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 < Mn < 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.
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Fischer et al. (1994) studied this question.
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