Ethylene-rich diene-coupled copolymers and their preparation process

Abstract

The invention relates to a copolymer of a 1,3-diene and an olefin containing more than 50 mole percent of ethylene units, the olefin being ethylene or a mixture of ethylene and an α-monoolefin, which copolymer is a coupled copolymer, the copolymer chains being linked together by a group containing at least two motifs of formula 1, –(CH2-CH(CH3)-CO-O)-, each copolymer chain being linked to a distinct motif of formula 1 via a covalent bond between a carbon atom of a monomer unit of the copolymer chain and the carbon atom of the methylene group of the motif of formula 1.

Description

Description of the invention: Diene coupled copolymers rich in units ethylene and their preparation process The field of the invention is that of polymers rich in ethylene units and containing units of a 1,3-diene. Diene polymers rich in ethylene units are known, for example, from patent applications WO 2007054223 and WO 2007054224. Such copolymers are, for example, intended for use in a tire tread. The high molar content of ethylene units in these copolymers, which is greater than 50%, makes these copolymers less sensitive to oxidation phenomena than the diene polymers traditionally used in rubber compositions, namely polybutadienes, polyisoprenes, and copolymers of butadiene and styrene. It has been found that these copolymers containing 1,3-diene units and more than 50 mol% of ethylene units have a tendency to flow under their own weight. This cold flow is not controlled and can pose difficulties in the use of these copolymers, particularly when storing them in the form of bales or in storage boxes. To overcome this problem, it has been proposed in patent application WO 2021 / 123592 to branch the copolymer chain during its growth in the polymerization reaction. There is still a need to provide other processes capable of preparing new copolymers rich in ethylene units which contain 1,3-diene units and which have a lower propensity to flow. Continuing its efforts to remedy these storage flow problems, the Applicant has developed new coupled copolymers through the use in their preparation process of a coupling agent comprising at least two methacrylate functions. Thus a first subject of the invention is a copolymer of a 1,3-diene and an olefin, the olefin being ethylene or a mixture of ethylene and an α-monoolefin, which copolymer contains more than 50 mol% of ethylene unit and is a coupled copolymer, the chains of the copolymer being linked together by a group containing at least two units of formula 1 —(CH,-CH(CH-)-CO-O)- formula 1, each copolymer chain being linked to a distinct unit of formula 1 via a covalent bond between a carbon atom of a monomer unit of the copolymer chain and the carbon atom of the methylene group of the unit of formula 1. A second subject of the invention is a process for preparing a coupled copolymer of a 1,3-diene and an olefin, the copolymer containing more than 50 mol% of ethylene unit, which process comprises the successive steps a), b) and c), - step 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 one metallocene of formula (Ia) and an organomagnesium co-catalyst, {P(Cp!")(Cp*)Nd(BHa4)(1+yy-Ly-N,} (Ja) Cp' and Cp', identical or different, being chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted, Being a group bridging the two groups Cp! and Cp°, 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, whole number or not, being equal to or greater than 0, y, integer, being equal to or greater than 0, the olefin being ethylene or a mixture of ethylene and an α-monoolefin - step b) being the reaction of a coupling agent, compound containing at least two methacrylate functions of formula CH,=C(CH,)CO-O- with the reaction product of the polymerization of step a), - step c) being a chain termination reaction. A third subject of the invention is a polymer composition which contains a 2-branch copolymer and a 3-branch copolymer in accordance with the invention or capable of being obtained by the process in accordance with the invention. Detailed description Any interval of values ​​designated by the expression "between a and b" represents the domain of values ​​greater than "a" and less than "b" (i.e., excluding the limits a and b), while any interval of values ​​designated by the expression "from a to b" means the domain of values ​​from "a" to "b" (i.e., including the strict limits a and b). The compounds mentioned in the description may be of fossil or bio-sourced origin. In the latter case, they may be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. In the same way, the compounds mentioned may also come from the recycling of materials already in use, that is to say, they may be, partially or totally, resulting from a recycling process, or obtained from raw materials themselves resulting from a recycling process. The expression "based on" used to define the constituents of the catalytic system means the mixture of these constituents, or the product of the reaction of some or all of these constituents with each other. The copolymer according to the invention has the essential characteristic of being a copolymer of a 1,3-diene and an olefin. The olefin is ethylene or a mixture of ethylene and an α-monoolefin. The constituent units of the copolymer are those resulting from the polymerization of the 1,3-diene and the olefin. In the case where the olefin is ethylene, the constituent units are those resulting from the polymerization of the 1,3-diene and ethylene and the copolymer is a copolymer of ethylene and a 1,3-diene. In the case where the olefin is a mixture of ethylene and an α-monoolefin, the constituent units are those resulting from the polymerization of 1,3-diene, ethylene and α-monoolefin and the copolymer is a copolymer of ethylene, a 1,3-diene and an α-monoolefin. Preferably, the α-monoolefin is styrene. The copolymer also has the essential characteristic of containing more than 50 mol% of ethylene unit. The copolymer preferably contains more than 60 mol% of ethylene unit, more preferably more than 65 mol% of ethylene unit. The copolymer preferably contains less than 90 mol% of ethylene unit, more preferably at most 85 mol% of ethylene unit, even more preferably at most 80 mol% of ethylene unit. The levels of ethylene unit in the copolymer are expressed relative to all the units resulting from the polymerization of the 1,3-diene and the olefin. |,3-diene is a single compound, i.e., a single (in English "one") 1,3-diene, or a mixture of 1,3-dienes that differ from each other in chemical structure. Suitable 1,3-dienes include 1,3-dienes with 4 to 20 carbon atoms, Preferably, the 1,3-diene is 1,3-butadiene, isoprene, myrcene, fB-farnesene or mixtures thereof such as a mixture of at least two of them. The mixture of at least two of them is advantageously a mixture which contains 1,3-butadiene. According to a particular embodiment of the invention, the 1,3-diene is a mixture of 1,3-dienes which contains 1,3-butadiene. According to another particularly preferred embodiment of the invention, the copolymer in accordance with the invention contains 1,3-butadiene units and cyclic units, 1,2-cyclohexane units. The 1,2-cyclohexane units are of formula (I). The cyclic units result from a particular insertion of the ethylene and 1,3-butadiene monomers into the polymer chain, in addition to the conventional ethylene units. and 1,3-butadiene, respectively CHz-CH;)-, (CH,-CH=CH-CH)- and (CH> - CH(C=CH;))-. The mechanism for obtaining such a microstructure is for example described in the document Macromolecules 2009, 42, 3774-3779. sha—"0H2 Ë \ 2Hz, Or: ; ; “om 0H “ Pa A: When the copolymer according to the invention contains 1,2-cyclohexane units, it preferably contains at most 15 mol% thereof, the percentage being expressed relative to all the units resulting from the polymerization of the 1,3-diene and the olefin. Such a copolymer can be prepared by the process according to the invention according to the method in which the metallocene of the catalytic system has as ligand two fluorenyl groups, substituted or not. Preferably, the copolymer according to the invention is a copolymer of ethylene and a 1,3-diene, in which case the monomer units constituting the copolymer are those resulting from the copolymerization of ethylene and 1,3-diene. Very preferably, the copolymer according to the invention is a copolymer of ethylene and 1,3-butadiene or a copolymer of ethylene, 1,3-butadiene and myrcene or a copolymer of ethylene, 1,3-butadiene and β-farnesene. According to any one of the embodiments of the invention, the copolymer according to the invention is preferably a random copolymer. In other words, the monomer units constituting the copolymer chains (or branches, in English "arms") of the random copolymer according to the invention are distributed statistically in the copolymer chains.Such a copolymer may be prepared by the process according to the invention according to the mode in which the polymerization reaction is carried out at constant pressure in monomers in a reactor and a continuous addition of each of the monomers or one of them is carried out in the reactor. Advantageously, the copolymer according to the invention is a random copolymer of ethylene and 1,3-butadiene or a random copolymer of ethylene, 1,3-butadiene and myrcene or a random copolymer of ethylene, 1,3-butadiene and β-farnesene. The copolymer according to the invention also has the further characteristic of being coupled. The copolymer chains constituting the copolymer according to the invention are linked together by a group containing at least two units of formula 1 —(CH,-CH(CH,)-CO-0)- formula 1, each copolymer chain being linked to a distinct unit of formula 1 by through a covalent bond between a carbon atom of a monomer unit of the copolymer chain and the carbon atom of the methylene group of the unit of formula 1. In other words, the group which links the copolymer chains together can be represented by the following formula Z'-[O-CO-CH(CH;)-CH>-],-, Z' being a group of valence v, v being an integer at least equal to 2, preferably ranging from 2 to 3. Preferably, the copolymer in accordance with the invention is a copolymer coupled with 2 branches or with 3 branches. According to a preferred embodiment of the invention, the coupled copolymer is a 2-branch coupled copolymer, the two copolymer chains constituting the coupled copolymer being linked together by a group containing two units of formula 1. The 2-branch coupled copolymer preferably corresponds to formula 2 [P-CH.