International audienceA short review on the role of photocatalysts in photopolymerization reactions is presented. A special emphasis is done on photoredox catalysts leading to i) high performance initiating systems for polymerization upon low light intensity for the use of light emitting diodes (LEDs) and/or visible light or ii) Controlled Radical PhotoPolymerization (CRP2) processes with formation/reactivation of dormant species triggered by light

Photopolymerization, or the use of light to trigger polymerization, is one of the most exciting technologies for advanced manufacturing of polymers. One of the key components in the photopolymerization processes is the photoactive compound that absorbs the light, generating the active species that promotes the polymerization and largely determines the final properties of the material. The field of photopolymerization has been dominated by photoradical generators to mediate radical reactions. In the last decade, to expand the number of polymers that can be prepared by photopolymerization, intensive research has been devoted to the synthesis and utilization of photoactive molecules that are able to generate a base or an acid upon irradiation. These organic compounds are known to promote not only the ring‐opening polymerization of various heterocyclic monomers such as lactones, carbonates, or epoxides but also to trigger the step‐growth synthesis of polyurethanes. This Minireview highlights the recent advances in the development of organic photobase and photoacid generators, with the aim of encouraging the wider application of these photoactive compounds in the photopolymerization area and to expand the use of these polymers in advanced manufacturing processes.

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A benzophenone-naphthalimide derivative (BPND) bearing tertiary amine groups has been developed as a highperformance photoinitiator in combination with 2,4,6-tris(trichloromethyl)-1,3,5-triazine or an iodonium salt for both the free radical polymerization (FRP) of acrylates and the cationic polymerization (CP) of epoxides upon exposure to near UV and visible LEDs (385-470 nm). BPND can even produce radicals without any added hydrogen donor. The photochemical mechanisms are studied by molecular orbital calculations, steady state photolysis, electron spin resonance spin trapping, fluorescence, cyclic voltammetry and laser flash photolysis techniques.These novel BPND based photoinitiating systems exhibit an efficiency higher than that of the well-known camphorquinonebased systems (FRP and CP) or comparable to that of bis(2,4, 6-trimethylbenzoyl)-phenylphosphineoxide (FRP at k 455 nm).

International audienceA strong drawback of the photoinitiators of cationic polymerization or photoacids is the photosensitivity for short and energetic wavelengths preventing their general use (specialized photochemical equipment with safety concerns must be used). In the present paper, a novel iodonium salt bearing a naphthalimide moiety (naphthalimide-Ph-I+-Ph) is proposed as a one-component photoinitiator/photoacid operating at longer and safer wavelengths (i.e. violet light emitting diodes at 365, 385 nm and 395 nm). It allows the polymerization of various formulations (methacrylates, epoxides, vinyl ethers). A high reactive function conversion for multifunctional monomers can be achieved: e.g. 50% for a diepoxide under air, >90% for a divinylether (with a very high rate of polymerization Rp), almost 100% for an epoxide/vinyl ether blend (very high Rp) under air, and 85% for methacrylates (high Rp) in laminate (43% under air). These results are above the ones obtained with a thianthrenium salt chosen as a reference e.g. a lower epoxy conversion ∼25% and a clearly lower Rp for the diepoxide polymerization. ESR-spin trapping, laser flash photolysis, steady state photolysis and molecular orbitals calculations support the formation of Ph˙ and naphthalimide-Ph-I˙+ as well as the generation of H+, thereby explaining the photoinitiation step mechanism

A series of naphthalimide derivatives containing tertiary amine groups (DNNDs) have been prepared.

Four N-[2-(dimethylamino)ethyl]-1,8-naphthalimide derivatives (ANNs) with different substituents in the naphthalimide skeleton have been synthesized and can be used as versatile photoinitiators under various LEDs.

The photochemical mechanism of the radical generation from photoinitiating systems based on 1, 8‐naphthalimide derivatives (ANDs; with tertiary amine moieties) are investigated by using various approaches including cyclic voltammetry, steady‐state photolysis, and electron spin resonance spin‐trapping techniques. It reveals that radicals can be produced from ANDs alone or ANDs/additive (e. g. iodonium salt or chloro triazine) combinations. The generated radicals and cations can initiate both free‐radical and cationic photopolymerization reactions under irradiation with various light‐emitting diodes or a halogen lamp. For most of the AND‐based photoinitiating systems, more than 60 % of acrylate or epoxide conversions were attained, and were even higher than those obtained by using commercial photoinitiators, for example, bisacylphosphine oxide or camphorquinone. More interestingly, the AND1‐based photoinitiating system can also initiate concomitant cationic/radical polymerizations and can be used for the synthesis of interpenetrated polymer networks.