The effect of polymerization temperature on molecular weight, crystallinity, and electrical conductivity of polyaniline

The influence of the polymerization temperature (from - 50 to + 50 degrees C) on molecular weight, crystallinity, and electrical conductivity of polyaniline has been investigated. Aniline was oxidized in aqueous medium with ammonium peroxodisulfate at equimolar and excess concentrations of hydrochloric acid. The reaction mixture freezes below - 10 degrees C and the polymerization of aniline then proceeds in the solid state. As the reaction temperature decreases, both the molecular weight of polyaniline (determined by gel permeation chromatography) and its crystallinity (observed by X-ray diffraction) increase. The morphology of polyaniline changes from granular (reaction in a liquid medium) to macroporous (polymerization in the frozen state). Electrical conductivity of polyaniline is higher for samples prepared under more acidic conditions. It was found to be independent of the polymerization temperature and, consequently, of the molecular weight. (C) 1998 Elsevier Science S.A. All rights reserved.