RUBBER COMPOSITION

Description

[0001] The field of the invention is that of rubber compositions which are usable in particular for the manufacture of tires and which comprise a reinforcing filler and a highly saturated diene elastomer.

[0002] A tire must meet a large number of known, often conflicting, technical requirements, including low rolling resistance, high wear resistance, and high grip on both dry and wet roads. This compromise of properties, particularly in terms of rolling resistance and wear resistance, has been improved in recent years in energy-efficient "Green Tires," intended primarily for passenger vehicles, thanks in particular to the use of new, low-hysteresis rubber compounds characterized by being reinforced mainly with highly dispersible silicas known as "HDS" (Highly Dispersible Silica), capable of competing, in terms of strengthening power, with conventional tire-grade carbon blacks.

[0003] The Applicant described in document WO 2014114607 the use of highly saturated diene elastomers in tire rubber compositions to modify the performance trade-off between rolling resistance and wear. These highly saturated diene elastomers contain units of 1,3-diene and more than 50 mole percent of ethylene units.

[0004] Continuing its efforts, the Applicant developed a new low-hysteretic rubber compound containing a weakly saturated diene elastomer and a reinforcing filler containing silica or carbon black, again with the aim of reducing the rolling resistance of a tire. Indeed, contrary to expectations, it developed a low-hysteretic rubber compound comprising a highly saturated diene elastomer containing, as a functional group at the end of the elastomer chain, a single monomer unit of a methacrylate bearing an amine group.

[0005] Thus, a first object of the invention is a rubber composition comprising a highly saturated diene elastomer containing units of a 1,3-diene and more than 50 mole percent of ethylene units and bearing at one of its chain ends a functional group of formula -CH2-CH(CH3)-COOZ, Z being a hydrocarbon group substituted by a tertiary amine function, a crosslinking system and a reinforcing filler comprising silica or carbon black, the highly saturated diene elastomer being a copolymer of ethylene and a 1,3-diene or a copolymer of ethylene, a 1,3-diene and an α-monoolefin.

[0006] A second object of the invention is a tire which includes a tread, which tire includes a rubber composition according to the invention, preferably in its tread. Detailed description

[0007] 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).

[0008] The abbreviation "pce" means parts by weight per hundred parts of elastomer (of the total elastomers if more than one elastomer is present).

[0009] In the present description of the invention, the formalism alkyl(Cn-Cm) is used to denote an alkyl radical having n to m carbon atoms, where n is an integer greater than or equal to 1 and m is an integer greater than n. For example, alkyl(C1-C2) denotes an alkyl radical having 1 to 2 carbon atoms. Similarly, alkoxy(Cn-Cm) denotes an alkoxy radical having n to m carbon atoms.

[0010] 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.

[0011] In the present invention, the term "pneumatic" (in English, "tire") refers to a pneumatic or non-pneumatic tire. A pneumatic tire typically comprises two beads for contact with a rim, a crown consisting of at least one crown reinforcement and a tread, and two sidewalls. The tire is reinforced by a carcass reinforcement anchored in the two beads. A non-pneumatic tire, on the other hand, typically comprises a base, designed, for example, for mounting on a rigid rim, a crown reinforcement connecting to a tread, and a deformable structure, such as spokes, ribs, or dimples, this structure being arranged between the base and the crown. Such non-pneumatic tires do not necessarily include sidewalls. Non-pneumatic tires are described, for example, in documents WO 03 / 018332 and FR2898077.According to any one of the embodiments of the invention, the tire according to the invention is preferably a pneumatic tire.

[0012] The expression "based on" used to define the constituents of the catalytic system (or catalytic composition) means the mixture of these constituents, or the product of the reaction of some or all of these constituents with each other.

[0013] The elastomer useful for the purposes of the invention is a highly saturated diene elastomer, since the ethylene units represent more than 50% by mole of all the monomer units of the highly saturated diene elastomer. Preferably, the highly saturated diene elastomer is a random copolymer.

[0014] The term "ethylene unit" is known to refer to the (CH₂-CH₂)- motif resulting from the insertion of ethylene into the elastomer chain. Ethylene units in highly saturated diene elastomers preferably constitute at least 60 mole percent of all monomer units in the highly saturated diene elastomer, and more preferably at least 65 mole percent. Even more preferably, ethylene units in highly saturated diene elastomers constitute at least 70 mole percent of all monomer units in the highly saturated diene elastomer.

[0015] Preferably, the ethylene units in the highly saturated diene elastomer represent less than 90% by mole of all the monomer units in the highly saturated diene elastomer. More preferably, the ethylene units represent at most 85% by mole of all the monomer units in the highly saturated diene elastomer. Even more preferably, the ethylene units represent at most 80% by mole of all the monomer units in the highly saturated diene elastomer.

[0016] In an advantageous embodiment, the highly saturated diene elastomer comprises from 60% to less than 90 mol% ethylene units, particularly from 60% to 85 mol% ethylene units, the mol% being calculated on the basis of all the monomer units of the highly saturated diene elastomer. More advantageously, the highly saturated diene elastomer comprises from 60% to 80 mol% ethylene units, the mol% being calculated on the basis of all the monomer units of the highly saturated diene elastomer.

[0017] According to another advantageous embodiment, the highly saturated diene elastomer comprises from 65% to less than 90 mol% ethylene units, particularly from 65% to 85 mol% ethylene units, the mol% being calculated on the basis of all the monomer units of the highly saturated diene elastomer. More advantageously, the highly saturated diene elastomer comprises from 65% to 80 mol% ethylene units, the mol% being calculated on the basis of all the monomer units of the highly saturated diene elastomer.

[0018] According to yet another advantageous embodiment of the invention, the highly saturated diene elastomer comprises from 70% to less than 90 mol% ethylene units, particularly from 70% to 85 mol% ethylene units, the mol% calculated on the basis of all the monomer units of the highly saturated diene elastomer. More advantageously, the highly saturated diene elastomer comprises from 70% to 80 mol% ethylene units, the mol% calculated on the basis of all the monomer units of the highly saturated diene elastomer.

[0019] The highly saturated diene elastomer also includes 1,3-diene units resulting from the polymerization of a 1,3-diene. The term "1,3-diene unit" or "diene unit" is known to refer to units resulting from the insertion of 1,3-diene by a 1,4-addition, a 1,2-addition, or a 3,4-addition, as in the case of isoprene, for example.

[0020] According to one embodiment of the invention, the 1,3-diene units represent at least 35% by mole of the monomer units of the highly saturated diene elastomer.

[0021] According to another embodiment of the invention, the 1,3-diene units represent less than 35% by mole of the monomer units of the highly saturated diene elastomer.

[0022] Highly saturated diene elastomers may contain units of an α-monoolefin. An α-monoolefin is defined as an α-olefin containing at least three carbon atoms and having a single carbon-carbon double bond; double bonds in aromatic compounds are not considered. For example, styrene is considered an α-monoolefin. The α-monoolefin is preferentially aromatic, most preferably styrene or a styrene whose benzene ring is substituted by one or more alkyl groups. Even more preferably, the α-monoolefin is styrene.

