Introduction of Silicone Resin (II)


3. High Performance Silicone Resin


The universal silicone resin prepared by the above mature process and formula can meet most of the conventional use requirements, but because of some inherent defects of the existing old silicone resin, it can not fully meet the higher use requirements. In order to meet the stringent application requirements of higher performance, it is urgent to improve the synthesis process and formulation of old products. At the same time, it is necessary to research and develop new silicone resins with higher performance according to the development needs of modern new technologies.


3.1 Highly Curable Active Methylphenyl Silicone Resin


Methyl phenyl silicone resin is one of the most widely used products in organic silicone resin. The existing methyl phenyl silicone resins at home and abroad generally have some shortcomings, such as low curing activity, weak adhesion of cured coatings to substrates, and easy re-adhesion of cured coatings. These stubborn defects greatly limit the application of silicone resin.


General-purpose methyl phenyl silicone resins are generally made from methyl chlorosilane and phenyl chlorosilane by co-hydrolysis, washing, concentration and thermal condensation. Hydrolysis of organochlorosilane releases HCl, which dissolves in water to form strong acidic medium. Under acidic conditions, the hydrolysis of organochlorosilane produces not only silanol polymers, but also ring or cage inert organochlorosilane polymers. The subsequent thermal condensation reaction consumes most of the highly reactive groups in the silicone alcohol, so the curing reaction activity of the silicone resin is low, and the adhesion of the cured film to the substrate is weak. Organochlorosilane monomers are hydrolyzed in acidic medium, and the ring or cage inert organic silicone polymers are residual in the silicone resin polymer, which is equivalent to the latent solvent of the silicone resin. After curing, due to the migration and swelling of the inert organic silicone ring or cage oligomers, the silicone resin coating returns to adhesion.


In order to overcome the above shortcomings of methylphenyl silicone resin, the author improved the synthesis process. The main key technologies are: (1) regulating the condensation reaction conditions of silicone alcohol so as to retain enough reactive groups in the silicone resin polymer to improve the curing reaction activity and bonding performance of the silicone resin; and (2) eliminating the residue in the silicone resin polymer. The inert ring or cage silicone oligomers can improve the yield of silicone resin synthesis and eliminate the stubborn shortcomings of easy re-adhesion after curing.


The condensation of methyl phenyl silicone resin was catalyzed by special catalysts. The selective catalytic properties of nucleophilic reaction led to the preferential activation of the phenyl substitution position in the molecular chain of methyl phenyl silicone alcohol, which led to the condensation of the silicone hydroxyl group at the phenyl substitution position prior to the methyl substitution position to form methyl phenyl silicone. The polymer chain of the resin retains part of the methyl substituted silicone hydroxyl group in the polymer. In the curing process of silicone resin, the reaction activity of methyl substituted silicone hydroxyl is obviously higher than that of phenyl corresponding silicone hydroxyl, thus obtaining methyl phenyl silicone resin with high reaction activity. The silicone hydroxyl group retained in the silicone resin polymer with large proportion, low steric resistance and high reactive methyl substitution position improves the adhesion of the cured silicone resin to the substrate.


Another function of special catalysts is to catalyze the ring opening reaction of polycondensation process. Inert organosilicon macrocycles and cage polymers formed during the hydrolysis of organochlorosilicon also participate in polycondensation by ring opening under the action of specific catalysts, eliminating inert macrocycles and cage polymers, thus completely solving the fundamental defects of easy re-adhesion after curing of thermocondensable silicone resin; at the same time, special catalysts promote inertia. Sex ring oligomers or cage oligomers participate in the polymerization, which is also conducive to the precise control of the composition of silicone resin and the improvement of product yield.


The above selective catalysts have strong catalytic activity, fast catalytic condensation reaction speed and high curing activity of the silicone resin obtained by condensation reaction. In order to ensure that the synthesis reaction proceeds smoothly and the curing activity and storage stability of the silicone resin are taken into account, the production of high curing active silicone resin should be carried out at relatively low heating temperature. In order to control the condensation reaction process, effective monitoring methods must be matched. Three methods for monitoring the end point of the condensation reaction of silicone resin and evaluating the properties of silicone resin were determined: 1) to evaluate the degree of condensation reaction by measuring the amount of water released in the process of the condensation reaction of silicone alcohol; 2) to determine the molecular weight growth of polymers by measuring the relative viscosity of materials in the process of the reaction; 3) to determine the molecular weight growth of polymers by measuring the content of water released in the process of the condensation reaction The gelation time was used to evaluate the curing properties of silicone resin.
Silicone Innovation Institute