RUBBER COMPOSITION

Description

[0001] The present invention relates to diene rubber compositions intended for use in a tire which contain predominantly, as an elastomer, a copolymer of ethylene and 1,3-diene.

[0002] The diene rubber compositions traditionally used in tires are rubber compositions reinforced by highly unsaturated diene elastomers such as polybutadienes, polyisoprenes, butadiene and styrene copolymers.

[0003] It has been proposed, notably in document WO 2014114607, to use ethylene-1,3-butadiene copolymers in tire rubber compositions. These copolymers are synthesized by copolymerizing ethylene and 1,3-butadiene in the presence of a catalytic system including a rare-earth metallocene. Rubber compositions reinforced with ethylene-1,3-butadiene copolymer are described, in particular, to improve the performance trade-off of a tire, namely wear resistance and rolling resistance. These diene rubber compositions, once crosslinked, exhibit a much higher stiffness than traditionally used diene rubber compositions and may therefore prove unsuitable for certain applications. There is thus a need to significantly reduce the cured stiffness of such compositions containing ethylene-based diene rubber.

[0004] It is known that decreasing the curing stiffness of a diene rubber compound reduces the pressure density of the compound. Unfortunately, this also results in an increase in the hysteresis of the rubber compound.

[0005] The Applicant has discovered a reinforced rubber composition based on a copolymer of ethylene and 1,3-diene which does not have the disadvantages mentioned, since it presents an improved compromise between stiffness and hysteresis properties.

[0006] Thus, a first object of the invention is a rubber composition which comprises a reinforcing filler, a crosslinking system and more than 50 to 100 parts of an elastomer which is a copolymer of ethylene and a 1,3-diene of formula (I), CH2=CR-CH=CH2(l) the symbol R representing a hydrocarbon chain having 3 to 20 carbon atoms.

[0007] Another object of the invention is a tire comprising a tread, which tire includes a rubber composition according to the invention, preferably in the tread. Detailed description

[0008] 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., excluding the bounds a and b), 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). The abbreviation "pce" means parts by weight per hundred parts by weight of elastomer (of the total elastomers if multiple elastomers are present).

[0009] 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.

[0010] Unless otherwise stated, the rates of units resulting from the insertion of a monomer into a copolymer are expressed as a mole percentage relative to the total monomer units of the copolymer.

[0011] The compounds mentioned in the description may 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. These include, in particular, elastomers, plasticizers, fillers, etc.

[0012] Since 1,3-diene of formula (I) as defined above and useful for the needs of the invention is a substituted 1,3-diene, the 1,3-diene can give rise to units of configuration 1,2 represented by formula (1), of configuration 3,4 represented by formula (2) and of configuration 1,4 whose trans form is represented below by formula (3).

[0013] As is also well known, the ethylene unit is a pattern unit -(CH2-CH2)-.

[0014] The copolymer useful for the purposes of the invention is a copolymer of ethylene and 1,3-diene, which implies that the monomer units of the copolymer are units resulting from the polymerization of ethylene and 1,3-diene. The copolymer therefore comprises ethylene units and 1,3-diene units. According to any one embodiment of the invention, the 1,3-diene is a single compound, that is to say, a single 1,3-diene of formula (I), or is a mixture of 1,3-dienes of formula (I), the 1,3-dienes of the mixture being differentiated from one another by the group represented by the symbol R. The copolymer useful for the purposes of the invention is advantageously a statistical copolymer according to any one embodiment of the invention.

[0015] Preferably, the copolymer contains ethylene units that represent between 50% and 95% by mole of the monomer units of the copolymer, that is, between 50% and 95% by mole of the ethylene units and the 1,3-diene units. Most preferably, the copolymer contains ethylene units that represent at least 60% by mole of the ethylene units and the 1,3-diene units. More preferably, the copolymer contains ethylene units that represent at least 70% by mole of the ethylene units and the 1,3-diene units. Preferably, the copolymer contains ethylene units that represent at most 90% by mole of the ethylene units and the 1,3-diene units.

[0016] According to a particular embodiment of the invention, the copolymer contains ethylene units which represent at most 85% by mole of the ethylene units and the 1,3-diene units.

[0017] According to a preferred embodiment of the invention, in the copolymer according to the invention, the ethylene units represent 60 to 90% by mole of the ethylene units and the 1,3-diene units, advantageously 70 to 90% by mole of the ethylene units and the 1,3-diene units.

[0018] According to another particular embodiment of the invention, in the copolymer according to the invention, the ethylene units represent from 60 to 85% by mole of the ethylene units and the 1,3-diene units, advantageously from 70 to 85% by mole of the ethylene units and the 1,3-diene units.

[0019] In formula (I) of 1,3-diene, the hydrocarbon chain represented by the symbol R is an unsaturated chain of 3 to 20 carbon atoms. Preferably, the symbol R represents a hydrocarbon chain having 6 to 16 carbon atoms.

[0020] The hydrocarbon chain represented by the symbol R can be saturated or unsaturated. Preferably, the symbol R represents an aliphatic chain, in which case, in formula (I) of 1,3-diene, the hydrocarbon chain represented by the symbol R is an aliphatic hydrocarbon chain. It can be a linear or branched chain, in which case the symbol R represents a linear or branched chain. Preferably, the hydrocarbon chain is acyclic, in which case the symbol R represents an acyclic chain. Better still, the symbol R represents an unsaturated, branched, acyclic hydrocarbon chain. The hydrocarbon chain represented by the symbol R is advantageously an unsaturated, branched, acyclic chain containing from 3 to 20 carbon atoms, particularly from 6 to 16 carbon atoms. Most advantageously, 1,3-diene is myrcene or β-farnesene.

