Exploring steric effect of electron-donating group in palladium and nickel mediated ethylene polymerization and copolymerization with polar monomers

Abstract

The influence of steric effect of electron-donating substituents on the phosphine-sulfonate palladium and nickel catalysts was rarely studied in olefin (co)polymerizations. In this contribution, a family of flexible cyclohexyl/rigid aromatic phosphine-sulfonate palladium and nickel catalysts was designed, synthesized, and comprehensively identified by varying number, position, and size of alkoxy groups on aromatic substituents of phosphine. In ethylene polymerization, the steric effect of alkoxy substituents in palladium and nickel catalysts plays an important role on tuning polymer molecular weight, which gives the high molecular weight of 380 kg mol−1 at 80 °C in the palladium system and also provides very high catalytic activity of 16000 kg mol-1 h−1 at 70 °C in the nickel system. In ethylene copolymerization with polar monomers, the decrease of steric bulk leads to an increase on the co-monomer incorporation in the obtained copolymers. As a result, the copolymerization of ethylene with methyl acrylate, and acrylic acid using palladium catalysts affords the high incorporation of 9.5 mol% and 8.3 mol%, respectively; and the nickel promoted ethylene copolymerization with vinyl trimethoxysilane, and 6-chloro-1-hexene gives the incorporation of 3.7 mol% and 5.0 mol%, respectively.