Metal salen complexes as ethylene polymerization catalysts — effect of catalytic system composition on its activity and properties of polymerization products

摘要

The series of salen-type complexes differing in the metal center (M = Ti, Zr, V) and in the coordination spheres (different substituent at salen ligands) after activation with methylalumoxane (MAO) or Et2AlCl were studied as catalytic systems in ethylene polymerization. The vanadium and titanium complexes were found to be more active in combination with alkylaluminum compound (Et2AlCl) then with MAO, while zirconium complex was active only in combination with MAO. The activity of complexes activated by Et2AlCl decreases in the order V > Ti Zr ≈ 0, and when MAO is used as the cocatalyst the activity changes the order: Ti > Zr > V. The substituent type in the salen ligand also affects the catalyst activity; the best results were obtained for the catalyst having Cl or Br as substituents. The type of substituent has no significant effect on polyethylene properties, while the type of cocatalyst and the type of metallic centre play here the essential role. The salen titanium complexes in combination with Et2AlCl usually produce low molecular weight polyethylene with narrow polydispersity, also accompanied by oligomers. Other catalytic systems give linear high molecular weight polyethylene (M_w = 200 000—700 000).