Methyl methacrylate-methacrylic acid (MMA-MAA) copolymers were prepared from the polymerization reaction of the methyl methacrylate (MMA) monomer with concentrated nitric acid (65% HNO3) at different reaction times in the absence of other reagents in the reaction mixture. The hydrolysis degrees of the MMA-MAA (sodium salts) copolymers estimated by thermogravimetry (TG) corroborated the data obtained by chemical titration. By calorimetry (DSC), a relationship between the glass transition temperature (T-g) and the hydrolysis degree was obtained. The results presented a deviation from linear behavior and it was related to the strength of the interactions involved in the copolymer chains. The equation that relates the glass transition temperature to the interaction parameter, chi, for miscible binary polymer blends was applied for the MMA-MAA copolymers and demonstrated the composition dependence of chi. The molecular mobility was determined by nuclear magnetic resonance (NMR) in the solid state and through the proton spin-lattice relaxation time in the rotating frame. The NMR data were in a good agreement with the results obtained by calorimetry.