Removal of N‐methylpyrrolidone hydrogen‐bonded to polyaniline free‐standing films by protonation–deprotonation cycles or thermal heating

Free‐standing films of polyaniline (PANI), in an emeraldine base state, prepared by evaporation of polymer solutions in N‐methylpyrrolidone (NMP) retain solvent even under dynamic vacuum drying as indicated by transmission Fourier transform infrared (FTIR) spectroscopy, where a band at 1670 cm−1 is clearly observed. Upon protonation–deprotonation cycles in aqueous media the weight of the dry base film decreases indicating gradual loss of NMP. Transmission FTIR spectra shows also the washing out of NMP with a clear decrease in intensity of the hydrogen‐bonded >CO stretching band (1670 cm−1) of NMP. During this process the bands between 3500 and 3200 cm−1, assigned to >NH stretching in the PANI backbone, change intensity suggesting that intermolecular hydrogen‐bonded >NH, with carbonyl oxygen of NMP, is replaced by free >NH. This is clear evidence of specific interaction of NMP with the emeraldine base. A similar loss of NMP is observed during heating but evidence of polymer degradation is also present. A mechanism is proposed to account for the loss of hydrogen‐bonding ability upon protonation which requires delocalization of the radical cations in the protonated films.