Experimental evidence for hydrogen bonding in polyaniline: Mechanism of aggregate formation and dependency on oxidation state

Aggregation in the nondoped polyaniline, emeraldine base (EB), as observed by GPC in a N-methyl-2-pyrrolidinone (NMP) solution, was found to be closely related to the fraction of the imine nitrogen atoms in the nondoped polymer, i.e., to the oxidation state of the polymer. As EB was reduced to leucoemeraldine base (LEB), the degree of aggregation was significantly reduced. The results of gel permeation chromatography (GPC) and infrared studies suggest that the aggregation of the polymer is due to interchain hydrogen bonding between the imine and amine nitrogen sites on adjacent polymer molecules. The degree of hydrogen bonding and, thus, aggregation found in the polymer is greatly affected by solvents, LiCl, and the oxidation state of the polymer.