In this work, thermal degradation of copolymers of poly(methy methacrylate) namely, poly(methyl methacrylate-co-n-butyl acrylate), P(MMA-co-nBu), poly(methyl methacrylate-co-n-benzyl methacrylate) P(MMA-co-BzMA, and poly(methyl methacrylate-co-isobornyl acrylate), P(MMA-co-IBA) were investigated via direct pyrolysis mass spectrometry. It was determined that whether an available gamma-H with respect to the carbonyl groups is present or not determines the thermal degradation mechanisms of polyacrylates and polymethacrylates. Cis elimination reactions become preferential as the first step of thermal decomposition and lead to a multi-step degradation mechanism involving trans-esterification reactions together with elimination of molecules such as alcohols, CO2, CO and H2O if gamma-Hs to the carbonyl group is present. On the other hand, if there is no gamma-H, thermal degradation proceeds by depolymerization yielding mainly the corresponding monomer. Consequently, PMMA and PBzMA decompose by depolymerization mechanisms and in contrast, thermal degradation of PnBA, and PIBA occurs through various reaction pathways involving random chain scissions, cis-elimination and trans-esterification reactions and elimination of CO2 and CO. (C) 2015 Elsevier B.V. All rights reserved.