[0023] 1,3-diene 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. 1,3-dienes with 4 to 20 carbon atoms are suitable as 1,3-dienes. Preferably, the 1,3-diene is 1,3-butadiene, isoprene, myrcene, β-farnesene, or mixtures thereof, such as a mixture of at least two of these. The mixture of at least two of these is advantageously a mixture that contains 1,3-butadiene. The mixture of 1,3-dienes is preferably a mixture of 1,3-butadiene and myrcene or a mixture of 1,3-butadiene and β-farnesene.

[0024] According to a particularly preferred embodiment of the invention, 1,3-diene is a mixture of 1,3-butadiene and myrcene or a mixture of 1,3-butadiene and β-farnesene.

[0025] According to another particularly preferred embodiment of the invention, 1,3-diene is 1,3-butadiene.

[0026] Advantageously, the highly saturated diene elastomer is a copolymer of ethylene and a 1,3-diene, in which case the constituent units of the highly saturated diene elastomer are those resulting from the polymerization of a 1,3-diene and ethylene. In particular, the highly saturated diene elastomer is a copolymer of ethylene and 1,3-butadiene, or a copolymer of ethylene, 1,3-butadiene, and myrcene, or a copolymer of ethylene, 1,3-butadiene, and β-farnesene. More advantageously, the highly saturated diene elastomer is a statistical copolymer of ethylene and 1,3-butadiene or a statistical copolymer of ethylene, 1,3-butadiene and myrcene or a statistical copolymer of ethylene, 1,3-butadiene and β-farnesene.

[0027] According to a particularly preferred embodiment of the invention, in particular when the 1,3-diene is 1,3-butadiene or a mixture of 1,3-dienes of which one is 1,3-butadiene, the highly saturated diene elastomer contains 1,2-cyclohexane motifs, cyclic motifs of formula (I).

[0028] The presence of a saturated 6-membered cyclic motif, 1,2-cyclohexane, of formula (I) in the highly saturated diene elastomer can result from a series of very specific insertions of ethylene and 1,3-butadiene into the polymer chain during its growth. The mechanism for obtaining such a microstructure is described, for example, in Macromolecules 2009, 42, 3774-3779. When the highly saturated diene elastomer contains motifs of formula (I), it preferentially contains at most 15% by mol, the percentage being expressed relative to all monomer units.

[0029] The highly saturated diene elastomer also has the characteristic of carrying at one of its chain ends a functional group of the formula -CH2-CH(CH3)-COOZ. The functional group is typically covalently attached to the chain end of the highly saturated diene elastomer, one of the carbon atoms of the methylene (CH2) of the functional group being covalently bonded to a carbon atom constituting the terminal monomer unit of the highly saturated diene elastomer.

[0030] The symbol Z denotes a hydrocarbon group substituted by a tertiary amine function. Preferably, Z denotes a saturated acyclic hydrocarbon group substituted by a tertiary amine function, the saturated acyclic hydrocarbon group substituted by a tertiary amine function advantageously being an alkyl group having 1 to 3 carbon atoms. The tertiary amine function is preferably an N,N-dialkylamino group, the alkyl groups substituting the nitrogen atom preferably each having 1 to 3 carbon atoms, more preferably 1 or 2 carbon atoms. The alkyl groups substituting the nitrogen atom are preferably identical according to any one of the embodiments of the invention.

[0031] According to a particularly preferred embodiment, Z designates an N,N-dialkyl(C1-C3)aminoalkyl(C1-C3) group, preferably 2-(N,N-dimethylamino)ethyl, 2-(N,N-diethylamino)ethyl or 2-(N,N-diisopropylamino)ethyl, more preferably 2-(N,N-dimethylamino)ethyl.

[0032] The functionally highly saturated diene elastomer useful for the purposes of the invention can be prepared by a process which comprises the successive steps a), b) and c), Step a) being the polymerization of a monomeric mixture containing 1,3-diene and ethylene and optionally α-monoolefin in the presence of a catalytic system based on at least one metallocene of formula (la) and an organomagnesium compound {P(Cp 1< )(Cp 2< )Nd(BH 4 ) (1+y)- L y -N x} (la) Cp 1< and Cp 2<, 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, Nd denoting the neodymium atom, L representing an alkali metal chosen from the group consisting of lithium, sodium and potassium, N representing a molecule of an ether, x, an integer or not, being equal to or greater than 0, y, an integer, being equal to or greater than 0, the olefin being ethylene or a mixture of ethylene and an α-monoolefin,step b) being the reaction of a methacrylate with the reaction product of the polymerization of step a), step c) being a chain termination reaction.

[0033] Step a) of the process is a polymerization reaction of a monomer mixture containing 1,3-diene and ethylene and optionally α-monoolefin which allows the preparation of the chains of the highly saturated diene elastomer, growing chains intended to react in the next step, step b), with a functionalizing agent, a methacrylate.

[0034] Preferably, the monomer mixture of step a) contains more than 50 mole percent of ethylene, the percentage being expressed relative to the total number of moles of monomers in the monomer mixture of step a). When the monomer mixture contains an α-monoolefin, such as styrene, it preferably contains less than 40 mole percent of the α-monoolefin, the percentage being expressed relative to the total number of moles of monomers in the monomer mixture of step a). Preferably, the monomer mixture of step a) is a mixture of 1,3-diene and ethylene.

[0035] The copolymerization of the monomer mixture can be carried out in accordance with patent applications WO 2007054223 A2 and WO 2007054224 A2 using a catalytic system composed of a metallocene and an organomagnesium compound.

[0036] In this application, the term metallocene means an organometallic complex in which the metal, in this case the neodymium atom, is linked to a molecule called a ligand and consisting of two Cp 1< and Cp 2< groups linked together by a P bridge. These Cp 1< and Cp 2< groups, identical or different, are chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, these groups being able to be substituted or unsubstituted.

[0037] According to the invention, the metallocene used as a basic constituent in the catalytic system corresponds to the formula (la) {P(Cp 1< )(Cp 2< )Nd(BH 4 ) (1+y)- L y -N x} (la) P being a bridging group between the two groups Cp 1< and Cp 2<, and comprising a silicon or carbon atom, Cp 1< and Cp 2<, identical or different, being chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted, Nd denoting the neodymium atom, L representing an alkali metal chosen from the group consisting of lithium, sodium and potassium, N representing a molecule of an ether, x, an integer or not, being equal to or greater than 0, y, an integer, being equal to or greater than 0.

[0038] Any ether that has the ability to complex alkali metal is suitable as an ether, including diethyl ether, methyltetrahydrofuran, and tetrahydrofuran.

[0039] Examples of substituted cyclopentadienyl, fluorenyl, and indenyl 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, fluorenes, and indenes, because these are either commercially available or easily synthesized.

[0040] Examples of substituted fluorenyl groups include those substituted at positions 2, 7, 3, or 6, particularly 2,7-ditertiobutyl-fluorenyl and 3,6-ditertiobutyl-fluorenyl. Positions 2, 3, 6, and 7 respectively designate the positions of the carbon atoms in the rings, as shown in the diagram below, with position 9 corresponding to the carbon atom to which the P-bridge is attached.

