No abstract

This study reports for the first time the use of β-carotene as a natural photosensitizer for both the cationic photopolymerization and thiol-ene click reactions under visible-light irradiation. In an all-green synthesis approach, this performing dye-based system leads to the cationic and thiol-ene polymerization of bio-based monomers, mono- and di-epoxy limonene, with very high final conversions, and appears as efficient as the common visible-light photosensitizers used in free-radical or cationic photopolymerization, that is, thioxanthone derivatives or camphorquinone. Effective antibacterial and tack-free coatings have been synthesized through the incorporation of a natural antibacterial agent (eugenol) in the limonene-derived polymer network. The antibacterial assays have demonstrated a tremendous effect of the eugenol-containing coatings against the adhesion of Escherichia coli (Gram negative) and Staphylococcus aureus (Gram positive).

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 networks have been synthesized either by CP and the thiol–ene process with di­(ethylene glycol) divinyl ether/trithiol or by a concomitant free-radical and cationic photopolymerization with an epoxide/acrylate blend mixture upon LED@455 or 470 nm exposure. Interestingly, the resulting quinizarin-derived materials showed antiadherence properties under visible-light exposure even after two cycles of antibacterial experiments. Quinizarin derivatives can not only initiate photopolymerization but also generate singlet oxygen on the surface of the materials for preventing the adhesion and proliferation of bacteria under visible-light activation.