Synthesis of Siloxanes Containing Vinyl and Epoxy Group and its Enhancement for Adhesion of Addition-Cure Silicone Encapsulant

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Abstract
Three types of siloxanes containing vinyl and epoxy group, (3-glycidoxypropyl) allyloxydimethoxysilane (GAMS), [2, 2-bis (allyloxymethyl) butoxy] (3-glycidoxypropyl) dimethoxysilane (AGMS) and [3-allyloxy-2, 2-bis (allyloxymethyl) propoxy] (3-glycidoxypropyl) dimethoxysilane (AAGMS) were prepared by the transetherification of 3-glycidoxypropyltrimethoxysilane with allyl alcohol, trimethylolpropane diallyl ether and pentaerythritol allyl ether, respectively. The chemical structures were characterized by Fourier transform infrared (FTIR) spectroscopy and 1H nuclear magnetic resonance (1H-NMR) spectroscopy. GAMS, AGMS and AAGMS were used as adhesion promoter for addition-cure silicone encapsulant (ASE) with a large amount of alumina (Al2O3) as thermally conductive fillers. It was found that the adhesion promoters not only greatly improved the adhesion strength of ASE but also significantly enhanced the mechanical strength of ASE. Among them, AAGMS gave the best adhesion strength and mechanical strength of ASE. The shear strength and tensile strength of ASE were increased from 0.34 and 2.23 MPa to 1.14 and 3.27 MPa with addition of 1.5 phr AAGMS, which was about 335% and 147% higher than that of ASE without adhesion promoter, respectively. The scanning electron microscopy (SEM) results showed that the adhesion promoters could improve the compatibility between Al2O3 particles and ASE matrix. Additionally, the viscosity of ASE with less than 3.5 phr AAGMS did not exceed 5000 mPa•s, which could meet the requirements of electronic encapsulation.

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