The orientation behaviour of high-molecular polyacrylonitrile☆

Abstract High-temperature drawing is the most commonly used method of increasing the strength of polymeric films and fibres. The strengthening effect is due to the fact that thermal drawing is accompanied by a reorganization of the polymer structure resulting in preferential orientation of the macromolecular chains in the direction of the stretching axis. The orientation processes and the development of fibrillar structure are influenced by the length of the macromolecules (or the molecular weight, M ) of the original polymer. A rise in M up to a certain limit, according to the authors of [1], greatly increases the orientation capacity of the polymer undergoing drawing, but with the ordinary methods of drawing a saturation point is reached in regard to the orientation capacity if M is increased to values of the order of 10,000. A number of authors have dealt with the problem of the effect of further increase in M on the orientation capacities of polymers, including that of polyacrylonitrile (PAN) [2, 3]. However, these authors generally investigated PAN with values of M below 10 6 [4], in view of the difficulty of obtaining higher values of M for PAN synthesized by the usual methods. It was therefore of interest to investigate PAN with M exceeding 10 6 using samples synthesized by the method described in [5].