Coumarin derivatives as dual photo/thermal initiators for free radical polymerization and 3D printing

Abstract

In this study, five coumarin derivatives (Coums) were developed and synthesized to serve as visible light photoinitiators for the free radical photopolymerization of acrylates upon irradiation with a 405 nm LED. Their photoinitiating abilities were compared to that of a commercial photoinitiator, ketocoumarin (KC). By incorporating the ethyl 4-(dimethylamino)benzoate (EDB)/di-tert-butylphenyliodonium hexafluoro-phosphate (Iod) combination into the photoinitiating system, some of the resulting three-component Coums/EDB/Iod systems could lead to higher photopolymerization conversions than that obtained with the reference KC/EDB/Iod system. Parallel to their photoinitiating abilities, the different compounds also possess excellent thermal initiation capabilities, allowing their use as dual photo/thermal initiators. A comprehensive investigation of the photochemical mechanism was conducted utilizing various experimental techniques, including steady state photolysis, fluorescence quenching, cyclic voltammetry, and electron spin resonance spin trapping. Due to their excellent photoinitiation performance, the Coums/EDB/Iod combinations were successfully applied to 3D printing using different printing technologies.