[0041] 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, most notably the tetramethylcyclopentadienyl group. Position 2 (or 5) refers to the position of the carbon atom adjacent to the carbon atom to which the π-bridge is attached, as shown in the diagram below. It is worth noting that a substitution at position 2 or 5 is also referred to as an alpha-bridge substitution.

[0042] Examples of substituted indenyl groups include those substituted at position 2, particularly 2-methylindenyl and 2-phenylindenyl. Position 2 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.

[0043] Preferably, Cp1 and Cp2, whether identical or different, are alpha-substituted cyclopentadienyls, substituted fluorenyls, substituted indenyls, or fluorenyls of formula C13H8 or indenyls of formula C9H7. More preferably, Cp1 and Cp2, whether identical or different, are chosen from the group consisting of substituted fluorenyl groups and the unsubstituted fluorenyl group of formula C13H8. Advantageously, Cp1 and Cp2 are identical and each represent an unsubstituted fluorenyl group of formula C13H8, represented by the symbol Flu.

[0044] Preferably, the P-bridge connecting the Cp1< and Cp2< groups has the formula ZR1R2, in which Z represents a silicon or carbon atom, and R1 and R2, which may be the same or different, each represent an alkyl group comprising from 1 to 20 carbon atoms, preferably a methyl group. In the formula ZR1R2, Z advantageously represents a silicon atom, Si.

[0045] Better, the metallocene has the formula (I-1), (I-2), (I-3), (I-4) or (I-5): [Me 2 Si(Flu) 2 Nd(µ-BH 4 ) 2 Li(THF)] (I-1) [{Me 2 SiFlu 2 Nd(µ-BH 4 ) 2 Li(THF)} 2 ] (I-2) [Me 2 SiFlu 2 Nd(µ-BH 4 )(THF)] (I-3) [{Me 2 SiFlu 2 Nd(µ-BH 4 )(THF)} 2 ] (I-4) [Me 2 SiFlu 2 Nd(µ-BH 4 )] (I-5) where Flu represents the C 13 H 8 group.

[0046] The metallocene used in the synthesis of 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 A2 or WO 2007054223 A2. The metallocene can be prepared conventionally by a process similar to that described in patent applications WO 2007054224 A2 or WO 2007054223 A2, specifically by reacting, under inert and anhydrous conditions, the salt of an alkali metal of the ligand with a rare-earth borohydride, neodymium, in a suitable solvent, such as an ether like diethyl ether or tetrahydrofuran, or any other solvent known to those skilled in the art.After the reaction, the metallocene is separated from the reaction byproducts using techniques known to those skilled in the art, such as filtration or precipitation in a second solvent. The metallocene is then dried and isolated in solid form.

[0047] The organomagnesium compound, another basic constituent of the catalytic system, is the co-catalyst of the catalytic system. Typically, the organomagnesium compound can be a diorganomagnesium compound or a halide of an organomagnesium compound. Preferably, the organomagnesium compound has the formula (IIa) or (IIb), where R3 and R4, identical or different, represent a carbon group, and X is a halogen atom. MgR3R4 (IIa) XMgR5 (IIb)

[0048] A carbon group is defined as a group containing one or more carbon atoms. The carbon group can be a hydrocarbon group (hydrocarbyl group) or a heterohydrocarbon group, that is, a group containing one or more heteroatoms in addition to carbon and hydrogen atoms. The compounds described as transfer agents in patent application WO2016092227 A1 are suitable examples of organomagnesium compounds with a heterohydrocarbon group. The carbon groups represented by the symbols R3< and R4< are preferably hydrocarbon groups.

[0049] The carbon groups represented by R3< and R4< can be aliphatic or aromatic. They can contain one or more heteroatoms such as an oxygen, nitrogen, silicon, or sulfur atom. Preferably, they are alkyl, phenyl, or aryl. They can contain from 1 to 20 carbon atoms.

[0050] The alkyls represented R 3< and R 4< can contain 2 to 10 carbon atoms and include ethyl, butyl, octyl.

[0051] The aryls represented R 3< and R 4< can contain 7 to 20 carbon atoms and are notably a phenyl substituted by one or more alkyls such as methyl, ethyl, isopropyl.

[0052] R 3< and R 4< are preferentially alkyls containing 2 to 10 carbon atoms, phenyls or aryls containing 7 to 20 carbon atoms.

[0053] According to a particular embodiment of the invention, R3< comprises a benzene ring with two substituted carbon atoms, one of which is substituted by a methyl, ethyl, or isopropyl group, or forms a ring with its nearest carbon atom, the second carbon atom being substituted by a methyl, ethyl, or isopropyl group, the magnesium atom being in the ortho position with respect to each of said two carbon atoms, and R4< is an alkyl group. According to this particular embodiment, R3< is advantageously 1,3-dimethylphenyl, 1,3-diethylphenyl, mesityl, or 1,3,5-triethylphenyl, and R4< is advantageously ethyl, butyl, or octyl.

[0054] According to another particular embodiment of the invention, R 3< and R 4< are alkyls containing 2 to 10 carbon atoms, in particular ethyl, butyl, octyl.

[0055] For example, the following are suitable organomagnesium compounds: butylethylmagnesium, butylloctylmagnesium, ethylmagnesium chloride, butylmagnesium chloride, ethylmagnesium bromide, butylmagnesium bromide, octylmagnesium chloride, octylmagnesium bromide, 1,3-dimethylphenylbutylmagnesium, 1,3-diethylphenylethylmagnesium, butylmesitylmagnesium, ethylmesitylmagnesium, 1,3-diethylphenylbutylmagnesium, 1,3-diethylphenylethylmagnesium, 1,3-diisopropylphenylbutylmagnesium, 1,3-disopropylphenylethylmagnesium, 1,3,5-triethylphenylbutylmagnesium, 1,3,5-triethylphenylethylmagnesium, 1,3,5-triisopropylphenylbutylmagnesium, 1,3,5-triisopropylphenylethylmagnesium.

[0056] The compounds of formula (IIa) and (IIb), which are Grignard reagents, are well known; some are even commercial products. For their synthesis, one can also refer, for example, to the series of volumes in "Organic Synthesis".

[0057] Like any organomagnesium compound, the organomagnesium compound constituting the catalytic system, in particular of formula (IIa) or (IIb), can be in the form of a monomeric entity or in the form of a polymer entity. By way of illustration, the organomagnesium (IIa) can be in the form of a monomeric entity (MgR3<R4<)1 or in the form of a polymer entity (MgR3<R4<)p, p being an integer greater than 1, in particular a dimer (MgR3<R4<)2.

[0058] Furthermore, whether in the form of a monomeric or polymer entity, the organomagnesium can also be presented as an entity coordinated to one or more molecules of a solvent, preferably an ether such as diethyl ether, tetrahydrofuran or methyltetrahydrofuran.

[0059] According to any one of the embodiments of the invention, the organomagnesium is preferably of formula (IIa).

[0060] The amounts of co-catalyst and metallocene involved in the reaction are such that the ratio between the number of moles of Mg of the co-catalyst and the number of moles of the rare earth of the metallocene, neodymium, preferably goes from 0.5 to 200, more preferably from 1 to less than 20. The range of values ​​from 1 to less than 20 is particularly more favorable for obtaining copolymers with high molar masses.

