Stabilizer effects of two types (homopolymer and copolymer) of commercially available polyoxymethylenes containing two different stabilizer packages under various aging conditions have been studied by the application of thermogravimetric analysis coupled with mass spectrometry. Increasing yellowness during thermooxidative aging has been observed. Investigations of the melt volume rate have proved that the UV-stabilized materials exhibit a higher increase in the melt volume rate after oven aging, which is caused by reactions of the additives, than the solely heat-stabilized materials. The thermogravimetric analysis/mass spectrometry investigations have proved broad synergy effects between the heat- and UV- stabilizer systems. The formation of chains with thermally stable end groups or of cyclic products proceeds during aging, particularly in the presence of UV stabilizers. This formation might be the result of intermolecular transacetalization reactions. The degradation behavior of UV-irradiated homopolymer and copolymer samples has also been investigated. Oven storage and weathering cause comparable shifts in the derivative thermogravimetry traces, so similar damage reactions can be suggested. (c) 2007 Wiley Periodicals, Inc.