The new LED-Sensitive photoinitiators of Polymerization: Copper complexes in free radical and cationic photoinitiating systems and application in 3D printing

A ligand (A1) and four copper complexes (Cu1, Cu2, Cu3 and Cu4) were examined as photosensitizers in various photoinitiating systems (PISs). Interestingly, excellent photochemical reactivities were determined with the different compounds. Especially, notable photoinitiation abilities were determined upon exposure to LED@405 nm during the free radical polymerization of acrylates and the cationic polymerization of epoxides when combined with an iodonium salt and an amine. With regards to their remarkable reactivities, the different photoinitiating systems were applied to 3D printing experiments. By combining steady state photolysis and electron spin resonance spin trapping, the chemical mechanism supporting the polymerization processes could be fully detailed and proved. Among all PISs studied, the three-component PISs furnished the best monomer conversions during the free radical polymerization of trimethylolpropane triacrylate (TMPTA) and the cationic polymerization of (3,4-epoxycyclohexane)methyl 3,4-epoxycyclohexylcarboxylate (EPOX) monomers. The conversion process was monitored by real-time Fourier transform infrared spectroscopy (RT-FTIR). Three-component PISs based on A1, Cu1 and Cu2 showed better performances than those based on Cu3, Cu4 and the different twocomponent PIS (comprising only the iodonium salt or the amine) in FRP experiments. Based on the outstanding photoinitiation abilities of A1 and Cu1 with both TMPTA and EPOX, smooth and regular 3D patterns could be obtained by direct laser write experiments by generating interpenetrating polymer networks (IPN) with the blend of these two monomers.