Control of aggregation and crystallinity in polyaniline

Abstract

Interchain H-bonding between amine and imine sites in emeraldine base (EB) results in aggregate formation. The aggregation is present in the as synthesized EB; the level of aggregation is dependent on the polymerization conditions. Reduction of EB to the leucoemeraldine form eliminates the imine sites and thus, the interchain H-bonding and the aggregation are also eliminated. The degree of aggregation in the EB powder determines the solubility and solution characteristics of the polymer. Solvents such as m-cresol and additives such as LiCl which dope EB are most efficient at solvating the polymer and thus, deaggregating the chains. Deaggregation facilitates chain expansion. The degree of aggregation and chain expansion in EB solutions significantly impact the overall properties of both the non-doped and doped polymer such as the optical absorption, conductivity and degree of crystallinity. Crystalline EB films are attained from solutions consisting of low polymer concentration where the polymer is well solvated and highly deaggregated. Highly, crystalline non-stretched EB films are attained by the introduction of a plasticizer which imparts local mobility allowing the chains to crystallize.