Effect of Elevated Temperature on the Reactivity and Structure of Polyaniline

Abstract

The structure and oxidation state of emeraldine base polyaniline (PANI) in N-methylpyrrolidinone solutions that have been heated to 120−190 °C have been characterized by solid-state NMR, UV/vis, FTIR, and GPC. The spectroscopic studies reveal that the polymer is completely converted to its fully reduced leucoemeraldine form after heating at 175−190 °C for only 2 h, and bubbling oxygen gas through the solutions after heating results in partial reoxidation of the polymer. Cross-links, consisting of phenazine structures, have been identified in PANI films cast from heated NMP solutions by 15N interrupted decoupling solid-state NMR. After heating, the polymer is partially cross-linked with the cross-link density increasing with annealing temperature, and the non-cross-linked regions are the reoxidizable portions of the polymer. A mechanism by which the cross-linking reaction of PANI leads to the polymer reduction is discussed.