Mechanism of Charge-Transfer Polymerizations: Photopolymerization of a N-Vinylcarbazole-Maleic Anhydride System

Photochemical reactions of electron donor electron acceptor systems that involve monomers as one or both components often lead to polymerizations. Such polymerizations as initiated by means of charge-transfer interactions of monomers in the electronically excited state have been termed photoinduced charge-transfer polymerizations [1]. Among vinyl monomers, N-vinylcarbazole (VCZ) has been studied most extensively, and a complete picture including primary processes and follow-up reaction pathways of the photochemical reaction of the VCZ electron acceptor system has been brought to light [1-9]. The photochemical reaction of the VCZ electron acceptor system takes several courses, namely, cationic homopolymenzation of VCZ, cyclodimerization of VCZ to give traps-l,2-dicarbazol-9-ylcyclobutane, and free radical homopolymerization of VCZ or free radical copolymerization of VCZ with an electron acceptor monomer. The multiplicity and solvent control of these reaction courses are explained in terms of common intermediates, VCZ radical cation generated by photochemical electron transfer and VCZ dimer radical cation formed by the reaction of the VCZ radical cation with the VCZ monomer. In the present study, we have studied in detail photochemical reactions of the VCZ electron acceptor monomer system. Maleic anhydride (MAn) was used as an electron acceptor monomer, and the photochemical reaction of the VCZ MAn system was compared with that of the VCZ fumaronitrile (FN) system [6].