POLYMER COMPOSITION WITH A BRANCHED THERMOPLASTIC ELASTOMER AND A THERMOPLASTIC STYRENE POLYMER

Description

[0001] The present invention relates to a polymeric composition comprising a particular styrenic thermoplastic elastomer and a styrenic thermoplastic polymer, as well as to a tire comprising layers or parts formed from such a composition, said layers or parts being able to be in particular all or part of a tread.

[0002] In a conventional tire, the tread generally comprises mainly by weight one or more diene elastomers.

[0003] A constant objective of tire manufacturers is to improve tire grip on wet surfaces. At the same time, another objective is to reduce tire rolling resistance. However, these two objectives are difficult to reconcile in that improving grip requires increasing hysteretic losses, while improving rolling resistance requires reducing hysteretic losses. There is therefore a performance compromise to be optimized.

[0004] Therefore, the applicants have previously developed tires with a tread comprising a thermoplastic elastomer. These tires offer a very good compromise between grip and rolling resistance performance.

[0005] But the room temperature stiffness of the treads can still be improved.

[0006] Furthermore, thermoplastic elastomer treads are easy to use due to their low viscosity at temperature.

[0007] However, on the finished tire, the low high temperature stiffness sought for implementation may then be a problem for the tire's performance, particularly in use at high temperatures. Indeed, during tire usage cycles such as braking, this can result in extreme cases in a softening of the tread which would have the consequence of reducing the endurance of the tread.

[0008] This way, the temperature resistance performance of the treads can be further improved.

[0009] Therefore, there is a need to improve the temperature resistance of thermoplastic elastomer treads, i.e. to limit the drop in rigidity when the temperature increases, without degrading the possibilities of implementing these treads.

[0010] Furthermore, it is advantageous for the tread to have good mechanical properties, particularly in terms of rigidity for a given breaking elongation.

[0011] Finally, the formulations of elastomer compositions are often complex to provide a certain rigidity. There is therefore also a need to simplify these formulas.

[0012] The applicants have now unexpectedly discovered that a polymeric composition comprising a) 50 to 100 pce of one or more branched thermoplastic elastomers each comprising an unsaturated elastomer block and at least three styrenic thermoplastic blocks, the styrenic thermoplastic blocks of each branched thermoplastic elastomer representing from 15 to 50%, by weight of the weight of each branched thermoplastic elastomer, b) 10 to 100 pce of one or more styrenic thermoplastic polymers with a weight-average molecular mass of between 25,000 and 300,000 g / mol, preferably between 50,000 and 200,000 g / mol, making it possible to meet the constraints previously formulated, namely improvement of rigidity at room temperature, thermal stability, improvement of mechanical properties and simplification of the formulation.

[0013] Thus, the subject of the invention is a polymeric composition comprising a) 50 to 100 pce of one or more branched thermoplastic elastomers each comprising an unsaturated elastomer block and at least three styrenic thermoplastic blocks, the styrenic thermoplastic blocks of each branched thermoplastic elastomer representing from 15 to 50%, by weight of the weight of each branched thermoplastic elastomer, b) 10 to 100 pce of a styrenic thermoplastic polymer with a weight-average molecular mass of between 25,000 and 300,000 g / mol, preferably between 50,000 and 200,000 g / mol.

[0014] In the present invention, any interval of values ​​designated by the expression "between a and b" represents the domain of values ​​going from more than a to less than b (i.e., limits a and b excluded) while any interval of values ​​designated by the expression "from a to b" means the domain of values ​​going from a up to b (i.e., including the strict limits a and b).

[0015] In the present application, the term "part per cent of elastomer" or "pce" means the part by weight of a constituent per 100 parts by weight of the elastomer(s) of the elastomeric matrix, i.e. of the total weight of the elastomer(s), whether thermoplastic or non-thermoplastic, present in the elastomeric matrix. Thus, a constituent at 60 pce will mean, for example, 60 g of this constituent per 100 g of elastomer of the elastomeric matrix.

[0016] Thermoplastic elastomer (TPE) is understood to mean, as is known, a polymer with an intermediate structure between a thermoplastic polymer and an elastomer.

[0017] A thermoplastic elastomer generally consists of one or more rigid "thermoplastic" segments connected to one or more flexible "elastomeric" segments.

[0018] The branched thermoplastic elastomer(s) present in the composition according to the invention are thus made up of a flexible “elastomer” segment and at least three rigid “thermoplastic” segments.

[0019] Thus, the branched thermoplastic elastomer(s) of the composition according to the invention comprise an elastomer block and at least three thermoplastic blocks.

[0020] Typically, each of these segments or blocks contains at least more than 5, usually more than 10, basic units.

[0021] In the present application, when reference is made to the glass transition temperature of a thermoplastic elastomer, this is the glass transition temperature relative to the elastomer block (unless otherwise indicated). Indeed, as is known, thermoplastic elastomers have two glass transition temperature peaks (Tg, measured according to ASTM D3418), the lower temperature being relative to the elastomer part of the thermoplastic elastomer, and the higher temperature being relative to the thermoplastic part of the thermoplastic elastomer. Thus, the flexible blocks of thermoplastic elastomers are generally defined by a Tg less than or equal to room temperature (25°C), while the rigid blocks have a Tg greater than or equal to 80°C.To be both elastomeric and thermoplastic in nature, the thermoplastic elastomer must have blocks that are sufficiently incompatible (i.e. different due to their respective mass, polarity or Tg) to retain their own properties as elastomeric or thermoplastic blocks.