-CH(CH-)-CO-O1]--Z; formula 2 P denoting a copolymer chain, Z representing a divalent hydrocarbon group or a divalent hydrocarbon group which contains one or more functions chosen from the ether function and the thioether function, the divalent group possibly being substituted by one or more methacrylate functions of formula CH,=C(CH,)CO-O-. According to a first variant, the copolymer coupled with 2 branches corresponds to the formula 2 |P-CH--CH(CH-)-CO-O]--Z; formula 2 P denoting a copolymer chain, Z representing a divalent hydrocarbon group or a divalent hydrocarbon group which contains one or more functions chosen from the ether function and the thioether function. A hydrocarbon group which contains one or more functions chosen from the ether function and the thioether function means a hydrocarbon chain which is interrupted by one or more oxygen or sulfur atoms to form ether or thioether bonds respectively. Advantageously, Z is an acyclic group. Z may be a linear or branched group. The number of carbon atoms in Z is not limited in itself. Z may contain up to 20 carbon atoms. Preferably, Z is an alkanediyl or an alkanediyl which contains one or more ether functions. Preferably, the alkanediyl of Z contains 1 to 10 carbon atoms, more preferably 2 to 8 carbon atoms. Suitable alkanediyl groups of Z include, in particular, 1,2-ethanediyl, 1,1-ethanediyl, 1,3-propanediyl, 1,2-propanediyl, 1,4-butanediyl, 1,3-butanediyl, 1,5-pentanediyl, 2,2-dimethyl-1,3-propanediyl, 1,6-hexanediyl, 2,5-hexanediyl, 1,4-cyclohexanediyl, 1,4-cyclohexanediyl di-methylene. Also suitable are divalent groups, preferably alkanediyls, interrupted by one or more oxygen atoms to form ether bonds such as the divalent groups of formula —(CH,-CH;-O),-CH,-CH,-, (CH,-CH, - CH,-O),-CH,-CH,-CH,- in which n is an integer greater than or equal to 1, in particular ranging from 1 to 10, more particularly ranging from 1 to 2. According to a second variant, the 2-branch coupled copolymer is of formula 2 in which the divalent hydrocarbon group of Z, is further substituted by one or more methacrylate functions of formula CH,=C(CH,)CO-O-, preferably by a methacrylate function of formula CH=C(CH-)CO-O-. According to the second variant, Z, is preferably an alkanediyl substituted by a methacrylate function. Advantageously in formula (2), Z is an alkanediyl or an alkanediyl substituted by a methacrylate function. According to another preferred embodiment of the invention, the coupled copolymer is a 3-branch coupled copolymer, the three copolymer chains constituting the coupled copolymer being linked together by a group containing three units of formula 1. Preferably, the 3-branch coupled copolymer corresponds to formula 3 [P-CH.-CH(CHz)-CO-O1];-Z; formula 3 P denoting a copolymer chain, Za representing a trivalent hydrocarbon group or a trivalent hydrocarbon group which contains one or more functions chosen from the ether function and the thioether function. Advantageously, Z; is an acyclic group. Z; may be a linear or branched group. The number of carbon atoms in Z; is not limited per se. Z; may contain up to 20 carbon atoms. Preferably, Z; is an alkanetriyl or an alkanetriyl that contains one or more ether functions. An alkanetriyl is typically a saturated hydrocarbon trivalent aliphatic group. Preferably, the alkanetriyl of Z; contains 3 to 10 carbon atoms, more preferably 3 to 8 carbon atoms. Suitable alkanetriyl groups of Z include, in particular, propane-1,2,3-triyl, 2-methylpropane-1,2,3-triyl, 2-ethylpropane-1,2,3-triyl, propane-1,1,1-triyltrimethylene, 1,2,5-pentanetriyl groups. Also suitable are trivalent groups, preferably alkanetriyls, containing oxyalkylene chains such as oxyethylene, oxypropylene, or polyoxyalkylene chains such as polyoxyethylene, polyoxypropylene. Mention may be made of propane-1,2,3-triyl, 2-methylpropane-1,2,3-triyl, 2-ethylpropane-1,2,3-triyl, propane-1,1,1-triyltrimethylene groups containing one or more oxyalkylene or polyoxyalkylene chains, in particular oxyethylene or polyoxyethylene. For example, propane-1,2,3-triyl, 2-methylpropane-1,2,3-triyl or 2-ethylpropane-1,2,3-triyl groups containing three oxyethylene or polyoxyethylene chains in the 1,2,3 position, the propane-1,1,1-triyltrimethylene group containing three oxyethylene or polyoxyethylene chains in the 1,1,1 position, are suitable. The figures of such groups are shown below, in which n, m and p are integers greater than or equal to 1, in particular ranging from 1 to 10, more particularly ranging from 1 to 2. The 7% AP TT &ùi ax 3, N. A Sn” + To L + SA id Sa Ms ba va: 44 a” di. ; 4 = de * ei LS J PA” 0 RS _ ; 04, SL D” Part Pro” . ST A ra 0 ; “ù dns} LNH KL ef (Pom V de > vs le les »es alkanetrivles containing a group Also suitable are, for example, alkanetriyl groups containing a ©-alkoxypoly(oxyalkylene) group such as -methoxypoly(oxyethylene). Examples of these are 2-(w-methoxypoly(oxyethylene))propane-1,2,3-triyl, 1-(methoxypoly(oxyalkylene))methane-1,1,1-triyltrimethylene. Advantageously in formula (3), Z; represents an alkanetriyl. According to any one of the embodiments, the copolymer in accordance with the invention is preferably an elastomer and is intended to be used in a rubber composition. In particular, the 2-branch coupled copolymer and the 3-branch coupled copolymer are preferably elastomers. A 3-branch coupled copolymer in accordance with the invention is particularly preferred, since it has an advantageous compromise between its macrostructure and its rheological properties, in particular viscosity, compared to an uncoupled copolymer, a single-branch polymer, or a 2-branch coupled copolymer, the branches of the uncoupled copolymer and of the 2-branch coupled copolymer being of composition and length substantially identical to the branches of the 3-branch coupled copolymer. A polymer composition, a mixture containing a 2-arm coupled copolymer and a 3-arm coupled copolymer in accordance with the invention is particularly preferred, since it also has improved rheological properties compared to an uncoupled copolymer or a 2-arm coupled copolymer, the arms of the uncoupled copolymer and of the 2-arm coupled copolymer being of composition and length substantially identical to the arms of the 3-arm coupled copolymer. A blend containing a 2-arm coupled copolymer and a 3-arm coupled copolymer which are in accordance with the invention and which are both elastomers is also particularly preferred. The copolymer in accordance with the invention can be prepared by a process, another subject of the invention, which comprises the successive steps a), b) and c), - step 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 one metallocene of formula (Ia) and an organomagnesium compound {P(Cp')(Cp”)Nd(BH4)u+,y-Ly-N,} (a) Cp' and Cp”, identical or different, being chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted, Being a group bridging the two groups Cp' and Cp°, 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, whole number or not, being equal to or greater than 0, y, integer, being equal to or greater than 0, the olefin being ethylene or a mixture of ethylene and an α-monoolefin, - step b) being the reaction of a coupling agent, compound containing at least two methacrylate functions of formula CH,=C(CH,)CO-O- with the reaction product of the polymerization of step a), - step c) being a chain termination reaction. Step a) of the process according to the invention is a polymerization reaction of a monomer mixture of a 1,3-diene and an olefin which makes it possible to prepare the copolymer chains of a 1,3-diene and an olefin, growing chains intended to react in the following step, step b), with a coupling agent. The 1,3-diene in the monomer mixture of step a) is a single compound, i.e., a single (in English "one") 1,3-diene, or a mixture of 1,3-dienes which differentiate from each other by chemical structure. Suitable 1,3-dienes include 1,3-dienes having 4 to 20 carbon atoms, such as 1,3-butadiene, isoprene, myrcene, B-farnesene and mixtures thereof. The 1,3-diene is preferably 1,3-butadiene, isoprene, myrcene, B-farnesene or mixtures thereof, in particular a mixture of at least two of them. More preferably, the 1,3-diene is 1,3-butadiene or a mixture of 1,3-dienes which contains 1,3-butadiene which is preferably a mixture of 1,3-butadiene and myrcene or a mixture of 1,3-butadiene and B-farnesene. According to a first variant of the invention, the olefin of the monomer mixture of step a) is ethylene. According to this variant, the monomer mixture is a mixture of a 1,3-diene and ethylene and the reaction product of the polymerization of step a) is a polymer chain whose constituent units result from the insertion of ethylene and 1,3-diene into the growing chain. The copolymer prepared by this first variant is a copolymer of ethylene and a 1,3-diene. According to a second variant of the invention, the monomer mixture of step a) is a mixture of a 1,3-diene and an olefin which is itself a mixture of ethylene and an α-monoolefin. According to this variant, the reaction product of the polymerization of step a) is a polymer chain whose constituent units result from the insertion of ethylene, the α-monoolefin and the 1,3-diene into the growing chain. The α-monoolefin is preferably styrene or a styrene whose benzene ring is substituted by alkyl groups, more preferably styrene. The copolymer prepared by a preferred embodiment of the second variant is a copolymer of ethylene, a 1,3-diene and styrene. Preferably, the monomer mixture of step a) contains more than 50 mol% of ethylene, the percentage being expressed relative to the total number of moles of monomers of the monomer mixture of step a). When the monomer mixture contains an α-monoolefin, such as styrene, it preferably contains less than 40 mol% of the α-monoolefin, the percentage being expressed relative to the total number of moles of monomers of the monomer mixture of step a). The copolymerization of the monomer mixture can be carried out in accordance with patent applications WO 2007054223 A2 and WO 2007054224 A2 using a catalyst system composed of a metallocene and an organomagnesium. In the present application, metallocene means an organometallic complex in which the metal, in this case the neodymium atom, is linked to a molecule called ligand and consisting of two groups Cp! and Cp? linked together by a P bridge. These groups Cp' and Cp”, which may be identical or different, are chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, these groups being able to be substituted or unsubstituted. According to the invention, the metallocene used as a basic constituent in the catalytic system corresponds to formula (Ia) {P(Cp')(Cp”)Nd(BH,)u+p-Ly-N,} (la) Being a group bridging the two groups Cp! and Cp?, and comprising a silicon or carbon atom, Cp! and Cp°, identical or different, being chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted, 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, whole number or not, being equal to or greater than 0, y, an integer, being equal to or greater than 0. Any ether that has the power to complex the alkali metal is suitable as an ether, especially diethyl ether, methyltetrahydrofuran and tetrahydrofuran. Examples of substituted cyclopentadienyl, fluorenyl and indenyl groups include those substituted by alkyl radicals having 1 to 6 carbon atoms or by aryl radicals having 6 to 12 carbon atoms or by trialkylsilyl radicals such as SiMez. The choice of radicals is also guided by the accessibility of the corresponding molecules, namely substituted cyclopentadienyl, fluorenyl and indene, because the latter are commercially available or easily synthesized. As substituted fluorenyl groups, mention may be made of those substituted in position 2, 7, 3 or 6, particularly 2,7-ditertiobutyl-fluorenyl, 3,6-di-tert-butyl-fluorenyl. Positions 2, 3, 6 and 7 respectively designate the position of the carbon atoms of the rings as shown in the diagram below, with position 9 corresponding to the carbon atom to which the P bridge is attached. "4 if ; art, Eee GE, 23 / 7% PA born j; Fu sd pr 8 Ÿ 4 8 A 'UA- AAA AAA EN Aria TAa Rent us EL Examples of substituted cyclopentadienyl groups include those substituted in both the 2- (or 5-) and 3- (or 4-) positions, particularly those substituted in the 2-position, more particularly the tetramethylcyclopentadienyl group. The 2- (or 5-) position refers to the position of the carbon atom that is adjacent to the carbon atom to which the P bridge is attached, as shown in the diagram below. Remember that a substitution in position 2 or 5 is also called an alpha substitution of the bridge. 