A simple method to estimate the oxidation state of polyanilines

The electrical conductivity and other properties of polyaniline (PANI) and its derivatives are highly dependent on its oxidation states. In order to o btain a simple method to determine the oxidation state, a systematic study was performed to investigate the interconversion between pernigraniline (PB ) PANI form to emeraldine (EB) one, and from EB to leucoemeraldine (LEB), b y ultraviolet/visible (UV/Vis) spectroscopy. UV/Vis spectra were carried ou t for different oxidation degrees of PANI/N-methyl-2-pyrrolidinone (NMP) so lutions. The redox states interconversion was made in NMP solutions in ambi ent air and/or inert atmosphere. LEE base presents only one peak in the abs orbance spectra, associated with the pi-pi* transition, while the other two forms, EB and PB, exhibit another peak of lower energy. This second peak, related to a molecular exciton in EB, has its maximum intensity diminished as the EB is reduced or oxidized. By plotting the relative intensity of the se peaks vs. the oxidation degree, it was possible to identify, with a reas onable accuracy, the oxidation state of PANIs. This method was also applied to poly(o-methoxyaniline) (POMA). (C) 2000 Elsevier Science S.A. All right s reserved.