Electrochemistry and contact angle measurements on polymer films of ω-(3-pyrrolyl)-alkanoic acids in aqueous solution

Films of poly(3-(pyrrolyl)-carboxylic acid), poly(3-(pyrrolyl)-butanoic acid) and poly(3-(pyrrolyl)-pentanoic acid) were prepared by electrochemical polymerisation of the monomers in acetonitrile. All three give stable voltammetry in aqueous solutions. In the case of poly(3-(pyrrolyl)-carboxylic acid) and poly(3-(pyrrolyl)-butanoic acid) this voltammetry is pH dependent. Measurement of the advancing contact angle using buffered solutions of different pH is shown to be a sensitive technique for the characterisation of the surfaces of these conducting polymer films. These contact angle titrations provide information about the acidity of the carboxylic acid groups at the surface of the polymer film. We find that the surface acid groups are about 1.5 pKa units less acidic than simple carboxylic acids in solution but that the pH titration curves are not broadened as is usually observed for surface bound carboxylate groups.