THE INTRINSIC REDOX STATES IN POLYPYRROLE AND POLYANILINE - A COMPARATIVE-STUDY BY XPS

X-ray photoelectron spectroscopy provides a useful tool for the critical comparison of the chemical nature of the nitrogens corresponding to the various intrinsic redox states of electroactive polypyrrole (PPY) and polyaniline (PAN) and their N-substituted derivatives. Proton modifications of the PPY nitrogens can give rise to a number of intrinsic redox states corresponding to various proportions of the imine-like (=N-) and amine-like (-NH) nitrogens, similar to those observed in PAN. For complexes prepared from oxidative polymerizations, the intrinsic oxidation level of PAN is always about twice that of PPY (50% vs. 25%). The behaviours of the nitrogens of the corresponding redox states in both polymers towards oxidation, reduction, protonation and charge transfer interactions are grossly similar. However, the amine nitrogens in the emeraldine (EM) oxidation state of PAN (50% =N- structure) are more susceptible to protonation in the presence of excess protonic acids than those of the 25% deprotonated PPY (DP-PPY). Finally, the doping level in poly(N-methylaniline) (PMAN) is twice that of poly(N-methylpyrrole) (PMPY). The base polymers of PMAN and PMPY exist only in the fully reduced state and are susceptible to reoxidation. The nitrogens of PMAN, but not PMPY, are also susceptible to protonation.