Cationic photoinitiators are another kind of very important photoinitiators, including diazo salt, diaryliodonium salt, triarylthionium salt, alkyl thionium salt, ferric aromatic salt, sulfonioxyl ketone and triarylsiloxyether. Its basic function is characterized by photoactivation of molecules to the excited state, a series of molecular decomposition reactions, and finally produce super proton acid (also called Bronsteric acid), as cationic polymerization of active species and trigger epoxy compounds, vinyl ether, lactone, acetal, ring ether polymerization.
Cationic photoinitiators can be divided into onium salts, metal-organic compounds and organosilanes, among which iodonium salts, sulfonium salts and ferric arenes are the most representative ones. The photolysis of diaryl iodonium salt I-250 can produce both homolysis and heterolysis at the same time, and produce superacid and active radical. Therefore, in addition to cationic photopolymerization, iodonium salt can also induce radical polymerization, which is the common characteristic of iodonium salt and sulfonium salt.
