Copolymerization of Ethylene and Methyl Acrylate by Pyridylimino Ni(II) Catalysts Affording Hyperbranched Poly(ethylene-co-methyl acrylate)s with Tunable Structures of the Ester Groups

Abstract

The introduction of polar functional groups into the polyolefin skeleton is a challenging goal of high interest, and coordination-insertion polymerization represents the most powerful and environmentally friend approach to achieve it. Until now the most considerable catalysts are based on Pd­(II) complexes and only a few examples on Ni­(II) derivatives have been reported. We have now investigated a series of Ni­(II) complexes with four pyridylimino ligands, both aldimines and ketimines, differing for the substituent present in position 6 on the pyridine ring (either a methyl group or a 2,6-dimethyl-substituted phenyl ring). These complexes generated active catalysts for the copolymerization of ethylene with methyl acrylate, yielding low-molecular weight, hyperbranched copolymers with the polar monomer content ranging between 0.2 and 35 mol % and inserted in a variety of modes, some of which were never observed before. The way of incorporation of the polar monomer goes from “in-chain only” to “everywhere but in-chain”, and it is dictated by both the activation mode and the solvent used to dissolve the nickel precatalyst.

Iminopyridine Ni(II) Catalysts Affording Oily Hyperbranched Ethylene Oligomers and/or Crystalline Polyethylenes Depending on the Reaction Conditions: Possible Role of In Situ Catalyst Structure Modifications

“…Ligands L1-L6 and complexes 1-4 were synthesized as described in our previous papers [20][21][22]. Complexes 5-6 were synthesized following a procedure previously reported for similar complexes [23].…”

Rigidifying Cation-Tunable Nickel Catalysts Increases Activity and Polar Monomer Incorporation in Ethylene and Methyl Acrylate Copolymerization

“…The color of each dot (red, yellow, or green) indicates the relative activity of that catalyst. The nickel complexes chosen are supported by different bidentate ligands, including keto-phosphine ( A ), aryloxyphosphine ( B , C , and J ), imino-pyridine ( D ), keto-imine ( E ), bisphosphine mono-oxide ( F , G , and H ), and diimine ( I ) donors. The plot in Figure revealed several interesting trends.…”

Modulation of N^N′-bidentate chelating pyridyl–pyridylidene amide ligands offers mechanistic insights into Pd-catalysed ethylene/methyl acrylate copolymerisation

“…The latter results are remarkably different with respect to those obtained with Ni(II) catalysts having 6-substituted pyridylimino ligands, which lead to low molecular weight ethylene/MA copolymers. 32 Complex 10, however, gave more promising results and revealed activity of the palladium centre in this complex. Fig.…”