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

1. Dimethyl silicone rubber (abbreviated as methyl silicone rubber)

To prepare high molecular weight linear dimethylpolysiloxane rubber, high-purity raw materials are required. To ensure the purity of the raw materials, in industry, dimethyl dichlorosilane with a content of 99.5% or more is first subjected to acid catalyzed hydrolysis and condensation in ethanol water medium, and the bifunctional siloxane tetramer, namely octamethylcyclotetrasiloxane, is separated. Then, the tetramer is catalyzed to form high molecular weight linear dimethylpolysiloxane.

Dimethyl silicone rubber raw rubber is a colorless and transparent elastomer, usually vulcanized with highly active organic peroxides. Vulcanized rubber can be used within the range of -60~+250 ℃. Dimethyl silicone rubber has low vulcanization activity, large permanent deformation under high temperature compression, and is not suitable for making thick products. Thick products are difficult to vulcanize, and the inner layer is also prone to foaming. Due to the superior performance of methyl vinyl silicone rubber containing a small amount of vinyl groups, dimethyl silicone rubber has gradually been replaced by methyl vinyl silicone rubber. Other types of silicone rubber currently produced and applied contain not only dimethyl siloxane structural units, but also more or less other bifunctional siloxane structural units. However, their preparation methods are not substantially different from those of dimethyl silicone rubber. The preparation method is generally to hydrolyze and condense a certain bifunctional silicone monomer under favorable conditions for ring formation, and then add octamethylcyclotetrasiloxane in the required proportion, and then react together under the action of a catalyst to obtain it.

2. Methyl vinyl silicone rubber (abbreviated as vinyl silicone rubber)

Due to the presence of a small amount of vinyl side chains, this type of rubber is easier to cure than methyl silicone rubber, providing more types of peroxides for vulcanization and greatly reducing the amount of peroxides used. Compared with dimethyl silicone rubber, the use of silicone rubber containing a small amount of vinyl group can significantly improve the resistance to compression permanent deformation. The low compression deformation reflects better support as a seal at high temperatures, which is one of the necessary requirements for O-rings and gaskets. Methyl vinyl silicone rubber has good processability and is easy to operate. It can be made into thick products and has a smooth surface when pressed or rolled into semi-finished products. It is currently a commonly used type of silicone rubber.

3. Methyl phenyl vinyl silicone rubber (abbreviated as phenyl silicone rubber)

This type of rubber is obtained by introducing diphenylsiloxane or methylphenylsiloxane units into the molecular chain 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 will cause the rubber to become stiff. Introducing an appropriate amount of large volume functional groups can disrupt the regularity of polymer chains, thereby reducing the crystallization temperature of the polymer. Additionally, the introduction of large volume functional groups can alter the intermolecular forces between polymer molecules, thereby 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 ℃, and it is currently the best rubber with low temperature performance. Low phenyl silicone rubber combines the advantages of vinyl silicone rubber, and the interest rate is not very high, so there is a trend to replace vinyl silicone rubber. When the benzene content is greatly increased, the rigidity of the molecular chain will increase, resulting in a decrease in cold resistance and elasticity, but the resistance to erosion and radiation will be improved. A benzene content of C6H5/Si=20-34% is the characteristic of medium phenyl silicone rubber with erosion resistance, while high phenyl silicone rubber (C6H5/Si=35-50%) has excellent radiation resistance.

4. Fluorosilicone and nitrile silicone rubber:

Fluorosilicone rubber is a type of silicone rubber with fluorinated alkyl groups introduced into its side chains. The commonly used fluorosilicone rubber is one containing methyl, trifluoropropyl, and vinyl groups.

Fluorosilicone rubber has good heat resistance and excellent oil and solvent resistance. It has good stability against various fuel oils, lubricants, hydraulic oils, and some synthetic oils such as fatty hydrocarbons, aromatic hydrocarbons, chlorinated hydrocarbons, and petroleum based oils at room temperature and high temperature. These are the low-temperature properties that pure silicone rubber cannot match, which is a great improvement for pure fluororubber. The temperature range for maintaining elasticity of fluorosilicone rubber containing trifluoropropyl groups is generally -50 ℃~+200 ℃. Its resistance to high and low temperatures is inferior to that of vinyl silicone rubber, and it will produce toxic gases when heated above 300 ℃. The electrical insulation performance is much worse than that of vinyl silicone rubber. Adding an appropriate amount of low viscosity hydroxyl fluorosilicone oil to the rubber material of fluorosilicone rubber, heat treating the rubber material, and then adding a small amount of vinyl silicone rubber can significantly improve the process performance, which is conducive to solving problems such as adhesive roller sticking and serious structural storage of the rubber material, and can extend the effective service life of the rubber material. The introduction of methylphenylsiloxane chains into the above-mentioned fluorosilicone rubber can help improve its low-temperature resistance and good processability.