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. Till 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.