Grignard coupling-based synthesis of vinyl-substituted hydridopolycarbosilane: effect of starting material and polymerization behavior

Despite the multitude of available alternatives, the Grignard coupling-based synthesis of polycarbosilanes remains attractive, offering the benefit of easy structural design. Moreover, this method allows one to obtain a polymer precursor with the stoichiometric Si : C ratio required for SiC ceramic production and is also suited for the synthesis of polymers containing curable functional groups (e.g., allyl and vinyl). Herein, vinyl-substituted hydridopolycarbosilane was synthesized from three different starting materials (Cl3SiCH2Cl, (MeO)3SiCH2Cl, and (EtO)3SiCH2Cl) using Grignard coupling, and the effects of starting material on polymer growth behavior were investigated. The alkoxysilane starting materials had the advantage of being safe to handle, but had a limitation in polymer growth. The largest molecular weight was observed for Cl3SiCH2Cl, although side reactions occurred. This behavior was ascribed to the retention of unreacted –SiCH2Cl groups contributing to polymer growth via coupling with neighboring polymer chains.