The monomer for the preparation of silicone resin is chlorosilane, which can be alcoholyzed to obtain the corresponding alkoxy silane. They are widely used monomer components because they are not corrosive, and have greater hydrolysis stability, easy preservation and easy separation than the corresponding chlorosilane. By changing the number of functional groups in 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 meet different applications.
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 substitutional cardinal order, Si is the number of silicon atoms). Take the hydrolysis condensation of methyl chlorosilane as an example:
When R/Si> 2, that is, with (CH3) 2SiCl and (CH3) 3SiCl mixed co-hydrolysis, the formation of low molecular weight oily polymer, namely silicon oil. When R/Si=2, that is, with pure (CH3) 2SiCl2 hydrolysis condensation, the generation of high molecular weight linear polymer that is said behind the base material of silicone rubber adhesive, also known as silicon rubber.
When R/Si< 2, namely (CH3) 2SiCl2,CH3SiCl3 co-hydrolysis. Or CH3SiCl3,(CH3)2SiCl2 and SiCl4 co-hydrolytic polycondensation, the formation of a network structure of the polymer, namely silicone resin, appropriate change in the value of R/Si, can get different properties of silicon-containing polymer. When R/Si is small, that is, the ratio of tri-functional or four-functional silicon-oxygen unit is high, after curing, the cross-linking degree is high, and the silicone resin is hard and brittle; The R/Si is large, that is, the ratio of bifunctional silicon-oxane unit is high, and the flexibility of the cured silicone resin is good. The R/Si usually used is between 1.2-1.5.
Silicone resin is different from silicone oil and silicone rubber, the glass transition temperature (Tg) of the cured silicone resin > 200℃, whereas typical silicone rubber; 60 ℃. Methyl silicone resin has the lowest carbon content, it has a very high heat resistance, silicon atoms connected to the methyl group the least steric resistance, resin crosslinking degree is high, high hardness, small thermoplasticity, as a waterproof, moisture-proof adhesive is very ideal. However, pure methyl silicone resin has poor compatibility with pigments and small thermal elasticity. The introduction of phenyl in polymethyl siloxane can improve the thermal elasticity of the product and the miscibility of pigments, as well as the adhesive property of various substances, and can also improve its thermal stability. The properties of methylphenyl silicone resins depend mainly on two factors: one is the R/Si mentioned above, and the ratio of methyl to phenyl group (CH3/C6H5) is closely related.


From the above three kinds of silicone resin can be seen: silicon atoms connected to the type of organic groups have a great impact on the performance of the resin, when methyl, can give silicone resin thermal stability, demoulding, hydrophobicity, arc resistance; Is phenyl, endowing the resin oxidation stability, it can destroy the crystallization of the polymer in a certain range; When it is vinyl, it can improve the curing properties of silicone resin and bring coupling; When it is tetrachlorobenzene, it can improve the lubricity of the polymer; When it is phenyl ethyl group, the miscibility of silicone resin and organic matter can be improved. When it is ammonia propyl, it can improve the solubility of the polymer and bring coupling. The hydrophobicity of silicone resin can be improved when it is amyl group. Therefore, different organic groups can be introduced into the preparation process of silicone resin. In order to improve the adhesion of silicone resins, silicone resins can be copolymerized with polyester, epoxy, phenolic, etc. Silicone-polyester copolymer can be prepared by condensation reaction of polyester containing hydroxyl and silane containing alkoxy group (or siloxane), or silane containing silicon hydroxyl group (or siloxane).


There are many ways to synthesize organosilicone - epoxy copolymer, but most of them are based on commercial epoxy resin as raw material, according to different requirements, choose appropriate varieties and low molecular weight organosilicone resin containing alkoxy group or hydroxyl group for copolycondensation reaction to prepare copolymer.


Silicone - phenolic copolymers can also be prepared by copolycondensation of soluble silicone resin with phenolic resin, or by copolycondensation of organic acetylsilane with low molecular weight phenolic resin.