| abstract |
A process for preparing an ethylene polymer by a two-stage polymerization of ethylene or ethylene and an alpha -olefin in an inert hydrocarbon at 50 DEG -100 DEG C. using a coordination polymerization catalyst containing a solid component and an organoaluminum compound, said solid component containing a transition metal compound, which process comprises: (a) in a first stage, producing 10-90% by weight based on the total polymer quantity of a polymer having a melt index in the range of 0.0001 to 0.5 g/10 min as measured according to ASTM D 1238-73, Condition E, using as said solid component a solid product obtained by supporting chromium trioxide or a compound which on calcining forms chromium oxide at least partially, on an inorganic oxide carrier followed by calcining, and using as said organoaluminum compound a compound of the general formula <IMAGE> wherein R is a hydrocarbon radical having 1 to 18 carbon atoms and n is 2</=n</=100; and (b) in a second stage, producing 90-10% by weight based on the total polymer quantity of a polymer having a melt index in the range of 0.01 to 50 g/10 min as measured according to ASTM D 1238-73, Condition E, using as said solid component a solid material containing at least magnesium and titanium, and using as said organoaluminum compound a compound of the general formula AlR'pX3-p wherein R' is a hydrocarbon radical having 1 to 20 carbon atoms, X is halogen and/or alkoxy and p is 0<p</=3, in the presence of the polymer obtained in the first stage. |