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Synthesis and structural characterization of a nickel(II) precatalyst bearing a β-triketimine ligand and study of its ethylene polymerization performance using response surface methods

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Abstract

The reaction of N-(4-(mesitylamino)pent-3-en-2-ylidene)-2,4,6-trimethylbenzenamine (1) with n-butyl lithium and then with N-(2,4,6-trimethyl-phenyl)-acetimidoyl chloride yields a new β-triketimine ligand, N-(4-(mesitylamino)-3-(1-(mesitylimino)ethyl)pent-3-en-2-ylidene)-2,4,6-trimethylbenzenamine, 2. The addition of 2 to nickel (II) dibromide 1,2-dimethoxyethane (NiBr2(DME)) in the presence of [Na]+[3,5-(CF3)4C6H3]4B] (NaBAr'4) gives a five-coordinate dimeric complex [(2.NiBr)2].2 [(BAr'4)], 3. The structure of 3 has been determined by single crystal X-ray diffraction. This complex generates catalytically active species for the homopolymerization of ethylene in combination with methylaluminoxane to produce elastomeric, branched polyethylene. The effect of factors (temperature, pressure, and cocatalyst to catalyst molar ratio (CC)) on the polymerization process has been investigated using regression models of responses (catalyst activity, crystallinity, and weight-average molecular weight of polymer (Mw)) and visualized via the response surface method (RSM). Activity and Mw responses show a second-order variation with temperature and vary linearly with pressure. Conversely, crystallinity follows a second-order model while varying temperature, pressure, and CC. Furthermore, a set of polymerization conditions for reaching desirable responses was predicted and then experimentally verified. The activities achieved challenge the best reported activities for Ni(II) catalysts with β-connected imine ligand supports, but fall short of those for α-diimines. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

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