Infrared (IR) optical technologies are necessary in transportation, military, and medical applications. After the report of seminal research for inverse vulcanization of elemental sulfur (ES), low-cost and reprocessable inverse vulcanized sulfur-rich copolymers showed great potential as IR optical materials. However, the trade-off relationship between IR optical and thermomechanical properties limits inverse vulcanized sulfur-rich copolymers for IR optical applications. The high content of S–S bonds (70−90 wt % of sulfur content) can enhance the IR optical properties of sulfur-rich copolymers, while abundant polysulfide chains induce low glass transition temperature (T_g) of the sulfur-rich copolymer, making its application as an IR optical material very challenging. Herein, we present sulfur-rich copolymers with a microphase separation strategy to address the trade-off relationship between infrared transparency and thermomechanical properties. Dropwising self-crosslinkable 1,3,5-trivinylbenzene (TVB) into molten sulfur, the ES can be inverse vulcanized to microphase-separated poly(sulfur-random-TVB)s (poly(S-r-TVB)s). The microphase-separated TVB-rich domains show a modulus of ≈2.0 GPa and a high T_g of 92.6 ^oC, even with the high sulfur content of 80 wt %. Thermomechanically reinforced poly(S-r-TVB)s with reprocessablility by abundant polysulfide chains as well as excellent IR transparency and high refractive index, provide great promise for IR optical applications.

Schematic illustrations of microphase-separated poly(S-<i>r</i>-TVB)s. Microphase-separated poly(S-<i>r</i>-TVB)s exhibit robust thermomechanical properties via self-crosslinked 1,3,5-trivinylbenzene (TVB)-rich domains while maintaining excellent infrared (IR) optical properties via polysulfide-rich domains.

Schematic illustrations of microphase-separated poly(S-r-TVB)s. Microphase-separated poly(S-r-TVB)s exhibit robust thermomechanical properties via self-crosslinked 1,3,5-trivinylbenzene (TVB)-rich domains while maintaining excellent infrared (IR) optical properties via polysulfide-rich domains.

Jae Hyuk Hwang

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