ON THE PHOTOLYSIS OF CHAIN-CHLORINATED POLYSTYRENE

Copolymers of styrene and alpha-chlorostyrene containing 19%-95% alpha-chlorostyrene, prepared by photochlorination of polystyrene (PSt), were irradiated with UV light at lambda(inc) = 254 nm (continuous irradiation) or at lambda(inc) = 266 nm (flash photolysis). The major photochemical reactions occurring in films of highly chlorinated polymer (CPSt-95, gamma(Cl) = 0.95 Cl atoms per repeating unit) are chlorine release (phi(HCI) = 2 X 10(-2)) and the accompanying formation of carbon-carbon 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), triplets (tau approximate to 65 ns) and benzyl-type radicals (tau greater than or equal to 5 ms). The quantum yields of chlorine release and formation of benzyl-type radicals, measured in tetrahydrofuran solution, are of equal magnitude (about 0.2). By contrast, photochemical reactions in copolymers of low chlorine content resemble those induced in polystyrene, e.g. at gamma(Cl) = 0.19 intermolecular cross-linking dominates over main-chain cleavage and renders the polymer insoluble.