RUBBER COMPOSITION BASED ON A MODIFIED DIENE EASTOMER

Description

technical field

[0001] The invention relates to a rubber composition comprising a modified diene elastomer and silica as a reinforcing filler. Previous technique

[0002] Since fuel economy and the need to preserve the environment have become a priority, it is desirable to produce mixtures with as low hysteresis as possible so that they can be used in the form of rubber compositions for the manufacture of various semi-finished products used in the composition of tires, such as underlayers, sidewalls, treads, and in order to obtain tires with reduced rolling resistance.

[0003] Ideally, for example, a tire tread should meet a large number of technical requirements, often contradictory, including high wear resistance while offering the tire low rolling resistance.

[0004] Furthermore, the reduction of the hysteresis of the mixtures, which guarantees a reduction in rolling resistance, must also be done while preserving intact the suitability for implementation, in particular when raw, of the mixtures, while maintaining the creep resistance of the elastomers.

[0005] To achieve the goal of reducing hysteresis, numerous solutions have already been tested. In particular, one can mention the modification of the structure of diene polymers and copolymers at the end of polymerization by means of modifying, coupling or star-forming agents in order to obtain good interaction between the modified polymer and the filler, whether it be carbon black or a reinforcing inorganic filler.

[0006] In the context of mixtures containing a reinforcing inorganic filler such as silica, it has been proposed to use diene polymers functionalized by alkoxysilane derivatives, in particular by combining or not the functionalization by alkoxysilane functions with the functionalization by other functions, in particular amine, imine, epoxy or thiol functions.

[0007] Functionalization with alkoxysilane compounds bearing an amine group has been widely described in the patent literature. End-functionalized elastomers with alkoxysilane groups bearing an amine have been combined with both silica and carbon black, or even a mixture of these two fillers, in rubber compositions intended for tire manufacturing.

[0008] The Applicant, in document WO 2009133068 A1, described a functionalized diene elastomer essentially consisting of a coupled species of an elastomer possessing, within its chain, a group bearing an alkoxysilane function and an amine function, the silicon atom of this group linking the two parts of the diene elastomer chain. This functionalized elastomer in the middle of the chain confers improved mechanical and dynamic properties to the composition containing it, notably improved hysteresis, while maintaining satisfactory raw processing, particularly for use in tire treads.

[0009] Documents EP 2 003 146 A2, US 2014 / 0243476A1 describe diene elastomers modified with modifying agents possessing at least one silicon atom and at least one nitrogen atom. JP 2016017097A describes diene elastomers modified with modifying agents possessing at least one silicon atom and at least one nitrogen atom, bearing an amine functional group at the ends of chains not bonded to the modifying agent. These documents propose improvements to the mechanical and dynamic properties of rubber compositions with low reinforcing filler content intended for tire applications, and highlight in particular gains in wet grip, improved heat dissipation, reduced rolling resistance, and abrasion resistance.US2016 / 159957 A1 and US2016 / 194411 A1 documents describe diene elastomers modified by modifying agents comprising one or more silica atoms.

[0010] To achieve specific tire performance levels, it may be necessary to use varying amounts of reinforcing filler in the rubber compounds that make up the different parts of the tire. However, using a high amount of filler to achieve certain performance levels is incompatible with the desired reduction in rolling resistance. Indeed, using a high percentage of reinforcing filler in the compound used to manufacture the tread frequently, and often prohibitively so, negatively impacts rolling resistance properties, accompanied by a significant increase in hysteresis losses in the rubber compound.

[0011] The technical problem that the present invention aims to solve is to mitigate the effect of increasing the reinforcing charge ratio on the dynamic properties of rubber compositions and their implementation for the purpose of using these compositions for the manufacture of tires with reduced rolling resistance.

[0012] Continuing its research, the Applicant discovered that the use of certain specific modified diene elastomers in rubber compositions reduces the impact of increased reinforcing filler content on the performance / hysteresis trade-off. This makes it possible to supply tire rubber compositions with a high reinforcing filler content while minimizing the effect of this high content on the hysteresis and performance properties of the compositions. Description of the invention

[0013] The invention therefore relates to a rubber composition based on at least one reinforcing filler comprising silica and an elastomeric matrix comprising a modified diene elastomer, characterized in that the silica content is greater than or equal to 80 pce, the modified diene elastomer content is greater than or equal to 75 pce, and the modified diene elastomer comprises macromolecules comprising within their structure an n-functional branching unit, n being at least 1, preferably at least 3, consisting of a group comprising at least two silicon atoms substituted by elastomeric branches and linked together via a hydrocarbon group of valence at least 2, polymeric or non-polymer, which may include at least one heteroatom selected from N, O, P, S, the link between a silicon atom and this hydrocarbon group of valence at least 2 being made via a divalent spacer group. Detailed description

[0014] In this description, unless expressly stated otherwise, all percentages (%) are percentages by mass. Furthermore, any range of values ​​designated by the expression "between a and b" represents the range of values ​​from greater than a to 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). In this context, when a range of values ​​is designated by the expression "from a to b," it also refers to the range represented by the expression "between a and b."

[0015] The expression "based on" composition means a composition comprising the mixture and / or reaction product of the different constituents used, some of these basic constituents being likely to, or intended to, react with each other, at least in part, during the different phases of manufacturing the composition, in particular during its crosslinking or vulcanization.

[0016] In this description, the abbreviation "pce" means parts by weight per hundred parts by mass of elastomers present in the elastomer matrix, the elastomer matrix being the totality of elastomers present in the rubber composition.

[0017] In this application, "majority" or "majority" in relation to a compound means that this compound is the major component among the compounds of the same type in the composition; that is, it is the one that represents the largest weight fraction among the compounds of the same type. Similarly, a functional species of a modified diene elastomer referred to as the major component is the one representing the largest weight fraction among the functionalized species constituting the diene elastomer, relative to the total weight of the modified diene elastomer. In a system comprising a single compound of a certain type, this compound is the major component within the meaning of the present invention.

[0018] In this description, Mooney viscosity means the Mooney viscosity ML(1+4)100 °C of a compound, in particular the modified diene elastomer of the invention, measured according to ASTM D1646.

[0019] In this description, where no further details are given, primary or secondary amine means a primary or secondary amine that is protected or unprotected by a protecting group known to a person skilled in the art.

[0020] In this description, a modified diene elastomer is understood to be a mixture of macromolecules resulting from the reaction of a living diene elastomer with a modifying agent comprising at least two reactive functions with respect to the reactive end of the living diene elastomer, this compound comprising several heteroatoms including at least two silicon atoms.

[0021] Those skilled in the art will understand that a modification reaction with an agent possessing more than one reactive function with respect to the living elastomer results in a mixture of macromolecules functionalized at the chain ends and in the middle of the chain (also called coupled macromolecules), constituting the linear functional species of the modified elastomer, and macromolecules with at least three branches and at most as many branches as there are reactive functions on the modifying agent, constituting the branched species of the modified elastomer. Depending on the operating conditions, primarily the molar ratio of the modifying agent to the living chains and the number of its reactive functions, certain species are more or less present, or even predominant, in the mixture.

[0022] In this description, the term "monomer unit", whether diene or otherwise, is understood as a repeating unit of the polymer derived from the monomer in question.

[0023] In this description, the expression "branching unit" is understood as a non-repeating unit (there is only one in the polymer), resulting from the modifying agent on which the living diene elastomer chain(s) have reacted, and from which the diene elastomer chain(s) emanate.

[0024] It should be noted that, within the scope of the invention, the monomers used for the synthesis of the modified diene elastomer, as well as the compounds in the rubber composition, may be of fossil or bio-based origin. In the latter case, they may be partially or totally derived from biomass or obtained from renewable raw materials derived from biomass.

[0025] Thus, the invention relates to a rubber composition based on at least one reinforcing filler comprising silica and an elastomeric matrix comprising a modified diene elastomer, characterized in that the silica content is greater than or equal to 80 pce, the modified diene elastomer content is greater than or equal to 75 pce, and the modified diene elastomer comprises macromolecules comprising within their structure an n-functional branching unit, n being at least 1, preferably at least 3, consisting of a group comprising at least two silicon atoms substituted by elastomeric branches and linked together via a hydrocarbon group of valence at least 2, polymeric or non-polymer, which may include at least one heteroatom selected from N, O, P, S, the link between a silicon atom and this hydrocarbon group of valence at least 2 being made via a divalent spacer group.

