液态聚硅烷高压合成聚碳硅烷先驱体的组成与结构表征

Composition and Structure Characterization of Polycarbosilane Precursor Synthesized from Liquid Polysilane Under High Pressure

以液态聚硅烷(LPS)为原料,首次在高温高压条件下制备了聚碳硅烷(PCS)先驱体,对其组成及结构进行了表征。研究表明,LPS高压合成的PCS是以Si-C为主链的聚合物。其重均分子量为2861,分子量分布系数为1.92,实验式为SiC1.89H4.81O0.05,主要含有由Si-CH3,Si-CH2-Si,Si-H组成的SiC4,SiC3H等结构单元,C-H／Si-H值约为9.83,SiC3 H／SiC4值约为0.48,是支化度较高的分子。高压合成的PCS比常压PCS有高的分子量及Si-H键含量,比常压合成体现出了PCS先驱体的优异性。

The polycarbosilane (PCS) precursor for SiC fiber was synthesized in an autoclave with liquid polysilane (LPS), which was obtained by thermal decomposition of polydimethylsilane (PDMS). The composition and structure of the PCS were characterized. The results showed that the PCS was the general term for organosilicon polymers with a Si-C backbond. The weight average molecular weight (Mw) of PCS was about 2861, and the polydispersity index, Mw/Mn(weight average to number average molecular weight), was about 1.92. Elemental analysis gave an empirical formula of SiC1.89 H4.81O0.05. IR and NMR showed the presence of SiC4 and SiC3 H structure units containing Si-CH3, Si-CH2Si and Si-H groups. From the ratio of C-H and Si-H intensity areas in 1H-NMR spectra, the value of C-H/Si-H was about 9.83. From 29Si-NMR spectra, the ratio of SiC3 H to SiC4 units was about 0.48. The PCS synthesized under high pressure was better for precursor for SiC fiber than that of synthesized under normal pressure, because the PCS synthesized under high pressure had higher molecular weight and Si-H bond content.