3 = FU at >, \ vS 1} # As substituted indenyl groups, mention may be made in particular of those substituted in position 2, more particularly 2-methylindenyl, 2-phenylindenyl. Position 2 designates the position of the carbon atom which is adjacent to the carbon atom to which the P bridge is attached, as shown in the diagram below. P Preferably, Cp! and Cp”, which may be identical or different, are cyclopentadienyls substituted in the alpha position of the bridge, substituted fluorenyls, substituted indenyls or fluorenyl of formula C;3H; or indenyl of formula C,H,. More preferably, Cp' and Cp”, which may be identical or different, are chosen from the group consisting of substituted fluorenyl groups and the unsubstituted fluorenyl group of formula C;3Hz. Advantageously, Cp! and Cp? are identical and each represent an unsubstituted fluorenyl group of formula C,;H;, represented by the symbol Flu. Preferably, the bridge P connecting the groups Cp! and Cp? is of formula ZR'R?, in which Z represents a silicon or carbon atom, R! and R?, identical or different, each represent an alkyl group comprising from 1 to 20 carbon atoms, preferably a methyl. In the formula ZR'R?, Z advantageously represents a silicon atom, Si. Better, the metallocene is of formula (I-1), (I-2), (I-3), (I-4) or (I-5): [Me:Si(Flu),Nd(u-BH,),Li(THF)] (I-1) [{Me-SiFlu,Nd(u-BH,)Li(THF)}”] (1-2) [Me:SiFlu,Nd(u-BH,)(THF)] (1-3) [{Me;SiFlu,Nd(u-BH,)(THF)}»] (-4) [Me:SiFlu,Nd(u-BH4)] (I-5) in which Flu represents the C,3H5 group. The metallocene useful for the synthesis of the catalytic system may be in the form of a crystallized or non-crystalline powder, or in the form of single crystals. The metallocene may be in a monomeric or dimeric form, these forms depending on the method of preparation of the metallocene, as for example described in patent application WO 2007054224 A2 or WO 2007054223 A2. The metallocene may be prepared in a conventional manner by a process analogous to that described in patent application WO 2007054224 A2 or WO 2007054223 A2, in particular by reaction under inert and anhydrous conditions of the salt of an alkali metal of the ligand with a borohydride of the rare earth, neodymium, in a suitable solvent, such as an ether, such as diethyl ether or tetrahydrofuran or any other solvent known to those skilled in the art.After reaction, the metallocene is separated from the reaction by-products by techniques known to those skilled in the art, such as filtration or precipitation in a second solvent. The metallocene is finally dried and isolated in solid form. The organomagnesium compound, another basic constituent of the catalytic system, is the co-catalyst of the catalytic system. Typically, the organomagnesium compound may be a diorganomagnesium compound or a halide of an organomagnesium compound. Preferably, the organomagnesium compound is of formula (IIa), (Ib), (IIc) or (IId) in which R, R*, RS, RB, identical or different, represent a carbon group, RA represents a divalent carbon group, X is a halogen atom, m is a number greater than or equal to 1, preferably equal to 1. MgRR* (Ila) XMgR° (IIb) R5-(Mg-R#),-Mg-RB (IIc) X-Mg-RA-Mg-X (IId). RA may be a divalent aliphatic hydrocarbon chain, interrupted or not by one or more oxygen or sulfur atoms or by one or more arylene groups. A carbon group is understood to mean a group that contains one or more carbon atoms. The carbon group may be a hydrocarbon group (hydrocarbyl group) or a heterohydrocarbon group, i.e. a group containing one or more heteroatoms in addition to carbon and hydrogen atoms. Suitable organomagnesium compounds having a heterohydrocarbon group are the compounds described as transfer agents in patent application WO2016092227 A1. The carbon group represented by the symbols R°, R°, R°, RB and RA are preferably hydrocarbon groups. Preferably, RA contains 3 to 10 carbon atoms, especially 3 to 8 carbon atoms. Preferably, RA is a divalent hydrocarbon chain. Preferably, RA is a branched or linear alkanediyl, a cycloalkanediyl or a xylenediyl radical. More preferably, RA is an alkanediyl. Even more preferably, RA is an alkanediyl having 3 to 10 carbon atoms. Advantageously, RA is an alkanediyl having 3 to 8 carbon atoms. Very advantageously, RA is a linear alkanediyl. 1,3-propanediyl, 1,4-butanediyl, 1,5-pentanediyl, 1,6-hexanediyl, 1,7-heptanediyl, 1,8-octanediyl are particularly suitable RA groups. The carbon groups represented by R°, R*, R5, RB, may be aliphatic or aromatic. They may contain one or more heteroatoms such as an oxygen, nitrogen, silicon or sulfur atom. Preferably, they are alkyl, phenyl or aryl. They may contain 1 to 20 carbon atoms. The alkyls represented R°, R*, R°, RP can contain 2 to 10 carbon atoms and are in particular ethyl, butyl, octyl. The aryls represented R°, R°, R°, RP can contain 7 to 20 carbon atoms and are in particular a phenyl substituted by one or more alkyls such as methyl, ethyl, isopropyl. R°, R*, R° are preferably alkyls containing 2 to 10 carbon atoms, phenyls or aryls containing 7 to 20 carbon atoms. According to a particular embodiment of the invention, R° comprises a benzene ring substituted by the magnesium atom, one of the carbon atoms of the benzene ring ortho to the magnesium being substituted by a methyl, an ethyl, an isopropyl or forming a cycle with the carbon atom which is its closest neighbor and which is meta to the magnesium, the other carbon atom of the benzene ring ortho to the magnesium being substituted by a methyl, an ethyl or an isopropyl and R* is an alkyl. According to this particular embodiment, R° is advantageously 1,3-dimethylphenyl, 1,3-diethylphenyl, mesityl, or 1,3,5 triethylphenyl and R* is advantageously ethyl, butyl, octyl. According to another particular embodiment of the invention, R* and R* are alkyls containing 2 to 10 carbon atoms, in particular ethyl, butyl, octyl. Preferably, Re is an alkyl containing 2 to 10 carbon atoms, in particular ethyl, butyl, octyl. Advantageously, RB comprises a benzene ring substituted by the magnesium atom, one of the carbon atoms of the benzene ring ortho to the magnesium being substituted by a methyl, an ethyl, an isopropyl or forming a ring with the carbon atom which is its nearest neighbor and which is meta to the magnesium, the other carbon atom of the benzene ring ortho to the magnesium being substituted by a methyl, an ethyl or an isopropyl. More preferably, RB is 1,3-dimethylphenyl, 1,3-diethylphenyl, mesityl, or 1,3,5-triethylphenyl. For example, suitable organomagnesium compounds are butylethylmagnesium, butyloctylmagnesium, ethylmagnesium chloride, butylmagnesium chloride, ethylmagnesium bromide, butylmagnesium bromide, octylmagnesium chloride, octylmagnesium bromide, 1,3-dimethylphenylbutylmagnesium, 1,3-diethylphenylethylmagnesium, butylmesitylmagnesium, ethylmesitylmagnesium, 1,3-diethylphenylbutylmagnesium, 1,3-diethylphenylethylmagnesium, 1,3-diisopropylphenylbutylmagnesium, 1,3-disopropylphenylethylmagnesium, 1,3,5-triethylphenylbutylmagnesium, 1,3,5-triethylphenylethylmagnesium, 1,3,5-triisopropylphenylbutylmagnesium, 1,3,5-triisopropylphenylethylmagnesium, 1,3-di(bromide of magnesium)-propanediyl, 1,3-di(magnesium chloride)-propanediyl, 1,5-di(magnesium bromide)-pentanediyl, 1,5-di(magnesium chloride) magnesium)-pentanediyl, 1,8-di(magnesium bromide)-octanediyl, 1,8-di(magnesium chloride)-octanediyl. The organomagnesium compound of formula (IIc) may be prepared by a process, which comprises reacting a first organomagnesium compound of formula X'Mg-R4-MgX" with a second organomagnesium compound of formula R5-Mg-X', X° representing a halogen atom, preferably bromine or chlorine, RP and RA being as defined previously. X° is more preferably a bromine atom. The stoichiometry used in the reaction determines the value of m in formula (IIc). For example, a molar ratio of 0.5 between the amount of the first organomagnesium compound and the amount of the second organomagnesium compound is favorable for the formation of an organomagnesium compound of formula (IIc) in which m is equal to 1, while a molar ratio greater than 0.5 will be more favorable for the formation of an organomagnesium compound of formula (IIc) in which m is greater than 1. To carry out the reaction of the first organomagnesium compound with the second organomagnesium compound, a solution of the second organomagnesium compound is typically added to a solution of the first organomagnesium compound. The solutions of the first organomagnesium compound and the second organomagnesium compound are generally solutions in an ether, such as diethyl ether, dibutyl ether, tetrahydrofuran, methyltetrahydrofuran or the mixture of two or more of these ethers. Preferably, the respective concentrations of the solutions of the first organomagnesium compound and the second organomagnesium compound are respectively 0.01 to 3 mol / L and 0.02 to 5 mol / L. More preferably, the respective concentrations of the first organomagnesium compound and the second organomagnesium compound are respectively 0.1 to 2 mol / L and 0.2 to 4 mol / L. The first organomagnesium and the second organomagnesium can be prepared in advance by a Grignard reaction from magnesium metal and a suitable precursor in a reactor. For the first organomagnesium and the second organomagnesium, the respective precursors are of formula X'-RA-X° and RB-X°, RA,R B and X' being as defined previously. The Grignard reaction is typically carried out by adding the precursor to