Rubber composition

Abstract

The invention relates to a rubber composition comprising a functional, highly saturated diene elastomer, the elastomer being a copolymer that contains more than 50 mol% ethylene units and units of a 1,3-diene and carries chain-end functional groups that contain a silanol or alkoxysilane function, a vulcanisation system, a reinforcing filler containing a silica, and an organofunctional silane coupling agent having at least one blocked thiol function, at least one thiol function and at least one function that is a hydroxy alkoxysilyl group or a cyclic dialkoxysilyl group. Such a composition has improved properties at break in the cured state.

Description

[0001] Rubber composition

[0002] The field of the present invention is that of rubber compositions which comprise a silica and a highly saturated diene elastomer and which are in particular intended for use in the manufacture of tires.

[0003] Silica-reinforced rubber compositions comprising a highly saturated diene elastomer are known from WO 2014114607 A1 and WO 2018224776 A1. The highly saturated diene elastomer is a copolymer of ethylene and a 1,3-diene such as 1,3-butadiene and has the characteristic of containing more than 50 mol% of ethylene unit. Due to its high ethylene content and low diene unit content of less than 50 mol%, it is largely distinguished from diene elastomers which are traditionally used in rubber compositions and which generally contain more than 50 mol% of diene unit, such as polybutadienes, polyisoprenes and copolymers of 1,3-butadiene or isoprene and styrene. In particular, it has the particularity of giving a rubber composition a different compromise of properties between rigidity and hysteresis.

[0004] There remains a need to further improve the fracture properties of silica-reinforced rubber compositions containing a highly saturated diene elastomer.

[0005] The inventors have discovered a novel silica-reinforced rubber composition containing a highly saturated diene elastomer and exhibiting improved cured fracture properties.

[0006] Thus, the invention relates to a rubber composition which comprises:

[0007] - a highly saturated functional diene elastomer, a copolymer which contains ethylene units and units of a 1,3-diene and which carries at the end of the chain a functional group which contains a silanol or alkoxysilane function, the ethylene units representing more than 50% by mole of the repeating units constituting the copolymer,

[0008] - a vulcanization system,

[0009] - a reinforcing filler which contains silica,

[0010] - and an organofunctional silane coupling agent having at least one blocked thiol function, at least one thiol function and at least one function which is a hydroxyalkoxysilyl group or a cyclic dia-Ikoxysilyl group and corresponding to the formula (1) (A)p(B) q (1) wherein A and B respectively represent a blocked mercaptosilane unit corresponding to formula (2) and a mercaptosilane unit corresponding to formula (3) in which

[0011] R3 is selected from a hydrogen atom, a linear or branched C1-C18 alkyl, a linear or branched C2-C18 alkenyl, each F is independently selected from linear or branched C1-C6 saturated divalent hydrocarbon groups, each Z bwhich forms a bridging structure between a silicon atom of one unit and a silicon atom of another unit, these units being able to be identical or different, is independently chosen from (-0-)o,s and [-0(R°CR°)fO-]o,5 with the symbols R°, identical or different, each representing a hydrogen atom or a C1-C3 alkyl and f being a number in a range from 2 to 15, each Z cwhich forms a cyclic structure with the silicon atom of a unit is a group of formula [-O(R°CR°)fO-]o,5 with R° and f as defined above, each X is independently selected from a hydrogen atom, a hydroxyl group, a C1-C6 alkyl group, a C1-C6 alkoxyl group and a group of formula HO(R°CR°)fO- with R° and f as defined above, with u+v+2w=3, u being a number equal to 0, 1, 2 or 3, v being a number equal to 1, 2 or 3 and w being a number equal to 0 or 1, p is a number in the range from 1 to 20, q is a number in the range from 1 to 20.

[0012] The invention also relates to a tire which comprises a rubber composition in accordance with the invention, preferably in its tread.

[0013] Description

[0014] Any interval of values ​​designated by the expression "between a and b" represents the domain of values ​​greater than "a" and 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 domain of values ​​from "a" to "b" (i.e., including the strict limits a and b).

[0015] The abbreviation "pce" means parts by weight per hundred parts of elastomer (of the total elastomers if several elastomers are present). 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, that is to say, they may be, partially or totally, derived from a recycling process, or obtained from raw materials themselves derived from a recycling process.

[0016] 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.

[0017] Unless otherwise stated, the ratios of units in a polymer are expressed as a molar percentage relative to the total number of constituent repeating units (CRUs) in the polymer.

[0018] The elastomer useful for the purposes of the invention is a copolymer, preferably random, which comprises ethylene units resulting from the polymerization of ethylene and units of a 1,3-diene resulting from the polymerization of a 1,3-diene.

[0019] As is well known, the expression "ethylene unit" refers to the -(CH2-CH2)- unit resulting from the insertion of ethylene into the elastomer chain. Also as is well known, the expression "unit of a 1,3-diene" or "diene unit" refers to the units resulting from the insertion of the 1,3-diene by a 1,4 addition, a 1,2 addition or a 3,4 addition in the case of isoprene for example. The units of a 1,3-diene are those for example of a 1,3-diene having 4 to 12 carbon atoms, such as 1,3-butadiene, isoprene, 1,3-pentadiene, an aryl-1,3-butadiene. Preferably, the 1,3-diene is 1,3-butadiene or a mixture of 1,3-dienes, one of which is 1,3-butadiene. More preferably, the 1,3-diene is 1,3-butadiene. The functional highly saturated diene elastomer is a copolymer rich in ethylene units, since the ethylene units represent more than 50 mol% of the constituent repeat units of the copolymer.

[0020] Preferably, the copolymer comprises at least 60 mol% of ethylene unit, preferably at least 65 mol% of ethylene unit.

[0021] Preferably, the copolymer comprises at most 85 mol% of ethylene unit. More preferably, it comprises at most 80 mol% of ethylene unit.

[0022] According to an advantageous embodiment, the copolymer comprises from 60% to 85% mol of ethylene unit. More advantageously, the copolymer comprises from 60% to 80% mol of ethylene unit.

[0023] According to another advantageous embodiment, the copolymer comprises from 65% to 85% mol of ethylene unit. More advantageously, the copolymer comprises from 65% to 80% mol of ethylene unit.

[0024] According to a particularly preferred embodiment, the copolymer contains units of formula (I) or units of formula (II).

[0025] -CH2-CH(CH=CH2)- (II)

[0026] The presence of saturated 6-membered cyclic unit, 1,2-cyclohexanediyl, of formula (I) in the copolymer may result from a series of very specific insertions of ethylene and 1,3-butadiene into the polymer chain during its growth. When the copolymer comprises units of formula (I) or units of formula (II), the molar percentages of the units of formula (I) and the units of formula (II) in the copolymer, respectively o and p, preferably satisfy the following equation (eq. 1) or equation (eq. 2), o and p being calculated on the basis of the totality of the constituent repeating units of the copolymer. 0 < o+p < 30 (eq. 1) 0 < o+p < 25 (eq. 2)

[0027] Preferably, the copolymer comprises units of formula (I) in a molar ratio greater than 0% and less than 15%, more preferably less than 10% molar, molar percentage calculated on the basis of all the repeating units constituting the copolymer. These preferred ranges of molar ratio of the units of formula (I) can apply to any of the embodiments of the invention. Preferably, the functional highly saturated diene elastomer is a copolymer of ethylene and 1,3-butadiene.

[0028] More preferably, the functional highly saturated diene elastomer is a copolymer of ethylene and 1,3-butadiene, which copolymer contains units of formula (I) or units of formula (II), in particular according to the contents indicated previously.

[0029] According to any of the embodiments of the invention, the copolymer is preferably a random copolymer.

[0030] The highly saturated functional diene elastomer also has the additional characteristic of being a copolymer which carries at the end of the chain a functional group which contains a silanol or alkoxysilane function.

