Molecular Rheology and Statistics of Long Chain Branched Metallocene-Catalyzed Polyolefins

We derive the rheologically relevant “priority” and “seniority” distributions of entangled segment topology from a kinetic model of long chain branch formation in metallocene-catalyzed polyolefins. For the model considered, the chemistry results in a two-parameter family of molecular distributions;...

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Bibliographic Details
Published in:Macromolecules 2001-03, Vol.34 (6), p.1928-1945
Main Authors: Read, D. J, McLeish, T. C. B
Format: Article
Language:English
Subjects:
Applied sciences
Exact sciences and technology
Organic polymers
Physicochemistry of polymers
Properties and characterization
Rheology and viscoelasticity
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Summary:We derive the rheologically relevant “priority” and “seniority” distributions of entangled segment topology from a kinetic model of long chain branch formation in metallocene-catalyzed polyolefins. For the model considered, the chemistry results in a two-parameter family of molecular distributions; convenient parameters are the typical strand molecular weight between cross-links and a branching probability. Only the branching probability controls the chain topologies. We comment on the different nature of the metallocene ensemble from the usual gelation ensemble that is a candidate model for standard low-density polyethylene. We calculate the extensional rheology of a model system within a decoupling approximation that permits a partial mapping onto the “multimode pompom” constitutive scheme.
ISSN:0024-9297
1520-5835
DOI:10.1021/ma001483u