Polycarbosilanes (PCSs) were synthesized at high temperature under high pressure with polydimethylsilane (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℃ 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.