[0031] Preferably, the silicon atom of the silanol or alkoxysilane function of the functional group carried at the end of the chain by the copolymer is attached directly to the terminal unit of the copolymer, which amounts to saying that the silicon atom of the silanol or alkoxysilane function of the functional group is linked by a covalent bond to a carbon atom of the terminal unit of the copolymer. The terminal unit to which the silicon atom is directly attached preferably consists of a methylene linked to an ethylene unit or to a 1,2-cyclohexanediyl unit, of formula (I), the Si atom being linked to the methylene. By terminal unit is meant the last unit inserted into the copolymer chain by copolymerization, a unit which is preceded by the penultimate unit, itself preceded by the antepenultimate unit.

[0032] According to a first variant of this mode, the functional group carried at the end of the chain by the copolymer is of formula (III-a)

[0033] If(OR 1 )3-y(R 2 )y(IH-a) the symbols R 1 , identical or different, representing an alkyl, the symbols R 2 , identical or different, representing a hydrogen atom, a hydrocarbon chain or a hydrocarbon chain substituted by a tertiary amine function, y being an integer ranging from 0 to 2.

[0034] According to a second variant of this mode, the functional group carried at the end of the chain by the copolymer is of formula (III-b) Si(OH)(R 2 )2(Hl-b) the symbols R 2 , identical or different, representing a hydrogen atom, a hydrocarbon chain or a hydrocarbon chain substituted by a tertiary amine function.

[0035] Among the hydrocarbon chains represented by the symbols R 2in formulas (III-a) and (III-b), alkyls may be mentioned, in particular those having 1 to 6 carbon atoms, preferably methyl or ethyl, more preferably methyl. Among the hydrocarbon chains substituted by a tertiary amine function represented by the symbols R 2 in formulas (III-a) and (III-b), we can cite alkanediyl chains, in particular those comprising at most 6 carbon atoms, in particular the 1,3-propanediyl group, the alkanediyl group carrying the tertiary amine function, in other words, one valence of the alkanediyl chain for the tertiary amine function, the other valence for the silicon atom of the silanol or alkoxysilane function.

[0036] Preferably, the symbols R 2, identical or different, each represent an alkyl having at most 6 carbon atoms or an alkanediyl chain having at most 6 carbon atoms and substituted by a tertiary amine function in formulas (III-a) and (III-b).

[0037] In formula (lll-a), the symbols R 1 are preferably an alkyl having at most 6 carbon atoms, more preferably methyl or ethyl, even more preferably methyl. If 3-y is greater than 1, the symbols R 1 are advantageously identical, in particular methyl or ethyl, more particularly methyl.

[0038] As a functional group of formula (III-a), mention may be made of the groups dimethoxymethylsilyl, dimethoxyethylsilyl, diethoxymethylsilyl, diethoxyethylsilyl, 3-(N,N-dimethylamino)propyldimethoxysilyl, 3-(N,N-dimethylamino)propyldiethoxysilyl, methoxydimethylsilyl, methoxydiethylsilyl, ethoxydimethylsilyl, ethoxydiethysilyl, 3-(N,N-dimethylamino)propylmethoxymethylsilyl, 3-(N,N-dimethylamino)propylmethoxyethylsilyl, 3-(N,N-dimethylamino)propylethoxymethylsilyl, 3-(N,N-dimethylamino)propylethoxyethylsilyl.

[0039] As a functional group of formula (III-b), mention may also be made of the silanol form of the previously mentioned functional groups which contain one and only one ethoxy or methoxy function, the silanol form being able to be obtained by hydrolysis of the ethoxy or methoxy function. Suitable groups for this purpose are dimethylsilanol, diethylsilanol, 3-(N,N-dimethylamino)propylmethylsilanol, 3-(N,N-dimethylamino)propylethylsilanol.

[0040] In formula (III-a), f is preferably equal to 1. For this preferred variant, groups are particularly suitable for which R 1 is methyl or ethyl, such as dimethoxymethylsilyl, dimethoxyethylsilyl, diethoxymethylsilyl, diethoxyethylsilyl, 3-(N,N-dimethylamino)propyldimethoxysilyl, 3-(N,N-dimethylamino)propyldiethoxysilyl. More preferably in formula (III-a), f is 1 and R 1is methyl. For this more preferred variant, dimethoxymethylsilyl, dimethoxyethylsilyl, 3-(N,N-dimethylamino)propyldimethoxysilyl groups are particularly suitable.

[0041] The copolymer, which carries at the end of the chain a functional group which contains a silanol or alkoxysilane function, can be prepared by the process described in the patent application filed under number PCT / FR2018 / 051305 or in the patent application filed under number PCT / FR2018 / 051306, which process comprises the following steps (a) and (b), and where appropriate step (c):

[0042] (a) the copolymerization of a monomer mixture in the presence of a catalytic system comprising an organomagnesium compound and a metallocene,

[0043] (b) the reaction of a functionalizing agent with the polymer obtained in step a),

[0044] (c) where appropriate a hydrolysis reaction.

[0045] Step a) is the preparation of a copolymer chain which contains 1,3-diene and ethylene units. The copolymer chain can be obtained according to different synthesis methods known to those skilled in the art, in particular depending on the targeted microstructure of the highly saturated diene elastomer. Generally, it can be prepared by copolymerization of a monomer mixture which contains 1,3-diene, preferably 1,3-butadiene, and ethylene, 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 random, 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.

[0046] When the copolymer chains have the desired microstructure or macrostructure, step b) is carried out to modify the chain end of the copolymer at the end of step a). The functionalizing agent is a compound of formula (IV), Fc 1 )^ (Rc 2 ) g (IV) the Fc symbols 1 , identical or different, representing an alkoxy group or a halogen atom, the symbols Rc 2 , identical or different, representing a hydrogen atom, a hydrocarbon chain or a hydrocarbon chain substituted by a tertiary amine function, g being an integer ranging from 0 to 2.

[0047] When the symbol Fc 1represents an alkoxy group, the alkoxy group is preferably methoxy or ethoxy. When the symbol Fc 1 represents a halogen atom, the halogen atom is preferably chlorine.

[0048] The functionalizing agent may be of formula (IV-1), formula (IV-2), formula (IV-3) or formula (IV-4), MeOSi(Fc 1 ) 3-g (Rc 2 ) g (IV-1) (MeO)2Si(Fc 1 ) 2-g (Rc 2 ) g (IV-2) (MeO)3Si(Fc 1 )i- g (Rc 2 ) g (IV-3) (MeO)3SiRc 2 (IV-4), in which the symbols Fc 1 and Rc 2 being as defined in formula (IV) for formula (IV-1) and (IV-2), g being an integer ranging from 0 to 2, for formula (IV-3), g being an integer ranging from 0 to 1. Among the hydrocarbon chains represented by the symbols Rc 2in formulas (III), (IV-1), (IV-2), (IV-3) and (IV-4), alkyls may be mentioned, preferably alkyls having at most 6 carbon atoms, more preferably methyl or ethyl, better still methyl.

[0049] Among the hydrocarbon chains substituted by a chemical function Fc 2 which are represented by the symbols Rc 2 in formulas (IV), (IV-1), (IV-2), (IV-3) and (IV-4), mention may be made of alkanediyl chains, preferably those comprising at most 6 carbon atoms, more preferably the 1,3-propanediyl group, the alkanediyl group carrying a tertiary amine function, in other words one valence of the alkanediyl chain for the tertiary amine function, the other valence for the silicon atom of the silanol or alkoxysilane function. g is preferably different from 0, which implies that the functionalizing agent comprises at least one Si-Rc bond 2 .

[0050] As functionalizing agent, mention may be made of the compounds dimethoxydimethylsilane, diethoxydimethylsilane, dimethoxydiethylsilane, diethoxydiethylsilane, (N,N-dimethyl-3-aminopropyl)methyldimethoxysilane, (N,N-dimethyl-3-aminopropyl)methyldiethoxysilane, (N,N-dimethyl-3-aminopropyl)ethyldimethoxysilane, (N,N-dimethyl-3-aminopropyl)ethyldiethoxysilane, trimethoxymethylsilane, triethoxymethylsilane, trimethoxyethylsilane, triethoxyethylsilane, (N,N-dimethylaminopropyl)trimethoxysilane, (N,N-dimethylaminopropyl)triethoxysilane, preferably dimethoxydimethylsilane, dimethoxydiethylsilane, (N,N-dimethyl-3-aminopropyl)methyldimethoxysilane, (N,N- dimethyl-3-aminopropyl)ethyldimethoxysilane, trimethoxyethylsilane, (N,N- dimethylaminopropyl)trimethoxysilane, more preferably trimethoxymethylsilane, trimethoxyethylsilane, (N,N- dimethylaminopropyl)trimethoxysilane.

