Polymer composition comprising a blend of thermoplastic elastomers

Abstract

The invention relates to a polymer composition comprising: a first block thermoplastic elastomer of formula A-B-A, where A is a thermoplastic block comprising predominantly, in moles, α-methylstyrene units, and B is a diene elastomer block comprising more than 95% by weight of diene units relative to the weight of the diene elastomer block; a second block thermoplastic elastomer of formula A'-B'-A', where A' is a thermoplastic block comprising predominantly, in moles, α-methylstyrene units, and B' is a statistical copolymer elastomer block comprising diene units and vinyl aromatic units. Such a composition has improved processability and maintained or even improved rigidity. The invention also relates to finished or semi-finished products which comprise this composition and are intended for the manufacture of tyres or a tread of a tyre comprising such a composition.

Description

[0001] Polymer composition comprising a mixture of thermoplastic elastomers

[0002] The present invention relates to a polymer composition comprising thermoplastic elastomers based on diene units and units comprising aromatic units.

[0003] Prior art

[0004] In the field of tires for motor vehicles, the Applicant has in the past 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.

[0005] Thermoplastic elastomers (or TPE) 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 association of the rigid thermoplastic blocks between them gives the material the behavior of a crosslinked elastomer. Indeed, the rigid nodules, formed by zones of association of thermoplastic blocks between them, act as crosslinking nodes. The material is therefore rigid and does not flow. On the other hand, when the temperature is raised above the glass transition temperature or the melting temperature of the rigid blocks, the polymer will be able to flow, allowing the material to be shaped. The latter regains its rigidity when the temperature returns to the operating temperature, lower than the Tg of the thermoplastic blocks.This particularity of TPE implies a very broad application potential.

[0006] Among the most widespread thermoplastic elastomers are styrenic block copolymers, known as styrenic 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 certain applications, the Tg value of polystyrene blocks is insufficient. Indeed, this value does not allow the use of these TPEs to be considered for the manufacture of certain objects subject in particular to specific conditions of use where temperatures exceed 100°C.

[0007] As other styrenic TPEs, copolymers having poly(a-methyl styrene) 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 the rigid poly(a-methyl styrene) blocks. These thermoplastic elastomers are widely described in the state of the art, in the academic literature or in patent documentation such as in document W02007112232A2 or document FR2243214. The Applicant has previously developed compositions for tires, in particular for tire treads, 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.

[0008] A constant objective of tire manufacturers is to improve the properties of the tread, which must meet a large number of technical requirements, including that of having a very good level of road behavior on a motor vehicle. To improve road behavior, as we know, a certain level of tread rigidity is sought.

[0009] It is therefore desirable that a TPE composition comprising rigid blocks based on α-methyl styrene, has good rigidity, particularly in the manufacture of tires. To this same end, the improvement of the processability and the shaping of such a TPE composition is constantly sought.

[0010] It is generally known that the use of plasticizers in combination with TPEs, in particular TPEs comprising α-methylstyrene-based blocks, makes it possible to improve 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 makes it possible to reduce its rigidity.

[0011] 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 retaining the rigidity of the composition.

[0012] Statement of the invention

[0013] This objective is achieved in that the inventors discovered during their research that a specific rubber composition comprising a first block TPE, comprising a diene flexible block and thermoplastic rigid blocks comprising α-methylstyrene units, and a second block TPE comprising a random copolymer flexible block comprising units (or units) of diene origin and units (or units) of vinylaromatic origin and thermoplastic rigid blocks comprising α-methylstyrene units exhibited improved processability, without this being to the detriment of the rigidity of the composition. These significant improvements in properties make it possible to achieve a very good level of compromise between processability and road behavior of tires comprising a tread based on such a TPE composition.

[0014] Thus, a first subject of the invention is a polymer composition comprising: a first thermoplastic elastomer with blocks of formula ABA, in which A is a thermoplastic block comprising predominantly by mole of α-methylstyrene units and B is a diene elastomer block comprising more than 95% by mass of the diene units relative to the mass of the diene elastomer block, a second thermoplastic elastomer with blocks of formula A' -B' -A', in which A' is a thermoplastic block comprising predominantly by mole of α-methylstyrene units and B' is a random copolymer elastomer block comprising diene units and vinylaromatic units.

[0015] The invention also relates to finished or semi-finished products comprising a polymer composition in accordance with the invention and intended for the manufacture of tires, in particular, a tread of a tire comprising such a composition.

[0016] The invention also relates to a tire comprising a polymeric composition in accordance with the invention in all or part of its tread.

[0017] Summary of the invention

[0018] The invention, described in more detail below, relates to at least one of the embodiments listed in the following points:

[0019] 1 Polymer composition comprising: a first thermoplastic elastomer with blocks of formula ABA, in which A is a thermoplastic block comprising predominantly by mole of α-methylstyrene units and B is a diene elastomer block comprising more than 95% by mass of the diene units relative to the mass of the diene elastomer block, a second thermoplastic elastomer with blocks of formula A' -B' -A', in which A' is a thermoplastic block comprising predominantly by mole of α-methylstyrene units and B' is a random copolymer elastomer block comprising diene units and vinylaromatic units. 2 Composition according to embodiment 1 in which the thermoplastic blocks A and A' comprise more than 95% by mole of α-methylstyrene units.