magnesium metal which is generally in the form of chips. Preferably, iodine (L) typically in the form of beads is introduced into the reactor before the addition of the precursor in order to activate the Grignard reaction in a known manner. Alternatively, the organomagnesium compound of formula (IIc) may be prepared by reacting an organometallic compound of formula M-R4-M and the organomagnesium compound of formula RB-Mg-X”, M representing a lithium, sodium or potassium atom, X°, RB and RA being as defined above. Preferably, M represents a lithium atom, in which case the organometallic compound of formula M-R4-M is an organolithium. The reaction of the organolithium and the organomagnesium is typically carried out in an ether such as diethyl ether, dibutyl ether, tetrahydrofuran, methyltetrahydrofuran, methylcyclohexane, toluene or a mixture thereof. The reaction is also typically carried out at a temperature ranging from 0°C to 60°C. The contacting is preferably carried out at a temperature between 0°C and 23°C. The contacting of the organometallic compound of formula MR#-M with the organomagnesium of formula RE-Mg-X" is preferably done by adding a solution of the organometallic compound M-R4-M to a solution of the organomagnesium RB-Mg-X°. The solution of the organometallic compound M-R4-M is generally a solution in a hydrocarbon solvent, preferably n-hexane, cyclohexane or methylcyclohexane, the solution of the organomagnesium RB-Mg-X” is generally a solution in an ether, preferably diethyl ether or dibutyl ether.Preferably, the respective concentrations of the solutions of the organometallic compound and the organomagnesium compound M-R4-M and RB-Mg-X" are respectively 0.01 to 1 mol / L and 0.02 to 5 mol / L. More preferably, the respective concentrations of the solutions of the organometallic compound and the organomagnesium compound M-R4-M and R5-Mg-X" are respectively 0.05 to 0.5 mol / L and 0.2 to 3 mol / L. Like any synthesis carried out in the presence of organometallic compounds, the syntheses described for the synthesis of organomagnesiums take place under anhydrous conditions under an inert atmosphere, in stirred reactors. Typically, solvents and solutions are used under anhydrous nitrogen or argon. Once the organomagnesium compound of formula (IIc) is formed, it is generally recovered in solution after filtration carried out under an inert and anhydrous atmosphere. It can be stored before use in its solution in airtight containers, for example capped bottles, at a temperature between -25°C and 23°C. Compounds of formula (IId) which are Grignard reagents are described for example in the book "Advanced Organic Chemistry" by J. March, 4% Edition, 1992, page 622-623 or in the book "Handbook of Grignard Reagents", Edition Gary S. Silverman, Philip E. Rakita, 1996, page 502-503. They can be synthesized by bringing magnesium metal into contact with a dihalogenated compound of formula X-RA-X, R4 being as defined according to the invention. For their synthesis, one can for example refer to the collection of volumes of "Organic Synthesis". Compounds of formula (IIa) and (IId) which are also Grignard reagents are well known, even some of them are commercial products. For their synthesis, one can also refer, for example, to the collection of volumes of "Organic Synthesis". Like any organomagnesium compound, the organomagnesium compound constituting the catalytic system, in particular of formula (IIa), (IIb), (Ic) or (IId) may be in the form of a monomeric entity or in the form of a polymeric entity. By way of illustration, the organomagnesium (IIc) may be in the form of a monomeric entity (R5-(Mg-R#),-Mg-R5), or in the form of a polymeric entity (R5-(Mg-RA )m-Mg-RE),, p being an integer greater than 1, in particular dimeric (RE-(Mg-R4), - Mg-R5),, m being as defined previously. Similarly, also by way of illustration, the organomagnesium compound of formula (IId) may be in the form of a monomeric entity (X-Mg-R4-Mg-X), or in the form of a polymeric entity (X-Mg-R4-Mg-X), p being an integer greater than 1, in particular dimeric (X-Mg-RA-Mg-X). Furthermore, whether in the form of a monomeric or polymeric entity, the organomagnesium compound can also be in the form of an entity coordinated to one or more molecules of a solvent, preferably an ether such as diethyl ether, tetrahydrofuran or methyltetrahydrofuran. In formulas (IIb) and (IId), X is preferably a bromine or chlorine atom, more preferably a bromine atom. According to any of the embodiments of the invention, the organomagnesium compound is preferably of formula (IIa). The quantities of co-catalyst and metallocene reacted are such that the ratio between the number of moles of Mg in the co-catalyst and the number of moles of the rare earth of the metallocene, neodymium, preferably ranges from 0.5 to 200, more preferably from 1 to less than 20. The range of values ​​from 1 to less than 20 is particularly more favorable for obtaining copolymers with high molar masses. According to a first embodiment, the catalytic system can be prepared in a traditional manner by a process analogous to that described in the patent application WO 2007054224 A2 or WO 2007054223 A2. For example, the co-catalyst, in this case the organomagnesium compound and the metallocene, are reacted in a hydrocarbon solvent, typically at a temperature ranging from 20 to 80°C for a period of between 5 and 60 minutes. The catalytic system is generally prepared in a hydrocarbon solvent, aliphatic such as methylcyclohexane or aromatic such as toluene, preferably in an aliphatic hydrocarbon solvent such as methylcyclohexane. Generally, after its synthesis, the catalytic system is used as is for step a). According to a second embodiment, the catalytic system can be prepared by a process analogous to that described in patent application WO 2017093654 A1 or in patent application WO 2018020122 A1: it is said to be of the preformed type. For example, the organomagnesium and the metallocene are reacted in a hydrocarbon solvent, typically at a temperature of 20 to 80°C for 10 to 20 minutes to obtain a first reaction product, then with this first reaction product, a preforming monomer is reacted at a temperature ranging from 40 to 90°C for 1 hour to 12 hours. The pre-forming monomer is preferably used in a molar ratio (pre-forming monomer / metal of the metallocene) ranging from 5 to 1000, preferably from 10 to 500. Before its use in polymerization, the pre-formed type catalytic system can be stored in an inert atmosphere, in particular at a temperature ranging from -20°C to room temperature (23°C).According to this second embodiment, the preformed type catalytic system has as its basic constituent a preformation monomer chosen from 1,3-dienes, ethylene and their mixtures. In other words, the so-called preformed catalytic system contains, in addition to the metallocene and the co-catalyst, a preformation monomer. The 1,3-diene as preformation monomer can be 1,3-butadiene, isoprene or a 1,3-diene of formula CH;=CRS-CH=CH,, the symbol RS representing a hydrocarbon group having 3 to 20 carbon atoms, in particular myrcene or B-farnesene. The preformation monomer is preferably 1,3-butadiene. The catalytic system is typically present in a solvent which is preferably the solvent in which it was prepared, and the concentration of rare earth metal, i.e. neodymium, of metallocene is then within a range preferably from 0.0001 to 0.2 mol / L more preferably from 0.001 to 0.03 mol / L. Like any synthesis carried out in the presence of organometallic compounds, the synthesis of metallocene, the synthesis of organomagnesium and the synthesis of the catalytic system take place under anhydrous conditions under an inert atmosphere. Typically, the reactions are carried out from solvents and anhydrous compounds under anhydrous nitrogen or argon. The polymerization of the monomer mixture is carried out in a reactor, preferably in solution, continuously or batchwise. The polymerization solvent is typically a hydrocarbon solvent, preferably aliphatic. As an example of an aliphatic hydrocarbon solvent, methylcyclohexane is particularly suitable. The monomer mixture can be introduced into the reactor containing the polymerization solvent and the catalytic system or conversely the catalytic system can be introduced into the reactor containing the polymerization solvent and the monomer mixture. The monomer mixture and the catalytic system can be introduced simultaneously into the reactor containing the polymerization solvent, in particular in the case of continuous polymerization. The polymerization is typically carried out under anhydrous conditions and in the absence of oxygen, in the optional presence of an inert gas.The polymerization temperature generally varies in a range from 40 to 150°C, preferably 40 to 120°C. A person skilled in the art adapts the polymerization conditions such as the polymerization temperature, the concentration of each of the reactants, the pressure in the reactor according to the composition of the monomer mixture, the polymerization reactor, the desired microstructure and macrostructure of the copolymer chain. The polymerization is preferably carried out at constant pressure in monomers. A continuous addition of each of the monomers or one of them can be carried out in the polymerization reactor, in which case the polymerization reactor is a fed reactor. This embodiment is particularly suitable for a random incorporation of the monomers. Preferably, the polymerization of step a) is a random polymerization, which results in a random incorporation of the monomers of the monomer mixture used in step a). Once the desired monomer conversion rate is reached in the polymerization reaction of step a), step b) is proceeded to. Step b) of the process according to the invention brings the reaction product of step a) into contact with a coupling agent, a compound containing at least two methacrylate functions of formula CH,=C(CH,)CO-O-. Step b) is a coupling reaction of the copolymer chains, one of the ends of which reacts with the coupling agent without there being any subsequent polymerization of the methacrylate functions. After deactivation of the reactive sites by a termination reaction of the polymer chain (step c), a copolymer of a coupled 1,3-diene and olefin is obtained, the chains of the copolymer being linked together by a group containing at least two units of formula 1 —(CH,-CH(CH-)-CO-O)- formula 1, each copolymer chain being linked to a distinct unit of formula 1 via a covalent bond between a carbon atom of the monomer unit terminal of the copolymer chain and the carbon atom of the methylene group of the unit of formula 1. The terminal monomer unit is typically the monomer unit constituting the chain end of the copolymer obtained at the end of step a) which reacts with the coupling agent. The methacrylates useful for the purposes