[0061] According to one embodiment, the catalytic system is prepared conventionally by a process analogous to that described in patent application WO 2007054224 A2 or WO 2007054223 A2. For example, the co-catalyst, in this case the organomagnesium compound, and the metallocene are reacted in a hydrocarbon solvent, typically at a temperature 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, preferably in an aliphatic hydrocarbon solvent such as methylcyclohexane. Generally, after its synthesis, the catalytic system is used as is for step a).

[0062] According to another embodiment, the catalytic system is prepared by a process analogous to that described in patent application WO 2017093654 A1 or in patent application WO 2018020122 A1: it is said to be of the preformed type. For example, the organomagnesium compound and the metallocene are reacted in a hydrocarbon solvent, typically at a temperature of 20 to 80°C for 10 to 20 minutes to obtain a first reaction product, then a preformed monomer is reacted with this first reaction product at a temperature ranging from 40 to 90°C for 1 to 12 hours. The preforming monomer is preferably used with a molar ratio (preforming monomer / metal of the metallocene) of 5 to 1000, preferably 10 to 500. Before its use in polymerization, the preformed type catalytic system can be stored under an inert atmosphere, in particular at a temperature ranging from -20°C to room temperature (23°C).The preformed catalytic system has as its basic component a preforming monomer chosen from among 1,3-dienes, ethylene, and mixtures thereof. In other words, the so-called preformed catalytic system contains, in addition to the metallocene and the cocatalyst, a preforming monomer. The 1,3-diene used as the preforming monomer can be 1,3-butadiene, isoprene, or a 1,3-diene with the formula CH₂=CR₆<-CH=CH₂, the symbol R₆< representing a hydrocarbon group having 3 to 20 carbon atoms, particularly myrcene or β-farnesene. The preforming monomer is preferably 1,3-butadiene.

[0063] The catalytic system typically occurs in a solvent which is preferentially the solvent in which it was prepared, and the concentration of rare earth metal, i.e. neodymium, of metallocene is then in a range preferably from 0.0001 to 0.2 mol / L more preferably from 0.001 to 0.03 mol / L.

[0064] As with all syntheses carried out in the presence of organometallic compounds, the synthesis of the metallocene, the synthesis of the organomagnesium compound, and the synthesis of the catalytic system take place under anhydrous conditions in an inert atmosphere. Typically, the reactions are conducted using solvents and anhydrous compounds under anhydrous nitrogen or argon.

[0065] The polymerization of the monomer mixture is preferably carried out in solution, either continuously or batchwise. The polymerization solvent is typically a hydrocarbon solvent, preferably aliphatic. Methylcyclohexane is a particularly suitable example of an aliphatic hydrocarbon solvent. The monomer mixture can be introduced into the reactor containing the polymerization solvent and the catalytic system, or conversely, the catalytic system can be introduced into the reactor containing the polymerization solvent and the monomer mixture. The monomer mixture and the catalytic system can be introduced simultaneously into the reactor containing the polymerization solvent, particularly in the case of continuous polymerization. Polymerization is typically carried out under anhydrous conditions and in the absence of oxygen, possibly in the presence of an inert gas.The polymerization temperature generally varies in a range of 40 to 150°C, preferably 40 to 120°C. A person skilled in the art adapts the polymerization conditions such as the polymerization temperature, the concentration of each of the reactants, the reactor pressure according to the composition of the monomer mixture, the polymerization reactor, and the desired microstructure and macrostructure of the copolymer chain.

[0066] Polymerization is preferably carried out at constant pressure in monomers. A continuous addition of each or one of the monomers can be made to the polymerization reactor, in which case the polymerization reactor is a fed reactor. This embodiment is particularly suitable for the statistical incorporation of monomers. Preferably, the polymerization in step a) is a statistical polymerization, resulting in the statistical incorporation of monomers from the monomer mixture used in step a).

[0067] Once the desired monomer conversion rate is achieved in the polymerization reaction of step a), step b is carried out.

[0068] Step b) of the process according to the invention brings together a functionalizing agent, a methacrylate, with the reaction product of step a) to introduce the functional group useful for the purposes of the invention, a methacrylate monomer unit, at one end of the chain of the highly saturated diene elastomer produced at the end of step a). Step b) is a functionalization reaction of the chain end of the highly saturated diene elastomer without subsequent polymerization of the methacrylate.

[0069] Methacrylate is a so-called functional methacrylate and has the formula CH2=CCH3COOR', R' being a hydrocarbon group substituted by a tertiary amine function.

[0070] The hydrocarbon group with the symbol R' is preferentially saturated. The number of carbon atoms in the hydrocarbon group with the symbol R' is not limited. The hydrocarbon group can contain up to 20 carbon atoms. Preferably, the hydrocarbon group with the symbol R' contains from 1 to 6 carbon atoms, more preferably from 1 to 3 carbon atoms. Preferably, the hydrocarbon group with the symbol R' is a saturated acyclic hydrocarbon group substituted by the aforementioned tertiary amine function.

[0071] Preferably, the methacrylate is of the formula CH2=CCH3COOR' in which R' is an alkyl, saturated acyclic hydrocarbon group, which is substituted by a dialkylamino group, in particular the methacrylate is an N,N-dialkyl(C1-C3)aminoalkyl(C1-C3) methacrylate, preferably 2-(dimethylamino)ethyl methacrylate, 2-(diethylamino)ethyl methacrylate, 2-(diisopropylamino)ethyl methacrylate, more preferably 2-(dimethylamino)ethyl methacrylate.

[0072] The methacrylates useful for the purposes of the invention may be commercial products. They are generally commercially available products. When methacrylates are packaged in the presence of a stabilizer, as is the case for most commercial methacrylates, they are typically used after removal of the stabilizer, which can be carried out in a well-known manner by distillation or by treatment on alumina columns.

[0073] Preferably, step b) is carried out in an aliphatic hydrocarbon solvent, such as methylcyclohexane. Advantageously, it is carried out in the reaction medium from step a). It is generally performed by adding methacrylate to the reaction product of step a) in its reaction medium under stirring.

[0074] Before adding the methacrylate, the reactor is preferably degassed and inert. Degassing the reactor removes residual gaseous monomers and also facilitates the addition of the methacrylate. Inertizing the reactor, for example with nitrogen, prevents the carbon-metal bonds present in the reaction medium, which are necessary for the copolymer functionalization reaction, from being deactivated. The methacrylate can be added pure or diluted in a hydrocarbon solvent, preferably aliphatic such as methylcyclohexane. The methacrylate is left in contact with the reaction product from step a) for the time required for the functionalization of the copolymer chain end. The functionalization reaction can typically be monitored by chromatographic analysis to track methacrylate consumption.The functionalization reaction is preferably carried out at a temperature of 23 to 120 °C, for 1 to 60 minutes with stirring. The functionalization reaction is preferentially conducted with a molar excess of methacrylate relative to the number of moles of neodymium and magnesium. To achieve near-quantitative functionalization, the molar ratio of methacrylate to neodymium and magnesium is greater than 2, and in particular greater than or equal to 4. The molar ratio of methacrylate to neodymium and magnesium is preferentially from 4 to 50, and more preferably from 4 to 10.

