Polymer composition comprising a mixture of thermoplastic elastomers

Abstract

The invention relates to a polymer composition comprising a first block thermoplastic elastomer of formula ABA, wherein A is a thermoplastic block consisting predominantly by mole of α-methylstyrene units and B is a diene elastomer block consisting of more than 95% by mass of diene units relative to the mass of the diene elastomer block; and a second block thermoplastic elastomer of formula A'-B'-A', wherein A' is a thermoplastic block consisting predominantly by mole of α-methylstyrene units and B' is a statistical copolymer elastomer block consisting of diene units and vinylaromatic units. Such a composition exhibits improved processability and maintained or even improved stiffness. The invention also relates to finished or semi-finished products comprising this composition for the manufacture of tires, or to a tire tread comprising such a composition.

Description

Title of the invention: Polymer composition comprising a mixture of thermoplastic elastomers. Technical field

[0001] The present invention relates to a polymer composition comprising thermoplastic elastomers based on diene units and units comprising aromatic motifs. Previous technique

[0002] In the field of motor vehicle tires, the Applicant has previously developed rubber compositions comprising at least one thermoplastic elastomer. These tires offer a very good compromise between grip and rolling resistance performance, as well as good road handling.

[0003] Thermoplastic elastomers (or TPEs) are elastomers of great interest in many fields due to their combined properties, linked on the one hand to the flexible elastomer block and on the other hand to the rigid thermoplastic block. Furthermore, the bonding of the rigid thermoplastic blocks gives the material the behavior of a cross-linked elastomer. Indeed, the rigid nodules, formed by areas where the thermoplastic blocks bond together, act as cross-linking nodes. The material is therefore rigid and does not flow. However, when the temperature is raised above the glass transition temperature or the melting temperature of the rigid blocks, the polymer will flow, allowing the material to be shaped. The material regains its rigidity when the temperature returns to the operating temperature, which is lower than the glass transition temperature (Tg) of the thermoplastic blocks.This characteristic of very small businesses implies a very wide range of potential applications.

[0004] Among the most widespread thermoplastic elastomers are styrene block copolymers, known as styrene TPEs. The glass transition temperature (Tg) of polystyrene blocks is around 80°C to 100°C, depending on the size of the polystyrene blocks. For some applications, the Tg value of polystyrene blocks is insufficient. Indeed, this value does not allow for the use of these TPEs in the manufacture of certain objects subjected, in particular, to specific operating conditions where temperatures exceed 100°C.

[0005] As other styrenic TPEs, copolymers having poly(α-methylstyrene) blocks instead of polystyrene blocks have been proposed because they have the advantage of exhibiting high thermal resistance attributed to the high Tg of approximately 150-170°C of rigid poly(α-methylstyrene) blocks. These thermoplastic elastomers are widely described in the state of the art, in academic literature, and in patent documentation such as document WO2007112232A2 or document FR2243214.

[0006] The Applicant has previously developed compositions for tires, in particular for tire tread, comprising a thermoplastic elastomer, as in document WO20122152686 or more recently, in document WO2023202915A1 describing a TPE matrix comprising a triblock TPE having a diene elastomer block and two thermoplastic blocks comprising α-methylstyrene units.

[0007] A constant objective of tire manufacturers is to improve the properties of the tread, which must meet a large number of technical requirements, notably that of having a very good level of road handling on motor vehicles. To improve road handling, as is known, a certain level of tread rigidity is sought.

[0008] It is therefore desirable that a TPE composition comprising rigid blocks based on α-methylstyrene exhibit good rigidity, particularly in the manufacture of tires. To this same end, improvements in the processability and shaping of such a TPE composition are constantly being sought.

[0009] It is generally known that the use of plasticizers in combination with TPEs, in particular TPEs comprising α-methylstyrene blocks, improves their processability and shaping, as indicated in document WO2012152686 or in document WO2015 / 113966. However, it is also accepted that the use of plasticizers in a TPE composition reduces its rigidity.

[0010] An objective of the present invention is to improve the processability of a thermoplastic block TPE rubber composition comprising α-methylstyrene units, while improving or at least maintaining the rigidity of the composition. Description of the invention

[0011] This objective is achieved in that the Inventors discovered during their research that a specific rubber composition comprising a first block TPE, comprising a flexible diene block and rigid thermoplastic blocks comprising α-methylstyrene units, and a second block TPE comprising a flexible statistical copolymer block comprising units (or motifs) of diene origin and units (or motifs) of vinylaromatic origin and rigid thermoplastic blocks comprising α-methylstyrene units exhibited improved processability, without this being at the expense of the rigidity of the composition.

[0012] These significant improvements in properties make it possible to achieve a very good level of compromise between processability and road behavior of tires having a tread based on such a TPE composition.

[0013] Thus, a first object of the invention is a polymer composition comprising: - a first thermoplastic block elastomer of formula ABA, in which A is a thermoplastic block comprising predominantly by mole α-methylstyrene units and B is a diene elastomer block comprising more than 95% by mass of diene units relative to the mass of the diene elastomer block, - a second thermoplastic block elastomer of formula A'-B'-A', in which A' is a thermoplastic block comprising predominantly by mole α-methylstyrene units and B' is a statistical copolymer elastomer block comprising diene units and vinylaromatic units.

[0014] The invention also relates to finished or semi-finished products comprising a polymer composition according to the invention and intended for the manufacture of tires, in particular, a tire tread comprising such a composition.

[0015] The invention also relates to a tire comprising a polymeric composition according to the invention in all or part of its tread. Summary of the invention

[0016] The invention, described in more detail below, relates to at least one of the embodiments listed in the following points:

[0017] 1 Polymer composition comprising: - a first thermoplastic block elastomer of formula ABA, in which A is a thermoplastic block comprising predominantly by mole α-methylstyrene units and B is a diene elastomer block comprising more than 95% by mass of diene units relative to the mass of the diene elastomer block, - a second thermoplastic block elastomer of formula A'-B'-A', in which A' is a thermoplastic block comprising predominantly by mole α-methylstyrene units and B' is a statistical copolymer elastomer block comprising diene units and vinylaromatic units.

[0018] 2 Composition according to embodiment 1 in which the thermoplastic blocks A and A' comprise more than 95% by moles of α-methylstyrene units.

