SINGLET OXYGEN FORMATION IN A SOLID ORGANIC POLYMER UPON IRRADIATION OF THE OXYGEN POLYMER CHARGE-TRANSFER BAND

Singlet molecular oxygen (1ΔgO2) phosphorescence has been observed at 1270 nm in a time-resolved experiment subsequent to pulsed UV laser photolysis of the oxygen (3ΣgO2)-polymer charge-transfer (CT) absorption band of solid polystyrene samples. These data indicate that the polymer-oxygen CT potential surface (polymer*+02*_) is coupled to the potential surface of the polymer-(1ΔgO2) complex. Continued photolysis into the CT absorption band results in the formation of products that act as (1ΔgO2) photosensitizers, thus providing a second, independent channel for (1ΔgO2) formation. By monitoring the time-resolved (1ΔgO2) phosphorescence, we are able to distinguish between (1ΔgO2) produced in a photosensitized reaction and ^02 produced from the oxygen-polymer CT state. Unless rigorous steps are taken in the preparation and subsequent handling of the polymer sample, a substantial portion of the (1ΔgO2) produced upon UV irradiation of the oxygenated polymer originates from a photosensitized process. (1ΔgO2) has also been observed subsequent to UV photolysis of the oxygen-polymer CT band in a poly(dimethylsiloxane) oil and rubber. The polymer data are supported by independent time-resolved studies of (1ΔgO2) phosphorescence in a low molecular weight 130 K organic glass. Our results provide direct experimental support for a mechanism of light-induced (1ΔgO2) formation in a bulk polymer that obviates the necessity of invoking a photosensitizer. Thus, we conclude that, no matter how clean or impurity-free a particular solid polyolefin can be prepared, it is still possible to produce (1ΔgO2) upon irradiation. These data should be useful in understanding events that initiate polymer photodegradation. © 1990, American Chemical Society. All rights reserved.