Although the catalytic activity of hexaphenylcyclo-trisilazane trilithium salt is much lower than that of hexamethylcylotrisilazane trilithium salt due to the inductive and steric effect of phenyl group

the thermal and hydrolytic stability of hexaphenylcyclo-trisilazane is much higher than that of hexamethylcyclotrisilazane. By using a polar solvent

such as 1

4-dioxane

etc.

hexaphenylcyclo-trisilazane trilithium salt is prepared through the reaction of hexaphenylcycoltrisilazane and n-BuLi at low temperature. Ring-opening polymerization of cyclosioloxane using hexaphenylcyclotrisilazane trilithium salt as a catalyst and THF

Diglyme of DMSO as a promoter is carried out. The polymer is characterized by 1H-NMR

29Si-NMr

GPC limiting viscosity number measurement. Nitrogen content of the polymer is determined by means of coulometric titration. It is confirmed hat the polymer contains hexaphenylclotrisilazane. The relation between the weight-average molecular weight and the limiting viscosity number of the polymer has been studied.