Synthesis and application of binuclear α-diimine nickel/palladium catalysts with a conjugated backbone
A series of binuclear nickel/palladium catalysts C4–C7 with conjugated α-diimine ligands were designed, prepared and fully characterized. The binuclear nickel complexes C6 and C7 were activated by modified methylalumoxanes (MMAO) to generate highly active ethylene polymerization catalysts with activities up to 1050 kg [mol (Ni) h]−1. The activity of C7 is twice that of the mononuclear analogue under the same conditions. The effects of the catalyst structure, cocatalyst ratio, polymerization time, solvent and feeding monomer on the catalytic activities, molecular weight and branching structures of the resulting polymers were evaluated. The binuclear palladium complexes C4–C5 produced polyethylene with two separate peaks in GPC curves in ethylene polymerization. In contrast, the mononuclear analogue C3 produces polyethylene with a unimodal GPC curve. Probably, two active species are generated in the binuclear palladium catalyst system and are responsible for the bimodal feature of the GPC curves. The performance of the binuclear palladium complexes in ethylene/methyl acrylate copolymerization was also investigated.