Novel ketone derivative-based photoinitiating systems for free radical polymerization under mild conditions and 3D printing

Photopolymerization of acrylates under mild conditions is promising not only for academic research but also for industrial applications. However, it still remains a huge challenge to develop effective photoinitiators or photoinitiating systems for the free radical polymerization of acrylates under visible light-emitting diode (LED) irradiation. In this work, twelve novel ketone derivatives containing either tertiary amines or anthracenes as peripheral substituting groups (noted as Ami-1-Ami-6 and Anth-1-Anth-6) were elaborately synthesized and proposed for the polymerization of di(trimethylolpropane) tetraacrylate (TA), a tetrafunctional polyether acrylate, under both thin and thick film conditions under LED@405 nm irradiation. Remarkably, eight of the selected ketones (Ami-2, Ami-6, Anth-1-Anth-6) had never been synthesized before. In combination with an amine and/or an iodonium salt (Iod), these ketones could form distinct photoinitiating systems, among which the Ami-2/amine/Iod system could lead to the highest final conversion of acrylates under the thick film (~1.4 mm) conditions while the Ami-6/amine/Iod system could induce the highest final conversion of acrylates under the thin film (~25 µm) conditions. The photosensitivity of Ami-2 and Ami-6 was systematically investigated by steady state photolysis and fluorescence quenching experiments. Finally, the photocuring 3D printing technique was applied to TA, and both Ami-2- A nd Ami-6-based photoinitiating systems could be used to fabricate macroscopic 3D patterns with excellent spatial resolution.