High Refractive Index Copolymers with Improved Thermomechanical Properties via the Inverse Vulcanization of Sulfur and 1,3,5-Triisopropenylbenzene

The synthesis of a novel high sulfur content material possessing improved thermomechanical properties is reported via the inverse vulcanization of elemental sulfur (S₈) and 1,3,5-triisopropenylbenzene (TIB). A key feature of this system was the ability to afford highly cross-linked, thermosetting materials, where the use of TIB as a comonomer enabled facile control of the network structure and dramatically improved the glass transition temperature (relative to our earlier sulfur copolymers) of poly­(sulfur-random-(1,3,5-triisopropenylbenzene)) (poly­(S-<i>r</i>-TIB)) materials over a range from <i>T</i> = 68 to 130 °C. This approach allowed for the incorporation of a high content of sulfur–sulfur (S–S) units in the copolymer that enabled thermomechanical scission of these dynamic covalent bonds and thermal reprocessing of the material, which we confirmed via dynamic rheological characterization. Furthermore, the high sulfur content also imparted high refractive index (<i>n</i> > 1.75) and IR transparency to poly­(S-<i>r</i>-TIB) copolymers, which offered a route to enhanced optical transmitting materials for IR thermal imaging applications with improved thermomechanical propertie