Design of keto-coumarin based photoinitiator for Free Radical Photopolymerization: Towards 3D printing and photocomposites applications

In this article, ten organic dyes based on keto-coumarin (KC) derivatives (MeO-Coum1, MeO-Coum10) have been synthesized and characterized as high performance photoinitiators for the Free Radical Photopolymerization (FRP) of acrylates upon visible light exposure using a LED @405nm. The addition of Iodonium salt (Iod), amine [ethyl dimethylaminobenzoate (EDB) or N-phenylglycine (NPG)] and Iod/NPG couple in the photocurable resins have been carried out in order to prove their influences on the improvement on the photoinitiating abilities of keto-coumarins. The different dyes showed a very high ability to initiate the FRP by introduction of these additives, using Two or Three-component photoinitiating systems based on MeO-Coum/Iod or amine (0.1% or 0.4%/1% w/w) or MeO-Coum/Iod/NPG (0.1% or 0.4%/1%/1% w/w/w) respectively. In fact, these photoinitiators have been tested in different applications. For example: in direct laser write to generate 3D patterns using a laser diode @405nm, or for the photocomposite synthesis based on glass fibers. To characterize the initiation ability and to explain the reaction mechanisms in the photoinitiation step, several techniques have been used, such as UV-visible absorption spectroscopy and steady state photolysis, fluorescence emission, RT-FTIR, cyclic voltammetry and Electron Spin Resonance (ESR) spectroscopy.