conditions to form polynorbornadiene or poly(1,3-cyclopentenylvinylene), a highly unsaturated polyalkenamer (Eq. 8.85).

441 This reaction has been carried out first by Sartori, Valvassori and Faina ~ in the presence of various V- and Ti-based catalysts. The polymer structure, determined by IR spectroscopy, indicated mostly trans stereoconfiguration at the double bonds. Subsequently, Calderon and coworkers ~s~ employed particularly active catalysts for norbornadiene polymerization consisting of WCI6 with or without organometallic compounds. However, the structure of the polymers could not be determined accurately because significant amounts of gel formed on the polymer particles. In another series of polymerization reactions, Schulz 262 used several Ziegler-Natta catalysts which showed to be very active. Notwithstanding, in most cases, both types of polymers, namely ring-opened and vinyl products, were formed by the two reaction pathways of one of the double bonds of the monomer. Significant work on the norbornadiene polymerization, under the influence of a variety of transition metal-based catalysts, was carried out more recently by Ivin~s3 and Rooney. 2~ A number of homopolymers of norbomadiene and copolymers with norbomene have been synthesized in various yields ranging from 15% to 95%. By employing hex-1-erie as chain transfer agent, the molecular weight of these polymers has been regulated to levels that permitted high solubilities in suitable solvents. As a results, they obtained high.quality ~SC and ~H NMR spectra of these polynorbomadienes, analogous to those of polynorbornenes reported earlier. It is important to note that these spectra have been fully assigned and the detailed microstructures of the homopolymers e.g., cis-trans configuration, o~, and m-r diads, have been unequivocally established. Some relevant data obtained with a number of catalysts are given in Table 8.20. As this Table obviously illustrates, the fraction of main-chain cis double bonds, o~, ranged from o~ = 0.9 to a minimum of just under o~ = 0.4, and no catalyst system tried produced polymer with a lower value of o~. It is quite remarkable that OsCl3 as a catalyst afforded essentially all-cis polymers of norbornadiene, in contrast to norbornene, where the cis content was 93% overall recovered yield over two

523 steps) (Eq. 9.14).

F~

(MeCOhO py, 80"C-~

IVleOH TMS

TIVIS

140

OH

. I:.....~

MeCO0

.....~n

(9.14)

OOCMe

Pyrolysis of poly(cis-5,6-bis(acetoxy)-l,3-cyclohexadiene) to high-quality PPP occurred at 310-340~ on NaCI crystals in high yield.(Eq. 9.15).

coc( 'ooc

(9.15)

-2n MeCOOH

The use of acyl derivatives of cis-5,6-bis(hydroxy)-l,3-cyclohexadiene resulted only in aromatization of the monomers and deactivation of the catalyst (Eq. 9.16). n

RCOd \ OOCR

(ANiTFA)2> -2n RCOOH

n

n

_

15% HCl

_

=

(9.106(:)

C~

Tautomerization of the polynaphthoquinonc, under the above conditions, and reoxidation will produce similar polyacetylene backbone polymers (Eq.9.106d).

w D ,

=

(9.1o~)

monomers. Ring-opening polymerization of bis(thiomethyl) derivative of exo, endo-5,6-dimethylnorbornene occurred Sulphur-containing

with the molybdenum initiator Mo(=CHCMe2Ph)(=NAr)(OtBu)2, (At=-2,6'Pr2-C6H3) to give the corresponding polymer of a low polydispersity (PDI < I. l 0) and Tg value of ca. 45~ (Eq. 9.107).

~

CI'I2-SC H3

CH2-SCH3

Mo(CHC MezPhXNArXOtBu)z

(9.1o7)

H3CS-H2C CH2-SCH3

Copolymers with methyltetracyclododecene were also prepared by Schrock and coworkers ~3~ and used to bind metals, e.g., Zn and Cd, in a dative fashion. Interesting results reported Schimetta and Stelzer~4 on the ringopening polymerization of a norbomcncdixanthate, exo, exo-

592 bicyclo[2.2.1 ]hept-5-ene-2,3-bis(S-methyl dithiocarbonate), using the molybdenum carbene initiator Mo(=CHtBu)(=NArXOtBu)2 (Ar=-2,6-'Pr2C6H3).This monomer was readily polymefized with different initiator concentrations to form in high yields poly(bicyclo[2.2.1]hept-5-ene-2,3bis(S-methyl dithiocarbonate) (Eq. 9.108).

s II

Mo(CHtBu) (NAr) (OtBu) 2 OC,-SQ-I 3

= CS_~ "/-'~~O'~~nn ~ H3

s It

s N

(9.108)

-~;H 3

The typical molecular weight distribution was larger for the thia analog (MJM,=1.3) than for the corresponding oxa analog (M,~,K=1.09). However, the molecular weighs increased linearly with the monomer concentration (Table 9.28). Table 9.28 Polymenzauon of exo, exo-bicyclo[2.2.1 ]hept-5-ene-2,3-bis(S-methyl dithiocarbonate) (M) using the molybdenum carbene initiator Mo(=CHtBu)(=NAr)(OtBu)z (I)~

[M][I]

Yield,%

Uw

MJM,

50:1 100-1 200:1

80

30000 60000 114000

1.3 1.4 1.4

90 93

'Data from reference~, bMolecular ratao of monomer and initiator, r against polystyrene standard. Spectroscopic measurements by IR and NMR methods of poly(bicyclo[2.2, l]hept-5-ene-2,3-bis(S-methyl dithiocarbonate) indicated a highly stereoregular polymer with entirely trans stereoeoniiguration of the double bond connections. Thermal elimination of S-methyl dithiocarbonates from poly(bicyclo[2.2.1 ]hept-5-ene-2,3-bis(S- methyl dithiocarbonate) to form poly(cyclopentadienylenevinylene) (Eq. 9.109)

593 n

H3CSS

=

~

(9.109)

SCH3 S

occurred at a lower temperature as compared with the methyl carbonate

analog. Though the accurate structural analysis of the final product poly(cyclopentadienylenevinylene) by NMR method was not carried out due to its insolubility, the polyconjugated structure was based on UV spectra available. Nitrogen-containing monomers. The development of well-defined alkylidene compounds that are both tolerant of functional groups and provide a living initiator for polymerization of strained cycloolefins has spawned further growth in the field of nitrogen-containing polymers. Studies by Perrot and N o v a k 9 o n the highly functionalized N-benzyl cyclobut-3-ene-l,2-dicarboxylic imide showed that this monomer readily polymerized under the influence of the Mo Schrock initiators Mo(=CHR')(=NAr)(OR '') (where Ar = 2,6-'Pr2C6H3 and R ' = R'' = C(CH3)3; R' = C(CH3)2Ph, R' ' = C(CF3hCH3 or R' = C(CH3)2Ph, R' ' = C(CH3h) to produce a highly functionalized polymer, consisting of an imide substituted 1,4-polybutadiene. It is noteworthy that, under these conditions, the polymerizations were quatitative regardless of the monomer:initiator ratio and monodisperse polymers with narrow molecular weight distributions could be prepared. Norbornene substituted with CH2NHR groups in the position 5 has been polymerized using various ROMP catalysts. Ring-opened polymers of substituted norbornene bearing the amino groups in the cyclopentylenevinylene repeat unit have been thus prepared (Eq. 9. 110). n

~7~

CH2 NHR

ROMP

.---

(9.110)

\

CH2NHR When R is H, Me, or 'Pr, appropriate catalytic systems are W(=CPh2)(CO)~tAICI2/O2 and W(CO)3(mesitylene)/EtAICl2/O2 in chlorobenzene at 25~ working with a large excess of cocatalyst (W/AI = 1/140). These polymers have 50% cis double bonds and can be rendered

594 soluble in water by quatemization of the amine groups. TM They can also be made more soluble if pent-l-ene is used as a chain transfer agent. The monomer with R = C6H4NHC6Hs has been used efficiently in copolymers with dicyclopentadiene to act as a built-in antioxidant. ~32 N-Substituted 5,6-bis(methylamino)norbomene has been polymerized with molybdenum initiators to give poly(5,6bis(methylamino)norbomene) ~: (Eq. 9.111).

H2NHR CH2NHR

[Mo] .~

~ RHNH2C

(9.111) CH2NHR

where R is C(CH3)3 or Si(CH3h. These amino-containing polymers have been used to complex Sn(IV), Sn(II) or Pb(II) for manufacture of semiconductor clusters of a predictable size. ~33 Norbornene derivatives bearing the amide group or N-substituted amides have been polymerized with W-based catalysts. 2a~3"3S For instance, 5-dimethylamidonorbom-2-ene reacted for 17 hr under the influence of WCIdEt3Al (1:2) and W(OPh)dEt3Al in chlorobenzene at 70~ using a molar ratio monomer:W of 200, to produce in high yield poly(4dimethylamido- 1,3-cyclopentylenevinylene) 33 (Eq. 9.112).

V h/Et l

W(OPh)ejEt3A/

n

(9.112) \

CON(CH3)2 Glycopolymers were prepared by ring-opening metathesis polymerization of a series of N-sugar-substituted norbomene-5-amides using the ruthenium carbene initiators~34(R3P)3CI2Ru=CHCH=CPh2(R = Ph or Cy) (Eq. 9.113). O

n ]~~NHgluRR'

[Ru] =

~

(9.113) \

NHgluRR'

595 where NHgluRR' =

OR RO'7~OR ~ i I ~ ~O H

and RR ' = H (NBEglu(H)4,-COCH3 (NBEglu(Ac),,-CH2Ph (NBEgluBn),, -SiEh (NBEglu(SiEh)4 and R = H and R ' = -CPh3 (NBEglu(Tr)). The ring-opening polymerization of 2-((• carboxamido)-2-deoxy-D-glucopyranose (NBEglu(H)4) and the protected sugar derivatives based on this monomer, 2-((• carboxamido)-2-deoxy- 1,3,4,6-tetra-O-acetylD-glucopyranose (NBEglu(Ac)4), 2-((_)-exo- 5-norbomene-2-carboxamido)-2-deoxy- 1,3,4,6tetra-O-benzyl-D- glucopyranose (NBEglu(Bnh), 2-((+_)-exo-5-norbomene2-carboxamido)-2-deoxy- 1,3,4,6-tetra-O-triethylsilylD-glucopyranose (NBEglu(SiEh)4) and 2-((• 6-O-trityl-D-glucopyranose (NBEglu(Tr)) to produce high molecular weight polymers bearing carbohydrate moieties has been investigated by Fraser and Grubbs TM using the above mentioned ruthenium carbene initiators (R3P)2CI2Ru=CHCH=CPhz (R = cyclohexyl or phenyl). Under these conditions, these authors observed a totally different reactivity of the series of norbomene derivatives, depending on the nature of pendant sugar group. The unprotected sugar monomer, NBEglu(H)4, did not undergo efficient ring-opening metathesis polymerization in the presence of either catalyst in any of the solvent systems examined (Table 9.29). Table 9.29 Polymerization of 2-((f)-exo-5-norbomene-2-carboxamido)2-deoxy-D-glucopyranose (NBEglu(H)4 with (R3PhCIzRu=CHCH--CPhz (R = cyclohexyl (Cy)or phenyl (Ph))~ |

Catalyst

Solvent

Temp. Time [MI'[E]:[I] ~ days Ph 40 2:1 MeOH/CHzCIz 160:0:1 1 Ph 50 50:0:1 4:1 HzO/CHzCIz 4 Cy 50 3:2 MeOI'FCHzCIz 55:0:1 2 Cy 6:1 HzO/CH2CIz 50 35:3:1 1 9Data from reference~; bM = monomer, E = emulsifier, I = initiator

