Ethylene-rich diene triblock polymer with static block and two terminal polyethylene blocks

Description

[0001] The field of the present invention is that of diene copolymers rich in ethylene units.

[0002] It has been shown that statistical copolymers based on ethylene and 1,3-diene and rich in ethylene units exhibit interesting properties of stiffness, hysteresis, wear, and adhesion. See, for example, patent applications WO 2014114607 A1, WO 2016012259 A1, and WO 2016087248 A1.

[0003] Another advantage of these copolymers is the use of ethylene, a common and readily available monomer, accessible through fossil or biological sources. A further benefit of these copolymers is the presence of ethylene units along the polymer backbone. These units are significantly less susceptible than diene units to oxidative or thermo-oxidative degradation mechanisms, thus conferring improved stability and lifespan to the materials.

[0004] Controlling the rheology of a polymer is a key parameter in its industrialization and application. Manufacturing articles made entirely or partially from a polymer generally involves various operations such as mixing, extrusion, molding, etc., during which the polymer is subjected to a wide range of frequency stresses. The polymer's rheology must be suitable for these different operations to meet the quality criteria of the manufactured article and the productivity criteria in the manufacturing chain. In particular, high viscosity at low-frequency deformations is desirable to limit polymer flow phenomena. Solutions for increasing viscosity at low shear rates without affecting viscosity at higher shear rates are described, for example, in document WO 99 / 10421 A1.These methods involve crosslinking the polymer through radical reaction or modifying it with a polyfunctional coupling agent capable of inserting itself into CH bonds. Grafting associative functions onto a polymer is also a solution described in patent application WO 2008099125 A1 for improving the rheological properties of a polymer.

[0005] The Applicants discovered that it was possible to improve the rheological properties of statistical copolymers based on ethylene and 1,3-diene and rich in ethylene units without altering their mechanical, dynamic or thermal properties.

[0006] Thus, a first object of the invention is a triblock polymer of formula BAB in which the symbol A represents a so-called central block which is a statistical copolymer comprising units of a 1,3-diene and more than 50% by mole of ethylene units, and the symbols B each represent a so-called terminal block which is a polyethylene with a melting temperature above 90°C and a number-average molar mass greater than or equal to 2,000 g / mol and less than or equal to 10,000 g / mol, the rate of ethylene units in the central block being expressed as a mole percentage relative to the number of moles of monomer units constituting the central block.

[0007] A second object of the invention is a composition comprising a triblock polymer according to the invention and another component.

[0008] A third object of the invention is a method for synthesizing a triblock polymer according to the invention. Description

[0009] Any range of values ​​designated by the expression "between a and b" represents the range of values ​​greater than "a" and less than "b" (i.e., bounds a and b excluded) while any range of values ​​designated by the expression "from a to b" means the range of values ​​from "a" to "b" (i.e., including the strict bounds a and b).

[0010] The expression "based on" used to define the constituents of a catalytic system or composition refers to the mixture of these constituents, or the product of the reaction of some or all of these constituents with each other.

[0011] Unless otherwise stated, the rates of units resulting from the insertion of a monomer into a polymer are expressed as a mole percentage relative to the total number of monomer units that constitute the polymer.

[0012] The compounds mentioned in the description can be of fossil origin or bio-based. In the latter case, they may be partially or entirely derived from biomass or obtained from renewable raw materials derived from biomass. Similarly, the compounds mentioned may also come from the recycling of previously used materials; that is, they may be partially or entirely produced through a recycling process, or obtained from raw materials themselves derived from a recycling process.

[0013] The polymer according to the invention is a triblock with formula BAB. The central block, A, represents a block that is a statistical copolymer containing ethylene units and 1,3-diene units, meaning that the monomer units constituting the central block are statistically distributed within it due to the statistical incorporation of monomers into the growing polymer chain. The two other blocks, represented by B, are each a homopolymer, a polyethylene.

[0014] An ethylene unit is defined as a unit with the repeating unit -(CH₂-CH₂)-. The ethylene units present in block A, referred to as the central block, represent more than 50% by mole of the units constituting the central block. In this application, the proportion of ethylene units in the central block, that is, the number of moles of ethylene units in the central block, is expressed as a mole percentage relative to the number of moles of monomer units constituting the central block.

[0015] According to any one of the embodiments of the invention, the central block is preferably a statistical copolymer of ethylene and 1,3-diene, in which case the monomer units of the central block are those resulting from the copolymerization of ethylene and 1,3-diene and are statistically distributed in the central block.

[0016] According to the invention, the 1,3-diene whose monomeric units constitute the central block is a single compound, that is, a single 1,3-diene, or a mixture of 1,3-dienes that differ from one another in their chemical structure. The 1,3-diene is preferably 1,3-butadiene or isoprene, or a mixture of 1,3-dienes, one of which is 1,3-butadiene. More preferably, the 1,3-diene is 1,3-butadiene. Most preferably, the central block is a random copolymer of ethylene and 1,3-butadiene.