[0021] According to a preferred embodiment of the invention, 1,3-diene is myrcene.

[0022] According to another preferred embodiment of the invention, 1,3-diene is β-farnesene.

[0023] Preferably, the ethylene and 1,3-diene copolymer has a glass temperature below -35°C, preferably between -90°C and -35°C.

[0024] According to a first embodiment of the invention, the copolymer contains 1,3-diene units of the 1,2 or 3,4 configuration that represent more than 50% by mole of the 1,3-diene units. In other words, in the copolymer, the 1,3-diene units are more than 50% by mole of the 1,2 or 3,4 configuration units. In this embodiment, the remaining 100% by mole of the 1,3-diene units in the copolymer consists entirely or partially of 1,3-diene units of the 1,4 configuration. According to this first embodiment, preferably more than half of the 1,3-diene units of the 1,4 configuration are of the 1,4-trans configuration, and more preferably all of the 1,3-diene units of the 1,4 configuration are of the 1,4-trans configuration.

[0025] According to a second embodiment of the invention, in the copolymer, more than 50% of the 1,3-diene units are in the 1,4 configuration. In other words, the 1,3-diene units in the 1,4 configuration represent more than 50% by mole of the 1,3-diene units. In this embodiment, the remaining 1,3-diene units in the copolymer, up to 100% by mole, consist entirely or partially of 1,3-diene units in the 1,2 or 3,4 configurations. Preferably, the 1,3-diene units in the 1,4 configuration represent more than 70% by mole of the 1,3-diene units. Advantageously, more than half of the 1,3-diene units in the 1,4 configuration are in the 1,4-trans configuration, meaning that the 1,3-diene units in the 1,4-trans configuration represent more than 50% by mole of the 1,3-diene units in the 1,4 configuration.

[0026] The copolymer can be prepared by a process which includes the copolymerization of ethylene and 1,3-diene in the presence of a catalytic system based on at least one metallocene of formula (II) and one organomagnesium compound of formula (III) Cp1 and Cp2, identical or different, being chosen from the group consisting of the cyclopentadienyl group of formula C5H4, the unsubstituted fluorenyl group of formula C13H8, and the substituted fluorenyl groups, P being a bridging group between the two groups Cp1 and Cp2 and representing a ZR3R4 group, Z representing a silicon or carbon atom, R3 and R4, identical or different, each representing an alkyl group comprising from 1 to 20 carbon atoms, preferably a methyl group, y, an integer, being equal to or greater than 0, x, an integer or not, being equal to or greater than 0, L representing an alkali metal chosen from the group consisting of lithium, sodium, and potassium, N representing a molecule of an ether, preferably diethyl ether or tetrahydrofuran, R1 and R2, identical or different, representing a carbon group. p(Cp 1< Cp 2< ) Nd(BH 4 ) (1+y)- L y -N x (II) MgR 1< R 2< (III)

[0027] Examples of substituted fluorenyl groups include those substituted by alkyl radicals with 1 to 6 carbon atoms or by aryl radicals with 6 to 12 carbon atoms. The choice of radicals is also influenced by the availability of the corresponding molecules, namely the substituted fluorenes, because these are either commercially available or easily synthesized.

[0028] Examples of substituted fluorenyl groups include 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.

[0029] 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 ranging from 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. Generally, after its synthesis, the catalytic system is used as is in the process for synthesizing the copolymer according to the invention.

[0030] Alternatively, the catalytic system can be prepared by a process analogous to that described in patent application WO 2017093654 A1 or in patent application WO 2018020122 A1. According to this alternative, the catalytic system further contains a preforming monomer selected from a conjugated diene, ethylene or a mixture of ethylene and a conjugated diene, in which case the catalytic system is based at least on the metallocene, the organomagnesium and the preforming monomer. For example, the organomagnesium and metallocene are typically reacted in a hydrocarbon solvent at a temperature of 20 to 80°C for 10 to 20 minutes to obtain a first reaction product, then with this first reaction product the preforming monomer chosen from a conjugated diene, ethylene or a mixture of ethylene and a conjugated diene is reacted at a temperature of 40 to 90°C for 1h to 12h.The conjugated diene used as a preforming monomer is preferably a 1,3-diene such as 1,3-butadiene, isoprene, or a 1,3-diene of formula (I), particularly myrcene or β-farnesene. The catalytic system thus obtained can be used immediately in the process according to the invention or stored under an inert atmosphere before its use in the process according to the invention.

[0031] 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 a suitable solvent, such as an ether like diethyl ether or tetrahydrofuran, or any other solvent known to those skilled in the art. After reaction, the metallocene is separated from the reaction byproducts by techniques known to those skilled in the art, such as filtration or precipitation in a second solvent.The metallocene is ultimately dried and insulated in solid form.

[0032] 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.

[0033] The organomagnesium compound useful for the purposes of the invention has the formula MgR1<R2<, in which R1< and R2<, whether identical or different, represent a carbon group. A carbon group is understood to be a group containing one or more carbon atoms. Preferably, R1< and R2< contain 2 to 10 carbon atoms. More preferably, R1< and R2< each represent an alkyl group. The organomagnesium compound is advantageously a dialkylmagnesium compound, preferably butylethylmagnesium or butyloctylmagnesium, and even better, butyloctylmagnesium.

[0034] According to any one of the embodiments of the invention, the molar ratio of the organomagnesium to the Nd metal constituting the metallocene is preferably in the range of 1 to 100, more preferably greater than or equal to 1 and less than 10. The range of values ​​from 1 to less than 10 is in particular more favorable for obtaining copolymers with high molar masses.