Yield % 0 0 trace 99

596 The very low reactivity of this monomer was attributed to its poor solubility in all of the solvents compatible with the metathesis catalysts. In addition, the poly[NBEglu(H)4] product was also insoluble in these solvents systems and precipitated from the reaction mixture. This difficulty was overcome by using a different polymerization technique, namely, polymerization in the presence of ammonium halide salts as emulsifiers in an aqueous system. Reaction of NBEglu(H)4 in H20 containing dodecyltrimethylammonium bromide with the ruthenium carbene initiator, dissolved in a small amount of CHzCI2, resulted in polymer product in essentially quantitative yield. Of all the sugar monomers investigated, only the acetate-protected sugar monomer was efficiently polymerized by the less active (Ph3P)zCI2Ru=CHCH=CPhz catalyst (Table 9.30). Table 9.30 PolymerizaUon of 2-((+ )-exo-5-norbomene-2-carboxamido)2-deoxy- 1,3,4,6-tetra-O-ace~l-D-glue~yranose (NBEglu(Ac)4) with (R3P)zCIzRu=CHCH=CPhz(R = cyclohexyl (Cy) or phenyl (1~))~b Catalyst

Yield %

[M][I]

20 hr 20 hr 1 day 1 hr 5min 15min 15mm

110:1a 35:1 50:1~ 40:1 30:1 50:1 20:1 f

Ph Ph Cy Cy Cy Cy Cy I

|

gel 50 gel 71 68 gel gel

M~I0 "~

M,,xI0"

PDI ~

4r

1.87

2.63

1.40

1.34

3.02 2.70

2.25 2.09

1.31

Io

Xion conditions: CHzCIz:50 C; [M] = 0.14-0.18 M; "Data from'referencel"; bReactir By GPC, polystyrene calibration; a [M] = 0.5 M; ~25~ [M] = 0.45 M; f Cd'k.

r

In these experiments it was observed that the acetate polymers were very prone to gelation. The gels swelled upon addition of organic solvents such as CHzCI2, but they did not dissolve in any of a number of common polar or nonpolar solvents that were tested. With both catalytic systems, soluble poly[NBEglu(Ac)4] was obtained for lower monomer to catalyst feed ratios (

(11.2S3)

It was found that the metathesis polymerization of dicyclopentadiene, which is very fast and exothermic in these conditions, can be controlled by the addition of 5-cyano-2-norbomene. Though the cyano monomer delayed the polymerization at room temperature, at high temperatures the process was accomplished in reaction injection moulding time. The effect of incorporation of nitrile monomer onto the physical and mechanical properties of the copolymer was clearly outlined. The similar effect of 5cyanonorbomene has been encountered in the copolymerization reaction with methyltetracyclododecene carried out in the presence of W-based catalytic systems (Eq. 11.253a). n

f.~

CN

§ m

~

tCaAq "-

(11.253a)

819 Copolyalkenamers from 5-cyano-2-norbomene and a variety of substituted norbornenes have been prepared using classical W- and Mbased catalysts as well as more tolerant well-defined W and Mo alkylidene initiators ~ ' ~ (Eq. 11.254).

n

9rn

.=

(11.254) CN

R

where g is an alkyl, aryl, ester, amide, imide, halogen or anhydride group. With the aim of studying the influence that 5-cyano-2-norbornene will exert on the thermal and mechanical properties of the final product, copolymers of exo-5-norbomene-2,3-dicarboxy-N-phenylinfide and 5-cyano-2norbomene have been prepared by Asrar 22a with the classical tungsten/alkyl aluminium catalyst (Eq. 1 1.255).

/

n~CN+

J~ -COx m/.~co~N ~

[W/AIL ..~

N\

O(3 CO (11.255)

NC The glass transition temperatures, T s, of these copolymers ranged between those of the two homopolymers, increasing linearly with the N-phenylimJde content. The thermograms showed a change in the specific heat only at one temperature, indicating that random copolymers were produced which form a single-phase system. Block copolymers of mcthyltetracyclododecenr with methyl dithioether of trans 5,6-dimethyl-2-norbomcne were prepared by Schrock by living ring-opening metathesis polymerization in the presence of the molybdenum initiator Mo(=CHCMe2Ph)(--NAr)(O'Bu)2 (Ar = 2,6-C6Hr 'Pr2)2~ (Eq. I 1.256). e

+

m

~

~]

=

(11.256)

820 The products, characterized by GPC and tH NMR and TEM, exhibited a low polydispersity (PDI

[BF3]'['I'iCI4]

(12.4)

structure

The of poly(1,3-cyclohexadiene) synthesized with SnCIJCCI3COOH or BF3.OEt2 initiators in methylene chloride and benzene as solvents at 0~ has been more thoroughly examined by Imanishi and coworkers. ~3 The polymers were soluble with intrinsic viscosity [11] - 0.040.12 and softening range of 104-130~ The microstructure did not seem to be influenced by the nature of the initiator. According to NMR spectra, about 20% of the unsaturation was lost. The authors suggested that chainbranching might be responsible for this result. While there was strong evidence for 1,4- and 1,2-enchainmnents, no quantitative analysis as to the relative amounts of these structures was given. Polymerization of l-methylene-2-cyclohexene with various cationic initiators (BF3, BF3.EteO, TiCh, AICI3, EteAICI and VCh) gives rise to polymers with essentially 1,4-enchainments, accompanied by minor amounts of 1,2-1inkages~4'~s (Eq. 12. 5).

n H2C-----~--~

[Cat]

,E-cH2,~~.~

(12.5) chloroform

The white, powdery products were largely soluble in and benzene and could be solution cast to flexible films. The polymers were amorphous, with a softening range between 80-82~ Polymerization of 1vinylcyclohexene induced by BF3.EteO and SnCIVCCI3COOH (TCA) in toluene and methylene chloride at 0~ produced soluble, white, low molecular weight polymers, M,-- 1200 (DP--- 11) ~6. These properties remained almost unaffected by the reaction conditions. The structure of poly(l-vinylcyclohexene) was investigated by bromination, IR and NMR methods. The spectra indicated a preponderance of 1,4-enchainment accompanied by some 1,2-1inkages in the polymer prepared by SnCIdTCA

881 (Eq. 12.6).

SnCI4/TCA .._

+

(12.6)

Somewhat different occurred the polymerization of 4vinylcyclohexene in the presence of cationic initiators, for example, BF3, BF3.OEtz, and TiCh. The polymerization with BF3 gas in methylene chloride at -70~ led to 28% conversion of product, of which 85% was soluble and had an intrinsic viscosity [11] = 0.11. NMR spectroscopy indicated a polymer structure with at least two repeat units in about equal amounts ~v(Eq. 12.7). BF3

..=

[ §

~.~

(12.7)

Alternatively, the polymerization of 4-vinylcyclohexene with BF3.OEtz in methylene chloride at 0~ led to 35% conversion and to a completely soluble product of very low molecular weight (intrinsic viscosity [11] = 0.03). NMR spectra indicated c a . 80% cyclization.. The structure of oligomers obtained from d-limonene and tz-pinene in the presence of AICI3 probably corresponded to vinyl-type recurring units and equal amounts having bicycloheptane skeleton (Eq. 12.8)

y

i r

l

§

(12.8)

882 because ozone absorption indicated only 0.4-0.5 double bonds per repeat unit. ~8 The microstructure of polymers prepared from 1,3-cyr with TiCL~, TiCIdTCA, SnCIdTCA and BF3 initiators in methylene chloride and toluene as solvents at -78~ have been investigated by Imanishi et al. ~9 by infrared and NMR spectroscopy. The structures obtained with different initiator systems were essentially the same, however, the nature of the solvent significantly affected the enchainment. Thus, in methylene chloride, polymerization gives almost exclusively linear 1,4-enchainment and no branching (Eq. 12.9)

while in toluene there was 1,4-enchainment accompanied by branched polymer. Whether the branch sites were 1,2 or 1,4 units, that could not be determined. The products were white, amorphous powders of low intrinsic viscosity, [11] = 0.10 and softening range of 172-184~ The linear polymers obtained in toluene solvent were soluble in aromatic and chlorinated hydrocarbons, however, the branchy materials were insoluble, indicating cross-linking. The structure of polymers prepared from bicyclic and polycyclic olefins with cationic initiators is more complex due to the secondary reactions induced by the initiator on these type of monomers. Of such reactions, hydrogen migrations and skeleton rearrangements, under the influence of cationic initiators, are the most significant. A first example is the polymerization of u-pinene in the presence of various FriedeI-Crafis catalysts such as BF3, AICI3, AIBr3, ZrCL in toluene at 40-45~ leading to different polymers as a function of the catalyst employed. ~8 The oligomeric products resulted from ~-pinene in the presence of AICI3 at 40~ have similar properties (e.g. density and refractive index) to those obtained from d-limonene, it was suggested that they are limonene oligomers because prior to oligomerization, r is isomerized to d-limonene (Eq. 12.10).

883

AIC ~...~

AlCh

40oc v

.

40~

(12.10)

Norbornene gives readily polymers with cationic initiators having different bicyclic recurring units, depending on the initiator employed. In the presence of EtAICIz in ethyl chloride at o78~ and o100~ white, soluble solids were obtained (M~ = 1470 and 1940 and softening points 235~ and 260~ respectively) which were found to be amorphous by x-rays. It was inferred that the structure of polynorbornene was a mixture of bicyclic recurring units formed by isomerization of the norbornyl skeleton prior to propagation, e.g., syn, exo-norbornane along with normal 1,2-addition product 2~(Eq. 12.11).

[Cat]=

(12.11)

,

In contrast, polymerization of methylenenorbornene by the use of EtAICI2 and AIBr3 as catalysts at -78~ and VCh at -20~ in n-heptane gave a soluble, crystalline (by X-rays) polymer ([q] = 0.3, softening range 150160~ whose structure (by infrared spectra) corresponded to nortricyclic recurring units 2~ (Eq. 12.12).

n

%•

EtAICI2 -~

[ ,~~,., ~-]-n

(1212) "

The structure and physical properties of polynorbornadiene obtained with AICI3 in ethyl chloride and methylene chloride at various temperatures (+40~ to -123~ are sensitive to the polymerization temperature of norbornadiene. ~ The dependence of the benzene soluble fraction and molecular weights on the reaction temperatures can be observed in Table 12.1.

884 Table 12.1 Polymerization of norbomadiene with AICI3 at various temperatures' 9Ten~erature~ ~

Solvent Time, mm Yield, % Benzene soluble fraction, % Mn of soluble fraction Melting behavior Crystallmity (x-ray) Ts,~

+40

-123

-78

C2H~CI 37 17,2

C2H~CI 25 42.0 72.5 8680

C2H5C1 29 71.0 34.5 3680

Dec.

Dec.

100

5520 9850b Dec. Amorphous 320

CHzCI2 4 30.0 59 2980

'Data from reference 22;bPrcpar~ at - 12 7~

Only the polymer prepared at -123~ was completely soluble in benzene. The structure of the polymer was investigated by infrared and NMR spectroscopy and from these data it was concluded that linear polynorbornadiene essentially consisted of 2,6-disubstituted nortricyclene repeat units (Eq. 12. 13). AICI3 .~ "-

r

"l j

L

(12.13)

-1230C These authors suggested that cross-linked polymer, which is insoluble in common solvents, will arise at high temperatures by "2,3-type" reactions (Eq. 12.14).

[

AK~j +40~

] (12.14)

[

The physical transitions of the linear polynorbornadiene of M. = 9850 have been examined by torsion braid analysis, z3 The thermomechanical spectrum of this polymer, determined at less than 1 r in the range -180~

885 to +500~ revealed the glass transition temperature to be 320~ which is one of the highest known Ts for a hydrocarbon vinyl polymer. 5-Vinylnorbomene reacts at -78~ with EtAICI2 to form white powdery product with M~ ~ 4020, largely soluble (78%) in toluene. Analysis by infrared spectroscopy indicated the presence of 1,2 recurring units in the polymer but also a rearranged structure might be present, formed by the isomerization of the norbomene skeleton 2~(Eq. 12. 15).

m

(1215)

+

-71~C

]

At higher temperatures (-30~ predominantly insoluble polymer was produced with the above catalyst, indicating that a cross-linking reaction of the vinyl groups occurred under these conditions (Eq. 12.16). --

t

]

~--

E (1216)

+ ]

Likewise, polymerization of 5-isopropenylnorbomene with EtAICI2 in ethyl chloride in the range of temperatures-30~ to -100~ gave readily insoluble products, having a cross-linked structure (Eq. 12.17).

