Vanadium and Chromium Catalysts for Polymerization of Ethylene

In the present progress report literature data concerning homogeneous catalyst systems based on vanadium and chromium are reviewed and complemented by a combined study of the magnetic properties and the polymerization activity of such systems. The results show that vanadium forms active species as V (III ) and as V (II ), but chromium only as Cr (II ); models are suggested for the polymerization process. — A comparison with heterogeneous systems (Phillips catalyst) allows the establishment of some general principles concerning the activity of the catalyst and the properties of the polymers.