The formation of oligomers in the electrolyte upon polymerization of pyrrole

Pyrrole was polymerized by electrochemical and chemical oxidation of a solution of pyrrole and p-toluene sulfonic acid in acetonitrile. We have investigated the components formed within that electrolyte solution during the polymerization. Both, UV–VIS spectroscopy and size exclusion chromatography give evidence that pyrrole oligomers nP (n≤30) are formed in the solutions during the polymerization process. A model is proposed in which these oligomers act as intermediates of the polymerization reaction. Within that model the deviations from Faradayic behaviour at elevated current densities are explained. It also rationalizes the fact that polymer films with completely different properties can be realized by varying the experimental parameters.