[0022] Thus, the thermoplastic elastomer(s) that can be used according to the invention (therefore the elastomer block(s) of the thermoplastic elastomers) preferably have a glass transition temperature that is less than or equal to 25°C, more preferably less than or equal to 10°C. A Tg value higher than these minima can reduce the performance of the tread when used at very low temperatures; for such use, the glass transition temperature of the thermoplastic elastomers is more preferably still less than or equal to -10°C.

[0023] Also preferably, the glass transition temperature of the thermoplastic elastomers which can be used according to the invention is greater than -100°C.

[0024] The number-average molecular mass (Mn) of thermoplastic elastomers is preferably between 30,000 and 500,000 g / mol, more preferably between 40,000 and 400,000 g / mol. Below the indicated minima, the cohesion between the elastomer chains of thermoplastic elastomers, in particular due to their possible dilution (in the presence of an extender oil), risks being affected; on the other hand, an increase in the operating temperature risks affecting the mechanical properties, in particular the breaking properties, resulting in reduced performance "when hot". Furthermore, an excessively high Mn mass can be detrimental to implementation. Thus, it has been found that a value between 50,000 and 300,000 g / mol is particularly well suited to the use of thermoplastic elastomers in a tire tread.

[0025] The number-average molecular mass (Mn) and the weight-average molecular mass (Mw) of thermoplastic elastomers are determined in a known manner, by size exclusion chromatography (SEC). The sample is first solubilized in a suitable solvent at a concentration of approximately 2 g / l; then the solution is filtered through a 0.45 µm porosity filter before injection. The equipment used is a “WATERS alliance” chromatographic chain. The injected volume of the polymer sample solution is 100 µl. The detector is a “WATERS 2410” differential refractometer and its associated software for processing chromatographic data is the “EMPOWER” system. The conditions can be adapted by those skilled in the art.For example, in the case of styrenic thermoplastic elastomers, the sample is first solubilized in tetrahydrofuran at a concentration of approximately 1 g / L; then the solution is filtered through a 0.45 µm porosity filter before injection. The equipment used is a “WATERS alliance” chromatographic chain. The elution solvent is tetrahydrofuran, the flow rate is 0.7 mL / min, the system temperature is 35°C and the analysis time is 90 min. A set of four WATERS columns in series, with the trade names “STYRAGEL” (“HMW7”, “HMW6E” and two “HT6E”), is used. The injected volume of the polymer sample solution is 100 µL. The detector is a “WATERS 2410” differential refractometer and its associated software for processing chromatographic data is the “WATERS MILLENIUM” system. The calculated average molar masses are relative to a calibration curve produced with polystyrene standards.

[0026] The polydispersity index (Ip = Mw / Mn with Mw weight average molecular mass) of the thermoplastic elastomer(s) is preferably less than 3; more preferably less than 2, and even more preferably less than 1.5.

[0027] The branched thermoplastic elastomers which can be used according to the invention preferably each comprise in total less than 10 blocks (elastomer(s) and thermoplastic), preferably from 4 to 8, more preferably from 4 to 5.

[0028] Preferably, the blocks of branched thermoplastic elastomers usable according to the invention have masses, preferably weight-average molecular masses (Mw), greater than 2000 g / mol, preferably greater than 5000 g / mol, more preferably greater than 10000 g / mol.

[0029] The thermoplastic elastomers present in the composition according to the invention are in a branched form, also sometimes called ramified. These branched thermoplastic elastomers can then be composed of a branched elastomer block and thermoplastic blocks, located at the end of each of the branches of the elastomer block.

[0030] According to a particular embodiment, the branched thermoplastic elastomer(s) usable according to the invention are in a star-shaped form with at least three branches.

[0031] For example, the thermoplastic elastomers may then consist of a star-shaped elastomer block with at least three branches and a thermoplastic block, located at the end of each of the branches of the elastomer block. The number of branches of the central elastomer may vary, for example from 3 to 12, and preferably from 3 to 6.

[0032] According to another particular embodiment, the branched thermoplastic elastomers usable according to the invention are in a dendrimer form.

[0033] Thus, according to this embodiment, the thermoplastic elastomers may consist of a dendrimer elastomer block and thermoplastic blocks located at the end of each of the branches of the elastomer block. By dendrimer elastomer block is meant an elastomer block having at least two branches, each branch itself dividing into at least two sub-branches, such a division being able to be reproduced over several generations, like the branches of a tree.

[0034] As explained previously, the branched thermoplastic elastomer(s) present in the composition according to the invention comprise at least one unsaturated elastomer block and at least three thermoplastic blocks.

[0035] By unsaturated elastomer block, we mean that this block is derived at least in part from conjugated diene monomers, having a rate of units or motifs of diene origin (conjugated dienes) which is greater than 15% by mole.

[0036] We can also speak of an “essentially unsaturated” elastomer block.

[0037] A “highly unsaturated” elastomer block is also understood to mean an elastomer block having a content of units of diene origin (conjugated dienes) which is greater than 50% by mole.

