Amine and ammonolysis reactions
The main synthesis methods of low molecular weight polysilazanes are amination and ammonolysis polycondensation reaction. The main steps are as follows: ammonia gas is fed into the chlorosilane benzene solution prepared by dimethyl dichlorosilane (Me2SiCl2), methyl hydrogen dichlorosilane (MesiHCl2) and toluene, mechanical stirring continuous reaction, static precipitation, dry filtration, benzene solvent washing and fractionation. The results showed that the higher the content of Me2SiCl2 in chlorosilane benzene solution, the less time needed for ammonolysis reaction and the higher the molecular weight of reaction product. The low molecular weight polysilazane prepared by this method has an average molecular weight of 1300, but its chemical properties are less stable. The product can be quickly cross-linked, and the silicon nitride ceramics with high yield and mixed with pure silicon can be prepared by high temperature pyrolysis of the reaction product.
 Synthesis of cyclosilazanes
The results show that cyclotrisilazanes and cyclotetrasilazanes can be synthesized by ammonolysis of halosilane containing bifunctional groups, and polysilazanes can be synthesized by reaction of ammonia, amino dilithium and dichlorosilane. Tong Xiujun et al. took Me2SiCl2 as the reaction monomer, reacted with solid ammonium chloride and ammonia water, and recrystallized to obtain octamethylcyclotetrasilazane.