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

Radiation polymerization of N-vinylcarbaozle (VCz), in benzene solutions, i n vacuum or nitrogen-bubbled at different concentrations was carried out by Co-60 gamma-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 ch romatography was used to characterize molecular weight and distribution, Ox idation was found only when polymerization was conducted using nitrogen-bub bled solutions at lower concentration of VCz. The optimization to polymeriz e VCz was obtained based on the dependence of polymer yield on radiation do sage. Single layer electroluminescent device based on commercially radicall y polymerized poly(N-vinylcarbazole) shows inferiority in luminance and eff iciency, due to electronic traps resulted from heterogeneous end groups, wh en compared with that based on radiation-polymerized PVCz free of heterogen eous end groups. The effect of the different end groups may be confirmed by the divergent morphology when PVCz thin films were annealed above glass tr ansition temperature (T-g). (C) 2000 Published by Elsevier Science Ltd. All rights reserved.