Orientation and Crystal Transformation in Polybutene-1 under Stress Relaxation

Abstract

The stress relaxation and birefringence relaxation of polybutene-1 were simultaneously measured at different temperatures ranging from 14 to 80°C. The relaxation curves obtained could be well superposed by vertical and horizontal shifts at short relaxation times, during which little crystal transformation takes place. However, at long relaxation times, various nonsuperposed curves branched out from the master curve. Such branching out cannot be observed for polyethylene and polypropylene. The superposed part represents the orientation of crystallites of mod. II, whereas the nonsuperposed part must result from a crystal transformation. Thus, the relaxation processes in polybutene-1 involve the crystallite orientation and crystal transformation from mod. II to mod. I. The intrinsic birefringences for the mod. I and mod. II crystals could be evaluated from the strain-optical coefficients for the superposed and nonsuperposed parts along with orientation functions of mod. I and mod. II crystallites, as determined by X-ray methods.