Rubber composition comprising a highly saturated diene elastomer

Abstract

The invention relates to a rubber composition exhibiting improved endurance. This composition is based on at least 20 to 50 phr of a copolymer containing ethylene units and 1,3-diene units, the ethylene units in the copolymer representing between 50 mol% and 95 mol% of the monomer units of the copolymer; 50 to 80 phr of a polyisoprene comprising a content by weight of cis-1,4 bonds of at least 90% of the weight of the polyisoprene; a reinforcing filler; 0.5 to less then 10 phr of zinc stearate; and a vulcanisation system. The invention also relates to pneumatic tyres, at least one sidewall of which comprises a composition according to the invention.

Description

[0001] RUBBER COMPOSITION COMPRISING A HIGHLY SATURATED DIENE ELASTOMER

[0002] The field of the present invention is that of rubber compositions comprising a highly saturated diene elastomer, in particular intended for use in a tire, more particularly in a tire sidewall.

[0003] The sidewalls of a tire are exposed to both the action of ozone and deformation cycles such as flexing during tire rolling. Deformation cycles combined with the action of ozone can cause cracks or fissures to appear in the sidewall, which can reduce the tire's service life independently of tread wear. Therefore, rubber compositions that are highly cohesive are sought to constitute, for example, tire sidewalls due to their ability to withstand large deformations without breaking, even in the presence of incipient cracks.

[0004] To minimize the action of ozone on rubber compositions, it is known to use copolymers having less sensitivity to oxidation, such as for example highly saturated diene elastomers, elastomers comprising ethylene units at a molar content greater than 50% of the monomer units of the elastomer. The use of copolymers of ethylene and 1,3-diene in a sidewall composition is also for example described in document EP 2 682 423 A1 to increase the resistance to ozone. However, there appears to be a decline in the cohesion properties of the rubber composition when the molar content of ethylene in the copolymer is greater than 50%.

[0005] Furthermore, diene rubber compositions comprising copolymers of ethylene and 1,3-butadiene, once crosslinked, can have a much higher rigidity than the diene rubber compositions traditionally used as is apparent from document WO 2014 / 114607 AL. However, this increased rigidity, although favorable to improved wear resistance for use in treads, can sometimes prove unsuitable for certain applications, in particular in tire sidewalls.

[0006] It has therefore been sought to reduce the cured stiffness of such compositions comprising an ethylene-based diene rubber. To do this, it is known to reduce the bridge density of the rubber composition. However, this solution is accompanied by an increase in the hysteresis of the rubber composition, which is detrimental to rolling resistance. Document WO 2021 / 053296 A1 provided a solution for reducing the cured stiffness of compositions comprising an ethylene-based diene rubber without penalizing the hysteresis by using rubber compositions which comprise a copolymer of ethylene and a 1,3-diene of formula CH2=CR-CH=CH2, the symbol R representing a hydrocarbon chain having 3 to 20 carbon atoms. The reduction in cured stiffness results in an improvement in the endurance of the composition, in particular when it is used in a tire sidewall given the stresses to which it is subjected.

[0007] It would therefore be interesting for tire manufacturers to have rubber compositions, particularly usable in sidewalls, with lower cured rigidity in order to further improve the endurance of the composition.

[0008] Continuing its research, the Applicant unexpectedly discovered that the use of zinc stearate in a rubber composition based on a specific copolymer containing ethylene units and a 1,3-diene makes it possible to solve the aforementioned technical problem.

[0009] Thus, the invention relates to a rubber composition based on at least:

[0010] - 20 to 50 pce of at least one copolymer containing ethylene units and 1,3-diene units, the ethylene units in the copolymer representing between 50% and 95% by mole of the monomer units of the copolymer;

[0011] - 50 to 80 pce of polyisoprene comprising a mass rate of 1,4-cis bonds of at least 90% of the mass of the polyisoprene;

[0012] - a reinforcing charge;

[0013] - 0.5 to less than 10 pce of zinc stearate; and

[0014] - a vulcanization system.

[0015] The invention also relates to a pneumatic tire of which at least one sidewall comprises a composition according to the invention.

[0016] I- DEFINITIONS

[0017] The expression "based on" used to define the constituents of a catalytic system means the mixture of these constituents, or the product of the reaction of some or all of these constituents with each other.

[0018] The expression "rubber composition based on" means a rubber composition comprising the mixture and / or the in situ reaction product of the different constituents used, some of these constituents being able to react and / or being intended to react with each other, at least partially, during the different phases of manufacture of the composition; the composition can thus be in a totally or partially crosslinked state or in a non-crosslinked state.

[0019] By “elastomer matrix” is meant all the elastomers in the composition, including the copolymer defined below.

[0020] Unless otherwise indicated, the rates of units resulting from the insertion of a monomer into a copolymer are expressed as a molar percentage relative to the total monomer units of the copolymer.

[0021] By the expression "part by weight per hundred parts by weight of elastomer" (or pce), it is meant, within the meaning of the present invention, the part, by mass per hundred parts by mass of the elastomer matrix.

[0022] On the other hand, any interval of values ​​designated by the expression "between a and b" represents the range of values ​​from more than a to less than b (i.e., excluding the limits a and b), while any interval of values ​​designated by the expression "from a to b" means the range of values ​​from a to b (i.e., including the strict limits a and b). In this document, when an interval of values ​​is designated by the expression "from a to b", the interval represented by the expression "between a and b" is also and preferably designated.

[0023] The compounds mentioned in the description may be of fossil or bio-sourced origin. In the latter case, they may be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. Similarly, the compounds mentioned may also come from the recycling of materials already in use, i.e. they may be, partially or totally, derived from a recycling process, or obtained from raw materials themselves derived from a recycling process. This includes, in particular, polymers, plasticizers, fillers, etc.

[0024] Unless otherwise stated, all glass transition temperature “Tg” values ​​described herein are measured in a known manner by DSC (Differential Scanning Calorimetry) according to ASTM D3418 (1999).

[0025] II- DESCRIPTION OF THE INVENTION

[0026] II- 1 Elastomer matrix

[0027] The composition according to the invention is based on at least:

[0028] - 20 to 50 pce of a copolymer containing ethylene units and 1,3-diene units, the ethylene units in the copolymer representing between 50% and 95% by mole of the monomer units of the copolymer (hereinafter referred to as “the copolymer”);

[0029] - 50 to 80 pce of polyisoprene comprising a mass rate of 1,4-cis bonds of at least 90% of the mass of the polyisoprene.