[0026] By diene elastomer capable of being used as the modified diene elastomer in compositions according to the invention, shall be understood in a known way a synthetic elastomer consisting at least in part of diene monomer units, conjugated or not.

[0027] The term synthetic diene elastomer refers more specifically to: (a) - any homopolymer of a diene monomer, particularly a conjugated diene monomer, in particular any homopolymer obtained by polymerization of a conjugated diene monomer having from 4 to 12 carbon atoms; (b) - any copolymer obtained by copolymerization of one or more diene monomers with each other or with one or more vinylaromatic monomers.

[0028] In the case of copolymers (b), these contain from 20 to 99% by weight of diene units and from 1 to 80% by weight of units derived from vinylaromatic monomers.

[0029] Suitable conjugated dienes include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), and 2,3-di(C1-CS alkyl)-1,3-butadiene compounds such as 2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3-isopropyl-1,3-butadiene, an aryl-1,3-butadiene, 1,3-pentadiene, and 2,4-hexadiene. Preferably, the conjugated diene is a derivative of 1,3-butadiene, and more preferably 1,3-butadiene.

[0030] Suitable examples of vinylaromatic compounds include styrene, ortho-, meta-, para-methylstyrene, the commercial "vinyl-toluene" mixture, para-tert-butylstyrene, methoxystyrenes, chlorostyrenes, vinylmesitylene, divinylbenzene, and vinylnaphthalene. Styrene is the preferred vinylaromatic compound.

[0031] Preferably, the diene elastomer is chosen from the group consisting of polybutadienes (BR), synthetic polyisoprenes (IR), butadiene copolymers, isoprene copolymers, and mixtures of these elastomers. Such copolymers are more preferentially chosen from the group consisting of butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), isoprene-styrene copolymers (SIR), and isoprene-butadiene-styrene copolymers (SBIR), more particularly butadiene-styrene copolymers (SBR).

[0032] Dienic elastomers can have any microstructure that is a function of the polymerization conditions used.

[0033] Diene elastomers can be block, statistical, sequenced, microsequenced...

[0034] According to the invention, the modified diene elastomer comprises macromolecules comprising within their structure an n-functional branching unit, n being at least 1, preferably at least 3, consisting of a group comprising at least two silicon atoms substituted by elastomeric branches and linked together by means of a hydrocarbon group of valence at least 2, polymeric or not, which may comprise at least one heteroatom selected from N, O, P, S, the bond between a silicon atom and this hydrocarbon group of valence at least 2 being made by means of a divalent spacer group.

[0035] According to one embodiment of the invention, the number-average molar mass of the elastomeric branches of the modified diene elastomer is less than 150,000 g / mol, preferably from 40,000 g / mol to 100,000 g / mol.

[0036] According to one embodiment of the invention, the tips of the elastomeric branches of the modified diene elastomer, not bonded to a silicon atom, may bear a functional group comprising a nitrogen atom, preferably a cyclic or acyclic amine group. All or part of the tips of the elastomeric branches of the modified diene elastomer are functionalized with a cyclic or acyclic amine group; preferably at least 70 molar percent of the tips of the elastomeric branches of the modified diene elastomer are functionalized, relative to the number of moles of elastomeric branches.

[0037] According to one embodiment of the invention, the modified diene elastomer comprises macromolecules comprising in their structure at least two silicon atoms each substituted by at most three elastomeric branches and by at most three hydroxyl or alkoxy groups.

[0038] According to certain embodiments of the invention, the alkoxy groups substituting for the silicon atom can be partially or totally hydrolyzed to hydroxyl. According to these embodiments, all or at least 50 mol% of the alkoxy groups on the modified diene elastomer are hydrolyzed to hydroxyl. In particular, at least 80 mol% of the alkoxy functions on the modified diene elastomer are hydrolyzed to hydroxyl, or even 100%.

[0039] The alkyl radicals of the alkoxy groups substituting the silicon atoms are, independently of each other, chosen from among the alkyl radicals in C1-C10, or even in C1-C8, preferably from among the alkyl radicals in C1-C4, more preferably from among methyl and ethyl.

[0040] According to the invention, the branching unit comprises at least two silicon atoms, these atoms being linked together via a hydrocarbon group of at least 2 valences, polymeric or non-polymer, which may comprise at least one heteroatom selected from N, O, P, S, the bond between a silicon atom and this hydrocarbon group of at least 2 valences being made via a divalent spacer group. This spacer group can be defined as a divalent aliphatic hydrocarbon radical, saturated or unsaturated, cyclic or unsaturated, in the C1-C18 range, preferably a divalent hydrocarbon radical, linear or branched, aliphatic in the C1-C10 range, preferably, a divalent, linear, and saturated aliphatic group having from 3 to 8 carbon atoms, or an aromatic divalent hydrocarbon radical in the C6-C18 range.

[0041] According to the invention, the branching unit is n-functional, that is to say, at least n diene elastomeric branches are linked to this unit with n being at least 1 and preferably at most 9.

[0042] According to one embodiment of the invention, the hydrocarbon group of valence at least 2, polymeric or not, which may comprise at least one heteroatom chosen from N, O, P, S, has a maximum valence of 50, preferably its valence is less than or equal to 4, more preferably it is 2 or 3, more preferably still its valence is 2.

[0043] According to this preferred embodiment in which the valence of the hydrocarbon group is 2, the n-functional branching unit comprises two silicon atoms substituted by elastomeric branches linked together via the hydrocarbon group of valence 2, which may be polymeric or non-polymer and may include at least one heteroatom selected from N, O, P, or S. The bond between a silicon atom and this hydrocarbon group is made via a divalent spacer group. In this case, preferably, this hydrocarbon group of valence 2 comprises at least one nitrogen atom or at least one oxygen atom.

[0044] The different variants, preferred or not concerning the spacer group, the number of elastomer branches, the substitution of silicon atoms by alkoxy groups, the valence of the hydrocarbon group of the branching unit, the number of branches of the branching unit,... are combinable with each other.

[0045] The macromolecules of the modified diene elastomer of the invention correspond particularly to the following formula I: in which E represents a diene elastomer branch, the R radicals represent, independently of each other, an alkyl radical in C1-C10, or even in C1-C8, preferably an alkyl radical in C1-C4, more preferably methyl or ethyl, or a hydrogen atom, the R1 radicals represent, independently of each other, an aliphatic divalent hydrocarbon radical, saturated or unsaturated, cyclic or unsaturated, linear or branched, in C1-C18, preferably in C1-C10, more preferably linear and saturated in C3-C8, or an aromatic divalent hydrocarbon radical in C6-C18;the R2 radicals represent, independently of each other, an alkyl radical in C1-C10, or even in C1-C8, preferably an alkyl radical in C1-C4, more preferably methyl or ethyl, A represents a hydrocarbon group of valence k, polymeric or not, which may include at least one heteroatom chosen from N, O, P, S, m and n are independently of each other integers ranging from 0 to 3 and 1 is an integer equal to 0 or 1, with m+n+l = 3, preferably 1 equals 0, k is an integer of at least 2 and preferably of at most 5, preferably still of at most 4, more preferably 2 or 3, even more preferably 2. ;

[0046] According to variants of the invention, A represents a hydrocarbon group of valence k, very preferably 2, polymeric or not, comprising at least one nitrogen atom or at least one oxygen atom.

[0047] According to variants of the invention combinable with the previous ones, E represents a diene elastomer branch bearing at the end of the chain a group comprising a nitrogen atom, more particularly an amine function, cyclic or acyclic.

[0048] According to the invention, branched macromolecules consist of macromolecules whose branching points are all linked to at least three diene elastomer blocks. For reasons of feasibility and technical reality, these macromolecules preferably have the diene elastomer blocks distributed on either side of the n-functional branching unit, at the branching points. That is to say, all the elastomer blocks are not linked to the same branching point but are distributed over the two branching points.Thus, three-branch macromolecules may have two elastomeric branches at one end of the n-functional branching unit and one elastomeric branch at the other end, four-branch macromolecules may have two elastomeric branches at one end of the n-functional branching unit and two elastomeric branches at the other end or three elastomeric branches at one end of the n-functional branching unit and one elastomeric branch at the other end, and so on.

