ABSTRACT Title of Document: Degenerative Transfer Living Ziegler-Natta Polymerization of α-Olefins Yonghui Zhang, Doctor of Philosophy, 2005 Directed By: Professor Lawrence R. Sita Department of Chemistry and Biochemistry A degenerative transfer (DT) living Ziegler-Natta polymerization system based on 5 the cyclopentadienyl amidinate zirconium complex, (η -C5Me5)ZrMe2[N(t- Bu)C(Me)N(Et)] (19), has been studied in detail. Compound 19 is an active pre- catalyst for the living and stereospecific polymerization of α-olefins, upon activation by a stoichiometric amount of [PhNHMe2][B(C6F5)4] (18). With a substoichiometric amount of 18, degenerative transfer living Ziegler-Natta polymerization occurs. The extremely fast interconversion between an active cationic species and a dormant neutral species via a methyl (MeDeT) or chloride (ChloDeT) group is essential for degenerative transfer to occur (Rex>>Rp). Under MeDeT conditions, atactic polyolefins are produced due to the configurational instability of the amidinate ligand in its dormant state, with the rate of epimerization being much faster than the rate of propagation (Repi >>Rp). The configurational stability of all the zirconium species involved in ChloDeT ensures that this degenerative transfer living polymerization is stereospecific. 5 5 Methylating reagents (η -C5Me5)ZrMe2[N(t-Bu)C(t-Bu)N(Et)] (34) and (η - C5Me5)ZrMe2[NCH2(t-Bu)C(Me)N(Et)] (39) were synthesized to provide a means by which a fully activated polymerization system could be brought under degenerative transfer conditions. Adding 18 and 34 or 39 alternatively to a living polymerization system produces well-defined atactic-isotactic stereoblock polyolefins. This allows, for the first time, the production of stereoblock polyolefins with controlled block length, block tacticity and block placement within a polymer backbone. 5 Living stereoselective propylene polymerizations were carried out by {(η - C5Me5)ZrMe[N(t-Bu)C(Me)N(Et)]}[B(C6F5)4] (32). A mmmm of 73% and a σ value of 94% were determined, which is the highest among living propylene polymerizations reported to date. Under degenerative transfer conditions, atactic PP was produced. Using the developed methodology, a family of different atactic- isotactic stereoblock polypropylene (sb-PP) was synthesized with controlled block length, block tacticity for the first time. Preliminary data shows excellent elastomeric properties for the sb-PPs that are synthesized. The amidinate zirconium initiator was chemically immobilized to polystyrene- based solid support via deprotonation and nucleophilic addition reactions at the distal 5 position of (η -C5Me5)ZrCl2[N(t-Bu)C(Me)N(Et)] (40). Heterogeneous initiator (58) polymerizes α-olefins in a living and isospecific fashion. Also, a long shelf time was observed for 58 at room temperature. This is the first heterogeneous living Ziegler- Natta stereospecific catalyst reported to date. DEGENERATIVE TRANSFER LIVING ZIEGLER-NATTA POLYMERIZATION OF α-OLEFINS By Yonghui Zhang Dissertation submitted to the Faculty of the Graduate School of the University of Maryland, College Park, in partial fulfillment of the requirements for the degree of Doctor of Philosophy 2005 Advisory Committee: Professor Lawrence R. Sita Chair Professor Bryan W. Eichhorn Professor Jeffery T. Davis Associate Professor Lyle Isaacs Professor Kyu-Yong Choi © Copyright by Yonghui Zhang 2005 Dedication To my wife Jiemin and daughter Joyce. ii Acknowledgements I’d like to thank my advisor, Professor Lawrence R. Sita, for his supervision during my four years research at the University of Maryland. Professor Sita’s tremendous enthusiasm for chemistry, unique angles of observation, knowledge of organometallic chemistry and brilliant ideas have benefit my research significantly. I am also very grateful for his encouragement. I not only learned chemistry from him, but also how to be a scientist. It has been an incredible four years. My committee has given me great support not only for course work, but also for advice and suggestions. Among which, especially, Dr. Davis, Dr. DeShong, Dr. Eichhorn, Dr. Isaacs, Dr. Falvey, Dr. Morehead, Dr. Vedernikov and Dr. Rokita have been especially helpful. Without their help, this work would not be possible. Special thanks goes to the Sita group, both former and current members: Dr. Richard Keaton, Matthew B. Harney, Andrea E. Young, Lixin Wang, Dr. Denis A. Kissounko, Albert Epshteyn, Erin K. Reeder, Wei Zhang, Hao He and Samuel Hundert. I’d like to thank Dr. Keaton, Matthew and Lixin for their support, discussion and their partial contribution to this dissertation. NMR and X-Ray diffraction are the two major analytical techniques used in this dissertation. Without the help from Dr. Yiu-Fai Lam, Dr. Yinde Wang and Dr. James Fettinger, this work would be impossible. Finally, I would like to thank my family for their support, especially my parents Yizhong Zhang, Liujiao Chen and my wife Jiemin Lu. iii Table of Contents Dedication.. ................................................................................................................... ii Acknowledgements...................................................................................................... iii Table of Contents......................................................................................................... iv List of Abbreviations ................................................................................................... vi List of Figures ............................................................................................................. vii List of Schemes........................................................................................................... xii List of Tables .............................................................................................................. xv List of Numbered Compounds................................................................................... xvi Chapter 1 Introduction ................................................................................................. 1 1.1 Early Development of Ziegler-Natta Polymerization ........................................ 1 1.1.1 Discovery .................................................................................................... 1 1.1.2 Metallocene Initiators ................................................................................. 