The monomer of silicone resin is chlorosilane, which can be alcoholized to obtain the corresponding alkoxy silane. They are widely used monomer components because they are not corrosive and have greater hydrolytic stability, easy preservation, and easy separation than the corresponding chlorosilane. By changing the number of functional groups in the monomer and choosing different substituent groups, polymers with different degree of polymerization, branching degree and cross-linking degree can be prepared, and products with different properties can be obtained to adapt to different uses.
The number of functional groups in the monomer can be expressed by the ratio of R and Si of the monomer mixture, R/Si (R is the substituted cardinal number and Si is the number of silicon atoms). Take the hydrolytic condensation of methylchlorosilane as an example:
When R/Si> At 2, that is, (CH3) 2SiCl2 and (CH3) 3SiCl are mixed and cohydrolyzed to form an oily polymer with lower molecular weight, namely silicone oil. When R/Si=2, that is, pure (CH3) 2SiCl2 hydrolytic condensation, to generate high molecular weight linear polymer that is the base material of the silicone rubber adhesive, also known as silicone rubber.
When R/Si< 2, that is, (CH3) 2SiCl2,CH3SiCl3 co-hydrolysis. Or CH3SiCl3,(CH3)2SiCl2 and SiCl4 co-hydrolytic polycondensation, to generate the polymer network structure, namely silicone resin, appropriate change of R/Si value, can be obtained different properties of silicon-containing polymers. R/Si small, that is, three or four functional silicon - oxygen unit ratio is high, after curing, high crosslinking degree, silicone hard and brittle; The R/Si is large, that is, the ratio of bifunctic siloxane unit is high, and the flexibility of silicone resin after curing is good. The R/Si usually used is between 1.2 and 1.5.