[0049] The modified diene elastomer according to a preferred embodiment of the invention comprises at least 50% by weight of branched macromolecules relative to the total weight of the modified diene elastomer, preferably at least 80% by weight, the branched macromolecules being the set of macromolecules with at least three branches of the modified diene elastomer.

[0050] To illustrate this variant with formula I, the reader will understand that when the macromolecules of the modified diene elastomer of the invention correspond to formula I with k equal to 2, according to this variant, at least 50% by weight of macromolecules relative to the total weight of the modified diene elastomer, preferably at least 80% by weight, corresponds to formula I with k equal to 2 and the total number of E equal to at least 3.

[0051] According to another preferred embodiment of the invention, whether or not combined with the previous embodiment, the modified diene elastomer comprises at least 35% by weight of three-branched macromolecules, relative to the total weight of the modified diene elastomer, preferably at least 40%.

[0052] To illustrate this variant with formula I, the reader will understand that when the macromolecules of the modified diene elastomer of the invention correspond to formula I with k equal to 2, according to this variant, at least 35% by weight of macromolecules relative to the total weight of the modified diene elastomer, preferably at least 40% by weight, corresponds to formula I with k equal to 2 and the total number of E equal to 3.

[0053] The different variants and preferred aspects concerning the nature of the modified diene elastomer, the functionalization of the elastomer branches, their Mn, the alkoxy function, the number of silicon atoms, the spacer group and the group including at least one nitrogen atom, the proportion of branched macromolecules, the proportion of three-branch macromolecules ... are combinable with each other subject to their compatibility.

[0054] According to advantageous embodiments of the invention, the modified diene elastomer comprising macromolecules comprising within its structure a branching unit comprising at least two silicon atoms linked together via a hydrocarbon group of valence at least 2, polymeric or non-polymer, which may comprise at least one heteroatom selected from N, O, P, S, the bond between a silicon atom and this hydrocarbon group of valence at least 2 being made via a divalent spacer group, is such that at least one of the following characteristics is satisfied, at least two, at least three, at least four, at least five, at least six, at least seven, at least eight, at least nine and preferably all: The modified diene elastomer comprises two silicon atoms; the hydrocarbon group, polymeric or not, linking the silicon atoms together has a valence of 2 and may include at least one heteroatom chosen from N and O; the spacer groups are divalent, linear, and saturated aliphatic radicals, possessing from 3 to 8 carbon atoms; the alkoxy group(s) substituting one or more silicon atoms comprise 1 to 4 carbon atoms, preferably a methoxy or ethoxy radical; all or part of the alkoxy functions substituting one or more silicon atoms are hydrolyzed to hydroxyl groups; the diene elastomer is a butadiene-styrene copolymer; all or part of the ends of elastomeric branches not bonded to a silicon atom are functionalized, relative to the number of moles of chain end, by an amine function; the average Mn of the elastomeric branches is less at 150,000 g / mol, preferably from 40,000 g / mol to 100,000 g / mol,The modified diene elastomer comprises at least 50% by weight of macromolecules branched with at least three branches; the modified diene elastomer comprises at least 35% by weight of macromolecules branched with three branches.

[0055] The modified diene elastomer according to the invention can be obtained by a synthesis process comprising the reaction of a living diene elastomer, resulting from the polymerization of at least one diene monomer, with a specific modifying agent selected from molecules comprising at least two groups selected from trialcoxysilyls, dialcoxyalkylsilyls, trihalogenosilyls and dihalogenoalkylsilyls, preferably trialcoxysilyls or trihalogenosilyls, the alkoxysilyl or halogenosilyl groups being linked together via a hydrocarbon group of valence at least 2, polymeric or not, which may comprise at least one heteroatom selected from N, O, P, S, the link between a silicon atom and this group being made via a divalent spacer group.

[0056] The invention also relates to a rubber composition based on at least one reinforcing filler comprising a silica content greater than or equal to 80 parts per cent, preferably greater than or equal to 100 parts per cent, and an elastomeric matrix comprising a content of a modified diene elastomer greater than or equal to 75 parts per cent, the modified diene elastomer being obtained by this synthesis process including its particular, advantageous and preferential aspects described below.

[0057] The polymerization step according to the invention can be carried out by anionic polymerization initiated, for example, with an organic compound of an alkali or alkaline earth metal. The polymerization of at least one conjugated diene monomer according to these different methods generates elastomeric chains possessing a reactive site at the end of the chain. These are commonly referred to as living elastomers or living chains.

[0058] In anionic polymerization, the polymerization initiator can be any known anionic initiator. An initiator containing an alkali metal, such as lithium, is preferred. Suitable lithium-containing initiators include those with at least one carbon-lithium bond or at least one nitrogen-lithium bond. Representative compounds include aliphatic organolithium compounds such as ethyllithium, n-butyllithium (nBuLi), isobutyllithium, and lithium amides derived from a cyclic secondary amine, such as pyrrolidine and hexamethyleneimine. Such anionic polymerization initiators are known to those skilled in the art.

[0059] Polymerization can be carried out in a manner known per se, continuously or batchwise. It is generally performed at temperatures between 0°C and 110°C, and preferably from 40°C to 100°C, or even from 50°C to 90°C. The polymerization process can be carried out in solution, in a more or less concentrated or dilute medium. The polymerization solvent is preferably an inert hydrocarbon solvent, which may be, for example, an aliphatic or alicyclic hydrocarbon such as pentane, hexane, heptane, isooctane, cyclohexane, methylcyclohexane, or an aromatic hydrocarbon such as benzene, toluene, or xylene.

[0060] The monomers that can be used in the context of the invention are described above.

[0061] To refine the microstructure of diene elastomers, a modifying and / or randomizing agent may or may not be added in appropriate quantities. This is a matter of general knowledge for a person skilled in the art.

[0062] These variants concerning the polymerization step can be combined with the variants and preferred or alternative aspects described below.

[0063] The polymerization of at least one conjugated diene monomer according to the invention generates elastomeric chains having a reactive site at their chain ends. These live chains, or live elastomers, then react with the modifying agent during the modification step. The modifying agent comprises at least one reactive group with respect to the reactive site of the elastomer, in this case alkoxy groups or halogen atoms substituting for silicon atoms.

[0064] The amount of modifying agent intended to react with the living diene elastomer depends primarily on the type of modified diene elastomer desired. Generally, the molar ratio of reactive groups of the agent with respect to the living elastomer, to the metal of the polymerization initiator, is at least 0.1, preferably at least 0.15, more preferably at least 0.25, and at most 0.45, preferably at most 0.40, or even at most 0.35. Thus, according to a particularly advantageous variant of the modification step, the molar ratio of the modifying agent to the metal of the polymerization initiator has a value in the range of 0.25 to 0.40.

[0065] The conditions for adding and reacting the modifying agent with the elastomer are standard for anionic polymerization using alkoxysilane or halogenosilane compounds and are known to those skilled in the art. These conditions do not present any particular limitations.

[0066] For example, this reaction on living diene elastomers can take place at temperatures between -20°C and 100°C, by adding the modifying agent to the living elastomer chains or vice versa. This reaction can, of course, be carried out with one or more different modifying agents.

[0067] The mixing of the living elastomer with the modifying agent can be carried out by any suitable means, including any mixer with static agitation and / or any dynamic, fully stirred mixer known to those skilled in the art. The latter determines the reaction time between the living diene polymer and the modifying agent, which can vary from a few minutes, for example 2 minutes, to several hours, for example 2 hours.

[0068] According to variants of the invention, the modifying agent is chosen from silane compounds corresponding to formula II: A - [R1 - Si (Y) i R2 l ] k in which Y represent either a halogen atom, in particular chlorine, or an alkoxy OR group, R representing, independently of each other, a C1-C4 alkyl radical, preferably methyl or ethyl, R1 represent, independently of each other, a divalent aliphatic hydrocarbon radical, saturated or unsaturated, cyclic or unsaturated, linear or branched, in C1-C18, preferably in C1-C10, more preferably linear and saturated in C3-C8;R2 represent, independently of each other, an aliphatic hydrocarbon radical, saturated or unsaturated, cyclic or uncyclic, linear or branched, in C1-C18, preferably an alkyl radical C1-C4, more preferably methyl or ethyl, A represents a hydrocarbon group of valence k, polymeric or non-polymer, which may include at least one heteroatom chosen from N, O, P, S, i is an integer of 2 or 3 and 1 is an integer of 0 or 1, with i+l = 3, preferably 1 is 0, k is an integer of at least 2 and preferably of at most 50, preferably still of at most 4, more preferably 2 or 3, even more preferably 2. ;

[0069] According to variants of the invention, A represents a hydrocarbon group of valence k, preferably of valence 2, polymeric or not, comprising at least one nitrogen atom or at least one oxygen atom.

