A New Dealcoholization Method in the Synthesis of Vinyl Methyl Phenyl Silicone Resins for LED Encapsulation

Abstract

The oligosiloxane resins were synthesized through hydrolytic sol-gel reaction and remained many hydroxyl groups, which did great harm to the curing process and resulted in poor performance of the cured products. In previous works, epoxy-modified silicone resins were synthesized by dealcoholization, a reaction between 3-glycidoxypropylmethyldimethoxysilane and terminal hydroxyl groups in phenyl silicone resins. Although this method eliminated the hydroxyl groups, it caused a large loss of vinyl groups inevitably and a poor stability of cured products. In this study, methyltrimethoxysilane (MTMS) was used to eliminate hydroxyl groups containing in vinyl methyl phenyl silicone resins, which were synthesized through hydrolytic sol-gel reaction. Most of residual hydroxyl groups were deleted effectively and the great loss of vinyl groups were avoided in the dealcoholization reaction. Then, the methyl phenyl silicone materials were fabricated by hydrosilylation reaction between the synthesized vinyl methyl phenyl silicone resins and hydrogen-containing ones. The cured silicone materials showed excellent optical performance (~ 89.1% at 450 nm) and good adhesion performance. In addition, due to less vinyl loss in the vinyl methyl phenyl silicone resins, the cured methyl phenyl silicone materials exhibited higher cross-linking density, better thermal resistance (5% mass loss at 435 °C) and better mechanical properties (50 shore D) compared with the epoxy-modified phenyl silicone materials. The lumen depreciation (working 168 h at 50 mA) and reflow soldering tests further demonstrated the methyl phenyl silicone materials possessed good thermal stability. These results indicated that the methyl phenyl silicone materials could be used as a LED encapsulant with a good performance.