Relation between higher-order structure and crystalline phase transition of oriented isotactic polybutene-1 investigated by temperature-dependent time-resolved simultaneous WAXD/SAXS measurements

•Relationship between crystal phase transition and lamellar stacking structure has been revealed for the first time for the uniaxially-oriented isotactic polybutene-1.•The SAXS pattern could not be detected in the original form II sample, which started to be detected with the procedure of the phase transition from form II to form I, revealing the heterogeneous distribution of the long period and averaged thickness of the stacked lamellae.•The temperature dependence of the II-to-I phase transition rate was found to show the maximal point at around 30 °C, which was successfully interpreted quantitatively by developing a kinetic theory of the phase transition.

Drawing of isotactic polybutene-1 sample near the melting point gives the oriented form II sample with the complicated higher-order structure or the stacked lamellar structure. The small-angle X-ray scattering (SAXS) measurement may give us a useful information about the higher order structure in principle. However, it is almost impossible to detect the higher-order structure from the SAXS data, since the electron density of form II crystal is almost the same as that of the amorphous phase. The 2-dimensional SAXS pattern has started to be detected gradually as the crystalline phase transition from form II to form I was proceeded, since the form I has the higher electron density than the form II and amorphous phase. In this paper, the simultaneous time-resolved measurement of wide-angle and small-angle X-ray scattering data has been performed for the first time to reveal the lamellar stacking structure created in the form II sample by monitoring the phase transition from form II to I crystal. The thus-visualized lamellar stacking structure has been found to be different depending on the preparation condition of the oriented form II sample. The phase transition rate was also found to differ for the various types of samples depending on the temperatures of the experiment: the maximal point was located at around 30 °C. The phenomenological equation of the phase transition behavior, derived by modifying a classical theory of nucleation and growth of crystals, has succeeded to reproduce the observed temperature dependence of the phase transition rate.

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