Thermal stability of polypyrrole (PPY) synthesized by in situ doping polymerization in the presence of different naphthalene mono/disulfonic acid dopant like alpha-naphthalene sulfonic acid (alpha-NSA), beta-naphthalene sulfonic acid (beta-NSA), and 1,5-naphthalene disulfonic acid (1,5-NDSA) has been systematically investigated by thermogravimetric analysis (TG). It was found that the thermal stability of as-resulted PPY was greatly affected by type and concentration of dopant. In general, the order of their thermal stability was PPY-(beta-NSA) > PPY-(alpha-NSA) approximate to PPY-(1,5-NDSA). And high concentration of dopant (e.g., 1.2 mol/L) had a negative effect on the thermal stability. Among those three dopants, 1,5-NDSA had a unique influence on thermal stability and crystallinity of as-resulted PPY. In addition, all of room-temperature conductivity and crystallinity of PPY-(1,5-NDSA) changed dramatically after aging for 9 h under N-2 atmosphere and at 230 degrees C, which may be due to a partly dedoping process. These results were confirmed by elemental analysis, FTIR, X-ray photoelectron spectroscopy (XPS), and X-ray powder diffraction (XRD). (C) 2008 Wiley Periodicals, Inc.