Handbook of Engineering and Specialty Thermoplastics, vol. 4 - Nylons

Table of contents :
List of Contributors xi 1. Engineering and Specialty Thermoplastics: Nylons 1 P. M. Visakh and Sabu Thomas 1.1 Polyamide-imides 1 1.2 Polyetherimide (PEI) 2 1.3 Poly(Ether-Block-Amide) 2 1.4 Aromatic Polyamides 3 1.5 Polyaniline 5 1.6 Polyimides 6 1.7 New Challenges and Opportunities 8 References 9 2. Polyamide Imide 11 Zulkifl i Ahmad 2.1 Introduction and History 11 2.2 Polymerization 13 2.3 Properties 19 2.4 Processing 27 2.5 Applications 30 2.6 Recent development on blends and composite 33 2.7 Conclusions 38 Refernces 38 3. Polyphthalamides 43 J. I. Iribarren, C. Aleman, J. Puiggali 3.1 Introduction and History 43 3.2 Polymerization and Fabrication 47 3.3 Properties 53 3.4 Chemical Stability 61 3.5 Processing 66 3.6 Applications 68 3.7 Developments in polyphthalamide based blends and composites and their applications 71 References 75 4. Polyetherimide 79 Sabrina Carraccio, Concetto Puglisi, and Giorgio Montaudo 4.1 Introduction and Hystory 79 4.2 Polymerization 82 4.3 Properties 88 4.4 Stability 92 4.5 Special Additives 99 4.6 Processing 99 4.7 Applications 101 4.8 Environmental Impact and Recycling 102 4.9 Recent Developments in Polyetherimides Based Blends and Composities 102 References 105 5. Poly(ether-block-amide) Copolymers, Properties and Applications 111 Annarosa Gugliuzza 5.1 Introduction 111 5.2 Synthesis and Micro-phase Separated Morphology 113 5.3 Nomenclature, Properties and Relevant Area Applications 117 5.4 Compounding and Special Additives 122 5.5 Environmental Impact and Recycling 123 5.6 Poly ether-block-amides Membrane in Separation Processes 124 5.7 Poly(ether-block-amide) Membranes in Food 133 5.8 Concluding Remarks 135 References 136 6. Aromatic Polyamides (Aramids) 141 Jose M. Garcia, Felix C. Garcia, Felipe Serna, and Jose L. de la Pena 6.1 Introduction and History 142 6.2 Polymerization and Fabrication 145 6.3 Properties 149 6.4 Chemical Stability 154 6.5 Special Additives 154 6.6 Processing 157 6.7 Applications 158 6.8 Environmental Impact and Recycling 161 6.9 Recent Developments in Aromatic Polyamides and their Applications 162 7. Polyaniline 183 Melek Kiristi and Aysegul Uygun 7.1 Introduction and History 183 7.2 Polymerization and Fabrication 184 7.3 Properties 186 7.4 Chemical Stability 188 7.5 Compounding and Special Additives 189 7.6 Processing 195 7.7 Applications 197 7.8 Environmental Impact and Recycling 202 7.9 Recent Developments in Polyaniline Based Blends and Composites and their Applications 203 References 205 8. Polyimides: Synathesis, Properties, Characterization and Applications 211 Abdolreza Hajipour, Fatemeh Rafiee, Ghobad Azizi 8.1 Introduction 211 8.2 Synthesis and Properties of Polyimides 213 8.3 Characterization and Analysis of Polyimides 258 8.4 Applications 261 References 277 Index 289

Citation preview

Handbook of Engineering and Specialty Thermoplastics

Scrivener Publishing 3 Winter Street, Suite 3 Salem, MA 01970 Scrivener Publishing Collections Editors James E. R. Couper Richard Erdlac Norman Lieberman W. Kent Muhlbauer S. A. Sherif

Ken Dragoon Rafiq Islam Peter Martin Andrew Y. С Nee James G. Speight

Publishers at Scrivener Martin Scrivener ([email protected]) Phillip Carmical ([email protected])

Handbook of Engineering and Specialty Thermoplastics Volume 4 Nylons

Edited by

Sabu Thomas and Visakh P.M.

Scrivener

WILEY

Copyright © 2012 by Scrivener Publishing LLC. All rights reserved. Co-published by John Wiley & Sons, Inc. Hoboken, New Jersey, and Scrivener Publishing LLC, Salem, Massachusetts. Published simultaneously in Canada. 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, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 7504470, or on the web at www.copyright.com. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., Ill River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008, or online at http://www.wiley.com/go/perrnission. Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. For general information on our other products and services or for technical support, please contact our Customer Care Department within the United States at (800) 762-2974, outside the United States at (317) 572-3993 or fax (317) 572-4002. Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic formats. For more information about Wiley products, visit our web site at www.wiley.com. For more information about Scrivener products please visit www.scrivenerpublishing.com. Cover design by Russell Richardson Library of Congress Cataloging-in-Publication ISBN 978-0-470-63925-2

Printed in the United States of America 10

9 8 7 6 5 4 3 2 1

Data:

Contents List of Contributors 1.

2.

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Visakh. P. M and Sabu Thomas 1.1 Polyamide-imides 1.2 Polyetherimide (PEI) 1.3 Poly(Ether-Block- Amide) 1.4 Aromatic Polyamides: 1.5 Polyaniline 1.6 Polyimides 1.7 New Challenges and Opportunities References

1 2 2 3 5 6 8 9

Polyamide Imide

Zulkifli Ahmad

2.1 Introduction and History 2.2 Polymerization 2.3 Properties 2.3.1 Solubility 2.3.2 Crystallinity 2.3.3 Thermal 2.3.4 Mechanical 2.3.5 Opto-electronic 2.3.6 Hydrogen bonding 2.4 Processing 2.5 Applications 2.5.1 Membrane Material 2.5.2 Coatings 2.5.3 Electronic 2.5.4 Optical 2.6 Recent Developments on Blends and Composites 2.6.1 Blends 2.6.2 Composites 2.7 Conclusions References

11 11 13 19 19 19 22 24 25 26 27 30 30 31 32 33 33 33 34 38 38 V

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Polyphthalamides /. I. Iribarren, С. Aleman, J. Puiggali 3.1 Introduction and History 3.2 Polymerization and Fabrication 3.3 Properties 3.4 Chemical Stability 3.5 Processing 3.6 Applications 3.7 Developments in Polyphthalamide Based Blends and Composites and their Applications References

43

Polyetherimide Sabrina Carroccio, Concetto Puglisi, and Giorgio Montando 4.1 Introduction and History 4.2 Polymerization 4.2.1 Two Step Polymerization Reaction 4.2.2 One Step Processes 4.2.3 Synthesis Via Nucleophilic Substitution Reaction 4.2.4 Synthesis Via Exchange Reactions 4.3 Properties 4.3.1 Thermal Properties 4.3.2 Electrical Properties 4.3.3 Mechanical Properties 4.4 Stability 4.4.1 Hydrolitic Stability 4.4.2 Thermal Stability 4.4.3 Thermo and Photo Oxidative Stability 4.5 Special Additives 4.6 Processing 4.7 Applications 4.8 Environmental Impact and Recycling 4.9 Recent Developments In Polyetherimides Based Blends and Composities References

79

2.

2.

Poly(ether-foZocfc-amide) Copolymers Synthesis, Properties and Applications Annarosa Gugltuzza 5.1 Introduction

43 47 53 61 66 68 71 75

79 82 82 82 85 87 88 89 89 92 92 92 95 96 99 99 101 102 102 105

111 111

CONTENTS vi CONTENTS

5.2

Synthesis and Micro-phase Separated Morphology 5.3 Nomenclature, Properties and Relevant Area Applications 5.4 Compounding and Special Additives 5.5 Environmental Impact and Recycling 5.6 Poly ether-block-amides Membrane in Separation Processes 5.6.1 Treatment of Gaseous Streams 5.6.2 Water Permeable Poly(ether-block-amide) Membranes 5.6.3 Separation of Organic Compounds from Organic and Aqueous Streams 5.7 Poly(ether-block-amide) Membranes in Food 5.8 Concluding Remarks References 2.

2.

Aromatic Polyamides (Aramids) José M. Garcia, Felix C. Garcia, Felipe Serna, and José L.dela Pena 6.1 Introduction and History 6.2 Polymerization and Fabrication 6.2.1 Polymerization 6.2.2 Fabrication 6.3 Properties 6.4 Chemical Stability 6.5 Special Additives 6.6 Processing 6.6.1 Processing PMPI and ODA/PPPT 6.6.2 Processing of PPPT 6.7 Applications 6.8 Environmental Impact and Recycling 6.9 Recent Developments in Aromatic Polyamides and their Applications 6.9.1 Forthcoming and Future Application of Aramids 6.9.2 Polyamides with Improved Solubility Acknowledgments References Polyaniline Melek Kiristi and Ay segui Uygun 7.1 Introduction and History

113 117 122 123 124 126 130 131 133 135 136 141 142 145 145 149 149 154 154 157 157 157 158 161 162 163 171 174 174 183 183

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7.2 Polymerization and Fabrication 7.3 Properties 7.3.1 Electrical Properties of Polyaniline 7.3.2 Chemical Properties of Polyaniline 7.3.3 Mechanical Properties of Polyaniline 7.3.4 Optical Properties of Polyanilines 7.4 Chemical Stability 7.5 Compounding and Special Additives 7.6 Processing 7.7 Applications 7.8 Environmental Impact and Recycling 7.9 Recent Developments in Polyaniline Based Blends and Composites and their Applications References 2.

Polyimides: Synthesis Properties, Characterization and Applications Abdolreza Hajipour, Fatemeh Rafiee, Ghobad Azizi 8.1 Introduction 8.2 Synthesis and Properties of Polyimides 8.2.1 Two-step Poly(amic acid) Process 8.2.2 Bulky Substituent in Polymer Backbone 8.2.3 Polyimides with Flexible Ether Links 8.2.4 Polyimides Containing Trifluoromethyl Group 8.2.5 Polyimides Containing Pyridine 8.2.6 Polyimides Containing Silicon 8.2.7 Polyimides Containing Phosphine Oxide Group 8.2.8 Synthesis of Polyimides via Dithioanhydride and Diamine 8.2.9 Synthesis of Polyimides via Polyamic Acid Alkyl Esters 8.2.10 Synthesis of Polyimides via Polyamic Acid Trimethylsilyl Esters 8.2.11 Polyimides Containing Six Membered Rings 8.2.12 Synthesis of Polyimides via Dianhydride and Diisocyanate

184 186 186 186 187 188 188 189 195 197 202 203 205 211 211 213 213 215 217 221 228 233 233 235 236 238 239 241

CONTENTS

8.2.13 Preparation of Polyimides via Imide Exchange 8.2.14 Synthesis of Polyimides via Mitsunobu Reaction 8.2.15 Synthesis of Polyimides via Coupling by using Metals 8.2.16 Green Media for Preparation of Polyimides 8.2.17 Copolymers of Polyimides 8.3 Characterization and Analysis of Polyimides 8.4 Applications 8.4.1 Polyimides for Electronic Applications 8.4.2 Application of Polyimides in Membranes 8.4.3 Application of Polyimides in Fuel Cells 8.4.4 Polyimide Foams 8.4.5 Adhesives References Index

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243 244 245 246 251 258 261 262 270 273 275 276 277 289

List of Contributors Zulkifli Ahmad graduated with his doctoral degree from University of Reading, UK in 2005. His main research interest is the synthesis of high performance polymers with application in opto-electronic devices. He has published 50 papers in refereed journals and presented talks in several international conferences as well as authored a monograph on crystal structure of high performance polymers. At present he is at Universiti Sains Malaysia as an Associate Professor. Carlos Alemän earned his PhD in Sciences at the Technical University of Catalonia in 1994 and is currently a full professor there. He has received several awards including the Distinction of the Generalität de Catalunya to the University Research (2003), the В Research Award of MICINN (2006), and the ICREA-AC ADEMIA from ICREA Foundation (2007). He is group leader of the "Innovation in Materials and Molecular Engineering" (Chemical Engineering Department) and "Nanochemistry/Conducting" (CRNE) laboratories. Sabrina Carroccio is a researcher at the Institute of Chemistry and Technology of Polymers of the National Research Council (CNR), Catania, Italy. Her research interests on degradation of polymers include molecular characterization of macromolecules by advances mass spectrometry techniques, polymer pyrolysis, polymer thermo and photo oxidation mechanisms. EC. Garcia is a professor in the Department of Chemistry at the University of Burgos, Spain. He received his PhD at the University of Burgos, Spain in 2001. His research interest is in polymers with sensing capabilities in water environments. J.M. Garcia is a professor in the Department of Chemistry at the University of Burgos, Spain. He received his PhD in Chemistry at the Complutense University of Madrid, Spain, in 1995. Prof. Garcia is a co-author of more than 50 peer reviewed scientific publications, books and book chapters, and has a number of patents. His principal areas of research are high performance materials, functional polymers, and sensory polymers as sensing materials for water environments. XI

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Ghobad Azizi Ghahfarrokhi received his MS degree in 2008 in organic chemistry from Isfahan University of Technology, Isfahan, Iran, He is pursuing his PhD degree in organic chemistry and his research interests are organic synthesis in ionic liquid media, MW assisted reactions and organometallic catalyzed reactions. Annarosa Gugliuzza is a senior researcher at the Institute on Membrane Technology, ITM-CNR, Italy. She has a degree with honours in Chemistry and a PhD in Chemical Science. She is a membrane technologist with solid expertise in advanced materials and development of highly structured membranes with specific functions at molecular scale by sophisticated nanotechnologies, including self-assembly and layer-by-layer techniques. Abdolreza Hajipour received his MS degree in 1983 from Shiraz University Iran and his PhD degree in organic chemistry from Wollongong University, Australia in 1994. He is a Professor of Organic Chemistry at Isfahan University of Technology. His research interests cover the synthesis of novel optically active polymers, microwave-assisted organic and polymerization reactions, solid-state reactions, new reagents for oxidation and reduction of organic compounds. José I. Iribarren received his PhD in Sciences from the Technical University of Catalonia (Spain) in 1996. After many years developing his research activity in the structural characterization of chiral polyamides, in 2003 he joined the "Innovation in Materials and Molecular Engineering" group at the Technical University of Catalonia. His current research interests concern the protection against corrosion using conducting polymers. Melek Kiristi is a PhD candidate with research interests in the synthesis and application of conducting and biopolymers. She holds a BS degree from Suleyman Demirel University in Isparta, Turkey and a MS degree from Suleyman Demirel University in Isparta, Turkey. Giorgio Montaudo is a Professor in the Department of Chemistry, University of Catania, Italy. He has been the Director of ICTMPCatania of the CNR of Italy. Dr. Montaudo received a PhD in chemistry from the University of Catania and has been active in the field of the synthesis, degradation, and characterization of polymeric

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materials by mass spectrometry. He is the author of more than 300 publications in international journals and chapters in books. J.L. de la Pena is a Professor in the Department of Chemistry at the University of Burgos, Spain. He carried out his doctoral studies at the Institute of Polymer Science & Technology, Spanish National Research Council (CSIC), receiving his PhD in Chemistry at the Complutense University of Madrid, Spain, in 1972. His research interests cover all fields of polymer preparation and applications. Concetto Puglisi is a Research Manager in the Institute of Chemistry and Technology of Polymers of the Italian National Research Council (CNR). He received his degree in Industrial Chemistry at the University of Catania in 1978. His research activity include thermal degradation and oxidation mechanisms of polymers, mechanisms of chemical exchange of polymer blends in the molten state and application of advanced mass spectrometry techniques to the analysis of polymers. Jordi Puiggali earned his PhD in Industrial Engineering at the Technical University of Catalonia (UPC) in 1987 and is currently full professor at the same University. His research activity is mainly focused in the development of biodegradable polymers for biomedical applications and in the structural studies of polyamides and polyesters. He is group leader of the "Synthetic Polymers: Structure and Properties" (http://psep.upc.edu), "Macromolecular Chemistry" and "Nanochemistry" (http://www.upc.edu/crne) laboratories of the Chemical Engineering Department of the UPC. Fatemeh Rafiee received her MS degree in 2007 in organic chemistry from Isfahan University of Technology, Iran, She is pursuing her PhD degree in organic chemistry at the Isfahan University of Technology, Iran. Her research interests are organic synthesis in ionic liquid media, MW assisted reactions and organometallic catalyzed reactions. F. Serna is Associate Professor in the Department of Chemistry at the University of Burgos, Spain. He carried out his doctoral studies at the Institute of Polymer Science & Technology, Spanish National Research Council (CSIC), receiving his PhD in Chemistry at the Complutense University of Madrid, Spain, in 1985. His research interest is related with polymers for advanced technologies.

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Aysegul Uygun is a Professor of Chemistry at the Department of Chemistry in the Middle East Technical University, Turkey with expertise in polymer chemistry Her research interests include conducting polymers. Prof.Uygun has more than 50 publications in scientific journals. She received her PhD degree from Suleyman Demirel University in Isparta, Turkey She is the recipient of DFG and Fulbright Scholarships.

1 Engineering and Specialty Thermoplastics: Nylons State of Art, New Challenges and Opportunities Visakh. P. M1 and Sabu Thomas2 t2

School of Chemical Sciences, Mahatma Gandhi University, Kerala, INDIA 2 Centrefor Nanoscience and nanotechnology, Mahatma Gandhi University, Kerala, INDIA

Abstract

This chapter discuses a brief account on various types of nitrogen containing engineering polymers. Synthesis, morphology, structure, properties and applications of all different types of nitrogen containing engineering polymers are summarized in a concise manner. The new challenges and opportunities are also discussed.

1.1

Polyamide-imides

Polyamide-imides are thermoplastic amorphous polymers that have exceptional mechanical, thermal and chemical resistant properties. These properties put polyamide-imides at the top of the price and performance pyramid. Polyamide-imides are produced by Solvay Advanced Polymers under the trademark Torlon. Other high-performance polymers in this same realm are polyetheretherketones and polyimides. Polyamide-imides hold, as the name suggests, a positive synergy of properties from both polyamides and polyimides, such as high strength, melt processibility, exceptional high heat capability, and broad chemical resistance.

Sabu Thomas and Visakh P.M. (eds.) Handbook of Engineering and Specialty Thermoplastics, (1-10) © Scrivener Publishing LLC

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Polyamide-imide polymers can be processed into a wide variety of forms - from injection or compression molded parts and ingots - to coatings, films, fibers and adhesives. Generally these articles reach their maximum properties with a subsequent thermal cure process.

1.2 Polyetherimide (PEI) Polyetherimide (PEI) is an amorphous, amber-to-transparent thermoplastic with characteristics similar to the related plastic PEEK. Relative to PEEK, PEI is cheaper, but less temperature-resistant and lower in impact strength. Polyetherimide combines high temperature resistance, rigidity, impact strength, and creep resistance. Glass-fiber-reinforced PEI plastic grades are available for generalpurpose molding and extrusion; carbon-fiber-reinforced and other specialty grades also are produced for high-strength applications and PEI itself can be made into a high-performance thermoplastic fiber. PEI has found use in medical applications because of its heat and radiation resistance, hydrolytic stability, and transparency; in the electronics field, it is used to make burn-in sockets, bobbins, and printed circuit substrates; automotive uses include lamp sockets and under-hood temperature sensors; and PEI plastic sheeting is used in aircraft interiors. The PEI's history started in 1970, when USSR researchers (1) introduced the concept that the insertion of a flexible linkage into the polyimide chains considerably decreased glass transition temperatures without significantly lowering of thermal stability. Due to the wide range of PEI's applications, scientists continuously report studies concerning PEI synthesis from new monomers (2-4).

1.3

Poly(ether-block-amide)

Polyether block amide or РЕВА is a thermoplastic elastomer (TPE). It is also known under the tradename of РЕВAX® (Arkema). It is a block copolymer obtained by polycondensation of a carboxylic acid polyamide (PA6, PAH, PAI2) with an alcohol termination polyether (PTMG, PEG). РЕВА is a high performance thermoplastic elastomer. It is used to replace common elastomers - thermoplastic polyurethanes, polyester elastomers, and silicones - for these characteristics: lower density among TPE, superior mechanical

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and dynamic properties (flexibility, impact resistance, energy return, fatigue resistance) and keeping these properties at low temperature (lower than -40 °C), and good resistance against a wide range of chemicals. It is sensitive to UV degradation. Challenging high-performance polymeric materials are in high demand and poly(ether-block-amide) copolymers meet the requirements of advanced applications in various marketplaces. Thermoplastic elastomers with desired final properties can be tailored through addressed interplay of polymer segments having different chemical nature, length, and weight. Insightful investigations have suggested that the micro-phase separated morphology as the major factor for the outstanding properties of these copolymers that are not usually observed for each individual component. Excellent mechanical resistance enhanced chemical inertia and powerful perm-selective transport properties can be regarded as the result of the intricate interplay of the various constituents of these segmented copolymers. Excellent chemical, mechanical and transport properties of these polymers render them challenging systems for a broad range of applications, including high-performance waterproof breathable clothing, barrier films, engineered packaging, membrane separation processes. It is important to add that these materials are being used for many advanced industrial applications, including textile, packaging and medical devices. The latter appears to be a key issue to meet the requirements of advanced applications in textile, construction, food and waste processing, packaging and medical fields.

1.4 Aromatic Polyamides Poly(amide)s, most commonly called polyamides, are polymers incorporating the amide group in their repeating unit (-CO-NH-) (5). Aromatic polyamides, wholly aromatic polyamides, or aramids, are considered to be high-performance materials owing to their outstanding thermal and mechanical resistance. The high performance properties of these materials can be attributed to their fully aromatic structure and amide linkages, which give rise to stiff rod-like macromolecular chains that interact with each other via strong and highly directional hydrogen bonds. These physical links deeply favor the development of effective crystalline micro-regions or domains, resulting in a compact intermolecular packing and cohesive energy. The better-known

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commercial aramids, poly(p-phenylene terephthalamide) and poly (m-phenylene isophthalamide) are used in advanced technologies in every industrial field, and have been transformed into high-strength and flame resistant fibers and coatings with broad applications in advanced industrial products, such as heat and cut protective clothing, ballistic-protection products, sport fabrics, specialty paper products, transmission belts, friction products, industrial filters and membranes, and special pipes, among others. Owing to the above mentioned chemical and physical characteristics, they exhibit extremely high transition temperatures, which lie above their decomposition temperatures. They are sparingly soluble in common organic solvents and, accordingly, can only be transformed upon solution from polar aprotic solvents or strong inorganic acids. Hence, the expansion of the applications of aramids involves, from one side, increasing their solubility, thereby improving their transformability, and, from other side, incorporating new chemical functionalities in the polyamide backbone or lateral structure in order to provide key characteristics for their application in cutting edge technological fields. These fields are related with new electrochromic, luminescent or optically active materials, gas separation and ion exchange membranes, macromolecules with sensing and supramolecular capabilities, biomaterials for medical applications, materials with even higher mechanical and thermal resistance, etc. The first all-para oriented aramid, poly(p-benzamide) (PPBA), was marketed by Du Pont under the 'Fiber B' trade name. Production only lasted a few years, probably due to economic reasons. (6,7) Poly(p-phenylene terephthalamide) (PPTA)-based fabrics offer four times the protection of cotton fabrics and eight times the protection of leather based clothes, offering heat protection as well. The PPTA fibers are extremely cut-resistant, which makes them ideal for use in: cut-resistant gloves, leg protection (e.g., for forestry workers), anti-vandalism fabrics (e.g., for bus and train seats), etc. The excellent energy absorption properties, tenacity and impact resistance makes PPTA valid for helmets and soft (bullet-resistant vests) and hard (armored police and civilian vehicles) ballistics. The superior performance-to-weight ratio of aramids makes them useful for reinforcing high-performance tires, conferring the stability to the tires, durability and reduced fuel consumption. The aramids are used in passenger car tires, motorcycle tires, bicycle tires, truck and bus tires, agricultural tires, offroad tires, airplane tires and solid tires.

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Aramids encounter applications in the manufacture of hoses when hose specifications for bursting pressure, longevity, temperature and chemical resistance are extremely high. Transmission belts reinforced with aramids are used for applications demanding low creep, high dimensional stability, fatigue resistance, temperature resistance, precise synchronization and low operating noise belts, i.e., in the automotive industry. The thixotropic aramide-reinforced resins provide viscosity control for applications in a full range of temperatures, from cryogenic to 350 °C, and media, providing inertness in most common chemicals, including organic solvents. Moreover, the high strength, light weight and thermal stability of paper made with these polymers allows manufacturers of aerospace and marine equipment to produce safe components that perform better and last longer than their alloy equivalents. Aramids are used to reinforce ropes and cables wherever safety and protection are essential, showing significant advantages over other synthetic yarns and steels in ropes and cables. Aramids are used in a wide range of composite applications in the industrial, leisure, civil engineering, ground transportation and aerospace markets, with new applications added daily, i.e., sails and reinforced hulls of sailing boats in the marine industry, rotor blades and structural parts in aerospace industry, wind turbines in new energy fields, high-pressure vessels and circuit breakers in industrial components, lightweight parts for heavy-duty purposes in ground transportation, etc.

1.5

Polyaniline

Polyaniline (PANI) is a conducting polymer of the semi-flexible rod polymer family. Although the compound itself was discovered over 150 years ago, only since the early 1980s has polyaniline captured the intense attention of the scientific community. This is due to the rediscovery of its high electrical conductivity. Amongst the family of conducting polymers and organic semiconductors, polyaniline is unique due to its ease of synthesis, environmental stability, and simple doping/dedoping chemistry. Although the synthetic methods to produce polyaniline are quite simple, its mechanism of polymerization and the exact nature of its oxidation chemistry are quite complex. Because of its rich chemistry, polyaniline is one of the most studied conducting polymers of the past

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50 years. Poh/aniline (PANI) is a unique polymer among a family of conducting polymers and has semiconductor properties. It was first called as "aniline black" in organic form as part of melanin, like organic polymer in 1934. Melanin is a natural material protecting the skin by regulating UV exposure through a polyaniline interaction. In the end of 1990, PANI became evident that it was highly useful polymer and could be used in applications varying from smart windows to electronic chips. PANI can be configured to conduct across a wide range, from insulation to conductive purposes. It isflexibleappealing for manufacturing use and has granular form which can be mixed with an organic chemical and painted or sprayed onto a substance to form a smooth surface of polyaniline. From economic point of view, the PANI is significantly superior to other conducting polymers because the aniline monomer is less expensive than other monomers. The synthesis of PANI is simple and has many application fields. PANI has many potential applications in multidisciplinary fields because of its unique properties. PANI can be applied in different areas such as electronics, thermoelectric, electrochemical, electro-luminescence, chemical, membrane, coatings, sensors, and so on.

1.6

Polyimides

Polyimide (sometimes abbreviated PI) is a polymer of imide monomers. Polyimides have been in mass production since 1955. Typical monomers include pyromellitic dianhydride and 4,4'-oxydianiline. Polyimides (PI) are a class of thermally stable polymers that are often based on stiff aromatic backbones. Polyimides were first prepared by Bogert and Renshaw in 1908, and they were then widely used and rapidly developed in the early 1960s (8). Polyimides have received great attention as they are very useful for many high-tech applications (9). The use of polyimides as high-performance and high-temperature thermoplastic materials in various applications stems from the attractive combination of chemical, mechanical and physical properties. Polyimides have found wide usage as films, coatings, adhesives, and matrix resins due to their excellent electrical and mechanical properties, high thermal and chemical stability, good solvent resistance, and dimensional stability. They are generally used as flexible circuitry substrates, interlayer dielectrics and passivation and protective coatings in high density electronic

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packaging devices. The chemistry of polyimides is in itself a vast area with a large variety of monomers available and several methodologies available for synthesis. The most widely practiced procedure in polyimide synthesis is the two-step poly(amic acid) (PAA) process. It involves reacting a dianhydride and a diamine at ambient conditions in a dipolar aprotic solvent to yield the corresponding poly(amic acid), which is then cyclodehydrated to the polyimide either thermally or chemically The thermal imidization of the poly(amic acids) is especially useful when the final product is desired in a film or a coating form and chemical imidization is a useful technique for manufacturing molding powders. Most polyimides are infusible and insoluble due to their planar aromatic and hetero-aromatic structures and thus usually need to be processed from the solvent route. One step method- high temperature solution polymerization is employed for polyimides that are soluble in organic solvents at polymerization temperatures. The process involves heating a stoichiometric mixture of monomers in a high boiling solvent or a mixture of solvents at high temperature. The imidization proceeds rapidly at these temperatures and water generated due to the reaction is distilled off continuously as an azeotrope along with the solvent. The properties of polyimides can be dramatically altered by minor variations in the structure. The subtle variations in the structures of the monomer components have a tremendous effect on the properties of the final polyimide. The infusibility and limited solubility of unsubstiruted polyimides are characteristic properties which restrict synthesis, characterization, processing, and applications, particularly for a high molecular weight material. Thus, a variety of concepts for structural modifications such as bulky pendant groups, flexible alkyl side chains, alicyclic monomers, incorporation of pendent trifluoromethyl or trifluoromethoxy groups, noncoplanar biphenylene moieties, as well as flexible alkyl or aryl ether spacers have been used for the reduction of several types of polymer chain-chain interactions, chain packing and charge transfer electronic polarization interactions and thus to enhance the solubility and lower the phase transition temperatures. Another method is via copolymerization to synthesize copolymers to improve the processability. These copolymers can be synthesized from various aromatic monomers containing anhydride, carboxylic acid, and aromatic diamine by condensation. Polyimides may also be conveniently prepared by the reaction of a diisocyanate and a dianhydride. Other methods for synthesis of

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HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

polyimides are imide exchange, mitsunobu reaction, coupling by using organometals and etc. Because of the outstanding excellent electrical and mechanical properties, high thermal and chemical stability, good solvent resistance, low dielectric constants and dimensional stability, polyimides are already used for many important industrial applications under extreme temperature conditions such as films, fibers, foams, membranes, binders, varnishes, plastics, matrix resins in hightemperature composites, glues, adhesives and injection molding products. Also aromatic polyimides have long been recognized as attractive for applications in the electronic industries, wire and cable insulation, electrical component seal assemblies and components for nuclear power plants, military aircraft and the space shuttle, flexible circuits, semiconductor pads, microprocessor chip carriers, coil insulation, magnetic wire insulation and solar arrays. Shundrina et al (11) prepared new highly fluorinated aromatic polyimides based on hexafluoro-2,4-toluenediamine and commercially available dianhydrides (6FDA and ODPA) were synthesized by one-pot high temperature polycondensation in benzoic acid melt.

1.7 New Challenges and Opportunities The main difficulty in the preparation of polyetherimide is due to control of the stoichiometric ratio of the reactants during the melt polymerization technique process. The relatively high temperatures used in the melt polymerization reaction joint to the different volatilities of monomers (anhydrides, amines and chain termination agent) make the control of mixture stoichiometry very complicated. The ability of these polymers to embed different type and amount of organic and inorganic modifying agent opens new horizons towards the design of developed block copolymers with challenging desired features that can satisfy the increasingly needs of the market. Challenging performance in poly ether-block-amides polymers is achievable through molecular design of new monomers or blending of different polymers and/or creation of copolymers. There is lot of interest to make high performance nanocomposites using these polymers by mixing with nanofillers. Research is also progressing to prepare these polymers form bio based materials.

ENGINEERING AND SPECIALTY THERMOPLASTICS: NYLONS

9

References 1. N. A Androva, M.I Bessenov, LA Laius, A.R Rudakov, Polyimides, Thecnomic, Stamford, СТ Progress in Material Science Series, Vol. 7, Pag. 216,1970 2. B.K. Chen, Y. T. Fang, J.R Cheng, Macromol. Symp., Vol. 242, Pag.34,2006, 3. S. Kumar Sen, S. Maji, B.Dasgupta, S. Chatterjee, S. Banerjee, /. of Applied Polymer Science,Vol.113, Pag.1550,2009. 4. Flaim T.D, Y. Wang, R. Mercado, Optical system design, Vol. 5250, Pag.2342003. 5. J.M. Garcia, F.C. Garcia, E Sema, J. L. de la Pena, High-performance aromatic polyamides, Prog. Polym. Sci., Vol.35, Pag.623-686,2010. 6. R.J. Gaymans, "Polyamides", in M.E. Rogers, Т.Е. Long, eds., Synthetic Methods in Step-Growth Polymers, Hoboken, John Wiley & Sons, Inc., 2003. 7. H.G. Elias, "Macromolecules" in, Industrial Polymers and Synthesis, Voi 2, Weinheim, Wiley-VCH, 2007. 8. M.T. Bogert and R.R. Renshaw, 4-Amino-O-phtalic acid and some of its derivatives, /. Am. Chem. Soc, Vol.7 Pag.1135-1144,1908. 9. J.H. Jou and P.T. Huang, X-ray diffraction study of polyimide blends compatibility, Polym. }., Vol. 22 Pag.909,1990. 10. I. K. Shundrinaa, T. A. Vaganovaa, S. Z. Kusova, V. I. Rodionova, E. V. Karpovaa and E. V. Malykhin, Synthesis and properties of organosolublepolyimides based on novel perfluorinated monomer hexafluoro-2,4-toluenediamine (Article in Press)- http://dx.doi.Org/10.1016/j.jfluchem.2011.01.0082011

2 Polyamide Imide Zulkifli Ahmad School of Material and Mineral Resources Engineering, USM, Malaysia

Abstract

Polyamide imide is a high performance polymer possessing excellent thermal, chemical and mechanical properties. It finds a wide application in extreme environment such as separatory membrane material, coating as well as structural parts. However, it is this very nature which limits its processability. Several structural modifications have been performed so as to affect its flowability, improve solvent solubility and thermal tractability. This includes main chain copolymerization, grafting, blending and formation of nanocomposites. Synthesis of polyamide imide can be performed utilizing acid anhydride, acyl chloride and isocynate as initial monomers with diamine through substitution-condensation reaction. By choosing appropriate starting materials, final products can be tailor-made as to the required properties.