-

E\

I ~

-100"C

x]

§

]

(1217)

Evidently, in this molecule the reactivities of the two kinds of double bonds are comparable so that cross-linked polymer is formed even at a temperature of- 100~ Very low molecular weight oligomers (M~ - 540, softening point 85-95~ were obtained from 2,3-dihydro-era/o~icyclopentadiene with EtAICI/BuCI (11) initiator in methylene chloride at -78~ Infrared and

886 NMR spectroscopy indicated that polymerization occurred through hydride migration z4 (Eq. 12.18).

-78~

]~~~__ ] ,

,,,=

(12.18)

[

At the same time, white products with M~ of 1670 and 2150 and sottening points 265-280~ have been obtained from 5,6-dihydro-endodicyclopentadiene with EtAICI2/'BuCI (1"1) initiator in methylene chloride at-20~ and -78~ respectively. Infrared analysis showed no evidence for double bonds occurrence in the polymer chain and consequently the polymer structure seemed to involve double bond opening of the norbomene ring system with possible rearranged norbomyl repeat units (Eq. 12.19).

~

E~.~

-7s'c

§ [

[

[

(12.19)

Interestingly, cationic polymerization of exo- and endodicyclopentadiene in neat system with BF3.OEh at room temperature leads 25 to distinct poly(dicyclopentadiene)s as a function of the starting monomer. Thus, reaction of exo-dicyclopentadiene in the above conditions gives rise to poly(dicyclopentadiene) with 2,3-enchainment of the norbornene ring

(Eq. 12.20)

/~~

BF3/Et20 RT

.~~

(12.20)

[

whereas that of endo-dicyclopentadiene forms polymer with 2,7enchainment of the norbomene ring resulted by a Wagner-Meerwein rearrangement of the norbornene skeleton (Eq. 12.2 1).

B F 3/E t20

RT ~

[

3

(12.21)

887 By contrast, reaction of endo-dicyclopentadiene in methylene chloride diluent in the range of temperatures + 10~ to -78~ by the use of a variety of cationic initiators (e.g. AICI3, EtAICIz, EtAICI~BuCI, BF3, TiC~ SnCL~, EtzAIC~BuCI), gave white powdery, soluble polymers whose structures (by infrared and NMR spectroscopy) indicated norbomane and nortricyclene structures as repeat units z4(Eq. 12.22). "~'I~3"I~'~ [ (1222) +10to-l(XT13 The products have molecular weights in the range of ]300-4450 and softening points between 180~ and 320~ Tetracyclo[4.4.0.12,5. l ~ ~~ (di-endo-methylene octahydronaphthalene) has been polymerized with the catalyst EtAICI/BuCI in neat system at various temperatures (+ 10~ to -50~ to form white, powdery, low molecular weight polymers, M~ = 660-1070, having glass transition temperatures between 260~ and 275~ Structural analysis by ~3C NMR (see Figure 12.2, full spectrum (A) and olefinic region =v

C-7, C-IO PTCD

Qleltnic carbon

]

I

~H2 tn

1

C_H3

65 60 6 in p p m

55

50

t. 5

~.0

3.5

30

25

Z0

Figure 12.2. ~3CNMR spoctra ofpoly(tetracyclo[4.4.0.1~'5.1~.~o]dodec-3-ene) (PTCD) obtained with EtAICI~BuCI as catalyst (Adapted from Ref.~) (B)), revealed the presence of both 3,4- and 3,1 l-addition repeat units in the polymer chain (Eq. 12.23).

888

= +10t0-50~

*

(12.23)

[

Somewhat different occurred the reaction of tetracyclo[4.4.0.1 z,s. 1~~~ 2v (di-endo-methylene hexahydronaphthalene) with BF3.OEt2 in neat system at room temperature. It led to a completely soluble and saturated polymer of M~ = 1050, whose structure involved a half-cage recurring unit formed by a transannular reaction (Eq. 12.24).

n

BF31Et20 ~ RT

(12.24)

In

Indene and its derivatives are readily polymerized by a variety of cationic initiators (BF3, TiCh, SnCh, SbCI~, Ph3C+SbClf) to linear and branchy high molecular weight polymers whose structure corresponded mainly to a 1,2-addition reaction z8 (Eq. 12.25).

n [ ~ ~

BF3'TiCl4'SnCh'SbCI5

[

~n

(1225)

The softening points of such products were in the range 240-260~ Above these temperatures, the polymers exhibited a tendency to yellow and oxidize and could be molded into brittle films.

12.1.2. Anionic Polymers The structure of polymers obtained from cycloolefins by anionic polymerization is more well-defined as compared to the cationic polymers. The nature of anionic catalysts and of monomers prevent secondary isomerization or rearrangement reactions that would affect the polymer structure. As a results of these features, vinyl polymers formed by 1,2-

889 enchainment are normally produced from cycloolefins with one or more non-conjugated double bonds in the presence of anionic catalysts (Eq. 12.26).

[An] .~

n (C

[ /,,~. ~Jn "1

(12.26)

(CH2)x By contrast, polymers obtained from conjugated cyclic dienes with anionic initiators consist mainly of 1,4 recurring units (Eq. 12.27)

n (CH2~/

[An]

=---

rL/~- -/ \ Jn ~ (CH2)x

(12.27)

accompanied, in many cases, by a certain amount of 1,2 recurring units (Eq. 12.28). (CH2)~x

[An]

~

] [/ \] (CH2)x (CH2)~

(12.28)

Examples of such anionic polymers are those prepared from cyclopentadiene, 1,3-cyclohexadiene and 1,3-cyclooctadiene, under the action ofn-butyllithium ~ (Eq. 12.29). ~

n

nB uLi

..~

r ~

I

(12.29)

Of a particular interest is the structure of polymers produced from substituted and unsubstituted silacycloalkenes in the presence of anionic initiators. Thus, l,l-dimethyl-l-silacyclobutene gives with n-butyllithium and hexamethylphosphoramide as initiator a ring-opened polymer poly(1,1dimethyl-sila-cis-but-2-ene) 3~(Eq. 12.30). Me I

n

Me--S! I] [

nBuLtlHMPA=_THF,-78~

Me

[

sli~='w'~ i I Me

Jn

(12.30)

890 l-Silacyclopent-3-ene forms also poly(l-sila-cis-pent-3-ene) in the presence of methyllithium and hexamethylphosphoramide in tetrahydrofuran at a temperature of-78~ as evidenced by ~H-, ~3C- and ~Si-NMR spectroscopy sl (Eq. 12.31).

n

M

%H/O

L

EA

THF,-78~

~

[

HI H

-1

-In

(12.31)

Similar ring-opened polymers have been prepared from 1,l-dimethyl-1silacyclopent-3-ene 32 and l-methyl- 1-phenyl- l-silacyclopent-3-ene 33 under the action of n-butyllithium and hexamethylphosphoramide as a catalyst (Eq. 12.32-12.33).

n

Me /

]'1"1=, -78~

Me~s.~

nBuLi/HMPA ~ THF,-78~

ph/ ~

(12.32) Me Me

-'[---i--/---

.~

(12.33)

Ph

12.1.3. Ziegler-Natta Polymers It is expected that cycloolefins will form polymers by addition reaction in the presence of Ziegler-Natta catalysts. The structure of these polymers would generally correspond to a 1,2-type and 2,1-type cis insertion. Such structures have been found in the polymerization reactions of the majority of mono- and polycyclic cycloolefins with the classical Ziegler-Natta systems based on the transition metal salts and organometallic compounds. 4 Though with special Ziegler-Natta catalysts, e.g. metallocenebased systems or particular monomers, other polymer structures (by 1,3- to l,~addition reactions and with rearranged recurring units) can result. Using a large range of classical catalysts based on transition metal compounds and organometallic compounds, Natta and coworkers 35 found that cyclobutene can form poly(cyclobutylenamer) by vinyl

891 polymerization, polybutenamer by ring-opening reaction or both structures by the two competitive pathways, depending on the catalyst employed (Eq. 12.34).

VCI~HexaAI T~CL~E~I

nl il

=

r

I

-~

q

~

(12.34)

TiC~JEhAI

The vinyl and ring-opened structures of these poly(cyclobutene)s have been evaluated from infrared and NMR spectroscopy. More recent work on the structure of poly(cyclobutene) obtained with metallocene catalysts reported Kaminsky and coworkers. ~s For instance, poly(cydobutene) prepared with ethylenebis(TILindenyl)zirconium dichloride/ methylaluminoxane in toluene is a crystalline product as evidenced by the two peaks 1 and 2 of curve (A) in the X-ray spectrum (Figure 12.3)

(A)

10

16

22

2e o

28

Figure 12.3. X-ray spectrum of poly(cyclobutene) (PCB) powder prepared with the ethylmebis(rlLmdmyl)zir~ium di~loride/methylalummox~e eatalys't

(A~~

from gef.~

and exhibits a high melting point, Mp = 485~ The solid state ~3C NMR spectrum (B) displays also two characteristic peaks, 1 and 2, at/5 = 27 and 40 ppm, respectively, resulting from the CHz and CH groups of the fourmembered ring (Figure 12.4).

892 2

140

120

100

80

(~0

40

20

0

PS~

Figure 12.4. Solid state ~3CNMR spectnun (75 MHz) of poly(cyclobutene) (PCB) prepared with the ethylenebis(rlS-mdenyl)zirccmium dichloride/methylaluminoxane catalyst (Adapted from Ref.~. In a similar way, Natta and coworkers 37 showed that cyclopentene forms, in the presence of various classical transition metal catalysts, poly(cyclopentylenamer) by vinyl polymerization, polypentenamer by ringopening reaction or both structures by the two pathways, as a function of the catalyst employed (Eq. 12.3 5).

V~4/Et~,I

=

~

(12.35)

~CI4/EhJ~,I

The polymers were either amorphous or crystalline products, depending on the catalyst and reaction conditions. More recently, Kaminsky and

893 coworkers 38, using the chiral catalyst ethylenebis(TiS-indenyl)zirconium dichloride,/methylaluminoxane, prepared highly crystalline isotactic poly(cyclopentene) with a fairly high melting point (395~ (Figure 12.5, zone (A) and (B)). (A) (l) I~P

(B) (20)

(s~:, ~

~000 50"

jl-~tl~~

700 355" 600 570 3SO'"

.~

' 0 0 J' 0"9~ 320 2 22O 25O'-

100 200"

(~) (~

~9".5

~

(28)

Figure 12.5. X-ray diagram using synchrotron radiation of poly(cyclopmtme) (PCP) prepared with ethylenebis(rls-mdenyl)zirconium dichloride/methylaluminoxane (Adapted from Ref.3s). The product is insoluble in common hydrocarbons. Based on the infrared spectra, Debye-Sherrer photographs and ~3C NMR spectra in the solid state, these authors concluded that poly(cyclopentene) can be described by two distinct structures, I and II (Scheme 12.6).

j I

II

Scheme 12.6

894 The assignments of these two structures in the solid state ~3C NMR spectrum ofpoly(cyclopentene) can be observed in Figure 12.6 (A) and (B). C13 - S - NMR

l:~P C13 - AP.T,

- NMR

H -"fH

I

(B)

ii I

'

,

I"

,i

""1

iiii:........ "

""~'." "~ "e

"~~ ~176

(A)

180

140

100

60

20

-20

ppm

Figure 12.6. Solid state ~SCNMR spectrum (A) and (B) ofpoly(cyclopcntcne)~s In contrast to these data, Collins and coworkers 39 showed that cyclopentene in the presence of rac- ethylenebis(rlS-indenyl)zirconium dichloride/methylaluminoxane system forms oligomers and polymers by cis1,3 insertion of the monomer (Eq. 12.36)

~~

Et(Ind)2ZrCI2/MAO .~

(12.36)

whereas using the catalyst system rac-ethylenebis(clstetrahydroindenyl)zirconium dichloride./methylaluminoxane both cis- and trans-l,3 insertion structures can arise (Eq. 12.37).

