DSC and optical microscopy were used to determine the miscibility and crystallinity of blends of poly(ethylene oxide) (PEO) with poly(methyl vinyl ether-co-maleic acid) (PMVE-MAc). Single T-g was observed for all blends, indicating miscibility. The dependence of T-g on the weight per cent of PEO presents a negative deviation from linearity at high PEO content, associated to a greater blend free volume, mobility and flexibility than in pure PEG. A progressive decrease in the degree of crystallinity and in the size of the PEO spherullites as the PMVE-MAc is added is observed. FTIR provided evidence of specific interaction between the polymers. (C) 2001 Elsevier Science Ltd. AU rights reserved.