DIORGANOMAGNESIUM COMPOUND FOR A CATALYTIC SYSTEM

Description

[0001] The field of the present invention is that of organomagnesium compounds as well as that of catalytic systems which comprise organomagnesiums used as co-catalysts and which are intended to be used in the preparation of polyolefins, in particular copolymers of olefin and conjugated diene.

[0002] Catalyst systems based on rare earth metallocenes are described, for example, in patent applications EP 1 092 731, WO 2004035639, WO 2007054224 and WO 2018224776. They enable the synthesis of polyolefins, in particular copolymers of olefins and 1,3-dienes. They are also used in the preparation of copolymers of ethylene and functional 1,3-butadiene, as described in WO 2018224776. In these catalyst systems, the metallocene is activated by a co-catalyst that is part of the catalyst system. Suitable co-catalysts include organomagnesium, organoaluminium and organolithium. When the co-catalyst is an organomagnesium, it is typically a chloride of an organomagnesium or a diorganomagnesium in which the magnesium atom is bonded to two aliphatic groups, such as dibutylmagnesium, butylethymagnesium and butyloctylmagnesium.

[0003] The synthesis of block polymers comprising a homopolymer block of a 1,3-diene and a copolymer block of ethylene and 1,3-diene is also described in WO 2019077232. The process implemented in the synthesis of block polymers is the reaction of a living homopolymer obtained by anionic polymerization of a 1,3-diene and a rare earth metallocene, followed by the subsequent polymerization of a mixture of ethylene and a 1,3-diene.

[0004] Rare earth metallocenes used in catalytic polymerization are generally characterized through their catalytic activities expressed in kg of polymer per mol of catalyst per hour or their productivities expressed in grams of polymer per gram of catalyst.

[0005] The Applicant has discovered a novel asymmetric diorganomagnesium compound which has a first magnesium-carbon bond, which carbon is a carbon atom constituting a specific benzene ring, and a second magnesium-carbon bond, which carbon is a carbon atom constituting a polymer chain. In the synthesis of a block polymer comprising a homopolymer block of a 1,3-diene and a copolymer block of ethylene and 1,3-diene, the use of this novel asymmetric diorganomagnesium compound as a co-catalyst of a catalytic system based on a rare earth metallocene makes it possible to improve the catalytic activity and productivity.

[0006] Thus a first object of the invention is an asymmetric diorganomagnesium compound of formula (I) RB< -Mg-R A< (I) RA< being different from RB<, RA< being a polymer chain containing units of a first monomer selected from the group of monomers consisting of 1,3-dienes, aromatic α-monolefins and mixtures thereof, RB< comprising 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, with the proviso that if one of the 2 carbon atoms ortho is substituted by an isopropyl, the second carbon atom ortho is not substituted by an isopropyl.

[0007] A second subject of the invention is a catalytic system based at least on one metallocene of formula (IIIa) or (IIIb) and a diorganomagnesium compound in accordance with the invention as co-catalyst, {P(Cp 1< )(Cp 2< )Y} (IIIa) Cp 3< Cp 4< Y (IIIb) Y denoting a group comprising a metal atom which is a rare earth, Cp 1< , Cp 2< , Cp 3< and Cp 4< , identical or different, being chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted, P being a group bridging the two groups Cp 1< and Cp 2< , and comprising a silicon or carbon atom.

[0008] The invention also relates to a process for preparing a polymer which comprises a step of polymerizing a second monomer chosen from the group of monomers consisting of conjugated dienes, ethylene, α-monoolefins and their mixtures in the presence of a catalytic system in accordance with the invention. The polymer obtained by the process in accordance with the invention is a block polymer.

[0009] The invention also relates to a process for preparing an asymmetric diorganomagnesium compound in accordance with the invention which comprises: bringing a living anionic polymer of formula RA< Li into contact with a halide of an organomagnesium of formula RB< -Mg-X, reacting the living anionic polymer and the halide, RA< being a polymer chain containing units of a first monomer chosen from the group of monomers consisting of 1,3-dienes, aromatic α-monolefins and mixtures thereof, RB< comprising 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 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, provided that if one of the 2 carbon atoms in ortho is substituted by isopropyl, the second carbon atom in ortho is not substituted by isopropyl,X being a halogen selected from the group consisting of chlorine, fluorine, bromine and iodine. Detailed description of the invention

[0010] 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).

[0011] The abbreviation "pce" means parts by weight per hundred parts of elastomer (of the total elastomers if more than one elastomer is present).

[0012] 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.

[0013] 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.

[0014] The compound according to the invention of formula (I) has the essential characteristic of being a diorganomagnesium compound, called asymmetric and in the present invention called an asymmetric diorganomagnesium compound, since the two groups represented by the symbols RB< and RA< are different from each other. RB< -Mg-R A< (I)

[0015] The group represented by the symbol RA< is a polymer chain containing units of a first monomer selected from the group of monomers consisting of 1,3-dienes, aromatic α-monolefins and mixtures thereof. The 1,3-diene as the first monomer is preferably 1,3-butadiene, isoprene or a mixture thereof. The aromatic α-monolefin as the first monomer is an α-monolefin of formula CH 2 =CH-Ar, Ar representing an aromatic group, substituted or not. The Ar group is preferably phenyl or aryl. The aromatic α-monolefin as the first monomer is preferably styrene or a styrene substituted by one or more alkyl groups, more preferably styrene. Preferably, RA< represents a homopolymer chain of 1,3-butadiene, isoprene or styrene or a copolymer chain of monomers chosen from 1,3-butadiene, isoprene and styrene.

[0016] The group represented by the symbol RB< has the essential characteristic of comprising a benzene ring substituted by the magnesium atom. The two carbon atoms of the benzene ring ortho to the magnesium carry a substituent, identical or different. Alternatively, one of the two carbon atoms of the benzene ring ortho to the magnesium may carry a substituent, the other carbon atom of the benzene ring ortho to the magnesium may form a ring. The substituent is a methyl, an ethyl or an isopropyl. In the case where one of the two carbon atoms of the benzene ring ortho to the magnesium is substituted by an isopropyl, the second carbon atom of the benzene ring ortho to the magnesium is not substituted by an isopropyl. Preferably, the carbon atoms of the benzene ring ortho to the magnesium are substituted by a methyl or an ethyl.More preferably, the carbon atoms of the benzene ring ortho to magnesium are substituted by a methyl.

[0017] According to a preferred embodiment, the asymmetric diorganomagnesium compound corresponds to formula (II) in which RA< is a polymer chain as defined above, R 1 and R 5 , identical or different, represent a methyl or an ethyl and R 2 , R 3 and R 4 , identical or different, represent a hydrogen atom or an alkyl. Preferably, R 1 and R 5 represent a methyl. Preferably, R 2 and R 4 represent a hydrogen atom.

[0018] According to a preferred variant, R 1 , R 3 and R 5 are identical. According to a more preferred variant, R 2 and R 4 represent a hydrogen and R 1 , R 3 and R 5 are identical. In a more preferred variant, R 2 and R 4 represent a hydrogen and R 1 , R 3 and R 5 represent a methyl.

[0019] According to a preferred embodiment, the polymer chain represented by the symbol RA< is prepared by anionic polymerization.

