Cyclic Polymers PDF
Preview Cyclic Polymers
CYCLIC POLYMERS CYCLIC POLYMERS Edited by J. A. SEMLYEN Department of Chemistry, University of York, UK ELSEVIER APPLIED SCIENCE PUBLISHERS LONDON and NEW YORK ELSEVIER APPLIED SCIENCE PUBLISHERS LTD Crown House, Linton Road, Barking, Essex IGll 8JU, England Sole Distributor in the USA and Canada ELSEVIER SCIENCE PUBLISHING CO., INC. 52 Vanderbilt Avenue, New York, NY 10017, USA WITH 22 TABLES AND 152 ILLUSTRATIONS © ELSEVIER APPLIED SCIENCE PUBLISHERS LTD 1986 Softcover reprint of the hardcover 1s t edition 1986 British Library Cataloguing in Publication Data Cyclic polymers. 1. Polymers and polymerization 2. Cyclic compounds I. Semlyen, J. A. 547.7 QD381 Library of Congress Cataloging in Publication Data Cyclic polymers. Bibliography: p. Includes index. I. Polymers and polymerization. 2. Cyclic compounds. I. Semlyen, J. A. II. Title. QD38l.C93 1986 547'.5 85-16062 ISBN-13: 978-94-010-8354-6 e-ISBN-13: 978-94-010-8354-6 DOl: 10.1007/978-94-010-8354-6 The selection and presentation of material and the opinions expressed in this publication are the sole responsibility of the authors concerned Special regulations for readers in the USA This publication has been registered with the Copyright Clearance Center Inc. (Ccq, Salem, Massachusetts. Information can be obtained from the CCC about conditions under which photocopies of parts of this publication may be made in the USA. All other copyright questions, including photocopying outside of the USA, should be referred to the publisher. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publisher. Preface Synthetic polymers based on long chain molecules have been investigated intensively for over 50 years. They have found important applications as plastics, fibres, rubbers and other materials. The chain molecules may be simple linear structures or they may be branched or cross-linked. During the past decade, sharp fractions of the first synthetic cyclic polymer have been prepared. These fractions of cyclic poly(dimethyl- siloxane) consist of ring molecules containing hundreds of skeletal bonds. Some of their properties have been found to be quite different from those of the corresponding linear polymers. Synthetic cyclic polymers, including cyclic polystyrene, have joined the naturally occurring circular DNAs as examples of substantially large ring molecules. This book aims to review current knowledge of cyclic polymers and biological ring macromolecules. In addition, it discusses theories of cyclic macromolecules and describes cyclization processes involving long chain molecules. Since 1865, when Kekule proposed a simple ring structure for benzene, larger and larger ring molecules have been synthesized in the laboratory and discovered in nature. Many more examples are to be expected in the future. In time, large ring molecules should take their proper place alongside long chain molecules as one of the two possible constituent structural units of polymers. J. A. SEMLYEN v Contents Preface v List of Contributors ix I. Introduction J. A. SEMLYEN 2. Theory of Cyclic Macromolecules 43 WALTHER BURCHARD 3. Preparation of Cyclic Polysiloxanes 85 P. V. WRIGHT and MARTIN S. BEEVERS 4. Comparison of Properties of Cyclic and Linear Poly(dimethyl- siloxanes) 135 CHRISTOPHER J. C. EDWARDS and ROBERT F. T. STEPTO 5. Neutron Scattering from Cyclic Polymers 167 KEITH DODGSON and JULIA S. HIGGINS 6. Organic Cyclic Oligomers and Polymers 197 HARTWIG HOCKER 7. Circular DNA 225 J. C. WANG vii viii CONTENTS 8. Cyclic Peptides 261 ALAN E. TONELLI 9. Spectroscopic Studies ofCyclization Dynamics and Equilibria 285 MITCHELL A. WINNIK 10. Cyclization, Gelation and Network Formation 349 S. B. Ross-MuRPHY and ROBERT F. T. STEPTO Index 381 List of Contributors MARTIN S. BEEVERS Department of Chemistry, University of Aston in Birmingham, Gosta Green, Birmingham B4 7ET, UK WALTHER BURCHARD Institute of Macromolecular Chemistry, University of Freiburg, Stefan-Meier-Strasse 31, 7800 Freiburg im Breisgau, Federal Republic of Germany KEITH DODGSON Department of Chemistry, Sheffield City Polytechnic, Pond Street, Sheffield SI 1 WB, UK CHRISTOPHER J. C. EDWARDS Department of Polymer Science and Technology, University of Man- chester Institute of Science and Technology, PO Box 88, Manchester M60IQD, UK (Present address: Unilever Research, Port Sunlight Laboratory, Quarry Road East, Bebington, Wirral, Merseyside L633JW, UK) JULIA S. HIGGINS Department of Chemical Engineering, Imperial College ofS cience and Technology, Prince Consort Road, ILondon SW7 2BY, UK ix x LIST OF CONTRIBUTORS HARTWIG HOCKER Institute for Macromolecular Chemistry, University of Bayreuth, D- 8500 Bayreuth, Federal Republic of Germany SIMON B. Ross-MURPHY Unilever