[0038] The unsaturated elastomer blocks that can be used according to the invention can be chosen from: a) 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 conjugated dienes with each other or with one or more aromatic vinyl compounds having from 8 to 20 carbon atoms; c) a ternary copolymer obtained by copolymerization of ethylene, an α-olefin having from 3 to 6 carbon atoms with a non-conjugated diene monomer having from 6 to 12 carbon atoms, such as for example elastomers obtained from ethylene, propylene with a non-conjugated diene monomer of the aforementioned type such as in particular hexadiene-1,4, ethylidene norbornene, dicyclopentadiene; (d) a copolymer of isobutene and isoprene (butyl diene rubber), as well as halogenated, in particular chlorinated or brominated, versions of this type of copolymer.

[0039] Suitable conjugated dienes include, in particular, isoprene, 1,3-butadiene, piperylene, 1-methylbutadiene, 2-methylbutadiene, 2,3-dimethyl-1,3-butadiene, 2,4-dimethyl-1,3-butadiene, 1,3-pentadiene, 2-methyl-1,3-pentadiene, 3-methyl-1,3-pentadiene, 4-methyl-1,3-pentadiene, 2,3-dimethyl-1,3-pentadiene, 2,5-dimethyl-1,3-pentadiene, 2-methyl-1,4-pentadiene, 1,3-hexadiene, 2-methyl-1,3-hexadiene, 2-methyl-1,5-hexadiene, 3-methyl-1,3-hexadiene, 4-methyl-1,3-hexadiene, 5-methyl-1,3-hexadiene, 2,5-dimethyl-1,3-hexadiene, 2,5-dimethyl-2,4-hexadiene, 2-neopentyl-1,3-butadiene, 1,3-cyclopentadiene, methylcyclopentadiene, 2-methyl-1,6-heptadiene, 1,3-cyclohexadiene, 1-vinyl-1,3-cyclohexadiene, and a mixture of these conjugated dienes; preferably, these conjugated dienes are selected from isoprene, butadiene and a mixture containing isoprene and / or butadiene.

[0040] According to one variant, the monomers polymerized to form an unsaturated elastomer block may be copolymerized, in a statistical manner, with at least one other monomer so as to form an unsaturated elastomer block. According to this variant, the molar fraction of polymerized monomer other than a diene monomer, relative to the total number of units of the unsaturated elastomer block, must be such that this block retains its unsaturated elastomer properties. Advantageously, the molar fraction of this other comonomer may range from 0 to 50%, more preferably from 0 to 45% and even more preferably from 0 to 40%.

[0041] By way of illustration, this other monomer capable of copolymerizing with the first monomer may be chosen from ethylenic monomers such as ethylene, propylene, butylene, vinylaromatic monomers having from 8 to 20 carbon atoms as defined below or else, it may be a monomer such as vinyl acetate.

[0042] Suitable vinylaromatic compounds include styrenic monomers, namely methylstyrenes, para-tert-butylstyrene, chlorostyrenes, bromostyrenes, fluorostyrenes or para-hydroxystyrene. Preferably, the vinylaromatic comonomer is styrene.

[0043] Thus, according to one embodiment, the elastomer block may be a random copolymer of the styrene-butadiene type (SBR), this copolymer possibly being partially hydrogenated. This SBR block preferably has a Tg (glass transition temperature) measured by DSC according to the ASTM D3418 standard of 1999, less than 25°C, preferably less than 10°C, more preferably less than 0°C and very preferably less than -10°C. Also preferably, the Tg of the SBR block is greater than -100°C. SBR blocks having a Tg of between 20°C and -70°C and more particularly between 0°C and -50°C are particularly suitable. As is well known, the SBR block comprises a styrene content, a -1,2 bond content of the butadiene portion, and a -1,4 bond content of the butadiene portion, the latter consisting of a trans-1,4 bond content and a cis-1,4 bond content when the butadiene portion is not hydrogenated.Preferably, an SBR block is used in particular having a styrene content of, for example, in a range from 10% to 60% by weight, preferably from 20% to 50% by weight, and for the butadiene part, a content of -1,2 bonds of a range from 4% to 75% (mol%), and a content of -1,4 bonds of a range from 20% to 96% (mol%).

[0044] The hydrogenation rate is determined by NMR analysis. The spectra are acquired on a BRUKER Avance 500 MHz spectrometer equipped with a 1H-X 5 mm Cryoprobe. The quantitative 1H NMR experiment uses a single 30° pulse sequence and a 5-second repetition delay between each acquisition. 64 accumulations are performed. The samples (approximately 25 mg) are solubilized in CS2 approximately 1 mL, 100 µl of deuterated cyclohexane are added to lock during the acquisition. The chemical shifts are calibrated relative to the protonated impurity of CS2 δppm 1H at 7.18 ppm referenced on the TMS (δppm 1H at 0 ppm). The 1H NMR spectrum allows the microstructure to be quantified by integrating the signal massifs characteristic of the different patterns: Styrene from SBR and polystyrene blocks. It is quantifiable in the aromatic range between 6.0 ppm and 7.3 ppm for 5 protons (by removing the signal integral of the CS2 impurity at 7.18 ppm). PB1-2 from SBR. It is quantifiable in the ethylenic range between 4.6 ppm and 5.1 ppm for 2 protons. PB1-4 from SBR. It is quantifiable in the ethylenic range between 5.1 ppm and 6.1 ppm for 2 protons and by removing 1 proton from the PB1-2 unit. Hydrogenated PB1-2 from hydrogenation and having only aliphatic protons. The CH3 pendants of hydrogenated PB1-2 have been identified and are quantifiable in the aliphatics range between 0.4 and 0.8 ppm for 3 protons. Hydrogenated PB1-4 from hydrogenation and having only aliphatic protons. It will be deduced by subtraction of the aliphatic protons from the different patterns by considering it for 8 protons.

