Synthesis of High-Refractive-Index Epoxy-Modified Vinyl Methyl Phenyl Silicone Resins for Encapsulation of LEDs

A series of high-refractive-index epoxy-modified vinyl methyl phenyl silicone resins with different content of vinyl groups have been synthesized by a combination of hydrolytic and nonhydrolytic sol–gel processes to improve their adhesion. The products were characterized by Fourier-transform infrared spectroscopy and 1H nuclear magnetic resonance spectroscopy. The results showed that epoxy and vinyl groups were successfully introduced into the products while the content of hydroxyl groups was low. Then, epoxy-modified silicone materials were manufactured by addition reaction between the epoxy-modified vinyl methyl phenyl silicone resins and hydrogen-containing phenyl silicone resin. The epoxy-modified silicone materials were characterized by thermal aging (250°C for 2 h) experiments, light transmittance measurements, thermogravimetric analysis, red dye penetration tests, reflow soldering (270°C for 10 cycles), and lumen depreciation (50 mA for 165 h) tests. The results showed that the epoxy-modified silicone materials exhibited high transmittance (> 90%) and good thermal stability. The epoxy-modified silicone materials showed better resistance to high temperature and ultraviolet (UV) radiation than commercial epoxy resin (6103). The introduced epoxy groups greatly improved the adhesion of the silicone resin. The epoxy-modified silicone material prepared using epoxy-modified vinyl methyl phenyl silicone resin with higher content of vinyl groups showed better mechanical performance (50 Shore D). The epoxy-modified silicone material EVMPS-3′ is expected to be applicable in packaging of high-power light-emitting diodes (LEDs).