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The use of LEDs as novel and efficient light sources for the photopolymerization of various monomers (acylate, epoxy), interpenetrating polymer networks and thiols–ene, leads to the development of novel photoinitiating systems adapted for the LED emission.

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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

International audienceCu2+-doped zeolitic imidazolate framework (ZIF) crystals were efficiently prepared by reaction of Cu(NO3)2, Zn(NO3)2, and 2-methylimidazole in methanol at room temperature. Scanning electron microscopy, transmission electron microscopy and X-ray diffraction showed that the Cu/ZIF-8 particles were nanosized (between ca. 120 and 170 nm) and that the body-centered cubic crystal lattice of the parent ZIF-8 framework is continuously maintained, regardless of the doping percentage. Moreover, thermogravimetric analyses and specific BET surface area measurements demonstrated that the doping does not alter the high stability of ZIF-8 crystals and that the porosity only decreases at a high doping percentage (25% in Cu2+). The Cu/ZIF-8 material showed excellent catalytic activity in the [3 + 2] cycloaddition of organic azides with alkynes and in Friedländer and Combes condensations due to the high catalyst surface area and the high dispersion of Cu/ZIF-8 particles. Notably, the Cu/ZIF-8 particles not only exhibit excellent performance but also show great stability in the reaction, allowing their reuse up to ten times in condensation reactions. Our findings explored a simple and powerful way to incorporate metal ions into the backbones of open framework materials without losing their properties

Abstract:The present paper reviews some aspects concerned with the development of green technologies in the photopolymerization area: use of visible light sources (Xe and Hg-Xe lamps, diode lasers), soft irradiation conditions (household lamps: halogen lamp, fluorescence bulbs, LED bulbs), sunlight exposure, development of very efficient photoinitiating systems and use of renewable monomers. The drawbacks/breakthroughs encountered when going on the way of a greener approach are discussed. Examples of recent achievements are presented.

Photopolymerization under near-infrared (NIR) light is challenging due to the low energy of the absorbed photon but, if successful, presents significant advantages. For example, this lower energy wavelength is safer than UV light that is currently the standard photocuring light source. Also, NIR allows for a deeper light penetration within the material and therefore resulting in a more complete curing of thicker materials containing fillers for access to composites. In this study, we report the use of three-component systems for the NIR photopolymerization of methacrylates: (1) a dye used as a photosensitizer in the NIR range, (2) an iodonium salt as a photoinitiator for the free radical polymerization of the (meth)­acrylates, and (3) a phosphine to prevent polymerization inhibition due to the oxygen and to regenerate the dye upon irradiation. Several NIR-absorbing dyes such as a cyanine borate and a silicon–phthalocyanine are presented and studied. Systems using borate dyes resulted in methacrylate monomer conversion over 80% in air. We report three types of irradiation system: low-power LED at 660 and 780 nm as well as a higher power laser diode at 785 nm. The excellent performance reported in this work is due to the crucial role of the added phosphine.