Synthesis and chiroptical properties of water-processable polyaniline using methylcellulose as a molecular template

Optically active polyaniline (PANI) was synthesized using methylcellulose (MC) as a stabilizer and molecular template in HCl solution, in which ammonium persulfate was used as an oxidant; that is, the optical activity (helical conformation) was successfully induced into PANI by a water-soluble, non-ionic polymer. The synthesized PANI–MC composite was investigated by UV–VIS–NIR, FTIR, TGA and circular dichroism (CD) measurements. The UV–VIS–NIR spectra indicated that the characteristic peaks of PANI were existed in the as-synthesized, purified PANI–MC dispersion and the film of PANI–MC. FTIR spectra and TGA thermograms also suggested the interaction between PANI and MC. Most importantly, the bisignate CD bands of PANI–MC in water at ca. 395 and 459 nm were found to be consistent with that of optically active PANI doped with optically active polymeric acid derivatives. When the PANI–MC film was heat treated with increasing temperature, the CD spectrum indicated that the intensity almost unchanged until 120 °C, although there is a progressive dedoping while heating progress. In addition, PANI was still kept the emeraldine salt form even after heating the film to 200 °C for 10 min. The effect of addition of urea on the synthesizing PANI–MC aqueous dispersion was also investigated; the CD band of PANI–MC was decreased with increasing the urea concentration. Optically active PANI–MC also can disperse in various organic solvents, such as methanol, ethanol, DMF, DMSO and NMP. The CD spectra of PANI–MC indicated loss of its characteristic bisignate CD band and a weaken band exists at ca. 460 nm in each of these organic solvents. It means that the conformation of optically active PANI–MC was obviously changed and almost lost its optical activity. And it also exhibited that the optical activity of the water-processable PANI–MC was sensitive to the environment of solvents.