Contemporary Topics in Polymer Science: Volume 2 PDF
Preview Contemporary Topics in Polymer Science: Volume 2
Contemporary Topics in POLYMER SCIENCE Volume2 A Continuation Order Plan is available for this series. A continuation order will bring delivery of each new volume immediately upon publication. Volumes are billed only upon actual shipment. For further information please contact the publisher. Contemporary Topics in POLYMER SCIENCE Volume2 Edited by EH M. Pearce Polytechnic Institute of New York Brooklyn, New Y ork and John R. Schaefgen Pioneering Research Laboratory Textile Fibers Department E. I. du Po nt de Nemours and Company, Ine. Wilmington, Delaware PLENUM PRESS· NEW YORK AND LONDON Library of Congress Cataloging in Publication Data Main entry under title: Contemporary topics in polymer science. Proceedings of the biennial polymer symposia of the A.C.S. Division of Polymer Chemistry held at Key Biscayne, Florida, November 20-24, 1976 Includes indexes. 1. Polymers and polymerization-Congresses. I. Pearce, EH M. 11. Schaef gen, John R. IH. American Chemical Society. Division of Polymer Chem istry. QD380.C64 547'.84 77-21311 ISBN 978·1·4615'6739'4 ISBN 978·1'4615'6737'0 (eBook) DOI 10.1007/978'1'4615'6737'0 Proceedings of the Eighth Biennial Polymer Symposium of the Division of Polymer Chemistry held at Key Biscayne, Florida on November 20-24, 1976 © 1977 Plenum Press, New York Softcover reprint of the hardcover 1s t edition 1977 A Division of Plenum Publishing Corporation 227 West 17th Street, New York, N.Y. 10011 All righ ts reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written permission from the Publil'her PREFACE This marks the first publieation of the Division of Polymer Chemistry, Ine., Ameriean Chemieal Soeiety, bien nia1 polymer symposia. This new series will feature new and novel deve10pments in polymer seience and technology as presented at these symposia. This volume reports the proeeeding of the Eighth Bi ennia1 Polymer Symposium of the Division of Polymer Chem istry held at Key Biseayne, Florida on November 20 - 24, 1976. It is eoneerned with a number of developments having both scientifie and praetical significance. These inelude polymerie liquid erysta1 systems in the melt and in solu tion, polymer blends, and nove1 polymers in extended chain conformations produced by solid-state polymerization. Rates of eonformationa1 transitions and cis-trans isomeri zations in polymers, a new look at rubber elasticity theory and new synthetie procedures for stiffening polymer ehains are some of the new scientific developments. The book conc1udes with two approaches for the use of polymers in the important field of slow drug release. The authors are all we1l-known seientists and inelude Nobel Laureate Paul Flory, first recipient of the Polymer Division Award whieh was presented at this Symposium. Eli M. Pearee John R. Schaefgen v CONTENTS The Molecular Theory of Rubber Elasticity 1 (Polymer Division Award Address) P. J. Flory Liquid Crystalline Solutions from POlyhydrazides in Aqueous Organic Bases . . . . . . . 19 J. D. Hartzler and P. W. Morgan Properties of Rigid-Chain Polymers in Dilute and Concentrated Solutions . . . . 55 G. C. Berry Phase Equilibria in Rigid-Chain Polymer Systems " . • . . . . . . . 97 S. P. Papkov Liquid Crystal Polymers. II. Preparation and Properties of Polyesters Exhibiting Liquid Crystalline Melts . . • . . . . • . . . 109 F. E. McFarlane, V. A. Nicely, and T. G. Davis Problems in Compatibility Studies . . . • . . • • . 143 F. E. Karasz and W. J. MacKnight Compatibility and Phase Separation in Polymer Mixtures . . •. .• . . • . • • . 157 T. K. Kwei Some Studies on the Rates of Conformational Transitions and of Cis-Trans Isomerizations in Flexible Polymer Chains . • . • . . . . • . . • • • • . 171 H. Morawetz vii viii CONTENTS Topochemical Effects in Chemical Reactions of Crystalline Organic Compounds 189 J. B. Lando The Solid State Synthesis and Properties of Photoconducting, Metallic, and Superconducting Polymer Crystals • 205 R. H. Baughman Acetylene Containing Aromatic Heterocyclic Polymers 235 F. E. Arnold, F. L. Hedberg, and R. F. Kovar Biodegradable Polymers for Sustained Drug Delivery • . . . . • • . . . . • 251 A. Schindler, R. Jeffcoat, G. L. Kimmel, C. G. Pitt, M. E. Wall, and R. Zweidinger Design of Transdermal Therapeutic Systems 291 S. K. Chandrasekaran and J. E. Shaw Index 309 TRE MOLECUIAR TREORY OF RUBBER EIASTICITY Paul J. Flory Stanford University Stanford, California 94305 Once the existence of polymer chains as covalent