Direct pyrolysis mass spectrometry findings revealed that thermal decompositions of poly(n-butyl methacrylate), PnBMA, poly(n-butyl acrylate), PnBA, and poly(t-butyl acrylate), PtBA, follow different decomposition pathways. Among these polymers thermal degradation via depolymerization is only major decomposition routes for PnBMA. Thermal degradation of PnBA proceeds through simultaneous and subsequent processes, involving gamma-hydrogen transfer to carbonyl group from the main chain to carbonyl groups yielding mainly six-membered cyclic products and butanol. On the other hand, decomposition of PtBA starts by elimination of C4H8 by gamma-hydrogen transfer reactions from the t-butyl groups to the carbonyl groups producing poly(acrylic acid) chains by elimination of isobutene. Subsequent losses of H2O, CO2 and CO yield unsaturated linkages and crosslinked structures that decompose at elevated temperatures. (C) 2013 Published by Elsevier B.V.