Electropolymerization of 2,5-di-(-2-thienyl)-pyrrole in ethanolic medium. Effect of solution stirring on doping with perchlorate and chloride ions

The electrochemical behavior of 2,5-di-(-2-thienyl)pyrrole (SNS) on Pt has been studied from a 10 mM monomer solution in 0.2 M LiClO4+ethanol or in 0.2 hi LiCl-ethanol by cyclic voltammetry, chronopotentiometry and chronoamperometry. The monomer exhibits two similar consecutive oxidation processes. Uniformly. adherent and electroactive films of dark-blue poly(SNS) doped with ClO4-, or with Cl- are obtained at low potentials related to line first process. Reproducible film weights are found at 0.700 V versus Ag/AgCl during 360 s. The increase in transport rate of reactants by stirring the solution with a magnetic bar at 150 rpm accelerates the SNS electropolymerization, allowing to collect much more polymer weight than from the quiescent solution. The productivity of poly(SNS) doped with Cl- determined by 'ex situ' ultramicrogravimetry increases notably under stirring, although its percentage in Cl is similar to that found under quiescent conditions. This is ascribed to the production of a major proportion of longer linear molecules in polymer, consistent with its higher conductivity when it is synthesized under stirring. This effect is not so clear for the poly(SNS) doped with ClO4- due to the little influence of stirring upon its productivity and conductivity. The detection of short linear oligomers in the soluble fractions of polymers in thioglycerol by mass spectrometry-fast atom bombardment allows to propose a radical polycondensation as initial electropolymerization mechanism. (C) 2000 Elsevier Science Ltd, All rights reserved.