Vinylidene functionalization at the chain end of polyethylenes and copolymers containing ethylene units and units of a 1,3-diene.

Abstract

The present invention relates to a process for preparing a polymer containing ethylene units and bearing at the end of the chain a 1-arylethenyl group, which process comprises the polymerization of a monomer selected from ethylene and a monomer mixture containing ethylene and a 1,3-diene in the presence of a catalytic system and a 1-methyl-1-arylethene, the catalytic system being based on a neodymocene borohydride and an organomagnesium compound.

Description

Title of the invention: Vinylidene functionalization at the chain end of polyethylenes and copolymers containing ethylene units and units of a 1,3-diene.

[0001] The field of the present invention is that of end-chain functionalization processes of polyethylenes and copolymers containing ethylene units and units of a 1,3-diene.

[0002] The synthesis of polyethylenes and copolymers containing ethylene units and units of a 1,3-diene is widely described starting from the polymerization of ethylene or a mixture containing ethylene and a 1,3-diene. As described, for example, in documents EP 1 092 731, WO 2004035639, WO 2007054224, and WO 2018224776, the polymerization is carried out in the presence of a catalytic system based on a neodymocene and an organomagnesium compound. Modification of the chain end of these polymers to introduce a functional group is also known. For example, patent applications WO2016092237 and WO2013135314 describe the introduction of an amine, ether or vinyl function at their chain end using organomagnesium compounds bearing an amine, ether or vinyl function as a co-catalyst.In the patent applications, it has also been proposed to functionalize the chain end of these polymers by introducing a functionalizing agent such as an alkoxysilane, a nitrile, or a methacrylate at the end of the polymerization reaction.

[0003] The inventors have discovered a new process which makes it possible to introduce a vinylidene structure group at the end of the chain of these polymers by adding a 1-methyl-l-arylethene in the polymerization medium.

[0004] An object of the invention is a process for preparing a polymer containing ethylene units and bearing at the end of the chain an 1-arylethenyl group, which process comprises the polymerization of a monomer selected from ethylene and a monomer mixture containing ethylene and a 1,3-diene in the presence of a catalytic system and a 1-methyl-1-arylethenene, the catalytic system being based on a metallocene of formula (I) and a co-catalyst, an organomagnesium, P(Cp1Cp2)Nd(BH4)(1+y>Ly-Nx (I) Cp1 and Cp2, identical or different, being chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted, Pending a group bridging the two groups Cp1 and Cp2, and comprising a silicon or carbon atom, L represents an alkali metal chosen from the group consisting of lithium, sodium, and potassium, N representing a molecule of an ether, x, an integer or not, being equal to or greater than 0, y, an integer, being equal to or greater than 0.

[0005] Another object of the invention is a polymer containing ethylene units and bearing at the end of the chain an 1-arylethenyl group. Detailed description

[0006] 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., bounds a and b excluded) 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 bounds a and b).

[0007] Unless otherwise indicated, the rates of units resulting from the insertion of a monomer into a polymer are expressed as a molar percentage relative to the total units resulting from the polymerization of the monomers.

[0008] The compounds mentioned in the description may be of fossil origin or bio-based. In the latter case, they may be partially or totally derived from biomass or obtained from renewable raw materials derived from biomass. Similarly, the compounds mentioned may also come from the recycling of materials already used, that is to say, they may be partially or totally derived from a recycling process, or obtained from raw materials themselves derived from a recycling process.

[0009] 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.

[0010] In the present application, the term metallocene means an organometallic complex in which the metal, in this case the neodymium atom, is linked to a molecule called a ligand and consisting of two groups Cp1 and Cp2 linked together by a P-bridge. These groups Cp1 and Cp2, 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.

[0011] According to the invention, the metallocene used as a basic constituent in the catalytic system corresponds to the formula (I) {P(Cp1)(Cp2)Nd(BH4)(1+y>Ly-Nx} (I) Pending a group bridging the two groups Cp1 and Cp2, and comprising a silicon or carbon atom, Cp1 and Cp2, 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 represents an alkali metal chosen from the group consisting of lithium, sodium, and potassium, N representing a molecule of an ether, x, an integer or not, being equal to or greater than 0, y, an integer, being equal to or greater than 0.

[0012] In formula (I), the neodymium atom is bonded to a ligand molecule consisting of two groups Cp1 and Cp2 linked by a bridge P. Preferably, the symbol P, designated as the bridge, has the formula ZR'R2, where Z represents a silicon or carbon atom, and R1 and R2, which may be identical or different, represent an alkyl group comprising from 1 to 20 carbon atoms. More preferably, the bridge P has the formula SiR*R2, where R1 and R2 are identical and as defined above. Even more preferably, P has the formula SiMe2.

[0013] In formula (I), any ether that has the ability to complex the alkali metal is suitable, in particular diethyl ether, methyltetrahydrofuran, and tetrahydrofuran, preferably tetrahydrofuran. In formula (I), y can be equal to 0 or 1 and x can be equal to 0, 1, or 2.

[0014] Examples of substituted cyclopentadienyl, fluorenyl, and indenyl groups include those substituted with alkyl groups having 1 to 6 carbon atoms, aryl groups having 6 to 12 carbon atoms, or trialkylsilyl groups such as SiMe3. When the Cp1 and Cp2 ligands are substituted, they are preferentially substituted with methyl groups, butyl groups (particularly tert-butyl groups), or trimethylsilyl groups. The choice of groups is also guided by the availability of the corresponding molecules, namely the substituted cyclopentadienes, fluorenyls, and indenes, because these are either commercially available or easily synthesized.

[0015] Examples of substituted fluorenyl groups include those substituted at positions 2, 7, 3, or 6, particularly 2,7-ditertiobutyl-fluorenyl and 3,6-ditertiobutyl-fluorenyl. Positions 2, 3, 6, and 7 respectively designate the positions of the carbon atoms in the rings, as shown in the diagram below, with position 9 corresponding to the carbon atom to which the P-bridge is attached. P

[0016] Examples of substituted cyclopentadienyl groups include those substituted at position 2 (or 5) as well as at position 3 (or 4), particularly those substituted at position 2, more specifically the tetramethylcyclopentadienyl group. Position 2 (or 5) refers to the position of the carbon atom adjacent to the carbon atom to which the P-bridge is attached, as shown in the diagram below. It should be noted that a substitution at position 2 or 5 is also referred to as an alpha-bridge substitution.