[0017] As is known, a 1,3-diene can insert itself into a growing polymer chain by a 1,4 or 2,1 or even 3,4 insertion in the case of substituted dienes such as isoprene to give rise respectively to the formation of 1,3-diene units of configuration 1,4, 1,3-diene units of configuration 1,2 or of configuration 3,4. Preferably, the 1,3-diene units in the configuration 1,2 and the 1,3-diene units in the configuration 3,4 represent more than 50% by mole of the 1,3-diene units.

[0018] According to one embodiment of the invention, the central block contains 1,3-diene units of the 1,4 configuration, preferably 1,4-trans. Preferably, the 1,3-diene units of the 1,4-trans configuration represent more than 50% by mole of the 1,3-diene units of the 1,4 configuration. More preferably, the 1,3-diene units of the 1,4-trans configuration represent 100% by mole of the 1,3-diene units of the 1,4 configuration.

[0019] According to a particularly preferred embodiment of the invention, the central block contains units of 1,3-diene which are more than 50% by mole of 1,2 or 3,4 configuration units, the complement to 100% of the 1,3-diene units being 1,4-trans configuration units.

[0020] According to another particularly preferred embodiment of the invention, especially when the 1,3-diene is 1,3-butadiene or a mixture of 1,3-dienes, one of which is 1,3-butadiene, the central block further contains 1,2-cyclohexanediyl motif units or 1,4-cyclohexanediyl motif units, preferably 1,2-cyclohexanediyl motif units. The presence of these cyclic structures in the central block results from a very specific insertion of ethylene and 1,3-butadiene during their copolymerization. The mechanism for obtaining such a microstructure is described, for example, in Macromolecules 2009, 42, 3774-3779. The content of 1,2-cyclohexanediyl motif units and 1,4-cyclohexanediyl motif units in the central block varies according to the respective contents of ethylene and 1,3-butadiene in the central block.The core block typically contains less than 10 mole percent of 1,2-cyclohexanediyl and 1,4-cyclohexanediyl repeating units at the highest ethylene levels in the core block, and may contain more than 10 mole percent at the lowest ethylene levels in the core block, for example up to 15 mole percent, relative to the number of moles of monomer units constituting the core block. The 1,2-cyclohexanediyl repeating unit corresponds to the following formula.

[0021] Since the stiffness of a triblock polymer increases with the proportion of ethylene units in the core block, a triblock polymer with a particularly high proportion of ethylene units in the core block may be desirable for applications requiring high material stiffness. Preferably, the ethylene units in the core block represent more than 60 mole percent of the units constituting the core block, in which case the core block contains more than 60 mole percent of ethylene units. More preferably, the ethylene units in the core block represent at least 70 mole percent of the units constituting the core block, in which case the core block contains at least 70 mole percent of ethylene units.

[0022] According to a particular embodiment of the invention, the ethylene units in the central block represent at most 90% by mole of the units that constitute the central block, in which case the central block contains at most 90% by mole of ethylene units.

[0023] According to another particular embodiment of the invention, the ethylene units in the central block represent at most 85% by mole of the units that constitute the central block, in which case the central block contains at most 85% by mole of ethylene units.

[0024] The central block preferably has a glass transition temperature between -90°C and -20°C. More preferably, the glass transition temperature of the central block is between -60°C and -20°C, advantageously between -50°C and -30°C.

[0025] The central block preferably has a number average molar mass greater than or equal to 3,000 g / mol and less than or equal to 80,000 g / mol.

[0026] The terminal blocks (B) are characterized by the essential fact that each is a polyethylene with a number-average molar mass greater than or equal to 2,000 g / mol and less than or equal to 10,000 g / mol. The terminal blocks also have another essential characteristic: a melting point above 90°C, preferably above 90°C and below 140°C. Preferably, B represents a linear polyethylene.

[0027] The triblock according to the invention can be prepared according to a process, which includes the statistical copolymerization of a monomer mixture containing ethylene and 1,3-diene, followed by the subsequent polymerization of ethylene.

[0028] The catalytic system used in the block polymer synthesis process is advantageously a catalytic system based at least on a metallocene of formula (I) and an organomagnesium compound P(Cp 1< Cp 2< )Nd(BH 4 ) (1+y) Li y (THF) x (I)

[0029] Cp 1< and Cp 2<, identical or different, being chosen from the group consisting of cyclopentadienyl groups and fluorenyl groups, the groups being substituted or not, P being a group bridging the two groups Cp 1< and Cp 2< and representing a group 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, y, an integer, being equal to or greater than 0, x, an integer or not, being equal to or greater than 0.

[0030] In formula (I), the neodymium atom is bonded to a ligand molecule consisting of two groups, Cp1 and Cp2, linked by the P-bridge. Preferably, the symbol P, designated as the bridge, has the formula ZR1R2, where Z represents a silicon 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 P-bridge has the formula SiR1R2, where R1 and R2 are identical and as defined above. Even more preferably, P has the formula SiMe2.

