METHYLHYDRIDOPOLYSILAZANE AND ITS PYROLYTIC CONVERSION TO SI3N4/SIC CERAMICS

The present report explores the use of liquid-state nuclear magnetic resonance (NMR) spectroscopy for characterizing the methylhydridopolysilazane (MHPS) prepared by the Seyferth/Wiseman procedure and compares the structure of this polymer with other ceramic precursors derived from similar synthetic routes. X-ray diffraction, cross-polarization (CP), and single-pulse magic angle spinning (MAS) solid-state NMR spectroscopy 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 polymers is shown to affect the ceramic yield and phase development of these polysilazanes during pyrolysis. Ceramic yields approaching 90% are observed in these systems. CPMAS NMR is shown to be uniquely capable of identifying the hydrogen-rich environments and the onset of short-range SiC and Si3N4 phase development in these amorphous preceramic materials.