[0035] When the copolymer useful for the purposes of the invention is a copolymer having a microstructure as defined according to the first embodiment of the invention, it is prepared according to the process mentioned in this application using a metallocene of formula (II) in which Cp1 and Cp2, identical or different, are chosen from the group consisting of substituted fluorenyl groups and the unsubstituted fluorenyl group of formula C13H8. For this embodiment, the following metallocenes of formulas are particularly suitable, in which the symbol Flu represents the fluorenyl group of formula C13H8: [{Me2SiFlu2Nd(µ-BH4)2Li(THF)}2]; [Me2SiFlu2Nd(µ-BH4)2Li(THF)]; [Me2SiFlu2Nd(µ-BH4)(THF)]; [{Me 2 SiFlu 2 Nd(µ-BH 4 )(THF)} 2 ]; [Me 2 SiFlu 2 Nd(µ-BH 4 )].

[0036] When the copolymer useful for the purposes of the invention is a copolymer which has a microstructure as defined according to the second variant of the invention, it is prepared according to the process mentioned in this application using a metallocene of formula (II) in which Cp 1< denotes a cyclopentadienyl group Cp of formula C 5 H 4 and Cp 2< a fluorenyl group Flu of formula C 13 H 8.

[0037] A person skilled in the art also adapts 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, copolymerization, 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.

[0038] Polymerization is preferably carried out in solution, either continuously or batchwise. The polymerization solvent can be a hydrocarbon, aromatic, or aliphatic solvent. Examples of polymerization solvents include toluene and methylcyclohexane. Monomers 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 monomers. Copolymerization is typically carried out under anhydrous conditions and in the absence of oxygen, possibly with the addition of an inert gas. The polymerization temperature generally ranges from 30 to 150°C, preferably from 30 to 120°C. Preferably, copolymerization is carried out at a constant ethylene pressure.

[0039] During the polymerization of ethylene and 1,3-diene in a polymerization reactor, a continuous addition of ethylene and 1,3-diene can be carried out in the polymerization reactor, in which case the polymerization reactor is a fed reactor. This embodiment is particularly suitable for the synthesis of random copolymers.

[0040] Polymerization can be stopped by cooling the polymerization medium. The 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.

[0041] The rubber composition according to the invention comprises more than 50 to 100 parts per cent of an ethylene-1,3-diene copolymer of formula (I) as defined in any of the embodiments described above, including variations thereof. It is understood that the copolymer may consist of a mixture of copolymers that differ in their microstructure or macrostructure. When the proportion of the ethylene-1,3-diene copolymer of formula (I) is greater than 50 parts per cent and less than 100 parts per cent, the remainder to 100 parts per cent may be provided by another elastomer, in particular another diene elastomer known to those skilled in the art. This other diene elastomer may be an elastomer conventionally used in tire rubber compositions such as polybutadienes, polyisoprenes, 1,3-butadiene copolymers and isoprene copolymers.According to a preferred embodiment, the rubber composition comprises 100 parts per an ethylene copolymer and a 1,3-diene of formula (I).

[0042] The rubber composition according to the invention has another essential characteristic: it comprises a reinforcing filler. The rubber composition may include any type of so-called reinforcing filler, known for its ability to strengthen a rubber composition suitable for tire manufacturing. Examples include an organic filler such as carbon black, an inorganic reinforcing filler such as silica combined with a known coupling agent, or a mixture of these two types of filler. Such a reinforcing filler typically consists of nanoparticles with an average size (by mass) of less than one micrometer, generally less than 500 nm, most often between 20 and 200 nm, and more preferably between 20 and 150 nm.

[0043] The reinforcing filler content is adjusted by a person skilled in the art according to the intended use of the rubber compound. According to one embodiment of the invention, the reinforcing filler content in the rubber compound is greater than or equal to 30 parts per annum and less than or equal to 150 parts per annum, preferably greater than or equal to 35 parts per annum and less than or equal to 100 parts per annum. These reinforcing filler ranges defined in this embodiment allow the rubber compound to achieve an improved compromise between its reinforcing and stiffness properties, depending on the intended use of the rubber compound in a tire, particularly for a tread.

[0044] The reinforcing filler may be silica, carbon black, or a mixture of carbon black and silica. Preferably, silica constitutes more than 50% by mass of the reinforcing filler. More preferably, silica constitutes more than 85% by mass of the reinforcing filler.

[0045] The silica used may be any reinforcing silica known to those skilled in the art, in particular any precipitated or pyrogenated silica having a specific surface area BET and a specific surface area CTAB both less than 450 m² / g, preferably within a range of 30 to 400 m² / g, in particular 60 to 300 m² / g. In this presentation, the specific surface area BET is determined by gas adsorption using the Brunauer-Emmett-Teller method described in "The Journal of the American Chemical Society" (Vol. 60, page 309, February 1938), and more specifically according to a method adapted from the standard NF ISO 5794-1, Annex E of June 2010 [multipoint volumetric method (5 points) - gas: nitrogen - degassing under vacuum: one hour at 160°C - relative pressure range w / in: 0.05 to 0.17].

[0046] The CTAB specific surface area values ​​were determined according to the NF ISO 5794-1 standard, Annex G of June 2010. The process is based on the adsorption of CTAB (N-hexadecyl-N,N,N-trimethylammonium bromide) on the "external" surface of the reinforcing filler.

