硅氮烷添加剂的水解稳定性对硅橡胶热稳定性的影响

采用一种新的方法研究了硅氮烷水解反应的动力学规律 ,根据实验数据测出硅氮烷水解速率对硅氮烷的浓度符合一级动力学关系 .计算出了几种硅氮化合物与水蒸气反应的表观活化能 ,结果表明硅氮烷的结构与其水解反应的表观活化能有密切的关系 .硅原子或氮原子上带有较大空间位阻的基团后 ,其水解稳定性提高 .其中六苯基环三硅氮烷 4的水解表观活化能为 2 14kJ mol,而苯基硅氮聚合物 5的水解表观活化能更达到 2 91 3kJ mol.添加到硅橡胶中的硅氮化合物水解表观活化能越大 ,即水解稳定性越高 ,其改进硅橡胶热稳定性的效果越好 .将 4和 5添加到硅橡胶生胶中 ,35 0℃下老化 2 4h的热失重分别为 0 96 %和 0 6 % .

INFLUENCES OF HYDROLYSIS STABILITY OF SILAZANE ADDITIVES ON THERMAL STABILITY OF SILICONE RUBBER

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( E a) 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 E a 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.