Refractive Index Tunable Optical Films Based on In-Situ Nanoparticlization of Polynorbornene Block Copolymers
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Refractive index (RI) of the polymer films is largely affected by molar refraction of the elements within the polymers. Sulfur and fluorine are well-known elements for RI tuning, due to its significantly different molar refraction compared to typical hydrocarbon. While higher sulfur content increases the RI of a polymer film, fluorine content gives opposite trend of RI change. Herein, we report the synthesis of polynorbornene based block copolymers (BCPs) containing sulfur- and fluorine-rich blocks, and their application to RI-tunable optical films. Owing to intrinsic low solubility of both elements, sulfur- or fluorine-rich BCPs undergo in-situ nanoparticlization during the polymerization. Average size of the self-assembled nanoparticles under 100 nm prevents undesired light scattering, making films from those BCPs highly transparent. By controlling the monomer feed ratio, RI of the polymer films can be precisely tuned within a wide range.