Soluble preceramic polymer to BN ceramic, polyborazine, was synthesized via condensation of boron
trichloride and hexamethydisilazane followed by a polymerization process. The average molecular weight and structure
of the prepolymer during polymerization, mechanism of polymerization, pyrolysis process, and chemical composition of
the obtained ceramic were investigated using gel permeation chromatography, 1H NMR, infrared spectra, thermogravimetric
analysis and element analysis. The results indicate that hexamethydisilazane and NH3 were released during the
polymerization process. The average weight molecular and ceramic yield (1 000℃ in N2 ) of the polyborazine are 7
582 and 41． 6 wt%, respectively. The ceramic mainly formed at the temperature range of 400 to 600℃ and white BN
ceramic with low carbon content was obtained after pyrolyzed in NH3 at 800℃.