[0045] Microstructure quantification can be performed in mol% as follows: mol% of a unit = 1H integral of a unit / Σ(1H integrals of each unit). For example, for a styrene unit: mol% of styrene = (1H integral of styrene) / (1H integral of styrene + 1H integral of PB1-2 + 1H integral of PB1-4 + 1H integral of hydrogenated PB1-2 + 1H integral of hydrogenated PB1-4).

[0046] Preferably, in the thermoplastic elastomers useful for the purposes of the invention, the SBR elastomer block is hydrogenated in such a way that a proportion ranging from 10 to 80 mol% of the double bonds in the butadiene portion are hydrogenated. Preferably for the invention, the elastomer blocks of the branched thermoplastic elastomers have in total a number-average molecular weight ("Mn") ranging from 25,000 g / mol to 350,000 g / mol, preferably from 35,000 g / mol to 250,000 g / mol so as to give the thermoplastic elastomers good elastomeric properties and sufficient mechanical strength compatible with use in tire treads.

[0047] Preferably in the invention, the unsaturated elastomer block is chosen from the group consisting of polyisoprenes, polybutadienes, copolymers of butadiene and isoprene, copolymers of styrene and butadiene, and mixtures of these elastomers, these elastomers being non-hydrogenated or partially hydrogenated.

[0048] Particularly preferably, the unsaturated elastomer block is chosen from polybutadienes.

[0049] As explained previously, the branched thermoplastic elastomers present in the composition according to the invention also comprise at least three styrenic thermoplastic blocks.

[0050] By thermoplastic block is meant a block consisting of polymerized monomers and having a glass transition temperature, or a melting temperature in the case of semi-crystalline polymers, greater than or equal to 80°C, preferably varying from 80°C to 250°C, more preferably varying from 80°C to 200°C, and in particular varying from 80°C to 180°C.

[0051] Indeed, in the case of a semi-crystalline polymer, a melting temperature higher than the glass transition temperature can be observed. In this case, the melting temperature is taken into account for the above definition and not the glass transition temperature.

[0052] A styrenic thermoplastic block means a thermoplastic block comprising units derived from one or more styrenic monomers.

[0053] Preferably, the styrenic thermoplastic blocks each consist of more than 75% by weight, preferably more than 85% by weight, more preferably more than 95% by weight, better still 100% by weight, relative to the weight of the styrenic thermoplastic block, of units derived from one or more styrenic monomers.

[0054] Preferably, the styrenic monomer(s) are selected from styrene, o-, m- or p-methylstyrene, alpha-methylstyrene, beta-methylstyrene, 2,6-dimethylstyrene, 2,4-dimethylstyrene, alpha-methyl-o-methylstyrene, alpha-methyl-m-methylstyrene, alpha-methyl-p-methylstyrene, beta-methyl-o-methylstyrene, beta-methyl-m-methylstyrene, beta-methyl-p-methylstyrene, 2,4,6-trimethylstyrene, alpha-methyl-2,6-dimethylstyrene, alpha-methyl-2,4-dimethylstyrene, beta-methyl-2,6-dimethylstyrene, beta-methyl-2,4-dimethylstyrene, o-, m- or p-chlorostyrene, 2,6-dichlorostyrene, 2,4-dichlorostyrene, alpha-chloro-o-chlorostyrene, alpha-chloro-m-chlorostyrene, alpha-chloro-p-chlorostyrene, beta-chloro-o-chlorostyrene, beta-chloro-m-chlorostyrene, beta-chloro-p-chlorostyrene, 2,4,6-trichlorostyrene, alpha-chloro-2,6-dichlorostyrene, alpha-chloro-2,4-dichlorostyrene, beta-chloro-2,6-dichlorostyrene, beta-chloro-2,4-dichlorostyrene o-, m- or p-butylstyrene, o-, m- or p-methoxystyrene, o-, m- or p-chloromethylstyrene, o-, m- or p-bromomethylstyrene, styrene derivatives substituted by a silyl group, and mixtures of these monomers.,

[0055] Most preferably, the styrenic monomer(s) are chosen from styrene, alpha-methylstyrene, and mixtures of these monomers, and more preferably the styrenic monomer is styrene.

[0056] Advantageously, the styrenic thermoplastic blocks of each branched thermoplastic elastomer of the composition according to the invention represent from 20 to 50%, preferably from 20 to 40%, by weight of the weight of each branched thermoplastic elastomer.

[0057] As explained previously, the composition according to the invention comprises 50 to 100 pce of the branched thermoplastic elastomer(s) as described previously.

[0058] Preferably, said thermoplastic elastomer(s) represent from 70 to 100 pce, preferably from 80 to 100 pce of the composition according to the invention.

