In situ spectroelectrochemical studies were carried out on the polymerization of diphenylamine (DPA) and copolymerization of DPA with anthranilic acid (AA). Electropolymerization was performed in aqueous 2 M H2SO4 by applying a constant potential (0.80 V) on indium. tin oxide (ITO)-coated glass electrode. Spectral characteristics were followed for various feed ratios of the comonomers (DPA and AA) at different polymerization times. Two types of cation radicals could be observed for the electropolymerization with mixture of DPA and AA, corresponding to anilinium-type and N,N'-diphenylbenzidine-type, respectively. UV-visible spectra recorded for copolymerization inform that the peak position corresponding to DPB+. showed clear dependence on AA concentration in the feed. signifying the changes in the overall oxidation states of the polymer as a result of incorporation of AA units in the copolymer. The FTIR spectral analysis of the copolymer clearly reveals the incorporation of AA units into the polymer backbone during polymerization. The presence of a band at 1650 cm(-1) in FTIR spectra corresponding to the -C=O group of AA units and the improvement in thermal stability of the copolymer as observed from thermogravimetric analysis (TGA) favor the incorporation of AA units in the copolymer. (C) 2002 Elsevier Science B.V. All rights reserved.