[0031] Examples of substituted cyclopentadienyl and fluorenyl groups include those substituted by alkyl radicals with 1 to 6 carbon atoms, aryl radicals with 6 to 12 carbon atoms, or trialkylsilyl radicals such as SiMe3. The choice of radicals is also guided by the accessibility of the corresponding molecules, namely the substituted cyclopentadienes and fluorenes, because these are either commercially available or easily synthesized.

[0032] Examples of substituted cyclopentadienyl groups include those substituted at both position 2 (or 5) and position 3 (or 4), particularly those substituted at position 2, more specifically the tetramethylcyclopentadienyl group. In the present application, for the cyclopentadienyl 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.

[0033] Examples of substituted fluorenyl groups include those substituted at positions 2,7, 3, or 6, particularly the 2,7-ditertiobutyl-fluorenyl and 3,6-ditertiobutyl-fluorenyl groups. 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.

[0034] Preferably, Cp1 and Cp2 are identical and are chosen from the group consisting of substituted fluorenyl groups and the fluorenyl group. Advantageously, in formula (I), Cp1 and Cp2 each represent a substituted fluorenyl group or a fluorenyl group, preferably a fluorenyl group. The fluorenyl group has the formula C13H8. Preferably, the metallocene has the formula (Ia), (Ib), (Ic), (Id), or (Ie), in which the symbol Flu represents the fluorenyl group of formula C13H8. [{Me 2 SiFlu 2 Nd(µ-BH 4 ) 2 Li(THF)} 2 ] (Ia) [Me 2 SiFlu 2 Nd(µ-BH 4 ) 2 Li(THF)] (Ib) [Me 2 SiFlu 2 Nd(µ-BH 4 )(THF)] (Ic) [{Me 2 SiFlu 2 Nd(µ-BH 4 )(THF) 2 ] (Id) [Me 2 SiFlu 2 Nd(µ-BH 4 )] (Ie)

[0035] The organomagnesium compound used in the catalytic system as a co-catalyst is an organomagnesium compound of formula (II) or formula (III), RB< -(Mg-R A< ) m -Mg-R B< (II) X-Mg-R C< -Mg-X (III) RA< being an aliphatic hydrocarbon divalent chain, interrupted or not by one or more oxygen or sulfur atoms or by one or more arylene groups, 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, RC< being an aliphatic hydrocarbon divalent chain, interrupted or not by one or more oxygen or sulfur atoms or by one or more arylene groups, X being a halogen atom, m being a number greater than or equal to 1, preferably equal to 1.

[0036] The co-catalysts of formulas (II) and (III) both share the characteristic of having magnesium-carbon bonds involving distinct magnesium atoms. In formula (II), two magnesium atoms each share a first bond with a first carbon atom belonging to RB< and a second bond with a second carbon atom belonging to RA<. The first carbon atom is part of the benzene ring of RB<. The second carbon atom is part of the aliphatic hydrocarbon chain RA<, which may contain within its chain one or more heteroatoms chosen from oxygen and sulfur, or one or more arylene groups. In the preferred case where m equals 1, each magnesium atom therefore shares a first bond with a first carbon atom of RB< and a second bond with a second carbon atom of RA<.In formula (III), each magnesium atom therefore shares a first bond with a halogen atom and a second bond with a carbon atom of RC< .

[0037] In formula (II), RB< is characterized by a benzene ring substituted by a magnesium atom. The two carbon atoms of the benzene ring of RB< ortho to magnesium bear a substituent, either identical or different. Alternatively, one of the two carbon atoms of the benzene ring of RB< ortho to magnesium may bear a substituent, while the other carbon atom of the benzene ring of RB< ortho to magnesium may form a ring. The substituent is a methyl, an ethyl, or an isopropyl. If one of the two carbon atoms of the benzene ring of RB< ortho to magnesium is substituted by an isopropyl, preferably the second carbon atom of the benzene ring of RB< ortho to magnesium is not substituted by an isopropyl. Preferably, the carbon atoms of the benzene ring of RB< in ortho to magnesium are substituted by a methyl or an ethyl.More preferentially, the carbon atoms of the benzene ring of RB< in ortho to magnesium are substituted by a methyl.

[0038] The organomagnesium compound of formula (II) preferably corresponds to the formula (Ila-m) in which m is greater than or equal to 1, R1 and R5, identical or different, represent a methyl or an ethyl group, preferably a methyl group, R2, R3, and R4, identical or different, represent a hydrogen atom or an alkyl group, and RA< is an aliphatic hydrocarbon divalent chain, interrupted or not by one or more oxygen or sulfur atoms or by one or more arylene groups. Preferably, R1 and R5 represent a methyl group. Preferably, R2 and R4 represent a hydrogen atom.

[0039] The organomagnesium compound with formula (Ila-m) has formula (IIa-1) in the case where m is equal to 1.

[0040] According to a preferred variant, R1, R3, and R5 are identical in formula (IIa-m), specifically in formula (IIa-1). According to a more preferred variant, R2 and R4 represent hydrogen, and R1, R3, and R5 are identical. In a further preferred variant, R2 and R4 represent hydrogen, and R1, R3, and R5 represent methyl.

