TRANSITION OF BETA TO ALPHA PHASE IN ISOTACTIC POLYPROPYLENE

In samples of isotactic polypropylene, the influence of the nucleation agent chinacridine permanent red E3B on the crystallization rate and content of alpha and beta-modifications and on the rate and mechanism of the beta --> alpha-transition was investigated using x-ray diffraction, DSC microcalorimetry, and electron microscopy. It was found that, though E3B increases the content of the beta-phase, it is also a very efficient nucleation agent for the alpha-phase crystallization. The beta --> alpha-transition occurring above 140-degrees-C could be characterized by a gradual melting and annealing of the beta}phase, accompanied by a surface crystallization of the alpha phase on lateral faces of beta-lamellae by a mechanism similar to cross-branching of alpha-lamellae.