This paper studies the styrene-(mono-ethyl-maleate) copolymer using IR spectroscopy. The copolymer was obtained by styrene copolymerization with maleic anhydride, in ethanol as the reaction medium. The IR spectra recorded give information concerning the physico-chemical structure, the monomer ratio and emphasize the intermolecular interactions corresponding to the hydrogen bond associations. The elevated temperature studies (90-130 degrees C) allowed us to establish the equilibrium constants, the enthalphy and entropy variation, values of -4.2 kcal mol(-1) and -3.7 e.u. mol(-1), respectively, being obtained.