Issue 13, 2013

Revisiting the long-chain branch formation mechanism in metallocene catalyzed polyethylenes

Abstract

The effect of polymerization parameters, such as pressure (ethylene concentration), temperature and comonomer type and concentration, on several long-chain branched (LCB) ethylene homopolymers and ethylene/α-olefin copolymers was investigated with respect to their degree of long-chain branching. Common long-chain branched metallocene polyethylenes (LCB-mPEs) and comb-like LCB-PEs, which have high viscosity and significantly differ from conventional LCB-mPEs, have been used to evaluate different proposed mechanisms for LCB-formation based on available characterization methods. The correlations between polymerization parameters and degree of long-chain branching were compared with the correlations predicted by different formation mechanisms (intermolecular auto-copolymerization by re-incorporation of β-hydride terminated chains, intramolecular insertion of stored vinyl terminated chains, chain walking and σ-bond metathesis reactions) to elucidate which of these mechanisms is the correct one. The intermolecular auto-copolymerization mechanism was found to be the predominant mechanism behind LCB-formation in slurry phase polymerization. However, σ-bond metathesis reactions cannot be entirely ignored.

Graphical abstract: Revisiting the long-chain branch formation mechanism in metallocene catalyzed polyethylenes

Article information

Article type
Paper
Submitted
07 Mar 2013
Accepted
20 Apr 2013
First published
22 Apr 2013

Polym. Chem., 2013,4, 3774-3790

Revisiting the long-chain branch formation mechanism in metallocene catalyzed polyethylenes

V. Karimkhani, F. Afshar-Taromi, S. Pourmahdian and F. J. Stadler, Polym. Chem., 2013, 4, 3774 DOI: 10.1039/C3PY00319A

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