Isomer-Free Synthesis of Silicone Polyethers

Hydrosilylation is one of the most ubiquitous reactions in silicone chemistry, used to make and cure a variety of products that consumers interact with on a daily basis. A longstanding complication with this reaction is the propensity of platinum catalysts to isomerize terminal alkenes to internal alkenes that are far less reactive toward hydrosilylation. Here, we demonstrate that with the appropriate choice of Si–H substrate and control over the reaction conditions, these internal isomers can be reisomerized to the terminal alkene to then undergo hydrosilylation with Karstedt’s catalyst, an industry standard platinum catalyst. This ultimately leads to hydrosilylation products with no residual isomer content, on time scales relevant for industrial production. Only -SiMe₂H (M′) substrates were capable of producing isomer free products, with -SiMeH- (D′) units as substrates resulting in high (>13 mol %) residual isomerized alkenes. Using this technology, low-isomer silicone polyether materials were synthesized with a final isomer content <1 mol %. Due to the propensity of residual isomerized species to undergo hydrolysis to propionaldehyde and other malodorous acetals, this technology is expected to reduce the odor of residual alkenyl species in silicone polyether materials in a cost-effective manner for industrial production.