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-! 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.KEY WORDS Rheo-Optics I Crystal Transformation 1 Orientation I Stress Relaxation I Polybutene-1 I Intrinsic Birefringence 1As mentioned in a previous paper, 1 it is well known that the tetragonal crystal modification (mod. II) in polybutene-1 transforms into the hexagonal crystal modification (mod. I) when a fresh sample of this material is allowed to stand after preparation. 2 -9 The crystal transformation is also accelerated by stretching. 1 • 8 Therefore, the variation of the mechanical properties of this material with time can be fully understood only when this transformation is taken into consideration.observed under a constant strain. However, such an effect has not hitherto been studied at all.In a previous paper/ therefore, the infrared dichroism technique which had been developed by us was employed to elucidate the crystal transformation and orientation during stressstrain measurements; this technique was found to be very powerful for separating the contribution of the crystal transformation to the stress-strain behavior from that of the crystal orientation. It was anticipated from the results obtained in this study that the crystal transformation in polybutene-1 must also affect the stress relaxation and rhea-optical relaxation phenomena * To whom all communication should be addressed.In this paper, therefore, the stress relaxation and birefringence relaxation were simultaneously measured by means of the time-dependent birefringence method for a fresh polybutene-1 film in the course of aging at different temperatures. Combining results obtained by such viscoelastic and rhea-optical measurements with those from X-ray diffraction measurements, the effect of crystal transformation on the relaxation phenomena, which cannot be observed for polyethylene and polypropylene, 10 -12 was separated from that of crystallite orientation. The intrinsic birefringences for the modifications I and II crystals were also evaluated and discussed. EXPERIMENTAL Material and CharacterizationCommer...