Abstract
Long-chain branch (LCB) formation was measured in polyethylene homopolymers and 1-hexene–ethylene copolymers made using a variety of metallocene and chromium catalysts while the reaction ethylene concentration was varied. Kinetic analysis of this data indicates a marked difference between LCB formation versus short-chain branch (SCB) formation from the incorporation of 1-hexene comonomer. SCB generation exhibits first-order dependence on [comonomer/ethylene] concentration whereas LCB creation does not, which indicates different insertion pathways for the two. SCB formation follows the expected random intermolecular incorporation, whereas LCB generation is consistent with a different, and more selective, intramolecular mechanism of macromer incorporation. The latter holds that, once it is terminated by an active site, the macromer tends to remain coordinated to the site for a short time before either dissociation or insertion into a successor chain growing on the same site to form a LCB. In this way, struc...
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