Process for the preparation of ethylene-based polymers and catalyst system used therein

Ethylene copolymers prepared with comonomers selected from (a) α-olefins, (b) cycloolefins and (c) polyenes, having a content of ethylene units of between 80 and 99 mole%, a content of units derived from α-olefin, cycloolefin - and / or polyene comonomers of between 1 and 20 mole%, characterized in that (a) in the TREF assay (elution fraction at rising temperature) elute a quantity of at least 90% by weight of the copolymer within a temperature range of less than 50 ° C and (b) M./M ,,> 3, where M ,, is the weight average molecular weight and M 1 is the number average molecular weight, both determined by GPC.