[0017] As examples of substituted indenyl groups, those substituted at position 2 may be mentioned in particular, more specifically 2-methylindenyl and 2-phenylindenyl. Position 2 designates 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.

[0018] Preferably, Cp1 and Cp2, whether identical or different, are alpha-substituted cyclopentadienyls, substituted fluorenyls, substituted indenyls, or fluorenyls of formula C[3H8], or indenyls of formula C9H6. More preferably, Cp1 and Cp2, whether identical or different, are substituted fluorenyl groups or unsubstituted fluorenyl groups of formula Ci3H8. Advantageously, Cp1 and Cp2 are unsubstituted fluorenyl groups of formula Ci3H8, represented by the symbol Flu.

[0019] Better, the metallocene has the formula (1-1), (1-2), (1-3), (1-4) or (1-5): [Me2SiFlu2Nd(p-BH4)2Li(THF)] (I-1) [{Me2SiFlu2Nd(p-BH4)2Li(THF)}2] (1-2) [Me2SiFlu2Nd(p-BH4)(THF)] (1-3) [{Me2SiFlu2Nd(p-BH4)(THF)}2] (1-4) [Me2SiFlu2Nd(p-BH4)] (1-5) in which Flu represents the Ci3H8 group.

[0020] The metallocene useful for the synthesis of the catalytic system can be found under the Metallocene can be in the form of a crystalline or non-crystalline powder, or even as single crystals. It can be monomeric or dimeric, depending on the method of preparation, as described in patent applications WO 2007054224 A2 or WO 2007054223 A2. Metallocene can be prepared conventionally by a process similar to that described in patent applications WO 2007054224 A2 or WO 2007054223 A2, specifically by reacting, under inert and anhydrous conditions, the salt of an alkali metal ligand with a rare-earth borohydride, neodymium, in a suitable solvent, such as an ether like diethyl ether or tetrahydrofuran, or any other solvent known to those skilled in the art. After the reaction, the metallocene is separated from the reaction byproducts using techniques known to those skilled in the art, such as filtration or precipitation in a second solvent. The metallocene is then dried and isolated in solid form.

[0021] The organomagnesium compound, another basic constituent of the catalytic system, is the co catalyst of the catalytic system. Typically, the organomagnesium compound can be a diorganomagnesium compound or a halide of an organomagnesium compound. The organomagnesium compound can have the formula (Ia), (Ilb), (Ile), or (Ild), in which R3, R4, R5, and RB, whether identical or different, represent a carbon group, RA represents a divalent carbon group, X is a halogen atom, and m is a number greater than or equal to 1, preferably equal to to 1. MgR3R4 (lia) XMgR5 (Ilb) RB-(Mg-RA)m-Mg-RB (Ile) X-Mg-RA-Mg-X (Ild).

[0022] Ra can be an aliphatic hydrocarbon divalent chain, interrupted or not by one or more oxygen or sulfur atoms or one or more arylene groups.

[0023] A carbon group is understood to be a group that contains one or more atoms of carbon. The carbon group can be a hydrocarbon group (hydrocarbyl group) or a heterohydrocarbon group, that is, a group containing plus carbon and hydrogen atoms and one or more heteroatoms. As organomagnesium compounds with a heterohydrocarbon group, the compounds described as transfer agents in patent application WO2016092227 Al may be suitable. The carbon groups represented by the symbols R3, R4, R5, RB, and Ra are preferably hydrocarbon groups.

[0024] Preferably, RA contains 3 to 10 carbon atoms, in particular 3 to 8 carbon atoms.

[0025] 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. Most advantageously, RA is a linear alkanediyl. 1,3-propanediyl, 1,4-butanediyl, 1,5-pentanediyl, 1,6-hexanediyl, 1,7-heptanediyl, and 1,8-octanediyl are particularly suitable RA groups.

[0026] The carbon groups represented by R3, R4, 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 from 1 to 20 carbon atoms. The alkyl groups represented by the symbols R3, R4, R5, RB may be linear or branched. They are preferably linear according to any one of the embodiments of the invention.

[0027] The alkyls represented R3, R4, R5, RB can contain 2 to 10 carbon atoms and include ethyl, butyl, octyl.

[0028] The aryls represented R3, R4, R5, RB can contain 7 to 20 carbon atoms and are in particular a phenyl substituted by one or more alkyls such as methyl, ethyl, isopropyl.

[0029] According to a particular embodiment of the invention, R3 comprises a benzene ring substituted by a magnesium atom, one of the carbon atoms of the benzene ring ortho to the magnesium being substituted by a methyl, ethyl, or isopropyl group, or forming a ring with its nearest neighbor carbon atom meta to the magnesium, the other carbon atom of the benzene ring ortho to the magnesium being substituted by a methyl, ethyl, or isopropyl group, and R4 is an alkyl group. In other words, the aforementioned methyl, ethyl, and isopropyl substituents of the benzene ring are in an ortho position with respect to the magnesium atom according to this particular embodiment. R3 can be 1,3-dimethylphenyl, 1,3- diethylphenyl, mesityl, or 1,3,5-triethylphenyl and R4 can be ethyl, butyl, octyl.

[0030] According to another particular embodiment of the invention, R3 and R4 are alkyls containing 2 to 10 carbon atoms, in particular ethyl, butyl, octyl.

[0031] R5 is preferably an alkyl containing 2 to 10 carbon atoms, more preferably an ethyl, a propyl, a butyl, a pentyl, a hexyl, a heptyl or an octyl.

[0032] Rb may comprise a benzene ring substituted by a magnesium atom, one of the carbon atoms of the benzene ring ortho to magnesium being substituted by a methyl, ethyl, or isopropyl group, or forming a ring with its nearest neighbor carbon atom meta to magnesium, the other carbon atom of the benzene ring ortho to magnesium being substituted by a methyl, ethyl, or isopropyl group. RB may be 1,3-dimethylphenyl, 1,3-diethylphenyl, mesityl, or 1,3,5-triethylphenyl.