[0075] Once the end of the chain has been modified, step b) is followed by step c).

[0076] Step c), the chain termination reaction, is typically a reaction that deactivates the reactive sites still present in the reaction medium from step b). In step c), a chain termination agent is brought into contact with the reaction product of step b), generally in its reaction medium, for example, by adding the termination agent to the reaction medium after step b) or by pouring the reaction medium obtained after step b) onto a solution containing the termination agent. The termination agent is generally added in excess relative to the number of carbon-metal bonds such as C-Mg and C-Nd present in the reaction medium. The termination agent is typically a protic compound, a compound that contains a relatively acidic proton.Examples of terminating agents include water, carboxylic acids, particularly C2-C18 fatty acids such as acetic acid and stearic acid, aliphatic or aromatic alcohols such as methanol, ethanol, and isopropanol, and phenolic antioxidants.

[0077] After reaction with a protic compound, the process leads to the highly saturated diene elastomer bearing a tertiary amine function at one of its chain ends.

[0078] The highly saturated diene elastomer bearing a tertiary amine function at one of its chain ends can be separated from the reaction medium of step c) by processes well known to those skilled in the art, for example by an evaporation of the solvent under reduced pressure or by a steam stripping operation.

[0079] Preferably, the rubber composition contains more than 50 parts per cent of the highly saturated diene elastomer relevant to the invention, and more preferably at least 80 parts per cent of the highly saturated diene elastomer relevant to the invention. The remainder of 100 parts per cent may consist of all or part of a diene and ethylenic elastomer lacking the functional group relevant to the invention, with the formula -CH₂-CH(CH₃)-COOZ as described in this application. The rubber composition may also include an elastomer selected from the group of diene elastomers consisting of polybutadienes, polyisoprenes, butadiene copolymers, isoprene copolymers, and mixtures thereof. Advantageously, the proportion of the highly saturated diene elastomer relevant to the invention is 100 parts per cent.The highly saturated diene elastomer useful for the needs of the invention may consist of a mixture of highly saturated diene elastomers useful for the needs of the invention which differ from each other by their microstructures or by their macrostructures.

[0080] The rubber composition also has the essential characteristic of containing a reinforcing filler which includes silica or carbon black.

[0081] The silica used can be any reinforcing silica known to those skilled in the art, in particular any precipitated or pyrogenated silica having a BET surface area and a CTAB specific surface area both less than 450 m² / g, preferably from 30 to 400 m² / g, in particular between 60 and 300 m² / g. Examples of highly dispersible precipitated silicas (known as "HDS") include "Ultrasil" 7000 and "Ultrasil" 7005 from Degussa, "Zeosil" 1165MP, 1135MP and 1115MP from Rhodia, "Hi-Sil" EZ150G from PPG, "Zeopol" 8715, 8745 and 8755 from Huber, and high specific surface area silicas as described in application WO 03 / 016387.

[0082] In this presentation, the specific surface area BET is determined in a known manner by gas adsorption using the Brunauer-Emmett-Teller method described in "The Journal of the American Chemical Society, Vol. 60, page 309, February 1938, more precisely according to the French standard NF ISO 9277 of December 1996 (multipoint volumetric method (5 points) - gas: nitrogen - degassing: 1 hour at 160°C - relative pressure range) p / po: 0.05 to 0.17). The specific surface area CTAB is the external surface area determined according to the French standard NF T 45-007 of November 1987 (method B).

[0083] The physical state of the silica is irrelevant, whether it is in the form of powder, microbeads, granules, or spheres. Of course, the term "silica" also refers to mixtures of different reinforcing silicas, particularly highly dispersible silicas such as those described above.

[0084] Those skilled in the art will understand that, as an equivalent filler to the silica described in this paragraph, a reinforcing filler of another nature, particularly an organic one such as carbon black, could be used, provided that this reinforcing filler is coated with a layer of silica, or has functional sites on its surface, particularly hydroxyl sites, requiring the use of a coupling agent to establish the bond between the filler and the elastomer. For example, carbon blacks for tires, such as those described in patent documents WO 96 / 37547 and WO 99 / 28380, can be cited.

[0085] All carbon blacks are suitable, including those of the HAF, ISAF, SAF, FF, FEF, GPF, and SRF types conventionally used in tire rubber compounds (so-called tire-grade blacks). These carbon blacks can be used on their own, as commercially available, or in other forms, for example, as a carrier for certain rubber additives used in tire manufacturing.

[0086] According to one embodiment of the invention, the reinforcing filler comprises a mixture of silica and carbon black. When the rubber composition contains a mixture of silica and carbon black, the carbon black is preferably used at a concentration of less than 20 parts per million (ppm), more preferably less than 10 ppm (for example, between 0.5 and 20 ppm, particularly between 2 and 10 ppm). Within the indicated ranges, the coloring (black pigmenting agent) and UV-resistant properties of carbon black are utilized without compromising the typical performance provided by silica.

[0087] According to a particularly preferred embodiment of the invention, the reinforcing filler contains more than 50% silica by mass. More preferably, the reinforcing filler contains more than 50% silica by mass and contains carbon black at a rate less than or equal to 5 parts per cubic meter.

[0088] To couple silica to the elastomer, a coupling agent is used in a well-known manner, in particular a silane (or bonding agent) at least bifunctional intended to ensure a sufficient connection between the silica (surface of its particles) and the elastomer. Organosilanes or polyorganosiloxanes at least bifunctional are used in particular.

[0089] In particular, polysulfide silanes are used, described as "symmetric" or "asymmetric" depending on their particular structure, as described for example in applications WO03 / 002648 (or US 2005 / 016651) and WO03 / 002649 (or US 2005 / 016650).

[0090] In particular, without limitation, polysulfide silanes corresponding to the general formula (III) J - G - S x - G - J (III) are suitable, in which: x is an integer from 2 to 8 (preferably from 2 to 5); the symbols G, identical or different, represent a divalent hydrocarbon radical (preferably a C1-C18 alkylene group or a C6-C12 arylene group, more particularly a C1-C10 alkylene, especially C1-C4, in particular propylene); the symbols J, identical or different, correspond to one of the three formulas below: wherein: the radicals R1<, substituted or unsubstituted, identical or different, represent a C1-C18 alkyl, C5-C18 cycloalkyl, or C6-C18 aryl group (preferably C1-C6 alkyl, cyclohexyl, or phenyl groups, in particular C1-C4 alkyl groups, especially methyl and / or ethyl); the radicals R2<, substituted or unsubstituted, identical or different, represent a C1-C18 alkoxyl or C5-C18 cycloalkoxyl group (preferably a group selected from C1-C8 alkoxyles and C5-C8 cycloalkoxyles, more preferably a group selected from C1-C4 alkoxyles, especially methoxyl and ethoxyl).

[0091] In the case of a mixture of polysulfurized alkoxysilanes corresponding to formula (I) above, in particular common mixtures available commercially, the average value of "x" is a fractional number preferably between 2 and 5, more preferably close to 4. But the invention can also be advantageously implemented, for example, with disulfurized alkoxysilanes (x = 2).

