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 chronoampe rometry. The monomer exhibits two similar consecutive oxidation processes. Uniformly. adherent and electroactive films of dark-blue poly(SNS) doped wi th 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 duri ng 360 s. The increase in transport rate of reactants by stirring the solut ion with a magnetic bar at 150 rpm accelerates the SNS electropolymerizatio n, allowing to collect much more polymer weight than from the quiescent sol ution. The productivity of poly(SNS) doped with Cl- determined by 'ex situ' ultramicrogravimetry increases notably under stirring, although its percen tage in Cl is similar to that found under quiescent conditions. This is asc ribed to the production of a major proportion of longer linear molecules in polymer, consistent with its higher conductivity when it is synthesized un der 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 conduct ivity. 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 mech anism. (C) 2000 Elsevier Science Ltd, All rights reserved.