Cationic photoinitiators based on phenylethynyl onium salts

In comparison to radical photocuring, cationic photopolymerization can still be regarded as a niche technique, although it possesses various advantages such as a reduced shrinking behavior and the absence of inhibition by molecular oxygen. In UV-curable cationic systems, the photoinitiator (PI), which is still most frequently a diaryliodonium- or triarylsulfonium salt,1,2 plays a key role by generating the reactive species, a free acid, which initiates the polymerization.