Quinoxaline derivatives as long wavelength photosensitizers in photoinitiated cationic polymerization of diaryliodonium salts

The present paper is focused on visible light initiated cationic polymerizations. Photoinitiated polymerization of representative vinyl ether and oxirane monomers using two quinoxaline derivatives; namely (2-(2,3-dihydrobenzo [b][1,4]dioxin-6-yl)-3-(2,3-dihydrobenzo[b]-[1,4]dioxin-7-yl)-5-(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-8-(2,3-dihydrothieno[3,4-b][1,4]dioxin-7yl) quinoxaline) (DBQEd) and 2,3,5,8-tetra(thiophen-2-yl)quinoxaline (TTQ) are studied. Novel dyes based on the quinoxaline skeleton are employed as efficient photosensitizers in cationic photopolymerizations. Polymerizations were initiated at room temperature upon irradiation with long-wavelength UV and visible lights in the presence of diphenyliodonium hexafluorophosphate (Ph2I+PF6−). The progress of the polymerizations was monitored by optical pyrometry (OP). Solar irradiation is also employed to carry out the cationic polymerization of a diepoxide monomer in the presence of air.

DBQEd and TTQ are shown to work as excellent electron transfer photosensitizers for diaryliodonium salt photoinitiators. Their strong absorption characteristics and low oxidation potentials due to their extended conjugation facilitate the photoinitiated cationic polymerization of epoxides and vinyl ethers using long wavelength UV and visible light as well as solar irradiation.Figure optionsDownload as PowerPoint slideHighlights
► Two quinoxaline derivatives were employed as photosensitizers.
► Various epoxide and vinyl monomers were efficiently cationically photopolymerized.
► Polymerizations were carried out using long wavelength UV and visible light.
► Polymerizations displayed no induction period in the presence of the dye molecules.
► Subjection of a monomer to solar irradiation afforded fully cured polymer films.