PREPARATION AND PROPERTIES OF A PYRROLE-BASED ION-GATE MEMBRANE AS STUDIED BY THE EQCM

Polypyrrole ion-gate membranes were produced by electrochemical polyme rization of pyrrole onto a gold-covered quartz crystal from aqueous so dium tosylate solutions under varying experimental conditions with the aim of finding the optimum conditions for the use of such a membrane for the release of anionic drugs. The variables studied were the poten tial of polymerization, pH, temperature and the relative permittivity of the solution. The n Values determined for the polymerization reacti on were about 2.24 and they were found to be quite independent of the polymerization conditions used. The effect of temperature and the rela tive permittivity of the solvent on the doping levels and the ion exch ange properties was of minor importance. The cathodic reduction of the ion-gate membrane, however, showed that if mainly anions are to be re leased from the membrane the polymerization potential has to be above 900 mV (on the calomel electrode scale) and the pH of the electrolyte solution should be neutral or acidic. If this potential is kept below 800 mV and the pH of the solution in which reduction of the membrane i s performed is alkaline, cations should be the main species moving. Im pedance measurements and a separate determination of the apparent acti vation energy (6.8 kJ mol(-1)) confirmed that, in the oxidized state o f the membrane, ion transport within the film is the main rate-limitin g process. (C) 1998 Elsevier Science S.A.