[0019] 3 Composition according to embodiment 1 or 2 in which the thermoplastic blocks A and A' include styrene units.

[0020] 4 Composition according to embodiment 1 or 2 in which the thermoplastic blocks A and A' are homopolymers of α-methylstyrene.

[0021] 5 Composition according to any one of the preceding embodiments in which the thermoplastic blocks A represent at least 10% by mass relative to the mass of the first thermoplastic elastomer, preferably from 10 to 45% by mass and preferably again from 10% to 40% by mass, and thermoplastic blocks A' represent at least 10% by mass relative to the mass of the second thermoplastic elastomer, preferably from 10 to 45% by mass and preferably again from 10% to 40% by mass.

[0022] 6 Composition according to any one of the preceding embodiments in which the elastomer block B comprises from 0 to less than 5% by mass of units of one or more vinylaromatic monomers.

[0023] 7 Composition according to embodiment 6 in which the units of a vinyla- monomer The aromatic compounds of block B are chosen from styrene and α-methylstyrene.

[0024] 8 Composition according to any one of the preceding embodiments in which the elastomer block B consists mainly by mass of 1,3-butadiene units.

[0025] 9 Composition according to any one of the preceding embodiments in which the Elastomer block B is a polybutadiene block (BR).

[0026] 10 Composition according to any one of the preceding embodiments in which the The first thermoplastic elastomer is a copolymer poly(α-methylstyrene) - polybutadiene - poly(α-methylstyrene).

[0027] 11 Composition according to any one of the preceding embodiments in which the elastomer block B' comprises more than 5% by mass to less than 45% by mass, preferably more than 10% by mass to less than 40% by mass of vinylaromatic units, relative to the mass of block B', the vinylaromatic units preferably being styrene units.

[0028] 12 Composition according to any one of the preceding embodiments in which the Elastomer block B' comprises units of 1,3-butadiene and units of styrene.

[0029] 13 Composition according to any one of the preceding embodiments in which the B' elastomer block is a random copolymer of 1,3-butadiene and styrene.

[0030] 14 Composition according to any one of the preceding embodiments in which the the rate of the first thermoplastic elastomer is in the range of 20 to 80 pc, preferably 30 to 70 pc, the rate of the second thermoplastic elastomer is in the range of 20 to 80 pc, preferably 30 to 70 pc, and the total rate of the first thermoplastic elastomer and the second thermoplastic elastomer is greater than or equal to 80 pc and less than or equal to 100 pc.

[0031] 15 Composition according to any one of the preceding embodiments, which com position further comprises a homopolymer of α-methylstyrene (poly(α-methylstyrene)) in a mass proportion ranging from 5 to 45% by mass per ratio to the total mass of the composition.

[0032] 16 Composition according to any one of the preceding embodiments comprising at less one component selected from non-thermoplastic elastomers, reinforcing fillers selected from carbon blacks and other reinforcing fillers, organic and inorganic of siliceous type in particular silica, as well as mixtures of these fillers, elastomer / filler coupling agents, non-reinforcing fillers, processing agents, stabilizers, plasticizers, pigments, antioxidants, anti-fatigue agents, anti-ozonating waxes, adhesion promoters, reinforcing resins, crosslinking systems based on sulfur and / or peroxide and / or bismaleimides, crosslinking activators including zinc monoxide and stearic acid, guanidic derivatives, extending oils, silica coating agents.

[0033] 17 Finished or semi-finished product intended for the manufacture of tires comprising a composition according to any one of the previous designs.

[0034] 18 A tire comprising a tread, which tire comprises a composition according to any one of the realizations 1 to 16 in all or part of its tread. Definitions

[0035] In the present, unless expressly stated otherwise, all percentages (%) indicated are percentages (%) by mass.

[0036] On the other hand, any interval of values ​​designated by the expression "between a and b" represents the domain within the limits a and b (i.e. bounds 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 to b (i.e. including the strict bounds a and b).

[0037] In this description, "part per percent of elastomer" or "pce" means the mass portion of a constituent per 100 mass portions of the elastomer(s), i.e., of the total mass of the elastomer(s), whether thermoplastic or non-thermoplastic, in the composition. Thus, a constituent at 60 pce will mean, for example, 60 g of that constituent per 100 g of elastomer.

[0038] Poly(α-methylstyrene) is commonly understood to be a homopolymer of α-methylstyrene.

[0039] In the present description, "X units" (or "X motifs") or units of the X monomer of a polymer mean the monomer units that result from the polymerization of the X monomer. Thus, "α-methylstyrene units" are the units resulting from the polymerization of the α-methylstyrene monomer.

[0040] The carbon-containing compounds mentioned in the description may be of fossil origin or bio-based. In the latter case, they may be partially or These compounds can be entirely derived from biomass or obtained from renewable raw materials derived from biomass. Similarly, the compounds mentioned can also come from the recycling of previously used materials; that is, they can be partially or entirely produced through a recycling process, or obtained from raw materials themselves derived from a recycling process. This includes, in particular, monomers, polymers, etc. Detailed description of the invention

[0041] The polymer composition according to the invention comprises a first thermoplastic elastomer and a second thermoplastic elastomer.

[0042] The two TPEs useful for the needs of the invention are triblock elastomers, of formula ABA for the first with two rigid thermoplastic segments A comprising α-methylstyrene units connected by a flexible segment B made of a diene elastomer, and of formula A'-B'-A' for the second with two rigid thermoplastic segments A' comprising α-methylstyrene units connected by a flexible segment B' made of a statistical copolymer elastomer comprising diene units and vinylaromatic units.

[0043] The number-average molar mass (denoted Mn) of the TPEs of the invention is preferably between 30,000 and 500,000 g / mol, and more preferably between 40,000 and 400,000 g / mol. Below the indicated minimums, the cohesion between the TPE chains may be affected; furthermore, an increase in the operating temperature may affect the mechanical properties, particularly the fracture properties. Moreover, an excessively high Mn mass can be detrimental to processing. Thus, it has been found that a value in the range of 50,000 to 300,000 g / mol is particularly well-suited, especially for the use of TPE in a tire compound. An Mn in the range of 80,000 to 150,000 g / mol is even more preferable.

