Abstract: Catalyst system, suitable for the (co)polymerization of ethylene and optionally minor amounts of 1-alkenes and/or dienes at a temperature of at least 180.degree. C., to be prepared by combining at least two components A and B, which components comprise:A: one or more titanium compounds, one or more vanadium compounds, one or more aluminium compounds, one or more magnesium compounds and optionally one or more halogen compounds, in such amounts that the atomic ratio of magnesium to the sum of titanium and vanadium is between 0 and 10, the atomic ratio of aluminium to the sum of titanium and vanadium is at least 3, the atomic ratio of aluminium to magnesium is at least 1, and the atomic ratio of halogen to magnesium is at least 2,B: one or more organoaluminium compounds, which two components are, separately or in combination, supplied direct to the polymerization vessel.

Abstract: The process for (co)polymerization comprises polymerizing ethylene and optionally minor amounts of 1-alkenes and/or dienes at a temperature greater than 180.degree. C. in the presence of a catalyst system prepared by combining at least two components, A and B, which components comprise:A: one or more titanium compounds and one or more vanadium compounds, mixed with one or more organoaluminum compounds in such an amount that the atomic ratio of aluminum to the sum of titanium and vanadium is at least 3,B: one or more organoaluminum compounds,wherein one or both components A and b contain a chloride, and wherein the two components are fed, separately or in combination, direct to the reaction vessel in such an amount that the atomic ratio of the chlorine from components A and/or B to the sum of titanium and vanadium of component A is at least 6.

Abstract: A catalyst system is disclosed as a combination of at least two components comprising: component A which is one or more titanium compounds and one or more vanadium compounds mixed with one or more organoaluminum compounds in such in amount that the atomic ratio of aluminum to the sum of titanium and vanadium is at least 3; and component B which comprises one or more organoaluminum compounds,wherein one or both of components A and B contain a chloride, and wherein during use such two components are fed, separately or in combination, directly to the reaction vessel in such an amount that the atomic ratio of the chlorine from components A and/or B to the sum of titatium and vanadium of component A is at least 6. The catalyst system is suitable for copolymerizing ethylene and optionally minor amounts of 1-alkenes and/or dienes at high polymerization temperatures.