Structure and properties of polycarbosilane synthesized from polydimethylsilane under high pressure

Abstract

Abstract The polycarbosilane (PCS), which is the precursor of SiC fiber, was synthesized under high pressure by thermal decomposition of polydimethylsilane. The composition, structure, and properties of the PCS were characterized by the measurements of softening point, elemental analysis, IR, GPC, NMR, TG‐DTG‐DTA, XRD, and oxidative reaction activity, respectively. Structure model of the PCS was therefore inferred. The results showed that the PCS was the polymer with a SiC backbone with M n about 1587. IR and NMR showed the presence of SiC 4 and SiC 3 H structure units containing SiCH 3 , SiCH 2 Si, and SiH groups. The ratio between H in CH bond and H in SiH bond was about 8.84 with SiC 3 H/SiC 4 and about 0.51 from 1 H NMR and 29 Si NMR, respectively. Elemental analysis gave an empirical formula of SiC 1.87 H 7.13 O 0.03 . TG analysis showed that the ceramic yield of the PCS at 1200°C in a N 2 flow was about 78.9%. β‐SiC microcrystal could be obtained when PCS was pyrolyzed at 1250°C with the crystal size about 37.5 Å. Compared with the PCS with similar softening point synthesized under normal pressure, the PCS synthesized under high pressure had approximate elemental composition, higher SiH bond content and reaction activity, higher molecular weight, and higher ceramic yield, but lower ratio of SiC 3 H and SiC 4 . © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1188–1194, 2006