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

Silicone resins are generally prepared from organosilanes by hydrolysis and polycondensation in the presence of a solvent. Synthetic raw materials are generally chlorosilane or alkoxysilane. The specific processes are as follows: first, the silane is hydrolyzed to silanol under certain conditions; second, the silanol undergoes a condensation polymerization reaction; For example, Xu Xiaoqiu etc. first hydrolyzed methylphenyldiethoxysilane, cracked into methylphenyl ring body at high temperature, and then synthesized anionic ring-opening polymerization to synthesize colorless and transparent phenyl vinyl silicone oil with a refractive index above 1.5. Wu Tao et al. Used anionic ring-opening polymerization method to prepare vinyl-terminated methylbenzene from a cyclic methylphenylsiloxane containing a dimethylsiloxane chain and a vinyl double-end cap under the action of a basic catalyst. Base silicone oil. Wu Chuan et al. Used acid-catalyzed octamethylcyclotetrasiloxane (D4), or mixed 1,3,5,7-tetramethylcyclotetrasiloxane (D4H) with methylphenyl in toluene Polymerization in a solvent to prepare a silicone hydrogen-containing silicone oil as a cross-linking agent. The ratio of the amount of Ph to Si is 0.30 to 0.60, the active hydrogen mass fraction is 0 to 0.5%, the refractive index is 1.39 to 1.51 (25 ° C), and the dynamic viscosity is 100 to 550 mPa · s. Wang Xiaolu and others synthesized a phenylvinyl transparent silicone resin using a solvent-free method; vinyl trimethoxysilane, hydroxyl-terminated polydimethylsiloxane, diphenyldimethoxysilane, and phenyltrimethoxysilane were selected as A raw material, a hydrochloric acid aqueous solution is used as a catalyst, and a hydrolysis and condensation reaction is performed to synthesize a high refractive index transparent silicone resin having flowability at room temperature. In order to reduce the surface tension of the LED encapsulant and make it easy for vacuum defoaming, Yang Xiongfa and others prepared a transparent vinyl silicone oil containing methyltrifluoropropylsiloxane chain links and methylphenylsiloxane chain links. Huang Ronghua et al. Used methyl vinylchlorosilane, phenylchlorosilane, methylchlorosilane, and phenylchlorosilane as raw materials, and capped with methyl capping agent and vinyl capping agent to synthesize phenyl vinyl silicone resin. Then filtering with a filter having a pore size of 0.45 μm can effectively remove small residual hydrochloric acid particles, improve product transparency, and obtain a colorless and transparent vinyl phenyl silicone resin.