Visible, Mid- and Long-Wave Infrared Transparent Sulfur-Rich Polymer with Enhanced Thermal Stability

High sulfur content polymers (HSCPs) are regarded as promising materials for infrared (IR) optics, especially the long-wave IR range, due to intrinsic properties of sulfur, but the poor thermal stability of HSCPs limits their reliable utilization in wider IR applications. We herein present a new HSCP, poly(sulfur- co -hexavinyl disiloxane) (pSHVDS), prepared directly from elemental sulfur through sulfur vapor chemical deposition (sCVD). By employing hexavinyl disiloxane (HVDS) comonomer with high functionality ( f = 12) and weak absorption in the IR range, despite the poor compatibility between sulfur and HVDS, the sCVD process enables the preparation of highly cross-linked HSCP with 68 wt % sulfur. Furthermore, the combination of high refractive index (RI) of 1.842, high glass transition temperature ( T g ) of 151 °C, and high transparency in visible, mid- and long-wave IR range is achieved successfully, which is an unprecedentedly unique property compared to HSCPs reported to date. These favorable properties of pSHVDS render the material ideal for antireflection applications in IR optics, and conformal pSHVDS coatings on germanium IR lenses significantly improved the transmittance in mid- and long-wave IR regions. The developed polymer will lead the new possibility for polymer based optical devices, especially in the IR range.