Synthesis of ceramic precursor polycarbosilane (PCS) under supercritical fluids (SCFs) state

Abstract

Using xylene as supercritical fluids (SCFs) media and polydimethylsilane (PDMS) as raw material, the ceramic precursor polycarbosilane (PCS) with moderate molecular weight and narrow molecular weights distribution was synthesized under high pressure and temperature in autoclave. Softening-point test, Fourier transform infrared spectroscopy (FT-IR), gel permeation chromatography (GPC), element analysis and the yield test of PCS were adopted to characterize the SCFs-method and compared with two other PCS synthesis methods named normal-pressure high-temperature (NP) method and high-pressure hith-temperature (HP) method. The results indicate that the PCS maintains a high Si-H content and its chemical formula is SiC1.91H7.27O0.05. The yield is 63.5 wt% which has been improved by about 20 wt%, the softening-point is 180–220°C, the number average molecular weight is 1477 and the molecular weights distribution index is 1.61. The synthesis method via supercritical fluids with good diathermancy and reaction uniformity is a new feasible method of synthesizing PCS with good qualities.