Aggregation and interchain "self" doping in emeraldine base

We report gel permeation chromatography, electron paramagnetic resonance and optical absorption measurements on the emeraldine base (EB) form of polyaniline synthesized using different oxidant/aniline ratios in the range of 0.25 to 1.0. A concentration of localized paramagnetic defects and sub bandgap absorption is observed which correlate with the fraction of aggregated EB suggesting that radical formation is occurring within the aggregates. This correlation is observed in EB synthesized at different oxidant/aniline ratios and in heat treated EB. Further, we propose that interchain interactions within the aggregates give rise to a form of "self" doping in EB.