[0047] Any type of precipitated silica can be used, including highly dispersible precipitated silicas (known as "HDS" for "highly dispersible" or "highly dispersible silica"). These precipitated silicas, whether highly dispersible or not, are well known to those skilled in the art. Examples include the silicas described in applications WO03 / 016215-A1 and WO03 / 016387-A1. Among the commercial HDS silicas, one can notably use the silicas “Ulsil ®< 5000GR”, “Ulsil ®< 7000GR” from the company Evonik, the silicas “Zeosil ®< 1085GR”, “Zeosil ®< 1115 MP”, “Zeosil ®< 1165MP”, “Zeosil ®< Premium 200MP”, “Zeosil ®< HRS 1200 MP” from the Solvay Company.As non-HDS silica, the following commercial silicas may be used: “Ultrasil ®< VN2GR”, “Ultrasil ®< VN3GR” silicas from Evonik, “Zeosil ®< 175GR” silica from Solvay, “Hi-Sil EZ120G(-D)”, “Hi-Sil EZ160G(-D)”, “Hi-Sil EZ200G(-D)”, “Hi-Sil 243LD”, “Hi-Sil 210”, “Hi-Sil HDP 320G” silicas from PPG.

[0048] Silica can be a mixture of different silicas, in which case the proportions of silica in the reinforcing filler refer to the total of all the silicas.

[0049] All carbon blacks are suitable, including those conventionally used in tires or their treads. Among these, particularly the reinforcing carbon blacks of the 100, 200, and 300 series, or the 500, 600, and 700 series (ASTM D-1765-2017 grades), such as N115, N134, N234, N326, N330, N339, N347, N375, N550, N683, and N772. 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.

[0050] Carbon black can be a mixture of different carbon blacks, in which case the carbon black rates refer to the total of all the carbon blacks.

[0051] Preferably, carbon black is used at a concentration of 20 parts per cubic meter (ppm) or less, more preferably 10 parts per cubic meter (ppm) or less (for example, the carbon black concentration may be in the range of 0.5 to 20 parts per cubic meter, in particular from 1 to 10 parts per cubic meter). Advantageously, the carbon black concentration in the rubber composition is 5 parts per cubic meter or less. Within the indicated ranges, the coloring (black pigmenting agent) and UV-resistant properties of carbon black are benefited without compromising the typical performance provided by silica.

[0052] To couple the reinforcing inorganic filler, in this case silica, to the elastomer, a coupling agent (or bonding agent) with at least two functional groups can be used in a well-known manner. This ensures sufficient chemical and / or physical connection between the inorganic filler (the surface of its particles) and the elastomer. In such cases, the rubber compound includes a coupling agent to bind the silica to the elastomer. Organosilanes or polyorganosiloxanes with at least two functional groups are used in particular. "Two functional groups" refers to a compound possessing a first functional group capable of interacting with the inorganic filler and a second functional group capable of interacting with the elastomer.

[0053] Polysulfide silanes, described as "symmetric" or "asymmetric" depending on their specific structure, are used, as described, for example, in applications WO03 / 002648-A1 (or US2005 / 016651-A1) and WO03 / 002649-A1 (or US2005 / 016650-A1). In particular, but not limited to, polysulfide silanes conforming to the following general formula (IV), in which: Z - A - S x - A - Z (IV) are suitable. x is an integer from 2 to 8 (preferably from 2 to 5); the symbols A, whether 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 a C1-C4 alkylene, in particular propylene); the symbols Z, whether identical or different, correspond to one of the three formulas below: in which: the radicals R< , substituted or unsubstituted, identical or different from each other, represent a C1-C18 alkyl group, a C5-C18 cycloalkyl group or a C6-C18 aryl group (preferably C1-C6 alkyl groups, cyclohexyl or phenyl, in particular C1-C4 alkyl groups, more particularly methyl and / or ethyl), the radicals R< , substituted or unsubstituted, identical or different from each other, represent a C1-C18 alkoxyl group or a C5-C18 cycloalkoxyl group (preferably a group selected from C1-C8 alkoxyls and C5-C8 cycloalkoxyls, more preferably a group selected from C1-C4 alkoxyls, in particular methoxyl and ethoxyl), or a hydroxyl group, or such that 2 Rb radicals represent a dialkoxyl group in C3-C18.

[0054] In the case of a mixture of polysulfurized alkoxysilanes corresponding to formula (V) above, in particular common mixtures available commercially, the average value of "x" is a fractional number preferably in the range of 2 to 5, more preferably close to 4.

[0055] 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, marketed under the name "Si69" by the company Evonik, or the disulfide of bis-(triethoxysilylpropyl), abbreviated TESPD, with the formula [(C 2 HSO) 3 Si(CH 2 ) 3 S] 2, marketed under the name "Si75" by the company Evonik, is used.We will also cite as preferential examples the polysulfides (in particular disulfides, trisulfides or tetrasulfides) of bis-(monoalkoxyl(C1-C4)-dialkyl(C1-C4)silylpropyl), more particularly the tetrasulfide of bis-monoethoxydimethylsilylpropyl as described in the aforementioned patent application WO02 / 083782-A1 (or US7217751-B2).

[0056] Of course, mixtures of the coupling agents described above could also be used.

[0057] The coupling agent content in the composition of the invention is advantageously less than or equal to 25 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 reinforcing inorganic filler. Its content is preferably in the range of 0.5% to 20 parts per liter, and more preferably in the range of 3% to 15 parts per liter. This content is readily adjusted by a person skilled in the art according to the amount of reinforcing inorganic filler used in the composition of the invention.

[0058] The crosslinking system useful for the purposes of the invention is preferably a vulcanization system, that is to say, based on sulfur and a primary vulcanization accelerator. The sulfur is typically supplied in the form of molecular sulfur or a sulfur donor, preferably in molecular form. Molecular sulfur is also referred to as molecular sulfur. A sulfur donor is defined as any compound that releases sulfur atoms, combined or not in the form of a polysulfide chain, capable of inserting themselves into the polysulfide chains formed during vulcanization and bridging the elastomeric chains. Various known secondary accelerators or vulcanization activators, such as zinc oxide, stearic acid, guanidine derivatives (in particular diphenylguanidine), etc., are added to the vulcanization system and incorporated during the first non-productive phase and / or during the productive phase.The sulfur content is preferably between 0.5 and 3.0 parts per annum, and that of the primary accelerator is preferably between 0.5 and 5.0 parts per annum. These preferred levels can be applied to any of the embodiments of the invention.

