Coumarin Derivatives as Photoinitiators in Photo-oxidation and Photo-reduction Processes and Kinetic Model for Simulations of the Associated Polymerization Profiles

International audienceIn this work, the design of an original series of coumarin derivatives (CoumC1-CoumC13) is presented. Chemical structures of these coumarins were selected by molecular modelling to ensure both excellent light absorption properties and high potential photoreactivity (high excited state energy). As a striking result of this in-silico design, 8 of the 13 proposed coumarins were never presented and were specifically proposed for this work, evidencing the interest of the structures. New multi-component photoinitiating systems (PISs) based on these coumarins are proposed for the free radical polymerization (FRP) of (meth)acrylates and examined upon visible light irradiation using the light emitting diode (LED) as a safe and economical irradiation source. The proposed systems are based on coumarins which act as remarkable photoinitiators/photosensitizers (PIs/PSs) combined with N-phenylglycine (NPG) and/or iodonium salt (Iod) as co-initiators in order to generate the reactive species (radicals) that will initiate the photopolymerization recation. Investigation of the chemical mechanisms suggested by the different interactions that take place as well as the photophysical and photochemical properties of coumarins are provided. The access 2 to high polymerization rates (Rp), excellent photoinitiating abilities and great reactive function conversions (FC) is possible with these structures based on the coumarin core. Coumarins show high efficiency for the FRP of (meth)acrylates by reaction with iodonium salt (a photo-oxidation process) or with amine (a photo-reduction process). These compounds were used in 3D printing resins but also for the preparation of photocomposites. In this latter case, an excellent depth of cure was noted as remarkable behavior. To rationalize the experimental results, a kinetic model for a three-component system has been established to analyze the role of oxygen in the monomer conversions and the conversion enhancement observed while using an amine as a co-initiator