(7) Thermal stability without curing

It refers to putting the uncured silicone rubber plane sealant in the high temperature environment for a certain period of time, and then it can still be cured under the standard conditions. It is clarified that the silicone rubber plane sealant is stable under the temperature conditions. If the thermal stability temperature of sealant is ≥ 100 ℃, it means that the uncured sealant can continue to cure after heating at 100 ℃.

According to the different content of phenyl (phenyl: silicon atom) in silicone rubber, it can be divided into low phenyl, medium phenyl and high phenyl silicone rubber. When the rubber crystallizes or approaches the glass transition point or the two conditions overlap, the rubber will show a stiff state. The introduction of large volume groups can destroy the regularity of the polymer chain, which can reduce the crystallization temperature of the polymer. At the same time, because the introduction of large volume groups changes the force between the polymer molecules, it can also change the glass transition temperature. Low phenyl silicone rubber (C6H5 / Si = 6 ~ 11%) has excellent low temperature resistance due to the above reasons, and has nothing to do with the type of phenyl monomer used. The brittleness temperature of vulcanizate is - 120 ℃, which is the best rubber at low temperature. Low phenyl silicone rubber has the advantages of vinyl silicone rubber, and the cost is not very high, so it has the trend of replacing vinyl silicone rubber. When the content of phenyl is increased, the rigidity of molecular chain will be increased, which will lead to the decrease of cold resistance and elasticity, but the ablation resistance and radiation resistance will be improved. When the content of phenyl reaches C6H5 / Si = 20-34%, the medium phenyl silicone rubber has the characteristics of ablation resistance, while the high phenyl silicone rubber (C6H5 / Si = 35-50%) has the excellent radiation resistance.