{B[C2H4Si(CH3)NH]2[C2H4Si(CH3)N(SiH2Ph)]}n: The First Polyborosilazane Precursor for Silicoboron Carbonitride Stable to 2200 °C

{B[C2H4Si(CH3)NH]2[C2H4Si(CH3)N(SiH2Ph)]}n was synthesized by base-catalyzed dehydrocoupling reaction of {B[C2H4Si(CH3)NH]3}n with phenylsilane. Pyrolysis of the new polyborosilazane precursor to 1050 °C gave an amorphous material Si3.9B1.0C11N3.2, which could resist thermal degradation to 2200 °C in argon.