Synthesis of Hyperbranched Polyethylene and Carboxylate Functionalized Polyethylene Using Bis(benzocyclopentyl) α-Diimine Pd(II) Catalysts with Axial Substituent-Constrained Strategy

Preparation of hyperbranched polyethylene and its polar functionalized polyethylene by chain walking polymerization technology is convenient and efficient. In this work, two bis(benzocyclopentyl) α-diimine ligands with different backbones and the corresponding Pd(II) catalysts were designed and synthesized. The axially open palladium catalysts enabled the polymerization of ethylene to afford hyperbranched polyethylene with low molecular weights (2.58-8.21 kg/mol) and high branching densities (111-142/1000C). Moreover, hyperbranched E-MA copolymers with high MA incorporation ratios (up to 20.7 mol%) were obtained by copolymerization of ethylene with MA using these Pd(II) catalysts. In addition, the polyethylene and E-MA copolymers obtained from the catalyst with butyl backbone exhibited significantly higher molecular weights with remarkably higher catalytic activities compared to those obtained from the acenaphthene backbone catalyst. Most interestingly, the axial substituent-constrained strategy of o-aryl bis(benzocyclopentyl) substituents provides a more open axial space, facilitating the insertion of methyl acrylate, and the formation of branching, compared to the conventional chain o-aryl alkyl substitution.