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A novel high refractive index and highly transparent silicone resin-type material for the packaging of high-power lightemitting diodes (LEDs) is introduced, which was synthesized by hydrosilylation of vinyl end-capped methylphenyl silicone resin and methylphenyl hydrosilicone oil catalyzed by Karstedt's catalyst. The vinyl end-capped methylphenyl silicone resins were prepared by hydrolysisÀpolycondensation method from methylphenyl diethoxysilane (MePhSi(OEt) 2 ), phenyl triethoxysilane (PhSi(OEt) 3 ), and vinyl dimethylethoxy silane (Me 2 ViSiOEt) in toluene/water mixture catalyzed by cation-exchange resin. The vinyl end-capped methylphenyl silicone resins were characterized by 1 H-NMR and Fourier-transform infrared. The performances of the cured silicone resintype materials for LED packaging have been examined in detail.

Transparent flexible silicone materials are useful in electronics, sensors, coatings, and so forth. However, to the best of our knowledge, the tensile strength of unreinforced silicone rubber is lower than 0.4 MPa, and the highest tensile strength of highly transparent silicone-modified materials is no more than 1.5 MPa. The poor mechanical property limits their further application in electronic devices. Here, a kind of UV-cured transparent flexible silicone materials with tensile strength as high as 2.2 MPa were prepared by a UV-initiated thiol−ene reaction of a sulfur-containing hyperbranched polycarbosilane and a thiol silicone resin. Interestingly, their tensile strength can increase from 2.2 to 5.6 and 5.7 MPa after being immersed in an aqueous solution of 10 wt % hydrochloric acid and 10 wt % NaCl for 7 days, respectively. It is argued that the increase of the tensile strength of cured films may be attributed to the −SiOCH 3 of the residual 3-trimethoxysilylpropanethiol in the sulfur-containing hyperbranched polycarbosilane. The performances of the cured materials were investigated in detail. These silicone materials exhibit transparency higher than 95% (wavenumber in the range of 400−800 nm), and the initial thermal decomposition temperatures of the cured materials are about 340 °C. These materials also show good anticorrosion property, and the mass loss of the materials immersed in the aqueous solution mediums is no more than 0.39 wt % even for 15 days.

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