Silicones are mainly divided into four categories: silicone rubber, silicone resin, silicone oil, and silicone coupling agent.
Silicone rubber is mainly divided into room temperature vulcanized silicone rubber, high temperature vulcanized silicone rubber, and liquid silicone rubber. Silicone rubber is composed of silicon and oxygen atoms to form the main chain. The side chain is a carbon-containing group. The maximum amount of silicone rubber is the side chain of ethylene. It is heat-resistant and cold-resistant. The service temperature is between 100 ℃ and 300 ℃. Excellent weather resistance and ozone resistance for good insulation. The disadvantages are low strength, poor tear resistance, and poor wear resistance.
Silicone resin is a cross-linked semi-inorganic polymer with silicon-oxygen-silicon as the main chain and organic groups connected to silicon atoms. Polyorganosiloxane with a highly cross-linked network structure is a highly branched polymer (compared to linear silicone oil) that can be cured into a solid state. It has the dual characteristics of organic resin and inorganic materials, and has unique physical and chemical properties. The performance of the final processed silicone resin product depends on the number of organic groups contained (that is, the ratio of R to Si).
The monomer for preparing silicone resins is chlorosilanes, and these chlorosilanes can all be alcoholyzed to obtain the corresponding alkoxysilanes. Because they are not corrosive, they have greater hydrolytic stability, easy to store, and easy to separate than the corresponding chlorosilanes, and are widely used monomer components. By changing the number of functional groups in the monomer and choosing different substituents, polymers with different degrees of polymerization, branching and cross-linking can be prepared, and products with different properties can be obtained to suit different uses. The number of functional groups in a monomer can be expressed by the ratio of R to Si of the monomer mixture R/Si (R is the number of substituents and Si is the number of silicon atoms). Generally, silicone resins with practical value have the ratio of R to Si in the molecular composition between 1.2 and 1.6. The general rule is that the smaller the value of R: Si, the more the obtained silicone resin can be cured at a lower temperature; the larger the value of R: Si, the greater the value of R: Si, the higher the temperature of the obtained silicone resin is to cure it. If the paint film is baked for a long time at a high temperature of 250°C, the hardness of the paint film obtained is poor, but the thermal elasticity is much better than the former. Silicone resin also has excellent moisture resistance, water resistance, rust resistance, cold resistance, ozone resistance and weather resistance. It has good corrosion resistance to most water-containing chemical reagents such as dilute mineral acids, but has poor resistance to solvents.