[0033] For example, suitable organomagnesium compounds include butylethylmagnesium, butylloctylmagnesium, ethylmagnesium chloride, butylmagnesium chloride, pentylmagnesium chloride, ethylmagnesium bromide, butylmagnesium bromide, pentylmagnesium bromide, octylmagnesium chloride, octylmagnesium bromide, 2,6-dimethylphenylbutylmagnesium, 2,6-diethylphenylethylmagnesium, butylmesitylmagnesium, ethylmesitylmagnesium, 2,6-diethylphenylbutylmagnesium, 2,6-diethylphenylethylmagnesium, 2,6-diisopropylphenylbutylmagnesium, 2,6-diisopropylphenylethylmagnesium, 2,4,6-triethylphenylbutylmagnesium, 2,4,6-triethylphenylethylmagnesium, 2,4,6-triisopropylphenylbutylmagnesium, 2,4,6-triisopropylphenylethylmagnesium, l,3-di(magnesium bromide)-propanediyl, l,3-di(magnesium chloride)-propanediyl, l,5-di(magnesium bromide)-pentanediyl, l,5-di(magnesium chloride)-pentanediyl, l,8-Di(magnesium bromide)-octanediyl, 1,8-di(magnesium chloride)-octanediyl.

[0034] The organomagnesium compound of formula (Ile) can be prepared by a process comprising the reaction of a first organomagnesium compound of formula X'Mg-RA-MgX' with a second organomagnesium compound of formula RB-Mg-X', where X' represents a halogen atom, preferably bromine or chlorine, and RB and RA are as defined previously. X' is more preferably a bromine atom. The stoichiometry used in the reaction determines the value of m in formula (Ile). 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 to the formation of an organomagnesium compound of formula (Ile) in which m is equal to 1, whereas a molar ratio greater than 0.5 will be more favorable to the formation of an organomagnesium compound of formula (Ile) in which m is greater than 1.

[0035] 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 and second organomagnesium compounds are generally solutions in an ether, such as diethyl ether, dibutyl ether, tetrahydrofuran, methyltetrahydrofuran, or a mixture of two or more of these ethers. A hydrocarbon, aliphatic, or aromatic solvent may be added to the ether as a co-solvent. Preferably, the respective concentrations of the solutions of the first and second organomagnesium compounds are 0.01 to 3 mol / L and 0.02 to 5 mol / L, respectively. More preferably, the respective concentrations of the first organomagnesium and the second organomagnesium are respectively 0.1 to 2 mol / L and 0.2 to 4 mol / L.

[0036] The first organomagnesium reagent and the second organomagnesium reagent, Grignard reagents, can be prepared beforehand from magnesium metal and a suitable halogenated precursor in a reactor. For the first and second organomagnesium reagents, the respective precursors have the formulas X'-RA-X' and RB-X', RA, Rb, and X' being as defined previously. The preparation of the Grignard reagents is typically carried out by adding the precursor to magnesium metal, which is generally in the form of chips. Preferably, iodine (I2), 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.

[0037] Alternatively, the organomagnesium compound of formula (Ile) can be prepared by reacting an organometallic compound of formula M-RA-M and the organomagnesium compound of formula RB-Mg-X', where M represents a lithium, sodium, or potassium atom, and X', RB, and RA are as defined previously. Preferably, M represents a lithium atom, in which case the organometallic compound of formula M-RA-M is an organolithium compound.

[0038] The reaction of the organolithium compound and the organomagnesium compound 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. Contacting is preferably carried out at a temperature between 0°C and 23°C. Contacting the organometallic compound of formula M-RA-M with the organomagnesium compound of formula RB-Mg-X' is preferably achieved by adding a solution of the organometallic compound M-RA-M to a solution of the organomagnesium compound. RB-Mg-X'. The solution of the organometallic compound M-RA-M is generally a solution in a hydrocarbon solvent, preferably hexane, cyclohexane, or methylcyclohexane; the solution of the organomagnesium compound 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-RA-M and RB-Mg-X' are 0.01 to 1 mol / L and 0.02 to 5 mol / L, respectively. More preferably, the respective concentrations of the solutions of the organometallic compound and the organomagnesium compound M-RA-M and RB-Mg-X' are 0.05 to 0.5 mol / L and 0.2 to 3 mol / L, respectively.

[0039] As with any synthesis carried out in the presence of organometallic compounds, the syntheses described for the synthesis of organomagnesium compounds take place under anhydrous conditions in an inert atmosphere, in stirred reactors. Typically, solvents and solutions are used under anhydrous nitrogen or argon.

[0040] Once the organomagnesium compound of formula (Ile) is formed, it is generally recovered in solution after filtration conducted under an inert and anhydrous atmosphere. It can be stored in solution in airtight containers, for example capped bottles, at a temperature between -25°C and 23°C before use.

[0041] Compounds of formula (Ild), which are Grignard reagents, are described, for example, in J. Mardi's "Advanced Organic Chemistry," 4th Edition, 1992, pages 622-623, or in the "Handbook of Grignard Reagents," edited by Gary S. Silverman and Philip E. Rakita, 1996, pages 502-503. They can be synthesized by contacting magnesium metal with a dihalogenated compound of formula X-Ra-X, Ra being as defined according to the invention. For their synthesis, reference may be made, for example, to the "Organic Synthesis" series of volumes.

[0042] The compounds of formula (lia) and (Ilb), which are also Grignard reagents, are well known; some of them are even commercial products. For their synthesis, one can, for example, refer to the collection of volumes of "Organic Synthesis".

[0043] Like any organomagnesium compound, the organomagnesium compound constituting the catalytic system, in particular of formula (Ha), (Ilb), (Ile) or (Ild) can be in the form of a monomeric entity or in the form of a polymer entity. By way of illustration, the organomagnesium (Ile) can be in the form of a monomeric entity (RB-(Mg-RA)m-Mg-RB)i or in the form of a polymer entity (RB-(Mg-RA)m-Mg-RB)p, p being an integer greater than 1, in particular a dimer (RB-(Mg-RA)m-Mg-RB)2, m being as defined above. Similarly, also by way of illustration, the organomagnesium compound with formula (Ild) can exist as a monomeric entity (X-Mg-RA-Mg-X)i or as a polymer entity (X- Mg-RA-Mg-X)p, where p is an integer greater than 1, in particular the dimer (X-Mg-RA-Mg-X)2.

