In this study, poly(o-anisidine) [POA], poly(o-anisidine-co-aniline) [POA-co-A], and polyaniline [PANi] were chemically synthesized using a single polymerization process with aniline and o-anisidine as the respective monomers. During the polymerization process, p-toluene sulfonic acid monohydrate was used as a dopant while ammonium persulfate was used as an oxidant. N-methyl-pyrolidone (NMP) was used as a solvent. We observed that the ATR spectra of POA-co-A showed features similar to those of PANi and POA as well as additional ones. POA-co-A also achieved broader and more extended UV-vis absorption than POA but less than PANi. The chemical and electronic structure of the product of polymerization was studied using Attenuated Total Reflectance spectroscopy (ATR) and UV-visible spectroscopy (UV-vis). The transition temperature of the homopolymers and copolymers was studied using differential scanning calorimetry and the viscosity average molecular weight was studied by using dilute solution viscometry. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 3123-3130, 2010