SYNTHESIS AND CHARACTERIZATION OF THERMOPLASTIC POLYPHENOXYQUINOXALINES A Dissertation Presented to The Graduate Faculty of the University of Akron In Partial Fulfillment of the Requirement for the Degree Doctor of Philosophy Haci Bayram Erdem May, 2008 © 2008 HACI BAYRAM ERDEM ALL RIGHTS RESERVED SYNTHESIS AND CHARACTERIZATION OF THERMOPLASTIC POLYPHENOXYQUINOXALINES Haci Bayram Erdem Dissertation Approved: Accepted: ______________________________ _____________________________ Advisor Department Chair Frank W. Harris Mark D. Foster ______________________________ _____________________________ Committee Member Dean of the College Stephen Z. D. Cheng Stephen Z. D. Cheng ______________________________ _____________________________ Committee Member Dean of the Graduate School Judit Puskas George R. Newkome ______________________________ _____________________________ Committee Member Date Roderic P. Quirk ______________________________ Committee Member David A. Modarelli ii ABSTRACT This research was divided into two main parts. In the first part, a new facile route to relatively inexpensive thermoplastic polyphenoxyquinoxalines was developed. The synthetic route involves the aromatic nucleophilic substitution reaction of bisphenols with 2,3-dichloroquinoxaline. The dichloro monomer was prepared in two steps. In the first step, oxalic acid was condensed with o-phenylenediamine to give 2,3- dihydroxyquinoxaline. In the second step, 2,3-dihydroxyquinoxaline was treated with thionyl chloride to give 2,3-dichloroquinoxaline. This monomer was successfully polymerized with bisphenol-A, bisphenol-S, hexafluorobisphenol-A and 9,9-bis(4- hydroxyphenyl)fluorenone. Hydroquinone and biphenol, however, can not be polymerized to high molecular weight polymers because of the premature precipitation of crystalline oligomers. The glass transition temperatures of the high molecular weight polymers prepared from a series of bisphenols range from 191 °C to 279 °C, and their thermal decomposition temperatures are around 500 °C. The polymers are soluble in a wide range of solvents and can be solution-cast into thin films that are colorless and transparent. The polymers have tensile strengths ranging from 61 to 107 MPa, and tensile moduli ranging from 3.5 to 2.3 GPa. The synthesis of polymer obtained from 2,3- dichloroquinoxaline and bisphenol-A was scaled up to afford 500 g of material. This polymer is a thermoplastic with a melt-viscosity less than 1000 Pa.s. at 300 °C. The notched Izod impact strength of injection-molded samples of this polymer is 40.7 J/m. iii In the second part of this research, the synthetic method has been modified to allow the preparation of quinoxaline containing polyimides. Thus, 2,3- dichloroquinoxaline was treated either with p-nitrophenol followed by reduction of nitro groups, or with p-aminophenols to directly obtain the desired 2,3-(4- aminophenoxy)quinoxaline. This diamine was polymerized with 3,3’,4,4’- biphenyldianhydride, 4,4’-oxydiphthalic anhydride and 2,2’-bis(3,4- dicarboxyphenyl)hexafluoropropane dianhydride. The polymerizations were carried out by the two step method. The poly(amic acid) intermediates were thermally imidized. Although they have high molecular weights judged by their inherent viscosities ranging from 0.51 to 1.01, thin films of all these polyimides were brittle. The glass transition temperatures of the polyimides range from 259 °C to 282 °C with thermal decomposition temperatures around 550 °C. The polyimide obtained from 2,3-(4- aminophenoxy)quinoxaline and 3,3’,4,4’-biphenyldianhydride was found to be semi- crystalline. iv ACKNOWLEDGEMENTS I would like to thank to my advisor Dr. Frank W. Harris for his support, guidance and especially his patience. It is an honor for me being his last Ph. D. student. I would also thank to my committee members, Dr. Judit E. Puskas (Chairman), Dr. Roderic P. Quirk, Dr. David A. Modarelli and Dr. Stephen Z. D. Cheng for their numerous corrections and suggestions. In addition, I would like to thank Dr. Brian Knapp for being my first trainer in Harris’ Group. It is him that I owe most my laboratory skills. I would also like to thank Dr. Dong Zhong and Dr. Limin Sun for being my next tutors. I gratefully acknowledge Dr. John D. Harvey for his help in the preparation of this thesis. Finally, I thank my parents, Sukru and Emine Erdem. It is them that I dedicate this dissertation. v TABLE OF CONTENTS Page LIST OF TABLES…………………………………………………….…………………..x LIST OF FIGURES……………………………………………………………………....xi LIST OF SCHEMES………………………….………………………………………...xiii CHAPTER I. INTRODUCTION………………………………………………………………………1 II. HISTORICAL BACKGROUND…………………………………………………...