Cationic Photopolymerization

Cationic curing needs a photo catalyst, which under UV light decomposes into a so-called “super acid”. Such a photo catalyst, suitable for the curing of TEGO® RC Silicon is available under the name TEGO^® PC 1465.

The cationic photopolymerization starts with the protonation of the exopy groups along the silicone backbone, forming a network like shown in the drawing.

The overall process of cationic cross-linking is not inhibited by oxygen, but less rapid than the radical polymerization. The reaction process can be slowed down by substrate ingredients. Problems may be expected on most papers (as they contain alkaline), on printing inks, aluminium, PVC, or sulphur and amine components present in film formulations. Air humidity can also influence the curing process.