[0041] In formulas (II) and (IIa-m), particularly in formula (IIa-1), RA< is a divalent aliphatic hydrocarbon chain that may contain within its chain one or more heteroatoms selected from oxygen and sulfur, or one or more arylene groups. Preferably, RA< is a branched or linear alkanediyl, a cycloalkanediyl, or a xylenediyl radical. More preferably, RA< is an alkanediyl.

[0042] Preferably, RA< contains 3 to 10 carbon atoms, in particular 3 to 8 carbon atoms.

[0043] Even more preferably, RA< is an alkanediyl group having 3 to 10 carbon atoms. Advantageously, RA< is an alkanediyl group having 3 to 8 carbon atoms. Very advantageously, RA< is a linear alkanediyl group. Particularly suitable RA< groups are 1,3-propanediyl, 1,4-butanediyl, 1,5-pentanediyl, 1,6-hexanediyl, 1,7-heptanediyl, and 1,8-octanediyl.

[0044] According to any one of the embodiments of the invention, m is preferably equal to 1 in formula (II), in particular in formula (Ila-m).

[0045] The organomagnesium compound of formula (II) can be prepared by a process that includes the reaction of a first organomagnesium compound of formula X'Mg-RAA -MgX' with a second organomagnesium compound of formula RBA -Mg-X', where X' represents a halogen atom, preferably bromine or chlorine, and RBA and RAA are as defined previously. X' is more preferably a bromine atom. The stoichiometry used in the reaction determines the value of m in formula (II) and in formula (IIa-m). For example, a molar ratio of 0.5 between the amount of the first organomagnesium and the amount of the second organomagnesium is favorable to the formation of an organomagnesium compound of formula (II) 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 (II) in which m is greater than 1.

[0046] 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. 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. 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 and second organomagnesium compounds are 0.1 to 2 mol / L and 0.2 to 4 mol / L, respectively.

[0047] The first organomagnesium compound and the second organomagnesium compound can be prepared beforehand by a Grignard reaction using magnesium metal and a suitable precursor. For the first and second organomagnesium compounds, the respective precursors have the formulas X'-RA< -X' and RB< -X', where RA< , RB< , and X' are as defined previously. The Grignard reaction is typically carried out by adding the precursor to magnesium metal, which is usually 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 to activate the Grignard reaction in a known manner.

[0048] Alternatively, the organomagnesium compound according to the invention can be prepared by reacting an organometallic compound of formula MRA -M and the organomagnesium compound of formula RBMg -Mg-X', where M represents a lithium, sodium, or potassium atom, and X', RBMg, and RAMg are as defined above. Preferably, M represents a lithium atom, in which case the organometallic compound of formula MRA -M is an organolithium compound.

[0049] The reaction of the organolithium and organomagnesium compounds is typically carried out in an ether such as diethyl ether, dibutyl ether, tetrahydrofuran, or methyltetrahydrofuran. The reaction is also typically conducted 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 with formula MR< -M with the organomagnesium compound with formula RB< -Mg-X' is preferentially achieved by adding a solution of the organometallic compound MR< -M to a solution of the organomagnesium compound RB< -Mg-X'. The solution of the organometallic compound MR< -M is generally a solution in a hydrocarbon solvent, preferably n-hexane, cyclohexane, or methylcyclohexane. The solution of the organomagnesium RB< -Mg-X' is generally a solution in an ether, preferably diethyl ether or dibutyl ether.Preferably, the respective concentrations of the solutions of the organometallic compound and the organomagnesium compound MR A< -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 MR A< -M and RB< -Mg-X' are 0.05 to 0.5 mol / L and 0.2 to 3 mol / L, respectively.

[0050] As with all syntheses 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.

[0051] Once the organomagnesium compound of formula (II) 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, such as capped bottles, at a temperature between -25°C and 23°C before use.

[0052] Like all organomagnesium compounds, the organomagnesium compound of formula (II) can exist as a monomeric entity (RB< -(Mg-RA< ) m -Mg-RA< ) ) 1 or as a polymeric entity (RB< -(Mg-RA< ) m -Mg-RA< ) p, where p is an integer greater than 1, in particular as a dimer (RB< -(Mg-RA< ) m -Mg-RA< ) ) 2, where m is as defined previously. Furthermore, whether in monomeric or polymeric form, it can also exist as a coordinated entity to one or more molecules of a solvent, preferably an ether such as diethyl ether, tetrahydrofuran, or methyltetrahydrofuran.

[0053] In formula (III), RC< is a divalent aliphatic hydrocarbon chain that may contain within its chain one or more heteroatoms selected from oxygen and sulfur, or one or more arylene groups. Preferably, RC< is a branched or linear alkanediyl, a cycloalkanediyl, or a xylenediyl radical. Even more preferably, RC< is an alkanediyl.

[0054] Preferably, RC< contains 3 to 10 carbon atoms, in particular 3 to 8 carbon atoms.

