Functional copolymer of a 1,3-diene and ethylene or a 1,3-diene, ethylene and an alpha-monoolefin

A process for the preparation of a copolymer of a 1,3-diene and of an olefin, the copolymer bearing, at one of its chain ends, a functional group of formula —CH2—CH(CH3)—COOZ, Z being a hydrogen atom or a carbon-comprising group, which process comprises the successive stages a), b) and c) and, optionally, a stage d),

• stage a) being the polymerization of a monomer mixture containing a 1,3-diene and an olefin in the presence of a catalytic system based at least on a metallocene of formula (Ia) and on an organomagnesium compound
• 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 a neodymium atom,
• L representing an alkali metal selected from the group consisting of lithium, sodium and potassium,
• N representing a molecule of an ether,
• x, which is or is not an integer, being equal to or greater than 0,
• y, which is an integer, being equal to or greater than 0,
• the olefin being ethylene or a mixture of ethylene and of an α-monoolefin,
• stage b) being the reaction of a methacrylate with the reaction product of the polymerization of stage a),
• stage c) being a chain termination reaction, and
• stage d) being a hydrolysis reaction.