Ethylene-rich diene block polymer having a random block and a polyethylene block

1. A diblock polymer composed of a first block and a second block, the first block being a statistical copolymer comprising units of a 1,3-diene and more than 50 mol % of ethylene units, the second block being a polyethylene with a melting point above 90° C. and a number-average molar mass greater than or equal to 2000 g/mol and less than or equal to 10 000 g/mol, wherein the 1,3-diene is 1,3-butadiene or a mixture of 1,3-dienes, one of which is 1,3-butadiene, and the first block contains 1,2-cyclohexanediyl units or 1,4-cyclohexanediyl units.

2. A diblock polymer according to claim 1 , wherein the first block is a statistical copolymer of ethylene and a 1,3-diene.

3. A diblock polymer according to claim 1 , wherein the first block contains more than 60 mol % of ethylene units.

4. A diblock polymer according to claim 1 , wherein the first block contains at most 90 mol % of ethylene units.

5. A diblock polymer according to claim 1 , wherein the first block contains at most 85 mol % of ethylene units.

6. A diblock polymer according to claim 1 , wherein the first block has a glass transition temperature between −90° C. and −20° C.

7. A diblock polymer according to claim 1 , wherein the first block has a number-average molar mass of greater than or equal to 3000 g/mol and less than or equal to 80 000 g/mol.

8. A diblock polymer according to claim 1 , wherein the first block contains units of the 1,3-diene in a 1,4 configuration.

9. A diblock polymer according to claim 1 , wherein the second block is a linear polyethylene.

10. A composition which comprises a diblock polymer according to claim 1 and another component.

11. A diblock polymer composed of a first block and a second block, the first block being a statistical copolymer comprising units of a 1,3-diene and more than 50 mol % of ethylene units, the second block being a polyethylene with a melting point above 90° C. and a number-average molar mass greater than or equal to 2000 g/mol and less than or equal to 10 000 g/mol, wherein the units of the 1,3-diene in a 1,2 configuration and the units of the 1,3-diene in a 3,4 configuration represent more than 50 mol % of the units of the 1,3-diene.

12. A diblock polymer according to claim 11 in which the 1,3-diene is 1,3-butadiene.

13. A process for preparing a diblock polymer, the diblock polymer composed of a first block and a second block, the first block being a statistical copolymer comprising units of a 1,3-diene and more than 50 mol % of ethylene units, the second block being a polyethylene with a melting point above 90° C. and a number-average molar mass greater than or equal to 2000 g/mol and less than or equal to 10 000 g/mol, and the process including a statistical copolymerization of a monomer mixture containing ethylene and a 1,3-diene, then the subsequent polymerization of ethylene, wherein a catalytic system based at least on a metallocene of formula (I) and an organomagnesium compound is used

P(Cp 1 Cp 2 )Nd(BH 4 ) (1+y) —Li y (THF) x

Cp 1 and Cp 2 , which are identical or different, being selected from the group consisting of cyclopentadienyl groups and fluorenyl groups, the groups being substituted or unsubstituted,

P being a group bridging the two Cp 1 and Cp 2 groups and representing a ZR 1 R 2 group, Z representing a silicon or carbon atom, R 1 and R 2 , which are identical or different, each representing an alkyl group comprising from 1 to 20 carbon atoms,

y, which is an integer, being equal to or greater than 0, and

x being equal to or greater than 0.