Polystyrene-b-poly(2-vinyl phenacyl pyridinium) salts as photoinitiators for free radical and cationic polymerizations and their photoinduced molecular associations

Polystyrene-b-poly(2-vinyl phenacyl pyridinium hexafluorophosphate) (PS-b-PVPP) was synthesized by reacting polystyrene-b-poly(2-vinyl pyridine) prepared by living anionic polymerization with phenacyl bromide followed by counter anion exchange reaction. The ability of PS-b-PVPP to act as a photoinitiator for both free radical and cationic polymerizations is demonstrated. In the free radical polymerization, the initiation step involves the decay of the excited state of the salt with homolytic bond rupture of the nitrogen–carbon bond. For the cationic polymerization, homolytic cleavage followed by electron transfer and/or heterolytic scission reactions are responsible for the generation of reactive species. Photoinduced switching behavior of PS-b-PVPP from ionic to neutral state was also demonstrated by surface analysis, particle size and film thickness measurements.