[0044] Furthermore, whether in the form of a monomeric or polymeric entity, the organomagnesium can also be in the form of an entity coordinated by one or more molecules of a solvent, preferably an ether such as diethyl ether, tetrahydrofuran or methyltetrahydrofuran.

[0045] In formulas (Ilb) and (Ild), X is preferably a bromine or chlorine atom.

[0046] According to one embodiment of the invention, the organomagnesium compound is an organomagnesium halide, preferably of formula (Ilb) or (Ild), more preferably of formula (Ilb), even more preferably of formula (Ilb) XMgR5, in which X is a chlorine or bromine atom, R5 an alkyl or aryl group, preferably an alkyl group. According to this most preferred embodiment, R5 is advantageously an alkyl group containing 2 to 10 carbon atoms, more preferably an ethyl, propyl, butyl, pentyl, hexyl, heptyl, or octyl group.

[0047] Advantageously, the organomagnesium is a dialkylmagnesium of formula MgR3R4 in which R3 and R4 are alkyls containing 2 to 10 carbon atoms, in particular ethyl, butyl, octyl, preferably R3 is butyl and R4 is octyl.

[0048] The quantities of co-catalyst and metallocene involved in the reaction 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 element in the metallocene, neodymium, preferably ranges from 0.5 to 200, and more preferably from 1 to less than 20. These preferred ranges can be applied to any of the embodiments of the invention. The range of values ​​from 1 to less than 20 is particularly favorable for obtaining polymers with high molar masses.

[0049] According to one embodiment, the catalytic system can be prepared conventionally by a process analogous to that described in patent applications WO 2007054224 A2 or WO 2007054223 A2. For example, the co-catalyst, in this case the organomagnesium compound, and the metallocene are typically reacted in a hydrocarbon solvent at a temperature ranging from 20°C to 80°C for a duration of between 1 and 60 minutes. The catalytic system is generally prepared in a hydrocarbon solvent, either aliphatic such as methylcyclohexane or aromatic such as toluene.

[0050] According to another embodiment, the catalytic system can be prepared by a process analogous to that described in patent application WO 2017093654 Al or in patent application WO 2018020122 Al: it is said to be of the preformed type. For example, an organomagnesium compound and a metallocene are typically reacted in a hydrocarbon solvent at a temperature of 20°C to 80°C for 10 to 20 minutes to obtain a first reaction product. This first reaction product is then reacted with a preforming monomer at a temperature of 40°C to 90°C for 1 to 12 hours. The preforming monomer is preferably used in a molar ratio (preforming monomer / metallocene metal) of 5 to 1000, preferably 10 to 500. Before its use in polymerization, the preformed catalytic system can be stored under an inert atmosphere, particularly at a temperature ranging from -20°C to room temperature (23°C). According to this second embodiment, the preformed catalytic system has as its basic constituent a preforming monomer selected from among 1,3-dienes, ethylene, and mixtures thereof.In other words, the so-called preformed catalytic system contains, in addition to the metallocene and the co-catalyst, a preforming monomer. The 1,3-diene as the preforming monomer can be 1,3-butadiene, isoprene, or a 1,3-diene with the formula CH2=CR6-CH=CH2, the symbol R6 representing a hydrocarbon group having 3 to 20 carbon atoms, in particular myrcene or 3-farnesene. The preforming monomer is preferably 1,3-butadiene.

[0051] 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 in a range preferably from 0.0001 to 0.2 mol / L more preferably from 0.001 to 0.03 mol / L.

[0052] As with any synthesis carried out in the presence of an organometallic compound, the synthesis of the metallocene, the synthesis of the organomagnesium compound, and the synthesis of the catalytic system take place under anhydrous conditions in an inert atmosphere. Typically, the reactions are conducted using solvents and anhydrous compounds in anhydrous nitrogen or argon.

[0053] According to one embodiment of the invention, the monomer is ethylene and the polymerization reaction product is a polymer whose constituent units result from the insertion of ethylene. In other words, the polymer chains formed are polyethylene chains.

[0054] According to another embodiment of the invention, the monomer is a monomer mixture containing ethylene and a 1,3-diene, and the polymerization reaction product is a polymer comprising ethylene units and 1,3-diene units. According to a first variant of this embodiment, the monomer mixture containing ethylene and a 1,3-diene is a mixture of ethylene and a 1,3-diene, and the polymerization reaction product is a polymer whose constituent units result from the insertion of ethylene and 1,3-diene. In other words, the chains The polymers formed are copolymer chains of ethylene and 1,3-diene. According to a second variant of this polymerization method, the monomer mixture containing ethylene and 1,3-diene is a mixture of ethylene, 1,3-diene, and a vinylaromatic compound of formula Ar'CH=CH2, where Ar' denotes an aryl group, and the vinylaromatic compound of formula Ar'CH=CH2 is preferably styrene. According to this alternative, the polymerization reaction product is a polymer whose constituent units result from the insertion of ethylene, 1,3-diene, and the vinylaromatic compound. In other words, the polymer chains formed are copolymer chains of ethylene, 1,3-diene, and a vinylaromatic compound, preferably copolymer chains of ethylene, 1,3-diene, and styrene.

[0055] The monomer mixture containing ethylene and a 1,3-diene preferably contains more than 50 mole percent of ethylene, the percentage being expressed relative to the total number of moles of monomers in the monomer mixture. When the monomer mixture contains a vinylaromatic compound of formula Ar'CH=CH2 such as styrene, it preferably contains less than 40 mole percent, the percentage being expressed relative to the total number of moles of monomers in the monomer mixture.

[0056] By a 1,3-diene of the monomer mixture, we mean a single compound, that is to say, a single 1,3-diene, or a mixture of 1,3-dienes that differ from one another in their chemical structure. Suitable examples of 1,3-dienes are those having from 4 to 20 carbon atoms, such as 1,3-butadiene, isoprene, myrcene, 3-farnesene, and mixtures thereof. The 1,3-diene is preferably 1,3-butadiene, isoprene, myrcene, 3-famesene, or mixtures thereof, in particular a mixture of at least two of them. Advantageously, 1,3-diene refers to 1,3-butadiene or a mixture of 1,3-butadiene and another diene chosen from isoprene, myrcene, and 3-famesene. Better still, 1,3-diene refers to 1,3-butadiene.

