Summary: Phase behaviour and specific interactions that occurred between poly (styrene-co-4-vinylpyridine) containing 20 mol % of 4-vinylpyridine (PS4VP20) and poly(styrene-co-itaconic acid) containing 17 mol % of itaconic acid (PSIA17) were investigated by differential scanning calorimetry (DSC) and Fourier Transform Infrared spectroscopy (FTIR).Due to favourable specific interactions among others, PSIA17/PS4VP20 system is miscible in the whole composition range, as evidenced by a single glass transition temperature (Tg), observed with each initial mixture, intermediate between those of the pure components. The Tg-composition dependence of this system fitted well the recent approach proposed by Brostow et al. (BCKV).Copolymerization of itaconic acid with styrene improved the thermal stability of PIA. The PSIA17/PS4VP20 blends showed a better thermal stability than their corresponding pure constituents. The degradation temperatures at maximum T dmax of these complexes are higher than those of pure constituents. Due to specific interactions that occurred between the two constituents of the blends, the anhydride amount observed with PSIA17 decreased.FTIR spectroscopy analysis confirmed qualitatively the occurrence of inter-polymer interactions from the appearance of new bands, characteristic of associated pyridine at 1607 cm À1 , pyridinium ion at 1638 cm À1 and liberated carbonyl groups of PSIA17 at 1725 cm À1. Quantitatively both fractions of liberated carbonyl and pyridinium species increased upon increasing PS4VP20 amount in the blend.