Thermal Imaging and Clandestine Surveillance using Low‐Cost Polymers with Long‐Wave Infrared Transparency

With increasing use of infrared imaging in medical diagnostics, military and civilian surveillance, and navigation of autonomous vehicles, there is a need for low‐cost alternatives to traditional materials used in infrared optics such as germanium. Sulfur‐rich copolymers hold promise, as they are made from low‐cost feedstocks and have a high refractive index. In this report, cyclopentadiene is copolymerized with sulfur to provide a plastic with the highest long‐wave infrared transparency reported to date for this class of materials. Diverse lens architectures are accessible through melt casting or reactive injection molding. The featured copolymer is black, which enabled its use as an infrared‐transparent blind for protection of thermal imaging equipment and clandestine surveillance. These findings portend expanded use of sulfur copolymers in infrared optics. A copolymer made from low‐cost cyclopentadiene and elemental sulfur has the highest long‐wave infrared transparency reported to date for a synthetic polymer. The material can be processed by reactive injection molding to access a variety of thermal imaging lenses and devices. New applications in thermal imaging for clandestine surveillance are reported.