[0057] The process can be a continuous process or a batch process. Polymerization is typically carried out in at least one polymerization reactor, for example in a single reactor or in several reactors, preferably in two or three reactors. Polymerization is preferably carried out in solution. The polymerization solvent is typically a hydrocarbon, aromatic, or aliphatic solvent, such as toluene, cyclohexane, methylcyclohexane, or a mixture of two or all three. The monomer, whether ethylene or a monomer mixture containing ethylene and a 1,3-diene, 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. The monomer and the Catalytic systems can be introduced simultaneously into the reactor containing the polymerization solvent, particularly in the case of continuous polymerization. A continuous addition of the monomer or one of the monomers of the monomer mixture can be carried out in the polymerization reactor, in which case the polymerization reactor is a fed reactor and the process is a continuous or semi-continuous process as described, for example, in patent applications WO2017 / 103543, WO2017 / 103544, WO2018 / 193194, and WO2018 / 193193. This embodiment is particularly suitable for the polymerization of a monomer mixture for statistical incorporation of the monomers. In the case of the polymerization of a monomer mixture, the polymerization is preferably a statistical polymerization, resulting in the statistical incorporation of the monomers of the monomer mixture.

[0058] Polymerization is typically carried out under anhydrous conditions and in the absence of oxygen, possibly in the presence of an inert gas. The polymerization temperature generally varies from 40°C to 150°C, preferably from 40°C to 120°C. Those skilled in the art adapt the polymerization conditions, such as the polymerization temperature, the concentration of each of the reactants, and the pressure in the reactor, according to the monomer being polymerized, the polymerization reactor, and the desired microstructure and macrostructure of the polymer chain.

[0059] Polymerization is preferably carried out at constant pressure in monomer form.

[0060] According to any one of the embodiments of the invention, 1-methyl-l-arylethene can be introduced into the polymerization reactor at any time. It can be introduced into the polymerization reactor before the monomer, at the same time as the monomer, or after the monomer, for example, during the polymerization reaction, at the beginning of the polymerization reaction, or at the end of the polymerization reaction. If it is introduced at the end of the polymerization reaction, it is introduced before the polymerization reaction is stopped, for example, by cooling the polymerization medium or by adding an alcohol, preferably an alcohol containing 1 to 3 carbon atoms, for example, ethanol or methanol.

[0061] The aryl group constituting 1-methyl-l-arylethene can be phenyl or a phenyl substituted by one or more alkyl groups, in particular methyl or ethyl.

[0062] 1-Methyl-l-arylethene of formula Me(Ar)-C=CH2, Ar denoting an aryl, is preferably 1-methyl-l-phenylethene of formula Me(Ph)C=CH2, also known as alpha-methylstyrene, in which case the functional group at the end of the polymer chain is CH2=C(Ph)-, Ph denoting a phenyl.

[0063] 1-Methyl-L-arylethene can be introduced into the polymerization reactor as a solution, i.e., diluted in a solvent, or neat (i.e., undiluted in a solvent), the solvent preferably being the polymerization solvent. The amount of 1-methyl-L-arylethene introduced into the polymerization reactor can vary considerably with respect to the number of moles of Nd and is adjusted by those skilled in the art according to the desired proportion of functional polymer chains formed in the polymerization medium. The higher the amount of 1-methyl-L-arylethene in the polymerization medium, the greater the proportion of functional polymer chains formed.When a person skilled in the art is seeking a rather low molar percentage of functional chains, they choose a ratio between the number of moles of 1-methyl-l-arylethene and the number of moles of Nd preferably less than or equal to 10, more preferably between 0.1 and 10, for example between 0.5 and 5 or between 1 and 5 or between 1 and 10 or between 5 and 10. When a person skilled in the art is seeking a rather high molar percentage of functional chains, they choose a ratio between the number of moles of 1-methyl-l-arylethene and the number of moles of Nd preferably greater than 10, more preferably between 50 and 500, for example between 100 and 500 or between 100 and 400.The ranges relating to the ratio between the number of moles of 1-methyl-l-arylethene and the number of moles of Nd, and cited as preferred or more preferred, including those mentioned by way of illustration of the cited ranges, may be applied to any of the described embodiments of the invention. Preferably, the ratio between the number of moles of 1-methyl-l-arylethene and the number of moles of Nd is greater than 0.1, preferably greater than 0.5, more preferably greater than 1. Preferably, the ratio between the number of moles of 1-methyl-l-arylethene and the number of moles of Nd is less than 500, preferably less than 400.

[0064] The process according to the invention leads to the preparation of a polymer which carries a functional group covalently attached to one of the ends of the polymer chain, the functional group comprising the CH2=C(Ar)- function, the symbol Ar designating an aryl, preferably a phenyl.

[0065] The functional polymer, another object of the invention, which can be prepared by the process according to the invention, is therefore a polymer bearing at its chain end the 1-arylethenyl function, a group with the formula CH2=C(Ar)-, the symbol Ar representing, in a known manner, an aryl group. The functional polymer is preferably a polyethylene bearing at its chain end the CH2=C(Ar)- function or a copolymer containing ethylene units and units of a 1,3-diene and bearing at its chain end the CH2=C(Ar)- function. The 1- arylethenyl, group of formula CH2=C(Ar)-, is preferentially the 1-phenylethenyl function, group of formula CH2=C(Ph)-, the symbol Ph representing the phenyl group.

[0066] According to a first variant of the functional polymer according to the invention, the polymer containing ethylene units is a polyethylene.

[0067] According to a second embodiment of the functional polymer according to the invention, the polymer containing ethylene units is a copolymer containing ethylene units and units of a 1,3-diene, preferably a copolymer of ethylene and a 1,3-diene or a copolymer of ethylene, a 1,3-diene and styrene. The 1,3-diene of the copolymer is preferably 1,3-butadiene, isoprene, myrcene, 3-farnesene or mixtures thereof, more preferably 1,3-butadiene.

[0068] The functional polymer containing ethylene units and units of a 1,3-diene preferentially contains more than 50% by mole of ethylene units, the percentage being expressed in relation to all the constituent units of the functional polymer.