[0020] 3 Composition according to embodiment 1 or 2 in which the thermoplastic blocks A and A' comprise styrene units.

[0021] 4 Composition according to embodiment 1 or 2 in which the thermoplastic blocks A and A' are homopolymers of α-methylstyrene.

[0022] 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 more preferably 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 and more preferably from 10% to 40% by mass.

[0023] 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.

[0024] 7 Composition according to embodiment 6 in which the units of a vinylaromatic monomer of block B are chosen from styrene and α-methylstyrene.

[0025] 8 Composition according to any one of the preceding embodiments in which the elastomer block B comprises predominantly by mass 1,3-butadiene units.

[0026] 9 Composition according to any one of the preceding embodiments in which the elastomer block B is a polybutadiene block (BR).

[0027] 10 Composition according to any one of the preceding embodiments in which the first thermoplastic elastomer is a poly(a-methyl styrene) - polybutadiene - poly(a-methyl styrene) copolymer.

[0028] 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 the block B', the vinylaromatic units preferably being styrene units.

[0029] 12 Composition according to any one of the preceding embodiments in which the elastomer block B' comprises 1,3-butadiene units and styrene units. 13 Composition according to any one of the preceding embodiments in which the elastomer block B' is a random copolymer of 1,3-butadiene and styrene.

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

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

[0032] 16 Composition according to any one of the preceding embodiments comprising at least one component chosen from non-thermoplastic elastomers, reinforcing fillers chosen 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 comprising zinc monoxide and stearic acid, guanidine derivatives, extending oils, silica covering agents.

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

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

[0035] Definitions

[0036] In this document, unless expressly stated otherwise, all percentages (%) indicated are percentages (%) by mass.

[0037] On the other hand, any range of values ​​designated by the expression "between a and b" represents the domain within the limits a and b (i.e., excluding the limits a and b) while any range of values ​​designated by the expression "from a to b" means the domain of values ​​from a to b (i.e., including the strict limits a and b).

[0038] In this description, the term "part per cent of elastomer" or "pce" means the part by mass of a constituent per 100 parts by mass of the elastomer(s), i.e. of the total mass of the elastomer(s), whether thermoplastic or non-thermoplastic, of the composition. Thus, a constituent at 60 pce will mean, for example, 60 g of this constituent per 100 g of elastomer.

[0039] Poly(a-methyl styrene) is commonly understood to mean a homopolymer of a-methylstyrene.

[0040] In the present description, "X units" (or "X units") or units of the monomer X of a polymer are understood to mean the monomer units which result from the polymerization of the monomer X. Thus, "α-methyl styrene units" are the units resulting from the polymerization of the α-methylstyrene monomer.

[0041] The carbon-containing compounds mentioned in the description may be of fossil or bio-sourced origin. In the latter case, they may be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. Similarly, the compounds mentioned may also come from the recycling of materials already in use, i.e. they may be, partially or totally, derived from a recycling process, or obtained from raw materials themselves derived from a recycling process. This includes, in particular, monomers, polymers, etc.

[0042] Detailed description of the invention

[0043] The polymer composition according to the invention comprises a first thermoplastic elastomer and a second thermoplastic elastomer.

[0044] The two TPEs useful for the purposes of the invention are triblock elastomers, of formula ABA for the first with two rigid thermoplastic segments A comprising α-methylstyrene units linked by a flexible segment B consisting of a diene elastomer, and of formula A' -B' -A' for the second with two rigid thermoplastic segments A' comprising α-methylstyrene units linked by a flexible segment B' consisting of a random copolymer elastomer comprising diene units and vinylaromatic units.

[0045] The number-average molar mass (denoted Mn) of the TPEs of the invention is preferably between 30,000 and 500,000 g / mol, more preferably between 40,000 and 400,000 g / mol. Below the indicated minima, the cohesion between the chains of the TPE risks being affected; on the other hand, an increase in the operating temperature risks affecting the mechanical properties, in particular the properties at break. Furthermore, an excessively high Mn mass can be detrimental to processing. Thus, it has been found that a value in a range of 50,000 to 300,000 g / mol is particularly well suited, in particular to use of the TPE in a tire composition. An Mn in a range of 80,000 to 150,000 g / mol is more preferred.

[0046] For TPEs, the number-average molar mass (Mn) of Telastomer TPE is determined by size exclusion chromatography (SEC) in a manner known to those skilled in the art using a calibration curve produced from polybutadienes (PB) standards.

[0047] 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.

[0048] As is known, TPEs exhibit two glass transition temperature (Tg) peaks, 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.

