Allyl-Substituted Hydridopolycarbosilane with Low Curing Temperature and High Ceramic Yield under a Redox Initiation System

Abstract

Liquid hydridopolycarbosilanes (LHPCS) is commonly used to produce ceramic matrix composites by polymer impregnation pyrolysis (PIP) process. Allyl-substituted hydridopolycarbosilanes (AHPCS) with different allyl contents of 10, 15, 20, 25 and 30 mol % (AHPCS-10%, AHPCS-15%, AHPCS-20%, AHPCS-25%, AHPCS-30%) were synthesized by Grignard coupling reaction. tert-Butyl peroxybenzoate (TBPB) + cobalt 2-ethylhexanoate (Co) were used as the redox initiation system for AHPCS curing and was compared with Karstedt catalyst and TBPB initiator. Based on differential scanning calorimetry analyses, the TBPB + Co initiation system significantly decreased the exothermic peak temperature of the free radical polymerization to 80°C. According to thermogravimetric analysis, the residual at 1000°C of cured AHPCS-20% in flowing nitrogen reached to 86.0%. Ceramized AHPCS were obtained by heat treated cured AHPCS at 1500°C for 2 h. Based on the X-ray diffraction patterns and transmission electron microscope photographs of the ceramic products, β-SiC was the main component of the ceramized AHPCS. Ceramized AHPCS-15% was the highest ceramic yield of 88.1% in the ceramized AHPCS. Thermogravimetric analyses revealed high thermal oxidation resistance of the ceramic AHPCS in flowing air up to 1000°C. Therefore, AHPCS under TBPB + Co initiation system with low-temperature curability and high ceramic yield, and its ceramic products have excellent thermal oxidation resistance, showing potential as SiC ceramic precursors for aerospace field.