[0092] Examples of polysulfurized silanes include polysulfides (especially disulfides, trisulfides or tetrasulfides) of bis-(alkoxyl(C1-C4)-alkyl(C1-C4)silyl-alkyl(C1-C4)), such as bis(3-trimethoxysilylpropyl) or bis(3-triethoxysilylpropyl) polysulfides. Among these compounds, in particular, the tetrasulfide of bis(3-triethoxysilylpropyl), abbreviated TESPT, with the formula [(C 2 H 5 O) 3 Si(CH 2 ) 3 S 2 ] 2 or the disulfide of bis-(triethoxysilylpropyl), abbreviated TESPD, with the formula [(C 2 H 5 O) 3 Si(CH 2 ) 3 S] 2, is used.

[0093] Examples of coupling agents other than polysulfurized alkoxysilane include bifunctional POSS (polyorganosiloxanes) or hydroxysilane polysulfides as described in patent applications WO 02 / 30939 (or US 6,774,255), WO 02 / 31041 (or US 2004 / 051210) or silanes or POSS bearing azo-dicarbonyl functional groups, as described for example in patent applications WO 2006 / 125532, WO 2006 / 125533, WO 2006 / 125534.

[0094] The coupling agent content is advantageously less than 30 parts per liter, it being understood that it is generally desirable to use as little as possible. Typically, the coupling agent content represents 0.5% to 15% by weight relative to the amount of silica. Its content is preferably between 0.5% and 16 parts per liter, and more preferably within the range of 3% to 10%. This content is easily adjusted by a person skilled in the art according to the amount of silica used in the composition.

[0095] Preferably, the total reinforcing filler content, whether silica, carbon black, or a mixture thereof, is between 30 and 200 parts per cent, more preferably between 40 and 160 parts per cent. Any of these ranges of total reinforcing filler content can be applied to any of the embodiments of the invention.

[0096] The rubber composition according to the invention may also contain, in addition to coupling agents, coupling activators, inorganic filler covering agents or more generally processing aids which, by improving the dispersion of the filler in the rubber matrix and lowering the viscosity of the compositions, can improve their processing ability in the raw state.

[0097] Another essential characteristic of the rubber composition is that it contains a crosslinking system. Chemical crosslinking allows the formation of covalent bonds between the elastomer chains. The crosslinking system can be a vulcanizing system or one or more peroxide compounds. According to any one embodiment of the invention, the crosslinking system is preferably a vulcanizing system.

[0098] The vulcanization system itself is based on sulfur (or a sulfur-donating agent) and a primary vulcanization accelerator. To this basic vulcanization system are added, incorporated during the first non-productive phase and / or during the productive phase as described later, various known secondary accelerators or vulcanization activators such as zinc oxide, stearic acid or equivalent compounds, and guanidine derivatives (in particular diphenylguanidine). Sulfur is used at a preferential rate of 0.5 to 12 parts per million (ppm), particularly 1 to 10 ppm. The primary vulcanization accelerator is used at a preferential rate of 0.5 to 10 ppm, more preferably 0.5 to 5 ppm.Any compound capable of accelerating the vulcanization of diene elastomers in the presence of sulfur can be used as an accelerator (primary or secondary), including thiazole-type accelerators and their derivatives, thiuram-type accelerators, and zinc dithiocarbamates. Preferably, a sulfenamide-type primary accelerator is used.

[0099] When chemical crosslinking is carried out using one or more peroxide compounds, the said peroxide compound(s) preferably represent 0.01 to 10 parts per 10%. Examples of peroxide compounds usable as chemical crosslinking systems include acyl peroxides, for example benzoyl peroxide or p-chlorobenzoyl peroxide; ketone peroxides, for example methyl ethyl ketone peroxide; peroxyesters, for example t-butylperoxyacetate, t-butylperoxybenzoate and t-butylperoxyphthalate; alkyl peroxides, for example dicumyl peroxide, di-t-butyl peroxybenzoate and 1,3-bis(t-butylperoxyisopropyl)benzene; and hydroperoxides, for example t-butyl hydroperoxide.

[0100] The rubber composition according to the invention may also include all or part of the usual additives commonly used in elastomer compositions intended to constitute external compounds of finished rubber articles such as tires, in particular treads, such as plasticizers or extension oils, whether the latter are aromatic or non-aromatic, in particular hydrocarbon plasticizing resins, very weakly or non-aromatic oils (e.g., paraffinic oils, hydrogenated naphthenic oils, MES or TDAE oils), vegetable oils, in particular glycerol esters such as glycerol trioleates, pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, antioxidants.

[0101] The rubber composition according to the invention can be manufactured in suitable mixers, using two successive preparation phases according to a general procedure well known to those skilled in the art: a first thermo-mechanical working or mixing phase (sometimes referred to as the "non-productive" phase) at high temperature, up to a maximum temperature between 130°C and 200°C, preferably between 145°C and 185°C, followed by a second mechanical working phase (sometimes referred to as the "productive" phase) at a lower temperature, typically below 120°C, for example between 60°C and 100°C, a finishing phase during which the chemical crosslinking agent, in particular the vulcanizing system, is incorporated.

[0102] In general, all the basic constituents of the composition included in the tire of the invention, with the exception of the crosslinking system, namely the reinforcing inorganic filler, the coupling agent where applicable, are intimately incorporated, by mixing, into the elastomer, during the first so-called non-productive phase, that is to say, these different basic constituents are introduced into the mixer and thermomechanically mixed, in one or more stages, until reaching the maximum temperature between 130°C and 200°C, preferably between 145°C and 185°C.

[0103] As an example, the first (non-productive) phase is carried out in a single thermomechanical step during which all the necessary components, any additional processing agents, and other miscellaneous additives, with the exception of the chemical crosslinking agent, are introduced into a suitable mixer, such as a standard internal mixer. The total mixing time in this non-productive phase is preferably between 1 and 15 minutes. After the mixture obtained in the first non-productive phase has cooled, the low-temperature crosslinking system is then incorporated, generally in an external mixer such as a roller mixer; the mixture is then blended (productive phase) for a few minutes, for example, between 2 and 15 minutes.

[0104] The final composition thus obtained is then calendered, for example in the form of a sheet or plate, particularly for characterization in the laboratory, or extruded in the form of a rubber profile usable as a semi-finished vehicle tire.

[0105] Thus, according to a particular embodiment of the invention, the rubber composition according to the invention, which can be either in the raw state (before crosslinking or vulcanization) or in the cured state (after crosslinking or vulcanization), is a semi-finished product which can be used in a tire, in particular as a tire tread.

[0106] In summary, the invention is advantageously implemented according to any one of the following embodiments 1 to 25: Embodiment 1: Rubber composition comprising a highly saturated diene elastomer containing units of a 1,3-diene and more than 50 mole percent of ethylene units and bearing at one of its chain ends a functional group of formula -CH2-CH(CH3)-COOZ, Z being a hydrocarbon group substituted by a tertiary amine function, a crosslinking system and a reinforcing filler comprising silica or carbon black, the highly saturated diene elastomer being a copolymer of ethylene and a 1,3-diene or a copolymer of ethylene, a 1,3-diene and an α-monoolefin.

