Synthesis and characterization of transparent high-refractive index polyurethanes

In this study, high-refractive index carbazole-based polyurethanes (CBPs) were prepared. Firstly, bifunctional carbazole derivatives (BCDs) were synthesized by reacting 9-(2-oxiranylmethyl)-9H-carbazole with bisphenol A. Then, CBPs were prepared by step-growth polymerization of BCDs and isophorone diisocyanate in the presence of dibutyltin dilaurate. The polymer solution was spin-coated on a silicon wafer or a glass plate, and the sample was dried under nitrogen to give a transparent film. The product was characterized by 1H-NMR, GPC, TGA and DSC. The refractive index of the film was measured by spectroscopic ellipsometry. The transmittance of polyurethane films was observed by a UV-visible spectrometer. The refractive index of CBPs was 1.62 on average at 400 to 750 nm. The results suggest that the polyurethane films are promising materials for application in display industry.