Poly(p-chlorostyrene), PCSt, and poly(p-chloro-a-methylstyrene), PCaMSt, are much less photosensitive than low molecular model compounds. The quantum yield of HCI formation $(HCI) -0.01 is much lower than 4(HCI) -0.18 determined for I-chloro-4-isopropylbenzene and l-t-butyl-4-chlorobenzene.
The preferential non-chemical deactivation of electronically excited states of PCSt and PCaMSt is very likely due to a strong interaction of neighboring pendant groups. This kind of interaction is reflected by singlet excimer emission. Although less photosusceptible than model compounds PCSt and PCaMSt are much more readily photolyzed than the non-chlorinated analogues poly(styrene), PSt, and poly(z-methylstyrene), PaMSt. This is inferred from high crosslinking yields obtained from exposure curves. Gel doses determined in this way increase in the order PCSt < PCaMSt < PSt (<PtiMSt, not crosslinkable). Crosslinking of PCSt and PCaMSt is thought to be mainly based on reactions of phenyl type radicals and in the case of PCSt also on those of benzyl type radicals, generated when hydrogens in a-position are split off. Flash photolysis studies revealed that chemical alterations of PCSt and PCaMSt originate essentially from excited triplet states.