Liquid poly(silylacetylene)siloxane resin as a novel precursor of silicon carbide and silicon oxycarbide ceramics

Liquid preceramic poly(silylacetylene)siloxane resin was synthesized via a two-step protocol including organometallic condensation and hydrolysis reactions. The preceramic resin was well soluble in acetone, toluene, and tetrahydrofuran (THF), etc. By thermal cure at 180-250°C a hard monolithic solid was formed through radical polymerization of secondary ethynyl groups. The poly(silylacetylene)siloxane resin was processed easily to various nonporous shapes to silicon carbide (SiC) and silicon oxycarbide (SiCO). SiCO ceramic was obtained at a yield of >75% by pressureless pyrolysis at 900-1200°C; while SiC ceramic was obtained at 1500°C at a yield of ≈67%. The molar ratio of Si/C in the SiC was found at 1:1.1-1:3, based on ICP-MS elemental analysis. X-ray diffraction (XRD) results revealed the typical β-SiC structure in the poly(silylacetylene)siloxane derived SiC ceramics. The SiC ceramics exhibited high thermo-oxidation resistance at elevated temperatures in air atmosphere.