A new method was applied to study kinetics of hydrolysis reactions of silazane compounds

which were used as additives in silicone rubbers to improve their thermal stability．It was shown that the hydrolysis reaction was a first-order reaction versus the concentration of the silazane compound．Activation energy(Ea) was calculated for reactions of several silazane compounds with water vapor．It was indicated that activation energy of hydrolysis was closely related with the structure of the silazane compound. The hydrolysis stability would increase when groups around silicon atom or nitrogen atom were of high steric hindrance．Hydrolysis activation energy of hexaphenylcyclotrisilazane 4 was 214 kJ／mol

and that of polymer 5 which contained cyclodisilazane in backbone was 291.3 kJ／mol．Thermal stability of silicone rubber could be improved more effectively when silazanes with higher Ea were used as additives．The weight loss of silicone rubber with compound 4 and 5 as additive was 0.96％ and 0.6％

respectively

when aged under 350℃ for 24 h．