Simultaneous In-Situ SAXS and WAXS Study of Crystallization and Melting Behavior of Metallocene Isotactic Poly(propylene)

Abstract

The isothermal crystallization and subsequent melting behavior of a metallocene isotactic poly(propylene) (m-iPP) was studied by simultaneous in-situ wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS), and differential scanning calorimetry (DSC). The m-iPP chosen was one which is known to produce large amounts of the γ modification under normal isothermal crystallization conditions. Both DSC and WAXS data show that during crystallization at 117°C, α and γ modifications appear at about the same time. Thermal analysis by immediate rescan after partial crystallization shows that m-iPP exhibits dual melting endotherms. WAXS scans show that during melting, the γ modification melts first at lower temperature, followed by α modification at higher temperature. Once γ crystals begin to melt, they do not undergo recrystallization, nor do they convert into α phase crystals. We also report changes in the SAXS parameters corresponding to the events observed in DSC and WAXS. Systematic changes in the scattering invariant and Bragg long period are seen during isothermal crystallization and melting of m-iPP.