Polymer composition comprising a blend of thermoplastic elastomers

Abstract

The invention relates to a polymer composition comprising a thermoplastic elastomer TPE and a thermoplastic polyethylene polymer PE, wherein the thermoplastic elastomer TPE is a thermoplastic block elastomer TPE1 of formula A-B-A, in which A is a thermoplastic block predominantly comprising, in moles, α-methylstyrene units and B is a diene elastomer block comprising more than 95 wt.-% diene units relative to the weight of the diene elastomer block, or a thermoplastic block elastomer TPE2 of formula A'-B'-A', in which A' is a thermoplastic block predominantly comprising, in moles, α-methylstyrene units and B' is a random copolymer elastomer block comprising diene units and vinylaromatic units, or a blend of both of the thermoplastic block elastomers TPE1 and TPE2, the polyethylene PE having a melting temperature, Tf, within a range from 100°C to 135°C; the invention also relates to a tire comprising such a composition in all or part of its tread.

Description

[0001] Title of the invention: Polymer composition comprising a mixture of thermoplastic elastomers.

[0002] technical field

[0003] The present invention relates to a polymer composition comprising thermoplastic elastomers.

[0004] Previous technique

[0005] In the field of motor vehicle tires, the Applicant has previously developed rubber compounds 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.

[0006] Thermoplastic elastomers (TPEs) are elastomers of great interest in many fields due to their combined properties, linked on the one hand to a flexible elastomer block and on the other hand to a 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 rises above the glass transition temperature or the melting temperature of the rigid blocks, the polymer can flow, allowing the material to be shaped. The material regains its rigidity when the temperature returns to its 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 potential for application.

[0007] Among the most common thermoplastic elastomers are styrene block copolymers, also known as styrene TPEs. The glass transition temperature (Tg) of polystyrene blocks is around 80°C to 100°C, depending on the block size. For some applications, the Tg value of polystyrene blocks is insufficient. In fact, this value makes it unsuitable for manufacturing certain objects subjected to specific operating conditions where temperatures exceed 100°C.

[0008] Other styrenic TPEs have been proposed, including copolymers with poly(α-methylstyrene) blocks instead of polystyrene blocks, because they offer the advantage of high thermal resistance attributed to the high Tg of approximately 150-170°C of the 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 WO2007112232A2 and FR2243214.

[0009] The Applicant has previously developed compositions for tires, including for tire tread, comprising a thermoplastic elastomer, as in document WO2012152686 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.

[0010] A constant objective for tire manufacturers is to improve the properties of the tread, which must meet a large number of technical requirements, notably that of providing excellent road handling on motor vehicles. To improve road handling, as we know, a certain level of tread rigidity is sought.

[0011] It is therefore desirable that a TPE composition comprising rigid blocks based on α-methylstyrene exhibit good rigidity, particularly in tire manufacturing. To this same end, improvements in the processability and shaping of such a TPE composition are constantly being sought.

[0012] It is generally known that the use of plasticizers in combination with TPEs, particularly TPEs containing 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.

[0013] 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.

[0014] Description of the invention

[0015] This objective is achieved in that the Inventors discovered during their research, in a surprising way, that a specific rubber composition comprising a block TPE, including a flexible diene block and rigid thermoplastic blocks including α-methylstyrene units, and a polyethylene (PE) thermoplastic polymer, which polyethylene (PE) has a melting temperature, Tf, in the range of 100°C to 135°C, exhibited improved processability, without this being at the expense of the rigidity of the composition.

[0016] These significant improvements in properties make it possible to achieve a very good level of compromise between the processability of a TPE composition and the road behavior of tires with a tread based on such a TPE composition.

[0017] Thus, a first object of the invention is a polymer composition comprising a thermoplastic elastomer TPE and a thermoplastic polyethylene polymer PE, which thermoplastic elastomer is a TPE1 block thermoplastic 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, or a TPE2 block thermoplastic 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, or a mixture of the two TPE1 and TPE2 block thermoplastic elastomers, which polyethylene PE thermoplastic polymer has a melting temperature, Tf,within a range of 100°C to 135°C.

[0018] 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.

[0019] The invention also relates to a tire comprising a polymer composition according to the invention, in particular, in all or part of its tread. Summary of the invention

[0020] The invention, described in more detail below, relates to at least one of the implementations listed in the following points:

[0021] 1. A polymer composition comprising a thermoplastic elastomer TPE and a thermoplastic polyethylene polymer PE, wherein the thermoplastic elastomer TPE is a block thermoplastic elastomer TPE1 of formula ABA, in which A is a thermoplastic block comprising predominantly α-methylstyrene units by mole 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, or a block thermoplastic elastomer TPE2 of formula A'-B'-A', in which A' is a thermoplastic block comprising predominantly α-methylstyrene units by mole and B' is a statistical copolymer elastomer block comprising diene units and vinylaromatic units, or a mixture of the two block thermoplastic elastomers TPE1 and TPE2, in which thermoplastic polyethylene polymer PE has a melting temperature, Tf, in the range of 100°C at 135°C.

