LIVING CARBOCATIONIC POLYMERIZATION OF ISOBUTYLENE BY EPOXIDE/LEWIS ACID SYSTEMS: THE MECHANISM OF INITIATION A Dissertation Presented to The Graduate Faculty of The University of Akron In Partial Fulfillment of the Requirement for the Degree Doctor of Philosophy Serap Hayat Soytaş May, 2009 LIVING CARBOCATIONIC POLYMERIZATION OF ISOBUTYLENE BY EPOXIDE/LEWIS ACID SYSTEMS: THE MECHANISM OF INITIATION Serap Hayat Soytaş Dissertation Approved: Accepted: Advisor Department Chair Dr. Judit E. Puskas Dr. Ali Dhinojwala Committee Member Dean of the College Dr. Roderic P. Quirk Dr. Stephen Z. D. Cheng Committee Member Dean of the Graduate School Dr. Joseph P. Kennedy Dr. George R. Newkome Committee Member Date Dr. Li Jia Committee Member Dr. Chrys Wesdemiotis ii ABSTRACT The objective of the work presented in this dissertation was to generate a fundamental understanding of the synthesis of star-branched polyisobutylenes (PIBs) arising from hexaepoxysqualene (HES)/Lewis acid (LA) initiating systems, using BCl3 and TiCl4 as LAs. The understanding of initiation and propagation mechanisms by HES is crucial to control the number of arms and arm lengths of star PIBs expected from this initiator. The initiation by monofunctional epoxides, such as α-methylstyrene epoxide (MSE), 1,2- epoxy-2,4,4-trimethylpentane (TMPO-1), and 2,3-epoxy-2,4,4-trimethylpentane (TMPO- 2), was investigated. In situ FTIR spectroscopy, which was highly utilized in this research, provided valuable information. Most importantly, the ability to identify the head group by in situ FTIR of growing PIB chains initiated by an epoxide, i.e. the –C–O–LA complex, contributed significantly to the understanding of initiation of IB polymerization. This technique allowed the monitoring of the rate of initiation with the multifunctional epoxy initiator. Previous research showed that TiCl4 gave 40% initiating efficiency in conjunction with the aromatic epoxy initiator MSE, whereas the aliphatic initiators TMPO-1 and TMPO-2 gave only 3 and 10% efficiency, respectively. In this research it was found that BCl3 is more efficient with the aliphatic initiator, TMPO-1, yielding an iii asymmetric telechelic PIB carrying an α-primary OH and an ω-tertiary Cl functional group with 70% initiator efficiency, while MSE gave only 1-4% efficiency. The TMPO- 2/BCl3 system gave 20% initiator efficiency. The various initiation mechanisms were discussed. IB polymerization was successfully initiated by HES in the presence of excess BCl3 and monitored by in situ FTIR spectroscopy. The gradual increase of the IR band assigned to the –C–O–BCl2 group demonstrated that slow initiation was occurring. Chain extension with the HES/BCl3 initiated PIB was achieved leading to high molecular weight PIBs in the presence of TiCl4. It was also demonstrated for the first time that BCl3 invariably leads to β-proton expulsion, leading to chain transfer in IB polymerization. In addition, 1,2-epoxycyclohexane and epoxycyclohexyl-functional siloxanes, i.e. epoxycyclohexylisobutyl polyhedral oligomeric silsesquioxane (POSS) and bis[3,4- (epoxycyclohexyl)ethyl]tetramethyldisiloxane, were found to be initiators for the polymerization of IB. 1,2-epoxycyclohexane/TiCl4 was an efficient initiating system for the IB polymerization yielding up to 45% initiator efficiency. It was proposed that initiation of IB polymerization involves an SN2 reaction between IB and TiCl4- coordinated epoxide. iv DEDICATION I dedicate this dissertation to the loving memory of my father, Ismail Hayat. v ACKNOWLEDGEMENTS I would like to express my gratitude to my advisor Dr. Judit E. Puskas for her guidance, support and encouragement throughout the course of this research. I would like to thank all my group members for their help. I would like to thank my graduate committee members, Dr. Roderic P. Quirk, Dr. Joseph P. Kennedy, Dr. Li Jia and Dr. Chrys Wesdemiotis. I would also like to thank Dr. David A. Modarelli for helpful discussions in computational approach of epoxide reactions, Dr. Goy Teck Lim for his help in TEM analysis, and Dr. Val Krukonis and Dr. Paula Wetmore for supercritical fluid fractionation. I would like to acknowledge financial support by LANXESS Inc., Canada, and by the National Science Foundation under DMR-0509687. I would like to thank The Ohio Board of Regents and The National Science Foundation (CHE-0341701 and DMR- 0414599) for funds used to purchase the NMR instrument used in this work. Finally, I would like to thank my family for their support throughout my education and my husband, Mehmet, whose unconditional love and support have helped to make this possible. vi TABLE OF CONTENTS Page LIST OF TABLES............................................................................................................. xi