CHARACTERIZATION OF VANADIUM-BASED OLEFIN POLYMERIZATION CATALYST PRECURSORS BY SOLID-STATE V-51-NMR

Several VOCl3-based ethylene polymerization catalyst precursors were prepared on silica and studied by solid-state V-51-NMR. The structure of the vanadium species in these samples, as determined by V-51-NMR, did not have any significant effect on the resultant polyethylene MI or MWD. This result is significant since conventional wisdom says the attachment of the transition metal to the silica plays a key role in polymer properties. VOCl3 reacted with hexamethyldisilazane-treated silica and with 250 degrees C dried silica results in double attachment of the vanadium to the silica, yet the catalysts which formed had different reactivities and produced polyethylene with different HLMIs. On the other hand, VOCl3 reacted with 600 degrees C dried silica results in single attachment of the vanadium to the silica, yet this catalyst had a similar reactivity and produced polymer properties similar to the doubly attached vanadium on 250 degrees C dried silica. Two theories are offered to explain the lack of correlation between catalyst precursor structure and catalyst performance. (C) 1995 John Wiley and Sons, Inc.