Preparation of polyethylene elastomers with increased high molecular weight and nearly perfect strain recovery by steric control of asymmetric α-diimine nickel catalyst

The use of alpha-diimine nickel catalysts to prepare high molecular weight branched polyethylene has matured, but few work reports consider high branch density and ultrahigh molecular weight. Herein, through a combination of asymmetric and steric control strategies, series of catalysts with a gradual increase number of N-aryl orthobenzhydryl substituent were prepared. Through the analysis of polymerization results, it is believed that large steric hindrance plays a significant role in improving the catalyst thermal stability and reducing the temperature sensitivity of the product branch density and molecular weight. Surprisingly, Ni4, which has three large benzhydryl groups and one small methyl group at the four sites of the N-aryl ortho-position, has high chain growth rate and strong chain walking ability, allows it to prepare highly branched polyethylene with ultra-high molecular weight at higher temperatures with high activity. Moreover, this type of polyethylene material exhibits excellent strain recovery capabilities (98.2 %).