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Heat resistance modification and application knowledge of silicone rubber
Polydimethylmethyl vinyl siloxane, commonly known as methyl vinyl silicone rubber.
Silicone rubber has good mechanical properties at high temperatures and is suitable for manufacturing molds. It can be used in fields such as precision casting and low melting point metal alloy casting.
Starting from the compatibility between silicone rubber and heat-resistant additives, cerium containing polysiloxane (POSC) with good compatibility with silicone rubber was synthesized using potassium hydroxide catalyzed ring opening polymerization of cyclotrisiloxane, methyl terminated dimethylpolysiloxane, and cerium chloride as raw materials. The infrared spectrum and silicon nuclear magnetic resonance spectrum showed that its structure was cerium containing polysiloxane.
The thermal degradation behavior of silicone rubber was studied and the apparent activation energy of its thermal degradation was calculated. The results showed that the thermal degradation apparent activation energy of silicone rubber after adding POSC was 125.5 kJ/mol, which was higher than the thermal degradation apparent activation energy of blank silicone rubber (51.0 kJ/mol), indicating that POSC improved the thermal stability of silicone rubber.
Methylphenyl vinyl silicone rubber is abbreviated as phenyl silicone rubber. This type of rubber is obtained by introducing diphenyl siloxane or methylphenyl siloxane chains into the molecular chains of vinyl silicone rubber.
According to the different phenyl content (phenyl: silicon atom) in silicone rubber, it can be divided into low phenyl, medium phenyl, and high phenyl silicone rubber. When rubber crystallizes or approaches the glass transition point, or when these two situations overlap, it can lead to a stiff state of the rubber. Introducing an appropriate amount of large volume groups can disrupt the regularity of the polymer chain, which can reduce the crystallization temperature of the polymer. At the same time, the introduction of large volume groups can change the intermolecular force of the polymer, thus also changing the glass transition temperature. Low phenyl silicone rubber (C6H5/Si=6-11%) has excellent low-temperature resistance due to the above reasons, and is independent of the type of phenyl monomer used. The brittleness temperature of vulcanized rubber is -120 ℃, making it the rubber with good low-temperature performance today. Low phenyl silicone rubber has the advantages of vinyl silicone rubber and the cost is not very high, so there is a trend to replace vinyl silicone rubber. When the phenyl content is greatly increased, the rigidity of the molecular chain will increase, leading to a decrease in cold resistance and elasticity. However, the resistance to ablation and radiation will be improved. The phenyl content of C6H5/Si=20-34% is the characteristic of medium phenyl silicone rubber with ablation resistance, while high phenyl silicone rubber (C6H5/Si=35-50%) has excellent radiation resistance.