Isothermal melt- and cold-crystallization kinetics and subsequent melting behavior in syndiotactic polypropylene: a differential scanning calorimetry study

The isothermal melt- and cold-crystallization kinetics and subsequent melting behavior of syndiotactic polypropylene (s-PP) were investigated using differential scanning calorimetry (DSC). The overall crystallization kinetics was determined by directly fitting the experimental data to the Avrami and Malkin macrokinetic models using a non-linear multi-variable regression program. When plotted as a function of crystallization temperature, the overall crystallization rate parameters for melt-crystallization process exhibited an unmistakable double bell-shaped curve, while those for cold-crystallization process showed the typical bell-shaped curve. Comparison of the overall crystallization rate parameters obtained for both melt- and cold-crystallization processes indicated that crystallization from the glassy state proceeded at a much greater rate than that from the melt state. Melting of samples isothermally crystallized at low and moderate crystallization temperatures exhibited multiple-melting phenomenon. Determination of the equilibrium melting temperature according to the “linear” and “non-linear” Hoffman–Weeks extrapolative methods provided values of ca. 145 and 182°C, respectively.