Annealing effects of dilute polyaniline/NMP solution

The annealing effects of a dilute polyaniline solution on chemical and physical properties were investigated. Emeraldine base (EB) of polyaniline prepared by the conventional procedure was dissolved in 1-methyl-2-pyrrolidinone (NMP). After heating at 60-140 degrees C for 2 h, the color of PANi solution changed from deep blue to various colors depending on the annealing temperature. This solution was filtered and cooled at -5 degrees C to preserve an undoped structure. Changes of physical and chemical properties were investigated using ultraviolet-visible (W-vis), Fourier transform infrared (FT-IR) spectroscopy, electron spectroscopy for chemical analysis (ESCA), and dynamic light scattering (DLS). By contrast to the previously reported reductive reaction, we concluded that the annealing of dilute EB/NMP solution resulted in cross-linking. This was indicated by the decrease of the mutual diffusion coefficient at infinite dilution (D-0) and the increase in the apparent hydrodynamic radius (R-h) Of EB with the annealing temperature evidenced by the DLS and the increase of the cyclic-N portion from ESCA results. The annealing also produces a polyelectrolyte chain, supported by FT-IR and DLS measurements.