Keywords: Polyamide imide, high performance polymer, polymerization, optoelectronic, coating, blending, composites

2.1 Introduction and History Polyamide imide (PAI) is a high performance polymer having extreme thermal and chemical properties. Essentially the recurring structure of a polyamide imide consist of

о

Sabu Thomas and Visakh P.M. (eds.) Handbook of Engineering and Specialty Thermoplastics, (11^2) © Scrivener Publishing LLC

11

12

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

A commercial polyamide imide Torion 4000T from Solvay Advanced Polymer is shown as below: 0

0

jail·Y

L С 6

A r - H N - Amide-imide C ^ ^ Vi ii A Imide- imide

C-NH-Ar-HN-Cr il Д

)

II 0

Y

Amide-amide

Their glass transition is beyond 250°C and most often do not display any melting temperature. They are also chemically stable and mostly insoluble in most organic solvents. These properties owed very much to the aromatic groups which make u p the polymer backbone. However, it is these very properties which limit its widespread application due to the intractability in processing and solubility. With the presence of both imide and amide groups in the polymer repeating units, PAI possesses properties between polyimides and polyamides which offer a good compromise between high thermal properties and processibility. In fact, polyimide are mostly processed using its polyamic precursor which has a lower thermal property and is soluble in most solvents. Several modifications were accomplished in order to overcome these difficulties such as incorporation of flexible linkages like ester and amide functionality. Blending with other polymers is an option to improve the desired properties of PAL Composites are often formed with the addition of various additives and inorganic fibres as fillers. As early as 1966, PAI was synthesized by reacting aryl polyisocyanate with trimellitic anhydride for the purpose of fabricating foam structure. [1] Following this, several mixtures of diacid were formulated with diisocyanate which gives polymeric products of different melt processability, viscosity, solvent solubility, molecular weight and fusibility. The utilization of acyl halide derivative of trimellitic anhydride with aromatic primary diamine occurred during late 60's. They were popularly used initially as wire coating materials such as magnet wire coating. Nowadays, due to their thermal and mechanical versatility, PAI are widely used in aerospace programs, automobile and electrical industries, insulations, coatings, solvent resistant membranes application and electronic devices.

POLYAMIDE IMIDE

2.2

13

Polymerization

Polymerisation of PAI can be performed via several routes: A. Acid Anhydride B. Acid Chloride C. Isocyanate A. Acid Anhydride General methodology is to produce imide linkage with terminal primary amine group followed by condensation to amide linkages by carboxylic group at the acyl carbon. The imide linkage can be brought about by addition reaction of a dianiline with a difunctional carboxylic group. The most useful of the latter is trimellitic acid anhydride(TMAA):

о Trimellitic acid anhydride

Since the successful Yamazaki-Higashi phosphorylation reaction [2], the direct synthesis of high-molecular-weight PAIs was made from the TMA-derived imide ring-bearing dicarboxylic acids and aromatic diamines utilising triphenyl phosphite (TPP) and pyridine as condensing agents [3,4] The formation of imide linkage occurs as depicted in the following reaction Scheme 2.1: Thefirststep involves nucleophilic addition-elimination of amine onto the carbonyl carbon of the anhydride. This step is performed at temperature 5-30 °C in polar aprotic solvent eg. NMP under nitrogen atmosphere. The resulted poly(amide amie acid) is subsequently imidized to affect ring closure with the released of water molecules. [5] The ring closure of polyamic acid is called imidization reaction. Several methods can be used for imidization[6]: 1. Distillation under reduced pressure for removing the solvent at decreasing temperature. 2. Adding dehydrating agent eg acetic anhydride to PAA solution with addition of catalyst eg pyridine or triethylamine. 3. Simultaneous removal of solvent and heat imidization by reduced pressure and heat treatment. This method

Scheme 2.1 General reaction scheme for the formation of polyamide imide.

N —R —NH P

16 СП

и п

с >

о ч

ri

s

w n

4

о

s

ч И

о

о о

tu

α

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

POLYAMIDE IMIDE

15

need to be performed stepwise so as to avoid trapped bubbles and thermal stress. 4. By heat treatment in the present of catalyst, azeotropic agent or dehydrating agent. Examples of common monomers used for synthesis of polyamide imide are shown in the following Figure 2.1:

(a)

Dianiline

NH

H3C Diaminodiphenylether

1,5-Bis (3-aminophenyl) -1,4-pentadien-3-one

1,3-Phenylene diamine

3

Isophorone diamine

2,2'-Dimethyl-4,4'-bis (4-aminophenoxy) biphenyl

3,3',5,5'-Tetramethyl-2,2-bis[4-(4-amino-phenoxy)phenyl]propane (b)

Dianhydride

fo-oi·fcAo>io}

О 0 4,4-Oxydiphthalicanhydride

0 0 0 0 3,3',4,4-Diphenylsulfonetetra 1,2,4,5-Ben2enetetra carboxylic dianhydride carboxylic dianhydride

3,3',4,4-biphenyltetra 4,4'-(Hexafluoroisopropylidene) carboxylic dianhydride diphthalic anhydride

3,3,4,4-benzophenonetetra carboxylic dianhydride

16 (c)

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS Diacid

к )t мели*™ JQ&&*

^0чР\

l c

о

- =^ ~~~"

4-(a-Methylnadimido)-benzoic acid

b

2-(4-Carboxyphenyl)-1,3-dioxoisoindoline -5-carboxylic acid

О

О

о

о

Oxy-bis(W-(4-phenylene)-trimellitic imide) Figure 2.1 Common dianililne, diamhydride and diacid monomers used for synthesis of polyamide imide.

B. Acid Chloride

TMAA can be converted into trimellitic acid chloride (TMAC) by phosgenation of TMAA. Both are reactive towards diamine. υ

0 II

II

HO-

с II О

UL·0 —* II 0

Cl-C II 0

II TMAC 0

The acid chloride is reacted with aromatic primary amine to give the intermediate polyamic acid with subsequent thermal curing to give the PAL The initial step to produce polyamic acid is performed at temperature 5-50 °C in polar aprotic solvent such as NMP, DMAC and DMF. The by-products when using acid chloride is hydrochloric acid which need to be neutralized before further processing. An as made thin film PAI was fabricated between monomers oxydianiline with trimellitic acid chloride utilizing vapor deposition polymerization. They were heated at 165 °C and 70 °C respectively under pressure 5 x 10"5 Torr. The film was deposited on glass substrate to initially give polyamide amie acid intermediate followed by thermal curing at 300 °C affording a high molecular weight PAI [7].

POLYAMIDE IMIDE

17

С. Diisocyanate Synthetic route utilizing diisocyanate is also common. This occur by condensation reaction with diacid monomer without undergoing the polyamic intermediate. [8] Carbon dioxide gas evolved during the course of the reaction which was normally performed in dipolar aprotic solvent at temperature 150 °C-120 °C. Polymerisation could be speed up using catalyst eg. dibutyltin dilaurate, potassium propiolactamate, potassium pyrrolidone, sodium methoxide, and phospholene-1-oxides. The course of reaction is as shown in Scheme 2.2 below: Examples of diisocyanate monomers used are:

0CN

/==

cH2

4 h\

/=\

h

NC0

^*=YNCO

iJ T

A

NCO

_..

. .. .

._ ,.

Dnsocyanatediphenylmethane r ' '

1,3-isocyanato-

' . ' 6-methyl-benzene

OCN-r^-NCO

\J

н3с сн 3 3

1,5-diisocyanato-1,3,3-

.. . ' . . trimethyl-cyclohexane

The method of polymerization could be performed either with or without catalyst at elevated temperature or using micro-wave radiation. [9] Molecular weight shows an optimum with time during refluxing. By introducing different ratio of amidedmide functionality different physical, thermal and mecanical properties could be made [10]. An equimolar ratio between the reactants ensure a high molecular weight products. On the other hand controlling molecular weight can be made using a chain stopper. This comprise of monocarboxylic acid and intramolecular anhydride structure. The former include benzoic acid, toluic acid and hexanoic acid while the latter include phthalic anhydride. Incomplete cycloimidization of poly(amide amie acid) intermediate might pose an uncontrollable post-curing step. A novel route leading to synthesis of high molecular weight of PAI without the need for cycloimidization step is utilizing the palladium-mediated carbonylation and coupling between aromatic diiodides and diamine. The reaction scheme is shown as below [11]: The reaction mechanism involved oxidative addition of a coordinatively unsaturated Pd(0) complex to iodo-imide to gives the Pd(+1) aryl intermediate, followed by CO insertion into the aryl-palladium bond to form acyl complex. Subsequent attack of

Ь + OCN—R—N00

+

H2N-R-NH2

Pd cat/CO ► Solvent/base

0

0

Y

«

0

-NH-

^L^j-R-N^-

m-CM-·"-*-

0

(

N—R —N

О

Scheme 2.3 Reaction scheme for Palladium mediated synthesis of Polyamide imide. (from ref 11)

О

Scheme 2.2 Synthesis of polyamide imide through isocyanate route.

ноос

-СО,

0

II

о

>

о

n

M

о

И

z a

О О

> a

oo

POLYAMIDE IMIDE

19

aniline leads to the formation of imide-amide and regeneration of the active Pd(0) catalyst. The PIAs prepared via this method have the advantages of a preformed imide linkage as well as providing for the option of a variable ratio of imide to amide groups.

2.3 Properties 2.3.1 Solubility Most of the polymers exhibited good solubility in polar aprotic solvents such as N-methyl-2-pyrroHdinone (NMP), N,Ndimethylacetamide (DMAc) ,Ν-dimethylformamide (DMF), and less polar solvents such as pyridine, cyclohexanone and tetrahydrofuran. As with the polyimides, the introduction of bulky pendant group eg. CH3, F> Br induced non-coplanarity onto the chain backbone. This reduce intechain interaction hence chain packing. As the result solvent molecule would be able to penetrate between the molecular chains and affect an increase in solubility. The incorporation of noncoplanar 2,2'-disubstituted biphenylene into a para-linkage polymer chain does not initially change the rigidity of backbone but reduces the interactions of polymer chains. The resulting noncoplanar conformation, decrease the intermolecular forces between the polymer chains which improves significantly the solubility and thermal stability of polymers [12]. Introduction of kinks structure were also observed to reduced solubility eg. hexafluoroisopropylidene and diphenylmethylene [29]. This is been exemplified in a series of analogous PAI bearing trifluoromethyl group showing better solubility than those bearing biphenyl and noncoplanar methyl units. 2.3.2 Crystallinity PAIs were amorphous in nature as shown by the broad and diffused peak intensity in wide angle diffraction pattern. [13] This amorphicity is closely related to the reduction in chain packing as the result of the present of bulky pendant group or kink linkages on the chain backbone. The presence of bulky adamantyl ring in the chain backbone prove the high amorphicity due to severe restriction of chain packing whose structure is shown below.[14]: The presence of ТЮ2 nanocomposite in a hexafluoroisopropyl PAI affect in a similar reduction in crystallization, possibly by interrupting a good chain packing through the mechanism of intercalation and

20

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

exfoliation [15]. This is substantiated by the corresponding decreased in level of crystallinity as the concentration of ТЮ2 is increased. See Fig 2.3 The tendency to display crystallinity is similarly observed to be dependent on the symmetrical nature of the monomers as well as crystallographic equivalent between bond angles of linkaging groups. This was illustrated in a series of PAI of general structures as shown in Fig 2.4 below: Refering to Fig 2.4 the level of crystallinity are in the order a < b < с < d < e [16]. The sulfone bridge adopted an open book conformation which affect a severe bend structure. This reduce an efficient packing between chains. In the case of d and e, both are more symmetrical than the others.The bond angles of ether and ketone are known to be crystallographic equivalent whose C-CO-C (ketone) is almost similar to C-O-C (ether) angle [17].

о

С

^Ο

ί^\

о

Г*>

Figure 2.2 The presence of adamantane side chain group reduce chain packing.

3

I 10

20 30 2Θ (degree)

40

Figure 2.3 WAXD pattern of hexafiuoroisopropyl PAI at varying Ti0 2 concentration.(From Ref 15)

50

(а)

u

/CNA^

(e)

(Ь)

C^f^/

(d)

~©-~©-OQr

WMQHhQrW

(с)

II

о

№ ^oòmOr0«*©-aor

II

о

o

Figure 2.4 Level of crystallinity is dependent on monomers incorporated into chain backbone of PAL

R' =

CN

-™Cbtj ^>"j

о

II II -C-R'-C-l

о

σ и о и ю

м

К

I

о

22

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

PAI could display liquid crystal properties by designing appropriate amide and imide moiety group in its recurring unit. The presence of rigid aromatic rings in PAI induced anisotropicity hence affecting liquid crystalline properties. This feature can be established by observing under polarized optical microscope for optical anisotropy at several temperature regions. The recurring structural unit of plyamide-imide will determine if the polymer display liquid crystal property as exemplified by the following isomerie examples [18]: Structure 1 does not display any liquid crystal properties as opposed to structure 2. This was attributed to the presence of amide and imide bond in a same recurring unit in structure 1 as opposed to structure 2 whose amide and imide bond occur individually at different recurring unit. The liquid crystalline temperature of the latter occur at 228-275 °C. This effect could be attributed to the ability for structure 2 to adopt different mesomorphic phases since the amide and imide linkages could orient independently from each other since they occur in different recurring units. 2.3.3 Thermal Tg for several series of PAI, measured either using DSC or DMA occurred in the range 275-326 °C. A bulky side group e.g. adamantyl induce chain rigidity which display an elevated Tg values.[13,19]. It was concluded that the Tg of PAI is comparatively higher than polyamide possibly due to rigidity of the amide group in the former.[16] Thermal degradation occurred in the range 446-505 °C for a 10% weight loss. Incorporation of trifluoromethyl group induce a much higher thermal degradation stability [12]. The char yield are in the range 66-72% attributable to a high content of aromatic group. It was claimed that a short MW PAI gives a high thermal stability but poor mechanical properties. On the other hand a high MW PAI have good mechanical properties but poor processability [18]. These polymers were fairly thermally stable up to or above 438 °C, and lost 10% weight in the range of 446-505 °C and 438-496 °C, in nitrogen and air respectively. The coefficient of thermal expansion, CTE of PAI are in the range 31.9-105.0 ppm/°C [19]. Free volume influence the CTE as it allows a free chain movement during thermal treatment. Free volume is increased with the introduction of flexible linkage, pendant bulky group, non-coplanar group, ether unit and aliphatic group which loosen the molecular packing in the polymer. Tg is also related to the free volume. An inverse relationship was observed between the Tg

CHg

сн.

сн.

сн.

Structure 2

M

Figure 2.5 Two PAI having different amide and imine moiety in recurring units which affect liquid crystal properties.

сн.

^^Mk^L
-©-r©-Ó

I II -Ar-N-C

where the PA without the imide moiety while the PI without the amide linkage. It can be seen that PAI displays a lower CTE followed by PI and finally PA. This is consistently related to their respective Tg. A plot of CTE against Tg of this series is shown in Fig 2.6 [19]. 2.3.4 Mechanical The PAI polymer films have a tensile strength in the range of 79-145 MPa, and a tensile modulus in the range of 2.1 and 3.3 GPa. [20] These polymers are very stiff with an elongation at break in the range of 6-16%. These properties are dependent on rigid moieties in the chain backbone eg. naphthalene unit as well as charge transfer complex formation between chains. Conversely the present of kink and flexible structures induced a lower tensile strength and modulus.eg diphenylmethylene [19].

120 100 80 60

ш 40 °

20 230

250

270

290 Tg(°C)

310

330

350

Figure 2.6 Relationship between CTE with Tg for a series of analogous PA (orange diamond), PI (Purple square) and PAI (green circle).

POLYAMIDE IMIDE

25

2.3.5 Opto-electronic The optical properties of the PAIs are investigated by UV-vis and photoluminescence (PL) spectroscopy. PAI polymers exhibit strong UV-Vis absorption bands at 290-310 and 320-345 nm in NMP solution, which are peculiar to the combinations of η-π* and π-π* transitions [19]. These transitions give rise to the typical yellowish brown colour due to extensive conjugation in the chain as well as strong interchain charge-transfer interaction between the arylamino donor (in the amide segment) and the trimellitimido acceptor. This charge transfer interaction can be illustrated in the following Fig 2.7. Introduction of fluoroalkyl groups into chain backbone so as to break conjugative system result in an improved transparency [13]. In solid state, the UV-vis absorptions of PAIs are nearly identical and show absorbance maxima around 311-318 nm. A series of mixed methoxy triphenyl amine (TPA) based PAIs exhibited fluorescence emission maxima around 363-366 nm in NMP solution [13]. These PAIs generally showed very low quantum yields due to the effectively charge-transfer complex formation caused by the extremely electron-donating methoxy TPA moiety to the electronaccepting trimellitimide unit. These polymers had 80% transmission wavelengths which were in the range of 484-516 nm and their cutoff wavelengths are in between 418 and 434 nm [13]. PAI shows a considerable high refractive index compared to other polymers. The refractive index of commercially available polymers are in the range 1.338 (fluorinated ethylene propylene) -1.77 (polyetheretherketone). A commercial PAI, Torlon AI-10, Solvay showed a RI of 1.656 at near infra-red region [26]. Based on Lorentz-Lorentz

Figure 2.7 Stacking of electron donating anhydride moiety to the electronaccepting trimellitimide unit.

26

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

formulation, RI is dependent on the molar permittivity as given by the following equation:

where Rm is the molar refractivity, Mw is the molecular weight, p is density and n is the refractive index. It can be shown that the RI is indirectly dependence on free volume of a material. In can be envisage that the high value of RI in PAI is due to the extensive presence of aromatic rings which affect densification of the polymer matrix. This affect reduced the speed of traversing light through the material [21]. Refractive index is related to dielectric constant at optical frequency by the Maxwell relationship π2 = ε where и is the refractive index and ε the relative permittivity. Based on Clausius-Mosotti equation, dielectric constant is dependent on molar free volume [22]. A series of PAI with bulky pendant group triphenylamine showed a dielectric constant in the range 3.63-4.93 at 1 kHz [19] Introduction of trifluoromethyl group induced a lowering of dielectric constant [13]. This is due to bigger fluorine size and high polarizability, affecting a higher bulk density and higher free volume. It was noted that in a series of analogous PA, PAI and PI polymers, the dielectric constant decrease in the order polyamide, polyamide imide and polyimide as shown in Table 2.1 [7]. In addition, the Ar structure with oxy-p-biphenyl displayed a higher dielectric constant in these series compared to p-phenyl unit. 23.6 Hydrogen Bonding Intra and interchain hydrogen bonding in PAI can be detected in FTIR occurring at 1666 cm"1 in the form of weak shoulder peak [24]. The possibility of forming hydrogen bonding render PAI hydrophilic which favour water absorption into the polymer matrix. This behavior promote hydrolytic degradation process. The role of hydrogen bonding was also observed to be detrimental in affecting phase homogeneity in PAI nanocomposites. In DM Ac, PAITiÖ2 nanocomposite displayed phase inhomogeneity because the solvent is able to form hydrogen bonding with the polymer chains thus affecting phase separation between the polymer and the fillers. However, in THF, only weak polar forces was present between

POLYAMIDE IMIDE

27

Table 2.1 Delectric constant of an analogous service of PA, PI and PAL Polymer -Ar-

Structure

Dielectric Constant 6-7

-NHArNHC-i(

J)—C-n

H

h O> [

-ArN

4.6

n

/°YV C O \ (

)

5-8

N-

5.2 3.57 4.07

the solvent and the polymer chains hence phase homogeneity is affected between the polymer with the filler [24].

2.4 Processing PAI can be process using extrusion, injection or compression molding and ingots to coatings, films, fibers and adhesives. Due to its extreme thermal properties, it suffer from flowability hence difficult to be processed using conventional processing methods. Introducing an increasing content of phthalic anhydride or forming blends with polyamide 6 or 66 do improved flowability but at the expense of thermal properties. Prior to processing, thorough drying is recommended to ensure a non-defective final products such as brittleness, voids and foaming. This is due to hygroscopic nature of PAI with the presence of amide functionality. Drying could last over 24h at 80 °C ensuring a water content at least 500 ppm. In injection molding, temperature regulation needs to be highly control as the material flow through various processing zones. A standard injection molding machine is as shown in the following Fig 2.8.

28

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

The barrel temperature increases as the melt flow from Feed zone, Middle zone, Front zone and noozle depending on the glass transition of the PAI. This in turn is determined by the percentage content of imide component. A typical temperature range is as shown below in Table 2.2: A typical modern reciprocating screw is employed with the barrel compression ratio in the range 1.1 to 1.5 to 1 ratio. PAI is popularly used as wire coating. This coating is processed using extrusion whose schematic drawing is shown in Fig 2.9. The polymer in the form of particulate is feed into a screw extruder where it is melted. The pressurized, molten polymer is forced into a crosshead where it surrounds heated wire stock, which then becomes coated as its passes through the crosshead and out a die. Thin film fabrication of PAI employ several preparation techniques which includes spin casting and vapor deposition. The latter offer an ultra-thin film of micron-scale thickness. During spin casting, poly(amide amie acid) intermediate is normally use than the PAI due to the better processability of the former. It was dissolved Table 2.2 Temperature range in various zones in injection moulding. Feed zone

304 °C

Middle zone

327 °C

Front zone

343 °C

Nozzle

371 °C

Mold

170-210 °C

Plastic granules

Hopper

Reciprocating screw

Heater

Barrel

».

Mold cavity

,

Moveable platen

Figure 2.8 Injection molding machine (from Wikipedia).

POLYAMIDE IMIDE

29

Figure 2.9 Schematic drawing of wire coating extrusion die: A, die body, cross head; B, guider tip; C, die; D, die retainingring; E, die retaining bolt; F, wire. (Modified figure based from P.N. Richardson, Introduction to Extrusion, Society of Plastic Engineers, Brookfields Centre, CT, USA, 1978).

into 5-10 % weight concentration prior to casting on suitable substrate. A typical procedure was performed at 500 rev/min for 20 s followed by spin at various speed at 20 s then heat treating at 65 °C in open air hot plate followed by 150 °C for 60 min. The thickness of the film is dependent on spin speed as shown in the following Fig 2.10. [25] An ultra-thin film of PAI could be obtained using vapour deposition polymerization. This is performed by evaporating the monomers under vacuum at respective evaporation temperature. For oxydianiline, evaporation easily affected individually at its evaporation temperature which become deposited onto the substrate. However, for other monomers eg p-phenylenediamine, terephthaloyl chloride and 4-(chloroformyl)phthalic anhydride, the heating should be performed together with other monomers involved since the formers have higher vapour pressure [23]. Subsequent heating at 300 °C afforderd a cured thermoplastic at thickness range 50-1000 nm. The exact mechanism of deposition is still unclear but apparently involved adsorption and desorption of monomers and thus-formed oilgomers during the thermal treatment. Foaming can be induced into PAI using a technique known as confine free rise. This technique does not require any additional foaming agent but those volatiles naturally present or evolved during extrusion process. [26] These volatiles include water, solvent and carbon dioxide derived during the condensation, imidization and other reactions. The foam formation is brought about by heating the composition at or slightly above glass transition temperature

30

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS 100 F

n

i—i i i i.

a. to

8 с

io =

о !c i-

:

1 I

I

I

100

1

I

I

I I I I

I

1000

I

I

1

1 I I I

10000

Spin speed [rpm]

Figure 2.10 Relationship of film thickness with spin speed during spin coating.

so as to affect softening and fusion. Residence time in the mold is adjusted at controlled time and temperature so as to avoid charring followed by cooling at below Tg to allow solidification. The foam structure is essentially in the form of interconnected open cell of density 15-50 %. While technically simple this method is only suitable for sample shape of simple geometry. For a more complicated and specific shapes, short shot method is employed [26].

2.5

Applications

2.5.1 Membrane Material Polymer membrane provides environmental friendly and cost effective separation technique compared to conventional distillation or absorption. Several advantages of polyamide-imide such as high thermal stability, good mechanical properties, easy processing and solvent resistance characteristics are suitable for use in membrane separation. This include the saparation of S02,N2,N2, C02,CH4. [27,28,29]. Better permeability and permselectivity has been an issue in designing the separatory membrane. The use of polyimides and polysulfones suffer from trade off between these two properties. [30,31]. From several theoretical modeling, it has been found that the PAI has broader and more permanent channels than PI. [29,32,33,35]. It was proposed that the para substituents is more rigid behaving like a permanent channel which better able to act as a molecular sieve hence perform better selectivity and diffusivity. [5] This is illustrated in the following structures in Fig 2.11:

POLYAMIDE IMIDE

31

о

NH-CO/CF 2 -CF 2 4—C-NH

Figure 2.11 PAI used as saparation membranes (from ref 5).

Each of these structures differ in the repeating unit of tetrafluoro ethylene unit as well as orto/para isomer of phenyl ring in the amide moiety. The samples b and с showed higher rigidity than a. This rigidity acts as a natural channel passageway for solute movement which result in improvement in selectivity and diffusibility. Diffusivity and selectivity also display same trend and these were attributed to the fractional free volume as the result of improve chain packing. Gas sorption is dependent on polar interaction and free volume. Experimental and theoretical study of sorption and diffusion of C0 2 and CH4 through PAI showed the former interact better with polar group of C-F [5,36,37]. A longer chain backbone also allows a more flexibility hence more dynamic free volume as reflected in lower Tg. This induced a better diffusibilty. Membrane permeability is influenced by the formation of polymer nanocomposites. [16] Except for C0 2 and H2, all other gases exhibited higher activation energy of diffusion for the ТЮ2 nano-composite membrane when compared with the pure poly (amide-mide), consistent with the picture of a more rigid or denser structure of the nanocomposites. The decrease in the activation energy for permeation in the case of C0 2 and H2 has been attributed to specific interactions of these gases with the ТЮ2 domains. 2.5.2 Coatings Formulations suitable for high strength, high-temperature adhesives based on PAI, have been developed. Excellent bond strengths

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HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

are observed with stainless steel, aluminum and titanium alloys, and PI films. [16] Siloxane-modified PAI resin compositions have been developed for the production of interlaminar adhesive films for wiring boards. The composition strongly adheres to the PI base layer and copper foil. [38,39] 2.5.3 Electronic Due to the thermal stability, low water absorption, high hydrolytic resistance and storage stability, PAI is utilized as a main ingredient for the formulation used for the purpose of electrical conduction, electrical resistance, dielectric and insulators, protective or bonding materials [40]. This include the fabrication of conductive or insulative circuit board, electronic device eg condenser or passive devices. The formulation comprised of PAI homogeneously dissolved in polar aprotic solvent eg. DMAc, DMF, NMP and granules. The last components was added to impart electrical properties which could be conductive granules eg. Au, Ag, Pd and Pt or insulative granules eg. Si02, SiO, Si3N4, SiC whichever required for the purpose of application. Several examples of PAI are shown in Fig 2.12: By controlling the amount of solvent components, viscosity of the composition could be tailor made. Inappropriate solvent content would result in poor processing, low adhesion and pinholes effect. A commercially available PAI from Fujifilm called EHirimide, is in the form of preimidized PAL It was mostly design for the purpose

II.

О

Figure 2.12 PAI polymers used for electronic device coatings.

POLYAMIDE IMIDE

33

of junction coating for discrete devices, glob top applications, general passivation and LCD alignment layers. It posses a remarkable thermal coefficient expansion of 53 ppm/ °C and dielectric constant of 3.5-3.8. Being a polymeric product, PAI is flexible. This property has been fully utilized for used in 'flexible metal-clad laminate' [41]. It does not curl under humid conditions due to low water absorption. Impairment on insulation property and solder heat resistence would be reduced as the result of low water absorption. It also exhibit excellent dimensional stability with low thermal expansion coefficient. 2.5.4 Opitcal PAI was observed as a viable candidate for optical waveguide. A waveguide guide waves which are electromagnetic or sound waves. In optical waveguides, typically dielectric waveguides with high dielectric permittivity such as polymeric materials were used which allows the use at optical frequencies. Waveguides comprised of a high index of refraction material known as core surrounded by a material with lower permittivity known as clad. The waves move by total internal reflection along the material fibers in zig-zag fashion. Several issues related to waveguide include optical loss and refractive index. PAI has significantly high refractive index. A commercial PAI Torlon AI-10, Solvay has a value of 1.656. (42) The average value for total propagation loss (scattering and absorption) was 0.2-0.3 dB/cm for the propagation of 830 nm light. This losses were within the acceptable range , indicating PAI is a feasible material for lowloss integrated optics.(43,44) A factor which contribute to this loss is the surface ripples during spin casting, surface roughness during etching of supercladding sidewalls and particulate inclusion within films. This loss can be further reduced using sub-micron filtering and reducing the surface roughness during etching [42].

2.6 Recent Developments on Blends and Composites 2.6.2 Blends "The vast majority of polymer pairs form two phase blends after mixing as can be surmised from the small entropy of mixing for very large molecules. These blends are generally characterized by opacity, distinct thermal transition and poor mechanical properties. However,

34

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

special precautions in the preparation in the two phase blends can yield composites with superior mechanical properties. These materials play a major role in polymer industry in several instances commanding a larger market than either of the pure components' [45]. For a good miscible blend, it will show only one Tg peak while that of immiscible would show two peaks corresponding to the Tg of the respective components. The temperature difference between these two peaks is proportional to the extent of miscibility between the two components. A prerequisite for a good mixing is a strong interaction hence good dispersion between the two components in the blend. This could be brought about by formation of chemical bond as in the covalent bond or secondary forces as in hydrogen, polar and van der Waal forces. The former afforded cross-linking and grafting. During processing as in injection molding, this will affect a severe increase in melt viscosity which would reduce efficient flow of the blended material. In the case of blending PAI with polyetherketone (РЕК), grafting will occur between the free end of amino group with that of carbonyl of РЕК to form a ketimine group. This can be avoided by adding hydrated inorganic salt having dehydration temperature between the Tg of the PAI and the polyether ketone. Thus during heating at above Tg of PAI but below that of РЕК, the presence of the salt prevent ketimine reaction since the system is under equilibrium. Once the Tg temperature is reached as that of РЕК, the hydrated salt will become dehydrated and this initiate grafting between PAI with РЕК through ketimine reaction. The latter process result in an improved mechanical properties of moulded end products [45]. 2.6.2 Composites Formation of composite ensures a synergesic effect from either components to affect an improvement in properties. Good miscibility in composite structures, however, is dependent on the interaction between the respective components which include hydrogen bonding, polar interaction and/or hydrophilicity-hydrophibicity. Agglomeration of filler will result leading to phase separation if such interaction are not optimized. Above a critical concentration of the filler would similarly affect agglomeration. Fabrication of composites can be performed using sol-gel technique. Incorporation of ТЮ2 and Si02 into PAI to form composite were attempted using solgel method.[15,24] This was performed by mixing homogeneously a solution of PAI with the solution of the tetraethyl titanate at several percentage concentrations with a small amount of acid catalyst

POLYAMIDE IMIDE OEt ЕЮ

I

Ti

OEt

н+

35

OH ►

I

HO

Ti

OEt

OH

OH

OH HO

I

Heat

OH OH HO

О

Ti—OH

I

Ti

''-О—Ti—О-

I о

"'—О—Ti— ОOH

I о

Scheme 2.4 Reaction scheine for hydrolysis and condensation of tetraethyl titanate to form highly cross link structure.

followed by curing of the dried film at elevated temperature. The first step involved the hydrolysis and polycondensation of the tetraethyl titanate to give a cross-link network of titanate. This can be represented schematically as in Scheme 2.4 below: The ethoxy group was hydrolysed with the presence of acid catalyst to form hydroxyl group. Each hydroxyl group will then condense with the neighboring hydroxyl to affect a gel form cross-link network. In a mixture of PAI solution, the solution was casted and allowed for postthermal curing to afford a tough polymeric composites. Recent trends lead to the fabrication of polymer nanocomposites. As opposed to the conventional composite which make up the scale size of micrometer, nanocomposites comprised of reinforcement at nanometer scale. This wül provide a high surface area to volume ratio which will affect an improved interiacial interaction between the polymer matrix with the reinforcing filler [46]. An attempt was made to form PAI nanocomposite using montromollinite [46]. This is a type of layered silicate whose formation of nanocomposite involved the mechanism of intercalation and exfoliation, (see Fig 2.13) This mechanism would induce a good wetting between the clay and polymer surfaces hence improve the miscibility. Hardness was increased as MMT was increased particularly through exfoliation mechanism as compared to intercalation. Chemically treated silicates using alkyl ammonium cations are used to make it less hydrophilic and therefore induce better miscibility with the hydrophobic polymer [46].

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HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

Figure 2.13 The mechanism for intercalation (a) and exfoliation (b) during formation of nanocomposite.

Carbon nanotube has been the focus of recent nanocomposite advancements due to its stiff and strongest man-made material. It also display a good electrical conductivity. Mixing the polymer with CNT afford a nanocomposite having elevated mechanical, thermal and electrical properties. Incorporating polymers onto CNT surfaces could either involved formation of covalent bond or non-covalent bond. 2.6.2.1 Covalent The former leads to grafting of preformed polymer chains onto the surface of either pristine, oxidized or pre-functionalized CNTs in the form of hydroxyl, amine or carboxylic acid [48,49]. This is made favorable in the case of curvature shape of CNT as the strained sp2 hybrid carbon could readily be converted to sp3 hybrid. In graphene, on the other hand, its planarity made this conversion highly unfavorable. This prefunctionalised carboxylic acid subsequently could be attached with polymer chains through imidisation or amidation. This can be illustrated schematically by the following Fig 2.14: Using this approach several amine and imide terminated PAI polymers were successfully grafted onto the oxidized CWNT. [49,50] 2.6.2.2 Non-covalent The non-covalent bonding with CNT leads to formation of nanocomposites. It involved physical adsorption and/or wrapping of polymers onto the surface of CNT. The conjugative π-system present in CNT will also induced π-stacking interaction with the available lone pair from the polymer. Hu et al. [50] prepared MWCNT-reinforced optically transparent polyimide nanocomposite films from acyl chloridefunctionalized MWCNTS in reaction with diamine and dianhydride.

