Radiation polymerization of N-vinylcarbazole and electroluminescent behavior of poly( N-vinylcarbazole)

Abstract

Radiation polymerization of N-vinylcarbaozle (VCz), in benzene solutions, in vacuum or nitrogen-bubbled at different concentrations was carried out by 60Co γ-ray radiation at a dose rate of 10.5 kGy/h. Unlike other vinyl compounds, VCz polymerizes at a higher radiation dosage; however, the side groups of carbazole are not eliminated from their sites. Gel permeation chromatography was used to characterize molecular weight and distribution. Oxidation was found only when polymerization was conducted using nitrogen-bubbled solutions at lower concentration of VCz. The optimization to polymerize VCz was obtained based on the dependence of polymer yield on radiation dosage. Single layer electroluminescent device based on commercially radically polymerized poly( N-vinylcarbazole) shows inferiority in luminance and efficiency, due to electronic traps resulted from heterogeneous end groups, when compared with that based on radiation-polymerized PVCz free of heterogeneous end groups. The effect of the different end groups may be confirmed by the divergent morphology when PVCz thin films were annealed above glass transition temperature ( T g).