[0069] According to a preferred embodiment of the invention, the functional polymer containing ethylene units and 1,3-diene units also contains 1,2-cyclohexane cyclic motifs. The 1,2-cyclohexane cyclic motifs have formula (IV). h2o—ch2 H2 < / \h2 Ch—CH

[0070] When the functional polymer contains 1,2-cyclohexane cyclic motifs, it is a functional polymer according to a particular embodiment of the invention in which the 1,3-diene is 1,3-butadiene or a mixture of 1,3-dienes, one of which is 1,3-butadiene, and in which the cyclic motifs result from a particular insertion of the ethylene and 1,3-butadiene monomers into the polymer chain, in addition to the conventional ethylene and 1,3-butadiene units, respectively -(CH2-CH2)-, -(CH2-CH=CH-CH2)-, and -(CH2-CH(CH=CH2))-. It is notably obtained by the process according to the invention in the embodiment in which the metallocene of the catalytic system has two fluorenyl groups, substituted or unsubstituted, as ligands. The mechanism for obtaining such a microstructure is described, for example, in Macromolecules 2009, 42, 3774-3779. When the functional polymer according to the invention contains 1,2-cyclohexane cyclic motifs, it contains... preferably at most 15% by mole, the percentage being expressed in relation to all the constituent units of the functional polymer.

[0071] According to any one of the embodiments of the invention, the functional polymer according to the invention and containing ethylene units and units of a 1,3-diene is preferably statistical.

[0072] The functional polymer according to the invention, whether polyethylene or a copolymer, can be used in compositions containing one or more ingredients or constituents other than the functional polymer according to the invention, for example additives traditionally used in polymer compositions such as antioxidants, plasticizers, pigments, fillers.

[0073] In summary, the invention can be implemented according to any one of embodiments 1 to 37:

[0074] Mode 1: A process for preparing a polymer containing ethylene units and bearing a 1-arylethenyl group at the chain end, which process comprises the polymerization of a monomer selected from ethylene and a monomer mixture containing ethylene and a 1,3-diene in the presence of a catalytic system and a 1-methyl-1-arylethenene, the catalytic system being based on a metallocene of formula (I) and a co-catalyst, an organomagnesium compound, P(Cp1Cp2)Nd(BH4)(1+y>Ly-Nx (I) Cp1 and Cp2, identical or different, being chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted, Pending a group bridging the two groups Cp1 and Cp2, and comprising a silicon or carbon atom, L represents an alkali metal chosen from the group consisting of lithium, sodium, and potassium, N representing a molecule of an ether, x, an integer or not, being equal to or greater than 0, y, an integer, being equal to or greater than 0.

[0075] Mode 2: Process according to mode 1 in which 1-methyl-l-arylethene is 1-methyl-1-phenylethene.

[0076] Mode 3: Method according to mode 1 or 2 in which the symbol P corresponds to the formula ZR'R2, Z representing a silicon or carbon atom, R1 and R2, identical or different, representing an alkyl group comprising from 1 to 20 carbon atoms.

[0077] Mode 4: Method according to any one of modes 1 to 3 in which P has the formula SiMe2.

[0078] Mode 5: A process according to any one of modes 1 to 4 in which Cp1 and Cp2, identical or different, are substituted fluorenyl groups or unsubstituted fluorenyl groups of formula C[3H8.

[0079] Mode 6: Process according to any one of modes 1 to 5 in which the metallocene has the formula (1-1), (1-2), (1-3), (1-4) or (1-5): [Me2SiFlu2Nd(p-BH4)2Li(THF)] (I-1) [{Me2SiFlu2Nd(p-BH4)2Li(THF)}2] (1-2) [Me2SiFlu2Nd(p-BH4)(THF)] (1-3) [{Me2SiFlu2Nd(p-BH4)(THF)}2] (1-4) [Me2SiFlu2Nd(p-BH4)] (1-5) in which Flu represents the Ci3H8 group.

[0080] Mode 7: Process according to any one of modes 1 to 6 in which the metallocene is of (1-1) or (1-2).

[0081] Mode 8: Process according to any one of modes 1 to 7 in which the organomagnesium compound is a dialkylmagnesium compound of formula MgR3R4 in which R3 and R4 are alkyls containing 2 to 10 carbon atoms.

[0082] Mode 9: Process according to mode 8 in which R3 is butyl and R4 is octyl.

[0083] Mode 10: A method according to any one of modes 1 to 9 in which the ratio The ratio between the number of moles of Mg in the co-catalyst and the number of moles of the rare earth metallocene, neodymium, ranges from 0.5 to 200.

[0084] Mode 11: A process according to any one of modes 1 to 10 in which the ratio between the number of moles of Mg of the co-catalyst and the number of moles of the rare earth of the metallocene, neodymium, ranges from 1 to less than 20.

[0085] Mode 12: A process according to any one of modes 1 to 11 in which the monomer mixture containing ethylene and a 1,3-diene is a mixture of ethylene and a 1,3-diene or a mixture of ethylene, a 1,3-diene and styrene.

[0086] Mode 13: A process according to any one of modes 1 to 12 in which the monomer mixture containing ethylene and a 1,3-diene contains more than 50 mole percent of ethylene.

[0087] Mode 14: A process according to any one of modes 1 to 13 in which the 1,3-diene is 1,3-butadiene, isoprene, myrcene, [3-famesene or mixtures thereof.

[0088] Mode 15: Process according to any one of modes 1 to 14 in which the 1,3-diene is 1,3-butadiene.

[0089] Mode 16: A process according to any one of modes 1 to 15, which process is a continuous process.

[0090] Mode 17: A process according to any one of modes 1 to 15, which process is a batch process.

[0091] Mode 18: A process according to any one of modes 1 to 17, in which the polymerization is carried out in a single reactor.

[0092] Mode 19: A process according to any one of modes 1 to 17, in which the polymerization is carried out in two or three reactors.

[0093] Mode 20: A process according to any one of modes 1 to 19, in which the polymerization is carried out in a hydrocarbon solvent.

[0094] Mode 21: Process according to any one of modes 1 to 20, in which the polymerization is carried out in toluene.

[0095] Mode 22: A process according to any one of modes 1 to 21, in which the polymerization is carried out in cyclohexane, methylcyclohexane or a mixture thereof.

[0096] Mode 23: A method according to any one of modes 1 to 22, wherein the ratio between the number of moles of 1-methyl-l-arylethene and the number of moles of Nd is less than or equal to 10.

