The low temperature properties of silicone rubber are mainly affected by its crystallization properties and glass transition temperature. The low temperature properties of silicone rubber are improved by the introduction of phenyl group with larger steric resistance and the change of polymer molecular chain flexibility. For most crystalline silicone rubbers, although there is a low glass transition temperature, the higher crystallization temperature (generally higher than Tg) limits the temperature range of its use to more than -100℃. With the introduction of rigid phenyl groups, Tg increases, low temperature crystallization efficiency decreases, and low temperature performance improves. At low temperature, the volume of silicone rubber shrinks, the distance between molecular chains decreases, and the intermolecular force increases. At low temperature, crystalline micro-region of crystalline silicone rubber acts as a cross-linking point, and the tensile strength and tensile modulus of rubber are increased, while the elongation at break is decreased. At low temperature, the low temperature crystallization and crystal orientation of silicone rubber have a comprehensive effect on the tensile strength of silicone rubber. The introduction of phenyl inhibits the crystallization to reduce the orientation, and increases the tensile strength and elongation at break. It has been verified by literature that the tensile strength of phenyl silicone rubber reaches 22.1MPa and the elongation at break reaches 145% at -70℃.

There are two aging forms of silicone rubber at high temperature, one is the siloxane chain segment silicon-oxygen bond fracture rearrangement; The other is methyl, vinyl and other organic side group oxidation, both forms may cause molecular chain crosslinking, rubber hardness due to crosslinking density increases, resulting in silicone rubber to lose elasticity and even cracking, so high temperature resistance is one of the hot research of silicone rubber. The phenyl group was introduced into the side group of silicone rubber to form steric hindrance on the polysiloxane chain segment and inhibit cyclic degradation. On the other hand, the thermal oxygen stability of phenyl is much higher than that of methyl, so the introduction of phenyl can prevent the cross-linking or degradation of the main chain caused by the oxidative decomposition of side chain groups to a certain extent, and improve the high temperature resistance of silicone rubber. The high temperature resistance of silicone rubber is mainly reflected in the high temperature stability and the change of performance after hot air aging. Zhou Lizhuang et al. used phenyl silicone oil and iron oxide as heat resistant additives to enhance the heat resistance of silicone rubber, and found that 10 parts of phenyl silicone oil with a mass fraction of 10.2% and 6 parts of iron oxide acted together, which had the best effect on improving the heat resistance of silicone rubber. After aging at 300℃ for 48h, The hardness and tensile strength retention rates of silicone rubber were 96.23% and 86.7%, respectively. Zhang Yan et al. modified phenyl silicone rubber by mechanical strengthening of glass fiber, adding heat resistant agent of iron oxide and insulating glass ball and other fillers, and measured that the thermal decomposition temperature of modified phenyl silicone rubber could reach 445℃, which was much higher than that of ordinary silicone rubber. Su Zhengtao et al. conducted hot-air aging tests on PS5360 phenyl silicone rubber at 200℃, 250℃ and 300℃ respectively. Under the premise of ensuring the performance of phenyl silicone rubber, it was determined that its working life was 1200h, 360h and 48h respectively, and its heat-resistant aging performance was good.


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