Coumarin derivatives as versatile photoinitiators for 3D printing, polymerization in water and photocomposite synthesis

The goal of this paper concerns the first evaluation of two recently reported coumarins to initiate photopolymerization reactions. These two compounds (CoumA and CoumB) are proposed as high performance visible light photoinitiators and evaluated as photoredox catalysts (PCs), in the presence of an iodonium salt or with an amine, for both the free radical polymerization (FRP) of (meth)acrylates and the cationic polymerization (CP) of epoxides upon visible light exposure using an LED at 405 nm. These coumarin derivatives showed a high photoinitiation ability i.e. excellent polymerization rates and high final monomer conversions were obtained. The photophysical and photochemical properties of the coumarin derivatives were studied in terms of absorption, steady state photolysis and fluorescence spectroscopy. The photoinitiation mechanisms of the coumarin derivatives were discussed from fluorescence quenching, redox behavior and cyclic voltammetry experiments. A full picture of the involved photochemical mechanisms is provided. Coumarin-based systems are high performance photoinitiators, and their use in new photosensitive 3D printing resins will also be presented. Remarkably, CoumB is also found to be very efficient for the preparation of hydrogels under mild conditions due to its high solubility in water i.e. CoumB corresponds to a high-performance water soluble photoinitiator. Finally, the usage of the new coumarin derivatives for photocomposite synthesis with glass fibers (thick samples with a good depth of cure) using a near-UV conveyor (LED @395 nm) is particularly outlined.