[0070] Examples of molecules in which group A represents a valence 2 hydrocarbon group, polymeric or not, comprising at least one nitrogen atom or at least one oxygen atom, include the compounds bis(triethoxysilylalkyl)methylamine, bis(triethoxysilylalkyl)ethylamine, bis(triethoxysilylalkyl)propylamine, bis(triethoxysilylalkyl)butylamine, bis(triethoxysilylalkyl)phenylamine, and the trimethoxysilyl compounds corresponding to these trimethoxysilyl compounds, the compounds bis(trimethoxysilylalkyl) N-trimethylsilylamine, bis(triethoxysilylalkyl) N-trimethylsilylamine, in which the alkyl radical is at C1-C10, preferably at C3-C8.

[0071] Examples of molecules in which group A represents a valence 2 hydrocarbon group, polymeric or not, comprising at least one nitrogen atom or at least one oxygen atom, include the compounds bis(trimethoxysilylalkyl)piperazine, bis(triethoxysilylalkyl)piperazine, bis(trimethoxysilylalkyl)imidazolidine, bis(triethoxysilylalkyl)imidazolidine, bis(trimethoxysilylalkyl)hexahydropyrimidine, bis(triethoxysilylalkyl)hexahydropyrimidine, in which the alkyl radical is at C1-C10, preferably at C3-C8.

[0072] Examples of molecules in which group A represents a valence 2 hydrocarbon group, polymeric or not, comprising at least one nitrogen atom or at least one oxygen atom, include the compounds poly(oxy-1,2-ethanediyl)-α-[3-(triethoxysilyl)alkyl]-ω-[3-(triethoxysilyl)alkoxy], poly(oxy-1,2-ethanediyl)-α-[3-(trimethoxysilyl)alkyl]-ω-[3-(trimethoxysilyl)alkoxy], and poly[oxy(methyl-1,2-ethanediyl)]-α-[3-(trichlorosilyl)alkyl]-ω-[3-(trichlorosilyl)alkoxy], in which the alkyl radical and the alkoxy radical are at C1-C10, preferably at C3-C8.

[0073] Following these polymerization and functionalization steps, the synthesis process of the modified diene elastomer according to the invention can continue in a manner known per se by the steps of recovery of the modified elastomer.

[0074] According to the invention, the rubber composition comprises an elastomeric matrix including at least 75 parts per million of modified diene elastomer as described above, preferably at least 80 parts per million, and more preferably 100 parts per million of modified diene elastomer. The modified diene elastomer may be a mixture of several modified diene elastomers as described above.

[0075] According to one embodiment of the invention, the elastomeric matrix may also comprise less than 25 parts per million, preferably less than 20 parts per million, of at least one diene elastomer other than the modified diene elastomer described above. As a complementary diene elastomer, any diene elastomer, whether natural or synthetic, may be mentioned. In particular, the diene elastomer may be selected from the group consisting of polybutadienes (BR), natural rubber (NR), synthetic polyisoprenes (IR), butadiene copolymers, isoprene copolymers, and mixtures of these elastomers. Butadiene copolymers are particularly selected from the group consisting of butadiene-styrene copolymers (SBR).

[0076] According to the invention, the rubber composition also comprises at least 80 parts per cent of silica, preferably at least 100 parts per cent, and preferably at most 200 parts per cent, more preferably at most 150 parts per cent, the optimal rate being known to differ according to the particular applications intended.

[0077] The silica used can be any reinforcing silica known to those skilled in the art, in particular any precipitated or pyrogenated silica having a BET surface area and a CTAB specific surface area both less than 450 m2 / g, preferably from 30 to 400 m2 / g, especially between 60 and 300 m2 / g, even more preferably between 130 and 300 m2 / g, or even between 130 and 250 m2 / g.

[0078] In addition to silica, any other type of reinforcing filler known for its ability to strengthen a rubber composition usable for the manufacture of tire treads can be used, for example carbon black or another reinforcing inorganic filler, or a mixture of these fillers.

[0079] All carbon blacks, used individually or in mixtures, are suitable as carbon blacks, including those of the HAF, ISAF, and SAF types conventionally used in tire treads (so-called tire-grade blacks). Among these, particularly the reinforcing carbon blacks of the 100, 200, or 300 series (ASTM grades), such as N115, N134, N234, N326, N330, N339, N347, and N375, are recommended.

[0080] In this application, the term "reinforcing inorganic filler" should be understood, by definition, as any inorganic or mineral filler, regardless of its color and origin (natural or synthetic), capable of reinforcing, by itself and without any means other than an intermediate coupling agent, a rubber composition intended for the manufacture of tires; such a filler is generally characterized, in a known way, by the presence of hydroxyl groups (-OH) on its surface.

[0081] Suitable inorganic reinforcing fillers include siliceous mineral fillers, in addition to silica (SiO2), aluminous fillers, and reinforcing titanium oxides, for example those described in US 6 610 261 and US 6 747 087. Among the aluminous mineral fillers, alumina (Al2O3) and aluminum (oxide)hydroxides are particularly suitable.

[0082] Reinforcing fillers of other types, such as carbon black, are also suitable, provided that these fillers are coated with a silica layer or have functional sites on their surface, particularly hydroxyl sites, requiring the use of a coupling agent to establish the bond between the filler and the elastomer. For example, carbon blacks for tires, such as those described in patent documents WO 96 / 37547 and WO 99 / 28380, can be cited.

[0083] The physical state of the reinforcing inorganic filler, including silica, is irrelevant, whether it is in the form of powder, microbeads, granules, spheres, or any other suitable densified form. Of course, the term "reinforcing inorganic filler" also includes mixtures of different reinforcing fillers, particularly highly dispersible siliceous fillers as described above.

[0084] According to an advantageous embodiment of the invention, the reinforcing filler is predominantly silica, that is to say, it comprises more than 50% by weight of the total weight of the reinforcing filler, of silica.

[0085] According to this variant, when carbon black is also present, it can be used at a rate of less than 20 pc, more preferably less than 10 pc, and at a rate greater than 0.5 pc, notably greater than or equal to 1.

[0086] The use of silica as a reinforcing filler may require the use of a coupling agent to establish the bond between the filler and the elastomer. Organosilanes, particularly polysulfurized alkoxysilanes or mercaptosilanes, or at least bifunctional polyorganosiloxanes, can be used as coupling agents.

[0087] Such a coupling agent should not be confused with the modifying agent used for the synthesis of the modified diene elastomer described previously.

[0088] When the composition according to the invention includes a coupling agent, its quantity depends on that of the reinforcing inorganic filler. Its proportion is easily adjusted by a person skilled in the art according to the proportion of this filler; it is typically in the range of 0.5% to 15% by weight relative to the quantity of reinforcing inorganic filler other than carbon black, preferably from 6% to 12% by weight.

[0089] The rubber composition according to the invention may also contain coupling activators, filler covering agents or more generally processing aids which, by improving the dispersion of the filler in the elastomer matrix and lowering the viscosity of the composition, may improve its processing ability in the raw state, these agents being for example hydrolyzable silanes such as alkylalkoxysilanes, polyols, polyethers, primary, secondary or tertiary amines, hydroxylated or hydrolyzable polyorganosiloxanes.

[0090] Rubber compositions according to the invention may also contain reinforcing organic fillers that may replace all or part of the carbon blacks or other reinforcing inorganic fillers described above. Examples of reinforcing organic fillers include functionalized polyvinyl organic fillers as described in applications WO-A-2006 / 069792, WO-A-2006 / 069793, WO-A-2008 / 003434, and WO-A-2008 / 003435.

