1. Chemical structure

(1) Main chain and side groups
The main chain is the most basic skeleton of silicone rubber and has a decisive impact on the thermal aging of silicone rubber. The main chain is composed of silicon oxygen bonds connected and arranged in a spiral structure, with high polarity and flexibility. Therefore, at high temperatures, the degradation of the main chain and oxidation of the side groups are prone to occur, leading to the gradual softening of silicone rubber and its loss of use value. If the main chain of silicone rubber is composed of different structures, its heat resistance performance also varies greatly. Introducing groups such as phenylene, cyclodisilazane, phenyletherene, phenylene, and carbodecaboroalkyl into the main chain can greatly inhibit the possibility of cyclization degradation reactions and improve the overall heat resistance of the material. For the side groups, when the side groups of vinyl silicone rubber are phenyl, methyl, ethyl, propyl, and butyl, oxidation will occur sequentially in a high-temperature environment, resulting in a decrease in the heat resistance of the material. In addition, according to research, when the side chain alkyl groups increase, 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)  Terminal group
When the end group of methyl silicone rubber is hydroxyl, intermolecular condensation reactions occur at lower temperatures, which promote the fracture of the main chain and thereby affect the heat resistance of the material. At higher temperatures, a back biting reaction occurs, resulting in irregular degradation, which ultimately affects the heat resistance of silicone rubber through two aspects: the breakage of silicone benzene bonds and silicone oxygen bonds.

2. Semi inorganic polymer composite materials
Silicone rubber, as a semi inorganic polymer composite material, has different effects on the heat resistance of silicone rubber when different fillers are added. For example, certain amphoteric metal compound fillers can absorb acidic or alkaline substances in silicone rubber, which can effectively reduce the catalytic degradation of these substances to silicone rubber. This measure can effectively reduce the possibility of thermal aging of silicone rubber, and the commonly used material is generally aluminum oxide. Overall, fillers are not only excellent fillers, but also can better improve the heat resistance of silicone rubber when used properly.

3. Environmental factors
The use of water in the environment, including water vapor, can trigger the fracture of silicon oxygen bonds in silicone rubber, ultimately generating silicon hydroxyl groups. As is well known, the presence of silicon hydroxyl groups has a negative impact on the heat resistance of silicone rubber. Furthermore, it is interesting to note that when filling silicone rubber, the hydrolysis and rearrangement of siloxanes have the same impact on mechanical properties, making it difficult to effectively determine the presence of hydrolysis through mechanical property analysis. However, the difference in heat resistance can provide a basis for its determination. The presence of acids and alkalis in the silicone rubber system will have a catalytic degradation effect on the silicone rubber. In addition, oxygen and ozone in the environment also have certain adverse effects on the thermal degradation of silicone rubber. If there is cyclic stress under load in the same application environment, it will accelerate the degradation of dimethylsiloxane and diphenylsiloxane copolymer elastomers, resulting in a decrease in the heat resistance of the material. Moreover, the composition of these two component copolymers is different, and the degradation mechanism is also different.