Synthesis of 1,2-bis(imidazolidin-2-imine)benzene nickel complexes and their application for norbornene (co)polymerization with styrene

Abstract

A series of 1,2-bis(imidazolidin-2-imine)benzene nickel complexes with different substituents on the imidazolidin-2-imine or benzene ring was synthesized and characterized. The complexes exhibited a tetrahedral configuration, and Ni2 bearing a phenyl substituent on the imine ligand provided highest steric hinderance around nickel center with a buried volume percentage of 53.1%. The nickel complexes in the presence methylaluminoxane (MAO) were highly active for the addition polymerization of norbornene and exhibited good thermal stability, where Ni3 bearing fluorine substituent on the benzene ligand backbone showed highest activity of 1.68 × 106 g·mol−1·h−1 at 100 °C to produce high molecular weight polynorbornene (1.2 × 105 g·mol−1). Most importantly, the catalysts promoted the copolymerization of norbornene and styrene with high activity (～105 g·mol−1·h−1), high molecular weight (~104 g·mol−1), and tunable styrene content (up to 17 mol%) and glass transition temperature. The linear relationship between the glass transition temperature and styrene content indicated the formation of the uniform copolymers. A preference for the norbornene insertion in each catalytic system was investigated by the evaluation of the monomer reactivity ratios.