Concerted flexible and steric strategy in -diimine nickel and palladium mediated insertion (Co-)Polymerization

To address the issues of poor thermostability of catalyst and low polymer molecular weight resulted from chain transfer at high temperature in olefin polymerization, versatile strategies have been utilized in the benchmark alpha-diimine nickel and palladium catalysts. In this contribution, a concerted flexible and steric strategy was highlighted in the alpha-diimine nickel and palladium catalysts. Compared to the seminal Brookhart catalyst, these newly generated nickel catalysts exhibited improved thermostability over a wide range of temperature from 30 degrees C to 130 degrees C, showed higher catalytic activities, and produced significantly higher (4.7-5.8 times) molecular weight polymers in ethylene polymerization, which are highly branched polyethylenes (76-110/1000C, SR = 72 %). Notably, high molecular weight polyethylene (up to 219 kg mol(-1)) was even afforded at 130 degrees C, which is extremely challenging when the flexible substituent is used in alpha-diimine system. The corresponding palladium analogues by using the same strategy further produced high molecular weight ethylene-methyl acrylate copolymers (up to 137 kg mol(-1)) at the difficult 70 degrees C in the copolymerization of ethylene and methyl acrylate. The incorporation of methyl acrylate could be tuned (0.6-2.9 mol%), where methyl acrylate units distribute both in the main chain and at the end of branches (15 %:85 %).