Ionic Polymerization and Living Polymers

380 Pages·1993·7.42 MB·English

by  Michael Szwarc, Marcel Van Beylen (auth.)

Ionic
Polymerization
and Uving
Polymers
Michael Szwarc
Marcel Van Beylen
m
SPRINGER-SCIENCE+BUSINESS MEDIA, B.V.
© 1993 Springer Science+Business Media Dordrecht
Originally published by Chapman & HalI, Inc. in 1993
Softcover reprint of the hardcover 1s t edition 1993
AlI rights reserved. No part of this book may be reprinted or reproduced or utilized
in any form or by any electronic, mechanical or other means, now known or
hereafter invented, including photocopying and recording, or by an information
storage or retrieval system, without permission in writing from the publishers.
Library of Congress Cataloglng-in-Publicatlon Data
Szwarc, Michael.
Ionic polymerization and living polymers I Michael Szwarc and
Marcel Van Beylen.
p. cm.
Includes index.
ISBN 978-94-010-4649-7 ISBN 978-94-011-1478-3 (eBook)
DOI 10.1007/978-94-011-1478-3
1. Additional polymerization. I. Van Beylen, Marcel. m. Title.
QD281.P6S99 1993
547'.28--dc20 92-2344
CIP
British Lil>rary Cataloguing in Publication Data also available.
to Marysia and Chris
Contents
Preface ix
1. Introduction 1
1. Comparison of Ionic and Radical Polymerizations 1
2. Developments of Ionic Polymerization 5
3. Living and Dormant Polymers 12
3.1. Definition of Living Polymers and Their Stability 12
3.2. The "Seeding" Technique 19
3.3. Dormant Polymers; Rate Constant of Propagation 21
3.4. Determination of the Concentration of Living
Polymers 22
3.5. Synthetic Value of Living Polymerization 24
4. Polymerizability and the Monomer-Living Polymer
Equilibria 25
2. Ionic Species 39
1. Formation of Ions 39
2. Ionophores and Ionogens, Ion-Pairs, and Covalent
Species 41
3. Free Ions and Ion-Pairs 43
4. Different Types of Ion-Pairs 48
5. Equilibria Between Free Ions and Ion-Pairs:
Conductance Studies 58
6. Heat and Entropy of Dissociation of Ion-Pairs 64
7. Triple Ions 65
8. Higher Ionic Aggregates 70
9. Dynamics of Interconversions Between Ionic Species 72
3. Initiation and Propagation of Ionic Polymerization 87
1. General Remarks 87
2. Initiation and Propagation Induced by Salts 89
2.1. Initiation and Propagation of Polymerization by
Free Ions 89
v
vi / Contents
2.2. Initiation and Propagation of Polymerization by
Ion-Pairs 92
2.3. Initiation and Propagation of Cationic
Polymerization by Free Ions and Ion-Pairs 130
2.4. Role of the Solvent 141
2.5. Initiation and Propagation of Ionic Polymerization
in the Gaseous Phase 144
3. Initiation and Propagation Involving Lithium Alkyls 147
3.1. Structure of Alkyl Lithiums 147
3.2. Initiation of Anionic Polymerization by Alkyl
Lithiums 150
3.3. Interaction of Alkyl Lithiums with Solvating or
Complexing Agents 157
3.4. Bifunctional Lithium Initiators 158
3.5. Propagation of Polystyrene Initiated by Alkyl
Lithiums 159
3.6. Propagation of Lithium Polydienes 162
3.7. Stereochemistry of Propagation of Lithium
Polydienes 165
3.B. Effect of Solvating Agents on Propagation Induced
by Alkyl Lithiums 169
4. Initiation of Cationic Polymerization by Protonic
Acids: Role of Esters (Including Halides) 172
4.1. General Observations 172
4.2. Self-Associations of Protonic Acids and the
Homoconjugation 174
4.3. Mechanism of Protonation of Monomers 177
4.4. Problem of Covalent-Ionic Equilibria 179
4.5. Esters Derived from Vinyl Monomers 186
4.6. Stopped-Flow Experiments 194
4.7. Living Cationic Polymerization 202
4.B. Uniformity of Polymers 210
4.9. Some Comments on the Kinetics of
Polymerization of Vinyl Ethers Initiated by the
HI-I2 System 212
4.10. Some Experimental Results 213
5. Initiation of Polymerization by Lewis Bases and Acids:
Problem of Zwitterions 215
5.1. Lewis Bases 215
5.2. Lewis Acids 218
5.3. Spontaneously Initiated Zwitterionic
Copolymerizations 221
6. Initiation of Cationic Polymerization by Friedel-Crafts
Reagents in Conjunction with Co-initiators 223
