Synthesis of thermoplastic polyethylene elastomers and ethylene–methyl acrylate copolymers using methylene-bridged binuclear bulky dibenzhydryl α-diimine Ni(II) and Pd(II) catalysts

Abstract

Binuclear olefin polymerization catalysts have recently attracted extensive interest in the field of polyolefin synthesis due to their excellent catalytic performance. In this work, we designed and synthesized a class of methylene-bridged binuclear bulky dibenzhydryl α-diimine Ni(II) and Pd(II) catalysts and applied them to ethylene polymerization and copolymerization. The Ni(II) complexes exhibited high activities (ca. 106 g·mol−1·h−1) and yielded highly branched (79–92/1000C) polyethylenes with very high molecular weights (Mn up to 44.57 × 104 g/mol) in ethylene polymerization. The obtained polyethylene products demonstrated excellent strain recovery (SR up to 84%). Meanwhile, the corresponding Pd(II) complexes also displayed high activities (well above 105 g·mol−1·h−1), and generated highly branched (90–92/1000C) polyethylene with high molecular weights (Mn up to 27 × 104 g/mol) in ethylene polymerization. More importantly, these Pd(II) complexes led to generating highly branched (93–101/1000C) polar functional copolymers with moderate molecular weights (Mn up to 6 × 104 g/mol) and moderate incorporation ratios (ca. 1 mol%) in ethylene–methyl acrylate copolymerization. Compared with mononuclear α-diimine Ni(II) and Pd(II) catalysts, the binuclear catalysts possessed higher thermal stability and activity, generated higher molecular weights polyethylene.