Synthesis and Pyrolysis of Thermosetting Copolymer of Polysilastyrene and Perhydropolysilazane

Abstract

Copolymer of polysilastyrene and perhydropolysilazane was obtained by the reaction of polysilastyrene with zirconium n-butoxide and perhydropolysilazane. Zirconium n-butoxide and perhydropolysilazane were essential to render the thermosetting property. The thermosetting copolymers were converted into silicon carbide-based ceramics by pyrolysis at 1000°C in a stream of N2 with about 80 mass% ceramic yield. The main phase of the pyrolysis product at 1500°C in N2 was small crystallite β-SiC. Free carbon, based on rule-of-mixtures composition in the final ceramics could be reduced by varying the ratio of polysilastyrene/perhydropolysilazane. The copolymer was dry spun and pyrolyzed to produce a ceramic fiber. Pyrolysis in N2 at 1500°C yielded a silicon carbide-based fiber. Tensile strength of 1.0 GPa and elastic modulus of 190 GPa were obtained for the fiber from 10 to 12μ in diameter. Crystallization to α-Si3N4, β-Si3N4, β-SiC, and ZrN proceeded on annealing in N2 at 1700°C for 1 h.