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The structural changes of a polymeric hindered amine light stabilizer (HALS), Adekastab LA-68LD (MW=1900) added in PP materials during UV-irradiation were investigated by reactive thermal desorption-gas chromatography (RTD-GC) in the presence of tetramethylammonium hydroxide [(CH3)4NOH, TMAH]. Not only the products formed from the residual intact HALS, but also those from its oxidized moiety (nitroxyl radical) were observed on the resulting chromatograms without the use of any troublesome sample pretreatment such as solvent extraction. The changes in the yields of these key products were then examined as a function of UV-exposure time. As a result, it was revealed that the amount of the nitroxyl radical increased in the initial stage of UV-irradiation but then slightly decreased mainly because of further decomposition into the smaller compounds, whereas that of the intact HALS monotonously decreased during exposure. [Copyright &y& Elsevier]