….3 2.1 High Temperature/High Performance Polymers…………………………………...3 2.2 Synthesis of Polyquinoxalines (PQs) and Polyphenylquinoxalines (PPQs)………..4 2.2.1 Quinoxalines…………………………………………………………………...4 2.2.2 Polyquinoxalines (PQs) …………………………………………………….…5 2.2.3 Polyphenylquinoxalines(PPQs)………………………………………………..5 2.2.4 Properties of PQs and PPQs……………………………………………………6 2.2.4.1 Isomerism in PQs and PPQs………………………………………………7 2.2.4.2 Thermal Properties of PQs and PPQs……………………………………..8 2.3 Synthesis of Polyarylethers by Aromatic Nucleophilic Substitution Reaction…...10 2.3.1 Aromatic Nucleophilic Substitution Reactions……………………………....10 2.3.2 Development of Polymerizations by Aromatic Nucleophilic Substitution Reactions………………………………………………………………………....12 2.3.2.1. Strong Base vs. Weak Base Process in Polymerizations by SNAr……....17 vi 2.3.2.2 Reductive Dehalogenation Reactions……………………………………19 2.3.2.3 Cyclization in the Synthesis of Polysulfones……………………..…….21 2.3.3. Synthesis of Polyaryletherketones…………………………………………..23 2.3.4 Synthesis of Polyaryletherimides…………………………………………….24 2.3.5 Synthesis of Polyarylsulfides………………………………………………...26 2.3.6 Synthesis of Poly(aryletherphenyl quinoxalines) by SNAr Reaction………...27 2.4 Polyimides………………………………………………………………………...34 2.4.1 Synthesis of Polyimides……………………………………………………...34 2.4.1.1 Introduction………………………………………………………….…..34 2.4.1.2 Two-Step Method………………………………………………………..35 2.4.1.2.1 Thermal Imidization………………………………………………...37 2.4.1.2.2 Chemical Imidization………………………………………………..39 2.4.1.3 One-Step Method………………………………………………………...41 2.3.1.4 Synthesis of Polyimides by Transimidization…………………………...42 2.4.3 Poly (imide-aryl ether quinoxalines)………………………………………....43 2.4.4 Poly (ether imide)s Having Ortho-Linked Aromatic Units in the Main Chain.......................................................................................................................46 III.EXPERIMENTAL……………………………………………………...…………….50 3.1. Chemical Instrumentation………………………………………………………...50 3.2 Reagents and Solvents………………………………………………………...…..52 3.2.1 Reagents………………………………………………………………………52 3.2.2 Solvents…………………………………………………………………..…..53 3.3 Synthesis of Small Molecules……………………………………………………..54 vii 3.3.1 2,3-Dihydroxyquinoxaline (76a)……………………………………...……………54 3.3.2 2,3-Dichloroquinoxaline (75)…………………………………………..…….54 3.3.3 2,3-Diphenoxyquinoxaline (79)…………………………………………...….55 3.3.4 2,3-Bis(4-aminophenoxy)quinoxaline (94a)………………………………….55 3.3.5 2,3-Bis(4-nitrophenoxy)quinoxaline (97a)………………………………..….56 3.3.6 12H-Quinoxalino[2,3-b][1,4]benzoxazine (98)……………………………....57 3.3.7 2,3-Bis(2-aminophenoxy)quinoxaline (97b)……………………………….…58 3.3.8 2,3-Bis(2-nitrophenoxy)quinoxaline (94b)……………………………..…….58 3.4 Synthesis of Polymers (Macromolecules)………………………………………...59 3.4.1 Synthesis of Polyphenoxyquinoxalines……………………………………....59 3.4.1.1 Polymerization of 2,3-Dichloroquinoxaline with Bisphenol-A Using 100 % Excess Potassium Carbonate…………………………………....59 3.4.1.2 Polymerization of 2,3-Dichloroquinoxaline with Bisphenol-A Using 25 % Excess Potassium Carbonate…………………………………..…60 3.4.1.3 Polymerization of 2,3-Dichloroquinoxaline with 9,9’-Bis(4-hydroxyphenyl)fluorene…...………………………………………61 3.4.1.4 Polymerization of 2,3-Dichloroquinoxaline with Bisphenol-S……...…..62 3.4.1.5 Polymerization of 2,3-Dichloroquinoxaline with Hexafluorobisphenol-A………………………………………………………..63 3.4.1.6 Polymerization of 2,3-Dichloroquinoxaline with Hydroquinone…….….63 3.4.1.7 Polymerization of 2,3-Dichloroquinoxaline with Biphenol……………...64 3.4.1.8 Polymerization of 2,3-Dichloroquinoxaline with Bisphenol-A (50 %) and Hydroquinone (50 %)………………………………65 3.4.1.9 Polymerization of 2,3-Dichloroquinoxaline with Bisphenol-A (50 %) and Biphenol (50 %)……………………………….……66 3.4.2 General Procedure for the Synthesis of Polyimides………………………….66 viii 3.5 General Procedure for the Preparation of Thin Films for Tensile Testing………..67 3.6 General Procedure for the Sample Preparation Using Injection Molding………...67 IV. RESULTS AND DISCUSSION……………………………………………………..68 4.1 Synthesis and Characterization of Polyphenoxyquinoxalines…………………….68 4.1.1 Introduction…………………………………………………………………...68 4.1.2 Synthesis of 2,3-Dichloroquinoxaline………………………………………..69 4.1.3 Model Reaction with 2,3-Dichloroquinoxaline…………………..…………..74 4.1.4 Optimization of Polymerization Conditions…………………………….……76 4.1.5 Synthesis of Polyphenoxyquinoxalines……………………………….….…..85 4.1.6 Thermal Properties of Polyphenoxyquinoxalines……………………….…....90 4.1.7 Solubilities of the Polyphenoxyquinoxalines…………………………………92 4.1.8 Optical Properties of Polyphenoxyquinoxalines……………………….……..93 4.1.9 Tensile Properties of Polyphenoxyquinoxalines……………………………...97 4.1.10 Melt Processability of Polyphenoxyquinoxaline 85………..……………....99 4.1.11. Tensile Properties of Injection Molded Samples of 85 …...…………………....100 4.1.12. Impact Properties of Injection Molded Samples of 85……..……………..102 4.2 Poly(imide-aryl