Polyaniline (PANI) was synthesized by the well-known oxidative polymerization of aniline with ammonium peroxodisulfate as the oxidant. The morphological, structural, thermal, optical, magnetic, and electrical properties were characterized with scanning electron microscopy, X-ray diffraction, Fourier transform infrared, thermogravimetric analysis, differential scanning calorimetry, ultraviolet-visible spectroscopy, room-tempera tu re magnetic measurements, and low-temperature electrical transport measurements by the standard four-probe method. Greater thermal stability and crystallinity were observed in doped PANI versus pure PANI. Magnetic measurements showed that the magnetic susceptibility was field-dependent. Positive and negative susceptibility values were observed. This may have been due to the interactions of magnetic ions among interchains or intrachains of the polymer matrix. The alternating-current (ac) conductivity was measured in the temperature range of 77-300 K in the frequency range of 20 Hz to 1 MHz. The frequency-dependent real part of the complex ac conductivity was found to follow the universal dielectric response: sigma'(f) proportional to f(s) [where sigma'(f) is the frequency-dependent total conductivity, f is the frequency, and s is the frequency exponent] The trend in the variation of the frequency exponent with temperature corroborated the fact that correlated barrier hopping was the dominant charge-transport mechanism for PANI-CoCl2. An anomalous dependence on temperature of the frequency exponent was observed for PANI-CuCl2. This anomalous behavior could not be explained in terms of existing theories. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 2911-2917, 2010