ELECTROCHEMICAL INVESTIGATIONS OF A SUBSTITUTED OXIDATION STABLE POLYPYRROLE

The polar substituted polypyrrole, poly(5-acetamido-4,5,6,7-tetrahydro-2H-benzo[c]pyrrole), can be oxidized up to a degree of oxidation of 0.8 charges per pyrrole ring without substantial degradation. Its cyclic voltammogram (CV) shows two redox peaks. Variation of the sweep rate of the CVs and in situ gravimetric experiments show that the second anodic peak is associated with a swelling of the polymer. In situ u.v.-vis and e.p.r. spectra are in accordance with existing theories on the electronic properties of polypyrrole. While the neutral polymer is an insulator, the electrical conductivity increases to a maximum of 4 x 10(-3) S cm-1 when the polymer is 'half oxidized in a linear potential sweep, and then decreases to less than 10(-4) S cm-1 when fully oxidized. The potential dependence of the conductivity is completely reversible. The maximum of the conductivity occurs when polarons and bipolarons have the same concentration. This supports a hopping model of the conductivity in which charge transfer occurs between polarons and bipolarons.