Complications in the 355 nm Pulsed-Laser Polymerization of N-Vinylcarbazole

The propagation kinetics of N-vinylcarbazole (NVC) were carefully investigated via the IUPAC-recommended pulsed-laser polymerization/size-exclusion chromatography technique (PLP-SEC) in the temperature range between –20 and 20°C using 355 nm pulsed irradiation and the photo initiator 2,2-dimethoxy-2-phenylacetophenone (DMPA) as a source of primary radicals. Using this experimental approach, propagation rate coefficients, k_p, were not accessible for temperatures exceeding 20°C. There is strong evidence that the monomer itself is excited by pulsed-laser light of 355 nm, thus contributing to the polymerization process via the formation of free radicals. In addition, UV light-induced cationic polymerization processes can not be ignored as a possible side reaction. NVC polymer also absorbs strongly at 355 nm and we speculate that this may lead to bond scission and branch network formation in the PLP process. Laser-controlled molecular weight distributions are only obtained for reaction temperatures below 20°C. The apparent Arrhenius parameters, E_A and A, are 22.8 kJ·mol^–1 and 3.6×10⁷ L·mol^–1·s^–1, respectively. These results are divergent from recent literature data.