[0044] For TPE, the number-average molar mass (Mn) of TPE telatomer is determined by size exclusion chromatography (SEC) in a manner known to those skilled in the art using a calibration curve made from polybutadiene (PB) standards.

[0045] The value of the polymolecularity index Ip (reminder: Ip = Mw / Mn with Mw average molar mass by weight and Mn average molar mass by number) of the TPE is preferably less than 3, more preferably less than 2, even more preferably less than 1.5.

[0046] As is known, TPEs exhibit two peaks of glass transition temperature (Tg), the lower temperature being relative to the elastomer part of the TPE, and the higher temperature being relative to the thermoplastic part of the TPE. I- The first thermoplastic elastomer

[0047] The first thermoplastic elastomer used for the implementation of the invention is a block copolymer of formula ABA, in which A is a thermoplastic block comprising predominantly by mole α-methylstyrene units and B is a diene elastomer block comprising more than 95% by mass of diene units relative to the mass of the diene elastomer block. The diene elastomer block "B" or B block

[0048] Block B of the first TPE, for the purposes of the invention, is a diene elastomer. A diene elastomer is defined as an elastomer derived at least in part (i.e., a homopolymer or a copolymer) from diene monomers (monomers bearing two carbon-carbon double bonds, conjugated or not). Block B generally has a Tg below 0°C and very preferably below -10°C. A Tg value above these values ​​may reduce the performance of the composition when used at very low temperatures. Preferably, the Tg of the elastomer block of the TPE is above -100°C. The essential characteristic of block B is that it contains predominantly diene units by mass. In other words, the diene units of block B represent the highest weight fraction of the constituent units of block B.

[0049] Preferably, block B is any homopolymer obtained by polymerization of a conjugated diene monomer having 4 to 15 carbon atoms, or a copolymer obtained by copolymerization of one or more conjugated dienes having 4 to 15 carbon atoms between them or possibly by copolymerization with one or more vinylaromatic monomers having 8 to 20 carbon atoms.

[0050] Suitable conjugated dienes for use according to the invention include, in particular, 1,3-dienes such as 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-di(alkyl in Ci-C5)-1,3-butadiene such as 2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3-isopropyl-1,3-butadiene, phenyl-1,3-butadiene and 1,3-pentadiene.

[0051] More preferably, block B comprises monomer units of a 1,3-diene having 4 to 12 carbon atoms. Even more preferably, block B comprises units of 1,3-butadiene.

[0052] Block B is preferably a polybutadiene (BR), or a 1,3-butadiene copolymer, in particular a copolymer of 1,3-butadiene and a vinyl-aromatic monomer.

[0053] Suitable vinylaromatic monomers include, in particular, styrene, Ta-methylstyrene, ortho-, meta-, para-methylstyrene, and the commercial mixture "vinyl- toluene", para-tert-butylstyrene, methoxystyrenes, vinylmesitylene, div-nylbenzene and vinylnaphthalene. The vinylaromatic monomer is preferentially styrene or α-methylstyrene, more preferably α-methylstyrene.

[0054] According to a particularly preferred embodiment of the invention, the elastomer block B comprises predominantly by mass units of 1,3-butadiene, preferably block B is a polybutadiene block.

[0055] According to one embodiment of the invention, the elastomer block B comprises from 0 to less than 5% by mass of units of one or more vinylaromatic monomers. According to this preferred embodiment of the invention, the units of a vinylaromatic monomer in the elastomer block B are advantageously chosen from styrene and α-methylstyrene, more advantageously α-methylstyrene.

[0056] Preferably, the elastomer block B has a number-average molar mass (“Mn”) of at least 25,000 g / mol, preferably at least 35,000 g / mol and at most 350,000 g / mol, preferably at most 250,000 g / mol, so as to impart good elastomeric properties and satisfactory mechanical strength to the thermoplastic elastomers. The number-average molar mass of the elastomer block B of the thermoplastic elastomer can be determined by size-exclusion chromatography in a manner known to those skilled in the art using a calibration curve prepared from polybutadiene standards. The thermoplastic block "A" or block A

[0057] The first thermoplastic elastomer useful for the purposes of the invention comprises two terminal thermoplastic, or rigid, blocks comprising α-methylstyrene units.

[0058] Preferably, the thermoplastic blocks A each have a number-average molar mass (“Mn”) of at least 5,000 g / mol, preferably at least 7,000 g / mol, and at most 100,000 g / mol, preferably at most 50,000 g / mol. The number-average molar mass of the thermoplastic blocks A can be determined by size-exclusion chromatography in a manner known to those skilled in the art and is expressed herein relative to polystyrene standards.

[0059] According to the invention, the thermoplastic blocks A comprise predominantly, by mole, α-methylstyrene units to provide good thermal resistance to the thermoplastic elastomer, as well as to the composition according to the invention. In other words, the α-methylstyrene units of block A represent the highest mole fraction of the constituent units of block A. The thermoplastic block A preferably comprises more than 95% by mole of α-methylstyrene units, a percentage expressed relative to all the monomer units constituting block A.

[0060] When the thermoplastic blocks A further comprise units derived from at least one other monomer, this monomer may be vinylaromatic, preferably it is the styrene. These units derived from another monomer can also be a conjugated diene.

[0061] According to a particularly preferred embodiment of the invention, the thermoplastic blocks A are essentially composed of α-methylstyrene units, that is to say, the thermoplastic blocks A do not comprise any units of a monomer other than α-methylstyrene. Thus, improved thermal resistance at higher temperatures is observed in the thermoplastic elastomer, as well as in the composition containing it. For this reason, the thermoplastic blocks A have a Tg that is preferably greater than or equal to 100°C, more preferably at least 120°C, and even more preferably at most 200°C, advantageously varying from 100°C to 200°C, preferably from 120°C to 180°C.

[0062] The minimum proportion of thermoplastic blocks A in the first plastic elastomer can vary depending on the conditions of use of the composition according to the invention and is adjusted by a person skilled in the art. Preferably, the two thermoplastic blocks A represent at least 10% by mass relative to the mass of the first thermoplastic elastomer, preferably from 10% to 45% by mass, more preferably from 10% to 40% by mass.

