Polymerization mechanism and physicochemical properties of electrochemically prepared polyindole tetrafluoroborate

Abstract

Polyindole tetrafluoroborate [(PI)BF4] was obtained from a acetonitrile/benzonitrile solution containing 0.2 M indole and 0.1 M tetraethylammonium tetrafluoroborate, supplying a potential of 0.7 V. Cyclic voltammetry measurements suggested that the electrode reaction in the indole solution was a reversible reaction and the number of related electrons was 2. The measurements suggested that an electropolymerization of indole proceeded by the formation of radical cations as intermediates. Thermal analyses of polyindole- and polyaniline-based systems were performed at 25-800°C. The TGA results indicated that most polyindole-based polymers were mainly decomposed at higher temperatures than those of the polyaniline-based systems. Also, the maximum values of the reaction rate of thermal decomposition (Rmax) for the polyindole-based systems were not seriously affected by the kind of dopants. On the other hand, the Rmax values of the polyaniline-based ones depended on the kind of electron acceptor. The electrical conductivity for (PI)BF4 was measured in the temperature range from -150 to 25°C. The resulting values of log σ at 25°C and Ea value as calculated, from the Arrhenius plot were -2.43 S/cm and 0.4057 eV, respectively. The conductivity measurements suggested that possibly the conduction mechanism and charge carriers were hopping conduction and polarons, respectively, which then caused the BF4- anion to act as an electron acceptor. The ESR measurements for the (PI)BF4 powder were performed at 25°C, so the values of ΔHpp, g, and spectral ratio were obtained. ？ 1992 American Chemical Society.