Photo-oxidation of polymers—VIII. The photo-oxidation of polystyrene containing aromatic ketones

Abstract

Aromatic ketones have been used to initiate the photo-oxidation of polystyrene at wavelengths > 300 nm. Quantum yields of oxygen absorption have been measured. The results indicate that only ketones with a lowest 3( n-n ∗) state are efficient and that hydrogen abstraction is the initial step of the process. Up to four oxygen molecules are consumed for each ketone molecule transformed into the corresponding pinacol. The similarity of chemical effects observed in the present case and in the photo-oxidation of pure polystyrene irradiated at 254 nm suggests that they result from the sensitized decomposition of hydroperoxide groups in both cases. Quantitatively the transfer of energy from excited aromatic ketones is, however, 5 times more efficient than the transfer from excited phenyl groups. Chain scission and decrease of the ultimate tensile strength are directly connected. This indicates that the controlled photodegradation of polystyrene can be achieved by using different aromatic ketones and various concentrations depending on the sensitivity required in a selected wavelength range.