structures became established a half century ago, the understanding of the molecular basis of the high elasticity characteristic of rubber-like substances presented itself as a foremost challenge . The first attemPtJ, 2 to explain this remarkable property may be said to date from the beginning of molecular theory as applied to polymers. Al though the subject today is old, it is of continuing interest and one in which much remains to be done before an ac ceptable state of completion will have been attained. The theory of rubber elasticity is cent ral to polymer science. This property of recoverable, high extensibility is manifested under suitable conditions by virtually all macromolecular substances consisting predominantly of long chains. Moreover, it is exhibited exclusively by materials so constituted. Rubber elasticity is essential to the functioning of elastic proteins and of muscle. It is operative also in the deformation of semi-crystalline polymers, generally not included in the category of rubbers. The molecular theory of rubber elasticity rests on the premise that the stored elastic free energy , and the force that derives therefrom, originate within the molecular chains comprising the structure, usually a covalent net- 2 P.J. FLORY work. The stress comprises the sum of the responses of the chains to the alteration of their configurations resulting from the macroscopic strain. Interactions between chains, although large, are asserted to be of no importance on the grounds that they are not altered appreciably by the strain (which orients individual chain units only minutelyon the average) • The validity of this latter assertion, or approximation, has long been contested • The results of recent experimen tal investigations on rubber ela sticity (cf. seq .) , when compared with theory, provide incontrovertible con firmation of this basic premise. Equally compelling in direct support is provided by recent studies 3 confirming earlier predictions4 that the configurations of linear polymer chains in the amorphous state are random; i.e., theyare unperturbed by interactions with their neighbors, the pro fusion of such interactions notwithstanding. 5 ,6 This being true, it must follow conversely that interactions with neigh bors do not depend appreciably on the chain configuration . Hence, when the chains undergo orientation by strain, these interactions do not contribute to the elastic free energy , and to the stres s . This premise, now securely established, provides us with a simplification that turns an otherwise vastly com plicated si.tuation into one that is tractable. Since it is legitimate to disregard intermolecular effects, one may reasonably approach the problem by first considering a single linear chain. Elasticity of an Isolated Chain Chains of the usuallength between junctions in a rub ber network consist of several hundred skeletal bonds. The distribution function Wer) for the vector r. connecting the ends of a chain of this length is satisfactorily approximated by the Gaussian function? 1. e. , MOLECULAR THEORY OF RUBBER ELASTICITY 3 W(r) = (3/2TT(r2)0)3/2 eXp[-(3/2(r2)0)r2] (I) where (r2)0 is the mean-square separation of the ends of the free chain. It follows that the free energy of the chain is given by = A(r) C - kT ..en W(r) (2) where k is Boltzmann s constant; C is a constant and C (T) I is a function of temperature. The distribution function W(r) relates directly to the free energy and not to the entropy contribution -T8 as assumed in early expositions on rubber elasticity.4,9-13 Confusion arising from this mistaken identification continues. 14 The average retractive force exhibited by the chain held at fixed length r is 2 -I f= [dA(r)/dr]T = 3kT(r )0 r (3) Thus, the average force is directly proportional to r. It is also proportional to the absolute temgerature T, and to the inverse of the molecular parameter (r2)0 that characterizes the chain at the chosen temperature T. Proportionality of I to r, which underlies the analysis of networks, follows directly from the assertion that W(r) is Gaussian; in fact, eq. I may be derived from eq. 3. Elasticity of Networks In a network the effects of the macroscopic strain are transmitted to the chains through the junctions at which the ends of chains are multiply joined. The lengths r of the chains are determined by the relative locations of the pairs of junctions joined by linear chains. Hence, the displace ments of the junctions by the strain is the issue of pivotal concern.
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