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Polyacrylonitrile Copolymers: Effects of Molecular Weight, Polydispersity, Composition, and Sequencing on Thermal Ring- Closing Stabilization

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Polyacrylonitrile Copolymers: Effects of Molecular Weight, Polydispersity, Composition, and Sequencing on Thermal Ring- Closing Stabilization The University of Southern Mississippi The Aquila Digital Community Dissertations Fall 12-1-2015 Polyacrylonitrile Copolymers: Effects of Molecular Weight, Polydispersity, Composition, and Sequencing on Thermal Ring- Closing Stabilization Jeremy D. Moskowitz University of Southern Mississippi Follow this and additional works at: https://aquila.usm.edu/dissertations Part of the Polymer and Organic Materials Commons, Structural Materials Commons, and the Structures and Materials Commons Recommended Citation Moskowitz, Jeremy D., "Polyacrylonitrile Copolymers: Effects of Molecular Weight, Polydispersity, Composition, and Sequencing on Thermal Ring-Closing Stabilization" (2015). Dissertations. 173. https://aquila.usm.edu/dissertations/173 This Dissertation is brought to you for free and open access by The Aquila Digital Community. It has been accepted for inclusion in Dissertations by an authorized administrator of The Aquila Digital Community. For more information, please contact [email protected]. POLYACRYLONITRILE COPOLYMERS: EFFECTS OF MOLECULAR WEIGHT, POLYDISPERSITY, COMPOSITION, AND SEQUENCING ON THERMAL RING-CLOSING STABILIZATION by Jeremy Daniel Moskowitz A Dissertation Submitted to the Graduate School and the School of Polymers and High Performance Materials at The University of Southern Mississippi in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy December 2015 ABSTRACT POLYACRYLONITRILE COPOLYMERS: EFFECTS OF MOLECULAR WEIGHT, POLYDISPERSITY, COMPOSITION, AND SEQUENCING ON THERMAL RING-CLOSING STABILIZATION by Jeremy Daniel Moskowitz December 2015 Controlled polyacrylonitrile (PAN)-based carbon fiber precursors with defined molecular weights, polydispersities, compositions, and architectures have been prepared for their study on thermal ring-closing stabilization behavior. PAN and its copolymers of number average molecular weights exceeding 170,000 g/mol were successfully synthesized via low temperature reversible addition-fragmentation chain transfer (RAFT) polymerization. RAFT polymerizations of PAN-based precursors were compared to conventional free radical solution polymerizations with a focus on the effects of molecular weight and polydispersity on structural evolution and cyclization efficiency. When RAFT polymerization was extended to copolymers, it was found that RAFT copolymers achieved greater cyclization intensities and improved thermal stability as compared to analogous uncontrolled free radical copolymers. The greater thermal stability was attributed to the more controlled polymerization method and the reduction of chain transfer and small molecule defects. New comonomers were introduced for PAN-based precursors and explored in relation to traditional comonomers. N-isopropylacrylamide (NIPAM) was found to be a promising comonomer by simultaneously serving as a mediator to thermal cyclization as well as a plasticizer to facilitate processing and spinning. Utilizing RAFT polymerization ii in combination with a semibatch reaction technique the copolymer sequencing of p(AN- co-NIPAM) was systematically investigated. Results suggest that adjusting the feed rate of each comonomer affects the comonomer distribution along the backbone by offering tunable cyclization behaviors. Attempts were made to mediate tacticity of PAN to study effects of tacticity on cyclization. A series of Lewis acids and fluoroalcohols were employed as additives in the polymerization, but no changes in tacticity were observed. A 98/2 p(acrylonitrile-co-NIPAM) fiber was prepared from conventional free radical solution polymerization. The fiber morphology, characterized by Transmission Electron Microscopy (TEM), displayed minimal defects at the nanoscale with a characteristic ribbon-like wavy pattern. The degree of orientation in the fibers was found to exceed that of a commercial-grade PAN-based precursor. The thermo-oxidative stability of the lab-produced fiber shared similar characteristics to commercial fibers and has set the benchmark for future designs of PAN-based carbon fiber precursors. iii COPYRIGHT BY JEREMY DANIEL MOSKOWITZ 2015 POLYACRYLONITRILE COPOLYMERS: EFFECTS OF MOLECULAR WEIGHT, POLYDISPERSITY, COMPOSITION, AND SEQUENCING ON THERMAL RING-CLOSING STABILIZATION by Jeremy Daniel Moskowitz A Dissertation Submitted to the Graduate School and the School of Polymers and High Performance Materials at The University of Southern Mississippi in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Approved: ________________________________________________ Dr. Jeffrey Wiggins, Committee Chair Associate Professor, School