Methyl methacrylate-methacrylic acid (MMA-MAA) copolymers, prepared by the action of concentrated nitric acid (65% HNO3) on methyl methacrylate in absence of other reagents, were characterized using calorimetry (DSC) and infrared (FTIR) analyses. DSC curves of ester/acid copolymers suggested the anhydride formation at similar to 200 degrees C, which was corroborated by thermogravimetry (TG). This structure was assigned by FTIR spectra. The results obtained by DSC data are in good agreement with the hydrolysis degree of the MMA-MAA copolymers obtained from chemical titration. The molecular weight of the copolymers were estimated by viscometry.