[0022] 2. Composition according to embodiment 1, wherein the thermoplastic blocks A and A' independently comprise more than 95 mole percent of α-methylstyrene units.

[0023] 3. Composition according to any one of embodiments 1 to 2 in which the thermoplastic blocks A and A' independently comprise styrene units.

[0024] 4 Composition according to any one of embodiments 1 to 2 in which the thermoplastic blocks A and A' are independently of each other α-methylstyrene homopolymers.

[0025] 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 thermoplastic block elastomer TPE1, preferably from 10 to 45% by mass, preferably again from 10% to 40% by mass, and independently the thermoplastic blocks A' represent at least 10% by mass relative to the mass of the thermoplastic block elastomer TPE2, preferably from 10 to 45% by mass and preferably again from 10% to 40% by mass.

[0026] 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.

[0027] 7. Composition according to embodiment 6 in which the vinylaromatic monomer units of block B are selected from styrene units, α-methylstyrene units and mixtures thereof.

[0028] 8. Composition according to any one of the preceding embodiments in which the elastomer block B comprises predominantly 1,3-butadiene units, preferably block B is a polybutadiene block (BR).

[0029] 9. 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.

[0030] 10. 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.

[0031] 11. Composition according to any one of the preceding embodiments in which the elastomer block B 1 is a random copolymer of 1,3-butadiene and styrene.

[0032] 12. Composition according to any one of the preceding embodiments, wherein the thermoplastic polyethylene polymer is selected from the group consisting of high-density polyethylenes (HDPE), low-density polyethylenes (LDPE), linear low-density polyethylenes (LLDPE), medium-density polyethylenes (MDPE), very high molecular weight polyethylenes (UHMWPE), very low-density polyethylenes and mixtures of these polyethylenes (VLDPE).

[0033] 13. Composition according to any one of the preceding embodiments, wherein the thermoplastic polyethylene polymer is non-crosslinked HDPE polyethylene.

[0034] 14. Composition according to any one of the preceding embodiments, wherein the thermoplastic polyethylene polymer has a density in the range of 940 to 970 kg / m³ 3 , preferably in a range of 940 to 965 kg / m 3measured at 23°C according to ISO 1183-2019.

[0035] 15. Composition according to any one of the preceding embodiments, wherein the thermoplastic polyethylene polymer has a melt flow index at 190°C under 5 kg in the range of 2 to 25 g / 10 min, preferably in the range of 2.5 to 22 g / 10 min, measured according to ISO 1133-1-2012.

[0036] 16. Composition according to any one of the preceding embodiments, wherein the mass fraction of the thermoplastic polyethylene polymer is in the range of 4 to 90 parts per annum, preferably 25 to 70 parts per annum, preferably 30 to 45 parts per annum.

[0037] 17. Composition according to any one of the preceding embodiments, wherein the proportion of thermoplastic elastomer in the composition is 100 parts per cent.

[0038] 18. Composition according to any one of the preceding embodiments, wherein the proportion of the thermoplastic polyethylene polymer in the composition is in the range of 4 to 50 parts per cent.

[0039] 19. Composition according to any one of the preceding embodiments, which 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.

[0040] 20. Composition according to any one of the preceding embodiments comprising at least one component selected from non-thermoplastic elastomers, reinforcing fillers selected from carbon blacks and other reinforcing fillers, organic and inorganic of the 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, guanylic acid derivatives, extending oils, silica coating agents. 21.Finished or semi-finished product intended for the manufacture of tires comprising a composition according to any of the preceding realizations.

[0041] 22. Tire comprising a tread, which tire comprises a composition according to any one of the embodiments 1 to 20 in all or part of its tread.

[0042] Definitions

[0043] In this document, unless expressly stated otherwise, all percentages (%) shown are percentages (%) by mass.

[0044] On the other hand, any interval of values ​​designated by the expression "between a and b" represents the domain inside the limits a and b (that is, 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 (that is, including the strict bounds a and b).

[0045] In this description, "parts per percent of elastomer" or "pce" means the mass fraction of a constituent per 100 parts per mass of the elastomer(s), that is, of the total mass of the elastomer(s), whether thermoplastic or non-thermoplastic, in the composition. Thus, a constituent with a 60 pce value would mean, for example, 60 g of that constituent per 100 g of elastomer.

[0046] Poly(α-methylstyrene) is commonly understood to be a homopolymer of α-methylstyrene.

[0047] In this description, "X units" (or "X motifs") or units of the X monomer of a polymer are the monomer units that result from the polymerization of monomer X. Thus, "α-methylstyrene units" are the units resulting from the polymerization of the α-methylstyrene monomer.

[0048] The carbon-containing compounds mentioned in the description can be of fossil origin or bio-based. In the latter case, they may be partially or entirely derived from biomass or obtained from renewable raw materials derived from biomass. Similarly, the compounds mentioned may also come from the recycling of previously used materials; that is, they may 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.

