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Organosilicon resin is a highly crosslinked net structure of polyorganosiloxane, usually a mixture of methyl three chlorosilane, two methyl two chlorosilane, phenyl three chlorosilane, two phenyl two chlorosilane, or methyl phenyl two chlorosilane. In the presence of organic solvents such as toluene, water is decomposed at a lower temperature and acidity is obtained. Hydrolysate. The initial product of hydrolysis is a mixture of cyclic, linear and cross-linked polymers, and usually contains quite a lot of hydroxyl groups. The hydrolysate is washed by water and the acid is removed. The neutral primary polycondensation is heated in the air or further condensed in the presence of the catalyst, finally forming a highly cross linked three-dimensional network structure.
Silicone resin and modified organosilicon resin products are widely used in defense industry, electrical industry, leather industry, light industrial products, rubber plastic materials, food hygiene and other industries for their excellent thermal oxidation stability, electrical insulation, weatherability, waterproof, salt fog, mould proof and biocompatibility. An alternative role. China's organic silicon industry has developed greatly since the early 1950s, and has made great progress in material properties, mechanisms and applications. Compared with the advanced countries, China's technology gap is relatively small, but the gap in application is relatively large. With the increasing demand for high temperature resistant materials, organosilicon polymer, as a kind of outstanding material, can be modified and matched with organic and inorganic materials to realize the integration of structure and function. The prospect of application in high and new technology industry and cutting-edge field is very broad .
Curing is usually achieved by siloxane condensation to form silicon oxygen links. When condensation reaction is going on, the reaction rate decreases because of the steric hindrance and poor fluidity due to the gradual decrease of silanol concentration. Therefore, to completely solidify the resin, the reaction must be accelerated by heating and adding catalyst. Many substances can play a catalytic role in the condensation reaction of silanol, which include soluble organic salts of acids and bases, lead, cobalt, tin, iron and other metals, and organic compounds such as two butyl laurate tin, and so on.
The final product of silicone resin depends on the number of organic groups contained in it, that is, the ratio of R to Si. The silicone resin, which is of practical value, has a ratio of R to Si between 1.2 and 1.6. The general rule is that the smaller the value of R:Si, the more the obtained silicon resin can be cured at a lower temperature. The greater the value of R:Si, the obtained silicon resin must be cured at a high temperature at 200~250 C for a long time, and the hardness of the film is poor, but the thermal elasticity is much better than the former.
In addition, the ratio of methyl group to phenyl group in organic group also has great influence on the properties of silicone resin. The lower the content of phenyl group in organic group is, the softer the film is, the faster the condensation is, the higher the phenyl content is, the harder the film is, the more thermoplastic it is. The content of phenyl is between 20 and 60%, and the bending resistance and heat resistance of the film are the best. In addition, the introduction of phenyl can improve the compatibility of silicon resin with the pigment, and also improve the compatibility of silicon resin with other organosilicon resins and the adhesion of silicone resin to various substrates.