[0097] Mode 24: A method according to any one of modes 1 to 23, wherein the ratio between the number of moles of 1-methyl-l-arylethene and the number of moles of Nd is between 0.1 and 10.

[0098] Mode 25: A process according to any one of modes 1 to 24, wherein the ratio between the number of moles of 1-methyl-l-arylethene and the number of moles of Nd is between 0.5 and 5.

[0099] Mode 26: A process according to any one of modes 1 to 25, wherein the ratio between the number of moles of 1-methyl-l-arylethene and the number of moles of Nd is between 1 and 5.

[0100] Mode 27: A process according to any one of modes 1 to 26, wherein the ratio between the number of moles of 1-methyl-l-arylethene and the number of moles of Nd is between 1 and 10.

[0101] Mode 28: A process according to any one of modes 1 to 27, wherein the ratio between the number of moles of 1-methyl-l-arylethene and the number of moles of Nd is between 5 and 10.

[0102] Mode 29: A process according to any one of modes 1 to 22, wherein the ratio between the number of moles of 1-methyl-l-arylethene and the number of moles of Nd is greater than 10.

[0103] Mode 30: A process according to mode 29, in which the ratio between the number of moles of 1-methyl-l-arylethene and the number of moles of Nd is between 50 and 500, for example between 100 and 500 or between 100 and 400.

[0104] Mode 31: Polymer containing ethylene units and bearing the 1-arylethenyl function at the end of the chain.

[0105] Mode 32: Polymer according to mode 31 in which the 1-arylethenyl function is the 1-phenylethenyl function.

[0106] Mode 33: Polymer according to mode 31 or 32, which polymer containing ethylene units is a copolymer of ethylene and a 1,3-diene or a copolymer of ethylene, a 1,3-diene and styrene.

[0107] Mode 34: Polymer according to mode 33 in which the 1,3-diene is 1,3-butadiene, isoprene, myrcene, [3-famesene or mixtures thereof.

[0108] Mode 35: Polymer according to mode 33 in which the 1,3-diene is 1,3-butadiene.

[0109] Mode 36: Polymer according to any one of modes 33 to 35, which polymer is a statistical copolymer.

[0110] Mode 37: Polymer according to mode 31 or 32, which polymer containing ethylene units is a polyethylene.

[0111] The aforementioned features of the present invention, as well as others, will be better understood upon reading the following description of several examples of embodiments of the invention, given by way of illustration. Examples

[0112] Nuclear magnetic resonance (NMR): The prepared polymers were characterized by ¹H NMR spectroscopy. NMR spectra were recorded on a Brüker Avance III 500 MHz spectrometer equipped with a 5 mm BBFOz-grad "broadband" cryo-probe. The quantitative ¹H NMR experiment used a single 30° pulse sequence with a 5-second repetition delay between acquisitions. 64 to 256 accumulations were performed. The ¹H chemical shift axis was calibrated with respect to the protonated solvent impurity (CDC13) at δm = 7.20 ppm.

[0113] Size exclusion chromatography (SEC RI) analysis: Size exclusion chromatography (SEC) allows the fractionation of polymer chains in a solvent according to their hydrodynamic volume. Like any chromatographic system, the technique is based on the elution of a solute (the polymer) through a column containing a stationary phase. The system consists, in this order, of a solvent reservoir, a pumping system, an injector, a set of columns, and detectors. The measurement chain is equipped with a Waters Alliance e2695 module and a Waters fRI410 refractometer. The mobile phase is eluted at a flow rate of 1 mL / min. The polymer is solubilized in THF at a concentration of 1 g / L, then stirred for a minimum of 2 h and filtered through a 0.45 µm filter. A volume of 100 pL is injected through a set of three AGELENT (MIXED B LS) size-exclusion chromatography columns. The columns are temperature-controlled in an oven at 35°C. The stationary phase of the columns The analysis is based on a polystyrene gel with controlled porosity. The polymer chains are separated according to the hydrodynamic volume they occupy when dissolved in the solvent. The larger the volume, the less accessible the column pores are to them, and the shorter their elution time. Detection is performed using a refractometer (RI) thermostated at 35°C. Each elution volume is associated with a mass via Moore calibration (using certified standards: standard polystyrenes from the Polymer Standard Service (Mainz)). The WATERS: EMPOWER software is used for data acquisition and analysis. It is then possible to determine the number-average molar masses (Mn), the mass-average molar masses (Mw), and the dispersity (D = / Ma).

[0114] Syntheses of an ethylene and 1,3-butadiene copolymer according to the invention: Metallocene [{Me2SiFlu2Nd(p-BH4)2Li(THF)}]2 is prepared according to the procedure described in patent application WO 2007054224. BOMAG butyl methylmagnesium (20% in heptane, at 0.88 mol L1) comes from Chemtura and is stored in a Schlenk tube under an inert atmosphere. The ethylene, of N35 grade, comes from the company Air Liquide and is used without prior purification. 1,3-Butadiene is purified over alumina guards. Alpha-methylstyrene (AMS) from Sigma Aldrich is pre-purified on alumina. The methylcyclohexane (MCH) solvent from Total is dried and purified on an alumina column in a solvent fountain from mBraun and used under an inert atmosphere.

[0115] The polymerization reaction is carried out under an inert atmosphere in a 500 mL glass reactor equipped with a stirring paddle. 300 mL of previously degassed MCH, alpha-methylstyrene, and a 0.662 mol / L BOMAG solution in MCH are successively introduced into the reactor, with the ratio of the number of moles of BOMAG to the number of Nd atoms in the catalytic system being 2.8. The reactor is heated to 80°C, and the initial reactor pressure is 4 bar. The monomers, ethylene and 1,3-butadiene, are then introduced into the reactor as a gaseous mixture containing 20 mol% 1,3-butadiene. The catalytic system is injected into the reaction medium.

[0116] For each of the syntheses (tests 1 to 3), the polymerization conditions are shown in Table 1.

[0117] At a given polymerization time, the reaction mixture is transferred to a container containing 2 to 3 mL of ethanol. The copolymer is then antioxidantized and subsequently dried in a vacuum oven under a stream of nitrogen at 60°C.

