A terpolymer, obtained by the free-radical terpolymerization of 2-(N,N-dimethylamino)ethyl methacrylate (DMMA), methyl methacrylate(MMA), and isobutyl methacrylate (IBMA), was allowed to react with hydrogen peroxide, chloroacetic acid, and diethyl sulfate to form the corresponding modified terpolymers: (1) N,N-dimethyl-N-(2-methacryloyloxyethyl)amine N-oxide, MMA and IBMA (DMANO series); (2) N-(carboxymethyl)-N,N-dimethyl-N-(2-methacryloyloxyethyl)ethyl ammonium, MMA and IBMA (CDME series); and (3) N-(ethyl)-N,N-dimethyl-N-(2-methacryloyloxyethyl)ethyl ammonium ethylsulfonate, MMA and IBMA (EDMEES series), respectively. The terpolymer compositions were determined using C-13 NMR spectrometry. Surface free energies of the terpolymers were estimated by measuring the contact angles of water and methylene iodide on the three series films (DMANO, CDME, and EDMEES), and the effect of the N-oxide group on wettability was discussed. It was found that the upper surface of the films for the DMANO and CDME series are more hydrophobic than that for the EDMEES series. Notably, elongation to break for the DMANO series was relatively larger than that for the CDME series because of the water bound to the N-oxide functional group. (c) 2005 Wiley Periodicals, Inc.