According to its refractive index, it can be divided into low refractive index (1.4) and high refractive index (1.5). The refractive index of 1.4 is mainly methyl type silicone material, and the refractive index of 1.53 is mainly phenyl type silicone material. Since the higher the refractive index of the organic silicon material, the higher the light extraction efficiency, so the refractive index of the organic silicon material should be increased as much as possible.


Silicone resins are generally prepared by hydrolyzing and polycondensing organosilanes in the presence of solvents. The synthetic raw material is generally chlorosilane or alkoxysilane. The specific process is as follows: firstly, silane is hydrolyzed into silanol under certain conditions, secondly, the silanol itself undergoes polycondensation reaction, and thirdly, it is neutralized by washing with water and concentrated to remove small molecules to obtain silicone resin. For example, Xu Xiaoqiu first hydrolyzed methyl phenyl diethoxy silane and cracked it into methyl phenyl ring body at high temperature, and then synthesized colorless and transparent phenyl vinyl silicone oil with a refractive index of 1.5 or more through anionic ring-opening polymerization. Wu Tao et al. used anionic ring-opening polymerization method to prepare vinyl-terminated methylbenzene from cyclic methyl phenyl siloxane containing dimethyl siloxy chain links and vinyl double caps under the action of alkaline catalysts. Base silicone oil. Wu Chuan et al. used acid catalysis, octamethylcyclotetrasiloxane (D4), or mixed 1,3,5,7-tetramethylcyclotetrasiloxane (D4H) and methylphenyl in toluene Polymerize in solvent to prepare crosslinking agent organosilicon hydrogen-containing silicone oil. The ratio of the amount of Ph to Si is 0.30～0.60, the mass fraction of active hydrogen is 0～0.5%, the refractive index is 1.39～1.51 (25℃), and the dynamic viscosity is 100～550 mPa·s. Wang Xiaolu et al. used a solvent-free method to synthesize phenyl vinyl transparent silicone resin; selected vinyl trimethoxy silane, hydroxyl-terminated polydimethylsiloxane, diphenyl dimethoxy silane, and phenyl trimethoxy silane as The raw material, hydrochloric acid aqueous solution as a catalyst, undergoes hydrolysis and condensation reaction to synthesize a high refractive index transparent silicone resin with fluidity at room temperature. In order to reduce the surface tension of the LED packaging glue and make it easy to vacuum degas, Yang Xiongfa et al. prepared transparent vinyl silicone oil containing methyl trifluoropropyl siloxane chain links and methyl phenyl siloxane chain links. Huang Ronghua and others used methyl vinyl chlorosilane, phenyl chlorosilane, methyl chlorosilane, and phenyl chlorosilane as raw materials, and used methyl capping agent and vinyl capping agent to block the ends to synthesize phenyl vinyl silicone resin. Then it is filtered with a filter membrane with a pore size of 0.45 μm, which can effectively remove the small particles of residual hydrochloric acid, improve the transparency of the product, and obtain a colorless and transparent vinyl phenyl silicone resin.