Abstract
A random propylene-based copolymer containing 1.0 mol% 1-butene as co-unit, synthesized with Ziegler-Natta catalyst and then fractionated to make the sample having a uniform in molecular microstructure, was investigated by differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXD), and atomic force microscopy (AFM). In the DSC curves, one can see clearly the endothermic peaks corresponding to the melting of α-iPP crystals and a group of broad endothermic peaks associated to the melting of the γ-iPP crystals. Wide-angle X-ray diffraction results indicate that both the α and γ modifications can be formed in the copolymer in a wide temperature range. The γ fraction increases first with increasing the crystallization temperature at the expense of its α component, which has been explained according to crystalline structures of iPP in its α and γ forms, and then decreases with increasing crystallization temperature as the crystallization of iPP in its γ phase has been suppressed at high temperatures. The γ-iPP content in the copolymer reaches maximum at the temperature of 130 °C. The in situ X-ray diffraction characterization on the isothermal crystallization process at 130 °C indicates that, as long as the γ-iPP can be detected, it takes always ca. 25% of the overall crystallinity. This leads to the conclusion that α- and γ-iPP crystals grow simultaneously during the crystallization process. The fact that the α and γ phases cannot be distinguished by morphological observation leads to the conclusion that they may intermix within one spherulite.
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The financial support of the Outstanding Youth Fund (No. 20425414), the National Natural Science Foundations of China (No. 50521302, 20423003, 20574079, and 20604031), and the 973 programs from MOST of China are gratefully acknowledged.
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Gou, Q., Li, H., Yu, Z. et al. Crystallization behavior of a propylene-1-butene random copolymer in its α and γ modifications. Colloid Polym Sci 285, 1149–1155 (2007). https://doi.org/10.1007/s00396-007-1669-x
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DOI: https://doi.org/10.1007/s00396-007-1669-x