-RNH,

RNH,

CONHR (-COOR)

CONHR (-COOR)

CONHR (-COOR) CONHR (-COOR) CONHR (-COOR)

Figure 2.14 Oxidation of CNTs and derivatization reaction with amines or alcohols.(Adapted from ref 38).

COCI

SOCI,

COOH

COOH

Oxidation

vi

и

О

о w

5

о

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HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

The prepared MWCNT-poly (amie acid) were immidized by heating in a subsequent step. An in situ polymerization of polyimide in a sonocated pre-treated CNT was attempted by Jiang et al [51] to give a nanocomposite of improved electrical conductivities. The preceding section describes several efforts that were performed to introduce imide and amide functionality [49] onto CNT either through covalently bound grafting or formation of nanocomposites. Despite absence of corresponding work on polyamide imide to date, the feasibility of this process should be amenable.

2.7

Conclusions

Polyamide imide displayed several excellent thermal, chemical and mechanical properties. They are very suitable for use as high performance polymer in the area of coating, structural building in aeronautic and aerospace, filtration and electronics. Several strategies were employed in order to overcome the problem of its flowability and processability. These includes reducing the chain rigidity by incorporating flexible linkages on the chain backbone, blending and formation of composites. These modifications affect a reduction in level of crystallinity hence improved solubility in several polar and non-polar solvents. There is a trade-off between the desired properties at the expanse of some others hence a careful balance in modification is required. An intensive simulation studies should supplement several data gathered regarding the behavior of this polymer. A wider scope for applications in challenging areas would be envisaged with further modifications of this interesting polymer. A great challenge is awaiting in the area of opto-electronic applications. It is yet to be established the fabrication of tunable refractive index of PAI for particular use in optical waveguide and integrated optic as well as the dielectric properties whose wide application in electronics still remains unexplored. This includes the level of structural modification, blending and composite formation until the processing steps.

References 1. H.E.Frey, Foam resins prepared from aromatic anhydrides and isocyanates, US Patent 3300420, Jan 24,1967; M. Izumi et al, Method for preparing soluble Polyamideimide, US Patent 3803100, assigned to Sumitomo Electric Industry Ltd, Apr 9,1974; Denise R Pauze et al, Polyamides-imides, US Patent 3817926,

POLYAMIDE IMIDE

2.

3. 4.

5. 6. 7. 8. 9. 10.

39

assigned to General Electric Co., US, June 18,1974; Disque Donny R., Koerner Ernest C, Modified amide-imide resins and method of making the same US Patent 3884880, assigned to Phelps Dodge Magnet Wire Corporation, 20 May 1975. Yamazaki N, Matsumoto M, Higashi F. Studies on reactions of the N-phosphonium salts of pyridines. XIV. Wholly aromatic polyamides by the direct polycondensation reaction by using phosphites in the presence of metal salts.} Polym Sci Polym Chem Ed 1975;13:1373-80. Yang C-P, Hsiao S-H. Preparation of poly(amide-imide)s by means of triphenyl phosphite, 1. Aliphatic-aromatic poly(amide-imide)s based on trimellitimide. Makromol Chem 1989;190:2119-31. Hsiao S-H, Yang C-P. Preparation of polyamide-imides via the phosphorylation reaction. II. Synthesis of wholly aromatic polyamide-imides from N-[p(or m)carboxyphenyl]trimellitimides and various aromatic diamines. / Polym Sci A: Polym Chem 1990;28:1149-59. Yu Chen, Qing Lin Liu, Ai Mei Zhu, Qiu Gen Zhang, Jian Yang Wu, Molecular simulation of C 0 2 / C H 4 permeabilities in polyamide-imide isomers, Journal of Membrane Science 348 (2010) 204-212. Wayne R Sorenson, Wilfred Sweeny, Tod W Campbell, Preparative methods of Polymer Chemistry, 3 rd Ed., Wiley Intersciencew, 2001. Yoshikazu Takahashi and Masayuki Iijima, Preparation of Ultrathin Films of Aromatic Polyamides and Aromatic Poly(amide-imides) by Vapor Deposition Polymerization, Macromolecules 1991,24, 3543-3546. M. Nakano and T. Koyama. Novel polyimidamide resin. US Patent 3 541 038, assigned to Hitachi Chemical Co. Ltd, November 17,1970. Mallakpour, S., Rafiemanzelat, F., Diisocyanate route as a convenient method for the preparation of novel optically active poly(amide-imide)s based on N-trimellitylimido-S-valine, European Polymer Journal 41 (2005) 2945-2955. Lin JH, Yang CP. / Polym Sci Part A: New poly(amide-imide)s syntheses. XVII. Preparation and properties of poly(amide-imide)s derived from 3,3-Bis[4-(4aminophenoxy)phenyl]phthalimidine and various bis(trimellitimide)s, Polym Chem 1996;34:747.; Kakimoto M, Akiyama R, Negi YS, Imai Y, Synthesis and characterization of aromatic polyimide and polyamide-imide from 2,5-bis(4-isocyanatophenyl)-3,4-diphenylthiophene and aromatic tetra- and tricarboxylic acids, / Polym Sci Part A: Polym Chem 1988;26:99.; Kricheldorf HR, Gurau MJ. LC polyimides. XXI. Thermotropic poly(amide-imide)s based on trimellitimides, / Polym Sci Part A: Polym Chem 1995;33:2241.; Oishi Y, Kakimoto MA, Imai Y. Synthesis of aromatic polyamide-imides from Ν,Ν'bis(trimethylsilyl)-substituted aromatic diamines and 4-chloroformylphthalic anhydride, / Polym Sci Part A: Polym Chem 1991;29:1925.; Yang CP, Chen WT. New poly (amide-imide) syntheses. IX. Preparation and properties of poly(amide-imide)s derived from 2,7-bis (4-aminophenoxy) naphthalene and various bis (trimellitimide)s, / Polym Sci Part A: Polym Chem 1994;32:1101.; Saxena A, Rao VL, Prabhakaran PV, Ninan KN. Synthesis and characterization of polyamides and poly(amide-imide)s derived from 2,2-bis(4-aminophenoxy)benzonitrile, Eur Polym]2003 39:401.

11. Perry RJ, Turner SR, Blevis RW. Palladium-Catalyzed Formation of PolyGmideamides). 1. Reactions with Diiodo Imides and Diamines, Macromolecules (1994);27:4058.

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12. Liaw DJ, Chang FC, Leung MK, Chou MY, Muellen K. High Thermal Stability and Rigid Rod of Novel Organosoluble Polyimides and Polyamides Based on Bulky and Noncoplanar Naphtha lene-Biphenyldiamine, Macromolecules, (2005);38:4024. 13. Der-Jang Liaw, Wen-Hsiang Chen, High glass transitions of novel organosoluble polyamide-imides based on noncoplanar and rigid diimide-dicarboxylic acid, Polymer Degradation and Stability 91 (2006) 1731-1739. 14. Lia DJ, Lia BY. Synthesis and characterization of new polyamide-imides containing pendent adamantyl groups Polymer 2001;42:839. 15. Hu, Q., Marand E., and. Wilkes, G.L., In situ formation of nanosized TiO2 domains within a poly (amide- imide) by a sol-gel process, J. Appi. Polym. Sci., (1997) submitted. 16. Akanksha Saxena, Rao, V.L., Prabhakaran, P.V., Ninan, K.N., Synthesis and characterization of polyamides and poly(amide-imide)s derived from 2,2-bis(4aminophenoxy). benzonitrile, European Polymer Journal 39 (2003) 401-405. 17. Dawson PC. and Blundell D.J., X-ray data for poly(aryl ether ketones) Polymer 1980,231,577. 18. Shibuya Atsushi, Okawa Yuichi, Tamai Shoji, Ohta Masahiro , Yamaguchi, Akihiro, Liquid crystal polyamide-imide copolymer, US Patent 5821319, assigned to Mitsui Chemicals, Ine, 13 October 1998. 19. Der-Jang Liaw, Pei-Nan Hsu, Wen-Hsiang Chen, and Shu-Ling L, High Glass Transitions of New Polyamides, Polyimides, and Poly(amide-imide) s Containing a Triphenylamine Group: Synthesis and Characterization, Macromolecules 2002,35,4669^676 20. Cassidy PE., Thermally stable polymers: synthesis and properties. New York: Dekker; 1980. Wilson D, Stenzenberger HD, Hergenrother PM, editors. Polyimides. London: Blackie; 1990., Ghosh MK, Mittal KL, editors. Polyimides: fundamental and applications. New York: Dekker; 1996. Crichly JP, Knight GJ, Wright WW., Heat resistant polymers. New York: Plenum Press; 1983. Mittal KL, editor. Polyimides: synthesis, characterization and application. New York: Plenum Press; 1984. 21. Jie Xu,, Biao Chen, Qijin Zhang, Bin Guo,Prediction of refractive indices of linear polymers by a four-descriptor QSPR model Polymer (2004), 45,8651-8659). 22. Blythe, T and Bloor, D., Electricdal properties of Polymers, Cambridge University Press 2nd Ed., 2005. 23. Ajit Ranade, Nandika Anne D'Souza- and Bruce Gnade. Exfoliated and intercalated polyamide-imide nanocomposites with montmorillonite Polymer 43 (2002) 3759-3766. 24. Hu, Q., Marand, E., Dhingra, S., Fritsch, D. Wen, J., Wilkes, G., Poly(amideimide)/Ti02 nano-composite gas separation membranes:Fabrication and characterization, Journal of Membrane Science 135 (1997) 65-79. 25. Bryce, R.M., Nguyen, H.T., Nakeeran, P., Clement, Т., Haugen, C.J., Tykwinskic, R.R.,DeCorbya, R.G., McMullina, J.N., Polyamide-imide polymer thin films for integrated optics, Thin Solid Films 458 (2004) 233-236. 26. Friel Jr., Thomas C. O'lenick Jr., Anthony J. Alkoxylated bis-amide defoaming compounds, US Patent 4960549,2 October, 1990. 27. Chung, T.S., Ren, J., Wang, R.,. Li, D, Liu, Y, Pramoda, K.P. , Loh, W.W. , Development of asymmetric 6FDA-2,6DAT hollow fiber membranes for

POLYAMIDE IMIDE

28. 29. 30. 31. 32.

33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44.

41

C 0 2 / C H 4 separation Part 2. Suppression of plasticization, /. Membr. Sci. 214 (2003) 57-69. Cao, C , Chung, T.S., Lui, Y, Wang, R., Pramoda, K.P., Chemical cross-linking modification of 6FDA-2,6-DAT hollow fiber membranes for natural gas separation, /. Membr. Sci. 216 (2003) 257-268. Sridhar, S., Smitha, В., Mayor, S., Prathab, В., Aminabhavi, T.M., Gas permeation properties of polyamide membrane prepared by interfacial polymerization, /. Mater. Sci. 42 (2007) 9392-9401. Aitken, C.L., Koros, W.J., Paul, D.R., Effect of structural symmetry on gas transport properties of polysulfones, Macromolecules 25 (1992) 3424-3434. Coleman, M.R., Koros, W.J., Conditioning of fluorine-containing polyimides. 2.Effect of conditioning protocol at 8% volume dilation on gas transport properties, Macromolecules 32 (1999) 3106-3133. Hofmann, D., Fritz, L., Ulbrich, J., Schepers, C , Bohning, M., Detailedatomistic molecular modeling of small molecule diffusion and solution processes in polymeric membrane materials, Macromol. Theory Simul. 9 (2000) 293-327. S. Neyertz, D. Brown, Influence of system size in molecular dynamics simulations of gas permeation in Glassy polymers, Macromolecules 37 (2004) 10109-10122. Grossman Steven J. Onder Kemal , Copolyamide-imides, US Patent 4467083, assigned to The Upjohn Company, 21 August 1984. D. Hofmann, J. Ulbrich, D. Fritsch, D. Paul, Molecular modeling simulation of gas transport in amorphous polyimide and poly (amide imide) membrane materials, Polymer 37 (1996) 4773-4785. S.A. Stern, Y. Liu, W.A. Feld, Structure/permeability relationships of polyimides with branched or extended diamine moieties, /. Polym. Sci. Part B: Polym. Phys.31 (1993) 939-951. S. Neyertz, Tutorial:, Molecular dynamics simulations of microstructure and transport phenomena in glassy polymers, Soft Mater. 4 (2006) 15-83. H. R. Lubowitz and С. Н. Sheppard. Oligomers with multiple chemically functional end caps. US Patent 5 969 079, assigned to The Boeing Company (Seattle, WA), October 19,1999. M. Nakano and T. Koyama. Novel polyimidamide resin. US Patent 3 541 038, assigned to Hitachi Chemical Co. Ltd, November 17,1970. Ohmura, Kaoru, Shibasaki, Ichiro, Kimura, Takeo, Polyamide-imide compositions and articles for electrical use prepared therefrom, US Patent 4377652, assigned to Asahi Kasei Kogyo Kabushiki Kaisha (Osaka, JP), August 2,1979. Kurita Tomoharu , Suzuki Shinji Jnukai Cyuji , Polyamide-imide resin, flexible metal-clad laminate, and flexible printed wiring board, US Patent 7728102 B2 assigned to Toyo Boseki Kabushiki Kaisha (Osaka, JP), January 6,2010. R.M.Bryce, H.T.Nguyen, P.Nakeerana, T.Clement a, C.J.Haugen , R.R.T ykwinskic. R.G. DeCorbyb, J.N. McMullin Polyamide-imide polymer thin films for integrated optics, Thin Solid Films 458 (2004) 233-236. L.-S. Tan, in: J.E. Mark (Ed.), Polymer Data Handbook, Polyiamide imide), 1st ed, Oxford University Press, Oxford,1999, p.260. S.Ramachandran, S.G.Bishop, Low loss photoinduced waveguides in rapid thermally annealed films of chalcogenide glasses, Appi. Phys.Lett. 74 (1999)13.

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45. Olabisi, Robesonand Shaw, Polymer-polymer miscibility, Academic Press New York, N.Y., p7 (1979). 46. Vaia RA, Polymer melt intercalation in mica type layered silicates,PhD Tesis USA, Cornell University, May 1995. 47. Zdenko Spitalskya, Dimitrios Tasisb, Konstantinos Papagelisb, Costas Galiotis, Carbon nanotube-polymer composites: Chemistry, processing,mechanical and electrical properties, Progress in Polymer Science 35 (2010) 357-401. 48. Ge JJ, Zhang D, Li Q, Hou H, Graham MJ, Dai L, et al. Multiwalled carbon nanotubes with chemically grafted polyetherimides. J Am Chem Soc 2005;127:9984-5., Qu L, Lin Y, Hill DE, Zhou B, Wang W, Sun X, et al. Polyimide functionalized carbon nanotubes: synthesis and dispersion in nanocomposite films. Macromolecules 2004;37:6055-60. 49. Jason J. Ge, Dong Zhang, Qing Li, Haoqing Hou, Matthew J. Graham, Liming Dai, Frank W. Harris, and Stephen Z. D. Cheng, Multiwalled Carbon Nanotubes with Chemically Grafted Polyetherimides J. Am. Chem. Soc. 2005, 127, 9984-9985, Kim HS, Park BH, Yoon JS, Jin HJ. Nylon 610/functionalized multiwalled carbon nanotubes composites by in situ interfacial polymerization. Mater Lett 2007;61:2251-4. Liangwei Qu, Yi Lin, Darron E. Hill, Bing Zhou, Wei Wang, Xianfeng Sun, Alex Kitaygorodskiy, Myra Suarez, John W. Connell, Lawrence F. Allard, and Ya-Ping Sun, Polyimide-Functionalized Carbon Nanotubes: Synthesis and Dispersion in Nanocomposite Films Macromolecules 2004,37,6055-6060. 50. Hu N, Zhou H, Dang G, Rao X, Chen C, Zhang W. Efficient dispersion of multiwalled carbon nanotubes by in situ polymerization. Polym bit 2007;56:655-9. 51. Xiao wen Jiang, Yuezhen Bin, Masaru Matsuo Electrical and mechanical properties of polyimide-carbon nanotubes composites fabricated by in situ polymerization, Polymer 46 (2005) 7418-7424.

3 Polyphthalamides J. I. Iribarren, C. Alemän, J. Puiggali Departament d'Enginyeria Quimica, Universität Politècnica de Catalunya, Barcelona, Spain

Abstract

Polyphthalamides are polymers with intermediate characteristics between polyaramides and easily processable aliphatic polyamides (nylons) due their chemical constitution based on aliphatic and aromatic monomers. Specifically, at least a 55 molar percentage of their dicarboxylic acid units correspond to terephthalic and/or isophthalic acids. Selection of components and synthesis conditions may provide materials with a wide range of physical and thermal properties, which in turn depend on their different crystallinities. Polyphthalamides constitute nowadays a family of thermoplastic polymers with outstanding performance at high temperatures and excellent mechanical properties. These materials can therefore be employed among other uses to replace metals in high temperature automotive applications and as housing for high temperature electrical connectors. Keywords: Polyphthalamides, semiaromatic polyamides, terephthalic acid, isophthalic acid, high performance materials, thermoplastic polymers

3.1 Introduction and History Polyamides (PAs) are thermoplastic polymers that can be obtained by the polycondensation of diacids and diamines or by the ring opening polymerization of cyclic amides denoted lactams. PAs are typically named according to the chemical constitution of the monomers. For example, PA 66 is a very well known aliphatic PA

Sabu Thomas and Visakh P.M. (eds.) Handbook of Engineering and Specialty Thermoplastics, (43-78) © Scrivener Publishing LLC

43

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HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

that results from the condensation of hexamethylenediamine and hexanedioic or adipic acid, while caprolactam is used to prepare PA 6. Figure 3.1a shows the chemical structure of some well-known aliphatic PAs.

(a)

H PA 6

О

-^N_(CH2)_cj-

H PA 66

н

о

- i . N _ ( C H 2 ) 6 — N—C—(CH 2 )—C-^

H PA 46

о

Н О

О

- ^ N _ ( C H 2 ) — N — C — ( CH 2 ) 4 —C^-n

(b) Terephthalic acid

HOOC—\ V - COOH

COOH Isophthalic acid

IL ^?ч. ^^^COOH

(c)

H PA6T

(d)

PA 61

|N-(CH

H

2

О

)-N-C-{]bc}

H O ^ .

n

О

-|Ν- Ρ 2 ) Γ Ν-{Χίϋ| η

Figure 3.1 Chemical structure of: (a) selected aliphatic polyamides; (b) terephthalic and isophthalic acids; (c) polyphthalamide obtained by combination of terephthalic acid and hexamethylenediamine; and (d) polyphthalamide obtained by combination of isophthalic acid and hexamethylenediamine.

POLYPHTHALAMIDES

45

Due to their constitution, aliphatic PAs (also denoted nylons) are closely related to proteins since both present NH· 0=C hydrogen bonds, which play a key role in determining their structural characteristics and properties. By changing the ratio between the number of amide groups and methylene units, both the structure and properties of aliphatic PAs can be dramatically modified [1,2]. However, the structure and properties of PAs can be also significantly changed by using aromatic monomers rather than aliphatic ones. Thus, fully aromatic PAs, known as polyaramides, are derived from the condensation of both aromatic diacids and diamines. Examples of fully aromatic PAs are poly(p-phenylene terephthalamide) and poly(ra-phenylene terephthalamide), usually abbreviated PPPTA and PMPTA, respectively. An intermediate situation between aliphatic and fully aromatic PAs occurs when aromatic diacids, like terephthalic and isophthalic acids, are combined with aliphatic PAs. The resulting polyamides are known as semiaromatic PAs because their constitutional repeating units involve both aliphatic and aromatic fragments that results from the combination of aromatic and aliphatic monomers, respectively. Among semiaromatic PAs, the most important class corresponds to the polyphthalamides, hereafter abbreviated as PPAs. Thus, the PPAs are directly related with a type of semiaromatic PAs derived from phthalic acids. More specifically, isophthalic acid, terephthalic acid (Figure 3.1b) or even the two are present in polymer chains with a well-defined rate. Indeed, the definition provided from ASTM D-5336 standard establish that "a polyphthalamide is a polyamide in which the residue of terephthalic acid or isophthalic acid or combination of two comprise at least 55 molar percent of the dicarboxylic acid portion of repeating structural unit in

the polymer chain". On the basis of the chemical constitution of aliphatic PAs and terephthalic and isophthalic acids, PPAs with different chemical structures can be obtained by combining them. Some examples are given in Figures 3.1c and 3.1d, which represent the chemical structures of the PPAs derived from the combination of hexamethylenediamine with terephthalic acid (PA 6T) or isophthalic acid (PA 61), respectively. In addition to form PA 6T, the building block constituted by hexamethylenediamine and terephthalic acid co-monomers can be assembled with the constitutional repeating unit of PA 66 to obtain the PA 6T/66 (Figure 3.2). A derivative of PA 6T/66 is PA 6T/DT

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HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

(Figure 3.2), in which the adipic acid and hexamethylenediamine of the 66 building block are replaced by terephthalic acid and 2-methylpentamethylene diamine, respectively. The PA 6T/6I/66 is similar to a terpolymer made of three building bocks (Figure 3.2), which correspond to the constitutional repeating units of PA 6T, PA 61 and PA 66. It is worth noting that PPAs involving two building blocks, as PA 6T/66 and PA 6T/DT, does not necessarily involve the 50%-50% proportion. Specifically, the replacement of at least 55 % of the adipic acid in the PA 66 chain by the terephthalic acid is the condition that must be fulfilled to consider the resulting PA 6T/66 as a PPA. In the case of PA 6T/DT, any ratio of the 6T and DT building blocks will meet the requirement of PPA definition, even though in practice this ratio is determined by the optimization of the polymer properties. Some of these polymers are considered high performance materials and their properties are somewhat worse than those of the fully

- N -(СНЖ- N - i - Q - i - J ^ - f N - C H 2 - C H - (CH2)3- N СНз

6T building block

c H

Q ^ c 4

DT building block

6T/DT

I

H

Н о

I

I

О

|

I

A I —N—(CH 2 ) e —N — C - ^ - c 4

, n

H

I

H

I

Q

0

Ϊ

II ,

-j-N—(CH 2 ) 6 — N — C ~ (CH2) — C-f^

6T building block

66 building block 6T/66

H

H

О

0

-N— (CH2)6— N— C-\J~C-in

н

6T building block

H

,1

,, H

I

и

г)

О

Ϊ ?

- j - N — (CH2) — N — C—(CH 2 ) 4 — C ^ Q

^

О

66 building block ы

- j - N —CH2—CH—(CH2)3— N — С CH 3 61 building block 6T/6I/66

Figure 3.2 Chemical structure of the building blocks contained in PA 6T/66 and 6T/DT copolymers, and PA 6T/6I/66 terpolymer.

n

POLYPHTHALAMIDES

47

aromatic PAs, their average properties being intermediate between those of aliphatic PAs and fully aromatic PAs. However, PPAs are easier to synthesize and transform from an industrial view point. Historically, PPAs were introduced in market by Amoco Company in 1991 under the name of Amodel®. This plastic is currently supplied from Solvay Advanced Polymers (Plast.Rubb.Wkly. No pl573, Feb 1995) under a great number of different formulations with applications in automotive electric and electronic sector. At present time, PPAs are commercialized with a few different denominations. Ultramide T®, from BASF [3] is made of a copolymer of PA 6 with PA 6T (PA 6/6T). In Arlen®, from Mitsui Petrochemical and Amodel® (Solvay Advanced Polymers), terephthalic acid of PA6T is partially replaced by isophthalic acid or adipic acid, or even mixtures of them. Addition of co-monomers to PA 6T produces a reduction of the melting temperature and, therefore, the processability of the copolymer is easier than that of the homopolymer. This strategy has been used to obtain products not only with lower melting point than aliphatic PAs but also with significantly lower moisture absorption. Zytel® HTN from Dupont, in which the hexamethylenediamine of PA 6T is replaced by 2-methyl-l,5-pentanediamine [4], Grivory HT3® and Grivoyi GVX® manufactured by EMS-Grivory company, and Trogamid T® from Evonik company, which results from the copolycondensation between 2,2,4/2,4,4-trimethyl-hexamethylenediamine and terephthalic acid, are other commercial PPAs with interesting technological applications. PAs with high melting temperatures are typically derived from polymerization reactions at high temperatures. Unfortunately, this process also produces undesired products arising from side reactions that, in many cases, lead to cross-linking of polymer chains and gel formation. In spite of these reactions are relatively easy to control, polycondensation processes using aromatic diacids have lower reaction kinetics with less favorable equilibrium conditions to obtain final products. Thus, the use of high reaction temperatures for the production of PPAs results in an important presence of collateral products of polymerization.

3.2 Polymerization and Fabrication The general procedure to obtain PPAs at both laboratory and industrial scales is the polycondensation from diamines and diacids. As

48

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

it was previously mentioned, aromatic acids have a significant tendency to produce undesirable chemical compounds derived from side reactions. Additionally, diamines can react with themselves generating trifunctional compounds. For example, hexamethylenediamine is able to react with itself producing bis-hexamemylenetriamine. Furthermore, some diamines can generate monofunctional amine products as a consequence of cyclization reaction. This is the case of tetramethylenediamine. All these side reactions are very important when large amounts of free amine functionality is exposed to high temperatures during the reaction. In order to avoid this limitation, the residence time of the reactants is controlled, which allows to minimize the amount of diamine necessary for the reaction. Furthermore, water levels are maintained as low as possible, favoring the displacement of the equilibrium towards the product formation. Several authors have pointed out the more important problems related with the use of aromatic diacids to produce linear PPAs by melt polycondensation [5], which may result in a detriment of the properties of the yielded material. However, for some applications, as for example fiber formation, materials with acceptable properties can be produced. This is the case of copolymers PA 6T/6I containing 60-80% of terephthalic acid and 40-20% of isophthalic acid, which allow the formation of fibers with good mechanical properties [6,7]. At the industrial scale, polymerizations processes are usually carried out in autoclave reactors. The residence time, pressure and temperature are precisely controlled to obtain PPAs with optimized properties [8]. In order to prevent the formation of oligomers, reactants are firstly mixed to form a homogeneous phase in aqueous solution and, subsequently, the temperature is increased. Simultaneously, pressure is controlled to be high, which permits to maintain a homogeneous phase with the minimum amount of water. Finally, when the polymerization temperature is raised, pressure is reduced and the polycondensation occurs. Phosphorus catalysts are used to reduce both polymerization times and participation of side reactions. Autoclave reactors in batch processes above mentioned have to be accurately cleaned in order to avoid the presence of residues, as for example particles which may lead to heterogeneous products with unacceptable properties for selected applications. This problem is minimized by adding a small concentration of adipic acid (maximum 15 %) while the isophthalic acid proportion is kept around 30-40 %.

POLYPHTHALAMIDES

49

PPAs copolymers and terpolymers based in 6T, 61 and 66 building blocks were found to be suitable for conventional processing, as injection molding, allowing to obtain a great variety of products and articles. These materials are prepared by considering a process that allows working with different compositions of polymers with crystalline properties. This novel procedure consists on the combination of the diacid and diamine components in water, the mixture being subsequently heated. This produces the reaction of the components giving place to the formation of a homogeneous solution if the water content is lower than 17 %. Temperature, degree of conversion and water content must be precisely controlled in order to avoid "phase out" phenomena. The use of water as solvent facilitates the existence of a homogeneous solution in a wide range of temperatures. This solution with low water content is then fed to an operating zone wherein the temperature is comprised between 275 °C and 330 °C to allow the amidation reaction to reach the equilibrium. The pressure is kept sufficiently high to avoid the vaporization of water or solvent. The conditions applied in this zone (that is, temperature, residence time and water content) are very important for the success of overall polymerization process. The residence time is controlled to minimize side reactions as the water proportion too. Then, the heated and pressurized mixture is placed in an operating zone of low pressure to form the prepolymer droplets by the vaporizations of the solvent. Degradation in reactor walls is minimized by the high speed, which avoids the deposition of the poh/condensate for sufficient time. The catalytic activity increases significantly in this step and the kinetics is similar to conventional PAs, showing a clear dependence of acid concentration. Amoco Corp., Monsanto Corp. and Dupont are the companies that mainly developed this technology. Notwithstanding, there are other industrial alternatives to prepare partially aromatic PAs that are an extension of the conventional continuous processes used for the preparation of aliphatic PAs [9,10]. For example, Ultramid T® from BASF is prepared by using one of these methodologies. Monomers are combined in solution with 50 % of water at a temperature of 80 °C. Next, water is removed with an evaporator by applying a pressure of 75 psi and a temperature of 295 °C, the residence time being one minute. Both the short residence time and the considerable polymerization rate lead to minimize the side reactions. Although some amounts of volatile monomers are evaporated in this step, they are present

50

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

with the prepolymer while they are being separated. The volatilized monomers are then transferred to the molten prepolymer, the required residence time being of about ten minutes at 290 °C. After this, the stream is rectified to concentrate the monomers, which are returned to the earlier step of the continuous process. The steady state is necessary to obtain a reproducible stoichiometry. Comparison of the importance of the side reactions in Amoco Corporation and BASF's processes is difficult because both operate in optimal conditions (e.g. low residence time) to avoid them. Thus, the main differences between processes concern details about separation and residence time in the later steps (i.e. when monomers and water are in contact with the prepolymer and the final polymer is obtained). A high loss of monomer during reaction may occur when it has hindered amine groups since they have a lower reaction rate. The molecular weight is also limited in this case because the branched amines tend to form cycles. Thus, the resulting polymers crystallize more slowly and their applications are restricted to the formation of fibers and transparent products. In the laboratory, semiaromatic PAs similar to PA 6T have been recently obtained by polycondensation of terephthalic acid with diamines having a variable number of methylene groups [11]. The PAs derived from these monomers are denoted PA nT, where n indicates the number of methylene groups in the diamine. PAs nT with n ranging from 9 to 13 exhibit good processability. The general scheme of this synthesis is shown in Figure 3.3. As it can be seen, usually a prepolymerization followed by the solid state polymerization is used for the preparation of these materials. Diamines containing a large number of methylene units (i.e. more than 9 CH2 groups) are prepared by cyanating and aminating the n HOOC-/}>-COOH

+

n H2NCH2CH2(CH2)XCH2CH2NH2 .

Ο

θ Θ COOH3NCH2CH2(CH2)xCH2CH2NH2

Solid-state polymerization

—ÌOC-/

70 °C

Prepolymerization ► Prepolymer

yCOHNCH 2 CH 2 (CH 2 ) x CH 2 CH 2 NH

x = 6,7,8,9 Figure 3.3 Synthesis of long chain polyphthalamides.

POLYPHTHALAMIDES

51

corresponding diacids. Their intrinsic viscosities are comprised between 1.75 and 1.93 dL/g, yielding polymers with acceptable molecular weights. Furthermore, the water absorption capacity of these materials is lower than that of PA nT with n < 9. The low economic cost associated to the preparation of diamines with large segments has a positive impact in the final price of the resulting semiaromatic PAs. Other formulations have been obtained by step growth polymerization of 2-methyl-l,5-pentanediamine and isophthalic acid or terephthalic acid, or even a mixture of the two diacids. The resulting polymers are random copolymers, their chemical formula being displayed in Figure 3.4 [12]. The molecular weight of these polymers ranges from 20,000 to 30,000. Copolymers containing different molar compositions of the two diacids exhibit an amorphous behavior, while the polymer involving terephthalic acid presents an opaque aspect. Recently, Yang et al. [13,14] synthesized semiaromatic PAs that incorporated the naphthalene ring into the constitutional chemical unit (Figure 3.5). For this purpose, a prepolimerization was initially performed combining 2,6-naphthalenedicarboxylic acid with the 1,10-decanediamine, 1,11-undecanediamine, 1,12-dodecanediamine or 1,13-tridecane diamine, the following step being the solid state polymerization. The viscosities measured for the resulting materials, which were denoted PA nN (where n refers to the number of methylene units in the diamine fragment), were around 1.8-1.9 dL/g. Furthermore, it was found that water absorption decreases with the length of aliphatic segment of the diamine. H

(a)

H

I

!

о

Il / = \

- j - N — C H 2 — C IH — ( C H 2 ) 3 — N — с—amide) Copolymers Synthesis, Properties and Applications Annarosa Gugliuzza Research Institute on Membrane Technology-National Research Council, ITM-CNR, Rende, Italy

Abstract

Challenging high-performance polymeric materials are in big demand and poly(ether-WocA:-amide) copolymers meet the requirements of advanced applications in various marketplaces. Thermoplastic elastomers with desired final properties can be tailored through the interplay of polymer segments having different chemical nature, length, and weight. Investigations suggest that the micro-phase separated morphology is the actual responsible reason for the outstanding properties of these copolymers that are not usually observed for each individual component. Excellent mechanical resistance, as well as enhanced chemical inertia and powerful perm-selective transport properties, can be regarded as the result of the intricate interplay of the various constituents of these segmented copolymers. The potential impact of these copolymers for successful strategic applications, including textile, gas separation, packaging, is examined throughout the chapter.