[0020] The asymmetric diorganomagnesium compound in accordance with the invention can be prepared by a process, another subject of the invention, which process comprises the following steps: bringing a living anionic polymer RA< Li into contact with a halide of an organomagnesium of formula RB< -Mg-X, the reaction of the living anionic polymer and the halide, X being a halogen selected from the group consisting of chlorine, fluorine, bromine and iodine, R B and R HAS being as defined above.

[0021] X is preferably a bromine atom or a chlorine atom. X is more preferably a bromine atom.

[0022] The living anionic polymer useful for the synthesis of organometallic compounds of formula RA< Li is typically a polymer chain bearing a carbanion. It generally results from the initiation and propagation reactions of a polymer chain in the anionic polymerization of the first monomer. 1,3-dienes, aromatic α-monolefins and their mixtures which can be used as the first monomer are well known to polymerize or copolymerize together anionically and to form living polymer or copolymer chains. The polymerization processes of these monomers are also well known and widely described.

[0023] The living anionic polymer is therefore obtained conventionally by anionic polymerization of the first monomer in a solvent, called the polymerization solvent. The polymerization solvent can be any hydrocarbon solvent known to be used in the polymerization of 1,3-diene monomers and aromatic α-monolefins. The polymerization solvent is preferably a hydrocarbon solvent, preferably an aliphatic one, such as hexane, cyclohexane or methylcyclohexane.

[0024] The polymerization solvent of the first monomer may include an additive to control the microstructure of the polymer chain and the rate of the polymerization reaction. This additive may be a polar agent such as an ether or a tertiary amine. The additive is most often used in small quantities, in particular to limit the deactivation reactions of the propagating sites of the anionic polymerization. The quantity of additive in the polymerization solvent, traditionally indexed to the number of carbon-metal bonds in the polymerization medium, is adjusted according to the desired microstructure of the polymer chain and therefore depends on the complexing power of the additive.

[0025] The ratio between the amount of solvent and the amount of first monomer useful for the formation of the living polymer is chosen by a person skilled in the art according to the desired viscosity of the living polymer solution. This viscosity depends not only on the concentration of the polymer solution, but also on many other factors such as the length of the polymer chains, the nature of the counterion of the living polymer, the intermolecular interactions between the living polymer chains, the complexing power of the solvent, the temperature of the polymer solution. Consequently, a person skilled in the art adjusts the amount of solvent on a case-by-case basis.

[0026] In the initiation reaction of the polymerization reaction, a compound known as an initiator for the anionic polymerization of the monomers useful for the purposes of the invention is used. Preferably, the initiator is a compound which has a carbon-metal bond. The initiator is used at a rate chosen according to the desired chain length of the living polymer and can therefore vary to a wide extent.

[0027] The living polymer is generally prepared by polymerization of the first monomer initiated by an initiator which is a lithium compound. As a lithium initiator, mention may be made of organolithium compounds, such as n-butyllithium, sec-butyllithium and tert-butyllithium commonly used in the anionic polymerization of the monomers useful for the purposes of the invention.

[0028] The polymerization temperature to form the living polymer can vary widely. It is chosen based on the stability of the carbon-metal bond in the polymerization solvent, the relative rate coefficients of the initiation reaction and the propagation reaction, and the desired microstructure of the living polymer. Traditionally, it varies in a range from -20 to 100°C, preferably from 20 to 70°C.

[0029] Preferably, the living anionic polymer is a living polymer obtained by anionic polymerization of 1,3-butadiene, isoprene, styrene or mixtures thereof. In other words, the first monomer is preferably 1,3-butadiene, isoprene, styrene or mixtures thereof.

[0030] The living anionic polymer can be a homopolymer or a copolymer in the case where the first monomer is a mixture of monomers. The copolymer can be random or block, since the incorporation of the comonomers can be controlled with known operating conditions of anionic polymerization processes. For example, it is known that the polarity of the polymerization solvent and the mode of feeding the comonomers into the anionic polymerization medium influence the relative incorporation of the comonomers.

[0031] In the preparation of the asymmetric diorganomagnesium compound according to the invention, the contacting of the living anionic polymer with the halide of an organomagnesium is preferably carried out by adding a solution of the living anionic polymer RA< Li to a solution of the halide of an organomagnesium RB< -Mg-X. The solution of the living anionic polymer RA< Li is generally a solution in a hydrocarbon solvent, preferably aliphatic such as n-hexane, cyclohexane or methylcyclohexane. The solution of the halide of an organomagnesium RB< -Mg-X is generally a solution in an ether, preferably diethyl ether or dibutyl ether. The concentration of the living anionic polymer RA< Li is preferably 0.01 to 1 mol of lithium equivalent / L, more preferably 0.05 to 0.2 mol of lithium equivalent / L, that of the solution of the organomagnesium RB< -Mg-X preferably 1 to 5 mol / L, more preferably 2 to 3 mol / L.

[0032] The reaction between the living anionic polymer RA< Li and the halide of an organomagnesium RB< -Mg-X is 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.

[0033] As with any synthesis carried out in the presence of organometallic compounds, the contact and reaction take place under anhydrous conditions under an inert atmosphere. Typically, solvents and solutions are used under anhydrous nitrogen or argon. The various stages of the process are generally carried out under stirring.

[0034] Once the asymmetric diorganomagnesium is formed, it is generally recovered in solution after filtration conducted under an inert and anhydrous atmosphere. The asymmetric diorganomagnesium solution is typically stored before use in airtight containers, for example capped bottles, at a temperature between -25°C and 23°C.

[0035] Like any organomagnesium compound, the diorganomagnesium compound RB< -Mg-R A< useful for the purposes of the invention may be in the form of a monomeric entity (RB< -Mg-R A< ) 1 or in the form of a polymeric entity (RB< -Mg-R A< ) p , p being an integer greater than 1, in particular dimer (RB< -Mg-R A< ) 2 . Furthermore, whether it is in the form of a monomeric or polymeric entity, it may 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.

[0036] The asymmetric diorganomagnesium compound in accordance with the invention is particularly intended to be used as a co-catalyst in a catalytic system comprising an organometallic complex and useful for the polymerization or copolymerization of olefins or dienes. The organometallic complex is typically a rare earth metallocene or hemimetallocene.

[0037] The asymmetric diorganomagnesium compound has the role of activating the organometallic complex with respect to the polymerization reaction, in particular in the polymerization initiation reaction. It can replace the co-catalyst of the catalytic systems described for example in documents EP 1092731 A1, WO 2004035639 A1,

[0038] WO 2005028526 A1, WO2007045223 A2, WO2007045224 A2.

[0039] In particular, the asymmetric diorganomagnesium compound according to the invention is one of the essential constituents of a catalytic system, another subject of the invention. Used as a co-catalyst in the catalytic system, the asymmetric diorganomagnesium compound makes it possible to increase the catalytic activity of the catalytic system in the synthesis of block polymers. The polymers are typically copolymers of dienes and olefins. As olefins, mention may be made in particular of ethylene and α-olefins, in particular those having 3 to 18 carbon atoms. As dienes, 1,3-dienes are particularly suitable, more particularly 1,3-dienes having 4 to 24 carbon atoms such as 1,3-butadiene and isoprene.

[0040] The catalytic system in accordance with the invention therefore has as basic constituents the asymmetric diorganomagnesium compound in accordance with the invention and a metallocene of formula (IIIa) or (IIIb) {P(Cp 1< )(Cp 2< )Y} (IIIa) Cp 3< Cp 4< Y (IIIb) Y denoting a group comprising a metal atom which is a rare earth, Cp 1< , Cp 2< , Cp 3< and Cp 4< , identical or different, being chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted, P being a group bridging the two groups Cp 1< and Cp 2< , and comprising a silicon or carbon atom.

