ORIENTATION STUDIES IN POLYACRYLONITRILE FILMS UNIAXIALLY DRAWN IN THE SOLID-STATE

Pobacrylonitrile (PAN) films were made by casting a dimethyl sulphoxide (DMSO) solution. After drying, the films were uniaxially drawn by an essentially solid-state drawing procedure. Using polarised-infrared (IR) spectroscopy, the dichroism of the nitrile-stretching vibration was monitored as a function of draw ratio. The dichroism results were converted to plots of chain-orientation factor versus draw ratio. For this, alpha, the transition-moment angle of the vibration, has to be known. Though a value of 68-73 degrees has been suggested in the literature, for the present samples ct cannot be 70 degrees or less, and 73 degrees is the most appropriate. The meaning and nature of the transition-moment angle in the context of a flexible-chain polymer molecule is discussed. The IR spectrum also showed dichroism in the S=O stretch and the -CH3 rocking vibrations from the (residual) DMSO present in the film, indicating that the solvent molecules were also orientated. It is proposed that this occurred due to dipolar interactions between the S=O and the C drop N groups, which led to solvent molecules being bound to the polymer chains. X-ray diffraction studies indicated 'lateral-ordering' consisting of hexagonally packed, rod-like chains with no c-axis order. The diffraction patterns obtained here were the 'standard' ones for PAN, in contrast to those observed previously in solvent-containing PAN gels.