Keywords: Pebax®, membranes, elastomers, block copolymers, nanocomposite materials, gas separation, pervaporation, food packaging, breathability, textile

5.1

Introduction

The p o l y m e r s are w i d e l y u s e d in m a n y fields of the m a n u f a c t u r i n g i n d u s t r y from simple objects to a d v a n c e d textile, coatings, m e m branes, medical prostheses a n d high-tech devices [1]. Challenging Sabu Thomas and Visakh P.M. (eds.) Handbook of Engineering and Specialty Thermoplastics, (111-140) © Scrivener Publishing LLC

111

112

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

performance is achievable through molecular design of new monomers [2] or blending of different polymers [3-4] and /or creation of copolymers [5]. The first approach takes the advantage of programmed properties, even if it is too expensive and timeconsuming and, hence, not economically competitive. More attractively however, there are two other possible routes to engineered functional polymer materials: to mix two or more polymers or create tailor-made copolymers. The blending of polymers is rather limited, because low compatibility and/or immiscibility of the materials could induce macro-phase separation yielding systems poor in reproducibility and uniform properties. The formation of covalent linkages between different polymer segments is a powerful tool to prevent macro-phase separation and integrate diverse and reliable properties in unique systems. Rather, copolymers and much more block copolymers can exhibit complex structures (i.e., spheres, cylinders or lamellae, random arrangements and so on) on the nanometer length scale for the occurrence of micro-phase separations caused by the immiscibility of individual components [6-7]. In this case, we take advantage over preventing formation of macro domains and desired systems, depending on chemical and structural features as well as ratio, weight and relative position of the components. An example of high-performance copolymers, whose outstanding properties can be regarded as a result of nano and micro-segregations of the segmented blocks forming the polymer backbone, is represented by the family of poly(ether-block-amide)s commercialized under the trademark РЕВAX® [8]. These resins are appreciable for their water resistance, permeability and hardness from rubbers (70 Shore A) to nylons (72 Shore D). The linear backbone of these copolymers consists of polyether (soft) and polyamide (hard) blocks linked together via ester bonds (Scheme 1). The flexibility and versatility of this new generation of copolymers derives essentially from intrinsic micro-phase separated morphology caused by difference of polarity, crystallinity and well-established three-dimensional networks, involving hydrogen-bonding, polar and no polar intermolecular interactions between hard and soft domains [6,9]. The thermoplastic character above the melting temperature (Tm) as well as the reversible cross-linking of these block copolymers enable one to process and reprocess them as a melt by injection, molding, extrusion, casting or more simply melt blended with other

POLY(ETHER-BLOCK-AMIDE) COPOLYMERS

о Il

о II

HO-fC—РА—С—О—РЕ—O^H

113

Hard block (PA) Soft block (PE)

PA = Nylon 6,12 PE = Poly(tetramethylene oxide) (PTMO), Poly(ethylene oxide) (PEO)

Scheme 5.1 Schematic representation of the individual components (hard and soft) of poly(ether-Wocfc-amide) elastomers.

polymers. At service temperature PA blocks act as hard segments below their glass temperature (T ) or Tm, whereas the soft segments (PE) exist normally above respective T or Tm as a rubbery phase. Depending on PA/РЕ ratio, the hard block works as physical crosslink site for the rubbery phase of the soft segments. At elevated temperatures, the hard block softens or melts enabling these elastomers to be processed as thermoplastics. Differently from thermoset materials these block copolymers can be remelted because of their reversible cross-linking character. For this reason, they are called thermoplastic elastomers (TPE) and have been classified as "virtually cross-linked' elastomers [10]. The final performance of these thermoplastic elastomers can be modulated by changing nature, length and ratio of the polyether and polyamide blocks, resulting in attractive material for specific advance applications [11-12].

5.2 Synthesis and Micro-phase Separated Morphology The family of poly(ether-b/ocÄ:-amide)s is the result of extensive research activities devoted to achieve a flexible nylon through the introduction of flexible segment chains into the backbone of the polymer. Nylon 6 (N6) and nylon 12 (N12) as well as PEO and PTMO are the real precursors of these copolymers. A pioneering work on the synthesis of thermoplastic elastomers via formation of covalent linkages involving the formation of amide, urethane or urea has been carried out in 1970s [13-14]. In the early 1980s, the effective synthesis of thermoplastic poly(ether-block-amide)s with sufficiently high molecular weight has been proposed by Atochem [15].

114

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

Dicarboxylic acid and polyethers react at high temperature (250°C) in presence of tetraalkoxide catalysts Ti(OR)4 forming an ester linkage between hard and soft blocks. The catalyst facilitates the melt polycondensation of carboxylic acid terminated amide blocks with polyoxyalkylene glycols. High vacuum is applied to remove water and by-products, while adipic acid terminates the carboxylic acid of nylon. According to this synthetic pathway, Peyravi et al [16]. has recently proposed the synthesis of copolyetheramides in order to investigate the micro-phase separation induced by the change in PA and PEO crystalline domains content. Different chemical compositions and block lengths have been achieved from nylon N6, PEO and hexamethylenediamine (HMD) and adipic acid (AA) in different stoichiometric ratio through three synthetic steps: end-capping of N6, chain extension of carboxyterminated N6 and PEO and polycondensation in the presence of Ti(OBu)4. It has been observed how the incompatibility of two blocks forming the polymer backbone induces phase segregation comparable to the dimension of the same blocks. As aforementioned, the separation occurs on a local scale because hard and soft segments are covalently linked. The degree of segregation is usually expressed by the segregation power parameter (χΝ), where χ is the Flory interaction parameters of two block materials and N is the degree of polymerization. The extension of the segregation can be caused by thermal treatment and/or combination of hard and soft segments having various chemical nature and length [9]. In order to investigate correctly the phase behavior of poly(etherblock-amide), it is necessary to consider three important transition temperatures (Scheme 5.2): a) T that is the temperature below which glassy structures prevent free motion of the polymer segment chains. b) Tm that is the temperature above which a single segment or the overall copolymer is molten. c) Order-disorder transition temperature (TODT) that corresponds to an order-disorder transition and distinguishes from organized and unorganized phases. In this respect, the formation and dispersion of two crystalline domains in block PEO/PA6, one rich in N6 and another in PEO, have been explored in relation to the rising PEO/PA ratio, resulting

POLY(ETHER-BLOCK-AMIDE) COPOLYMERS

115

Molten single disordered phase

T°C

Crystallization of hard block

Cooling

Scheme 5.2 Schematic representation of morphology changes and separated states induced by thermal treatments of the copolymer.

in a decrease in the onset of the crystallization to lower temperature, ascribed to the deformation and/or chain folding of hard segments (PA) [16-17]. The separated multiphase morphology of Pebax® copolymers has abundantly been investigated by means of different technical approaches [18-20], providing useful indication about the changes of the polymer properties at the solid state. Concerning with PEO/PA12 and PEO/PA11 block copolymers, the chain conformation in the crystal phase has also been investigated by nuclear magnetic resonance (NMR) and X-ray diffraction, revealing crystallites of PA surrounded by interracial amorphous PA and PE [21]. Similarly, the solid state structure-property behavior of a series of poly(ether-biodc-amide) PEBAX® based on N12 and PTMO (XX33) has been examined with different hard segment contribution, yielding indication about the formation of PA lamellar crystals in both melt and solution cast films and a micro-phase segregation over a broad range of temperature [22]. At higher content in PA spherulitic superstructures have expressly been investigated in the bulk and on the surfaces of the examined samples, causing an incomplete

116

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

recovery of the original sample dimensions upon release of the applied deformation. Consistent results suggest undoubtedly the coexistence of a well-defined polyamide crystalline phase, polyamide amorphous phase, and polyether amorphous phase. However, the literature is poor in information about the rheology and structure of these thermoplastic elastomers in the molten state [23]. Yang and co-workers [24] have recently studied the viscoelastic behavior of this type of segmented copolymers by rheological and infrared analyses, evaluating the transformation of the melt from a weak structure to a stiff structure with rising temperature. Small spherical domains forming homogeneous micro-phase separated morphology have been observed just above the melting point of PA crystallites, whereas coarser spherical domains dispersed in stiff structures have been detected at higher temperatures. This behavior can be well-understood if related to the thermal history of the samples and the role of hydrogen bonding in the reorganization of the polymeric segments. At higher temperature, the hydrogen bonding dissociation causes demixing of the soft and hard domains, resulting in stiff micro-phase separated morphology for effect of changes on visco-elasticity. A short length scale reorganization of hydrogen bonding was also found to induce a phase transition from the semi-crystalline state (pre-existing ordered-state) to the micro-phase separated morphology for PA12/PTMG block copolymer [9]. In particular, a weak segregation was found to take place between T and T„„T. When cooled -Γ

m

ODT

from a temperature above TODT down to a temperature above Tm, a very low segregation was detected. Differently, significant segregation was observed starting with semi-crystalline sample in an order state. The heating of semi-crystalline samples below TODT caused the melt of semi-crystalline lamellae producing unfolding of the segments and formation of any domain spacing. Because of the formation of hydrogen bonding between PA-rich and PE-rich domains, the mix was not full and led to appreciable phase segregation. The same systems brought above TODT exhibited a homogeneous disorder phase. Chain-folded crystals of the hard phase with enhanced interconnectivity of the hard phase as well as continuity of the soft phase can be regarded as a result of addressed combination of individual components and morphological arrangements and/or thermal treatments mainly governed by hydrogen-bonding.

POLY(ETHER-BLOCK-AMIDE) COPOLYMERS

117

5.3 Nomenclature, Properties and Relevant Area Applications The broad family of the poly(ether-i»/ocA:-amide)s is generally classified in grades depending on chemical nature and ratio of hard and soft blocks as well as modifiers that improve processability and final performance of the materials [8]. The various series of polymers can be distinguished on the basis of indication resumed in specific nomenclatures. There are two general schemes adopted (Scheme 5.3). The first one gives information about hardness, series and additives (Scheme 5.3a). In this scheme, the first number stays for the Shore D hardness, the second number for the series, the third number indicates the presence of stabilizers and the final number is a code. The second type of nomenclature is usually associated to special grades developed to meet precise requests of the market (Scheme 5.3b). Poly(ether-WocA:-amide) elastomers have replaced more traditional cross-linked materials, revealing themselves as breakthrough polymers for outstanding and innovative solutions. Considering that the functionality of any object arises from intricate interplay of

(b) •

MX

•

MV

•

MH

•

MP

•

SA 01 (optional)

code •

SN01 (optional)

Examples: MX 1205 SN 01 MV 3000 SA 01 MH 1657 MP 1878 SA 01

Scheme 5.3 Different types of nomenclature adopted for poly(ether-iWocfc-amide) elastomers.

53

55 57

Pebax®3533

Pebax®4033

Pebax®5533

Pebax®1074

Pebax®4011

70PTMEO/PA12 1

53PTMEO/PA12*

30PTMEO/PA12 +

55PEO/PA12*

57PEO/PA6*

'Data reported from [25-26] I Data reported from (27) \Data reported from (28)

70

Pebax®2533

80РТМЕО/РА12*

"PE

30

80

Content [wt.%]

w

Trademark Acronym

Polymer g m

'

11 13

-53

201

156

160

159

-1 20

142

126

7

9

[°C]

'

[°C]

m

λ

T (PA)

T (PE)

-55

-65

-78

-72

-77

[°C]

T

Table 5.1 Selected properties of poly(ether-block-amide) copolymers. с

51

40

30

32

20

14

Crystallinity in PA block [wt.%]

С

о

СП I—I

>

о

В

и о

о

и

w оz

о

о

О

S

Z

oo

POLY(ETHER-BLOCK-AMIDE) COPOLYMERS

119

its constituents, any variation in the polyamide block nature, length and ratios can bring to complex systems, whose properties can not be detected for each single component. In this respect, to modify structural and physicochemical features means to change melting point, glass transition temperature, crystallinity, specific gravity, chemical and mechanical resistance, hydrophilic and antistatic properties (Tables 5.1-5.5). These changes render the poly(etherblock-amides)flexible,versatile and easy to process and recycle. The enhanced performance of these block copolymers is well reflected by the good solvent resistance, outstanding mechanical properties at broad range of service temperatures, and attractively selective transport properties. The class of poly(ether-biocfc-amide) is considered innovative and promising for breakthrough applications, that include smart breathable coatings for textile, barrier films, advanced chemical separation and biomedicai devices, mechanical parts, cables and wires, antistatic sheets or belts and automotive, intelligent food packaging materials, virus-proof surgical sheeting, and garments impact modifier. Hereafter, the most representative properties for any special grades of PEBAX® are reported in Tables 5.1-5.5. The mechanical response exhibited by the PEBAX XX33 series is consistent with their segment composition (Table 5.4). The increase in the interconnectivity of the hard segments (PA) causes a systematic increase in modules and tensile strength, whereas an increase in soft segments (PE) results in higher elongation. These thermoplastic elastomers exhibit substantially low energy loss, high elastic memory, great ability to withstand cyclic deformation (repeated strain) under severe conditions, slow change of the modulus with temperature and no break to impact especially for softer grades (55D Shore hardness and below), resulting in high durable materials to use in the fabrication of electronic devices, high-performance sporting goods and so on. If the mechanical strength of these copolymer depends on the hard amide block content, their ability to permeate selectively gases and vapors is mainly determined by the distribution and interconnectivity of soft ether segment domains. Table 5.5 offers just a cursory insight into the different behavior of any block copolymers in gases and water vapor transport. Undoubtedly, the chemical composition together with separated morphology confers to the segmented copolymers a more or less hydrophobic character, which can significantly influence their affinity to specific penetrating molecules

120

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

Table 5.2 Chemical resistance of poly (ether-block-amide) copolymers. Solvent

Result

Solvent

Result

-

Benzene

+/-

Butanol (80°C)

Aceton

Solvent

Result +

Boiling water*

-

Dimethylformamide

+/-

Freon

+

Caustic soda (10%)

-

Dimethylacetamide

+/-

Formic acid/ sulphuric acid

+

Chloroform

-

Kerosene**

+/-

Iso-propanol (70°)

+

Ethanol

-

N-Methylpirrolidinone

+/-

Phosphate-ester fluid

+

Ethylene glycol

-

Perchloroethylene

+/-

n-Propanol (80°C)

+

Isooctane

-

Star petrol**

+/-

Trichloroethane

+

Methanol

-

Xylene

+/-

Methylene chloride

-

Parafin

-

Skip detergent (30g/l)

-

Sulphuric acid (10%)

-

Zinc chloride (50%)*

-

g-Butylolactone

-

*at 100°C ** at low hardness Table 5.3 Comparison of physicochemical and mechanical properties estimated for special grades of poly(ether-b/ocA>amide) elastomers. Properties/Grades HARDNESS (SHORE D)

4033

MV1074

MX1205

MH1657

42

40

42

42

75

90

78

80

DENSITY (g/cm3)

1.01

1.07

1.01

1.14

MELTING POINT (°C)

168

158

147

195

SENSITIVITY AT H%

0.5%

1.7

0.5%

4.5%

Mechanical part

Breathable film

FLEXURAE MODULUS (MPa)

APPLICATIONS Data reproduced from (8)

Impact Antistatic modifier additive

1400 348 327 223

% Psi Ft-lb/in.

Mg/1000 Cycles Lb/in op

°F op

D638

D638

D790

D256

D1044

D624C

D3418

D1525

D648

D395A

Tensile Strength, Ultimate

Elongation, Ultimate

Flexural Modulus

Izod Impact, Notched 20 -40 °C

Abrasion resistance H 1811000g

Tear resistance Notched

Melting point

Vicat Softening Point

HDT66psi

Compression Set (24hr 160°F)

Data reproduced from 18], *20 °C, 65 % RH

29

Psi

D2240

Hardness

1.4 1.4

107000

360

9210

72D

D570

1.02

7233

Water Absorption Equilibr. (20 °C, 50 % RH) 24 hr immersion

%

Units

D792

Method

ASTM

Specific gravity

Property

300

400

6

208

329

345

6

194

322

342

850

84

57 900

NB 1.5

NB 0.95

49000

8100

8300 67000

63D

1.01

6333

69D

0.64 0.83

1.02

7033

40D

55D

25D 4950 640 2100

35D 5600 580 2800

108 62

54 21 10

140 115

165 126

270 151

291

298

306 334

220

260 400 650 334

161

104 94

NB NB

0.5 1.2

0.5 1.2

NB NB

1.01

2533

1.01

3533

93

NB NB

13000

29000 NB NB

390

430

5700

0.5 1.2

0.5 1.2

7300

1.01

4033

1.01

5533

-

-

-

-

-

-

-

-

-

40

4.5*

1.10

4011

Table 5.4 C o m p a r i s o n of physicochemical a n d mechanical Droperties estimated for the series P E B A 3 3 a n d P E B A 4 0 1 1 .

NJ

ел

и

о

О

П

О И

n

О

Cd

M

POLY(ETHER-BLOCK-AMIDE) COPOLYMERS 123

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HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

Table 5.5 Transport properties estimated for three different special grades of PEBAX®-based films with thickness of 25 urn. GRADE

Permeability H2O· 1

glim -day)

co;* 2

ml/(m -day-atm)

o2" 2

N2" 2

ml/(m -day-atm)

ml/(m -day-atm) 3000 3900

MV 3000

20000

177000

MV6100

6000

72000

18500 6500

MX1205

1800

175000

24000

650

Data reported from [8] 'Measurements carried out at 38 °C and 50 %RH by Cup method ** Measurements carried out at 23 °C by using dried gases

yielding selective transport. The latter appears to be a key issue to meet the requirements of advanced applications in textile, construction, food and waste processing, packaging and medical fields. In the sections 6,7, an overview about transport properties and performance of poly(ether-block-amide) elastomers in important separation processes is given.

5.4 Compounding and Special Additives The polymers, including poly(ether-b/ocA:-amide), are coming to be more competitive for their lower costs of production and enhanced performance in terms of appearance, functionality, performance, safety, effectiveness, and processing efficiency. Important segments, including electronics, automotive, aerospace, packaging and separation processes, tend to differentiate their products from design to manufacturing through the use of additives enabling renewed materials for advanced applications. Poly(ether-block-amide) copolymers have ability to embed additives with specific activity and at various loading, resulting in enhanced performance for specific applications. Antistatic additives are usually incorporated in these copolymers in order to render them plastics antistatic, electrically and thermally conductive enabling to replace metals or non-conductive plastics in electronics, computer, automotive, medical devices and so on [29]. Antistatic agents find safely applications when a suitable

POLY(ETHER-BLOCK-AMIDE) COPOLYMERS Conductive

Static dissipative

Antistatic

123

Isolative

SURFACE RESISTIVITY (Ohms/sq) Very fast charge decay Damages of sensitive parts

Very slow charge decay Risk of electrostatic discharge Dust attraction force

Scheme 5.4 Schematic representation of surface resistivity ranges [30].

control of charge decay is, for example, requested. Very fast charge decay can damage sensitive electronic components, whereas very slow charge decay can cause dust attraction forces and uncontrolled electrostatic discharge (Scheme 5.4). It has been demonstrated that any of the grades of PEBAX® induce immediate and permanent antistatic effects reducing the surface resistivity from 109 to 1012 Ohms/sq. Special grades of antistatic PEBAX® can also be dissolved as additives in a large number of thermoplastic matrixes preserving physical properties of the host matrix and preventing phenomena such as sloughing, blooming and offgassing [31-32]. In this respect, it has been observed that blends of Pebax® with ABS resins promote a reduction of the surface resistivity below to 1010 Ω with rising content of РЕВА and ratio of polyether [29]. Other frequent special additives incorporated in Pebax® are antiUV agents and/or an antioxidant in order to prevent or limit degradation due to UV light exposure as well as to extend the shelf-life, preserving mechanical and chemical properties of the materials. The incorporation of additives such as coloring agents, fluidizing agents, anti-abrasion agents, demoulding agents, antimicrobial preservatives, filler salts, fungicides, insect and moth repellant agents, germicides, hydrotropes, metallic salts is also addressed at enhancing the processability and performance of these thermoplastic elastomers for advanced industrial applications, including textile, packaging and medical devices.

5.5 Environmental Impact and Recycling The family of poly(ether-b/ocfc-amide) has usually from 20 % to 95 % of renewable content [33]. High-performance combined with low

124

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density render further this class of thermoplastic elastomers attractive under the profile of the lifecycle and recycle of their applications. Extended lifetime of the products and reduced weight of applications (20 % than competitive plastics) meet the requirements of eco-sustainability and economical benefits. Indeed, the introduction of flexible segments takes advantages over crack propagation and low impact strength, yielding optimized thermal, mechanical and chemical properties. The control of the phase segregation directs the final performance prolonging their efficiency with time. Recently, polyether block amide (PEBA)-type materials have been realized from a natural vegetable oil extracted from a non-edible crop. These bio-based materials exhibit outstanding features of РЕВА due to a favorable crystalline structure of the polyamide 11, taking advantage of a greener production with reduced fossil energy and greenhouse gas emissions when compared with more traditional manufacturing processes.

5.6 Poly ether-bfocfc-amides Membrane in Separation Processes Poly(ether-bZocfc-amide) elastomers represent an attractive class of materials for their intrinsic rheology, mechanical and chemical resistance as well as processability and reliability. Moreover, the possibility to control the density polymer packing through directed segregation of micro-domains as well as the variety of chemical composition of the segmented chains provide unusual transport properties to these copolymer, yielding attractive interfaces for advanced separation processes inspired to the basics of the membrane technology. In this respect, a membrane is defined as a permselective interface through which chemical species can selectively be transported from one phase to the other under controlling mechanisms that depend on intrinsic chemical and structural features of the membrane as well as composition of the streams and operating conditions [34] (Scheme 5.5). Key parameters that dictate the performance of a membrane are the productivity expressed as the mass transfer of chemical compounds per unit of volume and the selectivity expressed as the ability of the membrane to discern from penetrating molecules, which can be different for structure, size, chemistry, condensability and

POLY(ETHER-BLOCK-AMIDE) COPOLYMERS Upstream

125

Downstream Mfeed > Mpermeate

^feed

^permeate

Membrane thickness

Scheme 5.5 Representation of the transport of chemical species through a permselctive membrane.

affinity. Depending on structural and chemical features of the membrane and composition of the feed, thermodynamic and kinetic parameters can decide the controlling transport mechanism, determining the successful outcomes of the overall membrane operations [35]. The productivity (P) of a membrane is usually expressed as permeability, which can be written as „

Flux ■ thickness

/t- -t \

дμ Where the flux is given by the (amount of permenat)/ (membrane-area time) ratio, thickness is referred to the selective layer of the membrane and 3μ (i.e., difference in concentration, pressure, temperature, electrostic potential and so on) is the driving force gradient for mass transfer [36]. The efficiency of a membrane process is well expressed by a separation factor defined as selectivity parameter (a) and is referred to the preferentially permeated species. G=

C^/Q 1 ^ B / ^-B

i52)

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Where С is the composition of the permeated species (A and B) and С is the composition of the species in the feed, respectively. High-performance poly(ether-bZocic-amide) membranes have been developed for the treatment of gaseous mixtures, separation of organic compounds, purification of waste water streams or more simply recovery of flavors and aromas [37]. Hereafter, an overview of the various applications involving poly(ether-bZocfc-amide) membranes is given. 5.6.1

Treatment of Gaseous Streams

Segmented poly(ether-block-amide) copolymers have good filmforming ability and interesting transport properties. The strong physical cross-linking combined to the high mobility and chemical affinity of the soft segments enables the application of PEBA-based membranes suitable for the separation of condensable and acid gases from nonpolar gases [26-27]. In this case, the permeability [cm3(STP) -cm(cm2s-cm Hg)1] is given by the steady-state gas flux film [cm3(STP) (cm2-s)"T] measured through the membrane of thickness / (cm) under an applied trans-membrane pressure difference (ЛР=р2-р1), where and p2 and рг are the feed (i.e., high) pressure and permeate (i.e., low) pressure (cmHg), respectively. In a gas mixture, p2 and p3 refer to the partial pressures of permeant species on the high and low pressure sides of the film, respectively. The permeability can be regarded as a result of kinetic and thermodynamic contributions described by the diffusion-solution model (P=DS), where D (cmV) is a concentration-averaged effective diffusivity, while S (cm3cm3 olcmHg1) is the solubility coefficient defined as CJp2, where C2 is the gas concentration dissolved in the upstream (i.e., high pressure) side of the film. Therefore, the ideal selectivity for the species i relative to species / can be defined as the ratio of the respective permeability, which is the result of a diffusivity selectivity (DJD) and solubility selectivity (SJS), respectively [38-39] X

Various grades of PEBAX® have been used to tailor dense solvent-cast or melt extruded self-standing membranes for the

POLY(ETHER-BLOCK-AMIDE) COPOLYMERS

127

separation of carbon dioxide from streams containing nitrogen or hydrogen [25-26]. These membranes exhibited a selectivity for the gas-pair C0 2 /H 2 and C0 2 /N 2 higher than those measured for conventional rubbery and glassy polymers, and copolymers (Fig. 5.1), resulting attractive films to isolate C0 2 from emission sources such as power plants and chemical industries responsible for the global warming [40]. Strong interactions between the quadrupolar C0 2 and linkages in the polyether segments have been suggested to direct a preferential solubility of carbon dioxide in the polymer matrixes. The affinity

Figure 5.1 Selectivity values estimated for the gas-pair (a) C0 2 /N 2 and (b) C0 2 / H2 through different grades of Pebax® [26].

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HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

of rubbery polymers such as PEO to C 0 2 relative to nonpolar gases has been evaluated [41]. Significant separation factors of 61 for gas-pair C 0 2 / N 2 and 500 for S 0 2 / N 2 have been measured and the different gas permeation behavior through the various grades of Pebax® has also been discerned in relation to the contribution of the permeable continuous phase formed by PE block and the impermeable regions formed by PA discrete particles [27]. The blending of PEBAX® with a liquid absorbent such as polyethylene glycolether brings about an increase in 8-fold carbon dioxide permeability and enhanced selectivity (14.9), due to a combined effect of increased diffusivity and solubility [42]. Mixed matrixes have been developed by incorporating multiwalled carbon nanotubes (MWNT) in PEBAX®-based membranes [43], revealing an enhanced selectivity especially at 2.0 wt.% of CNT loading (Fig. 5.2). Pebax® membranes containing silica exhibited C 0 2 / N 2 selectivity of 79 [44], whereas separation factor C 0 2 / H 2 of 52.3 and C 0 2 permeability of 136 Barrer at 8 atm and 35 °C have been achieved introducing 3-hydroxy-3-methylbutyldimethylsiloxy (POSS) in PEBAX® [45] (Scheme 5.6). In this case, POSS nanoparticles induce the formation of cavity in the bulk of the membranes, whereas C 0 2 induce plasticization at higher pressure, determining an increase in free volume and higher mobility of the polymer segment chains, respectively.

- Uncross-linked PEBAX - Cross-linked PEBAX

(a)

1

2 3 4 CNT loading, [wt. %]

(b)

■ Uncross-linked PEBAX - Cross-linked PEBAX

1

2

3

4

CNT loading, [wt. %]

Figure 5.2 Selectivity values estimated for the gas-pair (a) H 2 /N 2 and (b) C0 2 /H 2 through Pebax® membranes incorporating CNTs [43].

POLY(ETHER-BLOCK-AMIDE) COPOLYMERS

129

In order to build u p predictive models enabling one to tailor poly (ether-block-amide) membranes with desired transport properties, Molecular Dynamic (MD) simulations have been implemented and the collected data have been compared with experimental insights achieved for 80PTMO20PA dense films [46-48] (Table 5.6). Amorphous atomistic bulk structures of the copolymer have been constructed, giving a good representation of the WAXD pattern of the membranes and of the transport of different gas molecules (Scheme 5.7). о HO - ( C4H80 kb-iC-

о о Il II -С — C4H8 — С -

0^Η22 - NH )

ί онес4;

он

Osi^^sr ;ί

J*

sV-0

/\

R

H,C

/ 4

о R V.

CH.

jQ

R

^ /° = о 1

.он

^

Scheme 5.6 Chemical structure of РЕВАХ® and nanoparticle silica (a) Octa (3-hydroxy-3-methyl butyldimethylsiloxy) POSS (POSS-OH) and (b) Octa amie acid POSS (POSS-acid) [45]. Table 5.6 Comparison between experimental and theoretical diffusivity and solubility selectivity data estimated for no polar and polar gases (48). Gas

Theoretical Selectivity

Experimental Selectivity D D

/

N2

s/sN2

H

@25°C

s/sN2

D/D N 2 (-)

(-)

(-)

TST

MD

TST

GCMC

85.92

23.92

0.37

0.29

0.073

2.24

19.26

5.99

22.29

0.46

co 2

2.09

23.61

o2 сн 4

1.81

1.39

3.27

2.22

2.12

1.50

0.80

3.986

3.36

0.94

3.75

3.10

H2

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HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

Scheme 5.7 Simulation copolymerizaton and production of atomistic boxes of poly(ether-block-amide)80PTMEO/PA12.

5.6.2

Water Permeable Poly(ether-block-amide) Membranes

The ability of poly(ether-frZocfc-amide) membranes containing high content of hydrophilic blocks to transport water vapor is a relevant topic, if we consider their use in clothing, medical or surgical textiles or gloves, and under-roof film protection (46,49-50). Many attempts have been done in order to find relationships between the polymer structure and the water vapor transport through poly(ether-blockamide) membranes, evaluating the role of chemical functionality and flexibility of the polymer segment chains [51-53]. Organic fillers have been embedded in 80PTMO20PA membranes in order to improve the selectivity of the matrixes (Figure 5.3) [51]. Experimental and theoretical studies have been combined in order to identify the controlling mechanisms for the water vapor transport, yielding useful indication about the role of host-guest intermolecular interactions established at the water-modifier, modifier-polymer, water-polymer, polymer-polymer and modifiermodifier (47,54). A domino effects caused by amphiphilic modifiers, i.e. aromatic sulphonamides, on the hydrophilicity of the overall polymer mixed matrixes revealed the critical role of hydrogen bonding involved in various adducts, which regulate the water sorption process. The ability of various grades of Pebax® to separate water from methanol vapors has also been evaluated, evidencing how the equilibrium sorption of water and methanol in the various matrixes is comparable and almost independent on PTMO content, whereas

POLY(ETHER-BLOCK-AMIDE) COPOLYMERS

131

(а)1б0

80PTMEO/PA12

25°C 0

10000 20000 30000 40000 50000 Water vapour permeability, [barrer]

0

10000

20000

30000

40000

Water vapour Permeability, [barrer]

Figure 5.3 Selectivity values for H 2 0/C0 2 and H 2 /N 2 vs. water vapor permeability estimated for 80PTMEO/PA12 membranes containing organic fillers. Data adapted from [51].

a decrease in diffusivity can be appreciated with rising glassy polyamide [28]. The diffusion of water and methanol is demonstrated to decrease exponentially with the inverse fractional free volume of the polymer, which is defined as the ratio of the specific free volume to the observed specific volume [55]. The sorption of water vapor has been studied in poly(etherblock-amide) membranes containing AgBF4 nanoparticles formed in situ, resulting in various degree of uptake as a function of the changes in number, size and distribution of silver nanoparticles in the hybrid material [56]. The performance of poly(ether-block-amide) composite membranes has also been evaluated in ultrafiltration processes for water nanofiltration, achieving composite films with a molecular weight cut-off between 800 and 4500 g/mol and water permeability between 2.3 and 9.4 L/(hm 2 bar) [57]. The membranes coated by PEBAX® resulted less susceptible to fouling than commercial membranes, taking advantage of the treatment of oils/water emulsions wastes. 5.6.3

Separation of Organic Compounds from Organic and Aqueous Streams

Poly(ether-block-amide) membranes find also large application in separation of azeotropes, isotropes and compounds having close boiling temperature [58] or aroma and volatile compound [59-61]

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HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

recovery and dehydration of organic solvents [62] and the removal of organics from aqueous and non aqueous streams [63-68]. Among the various membrane processes, the pervaporation is one of the most exploited technologies for these types of applications [69-72]. This saving-energy and cost-effective membrane technology allows to separate various components in mixtures by different diffusional flow through thin a membrane and an evaporative phase change like to a simple flash step. The transport occurs under a partial pressure gradient across the membrane. A vacuum is usually applied to downstream (permeate) side and coupled with quick condensation of the permeating vapors. The selectivity is controlled by mutual affinity between membrane and chemical compounds. The flux corresponds to the amount of permeate per unit area per unit time, whereas the selectivity is defined as enrichment factor (/?) and is expressed as the ratio of concentrations in the feed (c/) and permeate (c."), respectively. The good separation characteristics of РЕВА membranes in pervaporation processes have extensively been discussed by Cen [73] in relation to the sorption and diffusion properties. Higher solubility has been estimated for halogenated hydrocarbons, aromatic hydrocarbons and aniline, followed by ethers, ethanol and methanol. The lowest sorption of around 0.2 % of water results in attractive use of these materials to remove organics from waste streams by membrane technology. Yildirim and coworkers [58] used various grades of PEBAX® membranes to disrupt azeotropic behaviour of the benzene/cyclohexane mixtures by pervaporation. Particularly, the hardness of the matrixes was examined in order to control swelling phenomena which affect the selectivity of the separation process. In this respect, the introduction of silica particles in block copolymer PEBAX® membranes has been proposed to prevent or reduce swelling phenomena during phenol/water separations [74], confirming how polymer-nano-inorganic particles composite membranes exhibit generally enhanced mechanical and chemical resistance, thermal stability and improved transport properties. In this respect, the high performance of Pebax® membrane for recovery of phenol from aqueous streams has extensively been demonstrated by Böddeker and coworkers [75], confirming the feasibility to scale up the process to pilot plant by using 40 L batch of aqueous phenol solution with an initial phenol content of 2 wt%. Membrane modules with an available area of 2.3 m2 enabled a recovery of 10kg/ day at 50°C and after 24 h.