[0051] The functionalizing agent is typically added to the polymerization medium resulting from step a). It is typically added to the polymerization medium at a monomer conversion rate chosen by a person skilled in the art according to the desired macrostructure and microstructure of the copolymer. Since step a) is generally carried out under ethylene pressure, degassing of the polymerization reactor may be carried out before adding the functionalizing agent. The functionalizing agent is added under inert and anhydrous conditions to the polymerization medium, maintained at the polymerization temperature. 0.25 to 10 moles of functionalizing agent are typically used per 1 mole of co-catalyst, preferably 2 to 4 moles of functionalizing agent per 1 mole of co-catalyst.

[0052] The functionalizing agent is brought into contact with the polymerization medium for a sufficient time to allow the functionalization reaction. This contact time is judiciously chosen by a person skilled in the art depending on the concentration of the reaction medium and the temperature of the reaction medium. Typically, the functionalization reaction is carried out with stirring, at a temperature ranging from 17 to 80°C, for 0.01 to 24 hours.

[0053] Once functionalized, the copolymer can be recovered, in particular by isolating it from the reaction medium. The techniques for separating the elastomer from the reaction medium are well known to those skilled in the art and chosen by those skilled in the art according to the quantity of copolymer to be separated, its macrostructure and the tools available to those skilled in the art. Examples include techniques for coagulation of the copolymer in a solvent such as methanol, techniques for evaporation of the solvent from the reaction medium and residual monomers, for example under reduced pressure.

[0054] When the functionalizing agent is of formula (IV), (IV-1) or (IV-2) and g is equal to 2, step b) may be followed by a hydrolysis reaction to form a copolymer carrying a silanol function at the chain end. The hydrolysis may be carried out by a step of stripping the solution containing the copolymer at the end of step b), in a manner known to those skilled in the art.

[0055] Step c) is an optional step depending on whether or not it is desired to hydrolyze the alkoxysilane function of the functional group carried at the end of the chain by the copolymer into a silanol function. Preferably, step c) is carried out before separating the copolymer from the reaction medium at the end of step b) or simultaneously with this separation step.

[0056] The rubber composition may contain, in addition to the functional highly saturated diene elastomer, a second diene elastomer. A diene elastomer is understood to mean an elastomer consisting at least in part (i.e., a homopolymer or a copolymer) of diene monomer units (monomers bearing two carbon-carbon double bonds, conjugated or not). The second elastomer may be chosen from the group of highly unsaturated diene elastomers consisting of polybutadienes, polyisoprenes, butadiene copolymers, isoprene copolymers and their mixture. A highly unsaturated elastomer is an elastomer which contains more than 50 mol% of diene units.

[0057] Preferably, the level of the functional highly saturated diene elastomer in the rubber composition is at least 50 parts by weight per hundred parts of elastomer of the rubber composition (phr). More preferably, the level of the functional highly saturated diene elastomer in the rubber composition varies in a range from 80 to 100 phr. Even more preferably, it varies in a range from 90 to 100 phr. It is advantageously 100 phr. The functional highly saturated diene elastomer may be a single functional highly saturated diene elastomer or a mixture of several functional highly saturated diene elastomers which differ from each other by their microstructures or by their macrostructures.In the case where the rubber composition contains several functional highly saturated diene elastomers which differ from each other by their microstructures or by their macrostructures, the level of the functional highly saturated diene elastomer in the rubber composition relates to the mixture of functional highly saturated diene elastomers.

[0058] The silica used may be any reinforcing silica known to those skilled in the art, in particular any precipitated or pyrogenic silica having a BET specific surface area and a CTAB specific surface area both less than 450 m 2 / g, preferably within a range of 30 to 400 m 2 / g, especially from 60 to 300 m 2 / g. In this paper, the BET specific surface area is determined by gas adsorption using the Brunauer-Emmett-Teller method described in "The Journal of the American Chemical Society" (Vol. 60, page 309, February 1938), and more precisely according to a method adapted from the standard NF ISO 5794-1, annex E of June 2010 [multipoint volumetric method (5 points) - gas: nitrogen - vacuum degassing: one hour at 160°C - relative pressure range p / in: 0.05 to 0.17], The CTAB specific surface area values ​​were determined according to the standard NF ISO 5794-1, annex G of June 2010. The method is based on the adsorption of CTAB (N-hexadecyl-N,N,N-trimethylammonium bromide) on the "external" surface of the reinforcing filler.

[0059] Any type of precipitated silica may be used, in particular highly dispersible precipitated silicas (called "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, it is possible to use in particular 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.

[0060] The reinforcing filler may include any type of so-called reinforcing filler other than silica, known for its ability to reinforce a rubber composition usable in particular for the manufacture of tires, for example a carbon black. Suitable carbon blacks include all carbon blacks, in particular the blacks conventionally used in tires or their treads. Among the latter, we will mention more particularly 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 N115, N134, N234, N326, N330, N339, N347, N375, N550, N683, N772. These carbon blacks can be used in their isolated state, as commercially available, or in any other form, for example as a carrier for some of the rubber additives used.When carbon black is used in the rubber composition, it is preferably used at a rate less than or equal to 10 phr (for example, the carbon black rate may be in a range from 1 to 10 phr).

[0061] Advantageously, the carbon black content in the rubber composition is less than or equal to 5 pce. Within the indicated ranges, the coloring (black pigmenting agent) and anti-UV properties of carbon blacks are benefited from, without otherwise penalizing the typical performance provided by silica.

[0062] Silica preferably represents more than 50% by mass of the reinforcing filler. In other words, the proportion of silica in the reinforcing filler is greater than 50% by weight of the total weight of the reinforcing filler. More preferably, silica represents more than 85% by mass of the reinforcing filler.

[0063] The total reinforcing filler content may vary over a wide range, for example from 30 phr to 150 phr. According to a first embodiment, the total reinforcing filler content varies over a range from 30 phr to 60 phr. According to a second embodiment, the total reinforcing filler content varies over a range from more than 60 phr to 150 phr. The first embodiment is preferred over the second embodiment for use of the rubber composition in a tread having very low rolling resistance. Any of these ranges of total reinforcing filler content may be applicable to any of the embodiments of the invention.

[0064] To couple the silica to the functional highly saturated diene elastomer, a coupling agent (or bonding agent) is used, a silane, at least bifunctional, intended to ensure a sufficient connection, of a chemical and / or physical nature, between the silica and the diene elastomer. The rubber composition according to the invention comprises, as coupling agent, an organofunctional silane having at least one blocked mercaptosilane unit, at least one mercaptosilane unit and at least one function which is a hydroxyalkoxysilyl group or a cyclic dialkoxysilyl group. The organofunctional silane corresponds to the following formula (1): (A) P (B) q (1) in which

[0065] - A is a symbol representing a blocked mercaptosilane unit corresponding to the formula (2) - B is a symbol representing a mercaptosilane unit corresponding to the formula (3)

[0066] In formula (2), R3 is selected from a hydrogen atom, a linear or branched C1-C18 alkyl, a linear or branched C2-C18 alkenyl,

[0067] In formulas (2) and (3), each F is independently selected from linear or branched C 1 -C 6 saturated divalent hydrocarbon groups, each Z b which forms a bridging structure between a silicon atom of one unit and a silicon atom of another unit, these units being able to be identical or different, is independently chosen from (-0-)o,s and [-0(R 0 CR°)fO-]o,s with the symbols R°, identical or different, each representing a hydrogen atom or a C1-C3 alkyl and f being a number in a range from 2 to 15, each Z cwhich forms a cyclic structure with the silicon atom of a unit is a group of formula [-O(R°CR°)fO-]o,5 with R° and f as defined above, each X is independently selected from a hydrogen atom, a hydroxyl group, a C1-C6 alkyl group, a C1-C6 alkoxyl group and a group of formula HO(R°CR°)fO- with R° and f as defined above, with u+v+2w=3, u being a number equal to 0, 1, 2 or 3, v being a number equal to 1, 2 or 3 and w being a number equal to 0 or 1. p is a number in a range from 1 to 20, q is a number in a range from 1 to 20.

