The compounds containing Si -- N bond structure mainly include small silazanes and polysilazanes, in which the small silazanes are further divided into linear silazanes [RNSI (NR2) 4-N] and ring silazanes [(R2sin) N]. Polysilazanes consist mainly of three types of bonds:
Silazanes small molecular compounds are the raw materials for the preparation of polysilazanes. The main preparation methods are the reaction method of chlorosilane and amine and the reaction method of silazanes and butyl lithium. The former is the most commonly used method, in which the amine can be used as the absorbent of HCl released in the reaction, and the steric hindrance of substituents on the amine and silicon has an obvious effect on the difficulty of the reaction and the distribution of products. The reaction of silazanes with butyl lithium for the latter is a very effective way to prepare new linear silazanes or cyclosilazanes. The reaction formula is as follows:
Polysilazanes can also be directly prepared by ammonolysis reaction of dialkyl dihalosilanes, which is very similar to the preparation of polysiloxanes by hydrolysis reaction of dialkyl dihalosilanes. The preparation equation is as follows:
Cyclic polysilazanes can be prepared by ammonolysis reaction of silicon tetrachloride with 2, 2, 2-trifluoroethylamine and then with trimethyl aluminum.