Synergistic Influence of Methoxy and Benzhydryl Groups in Α-Diimine Nickel Precatalysts for Facile Synthesizing UHMW PE Elastomers

Concerted effect of steric and electronic substituents is a powerful strategy to enhance the catalytic performance of alpha-diiminonickel precatalysts for ethylene polymerization, but less investigated so far. In this study, the synthesis of a series of unsymmetrical alpha-diiminonickel complexes, featuring the sterically crowded 2,6-dibenzhydryl-3,4,5-trimethoxyphenylimine and 2,4,6-(alkyl)phenylimine units, is described. Some of these complexes, including ligand and abnormal organic compound are presented in X-ray structures. All the nickel complexes, extensively studied with two alkylating reagents (Me2AlCl and MMAO), demonstrated excellent catalytic performance, with activity level in the range of 10(6)-10(7) g mol(-1) h(-1) across a broad temperature range (30 degree celsius-90 degree celsius). Of significant note, concerted effect of three OMe substituents and two benzhydryl groups present at the same imine unit, significantly improved chain propagation and thereby facilitated the synthesis of ultra-high molecular weight (up to 1.2 x 10(6) g mol(-1)) polyethylene with high branching degree (up to 205/1000C) and narrow polymer molecular weight distributions (D = < 1.80). Moreover, the obtained polyethylene, especially the ultra-high MW samples, exhibited excellent material properties (up to sigma(b) = 7.58 MPa with epsilon(b) = 1025 % and E = 5.32 MPa), along with elastic recovery rates of 59-65 %. These properties of obtained polyethylene highlight characteristics of typical thermoplastic polyolefin elastomers.