[0068] For the purposes of the present invention, the term "organofunctional silane" means a silane or a mixture of silanes having the characteristic of possessing at least one blocked, i.e. protected, thiol function, one thiol function, i.e. unprotected, and at least one function which is a hydroxylalkoxysilyl group or a cyclic dialkoxysilyl group.

[0069] By "mercaptosilane unit" is meant a unit which contains at least one silicon atom and a thiol function (—SH) linked to a carbon atom.

[0070] A "blocked mercaptosilane unit" means a unit that contains at least one silicon atom and at least one blocked thiol function. A blocked thiol function can, for example, be a thioester group -S-(CO)-R.

[0071] In the compound of formula (1), the sequence of the blocked mercaptosilane repeating units (A) and the mercaptosilane repeating units (B) is indifferent. In particular, this sequence may be alternating (for example ABABAB), block (for example AAAB- BB) or statistical, that is to say that the sequential distribution of said units (A) and (B) obeys known statistical laws. By hydroxyalkoxy group used in the name hydroxyalkoxysilyl, is meant a monovalent group of formula HO(R°CR°)fO- which substitutes the silicon atom, R° and f being as defined previously.

[0072] A cyclic dialkoxysilyl group means a group in which a silicon atom is bonded to two oxygen atoms each bonded to a separate carbon atom of the same alkylene group.

[0073] By "bridging structure" we mean a chemical structure made of covalent bond(s) allowing two repeating units to be linked together, these repeating units being able to be identical or different.

[0074] The denomination in C n -C m qualifying a group refers to the number of carbon atoms constituting the group which contains n to m carbon atoms, n and m being integers with m greater than n.

[0075] Preferably, R3 in formula (2) is selected from hydrogen, C1-C10 alkyls and C2-C10 alkenyls. More preferably, R3 in formula (2) is linear C6-C8 alkyl. Even more preferably, the symbol R3 in formula (2) is heptyl (C7H15-).

[0076] Preferably, each R4 in formulas (2) and (3) is independently a linear C1-C4 alkylene. More preferably, each R4 is propylene.

[0077] Preferably, each Z b in formulas (2) and (3) is independently selected from the group consisting of the units of formula (-0-)o,s, [-OCH2CH2CH20-]o,s, [- OCH2CH2CH2CH20-]O,5 and [-OCH2CH(CH3)CH20-]o,s. More preferably, Z b in formulas (2) and (3) is of formula (-0-)o,s or of formula [-OCH2CH(CH3)CH20-]o,s.

[0078] Preferably, each Z c in formulas (2) and (3) is independently selected from the group consisting of the units of formula [-OCH2CH2CH20-]o,s, [-OCH2CH2CH2CH20-]o,s and [-OCH2CH(CH3)CH20-]O,5. More preferably, each Z c in formulas (2) and (3) is of formula [-OCH2CH(CH3)CH20-]o.5.

[0079] Preferably, each X in formulas (2) and (3) is independently selected from the group consisting of hydroxyl, methoxy, ethoxy, methyl, ethyl, 3-hydroxypropoxy, 3-hydroxy-2-methylpropoxy and 4-hydroxybut-1-oxy. More preferably, each X in formulas (2) and (3) is the same and is selected from the group consisting of hydroxyl, methoxy, ethoxy and 3-hydroxy-2-methylpropoxy.

[0080] Very advantageously, in formulas (2) and (3), R3 is heptyl (C7H15-), each R4 is propylene, each Z b is of formula (-0-)o,s or [-OCH2CH(CH3)CH20-]o,s, each Z c is of formula [-OCH2CH(CH3)CH20-]o, 5, each X is selected from the group consisting of hydroxyl, methoxy, ethoxy and 3-hydroxy-2-methylpropoxy, with u+v+2w=3, u being 0, 1, 2 or 3, v being 1, 2 or 3 and w being 0 or 1.

[0081] The notations (-O-)o,s and [-O(R°CR°)fO-]o,5 refer to half of a siloxane bond and half of a bridging dialkoxy group respectively. These notations are used in conjunction with a silicon atom of the repeating units of the oligomer. They denote half of an oxygen atom, namely half of the oxygen atom that is bonded to the silicon atom of a repeating unit or half of a dialkoxy group, namely half of the atom of the dialkoxy group that is bonded to the silicon atom of a repeating unit; it being understood that the other half of the oxygen atom or the dialkoxy group respectively is bonded to another silicon atom of another repeating unit of the structure of the oligomer; the repeating units may be the same or different. Thus, (-0-)o,s forms a siloxane bond between two silicon atoms each belonging to a repeating unit.[— O( R°CR°)fO— ]o,s can form either a bridging structure (this intermolecular structure being represented by Z. b ) between two silicon atoms each belonging to a repeating pattern, or a cyclic structure (this intramolecular structure being represented by Z c ), the two oxygen atoms of [-O(R°CR°)fO-]o,5 being bonded to the silicon atom of the unit. Those skilled in the art will understand that in the compound of formula (1), the bridging structures may be identical or different between the repeating units. For example, the bridging structures may be of the type -Si-O(R°CR°)fO-Si- or a mixture of bridging structures of the type -Si-O(R°CR°)fO-Si- and of the type —Si— O— Si— .

[0082] Preferably, the organofunctional silane has a molar percentage of blocked mercaptosilane units (A) ranging from 20 to 80% and a molar percentage of mercaptosilane units (B) ranging from 80 to 20%. More preferably, the organofunctional silane has a molar percentage of blocked mercaptosilane units (A) ranging from 40 to 60% and a molar percentage of mercaptosilane units (B) ranging from 60 to 40%. Even more preferably, the organofunctional silane has a molar percentage of blocked mercaptosilane units ranging from 50 to 55% and a molar percentage of mercaptosilane units ranging from 50 to 45%.The molar percentage of blocked mercaptosilane units and that of mercaptosilane units of the organofunctional silane are calculated relative to the total number of thiol units, whether blocked or not, in the organofunctional silane and they can be determined by any method well known to those skilled in the art, such as for example analysis. 1 H NMR.

[0083] The coupling agent, the organofunctional silane, can be obtained from a synthesis process comprising at least one step (a) of trans-esterification reaction of a diol compound of formula (9) with at least one blocked mercaptosilane compound of formula (10) and with at least one mercaptosilane compound of formula (11): HO(R°CR°)fOH (9)

[0084] (RO)3SiR4SC(=O)R3(10)

[0085] (RO)3SiR4SH (11) R° and f being as defined previously, namely R°, identical or different, representing a hydrogen atom, a methyl, an ethyl or a propyl and f a number in a range from 2 to 15,

[0086] R, identical or different, representing a linear C1-C6 alkyl group, R3 and R4 being as defined above, namely R4 representing a linear or branched C1-C6 saturated divalent hydrocarbon group, R3 representing a hydrogen atom, a linear or branched C1-C8 alkyl, or a linear or branched C2-C18 alkenyl.

[0087] The transesterification reaction is a reaction well known to those skilled in the art and can be carried out in the presence of a transesterification catalyst, such as, for example, strong acids.

[0088] Preferably, in the process described above, the diol compound of formula (9) is chosen from HOCH2CH2CH2OH, HOCH2CH2CH2CH2OH and HOCH2CH(CH3)CH2OH. More preferably, in the process described above, the diol compound of formula (4) is HOCH2CH(CH3)CH2OH.

[0089] Preferably, the compounds of formula (10) and (11) used in the implementation of the process described above are those in which the group R is chosen from methyl, ethyl, propyl, iso-propyl, n-butyl, iso-butyl

[0090] Preferably, the compounds of formula (10) used in the implementation of the process described above are those in which R3 represents a hydrogen atom, a linear or branched C1-C10 alkyl, or a linear or branched C2-C10 alkenyl. More preferably, the compounds of formula (10) used in the implementation of the process described above are those in which R3 is a linear C6-C8 alkyl. Even more preferably, the compounds of formula (10) used in the implementation of the process described above are those in which R3 is heptyl (C7H15-).

