ELECTROCHEMICAL INVESTIGATIONS OF A SUBSTITUTED OXIDATION STABLE POLYPYRROLE

The polar substituted polypyrrole, -acetamido-4,5,6,7-tetrahydro-2H-be nzo[c]pyrrole), can be oxidized up to a degree of oxidation of 0.8 cha rges per pyrrole ring without substantial degradation. Its cyclic volt ammogram (CV) shows two redox peaks. Variation of the sweep rate of th e 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 an d e.p.r. spectra are in accordance with existing theories on the elect ronic properties of polypyrrole. While the neutral polymer is an insul ator, 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. T he potential dependence of the conductivity is completely reversible. The maximum of the conductivity occurs when polarons and bipolarons ha ve the same concentration. This supports a hopping model of the conduc tivity in which charge transfer occurs between polarons and bipolarons .