of the invention as coupling agents may be bismethacrylates or trismethacrylates. They may be commercial products. They are preferably commercially available products. When the methacrylates are packaged in the presence of a stabilizer, as is the case for most commercial methacrylates, they are typically used after removal of the stabilizer, which may be carried out in a well-known manner by distillation or by treatment on alumina columns. According to a first preferred embodiment of the invention, the coupling agent is a bismethacrylate, a compound which contains two methacrylate functions, preferably of formula 3 [CH-=C(CH-)-CO-01],-Z; formula 3 Za representing a divalent hydrocarbon group or a divalent hydrocarbon group substituted by one or more functions chosen from the ether function and the thioether function. Advantageously, Z; is an acyclic group. Z3; may be a linear or branched group. The number of carbon atoms in Z3 is not limited in itself. Z; may contain up to 20 carbon atoms. Preferably, Z; is an alkanediyl or an alkanediyl substituted by one or more ether functions, more preferably an alkanediyl. Preferably, the alkanediyl of Z; contains 1 to 10 carbon atoms, more preferably 2 to 8 carbon atoms. Suitable alkanediyl groups of Z; include, in particular, 1,2-ethanediyl, 1,1-ethanediyl, 1,3-propanediyl, 1,2-propanediyl, 1,4-butanediyl, 1,3-butanediyl, 1,5-pentanediyl, 2,2-dimethyl-1,3-propanediyl, 1,6-hexanediyl, 2,5-hexanediyl, 1,4-cyclohexanediyl, 1,4-cyclohexanediyl dimethylene. Also suitable are divalent hydrocarbon groups, preferably alkanediyls, interrupted by one or more oxygen atoms to form ether bonds such as the divalent groups of formulas —(CH,-CH,-O),-CH,-CH--, (CH;-CH,-CH,-O),-CH-CH,-CH,- in which n is an integer greater than or equal to 1, in particular ranging from 1 to 10, more particularly ranging from 1 to 2. By way of illustration of bismethacrylates containing polyoxyalkylene chains, mention may be made of triethylene glycol dimethacrylate, dipropylene glycol dimethacrylate, neopentyl glycol propoxylate dimethacrylate, bisphenol A ethoxylate dimethacrylate, For reasons of commercial availability, the coupling agent is advantageously diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, thiodi-2,1-ethanediyl bismethacrylate, ethylidene dimethacrylate, 1,2-propanediol dimethacrylate, 1,3-propanediol dimethacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol dimethacrylate, neopentyl glycol dimethacrylate, 1,4-cyclohexanediol dimethacrylate or cyclohexane-1,4-dimethanol dimethacrylate, more preferably diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, ethylidene dimethacrylate, 1,2-propanediol dimethacrylate, 1,3-propanediol dimethacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol dimethacrylate or neopentyl glycol dimethacrylate, even more preferably ethylidene dimethacrylate, 1,2-propanediol dimethacrylate, 1,3-propanediol dimethacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol dimethacrylate or neopentyl glycol dimethacrylate. According to a second preferred embodiment of the invention, the coupling agent is a trismethacrylate, a compound which contains three methacrylate functions, preferably of formula 4 [CH,=C(CH:)-CO-O1];- Z4 formula 4 Za representing a trivalent hydrocarbon group or a trivalent hydrocarbon group substituted by one or more functions chosen from the ether function and the thioether function. Advantageously, Z4 is an acyclic group. Z4y may be a linear or branched group. The number of carbon atoms in Z4 is not limited per se. Z4 may contain up to 20 carbon atoms. Preferably, Z4 is an alkanetriyl or an alkanetriyl substituted by one or more ether functions, more preferably an alkanetriyl. An alkanetriyl is typically a saturated trivalent aliphatic hydrocarbon group. Preferably, the alkanetriyl of Z4 contains 3 to 10 carbon atoms, more preferably 3 to 8 carbon atoms. Suitable alkanetriyl groups of Z4 include, in particular, propane-1,2,3-triyl, 2-methylpropane-1,2,3-triyl, 2-ethylpropane-1,2,3-triyl, propane-1,1,1-triyltrimethylene, 1,2,5-pentanetriyl groups. Also suitable are trivalent groups, preferably alkanetriyls, containing oxyalkylene chains such as oxyethylene, oxypropylene, or polyoxyalkylene chains such as polyoxyethylene, polyoxypropylene. Mention may be made of propane-1,2,3-triyl, 2-methylpropane-1,2,3-triyl, 2-ethylpropane-1,2,3-triyl, propane-1,1,1-triyltrimethylene groups containing one or more oxyalkylene or polyoxyalkylene chains, in particular oxyethylene or polyoxyethylene. For example, propane-1,2,3-triyl groups are suitable, 2-methylpropane-1,2,3-triyl or 2-ethylpropane-1,2,3-triyl containing three oxyethylene or polyoxyethylene chains in the 1,2,3 position, the propane- group 1,1,1-triyltrimethylene containing three oxyethylene or polyoxyethylene chains in the 1,1,1 position. The figures of such groups are shown below, in which n, m and p are integers greater than or equal to 1, in particular ranging from 1 to 10, more particularly ranging from 1 to 2. fa. 0 A Se Fa * f das ; Lo 0 AR Ï | ready sf” SN ta, ET pe 3 ve etT . 'er Set S ai ; 006 { ; &. s A Î A ee Je fi i ï - fr i ÿ 0 ES Le ner” A Le swf Also suitable are, for example, alkanetriyl groups containing a ©-alkoxypoly(oxyalkylene) group such as w-methoxypoly(oxyethylene). Examples include 2-(w-methoxypoly(oxyethylene))propane-1,2,3-triyl, 1-(methoxypoly(oxyalkylene))methane-1,1,1-triyltrimethylene. For reasons of commercial availability, the coupling agent is advantageously glycerol trimethacrylate, also known as propane-1,2,3-triyl tris(2-methylacrylate), 1,1,1-trimethylolpropane trimethacrylate or 1,2,5-pentanctriyl trismethacrylate. Preferably, step b) is carried out in an aliphatic hydrocarbon solvent, such as methylcyclohexane. Advantageously, it is carried out in the reaction medium resulting from step a). It is generally carried out by adding the coupling agent to the reaction product of step a) in its reaction medium with stirring. Before adding the coupling agent, the reactor is preferably degassed and inerted. Degassing the reactor removes residual gaseous monomers and also facilitates the addition of the coupling agent to the reactor. Alternatively, the coupling agent can be injected into the reactor by overpressure. Inerting the reactor, for example with nitrogen, prevents the carbon-metal bonds present in the reaction medium and necessary for the coupling reaction of the copolymer chains from being deactivated. The coupling agent can be added pure or diluted in a hydrocarbon solvent, preferably aliphatic such as methylcyclohexane or aromatic. such as toluene. The coupling agent is left in contact with the reaction product of step a) for the time required for the coupling reaction. The coupling reaction can typically be monitored by chromatographic analysis to track the consumption of the coupling agent. The coupling reaction is preferably carried out at a temperature ranging from 23 to 120 °C, for 1 to 60 minutes with stirring. The coupling reaction is preferably carried out with a molar equivalent of methacrylate function relative to the number of carbon-magnesium bonds per mole of co-catalyst in the catalytic system.The ratio between the number of molar equivalents of methacrylate function and the number of carbon-magnesium bonds per mole of co-catalyst can however vary according to the desired rate of coupled polymer in the polymer obtained at the end of step c), according to the desired number of branches in the coupled copolymer and, in the case of obtaining a mixture of coupled copolymers having a different number of branches, according to their respective proportion. A ratio close to 1, typically varying from 0.85 to 1.05, favors the highest coupling rates. Advantageously, step b), coupling reaction, is carried out with a ratio between the number of molar equivalents of methacrylate function and the number of carbon-magnesium bonds per mole of co-catalyst varying from 0.85 to 1.5. Typically in a diorganomagnesium such as butyloctylmagnesium (BOMAG) there are two carbon-magnesium bonds per mole of magnesium.One mole of a compound having two methacrylate functions is equivalent to two molar equivalents of methacrylate function; more generally, one mole of a compound having n methacrylate functions is equivalent to n molar equivalents of methacrylate function, n being an integer greater than or equal to 2. Once the chain end is modified, step b) is followed by step c). Step c), chain termination reaction, is typically a reaction which deactivates the reactive sites still present in the reaction medium resulting from step b). In step c), a chain terminating agent is brought into contact with the reaction product of step b), generally in its reaction medium, for example by adding the terminating agent to the reaction medium at the end of step b) or by pouring the reaction medium obtained at the end of step b) onto a solution containing the terminating agent. The terminating agent is generally in stoichiometric excess. The terminating agent is typically a protic compound, a compound which comprises a relatively acidic proton. As a terminating agent, mention may be made of water, carboxylic acids, in particular C1C fatty acids such as acetic acid, stearic acid, aliphatic or aromatic alcohols, such as methanol, ethanol, isopropanol, phenolic antioxidants. After reaction with a protic compound, the process leads to a coupled copolymer in accordance with the invention. The copolymer prepared according to the process in accordance with the invention can be separated from the reaction medium of step c) according to methods well known to those skilled in the art, for example by an operation of evaporation of the solvent under reduced pressure or by a steam stripping operation. The process using a coupling agent having two methacrylate functions preferentially leads to the preparation of a 2-branch coupled copolymer, whereas the process using a coupling agent having three methacrylate functions preferentially leads to the preparation of a 3-branch coupled copolymer or to the preparation of a mixture containing a 2-branch coupled copolymer and a 3-branch coupled copolymer. The process according to the invention has the advantage of leading to the preparation of coupled copolymer without there being any polymerization of the methacrylate functions, which results in the absence of the formation of polymethacrylate either in the form of block polymer or in the form of homopolymer. Consequently, the coupled copolymer according to the invention is obtained without being contaminated by polymethacrylate whether in the form of block copolymers or homopolymers. In summary, the invention may be implemented according to any of the following embodiments 1 to 52: Mode 1: Copolymer of a 1,3-diene and an olefin, the olefin being ethylene or a mixture of ethylene and an ε-monoolefin, which copolymer