THE INFLUENCE OF REGIO-IRREGULARITIES AND STEREOIRREGULARITIES ON THE CRYSTALLIZATION BEHAVIOR OF ISOTACTIC POLY(PROPYLENE)S PREPARED WITH HOMOGENEOUS GROUP-IVA METALLOCENE METHYLALUMINOXANE ZIEGLER-NATTA CATALYSTS

Poly(propylene)s with narrow molecular weight distributions were prepared with various methylaluminoxane-activated metallocene-based Ziegler-Natta catalysts to study the influence of randomly incorporated regio- and stereoirregularities on the crystallization behavior. As a function of the metallocene type and the polymerization temperature, the molecular weights varied between 11500 < M(n)BAR < 63 000, melting temperatures of annealed samples between 125 to 158-degrees-C, and the corresponding degrees of crystallinity, as measured by wide-angle X-ray scattering, between 49 and 67%. While the virgin poly(propylene)s exhibited exclusively the alpha-modification, annealing and melt crystallization favored the development of the gamma-modification. The Microstructure analysis by C-13 NMR spectroscopy revealed a linear correlation between the content of the gamma-modification and the average length of the isotactic segments.