[0091] The rubber composition according to the invention may also contain at least one plasticizer. In a manner known to those skilled in the art of tire rubber compositions, this plasticizer is preferably selected from high glass transition temperature (Tg) hydrocarbon resins, low Tg hydrocarbon resins, plasticizing oils, and mixtures thereof.

[0092] According to an advantageous embodiment of the invention, the total plasticizer content in the composition is greater than or equal to 20 parts per cent, preferably greater than or equal to 50 parts per cent, and advantageously not more than 100 parts per cent.

[0093] By definition, a high Tg hydrocarbon resin is a solid at room temperature and pressure (20°C, 1 atm), while a plasticizing oil is liquid at room temperature and a low Tg hydrocarbon resin is viscous at room temperature. Tg is measured according to ASTM D3418 (1999).

[0094] High Tg hydrocarbon resins are known to be thermoplastic hydrocarbon resins with a Tg value above 20°C. Preferred high Tg hydrocarbon resins usable within the scope of the invention are well known to those skilled in the art and are commercially available.

[0095] The plasticizer may also contain a plasticizing oil (or extending oil) that is liquid at 20°C, said to be "low Tg", that is to say, which by definition has a Tg below 20°C, preferably below 40°C.

[0096] Any extending oil, whether aromatic or non-aromatic, known for its plasticizing properties with respect to elastomers, is suitable. At room temperature (20°C), these oils, which vary in viscosity, are liquids (that is, substances that can eventually take the shape of their container), unlike high-Tg hydrocarbon resins, which are solid at room temperature.

[0097] Particularly suitable are plasticizing oils chosen from the group consisting of naphthenic oils (low or high viscosity, including hydrogenated or non-hydrogenated), paraffinic oils, MES (Medium Extracted Solvates) oils, TDAE (Treated Distillate Aromatic Extracts) oils, RAE (Residual Aromatic Extract) oils, TRAE (Treated Residual Aromatic Extract) oils and SRAE (Safety Residual Aromatic Extract) oils, mineral oils, vegetable oils, ether plasticizers, ester plasticizers, phosphate plasticizers, sulfonate plasticizers and mixtures of these compounds.

[0098] The rubber composition according to the invention may also include all or part of the usual additives and processing agents known to those skilled in the art and commonly used in tire rubber compositions, in particular tread rubber compositions, such as, for example, non-reinforcing fillers, pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, antioxidants, anti-fatigue agents, reinforcing resins (such as described, for example, in application WO 02 / 10269), a crosslinking system, for example based on sulfur and other vulcanizing agents, and / or peroxide and / or bismaleimide.

[0099] According to highly advantageous variants of the invention, the rubber composition is such that *The modified diene elastomer described above exhibits at least one, two, three, four, five, six, seven, eight, or nine of the following characteristics, and preferably all of them: the modified diene elastomer comprises two silicon atoms; the hydrocarbon group, polymeric or non-polymer, linking the silicon atoms together has a valence of 2 and may comprise at least one heteroatom selected from N and O; the spacer groups are divalent, linear, saturated aliphatic radicals with 3 to 8 carbon atoms; the alkoxy group(s) substituting for one or more silicon atoms comprise 1 to 4 carbon atoms, preferably a methoxy or ethoxy radical; all or part of the alkoxy functions substituting for one or more silicon atoms are hydrolyzed to hydroxyl groups; the diene elastomer is a copolymer. butadiene-styrene,all or part of the ends of elastomeric branches not bonded to a silicon atom is functionalized, relative to the number of moles of chain end, by an amine function; the average Mn of the elastomeric branches is less than 150,000 g / mol, preferably from 40,000 g / mol to 100,000 g / mol; the modified diene elastomer comprises at least 50% by weight of macromolecules branched with at least three branches; the modified diene elastomer comprises at least 35% by weight of macromolecules branched with three branches; *it comprises 20 parts per million, preferably 50 parts per million, of at least one plasticizer; *it comprises a crosslinking or vulcanizing system.

[0100] The rubber composition according to the invention is manufactured in suitable mixers, using two successive preparation phases well known to those skilled in the art: A first thermomechanical working or mixing phase (the so-called "non-productive" phase), which can be carried out in a single thermomechanical step, during which all the necessary constituents, including the elastomer matrix, fillers, and any other miscellaneous additives, with the exception of the crosslinking system, are introduced into a suitable mixer such as a standard internal mixer (e.g., a Banbury type mixer). The incorporation of the filler into the elastomer can be carried out in one or more stages by thermomechanical mixing. A second mechanical working phase (the so-called "productive" phase), which is carried out in an external mixer such as a roller mixer, after the mixture obtained during the first non-productive phase has been cooled to a lower temperature, typically below 120°C, for example, between 40°C and 100°C.The crosslinking system is then incorporated, and the whole thing is then mixed for a few minutes, for example between 5 and 15 minutes.

[0101] The non-productive phase is carried out at high temperature, up to a maximum temperature between 110°C and 200°C, preferably between 130°C and 185°C, for a duration generally between 2 and 10 minutes.

[0102] The final composition thus obtained is then calendered, for example in the form of a sheet or plate, particularly for characterization in the laboratory, or extruded in the form of a semi-finished (or profile) of rubber usable, for example, as a tire tread for a vehicle.

[0103] The composition 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 that can be used in a tire.

[0104] 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.

[0105] Due to the maintenance of the compromise of hysteresis / raw implementation properties despite a high load rate which characterizes a reinforced rubber composition according to the invention, it will be noted that such a composition can constitute any semi-finished product of the tire and in particular the tread, reducing in particular its rolling resistance, while improving its performance related to the high rate of reinforcing load.

[0106] The invention therefore ultimately relates to a tire comprising a semi-finished article made up in whole or in part of a composition according to the invention, in particular a tread.

[0107] 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. Examples I - Measurements and tests used Determination of the Mn value of the branch before coupling or star pairing by size exclusion chromatography

[0108] The SEC (Size Exclusion Chromatography) technique 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.

[0109] While not an absolute method, SEC allows us to understand the molar mass distribution of a polymer. From commercial standard products, the various number-average molar masses (Mn) and weight-average molar masses (Mw) can be determined, and the polymolecularity index (Ip = Mw / Mn) calculated via a Moore calibration.

[0110] There is no special treatment of the polymer sample prior to analysis. It is simply solubilized in the elution solvent at a concentration of approximately 1 gL-1. The solution is then filtered through a 0.45µm porosity filter before injection.

[0111] The equipment used is a WATERS Alliance chromatographic system. The elution solvent is either tetrahydrofuran or tetrahydrofuran + 1% vol. diisopropylamine + 1% vol. triethylamine, with a flow rate of 1 mL / min, a system temperature of 35°C, and an analysis time of 30 min. A set of two WATERS columns, commercially known as "STYRAGEL HT6E," is used. The injected volume of the polymer sample solution is 100 µL. The detector is a WATERS 2410 differential refractometer, and the chromatographic data processing software is the WATERS EMPOWER system.

[0112] The calculated average molar masses are relative to a calibration curve made for SBRs with the following microstructure: 25% mass of styrene type motifs, 23% mass of 1-2 type motifs and 50% mass of 1-4 trans type motifs. Determination of linear macromolecule and branched macromolecule levels by high-resolution size exclusion chromatography (high-resolution SEC).

[0113] High-resolution SEC is used to determine the mass percentages of the different chain populations present in a polymer sample.

[0114] There is no special treatment of the polymer sample prior to analysis. It is simply solubilized in the elution solvent at a concentration of approximately 1 gL-1. The solution is then filtered through a 0.45 µm porosity filter before injection.

[0115] The equipment used is a "WATERS alliance 2695" chromatographic system. The elution solvent is tetrahydrofuran, the flow rate is 0.2 mL / min, and the system temperature is 35 °C. A set of three identical columns in series is used (Shodex, 300 mm long, 8 mm diameter). The theoretical number of plates in the column set is greater than 22,000. The injected volume of the polymer sample solution is 50 µL. The detector is a "WATERS 2414" differential refractometer, and the chromatographic data processing software is the "WATERS EMPOWER" system.

[0116] The calculated molar masses are relative to a calibration curve made for SBRs with the following microstructure: 25% mass of styrene type motifs, 23% mass of 1,2 type motifs and 50% mass of 1,4-trans type motifs. Determination of Mooney viscosity

[0117] For polymers and rubber compositions, Mooney viscosities ML(1+4)100 °C are measured according to ASTM D-1646.

