PHOTOLYSIS OF CHLORINE-SUBSTITUTED POLYSTYRENE AND POLY-ALPHA-METHYLSTYRENE

Poly(p-chloro styrene), PCSt, and poly(p-chloro-alpha-methylstyrene), PC alpha MSt, are much less photosensitive than low molecular model co mpounds. The quantum yield of HCl formation phi(HCl) similar to 0.01 i s much lower than phi(HCl) similar to 0.18 determined for 1-chloro-4-i sopropylbenzene and 1-t-butyl-4-chlorobenzene. The preferential non-ch emical deactivation of electronically excited states of PCSt and PC al pha MSt is very likely due to a strong interaction of neighboring pend ant groups. This kind of interaction is reflected by singlet excimer e mission. Although less photosusceptible than model compounds PCSt and PC alpha MSt are much more readily photolyzed than the non-chlorinated analogues poly(styrene), PSt, and poly(alpha-methylstyrene), P alpha MSt. This is inferred from high crosslinking yields obtained from expo sure curves. Gel doses determined in this way increase in the order PC St<PC alpha MSt<PSt (<P alpha MSt, not crosslinkable). Crosslinking of PCSt and PC alpha MSt is thought to be mainly based on reactions of p henyl type radicals and in the case of PCSt also on those of benzyl ty pe radicals, generated when hydrogens in alpha-position are split off. Flash photolysis studies revealed that chemical alterations of PCSt a nd PC alpha MSt originate essentially from excited triplet states.