[0063] In the context of the invention, the polymer composition may comprise one or more first thermoplastic elastomers of formula ABA. In the case where there are several, they are differentiated by their macrostructure or their microstructure.

[0064] Advantageously, the first TPE is a triblock thermoplastic elastomer of formula ABA in which the A blocks each represent a poly(α-methylstyrene) thermoplastic block and the B block is a diene elastomer block, the B block being in particular a homopolymer of a 1,3-diene or a copolymer of a 1,3-diene, the 1,3-diene being as defined above and in particular 1,3-butadiene, preferably 1,3-butadiene. II- The second thermoplastic elastomer

[0065] The second thermoplastic elastomer used for the implementation of the invention is a block copolymer of formula A'-B'-A', in which A' is a thermoplastic block comprising predominantly by mole α-methylstyrene units and B' is a statistical copolymer elastomer block comprising diene units and vinylaromatic units, in particular a statistical (1,3-diene-co-vinylaromatic) copolymer elastomer block. The diene elastomer block “B’” or B’ block

[0066] Block B' of the second TPE, for the purposes of the invention, can be any statistical copolymer comprising diene units and vinylaromatic units, in particular styrene units, known to those skilled in the art. It possesses gen- The Tg value is generally below 0°C and very preferably below -10°C. A Tg value above these values ​​may reduce the performance of the composition according to the invention when used at very low temperatures. Also preferably, the Tg of block B' is above -100°C.

[0067] By statistical copolymer elastomer formed of diene units and styrene units (or elastomer block "B'") is meant a statistical copolymer elastomer derived at least in part from diene monomers (monomers bearing two carbon-carbon double bonds, conjugated or not) and at least in part from vinylaromatic monomers, monomers of formula ArCH=CH2 or Ar-CMe=CH2, the symbol Ar representing an aromatic group.

[0068] Preferably, block B' is an elastomer obtained by statistical copolymerization of one or more conjugated dienes having 4 to 15 carbon atoms with one or more vinylaromatic monomers having 8 to 20 carbon atoms.

[0069] Suitable conjugated dienes for use according to the invention include, in particular, 1,3-dienes such as 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-di(alkyl in Ci-C5)-1,3-butadiene such as 2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3-isopropyl-1,3-butadiene, phenyl-1,3-butadiene and 1,3-pentadiene.

[0070] Preferably, block B' comprises 1,3-diene units having 4 to 12 carbon atoms, more particularly, block B' comprises 1,3-butadiene units.

[0071] Suitable vinylaromatic monomers include styrene, Ta-methylstyrene, ortho-meta-, para-methylstyrene, the commercial "vinyl-toluene" mixture, para-tert-butylstyrene, methoxystyrenes, vinylmesitylene, div-nylbenzene and vinylnaphthalene.

[0072] According to one embodiment of the invention, the elastomer block B' comprises units of styrene or α-methylstyrene or both units of styrene and units of α-methylstyrene, preferably units of styrene.

[0073] Block B' is preferably a random copolymer comprising 1,3-butadiene units and styrene units. More preferably, block B' is a random copolymer of 1,3-butadiene and styrene.

[0074] According to one embodiment of the invention, the elastomer block B' advantageously comprises more than 5% by mass to less than 45% by mass, preferably more than 10% by mass to less than 40% by mass of styrene relative to the mass of block B'.

[0075] Preferably for the invention, block B' has a number-average molar mass (“Mn”) of at least 25,000 g / mol, preferably at least 35,000 g / mol and at most 350,000 g / mol, preferably at most 250,000 g / mol, so as to impart good elastomeric properties to the second thermoplastic elastomer and a satisfactory mechanical strength, as well as the composition according to the invention. The number-average molar mass of block B' can be determined by size-exclusion chromatography in a manner known to those skilled in the art using a calibration curve prepared from polybutadiene standards. The thermoplastic block "A'" or block A'

[0076] The second triblock thermoplastic elastomer A'-B'-A' according to the invention comprises two terminal thermoplastic, or rigid, blocks, block A' comprising α-methylstyrene units.

[0077] Preferably, the thermoplastic blocks A' each have a number-average molar mass ("Mn") of at least 5,000 g / mol, preferably at least 7,000 g / mol, and at most 100,000 g / mol, preferably at most 50,000 g / mol. The number-average molar mass of the blocks A' can be determined by size-exclusion chromatography in a manner known to those skilled in the art and is expressed herein relative to polystyrene standards.

[0078] According to the invention, the thermoplastic blocks A' comprise predominantly by mole of α-methylstyrene units to provide good thermal resistance to the thermoplastic elastomer, as well as to the composition according to the invention. Each thermoplastic block A' preferably comprises more than 95% by mole of α-methylstyrene units.

[0079] When the thermoplastic blocks A' further comprise units of at least one other monomer, this monomer may be vinylaromatic, preferably styrene. These units of another monomer may also be a conjugated diene.

[0080] According to a particularly preferred embodiment of the invention, the thermoplastic blocks A' are essentially composed of α-methylstyrene units, that is to say, the thermoplastic blocks A' do not comprise any units of a monomer other than α-methylstyrene. Thus, improved thermal resistance at higher temperatures is observed in the thermoplastic elastomer, as well as in the composition according to the invention. For this reason, the thermoplastic blocks A' exhibit a Tg that is preferably greater than or equal to 100°C, more preferably at least 120°C, and even more preferably at most 200°C, advantageously varying from 100°C to 200°C, preferably from 120°C to 180°C.

[0081] The minimum proportion of thermoplastic blocks A' in the second plastic elastomer can vary depending on the conditions of use of the composition according to the invention and is adjusted by a person skilled in the art. Preferably, the thermoplastic blocks A' represent at least 10% by mass relative to the mass of the thermoplastic elastomer, preferably from 10% to 45% by mass, more preferably from 10% to 40% by mass.

[0082] Advantageously, the second TPE is a triblock thermoplastic elastomer of formula A'-B'-A' in which the A' blocks each represent a poly(α-methylstyrene) thermoplastic block, the B' block is a statistical copolymer elastomer block of a 1,3-diene and a vinylaromatic monomer, the 1,3-diene being as defined above, preferably 1,3-butadiene and the vinylaromatic monomer being as defined above, preferably styrene.