[0030] By "copolymer containing ethylene units and 1,3-diene units" is meant any copolymer comprising, within its structure, at least ethylene units and 1,3-diene units. According to the invention, the 1,3-diene may be a single compound, i.e. a single (in English "one") 1,3-diene or be a mixture of 1,3-dienes.

[0031] The copolymer may also comprise monomer units other than ethylene units and 1,3-diene units, but this is not preferred. For example, the copolymer may also comprise alpha-olefin units, in particular alpha-olefin units having from 3 to 18 carbon atoms, advantageously having 3 to 6 carbon atoms. For example, the alpha-olefin units may be selected from the group consisting of propylene, butene, pentene, hexene or mixtures thereof.

[0032] As is well known, the expression "ethylene unit" refers to the -(CH2-CH2)- motif resulting from the insertion of ethylene into the copolymer chain.

[0033] As is known, the expression "1,3-diene unit" refers to the units resulting from the insertion of 1,3-diene by a 1,4 addition, a 1,2 addition or a 3,4 addition in the case of a substituted diene such as isoprene for example.

[0034] Preferably, the 1,3-diene units are selected from the group consisting of butadienes, isoprene units and mixtures of these 1,3-diene units. In particular, the 1,3-diene units of the copolymer may be 1,3-diene units having 4 to 24 carbon atoms, for example 1,3-butadiene, 2-methyl-1,3-butadiene (or isoprene) units or units of formula CH2=CR-CH=CH2, the symbol R representing a hydrocarbon chain having 3 to 20 carbon atoms.

[0035] The copolymer useful for the purposes of the invention is advantageously a random copolymer according to any one of the embodiments of the invention. Very advantageously, the copolymer is an atactic polymer according to any one of the embodiments of the invention.

[0036] Preferably, the copolymer has a glass transition temperature of less than -35°C, preferably between -90°C and -35°C, more preferably between -70°C and - Advantageously also, the copolymer contains ethylene units which represent from 60% to 90% by mole of the monomer units of the copolymer, i.e. from 60% to 90% by mole of the ethylene units and the 1,3-diene units. Very preferably, the copolymer contains ethylene units which represent from 70% to 85% by mole of the monomer units of the copolymer.

[0037] Particularly advantageously, the copolymer is a copolymer containing ethylene units and units of a 1,3-diene of formula (I), the ethylene units in the copolymer representing between 50% and 95% by mole of the units, CH2=CR-CH=CH2 (I), the symbol R representing a hydrocarbon chain having 3 to 20 carbon atoms.

[0038] 1,3-Diene of formula (I) is a substituted 1,3-diene, which can give rise to units of 1,2-configuration represented by formula (1), 3,4-configuration represented by formula (2) and 1,4-configuration whose trans form is represented below by formula (3).

[0039] 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.

[0040] The hydrocarbon chain represented by the symbol R may be a saturated or unsaturated chain. 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 may be a straight or branched chain, in which case the symbol R represents a straight or branched chain. Preferably, the hydrocarbon chain is acyclic, in which case the symbol R represents an acyclic chain. More preferably, the symbol R represents an unsaturated and branched acyclic hydrocarbon chain. Thus, the hydrocarbon chain represented by the symbol R is advantageously an unsaturated and branched acyclic chain containing from 3 to 20 carbon atoms, in particular from 6 to 16 carbon atoms. Very advantageously, the 1,3-diene is myrcene, P-famesene or a mixture of myrcene and P-farnesene.Even more advantageously, the 1,3-diene is myrcene. Advantageously, the copolymer contains units of the 1,3-diene of formula (I) which represent between 10% and 40%, preferably between 15% and 30%, in moles of the monomer units of the copolymer.

[0041] The copolymer containing ethylene units and units of a 1,3-diene of formula (I) may comprise a second 1,3-diene chosen from 1,3-butadiene, isoprene or a mixture thereof. In this case, the copolymer is a copolymer of ethylene, a 1,3-diene of formula (I) and a second 1,3-diene chosen from 1,3-butadiene, isoprene or a mixture thereof, the monomer units of the copolymer are units resulting from the polymerization of ethylene, the 1,3-diene of formula (I) and the second 1,3-diene. The copolymer may thus comprise ethylene units, units of the 1,3-diene of formula (I) and units of the second 1,3-diene. Advantageously, the second 1,3-diene of the copolymer is 1,3-butadiene.

[0042] When the copolymer containing ethylene units and units of a 1,3-diene of formula (I) contains units of the second 1,3-diene, these advantageously represent between 1% and 49%, preferably between 4% and 29%, preferably between 4% and 25%, in moles of the monomer units of the copolymer.

[0043] According to one embodiment of the invention, the copolymer contains more than 60% to 90% by mole of ethylene units and at most 20% by mole, preferably at most 15% by mole of units of the 1,3-diene of formula (I). According to this embodiment of the invention, the copolymer preferably contains less than 30% by mole of units of the second 1,3-diene or preferably contains less than 20% by mole of units of the second 1,3-diene.

[0044] When the second 1,3-diene is 1,3-butadiene or a mixture of 1,3-butadiene and isoprene, the copolymer may additionally contain 1,2-cyclohexanediyl unit units. The presence of these cyclic structures in the copolymer results from a very specific insertion of ethylene and 1,3-butadiene during polymerization. The content of 1,2-cyclohexanediyl unit units in the copolymer varies depending on the respective contents of ethylene and 1,3-butadiene in the copolymer. The copolymer preferably contains less than 15 mol% of 1,2-cyclohexanediyl unit units.

