Silicone resin is different from silicone oil and silicone rubber. The glass transition temperature (TG) of cured silicone resin is more than 200 ℃, while that of typical silicone rubber is less than - 60 ℃. Methyl silicone resin has the lowest carbon content, high heat resistance, minimum steric hindrance of methyl groups connected to silicon atoms, high crosslinking degree, high hardness and low thermoplastic property. It is ideal as a waterproof and moisture-proof adhesive. However, the compatibility between pure methyl silicone resin and pigment is poor, and the thermal elasticity is small. The introduction of phenyl into polymethylsiloxane can improve the thermal elasticity of the product, the miscibility of pigment, and the adhesion to various substances, and also improve its thermal stability.
The properties of methylphenyl silicone resin mainly depend on two factors: one is R / Si and the other is the ratio of methyl to phenyl (CH 3 / C 6H 5)
The types of organic groups connected by silicon atoms have a great influence on the properties of the resin. When it is methyl, it can endow the silicone resin with thermal stability, demoulding property, hydrophobicity and arc resistance; when it is phenyl, it can endow the silicone resin with thermal stability, demoulding property, hydrophobicity and arc resistance The results show that the oxidation stability of the resin can destroy the crystallinity of the polymer in a certain range; the vinyl group can improve the curing property of the silicone resin and bring coupling property; the tetrachlorophenyl group can improve the lubricity of the polymer; the phenylethyl group can improve the miscibility of the silicone resin with organic matter; the aminopropyl group can improve the water solubility of the polymer, At the same time, it brings coupling property; when it is amyl, it can improve the hydrophobicity of silicone resin. Therefore, different organic groups can be introduced into the preparation of silicone resin.
In order to improve the adhesion of silicone resin, silicone resin can be copolymerized with polyester, epoxy, phenolic, etc. silicone polyester copolymer can be prepared by condensation reaction of polyester containing hydroxyl group with silane (or siloxane) containing alkoxy group, or with silane (or siloxane) containing hydroxyl group.
There are many ways to synthesize organosilicon epoxy copolymer, but most of them are prepared from commercial epoxy resin by CO condensation reaction with low molecular weight organosilicon resin containing alkoxy or hydroxyl groups according to different requirements. Silicone phenolic copolymer can also be prepared by copolycondensation of soluble silicone resin and phenolic resin, or by copolycondensation of organic acetylsilane and phenolic resin with low molecular weight. The difference is: silicone rubber is a linear structure after molecular reinforcement, vulcanized and cross-linked into a three-dimensional structure. When the trace hydroxyl terminated is contained, the aging resistance is not good enough. The light transmittance of silica reinforcement is poor. Generally, its mechanical properties are better than that of silicone resin; it has large elasticity, softness, good heat and weather resistance, and small internal stress, but its disadvantages are large gap between molecular chains, high air permeability, oxygen permeability and moisture permeability. The bonding strength is generally in the range of - 50 - 200. Silicone resin is a three-dimensional structure with a larger structure. When it contains trace terminal hydroxyl groups, it is much better than silicone rubber. It has high hardness, good light transmittance, low air permeability, moisture permeability and oxygen permeability, and its mechanical properties are generally worse than those of silicone rubber.