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, pre pared by evaporation of polymer solutions in N-methylpyrrolidone (NMP) reta in solvent even under dynamic vacuum drying as indicated by transmission Fo urier transform infrared (FTIR) spectroscopy, where a band at 1670 cm(-1) i s clearly observed. Upon protonation-deprotonation cycles in aqueous media the weight of the dry base film decreases indicating gradual loss of NMP. T ransmission FTIR spectra shows also the washing out of NMP with a clear dec rease 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), assig ned to >N-H stretching in the PANI backbone, change intensity suggesting th at intermolecular hydrogen-bonded >N-H, with carbonyl oxygen of NMP, is rep laced by free >N-H. This is clear evidence of specific interaction of NMP w ith the emeraldine base. A similar loss of NMP is observed during heating b ut 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. (C ) 2001 Society of Chemical Industry.