3 1.2 Dynamic Polymerization Systems ................................................................... 12 1.2.1 Chain End Epimerization.......................................................................... 12 1.2.2 Site-Isomerization ..................................................................................... 16 1.2.3 Oscillating Metallocene ............................................................................ 21 1.2.4 Binary System........................................................................................... 25 1.3 Living Ziegler-Natta Polymerization and Post-Metallocene Polymerization.. 27 1.3.1 Living Polymerization .............................................................................. 27 1.3.2 Group 4 Post-Metallocene Initiators for Living Ziegler-Natta Polymerizations......................................................................................... 28 1.4 Sita System: More Detailed Picture................................................................. 38 Chapter 2 Methyl Group Degenerative Transfer Ziegler-Natta Polymerization 164 MeDeT .................................................................................................. 42 2.1 Background...................................................................................................... 42 2.2 Degenerative Transfer Ziegler-Natta Polymerization...................................... 43 2.3 Mechanistic Studies ......................................................................................... 49 2.4 Kinetic Analysis............................................................................................... 51 2.5 Origin of the Loss of Stereospecificity ............................................................ 57 2.6 Synthesis of Multi-Stereoblocks ...................................................................... 66 192 2.7 Hafnium MeDeT .......................................................................................... 75 2.8 Conclusions...................................................................................................... 79 2.9 Experimental .................................................................................................... 79 Chapter 3 Chloride Group Degenerative Transfer Ziegler-Natta Polymerization ChloDeT.................................................................................................... 91 3.1 Background...................................................................................................... 91 3.2 Stereospecific Degenerative Transfer Living Polymerization......................... 92 3.3 Halide Abstraction Reagents............................................................................ 96 3.4 Kinetic of ChloDeT.......................................................................................... 99 3.5 Applications of ChloDeT............................................................................... 101 3.6 Conclusion ..................................................................................................... 106 Chapter 4 Heterogeneous Living Ziegler-Natta Polymerization of α-olefins ......... 117 iv 4.1 Background.................................................................................................... 117 217 4.2 Deprotonation of Zirconium Amidinate .................................................... 119 4.3 Reaction with Electrophiles ........................................................................... 121 224 4.4 Preparation of the Solid-Supported Initiator .............................................. 126 4.5 Living Polymerization of 1-Hexene............................................................... 127 4.6 Conclusions.................................................................................................... 130 4.7 Experimental .................................................................................................. 130 Chapter 5 Living 1-Butene and Propylene Polymerization ..................................... 135 5.1 Background.................................................................................................... 135 5.2 Polymerization of 1-Butene Stereoblock ....................................................... 136 5.3 Polypropylene Polymerization....................................................................... 140 5.4 Kinetic Analysis............................................................................................. 145 5.5 Methylating Reagents .................................................................................... 151 5.6 Synthesis of PP Stereoblocks......................................................................... 152 5.7 Polypropylene Produced by Formamidinate Zirconium Complex ................ 160 5.8 Conclusions.................................................................................................... 163 5.9 Experimental .................................................................................................. 164 Chapter 6 Conclusions ............................................................................................. 171 References................................................................................................................. 173 v List of Abbreviations σ stereoselectivity of pro-chiral monomer insertion into the cationic propagating centers acac acetylaceton AFM atomic force microscopy i-Bu iso-butyl t-Bu tert-butyl CGC constrained geometry catalyst ChloDeT chloro group degenerative transfer 5 Cp cyclopentadienyl (η -C5H5) 5 Cp* pentamethylcyclopentadienyl (η -C5Me5) Cy cyclohexyl DMA dynamic mechanic analysis DSC diferential scaning calorimetry DP degre of polymerization DT degenerative transfer EXSY exchange NMR spectroscopy GC gas chromatography GPC gel permeation chromatography Ind indenyl MAO methylaluminoxane mMAO modified MAO MeDeT methy group degenerative transfer mmmm isotactic content for PP microstructure pentad analysis Mn number average molecular weight Mw weight average molecular weight PDI polydispersity index (Mw/Mn) PE polyethylene PH poly(1-hexene) PMCP poly(methylenecyclopentane) PO poly(1-octene) PP polypropylene a-PP atactic polypropylene el-PP elastomeric polypropylene iso-PP isotactic polypropylene sb-PP stereoblock polypropylene syndio-PP syndiotactic polypropylene PVCH poly(vinylcyclohexane) R any alkyl group Rp rate of propagation Repi rate of epimerization Rex rate of exchange Tm melting point vi