A novel high-refractive index episulfide-thiol polymer for nanoimprinting optical elements

A novel optical polymer with a high refractive index (n = 1.707 at 590 nm) was developed consisting of episulfide and thiol bifunctional monomers. The episulfide derivative of 9,9-bis(4-glycidyloxyphenyl)fluorene, synthesized by the reaction of an epoxide and inorganic thiocyanate, reacts by a ring-opening polymerization with 4,4-thiodibenzenethiol to produce the optical polymer with high transparency over the visible region of the spectrum and thermally stable up to 290 °C. The developed episulfide-thiol optical polymer can be thermally nanoimprinted at 160 °C with nanoscale size resolution. Different nanostructures including sub-micron and nanoscale size gratings, two-dimensional photonic crystals, and plano-convex semispherical microlenses were successfully nanoimprinted with excellent pattern fidelity and low defectivity. These results exhibit the episulfide-thiol optical polymer as a potential candidate for applications in optical and optoelectronic devices.