The effect of dimethylsulfoxide on the dissociation process of physical complexes of polyacrylonitrile in N,N-dimethylformamide

Abstract

The physical properties and gelation behavior of polyacrylonitrile (PAN) solutions were investigated in mixed solvents of N,N-dimethylformamide (DMF) and dimethylsulfoxide (DMSO). For the individual solubility parameters, DMSO had the polar term closer to PAN than DMF. Small-angle X-ray scattering profiles and Fourier transform infrared spectra of 20 wt% PAN solutions confirmed that the internal structure and intermolecular complexes between nitrile groups were broken up by the DMSO molecules. The slope of Cole-Cole plot, a measure of the solution heterogeneity, increased with the mole fraction of DMSO (X-DMSO) via three distinct zones. The homogenization was particularly noticeable in Zone 1 (0.0 < X-DMSO < 0.4) and Zone 3 (0.7 < X-DMSO < 1.0). The Huggins constant and UV-visible absorption at 268 nm of dilute solutions decreased sharply above X-DMSO of 0.7 in Zone 3. This indicated a marked increase of PAN solubility by dissociating the intramolecular complexes between nitrile groups. In Zone 1, the storage modulus of 20 wt% PAN solutions decreased but loss modulus remained almost constant with X-DMSO at lower frequency below 1 rad s(-1), indicating the weakening of the true entanglement points of the intermolecular complexes. The mechanism indicated that the intermolecular complexes between nitrile groups were dissociated by DMSO earlier than the intramolecular ones. (c) 2017 Society of Chemical Industry