POLY(ETHER-BLOCK-AMIDE) COPOLYMERS

133

Poly(ether-block-amide) membranes have also been used to recover alcohols from aqueous streams [76]. An unusual increase in permeability and selectivity has been observed with increasing content of soft block (PTMO) and polarity of the alcohols. Böddeker and coworkers [77] confirmed a concomitant increase in permeability and selectivity with rising polarity of alcohols during the recovery of butanol isomers from dilute aqueous by pervaporation.

5.7 Poly(ether-block-amide) Membranes in Food Packaging, treatment of waste streams as well as recovery of aroma and flavors represent any of the critical requirements to meet in food and beverage industrial processes. In food packaging, the control of atmosphere surrounding foods and beverage wrapped in plastics depends significantly on the respiratory of the enveloped food but also on the ability of the envelope to control selectively the transport of gas and vapors in and out of the package. Pebax elastomers well meet the requirements of high mechanical resistance, transparency, chemical inertia and controlled transport of oxygen, carbon dioxide, water, nitrogen and aromas [78]. Any of grades of PEBAX® have been molded in dense films and their transport properties have been tested at various relative humidity (RH %)[79], resulting in suitable films to store vegetable and fruit in modified atmosphere (Figure 5.4). (a) « 60000

E 20000

■ O2RH0% B C 0 2 RH0% □ 0 2 RH 100% aCO2RH100%

I 10

i& П , W/.

20 T, [ X ]

Figure 5.4 Carbon dioxide permeability (a) and carbon dioxide/oxygen selectivity (b) measured at various temperature (T °C) and relative humidity (RH%) through PEBAXMV3000 [79].

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HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

Enhanced mechanical, surface or optical properties of РЕВА films, preserving their high water permeability, have been achieved over the years through blends, multi-layer films and films containing inorganic particles with several patented applications in high performance packaging [80-81]. Water vapor and oxygen permeability through 80PTMO20PA matrixes have been changed by adding amphiphilic modifiers to casting solutions [51], yielding films with different H 2 0 / 0 2 separation factors (Figure 5.5). The recovery of aroma and fruit flavors is another key issue in food processing, considering that the composition of molecular compounds like esters, aldehydes and alcohols cause the typical juice flavor, including sensation of ripeness, sweetness a n d / o r grassy flavor typical [82]. The permeability of model-molecules like ethyl acetate, ethyl propionate or ethyl butyrate resembling aroma and flavors has been examined in relation to their high condensability and affinity to modified 80PTMOPA12 membranes [52-53]. The permeation of these compounds was addressed via controlling interactions established at penetrant-membrane surface interface. The sensitivity of these volatile compounds to heat can, however, be responsible for their lost. Usually, this drawback is overcome by implementing pervaporation processes. PTMO/PA copolymers exhibit high permeability to these esters, especially as PTMO forming the polymer backbone increases [60]. Sampranpiboon and coworkers [59] have also proposed the use of PEBA-based membranes for the recovery of aroma ethyl butyrate and isopropanol

о 30 wt.% » 50 wt.% • 70 wt.%

3,1

3,2

3,3

1/ТхЮ" 3 , [К" 1 ]

3,4

10000

20000

30000

Water vapour permeability, [barrer]

Figure 5.5 Water vapor permeability (a) and water vapor/oxygen selectivity values estimated for 80PTMOPA12 membranes embedding various organic fillers [51].

40000

POLY(ETHER-BLOCK-AMIDE) COPOLYMERS

135

in pineapple juice by pervaporation separation. Experimental findings based on evaluations about the influence of feed concentration and temperature highlighted the large affinity of РЕВА to ethyl butyrate in the entire concentration range studied (100-900 ppm), whereas a loss of isopropanol/water selectivity was observed. Any examples of PEBA-membrane-based-pervaporation to recovery thermo-sensitive aroma with high boiling temperature are also reported. Aroma with butter flavor like acetoin [83], aroma with cheese flavor like S-methylthiobutanoate [84-85] as well as natural vanillin (86) have been, for example, recovered with high enrichment factors by using pervaporation plants equipped by poly (ether-b/ocfc-amide) membranes. The use of composite membranes tailored by coating PEBAX® layers on polymeric porous supports such as polyamideimide (PAI) and polyacrylonitrile (PAN) has further confirmed a potential utilize of these elastomers in separation of acetone from edible oil/solvent mixtures [87-88]. PAI/Pebax® composite membranes processed in nanofiltration plants exhibited acetone fluxes ranging from 42 to 93.5 l/(hm2) with retention factors of 88-68 at 5 bar, whereas fluxes from 15 to 24.5 l/(hm2) with retention factors of 68-54 were estimated for PAN/Pebax® composite membranes.

5.8 Concluding Remarks Poly(ether-friocic-amide) copolymers represent a class of next generation materials with outstanding chemical, mechanical and transport properties that render them challenging systems for a broad range of applications, including high-performance waterproof breathable clothing, barrier films, engineered packaging, membrane separation processes. The special performance of these thermoplastic elastomers arises from the versatility of their structure, depending on nature, length, and weight of hard (PA) and soft (PE) segments forming the linear backbone of the polymers. Microphase separated morphology caused by incompatibility of the segments and/or thermally directed phase transitions can decide the final structure-property relationships, which are responsible for the enhanced properties of these materials, including key separations of various gaseous and liquid chemical species. Also, the ability of these elastomers to embed different type and amount of organic and inorganic modifying agent opens new horizons towards the

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design of developed block copolymers with challenging desired features that can satisfy the increasingly needs of the market.

References 1. Polymers, The Materials of Choice, Materials Science and Technology (MAST), 1995, www.matsel .matse.illinois.edu. 2. Heitz W., Bragging W., Freund L., Gailberg M., Greiner A., Jung H., Kampschilte, Niebner N., Osa F., Schmidt A-W., Wicker M., Synthesis of monomers and polymers by the Heck reaction, Macromolecular Chemistry and Physics, 189 (1988) 119-127. 3. Eidelman N., Characterization of Combinatorial Polymer Blend Composition gradients by FTIR Microspectroscopy, /. Res. Nati. Inst. Stand. Technol. 109 (2004), 219-231. 4. Ryan A.J., Polymer science: Designer polymer blends, Nature Materials, 1 (2002), 8-10. 5. Hadjichristidis N., Pispas S., Flouda G., (Eds), Block Copolymers: Synthetic Strategies, Physical Properties, and Applications, John Wiley &Sons, Inc., New Jersey, 2003. 6. Libler L., Theory of Microphase Separation in Block Copolymers, Macromolecules, 13/6 (1980), 1602-1617. 7. Luo C , Huang W., Han Y, Formation of two kinds of hexagonally arranged structures in ABC triblock copolymer thin films induced by a strongly selective solvent vapour, Macromol. Rapid Commun., 30 (2009), 000-000, DOI 10.1002/ marc200900427. 8. http://www.arkema.com. 9. Tavernier B, Influence of Processing Conditions on the Structure Development In Pebax®,Thesis Dissertation, Catolic University of Leuven (Belgium), 2009. 10. Schollenberger C.S., US PATENT 2,871,218,1955. 11. Brydson J.A., (Ed), Plastics Materials, Butterworth-Heinemann, Oxford, 1995. 12. Bhowmick A. K., Stephens, H.L., (Eds.) Handbook of Elastomers, Marcel Dekker, New York and Basel, 1988. 13. Lilaonitkul A. West J.C., Cooper S.L, Properties of polytetramethylene oxidepolytetramethylene terephthalate block copolymers, /. Macromol Sci-Phys., B12 (1976) 563-597. 14. Lilaonitkul A., Cooper S.L, Properties of polyester-polyester thermoplastic elastomers, Rubber Chem Technol., 50 (1977) 1-23. 15. http://www.matweb.com. 16. Peyravi M., Babaluo A. A., Akhfash Ardestani M.,. Razavi Aghjeh M. K, Pishghadam, S.R., Hadi P., Study on the Synthesis of Poly(ether-block-amide) Copolymer Based on Nylon6 and Poly(ethylene oxide) with Various Block Lengths, /. Appi. Polym. Sci., 118, (2010) 1211-1218. 17. Peyravi M., Akhfash Ardestani M., Babaluo A.A., Razavi Aghjeh M. K, Pishghadam, S.R., Jannatdousta E., Synthesis and characterization of nanostructured-segmented block copolyetheramide based on nylonó and

POLY(ETHER-BLOCK-AMIDE) COPOLYMERS

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poly(ethylene oxide), Chinese Journal of Polymer Science Vol. 28, No. 4, (2010), 597-605. Sauer B.B., Mclean R. S., Brill D. J., Londono D. J., Morphology and orientation during the deformation of segmented elastomers studied with small-angle X-ray scattering and atomic force microscopy, /. Polym, Sci., Part B, Polymer Physics, 40(16), (2002) 1727-1740. Sauer B.B., Mclean R.S., Thomas R. R., Nanometer resolution of crystalline morphology using scanning probe microscopy, Polymer International, 49(5) (2000) 449-452. Sauer В. В., Mclean R. S., Thomas R. R., Nanometer resolution of crystalline morphology using probe microscopy, /. Polym Int, 49 (2000) 449-452. Hatfield G. R., Guo Y, Killinger W.E., Andrejak R.A., Roubicek P.M., Characterization of Structure and Morphology in Two Poly(ether-blockamide) Copolymers, Macromolecules 26 (1993) 6350-6353. Sheth J.P., Wilkes G. L., Semicrystalline Segmented Poly(Ether-b-Amide) Copolymers: Overview of Solid-State Structure-property relationships and Uniaxial Deformaton Behavior in: Handbook of Condensation Thermoplastic Elastomers, S. Fakirov (Ed), Wiley-VCH Verlag GmbH & Co KGaA, Weinheim, 2005. Yang I. H., Tsai P. H., Rheological characterization and microphase-separated structure of a poly8ether-block-amide) segmented block copolymer, /. polym. Sci. part B: polymer Physics. 43 (2005) 3557-2567. Yang I. H., Tsai P. H., Rheology and structure change of poly(ether-blockamide) segmented block copolymer, /. Cent. South Univ. Technol. 14S1 (2007) 146-150. Bondar V I., Freeman B. D., Pinnau L, Gas Sorption and Characterization of Poly(ether-b-amide) Segmented Block Copolymers, ] Journal of Polymer Science: Part B: Polymer Physics, 37 (1999) 2463-2475. Bondar V. I., Freeman B. D, Pinnau I., Gas Transport Properties of Poly (ether-b-amide) Segmented Block Copolymers, Journal of Polymer Science: Part B: Polymer Physics, 38 (2000) 2051-2062. Kim J. H., Ha S. Y, Lee Y M., Gas permeation of poly(amide-6-b-ethylene oxide) copolymer,/. Membr. Sci., 190, (2001) 179-193. Rezac M., John Т., Pfromm P., Effect of copolymer composition on the solubility and diffusivity of water and methanol in a series of polyether amides. / Appi. Polym. Sci., 65 (1997) 1983-1993. Wang G., Xue В., Synthesis and characterization of poly(ether-block-amide) and application as permenat antistatic agent, /. Appi. Polym. Sci., 118/4 (2010) 2448-2453. h t t p : / / www.Pebax®.com. Dufton P., Thermoplastic Elastomers Market, (in Rapra Industry Analysis Report Series, Rapra Technology Limited, 2001. Brulé В., Babin, P., guilment, J., PATENT WO/2008/139111,2008. http://www.americanrecycler.com. Mulder M., Basic Principles of Membrane Technology, Kluwer Academic Publishers, Dordrecht, The Netherlands, 1991. Noble R., Stern S., Membrane Separations Technology, Principles and Applications, (Eds), Elsevier Science B.V, Amsterdam, The Netherlands, 1995.

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36. Bitter Т., Transport Mechanisms in Membrane Separation Processes. Plenum Press, New York and London, 1991. 37. Jonquiéres A., Clement R., Lochon P., Permeability of block copolymers to vapors and liquids, Prog. Polym. Sci. 27 (2002) 1803-1877. 38. Ghosal K., Freeman B. D., Gas separation using polymer membranes: an overview. Polymers for Advanced Technologies, 5 (1993) 673-697. 39. George S., Thomas S., Transport phenomena through polymeric systems, Progress in Polymer Science, 26 (2001) 985-1017. 40. Car A., Yave W., Peinemann K-V., Stropnik C , Tailoring Polymeric Membrane Based on Segmented Block Copolymers for C 0 2 Separation in Membrane Gas Separation, Freemann B. D., Yampolskii Y, (Eds), John Wiley and Sons Ltd, Chichester, UK, 2010. 41. Lin H., Freeman B.D., Gas solubility, diffusivity and permeability in poly (ethylene oxide), /. Membr. Sci. 239 (2004) 105-117. 42. Yave W., Car A., Peinemann K-V., Nanostructured membrane material design for carbon dioxide separation, /. Membr. Sci., 350 (2010) 124-129. 43. Murali R.S., Sridhar S., Sankarshana Т., Ravikumar Y.V.L., Gas Permeation Behavior of Pebax-1657 Nanocomposite Membrane Incorporated with Multiwalled Carbon Nanotubes, Ind. Eng. Chem. Res. 49 (2010) 6530-6538. 44. Xu Z., Yu L., Han L., Polymer-nanoinorganic particles composite membranes: a brief overview, Front. Chem. Emg. China, 373 (2009) 318-329. 45. Li Y, Chung T-S., Molecular-level mixed matrix membranes comprising Pebax® and POSS for hydrogen purification via preferential C 0 2 removal, Inter. /. Hydrogen Energy, 13/19 (2010) 10560-10568. 46. Gugliuzza A., Drioli E., New performance of a modified poly(amide-12b-ethylenoxide), Polymer, 44 (2003) 2149-2157. 47. Gugliuzza A., De Luca G., Tocci E., De Lorenzo L., Drioli E., Intermolecular Interactions as Controlling Factor for Water Sorption into Polymer Membranes, /. Phys. Chem. В 111 (2007) 8868-8878. 48. Tocci E., Gugliuzza A., De Lorenzo L., Macchione M., De Luca G., Drioli E., Transport properties of a co-poly(amide-12-b-ethylene oxide) membrane: A comparative study between experimental and molecular modelling results, /. Membr. Sci. 323 (2008) 316-327. 49. Flesher ]., Film élastomére thermoplastique permeable ä la vapeur d'eau a base de polyétheresteramide, son procède de fabrication et articles comprenant un tei film. EUR PATENT Appi 378,015,1990. 50. Gugliuzza A., Drioli E., Role of additives in the water vapor transport through co-poly (amide/ether) membranes: effects on surface and bulk polymer properties, Eur. Polym. ]., 40 (2004) 2381-2389. 51. Gugliuzza A., Drioli E., valuation of C 0 2 permeation through functional assembled mono-layers: relationships between structure and transport, Polymer, 46 (2005) 9994-10003. 52. Gugliuzza A., Fabiani R., Garavaglia M.G., Spisso A., Drioli E., Study of the surface character as responsible for controlling interfacial forces at membrane-feed interface, Journal of Colloid and Interface Science, 303 (2006) 388-403. 53. Gugliuzza A., Fabiani R., Garavaglia M.G., Spisso A., Drioli E., Corrigendum to "Study of the surface character as responsible for controlling interfacial

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54. 55. 56.

57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 67. 68. 69. 70.

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forces at membrane-feed interface" [J. Colloid Interface Sci. 303 (2006) 388^103], Journal of Colloid and Interface Science 306 (2007) 192-193. De Luca G., Gugliuzza A., Drioli E., Competititve Hydrogen-bonding Intercations in Modified Polymer membranes: A Density Functional Theory Investigation, /. Phys. Chem B, 113 (2009) 5473-5477. Rezac M.E., John Т., Correlation of penetrant transport with polymer free volume: additional evidence from block copolymers, Polymer 39 (1998) 599-603. Hamouda S.B., Nguyen Q. Т., Langevin D., Chappey C , Roudesli S., Polyamide 12-polytetramethyleneoxide block copolymer membranes with silver nanoparticles - Synthesis and water permeation properties, Reactive & Functional Polymers 67 (2007) 893-904. Nunes S.P., Sforqa M.L., Peinemann K-V., Dense hydrophilic composite membranes for ultrafiltration, /. Membr. Sci. 106 (1995) 49-56. Yildirim A.E., Hilmioglu N. D., Separation of benzene/cycloxane mixtures by pervaporation using РЕВА membranes, Desalination 219/[1-3] (2008) 14-25. Sampranpiboon P., Jiraratananon R., Uttapap D., Feng X, Huang R. Pervaporation separation of ethyl butyrate and isopropanol with polyether block amide (РЕВА) membranes, / Membr Sci, 173 (2000) 53-59. Djebbar M. K., Nguyen Q.T., Cle'ment Q.T., Germain Y., Pervaporation of aqueous ester solutions through hydrophobic poly(ether-block-amide) copolymer membranes, / Membr Sci 146 (1998) 125-133. Kujawsky W., Rozac R., Pervaporative removal of volatile organic compounds from multicomponent aqueous mixtures, Sep. Sci. TechnoL, 37 (2002) 3559-3575. Sridhar S., Kalyani S., Ravikumar Y.V.L., Muralikrishna T.S.V.N., Performance of composite membranes of poly(ether-block-amide) for dehydration of ethylene glycol and ethanol, Separation Science and Technology, 45 (2010) 322-330. Böddeker К, Bengston G, Pingel H. Pervaporation of isomerie butanols, J Membr Sci, 54 (1990) 1-12. Fouad E.A., Feng X., Use of pervaporation to separate butanol from diluite aqueous solutions: Effects of operating conditions and concentration polarization, /. Membr Sci 323/2 (2008) 428-435. Hilmioglu N.D., Yildirim A.E., Tulbentci S., A pervaporation application for treating methyl ier-butyl ether (MJBE)Contaminated Water/Wastewater, Green Energy and technology (2010) 555-563. Mandai M.K., Bhattacharya P.K., Poly(ether-block-amide) Membrane For Pervaporative Separation of Pyridine Present In Low Concentration In Aqueous Solution, /. Membr. Sci., 286 (2006) 115-124. Garcia Villaluenga J.P., Tabe-Mohammadi A., A review on the separation of benzene/cyclohexane misture by pervaporation processes, /. membr Sci, 169 (2000) 159-174. Sheng J, Separation of dichloroethane-trichloroethylene mixtures by means of a membrane pervaporation process, Desalination, 80 (1991) 85-95. Huang R.Y.M., (Ed), Pervaporation membrane separation processes, Elsevier, New York, 1991. Lipnizki F, Field RW, Ten PK. Pervaporation-based hybrid process: a review of process design, applications and economics. / Membr Sci, 153 (1999)183-210.

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71. Nguyen Q.T., Germain Y, Clement R.; Hirata Y, Pervaporation, a novel technique for the measurement of vapor transmission rate of highly permeable films, Polymer Testing, 20 (2001) 901-911. 72. Shao P., Huang R.Y.M., Polymeric membrane pervaporation, /. Membr Sci, 287 (2007) 162-179. 73. Cen Y, Staudt-Bickel C , Lichtenthaler R.N., Sorption properties of organic solvents in РЕВА membranes, /. Membr. Sci. 206 (2002) 341-349. 74. Sforga M.L., Yoshida I. V.P., Borges СР., Nunes A. P., Hybrid membranes based on Si02/Polyether-b-Polymaide: Morphology and applications,/. Appi., Polym., Sci., 178 (2001) 178-2001. 75. Böddeker К, Pingel H, Dede К. In: Bakish R, (Eds), Continuous pervaporation of aqueous phenol on a pilot plant scale, Proceedings of the Sixth International Conference on Pervaporation Processes in the Chemical Industry, Ottawa, Canada: Bakish Materials Corporation; September 27-30,1992, 514-9. 76. Morin M, Thompson E. Pervaporation of alcohol/water solutions through block copolymer membranes. In: Bakish R, (Eds), Proceedings of the Third International Conference on Pervaporation Processes in the Chemical Industry, Nancy, France: Bakish Materials Corporation; September 19-22,1988,349-54. 77. Böddeker K.W., Bengtson G., Pervaporation of low volatility aromatics from water, /. Membr Sci, 53 (1990) 143-158. 78. Frey A., Leroux R., Fischer L., US PATENT 5,888,597,1999. 79. Paz, H.M., Cucamp-Collin M.N., Lebrun M., Reynes M., Etude comparative de la pérmeabilité aux gaz d'emballages de fruits frais en film synthétique, fruits, 52 (1997) 331-338. 80. Tse S., Schroeder G., Iwanami Т., US PATENT 5,069,955,1991. 81. Kuratsuji Т., Maillet J., Yamamoto J., US PATENT 6,063,505,2000. 82. Lautenschlaeger F., US PATENT 4,594,250,1986. 83. Dettwiler В., Dunn I., Prenosil J., In: Bakish R, (Ed), Bioproduction of acetoin and butanediol: product recovery by pervaporation, Proceedings of the Fifth International Conference on Pervaporation Processes in the Chemical Industry Heidelberg, Germany: Bakish Materials Corporation; March 11-15, 1991,308-17. 84. Baudot A., Marin M., Dairy aroma compounds recovery by pervaporation, J Membr Sci, 120 (1996) 207-220. 85. Baudot A., Marin M., Pervaporation of aroma compounds: comparison of membrane performances with vapour-liquid equilibria and engineering aspects of process improvement, Trans IChemE, C75 (1997) 117-142. 86. Böddeker К, Gatfield I, Ja'hnig J, Schorm C. Pervaporation at the vapor pressure limit: Vanillin.} Membr Sci, 137 (1997) 155-158. 87. Zwijnenberg H.J., Krosse A.M., Ebert K , Peinemann K.V., Cuperus F.P., Acetone-stable nanofiltration membranes in deacidifying vegetable oil, JAOCS, 76/1 (1999) 83-87. 88. Peinemann K.V., Ebert K., Hicke H.G., Scharnagl N., Polymeric Composite Ultrafiltration Membranes for Non-aqueous Applications, Environmental Progress, 20/1 (2001) 17-22.

6 Aromatic Polyamides (Aramids) José M. Garcia, Felix C. Garcia, Felipe Sema, and José L. de la Pena Departamento de Quimica, Facultad de Ciencias, Universidad de Burgos, Burgos, Spain

Abstract

Aromatic polyamides, wholly aromatic polyamides, or aramids, are considered to be high-performance materials owing to their outstanding thermal and mechanical resistance. Their properties can be attributed to their fully aromatic structure and amide linkages, which give rise to stiff rod-like macromolecular chains that interact with each other via strong and highly directional hydrogen bonds. These physical links deeply favor the development of effective crystalline micro-regions or domains, resulting in a compact intermolecular packing and cohesive energy. The better-known commercial aramids, poly(p-phenylene terephthalamide) and poly(w-phenylene isophthalamide), are used in advanced technologies in every industrial field, and have been transformed into highstrength and flame resistant fibers and coatings with broad applications in advanced industrial products, such as heat and cut protective clothing, ballistic-protection products, sport fabrics, specialty paper products, transmission belts, friction products, industrial filters and membranes, and special pipes, among others. Owing to their above mentioned chemical and physical characteristics, they exhibit extremely high transition temperatures, which lie above their decomposition temperatures, are sparingly soluble in common organic solvents and, accordingly, can only be transformed upon solution from polar aprotic solvents or strong inorganic acids. Hence, the expansion of the applications of aramids involves, from one side, increasing their solubility, thereby improving their transformability, and, from other side, incorporating new chemical functionalities in the polyamide backbone or lateral structure in order to provide key characteristics for their application in cutting edge technological

Sabu Thomas and Visakh P.M. (eds.) Handbook of Engineering and Specialty Thermoplastics, (141-182) © Scrivener Publishing LLC

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fields. These fields are related with new electrochromic, luminescent or optically active materials, gas separation and ion exchange membranes, macromolecules with sensing and supramolecular capabilities, biomaterials for medical applications, materials with even higher mechanical and thermal resistance, etc. Keywords: Aromatic polyamides, aramids, high-performance polymers, heat-resistance materials, thermal resistance materials, outstanding mechanical properties, heat-protection products, cut-protection products, ballistic-protection products, friction products, specialty paper products, luminescent materials, electrochromic materials, optically active materials, gas separation membranes

6.1 Introduction and History Poly(amide)s, most commonly called polyamides, are polymers incorporating the amide group in their repeating unit (-CO-NH-) [1]. The amide linkage is widespread and found in natural occurring macromolecules, i.e., polypeptides and proteins, where it is known as a peptide bond, and in synthetic polymers as aliphatic and aromatic polyamides. Aliphatic polyamides are known as 'nylons', and aromatic polyamides are known by the acronym 'aramids'. The synthetic aromatic polyamides differ from the aliphatic nylons in the highly aromatic nature of the polymer backbone. Thus, according to the US Federal Trade Commission (FTC), wholly aromatic polyamides are synthetic polyamides, in which at least 85% of the amide groups are bound directly to two aromatic rings [2]. Both nylons and aromatic polyamides are considered engineering materials, but the aromatic structure of the main chain of the aramids endows these polymers with specialty characteristics. These characteristics make them less sensitive to oxidation and highly solvent resistant and give the materials superior thermal and mechanical resistance. Thus, they are classified as high-performance materials [1,3]. Demand is increasing for these materials for use as advantageous replacements for metals or ceramics in currently used applications or even as new materials in novel and cutting-edge technological applications [4-7].

AROMATIC POLYAMIDES (ARAMIDS)

143

The better-known commercial aramids are poly(p-phenylene terephthalamide) (PPPT) and poly(m-phenylene isophthalamide) (PMPI). Both of these polymers can be transformed into flameresistant, cut-resistant and high-tensile strength synthetic fibers, with technological applications in the field of coatings and fillers in the aerospace and armament industry, as asbestos substitutes, electrical insulation, bullet-proof body armor, industrial filters, and sport fabrics, among others. However, due to their chemical structure, they exhibit extremely high transition temperatures that are above their decomposition temperatures, are sparingly soluble in common organic solvents and, accordingly, can only be transformed in solution. As a consequence, recent basic and applied research has focused on enhancing their processability and solubility in order to broaden the scope of the technological applications of these materials. There is currently a huge research effort directed toward exploiting the special high-performance characteristics of the polyamides to obtain electro- or photoluminescent materials, reverse osmosis, gas or ion-exchange membranes, optically active materials, and nanocomposites with superior thermo-mechanical performance. The first all-para oriented aramid, poly(p-benzamide) (PPBA), was marketed by Du Pont under the 'Fiber B' trade name. Production only lasted a few years, probably due to economic reasons [8,9]. This polymer was replaced on the market by PPPT in 1970 under the trade name 'Kevlar®'. At the same time, Du Pont described an alternative to the all-para aramids and commercialized PMPI in 1967 [10]. Two decades after, the copolymerization of terephthaloyl dichloride (TPC) with p-phenylenediamine (PPD) and 3,4'-diaminodiphenyl ether (ODA) gave rise to a polymer with enhanced solubility, ODA/PPPT. The asymmetry of the monomer ODA and the copolymerization rendered a less ordered material with lower cohesive energy. Available since 1987, and commercialized under the tradename of Technora®, it is a very strong paraaramid fiber developed and produced by Teijin Limited. Scheme 6.1 shows the structure of the above mentioned aramids, which are now commercial aramids of great economic relevance, except PPBA, and some of the trade names they have used over the last 40 years. Scheme 6.2 depicts the monomers used in the synthesis of these polymers.

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Tradenames: Kevlar®, Twaron®

Scheme 6.1 Chemical structures and codes meta and ряга-aromatic polyamides.

Products marketed today

Copoly(p-phenylene/3,4'-oxydiphenylene terephthalamide) (ODA/PPPT) Tradename: Technora®

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Scheme 6.2 Chemical structures of monomers, diacids and diamines, used in the preparation of commercial meta and рягя-aramids.

6.2 Polymerization and Fabrication 6.2.1

Polymerization

The most common methods for the preparation of aromatic polyamides are: a) the reaction of diacid dichlorides with diamines at low temperature; and b) direct condensation reaction in a solution of aromatic diacids with diamines at high temperature. The solvents used in both methods are polar aprotic solvents like Ν,Ν-dimethylformamide (DMF), Ν,Ν-dimethylacetamide (DMA), N-methyl-2-pyrrolidone (NMP), and hexamethylphosphoramide (HMPA). Salts, such as LiCl, CaCL,, or a mixture of both, are often used as solubility promoters because the cations interact with the amide groups, diminishing the strength of the interchain hydrogen

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Scheme 6.3 Preparation of PMPI by low and high temperature solution methods.

bonds. As an illustrative example, Scheme 6.3 depicts the preparation of PMPI by low and high temperature solution methods. 6.2.1.1 Low Temperature Solution Methods The low temperature solution method is generally preferred when the diacid dichloride can be easily obtained from the corresponding aromatic diacid. A modification of this method includes the silylation of the diamines to increase the reactivity of the amino groups. The silylation-polymerization procedure is usually performed in situ to avoid the isolation and purification of the moisture sensitive silylated diamines [11]. The polycondensation reaction can also be carried out in a two-phase system at room temperature via the so-called interracial polymerization [12]. The diamine and the diacid dichloride monomers are dissolved in water and a water-immiscible solvent, respectively. A base and a surfactant are usually added to the aqueous media. The mixture of immiscible solutions, upon rapid stirring, gives rise to a polymer precipitate in seconds. The reaction is extremely fast and occurs in the interphase on the organic solvent side. The stoichiometry cannot easily be controlled in the interphase because the instantaneous concentration is diffusion dependent and depends only in part on the concentration of the monomers. Precipitation of the growing polymer chains usually produces polymers with a broad molecular weight distribution that are considered to be unsuitable for fibers or film-forming

AROMATIC POLYAMIDES (ARAMIDS)

147

materials [13]. Nevertheless, the tuning of the polymerization conditions, in terms of the organic solvent type, solvent volume, monomer concentration, and stirring rate, yields aromatic polyamides that have properties similar to those prepared via solution polycondensation methods. Films can then be cast from the solution, which has desirable chemical properties. Moreover, water insoluble diamines can be used as monomers for the polymerization of their water-soluble dihydrochloride derivatives [14]. The interfacial polycondensation has not achieved commercial importance. 6.2.2.2

High Temperature Solution Methods

If the diacid dichloride cannot be obtained from the corresponding aromatic diacid or is of poor quality, i.e., it is prone to give side reactions or is too much moisture or heat sensitive, the direct condensation between aromatic diacids and diamines can be used. The method was developed by Yamazaky and Higashi [15], and it is still not used for commercial purposes. Again, high-purity monomers are required, and an extra drawback is the side reactions that occur at the high temperatures used. Thus, to obtain an aromatic polyamide with side chains containing sensitive functional groups by this method, it is important to verify the absence of side reactions in the polymerization conditions. This can be carried out by the prior preparation of model compounds. The high-temperature solution procedure was recently modified by the introduction of microwave-assisted polycondensation. Microwave radiation (MW) is a non-conventional energy source, now widely used in organic chemistry, employed to promote chemical reactions in extremely fast and sometimes unconventional ways. Thus, the MW-assisted synthesis of polyamides was performed to promote the condensation of aromatic diacids and diamines under Yamazaki condition. The conventional heating system, i.e., temperature control oil bath, is replaced by the MW system, which reduces the reaction time from 4 h to approximately 2 min [16-19]. The polymers obtained by both methods have comparable inherent viscosities. MW has also been used to promote the polycondensation of diacids with aliphatic and aromatic diisocyanates, yielding semiaromatic polyamides and aramids [20]. The reaction was completed in less than five minutes, and the resultant polymers had T|inh values between 0.5 and 0.2 dL/g.

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Recent efforts have also been directed to the greener promotion of polycondensation under low- or high-temperature solution methods. Thus, the replacement of organic solvents by more environmental friendly versions is a topic of current interest in chemistry. Following this approach, the mixture of solvents used in the usual low temperature polycondensation (DMF, DMA, NMP) and in the Yamazaki polyamidation method (NMP and pyridine) can be replaced by ionic liquids. The ionic liquids have high thermal stability and low vapor pressure, are highly polar and have a high dielectric constant, which makes them suitable to dissolve the aromatic polyamides. Thus, eco-friendly aramids have been prepared using ionic liquids with triphenylphosphite (TPP) to promote the direct condensation of the acid and amide groups, avoiding the use of harmful solvents like pyridine and NMP, and to promote the reaction of diacid dichlorides and diamines at low temperatures [21-30]. Moreover, the polycondensation can be carried out by a conventional high-temperature heating method, using TPP as the condensation promoter, or employing MW, thus diminishing the reaction times from hours to minutes. Again, polymers having identical chemical structures and comparable inherent viscosities are obtained from both heating methods, suggesting that their molecular weights are similar. 6.2.1.3 Other Polymerization Methods Organic chemistry provides a wide set of synthetic methods to obtain aromatic or aliphatic-aromatic amide bonds, and some of them have been used to prepare polyamides. It is beyond the scope of this work to cover all of these procedures, and we refer the reader to the summary of reaction methods described by Gaymans [8], Fink [6], Sekiguchi and Coutin [31], and Vollbracht [7]. Among other methods, the following could be mentioned: wholly and partially aromatic polyamides prepared by the reaction of diacids with diisocyanates; the direct polycondensation of diacids with diamines using thionyl chloride as the activating agent; the condensation of diacids with the formamidinium salts of aromatic diamines; using diamines and CS2; the reaction of aromatic diacid phenyl esters with amines; the palladium-catalyzed carbonylation-polycondensation from dihaloaryl compounds and aromatic diamines [32,33]; etc.

