alpha-keto-beta-diimine nickel-catalyzed olefin polymerization: Effect of ortho-aryl substituents and preparation of stereoblock copolymers
Abstract
A series of -keto--diimine nickel complexes (Ar-N=C(CH3)-C(O)-C(CH3)=N-Ar)NiBr2; Ar=2,6-R-C6H3-, R=Me, Et, iPr, and Ar=2,4,6-Me-3-C6H3-) was prepared. All corresponding ligands are unstable even under an inert atmosphere and in a freezer.
Stable copper complex intermediates of ligand synthesis and ethyl substituted nickel complex were isolated and characterized by X-ray. All nickel complexes were used for the polymerization of ethene, propylene, and hex-1-ene to investigate their livingness and the extent of chain-walking.
Low-temperature propene polymerization with less bulky ortho-substituents was less isospecific than the one with isopropyl derivative. Propene stereoblock copolymers were prepared by iPr derivative combining the polymerization at low temperature to prepare isotactic polypropylene (PP) block and at a higher temperature, supporting chain-walking, to obtain amorphous regioirregular PP block.
Alternatively, a copolymerization of propene with ethene was used for the preparation of amorphous block.