The products of the thermal degradation at 95°C over 10 months of ω-saturated and non-saturated poly(methyl methacrylate) (pMMA) model compounds were identified with high accuracy via quadrupole ion trap and quadrupole ion trap-time of flight (Q-ToF) mass spectrometry. Analysis of the samples taken via these techniques indicated that degradation of vinyl terminated pMMA proceeds via the incorporation of oxygen via the formation of ethylene oxide type end groups, which subsequently rearrange under the expulsion of formaldehyde and 2-oxo-propionic acid methyl ester. The corresponding saturated model compounds were demonstrated to be stable over the same time period. The present findings highlight for the first time that poly(methyl methacrylate) degradation does not necessarily and exclusively proceed via radical intermediates. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.