The formation of polymer-solvent complexes of polyacrylonitrile from organic solvents containing carbonyl groups

The crystallisation behaviour on cooling of concentrated solutions of polyacrylonitrile (PAN) in two organic solvents, gamma butyrolactone (gBL) and ethylene carbonate (EC), was investigated. gBL is a liquid but EC is a crystalline solid at 20°C. Wide angle X‐ray diffraction studies showed that the peaks from the solvent‐containing gel films were different from those in the dry PAN powder. Polarised‐infrared spectroscopy measurements conducted on uniaxially‐drawn gel films indicated not only preferential orientation of the nitriles perpendicular to the draw direction but also orientation of the residual solvent in such a way as to suggest pairing of the gBL or EC molecule with the nitriles on the chains. It is suggested that the X‐ray diffractograms of the gels may be due to the formation of polymer‐solvent complexes during crystallisation of PAN from solvents with carbonyl groups. Differential scanning calorimetry showed gel‐melting endotherms on heating and crystallisation exotherms on cooling.