METHYLHYDRIDOPOLYSILAZANE AND ITS PYROLYTIC CONVERSION TO SI3N4 SIC CERAMICS/

The present report explores the use of liquid-state nuclear magnetic r esonance (NMR) spectroscopy for characterizing the methylhydridopolysi lazane (MHPS) prepared by the Seyferth/Wiseman procedure and compares the structure of this polymer with other ceramic precursors derived fr om similar synthetic routes. X-ray diffraction, cross-polarization (CP ), and single-pulse magic angle spinning (MAS) solid-state NMR spectro scopy were employed for characterizing temperature-induced short-range bonding and phase evolution in MHPS precursors to SiC/Si3N4 ceramics. The molecular weight and methyl substitution of the preceramic polyme rs is shown to affect the ceramic yield and phase development of these polysilazanes during pyrolysis. Ceramic yields approaching 90% are ob served in these systems. CPMAS NMR is shown to be uniquely capable of identifying the hydrogen-rich environments and the onset of short-rang e SiC and Si3N4 phase development in these amorphous preceramic materi als.