Contents / vii
6.1. General Features of Friedel-Crafts Reagents 223
6.2. Complexes of FC Reagents with Protogens 225
6.3. Initiation of Cationic Polymerization by FC
Reagents in Conjunction with Cationogens 227
7. Initiation of Polymerization by Electron Transfer and
Related Topics 230
7.1. General 230
7.2. Solutions of Alkali Metals 232
7.3. Structure and Properties of Solvated Electrons
and Negative Alkali Ions 234
7.4. Reactivity of Alkali Metal Solutions 236
7.5. Homogeneous Electron Transfer; Initiation of
Anionic Polymerization 239
7.6. Initiation of Anionic Polymerization by a
Heterogeneous Electron Transfer 247
7.7. Formation of Radical-Cations 249
7.8. Initiation of Cationic Polymerization by Electron
Transfer 251
7.9. Initiation of Radical Chain Process by Electron
Transfer 257
7.10. Two Simultaneous Homopolymerizations 259
7.11. Field Emission, Field Ionization, and Electrolysis 262
8. Polymerization Initiated by High Energy Radiation 264
8.1. Ionizing Radiation 264
8.2. Radiolysis of Monomers 265
8.3. Kinetics of Radiation-Induced Polymerization 267
8.4. Solvent Effects in ,,(-Initiated Polymerization of
Vinyl Ethers 270
9. Initiators Involving AI, Fe, Zn, and Other
Metallo-Organics 274
9.1. Al-Zn Oxyalkoxides 274
9.2. Pseudoanionic Polymerization of E-Caprolactone 277
9.3. Metalloporphyrins-Catalysts 282
9.4. Stereoselection and Stereoelection 284
9.5. Group-Transfer Polymerization 288
10. Activated Monomer Mechanism 292
10.1. Polymerization of NCA Initiated by Primary and
Secondary Amines 292
10.2. Polymerization Initiated by Aprotic Bases 293
10.3. The Activated Monomer Mechanism in Lactam
Polymerization 295
10.4. The Real Systems 297
10.5. Cationic Polymerization of Lactams 298
viii I Contents
10.6. Activated Monomer Propagation in Cationic Ring
Opening Polymerization of Cyclic Ethers 299
4. Elementary Steps of Polymerization Other Than Initiation
or Propagation 319
1. Termination 319
1.1. General Remarks 319
1.2. Unimolecular Termination 320
1.3. Bimolecular Termination Involving Two Growing
Polymers 324
1.4. Other Bimolecular Terminations 325
1.5. Proper Termination Caused by Solvents or
Impurities 325
2. Intramolecular Proton or Hydride Ion Transfers and
Other Isomerizations 326
3. "Wrong" Monomer Addition 328
4. Chain-Transfer 330
5. Proton Traps 332
6. Polymerization of Isobutene Initiated by Cumyl
Chloride and Its Analogues 333
7. Ring-Chain Competitions 334
7.1. Branching and Ring Formation 334
7.2. Ring-Chain Equilibrium 335
7.3. Overview of Earlier Observations 336
7.4. Simultaneous Polymerization of Propylene Sulfide
and Cyclization of Its Polymer 339
7.5. Alteration of Growing Polymer End-Groups 341
S. Ionic Copolymerization 347
1. General Schemes of Copolymerization and the
Crossover Constants 347
2. Reactivity and Basicity of Monomers 354
3. Reactivity Ratios: Composition of Copolymer and Feed 354
4. Copolymerization and Homopolymerization 358
5. System Li-Polystyryl and Li-Polybutadienyl in
Hydrocarbon Solvents 359
6. Consequences of Equilibria Between Unreacted
Aggregates and Reactive Nonassociated Polymers:
Mixed Dimerizations 361
7. Reversible Copolymerization:
System 2-Vinylnaphthalene-Styrene 366
8. Cationic Copolymerizations 373
Index 377
Preface
Two basic questions, namely "why" and "how," dominate the treatment
of any scientific or technological problem. In this work we are more often
concerned with the question "why" than "how." We try here to rationalize
and explain why the various ionic processes yielding polymeric molecules
proceed as observed, and how their rates and the equilibria established in
these systems are affected by the external conditions and by the structure
of the reagents. Moreover, we look upon anionic and cationic polymeri-
zations from a comparative point of view, stressing, wherever possible, the
similarity and differences between these two modes of the reaction.
