Get access

Isoselectivity Distribution of Isospecific Centers in Supported Titanium-Based Ziegler-Natta Catalysts

Authors

  • Yury V. Kissin,

    Corresponding author
    1. Department of Chemistry, Rutgers-The State University of New Jersey, 610 Taylor Road, Piscataway, New Jersey 08854-8087, USA
    • Department of Chemistry, Rutgers-The State University of New Jersey, 610 Taylor Road, Piscataway, New Jersey 08854-8087, USA.
    Search for more papers by this author
  • John C. Chadwick,

    Corresponding author
    1. Laboratory of Polymer Chemistry/Dutch Polymer Institute, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands (on secondment from Basell Polyolefins)
    • Laboratory of Polymer Chemistry/Dutch Polymer Institute, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands (on secondment from Basell Polyolefins).
    Search for more papers by this author
  • Ines Mingozzi,

    1. Basell Polyolefins, Centro Ricerche G. Natta, Piazzale Donegani 12, Ferrara 44100, Italy
    Search for more papers by this author
  • Giampiero Morini

    1. Basell Polyolefins, Centro Ricerche G. Natta, Piazzale Donegani 12, Ferrara 44100, Italy
    Search for more papers by this author

Abstract

Summary: This article describes the quantitative aspects of the isoselectivity distribution of isospecific centers in five supported titanium-based Ziegler–Natta catalyst systems containing different internal and external organic donors. Highly crystalline poly(propylene) fractions of the polymers (insoluble in o-xylene at 95 °C) were analyzed by analytical Tref and gel permeation chromatography (GPC) methods. Separation of the Tref curves into the peaks of sterically uniform components (each represented by the Lorentz function) showed that all these “isotactic” poly(propylene) fractions are nonuniform materials. Each highly crystalline fraction contains several distinct components that differ in stereoregularity. The [mmmm] values for different components (which have approximately the same isotacticity in different polymers) range from as high as 0.986–0.993 to much lower values, in the 0.935–0.955 range. The number of Tref components and their relative contents are substantially different for the crystalline fractions of the polymers produced with different catalyst systems; these parameters depend on the nature of the internal and the external electron donors in the catalysts. GPC analysis of the crystalline poly(propylene) fractions showed that each consists of four or five Flory components (the components produced by kinetically uniform active centers) with widely different average molecular weights, from ≈1 × 104 to ≈1.3 × 106. In general, the probabilities of chain transfer reactions for different active centers decrease with the increase in their isospecificity.

original image

Resolution of the Tref curve of the highly crystalline fraction of poly(propylene) prepared with catalyst system 3.

Ancillary