[0041] It should be remembered that rare earths are metals and refer to the elements scandium, yttrium and lanthanides whose atomic number varies from 57 to 71.

[0042] According to a first variant of the invention, the metallocene used as a basic constituent in the catalytic system in accordance with the invention corresponds to the formula (IIIa) {P(Cp 1< )(Cp 2< )Y} (IIIa) in which Y denotes a group comprising a metal atom which is a rare earth, Cp 1< and Cp 2< , identical or different, are chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted, P is a group bridging the two groups Cp 1< and Cp 2< , and comprising a silicon or carbon atom.

[0043] According to a second variant of the invention, the metallocene used as a basic constituent in the catalytic system in accordance with the invention corresponds to the formula (IIIb) Cp 3< Cp 4< Y (IIIb) in which Y denotes a group comprising a metal atom which is a rare earth, Cp 3< and Cp 4< , identical or different, are chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted.

[0044] As substituted cyclopentadienyl, fluorenyl and indenyl groups, mention may be made of 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 SiMe 3 . The choice of radicals is also guided by the accessibility of the corresponding molecules that are substituted cyclopentadienyl, fluorenyl and indene, because the latter are commercially available or easily synthesized.

[0045] As substituted fluorenyl groups, mention may be made in particular of 2,7-ditertiobutyl-fluorenyl, 3,6-ditertiobutyl-fluorenyl. Positions 2, 3, 6 and 7 respectively designate the position of the carbon atoms of the rings as shown in the diagram below, position 9 corresponding to the carbon atom to which the P bridge is attached.

[0046] As substituted cyclopentadienyl groups, mention may be made in particular of those substituted in position 2, more particularly the tetramethylcyclopentadienyl group. Position 2 (or 5) 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.

[0047] 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.

[0048] Preferably, the metallocene is of formula (IIIa).

[0049] According to a preferred embodiment of the invention, Cp 1< and Cp 2< are identical and are chosen from the group consisting of substituted fluorenyl groups and the unsubstituted fluorenyl group of formula C 13 H 8 . The catalytic system according to this preferred embodiment has the particularity of leading to copolymers of butadiene and ethylene which comprise, in addition to ethylene monomer units and butadiene units, 1,2-cyclohexane cyclic units of the following formula:

[0050] Advantageously, Cp 1< and Cp 2< are identical and each represent an unsubstituted fluorenyl group of formula C 13 H 8 , represented by the symbol Flu.

[0051] According to a preferred embodiment of the invention, the symbol Y represents the group Met-G, with Met denoting a metal atom which is a rare earth and with G denoting a group comprising the borohydride unit BH 4 or denoting a halogen atom chosen from the group consisting of chlorine, fluorine, bromine and iodine. Advantageously, G denotes a chlorine atom or the group of formula (IV): (BH 4 ) (1+y)- L y -N x (IV) in which L represents an alkali metal selected from the group consisting of lithium, sodium and potassium, N represents a molecule of an ether, x, an integer or not, is equal to or greater than 0, y, an integer, is equal to or greater than 0.

[0052] Very advantageously, G denotes the group of formula (IV).

[0053] Any ether that has the power to complex the alkali metal is suitable as an ether, especially diethyl ether and tetrahydrofuran.

[0054] According to any one of the embodiments of the invention, the metallocene metal useful for the purpose of the invention, in this case the rare earth, is preferably a lanthanide whose atomic number ranges from 57 to 71, more preferably neodymium, Nd.

[0055] The bridge P connecting the groups Cp 1< and Cp 2< preferably corresponds to the formula ZR 1< R 2< , in which Z represents a silicon or carbon atom, R 1< and R 2< , identical or different, each represent an alkyl group comprising from 1 to 20 carbon atoms, preferably a methyl. In the formula ZR 1< R 2< , Z advantageously represents a silicon atom, Si.

[0056] The metallocene useful for the synthesis of the catalytic system can be in the form of crystallized or non-crystalline powder, or in the form of single crystals. The metallocene can 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 or WO 2007054223. The metallocene can be prepared in a conventional manner by a process analogous to that described in patent application WO 2007054224 or WO 2007054223, in particular by reaction under inert and anhydrous conditions of the salt of an alkali metal of the ligand with a rare earth borohydride 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.

[0057] According to a particularly preferred embodiment, the metallocene is of formula (III-1), (III-2), (III-3), (III-4) or (III-5): [Me 2 Si(Flu) 2 Nd(µ-BH 4 ) 2 Li(THF)] (III-1) [{Me 2 SiFlu 2 Nd(µ-BH 4 ) 2 Li(THF)} 2 ] (III-2) [Me 2 SiFlu 2 Nd(µ-BH 4 )(THF)] (III-3) [{Me 2 SiFlu 2 Nd(µ-BH 4 )(THF)} 2 ] (III-4) [Me 2 SiFlu 2 Nd(µ-BH 4 )] (III-5) in which Flu represents the group C 13 H 8 .

[0058] The catalytic system in accordance with the invention can be prepared in a conventional manner by a process analogous to that described in patent application WO 2007054224 or WO 2007054223. For example, the asymmetric diorganomagnesium 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 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 rare earth metal in the metallocene is preferably from 1 to 100, more preferably from 1 to less than 10. The range of values from 1 to less than 10 is particularly more favorable for obtaining polymers with high molar masses. The catalyst system is usually prepared in a hydrocarbon solvent, aliphatic such as methylcyclohexane or aromatic such as toluene.Generally, after its synthesis, the catalytic system is used as is in the process for synthesizing the polymer in accordance with the invention.

[0059] Like any synthesis carried out in the presence of organometallic compounds, the synthesis of the metallocene, the synthesis of the asymmetric diorganomagnesium compound and the synthesis of the catalytic system take place under anhydrous conditions under an inert atmosphere. Typically, the reactions are carried out from anhydrous solvents and compounds under anhydrous nitrogen or argon.

[0060] The catalyst system is generally in the form of a solution in a hydrocarbon solvent. The hydrocarbon solvent can be aliphatic such as methylcyclohexane or aromatic such as toluene. The hydrocarbon solvent is preferably aliphatic, more preferably methylcyclohexane. Generally, the catalyst system is stored in the form of a solution in the hydrocarbon solvent before being used in polymerization. We can then speak of a catalyst solution which includes the catalyst system and the hydrocarbon solvent. The concentration of the catalyst solution is typically defined by the metallocene metal content in the solution. The metallocene metal concentration has a value preferably ranging from 0.0001 to 0.2 mol / L, more preferably from 0.001 to 0.03 mol / L.

[0061] The catalytic system according to the invention is intended to be used in a process for the synthesis of block polymers, in particular elastomers and usable in rubber compositions, for example for tires. The use of the catalytic system according to the invention in the block polymer process makes it possible to increase the productivity of the process due to an increase in the catalytic activity.

[0062] The process, another object of the invention, comprises a step of polymerization of a second monomer chosen from the group of monomers consisting of conjugated dienes, ethylene, α-monoolefins and their mixtures in the presence of the catalytic system conforming to the process for preparing a polymer.

