WIDE-RANGE COOLING CHARACTERISTICS OF A SELECTED ISOTACTIC POLYPROPYLENE

An increased knowledge of polymer crystallization kinetics and its eff ect on the crystalline structure is of particular importance at high c ooling rates. The aims of this study were to explore the range of util ity and complementarity of various methods (densitometry, microscopy, wide-angle x-ray diffraction [WAXD], and small-angle light scattering [SALS]) on the characterization of the crystalline structure of a high purity isotactic polypropylene (PP) in a wider cooling range than pre viously obtainable and to identify characteristic ranges of the struct ure as a function of cooling rate. High cooling rates, ranging to near ly 1000 degrees C/sec, were obtained using a special quench device. Th e transition between truncated and isolated spherulites at 10 degrees C/sec and the transition range between a pronounced cr-monoclinic and a mainly mesomorphic phase were identified. The sizes of spherulites ( ranging from partly truncated spherulites to a mesomorphic phase with no spherulites) were characterized by polarized optical microscopy and SALS. The influence of experimental conditions, such as beam diameter and sample thickness, on the SALS pattern was also investigated.