Quinizarin Derivatives as Photoinitiators for Free-Radical and Cationic Photopolymerizations in the Visible Spectral Range

We report the use of efficient visible-light sensitive allyl (QA) and epoxidized (QE) quinizarin derivatives as photoinitiating systems when combined with an appropriate electron donor (methyldiethanol amine, MDEA), an electron acceptor (iodonium salt, Iod), or a H donor (thiol derivative), for free-radical photopolymerization (FRP), cationic photopolymerization (CP), and a thiol–ene process. These systems have demonstrated excellent initiating properties under air or in laminated conditions under visible-light irradiation (LEDs@405, 455, and 470 nm or Xe lamp) for FRP, CP, or the thiol–ene process and appear more efficient than the well-known camphorquinone-based photoinitiating systems. As highlighted by electron paramagnetic resonance (EPR) and laser flash photolysis experiments, QA (or QE) acts either as an electron donor via a photoinduced electron transfer pathway with Iod or as a proton/proton-coupled electron transfer promoter with MDEA or a thiol derivative. Two types of interpenetrated polymer n...