The photostabilization of polystyrene (PS) films by 2-thioacetic acid benzothiazol with Sn(II), Cd(II), Ni(II), Zn(II), and Cu(II) complexes was investigated. The PS films containing complexes of concentration 0.5% by weight were produced by the casting method from chloroform solvent. The photostabilization activities of these compounds were determined by monitoring the carbonyl and hydroxyl indices with irradiation time. The changes in viscosimetric average molecular weight of PS with irradiation time were also tracked (using benzene as a solvent). The quantum yield of the chain scission (?cs) of these complexes in PS films was evaluated and found to range between 3.60 x 10-6 and 7.78 x 10-6. The results obtained showed that the rate of photostabilization of PS in the presence of the additive is in the following trend: Ni(L)2 > Cu(L)2 > Zn(L)2 > Cd(L)2 > Sn(L)2. According to the experimental results obtained, several mechanisms were suggested depending on the structure of the additive. Among UV absorption, peroxide decomposer and radical scavenger for photostabilizer additive mechanisms were suggested. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012