[0049] Detailed description of the invention

[0050] The polymer composition according to the invention comprises a thermoplastic elastomer and a thermoplastic polyethylene (or polyethylene) polymer.

[0051] Thermoplastic elastomer (TPE)

[0052] The TPE useful for the needs of the invention is selected from: a triblock thermoplastic elastomer (TPE1), of formula ABA with two rigid thermoplastic segments A comprising α-methylstyrene units linked by a flexible segment B made of a diene elastomer; a triblock thermoplastic elastomer (TPE2) of formula A'-B'-A' with two rigid thermoplastic segments A' comprising α-methylstyrene units linked by a flexible segment B' made of a statistical copolymer elastomer comprising diene units and vinylaromatic units; and a mixture of TPE1 and TPE2. The number-average molar mass (denoted Mn) of the TPE of the invention is preferably between 60,000 and 800,000 g / mol, more preferably between 80,000 and 600,000 g / mol.Below the specified minimum values, 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 observed that a value in the range of 80,000 to 400,000 g / mol is particularly well-suited, especially for the use of TPE in tire compounds. An Mn mass in the range of 100,000 to 300,000 g / mol is even more preferable.

[0053] For TPEs, the number-average molar mass (Mn) of the TPE elastomer is determined by size-exclusion chromatography (SEC) in a manner known to those skilled in the art using a calibration curve made from standard polybutadienes.

[0054] 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.

[0055] As is known, TPEs exhibit two peaks in 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.

[0056] The triblock thermoplastic elastomer TPE1, with formula ABA

[0057] The triblock thermoplastic elastomer denoted TPE1 useful for the implementation of the present invention is 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.

[0058] The diene elastomer block "B" or B block

[0059] Block B of the TPE, as used in 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, most 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 TPE elastomer block 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.

[0060] 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.

[0061] Suitable conjugated dienes according to the invention include, in particular, 1,3-dienes such as 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), and 2,3-di(alkyl Cl-C5)-1,3-butadiene such as, for example, 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. More preferably, block B comprises 1,3-diene monomer units having 4 to 12 carbon atoms. Even more preferably, block B comprises 1,3-butadiene units.

[0062] Block B is preferably a polybutadiene (BR) or a 1,3-butadiene copolymer, in particular a copolymer of 1,3-butadiene and a vinylaromatic monomer.

[0063] Suitable vinylaromatic monomers include styrene, α-methylstyrene, ortho-, meta-, para-methylstyrene, the commercial "vinyl-toluene" mixture, para-, tert-butylstyrene, methoxystyrenes, vinylmesitylene, divinylbenzene, and vinylnaphthalene. The vinylaromatic monomer is preferably styrene or α-methylstyrene, and more preferably α-methylstyrene.

[0064] 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.

[0065] 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.

[0066] 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, and 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 polybutadiene standard curve.

[0067] The thermoplastic block "A" or block A

[0068] The thermoplastic elastomer TPE1 useful for the purposes of the invention comprises two terminal thermoplastic, or rigid, blocks comprising α-methylstyrene units.

[0069] 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 here relative to polystyrene standards.

[0070] According to the invention, the thermoplastic blocks A comprise predominantly α-methylstyrene units by mole to provide good thermal resistance to the thermoplastic elastomer and 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.

[0071] When the thermoplastic blocks A further comprise units derived from at least one other monomer, this monomer may be vinylaromatic, preferably styrene. These units derived from another monomer may also be a conjugated diene. 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 for the thermoplastic elastomer, as well as for the composition containing it. For this reason, thermoplastic blocks A have a Tg which is preferably greater than or equal to 100°C, more preferably of at least 120°C, and even more preferably of at most 200°C, advantageously varying from 100°C to 200°C, preferably from 120°C to 180°C.

[0072] The minimum percentage of thermoplastic blocks A in the thermoplastic 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 thermoplastic elastomer, preferably from 10% to 45% by mass, more preferably from 10% to 40% by mass.

[0073] In the context of the invention, the polymer composition may comprise one or more thermoplastic elastomers TPE1 of formula ABA. In the case where there are several, they are differentiated by their macrostructure or microstructure.

[0074] Advantageously, TPE1 is a triblock thermoplastic elastomer of formula ABA in which blocks A each represent a poly(α-methylstyrene) thermoplastic block and block B is a diene elastomer block, block B 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, the 1,3-diene being preferably 1,3-butadiene.

[0075] The triblock thermoplastic elastomer TPE2, of formula A'-B'-A'

[0076] The triblock thermoplastic elastomer denoted TPE2 useful for the implementation of the present invention is 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.

[0077] The diene elastomer block “B’” or B’ block

[0078] Block B' of TPE2, as required by the invention, can be any statistical copolymer comprising diene units and vinylaromatic units, particularly styrene units, known to those skilled in the art. It 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 according to the invention when used at very low temperatures. Preferably, the Tg of block B' is above -100°C.