[0091] Preferably, the compounds of formula (10) and (11) used in carrying out the process described above are those in which each R4 is independently a divalent hydrocarbon group selected from the group consisting of linear C1-C4 alkylenes. More preferably, the compounds of formula (10) and (11) used in carrying out the process described above are those in which each R4 is propylene.

[0092] Preferably, the compounds of formula (10) and (11) used in the implementation of the process described above are those in which R3 is heptyl, R4 is propylene, R, identical or different (preferably identical), is chosen from methyl, ethyl, propyl, isopropyl, n-butyl, iso-butyl and the compound of formula (9) used in the implementation of the process described above is HOCH2CH(CH3)CH2OH.

[0093] Mixtures of compounds of formula (10) and mixtures of compounds of formula (11) may be used to synthesize the coupling agent, the organofunctional silane. The method of synthesizing the coupling agent may further comprise:

[0094] - at least one treatment step (b) of the products obtained in step (a) to convert part of the blocked thiol functions, if present in the products obtained in step (a), into thiol functions (—SH) and / or

[0095] - at least one treatment step (c) of the products obtained in step (a) to convert part of the thiol functions, if present in the products obtained in step (a), into blocked thiol functions and / or

[0096] - at least one step (d) of partial hydrolysis of the products obtained in step (a), of the products obtained in step (b) if this step is implemented in the process and of the products obtained in step (c) if this step is implemented in the process.

[0097] Treatment step (b) may, for example, be a step in which a strong base, for example, NaOEt, is used to convert the blocked thiol functions carried by the products obtained in step (a) into thiol functions. Treatment step (c) may, for example, be a step of esterification of the thiol functions of the products obtained in step (a) using a carboxylic acid (in particular C7H15COOH) or an acyl chloride (in particular C7H15COCl) to convert them into blocked thiol functions. Partial hydrolysis step (d) may take place when there is an excess of water relative to the products and reagents used in steps (a), and optionally steps (b) and (c) if present. The partial hydrolysis step makes it possible to obtain the compounds described above in which Z b represents (-0-)o,s or OH.

[0098] Those skilled in the art may refer in particular to document WO2007 / 098120 A2 which describes the process for obtaining the organofunctional silane coupling agent.

[0099] The organofunctional coupling agent may be obtained in the form of a mixture resulting from the implementation of the process described above and may be used in the rubber composition according to the invention in the form of this mixture. The mixture contains not only the organofunctional coupling agent, but also other silanes chosen from any one of the following compounds and mixtures thereof:

[0100] - a compound of formula (2') which is derived from formula (2), formula (2') differing from formula (2) in that Z b v is replaced by Z a t , Z ahaving the same definition as group X of formula (2), t being a number equal to 0, 1, 2 or 3 with u+t+2w= 3 and u and w having the same definition as in formula (2),

[0101] - a compound of formula (3') which is derived from formula (3), formula (3') differing from formula (3) in that Z b v is replaced by Z a t , Z a having the same definition as group X of formula (3), t being a number equal to 0, 1, 2 or 3 with u+t+2w= 3 and u and w having the same definition as in formula (3),

[0102] - a dimer consisting of two blocked mercaptosilane units of formula (2),

[0103] - a dimer consisting of two mercaptosilane units of formula (3),

[0104] - a dimer consisting of a blocked mercaptosilane unit (2) and a mercaptosilane unit of formula (3) - an oligomer consisting of blocked mercaptosilane units of formula (2),

[0105] - an oligomer consisting of mercaptosilane units of formula (3).

[0106] The organofunctional silane coupling agent is, for example, commercially available from Momentive. Inc. under the trade name “NXT-Z,” specifically “NXT-Z45.”

[0107] In the rubber composition according to the invention, the level of the organofunctional silane coupling agent is adjusted by a person skilled in the art according to the specific surface area of ​​the silica used in the rubber composition and according to the level of silica in the rubber composition. It preferably varies from 1 to 15 phr, more preferably from 1.5 to 10 phr, even more preferably from 2 to 5 phr.

[0108] The rubber composition according to the invention has the other essential characteristic of containing a vulcanization system, that is to say a sulfur-based crosslinking system. The sulfur is typically provided in the form of molecular sulfur or a sulfur donor agent, preferably in molecular form. Sulfur in molecular form is also referred to as molecular sulfur. A sulfur donor is understood to mean any compound which releases sulfur atoms, combined or not in the form of a polysulfide chain, capable of being inserted into the polysulfide chains formed during vulcanization and bridging the elastomer chains. In addition to the vulcanization system, various known secondary accelerators or vulcanization activators such as zinc oxide, stearic acid, guanidine derivatives (in particular diphenylguanidine), etc. are incorporated during the first non-productive phase and / or during the productive phase.The sulfur content is preferably between 0.5 and 4 pce, that of the primary accelerator is preferably between 0.5 and 5 pce. These preferential rates can apply to any of the embodiments of the invention.

[0109] Any compound capable of acting as a vulcanization accelerator (primary or secondary) that can act as a vulcanization accelerator for diene elastomers in the presence of sulfur may be used, in particular accelerators of the thiazole type and their derivatives, accelerators of the sulfenamide type for primary accelerators, and accelerators of the thiuram, dithiocarbamate, dithiophosphate, thiourea and xanthate type for secondary accelerators. Examples of primary accelerators include, in particular, sulfenamide compounds such as N-cyclohexyl-2-benzothiazyl sulfenamide ("CBS"), N,N-dicyclohexyl-2-benzothiazyl sulfenamide ("DCBS"), N-tert-butyl-2-benzothiazyl sulfenamide ("TBBS"), and mixtures of these compounds.

[0110] The primary accelerator is preferably a sulfenamide, more preferably N-cyclohexyl-2-benzothiazyl sulfenamide. Examples of secondary accelerators include thiuram disulfides such as tetraethylthiuram disulfide, tetrabutylthiuram disulfide ("TBTD"), tetrabenzylthiuram disulfide ("TBZTD") and mixtures of these compounds. The secondary accelerator is preferably a thiuram disulfide, more preferably tetrabenzylthiuram disulfide. The vulcanization is carried out in a known manner at a temperature generally between 130°C and 200°C, for a sufficient time which may vary, for example, between 5 and 90 min depending in particular on the curing temperature, the vulcanization system adopted and the vulcanization kinetics of the composition in question.

[0111] The rubber composition in accordance with the invention may also comprise all or part of the usual additives normally used in elastomer compositions intended for the manufacture of tires, in particular pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, antioxidants, plasticizers such as plasticizing oils or resins.

[0112] The rubber composition, before vulcanization, can be manufactured in suitable mixers, using two successive preparation phases according to a procedure well known to those skilled in the art: a first thermo-mechanical working or kneading phase (sometimes referred to as the "non-productive" phase) at high temperature, up to a maximum temperature of between 110°C and 190°C, preferably between 130°C and 180°C, followed by a second mechanical working phase (sometimes referred to as the "productive" phase) at a lower temperature, typically below 110°C, for example between 40°C and 100°C, a finishing phase during which the sulfur or sulfur donor and the vulcanization accelerator are incorporated.

[0113] For example, the first (non-productive) phase is carried out in a single thermomechanical step during which all the necessary constituents, any additional processing agents and other various additives, with the exception of the vulcanization system, are introduced into a suitable mixer such as a conventional internal mixer. The total mixing time in this non-productive phase is preferably between 1 and 15 min. After cooling the mixture thus obtained during the first non-productive phase, the vulcanization system is then incorporated at low temperature, generally in an external mixer such as a roller mixer, and the whole is then mixed (productive phase) for a few minutes, for example between 2 and 15 min.