[0045] The copolymer containing ethylene units and units of a 1,3-diene of formula (I) can be prepared by a process which comprises the copolymerization of ethylene, the 1,3-diene of formula (I) and the optional second 1,3-diene, in the presence of a catalytic system based at least on a metallocene of formula (II) and an organomagnesium compound of formula (III) in which:

[0046] - Cp 1 and Cp 2 , identical or different, being chosen from the group consisting of the cyclopentadienyl group of formula C5H4, the unsubstituted fluorenyl group of formula C13 L and the substituted fluorenyl groups,

[0047] - P being a group bridging the two Cp groups 1 and Cp 2 and representing a ZR group 3 R 4 , Z representing a silicon or carbon atom, R 3 and R 4 , identical or different, each representing an alkyl group comprising from 1 to 20 carbon atoms, preferably a methyl,

[0048] - y, integer, being equal to or greater than 0,

[0049] - x, whole number or not, being equal to or greater than 0,

[0050] - L representing an alkali metal chosen from the group consisting of lithium, sodium and potassium,

[0051] - N representing a molecule of an ether, preferably diethyl ether or tetrahydrofuran,

[0052] - R 1 and R 2 , identical or different, representing a carbon group.

[0053] Substituted fluorenyl groups include those substituted by alkyl radicals having 1 to 6 carbon atoms or by aryl radicals having 6 to 12 carbon atoms. The choice of radicals is also guided by the accessibility of the corresponding molecules, which are substituted fluorenes, because the latter are commercially available or easily synthesized.

[0054] As substituted fluorenyl groups, mention may be made more particularly of the 2,7-ditertiobutyl-fluorenyl and 3,6-ditertiobutyl-fluorenyl groups. Positions 2, 3, 6 and 7 respectively designate the position of the carbon atoms of the rings as shown in the diagram below, position 9 corresponding to the carbon atom to which the P bridge is attached. The catalytic system can be prepared in a traditional manner by a process similar to that described in patent application WO 2007054224 or WO 2007054223. For example, the organomagnesium compound and the metallocene are reacted in a hydrocarbon solvent, typically at a temperature ranging from 20 to 80°C for a period of between 5 and 60 minutes. The catalytic system is generally prepared in a hydrocarbon solvent, aliphatic such as methylcyclohexane or aromatic such as toluene. Generally, after its synthesis, the catalytic system is used as is in the process for synthesizing the copolymer in accordance with the invention.

[0055] Alternatively, the catalytic system may 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 preformation monomer chosen 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 compound and the preformation monomer. 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 with this first reaction product, the preformation monomer chosen from a conjugated diene, ethylene or a mixture of ethylene and a conjugated diene is reacted at a temperature ranging from 40 to 90°C for 1 to 12 hours.The conjugated diene as pre-formation monomer is preferably a 1,3-diene such as 1,3-butadiene, isoprene or a 1,3-diene of formula (I), in particular myrcene or P-famesene. The catalytic system thus obtained can be used immediately in the process according to the invention or can be stored under an inert atmosphere before its use in the process according to the invention.

[0056] The metallocene used to prepare the catalytic system may be in the form of a crystallized or non-crystalline powder, or in the form of single crystals. The metallocene may be in a monomeric or dimeric form, these forms depending on the method of preparation of the metallocene, as for example described in patent application WO 2007054224 or WO 2007054223. The metallocene may be prepared in a conventional manner by a process analogous to that described in patent application WO 2007054224 or WO 2007054223, in particular by reaction under inert and anhydrous conditions of the salt of an alkali metal of the ligand with a rare earth borohydride in a suitable solvent, such as an ether, such as diethyl ether or tetrahydrofuran or any other solvent known to those skilled in the art. After reaction, the metallocene is separated from the reaction by-products by techniques known to those skilled in the art, such as filtration or precipitation in a second solvent.The metallocene is finally dried and isolated in solid form. 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 under an inert atmosphere. Typically, the reactions are carried out from solvents and anhydrous compounds under anhydrous nitrogen or argon.

[0057] The organomagnesium useful for the purposes of the invention is of formula MgR'R. 2 in which R 1 and R 2 , identical or different, represent a carbon group. A carbon group is understood to mean a group which contains one or more carbon atoms. Preferably, R 1 and R 2 contain 2 to 10 carbon atoms. More preferably, R 1 and R 2 each represent an alkyl. The organomagnesium is advantageously a dialkylmagnesium, better butylethylmagnesium or butyloctylmagnesium, even better butyloctylmagnesium.

[0058] 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 within a range from 1 to 100, more preferably is 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.

[0059] When the copolymer useful for the purposes of the invention is a copolymer which has a microstructure as defined according to the first variant of the invention, it is prepared according to the process mentioned in the present application using a metallocene of formula (II) in which Cp 1 and Cp 2, identical or different, are chosen from the group consisting of substituted fluorenyl groups and the unsubstituted fluorenyl group of formula CBHS. For this variant, the metallocenes of the following formulas are particularly suitable, in which the symbol Flu has the fluorenyl group of formula C13H8: [{Me2SiFlu2Nd(p-BH4)2Li(THF)}2]; [Me2SiFlu2Nd(p-BH4)2Li(THF)]; [Me2SiFlu2Nd(p-BH4)(THF)]; [{Me2SiFlu2Nd(p-BH4)(THF)}2]; [Me2SiFlu2Nd(p-BH4)].

[0060] The skilled person also knows how to adapt 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 the skilled person, the copolymerization as well as the handling of the monomers, the catalytic system and the polymerization solvent(s) are carried out under anhydrous conditions and under an inert atmosphere. The polymerization solvents are typically hydrocarbon, aliphatic or aromatic solvents. The polymerization is preferably carried out in solution, continuously or batchwise. The polymerization solvent may be a hydrocarbon, aromatic or aliphatic solvent. Examples of polymerization solvents include toluene and methylcyclohexane.The monomers may be introduced into the reactor containing the polymerization solvent and the catalytic system or conversely the catalytic system may be introduced into the reactor containing the polymerization solvent and the monomers. The copolymerization is typically carried out under anhydrous conditions and in the absence of oxygen, in the optional presence of an inert gas. The polymerization temperature generally varies in a range from 30 to 150°C, preferably from 30 to 120°C. Preferably, the copolymerization is carried out at constant ethylene pressure.

[0061] During the polymerization of ethylene, 1,3-diene of formula (I) and the optional second 1,3-diene, in a polymerization reactor, a continuous addition of ethylene and

[0062] 1,3-diene of formula (I) and the optional second 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 copolymer.

[0063] The 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 stripping with water vapor.

[0064] The copolymer may also be a copolymer of ethylene and a 1,3-diene (preferably 1,3-butadiene), i.e. a copolymer consisting exclusively of ethylene units and 1,3-diene units (preferably 1,3-butadiene).