[0079] By statistical copolymer elastomer formed of diene units and styrene units (or elastomer block "B'") we mean 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.

[0080] 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. 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 Cl-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.

[0081] Preferably, block B' comprises 1,3-diene units having 4 to 12 carbon atoms; more particularly, block B' comprises 1,3-butadiene units.

[0082] Suitable vinylaromatic monomers include styrene, α-methylstyrene, ortho-meta-, para-methylstyrene, the commercial "vinyl-toluene" mixture, para-tert-butylstyrene, methoxystyrenes, vinylmesitylene, divinylbenzene and vinylnaphthalene.

[0083] 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.

[0084] Block B' is preferably a statistical copolymer comprising 1,3-butadiene units and styrene units. More preferably, block B' is a statistical copolymer of 1,3-butadiene and styrene.

[0085] 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'.

[0086] Preferably, for the invention, block B' has a number-average molar mass (Mn) of at least 45,000 g / mol, preferably at least 65,000 g / mol and at most 700,000 g / mol, preferably at most 500,000 g / mol, so as to impart good elastomeric properties and satisfactory mechanical strength to the thermoplastic elastomer, as well as to 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 polystyrene standards.

[0087] The thermoplastic block "A'" or block A'

[0088] The triblock thermoplastic elastomer TPE2 of formula A'-B'-A' according to the invention comprises two terminal thermoplastic, or rigid, blocks, block A' comprising α-methylstyrene units.

[0089] 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 here relative to polystyrene standards.

[0090] According to the invention, the thermoplastic blocks A' comprise predominantly α-methylstyrene units by mole 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.

[0091] 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. 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 for the thermoplastic elastomer, as well as for the composition according to the invention. For this reason, the thermoplastic blocks A' have a Tg which is preferably greater than or equal to 100°C, more preferably of at least 120°C, and even more preferably of at most 200°C, advantageously varying from 100°C to 200°C, preferably from 120°C to 180°C.

[0092] The minimum percentage of thermoplastic blocks A' in the thermoplastic elastomer can vary depending on the conditions of use of the composition according to the invention and is adjusted by those 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.

[0093] Advantageously, TPE2 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.

[0094] In the context of the invention, the polymer composition may comprise one or more thermoplastic elastomers A'-B'-A'. In the case where there are several, they are differentiated by their macrostructure or their microstructure.

[0095] The thermoplastic elastomer of the polymer composition according to the invention is TPE1 according to a first variant of the invention, is TPE2 according to a second variant of the invention and a mixture of the two thermoplastic elastomers TPE1 and TPE2 according to a third variant of the invention.

[0096] Quantity of thermoplastic elastomer (TPE)

[0097] According to the invention, the elastomer matrix may comprise at least one other elastomer, which is not the TPE elastomer, but this is neither necessary nor preferred. Thus, advantageously, in the polymer composition according to the invention, the proportion of the thermoplastic elastomer (TPE), whether TPE1 or TPE2 or a mixture of the two, is preferably 100 parts per cent.

[0098] When TPE is a mixture of TPE1 and TPE2, the mass percentage of TPE1 relative to the total mass of TPE1 and TPE2 is 50 to 90%.

[0099] According to a particular embodiment, the composition further comprises one or more thermoplastic poly(α-methylstyrene) homopolymers.

[0100] 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.

[0101] Polyethylene (PE) According to the invention, the polymer composition comprises at least one thermoplastic polyethylene (PE) polymer, which PE has a melting point (Tf) in the range of 100°C to 135°C. Advantageously, the Tf of PE is in the range of 120°C to 135°C.

[0102] Surprisingly, the Applicant found that it was possible to replace all or part of the reinforcing fillers conventionally used in rubber compositions, particularly those intended for tire manufacturing, with polyethylene and to obtain rubber compositions that exhibit significantly improved mechanical properties.

[0103] The number-average molar mass (denoted Mn) of PE is preferably between 30,000 and 200,000 g / mol, and even more preferably between 30,000 and 150,000 g / mol. Thus, it has been found that a value in the range of 40,000 to 100,000 g / mol, and preferably 50,000 to 70,000 g / mol, is particularly well-suited, especially for the use of PE according to the invention.

[0104] The number-average molar mass (Mn) of PE is determined in a manner known to those skilled in the art, by size exclusion chromatography (SEC) using a calibration curve made from standard polystyrenes.

[0105] Polyethylene (also called "PE") is a semi-crystalline polyolefin belonging to the family of thermoplastic polymers.

[0106] In the context of the present invention, the term "polyethylene" refers to ethylene homopolymers, that is, polymers obtained from ethylene as the sole monomer. However, it is not excluded that monomers of propylene, 1-butene, 1-hexene, or 1-octene may be present in this polymer. If these monomers are present, however, they are present as impurities and in small proportions, preferably less than 5% by mass relative to the total mass of the polyethylene and the impurities. Ethylene-propylene copolymers (also called EP, EPM, or EPR for "ethylene propylene rubber") are not included in the definition of polyethylene mentioned above.