[0059] In addition to the branched thermoplastic elastomer(s) as defined above, the composition according to the invention may contain other elastomers, such as diene elastomers or non-branched and / or non-styrenic thermoplastic elastomers, representing from 0 to 50 phr, preferably from 0 to 30 phr, more preferably from 0 to 20 phr.

[0060] It is also possible that the composition according to the invention comprises one or more non-thermoplastic elastomers.

[0061] Preferably, the branched thermoplastic elastomer(s) as defined above are the only elastomers in the composition. In other words, the branched thermoplastic elastomer(s) defined above, according to this preferred embodiment, represent 100 phr of the polymeric composition according to the invention.

[0062] As explained above, the polymeric composition according to the invention comprises 10 to 100 pce of one or more styrenic thermoplastic polymers with a weight-average molecular mass (Mw) of between 25,000 and 300,000 g / mol, preferably between 50,000 and 200,000 g / mol.

[0063] By thermoplastic polymer is meant a thermoplastic polymer having a glass transition temperature, or a melting temperature in the case of semi-crystalline polymers, greater than or equal to 80°C, preferably varying from 80°C to 250°C, more preferably varying from 80°C to 200°C, and in particular varying from 80°C to 180°C.

[0064] Indeed, in the case of a semi-crystalline polymer, a melting temperature higher than the glass transition temperature can be observed. In this case, the melting temperature is taken into account for the above definition and not the glass transition temperature.

[0065] It is clear that a thermoplastic polymer within the meaning of the present invention is not a thermoplastic elastomer.

[0066] A styrenic thermoplastic polymer means a thermoplastic polymer comprising units derived from one or more styrenic monomers.

[0067] The average molecular mass of a styrenic thermoplastic polymer is preferably understood to mean the weight-average molecular mass.

[0068] Preferably, the styrenic thermoplastic polymer(s) consist of more than 75% by weight, preferably more than 85% by weight, more preferably more than 95% by weight, better still 100% by weight, of units derived from one or more styrenic monomers.

[0069] The styrenic monomer(s) that can be used for the thermoplastic polymer(s) can be chosen from the styrenic monomers that can be used for the styrenic thermoplastic blocks of the branched thermoplastic elastomer(s) present in the polymer composition according to the invention and cited above.

[0070] Most preferably, the styrenic monomer(s) are chosen from styrene, alpha-methylstyrene, and mixtures of these monomers, and more preferably the styrenic monomer is styrene.

[0071] Preferably, said styrenic thermoplastic polymer(s) represent from 15 to 85 pce of the composition according to the invention.

[0072] According to a first particular embodiment, the said styrenic thermoplastic polymer(s) usable in the composition according to the invention represent from 50 to 85 pce of the composition according to the invention and have a molecular mass, preferably an Mw, of between 50,000 and 100,000 g / mol.

[0073] According to a second particular embodiment, the said styrenic thermoplastic polymer(s) which can be used in the composition according to the invention represent from 15 to 50 pce of the composition according to the invention and have a molecular mass, preferably an Mw, of between 120,000 and 200,000 g / mol.

[0074] The composition according to the invention may optionally comprise one or more thermoplastic polymers other than the styrenic thermoplastic polymers described previously.

[0075] When present in the composition, non-styrenic thermoplastic polymers preferably represent less than 30 pce, preferably between 10 and 25 pce.

[0076] These non-styrenic thermoplastic polymers may in particular be poly(para-phenylene ether) polymers (abbreviated as "PPE"). These PPE thermoplastic polymers are well known to those skilled in the art; they are resins that are solid at room temperature (20°C) and compatible with styrenic polymers, which are used in particular to increase the glass transition temperature of thermoplastic elastomers whose thermoplastic block is a styrenic block (see for example "Thermal, Mechanical and Morphological Analyses of Poly (2,6-dimethyl-1, 4 phenylene oxide) / Styrene-Butadiene-Styrene Blends", Tucker, Barlow and Paul, Macromolecules, 1988, 21, 1678-1685).

[0077] Preferably, the composition does not comprise a non-styrenic thermoplastic polymer.

[0078] The composition according to the invention may comprise a crosslinking system.

[0079] When the composition includes it, the crosslinking system may in particular be a so-called vulcanization system, i.e. based on sulfur (or a sulfur-donating agent) and a vulcanization accelerator. Various known secondary accelerators or vulcanization activators such as stearic acid, zinc oxide, guanidine derivatives, retarders or antireversion agents may be added to this basic vulcanization system.

[0080] The crosslinking system can also be based on one or more peroxides.

[0081] By the expression "based on", it is meant that the crosslinking system comprises a mixture and / or the reaction product of the different constituents used in the crosslinking system, and in particular the peroxide(s), some of these basic constituents being capable of, or intended to, react with each other or with the other constituents of the composition, at least in part, during the different phases of manufacture of the composition, in particular during its crosslinking.

[0082] The peroxide(s) that can be used according to the invention may be any peroxide known to those skilled in the art.

[0083] Preferably, the peroxide(s) that can be used according to the invention are chosen from organic peroxides.

