Synthesis mechanism of polycarbosilane at high temperature under high pressure

Polycarbosilanes (PCSs) were synthesized at high temperature under high pressure with polydimethylsilane (PDMS), liquid polysilane (LPS) and the soluble solid product from PDMS pyrolysis (LPCS), as raw materials, respectively. The PCSs synthesized at different temperatures from fifferent raw materials were characterized by IR, UV, NMR, and GPC, respectively. The structure evolution from raw material to PCs was found. On the other hand, the crude PCs was synthesized at 450 degrees C under high pressure with LPS. After dissolved and vacuum distilled at different temperature, fractions of PCSs with different molecular weights were obtained and characterized by IR. The synthesis mechanism of the PCs at high temperature under high pressure was proposed. The results showed that, during the synthesis process of PCs, Si-Si bonds were converted to Si-C bonds with the reaction temperature increasing, and the low molecular carbosilanes were therefore produced. The molecular weight of carbosilanes increased by dehydrogenation and dehydrocarbonation condensation between small carbosilane molecules, and then PCs was obtained.