Higher soluble nanostructured polyaniline was prepared by vapor-phase polymerization after passing aniline vapor through an aqueous acidic Solution of ammonium persulfate (PANI-V). Polyaniline was also synthesized by the conventional oxidative polymerization method (PANI-C) in an aqueous medium for the comparison of its properties with PANI-V. PANI-V exhibited lower conductivity but higher hydrophilicity and higher solubility (2-3 times) in. different solvents, such as tetrahydrofuran, N-methyl-2-pyrrolidone, dimethylsulfoxide, N,N-dimethyl formamide, and m-cresol at room temperature compared with that of PANI-C. The thermal stability of PANI-V was higher than that of PANI-C. In-depth investigations of the crystal structures of PANI-C and PANI-V were performed through powder X-ray diffraction analysis. The PANI-V showed a less ordered structure with a lower crystallinity and crystallite size and with a higher d-spacing and interchain separation compared with PANI-C. The unit cell volume of PANI-V was significantly higher with a greater number of atoms in the unit cell than that of PANI-C. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 331-340, 2009