[0055] Even more preferably, RC< is an alkanediyl group having 3 to 10 carbon atoms. Advantageously, RC< is an alkanediyl group having 3 to 8 carbon atoms. Very advantageously, RC< is a linear alkanediyl group. 1,3-propanediyl, 1,4-butanediyl, 1,5-pentanediyl, 1,6-hexanediyl, 1,7-heptanediyl, and 1,8-octanediyl groups are particularly suitable as RC< groups.

[0056] Compounds of formula (III) are well-known Grignard reagents. However, they are not known to be used as co-catalysts in catalytic systems for the preparation of triblock polymers. Grignard reagents of formula (III) are described, for example, in J. March'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 XRC<-X, where RC< is as defined according to the invention. For their synthesis, reference may be made, for example, to the "Organic Synthesis" series.

[0057] Like any organomagnesium compound, the organomagnesium compound of formula (III) can exist as a monomeric entity (X-Mg-R C< -Mg-X), or as a polymeric entity (X-Mg-R C< -Mg-X) p, where p is an integer greater than 1, in particular a dimer (X-Mg-R C< -Mg-X) 2. Furthermore, whether in the form of a monomeric or polymeric entity, it can also exist as an entity coordinated to one or more molecules of a solvent, preferably an ether such as diethyl ether, tetrahydrofuran, or methyltetrahydrofuran.

[0058] The catalytic system can be prepared conventionally by a process analogous to that described in patent applications WO 2007054224 or WO 2007054223. For example, the organomagnesium compound and the metallocene are typically reacted in a hydrocarbon solvent at a temperature of 20 to 80°C for a duration of 5 to 60 minutes. The catalytic system is generally prepared in a hydrocarbon solvent, either aliphatic such as methylcyclohexane or aromatic such as toluene.

[0059] The metallocene used to prepare the catalytic system can be in the form of crystalline or non-crystalline powder, or as single crystals. The metallocene can be monomeric or dimeric, depending on the method of preparation, as described in patent applications WO 2007054224 or WO 2007054223. The metallocene can be prepared conventionally by a process analogous to that described in patent applications WO 2007054224 or WO 2007054223, specifically by reacting, under inert and anhydrous conditions, the salt of an alkali metal of the ligand with a rare-earth borohydride, in this case 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.

[0060] As with any synthesis carried out in the presence of organometallic compounds, the synthesis of the metallocene and that of the catalytic system take place under anhydrous conditions in an inert atmosphere. Typically, the reactions are conducted using solvents and anhydrous compounds under anhydrous nitrogen or argon.

[0061] The catalytic system is generally introduced into the reactor containing the polymerization solvent and the monomers. To achieve the desired macrostructure of the triblock polymer, those skilled in the art adjust the polymerization conditions, particularly the molar ratio of the organomagnesium compound to the Nd metal constituting the metallocene. The amounts of co-catalyst and metallocene reacted are such that the ratio of the number of moles of Mg in the co-catalyst to the number of moles of rare-earth metal in the metallocene preferably ranges from 1 to 200, and more preferably from 1 to less than 20. The range of values ​​from 1 to less than 20 is particularly favorable for obtaining polymers with high molar masses. The catalytic system is generally prepared in a hydrocarbon solvent, either aliphatic such as methylcyclohexane or aromatic such as toluene.Generally, after its synthesis, the catalytic system is used as is in the polymer synthesis process according to the invention.

[0062] A person skilled in the art also adjusts the polymerization conditions and the concentrations of each of the reactants (components of the catalytic system, monomers) according to the equipment (tools, reactors) used to carry out the polymerization and the various chemical reactions. As is known to those skilled in the art, polymerization, as well as the handling of the monomers, the catalytic system, and the polymerization solvent(s), is performed under anhydrous conditions and in an inert atmosphere. Polymerization solvents are typically hydrocarbon, aliphatic, or aromatic solvents.

[0063] Polymerization is preferably carried out in solution, either continuously or batchwise, in a stirred reactor. The polymerization solvent may be a hydrocarbon, aromatic, or aliphatic solvent. Examples of polymerization solvents include toluene and methylcyclohexane. Advantageously, polymerization is carried out in solution in a hydrocarbon solvent.

[0064] The preparation of the central block is carried out by copolymerizing the mixture containing ethylene and 1,3-diene. The polymerization temperature generally varies from 30 to 160°C, preferably from 30 to 120°C. During the preparation of the central block, the temperature of the reaction medium is advantageously kept constant during copolymerization, and the total reactor pressure is also advantageously kept constant. The preparation of the central block is completed by stopping the supply of monomers, notably by dropping the reactor pressure, preferably to approximately 3 bar.

