The present invention relates to a process for producing
ethylene copolymers in a multistage process comprising at least one
slurry phase
polymerization stage and at least one
gas phase polymerization stage in the presence of
Ziegler Natta catalyst comprising a
solid catalyst component, a cocatalyst of a compound of group 13
metal and an external additive selected from alkoxysilanes of formula (I) R1nSi(OR2)4-n, (I) where n is an integer 0 to 3, each R1 are equal or different and are selected among H,
halogen,
alkyl groups of 1 to 6 10 carbon atoms optionally substituted with one or more
halogen atoms, alkenyl groups of 2 to 6 carbon atoms optionally substituted with one or more
halogen atoms, and
aryl groups of 6 to 12 carbon atoms optionally substituted with one or more halogen atoms, or the R1 groups can form with the Si atom they are linked to a ring of 3 to 8 ring atoms, provided that all R1 are not
hydrogen, R2 are equal or different and are selected among
alkyl groups of 1 to 6 carbon atoms optionally substituted with one or more halogen atoms, alkenyl groups of 2 to 6 carbon atoms optionally substituted with one or more halogen atoms, and
aryl groups of 6 to 12 carbon atoms optionally substituted with one or more halogen atoms, or the OR2 groups can form with the Si atom they are linked to a ring of 3 to 8 ring atoms, halogen is Br, CI or F. The invention further relates to the catalysts and use thereof in said multistage process r for producing
ethylene copolymers having melt flow
rate ratio FRR21 / 5 at least 40 and / or polydispersity index PDI of at least 27.