[0065] When the copolymer is a copolymer of ethylene and a 1,3-diene, it advantageously contains units of formula (IV) and / or (V). The presence of a saturated 6-membered cyclic unit, 1,2-cyclohexanediyl, of formula (IV) as a monomeric unit in the copolymer may result from a series of very specific insertions of ethylene and

[0066] 1,3-butadiene in the polymer chain during its growth.

[0067] -CH2-CH(CH=CH2)- (V)

[0068] For example, the copolymer of ethylene and a 1,3-diene may be devoid of units of formula (IV). In this case, it preferably contains units of formula (V).

[0069] When the copolymer of ethylene and a 1,3-diene comprises units of formula (IV) or units of formula (V) or units of formula (IV) and units of formula (V), the molar percentages of the units of formula (IV) and units of formula (V) in the copolymer, respectively o and p, preferably satisfy the following equation (eq. 1), more preferably equation (eq. 2), o and p being calculated on the basis of all the monomer units of the copolymer.

[0070] 0 < o+p < 25 (eq. 1)

[0071] 0 < o+p < 20 (eq. 2)

[0072] The copolymer of ethylene and a 1,3-diene (preferably 1,3-butadiene) can be obtained according to different synthesis methods known to those skilled in the art, in particular depending on the targeted microstructure of the copolymer. Generally, it can be prepared by copolymerization of at least one diene, preferably a 1,3-diene, more preferably 1,3-butadiene, and ethylene and according to known synthesis methods, in particular in the presence of a catalytic system comprising a metallocene complex. Mention may be made in this respect of catalytic systems based on metallocene complexes, which catalytic systems are described in documents EP 1 092 731, WO 2004035639, WO 2007054223 and WO 2007054224 in the name of the Applicant. The copolymer, including when it is statistical, can also be prepared by a process using a preformed type catalytic system such as those described in documents WO 2017093654 Al, WO 2018020122 Al and WO 2018020123 AL

[0073] The content of the copolymer is advantageously within a range from 20 to 45 phr, preferably from 31 to 45 phr. It is understood that the copolymer may be constituted by a mixture of copolymers which differ by their microstructure or by their macrostructure. Furthermore, the content of polyisoprene comprising a mass content of 1,4-cis bonds of at least 90% of the mass of the polyisoprene is advantageously within a range from 55 to 80 phr, preferably from 55 to 69 phr. Advantageously, the polyisoprene comprises a mass content of 1,4-cis bonds of at least 98% of the mass of the polyisoprene.

[0074] Preferably, the polyisoprene is selected from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR) and mixtures thereof. More preferably, the polyisoprene is a natural rubber.

[0075] In a particularly preferred manner, the total content of the copolymer and the polyisoprene is within a range from 90 to 100 phr, preferably from 95 to 100 phr. Preferably the total content of the copolymer and the polyisoprene is 100 phr, that is to say that the copolymer and the polyisoprene are the only elastomers in the composition.

[0076] II-2 Reinforcing charge

[0077] The composition according to the invention is based on at least one reinforcing filler. Such a reinforcing filler typically consists of nanoparticles whose average size (by mass) is less than one micrometer, generally less than 500 nm, most often between 20 and 200 nm, in particular and more preferably between 20 and 150 nm.

[0078] The reinforcing filler may comprise carbon black, silica or a mixture thereof. Advantageously, the reinforcing filler of the composition according to the invention comprises more than 50% by mass, preferably more than 80% by mass, of carbon black. More preferably, the reinforcing filler consists exclusively of carbon black, i.e. the carbon black represents 100% by mass of the reinforcing filler.

[0079] Suitable carbon blacks are all carbon blacks, including those conventionally used in tires or their treads. Among the latter, we will particularly mention the reinforcing carbon blacks of the 100, 200, 300 series, or the blacks of the 500, 600 or 700 series (ASTM D-1765-2017 grades), such as for example blacks NI 15, N134, N234, N326, N330, N339, N347, N375, N550, N683, N772. These carbon blacks can be used in the isolated state, as commercially available, or in any other form, for example as a carrier for some of the rubber additives used. Carbon blacks could, for example, already be incorporated into the diene elastomer, in particular isoprene elastomer, in the form of a masterbatch (see, for example, applications WO97 / 36724-A2 or WO99 / 16600-A1). Among the aforementioned carbon blacks, those having a BET specific surface area in a range from 21 to 69 m2 / g, preferably 33 to 60 m 2 / g, preferably 40 to 49 m 2 / g, are particularly preferred.

[0080] Thus, preferably, the reinforcing filler comprises more than 50% by weight, preferably more than 80% by weight, of at least one carbon black having a BET specific surface area within a range of 21 to 69 m 2 / g, preferably 33 to 60 m 2 / g, preferably 40 to 49 m 2 / g. The BET specific surface area of ​​carbon blacks is measured according to ASTM D6556-10 [multi-point method (minimum 5 points) - gas: nitrogen - relative pressure range P / P0: 0.1 to 0.3],

[0081] Any type of precipitated silica is suitable as silica, in particular 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, we can notably use the silicas “Ultrasil ® 5000GR”, “Ultrasil ® 7000GR” from the company Evonik, the silicas “Zeosil ® 1085GR”, “Zeosil® 1115 MP”, “Zeosil® 1165MP”, “Zeosil® Premium 200MP”, “Zeosil® HRS 1200 MP” from the company Solvay.As non-HDS silica, the following commercial silicas can be used: silicas “Ultrasil ® VN2GR”, “Ultrasil ® VN3GR” from Evonik, silica “Zeosil® 175GR” from Solvay, silicas “Hi-Sil EZ120G(-D)”, “Hi-Sil EZ160G(- D)”, “Hi-Sil EZ200G(-D)”, “Hi-Sil 243LD”, “Hi-Sil 210”, “Hi-Sil HDP 320G” from PPG.

