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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

1994; Wiley; Volume: 195; Issue: 4 Linguagem: Inglês

10.1002/macp.1994.021950426

1521-3935

David M. Fischer, Rolf Mülhaupt,

Organometallic Complex Synthesis and Catalysis

Abstract 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 13 C NMR spectroscopy revealed a linear correlation between the content of the γ‐modification and the average length of the isotactic segments.