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.

Carbazole structures are of high interest in photopolymerization due to their enhanced light absorption properties in the near-UV or even visible ranges. Therefore, type I photoinitiators combining the carbazole chromophore to the well-established phosphine-oxides were proposed and studied in this article. The aim of this article was to propose type I photoinitiators that can be more reactive than benchmark phosphine oxides, which are among the more reactive type I photoinitiators for a UV or near-UV light emitting diodes (LED) irradiation. Two molecules were synthesized and their UV-visible light absorption properties as well as the quantum yields of photolysis and photopolymerization performances were measured. Remarkably, the associated absorption was enhanced in the 350–410 nm range compared to benchmark phosphine oxides, and one compound was found to be more reactive in photopolymerization than the commercial photoinitiator TPO-L for an irradiation at 395 nm.

Reactions of 1,3-dimethylimidazol-2-ylidene-borane (diMe-Imd-BH3) and related NHC-boranes with diaryl and diheteroaryl disulfides provide diverse NHC-boryl monosulfides (diMe-Imd-BH2SAr) and NHC-boryl disulfides (diMe-Imd-BH(SAr)2). Heating in the dark with 1 equiv of disulfide favors monosulfide formation, while irradiation with 2 equiv disulfide favors disulfide formation. With heteroaryl disulfides, the NHC-borane in the primary NHC-boryl sulfide product migrates from sulfur to nitrogen to give new products with a thioamide substructure. Most substitution reactions are thought to proceed through radical chains in which homolytic substitution of a disulfide by an NHC-boryl radical is a key step. However, with electrophilic disulfides under dark conditions, a competing ionic path may also be possible.

Some efficient acylphosphine oxides have been used for many years as photoinitiators of radical polymerization. As very few new acylphosphine oxide compounds have been proposed these past years for the radical polymerization of methacrylates, the aim of this work is to use molecular modeling to select potentially reactive compounds before their synthesis to see whether acyldiphenylphosphine oxide (ADPO) molecules can compete or even work better than commercial and well-established acylphosphine oxides. Two of the common acylphosphine oxides, TPO-L and BAPO, used in industrial applications will be taken as references in this work, while new ADPO will be evaluated in photopolymerization reaction initiated upon LED at 395 nm. In fact, the photopolymerization industrial technology is evolving from the use of an energy-consuming Hg lamp toward the use of safer LEDs working typically in the 385−405 nm range. At least two of the compounds are competing or working better than the well-established systems in a reference benchmarked acrylic resin, evidencing the importance of molecular modeling for the design of new photoinitiators before their synthesis.

New photoinitiating systems based on boron-dipyrromethene dye (bodipy)/iodonium salt and optionally tris(trimethylsilyl)silane are proposed for the polymerization of divinylether and epoxy monomers upon visible-light exposure. The presence of the silane increases the epoxide rate of polymerization and conversion. Using acrylate/vinyl ether blends, the synthesis of cross-linked polymer networks (possessing two T g values: −11 and 111 °C) is also successfully achieved through concomitant cationic and radical polymerization pathways. The chemical mechanisms associated with these initiating systems are investigated by steady-state photolysis and ESR experiments.

International audienceA procedure for the production of N-heterocyclic carbene boryl radicals (NHC-BH2 center dot) upon visible light irradiation under soft conditions is presented. New acridine orange (dye)/diphenyl disulfide/NHC-BH3 and dye/sulfonium salt/NHC-BH3 three-component initiating systems are introduced for the efficient visible light photopolymerization of trimethylolpropane triacrylate. The new systems could be extendend to polymerization reactions in water (hydroxyethyl acrylate and hydroxyethyl methyl acrylate), which proceeded with strongly improved polydispersity. The chemical mechanisms are investigated through EPR and photolysis experiments

The B-S bond in N-heterocyclic carbene (NHC)-boryl sulfides can be cleaved homolytically to NHC-boryl or NHC-thioboryl and thiyl radicals using light, either directly around 300 nm or with a sensitizer at a longer wavelength (>340 nm). In contrast, the electrochemical reductive cleavage of the B-S bond is difficult. This easy photolytic cleavage makes the NHC-boryl sulfides good type I photopolymerization initiators for the polymerization of acrylates under air.

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