[0063] As the process involves the polymerization of a monomer, called the second monomer, in the presence of a catalytic system which comprises a co-catalyst consisting of a polymer chain RA<, the polymer chain RA< and the polymer chain resulting from the polymerization of the second monomer constitute the polymer synthesized by the process according to the invention. The polymers synthesized by the process according to the invention are therefore block, diblock or multiblock polymers. Indeed, the polymer chain RA< can be a homopolymer, a block polymer or a random polymer. The polymer chain resulting from the polymerization of the second monomer which results from the polymerization of the second monomer can be a random polymer or a block polymer, when the second monomer is a mixture of monomers.

[0064] Preferably, the second monomer is ethylene or a mixture of a 1,3-diene and ethylene, the 1,3-diene preferably being 1,3-butadiene, isoprene, or a mixture thereof. Depending on the microstructure and length of the polymer chains prepared by the process according to the invention, the polymer may be an elastomer.

[0065] The polymerization of the second monomer is preferably carried out in solution, continuously or batchwise. The polymerization solvent may be a hydrocarbon, aromatic or aliphatic solvent. Examples of polymerization solvents include toluene and methylcyclohexane. The second monomer may be introduced into the reactor containing the polymerization solvent and the catalytic system or conversely the catalytic system may be introduced into the reactor containing the polymerization solvent and the second monomer. The second monomer and the catalytic system may 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. It is adjusted according to the second monomer to be polymerized. If the second monomer is a mixture of monomers containing ethylene, the copolymerization is preferably carried out at constant ethylene pressure.

[0066] In the case where the polymerization of a second monomer is the polymerization of a mixture of ethylene and 1,3-diene in a polymerization reactor, a continuous addition of ethylene and 1,3-diene may be carried out in the polymerization reactor, in which case the polymerization reactor is a fed reactor. This embodiment is particularly suitable for a statistical or random incorporation of ethylene and 1,3-diene.

[0067] Once the desired conversion rate of the polymerization reaction of the second monomer is reached, the polymerization reaction is stopped by a terminating agent, such as a compound having an acidic proton, such as an alcohol. The block polymer can be recovered, in particular by separating it from the reaction medium, for example by coagulating it in a solvent causing it to coagulate or by removing the polymerization solvent and any residual monomer under reduced pressure or under the effect of steam distillation (stripping operation).

[0068] In summary, the invention is advantageously implemented according to any one of the following embodiments 1 to 32: Method 1: Asymmetric diorganomagnesium compound of formula (I) RB< -Mg-RA< (I) RA< being different from RB< , RA< being a polymer chain containing units of a first monomer chosen from the group of monomers consisting of 1,3-dienes, aromatic α-monolefins and mixtures thereof, RB< comprising 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, with the condition that if one of the 2 carbon atoms ortho is substituted by a isopropyl, the second carbon atom in ortho is not substituted by isopropyl.Mode 2: Asymmetric diorganomagnesium compound according to mode 1 in which the diorganomagnesium compound is of formula (II). R 1 and R 5 , identical or different, represent a methyl or an ethyl, R 2 , R 3 and R 4 , identical or different, being a hydrogen atom or an alkyl, RA< being defined according to mode 1. Mode 3: Asymmetric diorganomagnesium compound according to mode 2 in which R 1 and R 5 represent a methyl. Mode 4: Asymmetric diorganomagnesium compound according to mode 2 or 3 in which R 2 and R 4 represent a hydrogen atom. Mode 5: Asymmetric diorganomagnesium compound according to any one of modes 2 to 4 in which R 3 is identical to R 1 and to R 5 . Mode 6: Asymmetric diorganomagnesium compound according to any one of modes 1 to 5 in which the carbon atoms of the benzene ring ortho to magnesium are substituted by a methyl or an ethyl. Mode 7: Asymmetric diorganomagnesium compound according to any one of modes 1 to 6 in which the carbon atoms of the benzene ring ortho to magnesium are substituted by a methyl.Mode 8: Asymmetric diorganomagnesium compound according to any one of modes 1 to 7 in which RA< is a homopolymer chain of 1,3-butadiene, isoprene or styrene or a copolymer chain of monomers selected from 1,3-butadiene, isoprene and styrene. Mode 9: Asymmetric diorganomagnesium compound according to any one of modes 1 to 7 in which the polymer chain represented by the symbol RA< is prepared by anionic polymerization.Mode 10: Catalytic system based at least on: a metallocene of formula (IIIa) or (IIIb), a diorganomagnesium compound as co-catalyst, {P(Cp 1< )(Cp 2< )Y} (II) Cp 3< Cp 4< Y (IIIb) Y denoting a group comprising a metal atom which is a rare earth, Cp 1< , Cp 2< , Cp 3< and Cp 4< , identical or different, being chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted, P being a group bridging the two groups Cp 1< and Cp 2< , and comprising a silicon or carbon atom, the diorganomagnesium compound being an asymmetric diorganomagnesium compound defined in any one of modes 1 to 9. Mode 11: Catalytic system according to mode 10 in which the metallocene is of formula (IIIa).Mode 12: Catalytic system according to any one of modes 10 to 11 in which Cp 1< and Cp 2< are identical and are selected from the group consisting of substituted fluorenyl groups and the unsubstituted fluorenyl group of formula C 13 H 8 . Mode 13: Catalytic system according to any one of modes 10 to 12 in which Cp 1< and Cp 2< each represent an unsubstituted fluorenyl group of formula C 13 H 8 . Mode 14: Catalytic system according to any one of modes 10 to 13, in which the symbol Y represents the group Met-G, with Met denoting a metal atom which is a rare earth and G denoting a group comprising the borohydride unit BH 4 or denoting a halogen atom selected from the group consisting of chlorine, fluorine, bromine and iodine.Mode 15: Catalytic system according to mode 14 in which G denotes chlorine or the group of formula (IV) (BH 4 ) (1+y)- L y -N x (IV) in which L represents an alkali metal chosen from the group consisting of lithium, sodium and potassium, N represents a molecule of an ether, preferably diethyl ether or tetrahydrofuran, x, an integer or not, is equal to or greater than 0, y, an integer, is equal to or greater than 0. Mode 16: Catalytic system according to mode 15 in which G denotes the group of formula (IV). Mode 17: Catalytic system according to any one of modes 10 to 16 in which the rare earth is a lanthanide whose atomic number varies from 57 to 71. Mode 18: Catalytic system according to any one of modes 10 to 17 in which the rare earth is neodymium, Nd.Mode 19: Catalytic system according to any one of modes 10 to 18 in which the bridge P corresponds to the formula ZR 1< R 2< , Z representing a silicon or carbon atom, R 1< and R 2< , identical or different, each representing an alkyl group comprising from 1 to 20 carbon atoms, preferably a methyl. Mode 20: Catalytic system according to mode 19 in which Z is Si. Mode 21: Catalytic system according to any one of modes 10 to 20 in which the metallocene is (III-1), (III-2), (III-3), (III-4) or (III-5): [Me 2 Si(Flu) 2 Nd(µ-BH 4 ) 2 Li(THF)] (III-1) [{Me 2 SiFlu 2 Nd(µ-BH 4 ) 2 Li(THF)} 2 ] (III-2) [Me 2 SiFlu 2 Nd(µ-BH 4 )(THF)] (III-3) [{Me 2 SiFlu 2 Nd(µ-BH 4 )(THF)} 2 ] (III-4) [Me 2 SiFlu 2 Nd(µ-BH 4 )] (III-5) Flu representing the group C 13 H 8 .Mode 22: Catalytic system according to any one of modes 10 to 21 in which the ratio between the number of moles of Mg in the co-catalyst and the number of moles of rare earth metal in the metallocene is from 1 to 100. Mode 23: Catalytic system according to any one of modes 10 to 22 in which the ratio between the number of moles of Mg in the co-catalyst and the number of moles of rare earth metal in the metallocene is from 1 to 10. Mode 24: Catalytic system according to any one of modes 10 to 23, which catalytic system is in the form of a solution in a hydrocarbon solvent. Mode 25: Catalytic system according to mode 24 in which the hydrocarbon solvent is aromatic or aliphatic, preferably aliphatic, more preferably methylcyclohexane.Mode 26: Catalytic system according to any one of modes 24 to 25 in which the molar concentration of metal of the metallocene in the catalytic system has a value ranging from 0.0001 to 0.2 mol / L, preferably from 0.001 to 0.03 mol / L. Mode 27: Process for preparing a polymer which comprises a step of polymerization of a second monomer chosen from the group of monomers consisting of conjugated dienes, ethylene, α-monoolefins and their mixtures in the presence of a catalytic system defined in any one of modes 10 to 26. Mode 28: Process according to mode 27 in which the second monomer is ethylene or a mixture of a 1,3-diene and ethylene. Mode 29: Process according to mode 28 in which the 1,3-diene is 1,3-butadiene, isoprene or a mixture thereof.Method 30: A process for preparing an asymmetric diorganomagnesium compound defined in any one of methods 1 to 9 which comprises: contacting a living anionic polymer of formula RA< Li with a halide of an organomagnesium of formula RB< -Mg-X, reacting the living anionic polymer and the halide, X being a halogen selected from the group consisting of chlorine, fluorine, bromine and iodine, RA< and RB< being defined according to any one of methods 1 to 9. Method 31: A process according to method 30 wherein X is a bromine atom or a chlorine atom. Method 32: A process according to method 30 or 31 wherein X is a bromine atom.