[0082] To couple the silica to the diene elastomer, it is possible to use, in a well-known manner, an at least bifunctional coupling agent (or bonding agent) intended to ensure a sufficient connection, of a chemical and / or physical nature, between the inorganic filler (surface of its particles) and the diene elastomer. In particular, at least bifunctional organosilanes or polyorganosiloxanes are used. By "bifunctional", we mean a compound having a first functional group capable of interacting with the inorganic filler and a second functional group capable of interacting with the diene elastomer. For example, such a bifunctional compound may comprise a first functional group comprising a silicon atom, said first functional group being capable of interacting with the hydroxyl groups of an inorganic filler and a second functional group comprising a sulfur atom, said second functional group being capable of interacting with the diene elastomer.Preferably, when used, the organosilanes are chosen from the group consisting of polysulfurized organosilanes (symmetrical or asymmetrical) such as bis(3-triethoxysilylpropyl) tetrasulfide, abbreviated to TESPT, marketed under the name “Si69” by the company Evonik or bis-(triethoxysilylpropyl) disulfide, abbreviated to TESPD, marketed under the name “Si75” by the company Evonik, polyorganosiloxanes, mercaptosilanes, blocked mercaptosilanes, such as S-(3-(triethoxysilyl)propyl) octanethioate marketed by the company Momentive under the name “NXT Silane”. More preferably, the organosilane is a polysulfurized organosilane.

[0083] When a silica-elastomer coupling agent is used, the coupling agent content can easily be adjusted by a person skilled in the art. Typically, the coupling agent content is from 0.5% to 15% by weight relative to the amount of silica.

[0084] The level of reinforcing filler can easily be adjusted by a person skilled in the art depending on the use of the rubber composition. Advantageously, the level of reinforcing filler, in the composition according to the invention, is within a range from 15 to 80 phr, preferably from 20 to 55 phr, more preferably from 25 to 45 phr.

[0085] Preferably, the carbon black content in the composition according to the invention is within a range from 15 to 80 phr, preferably from 20 to 55 phr, more preferably from 25 to 45 phr, and the composition does not comprise any filler other than carbon black or comprises less than 10 phr, preferably less than 5 phr, more preferably the composition does not comprise any filler other than carbon black.

[0086] II-3 Plasticizing oil

[0087] The composition according to the invention may comprise a liquid plasticizing oil at 20°C having a Tg of less than -70°C, preferably within a range from -150°C to -78°C, preferably from -120°C to -80°C. This is particularly advantageous for further reducing the rigidity of the composition based on the elastomer matrix described above.

[0088] Liquid plasticizing oils at 20°C are called "low Tg" and are known for their plasticizing properties with respect to elastomers. At room temperature (20°C), low Tg plasticizers, more or less viscous, are liquids (i.e., as a reminder, substances having the capacity to eventually take the shape of their container), in contrast in particular to high Tg hydrocarbon resins which are by nature solid at room temperature. The liquid plasticizing oil at 20°C can be chosen from the group consisting of paraffinic oils, vegetable oils, ether plasticizers, ester plasticizers, phosphate plasticizers, sulfonate plasticizers and their mixtures. Preferably, it is chosen from the group consisting of paraffinic oils and their mixtures. Paraffinic “oils”, liquid at 20°C, should not be confused with paraffin “waxes” which are not liquid at this temperature.

[0089] Furthermore, paraffinic oils can be defined according to their crystallinity level. Advantageously, the paraffinic oil has a crystallinity level of less than 20%, preferably less than 10%, more preferably less than 5%, measured by differential scanning calorimetry at a temperature of 20°C. The ISO 1-1357-3 (2013) standard is used to determine the temperature and enthalpy of melting and crystallization of polymers used by differential scanning calorimetry (DSC). The reference enthalpy of polyethylene is 277.1 J / g (according to Hanbook of Polymer 4th edition, J. BRANDRUP, EH IMMERGUT, and EA GRULKE, 1999).

[0090] The polar liquid plasticizer may also be or comprise a vegetable oil comprising from 45% to 100% by weight of unsaturated fatty acid triester of glycerol, or a mixture of plasticizers comprising from 45% to 100% by weight of unsaturated fatty acid triester of glycerol. Particularly advantageously, the unsaturated fatty acid of the unsaturated fatty acid triester is a C12-C22 unsaturated fatty acid (i.e. comprising from 12 to 22 carbon atoms). Such triesters are well described for example in application WO 02 / 088238, as plasticizing agents in tire treads. The oil is preferably selected from the group consisting of sunflower oil, rapeseed oil and mixtures thereof.

[0091] Examples of liquid plasticizing oil at 20°C that can be used in the context of the present invention include the oils “Extensoil51” from the company REPSOL or “Tudalen 1968” from the company Hansen & Rosenthal, the isooctyl tallate “Plasthall 100” from the company Hallstar, the diisooctyl sebacate “Plasthall DOS” from the company Hallstar or the trioctyl phosphate “Disflamoll TOF” from the company Lanxess.

[0092] The level of liquid plasticizing oil at 20°C is preferably in the range of 5 to 25 pce, preferably 5 to 20 pce, preferably 10 to 20 pce.

[0093] II-4 Crosslinking system

[0094] The crosslinking system of the composition according to the invention is a vulcanization system, that is to say a sulfur-based crosslinking system. The sulfur can be provided in any form, in particular in the form of molecular sulfur, or a sulfur-donating agent. Those skilled in the art know how to adapt the quantity of sulfur-donating agent to obtain the desired quantity of sulfur in the composition. Preferably, the sulfur is provided in the form of molecular sulfur.

[0095] According to the invention, the composition comprises from 0.5 to less than 10 pce of zinc stearate. Preferably, the level of zinc stearate in the composition is within a range of from 0.5 to 5 pce, preferably from 1 to 5 pce.

[0096] The composition according to the invention advantageously does not comprise zinc oxide or comprises less than 2.9 pce, preferably less than 1 pce. Preferably, the composition does not comprise zinc oxide.

[0097] The composition according to the invention may comprise stearic acid but this is not obligatory. The level of stearic acid in the composition may be in a range from 0 to 10 phr. Preferably, the composition does not comprise stearic acid or comprises less than 2.9 phr, preferably less than 1 phr. When the composition does not comprise stearic acid or comprises less than 1 phr, it is preferable for the level of zinc stearate in the composition to be in a range from 2 to less than 10 phr, preferably from 2 to 5 phr.

[0098] Furthermore, at least one vulcanization accelerator is also present and, optionally and preferably, various known vulcanization activators may be used, such as stearic acid or equivalent compound such as stearic acid salts and transition metal salts, guanidine derivatives (in particular diphenylguanidine), or even known vulcanization retarders.