[0065] The preparation of the terminal blocks by subsequent polymerization of ethylene continues by applying ethylene pressure in the reactor. This pressure is maintained constant until the desired ethylene consumption is reached to achieve the desired number-average molar mass of the terminal block. The ethylene polymerization temperature is preferably set at the same temperature as that used for the preparation of the central block. The polymerization temperature for terminal block preparation generally ranges from 30 to 160°C, preferably from 30 to 120°C. The pressure for terminal block preparation generally ranges from 1 bar to 150 bar, preferably from 1 bar to 10 bar. The synthesis of the terminal blocks is complete when they reach the desired number-average molar mass.

[0066] Polymerization can be stopped by cooling the polymerization medium or by adding an alcohol, preferably one containing 1 to 3 carbon atoms, such as ethanol. The triblock polymer can be recovered using conventional techniques known to those skilled in the art, such as precipitation, evaporation of the solvent under reduced pressure, or steam stripping.

[0067] The triblock polymer according to the invention exhibits improved rheology compared to a random copolymer with the same microstructure and macrostructure as the central block of the triblock polymer. This improved rheology is manifested by a significant increase in polymer viscosity at low shear rates (typically below 10 rad / s), while having a minimal impact on viscosity at high shear rates (typically above 50 rad / s). This improved rheology allows for greater control over polymer flow during operations that stress the polymer at low shear rates, such as hot extrusion. This result is all the more surprising as it is obtained without any modification to the polymer's macrostructure or its thermal property, namely the glass transition temperature.Indeed, the triblock remains a linear chain, like the statistical copolymer with the same microstructure as the central block, and it retains the glass transition temperature of this same statistical copolymer. Preferably, the triblock polymer according to the invention is an elastomer.

[0068] The triblock polymer according to the invention can be used in a composition, another object of the invention, which further comprises another component. The other component may be a filler such as carbon black or silica, a plasticizer such as oil, a crosslinking agent such as sulfur or a peroxide, or an antioxidant. The other component may also be a polymer, in particular an elastomer. The composition may be a rubber composition. The aforementioned features of the present invention, as well as others, will be better understood upon reading the following description of several illustrative and non-limiting embodiments of the invention. Example :

[0069] High temperature size exclusion chromatography (HTSEC).High-temperature size exclusion chromatography (HT-SEC) analyses were performed using a Viscotek instrument (Malvern Instruments) equipped with three columns (PLgel Olexis 300 mm × 7 mm ID from Agilent Technologies) and three detectors (differential refractometer and viscometer, and light scattering). 200 µL of a 3 mg mL⁻¹ sample solution was eluted in 1,2,4-trichlorobenzene at a flow rate of 1 mL min⁻¹ at 150 °C. The mobile phase was stabilized with 2,6-di(tert-butyl)-4-methylphenol (400 mg L⁻¹). OmniSEC software was used for data acquisition and analysis. The number-average (Mn) and mass-average (Mw) molar masses of the synthesized ethylene-butadiene copolymers are calculated using a universal calibration curve calibrated from standard polystyrenes (peak molar masses Mp: 672 to 12,000,000 g mol⁻¹ ) of Polymer Standard Service (Mainz) using refractometer and viscometer detectors. Dispersion Ð ( Ð (Mw / Mn) is also calculated.

[0070] Nuclear magnetic resonance (NMR). High-resolution ¹H NMR spectroscopy of the copolymers was performed on a Bruker 400 Avance III spectrometer operating at 400 MHz equipped with a 5 mm BBFO probe. Acquisitions were made at 363 K. A mixture of tetrachloroethylene (TCE) and deuterated benzene (C₆D₆) (2:1 v / v) was used as the solvent. The samples were analyzed at a concentration of 17 g L⁻¹. Chemical shifts are given in ppm, relative to the deuterated benzene proton signal set at 7.16 ppm. The number of acquisitions was set at 512.

[0071] Differential scanning calorimetry (DSC).The analyses are carried out on a DSC 3+< instrument (Mettler Toledo) following a dynamic method comprising 9 temperature steps: Step 1: 20 to 180 °C (10 °C min -1< ), Step 2: isothermal 180 °C (5 min), Step 3: 180 to -80 °C (-10 °C min -1< ), Step 4: isothermal -80 °C (5 min), Step 5: -80 to 180 °C (10 °C min -1< ), Step 6: isothermal 180 °C (5 min), Step 7: 180 to -80 °C (10 °C min -1< ), Step 8: isothermal -80 °C (5 min), Step 9: -80 to 180 °C (10 °C min -1< ). The first two steps erase the sample's thermal history. Glass transition and melting point measurements are taken on the 9th step. The 7th step is also retained to obtain information on the sample's crystallization.

[0072] Rheological analysis.The analyses are performed on a MARS 60 rotational rheometer (Thermo Scientific) equipped with a lower flat / upper Peltier furnace assembly featuring 8 mm flat-flat geometries. The powdered samples are pressed into discs at 150 °C (1 to 1.5 mm thick) for 5 min, then cut into 8 mm diameter discs using a punch. These are then placed in the rheometer at 150 °C.