[0059] Any compound capable of acting as a vulcanization accelerator of diene elastomers in the presence of sulfur can be used as a vulcanization accelerator (primary or secondary), including thiazole-type accelerators and their derivatives, sulfenamide-type accelerators for primary accelerators, and thiurams, dithiocarbamates, dithiophosphates, thioureas and xanthates for secondary accelerators.

[0060] Crosslinking (or curing), where applicable vulcanization, is carried out in a known manner at a temperature generally between 130°C and 200°C, for a sufficient time which can vary for example between 5 and 90 min depending in particular on the curing temperature, the crosslinking system adopted and the crosslinking kinetics of the composition considered.

[0061] The rubber composition according to the invention may also include all or part of the usual additives commonly used in elastomer compositions for the manufacture of tires, including pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, antioxidants, and plasticizers.

[0062] According to a particular embodiment of the invention, the rubber composition further comprises a plasticizer. The plasticizer content in the rubber composition can vary considerably, particularly depending on the reinforcing filler content in the rubber composition and the nature of the plasticizer used. Preferably, it is greater than 10 parts per cubic centimeter and less than or equal to 100 parts per cubic centimeter, or more preferably greater than or equal to 30 parts per cubic centimeter and less than or equal to 90 parts per cubic centimeter.

[0063] According to a particularly preferred embodiment of the invention, the rubber composition comprises a hydrocarbon resin as a plasticizer. This embodiment is particularly preferred for use of the rubber composition in a tread. Hydrocarbon resins, also called hydrocarbon plasticizing resins, are polymers well known to those skilled in the art, essentially based on carbon and hydrogen but which may contain other types of atoms, for example oxygen, and are particularly useful as plasticizing or tackifying agents in polymer matrices. They are by nature at least partially miscible (i.e., compatible) at the rates used with the polymer compositions for which they are intended, so as to act as true diluents. They have been described, for example, in the book entitled "Hydrocarbon Resins" by R. Mildenberg, M. Zander, and G.Collin (New York, VCH, 1997, ISBN 3-527-28617-9), whose Chapter 5 is devoted to their applications, particularly in pneumatic rubber (5.5. "Rubber Tires and Mechanical Goods"). As is known, these hydrocarbon resins can also be described as thermoplastic resins in that they soften upon heating and can thus be molded. The softening point of hydrocarbon resins is measured according to ISO 4625 (Ring and Ball method). The Tg is measured according to ASTM D3418 (1999). The macrostructure (Mw, Mn, and Ip) of the hydrocarbon resin is determined by size exclusion chromatography (SEC): tetrahydrofuran solvent; temperature 35°C; concentration 1 g / l; flow rate 1 ml / min; solution filtered through a 0.45 µm porosity filter before injection; Moore calibration with polystyrene standards; set of 3 "WATERS" columns in series ("STYRAGEL" HR4E, HR1 and HR0.5); detection by differential refractometer ("WATERS 2410") and its associated operating software ("WATERS EMPOWER").

[0064] Hydrocarbon resins can be aliphatic, aromatic, or aliphatic / aromatic, meaning they are based on aliphatic and / or aromatic monomers. They can be natural or synthetic, and may or may not be petroleum-based (in which case they are also known as petroleum resins). Preferably, hydrocarbon plasticizing resins have a glass transition temperature above 20°C.

[0065] Advantageously, the hydrocarbon plasticizing resin exhibits at least one of the following characteristics, more preferably all of them: a Tg greater than 30°C; a number average molecular mass (Mn) between 300 and 2000 g / mol, more preferably between 400 and 1500 g / mol; a polymolecularity index (Ip) less than 3, more preferably less than 2 (reminder: Ip = Mw / Mn with Mw weight average molecular mass).

[0066] Preferably, the hydrocarbon plasticizing resin is chosen from the group consisting of cyclopentadiene homopolymer resins, cyclopentadiene copolymer resins, dicyclopentadiene homopolymer resins, dicyclopentadiene copolymer resins, terpene homopolymer resins, terpene copolymer resins, C5 cut homopolymer resins, C5 cut copolymer resins, C9 cut homopolymer resins, C9 cut copolymer resins, hydrogenated cyclopentadiene homopolymer resins and hydrogenated cyclopentadiene copolymer resins.

[0067] Preferably, the hydrocarbon plasticizing resin is a C9-cut copolymer resin or a dicyclopentadiene copolymer resin, hydrogenated or not. As a particular example, C9-cut copolymer resins and hydrogenated dicyclopentadiene resins are particularly suitable.

[0068] As a useful plasticizer for the purposes of the invention, one can also mention hydrocarbon liquid plasticizers known to soften a rubber composition by diluting the elastomer and the reinforcing filler of the rubber composition. Their Tg is typically below -20°C, preferably below -40°C. Any hydrocarbon extending oil or any hydrocarbon liquid plasticizer known for its plasticizing properties with respect to diene elastomers is usable. At room temperature (23°C), these plasticizers or oils, which vary in viscosity, are liquids (that is to say, substances that eventually take the shape of their container), unlike hydrocarbon plasticizing resins, which are solid by nature at room temperature.