[0107] The aforementioned features of the present invention, as well as others, will be better understood upon reading the following description of examples of embodiments of the invention, given by way of illustration and not limitation. Examples Nuclear magnetic resonance (NMR):

[0108] The functionalization products of the copolymers are characterized by 1H, 13C, 29Si NMR spectroscopy. The NMR spectra are recorded on a Brüker Avance III 500 MHz spectrometer equipped with a 5 mm BBFOz-grad "broadband" cryo-probe. 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 quantitative 13C NMR experiment uses a single 30° pulse sequence with proton decoupling and a 10-second repetition delay between each acquisition. 1024 to 10240 accumulations are performed. The two-dimensional 1H / 13C experiments are used to determine the structure of the functional polymers. The chemical shift axis 1< H is calibrated with respect to the protonated impurity of the solvent (CDCl 3 ) at δ 1H = 7.20 ppm.The chemical shift axis 13< C is calibrated with respect to the solvent signal (CDCl 3 ) at δ 13C = 77 ppm.

[0109] The chemical structure of each functional polymer is identified by NMR (1<H, 13<C). SEC 3D Analysis:

[0110] To determine the number-average molar mass (Mn), and where applicable the weight-average molar mass (Mw) and the polydispersity index (Ip, also denoted Ð = Mw / Mn) of polymers, we use the method below.

[0111] The number-average molar mass (Mn), weight-average molar mass (Mw), and polydispersity index of the polymer (hereafter referred to as the sample) are determined in absolute terms by triple-detection size exclusion chromatography (SEC). Triple-detection size exclusion chromatography has the advantage of directly measuring average molar masses without calibration.

[0112] The refractive index increment (dn / dc) of the sample solution is measured online using the peak area detected by the refractometer (RI) of the liquid chromatography equipment. To apply this method, it is essential to ensure that 100% of the sample mass is injected and eluted through the column. The RI peak area depends on the sample concentration, the RI detector constant, and the dn / dc value.

[0113] To determine the average molar masses, a previously prepared and filtered 1 g / L tetrahydrofuran solution is injected into the chromatography system. The equipment used is a Wyatt chromatography system. The elution solvent is tetrahydrofuran containing 250 ppm BHT (2,6-diter-butyl 4-hydroxytoluene), the flow rate is 1 mL / min, the system temperature is 35°C, and the analysis time is 60 min. The columns used are a set of three AGILENT columns, commercially known as "PL GEL MIXED B LS". The injected volume of the sample solution is 100 µL.The detection system consists of a Wyatt differential viscometer with the trade name "VISCOSTAR II", a Wyatt differential refractometer with the trade name "OPTILAB T-REX" with a wavelength of 658 nm, and a Wyatt multi-angle static light scattering detector with a wavelength of 658 nm and the trade name "DAWN HELEOS 8+".

[0114] For the calculation of the number-average molar masses and the polydispersity index, the value of the refractive index increment dn / dc of the sample solution obtained above is incorporated. The software used for processing the chromatographic data is Wyatt's ASTRA system. Determination of the glass transition temperature of polymers:

[0115] The glass transition temperature is measured using a Differential Scanning Calorimeter according to ASTM D3418 (1999). Dynamic properties:

[0116] Dynamic properties are measured on a viscoelastic analyzer (Metravib VA4000) according to ASTM D 5992-96. The response of a vulcanized composition sample (cylindrical specimen 4 mm thick and 400 mm² cross-section) is recorded under sinusoidal alternating simple shear loading at a frequency of 10 Hz, under standard temperature conditions (23°C) according to ASTM D 1349-99. A strain amplitude sweep is performed from 0.1% to 50% (forward cycle), then from 50% to 0.1% (return cycle). The result used is the loss factor tan(δ). For the return cycle, the maximum observed tan(δ) value, denoted tan(δ)max, is reported. The tan(δ)max values ​​are given on a scale of 100, with 100 assigned to the control composition (T). The lower the value of tan(δ)max, the lower the hysteresis of the rubber composition. Preparation of elastomers :

[0117] The metallocene [{Me 2 SiFlu 2 Nd(µ-BH 4 ) 2 Li(THF)}] 2 is prepared according to the procedure described in patent application WO 2007054224.

[0118] BOMAG butyl methylmagnesium (20% in heptane, at 0.88 mol L-1) comes from Chemtura and is stored in a Schlenk tube under an inert atmosphere.

[0119] The ethylene, of N35 grade, comes from the company Air Liquide and is used without prior purification.

[0120] 1,3-Butadiene and myrcene are purified on alumina guards.

[0121] The functionalizing agent used is 2-(dimethylamino)ethyl methacrylate from Sigma-Aldrich. Commercial methacrylate is used after purification over alumina guards and after bubbling with nitrogen.

[0122] The methylcyclohexane (MCH) solvent from BioSolve is dried and purified on an alumina column in a solvent fountain from mBraun and used under an inert atmosphere.

[0123] All reactions are carried out under an inert atmosphere.

[0124] Synthesis of ethylene, 1,3-butadiene, and non-functional myrcene copolymers: elastomer E1: In a 90 L stainless steel reactor, 64 L of MCH and a solution of BOMAG (23 mmol) in methylcyclohexane (0.01 mol / L) are introduced. The reactor is heated to 80°C, and the monomers are added at a controlled rate to maintain a constant monomer mixture composition in the polymerization medium. The ethylene flow rate is set at 40 g / min. Myrcene and butadiene are injected independently, and their flow rates are controlled by the ethylene flow rate according to a myrcene / ethylene mass ratio of 1.62 and a butadiene / ethylene mass ratio of 0.25.

[0125] When the reactor reaches a pressure of 8 bar, the catalytic system (6.25 mmol of Nd), preformed at a concentration of 0.007 mol / L and prepared according to the previous protocol, is introduced into the polymerization medium. The chain termination reaction is carried out by stopping with methanol when 5 to 6 kg of polymer have formed; the polymer is recovered after a stripping step. The polymer is then dried on a screw conveyor equipped with a single screw at 150°C.

[0126] The catalytic system is a preformed catalytic system. It is prepared in methylcyclohexane from the metallocene [Me₂Si(Flu)₂Nd(µ-BH₄)₂Li(THF)], the cocatalyst butylmagnesium (BOMAG), and a preforming monomer, 1,3-butadiene. It is prepared according to a preparation method conforming to paragraph II.1 of patent application WO 2017093654 A1.

