Effect of photooxidation on the surface properties of polystyrene

The effect of UV irradiation on the surface properties of polystyrene was s tudied. It was established that an increase in the exposure dose significan tly improves the water wettability of polystyrene; that is, its surface und ergoes hydrophilization under the action of photooxidation. It was found th at a partial relaxation (rearrangement) of the surface of the photooxidized polymer to the initial low-energy state takes place at the annealing tempe ratures which are appreciably below the glass transition temperature T-g of block polystyrene. An analogous effect was observed when evacuation of the photooxidized samples was carried out even at room temperature. Hence, alr eady at the early stages of photooxidation, rather low-molecular-mass polar products of degradation are formed in the surface layer of polystyrene. Th ese products plasticize the surface layer and markedly decrease its T-g. Th is conclusion is supported by the data of atomic force microscopy, which su ggest that, after sufficiently prolong UV irradiation, the surface layer of polystyrene behaves as a high-viscous liquid in contact with the edge of m icroscope.