Thermal vulcanization silicone rubber refers to silicone rubber with high relative molecular mass (400,000 to 600,000). The organic peroxide is used as a vulcanizing agent, and the organic peroxide is decomposed by heating to generate free radicals, which form cross-links with the organic side groups of the rubber, thereby obtaining a vulcanizate.

Varieties and Characteristics

Hot vulcanized silicone rubber is the earliest type of rubber, and there are many varieties developed so far, which are divided into the following 7 types according to different chemical compositions:

(1) Dimethyl silicone rubber

Dimethyl silicone rubber (polydimethylsiloxanerubber), referred to as methyl silicone rubber, is the oldest variety of silicone rubber. It can maintain good elasticity in the temperature range of -60 ~ 250 ℃. Due to the shortcomings of low vulcanization activity, poor process performance, easy foaming of thick-walled products during secondary vulcanization, and large compression deformation at high temperature, it has been replaced by methyl vinyl silicone rubber except for a small amount of fabric coating.

(2) Methyl vinyl silicone rubber

Methyl vinyl silicone rubber (methylvinylpolysiloxanerubber) referred to as vinyl silicone rubber, is made of dimethyl siloxane and a small amount of vinyl siloxane copolymerization, vinyl molar fraction is generally 0.001 ~ 0.003. The introduction of a small amount of unsaturated vinyl greatly improved the vulcanization process and finished product properties, especially heat aging resistance and high temperature compression deformation resistance. In the production of silicone rubber, methyl vinyl silicone rubber has the largest output, the widest application, and the most varieties and grades. Silicone rubber, low compression permanent deformation silicone rubber, conductive silicone rubber, thermally conductive silicone rubber, and non-two-stage vulcanized silicone rubber, granular silicone rubber, etc.) are also processed and matched based on it.

(3) Methyl vinyl phenyl silicone rubber

Methylvinylphenylpolysiloxanerubber (Methylvinylphenylpolysiloxanerubber) is referred to as phenyl silicone rubber, which is made by introducing diphenylsiloxane segments (or methylphenylsiloxane segments) into the molecular chain of vinyl silicone rubber. completed. When the phenyl molar fraction is 0.05 to 0.10, it is collectively referred to as low phenyl silicone rubber. At this time, the hardening temperature of the rubber is reduced to the lowest value (-115 °C), so that it has the best low temperature resistance performance, at -100 °C The following is still elastic. With the increase of the phenyl molar fraction, the rigidity of the molecular chain also increases, and the crystallization temperature increases. When the phenyl molar fraction is 0.15 to 0.25, it is collectively referred to as medium phenyl silicone rubber, which has the characteristics of flame resistance. When the phenyl molar fraction is above 0130, it is collectively referred to as high phenyl silicone rubber, which has excellent radiation resistance. Phenyl silicone rubber is used in applications requiring low temperature resistance, ablation resistance, high energy radiation resistance, heat insulation, etc. The production and application of medium phenyl and high phenyl silicone rubber are limited due to difficult processing and poor physical properties.

(4) Methyl vinyl trifluoropropyl silicone rubber

Methylvinylrtrifluoropropylpolysiloxanerubber, referred to as fluorosilicone rubber, is a fluoroalkyl group (usually trifluoropropyl) introduced into the molecular chain of vinyl silicone rubber, which has excellent oil resistance, Solvent resistance. For example, for aliphatic, aromatic and chlorinated hydrocarbon solvents, various petroleum-based fuel oils, lubricating oils, hydraulic oils and some synthetic oils, the operating temperature range is -50 ~ 250 ° C, at room temperature and high temperature. Good stability.

(5) Phenylene silicone rubber and phenylene ether silicone rubber

Phenylene silicone rubber and phenylene ether-based silicone rubber (phenylenepolysiloxanerubberandphenylatylenesiliconerubber) are new varieties of silicone rubber containing phenylene or phenylene ether-based chains in the molecular chain. They are developed to meet the requirements of nuclear power devices and navigation technology. Its main characteristics are high tensile strength, γ-ray resistance, high temperature resistance (above 300 ℃), but the cold resistance is not as good as low phenyl silicone rubber.

(6) Nitrile silicone rubber

Nitrile silicone rubber (nitrilsiliconerubber) is mainly an elastomer containing methyl-β-nitrile ethyl silicone link or methyl-γ-nitrile propyl silicone link in the molecular chain. Its main characteristics are similar to fluorine. Silicone rubber is similar in that it is oil resistant, solvent resistant and has good low temperature resistance. However, due to the factors that cause the hydrolysis of the nitrile group under the polymerization conditions, the reproducibility of the raw rubber is poor, and its application development is limited to a certain extent.

(7) Silicon boron rubber

Silicon boron rubber (boronsiliconerubber) is a new type of silicone rubber containing a decaborane cage structure on the main chain of the molecule. Work for several hours while still retaining elasticity at -54°C. It is suitable for sealing material in high-speed aircraft and spacecraft. In the late 1960s, the United States had a series of commercial grades of silicon boron rubber, but it was rarely reported after the 1970s. The main reason may be that the process performance of the rubber compound and the elasticity of the vulcanizate are very poor, and the synthesis of carbon and boron is very complicated and toxic. Big and expensive.