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The George and Josephine Butler Laboratory for Polymer Research, Department of Chemistry, University of Florida, Gainesville, USA
; Fax: +1-352-392-9741
; Tel: +1-352-392-7773
Dalton Trans., 2013,42, 9139-9147
16 Jan 2013,
01 Mar 2013
First published online
01 Mar 2013
Several analogues of the sterically expanded constrained geometry catalyst Me2Si(η1-C29H36)(η1-N-tBu)ZrCl2·OEt2 (2) were synthesized to assess the effect on branching and molecular weight for ethylene homopolymerization. Catalysts based on tetramethyltetrahydrobenzofluorene (TetH), ethylTetH, t-butylTetH, and octamethyloctahydrodibenzofluorenyl (OctH) bearing a diphenylsilyl bridge were prepared and characterized: Me2Si(η5-C21H22)(η1-N-tBu)ZrCl2 (3); Me2Si(η5-C23H26)(η1-N-tBu)ZrCl2 (4); and Me2Si(η5-C25H30)(η1-N-tBu)ZrCl2 (5); Me2Si(η5-C21H22)(η1-N-tBu)ZrMe2 (6); and Ph2Si(η5-C29H36)(η1-N-tBu)ZrCl2 (7). Complexes 4, 5, 6, and 7 were characterized by X-ray crystallography and displayed η5 hapticity to the carbon ring in each case, in contrast to 2. In comparison to 2, complexes 3, 4, 5, and 7 (in combination with methylaluminoxane = MAO) showed diminished branching, higher molecular weight, and higher polydispersity indices for obtained ethylene homopolymers. While 4/MAO produced the greatest molecular weight polymers, no branching was observed. Reactivity ratios were determined for the copolymerization of ethylene and 1-decene with 2/MAO. A value of rethylene = 14.9 and an exceedingly high value of r1-decene = 0.49 were found—in line with previous reports of this catalyst's unusual affinity for α-olefins.
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