895 (12.37)

Interestingly, this was the first report of a trans "insertion" product being formed in cycloolefin polymerization using homogeneous Ziegler-Natta catalysts. To reduce the melting point of poly(cyclopentene), copolymers with ethylene have been synthesized using ethylenebis(rlS-indenyl)zirconium dichloride/methylaluminoxane, Et(IndhZrCl2/MAO, as the catalyst 4~ (Eq. 12.37a). +

~

II

(12.37a)

Sequence analysis by ~3C NMR spectroscopy indicated the presence of 1,2cyclopentylene-cthylene units. In the spectra of copolymers with 28% mole cyclopentene monomer units, minor amounts of short blocks can be observed, consisting of two cyclopentene moieties (Figure 12.7). S

S

T

T

S

-CH)-CH)~CHz-CH C S ~ C :m C+

_

S

oh.,o

i Pc

+,l

l-

Slhl /SILO

br onc hk~g

Tu \+ 11 T ~

,,5

s

4o

3~

3o

2"5

porn

Figure 12.7. S3CNMR spectrum of c~olymer of cyclopentene (CP)

with ethylene (ET) prepared with ethylenebis0lS-mdenyl)zirconium dichloride/m~ylalummoxane (Adapted from Ref.4~

896 The fact that the polymer structure results from a transannular rearrangement of the monomer in the Ziegler-Natta polymerization was reported by Bokaris, Siskos and Zarkadis 4~ in the reaction of 1,5cyclooctadiene induced by cationic metaUocene catalysts CpzMCI~q~t3AI,EtzAICI, Et3AIzCI3 (M=Ti,Zr, Ht). By the use of infrared and ~H NMR spectroscopy, these authors showed that poly(1,5cyclooctadiene), obtained in the above conditions, contained bicyclo[3.3.0]octane or bicyclo[4.2.0]octane as repeat units (Eq. 12.38).

n

)

cp2uc~t~ =

or

(12.38)

The structure of polymers prepared from bicyclic and polycyclic olefins with the Ziegler-Natta systems depends largely on the catalyst employed. Relevant work has been conducted with norbomene and norbornene-like monomers in the presence of various Ziegler-Natta catalysts. Thus, in their early report, Anderson and Merckling 42 showed that norbornene under the action of TiCldLiHepdd gives rise to a mixture of saturated and unsaturated polymers whose structure was not fully elucidated at that time. Later on, Truett e t al. 43 proved that norbornene yields, with the above catalyst, saturated polynorbornene by vinyl polymerization and unsaturated polynorbornene by ring-opening polymerization (Eq. 12.39).

AI:TiI

The vinyl polymerization occurred when the molar ratio AI:Ti 1. Significantly, the unsaturated polymer displayed better elastomeric properties and a higher

897 crystallinity than the saturated polymer. More recent work on the polymerization and copolymerization reactions of bicyclic and polycyclic olefins using various Ziegler-Natta systems evidenced formation of vinyl polymers and copolymers by 1,2insertion mechanism ~ (Eq. 12.40)

C

(CH2)x

Z-N =

(CH2)x

(12.4o)

where n may be zero and an integer and x is an integer greater than 1. The copolymers with ethylene are amorphous and transparent with a glass transition temperature between 120~ and 160~ and they can be used as proper materials for optical discs and fibers. The structure of the norbornene-ethylene copolymers can be readily evaluated from the characteristic chemical shifts displayed in the ~3C NMR spectra (Figure 12.8). CH

2

-- C h a i n

r

!

3

Figure 12.8. ~3CNMR spectnun of norbomme-cthylene (NB/ET) copolymer prepared with ethylenebis(rls-mdmyl)zirconiumdichloride/methylalummoxane (Adapted from Ref.~

898 The variable content of norbornene incorporated into the copolymer norbomene/ethylene prepared with different metallocene catalysts is clearly illustrated by the splitting of each of the four characteristic norbomene ~3Csignals ~ (Figure 12.9).

P0qB/ET)

60

55

So

~

4o

3S

3o

2

1

55

So

~,

40

X~

~

ZS pore

Figure 12.9. ~3CNMR spectra ofnorbomene-ethylene (NB/ET) copolymers prepared with two zirconocene catalysts (l-MezSi[Ind]zZrCIzand 2PhzC[Fluo][Cp]ZrClz) (Adapted from Ref +6) The splitting of each norbomene ~3C signal in these spectra is due to the formation of short blocks of norbomene in the copolymer. For the copolymer 2 additional peaks in the range of 36-40 ppm can be observed. Based on the t3C NMR results of norbornene dimers and trimers it can be shown that these additional signals are a consequence of the formation of longer norbomene blocks. Further investigations by WAXS and differential scanning calorimetry confirmed the above results. The WAXS diagrams for polynorbomene and copolymers of norbomene with ethylene are

899 illustrated in Figures 12.10 and 12.11. Countrate, [a.u.]

./~'~176 9 !

Angle 2| Figure 12.10. WAXS diagrams for polynorbomene prepared with various zirconocene catalysts (I-Ph2C[Fluo][Cp]ZrCI2, 2-Me2Si0nd]2[Cp]ZrCl2)

(Adapted from Ref.") It can be observed that the copolymer prepared with Ph2C[Fluo][Cp]ZrCl2 as a catalyst, which exhibits only a glass transition temperature, has the WAXS pattern of an amorphous halo compound. In contrast to this Countrate [a.u.] !

o

~,

Io

15

2o

2-5

s-o

35

40

Angle 20 Figure 12.11. WAXS diagrams of norbomene,,ethylene copolymers prepared with various zirconocme catalysts (1-Me2Si[Ind]2ZrCl2; 2-Ph2C[Fluo][Cp]ZrCl2) (Adapted from Ref.46)

900 product, the WAXS diagrams of the copolymers prepared with Me2Si[Ind]2ZrCl2 and of polynorbomene prepared with Ph2C[Fluo][Cp]ZrCl2 and Me2Si(Fluo][Cp]ZrCl2 as catalysts, show two patterns due to the existence of the amorphous polynorbomene region. The formation of distinct blocks in these eopolymers has also been confirmed by DSC experiments. The structure of the copolymers prepared from dimethanooctahydronaphthalene and ethylene, in the presence of ethylenebis(rlLindenyl)zirconium dichloride/methylaluminoxane as the catalyst, 36 have been also evaluated by t3C NMR spectroscopy. The t3C chemical shifts assigned to dimethanooctahydronaphthalene skeleton in a copolymer with 7% mole of this monomer incorporated into the polymer chain are illustrated by spectrum (A) in Figure 12.12. f

P(DMON/ET) CH2

2

(A) i

sO

- 7o

LI

I

S 7

,i

!

eo

i

IJL

.

.

.

.

sO

.

.

!

40

3o

' "

pp,.

Figure 12.12.13C NMR spectrum of ~anooctahydronaphthaleneethylene (DMON/ET) copolymerprepared with ethylenebis(qLmdenyl)zirconium dichloride/methylalummoxaneas the catalyst (Adapted from Ref.

901 The copolymerization products are amorphous at room temperature, insoluble in hydrocarbons and display a high glass transition temperature. These materials have excellent transparency, thermal stability and chemical resistance and are suitable for optical applications.

12.1.4. ROMP Polymers The structure of polymers prepared by ring-opening metathesis polymerization (ROMP) commonly known as polyalkenamers concerns the position, steric nature, ratio and distribution (random or blocky) of the ~ o n - c a r b o n double bonds as well as the polymer tacticity (isotactic, syndiotactic, atactic and head-head, head-tail, tail-head enchainment). Ozonolysis. Of the chemical methods suitable to examine the structure of polyalkenamers, ozonolysis is one of the most convenient and precise methods for the determination of the double bonds in the polymer chain. Two approaches of this method have been widely employed i.e. total and partial ozonolysis. The first approach allowed Eleuterio 4~ to isolate cyclopentane-cis-l,3-dicarboxylic acid by the oxidative degradation of polynorbornene prepared with heterogeneous catalysts (Eq. 12.41).

[o]

n

(12.41)

This result unequivocally demonstrated for the first time that norbornene polymerization, under the action of heterogeneous molybdena catalysts, occurred by ring-opening at the C=C double bond of the monomer. By the same approach, Natta and coworkers 4s isolated the monomer units in the form of ot,co-di~xylic acids, e.g., glutaric acid in the case of polypentenamer (Eq. 12.42).

4-vv

[o]

n

I-IOs

(12. 42)

However, the oxidative ozonide cleavage used to obtain such acids was accompanied by undesired side reactions, which can be avoided by the reductive cleavage with NaBH4. This more convenient method was therefore preferred in succeeding work on the chemical degradation of

902 polyalkenamers. It is significant to note that the exclusive presence of ozonolysis products, having the same methylene sequence length as the starting cycloolefin, showed that no appreciable shift of double bonds accompanied the ring-opening polymerization reaction. Similar results obtained in the polymerization of alkyl substituted cycloolefins are also of particular relevance. The presence of ozonolysis products, having a methylene sequence length different from that of the starting cycloolefins, should indicate double bond migration, especially as a consequence of irradiation of polymers, stored over long period of time. Using the ozonization and reductive degradation, Dall'Asta and coworkers 49 demonstrated that the structure of copolymers prepared from isotopically labeled cyclopentene and cyclooctene was formed by ringopening polymerization. Thus, the nature of the final glycols resulted after ozonization and reduction indicated the positions of the carbon-carbon double bonds in the copolymer (Eq. 12.43).

(1Z43)

By a similar way, the products obtained by oxidative degradation of the copolymers prepared from t4C-labelled cyclobutene and 3methylcyclobutene indicated that the structure of the copolymer corresponded to ring-opening copolymerization.(Eq. 12.44).

.~j~.~

[CII~II = n~ , . ~ ~

,n ~

~

(12.44)

The second approach used by DaU'Asta and coworkers 5~ for structure determination of cycloolefin polymers is based on a partial ozonization technique. In this case, in addition to the normal ozonolysis products, dimeric and trimeric compounds will be formed, in which two or three monomer units are linked together by non-ozonized polyalkenamer double bonds. Examination of the nature of such dimeric and trimerir cz,r~ diols, resulted from copolyalkenamers, is an important method for the determination of the degree of randomness of copolyalkenamers. This method, applied to homo- and copolyalkenamers containing alioyl

903 substituents, allowed Dall'Asta and coworkers 5~ to draw important conclusions about the tacticity of substituted copolyalkenamers. Chemical degradation. An efficient chemical method for the structure determination is the polymer degradation induced by metathesis catalysts in the presence or in the absence of an acyclic olefin. Unsaturated polymers can be converted metathetically to fragments of low molecular weight by a controlled reaction with olefms. Since the scission of the polymer backbone occurs at the double bonds, analysis of the degradation products enables establishing the structure of the polymer. This technique has been first applied by Michailov and Harwood 52 to structure evaluation of 1,4-polybutadiene and styrene-l,4-polybutadiene copolymers, which were fragmented with excess 2-butene in the presence of WCIdEtOH/EtAICI2. The amount of 2,6-octadiene provided a measure of the 1,4-butadiene units (Eq. 12.45) ....

I

I

I

I

!

(12_45)

w--

! !

I

I

!

'

I

whereas the amount of 5-phenyl-2,8-decadiene and 4-phenylcyclohexene a measure of 1,4-butadiene-styrene-1,4-butadiene triads (Eq. 12.46).

.--

~

/5 / ,

!

r

....~

9~

.... 0246)

/X/ ii

At the same time, Hummel and coworkers 53 used an analogous technique to determine the possible double bond migration in the vulcanized polybutadiene and polypentenamer during vulcanization process or to measure the rate of penetration of swollen polymer gels by a solvent. A more selective approach has been applied by Thorn and coworkers s~ in the quantitative metathetic degradation of rubbers and sulphur cross-linked rubbers, including tires. These authors used Grubbs and Schrock tungsten alkylidene catalysts and 3-hexene as a scission agent. Metathetic

904 degradation of cis- and trans-1,4-polybutadiene showed that the fragments were not affected by the steric configuration of the polybutadiene sample. In both eases, the same ratio of the three possible isomers of deca-3,7-diene was observed after thermodynamic equilibrium was reached (Eq. 12.47). I I

....

I I

[W=O'F~

I

...." - , , ~ x j

=

§ ~

/

I

....

(12.47)

/

, I

'

I

The structure of the cyclic isoprene trimer (ttt-(CsHsh) obtained from polyisoprene degradation under the action of tungsten-carbene initiator W(=CHPh~ in the absence of acyclic olefins (Eq. 12.47a) ..

