Morphology of different types of isotactic polypropylene spherulites crystallized from melt

Abstract The morphology of melt-grown spherulites of isotactic polypropylene (iPP) has been investigated by use of a polarizing microscope. The low molecular weight iPP, isothermally crystallized at 150–160°C, was found to form new types of spherulites. The spherulites termed types I and II by Keith et al. 2 exhibit a simple Maltese cross on a polarizing microscope with crossed polars. However, the new spherulites do not exhibit such a Maltese cross. These spherulites have been named ‘pseudo-negative’, ‘pseudo-positive’, ‘neo-mixed’ and ‘flower-like’ according to their morphologies, respectively. The structure of iPP spherulites crystallized isothermally at 155°C, does not belong to the α 1 -form ( C 2 c ) group but to the α 2 -form ( P 2 1 c ) group.