Synthesis of an adhesion-enhancing polyhydrosiloxane containing acrylate groups and its cross-linked addition-cure silicone encapsulant

A novel adhesion-enhancing polyhydrosiloxane containing acrylate groups (MPMS-PHMS) was prepared via the hydrolysis of 3-methacryloyloxypropylmethyldimethoxysilane and the ring-opening polymerization of octamethylcyclotetrasiloxane and tetramethylcyclotetrasiloxane, and was used as cross-linker for addition-cure silicone encapsulant (ASE) with a large amount of alumina as thermally conductive fillers. The chemical structure of MPMS-PHMS was characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, silicon nuclear magnetic resonance spectroscopy, and gel permeation chromatography. The effect of MPMS-PHMS on the properties of ASE was investigated. The results indicated that when using MPMS-PHMS as cross-linker, the cross-linking density of ASE was much higher than that of ASE using commercial poly(hydromethylsiloxane) cross-linker. It was also found that MPMS-PHMS not only markedly improved the adhesion strength of ASE to aluminum substrate but also significantly enhanced the mechanical properties of ASE. Appropriately increasing cure temperature and prolonging cure time were favorable to improve the adhesion strength of ASE. The optimal content of MPMS-PHMS was 10 phr, and the suitable cure temperature and time were approximately between 130 and 150°C and 2 h, respectively.