[0069] The above-mentioned characteristics of the present invention, as well as others, will be better understood upon reading the following description of several exemplary embodiments of the invention, given for illustrative and non-limiting purposes. Examples of embodiments of the invention 1. Size exclusion chromatography (SEC):

[0070] Molar masses were determined by universal calibration using polystyrene standards certified by "Polymer Laboratories" and double detection with refractometer and viscometer coupling.

[0071] Without being an absolute method, SEC allows us to understand the distribution of molar masses of a polymer. From commercial standard products of the Polystyrene type, the different average molar masses in number (Mn) and in weight (Mw) can be determined and the polymolecularity index, also called dispersity, calculated (Ip = Mw / Mn). The polymer is solubilized in tetrahydrofuran (THF) at a concentration of 1 g / L, the solution is filtered through a filter with a porosity of 0.45 µm, then it is injected into a chromatograph equipped with 2 detectors, a "Waters 410" refractometer and a viscometer. using a "Waters 717" injector and a "Waters 515 HPLC" pump at a flow rate of 1 ml.min -1< in a series of "Polymer Laboratories" columns.

[0072] This series of columns, placed in a thermostatically controlled enclosure at 45°C, is composed of: 1 PL Gel 5 µm precolumn, 2 PL Gel 5 µm Mixed C columns, 1 PL Gel 5 µm-500 Å column. 2. Nuclear magnetic resonance (NMR) (synthesis of the polymer containing units of a first monomer):

[0073] Spectra were acquired on a Brüker Avance III 500 MHz spectrometer equipped with a BBIz-grad 5 mm “broadband” cryoprobe. Samples were solubilized in 1,2-dichlorobenzene d4. Calibration was performed on the protonated impurity of 1,2-dichlorobenzene at 7.20 ppm in 1H NMR. The quantitative 1H NMR experiment used a single 30° pulse sequence and a 5-second repetition delay between each acquisition. 3. Nuclear Magnetic Resonance (NMR) (block polymer synthesis):

[0074] The block polymers are solubilized in 1,2-dichlorobenzene d4. Calibration is performed on the protonated impurity of 1,2-dichlorobenzene at 7.20 ppm in 1H NMR.

[0075] The quantitative 1H NMR experiment uses a single 30° pulse sequence and a 5-second repetition delay between each acquisition. 64 to 256 accumulations are performed. The two-dimensional 1H / 13C experiments are used to determine the structure of polymer units. The 1H-13C HMBC (heteronuclear multiple bond correlation) experiment allows the detection of long-range correlations by J coupling between protons and carbon-13 nuclei.

[0076] The 1H NMR spectra and the edited 2D 1< H / 13< C 1< J HSQC NMR correlation spectrum allow the determination of the microstructure of the block polymer and the proportion of each block in the sample. Determination of the percentage of block polymer by DOSY:

[0077] The DOSY experiment, an NMR method, allows for the analysis of complex mixtures and the detection of traces. The aim of this experiment is to demonstrate that the block polymer represents the majority of the sample and that the presence of homopolymer is very low.

[0078] DOSY NMR analysis allows the separation of the species present, particularly in polymer matrices, by analyzing their diffusion coefficient in solution. The principle of the technique is as follows: The DOSY experiment consists of recording proton spectra by varying the G force of the applied gradients and thus the diffusion force. A linear increase in the intensity of the gradients will lead to an exponential decrease in the intensity of the NMR signal.

[0079] The DOSY experiment will give a two-dimensional map. The 2nd dimension F2 of the DOSY corresponds, after processing by the Fourier transform, to the 1H dimension. The 1st dimension F1 corresponds to the decrease of the NMR signal as a function of the applied gradient force. After processing the F2 dimension, the diffusion coefficient is extracted from equation (1), and a DOSY map is obtained. I = I 0 . exp − Dγ 2 G 2 δ 2 Δ − δ / 3

[0080] If the two matrices have an identical diffusion coefficient, this means that the two matrices have the same hydrodynamic radius, and are therefore grafted. On the other hand, if the two matrices have two different diffusion coefficients, this means that they are free from each other.

[0081] The equation that describes the diffusion coefficient is:

[0082] The experiment was conducted on samples of poly(butadiene-b-poly(ethylene-co-butadiene) synthesized according to the process according to the invention.

[0083] Recording two 1D 1H NMR spectra with a diffusion filter, one with a magnetic field gradient set at 90% of the maximum power of the gradient amplifier and the other at 1% of this value, allows, by comparison with the 1H NMR spectrum, to observe the part of signal loss due to spatial diffusion of molecules and relaxation of magnetization. The signal loss due to diffusion is then attributed to "small molecules" not grafted to the polymer matrix (reagents, antioxidants, solvents, etc.).

[0084] The chemical shift between 5.18 and 4.96 ppm is attributed to the 1,4-unit isoprene units, the chemical shift between 4.79 and 4.49 ppm is attributed to the 3,4-unit isoprene units. The chemical shift between 5.36-5.10 ppm is attributed to the 1,4-unit butadiene units, the signal between 5.63 and 5.36 ppm is attributed to the 1,2-unit butadiene units.

[0085] Chemical shifts between 6.0-5.63 ppm and 1.75-1.63 ppm are attributed to the 6-membered cyclic units, 1,2-cyclohexanediyl.

