Near-infrared light induced cationic polymerization based on upconversion and ferrocenium photochemistry

A novel near-infrared (NIR) photoinitiating system for cationic polymerization using upconversion nanoparticles (UCNPs) and ferrocenium salts is reported. The UV-A and visible light emitted by the UCNPs upon NIR irradiation, absorbed by the ferrocenium salts, results in the liberation of aromatic ligand and thus the formed active Lewis acid can efficiently induce the cationic polymerization of oxirane and vinyl monomers. Notably, high post polymerization efficiency in dark (>30%) was observed which can compensate the limited upconversion fluorescence efficiency and lead to an improved and uniform conversion of the monomers.