Influence of supported vanadium catalyst on ethylene polymerization reactions

BACKGROUND: In the research area of homogeneous Ziegler-Natta olefin polymerization, classic vanadium catalyst systems have shown a number of favourable performances. These catalysts are useful for (i) the preparation of high molecular weight polymers with narrow molecular weight distributions, (ii) the preparation of ethylene/R-olefin copolymers with high R-olefin incorporation and (iii) the preparation of syndiotactic polypropylenes. In view of the above merits of vanadium-based catalysts for polymerization reactions, the development of well-defined single-site vanadium catalysts for polymerization reactions is presently an extremely important industrial goal. The main aim of this work was the synthesis and characterization of a heterogeneous low-coordinate non-metallocene (phenyl)imido vanadium catalyst, V(NAr)Cl-3, and its utility for ethylene polymerization. RESULTS: Imido vanadium complex V(NAr)Cl-3 was synthesized and immobilized onto a series of inorganic supports: SiO2, methylaluminoxane (MAO)-modified SiO2 (4.5 and 23 wt% AVSiO(2)), SiO2- Al(2)O(3)1 MgCl2, MCM-41 and MgO. Metal contents on the supported catalysts determined by X-ray fluorescence spectroscopy remained between 0.050 and 0.100 mmolVg(-1) support. Thermal stability of the catalysts was determined by differential scanning calorimetry (DSC). Characterization of polyethylene was done by gel permeation chromatography and DSC. All catalyst systems were found to be active in ethylene polymerization in the presence of MAO or triisobutylaluminium/MAO mixture (Al/V = 1000). Catalyst activity was found to depend on the support nature, being between 7.5 and 80.0kg PE (molV)(-1) h(-1). Finally, all catalyst systems were found to be reusable for up to three cycles. CONCLUSION: Best results were observed in the case of silica as support. Acid or basic supports afforded less active systems. In situ immobilization led to higher catalyst activity. The resulting polyethylenes in all experiments had ultrabigh molecular weight. Finally, this work explains the synthesis and characterization of reusable supported novel vanadium catalysts, which are useful in the synthesis of very high molecular weight ethylene polymers. (C) 2007 Society of Chemical Industry.