[0114] The rubber composition may be calendered or extruded in the form of a sheet or plate, in particular for laboratory characterization, or in the form of a semi-finished (or profiled) rubber usable in a tire. The composition may be either in the raw state (before crosslinking or vulcanization), or in the cured state (before crosslinking or after vulcanization). It may constitute all or part of a semi-finished article, in particular intended to be used in a pneumatic or non-pneumatic tire which comprises a tread, in particular in the tread of the tire.

[0115] In summary, the invention is advantageously implemented according to any one of the following embodiments 1 to 34: Mode 1: Rubber composition which comprises:

[0116] - a highly saturated functional diene elastomer, a copolymer which contains ethylene units and units of a 1,3-diene and which carries at the end of the chain a functional group which contains a silanol or alkoxysilane function, the ethylene units representing more than 50% by mole of the repeating units constituting the copolymer,

[0117] - a vulcanization system,

[0118] - a reinforcing filler which contains silica,

[0119] - and an organofunctional silane coupling agent having at least one blocked thiol function, at least one thiol function and at least one function which is a hydroxyalkoxysilyl group or a cyclic dia-Ikoxysilyl group and corresponding to the formula (1) (A)p(B) q (1) wherein A and B respectively represent a blocked mercaptosilane unit corresponding to formula (2) and a mercaptosilane unit corresponding to formula (3) in which

[0120] R3 is selected from a hydrogen atom, a linear or branched C1-C18 alkyl, a linear or branched C2-C18 alkenyl, each F is independently selected from linear or branched C1-C6 saturated divalent hydrocarbon groups, each Z b which forms a bridging structure between a silicon atom of one unit and a silicon atom of another unit, these units being able to be identical or different, is independently chosen from (-0-)o,s and [-0(R°CR°)fO-]o,5 with the symbols R°, identical or different, each representing a hydrogen atom or a C1-C3 alkyl and f being a number in a range from 2 to 15, each Z cwhich forms a cyclic structure with the silicon atom of a unit is a group of formula [-O(R°CR°)fO-]o,5 with R° and f as defined above, each X is independently selected from a hydrogen atom, a hydroxyl group, a C1-C6 alkyl group, a C1-C6 alkoxyl group and a group of formula HO(R°CR°)fO- with R° and f as defined above, with u+v+2w=3, u being a number equal to 0, 1, 2 or 3, v being a number equal to 1, 2 or 3 and w being a number equal to 0 or 1, p is a number in the range from 1 to 20, q is a number in the range from 1 to 20.

[0121] Mode 2: Rubber composition according to mode 1 in which the ethylene units in the copolymer represent at least 60 mol% of the constituent repeat units of the copolymer.

[0122] Mode 3: Rubber composition according to any one of modes 1 to 2 in which the ethylene units in the copolymer represent at least 65 mol% of the constituent repeat units of the copolymer.

[0123] Mode 4: Rubber composition according to any one of modes 1 to 3 in which the ethylene units in the copolymer represent at most 85 mol% of the constituent repeat units of the copolymer.

[0124] Mode 5: Rubber composition according to any one of modes 1 to 4 in which the ethylene units in the copolymer represent at most 80 mol% of the constituent repeat units of the copolymer.

[0125] Mode 6: Rubber composition according to any one of modes 1 to 5 in which the silicon atom of the silanol or alkoxysilane function of the functional group carried at the end of the chain by the copolymer is attached directly to the terminal unit of the copolymer.

[0126] Mode 7: Rubber composition according to any one of modes 1 to 6 in which the functional group carried at the chain end by the copolymer is of formula (III-a) or (IIIb)

[0127] If(OR 1 )3-y(R 2 )y (lll-a)

[0128] Si(OH)(R 2 )2, (lll-b) the symbols R 1 , identical or different, representing an alkyl, the symbols R 2 , identical or different, representing a hydrogen atom, a hydrocarbon chain or a hydrocarbon chain substituted by a tertiary amine function, y being an integer ranging from 0 to 2.

[0129] Mode 8: Rubber composition according to mode 7 in which the symbols R 1 are methyl or ethyl, the symbols R 2 are methyl or ethyl or 1,3-propanediyl carrying a tertiary amine function.

[0130] Method 9: Rubber composition according to any one of methods 1 to 8 in which the 1,3-diene is 1,3-butadiene or a mixture of 1,3-dienes of which one is 1,3-butadiene, preferably 1,3-butadiene. Method 10: Rubber composition according to any one of methods 1 to 9 in which the copolymer contains units of formula (I) or units of formula (II).

[0131] -CH2-CH(CH=CH2)- (II)

[0132] Mode 11: Rubber composition according to any one of modes 1 to 10 in which the copolymer is a copolymer of ethylene and 1,3-butadiene.

[0133] Mode 12: Rubber composition according to any one of modes 1 to 11 in which the copolymer is a random copolymer.

[0134] Mode 13: A rubber composition according to any one of modes 1 to 12 wherein the level of functional highly saturated diene elastomer is at least 50 parts by weight per hundred parts of elastomer of the rubber composition (pce).

[0135] Mode 14: Rubber composition according to any one of modes 1 to 13 in which the level of functional highly saturated diene elastomer varies in a range from 80 to 100 pce.

[0136] Mode 15: Rubber composition according to any one of modes 1 to 14 in which the silica represents more than 50% by mass of the reinforcing filler.

[0137] Mode 16: Rubber composition according to any one of modes 1 to 15 in which the silica represents more than 85% by mass of the reinforcing filler.

[0138] Mode 17: Rubber composition according to any one of modes 1 to 16 in which the total rate of reinforcing filler varies in a range from 30 to 150 pce.

[0139] Mode 18: Rubber composition according to any one of modes 1 to 17 in which the total rate of reinforcing filler varies in a range from 30 pce to 60 pce.

[0140] Mode 19: Rubber composition according to any one of modes 1 to 18 wherein R3 in formula (2) is selected from hydrogen, C1-C10 alkyls and C2-C10 alkenyls.

[0141] Mode 20: Rubber composition according to any one of modes 1 to 19 in which R3 in formula (2) is a linear C6-C8 alkyl, more preferably is heptyl.

[0142] Mode 21: A rubber composition according to any one of modes 1 to 20 wherein each R4 in formulae (2) and (3) is independently a linear C1-C4 alkylene. Mode 22: A rubber composition according to any one of modes 1 to 21 wherein each F in formulae (2) and (3) is propylene.

[0143] Mode 23: Rubber composition according to any one of modes 1 to 22 in which each Z b in formulas (2) and (3) is independently selected from the group consisting of the units of formula (-0-)o,5, [-OCH2CH2CH20-]o,5, [-OCH2CH2CH2CH20-]o,5 and [- OCH2CH(CH3)CH20-]O,5.

[0144] Mode 24: Rubber composition according to any one of modes 1 to 23 in which each Z b in formulas (2) and (3) is of formula (-0-)o,s or [-OCH2CH(CH3)CH20-]o,s.

[0145] Mode 25: Rubber composition according to any one of modes 1 to 24 in which each Z cin formulas (2) and (3) is independently selected from the group consisting of the units of formula [-OCH2CH2CH20-]o,s, [-OCH2CH2CH2CH20-]o,s and [- OCH2CH(CH3)CH20-]O,5.

[0146] Mode 26: Rubber composition according to any one of modes 1 to 25 in which each Z c in formulas (2) and (3) is of formula [-OCH2CH(CH3)CH20-]o,s.

[0147] Mode 27: A rubber composition according to any one of modes 1 to 26 wherein each X in formulae (2) and (3) is independently selected from the group consisting of hydroxyl, methoxy, ethoxy, methyl, ethyl, 3-hydroxypropoxy, 3-hydroxy-2-methylpropoxy and 4-hydroxybut-1-oxy.

[0148] Mode 28: A rubber composition according to any one of modes 1 to 27 wherein each X in formulae (2) and (3) is the same and is selected from the group consisting of hydroxyl, methoxy, ethoxy and 3-hydroxy-2-methylpropoxy.

[0149] Mode 29: Rubber composition according to any one of modes 1 to 28 in which the organofunctional silane has a molar percentage of blocked mercaptosilane units (A) ranging from 20 to 80% and a molar percentage of mercaptosilane units (B) ranging from 80 to 20%.