[0118] An oscillating consistometer is used as described in ASTM D-1646. The Mooney plasticity measurement is performed according to the following principle: the raw (i.e., before firing) composition is molded in a cylindrical chamber heated to 100°C. After one minute of preheating, the rotor rotates within the specimen at 2 revolutions per minute, and the torque required to maintain this rotation after 4 minutes of rotation is measured. The Mooney plasticity ML(1+4) is expressed in Mooney units (MU, with 1 MU = 0.83 Nm). Differential calorimetry

[0119] The glass transition temperatures (Tg) of elastomers are determined using a differential scanning calorimeter, according to ASTM D3418 (1999). Dynamic properties

[0120] The dynamic properties, and in particular tan δ max, are measured on a viscoelastic analyzer (Metravib VA4000), according to ASTM D 5992-96. The response of a vulcanized composition sample (cylindrical specimen 2 mm thick and 79 mm² cross-section) is recorded under sinusoidal loading in alternating simple shear at a frequency of 10 Hz, under standard temperature conditions (23°C) according to ASTM D 1349-99. A strain amplitude sweep is performed from 0.1% to 50% peak-to-peak (forward cycle), then from 50% to 0.1% peak-to-peak (return cycle). The most important result is the loss factor tan δ. For the return cycle, the maximum observed value of tan δ, denoted tan δ max, is recorded. This value is representative of the hysteresis of the material and in this case of the rolling resistance: the lower the value of tan δ max, the lower the rolling resistance. II - Examples of elastomer preparations Preparation of polymer A: functional SBR - witness

[0121] In a 90-liter reactor, maintained under a nitrogen pressure of approximately 2 bar, containing 44 kg of methylcyclohexane, 1.74 kg of styrene and 5.84 kg of butadiene are injected, along with 1.07 L of a 0.36 mol / L tetrahydrofuran solution in methylcyclohexane. After neutralizing impurities in the solution to be polymerized by adding n-butyllithium, 716 mL of 0.06 mol / L n-butyllithium is added to the methylcyclohexane. Polymerization is carried out at 50°C.

[0122] After 45 minutes, the monomer conversion rate reaches 68%. This rate is determined by weighing an extract dried at 140°C under a reduced pressure of 200 mmHg. The pre-coupling Mn value, determined by SEC RI, is 120,000 g.mol⁻¹.

[0123] 1.19 L of a 0.018 mol·L⁻¹ N,N-dimethylaminopropyltrimethoxysilane solution in methylcyclohexane is then added (n(N,N-dimethylaminopropyltrimethoxysilane) / n(n-butyllithium) = 0.5). The solution is stirred at 50 °C for 30 minutes. It is then antioxidantized by adding 0.8 parts per cent (pc) of 4,4'-methylene-bis-2,6-tert-butylphenol elastomer and 0.2 parts per cent (pc) of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine elastomer. The resulting copolymer is separated from the solution by steam stripping and then drum-dried at 100 °C for 15 minutes.

[0124] The Mooney viscosity of the polymer is 70.

[0125] The distribution of species 1 branch, 2 branches, 3 branches, 4 branches, 5 branches and 6 branches (1b / 2b / 3b / 4b / 5b / 6b) determined by high-resolution SEC is as follows: 10 / 87 / 2 / 1 / 0 / 0. The glass transition temperature of this copolymer is - 63°C. Preparation of polymer B : Functional SBR according to the invention

[0126] In a 90-liter reactor, maintained under a nitrogen pressure of approximately 2 bar, containing 43 kg of methylcyclohexane, 1.67 kg of styrene and 5.91 kg of butadiene are injected, along with 1.01 L of a 0.36 mol / L tetrahydrofuran solution in the methylcyclohexane. After neutralizing impurities in the solution to be polymerized by adding n-butyllithium, 1628 mL of 0.06 mol / L n-butyllithium is added to the methylcyclohexane. Polymerization is carried out at 50°C.

[0127] After 40 minutes, the monomer conversion rate reaches 69%. This rate is determined by weighing an extract dried at 140°C under a reduced pressure of 200 mmHg. The value of the branch Mn before coupling, determined by SEC RI, is 52,000 g.mol⁻¹.

[0128] 1.38 L of a 0.022 mol·L⁻¹ bis(3-trimethoxysilylpropyl)-N-methylamine solution in methylcyclohexane is then added (n(bis(3-trimethoxysilylpropyl)-N-methylamine) / n(n-butyllithium) = 0.3). The solution is stirred at 50°C for 30 minutes. The solution is then antioxidantized by adding 0.8 parts per cent (pc) of 4,4'-methylene-bis-2,6-tert-butylphenol elastomer and 0.2 parts per cent (pc) of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine elastomer. The resulting copolymer is separated from its solution by devolatilization in an oven.

[0129] The Mooney viscosity of the polymer is 38.

[0130] The distribution of species 1 branch, 2 branches, 3 branches, 4 branches, 5 branches and 6 branches (1b / 2b / 3b / 4b / 5b / 6b) determined by high-resolution SEC is as follows: 2 / 11 / 48 / 33 / 5 / 1. The glass transition temperature of this copolymer is - 64°C. Preparation of polymer C : Functional SBR according to the invention

[0131] In a 90-liter reactor, maintained under a nitrogen pressure of approximately 2 bar, containing 44 kg of methylcyclohexane, 1.67 kg of styrene and 5.91 kg of butadiene are injected, along with 1.01 L of a 0.36 mol / L tetrahydrofuran solution in the methylcyclohexane. After neutralizing impurities in the solution to be polymerized by adding n-butyllithium, 999 mL of 0.06 mol / L n-butyllithium is added to the methylcyclohexane. Polymerization is carried out at 50°C.

[0132] After 42 minutes, the monomer conversion rate reached 68%. This rate was determined by weighing an extract dried at 140°C under a reduced pressure of 200 mmHg. The pre-coupling Mn value, determined by SEC RI, was 81,000 g.mol⁻¹.

[0133] 0.76 L of a 0.022 mol·L⁻¹ bis(3-trimethoxysilylpropyl)-N-methylamine solution in methylcyclohexane is then added (n(bis(3-trimethoxysilylpropyl)-N-methylamine) / n(n-butyllithium) = 0.26). The solution is stirred at 50°C for 30 minutes. The solution is then antioxidantized by adding 0.8 parts per cent (pc) of 4,4'-methylene-bis-2,6-tert-butylphenol elastomer and 0.2 parts per cent (pc) of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine elastomer. The resulting copolymer is separated from its solution by devolatilization in an oven.

[0134] The Mooney viscosity of the polymer is 71.

[0135] The distribution of species 1 branch, 2 branches, 3 branches, 4 branches, 5 branches and 6 branches (1b / 2b / 3b / 4b / 5b / 6b) determined by high-resolution SEC is as follows: 3 / 5 / 39 / 50 / 4 / 0. The glass transition temperature of this copolymer is - 64°C. Preparation of polymer D : Functional SBR amine at branch tips - witness

[0136] In a 90-liter reactor, maintained under a nitrogen pressure of approximately 2 bar, containing 44 kg of methylcyclohexane, 1.67 kg of styrene and 5.91 kg of butadiene are injected, along with 1.01 L of a 0.36 mol / L tetrahydrofuran solution in methylcyclohexane. After neutralizing impurities in the solution to be polymerized by adding n-butyllithium, 785 mL of 0.06 mol / L lithium hexamethyleneminine is added to the methylcyclohexane. Polymerization is carried out at 50°C.

[0137] After 49 minutes, the monomer conversion rate reaches 70%. This rate is determined by weighing an extract dried at 140°C under a reduced pressure of 200 mmHg. The value of the branch Mn before coupling, determined by SEC RI, is 113,000 g.mol⁻¹.

[0138] 1.22 L of a 0.018 mol.L-1 N,N-dimethylaminopropyltrimethoxysilane solution in methylcyclohexane is then added (n(N,N-dimethylaminopropyltrimethoxysilane) / n(lithia hexamethylenenimine) = 0.5). The solution is stirred at a temperature of 50°C for 30 minutes. The solution is then antioxidantized by the addition of 0.8 part per cent parts (pc) of 4,4'-methylene-bis-2,6-tert-butylphenol elastomer and 0.2 part per cent parts (pc) of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine elastomer. The copolymer thus treated is separated from its solution by a steam stripping operation, then dried on cylinder tools at 100°C for 15 minutes.

