Ethylene copolymers, process for the preparation of ethylene-based polymers and catalyst system used therein

A process for the preparation of ethylene polymers having the following characteristics:

• (a) Mw/Mn>4, where Mw is the weight average molecular weight and Mn is the number-average molecular weight, both determined by GPC;
• and
• (b) no more than one melting point is detectable by differential scanning calorimetry analysis;
• said process comprising the polymerization reaction of ethylene in the presence of a catalyst consisting of the reaction product of:
• (A) a mixture of racemic and meso isomers of a stereorigid metallocene compound of a transition metal belonging to Groups III, IV or V or the lanthanides in the Periodic Table of the Elements, with two cyclopentadienyl ligands connected to each other by a chemical bridge, and
• (B) at least one co-catalyst capable of activating both the racemic form and the meso form of the metallocene compound, selected from the alumoxanes and the compounds capable of forming an alkylmetallocene cation.