Aggregation and molecular conformation of doped polyaniline in chloroform solution

The UV/Vis spectrum of a freshly made chloroform solution of polyaniline (emeraldine base) doped by d,l-camphorsulfonic acid after filtration through a 0.22 μm filter has a localized polaron peak at ∼730 nm. After stirring for ∼72 hours at room temperature, this localized polaron peak shifts to ∼810 nm. A change in color from "blue-green" to green can be observed visually. The GPC chromatogram of the freshly made solution in CHCl3 shows a small high molecular weight peak (retention time, ∼31 min), in addition to the major polyaniline peak (retention time, ∼33 min). After ∼72 hours stirring, this small peak disappears. It is postulated that both the freshly-made and aged solutions are comprised of doped polyaniline, the former containing aggregates (due to H-bonding) of single molecules having larger hydrodynamic volumes than the polyaniline comprising the major peak. The polymer represented by the smaller "high molecular weight" peak slowly becomes disentangled in solution.