Effect of chemical functionalization on the electrochemical properties of conducting polymers. Modification of polyaniline by diazonium ion coupling and subsequent reductive degradation

Abstract

The electrochemical properties of polyaniline (PANI) can be altered by coupling the polymer with aryldiazonium ions. The ions are synthesized by diazotization of aromatic primary amines (1-aminoanthraquinone, sulphadiazine and 4-cyanoaniline) bearing functional groups which are then linked to the polyaniline backbone. All materials produced are electroactive, suggesting that the reaction involves coupling of the diazonium ion with the aromatic rings and not nucleophilic substitution by the aminic nitrogen of PANI on the aryl cations. The electrochemical properties of the modified polymers are different to those of PANI, likely due to electronic and steric effects of the attached groups. Reductive degradation of the azo linkages, using dithionite ion, removes the attached moieties leaving primary amino groups attached to the polyaniline backbone. In that way, the effect of the attached groups on the electrochemical properties of PANI is eliminated. FTIR spectroscopy measurement of the different polymers supports the proposed mechanism. Using the method a polymer containing redox (anthraquinone) groups, which could be used for charge storage, is obtained. Additionally a material containing sulphadiazine moieties, which can be released in vivo by bacterial activity, is also produced. The molecule is a well-known sulfa drug with bacteriostatic activity. The reaction sequence seems to be of general application to modify polyanilines, by attaching functional groups, and then to produce a PANI backbone bearing primary amino groups. Evidence is presented on the kinetic control of attached group removal.