反应温度对聚二甲基硅烷高压合成聚碳硅烷性能的影响

以聚二甲基硅烷(PDMS)为原料,在高压釜内高温高压合成了聚碳硅烷(PCS)先驱体.研究了反应温度对合成的PCS的Si—H键含量、支化度、Si—Si键含量、分子量及其分布、软化点及产率的影响.研究表明,随着反应温度的提高,分子量及软化点均明显增加,分子量分布变宽,支化度升高,Si—Si键含量明显降低.当反应温度低于460℃时,Si—H键含量及产率随反应温度的升高逐渐升高,当反应温度高于460℃时,由于分子间的缩合及热交联二者逐渐降低.在反应过程中PDMS首先转化为小分子量的PCS,然后是小分子PCS分子间发生脱氢及少量脱甲烷缩合使分子量长大.当反应温度高于450℃时,PCS分子量分布出现中分子量峰,Si—Si键含量较低,在室温空气中比较稳定.

INFLUENCE OF REACTION TEMPERATURE ON THE PROPERTIES OF POLYCARBOSILANE SYNTHESIZED FROM POLYDIMETHYLSILANE UNDER HIGH PRESSURE

The polycarbosilane(PCS) precursor for SiC fibers was synthesized in an autoclave from polydimethylsilane(PDMS).The influence of reaction temperature on the Si—H bond content,degree of branching,Si—Si bond content,molecular weight and distribution,softening point and yield of the PCS was investigated.The results showed that,with raising the reaction temperature the weight average molecular weight,degree of branching and softening point increased,the molecular weight distribution broadened and the Si—Si bond content decreased.The Si—H bond content and PCS yield increased with temperature in the range below 460℃ and decreased over 460℃.The conversion process included initially the formation of PCS by thermal decomposition of PDMS and then the increase in molecular weight by condensation among the PCS molecules.An medium molecular weight peak appeared while the reaction temperature was over 450℃,and the PCS was stable with low Si—Si bond contents in air at room temperature.