The scope of the known ionic polymerizations is too large to allow a
comprehensive treatment of all of them in a volume of moderate size.
Hence, some subjective selection of topics is inevitable and, not surpris-
ingly, those studied in the course of our own investigations gained most
of our attention.
The statements made in this monograph do not claim to be authoritative.
We expressed our opinions concerning some controversial subjects, trying
then to justify them by the results of reported experiments and by logical
arguments. We proposed a few experiments that might clarify the problems
under consideration or perhaps enlarge their scope. We did not hesitate
to outline some hypothetical schemes in the hope that they might induce
the reader to conceive better solutions for the debated questions.
It is not our intention to survey all the available literature. Some valuable
papers dealing with important subjects have been omitted due to lack of
space. For example, the microstructure of polymer chains and the pertinent
statistical considerations might have been discussed more extensively, but
the space restriction prevented further elaboration of this subject.
This monograph is composed of five chapters. In Chapter 1 the ionic
addition polymerization is contrasted with the more widely known radical
process. The historical development of ionic polymerizations is then briefly
outlined. The terms "living polymers" and "living polymerization" are
be
xl Preface
defined, the significance of "living polymers" for polymer science is stressed,
and its relation to the thermodynamic of propagation is elaborated.
We believe that a general discussion of the modes of formation of ions
and of their behavior in solution would be helpful for the readers of this
monograph. Therefore, we devoted Chapter 2 to a review of this subject,
emphasizing the problems of association of free ions into ion-pairs and still
higher aggregates.
The initiation and propagation of ionic polymerizations are the topics
covered in Chapter 3. Combined treatment of the propagation processes
and those concerned with the initiation seems justified. Indeed, propa-
gation may be looked upon as the initiation of further growth of polymeric
molecules induced by the active polymers. Other processes affecting the
course of polymerization, such as termination, chain-transfer, and back-
biting, are treated in Chapter 4, whereas Chapter 5 is devoted to ionic
copolymerization.
Finally, we wish to thank our friends and colleagues, Dr. S. Bywater,
Profs. K. Matyjaszewski, G. Olah, S. Penczek, A. Persoons, P. H. Plesch,
Dr. M. Sawamoto, Prof. V. Stannett, Prof. J. P. Vairon, and Dr. O. W.
Webster, listed here in alphabetic order, for their comments and discussions
most helpful in writing this book. One of us (M.V.B.) wishes to thank the
National Fund for Scientific Research of Belgium for their financial support
during the preparation of this monograph.
1
Introduction
1. Comparison of Ionic and Radical Polymerizations
Ionic polymerization, like the well-known radical polymerization, is a
chain polyaddition. It starts with a reaction of a monomer with a species
capable of forming an electrically charged or highly polar active group on
the added monomer molecule. Interaction of this group with another mol-
ecule of the monomer results in the formation of a covalent bond linking
these two species, and simultaneously regenerates the active group on the
newly added molecule. Such a repetitive covalent bonding of the monomer
molecules to the active end-group, and simultaneously the repeated re-
generation of the latter on the added unit, produces a growing polymer
chain.
Ionic polymerization is referred to as a classic cationic when the active
terminal group is positively charged, or as a pseudocationic (or a cationic
coordination) if this group forms the positive end of an active dipole. By
the same token we refer to ionic polymerization as a classic anionic when
the charge of the active group is negative, or as a pseudoanionic (or an
anionic coordination) when the active group forms the negative end of an
active dipole. Whenever electrically charged end-groups are formed, suit-
able counterions have to be present in the polymerizing system to ensure
its electric neutrality.
It is instructive to compare the radical and ionic modes of polymerization.
Radical polymerization is initiated by adding to a molecule of monomer a
small radical produced from a suitable initiator. The added radical then
forms the tail-group of the ultimately produced polymer, but its nature,
or the nature of the initiator, does not influence the propagation rate
constant, the selectivity, or the stereochemistry of the ensuing propagation.
All these features of radical propagation are determined by the nature of
1