[

.

~

~

"

..

[V~O~ =

(12.47a)

n

has been determined using a combination of analytical methods such as gas chromatography/m~s spectrometry (C_~B~tS) and ~3C NMR spectroscopy (see spectrum (A) in Figure 12.13). 55

5 3

2

5

u

leo

14o

.q_

12o

1oo

8o

60

zo

o pcm

Figure 12.13. ~3CNMR spectnun ofttt-(C~'l=)3 isomer obtained by melmhetic degradation of 1,4-polyisoprene with tungsten carbene catalysts"

905 The ~3C NMR spectrum shows five distinct lines due to two olefinic carbons and three different aliphatic carbons which evidenced the structure of ttt-(CsI'h)3 isomer. Oligomer analysis. An efficient method for the determination of the chemical structure of the fraction of oligomers obtained from cycloolefins and polyalkenamers consists of gel-permeation-chromatography (GPC) and combined techniques of gas chromatography and mass spectrometry (C~MS). In some cases, IH- and n3C-NMR spectroscopy give unambiguous data about the structure of the oligomeric compounds. This group of compounds may be of linear or macrocyclic nature and are normal coproducts in cycloolefin polymerization. The GPC evolution of the homologous series of cyclic oligomers obtained in the polymerization of cyclooctene and cyclododecene, ~s using WCIdMe4Sn as a catalyst, is illustrated by the chromatogram (A) and (B), respectively (Figures 12.14 and 12.15).

2 5

35

40

45

50

55

4

60

!

3

65

70

75

80

85

90

95

Figure 12.14. GPC of the homologous series of cyclic oligomers and polymer obtained from cyclooctcne (CO) using WCIdMe4Sn as a catalyst (Adapted from Ref.~s) It can be seen that all oligomers of cyclododecene up to nonamer are kinetically enhanced, while the polymer is only formed at the end of the reaction, at the expense of oligomers.

906

n

I /x II

9 - -

m

~

vg/n Figure 12.15. GPC of the homologous series of cyclic oligomers and polymer obtained from cyelododecene (CDD) using WCIdMe4Sn as a catalyst (Adapted from Ref. The cyclic nature of these oligomers can be evidenced by GC-MS from single components. For instance, the trimer of cyclododecene shows a molecular ion peak in the mass spectrum corresponding to 498 (m/e). The high intensity as compared with that of lower fragments is a first indication for the cyclic structure of the compound. Though the peak is not very characteristic as these values are typical for fragments of polyolefins. When the trimer is hydrogenated, the C36-product shows the molecular ion peak at 504 (m/e), corresponding to the formula C,H2,.~+, typical for a cycloalkane. Research on this line by the above techniques, carried out by Calderon and coworkers, s7 revealed the existence of butenamer units (Coils) in the macrocyclic oligomer fraction of polymers from 1,5cyclooctadiene. Also, by analysis of the oligomer fraction separated from polymers of l-substituted 1,5-cyclooctadienes, these authors found that the structures of these polymers were equivalent to an alternating copolymer of butadiene with isoprene (Eq. 12.48).

!

(1248)

i

Infrared spectroscopy. Infrared spectroscopy has been widely applied during early studies on the structure of polyalkenamers in order to reveal the presence of ring-opened structures and to determine the cis and trans vinylene content in these polymers. For several years the method was

907 based on absorptivity values previously established for cis- and trans-l,4polybutadiene without controlling their transferability to higher homologs. However, in a more detailed IR and NMR spectroscopic investigation of the structural units occurring in polyalkenamers, Tosi, Ciampelli and Dall'Asta st" determined more accurately the molar infrared absorptivities for several polyalkenamers (Table 12.2). Table 12.2 Molar absorptivities of infrared bands due to trans and cis double bonds in polyalkenamers'

Polyalkman~r

E~,(7.12 (mole.cm)"1

Polybtaman~r Polypmtmamcr Polyhoptcnamer Polyoctcnamcr Polydecenamer Polyd~amer 9Data from reference ~s

132 152 137 135 134 133

~m) (rnole.cm) "! 5.0 9.4 8.7 8.6

Inspection of the values from Table 12.2 surprisingly shows that the molar absorptivities vary considerably, depending on the length of the methylene sequence occurring between two successive double bonds. Analysis by this method of the structure of trans-polypentenamer, prepared by ring-opening polymerization of cyclopentene under the influence of the three-component catalyst WCl6/peroxide/EtAICl2 indicated that the amount of non-alkenamer units did not exceed 2-3%. Vinyl end groups were shown by infrared spectroscopy to be virtually absent in the high molecular weight polyalkenamers and to be present in the low molecular weight products only in amounts corresponding to the end groups, in accordance with the metathesis mechanism of ring-opening polymerization. The trans vinylene double bonds from polyalkenamers were generally determined by using infrared absorption band at 10.3 5 p whereas the cis vinylene double bonds either by using the infrared bands at 7.1 or at 13.7 p, or by assigning the complement to 100 per cent of the trans double bonds to the cis vinylene ones. Comparative examples with IR spectra of cis and trans polypentenamers obtained by Natta and coworkers 37 with Mo-and W-

908 based catalysts, respectively, are given in Figures 12.16 and 12.17.

x La) ~t| ~ .... 3...3~..~..~ zr

so

.... 5~ .... 6....6~...?...?~5...L.~...?.2~o. ~. ~L,~.m,~.~,5

---~

dO

40

cis-PPM

20 I

4000 ~

I

i

i=

3200 ~

I

*

2400 2000

"

9

IgO0

i

9

1600

9

t

9

1400

t

9

1200

t

9

1000

9

800

650

Wavenumber, cmt Figure 12.16. IR spectrum of cis-polypentenamer (PPM) prepared with MoCl~-based catalysts (Adapted from Ref.37) It is obvious that a clear distinction between the cis and trans structures of the two isomers can be observed by a rapid inspection of the two spectra.

x (~t) %

,d 5 . . . .

{,,, 33

a 45 $

5.5

6

6.5

7

7.5 8 83 99.510

II 12 131415

W 60 40 trlms--PPM

20 9

l

/

4000 3600 32(}0~

l

g

2400 ~

9

9

9

ISO0

t

9

I~

&

it

1400

it

9

1200

9

9

I000

9

t

900

9

~I~

Wavenumber, cm~ Figure 12.17. IR Spectrum of trans-polypentenamer (PPM) prepared with WCl~-basod catalysts (Adapted from Ref.37) The cis-polypentenamer displays the characteristic absorption bands at 7.1 2 and 13.8-13.9 g while the trans-polypentenamer at 10.35 g. Absorption bands in the region 8 and 8.5 It, characteristic of cyclopentane structures, are absent indicating the occurrence of a ring-opened polymer.

909 Investigation by infrared spectroscopy of the crystalline polyalkenamers showed a series of IR bands that are characteristic of crystallinity. This fact is illustrated for trans-polypentenamer in the wavenumber region of 400-2000 cm~ (Figure 12.18). 60 % G |._a__

6 l_

i

_l_

l

L

la__l

I

7 l

l

1

l

1 i

i

i

i

i I I lllllllt

8

9

lllllJllll

l

l

10 1.

I

A

l,

1G I

l

20 A

A

~

I

2G

l ~ t l ~

100

i. o

2ooo

t~

~o

~)o

I~

~obo

~o

~

,toe

Wavenumber, cm"t Figure 12.18. IR spoetrum of trans-polypentenarner (PPM) in the 400-2000 cm"~ region (-amorphous and "crystalline modification) (Adapted from Ref.~r*) Interestingly, some of these bands were found to be indicative of the specific type of crystalline modification present in the polymer. The structure of polyoctenamer with 62% trams content can be estimated from the FTIR spectrum of this polymer shown in Figure 12.19. 59 The absorption bands at 960 cm t (trans =C-H bending) and at 715 cm t (cis =C-H bending) give the ratio trans/cis using a factor of 0.10 for the trans band and 0.16 for the cis band. The FTIR spectrum of hydrogenated 62% polyoctenamer is comparable with that of polyethylene. In particular, the absorption bands at 3000 cm t (ethylenic C-H stretching) and at 960 cm" (the trans olefinic C-H bending), originally present in polyoctenamer, are completely eliminated by hydrogenation and the cis olefinic bending at 715 cm"~ is replaced by the CH2 rocking at 730 cm"t and 720 cm "t. From the ratio of the band at 730 cmt (assigned to the crystalline portion of the macromolecule) to that at 720 cm ~ (assigned to the amorphous portion of the macromolecule) it was possible to estimate the crystaUinity of the hydrogenated polyoctenamer.

910 Transmittance -/

ir \

/

..! !

POM ,,ooo

~oo

2obo

,~o

,oho

5o0

Wavenumbcr, cm" Figure 12.19. FTIR spoctrum of polyo~amcr (POM) with 62% trans conte~t and of its hydrogenated product (Adapted from Ref.59) The FTIR spectrum of polynorbornene ~9 with 80% trans content is given in Figure 12.20. The microstructure of polynorbornene can be roughly estimated by using the absorption band at 960 cm ~ due to trans out of plane =C-H bending and the cis in-plane =Coil bending at 1404 cm ~. Further estimation of the trans and cis content of polynorbornene can be clone by comparing the trans absorption band at 960 cm ~ with the cis absorption at 740 cm~. After hydrogenation, the FTIR spectrum of polynorbornene shows a complete absence of the cis band at 1400 cm~ and a very strong reduction of absorption band in the 740 cm ~ region also due to cis double bond while the trans absorption band at 960 cm "~ remains, but is strongly attenuated. This means that the cis portion of polynorbornene is more readily hydrogenated than the trans portion.

911 Tran~__~rn~ancr

'

w

I

9

9

l

!

:316O0

~0OO

2~OO

2OOO

lfl~o

mooo

ooo

Wavmumber, cm"t Figure 12.20. FTIR spectnnn of polynorbomenamer (PNB) with 80% t r a n s content and of its hydrogenated product (Adapted from Ref.'9)

tH NMR and t3C NMR spectroscopy. With the rapid advance in NMR spectroscopy, this technique has become one the principal methods for structural characterization of polyalkenamers. As early as 1965, Michelotti and Keaveney6~ reported the first ~H M R spectrum of polynorbornene, but some structural features were not discerned at that time with the available instrumentation. Subsequently, ~H NMR spectroscopy has been widely applied for evaluating the structure of polyalkenamers, namely to determine the number and types of protons present in the polymer chain. A first example is the ~H M R spectrum of polybutenamer where the CH2 and CH protons can be easily identified6~ (Figure 12.21). ...

--

t.4 2 -

.=.

mIND

pg~rn

Figure 12.21. ~H NMR spoctrum ofpolybutenamer (PBM) (Adaptod from Ref.6~).

912 In a similar way, the tH NMR spectrum of polypentenamer gives the type and amount of CH2 and CH protons in the polymer chain (Figure 12.22). Pr'M 1 I

-Cl-I--

planr~

Figure 12.22. ~H NMR spectnnn of polypent~amer (PPM) (Adapted from Ref.6~) Wide-line H NMR spectra, obtained at low temperatures provided a measure of the T s for several polyalkenamers. The apparent Tss of higher polyalkenamers were between those for polyethylene and polypentenamer, indicating Tss to be slightly below -100~ for these type of polymers. As ~3C NMR spectroscopy became readily available, more detailed information regarding the microstructure and tacticity of poly(cycloolefin)s was possible. Thus, chemical-shift additivity parameters for carbons in polypentenamer at various distances from the double bond were first reported by Chen 62 (Figure 12.23). m

_

|

..__.._...