AROMATIC POLYAMIDES (ARAMIDS)

6.2.2

149

Fabrication

As a general rule, aramids cannot be prepared by melt polycondensation, and they are commercially synthesized with low-temperature polycondensation methods, such as the Schotten-Baunmann reaction of acid chlorides and amines. PPPT and PMPI, or Kevlar® and Nomex®, respectively, are prepared commercially by the condensation of p-phenylenediamine (PPD) and terephthaloyl dichloride (TPC) or m-phenylenediamine (MPD) and isophthaloyl dichloride (IPC) using NMP as the solvent and CaCl 2 as the ionic component. The reaction is carried out continuously, and the viscosity of the solution is the parameter followed to control the polymerization. On the other hand, ODA/PPPT, or Technora®, is prepared commercially by the condensation of PPD and ODA (50% each) with TPC. The asymmetry of the monomer ODA and the copolymerization give rise to a less ordered material with lower cohesive energy. Thus, the polymer is prepared in NMP, without solubility promoters (salts), and upon neutralization of the evolved HC1 with Ca(OH) 2 ' the stable viscous isotropie solution is suitable for spinning. The number-average molecular weight (Mn) of aromatic polyamides generally ranges from lOxlO3 to 30x103 g/mol, which is typical of condensation polymers. The polydispersity of the polymers obtained is approximately two for lower molecular weight polymers and nearer to three for polymers with weight-average molecular weights (Mw) > 35 xlO3 g/mol [34]. The relation of the intrinsic viscosity of the aramids with their M w s, the so called Mark-Houwink equation, and a deeper description of the commercial preparation methods can be found in the review of Gallini [34].

6.3 Properties The high-performance properties of the aramids result from their chemical structure. The wholly aromatic structure with all-para substitutions of PPPT creates stiff rod-like macromolecules (Figure 6.1) with a high cohesive energy and a high crystallization tendency due to the very favorable intramolecular hydrogen bonds (Figure 6.2). Thus, PPPT fibers can be transformed into materials and composites with superior thermal and mechanical resistance. Taking this into account, aromatic polyamides with all-meta orientation in the

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phenylene ring, such as PMPI, have less linear structures and a concomitant reduction in cohesive energy and crystallization tendency. Thus, PMPI is a high-performance polymer, with high thermal and mechanical resistances. PMPI is a viable alternative to PPPT, only slightly underperforming it. Nevertheless, the extremely high transition temperatures of the commercial aramids, which lie above their decomposition temperatures, and their poor solubility in common organic solvents give rise to processing difficulties and limit their applications. Thus, considering the extraordinary characteristics of the chemically simplest aramids, PPPT and PMPI, the research efforts in the field of aromatic polyamides are twofold: a) by attempting to overcome the problems that are associated with the high cohesive energy of aromatic polyamides, which give rise to intractable materials due to their extremely low solubility and exceptionally high thermal transition temperatures; and b) by expanding the scope of their applications as high performance materials to new and promising areas of materials research, such as active optics, luminescence, ionic exchange, flame resistance, and fiber forming materials, all of which hold the promise of interesting results in fast-evolving areas of research. The physical properties and characteristics of the commercial aramid fibers, films and papers are summarized in Table 6.1. In comparing the properties of aramids and other synthetic yarns, the advantages of the former are: very high tenacity, high modulus of elasticity, low creep, resistance to high temperatures, good fatigue resistance, and good chemical resistance. The main advantages over steel are: low specific weight, high energy absorption, corrosion resistance, good dielectric behavior, non-magnetic properties and good fatigue resistance.

Figure 6.1 Rod-like structure of PPPT obtained upon molecular modeling of three structural units of the polymer (top: front view; bottom: lateral view).

Figure 6.2 Schematic representation of the structure of PPPT and the interchain high directional hydrogen bonds (bold bonds and atoms represent the structural unit).

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Characteristics, processing methods and applications

Flammability (LOI)

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AROMATIC POLYAMIDES (ARAMIDS) 157

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HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

6.4 Chemical Stability The wholly aromatic polyamides are considered chemically stable upon different exposure conditions to chemicals. Their fibers exhibit very good resistance to most hydrocarbons and organic solvents. However, strong aqueous acids, bases and sodium hypochlorite cause degradation of the materials if exposed for long periods of time at elevated temperatures. The resistance of aramid fiber yarn toward solvents and solutions of acids, bases, and oxidizing/ reducing chemicals is shown in Table 6.2 [39,40]. The light stability of materials is an important characteristic that has to be considered if they will be exposed to indoor light or sunlight. Aramids are sensitive to UV (ultraviolet) light, and unprotected yarns tend to discolor from yellow to brown upon prolonged exposure to sunlight, causing loss of mechanical properties. The property loss depends on the wavelength-the critical wavelength region for PPPT is 300-450 nm-exposure time, radiation intensity, and product geometry. Nevertheless, aramids show outstanding resistance to degradation by high-energy gamma radiation.

6.5 Special Additives Additives designed to enhance specific product performance, such as UV blockers or coloring agents and surface coatings of lubricating and antistatic agents, may be present in aramid compounding. As outlined in the previous section, aramids are sensitive to UV radiation. Nevertheless, the aramids are self-screening because external fibers form a protective barrier, shielding the interior fibers in a filament bundle or fabric. Further UV protection can be achieved by means of encapsulation by overbraiding with other fibers or by applying an extruded jacket over ropes or cables. The coatings, extrudates or films used to protect the fibers should have pigmentation absorbing in the 300-450 nm UV/Vis region. Aramid fibers can be colored. However, these kinds of fibers are difficult to dye using conventional techniques mainly because of their high crystallinity. Thus, low crystalline filament yarns are commercially available where dyed fibers are required, and the yarn and fabrics have slightly lower mechanical properties. Moreover, custom colored conventional staple or pulp wholly aromatic polyamides can be obtained with spun-in color.

ACIDS

Chemical

Formic

Acetic

Sulfuric

Nitric

Hydrochloric

(11-20)

1000

-(-)

100 21 90

(Continued)

-

1000 21 40

21

40

(-)

24 21

100

-

100 99

100 21

70 100

-(-) - (21-40)

100

41-80

24

21

70 21

41-80

100

21

70 10

21-40 (41-80)

100

11-20 (11-20)

100

21

(41-80)

100

21

10 10

(-)

24

21

37 21

81-100

10

71

37

1

41-80

1000

Strength Loss, %

Time, h

21

Temperature,

10

Concentration, %

Table 6.2 Chemical resistance of aramid yarns expressed in terms of percentage strength loss values of PMPI (values without brackets) and PPPT (between brackets).

1—1

AROMATIC POLYAMIDES (ARAMIDS) 157

3

Ferric chloride

121

10

99

121

99

10 5

Sodium chloride

SALT SOLUTIONS

21

71

0.4, pH=7 100

21

0.1

Sodium carbonate

Acetone, benzene, carbon tetrachloride, ethyl ether, ethyl alcohol, methylene chloride

Hydrogen peroxide

100

71

0.04, p H = l l

100

100

100

100

1000

100

1000

100

71

1000

0.01, pH=10

21

40

100 1000

21

40

100

21

99

10

1000

1000

0.01, pH=10

21

10

Sodium hydroxide

Sodium hypochlorite

21

28

Amonium hydroxide

ORGANIC SOLVENTS

OXIDIZING AND REDUCING AGENTS

BASES

2 1 ^ 0 (41-80)

11-20

11-20 (41-80)

-(-)

-(-)

-

(81-100)

11-20

11-20

-

11-20

-

81-100 (81-100)

- (41-80)

-

Table 6.2 Chemical resistance of aramid yarns expressed in terms of percentage strength loss values of PMPI (values without brackets) and PPPT (between brackets). (Continued)

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HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

AROMATIC POLYAMIDES (ARAMIDS)

157

Aliphatic and aromatic polyamides tend to collect electrical charges with the concomitant threat of sparking on discharge. The draining or dissipation of these charges from the polymeric surfaces is necessary for certain applications. Thus, the mixture of aramid fibrils with sulfonated poly(aniline) can yield an electrically conductive pulp to be used as reinforcement materials with extremely effective electrical charge dissipation properties [41].

6.6

Processing

The commercial aramids have very high melting points, even higher than the thermal degradation temperature, which prevent their transformation by conventional melt processing techniques, such as injection or extrusion. Thus, films and fibers, including pulp, staple and floe, are prepared from solutions of the polymers. 6.6.1 6.6.2.1

Processing PMPI and ODA/PPPT Wet Spinning of PMPI and ODA/PPPT

The fibers are produced by dissolving the dry PMPI or ODA/PPPT in an organic solvent and consecutive precipitation into a water coagulation bath. The amide solvent, generally DMA, DMF or NMP, and the water bath may contain different quantities of salts. The fibers obtained, after drawing and post-treatment, exhibit excellent mechanical properties. 6.6.1.2 Dry Spinning PMPI solutions in DMF/LiCl2 can be spun in an air column maintained at elevated temperatures higher than 200 °C. After that, the fibers are drawn, and the remaining solvent and salt are removed upon hot water washing. 6.6.2

Processing of PPPT

PPPT is not soluble in polar aprotic amide solvents and it has to be transformed in a concentrated solution, higher than 18 %, in 100 % sulfuric acid. The solution shows low relatively viscosity because of its lyotropic behavior and can be wet spun into a water coagulating

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bath at relatively low temperature. The fibers are then washed thoroughly with water, dried and subjected to a stretching process at high temperature to obtain highly ordered-high modulus fibers. A few years ago, a PPPT film was prepared and commercialized under the commercial trade name Aramica®. An optically anisotropie cast dope, prepared upon extrusion of a 10-15% solution of PPPT in concentrated sulfuric acid through a slit die onto a flat plate, was transformed into an isotropie phase by adjusting the temperature and/or humidity of the chamber. The isotropie dope was then immersed into the coagulation bath, washed and then dried. The drying process was carried out by maintaining a constant film width and length, and after that uni- or biaxial stretching could be performed. The thermal annealing highly improves the isotropie film properties, yielding non-flammable materials with excellent heat-resistance, superior tensile and tear strength, extremely high tensile modulus, and a thermal expansion coefficient near that of ceramics [42,43].

6.7

Applications

The wholly aromatic aramids are transformed into fibers upon wet or dry spinning, finding applications in advanced aromatic composites or high performance fiber derived products, such as filaments, yarns or fabrics. All applications rely on the thermal, chemical and mechanical resistance of the highly oriented and highly crystalline fibers. They have found applications, among others, in: Heat-protection products. The extreme heat resistance of aramids, both meta and para, makes them valid for application whenever very high temperatures present a serious threat. Thus, PPPT protects even at peak temperatures of 700 °C, and the staple fibers, filament yarns, and blends with other high-performance synthetic fibers can be used in gloves, blankets, or even entire suits that protect against intensive heat radiation, metal droplets, flying slag, flames or flares, red-hot sparks, high contact heat, etc. Cut-protection products. PPPT-based fabrics offer four times the protection of cotton fabrics and eight times the protection of leather based clothes, offering heat protection as well. The PPPT fibers are extremely cut-resistant, which makes them ideal for use in: cut-resistant gloves, leg protection (e.g., for forestry workers), anti-vandalism fabrics (e.g., for bus and train seats), etc.

AROMATIC POLYAMIDES (ARAMIDS)

159

Ballistic-protection products. The excellent energy absorption properties, tenacity and impact resistance makes PPPT valid for helmets and soft (bullet-resistant vests) and hard (armored police and civilian vehicles) ballistics. Tires. The superior performance-to-weight ratio of aramids makes them useful for reinforcing high-performance tires, conferring the stability to the tires, durability and reduced fuel consumption. The aramids are used in passenger car tires, motorcycle tires, bicycle tires, truck and bus tires, agricultural tires, off-road tires, airplane tires and solid tires. Hoses. Aramids encounter applications in this field when hose specifications for bursting pressure, longevity, temperature and chemical resistance are extremely high, i.e., in the automotive industry (radiator, air-conditioning, fuel, brake hoses, etc.), in the industrial and oil and gas hoses (extreme pressures, great depths, aggressive fluids and steam hoses, hoses that must meet stringent safety standards, etc). Transmission belts. Transmission belts reinforced with aramids are used for applications demanding low creep, high dimensional stability, fatigue resistance, temperature resistance, precise synchronization and low operating noise belts, i.e., in the automotive industry. Friction products. Friction materials containing PPPT are used in brake pads and linings as well as in clutch facings [44]. In addition, there are numerous industrial applications including elevators, cranes, and various other systems. Sealing materials (gaskets and braided packings). Aramidreinforced gaskets have found applications as sealants under working conditions when better residual stress at elevated temperatures, good dimensional stability, high tensile strength and longer durability are needed. In the same vein, aramid braided packings safely seal pumps and valves in applications where extreme chemical and thermal resistance is needed due to industrial, environmental or safety requirements. Adhesives, sealants and coatings. The thixotropic aramid-reinforced resins provide viscosity control for these applications in a full range of temperatures, from cryogenic to 350 °C, providing inertness in most common chemicals, including organic solvents. Specialty paper products. PPPT is a versatile material that fulfils the increasingly demanding requirements for technical paper in a wide variety of applications. These include friction paper for automatic

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transmission, printed wiring board, electrical and thermal insulation, and gasket paper for the automotive and chemical industries. Moreover, the high strength, light weight and thermal stability of paper made with these materials allows manufacturers of aerospace and marine equipment to produce safe components that perform better and last longer than their alloy equivalents. For example, the use of honeycomb cores made with PPPT paper for aerospace applications reduces the weight of components, helps reduce operating costs, and at the same time inhibits the galvanic corrosion between dissimilar materials, such as metals and graphite composites, due to the electrical insulating characteristics of the polyamides. Ropes and cables. Aramids are used to reinforce ropes and cables wherever safety and protection are essential, showing significant advantages over other synthetic yarns and steels in ropes and cables (i.e., mooring cables, hoisting cables, cables for deepsea applications, ropes for installing high-voltage cables, elevator cables, etc.). They have also found application in the fiber optic cable reinforcement. Thermoplastic pipes. The standard material of pipes installed to transport liquids and gases, i.e., in the oil and gas industries, continues to be steel. Nowadays, to overcome the corrosion of this material, PPPT-reinforced thermoplastic pipes have been developed. Aramid-rubber composites. Aramid fibers have been long used to reinforce all sorts of rubbers and thermoplastic elastomeric products as conveyor belts, air springs, anti-vibration products, etc. Hot gasfiltration.PMPI combine the thermal resistance with the physical properties of nylon and is used today to produce felts for a wide range of high-temperature filtration applications (up to 200 °C). Composites. Aramids are used in a wide range of composite applications in the industrial, leisure, civil engineering, ground transportation and aerospace markets, with new applications added daily, i.e., sails and reinforced hulls of sailing boats in the marine industry, rotor blades and structural parts in aerospace industry, wind turbines in new energy fields, high-pressure vessels and circuit breakers in industrial components, lightweight parts for heavy-duty purposes in ground transportation, etc. There are few examples of applications of wholly aromatic polyamides not related with fiber related products. Regarding this point, a major application of aromatic polyamides has for many years been in the field of reverse osmosis membranes:

AROMATIC POLYAMIDES (ARAMIDS)

161

Membranes. Aromatic polyamide, which forms an active layer, shows high salt rejection, high water permeability and high fouling tolerance [45]. The thin layer is obtained by the interfacial polycondensation of trimesoyl chloride with mefa-phenylene diamine, and polymerization takes place on a microporous polysulfone membrane. Among their other applications, these membranes are used in waste-water treatment, desalination of sea water and dialysis. Improvements in flux and salt retention are currently major topics in this field. For instance, very recently, zeolites and silica particles were incorporated in a thin film polyamide which resulted in composite membranes with improved performance compared to the performance of the pure polyamide membranes [46,47,48].

6.8 Environmental Impact and Recycling The aramids are inherently flame resistant, meaning that the burning of the materials usually stops upon eÜmination of the ignition source. For example, the limiting oxygen index (LOI) of PPPT is 29, being the LOI defined as the minimum fraction of oxygen in a mixture of oxygen and nitrogen that will support combustion after ignition. Thus, materials with LOI values higher than the air oxygen content (20.95 %) show a reduced or even zero tendency to propagate flame after removal of the igniting source. Furthermore, materials with a LOI greater than 28 are generally self-extinguishing [49]. Burning aramids produces gases similar to those of wool, mostly carbon dioxide, water and oxides of nitrogen, along with small amounts of hydrogen cyanide (14 mg of HCN per g of PPPT) and other toxic gases, depending on the burning. The diminishment of the weight of mass transport media is one of the most important goals of the transport industry. The composite materials have much lower specific density than metal and even advanced alloys. Thus, the use of aramid-reinforced composites in aerospace applications and in the car industry reduces the weight of cars and aircrafts, decisively diminishing the fuel consumption and the C0 2 emission and increasing the payload. For example, stiff and thin aramid sheets are used to make extremely strong lightweight honeycomb sandwich composite structures with an unrivalled strength-to-weight ratio, which are found in aircraft parts, such as tail-fins, engine nacelles and helicopter blades. Comparing the commonest reinforcing fibers, such as glass, carbon and aramids,

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HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

the latter has the lowest specific density (2.46,2.15 and 1.44 g/cm 3 , respectively). Nowadays, aramids are substituting for asbestos in friction materials, as vehicle brakes and clutches, because the latter has been prohibited in many countries. The former fibers are believed to be safer to health during manipulation, transformation and recovery. The recyclability of the aromatic polyamides fibers depends on how the polymers are processed into the product. Wholly aromatic polyamide fabrics used in textile applications, i.e., in bullet resistant vests, are easily recycled and returned to the market in non-ballistic related post consumer products such as gloves, brake pads, boat ropes, tire treads, etc. In this regard, the chemical companies that produce the aramids are working hard to increase the quality of the waste material supplied in order to be able to produce high quality goods. If aramid is processed as a composite material, in resins or rubber, then reprocessing is somewhat of a challenge. Even here, there is potential to be able to separate out the fibers from other materials by chemical methods. For example, the aramid fiber can be released and recycled from the epoxy matrix of aramid/epoxy composites by the chemical degradation of the epoxy matrix with 1,2,3,4-tetrahydronaphthalene [50].

6.9 Recent Developments in Aromatic Polyamides and their Applications Aromatic polyamides are unique materials insofar as their thermal and mechanical behavior is concerned. However, their extremely high transition temperatures and their poor solubility in common organic solvents or commercial polyamides, which lie above their decomposition temperatures, give rise to processing difficulties and limit their applications. As a consequence, basic and applied research is being carried out to enhance their processability and solubility in order to broaden the technological scope of applications associated with these materials. From a research point of view, these goals have been partly achieved, although further research is still needed. Moreover, basic and applied researchers should try to exploit the high performance

AROMATIC POLYAMIDES (ARAMIDS)

163

properties of the polyamides in new fields, i.e., optically active materials, photo- and electroluminescent materials, materials with even higher mechanical properties, polymers with a controlled structure, biodegradable materials, materials with molecular recognition capabilities, etc. 6.9.1

Forthcoming and Future Application of Aramids

Forthcoming applications depend on the correct selection of chemical structures. Thus, the structure-properties relationships are the key for future developments in cutting edge fields. Properties and application of aramids as optically active polymers, luminescent and electrochromic materials, gas separation and ion exchange membranes, and polymers with selective receptors and with environmental or medical applications are discussed here. This section is concluded with a discussion of polyamides with ever higher mechanical properties. The selected polyamide structures for these applications are depicted in Table 6.3. Optically active polyamides. Optically active polymers are interesting materials with application such as assembling chiral media for asymmetric synthesis, chiral stationary phases for resolution of enantiomers in Chromatographie techniques, chiral liquid crystals in ferroelectrics and nonlinear optical devices, etc. Regarding optically active aromatic polyamides, a simple approach has generally been followed to prepare these materials, starting from optically active monomers to yield polymers with asymmetric carbons in the main or in the lateral chain. Luminescent and electrochromic polyamides. Light-emitting phenomena are a characteristic of luminescence materials. Among the different types of luminescence, light-emitting aromatic polyamides that produce electroluminescence or photoluminescence upon exposure to an electric current or due to absorption of photons that cause re-radiation, have been described. The film formation properties and outstanding mechanical properties of aramids make these polymers suitable for the production of organic light-emitting diodes (OLEDs) and specifically polymer light-emitting diodes (PLEDs), and much work has been carried out to achieve materials suitable for these kinds of applications. Gas separation membranes. Gases are amongst the most important commercial products, and their separation and purification have a

164

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

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HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTIC

еда

H

o-


OR θ Θ C12H25SO4+ Na

\7 =\ NH

\ч //

NH

~\\

//

© NH

Θ

ΝΗ

e so.

so.

C12H25

Ci2H25

/=\

Θ4

//

+ NaCI

PANI-NaDBS

OR

NH л

/^ΝΗΛχ

© -I 1 S0 S044

/ S0„

C12H2

C12H2

PANI-SDS

+ NaCI J

Figure 7.3 Proposed interaction of PANI with NaDBS and SDS respectively (bipolaren form of PANI is depicted).

" -HN—С

О О © -NH =

\— NH-

/

\

•

@

"О

= NH —

i>

0=SO 3 ~ or S04~ (

SWNT

Figure 7.4 Hypothetical model for interactions between PANI-surfactantSWNTs using NaDBS and SDS (bipolaren form of PANI is depicted) [50].

POLYANILINE

193

X. Zhang et al. [51] synthesized of size-controllable PANI/CNT nanocables by in situ chemical oxidative polymerization directed with the cationic surfactant cetyltrimethylammonium bromide (СТАВ). Polyacylonitrile fibers (PAN) do not have functional groups for immobilization of macromolecules. From this point of view, PAN fibers surface can be modified by grafting with PANI to alter the final surface properties [52]. The PAN fibers surfaces were modified with chemical polymerization of conductive PANI in the presence of potassium dichromate as an oxidizing agent. The effect of aniline concentration on the grafting efficiency and on the electrical surface resistance of PAN/PANI composite fibers was investigated by Bayramoglu et al. [53]. The chemical deposition of silver particles in PANI powder has been carried out via the reduction of Ag+ ions by PANI in various concentrations of AgN0 3 aqueous solutions [54]. Moreover, recently there have been a number of publications on the synthesis nanostructured silver particles-polyaniline composites [55-60, 61]. The feasibility of the oxidation of aniline with silver nitrate to PANI-Ag composites (Fig. 7.5) have been illustrated in number of cases, aqueous solutions of nitric acid being a typical reaction medium [60]. A nanocomposite of PANI and bismuth telluride (Bi2Te3) was prepared using a simultaneous electrochemical reaction and deposition method [62]. In a two component nanocomposite, PANI and the inorganic thermoelectric material bismuth telluride (Bi2Te3)

•o

NH,

&+JNO: -

e

+ 10 n AgN0 3

NH NH

NO, + 10 n Ag + 8n.HN0 3

Figure 7.5 Aniline is oxidized with silver nitrate to PANI, metallic silver and nitric acid are by-products [60].

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HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

may yield high thermoelectric power and electrical conductivity of the material [63-65]. The schematic representation of the electrodeposition setup for PANI/Bi2Te3 composite is shown in Fig. 7.6. PANI doped with polystyrene sulfonate) (PANI-PSS), PANI doped with gold (PANI-Au) as well as PANI co-doped with poly(styrene sulfonate) and gold (PANI-Au-PSS) have been prepared using the interfacial polymerization method under similar conditions by Tang et al. [66]. Researchers, indicate that co-doping using poly(styrene sulfonate) and gold is an effective method to enhance the electrochemical and electrocatalytic activities of PANI in neutral solutions. A composite conductive polymer film, PANI coated polytetrafluoroethylene, PANI/PTFE, has been synthesized via a simple chemical oxidation polymerization by Zhou and co-workers [67]. A conductive composite film with high conductivity and extensibility was obtained by polymerizing aniline on the PTFE network. PANI/PTFE composite film in which the PTFE film acted as a support rather than a template, with a modifying dipping method also has been reported [68]. Number of dopants have been used to enhance the conductivity of PANI like Cu+ [69], Tellurium [70], Lithium [71], ТЮ2 [72], Pt [73], Pd [74] and Se [75]. Besides inorganic and synthetic polimerie PANI composites, natural polimer such as chitosan and cellulose/ PANI composites is attractive area for researches. Conductive composite of cellulose- PANI was

0.015NofTeO 2 in HN0 3 + 0.01 N of Bi(N03)3 in HN0 3 (Drop-wise addition)

Anode (Aluminum) Cathode (ITO glass) Saturated calomel electrode Polyaniline doped with Bi(N0 3 ) 3

Figure 7.6 Schematic representation of electrochemical deposition system for PANI/Bi2Te3 [62].

POLYANILINE

195

Figure 7.7 Schematic diagram of the process of preparing cellulose-PANI composite [76].

heterogeneously synthesized by chemical oxidative polymerization of aniline with native cellulose activated [76]. The preparation of cellulose-PANI composites could be described by a schematic illustration in Fig. 7.7. The cellulose-PANI conductive composite would be a promising material in application in electrode, gas sensor and membrane fields. Substituted PANI/chitosan (sPANI/Ch-H2S04) composites were electrochemically synthesized and investigated their biosensor properties by Yavuz et al. [76]. There is also exist in the literature that chemically synthesized substituted PANI /chitosan composites such as poly(N-methylaniline)/chitosan (PNMANI/Ch), poly (N-ethylaniline)/chitosan (PNEANI/Ch), poly(2-ethylaniline)/ chitosan (P2EANI/Ch) [78].

7.6

Processing

There are some processing methods to preparation of PANI and its derivatives. The main problem of conducting polymers is poor solubility in common organic solvent. It had been known that PANI salt only soluble in concentrated sulfuric acid until it was found that the functionalized protonic acids such as dodecylbenzensulfonic acid

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HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

(DBSA) together with phosphoric acid esters, etc., enabled PANI salts soluble in organic solvent [79]. Therefore, PANI can be process both in melt and solution processing. Melt processing method involves the mixing of different thermoplastic components with a polymer at a temperature beyond the melting point of the polymer [16]. PANI based conductive polymer compositions can be processed using this techniques. Plasticised compositions improve melt processing performance by lowering the melt-viscosity, lowering the processing temperature and shortening the processing time. The improved melt flow properties make, for example injection moulding of complex shapes easier [80]. The conducting thermoplastic films were fabricated by the melt processing techniques and are found to exhibit very low percolation threshold and high transparency. The functionalized sulfonic acid dopants were found to impart meltsolution processability and protonating ability to PANI [81]. The significant aspect is that plasticization of PANI could be simultaneously achieved during the process of protonation and the protonated PANI could be thermally processed and highly conducting free-standing flexible films. The melt mixing procedure has also been successfully employed to form elastomer- PANI composites [82-84]. An important example of protonic acids is dodecylbenzenesulfonic acid (DBSA), PANI -DBSA is normally used in melt blends, due to its relatively high thermal stability of PANI-DBSA [85-92]. Melt spinning method has been used to prepare conductive fibers. Soroudi at al [93] have combined blends of polypropylene with PANI and multi-walled carbon nanotubes and melt spun to fibre filaments. Polymer extrusion is a high volume manufacturing process in which raw material is melted and formed into a continuous profile. For instance, homogeneous films of n-dodecylbenzene sulfonic acid (DBSA)-doped PANI synthesized in the presence of a poly(styrene-acrylate) ionomer using a poly (n-butyl methacrylate) matrix were prepared by extrusion. These composites showed good sensing capability toward NH 3 and urea aqueous solutions [94]. Electroless metal plating (EMP) is a versatile method for surface metallization of plastics and ceramics [95, 96]. Various techniques, such as plasma modification [97], excimer UV laser [98] and dielectric barrier discharge [99] have been developed for modification of polymer surfaces. Beside those high energyirradiation methods, wet chemical methods such as nitration and sulfonation have been reported to be efficient in modification of

POLYANILINE

197

Figure 7.8 SEM images of H2S04-doped PANI fibers obtained from different PANI concentration in H2S04 solution: (a) 10.6 %, (b) 11.5 %, (c)14.0 % (inset is the corresponding higher magnification image) and (d) 17.9 %. The H2S04 concentration in the coagulation bath is 4 % [105].

relatively polar polymer surfaces [100]. Girginer et al. [101] indicated that PANI films well adhered to solid polystyrene surfaces by wet chemical methods. PANI coatings can provide significant corrosion protection to steel, copper and iron when exposed to severe corrosive environments [16]. Electrospinning is very simple and inexpensive to manufacture sub-micron fibers and nanofibers [102-104]. Sub-micron fibers (Fig. 7.8.) of pure PANI doped with sulfuric acid or hydrochloric acid were prepared by electrospinning [105].

7.7

Applications

PANI has many potential applications in multidisciplinary fields because of its unique properties. PANI can be applied in different areas such as electronics, thermoelectric, electrochemical, electroluminescence, chemical, membrane, coatings, sensors, and so on. Adsorption is one of the main techniques used to remove metal ions from wastewaters. The adsorbents commonly recommended for the removal of heavy metals range from industrial wastes to

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HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

agricultural waste products, biomaterials and activated carbon [106-108]. Polimerie adsorbents provides lower cost, simplicity of design and easiness of operation. There are plenty of imine and amine groups in PANI, Fig. 7.9, which can not only chelate cationic metal ions, but also adsorb anionic metal species through electrostatic interaction or hydrogen bonding [109]. That's the reason, PANI composites can be used as base material to remove heavy metals from aqueous solutions. For example, the PANI/polystyrene composite has been used as a adsorbent for remove mercury ions from aqueous solutions [108]. PANI Ce(IV) molybdate, cation-exchanger composite, is highly selective for the removal and separation of Cd(II) from other pollutants [110]. The PANI/poly (ethylene glycol), PANI/PEG, can be used as a good adsorbents for removal of total and hexavalent chromium in aqueous solutions [111]. PANI/Zirconium titanium phosphate, advanced nano-composite cation-exchanger, known that highly selective for toxic heavy metal ions Hg(II) and Pb(II) [112]. Humic acid, HA, that has high complex capacity with heavy metal ions, modified PANI composites as adsorbents of Hg(II) and Cr(VI) [113]. Fig. 7.10 shows the general scheme of the PANI/НА composite and the possible mechanism of mercury and chromium adsorption. It is widely accepted that nitrogen-containing functional groups act as adsorption sites for Hg(II) and Cr(VI) [108,116-118]. Microbial fuel cells (MFCs) are devices that directly generate electricity from various wastes, with the aid of microorganisms as catalysts [119-121]. There is requied for oxygen reduction reaction, an efficient catalyst to overcome the high overpotential for reduction of water. PANI can be used this area. For example PANI /carbon black, (PANI/C), composite-supported iron phthalocyanine (FePc), (PANI/C/FePc) has been investigated by Yuan et al. [122] as a catalyst for the oxygen reduction reaction in an air-cathode (MFCs). Qiao et al. also used PANI at CNT composite as an anode Benzenoid groups

и Figure 7.9 General scheme of polyaniline.

Quinoid groups

POLYANILINE

199

Figure 7.10 Mechanism for Hg(II) and Cr(VI) removal by PANI/HA. (a) Preparation of PANI/НА composite; (b) mercury adsorption; (c) chromium adsorption [113].

material and Escherichia coli as the microbial catalyst for MFCs [123]. Thanks to various remarkable characteristic properties of PANI is candidate for fabrication of variety of sensors such as biosensors, pH, humidity, chemical and toxic gase sensors. A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. The ability of FANI to change the electrical conductivity and color upon exposure to acidic, basic and some neutral medium finds its usefulness in the field of sensor, detector and indicator [124-139]. Humidity sensors have gained increasing applications in industrial processing and environmental control such as in automobile industry, medical field, agriculture paper and textile production, and food processing [140]. It is well known by many researches humidity sensitive nature of PANI and its

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derivative. For instance, Ramaprasad et al. [141] combined chitinPANI blend to gain low-cost, highly processable humidity sensors. Joubert and coworkers [142] processed composite films of PANI and polyacrylate from the crude dispersion in an aqueous dispersed medium and observed sensor performance, investigated kinetic of the synthesis as well. The results indicate that all the composites poly(BuA/ doped PANI) are suitable to detect ammonia pollution. Yang at al. [143] examined PANI inverse opals as sensors. The inverse opals were chemically synthesized via templating polystyrene colloidal crystals and then tested the responses of the PANI to dry gas flow, ethanol vapor, hydrogen chloride, and ammonia. Chlorine gas sensor was prepared by incorporating PANI in fluorinated ethylene propylene [127]. Doped PANI and substituted PANI are sensitive to ozone gas [144]. Similarly, PANI has been used to fabricate the sensors for liquefied petroleum gas [145]. Morover, PANI deposited single-walled CNT networks be used as solid state pH sensors [146]. PANI shows very high dielectric constant, which makes it useful as a capacitor and an energy storage device [147-150]. Energy storage systems are playing important roles in storing energy generated from sun and wind, or other renewable energy sources [151,152]. Supercapacitors are used for the applications where faster and higher power energy storage systems are needed because they have higher energy density than conventional capacitors, and higher power density and faster power delivery than batteries [152]. The composite of CNT/PANI shows improved energy storage capability as CNT is also a promising material for the fabrication of energy storage devices [153]. The fabrication of supercapacitor using CNT/PANI composite is presented in Fig. 7.11 Sahoo

Figure 7.11 Schematic illustration of the microstructures showing the flexible supercapacitor unit made of CNT/PANI composite [153].

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et al. [154] have studied CNT/PANI composite as a good quality supercapacitiors. An electrosynthesis process of hydrophilic PANI nanofiber electrode for electrochemical supercapacitor is described by Dhawale et al. [156]. The electrochemical study showed that the PANI electrode exhibits high stability with specific capacitance. CNTs are also widely used in actuators [157,158]. The addition of CNTs to PANI fibers increased the electromechanical actuation because the CNTs improved the mechanical, electronic, and electrochemical properties of the PANI fibers [159]. Electrochromic devices (ECs) change light transmission or reflection properties during electrochemical redox processes [160-162] and they can be used as large area displays, smart mirrors and windows. Smart or electrochromic window can control dynamic radiation, change color under applied potential, regulate energy through transmission in the ultraviolet and near infrared region. PANI has been successfully employed to fabricate electrochromic window [163-166]. The PANI based total electrochromic glass sandwich for electrochromic window may be constructed as presented in Fig. 7.12. Zhao et al. [167] reported PANI ECs with graphene electrodes working in acidic aqueous media. It was indicated that graphene electrodes showed significantly improved performances comparing those of the devices with ITO electrodes.

