Polymer complexation between poly(styrene-co-maleic acid), (SMA28) and (SMA50) containing 28 and 50mol% of maleic acid and poly(vinyl pyrrolidone) (PVP), has been investigated by differential scanning calorimeter (DSC), Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). All results showed that the ideal complex composition of SMA28/PVP and SMA50/PVP leads, respectively, to 2:1 and 1:1 mole ratio of interacting components. For the investigated systems, the T-g versus composition curve does not follow any of the usual proposed models for polymer blends. Withal, a new model proposed by Cowie et al. is used to fit the T-g data and it is found to reproduce the experimental results more closely. According to n and q obtained values, it seems reasonable to conclude that the inter-associated hydrogen bonds dominate in SMA28/PVP (2: 1) complexes. This effect is corroborated by the FTIR study as evidenced by the high displacement of the specific bands and ionic interactions have been clearly identified. Finally, a thermogravimetric study shows that ionic interactions increase the thermal stability of these complexes. (C) 2008 Elsevier B.V. All rights reserved.