Ethylene/propylene copolymers with the same composition but different sequence of monomer distribution were submitted to thermal degradation in an inert atmosphere, in the presence of oxygen and/or free radical initiators. The analysis of the reaction products, consisting of lower molecular weight macromolecules with double bonds and oxygenated functional groups, was performed by viscosimetric, FTIR, NMR, and differential scanning calorimetry (DSC) analysis. The presence of linear ethylene blocks of different length with distinct melting temperatures was detected by the self-annealing methods based on DSC. The results are used to evaluate the effect of the copolymer macromolecules' microstructure and the processing conditions on the degradation extent and the molecular structure of the degradation products. (C) 2004 Wiley Periodicals, Inc.