A novel soluble preceramic polymer to SiBNC ceramic, polyborosilazane (PBSZ), was synthesized via a cocondensation approach with a yield of about 91% (w%) by using dichloromethylsilane (MeHSiCl₂), boron trichloride (BCl₃) and hexamethydisilazane (HMDZ) as the starting materials. The chemical composition, structure and properties of the obtained polymer were investigated using element analysis, FT-IR, NMR, XPS, TMA and TG. The results indicate that the backbone of the polymer is —Si—N—B— linkage in the form of borazine ring and C is in the form of Si—CH₃ in the pendant or end group. The melting point, number average molecular weight and polydispersity index of PBSZ is 69 ℃, 10802 and 1.50, respectively. PBSZ shows good processability and PBSZ fibers with diameter of 15～20 μm can be obtained by melt spinning at 80 ℃ in N₂ atmosphere. The ceramic yield of the PBSZ at 1000 ℃ in nitrogen atmosphere is 63% (w%), which suggests that the as-achieved polymer can be used as a precursor to SiBNC ceramic fiber.

Key words: SiBNC ceramic, ceramic fiber, polyborosilazane, preceramic polymer, synthesis