The mechanism of photoprotection of polystyrene film by some ultraviolet absorbers

The efficiency of three commercial ultraviolet absorbers, a 2-hydroxy benzophenone, a 2-hydroxy benzotriazole, and a nickel chelate, in preventing the photo-oxidation of polystyrene films has been measured. When compared with the calculated screening and phosphorescence quenching efficiency, it is found that (i) the nickel chelate protects the substrate by UV screening alone and is a poor photoprotector, and (ii) the 2-hydroxy benzophenone and 2-hydroxy benzotriazole are more efficient photoprotectors and protect by triplet energy transfer from excited polymer carbonyl impurity groups in addition to UV screening.