International audienceA new alkoxyamine (methyl 2-((4-benzoylphenyl)((1-methoxy-2-methyl-1-oxopropan-2-yl)oxy)amino)-2-methylpropanoate 4) bearing a chromophore group directly linked to the aminoxyl function is proposed as a photoiniferter. This original compound decomposes under UV irradiation to generate the corresponding alkyl and nitroxide radicals. Drastic changes of the photophysical or photochemical properties of the starting chromophore are noted. Laser flash photolysis experiments showed both a singlet state cleavage and an efficient shortening of the triplet state lifetime of 4. MO calculations suggest a C?O bond homolytic dissociation under UV irradiation through both S1 and T1 pathways. However, an ESR study evidences that both N?O and C?O homolysis occur under UV irradiation. The efficiency of 4 as a conventional photoinitiator is close to that of 2,2?-dimethoxyphenyl acetophenone. When 4 was used as a photoiniferter in nitroxide-mediated photopolymerization (NMP2), a linear growth of the poly(n-butyl acrylate) chain, reaching 80% of conversion in \textless500 s, is observed combined with a reinitiation of the photopolymerization after the end of the irradiation: this is the first report showing a at least partial NMP2 process

Copper complexes are synthesized and evaluated as new photoredox catalysts/photoinitiators.

Organic−inorganic UV-curing of organosilanes containing epoxy and trialkoxysilyl functional groups in the same monomer was implemented using a diaryl iodonium salt as cationic photoinitiator. UV-generated Brönsted acids through photolytic degradation were found to be effective in catalyzing both epoxy ring-opening polymerization and alkoxysilane sol−gel polycondensation reactions. Competition between the formation of inorganic and organic phases was kinetically studied using real-time Fourier transform infrared spectroscopy (RT-FTIR). The nature of the hybrid monomer, the effect of changing the film thickness, the type of substrate and the influence of laminated conditions on the polymerization kinetics were assessed. 29Si and 13C solid state NMR measurements were also performed to investigate the structure of the UV-cured hybrid materials.

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).

New photosensitive alkoxyamines have been designed using molecular orbital calculations to improve the selective CO versus NO cleavage. The targeted light-sensitive alkoxyamine is synthesized in one step and its reactivity under UV has been investigated using both ESR and LFP. The ability of this alkoxyamine to control the photopolymerization of n-butyl acrylate is evidenced through a process called nitroxide-mediated photopolymerization NMP(2) . The selected alkoxyamine is finally used to prepare covalently bonded multilayered micropatterns. This original application highlights the high potential of this technique for some specific applications that require spatial control.

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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.

A performing photoinitiating system based on paprika spice was developed (i) to efficiently initiate, according to a green photoinduced process, the cationic polymerization of a biosourced and renewable monomer, e.g., gallic acid, and (ii) to synthesize environmentally friendly antibacterial coatings in a reduced time. A decrease of 100% of the adhered bacteria was demonstrated upon visible light illumination without any remaining live bacteria.