contains more than 50 mol% of ethylene unit and is a coupled copolymer, the chains of the copolymer being linked together by a group containing at least two units of formula | —(CH,-CH(CH-)-CO-O)- formula 1, each copolymer chain being linked to a distinct unit of formula 1 via a covalent bond between a carbon atom of a monomer unit of the copolymer chain and the carbon atom of the methylene group of the unit of formula 1. Mode 2: Copolymer according to mode 1, which copolymer is a 2-branch or 3-branch coupled copolymer. Mode 3: Copolymer according to mode 1 or 2, which copolymer corresponds to formula 2 [P-CH,-CH(CH-)-CO-O1]--Z; formula 2 P denoting a copolymer chain, Z representing a divalent hydrocarbon group or a divalent hydrocarbon group which contains one or more functions chosen from the ether function and the thioether function. Mode 4: Copolymer according to mode 3 in which Z is an alkanediyl or an alkanediyl which contains one or more ether functions. Mode 5: Copolymer according to mode 3 or 4 in which Z; is an alkanediyl. Mode 6: Copolymer according to mode 4 or 5 in which the alkanediyl of Z; contains 1 with 10 carbon atoms. Mode 7: Copolymer according to any one of modes 4 to 6 in which the alkanediyl of Z, is the group 1,2-ethanediyl, 1,1-ethanediyl, 1,3-propanediyl, 1,2-propanediyl, 1,4-butanediyl, 1,3-butanediyl, 1,5-pentanediyl, 2,2-dimethyl-1,3-propanediyl, 1,6-hexanediyl, 2,5-hexanediyl, 1,4-cyclohexanediyl or 1,4-cyclohexanediyl dimethylene. Mode 8: Copolymer according to any one of modes 3 to 7 in which the divalent hydrocarbon group of Z, is further substituted by one or more methacrylate functions of formula CH,=C(CH,)CO-O-. Mode 9: Copolymer according to mode 8 in which Zy is an alkanediyl substituted by a methacrylate function. Mode 10: Copolymer according to mode 1 or 2, which copolymer corresponds to formula 3 [P-CH.-CH(CH:)-CO-O1];-Z; formula 3 P denoting a copolymer chain, Z representing a trivalent hydrocarbon group or a trivalent hydrocarbon group which contains one or more functions chosen from the ether function and the thioether function. Mode 11: Copolymer according to mode 10 in which Z; is an alkanetriyl or an alkanetriyl which contains one or more ether functions. Mode 12: Copolymer according to mode 11 in which the alkanetriyl of Z; contains 3 to 10 carbon atoms. Mode 13: Copolymer according to any one of modes 10 to 12 in which Z; is an alkanetriyl. Mode 14: Copolymer according to any one of modes 10 to 13 in which the alkanetriyl of Z; is propane-1,2,3-triyl, 2-methylpropane-1,2,3-triyl, 2-ethylpropane-1,2,3-triyl, propane-1,1,1-triyltrimethylene or 1,2,5-pentanetriyl. Mode 15: Copolymer according to any one of modes 1 to 14, which copolymer contains more than 60 mol% of ethylene unit. Mode 16: Copolymer according to any one of modes 1 to 15, which copolymer contains more than 65 mol% of ethylene unit. Mode 17: Copolymer according to any one of modes 1 to 16, which copolymer contains less than 90 mol% of ethylene unit. Mode 18: Copolymer according to any one of modes 1 to 17, which copolymer contains at most 85 mol% of ethylene unit. Mode 19: Copolymer according to any one of modes 1 to 18, which copolymer contains at most 80 mol% of ethylene unit. Mode 20: Copolymer according to any one of modes 1 to 19 in which α-monoolefin is styrene. Mode 21: Copolymer according to any one of modes 1 to 20, which copolymer is a copolymer of ethylene and a 1,3-diene. Mode 22: Copolymer according to any one of modes 1 to 21, which copolymer is a random copolymer. Mode 23: Copolymer according to any one of modes 1 to 22 in which the 1,3-diene is 1,3-butadiene, isoprene, myrcene, B-farnesene or mixtures thereof. Mode 24: Copolymer according to any one of modes 1 to 23 in which the 1,3-diene is 1,3-butadiene. Mode 25: Copolymer according to any one of modes 1 to 24 in which the 1,3-diene is a mixture of 1,3-dienes which contains 1,3-butadiene. Mode 26: Copolymer according to any one of modes 1 to 25, which copolymer contains 1,3-butadiene units and 1,2-cyclohexane units. Mode 27: Copolymer according to any one of modes 1 to 26, which copolymer contains at most 15 mol% of the 1,2-cyclohexane units. Mode 28: Copolymer according to any one of modes 1 to 27, which copolymer is a copolymer of ethylene and 1,3-butadiene. Mode 29: Copolymer according to any one of modes 1 to 28, which copolymer is or a copolymer of ethylene, 1,3-butadiene and myrcene. Mode 30: Copolymer according to any one of modes 1 to 29, which copolymer is a copolymer of ethylene, 1,3-butadiene and B-farnesene. Mode 31: Copolymer according to any one of modes 1 to 30, which copolymer is an elastomer. Method 32: Process for the preparation of a coupled copolymer of a 1,3-diene and an olefin, the copolymer containing more than 50 mol% of ethylene unit, which process comprises the successive steps a), b) and c), - step 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 one metallocene of formula (Ia) and an organomagnesium co-catalyst, {P(Cp')(Cp*)Nd(BH4)(1+,y-Ly-N,} (Ja) Cp' and Cp”, identical or different, being chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted, Being a group bridging the two groups Cp' and Cp”, 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, whole number or not, being equal to or greater than A, y, integer, being equal to or greater than 0, the olefin being ethylene or a mixture of ethylene and an α-monoolefin, - step b) being the reaction of a coupling agent, compound containing at least two methacrylate functions of formula CH,=C(CH3)CO-O- with the reaction product of the polymerization of step a), - step c) being a chain termination reaction. Method 33: Process according to method 32 in which the coupling agent is a bismethacrylate or a trismethacrylate. Mode 34: Process according to mode 32 or 33 in which the coupling agent is of formula 3 or formula 4 [CH-=C(CH-)-CO-01],-Z; formula 3 [CH,=C(CH:)-CO-O1];- Z4 formula 4 Za representing a divalent hydrocarbon group or a divalent hydrocarbon group substituted by one or more functions chosen from the ether function and the thioether function, Za representing a trivalent hydrocarbon group or a trivalent hydrocarbon group substituted by one or more functions chosen from the ether function and the thioether function. Method 35: Process according to method 34 in which Z3 is an alkanediyl or an alkanediyl substituted by one or more ether functions, preferably an alkanediyl. Method 36: Process according to method 34 or 35 in which the alkanediyl of Z; contains 1 to 10 carbon atoms. Mode 37: A method according to any one of modes 32 to 34 wherein the coupling agent is diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, ethylidene dimethacrylate, 1,2-propanediol dimethacrylate, 1,3-propanediol dimethacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol dimethacrylate or neopentyl glycol dimethacrylate. Method 38: Process according to method 34 in which Z is an alkanetriyl or an alkanetriyl substituted by one or more ether functions. Method 39: Process according to method 34 or 38 in which the alkanetriyl of Z4 contains 3 to 10 carbon atoms. Mode 40: A process according to any of modes 32 to 34 wherein the coupling agent is glycerol trimethacrylate, 1,1,1-trimethylolpropane trimethacrylate or 1,2,5-pentanetriyl trismethacrylate. Mode 41: Method according to any one of modes 32 to 40 in which step b) is carried out with a ratio between the number of molar equivalents of methacrylate function and the number of carbon-magnesium bonds per mole of co-catalyst varying from 0.85 to 1.5. Mode 42: Process according to any one of modes 32 to 41 in which step b) is carried out in an aliphatic hydrocarbon solvent. Mode 43: Process according to any one of modes 32 to 42 in which the olefin is ethylene. Mode 44: A process according to any one of modes 32 to 43 wherein the 1,3-diene is 1,3-butadiene, isoprene, myrcene, [-farnesene or mixtures thereof. Mode 45: Process according to any one of modes 32 to 44 in which the 1,3-diene is 1,3-butadiene or a mixture of 1,3-dienes which contains 1,3-butadiene which is preferably a mixture of 1,3-butadiene and myrcene or a mixture of 1,3-butadiene and B-farnesene. Method 46: Process according to any one of methods 32 to 45 in which R' and R? each represent a methyl. Mode 47: Process according to any one of modes 32 to 46 in which Z represents a silicon atom. Method 48: Process according to any one of methods 32 to 47 in which the metallocene is of formula (I-1), (I-2), (I-3), (I-4) or (I-5): [Me:Si(Flu),Nd(u-BH,),Li(THF)] (I-1) [{Me-SiFlu,Nd(u-BH,)-Li(THF)}”] (1-2) |[Me-SiFlu,Nd(u-BH,)(THF)] (1-3) [{Me-SiFlu,Nd(u-BH,)(THF)}»] (-4) [Me-SiFlu,Nd(u-BH4)] (I-5) in which Flu represents the C,3H group;. Method 49: Process according to any one of methods 32 to 48 in which the organomagnesium compound is of formula (IIa) in which R* and R*, identical or different, represent a carbon group. MgR°R* (Ia). Mode 50: Process according to any one of modes 32 to 49 in which R* and Re are alkyl. Mode 51: Process according to any one of modes 32 to 50 in which R° and Re are alkyls containing 2 to 10 carbon atoms. Mode 52: A polymer composition which contains a 2-branch copolymer and a 3-branch copolymer, which copolymers are defined in any one of modes 1 to 31 or are obtainable by a process defined in any one of modes 32 to 51. The above-mentioned features of the present invention, as well as others, will be better understood by reading the following description of the exemplary embodiments of the invention, given for illustrative purposes. Examples Size exclusion chromatography (SEC): a) Principle of measurement: Size exclusion chromatography (SEC) separates macromolecules in solution according to their size using columns filled with a porous gel. Macromolecules are separated according to their hydrodynamic volume, with the largest being eluted first. Combined with 3 detectors (3D), a refractometer, a viscometer and a 90° light scattering detector, SEC allows the absolute molar mass distribution of a polymer to be understood. The various number-average (Mn), weight-average (Mw) absolute molar masses and the dispersity (D = Mw / Min) can also be calculated. b) Preparation of the polymer: Each sample is solubilized in tetrahydrofuran at a concentration of approximately 1 g / L. The solution is then filtered through a 0.45um porosity filter before injection. c) 3D SEC analysis: To determine the number-average molar mass (Mn), and where appropriate the weight-average molar mass (Mw) and the polydispersity index (Ip or also noted D = Mw / Mn) of polymers, the method below is used. The number-average molar mass (Mn), weight-average molar mass (Mw) and polydispersity index of the polymer (hereinafter referred to as sample) are determined absolutely by triple detection size exclusion chromatography (SEC). Triple detection size exclusion chromatography has the advantage