The structure of the system obtained after free radical copolymerization of ethyl acrylate and hydroxyethyl methacrylate comonomers has been studied using dynamic-mechanical and calorimetric techniques. According to the copolymerization theory it is known that the free-radical copolymerization reaction of two monomers may give rise to the formation of a copolymer having a chain composition different from the random mixture corresponding to the original solution. In our system, the dynamic-mechanical spectra suggest the existence of two main a relaxation processes in the copolymers. Conventional differential scanning calorimetry (DSC) heating scans show a single and broad glass transition located between those of the pure components. Segmental dynamics studies by subjecting the samples to isothermal annealing in the region of the glass transition and below it give information about the temperature range where conformational mobility is high enough and allow to infer conclusions about the composition distribution of the material. These results although qualitatively well correlated with the copolymerization theory, that predicts the composition of the system from the monomer feed ratios and the reactivity ratios of the monomers, provide a further insight in the final material architecture. (C) 2004 Elsevier Ltd. All rights reserved.