Crystallization with Nodular Aggregation near the Glass Transition Temperature for Syndiotactic Polypropylene

The isothermal crystallization from the melt state of syndiotactic polypropylene (sPP) has been studied by wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), and optical microscopy. The WAXD and SAXS results show the crystallization mechanism near the glass transition temperature in which the crystalline and mesomorphic nodules cover the entire sample with the formation of aggregation regions. For the SAXS analysis, the scattering function for the three-component system has been suggested. Furthermore, to analyze the growth kinetics of the aggregation region for sPP, the time-dependent structure factor combined with the homogeneous and inhomogeneous nucleation-and-growth kinetics has been suggested. The analysis shows that the growth kinetics of the aggregation region for sPP is the homogeneous nucleation-and-growth. The growth velocity of the aggregation region is a natural extrapolation of that of spherulite to the high supercooling region. These results might indicate that the crystallization with the nodular aggregation is a fundamental crystallization process near the glass transition temperature for polymers.