Ethylene Polymerization With Nickel Diimine Complexes Containing Pseudohalides

Abstract

Nickel-diimine complexes DADNiX 2 (DAD= 2,6-iPr 2-C 6 H 3-N=C(Me)-C(Me)=N-2,6-iPr 2-C 6 H 3) containing the non-chelating pseudohalide ligands isothyocyanate and isoseleniumcyanate (X= NCS 1 and NCSe 2) were synthesized and used in ethylene polymerization activated by methyaluminoxane (MAO) at temperatures from 0 to 50°C. Polymerizations with these complexes were compared with the analogous Ni-diimines halide (X= Br 3) as non-chelating ligand. All systems were very active in this polymerization. The increase of reaction temperature favored the increase in catalytic activity. The catalyst system 1/MAO was more stable than the others, showing the best catalytic activity at the molar ratio Al/Ni between 200 and 300. System 2/MAO showed to be the less stable and less active, particularly at 50°C. Polyethylenes obtained with systems 1, 2 and 3 show high molecular weights, are branched polymers, and predominately amorphous, but the majority still present DSC endothermal events related to melting of small crystals. When halide (Br) are compared with these pseudo-halides, different activities, polymerization kinetics and characteristics of the final polymer indicated modification in the active species caused by the non-chelating ligand. Polymer molecular weight and branching content was not significantly influenced by the non-chelating ligand, being much more dependent on the MAO/Ni molar ratio and polymerization temperature.