Abstract
A series of α-diimine Ni(II) complexes containing bulky phenyl groups, [ArN = C(Naphth)C = NAr]NiBr&sub2; (Naphth: 1,8-naphthdiyl, Ar = 2,6-Me&sub2;-4-PhC₆H&sub2; (C1); Ar = 2,4-Me&sub2;-6-PhC₆H&sub2; (C2); Ar = 2-Me-4,6-Ph&sub2;C₆H&sub2; (C3); Ar = 4-Me-2,6-Ph&sub2;C₆H&sub2; (C4); Ar = 4-Me-2-PhC₆H&sub3; (C5); Ar = 2,4,6-Ph&sub3;C₆H&sub2; (C6)), were synthesized and characterized. Upon activation with either diethylaluminum chloride (Et&sub2;AlCl) or modified methylaluminoxane (MMAO), all Ni(II) complexes showed high activities in ethylene polymerization and produced highly branched amorphous polyethylene (up to 145 branches/1000 carbons). Interestingly, the sec-butyl branches were observed in polyethylene depending on polymerization temperature. Polymerization of 1-alkene (1-hexene, 1-octene, 1-decene and 1-hexadecene) with C1-MMAO at room temperature resulted in branched polyolefins with narrow Mw/Mn values (ca. 1.2), which suggested a living polymerization. The polymerization results indicated the possibility of precise microstructure control, depending on the polymerization temperature and types of monomers.