Phenylene spacer between nickel centers in α-diimine binuclear catalysts for ethylene polymerization

To investigate dinuclearity and bridge effects on the catalyst performance and some polyethylene properties, two binuclear and a mononuclear α-diimine Ni(II)-based catalysts were comprised. Diphenyl Bi-Nuclear catalyst (DBNC) with a structure showed the highest activity (1750 g PE/mmolNi. h.) at the same ethylene polymerization condition while the bi-nuclear catalyst (BNC) illustrated moderate activity (1073 g PE/mmolNi. h.) and mono-nuclear catalyst (MNC) with no activity. This observation assigned to synergistic dinuclearity and cooperative effects which increased as the length, flexibility and thermal stability of bridge increased in DBNC (biphenyl methylene spacer). DSC thermograms revealed that polymer resulted using DBNC has insignificant crystallinity degree less than 1% with melting point at 117.2 °C, however, BNC yielded polyethylene with 24.7% crystallinity and Tm=123.0 °C. The vinyl content and branching of resulted PE in presence of catalyst DBNC were 21.2 and 101, however, these quantities decreased to 9.1 and 78 for catalyst BNC, respectively