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The Role of Hydrosilanes in the Preparation of Silicones

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The Role of Hydrosilanes in the Preparation of Silicones THE ROLE OF HYDROSILANES IN THE PREPARATION OF SILICONES Ph.D. Thesis – Mengchen Liao; McMaster University –Chemistry and Chemical Biology THE ROLE OF HYDROSILANES IN THE PREPARATION OF SILICONES By MENGCHEN LIAO B. ENG. A Thesis Submitted to the School of Graduate Studies In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy McMaster University © CopyriGht by MenGchen LIAO, April 2021 Ph.D. Thesis – Mengchen Liao; McMaster University –Chemistry and Chemical Biology Doctor of Philosophy (2021) McMaster University (Chemistry), Hamilton, Ontario TITLE: The Role of Hydrosilanes in the Preparation of Silicones AUTHOR: MenGchen Liao, B. EnG. (XianGtan University) SUPERVISOR: Dr. Michael A. Brook NUMBER OF PAGES: xvi, 262 Ph.D. Thesis – Mengchen Liao; McMaster University –Chemistry and Chemical Biology Abstract Silicone polymers (PDMS) are widely used for a large range of applications from automotive to cosmetic industries owing to their unique properties, such as electrical resistance, biocompatibility, and gas permeability. Conventionally, linear silicone polymers are produced by acid or base-catalyzed equilibration, leading to broad molecular weight dispersities, and high concentrations of a controversial monomer that requires removal. Therefore, in the first part of the research, we developed a new hydrolytic route to linear silicone polymers that is both simple and inexpensive. The small hydrosilane tetramethyldisiloxane (HSi(CH3)2OSi(CH3)2H) was polymerized to hydride-terminated PDMS (HSi-PDMS-SiH) using only water as a reagent, a process that has industrial potential. The product can further be converted into silicone block copolymers, elastomers, foams and resins. We broadened the studies to consider the incorporation of different functional groups (vinyl and alkoxy groups) into silicones, including developing methods to control their precise locations in polymers and to synthesize dendritic hyperbranched silicone polymers in a controllable manner. The ability of silanes to behave as functional reducing agents was examined. A series of model compound studies, including reduction with benzyl disulfide and tetrasulfide, were conducted to illustrate the mechanism of S-S bond cleavage using a catalytic amount of B(C6F5)3. The effect of sterics on the rates of hydrolysis of the product S-Si compounds allowed consideration of the use of this strategy to protect for thiol groups. In addition, the relative reactivities of hydrosilane with different functional groups including mercaptan (SH), disulfide (SS) and ethoxy i Ph.D. Thesis – Mengchen Liao; McMaster University –Chemistry and Chemical Biology (SiOEt) were also mapped out as follows: S-H>S-S>SiOEt. These investigations allowed us to exploit hydrosiloxanes for the reduction of the sulfur crosslinks in used rubber tires; current reuse methodologies either utilize harsh conditions or occur in low yields. ii Ph.D. Thesis – Mengchen Liao; McMaster University –Chemistry and Chemical Biology 父母之恩,云何可报?慈如河海,孝若涓尘。 ——致父母亲 iii Ph.D. Thesis – Mengchen Liao; McMaster University –Chemistry and Chemical Biology Acknowledgements This dissertation has been a labor of love, but it would never have been possible without the support and encouragement from my supervisor, Dr. Michael Brook who offered me tremendous and insightful commentaries and guidance that helped the project take shape. It is both an honor and a privilege to be your student. I would like to thank him and also everyone in my committee, Dr. Jose Moran- Mirabal and Dr. Ryan Wylie, for guiding this dissertation generously and shaping my intellectual life over the past five years. As with any research activity there were many, many challenges. I am very grateful that the committee stuck with me. Here, I would also like to thank Dr. Kirk Green, Dr. Bob Berno and Dr. Hilary Jenkins who offered me valuable suggestions for characterizations. To all the labmates in Brook’s lab, thank you for providing me a friendly and supportive working environment, Dr. Miguel Melendez, Scott Laengert, Dr. Alyssa Schneider, and the list go on. Especially, I would like to thank Dr. Yang Chen for offering me substantial advice and assistance along the way. I would also like to thank Dr. Sijia Zheng and Dr. Shuai Liang for being great friends to me and I have gained comfort and consolations from our endless conversations that propelled this project to completion. I would also like to take the chance to thank the friends that I met at McMaster, Dr. Fei Xu and Mr. Chenlong Xie, Dr. Jing Zhao and Dr. Wenwen Xu, Sheilan Sinjari (and more) for all the jokes and complaints! I would like to thank my friends Wenzhen Cao, Qing He, Weiwei Zhao and Jingshu Yin for all the delicious food and happy gatherings together. I would also like to thank Sheila for her support and encouragement throughout the process. iv Ph.D. Thesis – Mengchen Liao; McMaster University –Chemistry and Chemical Biology Moreover, I would like to express my sincere thanks to ‘ready-to-be’ Dr.