Synthesis, Characterization, and Pyrolytic Conversion of a Novel Liquid Polycarbosilane

Abstract

Partially ethynyl‐substituted ethynylhydridopolycarbosilane (EHPCS) is prepared by Grignard coupling of chloromethyltrichlorosilane, chloromethylmethyldichlorosilane, and ethynylmagnesium bromide, followed by reduction with lithium aluminum hydride. The as‐synthesized EHPCS, with a hyperbranched structure and an approximate formula of [SiH 1.35 (CH 3 ) 0.37 (C≡CH) 0.28 CH 2 ] n , has been characterized by GPC, FT‐IR, and 1 H, 13 C, and 29 Si NMR. The EHPCS can be cured readily in an inert atmosphere at 140°C for 6 h. Pyrolysis behavior and structure evolution of the cured EHPCS were studied by means of thermal gravimetric analysis‐differential scanning calormetry, FT‐IR, X‐ray diffraction, and elemental analysis. It is suggested that hydrosilylation, ethynyl group polymerization, dehydrocoupling, and demethanation are involved in the cross‐linking of EHPCS. The polymer–ceramic conversion is complete at 900°C, and it gives a stoichiometric and amorphous silicon carbide (SiC) with a yield of 78%. Further heating at 1200°C induces partial crystallization, forming locally ordered SiC 4 . The characteristic peaks of β‐SiC are observable above 1600°C.