[0086] The signal at 1.18 ppm is attributed to ethylene units. Raw materials:

[0087] Phenyl magnesium bromide in solution in diethyl ether at 3 mol / L, mesityl magnesium bromide in solution in diethyl ether at 1 mol / L, triisopropylphenyl magnesium bromide in solution in tetrahydrofuran at 0.5 mol / L are obtained from Sigma-Aldrich and used without prior purification. 4. Example 1 in accordance with the invention: Synthesis of a living polyisoprene:

[0088] 280 mL of degassed methylcyclohexane (MCH) is introduced into a 750 mL Steinie bottle. 5.64 g of isoprene is introduced into the reaction medium followed by 1 mL of sec-BuLi at 0.38 mol / L. The polymerization is maintained at 50°C for 2 h. The measured conversion, by dry matter content, is 96%.

[0089] For its characterization, the living polyisoprene is deactivated by the addition of degassed methanol. The polymer solution is dried in an oven at 50°C under vacuum with a nitrogen sweep for 48 hours.

[0090] The number-average molar mass of polyisoprene is 22350 g / mol (Ip = 1.09), the molar ratios of the 1,4 and 3,4 units of the isoprene units are 94.2% and 5.8%, respectively. The macrostructure and microstructure of polyisoprene are determined by size-exclusion chromatography and nuclear magnetic resonance, respectively, as described above in paragraphs 1 and 2, respectively. Synthesis of an asymmetric diorganomagnesium (polyisoprene-Mg-mesityl):

[0091] The asymmetric diorganomagnesium compound (polyisoprene-Mg-mesityl) is synthesized by lithium-magnesium metal exchange reaction. 0.3 mL of 1 mol / L mesityl-Mg-Br in dibutyl ether is introduced onto the lithiated living polyisoprene. The reaction medium is stirred for 1 hour at 23°C. Synthesis of a block polymer:

[0092] In a 500mL glass reactor, heated to 50°C, a solution containing 280 mL of the asymmetric diorganomagnesium polyisoprene-Mg-mesityl and 48.8 mg of metallocene [{Me 2 SiFlu 2 Nd(µ-BH 4 ) 2 Li(THF)}] 2 (76.3µmol) is introduced.

[0093] Then a gas mixture containing 20 mol% butadiene and 80 mol% ethylene is introduced into the reactor. The polymerization is carried out at 50°C and at an initial pressure of 4 bars absolute in the reactor.

[0094] The polymerization reaction is stopped, after formation of 9g of polymer, by cooling, degassing the reactor and adding methanol. The polymer is recovered and then dried. The weighed mass makes it possible to determine the average catalytic activity of the catalytic system expressed in kilograms of polymer synthesized per mole of neodymium metal and per hour (kg / mol.h).

[0095] The catalytic activity is 23 kg / mol.h.

[0096] The macrostructure and microstructure of the polymer are determined respectively by size exclusion chromatography according to the method described in paragraph 1 and by nuclear magnetic resonance, as described above in paragraph 2. The NMR results are shown in Table 1 which gives the molar percentage of the units in the diblock copolymer. The results of the SEC and NMR characterizations show that the polymer contains 30% by mass of polyisoprene and 70% by mass of a block copolymer consisting of a first polyisoprene block and a second random block of ethylene and 1,3-butadiene. Table 1 Unit dibloc Butadiene, 1,2-unit 11 Butadiene, 1,4-unit 5 Ethylene 82 1,2-cyclohexanediyl 2 Isoprene, 1,4-unit 93,9 ± 0,9 Isoprene, 3,4-unit 6,1 ± 0,2 5. Example 2 in accordance with the invention: Synthesis of a living polyisoprene:

[0097] 100 mL of methylcyclohexane (MCH) previously bubbled with nitrogen is introduced into a 500 mL reactor. 1 mL of sec-BuLi at 0.38 mol / L is introduced into the reactor. The reactor is heated to 50°C and then a mixture of isoprene (5.64 g) and MCH (100 mL) is introduced into the reactor.

[0098] Polymerization is maintained for 2 hours at 50°C to reach 100% conversion. Synthesis of an asymmetric diorganomagnesium (polyisoprene-Mg-mesityl):

[0099] 0.3 mL of 1 mol / L Mes-Mg-Br dissolved in 20 mL of MCH is introduced into the reactor containing the living anionic polyisoprene. The reaction medium is stirred for 1 hour at 50°C. Synthesis of a block polymer:

[0100] 48.8 mg of metallocene [{Me 2 SiFlu 2 Nd(µ-BH 4 ) 2 Li(THF)}] 2 (76.3µmol) in solution in 40 mL of MCH is introduced into the reaction medium containing the asymmetric diorganomagnesium (polyisoprene-Mg-mesityl). An additional 40 mL of MCH is used to rinse the steinie bottle containing the metallocene, then introduced into the reaction medium.

[0101] The reactor is then conditioned under vacuum, and then a gas mixture containing 20 mol% butadiene and 80 mol% ethylene is introduced into the reactor. The polymerization is carried out at 50°C, at an initial pressure of 4 bars absolute in the glass reactor.

[0102] The polymerization reaction is stopped, after the formation of 11g of polymer, by cooling, degassing the reactor and adding methanol. The polymer is recovered and then dried. The weighed mass makes it possible to determine the average catalytic activity of the catalytic system expressed in kilograms of polymer synthesized per mole of neodymium metal and per hour (kg / mol.h).

[0103] The catalytic activity is 37 kg / mol.h.

[0104] The macrostructure and microstructure of the polymer are determined respectively by size exclusion chromatography according to the method described in paragraph 1 and by nuclear magnetic resonance, as described above in paragraph 2. The NMR results are shown in Table 2 which gives the molar percentage of the units in the diblock copolymer. The results of the SEC and NMR characterizations show that the polymer contains 15% by mass of polyisoprene and 85% by mass of a block polymer consisting of a first polyisoprene block and a second random block of ethylene and 1,3-butadiene. Table 2 Unit dibloc Butadiene, 1,2-unit 8 Butadiene, 1,4-unit 4 Ethylene 84 1,2-cyclohexanediyl 4 Isoprene, 1,4-unit 93,8 ± 0,9 Isoprene, 3,4-unit 6,2 ± 0,1 6. Example 3 in accordance with the invention: Synthesis of a living polyisoprene:

[0105] 280 mL of degassed methylcyclohexane (MCH) is introduced into a 750 mL Steinie bottle. 5.64 g of isoprene is introduced into the reaction medium followed by 5.5 mL of n-BuLi at 0.06 mol / L. The polymerization is maintained at 50°C for 2 h. The measured conversion, by dry matter content, is 85%.

[0106] The number-average molar mass of polyisoprene is 22170 g / mol (Ip = 1.55), the molar ratios of the 1,4 and 3,4 units of the isoprene units are 94.1% and 5.9%, respectively. The macrostructure and microstructure of polyisoprene are determined by size-exclusion chromatography and nuclear magnetic resonance, respectively, as described above in paragraphs 1 and 2, respectively. Synthesis of an asymmetric diorganomagnesium (polyisoprene-Mg-mesityl):

[0107] The asymmetric diorganomagnesium compound (polyisoprene-Mg-mesityl) is synthesized by lithium-magnesium metal exchange reaction. 0.28 mL of 1 mol / L mesityl-Mg-Br in dibutyl ether is introduced onto the lithiated living polyisoprene. The reaction medium is stirred for 1 h at 23°C. Synthesis of a block polymer:

[0108] In a 500 mL glass reactor, heated to 80°C, a solution containing 280 mL of the asymmetric diorganomagnesium polyisoprene-Mg-mesityl and 42.4 mg of metallocene [{Me 2 SiFlu 2 Nd(µ-BH 4 ) 2 Li(THF)}] 2 (76.3 µmol) is introduced.