of measuring average molar masses directly without calibration. The value of the refractive index increment dn / de of the sample solution is measured online using the peak area detected by the refractometer (RI) of the liquid chromatography equipment. To apply this method, it must be ensured that 100% of the sample mass is injected and eluted through the column. The peak area RI depends on the sample concentration, the detector constant RI and the value of dn / dc. To determine the average molar masses, the previously prepared and filtered 1 g / L solution in tetrahydrofuran is used and injected into the chromatographic chain. The equipment used is a "Wyatt" chromatographic chain. The elution solvent is tetrahydrofuran containing 250 ppm of BHT. (2,6-diter-butyl 4-hydroxy toluene), the flow rate is | mL.min-!, the system temperature is 35° C and the analysis time is 60 min. The columns used are a set of three AGILENT columns with the trade name "PL GEL MIXED B LS". The injected volume of the sample solution is 100 uL. The detection system is composed of a Wyatt differential viscometer with the trade name "VISCOSTAR II", a Wyatt differential refractometer with the trade name "OPTILAB T-REX" with a wavelength of 658 nm, a Wyatt multi-angle static light scattering detector with a wavelength of 658 nm and with the trade name "DAWN HELEOS 8+". For the calculation of the number-average molar masses and the polydispersity index, the value of the refractive index increment dn / de of the sample solution obtained above is integrated. The software for processing the chromatographic data is the “ASTRA de Wyatt” system. Nuclear Magnetic Resonance (NMR): The copolymers are characterized by 'H, *C, Si NMR spectrometry. The NMR spectra are recorded on a Brüker Avance III 500 MHz Spectrometer equipped with a BBFOz-grad 5 mm "broadband" eryo-probe. The quantitative 'H NMR experiment uses a 30° single pulse sequence and a 5 second repetition delay between each acquisition. 64 to 256 accumulations are performed. The quantitative *C NMR experiment uses a 30° single pulse sequence with proton decoupling and a 10 second repetition delay between each acquisition. 1024 to 10240 accumulations are performed. The 'H chemical shift axis is calibrated relative to the protonated solvent impurity (CDCla) at 8,; = 7.20 ppm. The !'C chemical shift axis is calibrated relative to the solvent signal (CDCI3) at 8.4c = 77 ppm. The glass transition temperature (Tg) is measured using a differential scanning calorimeter according to ASTM D3418 (1999). Polymer crystallinity rate: ISO 11357-3:2011 is used to determine the temperature and enthalpy of melting and crystallization of polymers used by differential scanning calorimetry (DSC). The reference enthalpy of polyethylene is 277.1 J / g (according to Handbook of Polymer 4th Edition, J. BRANDRUP, EH IMMERGUT, and EA GRULKE, 1999) Viscosity: The dry polymer is redissolved in toluene at 0.1 g / dL. Viscosity measurement is carried out using an Ostwald viscometer immersed in a water bath at 25°C. The bath temperature is controlled using a circulating thermal bath. closed. The viscosity of the polymer is measured relative to the solvent in which it is dissolved. Measuring the viscosity of toluene in the Ostwald viscometer gives ty, an elution time between point A and B expressed in hundredths of a second. The viscosity measurement of the polymer in solution in toluene at 0.1 g / dL (C) in the Ostwald viscometer makes it possible to obtain t,, an elution time between point A and B expressed in hundredths of a second. The viscosity of the polymer, expressed in dL / g, is then calculated according to the following formula: visco = 1 / C x (t, - to) / to Preparation of copolymers: The metallocene [{Me:SiFlu:Nd(u-BH,),Li(THF)}] is prepared according to the procedure described in patent application WO 2007054224, BOMAG Butyloctylmagnesium (20% in heptane, at 0.88 mol L*) is sourced from Chemtura and stored in a Schlenk tube under an inert atmosphere. The ethylene, N35 grade, comes from Air Liquide and is used without prior purification. 1,3-Butadiene is purified on alumina guards. The coupling agent is trimethylolpropane trimethacrylate marketed by Sigma-Aldrich. Trismethacrylate is used after purification on alumina guards and after bubbling with nitrogen. The methylcyclohexane (MCH) solvent from BioSolve is dried and purified on an alumina column in a solvent fountain from mBraun and used under an inert atmosphere. All reactions are carried out under an inert atmosphere. All polymerizations and coupling reactions are carried out in a 500 mL disposable glass vessel reactor (Schott flasks) equipped with a stainless steel stirring blade. Temperature control is ensured by a thermostatically controlled oil bath connected to a double polycarbonate jacket. This reactor has all the necessary inlets and outlets for manipulations. In a 500 mL glass reactor containing MCH, the co-catalyst is added, followed by the metallocene. The amount of metallocene introduced is 40 mg, the amount of active BOMAG is 154 umol. The activation time is 10 minutes, the reaction temperature is 80°C. The polymerization is carried out at 80°C and at an initial pressure of 4 bar absolute in the 500 mL glass reactor containing 300 mL of polymerization solvent, methylcyclohexane, the catalytic system. 1,3-butadiene and ethylene are in- produced in the form of a gaseous mixture containing 20 mol% of 1,3-butadiene. At the desired conversion, either after the consumption of approximately 10 g of polymer monomers, either procedure A is carried out for the synthesis of uncoupled control copolymer, or procedure B for the synthesis of coupled copolymers in accordance with the invention. Procedure A: Synthesis of uncoupled control copolymer (example 1) The polymerization reaction is stopped by adding an excess of ethanol relative to the number of moles of magnesium and neodymium. The copolymer is recovered by precipitation in methanol, then dried at 60°C under vacuum under a stream of nitrogen. Procedure B: synthesis of coupled copolymers in accordance with the invention (examples 2 to 5) The coupling agent is introduced under an inert atmosphere by overpressure according to a molar content indicated in Table 1 and expressed in relation to the number of carbon-magnesium bonds per mole of co-catalyst of the catalytic system, active BOMAG (Coupling agent / C-Mg molar ratio). The reaction medium is stirred for 60 minutes at 80°C, then degassed and cooled. After degassing the reactor and cooling, ethanol is introduced into the reaction medium, in excess of the number of moles of magnesium and neodymium. The reaction medium is then precipitated in methanol, and the recovered polymer is dried at 60°C under vacuum under a stream of nitrogen until constant mass. It is then analyzed by SEC (THF) and NMR. The copolymerization reaction and coupling reaction conditions specific to each example, as well as the characteristics of the synthesized copolymers, are shown in Table | and Table 2. The 3D SEC method was used to determine the number- and mass-average molar masses, and the microstructure of the polymers was determined by NMR. The ethylene unit ratio, the 1,3-butadiene unit ratio in the 1,2 configuration (1,2 unit), in the 1,4 configuration (1,4 unit), and the 1,2-cyclohexane unit ratio (cycle unit) are expressed as a molar percentage relative to all the monomer units of the copolymer. 3D SEC analysis allows the determination of intrinsic viscosity values ​​at each number-average molar mass across the entire polymer distribution. From the Mark-Houvink-Sakurada relationship linking intrinsic viscosity to number-average molar mass according to the equation In(visco) = In(K) + aln(Mn), the coefficient œ can be calculated for a polymer population of average molar mass. It is known to those skilled in the art that the architecture of a polymer is related to the coefficient of. If this coefficient decreases, then this indicates that the viscosity of the polymer changes little as a function of its molar mass and that the polymer is architectural, i.e. star-shaped. The results are shown in Table 3. [Tables 1] Unit 1.4 (mol%) Example |Mass Ratio of |Time of [Unit |Molar Unit |Polymer |Polymeris |Ethylene|1.2 Drying Agent (% (% Coupling / |(g) (h) Mole) |Mole) C-Mg 03 11 2.1 77.3 4.3 4 1 9 43 76.4 5.2 [5 f. I 33 5.0 1 0 qr 13 78.7 |34 Ja 2 0.1 Il 33 783 |36 |s5 3 03 4 = 73 |as |51 4 1 9 ja 764 |s2 |6.1 FERRÉ EEE [Tables2] Example [Mn Mw There visco Tg / delta T Crystallinity | e (gmol) |(gmol) dL / g CC) (%) E 46300 |56100 [12 0.79 -31 / 6 = 2 [132300 [225000 |1.7 2.00 -31 / 7 2.6 3 81800 |111900 |14 145 -23 474 [143500 [292200 |20 2.09 -32 / 7 L7 [5 j14600 [283000 [19 | |is3 [327 jus [Tables3] [Example Coefficient Polymer population [Proportion of polymers | of architecture |(g / mol) coupled 1 0.62 32,000 - 77,000 2 0.64 90,000 - 208,000 62% 8 e |Polymer Population Coefficient |Architecture Proportion |(g / mol) coupled 0.62 32000-77000 0.64 90000-20800 [62% 0.49 213 000 - 539 000 38% 0.68 55 000 - 101 000 50% 0.53 103 000 - 266 000 50% The viscosity values ​​measured using an Ostwald viscometer and reported in Table 2 show that the polymers synthesized according to procedure B (reaction with the coupling agent trismethacrylate) have a higher viscosity than their uncoupled control (Example 1) and indicate that the reaction with the coupling agent leads to the formation of coupled polymers. The increase in the masses The average molar masses in number and mass reported in Table 2 confirm the formation of coupled chains, notably 2- and 3-branched, since the average molar masses increased by a factor of approximately 2 to 3. The observed viscosity increases reflect a change in the rheological properties of the polymer compared to its control, the uncoupled polymer. The coupled polymer has a lower propensity to flow. The results in Table 3, which result from the exploitation of the Mark-Houvink-Sakurada relationship, show that the reaction with the trismethacrylate coupling agent leads to a mixture containing 2-arm coupled polymers (having architecture coefficients greater than 0.6) and 3-arm coupled polymers (star polymers having architecture coefficients less than 0.6). It is also noted that a molar ratio between the number of methacrylate functions and the number of moles of magnesium close to 1, i.e. a molar ratio between the number of moles of the trismethacrylate coupling agent and the number of carbon-magnesium bonds per mole of co-catalyst equal to 0.3, is more favorable for obtaining a coupled polymer having 3 branches (star polymer). Finally, as reported in Table 2, the results of the DSC analysis indicate that each of the copolymers has a single Tg, as well as a relatively low delta T value, since it is 6°C or 7°C. All of these data demonstrate the production of statistical elastomers.

