Novel mechanism for the formation of long-chain branching in polyethylene

Abstract

Polyethylene produced by a vanadium-based polymerization catalyst contains long-chain branching as determined by NMR and rheology, even though the polymer has very low levels of vinyl unsaturation. A new mechanism is proposed for the formation of the long-chain branching, which involves CH bond activation of the polyethylene backbone through a σ-bond metathesis reaction, followed by ethylene insertion at the new VC bond. Consistent with the proposed CH bond activation mechanism, the polymerization catalyst was also found to insert ethylene into the CH bonds of alkanes such as heptane. A bridged metallocene catalyst was also found to activate CH bonds of alkanes suggesting this new mechanism may explain the formation of long-chain branching in some metallocene-produced polyethylene. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2889–2898, 1998