Palladium-Catalyzed Direct Preparation of Highly Branched Ethylene Oligomers and MA Functionalized Derivatives Using Dibenzhydryl Pyrazine-Imine Ligands

Abstract

This study reports the development of a class of dibenzhydryl-substituted pyrazine-imine Pd(II) catalysts (Pd1–Pd4) for the direct synthesis of highly branched ethylene oligomers (HBEOs) and their polar-functionalized derivatives. By transitioning from a conventional pyridine-imine to a more electron-deficient pyrazine-imine ligand backbone, the electrophilicity of the palladium center is enhanced, leading to intensified chain-walking behavior. These catalysts demonstrate high activity (up to 5.2 × 10⁵ g mol⁻¹ h⁻¹) for ethylene homopolymerization, producing HBEOs with precisely tunable molecular weights (342–479 g mol⁻¹) and high branching densities (43–52 branches per 1000C). The electronic nature of the para-aryl substituent significantly modulates polymerization behavior, influencing activity, molecular weight, and branching architecture. Furthermore, these catalysts efficiently copolymerize ethylene with methyl acrylate (MA) to yield MA-functionalized HBEOs (MFHBEOs) with controlled MA incorporation (0.37–6.10 mol%) while maintaining high branching density (37-53 branches per 1000C). Interestingly, the lubrication performance tests of the obtained HBEO revealed that it exhibits low kinematic viscosity (2.5 mm2/s) at 100°C, a low pour point (–50 °C), and a high viscosity index (158), suggesting its potential application in the field of automotive lubrication. This work establishes a robust structure–property relationship between catalyst electronic structure, polymer topology, and ultimate lubricant performance, providing an efficient catalytic strategy for the precision synthesis of high-performance polyolefin lubricant base oils.