An aza-cyclophane supported macrocyclic α-diimine nickel catalyst for ethylene polymerization

Abstract

α-Diimine nickel catalysts have attracted much attention in olefin polymerization over the past three decades, and the steric bulk strategy has become a common tool to regulate the related polymerization reactions. In contrast, the macrocyclic strategy is much less utilized in olefin polymerization due to the very difficult synthesis. In this contribution, a novel aza-cyclophane-based macrocyclic α-diimine nickel catalyst was synthesized via a simplified route with only 4 steps. Compared to the acyclic nickel analogue, this cyclic nickel pre-catalyst with the activation by a cocatalyst such as MAO or diethyl aluminum chloride (DEAC) exhibited remarkable advantages in ethylene polymerization including enhanced catalytic activity (9000 kg mol⁻¹ h⁻¹), superior thermostability (up to 130 °C), and notably higher polymer molecular weight (up to 29 times). Thus, ultrahigh molecular weight polyethylenes (UHMWPE: 1806 kDa) were produced by adjusting the cocatalyst and reaction solvent. This clearly indicated the effectiveness of the macrocyclic strategy. Notably, the use of a MgBu₂/DEAC binary cocatalyst enabled the formation of a heterogeneous solid-supported nickel catalytic system, further improving the catalytic activity and molecular weight in ethylene polymerization.