A de-doping/re-doping study of organic soluble polyaniline

Polyaniline (PAn·HA) doped with dinonylnaphthalene sulfonic acid (DNNSA) is highly soluble in organic solvents making it attractive from a processing viewpoint. In a number of applications, however, it is desirable to use specific counterions to obtain particular properties. The exchange of the DNNSA counterion has been investigated by a de-protonation/re-protonation cycle involving aqueous and methanolic base and acid solutions. More effective counterion exchange occurs when the polymer is de-protonated using the methanolic base solution, since the DNNSA counterion has limited solubility in water. De-protonation also occurs upon extended immersion in neutral methanol due to simple dissolution of the counterion. Re-protonation of the polyaniline to the emeraldine salt is possible using a wide range of acids to produce doped PAn·HA having simple counterions (e.g. Cl−), polymeric counterions (e.g. polyvinylphosphate) and even sulfonated polyaniline as the counterion. Re-doping is also achieved with neutral salt solutions, such as zinc nitrate. In most cases, the quality of the coatings is not compromised by the de-protonation/re-protonation cycle and the re-protonated polyanilines remained conductive and electroactive. However, significant conformational changes occur in the polymer following de-protonation/re-protonation as indicated by UV–visible–near-infrared spectral changes.