Figure 7.12 Schematic illustration of the construction of PANI based electrochromic window poly(2-acrylamido-2-methyl-propane-sulphonic acid) (PAMPS) is used as the solid state polymer proton conducting electrolyte [16].

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Figure 7.13 Schematic diagram of the growth mechanism of PANI/SÌ02 composite films [168].

A PANI/silica (SiOz) composite film was prepared via in situ electrodeposition method, and its electrochromic (EC) properties were studied by Chen et al. [168]. According to this research when PANI was electrodeposited in the presence of Si02 particles, the resulting PANI/Si0 2 composite films possessed higher surface areas, larger redox charge capacities, and higher doping levels, thus enhanced optical contrasts. The growth mechanism of the PANI/ Si02 composite film is investigated on the in situ EQCM technique as shown in Fig. 7.13.

7.8 Environmental Impact and Recycling Chemical, structural and other properties of PANI has been discussed in this chapter. PANI is a highly functional synthetic polymer which is unique among the family of π - conjugated polymers because of its ease of synthesis, good environmental stability and simple acid/base doping/dedoping chemistry. Due to this advantages PANI has found immense applications in diverse areas. PANI has also shown biocompatibility in several biological applications [169- 171]. Although PANI is a good canditate for many tomorrow's applications, common synthetic method of PANI still is not very environmentally friendly and utilizes harsh reagents in large quantities. Dias et al [172] have discovered a novel catalytic method

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0_ίΓ0_ ΝΗϊ or

o-

NH,

Mes catalyst Q|

H

Mes

H

iVN-_ Emeraldine base Base, - HX

Acid, + HX

H

/ vi_f~VN-^ v

H"

.At

Emeraldine salt (organic metal)

Figure 7.14 [MeB(3-(Mes)Pz)3]CuCl catalyzed oxidative polymerization of aniline dimmer [172].

that copper complex used as the catalyst. This method can be used produces high-quality PANI. This new route uses milder chemicals like hydrogen peroxide and generates only water as the byproduct. Therefore, this is an environmentally friendly, greener, approach for PANI synthesis that can be readily extended to a large scale industrial process. They have described a diffenrent route to PANI polimerization which involves aniline rather than the aniline dimer as the starting point (Fig. 7.14).

7.9 Recent Developments in Polyaniline Based Blends and Composites and their Applications PANI is one of the most used conducting polymer because of ease synthesis and stable electrical conductivity. It has many potential application fields such as battery electrodes, electrochromic,

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electronic devices and biosensors. Although these applications are some limitations, because of the electroactivitiy of PANI only in acidic solutions, to improve these restriction, PANI can be doped with negatively charged linearly polyelectrolytes such as poly(acrylic acid), poly(vinyl sulfonate), polystyrene sulfonate obtaining copolymers. These copolymers can be used in specially biosensor applications and the others. Nanostructures of PANI e.g. nanowires, nanospheres, nanorods, and nanotubes have provided a new ground to improve its properties and to show high performance with its environment [173]. For instance, in sensor applications, nanostructured PANI has greater sensitivity and faster response time thanks to higher effective surface area and shorter penetration depth for target molecules [174]. Nanostructured PANI, provide that suitable matrix for immobilization of biomolecules [173]. Since it acts as an effective mediator for electron transfer in redox or enzymatic reactions [175,176]. Dhand et al. [177] have investigated that chemically fabricated PANI nanospheres and electrophoretically deposited nanostructured PANI as platform towards the fabrication of cholesterol biosensor. Bo et al. [178] developed new DNA biosensor based on oxidized graphene and PANI nanowires (PANIw) modified glassy carbon electrode. It is showed that, under optimum conditions, the biosensor, ssDNA/ PANIw/Graphene/GCE, exhibited a fast amperometric response, high sensitivity and good storage stability for monitoring DNA. Carbon Nanotubes (CNTs) is one of the most interesting carbon materials and has different application fields in biosensors and electronics because of good electrical, chemical and mechanical properties. Recently, PANI/CNTs composites have been intensively prepared and investigated. These composites can be prepared by chemical and electrochemical methods and indicate enhanced properties according to PANI and CNTs. Multi-walled carbon nanotube (MWCNT)/polyaniline (PANI)/Mn02 (MPM) ternary coaxial structures are fabricated as supercapacitor electrodes via a simple wet chemical method [161]. Zhu at al. synthesized the water-soluble sulfonated multiwalled carbon nanotubes (sMWCNTs) via a diazotization [179]. On the basis, the novel composites of sMWCNT modified PANI nanorods (PANI/sMWCNT) were synthesized through in situ oxidative polymerization method in the HC10 4 solution. These PANI/ SMWCNT composites provided improved electrochemical properties compared to pure PANI.

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POLYANILINE 123. 124. 125. 126. 127. 128. 129. 130. 131. 132. 133. 134. 135. 136. 137. 138. 139. 140. 141. 142. 143. 144. 145. 146. 147. 148. 149. 150. 151. 152. 153. 154. 155. 156.

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Qiao, Y., Li, СМ., Bao, S.J. and Bao, Q.L. / Power Sources. 2007,170, 79-84. Irimia-Vladu, M. and Fergus, J.W. Synth Met. 2006,156,1401-7. Yan, X.B., Han, Z.J., Yang, Y, Tay, B.K. Sensor Actuator B. 2007,123,107-13. Dixit,V., Misra, S.C.K. and Sharma, B.S. Sensor Actuator B. 2005,104,90-3. Jain, S., Samui, A.B., Parti, M., Hande, V.R. and Bhoraskar, S.V. Sensor Actuator В. 2005,106, 609-13. Ando, M., Swart, С , Pringsheim, E., Mirsky, V.M. and Wolfbeis, O.S. Sensor Actuator B. 2005,108,528-34. Kim, J.S., Sohn, S.O. and Huh, J.S. Sensor Actuator B. 2005,108,409-13. Hosseini, S.H. and Entezami, A.A. Polym Advan Technol, 2001,12,482-93. Joshi, S.S., Lokhande, C D . and Han, S.H. Sensor Actuator B. 2007,123,240-5. Zou, Y., Sun, L. and Xu, F. Talanta. 2007, 72,437-^2. Nohria, R., Khillan, R.K., Su, Y, Dikshit, R., Lvov, Y. and Varahramyan, K. Sensor Actuator B. 2006,114,218-22. Huang, J., Virji, S., Weiller, B.H. and Kaner, R.B. / Am Chem Soc. 2003, 125, 314-5. Muthukumar, C , Kesarkar, S.D. and Srivastava, D.N. / Electroanal Chem. 2007, 602,172-80. Talaie, A., Lee, J. H., Lee, Y.K., Jang, J., Romagnoli, J.A., Taguchi, T. Thin Solid Films. 2000,363,163-6. Arora, K., Sumana, G., Saxena, V, Gupta, R.K., Gupta, S.K. and Yakhmi, J.V, Anal Chim Ada. 2007, 594,17-23. Ren, J., He, F., Zhang, L., Su, С and Liu, Z. Sensor Actuator B. 2007, 125,510-6. Andreu, Y, Marcos, S., Castillo, J.R. and Galban, J. Talanta. 2005, 65,1045-51. Chen, Z. and Lu, С Sens. Lett. 2005,3,274-295. Ramaprasad, A.T. and Rao, V. Sensors and Actuators B. 2010,148,117-125. Joubert, M., Bouhadid, M., Begue, D. Iratgabal, P., Redon, N., Desbrie, J. and Reynaud, S. Polymer, 2010,51,1716-1722. Yanga, L.Y. and Liau, W.B. Synthetic Met. 2010,160,609-614. Ando, M., Swart, C , Pringsheim, E., Mirsky, V.M. and Wolfbeis, O.S. Sensor Actuator B. 2005,108, 528-34. Joshi, S.S., Lokhande, C D . and Han, S.H. Sensor Actuator B. 2007,123, 240-5. Cai, H., Cao, X., Jiang, Y., He, P. and Fang, Y Anal Bioanal Chem. 2003, 375, 287-93. Lu, J., Moon, K.S., Kim, B.K. and Wong, C.P. Polymer. 2007,48,1510-6. Gupta, V. and Miura, N. Electrochim Ada. 2006;52:1721-6. Sung, J.H., Kim, S.J. and Lee, K.H.} Power Sources. 2004,126,258-67. Meng, С , Liu, С and Fan, S. Eledrochem Commun. 2009,11,186-9. Simon, P. and Gogotsi, Y. Nat. Mater. 2008, 7, 845-854. Miller, J.R and Simon, P. Science. 2008,321, 651-652. Meng, С , Liu, С and Fan, S. Eledrochem Commun. 2009,11,186-9. Sahoo, N.G., Rana, S., Chob, J.W., L., Lin, Chan, S.H. Progress in Polymer Sci. 2010, 35,837-867. Li, Q., Liuc, J., Zouc, J., Chunderc, A., Chenb, Y and Zhai, L. Journal of Power Sources. 2011,196, 565-572. Dhawale, D.S., Salunkhe, R.R., Jamadade, VS., Dubai, D.P, Pawar, S.M. and Lokhande C D . Current Applied Phys. 2010,10,904-909.

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157. Landi, B.J., Raffaelle, R.P., Heben, M.J., Alleman, J.L., VanDerveer, W. and Gennett, T. Nano Lett 2002,2,1329-32. 158. Koerner, H., Price, G., Pearce, N.A., Alexander, M. and Vaia, RA. Nature Mater 2004,3,115-20. 159. Mottaghitalab, V, Xi, В., Spinte, G.M. and Wallace, G.G. Synth Met. 2006,156, 796-803. 160. Rosseinsky, D.R. and Mortimer, R./. Adv. Mater. 2001,13, 783. 161. Somani, P.R. and Radhakrishnan, S. Mater. Chem. Phys. 2003, 77,117. 162. Mortimer, R.J. Dyer, A.L. and Reynolds, J.R. Displays. 2006,27,2. 163. Watanabe, A., Mori, K., Iwasaki, Y, Nakamura, Y, Niizuma, S. Macromolecules. 1987,20,1793-6. 164. Rodrigues, M.A., De Paoli, M.A. and Mastragostino, M. Electrochim Acta. 1991, 36, 2143-6. 165. Jelle, B.P., Hagen, G. Hesjevik, S.M., and Odegard, R. Mater Sei Eng В. 1992, 13,239-11. 166. Jelle, B.P., Hagen, G., Sungle. S. and Obegard, R. Synth Met. 1993,54,315-20. 167. Zhaoa, L., Zhaob, L., Xua, Y, Qiub, Т., Zhib, L. and Shi, G. Electrochimica Acta. 2009, 55,491-497. 168. Chen, W.K., Hu, C.W., Hsu, C.Y. and Ho, K.C. Electrochimica Acta. 2009, 54, 4408-1415. 169. Tahir, Z.M. Alocilja, E.C. and Grooms, D.L. Biosens. Bioelectron. 2005,20,1690. 170. Bidez, PR., Li, S., MacDiarmid, A.G., Venancio, E.C, Wei, Y, Lelkes, P.I. /. Biomater. Sci. Polym. Ed. 2006,17,199. 171. Kamalesh, S., Tan, P., Wang, ]., Lee, Т., Kang, E.T. and Wang, C.H. /. Biomed. Mater. Res. 2000,52,467. 172. Dias, H. V.R., Rajapakse, R. M. G., Krishantha, D. M. M., Fianchini, M., Wang, X. and Elsenbaumer, R.L. /. Mater. Chem. 2007,17,1762. 173. Forzani, E.S., Zhang, H., Nagahara, L.A., Amlani, I., Tsui, R. and Tao, N., Nano Lett. 2004, 4,1785-1788. 174. Zhao, M., Wu, X. and Cai, С. /. Phys. Chem. С 2009.113, 4987-4996. 175. Shi, L., Xiao, Y and Willner, I., Electrochem. Commun. 2004,6,1057-60. 176. Luo, YC. and Do, J.S., Biosens. Bioelectron. 2004,20,15-23. 177. Dhand, C , Das, M., Sumana, G., Srivastava, A.K., Pandey, M.K., Kim, CG., Datta, M. and Malhotra, B.D. Nanoscale. 2010,2, 747-754. 178. Bo, Y, Yang, H., Hu, Y, Yao, T. and Huang, S. Electrochimica Acta. 2010, doi: 10.1016/j. electacta.2010.12.034. 179. Zhu, Z., Wang, G., Sun, M., Li, X., Li, С and Zhu, Z.Z. Electrochimica Acta. 2011, 56,1366-1372.

8

Polyimides: Synthesis Properties, Characterization and Applications Abdolreza Hajipour12, Fatemeh Rafiee1, Ghobad Azizi 1 Pharmaceutical Research Laboratory, Department of Chemistry, Isfahan University of Technology, Iran 2 Department of Pharmacology, University of Wisconsin, Medical School, Madison, WI, USA

Abstract

Polyimides due to their excellent electrical and mechanical properties and high thermal, chemical and dimensional stability have received great attention. There are many different synthetic routes to polyimides, the most popular is the reaction of aromatic dianhydrides with aromatic diamines in aprotic polar solvents through precursor poly(amic acid) s that are subsequently converted to the polyimides. Other methods for synthesis of polyimides are containing reaction of a diisocyanate and a dianhydride, imide exchange, mitsunobu reaction, and coupling by using organometals. These polymers are already used for many important industrial applications such as films, fibers, foams, membranes, binders, varnishes, plastics, composites, glues, adhesives, injection molding products and in the electronic industries as an insulator for microelectronic devices. This chapter provides an overview of the most recent and exciting developments in the field of synthesis methods, modified properties, and novel applications of polyimides and their copolymers. Keywords: High performance polymers, polyimides, poly(amic acid), imidization, dianhydrides, diamines, diisocyanates

8.1

Introduction

Polyimides (PI) are a class of thermally stable polymers that are often based on stiff aromatic backbones. Polyimides were first prepared Sabu Thomas and Visakh P.M. (eds.) Handbook of Engineering and Specialty Thermoplastics, (211-288) © Scrivener Publishing LLC

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by Bogert and Renshaw in 1908, and they were then widely used and rapidly developed in the early 1960s [1]. Polyimides have received great attention as they are very useful for many high-tech applications [2]. The use of polyimides as high-performance and high-temperature thermoplastic materials in various applications stems from the attractive combination of chemical, mechanical and physical properties. Polyimides have found wide usage as films, coatings, adhesives, and matrix resins due to their excellent electrical and mechanical properties, high thermal and chemical stability, good solvent resistance, and dimensional stability. They are generally used as flexible circuitry substrates, interlayer dielectrics and passivation and protective coatings in high density electronic packaging devices [3-6]. The chemistry of polyimides is in itself a vast area with a large variety of monomers available and several methodologies available for synthesis. The most widely practiced procedure in polyimide synthesis is the two-step poly(amic acid) (PAA) process. It involves reacting a dianhydride and a diamine at ambient conditions in a dipolar aprotic solvent to yield the corresponding poly(amic acid), which is then cyclodehydrated to the polyimide either thermally or chemically. The thermal imidization of the poly(amic acids) is especially useful when the final product is desired in a film or a coating form and chemical imidization is a useful technique for manufacturing molding powders [7-8]. Most polyimides are infusible and insoluble due to their planar aromatic and hetero-aromatic structures and thus usually need to be processed from the solvent route. One step method high temperature solution polymerization is employed for polyimides that are soluble in organic solvents at polymerization temperatures. The process involves heating a stoichiometric mixture of monomers in a high boiling solvent or a mixture of solvents at high temperature. The imidization proceeds rapidly at these temperatures and water generated due to the reaction is distilled off continuously as an azeotrope along with the solvent [9]. The properties of polyimides can be dramatically altered by minor variations in the structure. The subtle variations in the structures of the monomer components have a tremendous effect on the properties of the final polyimide. The infusibility and limited solubility of unsubstituted polyimides are characteristic properties which restrict synthesis, characterization, processing, and applications, particularly for a high molecular weight material. Thus, a variety

POLYIMIDES

213

of concepts for structural modifications such as bulky pendant groups [10-12], flexible alkyl side chains [13-14], alicyclic monomers [15], incorporation of pendent trifluoromethyl or trifluoromethoxy groups [16-19], noncoplanar biphenylene moieties [20-23], as well as flexible alkyl or aryl ether spacers [24-25] have been used to reduction of several types of polymer chain-chain interactions, chain packing and charge transfer electronic polarization interactions and enhance the solubility and lower the phase transition temperatures. Another method is via copolymerization to synthesize copolymers to improve the processability. These copolymers can be synthesized from various aromatic monomers containing anhydride, carboxylic acid, and aromatic diamine by condensation [26-28]. Polyimides may also be conveniently prepared by the reaction of a diisocyanate and a dianhydride. Other methods for synthesis of polyimides are containing imide exchange, mitsunobu reaction, coupling by using organometals.

8.2 Synthesis and Properties of Polyimides The development of polymeric materials suitable for multi-purpose technological applications requires an ability to manipulate the morphological features of a given polymer to render the desired functional properties. Polyimides are high-performance polymers that have applications ranging from aerospace to microelectronics. Improvement of the polyimide properties has mainly relied on synthesizing new polymers [29]. 8.2.1

Two-step Poly(amic acid) Process

Since 1960, essentially the beginning of the search for high temperature polymers, more attention was focused on polyimides than any other high performance/high temperature polymers. This is primarily due to the availability of polyimide monomers (particularly aromatic dianhydrides and diamines), the ease of polymer synthesis, and their unique combination of physical and mechanical properties. Although there are many different synthetic routes to polyimides, the most popular is the reaction of an aromatic dianhydride with an aromatic diamine in an aprotic polar solvent such as N-methyl-2-pyrrolidone (NMP), Ν,Ν-dimethylacetamide (DMAc)

2.14

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

and Ν,Ν-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), to form a soluble precursor polyamide acid (amie acid) that is subsequently chemically or thermally converted to the polyimide. Most polyimides were and still are made by this method [30]. The synthesis route is shown in Figure 8.1. Aromatic polyimides are usually insoluble and infusible; their glass transition or melting temperatures, being very high, practically in the same range as their decomposition, make their processing possible only from poly(amic acid) precursors. However, poly(amic acid) is known to be in the equilibration with the constituent dianhydride and diamine [31]. Thus, molecular weight of the precursor polymer varies very sensitively with temperature variation and moisture contact, causing numerous problems in its quality control and process. The major problem for this two-step synthesis is the storage instability of poly(amic acid) solutions , which cause reduction in the molecular weight by hydrolysis and gelation of the solution by partial imidization and elimination of released water and formation of micro voids in the final product [32]. Therefore, many attempts have been made to improve the processing properties of aromatic polyimides, particularly their solubility and fusibility, by incorporation of more flexible units such as amide [33], ester [34], ether [35-37], or other flexibilizing linkages and also bulky pendant groups [10-12], trifluoromethyl groups [16-19] and noncoplanar biphenylene moieties [20-23] into the polymer backbone. The main concept behind all these approaches

О

О

но—IL^Jh— он Н (At) H N ^ > — < ^ - - ' N- Ar" О

О

Polyamic acid

——► — L N

Imidization idization

/

(M \Τ"^~^^^·Λ

l

О

О

Figure 8.1 General route for two-step synthesis of polyimides.

POLYIMIDES

215

is the reduction of polymer the inter-chain interactions and chain packing and enhances the chain mobility and processing. 8.2.2

Bulky Substituent in Polymer Backbone

Bulky substituents in the rigid backbone of polymer chain cause reduction in the interactions between polymer chains and chain packing. The intermolecular chain distance and chain rigidity of the polymer was increased as a result of the bulky pendant alicyclic structure, which restricted the dense packing and free rotation of the polymer chain. Hence, the obtained polymers showed good thermal stability as well as solubility [38]. Several Bulky substituents introduced in the polymer backbone. For example introduction of diamantine units into polyimide allows the polymer has good thermal stability and high T . Owing to the low hydrophilicity and polarity of diamantine, the resulting polyimide has low dielectric constant and low moisture absorbtion. Diamantane is a cycloaliphatic cage hydrocarbon (C14H20) containing an "extended cage" adamantine structure as shown in Figure 8.2. A diamantine-based polyimide was synthesized by two-step procedure starting from diamine 1 and various dianhydrides 2 as shown in Figure 8.3. In the first step, polyamic acids with inherent viscosity between 0.41 and 0.65 dl/g are formed. Then, the thermal conversion to polyimide was performed by heating to 250 °C in vacuum [39].

Figure 8.2 Structure of diamantine.

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The introduction of cardo groups into the backbone of polymers is an effective approach for improving solubility and thereby processability of polyimides. The presence of cardo groups such as fluorene, phthalide, phthalimidine, anthrone in the repeat unit of polyimide similarly results in enhanced solubility as well as high thermal properties of polymer. Cardo polyimides contain bulky bisphenylfluorene moiety as the loop like moiety have high glass transition temperature while providing high solubility in different organic solvents. This is so because the bulky fluorenyl cardo moiety hinders the molecular packing and reduces the rotational mobility of the main chain [40-42]. Fluorenyl cardo diamines containing different alkyl substituents were prepared by polycondensation of these cardo diamines with differen dianhydrides as shown in Figure 8.4. Most of fluorenyl cardo polyimides exhibited excellent solubility in common organic solvents such as m-cresol, chloroform, tetrahydrofuran (THF), NMP,DMAc,etc[43]. о Ar )

О

R.T.

►

О 1

NH2

Figure 8.3

Figure 8.4 Synthesis of fluorenyl cardo polyimides.

PPA

-H,0 320°C

►

POLYIMIDES

8.2.3

217

Polyimides with Flexible Ether Links

It has been generally recognized that flexible ether links inserted in the polyimide backbone enhance the solubility and moldability while lowering the phase transition temperatures by lowering the segmental rotational barrier and increasing the degree of freedom [44]. These flexible linkages inhibit packing and decrease the co-planarity of the aromatic rings, thus reducing inter and intra chain interactions to enhance solubility. The structure of resulting polyimide is, therefore, expected to provide balanced properties of thermal stability and processability (improve solubility with slight reduction in thermal properties). Poly (ether imide)s provide good processability owing to the presence of flexible ether links. The large class of poly(ether imide)s from bis(ether anhydride)s and various diamines developed by nucleophilic displacement reactions and ether formations such as nitrodisplacement reactions [45]. The synthesis route is shown in Figure 8.5.

Figure 8.5 Synthesis route for the synthesis of poly(ether imide) from its monomer.

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Structure alternation in the diamine has led to enhance solubility and acceptable thermal properties. Diamines 7 and 8 derived from their p-nitro phenol precursors by fluorine displacement are shown in Figure 8.6 [44]. Condensation of diamines 7 and 8 with various commercially available dianhydrides in NMP led to high molecular weight Poly (ether imide)s as shown in Figure 8.7. Combinations of the multi-ring flexible bis(ether amine)s with dianhydrides, particularly for those containing a flexibilizing bridge between two phthalic anhydride moieties, usually resulted in polyimides with a lowered T and higher solubility. Nucleophilic chlorodisplacement of an alkali metal bisphenolate with p-chloronitrobenzene, Followed by reduction of the resulting dinitro compound, was used for preparation of bis(ether amine) [32]. The synthesis route is shown in Figure 8.8.

H N

« -O~°4~r 0 ~O~ NHi

H N

2 ^CV 0 4~r°-O~ O^^QM^HQ-OHQ^NO,

2

reflux

Pd/C, EtOH

reflux

H N

* ^C^ o 4~r°~CH H2

Figure 8.6 Synthesis of diamines 7 from p-nitro phenol.

POLYIMIDES 2 1 9 Q

9

KD-1

NH

1.NMP '

2. NMP/Xylene^

Q

,9

-

NH,

Figure 8.8 Preparation route of bis(ether amine).

Diamine containing noncoplanar 2,2'-dimethyl-biphenylene and flexible aryl ether units, 2,2'-dimethyl-4/4'-bis(4-aminophenoxy) biphenyl, synthesized by nucleophilic substitution, followed by catalytic reduction with hydrazine-Pd/C and used for preparation of polyimides. Polyimides were synthesized from this diamine and various aromatic dianhydrides by the conventional two-step method which involved ring-opening polyaddition to form poly(amic acid)s and subsequently thermal or chemical cyclodehydration to polyimides [21]. The synthesis route is shown in Figure 8.9.

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HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

Ho.HCI

ΟΗ+ OoN

► HO

/ = \ ,

к2со3

^Qh-N0 2

NH,

DMAc R.T.

о

-► PAA

-H20

►

о

--о—O-OK> Figure 8.9 Synthesis of 2,2'-dimethyl-4,4'-bis(4-aminophenoxy)biphenyl and polycondensation with various dianhydrides.

Five benzene rings-containing diamine, a,a'-bis[3,5-dimethy l-4-(4-aminophenoxy)phenyl]-l,4-diisopropylbenzene (BDAPD) containingflexibleether and isopropylidene units, was reacted with various aromatic dianhydrides to prepare a series of polyimides as shown in Figure 8.10. Due to the presence of theflexiblemoieties on the polyimide backbone, there was a considerable decrease in the rigidity of polymer chain, which could be considered to be reduced the crystallinity and improved the solubility of polymer [46].

POLYIMIDES

221

Figure 8.10 Polyimide synthesis via, a,a'-bis[3,5-dimethyl-4-(4-aminophenoxy) phenyl]-l,4-diisopropylbenzene.

8.2.4

Polyimides Containing Trifluoromethyl Group

Polyimides containing the trifluoromethyl group in the main chain have much lower dielectric constants and water absorption, higher transparency, resistance to photochemical degradation, good solubility and gas permeation properties than observed for conventional polyimides. These groups decrease crystallinity, and color, while on the other hand they increase flame resistance, environmental stability, and optical transparency. Polyimides with low dielectric constant are used extensively as metal dielectric layer of the integrated circuit (1С). As the size of the 1С decreases, lower dielectric constants are needed. The best procedure for reduction the dielectric constant is the introduction of the bulky CF3 group into polyimide main chain, because F is the highest electronegative element and has low electric polarity Furthermore, the C-F bond is short enough and holds bonding atoms more close together and it can increase the interchain spaces to enhance solubility of polyimide. The dielectric constants in the range of 2.4-2.8 at 10 GHz have been achieved for polyimides containing the trifluoromethyl groups, while the 4,4'-oxydianiline and pyromellitic dianhydride system has a value of 3.2 at 10 GHz. With excellent physical and chemical properties, fluorinated polyimide can be expected to apply widely to the Electro-Optical and semiconductor industries. Substantially lower water absorption of polyimides

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HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

containing fluorinated alkyl groups, cause the higher humidity had relatively little influence on the electrical properties (19,47). Monomers containing hexafluoroisopropylidene groups, such as 4,4'-(hexafluoroisopropylidene) bis(phthalic anhydride) (6FDA) as shown in Figure 8.11, are used widely for this purpose. 6FDA is less reactive in the acylation of amines than pyromellitic dianhydride and gives polyimides with lower molecular weights [48]. Condensation of 6FDA with 4,4'-(alkylenediyldioxy)dianiline lead to polyimide with improved solubility and relatively low glass transition temperature. The synthesis route is shown in Figure 8.12. The diamine, l,l-bis(4-aminophenyl)-l-phenyl-2,2,2- trifluoroethane (3FDAM) and 2,2-bis[4-(4-aminophenoxy)phenyl] hexafluoropropane (4BDAF) that are shown in Figure 8.13, have exceptional thermal and mechanical properties [49].

Figure 8.11 Strycture of 4,4'-(hexafluoroisopropylidene) bis(phthalic anhydride). CF3

,P + H2N—£

Л-0-(СН2)п-0—£

Ρ Α Α ^

,)— Ν Η 2 = = ^ Ρ Α Α

0-(CH 2 )n

^ //

-*n= 4,6,10

Figure 8.12 Condensation of 6FDA with 4,4'-(alkylenediyldioxy)dianiline.

H N

CF1/=4

2 43^fC^ 3FDAM

_

NH2 H 2 N

—

o

CF3

41)- -0+ ! 0- o 4D b N H 2 CF,

4BDAF

Figure 8.13 Structure of l,l-bis(4-aminophenyl)-l-phenyl-2,2,2- trifluoroethane (3FDAM) and 2,2-bis[4-(4-aminophenoxy)phenyl] hexafluoropropane (4BDAF).

POLYIMIDES

223

The diamine l,l-bis[4-(4-aminophenoxy)phenyl]-l-phenyl-2,2,2trifluoroethane (3FEDAM) that is shown in Figure 8.14, has the CF3 group, which contributes to the high T , and ether links which provide sufficient chain mobility and proper symmetry to allow development of crystalHnity [47]. 3FEDAM has been prepared via method shown in Figure 8.15. The first step is a hydroxyalkylation reaction of trifluoroacetophenone with 4-nitrophenyl phenyl ether producing the 3F-dinitro compound, which is subsequently hydrogenated to afford the diamine, 3FEDAM. Fluorinated polyimide were prepared by the reaction of diamine with dianhydride to form the poly(amic acid) followed by thermal imidization, as illustrated in Figure 8.16.

н2ы

о

о

Ч~)~ Ч^Н^^ ^СН

н2

3FEDAMF

Figure 8.14 Structure of diamines l,l-bis[4-(4-aminophenoxy)phenyl]-l-phenyl2,2,2-trifluoroethane (3FEDAM).

+

2

1.ТЮН 25 C, 24h

H2N

0"°4^N°2 2.THF, EtOAc Pd/H2 50 C, 24h

-^O h o 4^Hvj^°^} h " N H 2 3FEDAM

Figure 8.15 Preparation of diamines 3FEDAM.

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HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

Aromatic diamine with cyclohexane cardo group substituted with trifluoromethyl group in the side chain, l,l-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]cyclohexane, was prepared through the nucleophilic substitution reaction of l,l-bis(4-hydroxyphenyl) cyclohexane and 2-chloro-5-nitrobenzotrifluoride in the presence of potassium carbonate, to yield the intermediate dinitro compound, followed by catalytic reduction with hydrazine and Pd/C to afford the diamine. The synthesis route is shown in Figure 8.17. Fluorinated polyimides were prepared from the diamine with various aromatic dianhydrides via thermal or chemical imidization of poly (amie acid) [50]. CF3

»^У^СУт^У^О-^^ NMP, R.T. 24 h PAA 1 h each at 25,100,200,300 0

-ок>£о~сИ

о.

о

fj +-3FEDAM-tQT j

Figure 8.16 Polycondensation of 3FEDAM with dianhydrides.

Figure 8.17 Preparation of diamine l,l-bis[4-(4-amino-2-trifluoromethylphenoxy) phenyl]cyclohexane.

POLYIMIDES

225

Polyimides derived from ether-bridged aromatic diamines with trifluoromethyl (3F) groups are soluble high temperature polymer materials with low moisture uptake, low dielectric constant, high optical transparency, and low birefringence. High-performance fluorinated polyimide containing naphthalene units was prepared from fluorinated bis(ether amine) monomer, 2,3-bis(4-amino-2-trifluoromethylphenoxy)naphthalene with various commercially available aromatic dianhydrides. Diamine was prepared through the nucleophilic aromatic substitution reaction of 2-chloro-5-nitrobenzotrifluoride and 2,3-dihydroxynaphthalene in the presence of potassium carbonate, followed by catalytic reduction with hydrazine and Pd/C as illustrated in Figure 8.18. These polyimides were highly soluble in a variety of organic solvents, and most of them afforded transparent, light-colored, and tough films with good tensile strengths [51]. This method had used for preparation of fluorinated diamine monomer, 9,9-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]fluorine as shown in Figure 8.19 [52]. A series of organosoluble and light-colored polyimides was synthesized from 2,3,3',4'-biphenyltetracarboxylic dianhydride (cc-BPDA) with various aromatic bis(ether amine)s bearing the

+

2 CI—Ì V-NO,

Pd/ С, ЕЮН

H,N-

r\

,CF3

F3C,

\ // \

//

-NH,

\ /

Figure 8.18 Preparation of diamine 2,3-bis(4-amino-2-trifluoromethylphenoxy) naphthalene.

226

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

CI ■CF3

KpCO, DMAc

NO,

Figure 8.19

PF,

0

H,N '2n +

\ \ /J V. V

Сч Ar.

°Ч\ /

NH,

DMAc

Alfa-BPDA

Figure 8.20 Polycondensation of (X-BPDA and aromatic bis(ether amine)s.

POLYIMIDES

227

pendent trifluoromethyl group via a thermal or chemical imidization. These polyimides show excellent solubility in the organic solvents. They are all soluble in the amide-type solvent like NMP, DMAc, DMF, ether-type solvents like Dioxane, THF and chloronated-solvent of CH2C12 and CHC13 [53]. The synthesis route is shown in Figure 8.20. Fluorinated aromatic dianhydride, 4,4'-[2,2,2-ггШиого-1-(3,5ditrifluoromethylphenyl) ethylidene] diphthalic anhydride (9FDA), was synthesized as shown in Figure 8.21, which was employed to polycondense with various aromatic diamines, to produce a series of fluorinated aromatic polyimides. The synthesis route is shown in Figure 8.21. The fluorinated polyimides obtained had inherent "- , -ζ 5 ν^' Ο Γ 3

Mg OLÌ

F,C

THF, ether

XX

CF,

CF3 KMnO. •ί^

TfOH

9FTM CF,

С02Н

H0 2 C

но2с·

'CF,

_н,о

-> a

CF. 9FTA

NMP

H2N-Ar-NH2 -H20 ^>PAA —► R.T.

