Copolymers of aniline and ethyl 3-aminobenzoate (3EAB) were synthesized by chemical polymerization in several mole ratios of aniline to functionalized aniline, and their physicochemical properties were compared to those of poly(aniline-co-3-aminobenzoic acid) (3ABAPANI) copolymers. The copolymers were characterized with UV-vis, FTIR, Raman, SEM, EPR, and solid-state NMR spectroscopy, elemental analysis, and conductivity measurements. The influence of the carboxylic acid and ester group ring substituents on the copolymers was investigated. The spectroscopic studies confirmed incorporation of 3ABA or 3EAB units in the copolymers and hence the presence of C=O group in the copolymer chains. The conductivity and EPR signals both decreased with increasing 3EAB content of the copolymers emeraldine salt (ES) form. The conductivity of the ES form of 3ABAPANI was found to be high (1.4 x 10(-1) S cm(-1)) compared with the conductivity (10(-2)-10(-3) S cm(-1)) of 3EABPANI (ES) copolymers. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1339-1347,2010