[0084] Particularly preferably, the peroxide(s) that can be used according to the invention are chosen from dialkyl peroxides such as di-tert-butyl peroxide (DTBP); dicumyl peroxide; tert-butylcumyl peroxide and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (DBPH), diacyl peroxides such as bis(2,4-di-chlorobenzoyl) peroxide (DCBP-50) and benzoyl peroxide (BP-50), acetal peroxides such as ethyl 3,3-di-(t-butylperoxy)butyrate), ester peroxides such as t-butyl peroxybenzoate and OO-(t-butyl) O-(2-ethylhexyl) monoperoxycarbonate, hydroperoxides such as t-amyl hydroperoxide, and mixtures of these compounds.

[0085] The composition can also be crosslinked by means of electron bombardment.

[0086] Preferably, this electronic bombardment is carried out by means of beta radiation.

[0087] Thus, preferably, the composition according to the invention is crosslinked by means of electron bombardment at an exposure level of at least 50 kGy, preferably ranging from 70 to 300 kGy.

[0088] Preferably, the polymeric composition according to the invention does not comprise a crosslinking system.

[0089] The polymeric composition according to the invention may also comprise one or more reinforcing fillers.

[0090] In particular, any type of filler normally used for the manufacture of tires can be used, for example an organic filler such as carbon black, an inorganic filler such as silica, or a blend of these two types of filler, in particular a blend of carbon black and silica.

[0091] Suitable carbon blacks are all carbon blacks conventionally used in tires (so-called tire-grade blacks). Examples include reinforcing carbon blacks of the 100, 200 or 300 series (ASTI grades), such as blacks N115, N134, N234, N326, N330, N339, N347, N375, or, depending on the intended applications, blacks of higher series (for example N660, N683, N772), or even N990.

[0092] By "reinforcing inorganic filler" is meant in the present application, by definition, any inorganic or mineral filler (whatever its color and origin (natural or synthetic), also called "white" filler, "clear" filler or even "non-black filler" as opposed to carbon black, capable of reinforcing on its own, without any other means than an intermediate coupling agent, a rubber composition intended for the manufacture of tires, in other words capable of replacing, in its reinforcing function, a conventional tire-grade carbon black; such a filler is generally characterized, in a known manner, by the presence of hydroxyl groups (-OH) on its surface.

[0093] The physical state in which the reinforcing inorganic filler is present is indifferent, whether in the form of powder, microbeads, granules, beads or any other suitable densified form. Of course, the term reinforcing inorganic filler also means mixtures of different reinforcing inorganic fillers, in particular highly dispersible siliceous and / or aluminous fillers as described below.

[0094] Suitable reinforcing inorganic fillers are, in particular, mineral fillers of the siliceous type, in particular silica (SiO2), or of the aluminous type, in particular alumina (Al2O3). 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 surface area and a CTAB specific surface area both of less than 450 m2 / g, preferably from 30 to 400 m2 / g. Examples of highly dispersible precipitated silicas (known as “HDS”) include “Ultrasil” 7000 and “Ultrasil” 7005 silicas from Evonik, “Zeosil” 1165MP, 1135MP and 1115MP silicas from Solvay, “Hi-Sil” EZ150G silica from PPG, “Zeopol” 8715, 8745 and 8755 silicas from Huber, and high specific surface silicas as described in application WO 03 / 16837.

[0095] To couple the reinforcing inorganic filler to the thermoplastic elastomer, it is possible, for example, to use in a known manner an at least bifunctional coupling agent (or bonding agent) intended to ensure a sufficient connection, of a chemical and / or physical nature, between the inorganic filler (surface of its particles) and the elastomer, in particular bifunctional organosilanes or polyorganosiloxanes.

[0096] The volumetric content of optional reinforcing filler in the composition (carbon black and / or reinforcing inorganic filler such as silica) is within a range from 0 to 30%, which corresponds approximately to a content of 0 to 100 phr for a composition without plasticizer. Preferably, the composition according to the invention comprises less than 30 phr of reinforcing filler and more preferably less than 10 phr.

[0097] According to a preferred variant of the invention, the composition does not contain a reinforcing filler.

[0098] In the same way, the composition according to the invention may contain one or more inert micrometric fillers such as the lamellar fillers known to those skilled in the art.

[0099] Preferably, the composition according to the invention does not contain a micrometric filler.

[0100] The composition according to the invention may also comprise various additives known to those skilled in the art. For example, one or more additives will be chosen from protective agents such as antioxidants or antiozonants, anti-UV agents, various processing agents or other stabilizers, non-reinforcing fillers.

[0101] Preferably, the composition according to the invention does not contain any of these additives.

[0102] The present invention also relates to a tire comprising at least one layer consisting of a polymeric composition as defined above.

[0103] For the purposes of the present invention, the term "layer" means a strip or any other three-dimensional element of relatively small thickness compared to its other dimensions, the ratio of the thickness to the largest of the other dimensions of which is less than 0.5, preferably less than 0.1.

[0104] Preferably, the layer is all or part of a tread.

[0105] The present invention finally relates to a tire comprising a tread comprising a polymeric composition as defined above in all or part of its tread.

[0106] The tread may be mounted on a tire in a conventional manner, said tire comprising, in addition to the tread, a crown, two sidewalls and two beads, a carcass reinforcement anchored to the two beads, and a crown reinforcement.

[0107] Optionally, the tire according to the invention may further comprise an underlayer or an adhesion layer between the sculpted portion of the tread and the crown reinforcement.

