Silicone resin curing is usually achieved by the condensation of silanol to form silicone chains. When the condensation reaction is carried out, due to the gradual reduction of silanol concentration, the steric hindrance is increased, and the fluidity is poor, resulting in a decrease in reaction rate. Therefore, to make the resin fully cured, it is necessary to heat and add a catalyst to accelerate the reaction. Many substances can catalyze the condensation of silanol, including acids and bases, soluble organic salts of lead, cobalt, tin, iron and other metals, and organic compounds such as dibutyltin dilaurate.
The performance of the final processed product of silicone depends on the number of organic groups contained (that is, the ratio of R to Si). Generally, silicone resins with practical value have a ratio of R to Si in their molecular composition between 1.2 and 1.6. The general rule is that the smaller the value of R: Si, the more the silicone resin can cure at a lower temperature; The larger the value of R: Si, the obtained silicone resin to cure it needs to be baked at a high temperature of 200~250℃ for a long time, the resulting film hardness is poor, but the thermoelasticity is much better than the former.
In addition, the ratio of methyl to phenyl groups in organic groups also has a great influence on the properties of silicone resins. The lower the content of phenyl in the organic group, the softer the resulting film, the faster the condensation, the higher the content of phenyl, the harder the resulting film, the more thermoplastic. The content of phenyl group is between 20 ~ 60%, and the bending resistance and heat resistance of the paint film are the best. In addition, the introduction of phenyl groups can improve the compatibility of silicone resins with pigments, as well as the compatibility of silicone resins with other organosilicone resins and the adhesion of silicone resins to various substrates.