The porphyrin-catalyzed, template-guided polymerization of aniline was carried out in an aqueous buffer solution. Hydrogen peroxide and iron(III) tetrasulfonated tetraphenyl porphyrin catalyzed the polymerization of aniline in the presence of sulfonated polystyrene as a template. The polymerization was carried out at different pHs ranging from I to 5. Ultraviolet-visible spectroscopy indicated the formation of a conducting form of polyaniline. The extent of the polymerization increased with decreasing pH of the solution. The maximum absorbance of the polaron band at 750 run was obtained at pH 2, but when the polymerization was performed with pH 4, this band shifted to a longer wavelength. These results confirmed that a longer chain length of polyaniline was obtained with pH 4. (c) 2006 Wiley Periodicals, Inc.