Liquid polycarbosilanes: synthesis and evaluation as precursors for SiC ceramic

Abstract

A series of liquid polycarbosilanes were successfully synthesized by a sequential Grignard coupling reaction of (chloromethyl)triethoxysilane and vinylmagnesium bromide, followed by the reduction with lithium aluminum hydride. The use of non-corrosive, easily handleable and storage stable (chloromethyl)triethoxysilane as starting material is an attractive advantage for this route. The as-synthesized polymers containing Si-CH=CH 2 and Si-H groups are storage stable and can be easily cured in an inert atmosphere. The ceramic yield of the cured polycarbosilane and the C/Si ratio of the derived ceramic were varied by adjusting the mole ratio of starting materials in feed. Among them, the polymer with the mole ratio of Si-CH=CH 2 to Si-H as 1:10 has the highest ceramic yield as 89.6% after cured at 220 o C and the C/Si ratio of the derived ceramic is 1.48. This kind of polycarbosilane shows high potential as SiC ceramic precursor in fabrication of SiC matrix by the precursor infiltration pyrolysis (PIP) process.

Evaluation of poly(methylsilane‐carbosilane) synthesized from methyl‐dichlorosilane and chloromethyldichloromethylsilane as a precursor for SiC

“…Figure shows the XRD patterns of pyrolyzed PMSCSs (B1, B2, B3) at 1000 °C. There are three major peaks appear at 2θ = 36°, 60°, and 72° in each sample, which indicate that β‐SiC is the only crystalline phase of SiC in this condition . According to the line width of XRD patterns, the SiC crystallites size of B1–B3 is about 2.0–1.3 nm.…”

“…The broad peaks ranging from 4.4 to 3.5 ppm were assigned to the Si H group . The multiplet at 6.5–5.5 ppm was assigned to protons in SiC H C H 2 . The peak of SiC H C H 2 in A3 was stronger than in A2 as designed.…”

“…[27][28][29] The multiplet at 6.5-5.5 ppm was assigned to protons in SiACH@CH 2 . 13,28 The peak of SiACH@CH 2 in A3 was stronger than in A2 as designed. Peaks at 6.98, 5.01, 2.27, and 1.43 ppm belong to the BHT.…”

Microscopic, mechanical and thermal properties of spark plasma sintered ZrB2 based composite containing polycarbosilane derived SiC

“…[17]. In general, maximum liquid polycarbosilanes were synthesized by Grignard coupling reaction between triethoxysilane and organomagnesium halide (Grignard reagent) and subsequently formed hyperbranched polycarbosilanes after crosslinking reaction of AB 2 -and AB 3 -type monomer units [18]. Moreover, the Si-CH 2 -Si and Si-CH 2 -should be produced by Grignard coupling reaction to form the carbon-carbon backbone of the polymer.…”

Highly effective free‐radical‐catalyzed curing of hyperbranched polycarbosilane for near stoichiometric SiC ceramics

“…Therefore, synthesis of preceramic polymer is one of the key issues in the field of preceramic polymer‐derived ceramics. Among various SiC precursors that contain both Si and C elements in their structure, liquid hyperbranched polycarbosilane (LHBPCS), which has low viscosity, low oxygen content and the ratio of Si to C approaching SiC stoichiometry, etc., is regarded as the most excellent one . LHBPCS was usually synthesized through Grignard coupling of chloroalkyl chlorosilane, followed by a reduction in the residual chlorine group.…”