(1)Main chain and side group
The main chain is the most basic skeleton of silicone rubber, the heat aging of silicone rubber has a decisive impact. The main chain is composed of silicone-oxygen bond connection and helical structure arrangement, there is a large polarity and flexibility, so at high temperatures are prone to degradation of the main chain and side group oxidation reaction, resulting in the gradual softening of silicone rubber, loss of value. The main chain of silicone rubber is composed of different structures, and its heat resistance is also very different. The introduction of phenylidene, cyclodisilazane, phenyl ether support, benzene support group, carbodecylboronyl and other groups in the main chain can greatly inhibit the possibility of cyclization degradation reaction and improve the overall heat resistance of the material. As for the side groups, when the side groups of vinyl silicone rubber are phenyl, methyl, ethyl, propyl, butyl, respectively, in the high temperature environment, oxidation will occur in order of priority, resulting in a decrease in the heat resistance of the material. In addition, according to the study when the side chain of the alkyl group increases, the thermal stability of the silicone rubber will also decrease. For example, the heat resistance of dimethyl silicone rubber is better than that of butyl silicone rubber.
(2) End group
When the end group of methyl silicone rubber is a hydroxyl group, an intermolecular condensation reaction occurs at low temperatures, which promotes the breakage of the main chain and affects the heat resistance of the material. At higher temperatures, the end-groups will undergo an occlusion reaction, resulting in irregular degradation and finally affecting the heat resistance of the silicone rubber through the breakage of silicone-phenylene and silicone-oxygen bonds.

Room termperature curing polysilazane, pls check IOTA 9150, IOTA 9150A. 
High termperature curing polysilazane, pls check IOTA 9108, IOTA 9118.