[0099] The sulfur may be used at a preferred rate of between 0.5 and 12 phr, in particular between 1 and 10 phr. The vulcanization accelerator is used at a preferred rate of between 0.5 and 10 phr, more preferably between 0.5 and 5.0 phr. Particularly advantageously, the composition comprises from 0.6 to 2 phr, preferably from 0.7 to 1.8 phr of sulfur and from 0.6 to 1 phr, preferably from 0.6 to 0.9 phr of at least one vulcanization accelerator.

[0100] The mass ratio of sulfur to vulcanization accelerator may be in a range from 0.75 to 3.00, preferably from 1.00 to 2.75, more preferably from 1.30 to 2.33. Any compound capable of acting as a vulcanization accelerator for diene elastomers in the presence of sulfur may be used as accelerator, in particular accelerators of the thiazole type and their derivatives, accelerators of the sulfenamide, thiuram, dithiocarbamate, dithiophosphate, thiourea and xanthate types. Examples of such accelerators include, but are not limited to, the following compounds: 2-mercaptobenzothiazyl disulfide (abbreviated as "MBTS"), N-cyclohexyl-2-benzothiazyl sulfenamide ("CBS"), N,N-dicyclohexyl-2-benzothiazyl sulfenamide ("DCBS"), N-tert-butyl-2-benzothiazyl sulfenamide ("TBBS"), N-tert-butyl-2-benzothiazyl sulfenimide ("TBSI"), tetrabenzylthiuram disulfide ("TBZTD"), zinc dibenzyldithiocarbamate ("ZBEC") and mixtures of these compounds.

[0101] Advantageously, the vulcanization accelerator is chosen from sulfenamide type accelerators and their mixtures, preferably chosen from the group consisting of CBS, TBBS, DCBS and their mixtures. Particularly advantageously, the vulcanization accelerator is CBS. Advantageously, also, the composition does not comprise a vulcanization accelerator other than sulfenamide type accelerators, preferably other than CBS.

[0102] II-5 Possible additives

[0103] The rubber compositions according to the invention may optionally also comprise all or part of the usual additives usually used in elastomer compositions for tires, such as for example plasticizers (such as plasticizing oils and / or plasticizing resins), pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, antioxidants, anti-fatigue agents, etc.

[0104] II-6 Preparation of compositions

[0105] The compositions usable within the framework of the present invention can be manufactured in suitable mixers, using two successive preparation phases well known to those skilled in the art:

[0106] - a first phase of working or thermomechanical mixing (so-called "non-productive" phase), which can be carried out in a single thermomechanical step during which all the necessary constituents are introduced into a suitable mixer such as a conventional internal mixer (for example of the "Banbury" type), in particular the elastomeric matrix, the reinforcing filler, any other various additives, with the exception of the crosslinking system. The incorporation of the possible filler into the elastomer can be carried out in one or more stages by thermomechanical mixing.In the case where the filler is already incorporated in whole or in part into the elastomer in the form of a masterbatch as described for example in applications WO 97 / 36724 or WO 99 / 16600, it is the masterbatch which is directly mixed and where appropriate the other elastomers or fillers present in the composition which are not in the form of a masterbatch are incorporated, as well as any other various additives other than the crosslinking system. The non-productive phase can be carried out at high temperature, up to a maximum temperature of between 110°C and 200°C, preferably between 130°C and 185°C, for a duration generally of between 2 and 10 minutes.

[0107] - a second phase of mechanical work (so-called "productive" phase), which can be carried out in an external mixer such as a roller mixer, after cooling the mixture obtained during the first non-productive phase to a lower temperature, typically below 120°C, for example between 40°C and 100°C. The crosslinking system is then incorporated, and everything is then mixed for a few minutes, for example between 5 and 15 min.

[0108] Such phases have been described for example in applications EP-A-0501227, EP-A-0735088, EP-A-0810258, WO00 / 05300 or WO00 / 05301.

[0109] The final composition thus obtained is then calendered, for example, in the form of a sheet or plate, in particular for characterization in the laboratory, or extruded (or co-extruded with another rubber composition) in the form of a semi-finished (or profiled) rubber usable, for example, as a tire sidewall. These products can then be used for the manufacture of tires, according to techniques known to those skilled in the art.

[0110] The composition can be either in the raw state (before crosslinking or vulcanization), or in the cooked state (after crosslinking or vulcanization), can be a semi-finished product which can be used in a tire.

[0111] The crosslinking of the composition can be carried out in a manner known to those skilled in the art, for example at a temperature between 130°C and 200°C, under pressure.

[0112] II-7 Rubber article

[0113] The present invention also describes a rubber article comprising at least one composition according to the invention. Preferably, the rubber article is a tire.

[0114] In the present invention, the term "tyre" means a pneumatic or non-pneumatic tire. A pneumatic tire usually comprises two beads intended to come into contact with a rim, a crown composed of at least one crown reinforcement and a tread, two sidewalls, the tire being reinforced by a carcass reinforcement anchored in the two beads. A non-pneumatic tire, for its part, usually comprises a base, designed for example for mounting on a rigid rim, a crown reinforcement, ensuring the connection with a tread and a deformable structure, such as spokes, ribs or cells, this structure being arranged between the base and the crown. Such non-pneumatic tires do not necessarily comprise a sidewall. 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 bandage.

[0115] More particularly, the invention also relates to a pneumatic tire comprising a rubber composition according to the invention, the composition being present in at least one sidewall of the pneumatic tire. The composition according to the invention may constitute part or all of the sidewall of the pneumatic tire.

[0116] The tire according to the invention can be intended to equip any type of vehicle, in particular motor vehicles, without any particular limitation.

[0117] III- EXAMPLES

[0118] III- 1 Measurements and tests used

[0119] III- 1.1 Determination of the microstructure of Ethylene-Myrcene copolymers (Elastomer El):

[0120] Spectral characterization and microstructure measurements of Ethylene-Myrcene copolymers are performed by Nuclear Magnetic Resonance (NMR) spectroscopy.

[0121] 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.

[0122] Experiments: 1H experiments are recorded using a radiofrequency pulse with a flip angle of 30°, the number of repetitions is 128 with a recycle delay of 5 seconds. 1H-13C HSQC (Heteronuclear Single Quantum Coherence) and HMBC (Heteronuclear Multiple-Bond Correlation) NMR correlation experiments are recorded with a number of repetitions of 128 and a number of increments of 128. The experiments are carried out at 25°C.