[0069] Examples of liquid hydrocarbon plasticizing agents include liquid diene polymers, polyolefin oils, naphthenic oils, paraffinic oils, DAE oils, and MES oils. Medium Extracted Solvates ), TDAE oils ( Treated Distillate Aromatic Extracts ) , RAE oils ( Residual Aromatic Extract oils ), TRAE oils ( Treated Residual Aromatic Extract ) and SRAE oils ( Safety Residual Aromatic Extract oils ), mineral oils, and mixtures of these compounds.

[0070] Preferably, the liquid hydrocarbon plasticizer is selected from the group consisting of liquid diene polymers, aliphatic polyolefin oils, paraffinic oils, MES oils, TDAE oils, TRAE oils, SRAE oils, mineral oils, and mixtures thereof. More preferably, the liquid hydrocarbon plasticizer is a liquid diene polymer, an aliphatic polyolefin oil, a paraffinic oil, a MES oil, or mixtures thereof.

[0071] The rubber composition, before crosslinking, 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 110°C and 190°C, preferably between 130°C and 180°C, followed by a second mechanical working phase (sometimes referred to as the "productive" phase) at a lower temperature, typically below 110°C, for example between 40°C and 100°C, a finishing phase during which the sulfur or sulfur donor and the vulcanization accelerator are incorporated.

[0072] 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 crosslinking system, 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 thus obtained during the first non-productive phase has cooled, the product is then incorporated at a low temperature, generally in an external mixer such as a roller mixer; the entire mixture is then blended (productive phase) for a few minutes, for example, between 2 and 15 minutes.

[0073] The rubber compound can be calendered or extruded into a sheet or plate, particularly for laboratory characterization, or into a semi-finished (or profiled) rubber product for use in a tire. The compound can be either in its raw state (before crosslinking or vulcanization) or in its cured state (after crosslinking or vulcanization), and can be a semi-finished product suitable for use in a tire.

[0074] The tire comprising a tread, another object of the invention, includes a rubber composition according to the invention, preferably in the tread.

[0075] The aforementioned features of the present invention, as well as others, will be better understood upon reading the following description of several examples of embodiments of the invention, given by way of illustration and not limitation. Example II.1 Tests and measurements: II.1-1 Determination of the microstructure of elastomers :

[0076] Spectral characterization and microstructure measurements of ethylene- and 1,3-myrcene copolymers are performed by Nuclear Magnetic Resonance (NMR) spectroscopy.

[0077] Spectrometer: For these measurements, a Bruker Avance III HD 400 MHz spectrometer is used, equipped with a Bruker cryo-BBFO z-grad 5 mm probe.

[0078] Experiments: The 1H experiments are recorded using a radiofrequency pulse with a 30° flip angle, with 128 repetitions and a 5-second replay interval. The 1H-13C HSQC (Heteronuclear Single Quantum Coherence) and HMBC (Heteronuclear Multiple-Bond Correlation) correlation NMR experiments are recorded with 128 repetitions and 128 increments. The experiments are performed at 25 °C.

[0079] Sample preparation: 25 mg of sample are solubilized in 1 mL of deuterated chloroform (CDCI3).

[0080] Sample calibration: The chemical shift axes 1<H and 13<C are calibrated with respect to the protonated impurity of the solvent (CHCl3) at δ1H = 7.2 ppm and δ13C = 77 ppm. Spectral assignment for ethylene- and 1,3-myrcene copolymers (see Chem 1): In the Chem 1 representation, the symbols R1 and R2 represent the attachment points of the unit to the polymer chain. In the Chem 1 representation, the signals of the 1,3-diene insertion forms A, B, and C were observed on the different recorded spectra. (Adapted from S. Georges) et al., (S. Georges, M. Bria, P. Zinck and M. Visseaux, Polymer 55 (2014) 3869-3878), the signal of the -CH= group no. 8" characteristic of the C form has chemical shifts 1< H and 13< C identical to the -CH= group no. 3.

[0081] The chemical shifts of the characteristic signals of motifs A, B and C are shown in Table 1. Motifs A, B and C correspond respectively to the 3,4 configuration units, the 1,2 configuration and the 1,4-trans configuration units.

[0082] Quantifications were performed from the integration of 1D 1< H NMR spectra using Topspin software.

[0083] The integrated signals for quantifying the different patterns are: Ethylene: signal at 1.2 ppm corresponding to 4 protons. Total myrcene: signal #1 (1.59 ppm) corresponding to 6 protons. Form A: signal #7 (4.67 ppm) corresponding to 2 protons. Form B: signal #8' (5.54 ppm) corresponding to 1 proton.

[0084] The quantification of the microstructure is carried out in molar percentage (% molar) as follows: % molar of a motif = 1H integral of a motif * 100 / Σ (1H integrals of each motif) Table 1 Table 1: Signal assignment 1< H and 13< C of Ethylene-Myrcene copolymers δ 1H (ppm) δ 13C (ppm) Group 5.54 146.4 8' 5.07 124.6 3 + 8" 4.97 - 4.79 112.0 9' 4.67 108.5 7 2.06 26.5 4 31.8 5 + 5' + 5" 2.0 - 1.79 44.5 8 1.59 25.9 and 17.0 1 1.2 36.8 - 24.0 CH2 ethylene

[0085] Quantifications were performed from the integration of 1D 1< H NMR spectra using Topspin software.

[0086] The integrated signals for quantifying the different patterns are: Ethylene: signal at 1.2 ppm corresponding to 4 protons, Total Myrcene: signal no. 1 (1.59 ppm) corresponding to 6 protons, Form A: signal no. 7 (4.67 ppm) corresponding to 2 protons, Form B: signal no. 8' (5.54 ppm) corresponding to 1 proton.

