Coupled polyethylenes or copolymers of ethylene and 1,3-diene, and process for the preparation thereof

A process for preparing a coupled polymer which contains more than 50 mol % of ethylene, expressed as a molar percentage relative to all of the monomer units of the polymer, the polymer being a polyethylene or a copolymer of ethylene and a 1,3-diene and optionally a vinylaromatic compound, which process comprises successive steps a), b) and c):

• step a) being a polymerization reaction of the monomers in the presence of a catalytic system based on at least one metallocene of formula (I) and an organomagnesium halide of formula (II)
• Cp1 and Cp2, which are identical or different, being chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted,
• P being a group bridging the two groups Cp1 and Cp2 and comprising a silicon or carbon atom,
• Nd denoting the neodymium atom,
• L representing an alkali metal chosen from the group consisting of lithium, sodium and potassium,
• N representing a molecule of an ether,
• x, which may or may not be an integer, being greater than or equal to 0,
• y, which is an integer, being greater than or equal to 0,
• X being a halogen atom and R being an alkyl,
• step b) being the reaction of the reaction product of step a) with a compound containing at least two nitrile functions,
• step c) being a hydrolysis reaction.