Polyaniline (PANI) doped with p-toluene sulfonic acid was synthesized by chemical polymerization method using (NH4)(2)S2O8 as an oxidizing agent. This is a single step polymerization process for the direct synthesis of the conducting emeraldine salt (ES) phase, without the need of doping, dedoping, and redoping of the polymer. Presence of a free carrier tail at higher wavelength, characteristic of extended coil conformation along with a sharp polaronic peak is observed in the UV-vis spectrum of doped PANI in m-cresol solvent. FT-IR studies show the characteristic peaks of ES phase along with a sharp peak at 1120 cm(-1) representing vibration band of the dopant ion. Clumps of small fibers resulting in a sponge-like structure was observed under scanning electron microscope. Thermal studies revealed a three-step decomposition pattern. Conductivity is found to increase with an increase in the temperature showing "thermal activation behavior." Decrease in resistance with increasing humidity is observed in a broad range of humidity. (c) 2005 Wiley Periodicals, Inc.