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Liquicl Crystalline Polymers Report of the Committee on Liquid Crystalline Polymers NATIONAL MATERIALS ADVISORY BOARD Commission on Engineering and Technical Systems National Research Council NMAB-453 National Academy Press 1990
NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. This report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Frank Press is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsiblity for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Robert M. White is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Samuel O. Thier is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Frank Press and Dr. Robert M. White are chairman and vice chairman, respectively, of the National Research Council. * ** * * * * ** ** * * * *** *** This study by the National Materials Advisory Board was conducted under Contract No. MDA903-89-K-0078 with the Department of Defense and the National Aeronautics and Space Administration. Library of Congress Catalog Card Number 90-60385. International Standard Book Number 0-309-04231-3. This report is available from the Defense Technical Information Center, Cameron Station, Alexandria, VA 22304-6145. S1 10 Cover: Schematic arrangement of molecules in the smectic phase (top left} and the nematic phase (bottom right) of a liquid crystalline material. Printed in the United States of America. F~stPrinung, J~mel990 Second Printing, S~p~mberl991
ABSTRACT The remarkable mechanical properties and thermal stability of fibers fabricated from liquid crystalline polymers (LCPs) have led to the use of these materials in structural applications where weight savings are critical. Advances in processing of LCPs could permit the incorporation of these polymers into other than uniaxial designs and extend their utility into new areas such as nonlinear optical devices. However, the unique feature of LCPs intrinsic orientational order is itself problematic, and current understanding of processing with control of orientation falls short of allowing manipulation of macroscopic orientation (except for the case of uniaxial fibers). This report reviews the current and desirable characteristics of LCPs and identifies specific problems and issues that must be addressed so that advances in the use of these unique polymers can be expedited. . · .
PREFACE The subject of liquid crystalline polymers (LCPs) transcends classical polymer chemistry and physics, and it extends the conventional boundaries of rheology and processing. Properties of these new materials are, on the one hand, reminiscent of amorphous metals, while simultaneously exhibiting attributes of organic single crystals. In this report we attempt to evaluate the potential of LCPs in selected areas, pointing out obstacles to further progress and suggesting where efforts in research and development might expedite LCP utilization in current and new technologies. Because the subject touches on a wide range of topics, we have attempted to make this report accessible by adhering to a parallel presentation scheme. Thus, insofar as possible, the key chapters of the report are divided into the following headings: Macromolecular Design and Synthesis Understanding and Theory Processing Mechanical Properties Blends and Composites Nonlinear Optical Properties When useful, the headings are subdivided further into sections on lyotropic (solution processed) and thermotropic (melt processed) LCPs. Occasionally, one of these sections may be partitioned into separate subsections, e.g., mainchain and sidechain LCPs. We have also tabulated a glossary of abbreviations and acronyms (Appendix B). The report is intended to enable persons unfamiliar with the field to obtain a general appreciation of LCPs in the context of conventional polymers (see Chapter 2, Background) and to proceed to contemporary issues associated with specific topics (e.g., nonlinear optical characteristics of LCPs). We include an appendix indicating approximate current federal funding levels for research on these new classes of polymers (Appendix A).
ACKNOWLEDGMENTS The committee is indebted to the liaison representatives for keeping the discussion of LCPs focused; special thanks also go to Stanley Wentworth for contributing the section in Chapter 3 on environmental stability. In addition, we are very appreciative of the following individuals who brought detailed technical material to committee meetings: Mohamed Zaidi, Alcoa; Harvey Ledbetter, Dow Chemical Company; John Blackwell, Case Western Reserve University; James Stamatoff, Celanese Corporation; Ian Ward, University of Leeds; Edwin Thomas, University of Massachusetts; Brian Kushner, BDM Corporation Paras Prasad, State University of New York at Buffalo; Richard Lytel, Lockheed Corporation, Palo Alto; Larry Dalton, University of Southern California; Judy Chen, Boeing Company, Seattle; Roger Morgan, MMI; James Wolf, Boeing; James Economy, University of Illinois; lames LyerIa, Andreas Muehlebach, and Do Yoon, IBM Corporation, San Jose; and Richard Lusignea and Adi Guitar, Foster-Miller, Inc. Finally, the chairman expresses earnest thanks to the committee members for their constructive contributions and enthusiastic participation in the writing of this report, and to Marlene Crowell, who provided secretarial support to the committee throughout the course of its deliberations. Edward T. Samulski Chairman · - V11
