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Keywords:

  • light scattering;
  • long-chain branching;
  • polyethylene;
  • rheology;
  • Ziegler-Natta polymerization

Summary

Comprehensive polymer architectural studies were carried out on a group of Ziegler-Natta (Z-N) polyethylene homopolymers via size-exclusion chromatography coupled with multi-angle light scattering (SEC-MALS) and rheology. Although Z-N resins are traditionally viewed as linear polymers, both SEC-MALS and rheology results strongly indicate that there are topological variations, presumably long-chain branching (LCB) or possibly hyper-branches, in this group of supposedly linear Z-N homopolymers. These Z-N homopolymers exhibit very complex elution behavior that resulted in anomalous elution profiles in SEC. It appeared that some high molecular weight (MW) and long-chain branched components followed a non-size exclusion separation mechanism on SEC columns, co-eluting with low MW and linear polyethylene components, causing a delayed elution. The possible origin of LCB in these Z-N polymers is also discussed.