1

,~o

,]o

,~o"

2

do

io pll~'n

Figure 12.23.13C NMR spectrum of polypentenamer (PPM) (Adapted from Ref.62)

913 From the characteristic ~3C NMR chemical shifts, the microstructure of a series of polyalkenamers can be accurately evaluated. Accordingly, the ~3C NMR chemical shifts of cis-polyalkenamers in CDCI3 at 60~ in ppm relative to tetramethylchlorosilane are given in Table 12.3. Table 12.3

~3CNMR Chemical Shifts of cis-Polyalkenamers in ppm relative to TMS"b

Polyalkenaater

Ct

C2

129.66

27.52

129.91

27.01

29.96

"129.88

27.25

29.72

29.02

129.88

27.33

29.85

29.29

133.95

38.70

33.32

42.77

Structure

Polybutenamer

1

C3

C4

2 Polypentenamer

1

3

1

3

Polyheptenamer

"0~'~

Polyoctenamer

~

1

4 v ~ ' ~ 3

] 2 1

4

~

4

Polynorbomene

'Data from reference

Solvent CDCI3 at 60~

The essential feature from these data is that the trans olefinic bonds are characterized by aUylic carbon resonances at ca. 5.0 ppm higher frequency than cis olefmic ones. For a more detailed information, the methylenic region of the ~3C NMR spectrum of 85.5% trans polypentenamer obtained with the catalytic system WC~epichlorohydrinfBu3Al, in toluene at a temperature of 0~ is illustrated in Figure 12.24 and that of 81.98% cis polypentenamer obtained with the catalytic system WCIdPI~Sn, in toluene at a temperature of-20~ in Figure 12.25. 64

914

trans-PPM

.{.- c N

1

2

2~

3"3

i2

i,

s'o

z~

2"8

i?

2"6

i5

Figure 12.24. Expanded ~3C NMR spectrum (methylene region, 25>C~-Ig>CH3. It is noteworthy that WCld(CH3)4Sn is also active in the metathesis of unsaturated compounds bearing certain functionalities. On the other hand, tetraphenyltin associated with WCI6 provides a highly active binary catalytic system for the polymerization of cyclopentene and cyclooctadiene. Higher cycl~lefins such as cyclooctene and cyclododecene were practically inactive under these conditions. However, these two r could be l~lymerized when small amounts of cyclepentene, cyclohexene or 1,5-cyclooctadiene were added to the catalyst (see Figure 4.21). Two alternate mechanisms for the generation of the initiating species have been envisaged for the two types of catalytic systems. The first mechanism, occurring with the alkyltin compounds, involves initially an alkylation step and subsequent ~-hydrogen elimination from the alkylated tungsten compound by one of the path (a) or (b), leading to metallacarbene species ~ (Scheme 15.13). WCl6 + (RCH2)4Sn

RCH WCI RCH=VVCI4

-~ RCH2WCIs + (RCH2)3SnCI RCH=WCl4

(b)

(RC H2)2VVC[4

O

=

-RCH 3

RCH=WCI4

c,,vvtc : .4

Scheme 15.13 The metallacarbene thus formed is able to initiate the polymerization process by subsequent coordination and insertion of cyclopentene. A similar mechanistic scheme for the generation of mngstac,arbene species by the interaction of WCI6 with (CH3)~Me has also been advanced by Thorn and coworkers. 88 In contrast to the tetraalkyltin compounds, tetraphenyltin can

1027 not generate directly m e t a l l a ~ n e species by the above reaction sequence since the phenylated derivative that would arise is devoid of hydrogen atoms in the cz position. The high activity of this system is rationalized by a reaction pathway in which the tungstaearbene species can arise directly from the cycloolefin and the phenylated tungsten compound as a result of the reductive elimination assisted by the cycloolefin ~ (Scheme 15.14).

WCl6 + (CsH5)4Sn~

C6H5WCI5 + (C6H5)3SnCI

C6H5WCI5 ~C61"15WCl5"0

0+99% can be easily reached. The selectivity of the hydrogenation step to cyclooctene is slightly less than 100% when commercial heterogeneous catalysts are employed. With rigorous temperature control and hydrogen metering a specially developed hydrogenation catalyst gives complete selectivity. However, a small degree of overhydrogenation to cyclooctane must be admitted, otherwise, traces of 1,5-cyclooctadiene can remain in the product that may hinder the sensitive polymerization process as results of its isomerization to 1,3-cyclooctadiene. The latter acts especially as a strong catalyst poison. The monomer with the purity necessary for polymerization contains 95-97% cyclooctene, the remaining being essentially cyclooctane. Synthesis of trans-polyoctenamer. On the industrial scale, polymerization of cyclooctene is performed in hexane as a solvent in the presence of a

1154 WCI6-based metathesis catalyst. 24 High purity monomer and anhydrous conditions are essential. The reaction is carried out adiabatically to complete conversion of monomer in almost 100% yield. The workup involves flash evaporation of the solvent with subsequent recycling. The final product is filtered in the melt, pelletized after cooling, and packed at a purity of >99.5% in bags. The content of impurities and low mass oligomers is very small. Properties of trans-polyoetenamer. Polyoctenamer has been produced over a wide range of molecular weights and cis:trans ratios of the double bonds. 24 The products exhibit bimodal molecular weight distribution with the first maximum corresponding to the low molecular weight oligomers. Depending on the reaction conditions, linear, unbranched polyoctenamers with an ideal poly(l-octenylene) structure in addition to macrocycles are formed in the polymerization process. As one double bond occurs at every eighth carbon atom of the chain or macrocycle, polymers with high chain mobility and low glass transition temperature will result. The crystallinity of the polyalkenamers depends strongly on their microstructure i.e., the ratio of cis:trans double bonds. The double bonds can be arranged in sequences and crystallites with defined melting temperatures will be formed. The crystallinity is thermally completely reversible and has a beneficial effect in blends of Vestenamer and other rubbers. During the mixing and extrusion the temperatures exceeds 50~ and the molten polyoctenamer improves the flow properties of the blend. After cooling the polymer recrystallizes and increases the green strength and shape stability. It was observed that the influence of the trans double bonds on the crystallinity is more pronounced than that of the cis double bonds. It is significant that recrystallization from the melt occurs within seconds; this property is very important in certain applications involving rubber processing. Several polyoctenamer grades are available commercially from Hials AG under the trade name Vestenamer. z5"3~The low molecular weight and crystallinity are chosen specifically so that they provide advantages in rubber processing due to their low melt viscosity. Typical properties of Vestenamer 8012 and Vestenamer 6213 are given in Table 18.4. In addition to these two types, a low molecular weight polyoctenamer has been offered to the coatings industry as Vestenamer L. The molecular weight of Vestenamer is kept intentionally low for a rubber. Due to its thermoplasticity, the viscosity in the molten state is unusually low compared to other solid rubbers. The Mooney viscosity ML

1155 Table 18.4. Properties of Vestezmmer 8012 and 6213' Property

Molecular mass, g/mol Glass transition temperature Tg, ~ Crystallmity (at 23 ~ % Melting point, ~ Startof d~osition, ~ Ratio trans:cisdouble bonds, % Mooney viscosityM L (l+4)(at I00 ~ Viscositynumber J(at23 ~ mL/g

Density,g/cm 3

Vestenamer

Vestenamer

8012

6213

100000 -65 30 54 275 80:20 eratures*

Temperature, ~

Tensile, kg/cm2 Elongation, % 100% Modulus, kg/cm2 200% Modulus, kg/cm2 300% Modulus, kg/cm2 Tear strength, kg/cm

+23

-20

-50

-70

-90

168 500 24

148 420 25 53 93 50

225 490 32 64 113 53

284 490 37 79 142 82

392 495 61 126 213 133

48 88

51

9 Data f r o m reference. 6z

It is noteworthy that the strong increase of the tensile strength and moduli is not accompanied by appreciable variation of the elongation at break, this fact indicating high elastomeric performances rather than stiffening of the material. The excellent properties of cis-polypentenamer at low temperatures are fully illustrated when comparing the dependence of the 100% modulus (Figure 18.22), the compression set (Figure 18.23), and the plot of hardness (Figure 18.24) as a function of temperature for various rubbers (e.g., transpolypentenamer, styrene~utadiene rubber 1500, polypropylene oxide,/allyl glycidyl ether and cis-1,4-polybutadiene). 63

1202 M ,oo, kg/cm2

200

/ t ./

100

4

5O

-70

-40

-20

-0

20

Temp., ~ Figure 18.22. Variation of 100% modulus with temperature for various elastomers (1-trans-Polypentenamer; 2- Styrene~utadiene Rubber 1500; 3-Polypropylene Oxide/Allyl Glycidyl F~er; cis-l,4-Polybutadiene; 5-cis-Polypentenamer) (Adapted from Ref.63). Compression, % 4

loo

80

60

I

1 / "

40 I

I

20

O

/

9

-80

9

-70

9

-60

a

-50-40

9

a

-30

f

9

-20

9

-10

9

0

,,

9

!0

20

A

30

Temp., ~ Figure ] 8.23. Dependence of compression set as a function of temperature for different rubbers (]-cis-Polypentenamer; 2-cis-Po]~outadiene 80%; 3-Smok~

Sheet; 4-Styrene/Butadiene Rubber). Conditioning 22 hr, Relaxation 30 mm (Adapted from Ref.63).

1203 Shore A 100

4

90

80

2

7O 6O

50 -80-70

-60-50-40-30

-20 -10

0

10

20

30

Ten~., ~ Figure 18.24. Variation of Shore A hardness with temperature for various rubbers

(l-cis-Polypemenamer; 2-cis-Polybutadiene; 3-Smoked Sheet; 4-StyreneJButadiene Rubber); Conditioning 70 hr (Adapted from Ref.63). It is obvious that cis-polypentenamer exhibits a much better low temperature behavior than general purpose rubbers, like natural rubber, styrene-butadiene rubber, or trans-polypentenamer, and displays even superior properties to the known low temperature rubbers, like cis-l,4polybutadiene and propylene oxide/allylglycidyl ether copolymer. 18.2.3. c/s-Polyoctenamer

cis-Polyoctenamer displays a series of particular physical properties. Thus, high cis-polyoctenamer has the same melting temperature as transpolypentenamer but exhibits a considerably higher crystallization rate at room temperature." To diminish the excess crystallization at room temperature, it is preferable to reduce the proportion of cis configuration to about 75-80%. Furthermore, the glass transition temperature (T o is lower (- 108~ than that of the trans-polypentenamer. cis-Polyoctenamer has poor processing properties, especially at temperatures below 100~ In these conditions, and particularly when the

1204 intrinsic viscosity of the polymer markedly exceeds [11] = 2, the material is dry and brittle and it is difficult to be processed. However, at temperatures between 100~ and 120~ it can be compounded with fillers, ingredients

and oil and the mixes are quite homogeneous. Significantly, sulphur cure is fast even at low sulphur doses. The influence of different oil loading on the vulcanization behavior and on some of the physical and dynamic properties of cis-polyoctenamer is illustrated in Table 18.22.

Table 18.22 Influence of oil loadmg on the cure behavior and physical-mechanical properties of cis-polyoctenamer '~b

Parameter

Sundex 790, phr Compound ML 1+4 at 100~ T2, mm T90, mm AL, m.lb Tensile, kg/cm2 Elongation, % M~0, kg/cm2 M3oo, kg/cm~ D1,% HIRHD HBU at 100~ A~

Value

72 7.5 32.5 95 182 340 77 160 5 75 26

5 62 10 37.5 90 189 370 76 152

I0 54 10 28.5 84 172 370 61 131

20 41 12.7 32.5 74 165 400 45 100

4

4

4

74 23

71 20

68 19

'Data from reference~9; I' Recipe: Polymer i00, SWC 0.5, ~;tearic acid'2, zinc oxide 5, ISAF black 50, Sundex 790 as indicated, Santocurr 0.8, Sulphur 1.0, Monsanto rheometer at 150~ Vulcanization 40 mm at 150~

Examination of the physical and dynamical properties of the reinforced cispolyoctenamer shows that the performances are similar to those of the conventional general purpose rubbers. The dependence of the elastomeric properties of cis-polyoctenamer with temperature is illustrated in Table 18.23.

