Process for preparing a Ziegler-Natta catalyst

Especially homogeneous supported Ziegler-Natta catalysts may be prepared in a simple one reaction vessel process from a magnesium hydrocarbyloxy starting material which is soluble in a hydrocarbon solvent. The process comprises: (I) reacting a magnesium hydrocarbyloxy compound with a chlorine-containing compound in a non-polar hydrocarbon solvent in which said magnesium hydrocarbyloxy compound is soluble whereby to produce a solution (A); and then either: (II) contacting the solution (A) with a chlorine containing tetravalent titanium compound to produce a solution (B); (III) impregnating solution (B) into a porous particulate support; or (II) impregnating solution (A) into a porous particulate support; and (III) contacting the solid support with a chlorine containing tetravalent titanium compound; or (II) impregnating solution (A) into a porous particulate support pretreated with a chlorine containing tetravalent titanium compound.