Synthesis and Characterization of Thianthrene-Based Epoxy with High Refractive Index over 1.7

A novel glycidyl resin 2,7-bis(-epoxypropylthio)thianthrene (4SEP) with high refractive index was synthesized and characterized by H-1 NMR, FT IR and FD-MS analyses. The kinetics of 4SEP cured with methylhexahydrophthalic anhydride (MeHHPA) was investigated by nonisothermal differential scanning calorimetry. The results revealed that the reactivity of 4SEP was higher compared with that of diglycidyl ether of bisphenol A (DGEBA) due to the weakened electron-withdrawing effect of thioether on the epoxy group. The thermal properties and refractive index of 4SEP/MeHHPA were investigated with differential scanning calorimetry, thermogravimetric analyses, Abbe refractometer, prism coupler, and compared with those of the DGEBA/MeHHPA. Experimental results showed that, due to the introduction of thianthrene and thioether units, the glass transition temperature (T-g) was slightly enhanced, while the thermal stability was reduced. The refractive index of 4SEP was over 1.7000, and the refractive index of 4SEP/MeHHPA was up to 1.6808.