[0107] Preferably, the polyethylene used in the context of the present invention is non-crosslinked polyethylene. For the purposes of this invention, "non-crosslinked polyethylene" means polyethylene that has not undergone a crosslinking reaction. It is therefore not crosslinked polyethylene, also known as PER (or "PEX" for "crosslinked PE"). PER crosslinked polyethylenes are obtained by polymerizing ethylene monomer followed by a crosslinking reaction, which can be crosslinking with a peroxide (PEX-A process), crosslinking by irradiation (PEX-C process), or crosslinking with silane and a crosslinking catalyst (PEX-B process). Of course, non-crosslinked polyethylene can undergo a crosslinking step after its incorporation into a rubber composition according to the invention, for example, during the curing of a tire comprising a rubber composition according to the invention.

[0108] Preferably, polyethylene is chosen from the group consisting of high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), ultra-high-molecular-weight polyethylene (UHMWPE), ultra-low-density polyethylene (VLDPE), and blends of these polyethylenes. High-density polyethylene is particularly preferred. Preferably, polyethylene, especially high-density polyethylene, has a density in the range of 940 to 970 kg / m³. 3 , more preferably in a range of 940 to 965 kg / m 3 , even more preferentially in a range of 950 to 970 kg / m3 The density is measured at 23°C according to ISO 1183-2019.

[0109] Preferably, polyethylene, especially high-density polyethylene, has a melt flow rate at 190°C under 5 kg within a range of 2 to 25 g / 10 min, preferably within a range of 2.5 to 22 g / 10 min, and more preferably within a range of 10 to 25 g / 10 min. The hot melt flow rate (MFR 190°C / 5 kg) ("MFR" for "Mass Flow Rate" is measured according to ISO 1133-1-2012 at 190°C through a standardized die under the action of a piston weighted with a mass of 5 kg).

[0110] Examples of PE

[0111] Examples of commercially available PE include Eraclene PE marketed by Versalis, Exxon HDPE PE marketed by ExxonMobil Chemical, HDPE marketed by SABIC, or any other PE from other suppliers.

[0112] Quantity of PE

[0113] In the context of the invention, the polymer composition may comprise one or more second PE polymers. In the case where there are several, they are differentiated by their macrostructure or microstructure.

[0114] In the polymer composition according to the invention, the PE content is preferably in the range of 4 to 90 parts per annum, preferably 25 to 70 parts per annum, preferably 30 to 45 parts per annum.

[0115] According to a particular embodiment, the composition further comprises one or more thermoplastic poly(α-methylstyrene) homopolymers.

[0116] 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.

[0117] Plasticizing hydrocarbon resin

[0118] According to a preferred embodiment of the present invention, the composition further comprises a plasticizing hydrocarbon resin, optionally hydrogenated, having a Tg (glass transition temperature) greater than or equal to 40°C, having an aromatic proton content less than or equal to 30 and a number-average molar mass (Mn) greater than or equal to 600 g / mol.

[0119] As is known to those skilled in the art, the term "resin" is reserved in this application, by definition, for a compound which is on the one hand solid at room temperature (23°C) (as opposed to a liquid plasticizing compound such as an oil), and on the other hand compatible (i.e. miscible at the rate used, typically greater than or equal to 5 pc) with the thermoplastic elastomers with which it is mixed.

[0120] Such a plasticizing hydrocarbon resin is for example chosen from cyclopentadiene homopolymer or copolymer resins (abbreviated CPD), dicyclopentadiene homopolymer or copolymer resins (abbreviated DCPD), terpene homopolymer or copolymer resins, C5-cut homopolymer or copolymer resins, C9-cut homopolymer or copolymer resins and mixtures of these resins. Among the copolymer resins above, special mention can be made of those chosen from the group consisting of (D)CPD / vinylaromatic copolymer resins, (D)CPD / terpene copolymer resins, terpene phenol copolymer resins, (D)CPD / C5 cut copolymer resins, (D)CPD / C9 cut copolymer resins, terpene / vinylaromatic copolymer resins, C5 cut / vinylaromatic copolymer resins, and mixtures of these resins.

[0121] The term "terpene" here encompasses, as is well known, the monomers α-pinene, β-pinene, and limonene. Suitable examples of vinylaromatic monomers include styrene, α-methylstyrene, ortho-methylstyrene, meta-methylstyrene, para-methylstyrene, vinyl-toluene, para-tert-butylstyrene, methoxystyrenes, chlorostyrenes, hydroxystyrenes, vinylmesitylene, divinylbenzene, vinylnaphthalene, and any vinylaromatic monomer derived from a C9 cut (or more generally from a C8 to C10 cut).

[0122] In particular, we can mention the resins chosen from the group consisting of terpene homopolymer or copolymer resins, C5 / C9 cup copolymer resins, and mixtures of these resins.

[0123] The plasticizing hydrocarbon resin useful for the needs of the invention may optionally be hydrogenated.