[0083] In the context of the invention, the polymer composition may comprise one or more second thermoplastic elastomers A'-B'-A'. In the case where there are several, they are differentiated by their macrostructure or their microstructure.

[0084] According to one embodiment of the invention, the percentage of the first thermoplastic elastomer is in the range of 20 to 80 parts per annum, preferably 30 to 70 parts per annum, and the percentage of the second thermoplastic elastomer is in the range of 20 to 80 parts per annum, preferably 30 to 70 parts per annum, and the total percentage of the first thermoplastic elastomer and the second thermoplastic elastomer is greater than or equal to 80 parts per annum and less than or equal to 100 parts per annum.

[0085] According to a particular embodiment, the composition further comprises one or more thermoplastic poly(α-methylstyrene) homopolymers.

[0086] According to a particular embodiment of the invention, the composition comprises a homopolymer of α-methylstyrene (poly(α-methylstyrene)) in a mass proportion ranging from 5 to 45% by mass relative to the total mass of the composition. Synthesis

[0087] The thermoplastic elastomers useful for the needs of the invention can be manufactured in a known manner according to various synthesis methods described in the prior art.

[0088] A first synthesis method consists, for example, of anionically polymerizing α-methylstyrene to simultaneously form the two thermoplastic blocks in the presence of polydienyldilithium as a polymerization initiator. For example, WO8505116A1 and EP0014947A1 describe such methods, which include the copolymerization of styrene and α-methylstyrene to generate the thermoplastic blocks. This yields a triblock copolymer of the type poly(α-methylstyrene-co-styrene)-β-polydiene-β-poly(α-methylstyrene-co-styrene). Similar synthesis methods can be considered for manufacturing poly(α-methylstyrene)-β-polydiene-poly(α-methylstyrene) triblock polymers using polydienyllithium as a polymerization initiator. Such a process is described for example in FR3045615.

[0089] A second method of synthesis consists of first anionically polymerizing α-methylstyrene. Then, in a second step, the diene monomer is polymerized onto the resulting live poly(α-methylstyrene) chains. This yields a poly(α-methylstyrene)-β-polydiene diblock polymer of which The dienyl end is active. To obtain a triblock thermoplastic elastomer, a coupling agent is added at this stage to couple the dienyl blocks of the chains. This step is carried out in a manner known per se. Coupling agents generally contain a silicon or tin atom, substituted by two groups reactive with respect to the carbanion end of the active polymer chains. Examples of coupling agents include dihalogenotins and dihalogenosilanes, notably dibutyltin dichloride or dimethyldichlorosilane, or dialcoxysilanes. The polymer resulting from the coupling step is a poly(α-methylstyrene)-β-polydiene-β-poly(α-methylstyrene) triblock.

[0090] Processes for implementing the second synthesis method are described, for example, in US4302559A. The synthesis of the block copolymer comprises a first step of polymerizing α-methylstyrene at low temperature in the presence of a first polar agent, called a polar activator, to form the poly(α-methylstyrene) block. In a second step, a small amount of conjugated diene is added to add a live polydienyl block of a few units to the end of the poly(α-methylstyrene) block, thus preventing the depolymerization of the α-methylstyrene. This is followed by a second addition of conjugated diene in the presence of another polar agent, called a polar activator, to allow the formation of the second block by subsequent polymerization of the conjugated diene while statistically inserting the residual α-methylstyrene into the polymer chain.To obtain the triblock copolymer, the polymer from the last polymerization step is coupled using a coupling agent. The central diene elastomer block of the triblock copolymer is, according to this synthesis method, a poly(butadiene-co-α-methylstyrene) statistical copolymer.

[0091] Other processes implementing this second method of synthesizing a poly(α-methylstyrene)-β-polydiene-β-poly(α-methylstyrene) triblock copolymer are described as yielding a central diene elastomer block free of α-methylstyrene. For example, in document FR2243214, the process consists, in a first step, of homopolymerizing α-methylstyrene in a concentrated medium at temperatures between 0°C and 40°C. Following this step, the conjugated diene and the solvent necessary for the synthesis of the poly(conjugated diene) block are added. After this final polymerization step, the resulting polymer is coupled using a coupling agent. More recently, WO2020070406A1 describes another process for the synthesis of a triblock poly(α-methylstyrene)-β-polydiene-β-poly(α-methylstyrene) copolymer in which the central diene elastomer block is also free of α-methylstyrene.

[0092] A person skilled in the art will understand that, depending on the method and conditions of synthesis of the thermoplastic elastomer, the product obtained may consist of, in addition The ABA triblock (or A'-B'-A' triblock) may contain other macromolecule populations such as thermoplastic polymers having the microstructure of block A (or A'), diene elastomers having the microstructure of block B (or B'), or diblock polymers of formula AB (or A'-B'), blocks A, A', B, and B' being as defined in this application. Thus, within the scope of the invention, those skilled in the art will understand that the product of the synthesis may comprise all of these populations when the triblock elastomer is not isolated at the end of its synthesis. The product resulting from the synthesis of the ABA triblock and the A'-B'-A' triblock may comprise at most 20% by mass of a diblock polymer of formula AB and a diblock polymer of formula A'-B', respectively. Similarly, the product resulting from the synthesis may include a thermoplastic polymer having the microstructure of block A in the case of synthesis of the ABA triblock (or A' in the case of synthesis of the A'-B'-A' triblock).

[0093] Polymerization can be carried out by a continuous process or a batch process.

[0094] The polymer composition according to the invention may further comprise at least one component selected from non-thermoplastic elastomers, reinforcing fillers selected from carbon blacks and other reinforcing fillers, organic and inorganic of siliceous type in particular silica, as well as mixtures of these fillers, elastomer / filler coupling agents, non-reinforcing fillers, processing agents, stabilizers, plasticizers, pigments, antioxidants, anti-fatigue agents, anti-ozonating waxes, adhesion promoters, reinforcing resins, crosslinking systems based on sulfur and / or peroxide and / or bis-maleimides, crosslinking activators including zinc monoxide and stearic acid, guanidic derivatives, extending oils, silica coating agents.

[0095] The present invention further relates to a finished or semi-finished product intended for the manufacture of tires comprising a polymer composition according to the invention.