Claims

Claims

1. Copolymer of a 1,3-diene and an olefin, the olefin being ethylene or a mixture of ethylene and a &-monoolefin, which copolymer contains more than 50 mol% of ethylene unit and is a copolymer coupled, the chains of the copolymer being linked together by a group containing at least two Formula 1 motifs —(CH,-CH(CH)-CO-O)- formula 1, each copolymer chain being linked to a distinct unit of formula 1 by through a covalent bond between a carbon atom of a monomer unit of the copolymer chain and the carbon atom of the methylene group of the formula 1 motif.

2. A copolymer according to claim 1, which copolymer is a co- 2-branch or 3-branch coupled polymer.

3. A copolymer according to claim 1 or 2, which copolymer meets formula 2 [P-CH,-CH(CH,)-CO-01]--Z, formula 2 P denoting a copolymer chain, Z. representing a divalent hydrocarbon group or a divalent group hydrocarbon which contains one or more functions chosen from the ether function and the thioether function, the divalent group being able to be substituted by one or more methacrylate functions of formula CH, =C(CH,)CO-O-

4. A copolymer according to claim 1 or 2, which copolymer meets formula 3 [P-CH,-CH(CH:)-CO-01];-Z; formula 3 P denoting a copolymer chain, Z- representing a trivalent hydrocarbon group or a trivalent group hydrocarbon which contains one or more functions chosen from the ether function and the thioether function.

5. Copolymer according to claim 3 or 4 in which Z, is an al- canediyl or an alkanediyl substituted by a methacrylate function, Z; is an alkanetriyl.

6. A copolymer according to any one of claims 1 to 5, which co- polymer is a copolymer of ethylene and a 1,3-diene.

7. A copolymer according to any one of claims 1 to 6, which co- polymer is a random copolymer.

8. A copolymer according to any one of claims 1 to 7 wherein 1,3-diene is 1,3-butadiene, isoprene, myrcene, 3-farnesene or their mixtures.

9. A copolymer according to any one of claims 1 to 8, which co- polymer contains 1,3-butadiene units and motifs 1,2-cyclohexane of formula (I). Cha CH5 # X exe! ​​po {4 ox-cn ; ;

10. A copolymer according to any one of claims 1 to 9, which co- polymer is an elastomer.

11. | Process for preparing a coupled copolymer of a 1,3-diene and a olefin, the copolymer containing more than 50 mol% of ethylene unit, which method comprises the successive steps a), b) and c), - step a) being the polymerization of a monomer mixture containing a 1,3-diene and an olefin in the presence of a catalytic system based on at least one metallocene of formula (Ia) and one organomagnesium, co-catalyst, {P(Cp'(Cp*)Nd(BH;)a+yy-Ly-N,} (a) Cp! and Cp”, identical or different, being chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted, Being a group bridging the two groups Cp! and Cp?, and including 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, whole number or not, being equal to or greater than 0, y, integer, being equal to or greater than 0, the olefin being ethylene or a mixture of ethylene and an a- monoolefin, - step b) being the reaction of a coupling agent, compound containing at least two methacrylate functions of formula CH,=C(CH)CO-O- with the reaction product of the polymerization of step a), - step c) being a chain termination reaction.

12. A method according to claim 11 wherein the coupling agent is a bismethacrylate or trismethacrylate.

13. A method according to claim 11 or 12 wherein the coupling agent is formula 3 or formula 4 [CH,=C(CH,)-CO-O1],-Z; formula 3 [CH,=C(CH,)-CO-O];- Z4 formula 4 Za representing a divalent hydrocarbon group or a divalent group hydrocarbon substituted by one or more functions chosen from the ether function and the thioether function, Za representing a trivalent hydrocarbon group or a trivalent group hydrocarbon substituted by one or more functions chosen from the ether function and the thioether function.

14. A method according to any one of claims 11 to 13 wherein step b) is carried out in an aliphatic hydrocarbon solvent.

15. A polymer composition which contains a 2-branch copolymer and a 3-branch copolymer, which copolymers are defined at one any of claims | to 10 or obtainable by a method defined in any one of claims 11 to 14.