[0124] The plasticizing hydrocarbon resin, optionally hydrogenated, according to the invention has a number-average molar mass (Mn) greater than or equal to 600 g / mol. Preferably, the plasticizing hydrocarbon resin, optionally hydrogenated, has a number-average molecular mass (Mn) in the range of 600 to 1500 g / mol.

[0125] Preferably, the plasticizing hydrocarbon resin, possibly hydrogenated, has a polymolecularity index Ip less than or equal to 2, preferably less than or equal to 1.8, preferably less than 1.7.

[0126] According to embodiments, the plasticizing hydrocarbon resin according to the invention, optionally hydrogenated, has a Tg within a range of 30°C to 150°C, as well as an average number molar mass Mn within a range of 600 to 1500 g / mol and an aromatic proton content within a range of 0 to 30%.

[0127] According to embodiments, the percentage of plasticizing hydrocarbon resin, possibly hydrogenated, is in a range of 5 parts to 70 parts, preferably from 5 to 55 parts.

[0128] The plasticizing hydrocarbon resins, possibly hydrogenated, which can be used according to the invention are commercially available under the references "A125" and "S135" marketed by DRT, under the reference NevChem 140 marketed by Neville Chemical, under the references PICCOTAC 8090 and PICCOTAC 9095 marketed by EASTMANN, under the reference Sylvatraxx 6720 marketed by KRATON.

[0129] The table below summarizes the characteristics of the commercial resins useful for the needs of the invention mentioned above.

[0130] 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.

[0131] One synthesis method involves, for example, the anionic polymerization of α-methylstyrene to simultaneously form the two thermoplastic blocks in the presence of polydienyldilithium as a polymerization initiator. For instance, 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 to produce 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.

[0132] A second synthesis method involves 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 with a live dien end. 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 that is well-known. Coupling agents generally contain a silicon or tin atom substituted with two reactive groups at the carbanion end of the live polymer chains. Examples of coupling agents include dihalogenotins and dihalogenosilanes, notably dibutyltin dichloride or dimethyldichlorosilane, as well as dialcoxysilanes.The polymer from the coupling step is a poly(a-methylstyrene)-b-polydiene-b-poly(a-methylstyrene) triblock.

[0133] Processes for implementing the second synthesis method are described, for example, in US4302559A. The synthesis of the block copolymer includes 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) random copolymer.

[0134] Other processes employing this second method for 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 required 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, W02020070406A1 describes another process for the synthesis of a triblock copolymer poly(a-methylstyrene)-b-polydiene-b-poly(a-methylstyrene) whose central diene elastomer block is also free of a-methylstyrene.

[0135] Those skilled in the art will understand that, depending on the method and conditions of synthesis of the thermoplastic elastomer, the resulting product may consist, in addition to the ABA triblock (or A'-B'-A' triblock), of 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 triblock A-BA (or A' in the case of synthesis of the triblock A'-B'-A').

[0136] Polymerization can be carried out using a continuous process or a batch process.

[0137] 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 bismaleimides, crosslinking activators including zinc monoxide and stearic acid, guanidic derivatives, extending oils, silica coating agents.

[0138] 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.

[0139] 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.

[0140] EXAMPLES OF THE INVENTION'S IMPLEMENTATION

[0141] I. Tests and measurements:

[0142] A - Measurement of the Mn of TPEs

[0143] The macrostructure (Mw, Mn, Ip) of TPEs is determined by size exclusion chromatography (SEC) based on ISO 16014 (Determination of average molecular mass and molecular mass distribution of polymers using size exclusion chromatography), ASTM D5296 (Molecular Weight Averages and molecular weight distribution of polystyrene by High performance size exclusion chromatography), and DIN 55672 (size exclusion chromatography).

[0144] For these measurements, the TPE sample is first solubilized in stabilized tetrahydrofuran 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 three AGILENT columns, consisting of a divinylbenzene polystyrene gel with controlled porosity, is used. The injected volume of the polymer sample solution is 100 pL. 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.

[0145] 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 column pores are to them and the shorter their elution time.

[0146] 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.

[0147] 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.

[0148] In the case of products resulting from the synthesis of block thermoplastic elastomers (thermoplastic block comprising α-methylstyrene—β-polydiene—β- 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 by integrating the RI signal from the SEC chromatograms. The mass proportion of each species is then expressed as a proportion of the integral of all the RI signals in the chromatogram.

[0149] 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 carrying out a calibration line by dosed addition of thermoplastic polymer comprising poly(α-methylstyrene) units, in a manner known to the person skilled in the art.

[0150] B - Differential Calorimetric Analysis (DSC) of TPEs:

[0151] The Tg characterization of the elastomer block and the thermoplastic blocks of the first and second thermoplastic elastomers TPE1 and TPE2 is performed by DSC measurement (Mettler Toledo DSC1 instrument). The instrument operates under a helium atmosphere. A 10 to 20 mg sample of thermoplastic elastomer is placed in a crucible commonly used by those skilled in the art for Tg measurements.

