Facile preparation of water-dispersible carboxylated polyaniline

Polyaniline (PANI), containing carboxylic groups, was prepared by covalent modification of PANI base, using various amounts of thiolactic acid (TLA). It was found that using the excess of TLA, compared to the stoichiometric amount required for modification of emeraldine form of PANI, did not lead to increase of substitution degree. Elemental analysis showed that in all studied conditions ≈6.5 wt% of carboxylic groups were introduced into PANI backbone. Change of PANI chemical structure as a result of modification by TLA was studied by electronic, vibrational and photoelectron spectroscopy. It was shown that TLA is covalently bound to PANI without significant amount of free TLA and the initial PANI base also becomes partially protonated. Conductivity of PANI-TLA materials (≈5 ×10–7 S cm–1) increased by 4 orders of magnitude, compared to PANI base (5 ×10–11 S cm–1). Due to the presence of carboxylic groups, TLA-modified PANI is dispersible in alkaline aqueous medium, which can enable eco-friendly ways of PANI deposition for the applications in sensors and anticorrosive coatings.