Effect of high‐pressure carbon dioxide on thermal conversion process of polydimethylsilane to Si–C backbone polymers

Polycarbosilane (PCS) is synthesized from polydimethylsilane (PDMS) by thermal condensation reaction in an inert atmosphere. In the new process described in this article, CO2 at high pressure (2-10 bar) was introduced into the system before the condensation reaction of PDMS. Si-C backbone formation process was accelerated at 340-360oC, and brown "PCS" liquid was obtained at 380oC. Polymer recovery increased from 60% (in a pressure vessel with a N-2 atmosphere) to >95% in CO2 atmosphere at 10 bar. The apparent viscosity also increased at high CO2 pressures. Spectrum analysis indicates the existence of the Si-CH2-Si, Si-O-Si bridges, and Si-H bonds in the heat-treated product. The viscous liquid "PCS" obtained at 380oC is stable up to 200oC. However, at temperatures of 200-600oC, the volatilization of macromolecular species proceeded, and the resulting ceramic yield at 1000oC was 29 mass%. In the CO2 treatment, product solidified at 420oC and ceramic yield increased to 56%. The volatilization of macromolecules, however, proceeded in two steps at 200-400oC and 600-800oC. When the product was heated beyond 400oC, it probably contained infinite PCS network with shorter chains.