聚碳硅烷的高温高压生成机理研究

分别以聚二甲基硅烷(PDMS)、液态聚硅烷(LPS)及PDMS裂解剩余物(LPCS)为原料,在不同的温度下高压合成聚碳硅烷(PCS),采用红外、紫外、核磁共振、分子量及其分布等分析PCS的组成、结构随温度的变化.同时,采用改变减压蒸馏温度的办法,对PCS进行分级,收集在不同蒸馏温度下的馏分,通过对一系列馏分进行了IR分析,以此推测PCS的转化过程.研究表明,PCS的生成过程是随着温度的升高,PDMS、LPS中键能较低的Si—Si键断裂,逐渐转变成为键能较高的Si—C键,转化为低分子的碳硅烷;随着温度的升高,碳硅烷分子间发生脱氢、脱甲烷缩合反应使产物的分子量逐渐长大,生成PCS.

SYNTHESIS MECHANISM OF POLYCARBOSILANE AT HIGH TEMPERATURE UNDER HIGH PRESSURE

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.