Date/Time
Date(s) - 10/12/2020
1:30 pm - 2:30 pm

Title: The Role of Hydrosilanes (SiH) in the Preparation of Silicones

Date: December 10th, 2020

Time: 1:30 p.m.

Zoom: link available from macchem@mcmaster.ca

Supervisor: Dr. Michael Brook

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 my 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 converted to commercial 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.1
We broadened the studies to consider the incorporation of different functional groups into silicones, including developing methods to control their precise locations in polymers. These included both silicone thiols and disulfides. A series of model compound studies, including with benzyl disulfide and tetrasulfide, were conducted to illustrate the mechanism of disulfide bond cleavage in up to 90% yield with <1 mol% B(C6F5)3.2 When exposed to catalytic amount of B(C6F5)3 (0.8 mol%), the relative reactivities of hydrosilane with different functional groups including mercaptan (SH), disulfide (SS) and ethoxy (SiOEt) were also mapped out. The relative reactivity of commercially available disulfide coupling agents was found to be S-H>S-S>SiOEt.
These investigations allowed us to exploit hydrosiloxanes for the reduction of the sulfur crosslinking sites in used rubber tires; current reuse methodologies either utilize harsh conditions or occur in low yields.

References
(1) Liao, M.; Schneider, A. F.; Laengert, S. E.; Gale, C. B.; Chen, Y.; Brook, M. A. Living Synthesis of Silicone Polymers Controlled by Humidity. Eur. Polym. J. 2018, 107 (July), 287–293.
(2) Zheng, S.; Liao, M.; Chen, Y.; Brook, M. A. Dissolving Used Rubber Tires. Green Chem. 2020, 22 (1), 94–102.