-Ing. Fengze Jiang for his encouragement and suggestions that consoled me during the last stage of my Ph.D. life. Last but certainly not least, I would like to thank my parents for their immense trust and supports throughout my life. Thank you for your hard work and sacrifice, thank you for being proud of me. And also, my grandparents, thank you for the encouragement and caring. 感谢祖父母，外祖父母在求学路上给予的鼓励与支持。 Even though there’s an end to the words, there is never an end to their meaning. v Ph.D. Thesis – Mengchen Liao; McMaster University –Chemistry and Chemical Biology Table of content Chapter 1: Introduction ........................................................................................ 1 1.1. Polysiloxanes: From a historical perspective ..................................... 1 1.2. Silicones: From structures to properties ............................................. 3 1.3. Silicones: Traditional chemistry for preparation .............................. 5 1.3.1. Synthesis of polydimethylsiloxanes fluids ...................................... 5 1.3.2. Syntheses of crosslinked silicone materials .................................... 8 1.4. Research frontiers for organosilicon – Develop methods to permit structural control and introduction of functional groups ........................... 12 1.4.1. Hydrosilane (SiH)- A synthetic handle ......................................... 13 1.4.2. B(C6F5)3- A strong Lewis acid catalyst ........................................ 13 1.4.3. The Piers-Rubinsztajn reaction ..................................................... 14 1.4.4. Other nucleophiles and relative reactivities .................................. 16 1.4.5. The metathesis of hydrosilanes with itself .................................... 17 1.4.6. Preparation of structured silicone copolymers via PR reaction .... 19 1.4.7. Preparation of branched silicones via PR reaction and then platinum- catalyzed hydrosilylation .............................................................................. 20 1.5. Research frontiers for organosilicon- Exploration into sulfur ....... 20 1.5.1. Thiol-functionalized silicones ....................................................... 20 1.5.2. Organosilicon in organic synthesis ............................................... 21 1.5.3. Organosilicon in vulcanized rubber synthesis .............................. 22 1.6. Thesis objectives .................................................................................. 24 1.6.1. New route to silicone materials using hydrosilane and water in the presence of B(C6F5)3 catalyst ........................................................................ 24 1.6.2. Spatially controlled silicones ........................................................ 26 1.6.3. Silylation and desilylation of sulfur compounds .......................... 27 1.7. References ............................................................................................ 29 Chapter 2: When Attempting Chain Extension, Even Without Solvent, It Is Not Possible to Avoid Chojnowski Metathesis Giving D3 ................................ 37 2.1. Abstract ................................................................................................ 37 2.2. Introduction ......................................................................................... 37 2.3. Experimental ....................................................................................... 42 2.3.1. Materials ....................................................................................... 42 2.3.2. Methods ......................................................................................... 42 2.4. Results .................................................................................................. 49 vi Ph.D. Thesis – Mengchen Liao; McMaster University –Chemistry and Chemical Biology 2.4.1. High molecular weight PDMS preparation using hydrolysis ....... 52 2.4.2. Managing Cyclics ......................................................................... 54 2.5. Conclusions .......................................................................................... 60 2.6. Acknowledgments ............................................................................... 60 2.7. References ............................................................................................ 61 2.8. Appendix 1- Supporting Information ............................................... 64 1 2.8.1. Calculation of polymer molecular weight (Mn) using H NMR ... 64 2.8.2. ‘Wet’
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