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

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.