Inverse Vulcanization Polymers with Enhanced Thermal Properties via Divinylbenzene Homopolymerization-Assisted Cross-Linking

Abstract

High-refractive-index sulfur-rich polymers with significantly improved thermal properties are prepared using divinylbenzene (DVB) as a comonomer in a modified, low-temperature inverse vulcanization with elemental sulfur. Differential scanning calorimetry and Fourier transform infrared studies reveal that under the modified inverse vulcanization conditions, homopolymerized DVB segments form, leading to high glass-transition temperatures (<i>T</i>_g > 100 °C) and thermal stability previously unattainable from the inverse vulcanization of bifunctional olefin comonomers. On the basis of the modified procedures, a three-step molding process of the inverse vulcanization product of DVB, poly(S-<i>r</i>-DVB), involving (1) prepolymer formation, (2) hot-press compression molding of the soft prepolymer, and (3) thermal annealing of the molded product is demonstrated. The molded high-sulfur-content poly(S-<i>r</i>-DVB) exhibits a high refractive index (<i>n</i> > 1.85), along with high midwave infrared transmittance. Combined with a high <i>T</i>_g, these properties render poly(S-<i>r</i>-DVB) with properties highly desirable in applications involving infrared optics.