9FDA

N—Ar-

Figure 8.21 Synthesis route of 9FDA and polycondensation with diamines.

228

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

viscosities ranged of 0.61-1.14 dL/g and were easily dissolved both in polar aprotic solvents and in low boiling point common solvents [54]. 8.2.5

Polyimides Containing Pyridine

Considering heteroaromatic rings introduced into the polymer backbone could provide certain properties presumed upon them, pyridine ring with heteroaromatic structure has been applied to design and synthesis of some monomers, as well as preparation of advanced polymers because its excellent stability resulting from corresponding nucleus structures and rigidity based on symmetry and aromaticity of pyridine ring. It was found that introduction of pyridine ring to the main chain of polyimide increase its solubility while maintaining its excellent thermal properties [55-56]. Polyamides with good thermo-stability and processability have been prepared by polycondensation of pyridine-containing diamine monomers with aromatic dianhydride monomers [57]. Heteroaromatic diamine 2,6-bis(3-aminobenzoyl)pyridine, has been synthesized from 2,6-bis(3-nitrobenzoy)pyridine, and corresponding polyimides have been prepared by the polycondensation of pyridine containing diamine with different commercially available aromatic tetracarboxylic dianhydrides. Cyclodehydration was carried out chemically by adding a mixture of acetic anhydride and pyridine into the poly(amic acid) solution with stirring at room temperature [57]. The synthesis route is shown in Figure 8.22. Diamine monomers resulting of 2,6-bis(4-aminophenoxy-4'benzoyDpyridine, which was derived from 2,6-bis(4,4'- dihydroxybenzoyDpyridine employed in preparation of the polyimides with several aromatic dianhydrides by two-step procedure [58]. The synthesis route is shown in Figure 8.23. Sulfonated polyimides (SPIs) containing pyridine ring in the polymer backbone were synthesized by the polycondensation of 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTDA), 5-(2,6-bis(4-arninophenyl)pyridin-4-yl)-2-methoxy benzene sulfonic acid (SDAM), and 4,4'-diaminodiphenyl ether (ODA) [59]. The synthesis route is shown in Figure 8.24. by incorporating the pyridine ring in polymer backbone, the strong intra and/or inter acid-base interactions would be formed between the sulfonic acid and pyridine functional groups to compare with the frequently reported weak H-bonding interactions, thereby suppressing membrane swelling.

POLYIMIDES

229

er

10

Figure 8.22 Synthesis of 2,6-Bis(3-aminobenzoyl)pyridine and polycondensation with different aromatic dianhydrides.

Pyridine-containing diamine, 2,6-bis[4-(4-aminophenoxy)phenoxy]pyridine (BAPP), was synthesized by a three step procedure, as shown in Figure 8.25. Pyridine-containing polyimide was prepared from the resulting diamine BAPP with 4,4'-oxydiphthalic

230

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

о Cl

о

li"*!Cl +

OEt

Cl—(ч

О

AICI,

Л—NO,

DMAc

О PAA

Figure 8.23 Synthesis of diamine 2,6-bis(4-aminophenoxy-4'-benzoyl)pyridine and preparation of polyimides with aromatic dianhydrides.

anhydride (ODPA) via a conventional two-step thermal imidization method. The resulting polyimide exhibits excellent solubility, filmforming capability and high thermal resistance [60]. In comparing with pyridme-containing diamines, pyridine-containing dianhydrides, which are need for synthesis polyimides containing

POLYIMIDES

+

231

.0_+i-x

so3H OMe Figure 8.24

HO

^O>_OH+CI^O_N°2

DMR K 2 C0 3 , 100C, 10h

H

°-4~5^ OH O hN ° 2 a

N ^ci

DMAc, K,CO,, 150 C, 24h

^Ν^Ο_Ο^Ο^°

Ν oH

GboHCj^0;

NH2NH2 H 2 0 Pd/ С, ЕЮН, 80 C, 6h

"^-ζ^-°^)-°

N

°4D bo 4D Ki

Figure 8.25

pyridine moieties were reported very few so far, due to purification hardness of pyridme-containing terra-acid intermediates. 4-phenyl2,6-bis[4-(3,4-dicarboxyphenoxy)phenyl]-pyridine dianhydride, forms a series of pyridine containing polyimides by reaction of dianhydrides with various aromatic diamines via a conventional two stage process undergoing ring-opening polycondensation to form the

232

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

poly(amic adid)s and further thermal or chemical imidization to form polyimides [55]. The synthesis route is shown in Figure 8.26. 2,6-bis[4-(3,4-dicarboxyphenoxy)benzoyl] pyridine dianhydride as shown in Figure 8.27, form pyridine-containing polyimides. For the thermal imidization, the poly(amic acid) solution was cast on a glass plate, followed by thermal curing. The chemical imidization was carried out by adding a mixture of an acetic

r\

KpCO, / PhH 0,N

O,

CN CN

O-

CN CHO

AcONH,/AcOH

HOOC

Figure 8.26 Synthesis of 4-phenyl-2,6-bis[4-(3,4-dicarboxyphenoxy) phenyl]-pyridine dianhydride.

POLYIMIDES

233

Figure 8.27 Structure of 2,6-bis[4-(3,4-dicarboxyphenoxy)benzoyl] pyridine dianhydride.

anhydride/pyridine to the PAA solution with stirring at room temperature, and then the mixture was heated [56]. 8.2.6

Polyimides Containing Silicon

Introduction of Si-C bonds into the polyimide main chain can cause to improved solubility and process ability of the polymers from their solutions. Because of the ionic character of the Si-C bond, thermal stability, electrical and mechanical properties of polyimides containing Si-C are improved. The bond energies of the C-C and Si-C bonds are similar. Although the silicon atom being less electronegative than the carbon atom. The polydimethylsiloxane repeating unit, have unusual properties such as high dynamic flexibility, high oxidative stability and excellent thermal stability. Introduction of flexible polysiloxane units into a polyimide backbone can yield processable, sUicon-containing polyimides, with good thermal mechanical properties. Therefore, polysiloxaneimide copolymers are attractive for aerospace applications as membranes and for electrolysis [61-63]. Diamine (4-aminophenyl) methylphenylsilane (obtained from 4-bromo-N,N-bis(trimethylsilyl)aniline can condensed with dianhydride monomers contained combinations of methyl and phenyl groups bonded to the silicon atom and yield corresponding polyimides by thermal cyclization of the respective poly(amic acid)s [64]. The synthesis route is shown in Figure 8.28. 8.2.7

Polyimides Containing Phosphine Oxide Group

Phosphine oxide moiety is known to be very good in enhancing adhession as well as thermal and mechanical properties and fire retardation properties of polymers. Triphenyl phosphine oxide moiety in the main chain of polyimide is known to give non-coplanar

234

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

Me3SiN

SiMe3 Ph H,N 2. PhMeSiCI2

^

/

Si-

\

//

NH,

Me (4-aminophenyl) methylphenylsilane

3. HCI 4. NaOH (5%)

1. Li, Et 2 0, N2 Br

2. R^jSiClj

►

3. HCI

Figure 8.28 Diamine (4-aminophenyl) methylphenylsilane and condensation with si containing dianhydride drived from 3,4- dimethyl bromobenzen.

structure, providing low birefringence. Phosphine oxide moiety provides a strong interacting site for imparting miscibility with several thermoplastic and thermosetting polymers. Due to the noncoplanar structure of triarylphosphine oxide and the intensely polar P=0 bond, polymers containing the phosphine oxide group are usually amorphous and have high refractive index [65-69]. The incorporation of the triarylphosphine oxide group into the main chain of polymers increases the solubility of the polymer in common organic solvents and improves the nonlinear optical properties of polymers due to the excellent electron- accepting ability of

POLYIMIDES

235

the tiiarylphosphine moiety. A remarkable feature of the phosphine oxide group is resistance to atomic oxygen [70-71]. Diamine, bis(3-arrunophenyl)-2,3,5,6-tetiafluoro-4-trifluoromethylphenyl phosphine oxide, was synthesized via Grignard reaction, followed by nitration and reduction and various polyimides were synthesized with dianhydrides, via conventional two-step reaction; preparation of poly(amic acid) followed by solution imidization [66]. The synthesis route is shown in Figure 8.29. Phosphorylation of organosoluble polyimides is the other method for creating the phosphorous containing polyimides. Polyimides with free hydroxyl groups can esterify with diphenylphosphoryl chloride to form pendent phosphate ester groups [72]. The synthesis route is shown in Figure 8.30. Direct nitration and reduction of triarylphosphine oxide give diamine bis (3-aminophenyl) phenylphosphine oxide as shown in Figure 8.31 that can use in the synthesis of phosphine oxide-based sulfonated polyimide [73]. 8.2.8

Synthesis of Polyimides via Dithioanhydride and Diamine

The preparation of polyimides by using dithioanhydrides in place of the dianhydrides proceeded at relatively lower temperatures of

" X V -4 // h

-5°C, 3h, R.T., 12h HN0 3 , H 2 S0 4

.0^0

-5°C, 3-4h RT, 24 h

F

CF, ,N

NH2

Abs, EtOh Pd/°C 50°C, H,

Figure 8.29 Synthesis of bis(3-aminophenyl)-2,3,5,6-tetrafluoro-4-trifluoromet hylphenyl phosphine oxide.

236

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

DMAc, PhH R.T., 24h PAA

Figure 8.30 Phosphorylation of free hydroxyl groups of polyimide.

100-140 °C with evolution of hydrogen sulfide, affording directly polyimides with high molecular weights as shown in Figure 8.32. Polyimides were prepared in a simple one-step synthesis from pyromellitic dithioanhydride and aromatic diamines in dimethylacetamide or other solvents. The reaction was strongly dependent on solvent and temperature [74]. 8.2.9

Synthesis of Polyimides via Polyamic Acid Alkyl Esters

An important improvement over the use of poly(amic acid)s as precursors is the derivatization of the acid side groups in the form of

POLYIMIDES

Pl-Q

Ο,Ν

NO,

237

P±Q Hp/Pd

Я5Р

S03Na

Figure 8.31 Synthesis of diamine bis (3-aminophenyl) phenylphosphine oxide. О s·

( Ar )

S

+

H2N-Ar-NH2

О

Figure 8.32 General route for preparation of polyimides by using dithioanhydrides.

alkyl esters. This derivatization improves the hydrolytic stability and solubility of the precursor polymers and results in more favorable imidization characteristics. poly(amic dialkylester) is known to show a thermal imidization behavior quite different from that of poly(amic acid). For example, poly(amie acid) of a polyimide is thermally imidized at a relatively low temperature, compared to its poly(amic dialkyl ester) [75]. Thus, poly (amie dialkyl ester) has gained great attention from academic and industry fields although its synthesis is relatively more complicate than that of poly (amie acid) [76]. These polymers were prepared by the polycondensation of bis(alkoxycarbonyl)-substituted aromatic dicarboxylic acids, derived from tetracarboxylic dianhydrides and alcohols, or their acid chlorides with aromatic diamines. These polyamic acid alkyl esters were then converted thermally to polyimides with the elimination of alcohols. The chemistry of the poly(amic ester) route is much more suitable for the synthesis of rigid polyimides. Linear

238

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

alkyl esters of polyamic acids were much more hydrolytically stable in solution than the polyamic acids and consequently showed little change in molecular weight with time. This enhanced stability has been attributed to the blocking of the ortho carboxylic acid group by an ester group. Unfortunately, the curing rates of linear alkyl esters are much slower than those of the corresponding free acids (up to 60 times slower for the n-butyl ester) [77-78]. Reaction of 2,5-bis(ethoxycarbonyl)terephthaloyl chloride with various substituted p-phenylenediamines and noncoplanar 4, 4'-diaminobiphenylene derivatives, yield to Polyamic acid alkyl esters. The substituted and noncoplanar diamines were selected to further improve the solubility of the poly(amic ester) precursors without significantly reducing their chain rigidity [79]. The synthesis route is shown in Figure 8.33. Acid activating groups such as N,N'-(phenylphosphino) bis[2(3H)-benzothiazolone was used in place of acid chloride as shown in Figure 8.34 [77]. 8.2.10

Synthesis of Polyimides via Polyamic Acid Trimethylsilyl Esters

The N-silylated diamine method has been applied to the synthesis of polyimides. Polyamic acid trimethylsilyl esters were synthesized о

У'

COpEt

HOpC.

ЕЮН

EtOpCl - ^ ^ - C O p H

Ck

HO,C EtO,C

C0 2 H

XX

C0 2 Et

/P

CO,Et EtO,C

О CK EtOpC

^COpEt _CI

+ H2N-Ar-NH2

NMP, 3% LiCI TMSCI

►

.

.COpEt H H N-Ar-N-

Figure 8.33 Preparation of polyamic acid alkyl ester from 2,5-bis(ethoxycarbonyl) terephthaloyl chloride and diamines.

POLYIMIDES

w /

о \

/

NH,

239

t-BuO

Υ1Ύ о

о

t-BuO

Figure 8.34 Activation of Acid with activating group.

starting from N-trirnetylsilyl-substituted aromatic diamines in place of the usual diamines with dianhydrides in two steps through the ring-opening polyaddition. In the second stage, the silylated precursor polymers were subjected to thermal imidization to convert them to polyirnides where trimethylsilanol was eliminated. These polyamic acid trimethylsilyl esters were stable in solution and remained unchanged for a long time when stored under anhydrous conditions. The thermal conversion to polyimides was readily achieved under the similar conditions that required for the parent polyamic acids. Since these N-silylated aromatic diamines dissolved quite readily in a wide range of organic solvents, compared with the corresponding aromatic diamines, the solution polyaddition could be carried out in various solvents. The polyamic acid silyl ester prepared by polyaddition had good solubility in various solvents including amide solvents and low boiling point solvents such as THF and chloroform [80]. The synthesis route is shown in Figure 8.35. 8.2.11 Polyimides Containing Six Membered Rings Varieties of six membered ring dianhydrides are used for preparation of polyimides, especially for fuel cell applications, six-membered ring

240

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

о Me3Si—N-Ar-N—SiMe3 + Q

о ( Т ^ У " О

H H -N—Ar-N Me,SiO

MeOH -MeOSiMe

H H -N—Ar-N N--*

Figure 8.35 General route for synthesis of polyimides via polyamic acid trimethylsilyl esters.

sulfonated polyimides are considered as promising candidates for proton exchange membrane materials because of their high thermal stability, high mechanical strength, good film-forming ability, superior chemical resistance and low fuel gas (or liquid) crossover [81-83]. The five-membered ring polyimides are generally unstable toward hydrolysis in acidic medium due to the ease of hydrolysis of imido rings whereas 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA) as shown in Figure 8.36 have been found to be stable toward both acid and water. Naphthalic polyimides are prepared by one-step, high temperature polycondensation reaction using m-cresol as the solvent. These anhydrides have a very low reactivity. Therefore, an acidic catalyst benzoic acid (BA) is added in the first step, and this may promote the formation of trans-isoimide. A basic catalyst like isoquinoloine (IQ) is then added to convert the trfns-isoimide into naphthalimide [84].

POLYIMIDES

241

Figure 8.36 Structure of 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA).

Figure 8.37 Structure of 4,4'-binaphthyl-l,l' / 8 / 8'-tetracarboxylic dianhydride (BTDA).

4,4'-binaphthyl-l,l',8,8'-tetracarboxylic dianhydride (BTDA) as shown in Figure 8.37 has two anhydride groups, which are located on the two twist noncoplanar naphthalene rings. As a result, the polyimides from 4,4'-binaphthyl-l,l',8,8'-tetracarboxylic dianhydride should possess a decreased positive charge density of carbonyl groups in the naphthalimide moieties compared with that from 1,4,5,8-naphthalene-tetracarboxylic dianhydride. This is favorable to depress the hydrolysis of the imide rings [81]. Bis(naphthalene anhydride)s display a reduced electrophilic reactivity, its polycondensation reaction has been shown to require a high reaction temperature (>180 °C) and the use of an organic acid or base as catalyst. Perylene-containing polyimides have been used in various fields. Perylenediimides are advantageous for their favorable photochemical behaviors, excellent thermal mal and photostabilities, electron acceptor and photoconductive properties, and application as laser dyes [85]. Polymer based on perylene-3,4,9,10-tetracarboxylic acidbis-(N,N'-dodecylpolyimide) as shown in Figure 8.38 is a photostable polymer [86]. 8.2.12

Synthesis of Polyimides via Dianhydride and Diisocyanate

Polyimides can be synthesized by direct polycondensation of dianhydrides with diisocyanates which are used in place of the parent diamines as shown in Figure 8.39 [87].

242

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

-NH,

m-Cresol Isoquiniline

LI

-N—(CH 2 ) 2

H —N—(CH 2 ) 2

Figure 8.38 Polyimide based on perylene-3,4,9,10-tetracarboxylic acid-bis-(N,N'-dodecylpolyimide). О О

О Ar

о

О + 0=C=N-R-N=C=0

о

О N О

О Ar

N-C-RО

Figure 8.39

Some polyimides were prepared by reacting equimolar amounts of the appropriate dianhydride and diisocyanate at ice-bath temperature in dimethylacetamide (DMAc). Here the reaction proceeds via the formation of a seven membered cyclic intermediate which on loss of carbon dioxide forms the polyimide. The synthesis route is shown in Figure 8.40 [88]. An optically active diisocyanate was prepared from the reaction of L-leucine and pyromellitic dianhydride (PMDA) and subsequent transformation of intermediate imide-containing diacid to diisocyanate. Solution polycondensation reaction of the prepared diisocyanate with various dianhydrides resulted in the preparation of novel optically active polyimides [89]. The synthesis route is shown in Figure 8.41.

POLYIMIDES

о

о

У

Ari

Ъ + 0=C=N—R-N=C=0

°

N —

—N

AcOH, 150°C

-Н2°

О

0-

о

Ν,Ν'-dimethyl pyromeUitic bisimide

H

2

N ^

^

Ο

^

^

χ

Ο

^

^ - N H ,

1, 4-bis(4-aminophenoxy) benzene diamine

_ О

\

//

^

/

Ö

Figure 8.42 Preparation of polyimides via imide exchange.

fast reaction in the dissolved state at room temperature, bisimide used instead dianhydride. Reaction of pyromeUitic dianhydride and MeNH2.HCl produce Ν,Ν'-dimethyl pyromeUitic bisimide. The Ν,Ν'-dimethyl pyromeUitic bisimide monomer does not react with l,4-bis(4-aminophenoxy) benzene diamine at room temperature, but the reaction does occur at elevated temperatures in the melt state [90].The synthesis route is shown in Figure 8.42. 8.2.14

Synthesis of Polyimides via Mitsunobu Reaction

Polyimides are commonly synthesized by the reaction of dianhydrides with diamines to provide poly(amic acid) precursor polymers, followed by a high-temperature imidization process to produce the desired polyimides. There is a direct and one-step reaction preparation of polyimide from diimide monomer and diol monomer through the Mitsunobu condensation as shown in Figure 8.43. By performing direct polymerization into polyimides under the mild Mitsunobu conditions, the harsh imidization process of the polyamic acid imidization process at high temperature can be avoided [91-94]. The polymerization reaction between the diimide and diol monomers executed by Mitsunobu reaction used diethyl azodicarboxylate

POLYIMIDES

245

ЕЮ2С N N C0 2 Et R OH

,PPh3 NUC

►

R NUC

Figure 8.43 General feature of mitsunobu reaction of alcohols and nucleophiles.

Figure 8.44 Use of Mitsunobu reaction for polymerization reaction between the diimide and diol monomers.

(DEAD) and triphenylphosphine in anhydrous tetrahydrofuran (THF) solvent as shown in Figure 8.44 [91]. 8.2.15

Synthesis of Polyimides via Coupling by using Metals

Coupling reaction with metals is other route for production of polyimides from less reactive monomers. For example, bis(naphthalenic anhydride)s had a reduced electrophilic reactivity so that their polycondensation reaction with diamines required high reaction temperature. But, in the presence of NiBr2, zinc dust and triphenylphosphine, polymerization was performed with naphthalimide dichloride in DMAc by Ni[0] catalytic coupling to prepare polyimides rapidly as shown in Figure 8.45 [95].

246

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS = \

,o

?F3 CI-Ar-OH

CI—Ar-0

K2C03, DMSO

NiBr2 / PPh3 / Zn DMAc, 90°C

-Ar-O-

/=\

.0

9F3

Figure 8.45 Catalytic coupling for preparation of polyimide by Ni(0).

Figure 8.46 Ni(0)- catalyzed coupling polymerization between binaphthalimide dichloride and aromatic dichloride.

Another example is reaction between binaphthalimide dichloride and aromatic dichlorides through a Ni[0]- catalyzed coupling polymerization as shown in Figure 8.46 [96]. 8.2.16

Green Media for Preparation of Polyimides

The majority of solvents commonly used in polymer synthesis represent highly flammable, volatile and toxic compounds. Thus, search for new solvents with adapted properties is an important topic of polymer chemistry. Water, supercritical fluids, such as carbon dioxide, and ionic liquids (ILs) [97-99] are considered as

POLYIMIDES

247

environmentally friendly reaction media and can be applied as solvents and catalysts in green chemistry processes. 8.2.16.1 Synthesis of Polyimides in Ionic Liquid Media Ionic liquids have been used as solvent for polymerization reactions. Free radical, atom transfer radical polymerization, cationic, cationic ring-opening, and metathesis polymerizations have been performed. However, there is only few example of polycondensation in ionic liquids [99]. In the synthesis of polyimides, diamine and dianhydride reacted generally in the amide type polar solvents such as DMF to obtain soluble poly(amic acid) as a prepolymer. Then, the solution of the prepared poly(amic acid) was heated in order both to proceed imidization and to remove solvents. In this step, the solvent was vaporized to the environment and was at risk of ignition. ILs, which have negligibly small vapor pressure, are expected as solvents for polyimide synthesis [100]. The results show that ionic liquids allow obtaining high molecular weight polyimides in the absence of any additional catalyst. Most of researches are based on free-radical polymerization because of its widely applicable possibility with small restriction. Against this, polycondensation, especially the synthesis of aromatic polyimides, is quite difficult in ILs [101]. Ambient-temperature ILs containing 1,3-dialkylimidazolium cations are very hopeful compounds as alternatives to conventional organic solvents. Important properties of these ILs are low volatility, ease of handling, increased rates of the reactions performed using them, possibility of recycling, and compatibility with various organic compounds. Ionic liquids bearing different cations and anions with asymmetrical l-methyl-3-alkylimidazolium cations and ILs with symmetrical 1,3-dialkylimidazolium cations are showed in Figure 8.47. Symmetrical 1,3-dialkylimidazolium cations lead to higher inherent viscosities. The polycyclization was occurred as homogeneous process in ILs having Et, Pr and Bu groups whereas ILs having longer alkyl groups cause rapid precipitation of this polymer. The ionic liquids containing halide anions are known as relatively polar ILs and show better solubilizing ability of many kinds of molecules. In addition, biological polymers were found to be soluble in some ILs containing halide anions. However, these halide

.248

HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS Asymmetrical -

Symmetrical

R, = CH 3

R, = R2 = C2HS, C3H7, i C3H7,

R2 = C2H5, C3H7, C4H9

C4H9, С^Н,,, C6H13, C12H25,

Y = Br, BF4, PF6, Tf2N

Figure 8.47 Ionic liquids bearing different cations and anions base on 1,3-dialkylimidazolium.

anion-containing ILs have a few drawbacks as solvents for polycondensation reactions. First, the melting point of halide-containing ILs is relatively high. Almost all of these ILs containing halide anions are solid at room temperature. It is quite important to lower the reaction temperature for PAA synthesis, because the molecular weight of PAA was reported to be lower when the reaction was carried out at higher temperature. Since the average molecular weight of PI clearly reflects the molecular weight of the prepolymer (PAA), the PAA should be prepared at a low temperature. These halidecontaining ILs needed heating when used as solvents. The ILs, having lower viscosity and lower melting point than those ILs having halide anions are quite favorable for the PAA syntheses. Second, halide-containing ILs are hydrophilic and hygroscopic. The reactivity of starting materials, especially anhydrous dicarboxylic acid, decreases considerably in the presence of water. Ionic liquids containing halide anions are generally hygroscopic, and thus, contaminated water considerably lowers the reactivity. Therefore, polycondensation in halide-containing ILs requires a special care to avoid humidity from the reaction systems. Hydrophobie ILs are much more favorable for this point of view. Even in the case of hydrophobic ILs, there are small amounts of water. However, these water molecules are not free but strongly hydrated. Last, halide containing ILs generally decompose around 200 °C. The thermal imidization of prepolymers should be carried out above 250 °C; otherwise imidization was not completely proceeded [100]. Ionic liquids can act as acid activating group in direct polyamide and poly(amide-imide). Probably, mobile imidazolium C2 hydrogen atom plays considerable role in this reaction. The usage of dicarboxylic acids in direct polycondensation instead of their significantly more toxic and more reactive derivatives, such as acid chlorides, is one of the main and important prerequisites for the study of such polymer synthesis in ionic liquids. The mechanism of

POLYIMIDES

R

/

N/

P(OPh)3

R2

N-R 2

249

R3COOH

PhCr) "^OPh PhO

H

%** R3 ^ L - OPh ПРИ

_ R4NH2 R,

\ /

M

2

Y

H

0

*"

3

>f

N

X + PhOH + HOP(OPh)2

О

12

Figure 8.48 Mechanism of activation of acid with ionic liquide in amide formation.

activation of acid with IL as showed in Figure 8.48. Initially intermediate IL—triphenyl phosphite complex is formed. Subsequent attack of carboxylic acid by such complex gives active acyloxyphosphonium salt. The interaction of this final salt and amine group results in obtaining amide [102]. 8.2.16.2 Synthesis ofPolyimides in Supercritical Carbon Dioxide Supercritical C0 2 is a viable and promising alternative to traditional solvents used in polymer synthesis. Much of this promise results from its fluid properties, effects on polymers, and environmental advantages. It is inexpensive, nonflammable, and nontoxic, making it an attractive solvent for large-scale synthesis. C0 2 can be easily recycled after use as a solvent to avoid any contribution to greenhouse effects. Because C0 2 is an ambient gas, the polymers can be isolated from the reaction media by simple depressurization, resulting in a dry polymer product. This feature eliminates energyintensive drying procedures required in polymer manufacturing to remove solvent and represents potential cost and energy savings for C02-based systems. While C0 2 is a good solvent for most nonpolar and some polar molecules of low molar mass, it is a poor solvent for most high molar mass polymers under mild conditions. The only polymers that show good solubility in C0 2 under mild conditions are amorphous fluoropolymers (polyfluoroalkyl acrylates, fluorine-substituted polyethers, some of the polyperfluoroolefines and also their block and random copolymers and several silicon polymers [103].

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HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

Since C0 2 in the presence of water admixture is acting as a weak acid, C0 2 may act as reaction medium and catalyst for this reaction. Polyimides were synthesized by high temperature one step polycyclization reaction of the corresponding diamines and dianhydrides as shown in Figure 8.49. Supercritical C0 2 reduces the melt viscosity that promotes a better elimination of low molecular mass reaction products and increases the polymer molecular weight. Supercritical C0 2 decreases T of polymers owing to its plasticizing action. Hence, the melting point of the polymers could be expected slightly to decrease [104]. 8.2.16.3 Microwave-assisted Condensation of Polyimides The reported works concerning preparation of polyimides under microwave conditions can be divided into four main areas: 1) Polycondensation of salt monomers composed of diamines and pyromellitic acid 2) Dehydration of poly(amic-acid)s as polyimide precursor 3) Polymerization of nadic-end capped or phenyl ethynyl-terminated imide oligomers and 4) Polycondensation of imide diacid chlorides with aliphatic and aromatic amines (poly(amide imide)). In the case of polycondensation of salt monomers, polyimides were obtained from salt monomers composed of diamines and pyromellitic acid or its diethyl ester in the presence of a small amount of a polar organic medium that acted as a microwave absorber as shown in Figure 8.50 [105]. Copolycondensation of 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), pyromellitic dianhydride, and 4,4'-oxydianiline (ODA) under microwave irradiation showed in Figure 8.51. Microwave irradiation accelerated the reaction rate. The inherent Dianhydride

+

Diamine

.

325 bar

Polyimide + H 2 0

130-180°C Super critical C0 2

Figure 8.49: One step polycondensation of diamines and dianhydrides in super critical conditions 0

n H3N-(CH2)^-NH3 + n

ΎΤ

ROOC^NXICL

""? » - nROH

' 4 L

C

H

0 J - Ö I } T

rf"^^

Figure 8.50 Microwave-assisted condensation of Salt monomers composed of diamines and pyromellitic dialkyl ester.

POLYIMIDES

251

»PAA

-Чх^з Figure 8.51 Copolycondensation of 3,3',4,4-benzophenonetetracarboxylic dianhydride (BTDA), pyromellitic dianhydride, and 4,4'-oxydianiline (ODA) under microwave irradiation.

О + 0=C=N

\

/

N=C=0

Solvent ■ -» Microwave

*-N

Figure 8.52 Microwave-assisted polycondensation of aromatic diisocyanates and dianhydrides.

viscosity (0.486 dL/g) of the polyamic acid prepared by a conventional heating was lower than that (up to 0.598 dL/g) of the polyamic acid prepared by microwave irradiation [106]. The microwave-assisted polycondensation of aromatic diisocyanates and dianhydrides for preparation of polyimide is shown in Figure 8.52 [107]. 8.2.17

Copolymers of Polyimides

The applications of the majority of polyimides are limited because of their infusibility and insolubility. Thus, for the processing of polyimides many copolyimides, such as poly(amide-imide)s/

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HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

poly(sulfone-imide)s, poly(ether-imide)s, poly(ester-imide)s [108] and other copolymers have been prepared. 8.2.17.1 Poly(urea-imide)s The introduction of ureylene linkage into polyimides is effective approaches to the modification of polyimides interface. However, the thermal stability of the polyurea-imides (PUI) is generally decreased in comparison with the corresponding homo polyimides due to the introduction of the ureylene linkage in the backbone. For example polyurea-imides were prepared by a three-step reaction procedure. First, the ureylene linkage chain-extended diamines (UCD) were synthesized by the reaction of 1 mol 2,4-diiso-cyanato toluene with 2 mol of a diamine in the presence of pyridine; the condensation polymerization then took place between UCD and 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) or pyromellitic dianhydride (PMDA), forming polyurea-amic acids (PUA). The polyurea-imides were finally obtained by imidizing the resulting PUA thermally. The modification of the polyimides' interfacial adhesion makes it of interest for adhesive applications [108]. The synthesis route is shown in Figure 8.53. 8.2.17.2 Poly(siloxaneimide)s (PSI) The polydimethylsiloxane repeating unit, -OSi(CH3)2-, is endowed with unusual properties such as high dynamic flexibility, high oxidative stability and excellent thermal stability. The incorporation of flexible polysiloxane into a PI backbone can yield processable H,N—Ar—NH,

:^4ΧΝ= >

Ö

< 5C, C«H,N Ξ-*. HPN—Ar-N-fl—N1И-гГ^Ч—NI-"—NH-Ar-I

* -Ar-N-LNH-гГ^Ч—Ν-Ί- N H - A r - N — Ì ^ ^ ^ j L f i - '

б

0

О 5

Аг-Ν-Ί—MH-rj^ »!—N—LNH-Ar-N

0

P (Ar

Figure 8.53 Three-step reaction procedure for synthesis of polyurea-imide.

POLYIMIDES

253

polysiloxaneimide (PSI) copolymers, silicon-containing polyimides, with good thermal mechanical properties. Therefore, PSI copolymers are attractive for aerospace applications as membranes and for electrolysis. Polysiloxaneimides (PSI) were synthesized by polycondensation of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) with oxydianiline (ODA) and ajrano-terminated siloxanes of varying molecular weights. Segments in PSI copolymers enhanced the thermo-oxidative stability [63]. The synthesis route is shown in Figure 8.54. 8.2.173

Poly(amide-imide)s

Replacement of polyimides by copolyimides such as poly(amideimide)s may be useful to tackle the intractability of polyimides. Poly(amide-imide)s are also expected to have the advantages of polyamides and polyimides, such as excellent mechanical and thermal properties as well as solvent resistance. A series of soluble poly(amide-imide)s were prepared from the diimide-dicarboxylic acid, 2,2-Ы5[4-(4-1птеШй|т^ор1\епоху)р]1еnyl]norbornane, and various diamines by the direct polycondensation in NMP containing CaCl2, using triphenylphosphite and pyridine as condensing agents. These poly(amide-imide)s were amorphous and were readily soluble in various solvents such as NMP, DMAc, DMF, DMSO, pyridine, cyclohexanone and tetrahydrofuran [109]. The synthesis route is shown in Figure 8.55 and Figure 8.56. 8.2.17.4

Poly(sulfone ether ester imide)s

Aromatic polymers that contain aryl ether or aryl sulfone linkages generally have lower glass transition temperatures, greater chain flexibility and tractability than their corresponding polymers without these groups in the chain Polymers containing both aryl ether and aryl sulfone linkages are amorphous, have low glass transition temperatures, and show excellent mechanical properties. The lower glass transition temperatures and also improved solubility are attributed to the flexible linkages that provide a polymer chain with a lower energy of internal rotation. Nowadays, poly(phenylene ether sulfone)s have been developed into commercial products due to their excellent thermooxidative stability, mechanical properties, and outstanding hydrolytic stability and recently many reports have been conducted in this field. A sulfone ether ester diamine was prepared by a threestep method. Reaction of 1,5-dihydroxy naphthalene with

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HANDBOOK OF ENGINEERING AND SPECIALTY THERMOPLASTICS

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