No abstract

Crystallization and melting behaviors of isotactic polypropylene (IPP) with low ethylene content during an isothermal process and on heating just after it are investigated by means of in-situ x-ray diffraction. At every isothermal temperature investigated here, the formations of both and phases are confirmed. The ratio of to increases with an increase in isothermal temperature. On heating just after the isothermal process, the starts melting at lower temperature than the . This may be due to the small crystallite size of the crystallization during the isothermal process. On cooling after the completion of the isothermal crystallization, the secondary crystallization accelerates, and the phase crystallizes predominantly. The fractionation is considered to occur in the primary crystallization during the isothermal process. The low molecular weight portion of the materials, which remained in amorphous regions of the spherulite during the isothermal process, crystallizes into the phase in the secondary crystallization. Furthermore, the fractionation behavior seems to be enhanced at higher temperature.