COMMITTEE ON LIQUID CRYSTALLINE POLYMERS CHAIRMAN EDWARD T. SAMULSKI, Department of Chemistry, University of North Carolina at Chapel Hill MEMBERS MORTON M. DENN, Department of Chemical Engineering, University of California at Berkeley DONALD B. DuPRE, Department of Chemistry, University of Louisville, Louisville, Kentucky NATHAN D. FIELD, Consultant, Elkins Park, Pennsylvania (formerly, Vice-President, R&D, Dartco Manufacturing, Inc.) ANSELM C. GRIFFIN III, Department of Chemistry and Polymer Science, University of Southern Mississippi, Hattiesburg MICHAEL JAFFE, Hoechst-Celanese Research Division, Summit, New Jersey STEPHANIE L. KWOLEK, Consultant, Wilmington, Delaware (formerly with the Du Pont Company, Fibers Department, Pioneering Research Laboratory) MALCOLM B. POLK, School of Textile Engineering, Georgia Institute of Technology, Atlanta DUSAN C. PREVORSEK, Polymer Laboratory, Allied-Signal Corporation, Morristown, New Jersey MONTGOMERY T. SHAW, Institute of Materials Science, University of Connecticut, Storrs UERICH SUTER, Institute for Polymers, Eidgenossische Technische Hochschule, Zurich, Switzerland DAVID J. WILLIAMS, Corporate Research Laboratories, Eastman Kodak Co., Rochester, New York LIAISON REPRESEN7~AT~ES NORBERT BIKALES, Polymers Program, National Science Foundation, Washington, D.C. TED HELMINIAK, Wright-Patterson Air Force Base, Ohio TERRY ST. CLAIR, Polymer Materials Branch, National Aeronautics and Space Administration, Langley Research Center, Hampton, Virginia 1X
DONALD UERICH, Air Force Office of Scientific Research, Bolling Air Force Base, Washington, D.C. STANLEY E. WENTWORTH, U. S. Army Materials Technology Laboratory, Watertown, Massachusetts KENNETH WYNNE, Division of Materials Research, National Science Foundation, Washington, D.C. NMAB STAFF STANLEY M. BARKIN, Associate Director and Program Officer MARLENE R. CROWELL, Project Assistant x
CONTENTS EXECUTIVE SUMMARY Page 1. CONCLUSIONS AND RECOMMENDATIONS 5 Macromolecular Design and Synthesis 5 Theoretical Understanding 7 Processing 8 Mechanical Properties 9 Blends ant! Composites 10 Nonlinear Optical Properties 10 2. BACKGROUND 13 Macromolecular Design and Synthesis Understanding and Theory Processing Mechanical Properties Blends and Composites Electro-Optical Properties 3. 4. PROPERTIES OF LIQUID CRYSTALLINE POLYMERS: CURRENT AND DESIRABLE CHARACTERISTICS Structural Properties Functional Properties Environmental Stability PROBLEMS AND ISSUES: RECOMMENDATIONS FOR FURTHER WORK Macromolecular Design and Synthesis Understanding and Theory Processing Mechanical Properties Blends and Composites Nonlinear Optical Properties X1 18 25 27 30 36 38 49 49 63 68 71 71 74 ~8 81 85 92
Page APPENDIXES A. A. Current Funding Levels/Sources for LCP Research 101 B. Glossary of Abbreviations 103 C. Biographical Sketches of Committee Members 105 X11
FIGURES AND TABLES Figures 2.1 Schematic indication of the differences between an isotropic and a liquid crystalline polymer fluid 2.2 An absence of translational order in the idealized nematic 2.3 Smectic stratification (lateral registration) in a polymer mesophase 2.4 Helicoidal cholesteric structure in a mainchain LCP 2.5 Condensation polymerization involving acidolysis 2.6 Representative potential thermotropic copolyesters Page 14 16 16 17 18 19 2.7 Synthesis of polyarylamides 20 2.8 Lyotropic polyamide unit structures 21 2.9 Synthesis of PBX polymers 22 2.11 2.12 4.1 4.2 Preparation of sidechain LCPs by free radical polymerization Preparation of sidechain LCPs by polyesterification Examples of preparation of sicIechain LCPs by derivitization of preformed polymers An illustration of the hierarchical morphology in fibers A plot of specific tensile strength vs. specific tensile modulus showing LCPs in context with other materials 23 23 24 34 56 Compressive strength vs. torsion modulus for some rigid rod polymers 82 Temperature dependence of dynamic mechanical tensile data (10 Hz) for HBA-HNA copolymers · · . x~ 84
Page Tables 2.1 3.1 3.2 Cold-forming methods for polymers Properties of Kevlar~ aramid fibers derived from lyotropic LCPs Yarn properties of some reinforcing fibers from LCPs 3.3 Properties of injection molded LCP ASTM bars 31 51 54 58 3.4 Classification of LCPs according to thermal behavior 59 3.5 3.6 Effect of gauge on flexural strength and modulus (ASTM Test Bars) 59 Comparison of barrier properties of LCPs and other polymer film 3.7 Important requirements for NLO applications 3.8 Requirements for SHG applications 3.9 Requirements for optical serial switching devices 3.10 NLO materials properties (inorganic and organic) 4.1A Properties of unidirectional epoxy composite with 60% fiber loading, 0° direction 62 63 64 64 67 86 4.1B Properties of unidirectional epoxy composite with 60% fiber loading 87 4.2 LCP-content blending regimes x~v 89