Investigation of spectral properties, thermal stability, and morphology in polyaniline doped with chlorocarboxylic acids

The morphology of polyaniline (PANI), granular or tubular, depends on the acidity conditions during the reaction rather than on the chemical nature of the acid. In reference to acetic acid in which media nanotubes had been observed, dichloroacetic acid (DCA) and trichloroacetic acid (TCA) were used to synthesize polyaniline by the oxidative polymerization technique. Characterization by Fourier-transform infrared ( FTIR), UV-visible, and electron paramagnetic (EPR) spectroscopy techniques indicated that the polymers are in the protonated emeraldine form and suggest that the protonation of PANI in media containing such acids was achieved with the help of sulfuric acid produced during the reaction from ammonium peroxydisulfate. The conductivity of polyaniline prepared in DCA was 0.04 S cm(-1) and 0.5 S cm(-1) in TCA. The thermal stability of polyaniline salts was tested by thermogravimetric analysis and a three-step decomposition pattern was observed. Wide-angle X-ray diffraction (WAXD) study showed enhanced crystallinity in polyaniline prepared in TCA. The morphology is discussed in relation to the formation of polyaniline nanotubes reported in the literature.