[0127] In a 500 mL Steinie bottle containing 380 mL of methylcyclohexane previously degassed with nitrogen, 5.7 mL of a butylmagnesium in heptane solution (0.88 M, 5.0 mmol) and 1.462 g of the complex {(Me₂Si(C₁₃H₈)₂)Nd(-BH₄)₂Li(THF)}₂ (number of moles of Nd, nNd = 2.3 mmol), prepared according to patent application WO2007 / 054224 (complex 1), are successively introduced. 17 mL of 1,3-butadiene (also referred to hereafter as butadiene) are added to the Steinie bottle at 17°C. The contents of the Steinie bottle are then heated to 80°C for 4 h with stirring. The resulting catalytic solution is stored in a freezer at -25°C. Synthesis of copolymers of ethylene, 1,3-butadiene and functional myrcene: elastomer E2:

[0128] Functional elastomers are prepared under the same synthesis conditions as their non-functional counterparts, with the difference that the chain termination reaction is replaced by a functionalization reaction described according to the functionalization procedure described below. Functionalization procedure:

[0129] When the desired conversion to monomers is reached (5 to 6 kg of polymer), the reactor contents are degassed. The functionalizing agent, methacrylate, is introduced into the polymerization medium under inert pressure at a rate of 40 equivalents relative to the number of moles of Nd and Mg introduced into the reactor. The reaction medium is stirred for 15 minutes at 80°C. The reaction medium is deactivated with methanol. The polymer is recovered after a stripping step. The polymer is then dried on a screw conveyor equipped with a single screw at 150°C. It is then analyzed by SEC (THF) and 1H, 13C NMR.

[0130] The characteristics of the prepared elastomers are shown in Table 1. SEC and NMR analyses confirm that the chain end of elastomer E2 is functionalized by a single methacrylate monomer unit bearing the amine function. Table 1 Elastomer % unit ethylene (mol) % unit butadiene (mol) % myrcene unit (mol) % cycle (1) (mol) Mn (g / mol) Tg (°C) E1 74 9 13 4 174000 -54 E2 73 10 13 4 180000 -54 (1) cyclic motif 1,2-cyclohexane of formula (I) Preparation of rubber compounds:

[0131] Rubber compositions whose formulation, expressed in parts per hundred weight of elastomer (ppm) as shown in Table 2, were prepared according to the following procedure: The elastomer, silica, coupling agent, and various other ingredients, with the exception of the vulcanizing system, were successively introduced into an 85 cm³ Polylab internal mixer (final fill level: approximately 70% by volume), with an initial tank temperature of approximately 100°C. A thermomechanical process (non-productive phase) was then carried out in a single step, lasting approximately 5 minutes, until a maximum "drop" temperature of 160°C was reached. The resulting mixture was collected, cooled, and then sulfur and the accelerator were incorporated in a mixer (homo-finisher) at 25°C, with the mixture being blended for approximately ten minutes (productive phase).The compositions thus obtained are then calendered either in the form of plates (thickness of 2 to 3 mm) or thin sheets of rubber for the measurement of their physical or mechanical properties, after vulcanization at 150°C.

[0132] Rubber composition C1 contains a highly saturated diene elastomer bearing a methacrylate monomer unit, elastomer E2, at the end of its chain. It conforms to the invention. Rubber composition T1 contains a highly saturated diene elastomer, E1, which has not been functionalized. It is synthesized according to the same procedure as elastomer E2, except that the functionalizing agent is not added and the reaction mixture is precipitated directly in methanol after degassing the reactor.

[0133] The results are shown in Table 3.

[0134] The C1 rubber composition exhibits much lower hysteresis than its control, composition T1. This decrease in hysteresis is attributed to the functionalization of the chain end of the highly saturated diene elastomer by a single monomer unit of a methacrylate bearing a tertiary amine function, since this result is obtained without the modification of the elastomer by the methacrylate being accompanied by the formation of a polymethacrylate block which would have led to a change in the glass transition temperature of the rubber composition and therefore to a change in certain properties of the rubber compositions, such as rheological properties, in particular stiffness. Table 2 Compositions (in pieces) T1 C1 E1 Elastomer 100 E2 Elastomer 100 Silica (1) 70 70 Carbon black (2) 2 2 Coupling agent (3) 7 7 DPG (4) 1.2 1.2 Ozone Wax (5) 2.5 2.5 Antioxidant (6) 3.8 3.8 Antioxidant (7) 1.6 1.6 Stearic acid (8) 3 3 ZnO (9) 0.9 0.9 Sulfur 0.9 0.9 CBS (10) 2.3 2.3 (1) Solvay-Rhodia's "Zeosil 1165 MP" in microbead form (2) N234 (3) Evonik's liquid silane (TESPT) "Si69" (4) Flexsys's "Perkacit DPG" diphenylguanidine (5) Sasol Wax's "VARAZON 4959" ozone-reducing wax (6) Flexsys's "Santoflex 6PPD" N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (7) Tetramethylquinone (8) Uniqema's "Pristerene 4931" stearic acid (9) Umicore's industrial-grade zinc oxide (10) Flexsys's "Santocure CBS" N-cyclohexyl-2-benzothiazol-sulfenamide Table 3 Composition T1 C1 tan(δ)max 23°C 100 90

Claims

1. Rubber composition that comprises a highly saturated diene elastomer containing 1,3-diene units and more than 50 mol% of ethylene units and bearing at one of its chain ends a functional group of formula -CH2-CH(CH3)-COOZ, Z being a hydrocarbon group substituted by a tertiary amine function, a crosslinking system and a reinforcing filler that comprises a silica or a carbon black, the highly saturated diene elastomer being a copolymer of ethylene and a 1,3-diene or a copolymer of ethylene, a 1,3-diene and an α-monoolefin.

2. Rubber composition according to Claim 1, wherein Z denotes a saturated acyclic hydrocarbon group substituted by a tertiary amine function.

3. Rubber composition according to Claim 2, wherein the saturated acyclic hydrocarbon group substituted by a tertiary amine function is an alkyl having 1 to 3 carbon atoms.

4. Rubber composition according to any one of Claims 1 to 3, wherein the tertiary amine function is an N,N-dialkylamino group.

5. Rubber composition according to Claim 4, wherein the alkyl groups substituting the nitrogen atom each have 1 to 3 carbon atoms, preferably 1 carbon atom or 2 carbon atoms.

6. Rubber composition according to any one of Claims 1 to 5, wherein Z denotes an N,N-di(C1-C3)alkylamino(C1-C3)alkyl group, preferably 2-(N,N-dimethylamino)ethyl, 2-(N,N-diethylamino)ethyl or 2-(N,N-diisopropylamino)ethyl, more preferably 2-(N,N-dimethylamino)ethyl.

7. Rubber composition according to any one of Claims 1 to 6, wherein the copolymer is a copolymer of ethylene and a 1,3-diene.

8. Rubber composition according to any one of Claims 1 to 7, wherein the ethylene units in the highly saturated diene elastomer represent less than 90 mol% of all of the monomer units in the highly saturated diene elastomer.

9. Rubber composition according to any one of Claims 1 to 8, wherein the 1,3-diene is 1,3-butadiene, isoprene, myrcene, β-farnesene or mixtures thereof.

10. Rubber composition according to any one of Claims 1 to 9, wherein the 1,3-diene is 1,3-butadiene or a mixture of 1,3-butadiene and myrcene or else a mixture of 1,3-butadiene and β-farnesene.

11. Rubber composition according to any one of Claims 1 to 10, wherein the copolymer contains 1,2-cyclohexane units of formula (I):

12. Rubber composition according to any one of Claims 1 to 11, wherein the highly saturated diene elastomer is a statistical copolymer.

13. Rubber composition according to any one of Claims 1 to 12, wherein the reinforcing filler contains more than 50% by mass of silica.

14. Tyre that includes a tread, said tyre comprising a rubber composition defined in any one of Claims 1 to 13, preferably in the tread of said tyre.