[0118] The catalytic system is a preformed catalytic system. It is prepared in methylcyclohexane from the metallocene, [Me2Si(Flu)2Nd(q-BH4)2Li(THF)], the co-catalyst, butylmagnesium (BOMAG), and a preforming monomer, 1,3-butadiene. It is prepared according to a preparation method in accordance with paragraph II. 1 of patent application WO 2017093654 A1: In a reactor containing 100 mL of the hydrocarbon solvent methylcyclohexane (MCH), the co-catalyst butylmagnesium (BOMAG) is added with a molar ratio of Mg / Nd = 2.2, followed by butadiene with a molar ratio of butadiene / Nd = 90. Metallocene [Me2Si(Flu)2Nd(q-BH4)2Li(THF)] is then added to the reaction mixture (0.71 mmol). The preformation takes place at a temperature of 80°C for 5 h. The resulting catalytic solution is stored at -5°C before use.

[0119] The copolymer thus prepared is statistically analyzed by SEC and NMR. The amount of copolymer recovered and the corresponding number-average molar mass determined by SEC analysis are given in Table 1. The chain end of the poly(ethylene-co-1,3-butadiene) (EBR) copolymer is identified by ¹H NMR analysis, and the microstructure of the copolymer is also determined by NMR analysis: the results of these characterizations are shown in Tables 2 and 3, respectively. Table 2 shows the chemical shifts of the 1-phenylethenyl functional group at the chain end of the EBR copolymer. Figure 1 represents an EBR copolymer chain bearing the 1-phenylethenyl functional group at its chain end.In Table 3, the abbreviations Et, B 1,4, B 1,2 denote the units -(CH2-CH2)-, -(CH2-CH=CH-CH2)-, and -(CH2-CH(CH=CH2)), respectively; cycles denote the 1,2-cyclohexane cyclic motifs of formula (IV). The amount of functional group attached to the chain end of the copolymer is determined by NMR analysis and is shown in Table 3. It is expressed in pmcm, micromoles per 100 g of monomer. For example, according to Table 3, the copolymer of test 1 contains 1393 micromoles of 1-phenylethenyl functional group per 100 grams of monomer, in other words, 13.93 mmols of 1-phenylethenyl functional group per kilogram of polymer.

[0120] Table 1: Tests [Nd] pmol / L Molar ratio [AMS] / [Nd] T°C Time (min) Copolymer mass (g) Mn (g / mol) 1 152 90 90 84 14 26900 2 152 180 80 80 14 25300 3 151 360 80 90 13.7 22400

[0121] Table 2: Atom number H 1 2 3 4 5 6 ô 1 H (ppm) 5.2 5.0 2.45 7.35 7.25 7.2

[0122] Formula 1

[0123] Table 3: Eth assays (mol%) %B 1.4 (mol%) %B 1.2 (mol%) cycles (m 01%) Functional group rate (pmcm) 1 76.8 5.4 5.7 12.1 1393 2 74.9 5.8 7.5 11.8 2326 3 75.0 5.7 7.3 12.0 3849

Claims

Demands

1. A process for preparing a polymer containing ethylene units and bearing a chain-end 1-arylethenyl group, wherein the process comprises the polymerization of a monomer selected from ethylene and a monomer mixture containing ethylene and a 1,3-diene in the presence of a catalytic system and 1-methyl-1-arylethenene, the catalytic system being based on a metallocene of formula (I) and a co-catalyst, an organomagnesium compound, P(Cp1Cp2)Nd(BH4)(1+y)_Ly-Nx (I), Cp1 and Cp2, identical or different, being selected 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, L representing an alkali metal chosen from the group consisting of lithium, sodium and potassium, N representing a molecule of an ether, x, an integer or not,y, an integer, being equal to or greater than 0.

2. A process according to claim 1 wherein 1-methyl-l-arylethene is 1-methyl-l-phenylethene.

3. A method according to claim 1 or 2 wherein the symbol P corresponds to the formula ZR*R2, Z representing a silicon or carbon atom, R1 and R2, identical or different, representing an alkyl group comprising from 1 to 20 carbon atoms.

4. A method according to any one of claims 1 to 3 wherein P has the formula SiMe2.

5. A method according to any one of claims 1 to 4 wherein Cp1 and Cp2, whether identical or different, are substituted fluorenyl groups or unsubstituted fluorenyl groups of formula Ci3H

6. 8* A process according to any one of claims 1 to 5 wherein the metallocene is of formula (1-1), (1-2), (1-3), (1-4) or (1-5): [Me2Si(Flu)2Nd(p-BH4)2Li(THF)] (I-1) [{Me2SiFlu2Nd(p-BH4)2Li(THF)}2] (1-2) [Me2SiFlu2Nd(p-BH4)(THF)] (1-3) [{Me2SiFlu2Nd(p-BH4)(THF)}2] (1-4) [Me2SiFlu2Nd(p-BH4)] (1-5) where Flu represents the CnH8 group.

7. A process according to any one of claims 1 to 6 wherein the organomagnesium compound is a dialkylmagnesium compound of formula MgR3R4 in which R3 and R4 are alkyls containing 2 to 10 carbon atoms, preferably R3 is butyl and R4 is octyl.

8. A method according to any one of claims 1 to 7 wherein the monomer mixture containing ethylene and a 1,3-diene is a mixture of ethylene and a 1,3-diene or a mixture of ethylene, a 1,3-diene and styrene.

9. A process according to any one of claims 1 to 8 wherein the 1,3-diene is 1,3-butadiene, isoprene, myrcene, [3-famesene or mixtures thereof, preferably 1,3-butadiene.

10. Polymer containing ethylene units and bearing the 1-arylethenyl function at the end of the chain.

11. Polymer according to claim 10 wherein the 1-arylethenyl function is the 1-phenylethenyl function.

12. Polymer according to claim 10 or 11, wherein polymer containing ethylene units is a copolymer of ethylene and a 1,3-diene or a copolymer of ethylene, a 1,3-diene and styrene.

13. Polymer according to claim 12 wherein the 1,3-diene is 1,3-butadiene, isoprene, myrcene, [3-farnesene or mixtures thereof.

14. Polymer according to claim 12 or 13, which polymer is a statistical copolymer.

15. Polymer according to claim 10 or 11, wherein polymer containing ethylene units is a polyethylene.