[0150] Mode 30: Rubber composition according to any one of modes 1 to 29 in which the organofunctional silane has a molar percentage of blocked mercaptosilane units (A) ranging from 40 to 60% and a molar percentage of mercaptosilane units (B) ranging from 60 to 40%.

[0151] Mode 31: Rubber composition according to any one of modes 1 to 30 in which the organofunctional silane has a molar percentage of blocked mercaptosilane units ranging from 50 to 55% and a molar percentage of mercaptosilane units ranging from 50 to 45%.

[0152] Method 32: Rubber composition according to any one of methods 1 to 31 in which the level of the organofunctional silane coupling agent varies from 1 to 15 phr. Method 33: Rubber composition according to any one of methods 1 to 32 in which the level of the organofunctional silane coupling agent varies from 1.5 to 10 phr, preferably from 2 to 5 phr.

[0153] Mode 34: A tire which has a tread, which tire comprises a rubber composition defined in any one of modes 1 to 33, preferably in its tread.

[0154] The above-mentioned characteristics of the present invention, as well as others, will be better understood upon reading the following description of several exemplary embodiments of the invention, given for illustrative and non-limiting purposes.

[0155] Examples

[0156] Breaking properties:

[0157] Tensile tests are used to determine the properties at break. Unless otherwise stated, they are carried out in accordance with French standard NF T 46-002 of September 1988, with a type H2 specimen, the tensile speed being 500 mm / min. The breaking stresses (in MPa) and the elongations at break (in %) are measured at 60°C ± 2°C according to standard NF T 46-002.

[0158] The results are expressed on a base of 100 relative to a control. A value higher than that of the control, arbitrarily set at 100, indicates an improved result, i.e. a measured quantity greater than that of the control.

[0159] Analysis of functional elastomers by nuclear magnetic resonance (NMR) analysis:

[0160] Copolymers of ethylene and 1,3-butadiene can be characterized by NMR spectrometry 1 H, 13 C, 29Yes. NMR spectra are recorded on a Brüker Avance III 500 MHz Spectrometer equipped with a BBIz-grad 5 mm “broadband” cryoprobe. The NMR experiment 1 Quantitative H, uses a single 30° pulse sequence and a 5 second repetition delay between each acquisition. 64 to 256 accumulations are performed. The NMR experiment 13 Quantitative C uses a 30° single-pulse sequence with proton decoupling and a 10-second repetition delay between each acquisition. 1024 to 10240 accumulations are performed. Two-dimensional experiments 1 H / 29 If are used for the purpose of determining the structure of functional polymers. The determination of the microstructure of copolymers is defined in the literature, according to the article by Llauro et al., Macromolecules 2001, 34, 6304-6311.

[0161] The final chemical structure of each functional polymer is identified by NMR ( 1 H and 29If). The microstructure of the elastomers is determined by NMR analysis 1 H, supplemented by NMR analysis 13 C when the resolution of the NMR spectra of the 1 H does not allow the attribution and quantification of all species.

[0162] NMR measurements are carried out at 25°C in the CDCh. Glass transition temperature of polymers:

[0163] The glass transition temperature (Tg) and the glass transition width ATg are measured using a differential scanning calorimeter according to ASTM D3418 (1999).

[0164] Mooney Viscosity:

[0165] Mooney viscosity is measured using an oscillating consistometer as described in ASTM D1646 (1999). The measurement is carried out according to the following principle: the sample analyzed in the raw state (i.e., before curing) is molded (shaped) in a cylindrical enclosure heated to a given temperature (100°C). After 1 minute of preheating, the rotor rotates within the specimen at 2 revolutions / minute and the torque needed to maintain this movement is measured after 4 minutes of rotation. Mooney viscosity (ML) is expressed in "Mooney units" (MU, with 1 MU = 0.83 Newton meters).

[0166] Preparation of a functional highly saturated diene elastomer, El:

[0167] All reagents are obtained commercially except the metallocene [{Me2SiFlu2Nd(p-BF hL THF)}] which is prepared according to the procedure described in patent application WO 2007054224.

[0168] Butyloctylmagnesium (BOMAG) (20% in heptane, at 0.88 mol L -1) 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. 1,3-Butadiene is purified on alumina guards. (N,N-Dimethyl-3-aminopropyl)methyldimethoxysilane is obtained from ABCR and is used without prior purification.

[0169] The solvent methylcyclohexane (MCH) from BioSolve is dried and purified on an alumina column in a solvent fountain from mBraun and used in an inert atmosphere. Methanol (99%, class 3, grade II) comes from Laurylas, CeDe (99.6% atom D) from Aldrich and is stored cold. All reactions are carried out in an inert atmosphere.

[0170] The highly saturated functional diene elastomer El is a copolymer prepared according to the following procedure:

[0171] In a 90 L stainless steel reactor, 64 L of MCH and a solution of BOMAG (23 mmol) in methylcyclohexane (0.01 mol / L) are introduced. The reactor is heated to 80°C and the monomers are added at a controlled flow rate in order to maintain the composition of the monomer mixture in the polymerization medium constant. The ethylene flow rate is set at 40 g / min and the butadiene is injected independently and the flow rate is controlled by the ethylene flow rate according to the butadiene / ethylene mass ratio equal to 0.55. When the reactor reaches a pressure of 8 bars, the catalytic system (6.25 mmol of Nd) preformed at a concentration of 0.007 mol / L prepared according to the protocol described in application WO 2017093654 A1 is introduced into the polymerization medium.The chain termination reaction is carried out by a functionalization reaction described according to the functionalization procedure when 5 to 6 kg of polymer are formed: the polymer is recovered after a stripping step. The polymer is then dried on a screw machine equipped with a single screw at 150°C.

[0172] Functionalization procedure:

[0173] When the desired monomer conversion is reached (5 to 6 kg of polymer), the contents of the reactor are degassed, the functionalizing agent, N, N dimethylaminopropyl-methyldimethoxysilane, is introduced into the polymerization medium under inert atmosphere by overpressure at a rate of 4 equivalents relative to the number of moles of Nd and Mg introduced into the reactor. The reaction medium is stirred for 15 minutes at 80°C. The reaction medium is deactivated with methanol. The polymer is recovered after a stripping step. The polymer is then dried on a screw machine equipped with a single screw at 150°C.

[0174] The catalytic system is a preformed catalytic system. It is prepared in methylcyclohexane from a metallocene, [Me2Si(Flu)2Nd(p-BH4)2Li(THF)] at 0.0065 mol / L, a co-catalyst, butyloctylmagnesium (BOMAG) whose BOMAG / Nd molar ratio is equal to 2.2, and a preformed monomer, 1,3-butadiene whose 1,3-butadiene / Nd molar ratio is equal to 90. The medium is heated to 80°C for a period of 5 hours. It is prepared according to a preparation method in accordance with paragraph 11.1 of patent application WO 2017093654 A1.

[0175] Preparation of rubber compositions:

[0176] The rubber compositions are prepared as follows:

[0177] The diene elastomer, then the silica, the silane coupling agent, and the various other ingredients except for the vulcanization system are introduced into a 400 mL internal mixer (final filling rate: approximately 70% by volume), whose initial tank temperature is approximately 80°C. Thermomechanical work (non-productive phase) is then carried out in one step, lasting approximately 5 min to 6 minutes for an average paddle speed of 100 rpm, until a maximum "fall" temperature of 160°C is reached. The mixture thus obtained is recovered, cooled, and then sulfur and a sulfenamide-type accelerator are incorporated on a mixer (homo-finisher) at 23°C, mixing everything (productive phase) for 5 minutes.

[0178] Rubber compositions C1 and T1 all contain a functional highly saturated diene elastomer according to the invention, a vulcanization system, a silica and a silane coupling agent. Rubber composition C1 which contains as coupling agent an organofunctional silane of formula (1) according to the invention, “NXT-Z45” marketed by the company Momentive, is in accordance with the invention. Composition T1 differs from composition C1 in that the coupling agent is a polysulfide silane, bis(3-triethoxysilyl propyl) tetrasulfide, abbreviated to TESPT of formula [(C2H5O)3Si(CH2)3S2]2 marketed under the name “Si69” by the company Evonik. Rubber composition T1 is not in accordance with the invention and is a control composition of C1.The total sulfur content is identical for the rubber compositions which are compared with each other, knowing that in the case of the rubber composition Tl, the coupling agent “Si69” releases free sulfur during its reaction with the elastomer, which represents a source of sulfur available for vulcanization, i.e. 0.3 pce.

