The First Vanadium-Oxide-Based UHMWPE Catalyst Supported on Chemically Modified Silica Gel

Novel vanadium-oxide-based catalysts supported on alumina, zirconia, or titania-modified silica, which are able to synthesize ultrahigh molecular weight polyethylene (UHMWPE), are successfully developed. Compared with the unmodified silica supported catalyst, the activities of the modified catalysts are substantially enhanced. By changing the polymerization temperature ( T p ) from 90 to 60 °C, the molecular weight of the produced UHMWPE can be easily regulated from 2 × 10 6 to more than 6 × 10 6 g mol −1 . It is the first time that chloride-free nonsingle site catalysts have been developed to synthesize UHMWPE within such a broad range of T p . Catalyst characterization by NH 3 -temperature-programmed desorption and pyridine-Fourier transform infrared spectroscopy reveals that the modified catalysts have increased acidity derived from both Lewis and Brønsted acid sites. The X-ray photoelectron spectroscopy characterization indicates that the vanadium on the modified catalysts is more electron deficient. Thus, the acidity of the catalysts and the electronic state of the vanadium play a critical role in determining the activity of the vanadium active sites for ethylene polymerization.