1205 Table 18.23 Variation of physical properties of cis-polyoctenamer vulcanizates with temperature ~b Temperature ~

Tensile strength kg/cm2

Elongation %

M200 k~n 2

M200

M300

kgcm

kg/. 2

70 50 23 0 -10 -20 -40 -50

117 139 161 157 192 207 300 310

360 360 360 360 360 370 380 360

24 25 23 22 27 41 115 135

57 59 60 70 93 123 200 218

104 107 119 136 168 193 256 283

'Data from refermce~ b Recipe:Polymer 100, SWC 0.5, Stearic acid 2, Zinc oxide 5, Nocton 10, I S , ~ 50, Sant~ure 0.8, Sulphur 1.0, Vulcanization 40 ~ at 150~ It is relevant to note that like cis-polypentenamer, cis-polyoctenamer does not exhibit significant variation of the elongation at break with temperature in the range of +70~ to -50~ However, unlike cis-polypentenamer, as it can be noted from the above data, the 100% modulus of cis-polyoctenamer considerably increases below -10~ this fact indicating rubber stiffening. Also, it is of interest to compare the aging resistance of cispolyoctenamer with that of several rubbers such as trans-polypentenamer, cis-1,4-polybutadiene and styrene-butadiene copolymer (Table 18.24). Table 18.24 Aging resistance of cis-polyoctenamer(COR)and several rubbers L~' |

Aging

TPR

COR

BR

SBR 15O0

days TS 4 8 16

93 86 83

69

TS

E

105 108 96

63 63 50

TS

E

TS

E

83 58 114 72 50 83 52 110 63 45 66 38 108 60 ' Aging resistance m air at 100~ ' Values of TS

' Data from reference' (tensile) and E (elongation) are percent of the original values.

1206 It is obvious that the behavior of cis-polyoctenamer is intermediate between that of cis-l,4-polybutadiene, on one hand, and trans-polypentenamer and styrene-butadiene copolymer, on the other hand. The higher aging resistance of cis-polyoctenamer compared to that of butadiene rubber was attributed to the lower content of double bonds in the former polymer while the lower aging resistance compared to that of trans-polypentenamer was assigned to the different configurations of the double bonds of the two polymers. From careful examination of the physical-mechanical properties of cis-polyoctenamer, it may be concluded that this rubber is to be considered as a special purpose rubber of the butadiene rubber type. However, in comparison to butadiene rubber, it displays poorer low temperature performances, but better aging resistance and stress crystallization (green strength).

18.2.4. Cyclorene Rubber A new flame resistant chlorine-containing elastomer that can be readily vulcanized with sulphur-based curatives has been developed since 1973 using as a monomer the Diels-Alder product of hexachlorocyclopentadiene with 1,5-cyclooctadiene. 65 This compound was copolymerized with additional 1,5-cyclooctadiene to give a family of copolymers with variable microstructures, chlorine content, melting points and glass transition temperatures as well as with a high solvent resistance (Eq 18.6). O

Due to its good solvent and weathering resistance, this product appeared to be capable of replacing polychloroprene (Neoprene) in many applications. Importantly, the copolymers thus manufactured showed to be compatible with conventional diene elastomers and could be vulcanized by sulphur and common sulphur donor curatives.

1207

18.3. Potential Applications Conventional and new polymers have become more and more accessible with the development of the versatile processes of ring-opening metathesis polymerization of cycloolefins.

18.3.1. Synthesis of Monodispersed Polyethylene Linear, monodispersed polyethylene is an extremely important practical and synthetic goal and provides the challenge of preparing essentially monodispersed, linear 1,4-polybutadiene. At present low polydispersity polyethylene is produced by the hydrogenation of 1,4polybutadiene prepared by the anionic polymerization of butadiene. However, this approach results in a somewhat branched polyethylene, since the 1,4-polybutadiene prepared by anionic polymerization generally contains C2 branches as a result of low levels of 1,2-polymerization of butadiene. With the advent of well-defined transition metal alkylider~e and metallacyclobutane complexes for living ring-opening metathesis polymerization (ROMP) of cycloolefins, synthesis of monodispersed, linear 1,4-polybutadiene by ring-opening metathesis polymerization of cyclobutene became feasible. Interesting studies by GnJbbs and coworkers ss showed that 1,4-polybutadiene with a polydispersity index of 1.03 can be manufactured by ring-opening polymerization of cyclobutene under the action of the alkylidene complex W(=CH'Bu)(=NAr)(O~Bu)2 (Ar=2,6diisopropylphenyl) in the presence of PMe3. Further hydrogenation of 1,4polybutadiene in the presence of appropriate hydrogenation catalysts will produce linear, low polydispersity polyethylene (Eq. 18.7).

18.3.2. Synthesis of 1,4-Polybutadiene 1,4-Polybutadiene is produced on a large industrial scale by anionic polymerization of 1,3-butadiene, under various conditions. The polymer obtained by this procedure contains generally a low level of C2 branched as a result of 1,2-polymerization of the monomer. An alternative, efficient route to prepare linear, monodispersed 1,4-polybutadiene, with a high steric

1208 purity, is available by ring-opening metathesis polymerization of cyclobutene, 1,5-cyclooctadiene and 1,5,9-cyclododecatriene 67 (Eq. 18.8). - -

(18.8)

The reaction is promoted selectively to cis-l,4-polybutadiene by TiCI,/Et3AI. 6~" Other catalysts such as TiCI4/(~-C,HT)4Mo, 6~ V(acac)3fEt3Al, 67c Cr(acac)3/Et3Al, 67c MoCI3/Et3AI,67c VCI4/BuLi, 67d MoCIs/(Tt-CaHT)4W,67e MoCIs/(Tt-C4H7)2Mo,67e WCl6/(~-c4n7)4W, 67e RuCI3,6?f Ph(MeO)C=W(CO) 5,67g Ph2C=W(CO)56"th and Mt(=CH'Bu)(=NAr)(O'Bu)2 (Mt = Mo or W, Ar=-2,6-diisopropylphenyl) 67iJ may give trans- or cis-l,4-pelybutadiene, depending on the catalyst and reaction conditions. With the availability of 1,5-cyclooctadiene and 1,5,9cyclododecatriene on the industrial sc~e by cyclodimerization and cyclotrimerization of butadiene, respectively, this method becomes of a great commercial interest.

18.3.3. Synthesis of 1,4-Polyisoprene Due to its outstanding elastomeric properties, synthesis of 1,4polyisoprene has stimulated intensive research work for a long period of time. Recent developments in the ring-opening metathesis polymerization catalysts prompted interesting studies for the synthesis of 1,4-polyisoprene by ring-opening metathesis polymerization of l-methylcyclobutene 68 and 1,5-dimethyl- 1,5-r 69 (Eq. 18.9).

(18.9)

1209 Polymerization of l-methylcyclobutene in the presence of the tungstencarbene catalyst Ph2C=W(CO)5 has been conducted by Katz and coworkers 6t" to appreciable yields of 1,4-polyisoprene having cis configuration at double bonds of ca. 90%. More recently, Wu and Cn'ubbs6~' prepared polyisoprene having an exclusively cis and head-to-tail structure by polymerization of l-methylcyclobutene with the well-defined alkylidene complexes of the type Mt(=CH(CH3)2R)(=NAr)(OC(CH3)n(CF3)3.~)2 (At = 2,6-diisopropylphenyl, Mt = Mo, R - Ph, n = 2). The polymer thus prepared showed properties similar to natural rubber. Unfortunately, at present the manufacture of 1,4polyisoprene through this procedure is limited by the availability of the starting materials, 1-methylcyclobutene and 1,5-dimethyl-1,5cyclooctadiene.

18.3.4. Alternating Copolymers Ring-opening metathesis polymerization of substituted cycloolefins afford a unique method for the synthesis of perfectly alternating copolymers of olefins. Starting from a substituted cyclobutene, a substituted polybutenamer can be prepared in a first step which by subsequent hydrogenation will provide the corresponding copolymer of the linear olefins. Thus, by ring-opening polymerization of 3-methylcyclobutene, in the presence of classical WCl6-based catalysts, poly(3-methylbutenamer) is obtained which by subsequent hydrogenation in the presence of Pd/C catalysts will form the alternating copolymer of ethylene and propylene 7~ (Eq. 18.10).

\ n U

[V l "-

~"-

(18.1@

Similar reactions of 3-ethylcyclobutene will produce the alternating copolymer of ethylene and l-butene whereas those of 3-propylcyclobutene will give rise to the alternating copolymer of ethylene and l-pentene. Alternating diene copolymers have been readily prepared by ringopening polymerization of monosubstituted 1,5-cyclooctadienes (R= CH3, C2H5, CI) in the presence of the ternary metathesis catalysts based on WCIffEtOH/EtAICI2.69 Interestingly, when the substituent was a CH3 group, the alternating copolymer of butadiene and isoprene was formed

1210 (Eq. 18.1 l) n

=

(18.11)

whereas when it was a chlorine atom, the alternating copolymer of butadiene and chloroprene was produce~ (Eq. 18.12). n

Cl

ROMP

(18.12)

If the starting material is 1,2-disubstituted 1,5-cyclooctadiene, an alternating copolymer of butadiene and disubstituted butadiene can be prepared. Obviously, the ring-opening reaction occurs at the more reactive, unsubstituted double bond of the cycle, due to the strong steric hindrance exerted by the substituents at other double bond.

18.3.5. Block Copolymers There are at present several experimental techniques which can be used to produce block copolymers from cycloolefins. The most straightforward synthesis that uses living systems derived from well-defined transition metal alkylidene and metallacyclobutane complexes involves growing the homopolymer with a desired molecular weight of one monomer and continuing the process with a second monomer until a final structure and molecular weight of the copolymer is obtained. A large number of diblock and triblock copolymers with very low polydispersities have been prepared by this method. Some examples are selected from the extensive work by GnJbbs and coworkers 7~ on the synthesis of diblock and triblock copolymers of norbornene with exo-dicyclopentadiene and benzonorbornadiene under the action of titanacyclobutane catalysts (Eq. 18.13-18.14). [ri]

...-~..--~

(18.13)

1211

[Til

"-----.--!~

(18.14)

as well as by Schrock and coworkers ~ on the synthesis of diblock and triblock copolymers of norbornene with substituted norbomene or polycyclic olefins in the presence of Ta, W and Mo catalysts (Eq. 18.15).

nf .m t

(1815)

l

Of a special interest are the block copolymers from halogen-n or ferrocene-containing monomers 74 in the presence of the Mo-alkylidene complex Mo(---CH'BuX=NAr)(OtBuh (Eq. 18.16-18.17).

n

+

[Mo]

m

--

F3C

(18.16)

CF3 F3C

9rn

Fe

, p

CF3

(1817)

1212 By this procedure, copolymerization of norbomene-like monomers having transition metals or main group metals, electroactive groups, etc. leads to products of potential use. Thus, block copolymers prepared from 5(ferrocenyl)-norbornene and 5-(trialkoxysilyl)norbomene were attached to electrode surfaces; redox-active materials with specific morphologies and prescribed dimensions were manufactured by this way. Block copolymers could be prepared by grafting living ring-opened polymers onto polymers that contain carbonyl groups, a method that takes advantage of the Wittig-like alkylidene transfer reactions 75 (Eq. 18.18).

According to several procedures, blocks that are not prepared by ring-opening metathesis polymerization could be added to ring opened polymers to provide a wide range of block copolymers with varying properties. Relevant examples reported GnJbbs and Risse, ~6 for instance, by growing a second block on a ring-opened polymer of norbornene by the use of group transfer polymerization (Eq. 18.19). (18,10) I

I

-2,-2

The silyl vinyl ether block can be modified by cleaving off the silyl groups. Treatment with tetrabutylammonium fluoride results in the formation of the hydrophobic-hydrophilic AB-diblock copolymer with poly(vinyl alcohol) as hydrophilic segment (Eq. 18.20). H

H

-S-

-S-

H

H

CH

O-t

1213 These block copolymers can potentially be applied as emulsifiers, flocculants, wetting agents, foam stabilizers and as polymeric dispersants for the stabilization of polymer blends. On coupling the anionic polymerization with ring-opening metathesis polymerization, Amass and coworkers ~ prepared block copolymers of styrene and cyclopentene (Eq. 18.21)

n

euLi

.=

Bu

"

mo

B

WCl6=

'[VV] (18.21)

and Feast and coworkers 7s grafted block copolymers of norbornene dicarboxylate with styrene (Eq. 18.22). o~ng:n,johcn~og~

Furthermore, changing the reaction mechanism from Ziegler-Natta polymerization to ring-opening metathesis polymerization, Cmabbs and coworkers ~9 prepared block copolymers of norbornene with ot-olefins in the presence of modified titanium catalysts (Eq. 18.23).

