Synthesis process:
Usually, various mixtures of methyltrichlorosilane, dimethyldichlorosilane, phenyltrichlorosilane, diphenyldichlorosilane or methylphenyldichlorosilane are hydrolyzed at a relatively low temperature in the presence of an organic solvent such as toluene to obtain an acidic hydrolyzate. The initial product of the hydrolysis is a mixture of cyclic, linear and cross-linked polymers, which usually also contains a considerable number of hydroxyl groups. The hydrolyzate is washed with water to remove the acid, and the neutral initial polycondensate is thermally oxidized in the air or further polycondensed in the presence of a catalyst to finally form a highly cross-linked three-dimensional network structure.


Features:
The number of organic groups contained in silicone resin, i.e., the R/Si value, is one of the main indicators for controlling the quality of silicone resin. The curing property, film flexibility, hardness, heat resistance and heat cracking resistance of organic silicone resin are all related to R/Si. Generally, the R/Si of linear silicone oil is slightly greater than 2, the R/Si of silicone rubber is close to 2, and the R/Si of silicone resin is around 1.0. The smaller the R/Si value, the better the curing performance of the silicone resin, the smaller the thermal weight loss, the harder the paint film, but the flexibility is reduced, the paint film becomes brittle, and the impact resistance is reduced; the larger the R/Si value, the silicone resin needs to be baked at high temperature (200-250℃) for a long time or cured with the help of a drying agent, so that the flexibility is better, the hardness of the paint film is poor, and it has better impact resistance.
In addition, the performance of silicone resin is also closely related to the type of organic group R. When the organic group is -CH3, it can give silicone resin thermal stability, hydrophobicity, demoulding properties, and arc resistance; when the organic group is -C6H5, it can give silicone resin oxidative stability and improve the thermal stability of the resin; when the organic group is -CH=CH2, it can improve the curing performance of silicone resin and give coupling properties; when the organic group is phenyl or ethyl, it can improve the miscibility of silicone resin with organic matter; when the organic group is -NH2(CH2), it can improve the water solubility of the polymer and give coupling properties; when the organic group is a long-chain alkyl, it can improve the hydrophobicity of silicone resin. Therefore, siloxane monomers with different groups can be selected to prepare silicone resins according to specific performance requirements.


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