Polymerizations of propylene with unsymmetrical (alpha-diimine)nickel(II) catalysts

Abstract

New unsymmetrical (a-diimine)nickel(11) catalysts having different pendent groups at the ortho positions on aromatic rings were synthesized and subjected to propylene polymerizations with MAO (methylaluminoxane). Structural analyses of the resulting polypropylenes by H-1 and C-13 NMR showed that the ortho substituents on aromatic rings of (alpha-diimine)nicket(II) catalyst affected significantly the polypropylene microstructure. While C-s symmetric catalyst afforded a syndiotactic polypropylene (rr triad content=66%) due to the syndiospecific chain end control, C-s symmetric catalysts produced much less stereoregular polypropylenes (rr triads content < 50%), presumably because of collision,of the isospecific site control with the syndiospecific chain end control.