Palladium-Catalyzed Direct Synthesis of Polar-Group Modified Hyperbranched Polyethylene Lubricant Base Oils

Conventional polar-functionalized polyolefin lubricants are generally prepared by postpolymerization grafting of polar groups onto nonpolar polyolefins. Herein, flexible imine-based palladium catalysts are developed for one-step copolymerization of ethylene with methyl acrylate (MA) to directly construct polar-functionalized hyperbranched polyolefin lubricants. A series of cycloalkyl- and isopropyl-substituted palladium catalysts were synthesized and characterized. These catalysts exhibited moderate activity (104 g mol-1 h-1) in ethylene homopolymerization, affording hyperbranched polyethylene oils with tunable branching density (55-116/1000C), molecular weight (283-1726 g/mol), viscosity (3.49-56.06 mm2/s at 100 °C), and high viscosity index (VI = 201-228). The catalyst framework and ortho-aryl substituents remarkably affected polymerization activity and molecular weight. Efficient ethylene-MA copolymerization produced polar-functionalized lubricants with MA incorporation up to 14.8 mol %. The obtained copolymers presented low viscosity (2.67 mm2/s at 100 °C), excellent viscosity index (VI = 196), and outstanding low-temperature fluidity (pour point < -50 °C). Catalyst steric and electronic effects exert more pronounced impacts on homopolymerization than copolymerization. This work provides a facile platform for designing high-performance lubricants with tailored polar functionalities and rheological properties.