Two studies were mainly focused on the measurement of electrochemical response time and the electron paramagnetic resonance (EPR) of the substituted polyaniline (PANI) complexes poly(o-phenetidine) (POP)-poly(styrene sulfonic acid) (PSSA) and poly(2-ethylaniline) (P2E)-PSSA, which were prepared by the electrochemical polymerization of the monomer (o-phenetidine or 2-ethylaniline) with PSSA, with indium tin oxide (ITO) as a working electrode in a 1M HC1 solution. Ultraviolet-visible spectra measurements showed evidence for the doped substituted PANI system to have a highly electrochemical response time recorded at a temperature of 298 K, and the results were further analyzed on the basis of the color-discolor model, which is typical of protonation systems. At the reaction time (3 s) and monomer concentration (0.6M) with PSSA (0.15 mu), the best electrochemical color/discolor time of the POP-PSSA complexes was 125/125 ms (thickness = 3.00 mu m), which was faster than that of the P2E-PSSA complexes. At the same thickness (10 mu m), the best electrochemical color/discolor time of the POP-PSSA complexes was 500/250 ms, which was faster than the P2E-PSSA complexes (750/500 ms). With regard to film growth rate, the POP-PSSA complexes (1.0 mu m/s) were faster than the P2E-PSSA complexes (0.79 [mu m/s); this was attributed to the substituted PANI having a steric effect and to good reactivity by the ethoxy group (-OC2H5) in the molecules. The EPR spectra of the two samples were recorded both at 298 and 77 K and were further analyzed on the basis of the polaron-bipolaron model. The narrower line width of the substituted PANI complexes arose due to polarons; that is, we propose that charge transport took place through both polarons and bipolarons. Compared to their salts, this could be attributed to the lower degree of structural disorder, the oxygen absorption on the molecules, and the steric effect by the side chain group.(c) 2005 Wiley Periodicals, Inc.