[0179] The formulations (in pce) of the rubber compositions are described in Table 1.

[0180] 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 after vulcanization at 150°C (cooked state), or in the form of profiles which can be used directly, after cutting and / or assembly to the desired dimensions, for example as semi-finished products for tires.

[0181] The results of the cured properties of the rubber compositions are shown in Table 2.

[0182] Table 2 shows that the elongation at break at 60°C of the rubber composition Cl is significantly increased compared to the control composition Tl. This result is obtained without the breaking stress at 60°C being degraded. Even the breaking stress at 60°C is also significantly improved. The rubber compositions according to the invention therefore exhibit a significant improvement in breaking properties.

[0183] Table 1

[0184] (1) Copolymer of ethylene and 1,3-butadiene containing 74 mol% of ethylene unit, 17% of butadiene unit in the form of 1,2 and 1,4 units and 9 mol% of 1,2-cyclohexanediyl unit, of Tg -39°C (AT 7°C) and of ML 60 and carrying at the chain end a Tl functional group which contains a silanol or alkoxysilane function

[0185] (2) “Zeosil 1165 MP” from Solvay-Rhodia in the form of microbeads

[0186] (3) Liquid silane triethoxysilylpropyltetrasulfide (TESPT) “Si69” from Evonik

[0187] (4) Silane Mercapto - Thiocarboxylate Oligomer (“NXT-Z45”) - CAS 922519-17-3 - Momentive company

[0188] (5) Diphenylguanidine “Perkacit DPG” from Flexsys

[0189] (6) Anti-ozone wax “VARAZON 4959” from the company Sasol Wax

[0190] (7) N-(l,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine “Santoflex 6PPD” from Flexys (8) Stearic acid “Pristerene 4931” from Uniqema

[0191] (9) Industrial grade Zinc Oxide from Umicore

[0192] (10) N-cyclohexyl-2-benzothiazol-sulfenamide “Santocure CBS” from Flexsys.

[0193] Table 2

Claims

Claims 1. Rubber composition which comprises: - a highly saturated functional diene elastomer, a copolymer which contains ethylene units and units of a 1,3-diene and which carries at the end of the chain a functional group which contains a silanol or alkoxysilane function, the ethylene units representing more than 50% by mole of the repeating units constituting the copolymer, - a vulcanization system, - a reinforcing filler which contains silica, - and an organofunctional silane coupling agent having at least one blocked thiol function, at least one thiol function and at least one function which is a hydroxyalkoxysilyl group or a cyclic dia-Ikoxysilyl group and corresponding to the formula (1) (A)p(B) q (1) wherein A and B respectively represent a blocked mercaptosilane unit corresponding to formula (2) and a mercaptosilane unit corresponding to formula (3) in which R3 is selected from a hydrogen atom, a linear or branched C1-C18 alkyl, a linear or branched C2-C18 alkenyl, each F is independently selected from linear or branched C1-C6 saturated divalent hydrocarbon groups, each Z b which forms a bridging structure between a silicon atom of one unit and a silicon atom of another unit, these units being able to be identical or different, is independently chosen from (-0-)o,s and [-0(R°CR°)fO-]o,5 with the symbols R°, identical or different, each representing a hydrogen atom or a C1-C3 alkyl and f being a number in a range from 2 to 15, each Z cwhich forms a cyclic structure with the silicon atom of a unit is a group of formula [-O(R°CR°)fO-]o,5 with R° and f as defined above, each X is independently selected from a hydrogen atom, a hydroxyl group, a C1-C6 alkyl group, a C1-C6 alkoxyl group and a group of formula HO(R°CR°)fO- with R° and f as defined previously, with u+v+2w=3, u being a number equal to 0, 1, 2 or 3, v being a number equal to 1, 2 or 3 and w being a number equal to 0 or 1, p is a number in a range from 1 to 20, q is a number in a range from 1 to 20.

2. Rubber composition according to claim 1 in which the functional group carried at the chain end by the copolymer is of formula (III-a) or (II-Ib) Si(OR 1 )3-y(R 2 ) y (lll-a) Si(OH)(R 2 )2, (lll-b) the symbols R 1, identical or different, representing an alkyl, the symbols R 2 , identical or different, representing a hydrogen atom, a hydrocarbon chain or a hydrocarbon chain substituted by a tertiary amine function, y being an integer ranging from 0 to 2.

3. Rubber composition according to any one of claims 1 to 2 in which the silicon atom of the silanol or alkoxysilane function of the functional group carried at the end of the chain by the copolymer is attached directly to the terminal unit of the copolymer.

4. Rubber composition according to claim 2 or 3 in which the symbols R 1 are methyl or ethyl, the symbols R 2 are methyl or ethyl or 1,3-propanediyl carrying a tertiary amine function.

5. Rubber composition according to any one of claims 1 to 4 in which the 1,3-diene is 1,3-butadiene or a mixture of 1,3-dienes of which one is 1,3-butadiene, preferably 1,3-butadiene.

6. A rubber composition according to any one of claims 1 to 5 wherein the copolymer is a copolymer of ethylene and 1,3-butadiene.

7. A rubber composition according to any one of claims 1 to 6 wherein the copolymer is a random copolymer.

8. Rubber composition according to any one of claims 1 to 7 in which the silica represents more than 50% by mass of the reinforcing filler, preferably more than 85% by mass of the reinforcing filler.

9. Rubber composition according to any one of claims 1 to 8 in which R3 in formula (2) is chosen from the hydrogen atom, C1-C10 alkyls and C2-C10 alkenyls, preferably is a linear C1-C8 alkyl, more preferably is heptyl.

10. A rubber composition according to any one of claims 1 to 9 wherein each R4 in formulas (2) and (3) is independently a linear C1-C4 alkylene, preferably propylene.

11. A rubber composition according to any one of claims 1 to 10 wherein each Z b in formulas (2) and (3) is independently selected from the group consisting of the units of formula (-O-)o,s, [— OCH2CH2CH2O— ]o,s, [-OCH2CH2CH2CH2O- ]o,5 and [-OCH2CH(CH3)CH20-]O,5, preferably is of formula (-0-)o,s or [- OCH2CH(CH3)CH20-]O,5.

12. A rubber composition according to any one of claims 1 to 11 wherein each Z c in formulas (2) and (3) is independently chosen from the group consisting of the units of formula [-OCH2CH2CH20-]o,s, [-OCH2CH2CH2CH20-]o,s and [-OCH2CH(CH3)CH20-]O,5, preferably is of formula [-OCH2CH(CH3)CH20-]o,s.

13. A rubber composition according to any one of claims 1 to 12 wherein each X in formulas (2) and (3) is independently selected from the group consisting of hydroxyl, methoxy, ethoxy, methyl, ethyl, 3-hydroxypropoxy, 3-hydroxy-2-methylpropoxy and 4-hydroxybut-1-oxy, preferably each X in formulas (2) and (3) is identical and is selected from the group consisting of hydroxyl, methoxy, ethoxy and 3-hydroxy-2-methylpropoxy.

14. Rubber composition according to any one of claims 1 to 13 in which the organofunctional silane has a molar percentage of blocked mercaptosilane units (A) ranging from 20 to 80% and a molar percentage of mercaptosilane units (B) ranging from 80 to 20%, preferably the organofunctional silane has a molar percentage of blocked mercaptosilane units (A) ranging from 40 to 60% and a molar percentage of mercaptosilane units (B) ranging from 60 to 40%, more preferably the organofunctional silane has a molar percentage of blocked mercaptosilane units ranging from 50 to 55% and a molar percentage of mercaptosilane units ranging from 50 to 45%.

15. A tire which comprises a tread, which tire comprises a rubber composition defined in any one of claims 1 to 14, preferably in its tread.

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