[0096] Another object of the invention is a tire comprising a tread, which tire comprises a polymer composition according to the present invention in all or part of its tread. EXAMPLES OF THE INVENTION'S IMPLEMENTATION I. Tests and measurements A - Measurement of the Mn of TPEs

[0097] The macrostructure (Mw, Mn, Ip) of TPEs is determined by chromatography size exclusion (SEC) based on ISO 16014 standards (Determination of average molecular mass and molecular mass distribution of polymers using size exclusion chromatographyf ASTM D5296 (Molecular Weight Averages and molecular weight distribution of polystyrene by High performance size exclusion chromatography and DIN 55672 (size exclusion chromatography).

[0098] For these measurements, the TPE sample is first solubilized in tetrahydrofuran stabilized at a concentration of 1 g / L; the solution is then filtered with PTFE filters with a porosity of 0.45 µm before injection. The equipment used is a WATERS Alliance chromatographic system. The elution solvent is tetrahydrofuran, the flow rate is 1 mL / min, the system temperature is 35°C, and the analysis time is 40 min. A set of Polypore columns made of a polystyrene divinylbenzene gel with controlled porosity (set of three AGILENT columns) is used. The injected volume of the polymer sample solution is 100 µL. The detector is a WATERS 2410 differential refractometer, also thermostated at 35°C, and its associated software for processing the chromatographic data is the WATERS Alliance system.

[0099] Polymer chains are separated according to the size they occupy when solubilized in the solvent: the larger the volume they occupy, the less accessible the pores of the columns are to them and the shorter their elution time.

[0100] The calculated number average molar masses are relative to a calibration curve made from commercial standard polystyrenes "PSS-pskitlh-3" in the case of thermoplastic polymers comprising α-methylstyrene units alone.

[0101] The calculated number average molar masses are relative to a calibration curve made from commercial standard polybutadienes "PSS-bdfkit" in the case of products comprising dibloc and / or tribloc thermoplastic elastomers containing butadiene units.

[0102] In the case of products resulting from the synthesis of block thermoplastic elastomers (thermoplastic block comprising α-methylstyrene-β-polydiene-β units; thermoplastic block comprising α-methylstyrene units) containing less than 10% by mass of thermoplastic polymer comprising poly(α-methylstyrene) units, the distribution of the different species in the product is determined from the integration of the RI signal of the SEC chromatograms. The mass proportion of each species is related to the integral of all the RI signals in the chromatogram.

[0103] In the case of products containing more than 10% by mass of thermoplastic polymer comprising poly(α-methylstyrene) units, the distribution of the different species of the product is carried out from the integration of the RI signal of the SEC chromatograms by modulating the RI response by the value of the specific increment of the refractive index dn / dc of each species or by constructing a calibration curve by adding measured amounts of thermoplastic polymer comprising units poly(α-methylstyrene), in a manner known to those skilled in the art.

[0104] B - Differential scanning calorimetry (DSC) analysis of TPE

[0105] The characterization of the Tg values ​​of the elastomer block and the thermoplastic blocks is carried out by DSC measurement using a Mettler Toledo DSC1 instrument. The instrument is operated under a helium atmosphere. A sample of 10 to 20 mg of thermoplastic elastomer is placed in a crucible commonly used by those skilled in the art to perform Tg measurements.

[0106] The sample is first placed in an isothermal environment at +25°C for 2 minutes and then cooled to -150°C at a rate of 50°C per minute. An isothermal environment of -150°C is then applied for 10 minutes. A first heating cycle then begins from -150°C to +10°C at a rate of 20°C per minute and continues from 10°C to 250°C at a rate of 50°C per minute. The sample then undergoes quenching to reach -150°C at the maximum rate allowed by the apparatus. The sample is then maintained in an isothermal environment at -150°C for 15 minutes. The second heating process then begins from -150°C to +10°C at a rate of 20°C per minute (measurement range of the Tg of the elastomer portion of the TPE) and continues from +10°C to +250°C at a rate of 50°C per minute (measurement range of the Tg of the thermoplastic blocks). In this measurement, only the second heating process is used.

[0107] C - Proton nuclear magnetic resonance (XH NMR)

[0108] The proportions of the different monomer units within the thermoplastic telastomer are determined by NMR analysis. Spectra are acquired on a 500 MHz BRUKER spectrometer equipped with a 5 mm BBIz-grad broadband probe. The quantitative ¹H NMR experiment uses a simple 30° pulse sequence and a 5-second repetition interval between each acquisition. The samples are solubilized in CDC13. The integration regions considered for quantification are the spectral signature regions of the monomer units known to those skilled in the art.

[0109] D- Viscosity measurement RPA (Rubber Process Analyzer)

[0110] The method for measuring G' and G” uses an oscillating disk rheology apparatus of the RPA type, such as the 2000LV device (Oscillating Disk Rheometer) supplied by Alpha Technologies®, equipped with the standard 200 in. lb (22.6 dNm) viscosity sensor. The RPA machine allows for the torsional stressing of a material sample enclosed in a chamber (or enclosure) with biconical walls.

[0111] To perform the measurement of G'(T) (elastic shear modulus), a sample of material approximately 30 mm in diameter and with a mass of approximately 5 g is placed in the chamber or enclosure of the RPA (a total volume of 5 cm³ is considered optimal; the quantity is sufficient when a small amount of sample escapes from each side of the chamber and is visible at the end of the test). At the end of this operation, the sample is perfectly molded within the closed chamber of the RPA.

[0112] A shaping operation is carried out by applying a temperature of 180°C to the sample enclosed in the RPA chamber for a time of 40 minutes with a deformation of 2.8% peak-to-peak at 1.7 Hz.

[0113] At the end of this operation, the sample is perfectly molded in the closed chamber of the RPA. The sample is then cooled to 40°C directly in the RPA chamber. It is then possible to begin measuring the value of G' at 5% peak-to-peak strain and 10 Hz in a temperature range varying from 40 to 200°C (ramp: 3°C / min).

[0114] A curve of variation of G' as a function of temperature is obtained, from which the modulus G' of the composition at 190°C can be extracted.

[0115] The shaping and measurement steps of G' are done without intervention, by programming the RPA machine.