--- Cp2Tt-

,. yc.2H4

(

08.23)

CIMa

Graft copolymers of practical interest could be readily produced by the ring-opening metathesis polymerization of cycloolefins in the presence of unsaturated polymers bearing unsaturation in the side chains (Eq 18.24).

rn x +

P,,~tl

(182,4)

1214 Thus, Medema e t al. so grafted cyclooctene on the unsaturated branches of the natural rubber in the presence of ReCIs/EhAI, Pampus and coworkers s~ obtained graft copolymers by ring-opening polymerization of cyclopentene with 1,2-polybutadiene, butadiene, styrene-butadiene copolymer and ethylene-propylene-dicyclopentadiene terpolymer whereas, Scott and Calderon 82 prepared graft copolymers from ethylene-propylene-diene terpolymer and 1,5-cyclooctadiene. 18.3.6. Comb and Star Copolymers

Comb copolymers can be produced by ring-opening polymerization of mono- and disubstituted cycloolefins with moderate to long side chainss3 (Eq. 18.25).

coA

n

lc

M

~D.

~

(18.2b~

Icth H3C,(O42I

CO2(O4 I OH3

Such products behave like hydrogels and can take up a moderate amount of water. Synthesis of a large number of star copolymers s4 is possible by ringopening metathesis polymerization using well-defined metathesis initiators and a cross-linking agent (Eq. 18.26) p

p

P

Reactive alkylidenes such as living poly(5-cyanonorbomene) can be quantitatively converted into living star polymers, which upon treatment with relatively unreactive monomers like 2,3bis(trifluoromethyl)norbornadiene give "heterostar" copolymers, since all the sites in the star core serve as initiators.

1215

18.3.7. Amphiphilic Star Block Copolymers Synthesis of amphiphilic star copolymers that consist of a hydrophobic polynorbornene "core" and hydrophilic functionalized polynorbomene "shell" has been effected by Schrock and coworkers s5 (Eq. 18.27). p.

P

[MI

A variety of star copolymers can be made by this procedure with functional groups in the shell, in the core, or in both, to suit whatever application is desired. Such amphiphilic star copolymers behave as model micelles in aqueous solution.

18.3.8. Macrocyclic Compounds Ring-opening metathesis polymerization affords an elegant and simple way to prepare macrocyclic compounds of the carbocyclic type from cycloolefins. This method has several advantages as compared to multi-step conventional methods. In the presence of metathesis catalysts cycloolefins produce macrocyclic compounds of various size as a function of the nature of the cycloolefin, catalytic system and reaction conditions ~~ (Eq. 18.2S). R

(

- (~~. -~

R .... ._~ ,,

F [1~

R = ( ~ _ . ~ . .......

. . _ /(CH2)x (18.28)

(CH2)x

Thus, starting from cyclooctene, Wassermann and coworkers ~s prepared unsaturated carbocycles having up to 120 carbon atoms in the molecule. The reaction proceeded under mild metathesis conditions, in the presence of the catalytic system WCIdEtAICIJEtOH at 5-20~ in benzene as a solvent. By subsequent catalytic hydrogenation, the corresponding saturated

1216 carbocycles were synthesized. Carbocyclic oligomerization products were also obtained by Calderon and coworkers s~ in the ring-opening metathesis polymerization of cyclooctene with the WCIdEtAICI2 catalyst under special conditions. Interestingly, the higher unsaturation degree in 1,5-cyclooctene and 1,5,9-cyclododecatriene as compared to cyclooetene led to a higher amount of carbocyclic compounds. Significantly, the carbocyclic nature of the oliogomeric compounds produced in cyclooctene metathesis was elegantly demonstrated by Hocker and Musch ss by detailed chromatographic and spectrometric investigation of the reaction products. A wide range of unsaturated carbocycles were also produced by Wolovsky and Nirs9 by the metathesis reaction of cyclododeeene in the presence of WCl6-based catalysts. The unsaturated oligomers separated in the first stage were subsequently reduced to the corresponding monoolefins which were further subjected to oligomerization in the presence of the same catalytic system. Carbocycles with 24, 36, or 48 carbon atoms were readily synthesized by this procedure.

18.3.9. Conducting Polymers Synthesis of poly(p-phenylene) (PPP), a remarkable material with good thermal stability, chemical resistance and electrical conductivity when doped, has been reported by Caubbs and coworkers 9~ to occur from stereoregular precursors made by transition metal catalyzed polymerization. Thus, cis-5,6-bis(trimethylsiloxy)-l,3-cyclohexadiene was polymerized by the Ziegler-Natta-type catalyst bis[(allyl)trifluoroacetatonickel(ll)] to give exclusively 1,4-poly(cis-5,6-bis(trimethylsiloxy)-l,3-cyr which after deprotection to the corresponding hydroxy polymer, followed by acylation to the acetoxy polymer, produced high-quality poly(p-phenylene) by the pyrolysis of the acetoxy compound (Eq. 18.29). (18.29) TMSO ~

TM~

OTt~

HO

CH

/k~

O~

As ring-opening metathesis polymerization of cycloolefins produces directly polymers with carbon-carbon double bonds in the backbone, this reaction is an attractive and powerful synthetic route for the preparation of materials with desired electrical and optical properties. One interesting example is the synthesis of the new product poly(diisopropylideneeyclobutene), a cross-

1217 conjugated polymer, by ring-opening metathesis polymerization of 3,4diisopropylidenecyclobutene 9~ (Eq 18.30).

n

--•

rri] ._ MeOH'-

(18 30)

The polymer could be spin-cast, formed flexible films, and, upon doping, exhibited moderate conductivities (10 .3 S cm~). The doped material was brittle and insoluble, but these undesirable properties could be altered by forming block copolymers. It is of interest that blocking this product with polynorbornene yielded a rubbery material with more desirable mechanical properties, though the electrical properties after doping were similar to the homopolymer (Eq. 18.31). t~'li +

m--~

65=C

(18.31)

Two major approaches were developed for the synthesis of polyacetylenes by ring-opening metathesis polymerization of cycloolefins. A first approach is the ring-opening polymerization of suitable monomers such as cyclooctatetraene and substituted cyclooctatetraenes in the presence of the tungsten alkylidene complex W(=CHtBu)(-NAr)[OCMe(CF3h]2, reported by Grubbs and coworkers 92 (Eq. 18.32). R n

R ~

These reactions, especially that from substituted cyclooctatetraene, produced interesting and potentially useful materials, which might have valuable applications.

1218 Another important route, discovered by Feast and coworkers, 93 involves the preparation of a "precursor polymer" in a first step followed by "polyacetylene" synthesis upon thermal treatment in a second one. For instance, 7, 8-hi s(tri fluoromet hyl)t ricyclo [4.2.2.02"s]dec.a-3,7, 9-t riene (TCDT-F6] could be ring-opened by classical olefin metathesis catalysts to give a precursor polymer from which hexafluoro-o-xylene was eliminated upon heating to produce polyacetylene (Eq. 18.33).

n

CFa

[Mr]

CF3

A

F3

(18.33)

CF3

n F3C

CFa

Of a significant synthetic value is the finding of Schrock and coworkers 94~ who demonstrated that it is possible, by using the tungsten and molybdenum alkylidene metathesis catalysts, to prepare a homologous series of polyenes that contain up to 15 double bonds by the ring-opening polymerization of TCDT-F6 in a controlled manner (Scheme 18. l). n

F3

[Mt]

[Mt]

F3 I

r

F3C

CF 3

F3C

nQ F3C

CF 3

nQ

CF3

F3C

Scheme 18.1

CF3

1219 The first double bond was trans, and warts propagation mechanism dominated (~75%). When pivaldehyde was used in the Wittig-like reaction, a series of "odd" polyenes containing 2x+ 1 double bonds resulted. If 4,4dimethyl-trans-2-pentanal was employed, then the resulting polyenes contain 2x+2 double bonds. Since evidence was accruing that relatively short conjugated sequences could sustain a soliton and could have significant third-order nonlinear optical properties, it was of fundamental interest to produce well-defined unsubstituted polyenes. Interesting variations have been imagined, including capping with para-substituted benzaldehydes, and di-or trialdehydes. Polyenes can be manufactured in diblock or triblock copolymers combined with polynorbomene or similar polymers. For example, Stelzer et al. 97 prepared a block copolymer of polyacetylene and polynorbomene from benzotricyclo[4.2.2.02"5]deca-3,7,9-triene (benzoTCDT) and norbornene using a titanacycle catalyst (Scheme 18.2).

011

Schen~ 18.2

The living polymer obtained from the Feast monomer could be further blocked with polynorbomene. Thermolysis of this product eliminated naphthalene to give rise controllable block lengths of polyacetylene within a polynorbornene matrix. Schrock and coworkers 98 prepared triblock copolymers by adding norbornene to W(=CH'Bu)(=Nar)(OtBu)2, followed by TCDT-F6, and norbornene again. Further heating generated the polynorbornene/polyene/polynorbomene triblock. Interestingly, between 10

1220 and 30 of these macromolecules "aggregated" when the polyene block contained more than approximately 20 double bonds, a phenomenon that was ascribed to cross-linking of polyene chains. When enough TCDT-F6 monomer was employed to generate a 50-ene in the triblock, then all of the macromolecules cross-link to yield dichloromethane-soluble red polymers with molecular weights approaching 500000 (vs. polystyrene). This process opened the possibility to control the size of the cross-linked portion of such copolymers and to prepare polyenes in the block copolymers that contain a wide variety of functionalities, redox centers (for self-doping), etc. Another application of living TCDT-F6 technique could be the generation of isolated polyenes diluted in a host polymer. 99 For this purpose, low concentration of polyTCDT-F6 in homopolymer should be homogeneously dispersed, as should the polyene chains generated from polyTCDT-F6 if the retro-Diels-Alder reaction is carried out in the solid state. If such films can be oriented by stretching before the retro-DielsAlder reaction is carried out, then an anisotropic distribution of polyenes with a known distribution of chain length could be produced. Such products would be valuable in the fundamental and applied third-order nonlinear optical fields. An alternate polymeric precursor route to polyaeetylene that did not involve elimination of molecular fragments was developed through the ringopening metathesis polymerization of the highly strained monomer, benzvalene (a valence isomer of benzene). The polymer precursor which was prepared from benzvalene using the tungsten alkylidene complex W(=CH'Bu)(=NAr)(O'Bu)2 formed soluble, tastable films and could be isomerized to polyacetylene upon treatment with mercury salts ~~176 (Eq. 18.34).

--~D. ~

(18.34)

A new interesting precursor route to high-quality poly(l,4phenylenevinylene) (PPV) by ring-opening metathesis polymerization of substituted bicyclo[2.2.2]octadienes reported recently C~ubbs and coworkers. ~~ Thus, starting from the bis(~xylic ester) of bicyclo[2.2.2]octa-5,8-diene-cis-diol, the precursor polymer was prepared by living ring-opening polymerization under the action of the molybdenum

1221 alkylidene complex Mo(=CHCMe2Ph)(=NArXOCMe2(CF3)h which by subsequent pyrolytic acid elimination provided poly(l,4-phenylenevinylene)

(Eq 18.35).

~OC(O)OO'l.sROMP O ) ~ H3CO(

A -~~

(18.35)

OC(O)OO'h

Significantly, the living metathesis polymerization of the starting bis(carboxylic ester) of bicyclo[2.2.2]octa-5,8-diene-cis-diol permitted direct control over the structure of poly(1,4-phenylenevinylene), and particularly the degree of polymerization, the narrow molecular weight distribution, the end group, and the sequence structure of the final copolymer. By a similar route poly(cyclopentadienylenevinylene) has been prepared by ring-opening metathesis polymerization of bis(carboxylic esters) of bicyclo[2.2.1 ]hept-5-ene-l,2-diol and subsequent thermal elimination reaction from the precursor polymers ~~ (Eq. 18.36).

n

~

A v-~ ~

(18.36)

The temperature needed for thermal elimination was reasonably reduced to