Effects of conformational change of polyacrylonitrile on the aging behavior of the solutions in N,N-dimethyl formamide

Abstract

Effects of chain conformation of polyacrylonitrile (PAN) on the aging behavior of the solutions in N,N-dimethyl formamide (DMF) were investigated over the range of aging temperature from 30 to 100 degrees C. Aging of PAN solutions reduced the hydrodynamic diameter and inherent viscosity at 0.5 g/dl. The absorption peak at 268 nm in the UV-vis spectra represented the dipole-dipole pairs of the physically associated nitrile (CN) groups, whose intensity increased with aging temperature above 60 degrees C. The results confirmed that aging of the solutions produced the contracted chain conformation with predominantly anti-parallel orientation of CN groups. Analyses of the temperature-dependent FTIR spectra and its two-dimensional correlation spectroscopy evidenced that thermal-induced conformational change of PAN to the contracted structure directly induced the reorientation of CN groups and resultant dipole-dipole pairs in the 70-100 degrees C range. In addition, the aging caused the release of the bound DMF molecules from CN groups. In the 30-60 degrees C range, however, the conformational change to the extended structure was followed by the increase of solvent entropy and resultant dissociation of solvent aggregates. Then, highly diffused DMF molecules separated the partially dissociated CN groups. (C) 2016 Elsevier Ltd. All rights reserved.