Several important types of silicone rubber are introduced below.

1. Methyl silicone rubber

Methyl silicone rubber is the earliest type of silicone rubber that has been put into commercial production. It can maintain good elasticity in the range of -60 to 200 °C, good aging resistance, excellent electrical insulation performance, and moisture-proof, shock-proof and physiological inert properties. .

Methyl silicone rubber is mainly used for the coating of strong objects, and can also be made into various extrusion and calendering products for electromechanical, aviation, automotive and medical industries. However, due to the low vulcanization activity of dimethyl silicone rubber, when it is used to manufacture thick products, it is difficult to vulcanize, the inner layer is easy to foam and the permanent deformation of high temperature compression is large, so it has been replaced by methyl vinyl silicone rubber.

2. Methyl vinyl silicone rubber

Since the introduction of a small amount of vinyl groups into the macromolecular structure of silicone rubber can greatly improve the vulcanization processability of silicone rubber, most of the currently used silicone rubbers contain vinyl groups. Methyl vinyl silicone rubber is the most common type of silicone rubber and currently dominates the production of silicone rubber at home and abroad. Due to the introduction of partially unsaturated vinyl groups on the side chain, its processability and physical and mechanical properties are superior to those of two-base silicone rubber. In addition to the general characteristics of dimethyl silicone rubber, it also has a wide operating temperature range and can maintain good elasticity in the range of 60 to 260 ° C. It is easier to vulcanize than dimethyl silicone rubber and has a smaller compression permanent Deformation, better solvent expansion resistance and high pressure steam resistance stability and excellent cold resistance, etc., and because of the use of peroxides with lower activity for vulcanization, it reduces the generation of bubbles during vulcanization and poor rubber stability. weakness. Therefore, methyl vinyl silicone rubber can generally be used to make products with larger thicknesses. Methyl vinyl silicone rubber is the most widely used variety of silicone rubber. In recent years, various high-performance and special-purpose silicone rubbers have emerged, mostly based on vinyl silicone rubber, such as high-strength silicone rubber, low Compression set silicone rubber, no post-vulcanization silicone rubber, heat-resistant conductive silicone rubber and medical silicone rubber, etc. In the aviation industry, methyl vinyl silicone rubber is widely used as a protective layer for gaskets, sealing materials and fragile and shock-proof parts; in the electrical industry, it can be used as advanced insulating materials such as electronic components, dynamic sealing rings for high temperature potentiometers, Sealing ring for underground long-distance communication equipment; in medicine, because methyl vinyl silicone rubber has little physiological response to the human body and is non-toxic, it is used for surgical plastic surgery, artificial heart valves, blood vessels, etc.

3. Methylphenyl vinyl silicone rubber

The introduction of a phenyl group on the side group of the polysiloxane can greatly reduce the crystallization temperature of the polymer due to the destruction of the regularity of the dimethylsiloxane structure and expand the low-temperature application range of the polymer material. Therefore, in addition to the small compression set, wide temperature range, oxidation resistance, weather resistance, shock resistance, moisture resistance and good electrical insulation properties of methyl vinyl silicone rubber, methyl phenyl vinyl silicone rubber also has excellent electrical insulation properties. Low temperature resistance, ablation resistance and radiation resistance. These properties vary with the phenyl content in the molecular chain. Generally speaking, when the phenyl content (ratio of phenyl to silicon atoms) is 5-10%, it is called low phenyl silicone rubber, which has unique cold resistance. It can still maintain the elasticity of rubber at -70 ~ -100 ℃, which is the best low-temperature performance among all rubbers. In addition, it has the advantages of methyl vinyl silicone rubber and the cost is not high, so it has great potential to replace methyl vinyl silicone rubber. based vinyl silicone rubber trends. When the phenyl content is 20-40%, it is said that the middle phenyl silicone rubber has both the advantages of methyl vinyl silicone rubber and the cost is not high, so there is a great tendency to replace methyl vinyl silicone rubber. When the phenyl content is 20 to 40%, it is called medium phenyl silicone rubber. It has excellent flame resistance and can self-extinguish once it catches fire. When the phenyl content is 40-50%, it is called high phenyl silicone rubber, which has excellent radiation resistance, and its resistance to γ-ray is 1xI08 roentgen. Generally speaking, with the increase of phenyl content, the rigidity of the molecular chain of silicone rubber gradually increases, and the low temperature resistance of silicone rubber gradually decreases, but with the increase of phenyl content, the flame resistance and radiation resistance of vulcanizate are improved. photogenic.