of Polymers and High Performance Materials ________________________________________________ Dr. Sarah Morgan, Committee Member Associate Professor, School of Polymers and High Performance Materials ________________________________________________ Dr. Charles McCormick, Committee Member Professor, School of Polymers and High Performance Materials ________________________________________________ Dr. Robson Storey, Committee Member Professor, School of Polymers and High Performance Materials ________________________________________________ Dr. Derek Patton, Committee Member Associate Professor, School of Polymers and High Performance Materials ________________________________________________ Dr. Karen S. Coats Dean of the Graduate School December 2015 DEDICATION This dissertation is dedicated to my family for their constant love and support. To my parents, Barry and Tammy Moskowitz, for teaching me invaluable life lessons and making me the person I am today. To my brothers and sisters, Josh, Kelsey, Jessica, and Stan, for always being at my side providing advice, and leading the way. To Rachel, for her motivation, pushing me to constantly better myself, and for believing in me and loving me. vi ACKNOWLEDGMENTS I would like to acknowledge my advisor, Dr. Jeffrey S. Wiggins, for providing me the opportunities to grow as a professional. I am sincerely grateful for his selfless devotion towards my success as a graduate student. Dr. Wiggins put me in the driver seat from day one and allowed me to make the most of my graduate school experience. My confidence as a polymer scientist emanated through his hands-off management style and intellectual freedom. I would also like to acknowledge my committee members: Dr. Derek Patton, Dr. Charles McCormick, Dr. Sarah Morgan, and Dr. Robson Storey, whom all have given academic guidance and insight. I am thankful to Dr. Bronwyn Fox and her research group and Dr. Matthew Weisenberger for their collaboration. I would like to thank Dr. William Jarrett and David Delatte for their assistance with laboratory instrumentation throughout the years. I am also appreciative of Dr. Richard Liang and his research group at FSU to allow me to use their X-Ray Scattering instrument. I would also like to recognize Jody Wiggins, Stephanie Patton, and Charlene McMillin for all their help with lab supplies and organizing events. I would like to thank industry partners Rob Maskell, Al Thomas, Longgui Tang, Matt Jackson, and Steve Christensen for providing direction in my research. I would like to thank my peers for making me a more well-rounded scientist and teaching me throughout my graduate career: Brooks Abel, Chris Childers, Mark Early, Phil Pickett, and Robert Peterson. Finally, I would like to acknowledge all of the current and past members from Wiggins Research Group, in particular John Misasi and Brian Greenhoe, for sticking together and making graduate school more enjoyable, and also my undergraduates for their contributions in the lab: Jonathan, Cade, and Anthony. vii TABLE OF CONTENTS ABSTRACT ......................................................................................................................... i DEDICATION .................................................................................................................... v ACKNOWLEDGMENTS ................................................................................................ vii LIST OF ILLUSTRATIONS .............................................................................................. x LIST OF TABLES ........................................................................................................... xvi LIST OF SCHEMES...................................................................................................... xviii CHAPTER I. INTRODUCTION ................................................................................................ 1 Carbon Fiber Composites Polyacrylonitrile (PAN)-Based Carbon Fiber Precursors Processing of PAN-based Precursors Polymer Precursor Properties and Their Effects on Carbon Fiber Processing Controlled/Living Radical Polymerization (CLRP) of PAN Copolymer Sequencing Tacticity Control of PAN Research Overview II. MATERIALS, METHODS, AND PROCEDURES .......................................... 21 Materials Synthesis of Polyacrylonitrile and its Copolymers Methods of Characterization III. HIGH MOLECULAR WEIGHT AND NARROW POLYDISPERSITY POLYACRYLONITRILE VIA LOW TEMPERATURE RAFT POLYMERIZATION ......................................................................................... 39 Abstract Results and Discussion Summary IV. STABILIZATION OF POLYACRYLONITRILE: CONVENTIONAL FREE RADICAL VERSUS CONTROLLED RAFT POLYMERIZATIONS ............. 62 viii Abstract Results and Discussion Summary V. AN INVESTIGATION OF N-ISOPROPYLACRLYAMIDE CONTAINING PAN-COPOLYMERS AND THE STABILIZATION BEHAVIOR OF PAN- BASED RAFT
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