[0087] The quantification of the microstructure is carried out in molar percentage (% molar) as follows: % molar of a motif = 1H integral of a motif * 100 / Σ (1H integrals of each motif). II.1-2 Determination of the glass transition temperature of polymers:

[0088] The glass transition temperature is measured using a Differential Scanning Calorimeter according to ASTM D3418 (1999). II.1-3 Rigidity and hysteresis of rubber compositions:

[0089] Dynamic properties are measured on a viscoelastic analyzer (Metravib VA4000), according to standard 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 an imposed stress of 0.7 MPa and a frequency of 10 Hz. The temperature sweep is performed from a minimum temperature below the Tg of the elastomers in the composition to a maximum temperature above 100°C. The results analyzed are the complex dynamic shear modulus (G*) and the loss factor (tand); the values ​​of G* are taken at 60°C and the loss factor (tand) at 20°C and 40°C.

[0090] Stiffness and hysteresis results are expressed as a percentage of 100 relative to a reference control. A value less than 100 indicates a lower value than that of the control. II.2 Polymer Synthesis :

[0091] In the synthesis of copolymers according to the invention, the 1,3-diene used is myrcene, 1,3-diene of formula (I) in which R is a hydrocarbon group having 6 carbon atoms of formula (I).

[0092] In myrcene, R corresponds to the formula CH2-CH2-CH=CMe2.

[0093] All reagents are commercially obtained except for the metallocenes [{Me 2 SiFlu 2 Nd(µ-BH 4 ) 2 Li(THF)}] is prepared according to the operating procedure described in patent application WO 2007054224.

[0094] Butylloctylmagnesium BOMAG (20% in heptane, C = 0.88 mol L⁻¹) is sourced from Chemtura and stored in a Schlenk tube under an inert atmosphere. The N35 grade ethylene is sourced from Air Liquide and used without prior purification. The myrcene (purity ≥95%) is obtained from Sigma-Aldrich.

[0095] Mooney viscosity is measured using an oscillating consistometer as described in ASTM D1646 (1999). The measurement is performed according to the following principle: the sample being analyzed in its raw state (i.e., before cooking) is molded (shaped) in a cylindrical chamber heated to a given temperature (100°C). After 1 minute of preheating, the rotor rotates within the specimen at 2 revolutions per minute, and the torque required to maintain this rotation is measured after 4 minutes of rotation. Mooney viscosity (ML) is expressed in "Mooney units" (MU, with 1 MU = 0.83 Newton-meters). 2.1- Ethylene and 1,3-butadiene copolymer: E1 elastomer

[0096] In a reactor containing methylcyclohexane, ethylene (Et), and butadiene (Bd) at 80°C in the proportions indicated in Table 2, butylclotylmagnesium (BOMAG) is added to neutralize impurities in the reactor, followed by the catalytic system (see Table 2). At this point, the reaction temperature is regulated to 80°C, and the polymerization reaction begins. The polymerization reaction proceeds at a constant pressure of 8 bar. The reactor is fed with ethylene and butadiene throughout the polymerization process in the proportions defined in Table 2. The polymerization reaction is stopped by cooling, degassing the reactor, and adding ethanol. An antioxidant is added to the polymer solution. The copolymer is recovered by drying in a vacuum oven until a constant mass is reached. The Mooney viscosity of E1 is 85.

[0097] The catalytic system is a preformed catalytic system. It is prepared in methylcyclohexane from a metallocene, [Me 2 Si(Flu) 2 Nd(µ-BH 4 ) 2 Li(THF)], a co-catalyst, butylloctylmagnesium (BOMAG), and a preforming monomer, 1,3-butadiene, in the amounts indicated in Table 2. It is prepared according to a preparation method in accordance with paragraph II.1 of patent application WO 2017093654 A1. 2.2- Ethylene and myrcene copolymer: E2 elastomer

[0098] The polymer is synthesized according to the following procedure: In a reactor containing methylcyclohexane, ethylene, and myrcene (My) at 80°C in the proportions indicated in Table 2, butylclotylmagnesium (BOMAG) is added to neutralize impurities in the reactor, followed by the catalytic system (see Table 2). At this point, the reaction temperature is regulated at 80°C, and the polymerization reaction begins. The polymerization reaction proceeds at a constant pressure of 8 bar. The reactor is fed with ethylene and myrcene throughout the polymerization process in the proportions defined in Table 2. The polymerization reaction is stopped by cooling, degassing the reactor, and adding ethanol. An antioxidant is added to the polymer solution. The copolymer is recovered by drying in a vacuum oven until a constant mass is reached. The Mooney viscosity of E2 is 17.

[0099] The catalytic system is a preformed catalytic system. It is prepared in methylcyclohexane from a metallocene, [Me 2 Si(Flu) 2 Nd(µ-BH 4 ) 2 Li(THF)], a co-catalyst, butylloctylmagnesium (BOMAG), and a preforming monomer, 1,3-butadiene, in the amounts indicated in Table 2. It is prepared according to a preparation method in accordance with paragraph II.1 of patent application WO 2017093654 A1.

[0100] The microstructure of the polymers and their properties are shown in Tables 3 and 4. 2.3 Preparation of rubber compositions:

[0101] Rubber compositions whose formulation, expressed in parts per cent (parts by weight per percent of elastomer), is shown in Table 5, were prepared according to the following procedure: the following is introduced into an internal mixer (final filling ratio: (approximately 70% by volume), with an initial tank temperature of approximately 80°C, the copolymer, the reinforcing filler, and various other ingredients, excluding the vulcanizing system, are successively mixed. A thermomechanical process (non-productive phase) is then carried out in a single step, lasting approximately 5 minutes, until a maximum "drop" temperature of 150°C is reached. The resulting mixture is collected, cooled, and then sulfur and the accelerator are incorporated in a mixer (homo-finisher) at 40°C, with the entire mixture blended for about ten minutes (productive phase). The resulting compositions are then calendered into either slabs (2 to 3 mm thick) or thin sheets of rubber for the measurement of their physical and mechanical properties.