[0109] Then a gas mixture containing 20 mol% butadiene and 80 mol% ethylene is introduced into the reactor. The polymerization is carried out at 80°C and at an initial pressure of 4 bars absolute in the reactor.

[0110] The polymerization reaction is stopped, after formation of 3 g of polymer, by cooling, degassing the reactor and adding methanol. The polymer is recovered and then dried. The weighed mass makes it possible to determine the average catalytic activity of the catalytic system expressed in kilograms of polymer synthesized per mole of neodymium metal and per hour (kg / mol.h).

[0111] The catalytic activity is 346 kg / mol.h.

[0112] The macrostructure and microstructure of the polymer are determined respectively by size exclusion chromatography according to the method described in paragraph 1 and by nuclear magnetic resonance, as described above in paragraph 2. The NMR results are shown in Table 3 which gives the molar percentage of the units in the diblock copolymer. The results of the SEC and NMR characterizations show that the polymer contains 50% by mass of polyisoprene and 50% by mass of a block copolymer consisting of a first polyisoprene block and a second random block of ethylene and 1,3-butadiene. Table 3 Unit dibloc Butadiene, 1,2-unit 8 Butadiene, 1,4-unit 11 Ethylene 81 1,2-cyclohexanediyl 0 Isoprene, 1,4-unit 94.1 ± 0,9 Isoprene, 3,4-unit 5.9 ± 0,2 7. Example 4 in accordance with the invention: Synthesis of a living polybutadiene:

[0113] 280 mL of degassed methylcyclohexane (MCH) is introduced into a 750 mL Steinie bottle. 5.64 g of butadiene is introduced into the reaction medium followed by 1 mL of sec-BuLi at 0.38 mol / L. The polymerization is maintained at 50°C for 2 hours. The measured conversion, by dry matter content, is 88%.

[0114] For its characterization, the living polybutadiene is deactivated by the addition of degassed methanol. The polymer solution is dried in an oven at 50°C under vacuum with a nitrogen sweep for 48 hours.

[0115] The number-average molar mass of polybutadiene is 23100 g / mol (Ip = 1.08), the molar ratios of the 1,4 and 1,2 units of the butadiene units are 92.8% and 7.2%, respectively. The macrostructure and microstructure of polybutadiene are determined by size-exclusion chromatography and nuclear magnetic resonance, respectively, as described above in paragraphs 1 and 2, respectively. Synthesis of an asymmetric diorganomagnesium (polybutadiene-Mg-mesityl):

[0116] The asymmetric diorganomagnesium compound (polybutadiene-Mg-mesityl) is synthesized by lithium-magnesium metal exchange reaction. 0.3 mL of 1 mol / L mesityl-Mg-Br in dibutyl ether is introduced onto the lithiated living polybutadiene. The reaction medium is stirred for 1 hour at 23°C. Synthesis of a block polymer:

[0117] In a 500mL glass reactor, heated to 80°C, a solution containing 280 mL of the asymmetric diorganomagnesium polybutadiene-Mg-mesityl and 45.1 mg of metallocene [{Me 2 SiFlu 2 Nd(µ-BH 4 ) 2 Li(THF)}] 2 (76.3µmol) is introduced.

[0118] Then a gas mixture containing 20 mol% butadiene and 80 mol% ethylene is introduced into the reactor. The polymerization is carried out at 80°C and at an initial pressure of 4 bars absolute in the reactor.

[0119] The polymerization reaction is stopped, after formation of 3 g of polymer, by cooling, degassing the reactor and adding methanol. The polymer is recovered and then dried. The weighed mass makes it possible to determine the average catalytic activity of the catalytic system expressed in kilograms of polymer synthesized per mole of neodymium metal and per hour (kg / mol.h).

[0120] The catalytic activity is 193 kg / mol.h.

[0121] The macrostructure and microstructure of the polymer are determined respectively by size exclusion chromatography according to the method described in paragraph 1 and by nuclear magnetic resonance, as described above in paragraph 2. The NMR results are shown in Table 4 which gives the molar percentage of the units in the diblock copolymer. The results of the SEC and NMR characterizations show that the polymer contains 30% by mass of polybutadiene and 70% by mass of a block copolymer consisting of a first block of polybutadiene and a second random block of ethylene and 1,3-butadiene. Table 4 Unit dibloc Butadiene, 1,2-unit 15.3 Butadiene, 1,4-unit 84.7 Ethylene 39 1,2-cyclohexanediyl 6 8. Example 5 not compliant: Synthesis of a living polybutadiene:

[0122] 50 mL of degassed toluene (MCH) is introduced into a 250 mL Steinie bottle. 2.5 g of butadiene is introduced into the reaction medium followed by 0.54 mL of n-BuLi at 0.19 mol / L. The polymerization is maintained at 60°C for 1.5 hours. The measured conversion, by dry matter content, is 91%.

[0123] For its characterization, the living polybutadiene is deactivated by the addition of degassed methanol. The polymer solution is dried in an oven at 50°C under vacuum with a nitrogen sweep for 48 hours.

[0124] The number-average molar mass of polybutadiene is 50750 g / mol (Ip = 1.08). The macrostructure is determined by size-exclusion chromatography, as described above in paragraph 1. Synthesis of a block polymer:

[0125] In a 500mL glass reactor, heated to 80°C, a solution containing 240 mL of toluene and 62.2 mg of metallocene [{Me 2 SiFlu 2 Nd(µ-BH 4 ) 2 Li(THF)}] 2 (96.5µmol) is introduced. The living polybutadiene solution, prepared in the previous paragraph, is added to the reactor and then a gas mixture containing 20 mol% of butadiene and 80 mol% of ethylene is introduced into the reactor. The polymerization is carried out at 80°C and at an initial pressure of 4 bars absolute in the reactor.

[0126] The polymerization reaction is stopped, after formation of 3 g of polymer, by cooling, degassing the reactor and adding methanol. The polymer is recovered and then dried. The weighed mass makes it possible to determine the average catalytic activity of the catalytic system expressed in kilograms of polymer synthesized per mole of neodymium metal and per hour (kg / mol.h).

[0127] The catalytic activity is 59 kg / mol.h.

[0128] The macrostructure of the polymer is determined by size exclusion chromatography according to the method described in paragraph 1. The result of SEC characterizations shows that the polymer contains 50% by mass of polybutadiene and 50% by mass of a block copolymer consisting of a first block of polybutadiene and a second statistical block of ethylene and 1,3-butadiene. 9. Example 6 not in accordance with the invention: Synthesis of a living polybutadiene:

[0129] 50 mL of degassed toluene (MCH) is introduced into a 250 mL Steinie bottle. 1 g of butadiene is introduced into the reaction medium followed by 0.54 mL of n-BuLi at 0.19 mol / L. The polymerization is maintained at 60°C for 1h30.

[0130] For its characterization, the living polybutadiene is deactivated by the addition of degassed methanol. The polymer solution is dried in an oven at 50°C under vacuum with a nitrogen sweep for 48 hours.

