In the rich and long-standing literature on the flow-induced formation of oriented precursors to polymer crystallization, it is often asserted that the longest, most extended chains are the dominant molecular species in the “shish” of the “shish-kebab” formation. We performed a critical examination of this widely held view, using deuterium labeling to distinguish different chain lengths within an overall distribution. Small-angle neutron-scattering patterns of the differently labeled materials showed that long chains are not overrepresented in the shish relative to their concentration in the material as a whole. We observed that the longest chains play a catalytic role, recruiting other chains adjacent to them into formation of the shish.

Relationship between the structure of injection-molded isotactic polypropylene and its tensile mechanical properties, necking and fracture behaviors in particular, was investigated in terms of micrometer-scale structural inhomogeneity of nanometer- and subnanometer-scale structures. To clarify the micrometer-scale inhomogeneity, we employed scanning microbeam wide-angle X-ray diffraction and small-angle X-ray scattering technique. Four isotactic polypropylene samples were studied, produced using different injection-condition and thermal treatments. The results of scanning microbeam X-ray scattering measurements showed the presence of two types of micrometer-scale structural inhomogeneity in addition to the orientation of molecules: the distribution of polymorphs and of crystalline ordering. The results of scanning microbeam X-ray scattering of deformed sample showed the disappearance of the β-form isotactic polypropylene crystals at the outer regions accompanied by the plastic deformation. It is indicated that the inhomogeneous distribution of crystalline ordering and the existence of different polymorphs are highly related to the tensile mechanical behavior.

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