LIST OF FIGURES .......................................................................................................... xii LIST OF SCHEMES...................................................................................................... xviii CHAPTER I. INTRODUCTION .........................................................................................................1 II. BACKGROUND ...........................................................................................................7 2.1. Controlled/Living Carbocationic Polymerization of IB ..........................................7 2.1.1. The Role of Additives in Living IB Polymerization......................................11 2.2. Ring-opening Polymerization (ROP) of Epoxides ................................................13 2.2.1. Cationic Polymerization of Epoxides.............................................................13 2.3. Epoxy Initiators for IB Polymerizations ................................................................18 2.4. Boron Trichloride as a Coinitiator in IB Polymerizations .....................................30 2.5. In situ FTIR Monitoring.........................................................................................32 2.6. Star-branched Polymers .........................................................................................34 2.6.1. Arm-first Method: Linking Agent..................................................................35 2.6.2. Arm-first Method: Microgel Core..................................................................40 2.6.3. Core-first Method...........................................................................................43 2.7. Characterization of Star Polymers .........................................................................51 vii 2.7.1. Dilute Solution Properties..............................................................................56 2.7.2. Glass Transition .............................................................................................57 III. EXPERIMENTAL.......................................................................................................59 3.1. Materials ................................................................................................................59 3.2. Instrumentation/Characterizations .........................................................................60 3.2.1. Fourier Transform Infrared (FTIR) Spectroscopy .........................................60 3.2.2. 1H and 13C Nuclear Magnetic Resonance (NMR) Spectroscopy ...................62 3.2.3. Size Exclusion Chromatography (SEC).........................................................62 3.2.4. Transmission Electron Microscopy (TEM) ...................................................63 3.3. Procedures..............................................................................................................63 3.3.1. Initiator Syntheses..........................................................................................63 3.3.2. Polymerizations..............................................................................................65 3.3.2.1. General Procedure ..................................................................................66 3.3.2.2. Real-time FTIR Monitoring....................................................................66 3.3.2.3. Screening Reactions ...............................................................................67 3.3.2.4. Two-stage Polymerizations ....................................................................68 IV. RESULTS AND DISCUSSION..................................................................................70 4.1. Investigation of the Mechanism of Initiation and Propagation of Epoxy-initiated IB Polymerizations using Monofunctional Epoxides...................70 4.1.1. Aromatic Epoxy Initiator: α-Methylstyrene Epoxide (MSE) ........................70 4.1.1.1. Real-time FTIR Monitoring of the Reaction of MSE with TiCl4 in the Absence of IB......................................................................71 4.1.1.2. Real-time FTIR Monitoring of the Reaction of MSE with TiCl4 in the Presence of IB.....................................................................79 viii 4.1.1.3. Real-time FTIR Monitoring of the Reaction of MSE with BCl3 in the Absence of IB ......................................................................84 4.1.1.4. The Reaction of MSE with BCl3 in the Presence of IB..........................90 4.1.2. Aliphatic Epoxy Initiator I: 1,2-Epoxy-2,4,4-trimethylpentane (TMPO-1) ......................................................................................................93 4.1.2.1. Real-time FTIR Monitoring of the Reaction of TMPO-1 with BCl3 in