Imidazole based dual photo/thermal initiators for highly efficient radical polymerization under air with a metal-free approach

By virtue of remarkable spatial resolution, a metal-free visible LED photopolymerization process, initiated by imidazole based charge transfer complexes under mild conditions (room temperature, without an inert atmosphere, monomer purification or stabilizer removal), is reported. For two multifunctional acrylate monomers, an outstanding photoinitiating ability was proved (up to 80% of acrylate function conversion) by combining imidazoles (electron donors) and iodonium salts (electron acceptors) under 405 nm LED irradiation. 3D printing experiments using a low intensity 3D printer are reported to demonstrate the performance of this CTC approach. Meanwhile, the thermal polymerization features a relatively low thermal initiating temperature, making the process more pursuable and also easier to achieve for thick samples in practice and/or polymerization in shadow areas (where light does not penetrate). As a new dual photo/thermal initiator, it showcases tremendous potential for 3D printing with high resolution and high-tech composites. This dual initiating system represents a new type of thermal initiator toward a safer way (peroxide-free) and provides a new pathway for surface repairing or modifying of direct laser writing in a low toxicity, facile manner.