Synthesis of silane oligomers containing vinyl and epoxy group for improving the adhesion of addition-cure silicone encapsulant

Two types of silane oligomers containing vinyl and epoxy group (PTGM and PTGE) as adhesion promoters were synthesized by the reaction of trimethylolpropane monoallyl ether with 3-glycidoxypropylmethyldimethoxysilane and 3-glycidoxypropylmethyldiethoxysilane, respectively. Fourier transform infrared spectroscopy, ¹H nuclear magnetic resonance spectroscopy, and gel permeation chromatography were used to characterize their chemical structures. The effect of adhesion promoters on properties of addition-cure silicone encapsulant (ASE) with lots of alumina (Al₂O₃) particles as thermally conductive fillers was investigated. The results showed that PTGM and PTGE could significantly improve both the adhesive strength and mechanical properties of ASE. The viscosity of ASE with no more than 3.0 phr PTGM and PTGE was below 5000 mPa s so that they were suitable for encapsulating process. Observation using scanning electron microscopy revealed that PTGM and PTGE could improve the dispersion of Al₂O₃ particles in silicone rubber matrix and enhance the bond between the particles and the matrix.