[0073] Example 1: Preparation of a co-catalyst, 1,5-di(magnesium bromide)-pentanediyl (DBMP). 1.25 g (50 mmol, 10 equivalents) of magnesium are inert in a 50 mL round-bottom flask fitted with a magnetic stir bar and a 10 mL dropping funnel. A 10 mg iodine bead is introduced onto the magnesium. 11 mL of sodium / benzophenone distilled MeTHF is introduced into the flask while stirring, and 9 mL is introduced into the dropping funnel. 0.68 mL of degassed and activated molecular sieve-dried 1,5-dibromopentane (5 mmol, 1 equivalent) is introduced into the dropping funnel. The haloalkane solution is added dropwise to the magnesium for 1 h. Stirring is maintained for 12 h at 20 °C. This solution is concentrated under vacuum and then diluted in 10 mL of toluene. The concentration of the pentanediyl group is estimated at 0.45 mol L⁻¹.

[0074] 1< H NMR (C 6 D 6 - 400 MHz - 298 K) δ: ppm = 2.06 (quin, J = 7.6 Hz, “b”), 1.80 (quin, J = 7.4 Hz, “c”), -0.05 (t, J = 7.7 Hz, “a”); quin for quintuplet.

[0075] Example 2: Preparation of a statistical copolymer of ethylene and reference 1,3-butadiene. 200 mL of toluene (Biosolve) purified on an SPS800 MBraun system are introduced into a 250 mL inert flask fitted with a magnetic stir bar. 0.31 mL (0.14 mmol) of a 1,5-di(magnesium bromide)pentanediyl (DBMP 0.45 mol L⁻¹) solution prepared according to Example 1 is introduced into the flask with stirring. 32 mg (50 µmol neodymium) of {(Me₂Si(C₁₃H₈)₂)Nd(-BH₄)[(-BH₄)Li(THF)]}₂ are then introduced into the flask.

[0076] The catalytic solution is transferred via a cannula into a 250 mL reactor under an inert atmosphere at 70 °C. The argon overpressure in the reactor is reduced to 0.5 bar, and then the reactor is pressurized to 4 bar with an ethylene / butadiene mixture with an 80 / 20 molar ratio, stirred at 1000 rpm. The pressure is maintained constant in the reactor using a reservoir containing the ethylene / butadiene mixture. After a pressure drop in the reservoir, equivalent to approximately 10 g of monomers for a target Mn of 72,000 g mol⁻¹, the feed is stopped, the reactor is degassed, and the temperature is lowered to 20 °C. The copolymer solution is precipitated in methanol with stirring in the presence of approximately 20 mg of 2,2'-Methylenebis(6-tert-butyl-4-methylphenol) as an antioxidant. The resulting copolymer is dried under vacuum at 70 °C for 4 h.

[0077] Example 3: Preparation of a triblock polymer according to the invention, with a central block of ethylene-1,3-butadiene copolymer and polyethylene terminal blocks: 200 mL of toluene (Biosolve) purified on an SPS800 MBraun system are introduced into a 250 mL inert flask fitted with a magnetic stir bar. 0.6 mL (0.25 mmol) of a 1,5-di(magnesium bromide)pentanediyl (DBMP 0.45 mol L⁻¹) solution prepared according to Example 1 is introduced into the flask while stirring. 16 mg (25 µmol neodymium) of {(Me₂Si(C₁₃H₈)₂)Nd(-BH₄)[(-BH₄)Li(THF)]}₂ are then introduced into the flask.

[0078] Preparation of the core block (Step 1): The catalytic solution is transferred via a cannula into a 250 mL reactor under an inert atmosphere at 70 °C. The argon overpressure in the reactor is reduced to 0.5 bar, and then the reactor is pressurized to 4 bar with an ethylene / butadiene mixture with an 80 / 20 molar ratio, stirred at 1000 rpm. The pressure is maintained constant in the reactor using a reservoir containing the ethylene / butadiene mixture. After a pressure drop in the reservoir equivalent to approximately 13 g of monomers, the feed is stopped, and the reactor is isolated until the pressure in the reactor reaches 2.8 bar to obtain 15 g of copolymer, corresponding to a target Mn of the core block of 60,000 g mol⁻¹.

[0079] Preparation of terminal blocks (Step 2): The reactor is again pressurized to 4 bars using a tank containing only ethylene, then approximately 3 g of monomers are consumed by pressure drop in the tank, resulting in a target Mn of the terminal blocks of 6,000 g mol -1 each.

[0080] The reactor is degassed and the temperature is lowered to 20 °C. The copolymer solution is precipitated in methanol with stirring in the presence of approximately 20 mg of 2,2'-Methylenebis(6-tert-butyl-4-methylphenol) as an antioxidant. The resulting copolymer is dried under vacuum at 70 °C for 4 h.

