The Blue-LED-Sensitive Naphthoquinone-Imidazolyl Derivatives as Type II Photoinitiators of Free Radical Photopolymerization

In this work, new naphthoquinone-based photoinitiators are synthesized and applied for the first time in free radical photopolymerization. In the presence of acrylate monomers, these PIs display excellent photoinitiation capabilities under blue-light LED@405 nm irradiation in a two-component photoinitiating system in which the additive is a common iodonium salt (bis-(4-tert-butylphenyl)iodonium hexafluorophosphate - Iod) or a tertiary amine (ethyl 4-dimethylaminobenzoate - EDB). In controlled tests, the polymerization performance of dye4/Iod is equal to or better than that of common commercial Type II photoinitiators (2-isopropylthioxanthone and benzophenone). Meanwhile, only a trace amount of photoinitiator is required (as low as 0.05%) to initiate the photopolymerization. It is worth noting that some of these compounds can also be used in one-component photoinitiating system (monocomponent Type II behavior) and exhibit high photoinitiation ability. A series of complementary characterization analyses of two new naphthoquinone dyes (i.e. dye 1 and dye 4) with very similar chemical structures are carried out to investigate the relevant photochemical mechanism. Finally, 3D printing experiments are carried out by a simple and convenient Direct Laser Write (DLW) technique.