Interaction of Polychloromethylsilanes with Ammonia and Ammonium Chloride

Polychloromethylsilanes were reacted with ammonia at various temperatures and pressures to achieve shape stabilization of preceramic green fibers. Besides the aspired cross-linking process, other reactions took place due to the interaction with NH4Cl, deposited as a byproduct at the polymer surface. FT/IR, 13C, 29Si, and 15N solid-state NMR investigations and X-ray powder diffraction were applied to follow the dynamics of the reaction and to characterize the obtained products. They prove that during annealing under argon back reactions occur. With annealing under ammonia, pressures up to 4 bar and temperatures >200 °C completely rearrange the polysilane into a polysilazane skeleton. The resulting silazane exhibits a cagelike structure. Reactions causing this rearrangement are discussed.