With the advantages offered by cationic photopolymerization (CP) such as broad wavelength activation, tolerance to oxygen, low shrinkage and the possibility of “dark cure”, it has attracted extensive attention in photoresist, deep curing and other fields in recent years. The applied photoinitiating systems (PIS) play a crucial role as they can affect the speed and type of the polymerization and properties of the materials formed. In the past few decades, much effort has been invested into developing cationic photoinitiating systems (CPISs) that can be activated at long wavelengths and overcome technical problems and challenges faced. In this article, the latest developments in the long wavelength sensitive CPIS under ultraviolet (UV)/visible light-emitting diodes (LED) lights are reviewed. The objective is, furthermore, to show differences as well as parallels between different PIS and future perspectives.

The oxygen inhibition and migration of micromolecules which stem from photoinitiators (PIs) remain two critical challenges to address in radical photocuring. In this work, we reported a one-step ternary copolymerization strategy to construct a one-component macromolecular photoinitiator (PPI) using polymerizable thioxanthone (TX), amine (N), and fluorinated alkane (F) as monomers. Then, we utilize the low surface energy of F unit and macromolecular skeleton to reduce oxygen inhibition and migration. Compared to micromolecule TX, PPI also exhibits a broad absorption in the 250–430 nm range, and a higher molar extinction coefficient. The effects of the TX, N, and F component ratios on the photoinitiation efficiency of PPI were systematically investigated, and the photopolymerization kinetics revealed that the increased content of F unit can eliminate the oxygen inhibition of PPI. As a result, PPI demonstrates the more superior photoinitiation efficiency compared to the traditional TX/N two-component macromolecule photoinitiation system. Migration experiments indicated that there is a 60% reduction in the migration rate for PPI compared to the TX/N photoinitiation system. This work provides an effective strategy to address oxygen inhibition and micromolecule migration issues in radical photocuring, showing potential applications in food and pharmaceutical packaging fields.

A novel photoinitiating system composed of osmium complexes, iodonium salts, and N -vinylcarbazole initiates free-radical and cationic polymerization under UV-Vis-NIR irradiation.