According to its vulcanization characteristics, silicone rubber can be divided into two types: hot vulcanized silicone rubber and room temperature vulcanized silicone rubber. According to the different performance and use, it can be divided into general type, ultra-low temperature type, ultra-high temperature type, high strength type, oil-resistant type, medical type and so on. According to the different monomers used, it can be divided into methyl vinyl silicone rubber, methyl phenyl vinyl silicone rubber, fluorosilicone, nitrile silicone rubber and so on.

1. Dimethyl silicone rubber

In order to prepare linear dimethylpolysiloxane rubber with high molecular weight, high purity raw materials are necessary. In order to ensure the purity of raw materials, the dimethyldichlorosilane with 99.5% content is usually purified by refined neptunium in industry, hydrolyzed and condensed in ethanol-water medium catalyzed by acid, and the bifunctional degree is separated. Siloxane tetramers, namely octamethylcyclotetrasiloxane, are then used to form linear dimethylpolysiloxane with high molecular weight under the action of catalyst.

Dimethyl silicone rubber raw rubber is a colorless and transparent elastomer, which is vulcanized by organic peroxide with higher activity. The vulcanizate can be used in the range of - 60 ~250 C. The vulcanization activity of dimethyl silicone rubber is low and the permanent deformation of high temperature compression is large. It is not suitable for making thick products. The vulcanization of thick products is difficult and the inner layer is easy to foam. Because the properties of methyl vinyl silicone rubber containing a small amount of vinyl are better than others, dimethyl silicone rubber has been gradually replaced by methyl vinyl silicone rubber. Other types of silicone rubber produced and applied nowadays contain more or less other bifunctional silicone structural units besides dimethylsiloxane structural units. However, there is no substantial difference between the preparation method of silicone rubber and that of dimethylsiloxane. The preparation method of silicone rubber is generally in favour of ring formation. The difunctional silicon monomers were hydrolyzed and condensated, then octamethylcyclotetrasiloxane was added according to the required proportion, and then synthesized under the action of catalyst.

2. Methyl vinyl silicone rubber

This kind of rubber contains a small amount of vinyl side chain, so it is easier to vulcanize than methyl silicone rubber, so that it has more kinds of peroxides for vulcanization, and can greatly reduce the amount of peroxides. Comparing with dimethyl silicone rubber, silicone rubber with a small amount of vinyl group can significantly improve the compression permanent deformation resistance. Low compression deformation reflects that as a seal, it has better support at high temperature, which is one of the requirements of O-rings and gaskets. Methyl vinyl silicone rubber is a kind of silicone rubber with good technological properties and easy operation. It can be made into thick products and smooth surface of extruded and calendered semi-finished products.

3. Methyl phenyl vinyl silicone rubber

The rubber is obtained by introducing diphenylsiloxane or methylphenylsiloxane segments into the molecular chain of vinyl silicone rubber.

According to the different content of phenyl in silicone rubber (phenyl: silicon atom), 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 be rigid. The regularity of polymer chains is destroyed by introducing a suitable amount of large groups, which can reduce the crystallization temperature of polymers. At the same time, the glass transition temperature can also be changed because the introduction of large groups changes the intermolecular force of polymers. 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 C. Nowadays, the rubber with the best low temperature performance is used. Low-phenyl silicone rubber has both the advantages of vinyl silicone rubber and the interest rate is not very high, so it has the tendency to replace vinyl silicone rubber. When the phenyl content is greatly increased, the rigidity of the molecular chain will increase, which will lead to the decrease of cold resistance and elasticity, but the ablation resistance and radiation resistance will be improved. The phenyl content up to C6H5/Si=20~34% is a medium-phenyl silicone rubber with ablation resistance, while the high-phenyl silicone rubber (C6H5/Si=35~50%) has excellent resistance. Radiation performance.

4. Silicone fluoride and silicone nitrile rubber:

Fluorosilicone rubber is a kind of silicone rubber with side chain introducing fluoroalkyl. The commonly used fluorosilicone rubber is fluorosilicone rubber containing methyl, trifluoropropyl and vinyl groups.

Fluorosilica gel has good heat resistance and excellent oil and solvent resistance, such as good stability to aliphatic hydrocarbons, aromatic hydrocarbons, chlorinated hydrocarbons, petroleum-based fuel oils, lubricants, hydraulic oils and some synthetic oils at room temperature and high temperature. These fluorosilicone rubber are better than pure silicone rubber. Low temperature performance is a great improvement for pure fluorine rubber. The temperature range of fluorosilicone rubber containing trifluoropropyl is generally - 50 ~200 C. The high and low temperature resistance of fluorosilicone rubber is worse than that of vinyl silicone rubber, and toxic gases will be produced when heated to above 300 C. The electrical insulation performance is much worse than that of vinyl silicone rubber. Adding proper amount of low-viscosity hydroxyl fluorosilicone oil, heat treatment of the rubber and a small amount of vinyl silicone rubber can improve the process performance significantly, which is beneficial to solving the problems of serious roll sticking and storage structure of the rubber, and prolong the effective service life of the rubber. The introduction of methyl phenyl silicone oxide chains into the fluorosilicone rubber mentioned above will contribute to the improvement of low temperature resistance and good processing performance.