Research, Colworth Laboratory, Colworth House, Sharnbrook, Bedford MK44 lLQ, UK J. A. SEMLYEN Department of Chemistry, University of York, Heslington, York, Y015DD, UK ROBERT F. T. STEPTO Department of Polymer Science and Technology, University of Man- chester Institute of Science and Technology, PO Box 88, Manchester M60 1QD, UK ALAN E. TONELLI AT & T Bell Laboratories, Murray Hill, New Jersey 07974, USA J. C. WANG Department of Biochemistry and Molecular Biology, Harvard University, 7 Divinity Avenue, Cambridge, Massachusetts 02138, USA MITCHELL A. WINNIK Lash Miller Laboratories, Department of Chemistry and Erindale College, University of Toronto, Toronto, Ontario, Canada M5S 1A1 PETER V. WRIGHT Department of Ceramics, Glasses and Polymers, University of Sheffield, Elmfield, Northumberland Road, Sheffield S10 2TZ, UK CHAPTER 1 Introduction J. A.SEMLYEN Department of Chemistry, University of York, UK LINEAR POLYMERS AND CYCLIC POLYMERS In the 1930s, Staudinger's macromolecular hypothesis was generally accepted and his long chain formulae for polystyrene, polyoxymethylene and other polymers became fully established.! As described by Flory, 2 ring structures had been assigned to some polymers earlier in the century but they were later shown to be erroneous. It soon became accepted that synthetic polymers were based on long chain molecules that could be linear, branched or cross-linked to form networks. The linear polymers could have mean molar masses of millions, corresponding to tens of thousands of skeletal bonds. 2 In this book, macromolecules based on large ring molecules rather than long chain molecules are described. Cyclic polymers are compared with linear polymers. Although well-characterized branched and network cyclic polymers have yet to be prepared, it is noted that cyclic polymers could have cyclic or linear branches and networks of rings could be catenated or have no free ends. Furthermore, there is a wide range of possibilities for types of polymer built from long chains and large rings. It will surely be a long time before a substantial number of such structures are synthesized and characterized. It might be asked, 'How many skeletal atoms (on average) must there be in the ring molecules before we have a cyclic polymer?' There are indications that cyclic poly(dimethyl siloxane) with about lOO skeletal atoms shows the properties expected of a polymer, whereas ring fractions containing substantially fewer skeletal atoms do not. The term macrocyclic 2 J. A. SEMLYEN (Greek, macros = long) is being used in the literature to describe rings with relatively few skeletal atoms, such as 15 or 20. These 'macrocyclics' do not show macromolecular behaviour and the term is a misnomer. They could be called medium rings or the term mesocyclic (Greek, mesos = middle or intermediate) might be used to describe them. The term macrocyclic could then be reserved for the cyclic polymers and ring macromolecules of the kind described in this book. Some cyclic macromolecules, including circular deoxyribonucleic acids (DNA) have been found to occur in nature. In Chapters 7 and 8, circular DNA and cyclic peptides are described. Some cyclic oligo saccharides have been discovered, including cycloamyloses (cyclodextrins) and a cyclic oligosaccharide composed of four, five and six trisaccharide repeat units. 3 Much larger cyclic polysaccharides may be found or synthesized in the future. Cyclic biological macromolecules have attracted considerable interest and are expected to become increasingly important in the years ahead. SOME DIFFERENCES BETWEEN THE PROPERTIES OF CYCLIC AND LINEAR POLYMERS Ring and chain macromolecules are topologically distinct, so there are many differences in their properties and behaviour. Some examples have been chosen to illustrate these differences in this chapter. Other examples are given later in the book (for example, the stabilization of supercoiling in large DNA rings in Chapter 7).. The Presence or Absence of End-groups A variety of chemical groups may terminate polymer chain molecules. The nature of these end-groups can be important. For example, they can react with other suitable molecules or they can be used to make analytical determinations as in end-group analysis. Ring polymers have no ends and no end-groups. The chemistry of end- groups developed by many research workers (see, for example, Ref. 4) is obviously not applicable to large ring molecules. In this connection, it is noted that the name cyclic poly(dimethyl siloxane) is a precise name for the ring polymer. Linear poly(dimethyl siloxane) carries HO-, (CH 3hSi- or other groups at the ends of the chain molecules. No reference is made to these groups in its name.
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