[0102] Composition C1, which contains elastomer E1, a copolymer of ethylene and 1,3-butadiene, is not a composition according to the invention. Composition C2, which contains elastomer E2, a copolymer of ethylene and myrcene, is a composition according to the invention. 2.4 Results:

[0103] The results are shown in Table 6.

[0104] Composition C2 exhibits lower stiffness than composition C1 without affecting its hysteresis properties. This result is obtained with a comparable diene content (14% for elastomer E1, 13% for elastomer E2) and a significantly higher ethylene content for E2 than for E1 (87% versus 78%). Despite the much higher ethylene content, the C2 rubber composition according to the invention offers an improved compromise between stiffness and hysteresis properties. Table 2 Synthesis Metallocene concentration (mmol / L) Alkylating agent concentration (mmol / L) preformed monomer / metal molar ratio Nd Dietary composition (%mol Eth / Bdt) Dietary composition (%mol Eth / Myr) E1 0.07 0.36 90 80 / 20 - E2 0.05 0.33 90 - 85 / 15 Table 3: Elastomer Ethylene (%mol) Butadiene (%mol) 1,2-cyclohexanediyl (%mol) Myrcene (%mol) Myrcene 1.4 (%mol / %mol myrcene) Myrcene 1.2 (%mol / %mol myrcene) Myrcene 3.4 (%mol / %mol myrcene) E1 78 14 8 - - - - E2 87 - - 13 31 7 62 Table 4: Elastomer Tg (°C) Crystallinity (%) E1 -40 5 E2 -58 17 Table 5 Composition C1 C2 E1 Elastomer 100 0 E2 Elastomer 0 100 Carbon black (1) 3 3 Silica (2) 76 76 Liquid plasticizing agent (3) 22 22 Plasticizing resin (4) 51 51 Antioxidant (5) 2 2 Anti-ozonating wax 2 2 Coupling agent (6) 6 6 Stearic acid (7) 2 2 DPG (8) 1.5 1.5 ZnO (9) 1 1 Accelerator (10) 2 2 Sulfur 1 1 (1) N234 (2) "Zeosil 1165 MP" from Solvay-Rhodia in microbead form (3) MES / HPD (Catenex SNR from Shell) (4) C9 / Dicyclopentadiene hydrocarbon resin "Escorez 5600" from EXXON (Tg = 55°C) (5) N-1,3-dimethylbutyl-N-phenyl-para-phenyldiamine ("Santoflex 6-PPD" from Flexsys) (6) TESPT ("Si69" from Evonik) (7) Stearine "Pristerene 4931" from Uniquema (8) Diphenylguanidine (9) Industrial grade zinc oxide from Umicore (10) N-cyclohexyl-2-benzothiazol-sulfenamide ("Santocure CBS" from Flexsys) Table 6 Composition C1 C2 G* 60°C 100 51 tanδ 20°C 100 95 tanδ 40°C 100 100

Claims

1. Rubber composition which comprises a reinforcing filler, a crosslinking system and more than 50 to 100 phr of an elastomer which is a copolymer of ethylene and of a 1,3-diene of formula (I),         CH2=CR-CH=CH2     (I) the symbol R representing a hydrocarbon chain having from 3 to 20 carbon atoms.

2. Rubber composition according to Claim 1, in which the copolymer contains ethylene units which represent between 50 mol% and 95 mol% of the ethylene units and of the units of the 1,3-diene.

3. Rubber composition according to either one of Claims 1 and 2, in which the copolymer contains ethylene units which represent at least 60 mol%, preferably at least 70 mol% of the ethylene units and of the units of the 1,3-diene.

4. Rubber composition according to any one of Claims 1 to 3, in which the copolymer contains ethylene units which represent at most 90 mol% of the ethylene units and of the units of the 1,3-diene.

5. Rubber composition according to any one of Claims 1 to 4, in which the copolymer contains ethylene units which represent at most 85 mol% of the ethylene units and of the units of the 1,3-diene.

6. Rubber composition according to any one of Claims 1 to 5, in which the symbol R represents an aliphatic chain.

7. Rubber composition according to any one of Claims 1 to 6, in which the symbol R represents a hydrocarbon chain having from 6 to 16 carbon atoms.

8. Rubber composition according to any one of Claims 1 to 7, in which the symbol R represents an acyclic chain.

9. Rubber composition according to any one of Claims 1 to 8, in which the symbol R represents a linear or branched chain.

10. Rubber composition according to any one of Claims 1 to 9, in which the copolymer has a glass transition temperature below -35°C, preferably between -90°C and -35°C, the glass transition temperature being measured by means of a differential calorimeter (differential scanning calorimeter) according to standard ASTM D3418 (1999).

11. Rubber composition according to any one of Claims 1 to 10, in which the copolymer contains units of the 1,3-diene of 1,2 or 3,4 configuration which represent more than 50 mol% of the units of the 1,3-diene.

12. Rubber composition according to any one of Claims 1 to 11, in which the 1,3-diene is myrcene or β-farnesene.

13. Rubber composition according to any one of Claims 1 to 12, in which the reinforcing filler is a silica, a carbon black or a mixture of a carbon black and a silica.

14. Rubber composition according to any one of Claims 1 to 13, which composition comprises a plasticizer, preferably a hydrocarbon plasticizing resin.

15. Tyre comprising a tread, which tyre comprises a rubber composition defined in any one of Claims 1 to 14.