[0108] Generally speaking, the tire according to the invention is intended to equip motor vehicles of the passenger car type, SUVs (“Sport Utility Vehicles”), two-wheelers (in particular motorcycles), airplanes, as well as industrial vehicles such as vans, heavy goods vehicles and other transport or handling vehicles.

[0109] Heavy goods vehicles include, in particular, metros, buses and road transport vehicles such as trucks, tractors, trailers and off-road vehicles such as agricultural or civil engineering machinery.

[0110] The process for preparing a tire as defined above generally includes the following steps: extrusion or co-extrusion of the tread, then installation of the extruded tread on the tire, then curing of the tire.

[0111] Thus, the tread of the tire according to the invention is first of all prepared in a conventional manner, by incorporating the different components into a twin-screw extruder, so as to achieve the fusion of the matrix and incorporation of all the ingredients, then use of a die to produce the profile.

[0112] The various components of the tread are in particular the thermoplastic elastomers seen previously which are available for example in the form of beads or granules.

[0113] The tread is then placed on the tire.

[0114] The tire is then baked. The tread is then usually sculpted into the tire baking mold. Examples Tensile tests

[0115] These tensile tests allow the determination of the elastic moduli and the properties at break and are based on the French standard NF T 46-002 of September 1988. A treatment of the tensile recordings also allows the plotting of the modulus curve as a function of the elongation. The modulus used here is the true secant modulus measured at first elongation, calculated by reducing it to the initial section of the specimen. The true secant moduli (or true stresses, in MPa) at 10% elongation, noted MSV10, are measured at first elongation at 23°C ± 2°C. G* module measurements

[0116] The dynamic complex modulus G* is measured on a viscoanalyzer (Metravib V A4000). The response of a composition sample (cylindrical specimen 4 mm thick and 400 mm2 in cross-section), subjected to sinusoidal stress in alternating simple shear, at an imposed stress of 0.7 MPa at a frequency of 10 Hz, is recorded as a function of temperature according to ASTM D 1349-99. In particular, the values ​​of the G* modulus at 23 and 80°C are recorded. Preparation of the compositions

[0117] The following compositions are prepared. The formulations are given in Table 1 and are expressed in pce, the SBS being considered here as an elastomer in its entirety.

[0118] Composition A0 is a reference composition, with the usual means of obtaining high modulus elastomer mixtures.

[0119] The composition C0 is given for comparison because it includes a linear type SBS.

[0120] Compositions C1 and C2 comply with the invention (star SBS + PS).

[0121] Similarly, composition C3 is given for comparison because it includes a PS with a molecular mass of less than 25000g / mol.

[0122] Finally, compositions C4 and C5 are in accordance with the present invention. Table 1 Compositions A0 C0 C1 C2 C3 C4 C5 Linear SBS (a) 100 SBS Star (b) 100 100 100 100 100 Low weight polystyrene (c) 76 Medium weight polystyrene (d) 22 22 76 High-weight polystyrene (e) 22 76 NR (f) 100 Carbon black (g) 75 Paraffinic oil (i) 3 Rosin (j) 2 Diphenylolpropane (k) 7 Formophenolic resin (h) 5 Cobalt resinate (l) 3 Hexamethoxymethylmelamine (m) 6 ZnO (n) 9 Stearic acid (o) 1 6PPD (p) 2 HMT (q) 3 Sulfur 5 CBS (r) 1 (a) SBS linear copolymer comprising 30% Kraton D1101 polystyrene (Mw=110000 g / mol) (b) SBS star copolymer comprising 31% Kraton D1184 polystyrene (Mw=200000 g / mol) (c) Polystyrene of Mw 1200g / mol: Scientific Polymer (d) Polystyrene of Mw 35000g / mol: Sigma Aldrich (e) Polystyrene of Mw 192000g / mol: Sigma Aldrich (f) Natural rubber (g) Carbon black N326 (denomination according to ASTM D-1765); (h) Novolac formophenolic resin (“Peracit 4536K” from Perstorp); (i) Paraffinic oil (Tudalen 1968 - Klaus Company, Dahkele) (j) Rosin (from Sigma-Aldrich Company) (k) Diphenylolproprane (from Chimprom Company) (l) Cobalt resinate (from Pfaltz and Bauer Company) (m) Hexamethoxymethylmelamine (Westco HMM from Western Reserve Chemical Company) (n) Zinc oxide (industrial grade - Umicore Company); (o) Stearin (Pristerene 4931 from Uniqema Company); (p) N-1,3-dimethylbutyl-N-phenylparaphenylenediamine (Santoflex 6-PPD from Flexsys Company);(q)Hexamethylenetetramine (from Degussa); (r) N-cyclohexyl-benzothiazyl sulphenamide (Santocure CBS from Flexsys).;

[0123] The mixtures are made using the internal mixer, according to the procedure indicated below: Temperature Actions 90°C Introduction to TPS 100°C Introduction of polystyrene 105°C Pestle blow 115°C Pestle blow 125°C Fall of the mixture

[0124] Once the mixtures have been obtained and dropped, they are shaped under pressure to be able to characterize them. Temperature: 130°C Time: approximately 1 min Pressure: approximately 30 bars 1. Dynamic properties

[0125] The mixtures are characterized in terms of dynamic properties. Table 2 illustrates both the G* modulus values ​​achieved and their temperature retention for the compositions according to the invention C1, C2, C4 and C5. Table 2 Composition G* 23°C (MPa) G* 80°C (MPa) Ratio (%) (G*80°C / G*23°C) A0 27,3 19 69,6 C0 7,9 1,5 19,0 C1 45,1 17,8 39,5 C2 38,8 23,6 60,8 C3 76,1 1,18 1,6 C4 120 29 24,2 C5 183 121 66,1

[0126] We note, by comparing the modulus levels of composition C1 (star SBS) with composition C0 (linear SBS), that these are much more significant and that the thermal stability (ratio G*(80°C) / G*(23°C)) is improved.

