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.