SOLVENT-FREE PREPARATION AND CHARACTERIZATION OF POLYANILINE DOPED WITH BRONSTED ACIDIC IONIC LIQUIDS

Two Bronsted acidic ionic liquids with an alkyl -SO3H functional group, 1-methyl-imidazoliumpropanesulfonic acid hydrogen sulfate ([MIMPS] [HSO4]) and pyridiumpropanesulfonic acid hydrogen sulfate ([PYPS] [HSO4]) were firstly synthesized. And then the polyamiline (PANO doped with these Bronsted acidic ionic liquids were synthesized by a solvent-free mechanochemical route. The structures and properties of PANI-[MIMPS] [HSO4] and PANI-[PYPS] [HSO4] were characterized. Because Bronsted acidic ionic liquid has four kinds of ionic form, in which hydrogen ion can exist independently, anilinium salt formed after the aniline was mixed with the ionic liquid. Reactions between anilinium salt and the oxidant, ammonium peroxydisulfate, resulted in PANI formation on grounding the reactants in a mortar. FTIR and UV-Vis-NIR spectroscopy indicated that PANI was formed in its doped, conductive emeraldine oxidation state and this was consistent with the green color of the products. The molar ratio of aniline monomer to ionic liquid was systematically varied in order to optimize the electrical conductivity of PANI. When the aniline monomer to ionic liquids ratio was 1:1, the highest electrical conductivity for the PANI-[MIMPS] [HSO4] (10.3 S/cm) and PANI-[PYPS] [HSO4] (8.8 S/cm) was obtained, respectively. The XRD patterns of the resultant PANI showed two broad peaks at 10.1 degrees, 27.1 degrees, two sharp peaks at 20.6 degrees, 25.4 degrees and a weak peak at 29.1 degrees, indicating that the resulting polymers were in the form of a highly doped emeraldine salts and have good crystallinity. Cyclic voltammograms of PANI showed two clear oxidation peaks in the forward scan and prominent reduction peaks in the reverse scan. The results demonstrated PANI-[MIMPS] [HSO4] had better crystallinity, conductivity and electrochemical activity compared with PANI-[PYPS] [HSO4].