[0123] Sample preparation: 25 mg of sample is solubilized in 1 mL of deuterated chloroform (CDCh).

[0124] Sample calibration: The chemical shift axes 'H and 13 C are calibrated against the protonated solvent impurity (CHCl3) at ôin = 7.2 ppm (for the most deshielded signal) and 813c = 77 ppm (for the least deshielded signal).

[0125] Spectral assignment for ethylene and 1,3-myrcene copolymers: In representations A, B, C below, the symbols Ri and R2 represent the attachment points of the unit to the polymer chain. The signals of the insertion forms of 1,3-diene A, B and C were observed on the different recorded spectra. According to S. Georges et al., (Polymer 55 (2014) 3869-3878), the signal of the -CH= group n°8” characteristic of form C shows chemical shifts X H and 13C identical to the group - CH= n°3. The chemical shifts of the characteristic signals of motifs A, B and C are presented in Table 1. Motifs A, B and C correspond respectively to the 3,4-configuration, 1,2-configuration and 1,4-trans-configuration units. Quantifications were carried out from the integration of 1D NMR spectra X H using Topspin software. The integrated signals for quantification of the different patterns are: Ethylene: signal at 1.2 ppm corresponding to 4 protons

[0126] Total myrcene: signal no. 1 (1.59 ppm) corresponding to 6 protons

[0127] Form A: signal no. 7 (4.67 ppm) corresponding to 2 protons

[0128] Form B: signal n°8' (5.54 ppm) corresponding to 1 proton

[0129] The quantification of the microstructure is carried out in molar percentage (mol%) as follows: mol% of a motif = 1H integral of a motif * 100 / X (1H integrals of each motif).

[0130] [Table 1] III- 1.2 Determination of the macrostructure of polymers by size exclusion chromatography (SEC): a) Principle of measurement:

[0131] Size exclusion chromatography (SEC) separates macromolecules in solution according to their size using columns filled with a porous gel. The macromolecules are separated according to their hydrodynamic volume, with the largest being eluted first. Combined with 3 detectors (3D), a refractometer, a viscometer and a 90° light scattering detector, SEC can be used to assess the absolute molar mass distribution of a polymer. The various number-average (Mn), weight-average (Mw) absolute molar masses and the polydispersity index (Ip = Mw / Mn) can also be calculated. b) Polymer preparation:

[0132] Each sample is solubilized in tetrahydrofuran at a concentration of approximately 1 g / L. The solution is then filtered through a 0.45 pm porosity filter before injection. c) 3D SEC analysis:

[0133] To determine the number-average molar mass (Mn), and where appropriate the weight-average molar mass (Mw) and the polydispersity index (Ip) of polymers, the method below is used.

[0134] The number-average molar mass (Mn), weight-average molar mass (Mw) and polydispersity index of the polymer (hereinafter referred to as sample) are determined absolutely by triple detection size exclusion chromatography (SEC). Triple detection size exclusion chromatography has the advantage of measuring average molar masses directly without calibration.

[0135] The refractive index increment dn / dc value 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 must be ensured 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.

[0136] To determine the average molar masses, the previously prepared and filtered lg / l solution is used and injected into the chromatographic system. The equipment used is a "WATERS alliance" chromatographic chain. The elution solvent is tetrahydrofuran containing 250 ppm of BHT (2,6-diter-butyl 4-hydroxy toluene), the flow rate is 1 mL.min' 1, the system temperature of 35°C and the analysis time of 60 min. The columns used are a set of three AGILENT columns with the trade name “PL GEL MIXED B LS”. The injected volume of the sample solution is 100 pL. The detection system is composed 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, a Wyatt multi-angle static light scattering detector with a wavelength of 658 nm and the trade name “DAWN HELEOS 8+”.

[0137] 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 integrated. The software for processing the chromatographic data is the “ASTRA de Wyatt” system.

[0138] Ill- 1.3 Dynamic Properties

[0139] The dynamic properties G' (10%) are measured at a temperature of 23 °C on a viscoanalyzer (Metravib VA4000), according to ASTM D 5992-96. The response of a sample of crosslinked composition (cylindrical specimen 4 mm thick and 400 mm 2 of section), subjected to sinusoidal stress in alternating simple shear, at a frequency of 10 Hz, under the defined temperature conditions, for example at 23°C according to standard ASTM D 1349-99. A strain amplitude sweep is carried out from 0.1 to 50% (forward cycle), then from 50% to 0.1% (return cycle). The results used are the dynamic shear modulus G”. For the return cycle, the dynamic shear modulus G'(10%) at 10% strain, at 23°C, is indicated.

[0140] It is recalled that, in a manner well known to those skilled in the art, the value of G' (10%) at 23°C is representative of the rigidity of the material. The performance results G'(10%) at 23°C are expressed on a base of 100, the value 100 being attributed to the control. For G' (10%) at 23°C a result greater than 100 indicates that the composition of the example considered is less rigid, reflecting, for a tire sidewall undergoing an imposed deformation, better endurance.

[0141] III- 1.4 Tearability

[0142] The tearability indices are measured at 60°C. In particular, the force required to achieve rupture (FRD, in MPa (in N / mm 2)) and the strain at break (DRD, in %) is measured on a specimen of dimensions 10 x 85 x 2.5 mm notched in the center of its length by 3 notches to a depth of 3 mm, to cause the specimen to break. Thus we can determine the Energy to cause the rupture (Rupture Energy) of the specimen which is the product of the FRD and the DRD.

[0143] III-2 Synthesis of polymers

[0144] In polymer synthesis, all reagents are obtained commercially except for metallocenes. BOMAG butylloctylmagnesium (20% in heptane, C = 0.88 mol.L' ') is obtained from Chemtura and is stored in a Schlenk tube under an inert atmosphere. Ethylene, grade N35, is obtained from Air Liquide and is used without prior purification. Myrcene (purity > 95%) is obtained from Sigma-Aldrich.

