Pyrromethene 567 Dye as Visible Light Photoinitiator for Free Radical Polymerization

In the present work we report on the photochemistry and photopolymerization activity of a new bimolecular photoinitiator system, which exhibits maximum sensitivity at 518 nm, consists of a sensitizer dye, pyrromethene 567 (PM567), and a radical generating reagent 3,3′,4,4′-tetra(tert-butylperoxycarbonyl)benzophenone (BTTB). The photosensitization of BTTB through the excitation of PM567 induces high polymerization rates, while different experiences have revealed that PM567 or BTTB, separately, are unable of initiating the polymerization of 2-hydroxyethyl methacrylate (HEMA) over extensive periods of time at 40 °C, either in the dark or under irradiation. The polymerization efficiency of this photoinitiator system, PM567/BTTB, was analyzed following the bulk polymerization kinetics of monomer HEMA by differential scanning photo-calorimetry. Photopolymerization rates and quantum yields were observed under isothermal conditions (40 °C) for continuous illumination polymerizations (at 518 nm) at different incident light intensities and different BTTB concentrations.

Scheme of the photosensitization process of the bimolecular photoinitiator system of PM567/BTTB.