[0139] The Mooney viscosity of the polymer is 62.

[0140] The distribution of species 1 branch, 2 branches, 3 branches, 4 branches, 5 branches and 6 branches (1b / 2b / 3b / 4b / 5b / 6b) determined by high-resolution SEC is as follows: 8 / 88 / 3 / 2 / 0 / 0. The glass transition temperature of this copolymer is - 63°C. Preparation of polymer E : Functional SBR amine at branch tips according to the invention

[0141] In a 90-liter reactor, maintained under a nitrogen pressure of approximately 2 bar, containing 43 kg of methylcyclohexane, 1.67 kg of styrene and 5.91 kg of butadiene are injected, along with 1.01 L of a 0.36 mol / L tetrahydrofuran solution in methylcyclohexane. After neutralizing impurities in the solution to be polymerized by adding n-butyllithium, 1376 mL of 0.06 mol / L lithium hexamethyleneminine is added to the methylcyclohexane. Polymerization is carried out at 50°C.

[0142] After 43 minutes, the monomer conversion rate reaches 70%. This rate is determined by weighing an extract dried at 140°C under a reduced pressure of 200 mmHg. The value of the branch Mn before coupling, determined by SEC RI, is 52,000 g.mol⁻¹.

[0143] 1.38 L of a 0.022 mol·L⁻¹ bis(3-trimethoxysilylpropyl)-N-methylamine solution in methylcyclohexane is then added (n(bis(3-trimethoxysilylpropyl)-N-methylamine) / n(lithia hexamethylenenimine) = 0.3). The solution is stirred at 50°C for 30 minutes. The solution is then antioxidantized by adding 0.8 parts per cent (pc) of 4,4'-methylene-bis-2,6-tert-butylphenol elastomer and 0.2 parts per cent (pc) of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine elastomer. The resulting copolymer is separated from its solution by devolatilization in an oven.

[0144] The Mooney viscosity of the polymer is 48.

[0145] The distribution of species 1 branch, 2 branches, 3 branches, 4 branches, 5 branches and 6 branches (1b / 2b / 3b / 4b / 5b / 6b) determined by high-resolution SEC is as follows: 3 / 11 / 48 / 32 / 5 / 2. The glass transition temperature of this copolymer is - 64°C. Preparation of polymer F : Functional SBR amine at branch tips according to the invention

[0146] In a 90-liter reactor, maintained under a nitrogen pressure of approximately 2 bar, containing 44 kg of methylcyclohexane, 1.67 kg of styrene and 5.91 kg of butadiene are injected, along with 1.01 L of a 0.36 mol / L tetrahydrofuran solution in methylcyclohexane. After neutralizing impurities in the solution to be polymerized by adding n-butyllithium, 1096 mL of 0.06 mol / L lithium hexamethyleneminine is added to the methylcyclohexane. Polymerization is carried out at 50°C.

[0147] After 48 minutes, the monomer conversion rate reached 69%. This rate was determined by weighing an extract dried at 140°C under a reduced pressure of 200 mmHg. The pre-coupling Mn value, determined by SEC RI, was 86,000 g·mol⁻¹.

[0148] 0.76 L of a 0.022 mol·L⁻¹ bis(3-trimethoxysilylpropyl)-N-methylamine solution in methylcyclohexane is then added (n(bis(3-trimethoxysilylpropyl)-N-methylamine) / n(lithianed hexamethylenenimine) = 0.27). The solution is stirred at 50°C for 30 minutes. The solution is then antioxidantized by adding 0.8 parts per cent (pc) of 4,4'-methylene-bis-2,6-tert-butylphenol elastomer and 0.2 parts per cent (pc) of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine elastomer. The resulting copolymer is separated from its solution by devolatilization in an oven.

[0149] The Mooney viscosity of the polymer is 86.

[0150] The distribution of species 1 branch, 2 branches, 3 branches, 4 branches, 5 branches and 6 branches (1b / 2b / 3b / 4b / 5b / 6b) determined by high-resolution SEC is as follows: 3 / 5 / 41 / 49 / 2 / 0. The glass transition temperature of this copolymer is - 63°C. III - Examples of preparations of rubber compositions

[0151] Elastomers A to F were used for the preparation of tread-type rubber compositions, each comprising silica as a reinforcing filler according to two different formulations.

[0152] Each of the following compositions is produced, firstly, by a thermo-mechanical process, then, in a second finishing stage, by a mechanical process.

[0153] Into an internal laboratory mixer of the ''Banbury' type, with a capacity of 400 cm3, which is filled to 70% and whose initial temperature is about 90°C, the following are successively introduced: the elastomer, two-thirds of the silica, the black, the coupling agent and the oil, then, about one minute later, the rest of the reinforcing charge, the resin, the antioxidant, the stearic acid and the anti-ozone wax, then, about two minutes later, the zinc monoxide.

[0154] The thermo-mechanical working stage is carried out for 4 to 5 minutes, until a maximum drop temperature of approximately 160°C.

[0155] The first aforementioned thermo-mechanical working time is thus carried out, it being specified that the average speed of the pallets during this first time is 50 rpm.

[0156] The mixture thus obtained is collected, cooled, and then, in an external mixer (homo-finisher), sulfur and accelerator are added at 30°C, with the mixture being mixed again for a period of 3 to 4 minutes (second aforementioned mechanical working stage).

[0157] The compositions thus obtained are then calendered, either in the form of plates (with a thickness ranging from 2 to 3 mm) or thin sheets of rubber, for the measurement of their physical or mechanical properties, or in the form of profiles directly usable, after cutting and / or assembly to the desired dimensions, for example as semi-finished products for tires, in particular for treads.

[0158] Crosslinking is carried out at 150°C for 40 min.

[0159] Each composition has the following formulation (expressed in parts per hundred parts of elastomer): Table 1 Ingredients Formulation 1 Formulation 2 Polymer 100 100 Silica 110 70 Carbon black 3 3 oil 13 0 Resin 59 46 Coupling agent 8.8 5.6 Stearic acid 3 3 Zinc oxide 1.5 1.5 DPG 2.3 1.5 Soluble sulfur 1 1 Accelerator 2.3 1.73 Antioxidant 3.6 2.8 Silica: Rhodia's "Zeosil 1165MP," HDS type. Carbon black: Cabot Corporation's ASTM N234 grade. Oil: Novance's "Lubrirob Tod 1880" sunflower oil with 85% oleic acid by weight. Resin: ExxonMobil's aromatic DCPD resin, Escorez 5600 or PR383. Coupling agent: Degussa's Silane TESPT Si69. DPG: Flexsys's "Perkacit" DPG. Accelerator: CBS: N-cylohexyl-2-benzothiazol-sulfenamide ("Santocure CBS" from Flexsys). Antioxidant: Flexsys's N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine.

[0160] The main difference between these two compositions is their filler content. Other differences are adjustments known to those skilled in the art when the filler content is modified. Thus, the total plasticizer content (oil + resin) is increased with the filler content to maintain a moderate modulus. The silane and DPG content is also adjusted to the silica filler content. IV - Results

[0161] The performance index is calculated using the following formula: 100 / (value of tan delta * value of mooney mixture).

[0162] The higher this index, the lower the rolling resistance and / or the lower the viscosity of the mixture, therefore the easier the implementation. Table 2 polymer Tan delta 23°C Mooney mix performance index Tan delta 23°C Mooney mix performance index Formulation 1 Formulation 1 Formulation 1 Formulation 2 Formulation 2 Formulation 2 A Witness 0.146 74 9.3 0.234 64 6.7 B Invention 0.147 59 11.5 0.231 47 9.2 C Invention 0.181 43 12.8 0.23 34 12.8 D Witness with amine function at branch tips 0.130 90 8.5 0.226 86 5.1 E Invention with amine function at the branch end 0.127 86 9.2 0.193 77 6.7 F Invention with amine function at the branch end 0.145 62 11.1 0.185 70 7.7

[0163] The examples above show that: Comparing composition 1A and composition 1B: the elastomer according to the invention exhibits a better performance index than the control elastomer. Comparing composition 2A and composition 2B, the elastomer according to the invention exhibits a better performance index.

