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

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.