[0081] The polymer characteristics are listed in Table 1. In Table 1, the ethylene unit content, the 1,3-butadiene unit content in the 1,2 configuration (1,2 units), in the 1,4 configuration (1,4 units), and the 1,2-cyclohexanediyl repeating unit content (ring units) are expressed as mole percentages relative to the total monomer units of the polymer. The rheological properties are listed in Table 2. [Table 1] Ex. ethylene unit unit 1.2 unit 1.4 unit cycle Tg (°C) Tf (°C) crystallinity rate (%) M n (g / mol) Ð 2 74,4 10,0 5,9 9,7 -35 - - 61400 1,9 3 81,9 6,7 4,0 7,4 -35 122 8,9 62600 2,9 [Table 2] Ex. G' at 0.1 Hz, at 150°C G' at 10 Hz, at 150°C 2 100 100 3 285 115

[0082] Comparison of Examples 2 and 3 shows that the G' value of the triblock polymer measured at low shear rates, typically below 10 rad / s, is amplified compared to the reference polymer. Indeed, at 0.1 Hz (i.e., 0.6 rad / s), it is nearly three times greater than the G' value of the reference polymer. For high shear rates, typically above 50 rad / s, the multiplicative factor is much smaller, being only 1.1 at 10 Hz (i.e., 62 rad / s). The use of a triblock polymer according to the invention, instead of a statistical polymer, does indeed allow for a significant increase in the polymer's viscosity at low shear rates, while the impact on viscosity is relatively small at high shear rates.This increase in viscosity at low shear rates makes it possible to limit the flow phenomena of the polymer in polymer transformation processes at low shear rates without significant modification of its rheological properties at high shear rates.

[0083] These results reflect an improvement in the rheology of a statistical copolymer of ethylene and a 1,3-diene without modifying the macrostructure of the triblock compared to the statistical copolymer and the microstructure of the statistical copolymer part, which allows the intrinsic properties of the statistical copolymer to be preserved in the triblock polymer as well.

Claims

1. Triblock polymer of formula B-A-B in which the symbol A represents a "central" block which is a statistical copolymer comprising units of a 1,3-diene and more than 50 mol% of ethylene units, and the symbols B each represent an "end" block which is a polyethylene with a melting point of greater than 90°C and a number-average molar mass of greater than or equal to 2000 g / mol and less than or equal to 10 000 g / mol, the content of the ethylene units in the central block being expressed as a molar percentage relative to the number of moles of monomer units constituting the central block.

2. Triblock polymer according to Claim 1, in which the central block is a statistical copolymer of ethylene and 1,3-diene.

3. Triblock polymer according to Claim 1 or 2, in which the central block contains more than 60 mol% of ethylene units, preferably at least 70 mol% of ethylene units.

4. Triblock polymer according to any one of Claims 1 to 3, in which the central block contains not more than 90 mol% of ethylene units.

5. Triblock polymer according to any one of Claims 1 to 4, in which the central block contains not more than 85 mol% of ethylene units.

6. Triblock polymer according to any one of Claims 1 to 5, in which the central block has a glass transition temperature of between -90°C and -20°C.

7. Triblock polymer according to any one of Claims 1 to 6, in which the central block has a number-average molar mass of greater than or equal to 3000 g / mol and less than or equal to 80 000 g / mol.

8. Triblock polymer according to any one of Claims 1 to 7, in which the 1,3-diene is 1,3-butadiene, isoprene or a mixture of 1,3-dienes, one of which is 1,3-butadiene, preferably 1,3-butadiene.

9. Triblock polymer according to any one of Claims 1 to 8, 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 the central block contains 1,2-cyclohexanediyl units or 1,4-cyclohexanediyl units, preferably 1,2-cyclohexanediyl units.

10. Triblock polymer according to any one of Claims 1 to 9, in which the polymer is an elastomer.

11. Composition which comprises a triblock polymer according to any one of Claims 1 to 10 and another component.

12. Process for synthesizing a triblock polymer defined in any one of Claims 1 to 10, which comprises the statistical copolymerization of a monomer mixture containing ethylene and a 1,3-diene, followed by the subsequent polymerization of ethylene in the presence of a catalytic system based on at least one metallocene of formula (I) and an organomagnesium reagent of formula (II) or (III)         P(Cp1Cp2)Nd(BH4)(1+y)Liy(THF)x     (I)         RB-(Mg-RA)m-Mg-RB     (II)         X-Mg-RC-Mg- X     (III) Cp1 and Cp2, which are identical or different, being chosen from the group consisting of cyclopentadienyl groups and fluorenyl groups, the groups being substituted or unsubstituted, P being a group bridging the two Cp1 and Cp2 groups and representing a ZR1R2 group, Z representing a silicon or carbon atom, R1 and R2, which are identical or different, each representing an alkyl group comprising from 1 to 20 carbon atoms, preferably a methyl, y, which is an integer, being equal to or greater than 0, x, which may or may not be an integer, being equal to or greater than 0, RA being a divalent aliphatic hydrocarbon-based chain, interrupted or not with one or more oxygen or sulfur atoms or with one or more arylene groups, RB comprising a benzene nucleus substituted with the 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, RC being a divalent aliphatic hydrocarbon-based chain, interrupted or not with one or more oxygen or sulfur atoms or with one or more arylene groups, X being a halogen atom, m being a number greater than or equal to 1 and preferably equal to 1.