Electrochemical behaviour of poly(2,5-di-(-2-thienyl)-thiophene): Properties of the reduced polymer

The oxidized poly(2,5-di-(-2-thienyl)-thiophene) (poly(SSS)) can be reduced, passing through a neutral state until a reduced, negatively charged state is reached by applying different potentials. Voltammetric and chronoamperometric results were confirmed by elemental analysis. Reduced polymers bearing 0.06 positive charges or 0.58 negative charges per monomeric unit after reduction at 0 or -2.6 V vs. SSCE respectively were obtained. An increasing content of ion pairs Li+ClO4- per monomeric unit was found in reduced poly(SSS) at increasing negative potential. During reduction, a weight loss ranging between 15 and 25% of the oxidized polymer mass was found. A small fraction of this loss was due to solubilization, the other fraction to counterions lost from the polymer. Magnitudes like the productivity of the polymerization charge, related to the reduced polymer mass, the density, conductivity and solubilities in several organic solvents of the different reduced states were determined. The reduction of the polymer at more negative potentials than -1V occurs together with other parallel reactions, as deduced from both the number of electrons consumed to reduce one monomeric unit and that calculated from elemental analysis results. IR studies point to alpha-alpha linkages as the main junction between monomeric units in the polymer. UV-vis studies of soluble fractions of reduced forms in different solvents indicate that the dimer is the main soluble species. A band diagram was proposed from UV-vis spectra obtained from solutions of monomer and soluble fractions of reduced and oxidized polymers in dichloromethane.