Substituent Effects on Conformational Changes in (+)-CSA Doped Polyaniline Derivatives

This paper reports substituent effects on the conformational changes in polyaniline (PAni) derivatives. PAni, poly-o-toluidine (POT), and poly-o-anisidine (POA) were formed by potentiodynamic electropolymerization in aqueous solution containing (+)-camphorsulfonic acid (CSA) as a dopant. UV-Vis spectroscopy and cyclic voltammetry measurements revealed that the methyl group showed a greater steric hindrance than the methoxy group. Further, the doping level decreased with increasing steric hindrance. The sign pattern of the circular dichroism (CD) bands for POA was opposite to that for PAni. However, no CD bands were observed in POT. The steric hindrance caused helical inversion, but at a high level of steric hindrance, the helical conformation could not be adopted, because of the reduced doping level. The reduced crystallinity was greatly affected by the decreased doping level. The steric effect influenced the polymer conformation and the doping level, thus determining the optical activity, morphology, and crystallinity of the PAni derivatives.