Copper photoredox catalysts for polymerization upon near UV or visible light: structure/reactivity/efficiency relationships and use in LED projector 3D printing resins

Copper complexes (CuCs) bearing pyridine–pyrazole ligands are synthesized and evaluated as new photoredox catalysts/photoinitiators in combination with an iodonium salt (Iod) for the free radical polymerization of (meth)acrylates and the cationic polymerization of epoxides upon visible light exposure using a Light Emitting Diode (LED)@405 nm. The structure/reactivity/efficiency relationships for the copper complexes are studied as well as the chemical mechanisms involved. The different substituents on the pyrazole moiety of the ligand allow tuning of the oxidation potential and the visible light absorbance of the complexes and to optimize the performance of the polymerization photoredox catalysts. The use of a novel additive (CARET) in a three-component system (CuC/Iod/CARET) highly improves the performance. Finally, the high performances of the Cu(I) complexes for the development of new 3D printing resins using an LED projector are demonstrated. Currently, LED projector printing is really advantageous in 3D printing i.e. this technology projects the profile of an entire layer at one time.