A Microphase Separation Strategy for the Infrared Transparency‐Thermomechanical Property Conundrum in Sulfur‐Rich Copolymers

Abstract With intrinsic optical and dynamic properties of polysulfide chains, inverse vulcanized copolymers have demonstrated immense potential for infrared (IR) optical applications. However, preparing highly IR‐transparent sulfur‐rich copolymers without sacrificing their thermomechanical properties remains challenging. To overcome the trade‐off relationship between IR optical and thermomechanical properties, an in situ microphase separation strategy for the inverse vulcanization of elemental sulfur utilizing self‐crosslinkable 1,3,5‐trivinylbenzene (TVB) is presented. Even with 80 wt% sulfur content, the microphase‐separated TVB‐rich domain self‐reinforces the copolymer with a noteworthy modulus of ≈2.0 GPa and a high glass transition temperature ( T g ) of 92.6 °C, while still exhibiting outstanding IR optical properties. This work is expected to provide insights into the fundamental structure–property relationships of sulfur‐rich copolymers and pave the way for various practical applications.