N-Vinylcarbazole is proposed as an additive for epoxy ring-opening polymerization ROP upon visible light exposure. This compound can convert hardly oxidizable radicals to carbon centered radicals by an addition process onto the N-vinylcarbazole double bond. The generated radicals can be further easily oxidized by an iodonium salt thereby leading to efficient initiating cations for the ROP of epoxides. Different visible light photoinitiating systems have been investigated: Type I photoinitiators (derived from phosphine oxides) and dye/iodonium salt couples. The underlying chemical mechanisms are investigated by electron spin resonance (ESR) experiments.

International audienceDifferent polyaromatic structures (truxene derivatives and tris(aza)pentacene) are presented as new metal-free organic photocatalysts (OPC) to promote free radical polymerization FRP and ring-opening polymerization (ROP) under halogen lamp, household LED bulb, and laser diode (405 nm). These OPCs exhibit interesting light absorption properties and lead, through an oxidative catalytic cycle, to the formation of radicals and ions that can initiate both free radical polymerization FRP and ring-opening polymerization ROP. Interestingly, excellent polymerization profiles are obtained even upon visible light exposure. Using these very soft irradiation conditions, acrylate/epoxide blends are also easily polymerized under air and lead to the formation of interpenetrated polymer networks IPN exhibiting no phase separation

International audienceThe photoredox catalysis approach is used to initiate the free radical promoted cationic photopolymerization of N-vinylcarbazole (NVK) under very soft irradiation conditions (halogen lamp, blue or green LED bulbs) using visible-light harvesting photocatalysts (mainly Ir(III) complexes) in iodonium salt and silane containing photoinitiating systems. The reactions were shown to proceed via an oxidative catalytic cycle where the generated free radicals are oxidized into cations. The effect of NVK on this catalytic cycle is discussed. Epoxy/NVK matrixes can also be polymerized. The luminescent properties of the synthesized polymers are presented

SummaryIn the present paper, the photoredox catalysis is presented as a unique approach in the field of photoinitiators of polymerization. The principal photocatalysts already reported as well as the typical oxidation and reduction agents used in both reductive or oxidative cycles are gathered. The chemical mechanisms associated with various systems are also given. As compared to classical iridium-based photocatalysts which are mainly active upon blue light irradiation, a new photocatalyst Ir(piq)2(tmd) (also known as bis(1-phenylisoquinolinato-N,C 2’)iridium(2,2,6,6-tetramethyl-3,5-heptanedionate) is also proposed as an example of green light photocatalyst (toward the long wavelength irradiation). The chemical mechanisms associated with Ir(piq)2(tmd) are investigated by ESR spin-trapping, laser flash photolysis, steady state photolysis, cyclic voltammetry and luminescence experiments.

International audienceA new iridium complex (nIr) was designed and investigated as a photoinitiator catalyst for radical and cationic polymerizations upon very soft irradiations (lights ranging from 457 to 532 nm). A ring-opening polymerization (ROP) of an epoxy monomer was easily promoted through the interaction between nIr and an iodonium salt (Iod) upon light. The addition of N-vinylcarbazole (NVK) enhances the performance. In radical polymerization, nIr can be efficient in combination with phenacyl bromide (PBr) and optionally an amine: these photoinitiating systems work according to an original oxidative cycle and a regeneration of nIr is observed. A control of the methyl methacrylate polymerization (conducted under a 462 nm light) with 1.2–1.6 polydispersity indexes was displayed. Surface modifications by direct laser write was also easily carried out for the first time through surface re-initiation experiments, i.e. the dormant species being reactivated by light in the presence of nIr; the polymer surfaces were analyzed by XPS. The chemical mechanisms were examined through laser flash photolysis, NMR, ESR and size exclusion chromatography experiment

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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.

An innovative model-based design strategy to synthesize well-defined sequence-controlled polymers is presented, enabling selection of both the most appropriate mediating agent and reaction conditions. In combination with experimental analysis, advanced kinetic Monte Carlo simulations are conducted, allowing a visualization of the connectivity of all monomer units of ca. 105 individual copolymer chains. The product quality can therefore be uniquely and unambiguously predicted for the first time at the molecular level, explicitly accounting for chain-to-chain deviations. The strategy is illustrated for BlocBuilder MA-initiated nitroxide-mediated polymerization, with styrene and N-benzyl­maleimide as comomomers, and is generally applicable for all reversible deactivation radical polymerization (RDRP) techniques. Further design of the nitroxide-mediating capabilities and the reaction conditions allows the realization of a targeted (multi)­functionalization pattern, including an increase of the contribution of trifunctionalized chains above 75%. The reported results are interpreted in terms of the individual activation–growth–deactivation cycles and provide an unprecedented mechanistic understanding of RDRP in general.