The miscibility and the thermal behaviour of binary mixtures of poly(styrene-co-methacrylic acid) containing 12 or 29 mol.% of methacrylic acid (SMA-12 or SMA-29) with poly(isobutyl methacrylate-co-4-vinylpyridine) containing 20 mol.% of 4-vinylpyridine (IBM4VP-20) as blends or interpolymer complexes were investigated by differential scanning calorimetry, thermogravimetry and FTIR spectroscopy. The results showed that, depending on the nature of the solvent used in the mixture and the density of the specific interacting species introduced within the polymer matrices, miscible polymer blends or interpolymer complexes were obtained. The single T-g observed with all the studied blends or interpolymer complexes is an evidence of their miscibility. The positive deviation of the T-g of the blends and the complexes from the weight average of the constituents T(g)s and the improved thermal stability of the SMA29/IBM4VP-20 complexes as compared to their corresponding blends is mainly due to the presence of stronger specific interactions of hydrogen bonding type that occurred between the carboxylic groups of the SMA-29 and the 4-vinylpyridine of the IBM4VP-20 and to the way these specific interactions are distributed. A quantitative analysis of these interactions was carried by FTIR above the glass transition temperature of the constituents of the (85/15) SMA-29/IBM4VP-20 blend in the 1850-1570 cm(-1) region. (C) 2007 Elsevier B.V. All rights reserved.