[0131] The number-average molar mass of polybutadiene is 17140 g / mol (Ip = 1.12). The macrostructure is determined by size-exclusion chromatography as described above in paragraph 1. Synthesis of a block polymer:

[0132] In a 500mL glass reactor, heated to 80°C, a solution containing 246 mL of toluene and 61.7 mg of metallocene [{Me 2 SiFlu 2 Nd(µ-BH 4 ) 2 Li(THF)}] 2 (96.5µmol) is introduced. The living polybutadiene solution, prepared in the previous paragraph, is added to the reactor and then a gas mixture containing 20 mol% of butadiene and 80 mol% of ethylene is introduced into the reactor. The polymerization is carried out at 80°C and at an initial pressure of 4 bars absolute in the reactor.

[0133] The polymerization reaction is stopped, after formation of 3 g of polymer, by cooling, degassing the reactor and adding methanol. The polymer is recovered and then dried. The weighed mass makes it possible to determine the average catalytic activity of the catalytic system expressed in kilograms of polymer synthesized per mole of neodymium metal and per hour (kg / mol.h).

[0134] The catalytic activity is 75 kg / mol.h.

[0135] The macrostructure of the polymer is determined respectively by size exclusion chromatography according to the method described in paragraph 1. The results of the SEC characterizations show that the polymer contains 30% by mass of polybutadiene and 70% by mass of a block copolymer consisting of a first block of polybutadiene and a second statistical block of ethylene and 1,3-butadiene.

[0136] Table 5 lists the catalytic activities and productivities depending on whether a process in accordance with the invention (examples 3 and 4) or not in accordance with the invention (examples 5 and 6) is used. Table 5 Example Co-catalyst Activity (Kg / mol / h) Productivity (g / g) 3 Pl-Mg-Mes 346 90 4 PB-Mg-Mes 193 75 5 PBLi 59 24 6 PBLi 75 29

[0137] The results show that the process according to the invention is a much more efficient process with respect to catalytic activity and much more productive than the process not according to the invention in the synthesis of block polymer. In summary, the use of a diorganomagnesium compound according to the invention as a co-catalyst makes it possible to significantly improve the catalytic activity and productivity in the synthesis of block polymer.

Claims

1. Asymmetric diorganomagnesium compound of formula (I)         RB-Mg-RA     (I) RA being different from RB, RA being a polymer chain containing units of a first monomer chosen from the group of monomers consisting of 1,3-dienes, aromatic α-monoolefins and mixtures thereof, RB comprising a benzene nucleus substituted with a magnesium atom, one of the carbon atoms of the benzene nucleus ortho to the magnesium being substituted with a methyl, an ethyl, an isopropyl or forming a ring with the carbon atom which is its closest neighbour and which is meta to the magnesium, the other carbon atom of the benzene nucleus ortho to the magnesium being substituted with a methyl, an ethyl or an isopropyl, on condition that if one of the two ortho carbon atoms is substituted with an isopropyl, the second ortho carbon atom is not substituted with an isopropyl.

2. Asymmetric diorganomagnesium compound according to Claim 1, in which the diorganomagnesium compound is of formula (II) R1 and R5, which may be identical or different, represent a methyl or an ethyl, preferably a methyl, R2, R3 and R4, which may be identical or different, being a hydrogen atom or an alkyl, RA being defined according to Claim 1.

3. Asymmetric diorganomagnesium compound according to either of Claims 1 and 2, in which the carbon atoms of the benzene nucleus ortho to the magnesium are substituted with a methyl or an ethyl, preferably a methyl.

4. Asymmetric diorganomagnesium compound according to any one of Claims 1 to 3, in which RA is a 1,3-butadiene, isoprene or styrene homopolymer chain or a copolymer chain of monomers chosen from 1,3-butadiene, isoprene and styrene.

5. Catalytic system based at least: - on a metallocene of formula (Illa) or (Illb), preferably (IIIa), - on a diorganomagnesium compound as cocatalyst,         {P(Cp1)(Cp2)Y}     (Illa)         Cp3Cp4Y     (IIIb) Y denoting a group including a metal atom which is a rare-earth metal, Cp1, Cp2, Cp3 and Cp4, which may be identical or different, being chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted, P being a group bridging the two groups Cp1 and Cp2 and comprising a silicon or carbon atom, the diorganomagnesium compound being an asymmetric diorganomagnesium compound defined in any one of Claims 1 to 4.

6. Catalytic system according to Claim 5, in which Cp1 and Cp2 are identical and are chosen from the group consisting of substituted fluorenyl groups and the unsubstituted fluorenyl group of formula C13H8.

7. Catalytic system according to either of Claims 5 and 6, in which the symbol Y represents the group Met-G, with Met denoting a metal atom which is a rare-earth metal and G denoting a group comprising the borohydride BH4 unit or denoting a halogen atom chosen from the group consisting of chlorine, fluorine, bromine and iodine.

8. Catalytic system according to Claim 7, in which G denotes chlorine or the group of formula (IV)         (BH4)(1+y)-Ly-Nx     (IV) in which L represents an alkali metal chosen from the group consisting of lithium, sodium and potassium, N represents a molecule of an ether, preferably diethyl ether or tetrahydrofuran, x, which may or may not be an integer, is greater than or equal to 0, y, which is an integer, is greater than or equal to 0.

9. Catalytic system according to any one of Claims 5 to 8, in which the rare-earth metal is a lanthanide, the atomic number of which ranges from 57 to 71, preferably neodymium.

10. Catalytic system according to any one of Claims 5 to 9, in which the bridge P corresponds to the formula ZR1R2, Z representing a silicon or carbon atom and R1 and R2, which may be identical or different, each representing an alkyl group comprising from 1 to 20 carbon atoms, preferably a methyl.

11. Catalytic system according to Claim 10, in which Z is Si.

12. Catalytic system according to any one of Claims 5 to 11, in which the metallocene is of formula (III-1), (III-2), (III-3), (III-4) or (III-5):         [Me2Si(Flu)2Nd(µ-BH4)2Li(THF)]     (III-1)         [{Me2SiFlu2Nd(µ-BH4)2Li(THF)}2]     (III-2)         [Me2SiFlu2Nd(µ-BH4)(THF)]     (III-3)         [{Me2SiFlu2Nd(µ-BH4)(THF)}2]     (III-4)         [Me2SiFlu2Nd(µ-BH4)]     (III-5) Flu representing the C13H8 group.

13. Process for preparing a polymer, which comprises a step of polymerization of a second monomer chosen from the group of monomers consisting of conjugated dienes, ethylene, α-monoolefins and mixtures thereof in the presence of a catalytic system defined in any one of Claims 5 to 12.

14. Process according to Claim 13, in which the second monomer is ethylene or a mixture of a 1,3-diene and of ethylene, the 1,3-diene preferably being 1,3-butadiene, isoprene or a mixture thereof.

15. Process for preparing an asymmetric diorganomagnesium compound defined in any one of Claims 1 to 4, which comprises: - the placing in contact of a living anionic polymer of formula RALi with an organomagnesium halide of formula RB-Mg-X, - the reaction of the living anionic polymer and of the halide, X being a halogen chosen from the group consisting of chlorine, fluorine, bromine and iodine, RA and RB being defined according to any one of Claims 1 to 4.