The influence of regio- and stereoirregularities on the crystallization behaviour 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 < 63 000, melting temperatures of annealed samples between 125 to 158°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 α-modification, annealing and melt crystallization favored the development of the γ-modification. The microstructure analysis by ¹³C NMR spectroscopy revealed a linear correlation between the content of the γ-modification and the average length of the isotactic segments.