[0164] Therefore, the elastomer according to the invention exhibits a better performance index regardless of the formulation and the loading rate used.

[0165] Comparing 1D and 1E: the elastomer according to the invention presents an improved performance compromise compared to this control which also includes an amine function at the end of the chain.

[0166] Comparing 2D and 2E, the elastomer according to the invention also exhibits an improved performance index compared to this control which also includes an amine function at the end of the chain.

[0167] Thus, the polymer according to the invention with an amine function at the end of the chain exhibits improved performance compared to a polymer that has an amine at the end of the chain but is not according to the invention.

[0168] Comparing 1B and 2B: we also note that the performance index of the polymer according to the invention is higher in Formulation 1 with the highest silica filler content.

[0169] By comparing 1E and 2E, we conclude that the elastomer with an amine function at the end of the chain according to the invention exhibits an improved performance index in Formulation 1 at high loading rates.

[0170] Finally, comparing 1B and 1E, we observe that the polymer according to the invention is particularly useful for achieving a low tan delta 23°C value, i.e. a low rolling resistance, when the polymer has an amine function at the end of the chain.

[0171] The examples above show that compositions comprising a modified diene elastomer according to the invention have a better low tan delta / low Mooney mixture compromise than compositions comprising a modified diene elastomer of the prior art, but especially that this gain on the hysteresis / Mooney compromise is all the stronger as the formulation contains a high level of silica.

[0172] This gain is also even greater when the specific polymer contains an amine function at the ends of the branches (comparison between polymer I and I HMN).

[0173] Furthermore, the use of a rubber compound according to the invention, comprising a high silica content of 80 parts per cubic centimeter or more, and a specific modified elastomer, unexpectedly allows for a low tan delta / low Mooney compromise compared to a compound with a lower silica content. The invention thus makes it possible to benefit from certain tire performance characteristics directly related to the increased reinforcing content, while minimizing the effect of this high content on the composition's processing properties and hysteresis, and therefore on the tire's rolling resistance.

Claims

1. Rubber composition based at least on a reinforcing filler comprising silica and on an elastomer matrix comprising a modified diene elastomer, characterized in that: - the content of silica is greater than or equal to 80 phr, preferably greater than or equal to 100 phr - the content of modified diene elastomer is greater than or equal to 75 phr, and - the modified diene elastomer comprises macromolecules comprising, within their structure, an n-functional branching unit, n having a value of at least 1, consisting of a group comprising at least two silicon atoms which are substituted by elastomer branches and connected together via a polymeric or non-polymeric hydrocarbon group with a valency of at least 2 which can comprise at least one heteroatom chosen from N, O, P, S, the bond between a silicon atom and this hydrocarbon group with a valency of at least 2 being produced via a divalent spacer group.

2. Composition according to Claim 1, characterized in that the elastomer branches of the modified diene elastomer have a number-average molar mass (Mn) ranging from 40 000 g / mol to 100 000 g / mol.

3. Composition according to Claim 1 or 2, characterized in that the end of the elastomer branches of the modified diene elastomer, which end is not bonded to a silicon atom, bears a functional group comprising a nitrogen atom.

4. Composition according to any one of Claims 1 to 3, characterized in that the n-functional branching unit within the structure of the modified diene elastomer comprises at least two silicon atoms each substituted by at most three elastomer branches and by at most three hydroxyl or alkoxy groups, which alkoxy groups are, independently of one another, C1-C10, indeed even C1-C8, preferably C1-C4, alkoxy groups, more preferentially methoxy and ethoxy groups.

5. Composition according to Claim 4, characterized in that all or part of the alkoxy groups borne by the modified diene elastomer are hydrolysed to give hydroxyl groups.

6. Composition according to any one of Claims 1 to 5, characterized in that the spacer group is a saturated or unsaturated, cyclic or non-cyclic, divalent aliphatic Ci-Cis hydrocarbon radical, preferably a linear or branched divalent aliphatic C1-C10 hydrocarbon radical, more preferentially a saturated and linear divalent C3-C8 hydrocarbon radical or a divalent aromatic C6-C18 hydrocarbon radical.

7. Composition according to any one of Claims 1 to 6, characterized in that the n-functional branching unit within the structure of the modified diene elastomer comprises two silicon atoms connected together via a polymeric or non-polymeric hydrocarbon group with a valency of at least 2 which can comprise at least one heteroatom chosen from N, O, P, S, preferably N or O.

8. Composition according to any one of Claims 1 to 7, characterized in that the macromolecules of the modified diene elastomer correspond to the following formula I: in which: - E represents a diene elastomer branch; - the R radicals represent, independently of one another, a C1-C10, indeed even C1-C8, alkyl radical, preferably a C1-C4 alkyl radical, more preferentially methyl or ethyl, or a hydrogen atom; - the R1 radicals represent, independently of one another, a saturated or unsaturated, linear or branched, cyclic or non-cyclic, divalent aliphatic C1-C18, preferably C1-C10, hydrocarbon radical, more preferentially a linear and saturated divalent aliphatic C3-C8 hydrocarbon radical, or a divalent aromatic C6-C18 hydrocarbon radical; - the R2 radicals represent, independently of one another, a C1-C10, indeed even C1-C8, alkyl radical, preferably a C1-C4 alkyl radical, more preferentially methyl or ethyl, - A represents a polymeric or non-polymeric hydrocarbon group with a valency k which can comprise at least one heteroatom chosen from N, O, P, S, - m and n are, independently of each other, integers varying from 0 to 3 and 1 is an integer having the value 0 or 1, with m + n + l = 3; preferably, 1 has the value 0, - k is an integer of at least 2 and preferentially of at most 5, more preferentially of at most 4, more preferentially 2 or 3, more preferentially still 2.

9. Composition according to Claim 8, characterized in that the modified diene elastomer corresponds to the formula I in which A represents a polymeric or non-polymeric hydrocarbon group with a valency k, preferentially 2, comprising at least one nitrogen atom or at least one oxygen atom.

10. Composition according to Claim 8 or 9, characterized in that the modified diene elastomer corresponds to the formula I in which E represents a diene elastomer branch bearing, at the chain end, a group comprising a nitrogen atom, more particularly a cyclic or acyclic amine functional group.

11. Composition according to any one of Claims 1 to 10, characterized in that the modified diene elastomer comprises at least 50% by weight, preferably at least 80% by weight, of branched macromolecules, with respect to the total weight of the modified diene elastomer.

12. Composition according to any one of Claims 1 to 11, characterized in that the modified diene elastomer comprises at least 35% by weight, preferably at least 40% by weight, of branched macromolecules having three branches, with respect to the total weight of the modified diene elastomer.

13. Composition according to any one of Claims 1 to 12, characterized in that at least one, at least two, at least three, at least four, at least five, at least six, at least seven, at least eight, at least nine and preferably all of the following characteristics is / are observed: - the modified diene elastomer comprises two silicon atoms, - the polymeric or non-polymeric hydrocarbon group connecting the silicon atoms together has a valency of 2 and can comprise at least one heteroatom chosen from N and O, - the spacer groups are saturated and linear divalent aliphatic radicals having from 3 to 8 carbon atoms, - the alkoxy group(s) substituting one or more silicon atoms comprises 1 to 4 carbon atoms; preferably, it is a methoxy radical or an ethoxy radical, - all or a part of the alkoxy functional groups substituting one or more silicon atoms are hydrolysed to give hydroxyl groups, - the diene elastomer is a butadiene / styrene copolymer, - all or a part of the ends of elastomer branches not bonded to a silicon atom are functionalized, with respect to the number of moles of chain end, by an amine functional group, - the mean Mn of the elastomer branches is less than 150 000 g / mol, preferably from 40 000 g / mol to 100 000 g / mol, - the modified diene elastomer comprises at least 50%, preferably at least 80%, by weight of branched macromolecules having at least three branches, - the modified diene elastomer comprises at least 35%, preferably at least 40%, by weight of branched macromolecules having three branches.

14. Composition according to any one of Claims 1 to 13, characterized in that it comprises 20 phr or more, preferably 50 phr or more, of at least one plasticizer.

15. Tyre comprising a semi-finished article constituted, in all or in part, by a composition according to any one of Claims 1 to 14.