[0116] It is recalled that, as is well known to those skilled in the art, the value of the RPA viscosity at 190°C is representative of the processability of the material: the lower the viscosity at 190°C, the easier the material is to shape.

[0117] E- Measurement of the complex dynamic shear modulus

[0118] Dynamic properties (after forming): Tensile test

[0119] The dynamic properties G*(10%) at 23°C are measured on a viscoelastic analyzer (Metravib VA4000), according to ASTM D 5992-96. The response of a cross-linked composite sample (cylindrical specimen 4 mm thick and 400 mm² cross-section) is recorded under sinusoidal alternating simple shear loading at a frequency of 10 Hz, under defined temperature conditions, for example, 23°C according to ASTM D 1349-99, or, where applicable, at a different temperature. A strain amplitude sweep is performed from 0.1 to 50% (forward cycle), then from 50% to 1% (reverse cycle). The results used relate to the complex dynamic shear modulus G*. For the return cycle, the value of the complex dynamic shear modulus G*(10%) at 10% strain, at 23°C, is indicated.

[0120] It is recalled that, as is well known to those skilled in the art, the value of G* 10% at 23 °C is representative of the stiffness of the material: the lower G* 10% at 23 °C is, the lower the stiffness.

[0121] II. Polymer synthesis and preparation of polymer compositions

[0122] In the following tests, the following designation will be adopted:

[0123] poly(α-methylstyrene) = PAMS

[0124] A - Synthesis of a first TPE, triblock polymer poly(α-methylstyrene)-β-polybutadiene-β-poly(α-methylstyrene) or TPE1

[0125] In an 80 L double-jacketed reactor, 2.0 L of cyclohexane, 0.106 L of tetrahydrofuran, and 5 kg of α-methylstyrene are successively introduced under constant nitrogen purging. All products have been previously purified and / or dried.

[0126] After the temperature has been brought to 17°C, 0.125 mol of sec-butyllithium is introduced into the reactor as a solution in cyclohexane at 0.13 mol / L. The molar ratio of activator (also called polar agent), in this case tetrahydrofuran / initiator, in this case sec-butyllithium, is 2.3.

[0127] After 33 minutes of polymerization at 17°C, the measured conversion of AMS is 32%. 0.675 kg of 1,3-butadiene is then introduced, and the reaction mixture is diluted with 23 L of cyclohexane. Next, 3.9 kg of 1,3-butadiene is added, and the temperature is raised to 40°C. The temperature is maintained at a maximum of 42°C. Polymerization lasts 102 minutes. The measured conversion of 1,3-butadiene is 92%. After polymerization, 0.06 moles of dimethyldichlorosilane are added with constant stirring. The reaction mixture is maintained at 40°C for 30 minutes.

[0128] Following this coupling step, a triblock polymer poly(α-methylstyrene)-β-polybutadiene-β-poly(α-methylstyrene) is synthesized. Next, 0.2 parts per million of an antioxidant, Irganox 1520L® (from BASF), is added. The antioxidantized polymer is separated from the solvent by steam stripping, and then the polymer is dried in a vacuum oven with nitrogen flushing at 60°C.

[0129] The Tg DSC of the polybutadiene flexible block -49°C (AT, glass transition width, being equal to 9°C).

[0130] Bl - Synthesis of a first second TPE, triblock polymer poly(a-methylstyrene)-b-poly(butadiene-co-styrene)-b-poly(a-methylstyrene) (or TPE2-1)

[0131] In an 80 L double-jacketed reactor, 2.1 L of cyclohexane, 0.106 L of tetrahydrofuran, and 5 kg of α-methylstyrene are successively introduced under constant nitrogen purging. All products have been previously purified and / or dried.

[0132] After the temperature has been brought to 17°C, 0.125 mol of sec-butyllithium is introduced into the reactor as a solution in cyclohexane at 0.13 mol / L. The molar ratio of activator, in this case tetrahydrofuran / initiator, in this case sec-butyllithium is 2.3.

[0133] After 50 minutes of polymerization of Ta-methylstyrene, the measured conversion of AMS is 50%. 0.42 kg of 1,3-butadiene and 0.26 kg of styrene are then introduced, followed by the addition of 39 L of cyclohexane to the reaction mixture. Next, 3.2 kg of 1,3-butadiene and 1.9 kg of styrene are introduced, and the temperature is raised to 40°C. The temperature is maintained at a maximum of 42°C. Polymerization lasts 145 minutes. The measured conversion is 74%.

[0134] After polymerization, 0.06 moles of dimethyldichlorosilane are added under constant stirring. The reaction mixture is maintained at 40°C for 30 minutes.

[0135] Following this coupling step, a triblock polymer Poly(α-methylstyrene)-β-butadiene-styrene-β-poly(α-methylstyrene) is synthesized. 0.2 parts per million of an antioxidant, Irganox 1520L® (from BASF), is added. The antioxidantized polymer is separated from the solvent by steam stripping, and then dried in a vacuum oven with nitrogen flushing at 60°C.

[0136] The Tg DSC of the flexible poly(butadiene-co-styrene) block -38°C (AT, glass transition width, being equal to 9°C).

[0137] B-2- Synthesis of a second TPE, triblock polymer poly(a- me- thylstyrene)-b-poly(butadiene-co-styrene)-b-poly(α-methylstyrene) (or TPE2-2)

[0138] In an 80 L double-jacketed reactor, 2.6 L of cyclohexane, 0.028 L of tetrahydrofuran, and 2 kg of alpha-methylstyrene are successively introduced under constant nitrogen purging. All products have been previously purified and / or dried.

[0139] After the temperature has been brought to 17°C, 0.15 mol of sec-butyllithium is introduced into the reactor as a solution in cyclohexane at 0.16 mol / L. The molar ratio of activator (tetrahydrofuran) to initiator (sec-butyllithium) is 2.3.

[0140] After 40 minutes of polymerization, the measured conversion is 34%. 0.567 kg of 1,3-butadiene and 0.24 kg of styrene are then introduced, after which the reaction mixture is diluted with 43.6 L of cyclohexane. Next, 3.8 kg of 1,3-butadiene and 1.6 kg of styrene are introduced, and the temperature is raised to 40°C. The temperature is maintained at a maximum of 42°C. Polymerization lasts 85 minutes. The measured conversion is 68%.

