Zhengfang Xie

Analysis and Characterization of Polycarbosilane

Abstract Polycarbosilane (PCS) synthesized at high temperature under high pressure from liquid polysilane was shown to be an organosilicon polymer with a Si–C backbone. MW of the PCS with a softening point of 209°C was about 2861. Elemental analysis gave an empirical formula of SiC1.86H7.50O0.02. IR and 29Si-NMR showed the presence of SiC4 and SiC3H structural units. The H mole ratio for C–H bond to Si–H bond was about 9.83, and the Si mole ratio for SiC3H to SiC4was about 0.94. TG analysis showed the ceramic yield of the PCS at 1200°C in N2 to be about 78.9%. β-SiC microcrystal was obtained when the PCS was pyrolyzed at 1250°C in N2 with a grain size of about 35.9 Å.

Facile synthesis of melt-spinnable polyaluminocarbosilane using low-softening-point polycarbosilane for Si-C-Al-O fibers

Melt-spinnable polyaluminocarbosilane (PACS) is of importance as the precursor to prepare the Si–C–Al–O ceramic fibers, which can be employed for the preparation of SiC fibers with high tensile strength and good thermal stability. In this work, low-softening-point polycarbosilane (LPCS) was synthesized by pyrolysis of polydimethylsilane and applied to prepare PACS precursors with variable aluminum content by the reaction with aluminum(III) acetylacetonate. GPC, 1H NMR, UV–Vis, FT-IR, 29Si NMR, 27Al MAS NMR, TGA, and elemental analysis were used to analyze the composition and structure of the PACS precursors. Finally, Si–C–Al–O fibers were obtained successfully by melt-spinning, curing, and final pyrolysis of the precursors. The method demonstrated in this work can be further extended to synthesize other melt-spinnable metal-containing polycarbosilane (PMCS, M: Zr, Ti, Fe, Co, et.) of high ceramic yield and adjustable M content by reacting LPCS with other corresponding metal-containing compounds.