Introduction of Silicone Resin (IV)


3.2 High Crosslinking Methyl Silicone Resin


Typical organosilicon resins are bulk organosilicon polymers with active reaction groups. In order to improve the hardness of cured silicone resin, the following two methods are often used: 1) improving the functionality of silicone resin polymer, i.e. reducing the R/Si value of silicone resin components; 2) all side chain groups of silicone resin polymer are methyl, which is the shortest chain organic group, while avoiding the use of phenyl and other side chain groups.


The synthetic route of methyl silicone resin has been described before. The high hardness silicone resin should be prepared, that is to say, to synthesize methyl silicone resin with high crosslinking degree or super high degree of intersection. In order to avoid crosslinking gel in hydrolysis process, it is not suitable to use methyl siloxane as raw material, only from alkoxy silane. In order to synthesize high crosslinking degree silicone resin which can be stored stably, besides acid treatment, the raw materials of low R/Si methyl silicone resin have a larger proportion of 3 and 4 functional components, even without 2 functional components. The reaction activity is relatively higher. Therefore, mild reaction should be chosen for hydrolysis and condensation reaction. Catalyzer.


The synthesis of high crosslinking degree, especially the super high degree of intersection of methyl silicone resin, is difficult to control the synthesis reaction process. The main problem is that the gel components are easily generated in the silicone solution obtained from the synthetic reaction, that is, colloidal gel particles are often found in silicone solution. During the storage period, the active sites of the lipid solution continue to be condensed and cross-linked. The gel particles produced during the synthesis process not only damage the storage stability of the silicone solution, but also may form "fish eyes" or "crystal spots" in the coating when applied, resulting in the optical distortion and the transmittance of the silicone grease film. The disadvantage seriously damages the performance of silicone resin.


It is necessary to avoid this kind of gel center in order to make the storage stable super high degree of crosslinking methyl silicone resin. The key technology lies in the effective control of the stable and balanced hydrolysis and condensation reaction. The feasible technical means are to adopt mild catalyst and mild controllable synthesis process to regulate the hydrolysis and condensation process of organosilicon monomers, so as to avoid excessive "preemptive" hydrolysis and "independent condensation" of four functional monomers, so as to prevent the formation of condensation. A stable polymer with a predefined composition is obtained. For example, a silicone resin prepolymer with good storage stability was prepared by a mild step-by-step hydrolysis process using methyltriethoxysilane and ethyl orthosilicate as the main raw materials, weak acid as catalyst and CH3/[Si]=0.85. For example, the methyl silicone resin prepared by the above process, with compound solvent and appropriate curing agent, the cured silicone resin coating has uniform and highly transparent film. The film adheres firmly to the base material. After curing, the hardness of the pencil reaches 6H.


From Silicone Innovation Institute