LLDPE with Exclusively Ethyl Branches by Tandem Catalysis with Single-Site Zr(IV)/Co(II) Catalysts

Abstract

Semicrystalline linear low density polyethylenes (LLDPEs) with exclusively ethyl branching (from 7 to 56 branches per 1,000 carbon atoms) were prepared from ethylene by homogeneous tandem catalytic systems comprising (imino)pyridine cobalt(II) dichlorides as oligomerization precursors, bis(cyclopentadienyl)zirconium(IV) dichloride as copolymerization precursor and methyaluminoxane as activator. The activity of the tandem systems was evaluated by varying either the molar fraction of the cobalt precursors or the ethylene pressure. The latter parameter was of crucial importance to control both the productivity and the extent of 1-butene incorporation. In particular, increasing the ethylene pressure from 2 bar to 4 bar changed the ''comonomer effect'' from positive to negative.

Olefin oligomerization, homopolymerization and copolymerization by late transition metals supported by (imino)pyridine ligands

“…The synthesis of late transition metal catalyst precursors (mostly from the first transition row) is a straightforward process, which involves the plain addition of the solid ligands to n-BuOH, THF, toluene or CH 2 Cl 2 solutions of either anhydrous or hydrated dihalides (Scheme 8) [1,2,[9][10][11][12]14,15,20,21,25,26,32,33,37,38,[47][48][49]53,54]. Irrespective of the metal, the dihalides are sparingly soluble in aromatic hydrocarbons, while they dissolve fairly well in polar solvents.…”

“…LLDPEs with exclusively ethyl branches (up to 56 C 2 br/1000 C), and higher turnover frequencies (over 139 kg (g of Zr × h × bar) −1 ) have been also prepared by means of a tandem protocol involving the same Co II oligomerization catalysts in combination with the more efficient and selective copolymerization system, Cp 2 ZrCl 2 [10]. All the LLDPEs produced by the Co II /Zr IV tandem catalysis are semicrystalline off-white solids and exhibit melting points Scheme 21.…”

“…Moreover, due to their good compatibility with various early and late metal copolymerization catalysts, (imino)pyridyl metal complexes can be used as oligomerization catalysts in tandem catalytic systems for the production in situ of ethylene-olefin copolymers (LLDPEs) as well as in reactor blending to give PEs with controlled molecular weight distribution [9][10][11][12].…”

Synthesis and characterization of some water soluble Zn(ii) complexes with (E)-N-(pyridin-2-ylmethylene)arylamines that regulate tumour cell death by interacting with DNA

“…[8][9][10][11] By simple modifications of the iminopyridyl architecture, the polymerization and/or oligomerization activities of the metal complexes can be tuned. All these merits make this class of complexes advantageous over other types of metal catalyst, such as metallocenes or geometry constrained species [12][13][14][15] . Consequently, synthesis of iminopyridyl based ligands has been a major research target in polymerization catalysis and there have been some studies with asymmetrical iminopyridyl based ligands 9,11,16 and also with long chain aliphatic substituents at the imino nitrogen atom.…”

Preparation of LLDPE through tandem ethylene polymerization using chromium and zirconium catalysts

“…Interestingly, a LLDPE with different branch lengths and densities can be effectively produced by selecting a suitable oligomerization catalyst and adjusting its concentration in the reaction medium. Along this line, to obtain high efficient, selective and active catalytic systems, the effect of catalyst ratios and reaction conditions has been extensively studied on the catalyst activity, incorporation efficiency, selectivity of catalyst oligomerization and resulting copolymer properties [6][7][8][9][10][11][12].…”