A Scalable Process for Synthesizing a Reactive Silicone-Acrylate Monomer

This study details the route selection, process development, and scale-up of a reactive silicone acrylate monomer, 3-(1,1,1,3,5,5,5-heptamethyltrisiloxane-3-yl)propyl methacrylate. A direct hydrosilylation reaction between allyl (meth)acrylate and 1,1,1,3,5,5,5-heptamethyltrisiloxane in the presence of Karstedt’s catalyst yielded the desired monomer in 46% yield. Two other byproducts were identified: an oxy-silyl ester and a propene hydrosilylated product. Prior to scale-up, the heat release associated with the hydrosilylation reaction was measured using a combination of isothermal reaction microcalorimetry and postreaction differential scanning calorimetry (DSC). The total heat release of hydrosilylation in the observed microcalorimetry experiment was −415 J/g. DSC studies detected the decomposition of the monomer at 280 °C, thereby revealing the risk of decomposition at elevated temperatures. Finding an inhibitor to prevent unwanted free radical polymerization of the monomer during scale-up and product isolation was crucial. 4-Hydroxy TEMPO was identified as the inhibitor of choice during the scale-up and distillation steps to isolate the monomer. Overall, the process optimization described here enabled a reliable, robust, and scalable method to produce multikilogram quantities of the 3-(1,1,1,3,5,5,5-heptamethyltrisiloxan-3-yl)propyl methacrylate monomer. This approach is also expected to be suitable for other reactive silicone-acrylate-based monomers.