Studies on the β‐form of isotactic polypropylene, 1. Characterization of the β‐form and study of the β‐α transition during heating by wide angle X‐ray diffraction

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The conditions for the formation of the β‐form of isotactic polypropylene in the presence of a β‐nucleator and the β‐α transition during heating were studied by wide angle X‐ray diffraction. A conditional crystallinity of the β‐form, X′β, and a structural disorder parameter, S, deduced from WAXD data were defined for the characterization of the β‐form in addition to the K value. The results show that X′β and S obviously depend on the content of β‐nucleator, and that the β‐α transition during heating essentially consists in the melting of the β‐form and the successive recrystallization to the α‐form.