1.Chemical structure
(1) Main chain and side groups
The main chain is the most basic skeleton of silicone rubber, the heat aging of silicone rubber has a decisive impact. The main chain consists of silicone-oxygen bonding and is arranged in a helical structure, there is a large polarity and flexibility, so it is easy to occur at high temperatures in the degradation of the main chain and the oxidation of the side groups of the reaction, resulting in the gradual softening of the silicone rubber, losing its 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 will occur in the bite reaction, resulting in irregular degradation, and finally through the silicone benzene bond and silicone-oxygen bond breakage of two aspects of the impact of heat resistance of silicone rubber.
2.Semi-inorganic polymer composite materials
Silicone rubber as a semi-inorganic polymer composite material, when adding different fillers will have different effects on the heat resistance of silicone rubber. For example, some amphoteric metal compounds filler can absorb the silicone rubber in the acidic or alkaline substances, which can effectively reduce the catalytic degradation of these substances on the silicone rubber, this measure can effectively reduce the possibility of thermal aging of silicone rubber, often used materials are generally alumina. In general, the filler is not only a good filler, properly used to better improve the heat resistance of silicone rubber.
3. Environmental factors
The use of water in the environment, including water vapor can be triggered in the silicone rubber silicone oxygen bond breakage, and finally generated silicone hydroxyl, and it is well known that the existence of silicone hydroxyl for the heat resistance of silicone rubber is an adverse effect. In addition, it is interesting to note that, when filling silicone rubber, the hydrolysis and rearrangement of siloxanes have the same effect on the mechanical properties, so it is difficult to determine whether there is hydrolysis through the analysis of the mechanical properties, but the difference in heat resistance can be used as a basis for its determination. Silicone rubber system in the presence of acid, alkali will play a catalytic degradation of silicone rubber in addition to the environment of oxygen, ozone on the thermal degradation of silicone rubber also has a certain adverse effect. At the same time, the application of the environment, such as the presence of load cyclic stress will accelerate the degradation of dimethylsiloxane and diphenylsiloxane copolymer elastomers, resulting in a reduction in the heat resistance of the material, and the two components of the copolymer composition is different, the degradation mechanism is also different.

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