On the Favorable Interaction of Metal Centered Radicals with Hydroperoxides for an Enhancement of the Photopolymerization Efficiency Under Air

Four metal-based photoinitiating systems (benzene-tricarbonylchromium(0), ArCr(CO)(3), cyclopentadienylmolybdenum tricarbonyl dimes, Cp(2)Mo(2)(CO)(6), diiron nonacarbonyl, Fe(2)(CO)(9), and bis-(cyclopentadienylruthenium dicarbonyl), Cp(2)Ru(2)(CO)(4)) are investigated by laser flash photolysis (LFP) and ESR-spin trapping (ESR-ST) experiments and checked as photoinitiators for both free radical promoted cationic photopolymerization (FRPCP) and free radical photopolymerization (FRP). New combinations with silanes instead of alkyl halides improve both the polymerization rates and the final conversions upon irradiation with UV/visible or visible light and laser diodes (405, 457, 473, and 532 nm) under air. The enhancement of the photopolymerization reaction under air in the presence of the selected compounds is ascribed to the reuse of the inherently present hydroperoxides through a set of reactions leading to additional initiating species. These systems are particularly attractive for FRPCP with excellent polymerization rates and final conversions.