Polysilazanes and Polysilanes

Polysilazanes have been shown to be excellent polymeric precursors to amorphous silicon carbonitride (SiCN), silicon nitride, silicon carbide (SiC) and their composites. The actual chemical and phase compositions of the ceramic products depend on the polymer composition and pyrolysis conditions, such as temperature, time and atmosphere. Polymeric silazanes consist of amorphous networks, which transform to amorphous SiCN ceramics by pyrolysis under inert atmosphere at around 1000 C. These ceramic products remain amorphous up to 1400 °C in an inert atmosphere [a.322]. However, at higher temperatures the non-stoichiometric SiCN matrix decomposes, with nitrogen loss, giving the thermodynamically stable phases, namely Si3N4 and SiC. Polysilanes, polycarbosilanes and polysilazanes are commonly used for the preparation of high-performance ceramics such as silicon carbide, silicon nitride and silicon carbonitride. 

Polysilanes have a continuous backbone of silicon atoms. Characteristics include lower solubility, higher glass transition temperatures and, perhaps most importantly, unique 

However, the activation energy of the thermal degradation reaction of copolymers in an N2 atmosphere was determined to be in the range of 180-105 kJ/mol and that of the same process in an O2 atmosphere in the range of 100-154 kj/mol. The activation energies of the degradation reactions of the copolymers were decreased in both N2 and O2 atmospheres 

Mole fraction of VTES in feed Mole fraction of VTES in copolymer M X 10-3 M X 10-3 Polydispersity Thermal E (kj/mol) Oxidative E (kJ/mol) 

The release of ammonia indicated the existence of transamination reactions corresponding to further crosslinking of the polysilazane precursor. The major mass loss (17.6%) occurred between 350 and 800 °C. This mass loss corresponds to the escape of hydrocarbons and traces of silicon species in the temperature range from 350 to 650 C. The masses of the 

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