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

Pobacrylonitrile (PAN) films were made by casting a dimethyl sulphoxid e (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 wa s monitored as a function of draw ratio. The dichroism results were co nverted to plots of chain-orientation factor versus draw ratio. For th is, alpha, the transition-moment angle of the vibration, has to be kno wn. Though a value of 68-73 degrees has been suggested in the literatu re, for the present samples ct cannot be 70 degrees or less, and 73 de grees is the most appropriate. The meaning and nature of the transitio n-moment angle in the context of a flexible-chain polymer molecule is discussed. The IR spectrum also showed dichroism in the S=O stretch an d the -CH3 rocking vibrations from the (residual) DMSO present in the film, indicating that the solvent molecules were also orientated. It i s proposed that this occurred due to dipolar interactions between the S=O and the C drop N groups, which led to solvent molecules being boun d 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-con taining PAN gels.