Methyl phenyl vinyl silicone rubber is one of the important materials in the aerospace industry, cutting-edge technology and other sectors of the national economy. Sealing rings, gaskets, pipes and bars for heat-aging or radiation-resistant parts.

4. Fluorosilicone rubber

Fluorosilicone rubber refers to γ-trifluoropropyl methyl polysiloxane. Fluorosilicone rubber has excellent chemical resistance, solvent resistance and lubricating oil resistance. This kind of silicone rubber has a small expansion rate in non-polar solvents, good cold resistance and thermal stability, and good fire resistance, so it is used in aircraft. , rockets, missiles, space flight, petrochemical used as contact hoses, gaskets, seals, fuel tanks, etc. with fuel oil and lubricating oil, and can also be used to make corrosion-resistant clothes, gloves, coatings, adhesives, etc. .

5. Nitrile Silicone Silicone Rubber

Because the side chain of the polymer molecule contains β-nitrile ethyl or γ-nitrile propyl strong polar groups, the intermolecular force is greatly increased, and the oil and solvent resistance properties are improved. At the same time, due to the introduction of a certain amount of nitrile alkyl groups, the regularity of the polymer structure is destroyed, and the cold resistance is also greatly improved. The type and content of nitrile alkyl groups have a great influence on performance. For example, silicone rubber containing 7.5 mole% γ-nitrile propyl group has similar low temperature performance to low phenyl silicone rubber (its glass transition temperature is -114.5 ° C), Oil resistance is better than phenyl silicone rubber. As the content of γ-nitrile propyl group increased to 33-50 mole %, the cold resistance decreased and the oil resistance improved. Replacing γ-nitrile propyl with β-nitrile ethyl can improve the heat resistance of nitrile silicone rubber, which can withstand 250 ℃ hot air aging.

The main advantage of nitrile silicone rubber is that it has excellent oil resistance and bath resistance, and can maintain elasticity in the range of -60 to 180 ° C. Therefore, it can be made into oil-resistant rubber products for the aviation industry, automobile industry and petroleum industry; also It can be used as environmental sealant and fuel tank sealant for high-performance aircraft, and can maintain sealing at -54°C to above 200°C. Nitrile silicone rubber can be processed with ordinary equipment.

6. Phenylene silicone rubber

The main feature of phenylene silicone rubber is that it has excellent radiation resistance. Its radiation resistance is 10 to 15 times that of general methyl vinyl silicone rubber and 5 to 10 times that of high phenyl silicone rubber. Therefore, it can be used for Aerospace industry, atomic energy industry and nuclear reactors are used as cables, sheaths, gaskets and heat shrinkable tubes that are resistant to high-energy radiation.

7. Ethyl silicone rubber

The diethyl silicone rubber prepared by introducing an ethyl group into the side chain of polysiloxane has the outstanding performance of particularly good cold resistance, which is better than dimethyl silicone rubber and general methyl vinyl silicone rubber. The higher the ethyl content, the better the cold resistance. However, the reactivity of ethyl group is higher than that of methyl group, so the heat resistance decreases with the increase of ethyl group content. As the ethyl silicone rubber used at low temperature, it is preferable to contain 8 mol% of diethylsiloxane chain units in the polymer. The use temperature of ethyl silicone rubber is generally -70--200 ℃.

8. Silicon nitrogen rubber

The main advantage of silicon-nitrogen rubber is that it has excellent thermal stability, it does not decompose at 430-480 °C, and some can even withstand high temperatures above 500 °C. The outstanding weakness of silicon-nitrogen rubber is its poor hydrolytic stability, which was once considered to have no future. It was later found that the polymer with cyclodisilazane incorporated into the main chain has good thermal stability. The cyclodisilazane-containing elastomer modified with silicon arylene does not lose weight when heated to 425° C. in air, but only loses 10% at 570° C., and has good hydrolysis stability.