Highly Branched Polyethylene from Ethylene Alone via a Single Zirconium-Based Catalyst.

A single zirconium-based constrained geometry catalyst (Me2Si(1-C29H36)(1-N-tBu)ZrCl2·OEt2/methylaluminoxane) has been employed to produce homopolymers of ethylene which contain degrees of branching unprecedented for early transition metal systems. A variable density of long branches is observed (10−50 branches per thousand carbon atoms) with strong dependences on both polymerization temperature and pressure. These branches are attributed to the exceptionally facile incorporation of long -olefin macromonomers formed in situvia the usual -hydride elimination of polymer chains. Additionally, a relatively constant low degree of ethyl branches is observed (∼5 branches per thousand carbon atoms) under all polymerization conditions; this is attributed to -hydride transfer to monomer followed by immediate reinsertion of the coordinated olefin-terminated polymer into the formed metal−ethyl bond. [ABSTRACT FROM AUTHOR]