[0127] This improvement in modulus and thermal stability (delayed drop at a higher temperature, which results in a higher G*(80°C) / G*(23°C) ratio) is even more marked with composition C2 (star-spangled SBS with a higher mass PS than in C1).

[0128] Similarly, a similar improvement in the modulus and thermal resistance properties of compositions C4 and C5 is observed compared to composition C3.

[0129] Thus, if we consider the modulus ratios between 80°C and 23°C (temperature stability criterion), we see that these are much higher when high mass polystyrene (C2 compared to C1 or C4 and C5 compared to C3) is used. In these cases, we also have temperature stabilities close to the A0 composition. 2. Mechanical properties

[0130] The same compositions are also characterized in terms of mechanical properties.

[0131] The results giving the elongations at break and the true secant moduli (TSM) are presented in Table 3. Table 3 Composition Elongation at Break (%) MSV 10% (MPa) Elongation at break (base 100) MSV 10% (base 100) A0 183 60,2 16 336 C0 1110 17,9 100 100 C1 1110 38,3 100 214 C2 1060 53 95 296

[0132] The better temperature stability is also accompanied by better mechanical properties seen in elongation. Thus, by comparing C1 to C0 (star vs. linear), we note that the rigidity (true secant modulus at low deformation) is doubled for the same elongation at break.

[0133] Similarly, comparing C2 to C1 (higher weight polystyrene compared to medium weight polystyrene), we note that the properties are further improved (higher modulus for almost identical elongation at break).

[0134] Similarly, C2 presents a more interesting property balance than A0, with a 10% MSV of the same order but much better elongation-to-break properties.

Claims

1. Polymer composition comprising a) 50 to 100 phr of one or more branched thermoplastic elastomers each comprising an unsaturated elastomer block and at least three thermoplastic styrene blocks, the thermoplastic styrene blocks of each branched thermoplastic elastomer representing from 15% to 50%, by weight of the weight of each branched thermoplastic elastomer, b) 10 to 100 phr of one or more thermoplastic styrene polymers having a weight-average molecular mass of between 25 000 and 300 000 g / mol, preferably between 50 000 and 200 000 g / mol.

2. Composition according to any one of the preceding claims, characterized in that the branched thermoplastic elastomer(s) are in a star-branched form comprising at least three branches or in a dendrimer form.

3. Composition according to any one of the preceding claims, characterized in that the thermoplastic styrene blocks each consist of more than 75% by weight, preferably of more than 85% by weight, more preferably of more than 95% by weight, better still of 100% by weight, relative to the weight of the thermoplastic styrene block, of units derived from one or more styrene monomers.

4. Composition according to any one of the preceding claims, characterized in that the thermoplastic styrene blocks of each branched thermoplastic elastomer represent from 20% to 50%, preferably from 20% to 40%, by weight of the weight of each branch thermoplastic elastomer.

5. Composition according to any one of the preceding claims, characterized in that said thermoplastic elastomer(s) represent from 70 to 100 phr, preferably from 80 to 100 phr of the composition.

6. Composition according to any one of the preceding claims, characterized in that the branched thermoplastic elastomer(s) represent 100 phr of the composition.

7. Composition according to any one of the preceding claims, characterized in that the thermoplastic styrene polymer(s) consist of more than 75% by weight, preferably of more than 85% by weight, more preferably of more than 95% by weight, better still of 100% by weight, of units derived from one or more styrene monomers.

8. Composition according to any one of Claims 3 à 7, characterized in that the styrene monomer of the thermoplastic styrene blocks is styrene.

9. Composition according to any one of the preceding claims, characterized in that the thermoplastic styrene polymer(s) represent from 15 to 85 phr of the composition.

10. Composition according to any one of the preceding claims, characterized in that said thermoplastic styrene polymer(s) that can be used in the composition according to the invention represent from 50 to 85 phr of the composition according to the invention and have a weight-average molecular mass of between 50 000 and 100 000 g / mol.

11. Composition according to any one of Claims 1 to 9, characterized in that said thermoplastic styrene polymer(s) that can be used in the composition according to the invention represent from 15 to 50 phr of the composition according to the invention and have a weight-average molecular mass of between 120 000 and 200 000 g / mol.

12. Composition according to any one of the preceding claims, characterized in that it comprises a crosslinking system selected from vulcanization systems and crosslinking systems based on one or more peroxides.

13. Composition according to any one of Claims 1 to 11, characterized in that it is crosslinked by means of electron bombardment.

14. Tyre comprising at least one layer consisting of a polymer composition as defined in any one of Claims 1 to 13.

15. Tyre comprising a tread comprising a polymer composition as defined in any one of Claims 1 to 13 in all or part of its tread.