[0145] The ethylene and myrcene copolymer: elastomer E1 was synthesized according to the procedure described below:

[0146] In a reactor containing methylcyclohexane at 80°C, as well as ethylene (Et) and myrcene (Myr) in the proportions indicated in Table 3, butyloctylmagnesium (BOMAG) is added to neutralize the impurities in the reactor, then the catalytic system (see Table 2). At this point, the reaction temperature is regulated at 80°C and the polymerization reaction starts. The polymerization reaction proceeds at a constant pressure of 8 bar. The reactor is supplied throughout the polymerization with ethylene and myrcene (Myr) in the proportions defined in Table 3. 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 to constant mass. The catalytic system is a preformed catalytic system.It is prepared in methylcyclohexane from a metallocene, [Me2SiFlu2Nd(p-BH4)2Li(THF)], a cocatalyst, butyloctylmagnesium (BOMAG), and a preformation monomer, 1,3-butadiene, in the contents indicated in Table 2. It is prepared according to a preparation method in accordance with paragraph II.1 of patent application WO 2017 / 093654 AL.

[0147] The microstructure of Telastomer El and its properties are shown in Table 3. For the microstructure, Table 3 shows the molar ratios of ethylene (Eth) units and myrcene units. Also shown is the molar ratio of myrcene units according to whether they are 1,4-configured, 1,2-configured, and 3,4-configured.

[0148] [Table 2] [Table 3]

[0149] III-3 Preparation of compositions

[0150] In the following examples, the rubber compositions were produced as described in point II-6 above. In particular, the “non-productive” phase was carried out in a 0.4 liter mixer for 3.5 minutes, for an average paddle speed of 50 revolutions per minute until a maximum drop temperature of 160°C was reached. The “productive” phase was carried out in a cylinder tool at 23°C for 5 minutes. The crosslinking of the composition was carried out at a temperature of 150°C, under pressure, for a period of 15 minutes.

[0151] III-4 Rubber composition tests

[0152] The examples presented below aim to compare the rigidity and tearability performances of compositions in accordance with the invention (C1 to C4) with a control composition (T1).

[0153] Table 4 presents the tested compositions (in pce), as well as the results obtained.

[0154] [Table 4]

[0155] (1) Natural rubber

[0156] (2) Elastomer El prepared according to the process described in point III-2 above

[0157] (3) Carbon black grade N550 according to ASTM D-1765

[0158] (4) Paraffin oil “Tudalen 1968” from the company Klaus Dahleke

[0159] (5) 2,2,4-trimethyl-l,2-dihydroquinoline “Pilnox TMQ” from Nocil

[0160] (6) Anti-ozone wax “VARAZON 4959” from the company Sasol Wax

[0161] (7) Nl,3-dimethylbutyl-N-phenylparaphenylenediamine “Santoflex 6-PPD” from Flexsys

[0162] (8) Industrial grade zinc oxide from Umicore

[0163] (9) Zinc stearate “Zinc stearate 2721” from the company Brenntag

[0164] (10) Stearic acid “Pristerene 4931” from Uniqema

[0165] (11) N-cyclohexyl-2-benzothiazyl sulfenamide “Santocure CBS” from Flexsys

[0166] The results presented in Table 4 above show that the substitution of zinc oxide with zinc stearate makes it possible to improve the stiffness performance of the composition, resulting in an improvement in the endurance of a tire sidewall comprising this composition. This effect is further improved when the composition does not comprise free stearic acid. It was further found that the tear resistance was also improved for the compositions in accordance with the invention, which is particularly interesting for tire sidewalls.

Claims

CLAIMS 1. Rubber composition based on at least: - 20 to 50 pce a copolymer containing ethylene units and 1,3-diene units, the ethylene units in the copolymer represent between 50% and 95% by mole of the monomer units of the copolymer; - 50 to 80 pce of polyisoprene comprising a mass rate of 1,4-cis bonds of at least 90% of the mass of the polyisoprene; - a reinforcing charge; - 0.5 to less than 10 pce of zinc stearate; and - a vulcanization system.

2. A rubber composition according to claim 1, wherein the copolymer containing ethylene units and 1,3-diene units is a copolymer containing ethylene units and units of a 1,3-diene of formula (I), CH2=CR-CH=CH2(I) the symbol R representing a hydrocarbon chain having 3 to 20 carbon atoms.

3. Rubber composition according to claim 2, the 1,3-diene of formula (I) is myrcene, P-famesene or a mixture of myrcene and P-famesene, preferably myrcene.

4. Rubber composition according to claim 2 or 3, in which the copolymer contains units of 1,3-diene of formula (I) which represent between 10% and 40%, preferably between 15% and 30%, by mole of the monomer units of the copolymer.

5. Rubber composition according to any one of the preceding claims, in which the level of the copolymer is in a range from 20 to 45 phr, and in which the polyisoprene is present at a level in a range from 55 to 80 phr.

6. A rubber composition according to any one of the preceding claims, wherein the polyisoprene is selected from the group consisting of natural rubber, synthetic polyisoprenes and mixtures thereof, preferably the polyisoprene is a natural rubber.

7. A rubber composition according to any preceding claim, wherein the reinforcing filler comprises more than 50% by mass of carbon black.

8. Rubber composition according to any one of the preceding claims, in which the level of reinforcing filler is within a range from 15 to 80 phr, preferably from 20 to 55 phr, preferably from 25 to 45 phr.

9. A rubber composition according to any one of the preceding claims, comprising a plasticizing oil liquid at 20°C having a glass transition temperature, Tg, below -70°C, preferably in a range from -150°C to -78°C, preferably from -120°C to -80°C.

10. Rubber composition according to claim 9, wherein the plasticizing oil liquid at 20°C is selected from the group consisting of paraffinic oils, vegetable oils, ether plasticizers, ester plasticizers, phosphate plasticizers, sulfonate plasticizers and mixtures thereof.

11. Rubber composition according to claim 9 or 10, in which the level of liquid plasticizing oil at 20°C is within a range of 5 to 25 phr, preferably 5 to 20 phr, preferably 10 to 20 phr.

12. Rubber composition according to any one of the preceding claims, in which the zinc stearate content is within a range from 0.5 to 5 phr, preferably from 1 to 5 phr.

13. A rubber composition according to any one of the preceding claims, the composition not comprising zinc oxide or comprising less than 2.9 phr, preferably less than 1 phr.

14. A rubber composition according to any one of the preceding claims, the composition not comprising stearic acid or comprising less than 2.9 phr, preferably less than 1 phr.

15. A pneumatic tire comprising a rubber composition defined in any one of claims 1 to 14, the composition being present in at least one sidewall of the pneumatic tire.

Images