Evidences of Long-Chain Branching in Ziegler-Natta Polyethylene Homopolymers as Studied via SEC-MALS and Rheology (PPT)

摘要

A comprehensive polymer architectural study was carried out on a group of Ziegler-Natta (Z-N) polyethylene homopolymers by means of SEC-MALS and rheology. It was discovered that, contrary to general belief that Z-N polymers are free of long-chain branching (LCB), these Z-N homopolymers clearly exhibited topological variations, presumably LCB of some sort or possibly hyperbranches. Also, these Z-N homopolymers had complex elution behavior on SEC columns; some high molecular weight and long-chain branched components follow a non size exclusion separation mechanism on SEC columns, resulting in anomalous relationships between elution time and molecular weight and between molecular weight and radius of gyration. Furthermore, the melt zero-shear viscosity of the high molecular weight fraction of these Z-N homopolymers had a significant negative deviation from the 3.4-power law, suggesting a hyperbranched chain topology.