Naphthoylenebenzimidazolone dyes as electron transfer photosensitizers for iodonium salt induced cationic photopolymerizations

Photoredox pairs, consisting of naphthoylenebenzimidazolone dyes and commercially available diphenyliodonium salts, are effective visible wavelength initiators for the cationic polymerization of cyclohexene oxide in air. The efficiencies of these initiator systems are based on the free energy change of the electron transfer from the naphthoylenebenzimidazolone dyes to the onium compounds. Experimental results show that the ability of tested photoredox pairs to initiate the photopolymerization strongly depends upon the oxidation potentials of the naphthoylenebenzimidazolone dyes and the reduction potentials of the iodonium salts. Additionally, the initiation species are formed from the hydrogen abstractions of the monomer by the radical cation of the dye and from the subsequent oxidations of the carbon-centered radicals of the monomer. Generally, photobleaching of the naphthoylenebenzimidazolone dyes also results from the further reduction of their protonated form.

► Two component initiator system for visible light initiated cationic polymerization.
► Naphthoylenebenzimidazolone dyes as oxidizable sensitizers.
► Iodonium salts as co-initiators.
► Initiation ability depends on oxidation potential of the dyes.
► Bleaching mechanism of dyes and initiation mechanism were proposed.