[0141] After polymerization, 0.072 moles of dimethyl-dichlorosilane are added under constant stirring. The reaction mixture is maintained at 40 °C for 30 minutes.

[0142] Following this coupling step, a triblock polymer poly(α-methylstyrene)-β-butadiene-styrene-β-poly(α-methylstyrene) is synthesized. 0.2 wt. of an antioxidant, Irganox 1520L® (from BASF), is added. The antioxidantized polymer is separated from the solvent by steam stripping, and then the polymer is dried in a vacuum oven with nitrogen flushing at 60°C.

[0143] The Tg DSC of the flexible poly(butadiene-co-styrene) block -48°C (AT, glass transition width, being equal to 9°C). C - Preparation of polymer compositions

[0144] For each composition, the TPE polymers are placed in a container with toluene at a ratio of 10% by volume of polymer in toluene and stirred for 24 hours at room temperature. The solution is then placed under a fume hood at room temperature for 24 to 36 hours, followed by drying in a vacuum oven at 60°C for 24 hours. The resulting film is shaped by pressing at 180°C for 10 minutes to obtain the necessary test specimens. to the characterizations.

[0145] Table 1 summarizes the components of the polymeric compositions, their characteristics and respective percentages in parts per unit area.

[0146] [Tables 1] Mn (kg / mol) (PB Calibration) Ml M2 M3 M4 M5 TPE1 130 100 50 50 70 30 TPE2-1 108 50 TPE2-2 81 50 30 70

[0147] AT = glass transition width

[0148] Tables 2 and 3 show the characteristics of the TPEs used in the examples.

[0149] [Tables2] Sample name n Microstructure % mass / TPE (1H NMR) %STY % PB 1.2% PB 1.4% AMS TPE1 0 51 33 16 TPE2-1 24 16.1 34.9 24 TPE2-2 16.3 21.1 41.4 21.2

[0150] [Tables3] Sample name Mn block PAMS Calibrati on PS Species distribution PAMS / dibloc / triblock (PB calibration) Mp PAMS % mass PAMS % mass diblock % mass triblock TPE1 10728 6,616 6.1 11.2 82.7 TPE2-1 15824 10,474 9.6 5.9 84.4 TPE2-2 8085 4252 3.8 6.3 89.9

[0151] AMS = α-methylstyrene PAMS = poly(α-methylstyrene) % STY = mass percentage of styrene units % PB 1.2 = mass percentage of butadiene units in the form of 1,2- units % PB 1.4 = mass percentage of butadiene units in the form of 1.4 units % AMS = mass percentage of α-methylstyrene units Mp = peak mass % mass = mass percentage. D - Results

[0152] Table 4 shows the results of the different polymer compositions, M1 to M5.

[0153] [Tables4] Ml M2 M3 M4 M5 Visco RPA at 190°C 100 96 53 82 60 G* 10% ret at 23°C 100 154 137 125 160

[0154] The results are presented on a basis of 100 relative to the ML control. Compared to composition M1 which includes TPE1 only, compositions M2 to M5 according to the invention exhibit lower viscosity and higher rigidity.

Claims

Demands

1. Polymer composition comprising: - a first thermoplastic block elastomer of formula A-BA, in which A is a thermoplastic block comprising predominantly by mole α-methylstyrene units and B is a diene elastomer block comprising more than 95% by mass of diene units relative to the mass of the diene elastomer block, - a second thermoplastic block elastomer of formula A'-B'-A', in which A' is a thermoplastic block comprising predominantly by mole α-methylstyrene units and B' is a statistical copolymer elastomer block comprising diene units and vinylaromatic units.

2. Composition according to claim 1 wherein the thermoplastic blocks A and A' comprise more than 95 mole percent of α-methylstyrene units.

3. Composition according to claim 1 or 2 wherein the thermoplastic blocks A and A' comprise styrene units.

4. Composition according to any one of claims 1 to 2 wherein the thermoplastic blocks A and A' are α-methylstyrene homopolymers.

5. Composition according to any one of the preceding claims wherein the thermoplastic blocks A represent at least 10% by mass relative to the mass of the first thermoplastic elastomer, preferably from 10 to 45% by mass, preferably again from 10% to 40% by mass and the thermoplastic blocks A' represent at least 10% by mass relative to the mass of the second thermoplastic elastomer, preferably from 10 to 45% by mass, preferably again from 10% to 40% by mass.

6. Composition according to any one of the preceding claims wherein the elastomer block B comprises from 0 to less than 5% by mass of units of one or more vinylaromatic monomers.

7. Composition according to any one of the preceding claims, wherein the elastomer block B comprises predominantly units of 1,3-butadiene, preferably block B is a polybutadiene block (BR).

8. Composition according to any one of the preceding embodiments wherein the elastomer block B' comprises more than 5% by mass to less than 45% by mass, preferably more than 10% by mass to less than 40% by mass of vinylaromatic units, relative to the mass of block B'.

9. Composition according to any one of the preceding claims wherein the elastomer block B' comprises more than 5% by mass to less than 45% by mass, preferably more than 10% by mass to less than 40% by mass of styrene relative to the mass of block B'.

10. Composition according to any one of the preceding claims wherein the elastomer block B' comprises units of 1,3-butadiene and units of styrene.

11. Composition according to any one of the preceding claims wherein the elastomer block B' is a statistical copolymer of 1,3-butadiene and styrene.

12. Composition according to any one of the preceding claims wherein the percentage of the first thermoplastic elastomer is in the range of 20 to 80 parts per cent, preferably 30 to 70 parts per cent, the percentage of the second thermoplastic elastomer is in the range of 20 to 80 parts per cent, preferably 30 to 70 parts per cent, and the total percentage of the first and second thermoplastic elastomers is greater than or equal to 80 parts per cent.

13. Composition according to any one of the preceding claims, wherein composition further comprises a homopolymer of α-methylstyrene in a mass proportion from 5 to 45% by mass relative to the total mass of the composition.

14. Finished or semi-finished product intended for the manufacture of tires comprising a composition according to any one of the preceding claims.

15. A tire comprising a tread, which tire comprises a composition according to any one of claims 1 to 13 in all or part of its tread.