High-refractive-index polymers of poly (carbazole phenoxy-based polyurethane) for a refractive index matching film in organic light-emitting diodes

A high-refractive index polymer of carbazole phenoxy-based polyurethane (CPP) was prepared by step-growth polymerization. Initially, bicarbazole phenoxy (BCP) derivatives were synthesized by the reaction between 9-(2-oxiranylmethyl)-9H-carbazole and 4,4′-(1-phenylethylidene)bisphenol. The step-growth polymerization of BCP and isophorone diisocyanate took place at 80°C in the presence of dibutyltin dilaurate as a catalyst affording the prepolymer with isocyanate end-groups. The CPP was obtained by the chain extension reaction of the prepolymer and bis-(2-hydroxyethyl) disulfide as an extender agent. The polymer was characterized by 1H NMR, FT-IR, and GPC. The CPP solution was spin-coated on a silicon wafer and dried under nitrogen. The transmittance of the CPP film was almost 100% as analyzed by a UV-visible spectrometer and the refractive index of the polymer was 1.63 as measured by spectroscopic ellipsometry. The result indicated that the high-refractive index CPP could be a promising material for optoelectronic device applications.