ON THE PHOTOLYSIS OF CHAIN-CHLORINATED POLYSTYRENE

Copolymers of styrene and alpha-chlorostyrene containing 19%-95% alpha -chlorostyrene, prepared by photochlorination of polystyrene (PSt), we re irradiated with UV light at lambda(inc) = 254 nm (continuous irradi ation) or at lambda(inc) = 266 nm (flash photolysis). The major photoc hemical reactions occurring in films of highly chlorinated polymer (CP St-95, gamma(Cl) = 0.95 Cl atoms per repeating unit) are chlorine rele ase (phi(HCI) = 2 X 10(-2)) and the accompanying formation of carbon-c arbon double bonds. Main-chain scission is a minor process of quantum yield phi(S) approximate to 2 X 10(-3), but brings about a decrease in the average molar mass of CPSt-95. Flash photolysis studies revealed the existence of singlet excimers (tau less than or equal to 20 ns), t riplets (tau approximate to 65 ns) and benzyl-type radicals (tau great er than or equal to 5 ms). The quantum yields of chlorine release and formation of benzyl-type radicals, measured in tetrahydrofuran solutio n, are of equal magnitude (about 0.2). By contrast, photochemical reac tions in copolymers of low chlorine content resemble those induced in polystyrene, e.g. at gamma(Cl) = 0.19 intermolecular cross-linking dom inates over main-chain cleavage and renders the polymer insoluble.