[0152] 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 is then quenched 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 cycle 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 cycle is used. C - Proton Nuclear Magnetic Resonance (NMR) 1 H):

[0153] The proportions of different monomer units within thermoplastic elastomers are determined by NMR analysis. Spectra are acquired on a 500 MHz BRUKER spectrometer equipped with a 5 mm BBIz-grad broadband probe. The NMR experiment 1 Quantitative H uses a simple 30° pulse sequence and a 5-second repetition delay between each acquisition. Samples are solubilized in CDCL. The integration regions considered for quantification are the spectral signature regions of monomer units known to those skilled in the art.

[0154] D- Viscosity measurement RPA (Rubber Process Analyzer)

[0155] The method for measuring G' and G" uses an oscillating disk rheometer (OSR), such as the 2000LV (Oscillating Disk Rheometer) supplied by Alpha Technologies®, equipped with a standard 200 in. lb (22.6 dNm) viscosity sensor. The OSR allows for the torsional stressing of a material sample enclosed in a biconical chamber.

[0156] 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). 3 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.

[0157] We carry out a shaping operation, by applying to the sample enclosed in the RPA chamber a temperature of 180°C for a time of 40 minutes with a deformation of 2.8% peak-to-peak at 1.7 Hz.

[0158] At the end of this operation, the sample is perfectly molded within the closed chamber of the RPA. The sample is then cooled to 40°C directly within the RPA chamber. It is then possible to begin measuring the G' value at 5% peak-to-peak strain and 10 Hz within a temperature range of 40 to 200°C (ramp: 3°C / min).

[0159] We obtain a curve of variation of G' as a function of temperature, from which we can extract the modulus G' of the composition at 190°C.

[0160] The shaping and measurement steps of G' are done without intervention, by programming the RPA machine.

[0161] It is worth recalling that, as is well known to those skilled in the art, the RPA viscosity value 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.

[0162] E- Measurement of the complex dynamic shear modulus

[0163] Dynamic properties (after forming): Tensile test

[0164] The dynamic properties G*(10%) at 23°C are measured on a viscoanalyzer (Metravib VA4000), according to ASTM D 5992-96. The response of a cross-linked sample (cylindrical specimen 4 mm thick and 400 mm long) is recorded. 2(of cross-section), subjected to a sinusoidal alternating simple shear load 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% (return cycle). The results used concern 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.

[0165] 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.

[0166] II. Polymer Synthesis and Preparation of Polymer Compositions

[0167] In the following tests, the following designation will be used: poly(α-methylstyrene) = PAMS Polyethylene = PE

[0168] A- Thermoplastic elastomer TPE

[0169] Synthesis of a triblock polymer poly(α-methylstyrene)-β-polybutadiene-β-poly(α-methylstyrene) or TPE1:

[0170] 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.

[0171] 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.

[0172] After 33 minutes of polymerization at 17°C, the measured AMS conversion is 32%. 0.675 kg of 1,3-butadiene is then added, 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 1,3-butadiene conversion 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.

[0173] 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 dried in a vacuum oven with nitrogen flushing at 60°C.

[0174] The Tg DSC of the polybutadiene flexible block -49°C (AT, glass transition width, being equal to 9°C)

[0175] A-2 - Synthesis of a second triblock polymer poly(α-methylstyrene)-β-poly(butadiene-co-styrene)-β-poly(α-methylstyrene) (or TPE2)

[0176] 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.

[0177] After the temperature was brought to 17°C, 0.15 mol of sec-butyllithium in a 0.16 mol / L cyclohexane solution was introduced into the reactor. The molar ratio of activator (tetrahydrofuran) to initiator (sec-butyllithium) was 2.3. After 40 minutes of polymerization, the measured conversion was 34%. 0.567 kg of 1,3-butadiene and 0.24 kg of styrene were then added, followed by dilution of the reaction mixture with 43.6 L of cyclohexane. Next, 3.8 kg of 1,3-butadiene and 1.6 kg of styrene were added, and the temperature was raised to 40°C. The temperature was maintained at a maximum of 42°C. Polymerization lasted 85 minutes. The measured conversion was 68%.

[0178] After polymerization, 0.072 moles of dimethyldichlorosilane are added under constant stirring. The reaction mixture is maintained at 40 °C for 30 minutes.

[0179] 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.

[0180] The Tg DSC of the flexible poly(butadiene-co-styrene) block -48°C (AT, glass transition width, being equal to 9°C).

[0181] B- Polyethylene PE

[0182] The PEs used in the examples of the invention are PEs from the Eraclene range marketed by Versalis, PEs from the Exxon HDPE range marketed by Exxonmobil chemical.

[0183] C- The plasticizing hydrocarbon resin

[0184] The resins used in the tests are chosen from the commercially known resins A125 and S135 marketed by DRT, NevChem 140 marketed by Neville Chemical, PICCOTAC 8090 and PICCOTAC 9095 marketed by Eastmann, Sylvatraxx 6720 marketed by Kraton, and Novarez TK100 marketed by Rain Carbon.

