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Studies have been made of electronic energy transfer from the triplet state of carbonyl groups in poly(methy1 vinyl ketone) (PMVK), using l-cis,3-cis-cyclooctadiene (COD) as a triplet quencher. About 70-7570 of the photochemical reaction leading to scissioning of the polymer originates from t h e triplet state. The lifetime of this state is estimated as 6 nsec. Phosphorescence quenching results show t h a t in solid solution a t 77"K, triplet migration takes place in poly(pheny1 vinyl ketone) ( P P V K ) , but not in PMVK or poly(methy1 isopropenyl ketone) under these conditions.

The quantum yield of chain scission was determined in the solid state for a number of polymers containing pendant ketone groups. Copolymers of methyl methacrylate with methyl vinyl ketone (PMMA-MVK) and styrene with phenyl vinyl ketone (PS-PVK) showed higher quantum yields with increasing temperature in the glassy state. Above the glass transition temperature (Tg) the quantum yield for chain scission increased rapidly to the same value as that obtained for the same polymer in solution. A homopolymer of phenyl vinyl ketone (PPVK) showed the opposite effect below Tg, but above Tg a constant quantum yield equal to the solution value was obtained. The variation in quantum yields is interpreted in terms of polymer chain mobility.The degradation of polymeric materials on outdoor exposure can often be attributed to photochemical reactions arising from absorption of ultraviolet radiation by ketone groups present on the polymeric backbone. In polyethylene, for example, the ketone groups are known to be formed by air oxidation on extrusion and moulding.It has been shown1"4 that ketones in polymeric material undergo some of the same photochemical reactions as their low molecular weight analogs. The most important t C.

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