Steric and temperature effects in unsymmetrical α‐diimine nickel‐catalyzed ethylene and 1‐octene polymerization

Abstract

In this contribution, a series of unsymmetric α‐diimine nickel complexes are synthesized. One side of these nickel complexes is the 2,4‐dimethyl‐6‐diphenylmethylaniline unit, and the steric effects are tuned by changing another aniline unit. These nickel complexes have high catalytic activities in ethylene (>106 g mol−1 h−1) and 1‐octene (104–105 g mol−1 h−1) polymerization, generating high‐molecular‐weight polyolefins (Mn > 104 g mol−1) with tunable branching densities (59–91/1000C). Steric effects and polymerization temperature can significantly affect the catalytic performance of the catalyst. Most importantly, catalysts with different steric hindrances have different temperature sensitivity. In general, catalysts with larger steric hindrances are more sensitive to temperature. This may be due to the fact that the rotation of some chemical bonds is blocked at low temperatures due to the larger volume of the substituents, resulting in more significant temperature sensitivity.