[0185] D- Preparation of Polymer Compositions:

[0186] Introduce TPE1 and TPE2 into an internal mixer with a volume of 85 cm³ 3 Once heated to a temperature of 120°C, the mixture is mixed at a paddle speed between 80 and 120 rpm. The mixture is then held above its melting point for at least four minutes.

[0187] Table 1 summarizes the components of the polymeric compositions, their characteristics and respective rates.

[0188] [Table 1]:

[0189] TPE1: triblock polymer poly(α-methylstyrene)-β-polybutadiene-β-poly(α-methylstyrene)

[0190] TPE2: triblock polymer poly(α-methylstyrene)-β-poly(butadiene-co-styrene)-β-poly(α-methylstyrene)

[0191] Resin: PICCOTAC 8090 marketed by Eastmann.

[0192] * HDPE HTA 001HP5 from Exxon Mobil

[0193] ** Eraclene MP 90 U BA from ENI Versalis

[0194] Table 2 shows the characteristics and microstructures of the TPEs used in the examples.

[0195] [Table 2]

[0196] AMS = α-methylstyrene

[0197] PAMS = poly(α-methylstyrene)

[0198] % STY = mass percentage of styrene units

[0199] % PB 1.2 = mass percentage of butadiene units in the form of 1,2- units

[0200] % PB 1.4 = mass percentage of butadiene units in the form of 1.4 units

[0201] % AMS = mass percentage of α-methylstyrene units

[0202] Mp = peak mass

[0203] % mass = mass percentage.

[0204] E - Results of Measurements Performed

[0205] Table 4 shows the results of measurements made on the different polymer compositions, M1 to M4.

[0206] [Table 4]

[0207] The results are presented on a basis of 100 relative to the control Ml. Compared to composition Ml which comprises TPE only, compositions M2 to M4 according to the invention exhibit lower viscosity and similar to higher rigidity.

Claims

DEMANDS 1. A polymer composition comprising a thermoplastic elastomer TPE and a thermoplastic polyethylene polymer PE, wherein the thermoplastic elastomer TPE is a block thermoplastic elastomer TPE1 of formula ABA, in which A is a thermoplastic block comprising predominantly α-methylstyrene units by mole 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, or a block thermoplastic elastomer TPE2 of formula A'-B'-A', in which A' is a thermoplastic block comprising predominantly α-methylstyrene units by mole and B' is a statistical copolymer elastomer block comprising diene units and vinylaromatic units, or a mixture of the two block thermoplastic elastomers TPE1 and TPE2, in which thermoplastic polyethylene polymer PE has a melting temperature, Tf, in the range of 100°C to 135°C.

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' are α-methylstyrene homopolymers.

4. Composition according to any one of the preceding claims wherein the thermoplastic blocks A and A', independently of each other, represent at least 10% by mass respectively with respect to the mass of TPE1 and the mass of TPE2, preferably from 10 to 45% by mass respectively with respect to the mass of TPE1 and the mass of TPE2, preferably again from 10% to 40% by mass respectively with respect to the mass of TPE1 and the mass of TPE2.

5. 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.

6. Composition according to claim 5 wherein the units of one or more vinylaromatic monomers of block B are selected from the styrene units, the α-methylstyrene units and their mixture.

7. Composition according to any one of the preceding claims wherein the elastomer block B is a polybutadiene block (BR).

8. 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 vinylaromatic units, relative to the mass of block B'.

9. Composition according to any one of the preceding claims wherein the vinylaromatic units of block B' are styrene units.

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 1 is a random copolymer of 1,3-butadiene and styrene.

12. Composition according to any one of the preceding claims, wherein the thermoplastic polyethylene polymer is selected from the group consisting of high-density polyethylenes (HDPE), low-density polyethylenes (LDPE), linear low-density polyethylenes (LLDPE), medium-density polyethylenes (MDPE), very high molecular weight polyethylenes (PE-UHMW), very low-density polyethylenes and mixtures of these polyethylenes (PE-VLD).

13. Composition according to any one of the preceding claims, wherein the thermoplastic polyethylene polymer is non-crosslinked HDPE polyethylene.

14. Composition according to any one of the preceding claims, wherein the thermoplastic polyethylene polymer has a density in the range of 940 to 970 kg / m³ 3 , preferably in a range of 940 to 965 kg / m 3 measured at 23°C according to ISO 1183-2019.

15. Composition according to any one of the preceding claims, wherein the thermoplastic polyethylene polymer has a melt flow index at 190°C under 5 kg in the range of 2 to 25 g / 10 min, preferably in the range of 2.5 to 22 g / 10 min, measured according to ISO 1133-1-2012.

16. Composition according to any one of the preceding claims, wherein the percentage of thermoplastic elastomer TPE in the composition is 100 pc.

17. Tire comprising a tread, which tire comprises a composition according to any one of claims 1 to 16 in all or part of its tread.

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