A Photoinitiation System for Conventional and Controlled Radical Polymerization at Visible and NIR Wavelengths

We report for the first time the use of phthalocyanine compounds, in conjunction with the common solvent N-methyl-2-pyrrolidone (NMP), as a photoinitiation system for radical polymerization under various visible and near-infrared wavelengths. A library of redox-inactive metallic phthalocyanine compounds were investigated for their ability to act as photosensitizers in these new two-component photoinitiation systems, for the radical polymerization of (meth)acrylate and (meth)acrylamide monomers. Conventional radical polymerization under these conditions was successful, and moreover, the addition of reversible addition-fragmentation chain transfer (RAFT) agents to these systems led to the production of polymers with molecular weights in agreement with theoretical predictions and molecular weight distributions typically lower than 1.15. In contrast to our previous systems described as photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) where RAFT agent is activated by the photocatalyst, we propose that the phthalocyanine compounds react via a reductive quenching pathway to oxidize NMP to an NMP radical, which can directly initiate the polymerization of monomers.