[0049] I- The first thermoplastic elastomer

[0050] The first thermoplastic elastomer used for implementing the invention is a block copolymer of formula ABA, in which A is a thermoplastic block comprising predominantly by mole of α-methyl styrene units and B is a diene elastomer block comprising more than 95% by mass of the diene units relative to the mass of the diene elastomer block.

[0051] The diene elastomer block “B” or B block

[0052] The B block of the first TPE, for the purposes of the invention, is a diene elastomer. By diene elastomer is meant 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). The B block generally has a Tg of less than 0°C and very preferably less than -10°C. A Tg value higher than these values ​​can reduce the performance of the composition when used at very low temperatures. Also preferably, the Tg of the elastomer block of the TPE is greater than -100°C. The B block has the essential characteristic of containing predominantly by mass diene units. In other words, the diene units of the B block represent the highest weight fraction of the constituent units of the B block.

[0053] 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 optionally by copolymerization with one or more vinylaromatic monomers having from 8 to 20 carbon atoms.

[0054] Suitable conjugated dienes which can be used in accordance with the invention are, in particular, 1,3-dienes such as 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-di(C1-C8 alkyl)-1,3-butadienes 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.

[0055] 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.

[0056] Block B is preferably a polybutadiene (BR), or a copolymer of 1,3-butadiene, in particular a copolymer of 1,3-butadiene and a vinylaromatic monomer.

[0057] Suitable vinylaromatic monomers include styrene, α-methyl styrene, ortho-meta-, para-methyl styrene, the commercial mixture "vinyl-toluene", para-tert-butyl styrene, methoxystyrenes, vinylmesitylene, divinylbenzene and vinylnaphthalene. The vinylaromatic monomer is preferably styrene or α-methyl styrene, more preferably α-methylstyrene.

[0058] According to a particularly preferred embodiment of the invention, the elastomer block B comprises predominantly by mass 1,3-butadiene units, preferably the block B is a polybutadiene block.

[0059] 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 of the elastomer block B are advantageously chosen from styrene and α-methylstyrene, more advantageously α-methylstyrene. 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 give the thermoplastic elastomers good elastomeric properties and satisfactory mechanical strength.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 produced from polybutadiene standards.

[0060] The thermoplastic block “A” or block A

[0061] The first thermoplastic elastomer useful for the purposes of the invention comprises two terminal thermoplastic, or rigid, blocks comprising α-methylstyrene units.

[0062] 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 expressed here relative to polystyrene standards.

[0063] According to the invention, the thermoplastic blocks A comprise predominantly in moles α-methylstyrene units in order to provide good thermal resistance to the thermoplastic elastomer, as well as to the composition in accordance with the invention. In other words, the α-methylstyrene units of the block A represent the highest molar fraction of the constituent units of the block A. The thermoplastic block A preferably comprises more than 95% in moles of α-methylstyrene units, a percentage expressed relative to all the constituent monomer units of the block A.

[0064] When the thermoplastic blocks A further comprise units derived from at least one other monomer, this may be vinylaromatic, preferably it is styrene. These units derived from another monomer may also be a conjugated diene.

[0065] According to a particularly preferred embodiment of the invention, the thermoplastic blocks A are essentially composed of α-methylstyrene units, that is to say that the thermoplastic blocks A do not comprise units of a monomer other than α-methylstyrene. Thus, better thermal resistance at higher temperatures of the thermoplastic elastomer is observed, as well as of the composition containing it. For this reason, the thermoplastic blocks A have a Tg which 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. The minimum rate of thermoplastic blocks A in the first plastic elastomer may vary depending on the conditions of use of the composition in accordance with 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.

[0066] 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.

[0067] Advantageously, the first TPE is a triblock thermoplastic elastomer of formula ABA in which the blocks A each represent a poly(a-methyl styrene) thermoplastic block and the block B is a diene elastomer block, the 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 and in particular 1,3-butadiene, preferably 1,3-butadiene.

[0068] II- The second thermoplastic elastomer

[0069] The second thermoplastic elastomer used for implementing the invention is a block copolymer of formula A' -B' -A', in which A' is a thermoplastic block comprising predominantly in moles α-methyl styrene units and B' is a random copolymer elastomer block comprising diene units and vinylaromatic units, in particular a random copolymer elastomer block (1,3-diene-co-vinylaromatic monomer).

[0070] The diene elastomer block “B'” or B' block

[0071] The B' block of the second TPE for the purposes of the invention may be any random copolymer comprising diene units and vinylaromatic units, in particular styrene units, known to those skilled in the art. It generally has a Tg of less than 0°C and very preferably less than -10°C. A Tg value higher than these values ​​may reduce the performance of the composition in accordance with the invention when used at very low temperatures. Also preferably, the Tg of the B' block is greater than -100°C.

[0072] By statistical copolymer elastomer formed from diene units and styrenic 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 Ar- CH=CH2 OR Ar-CMe=CH2, the symbol Ar representing an aromatic group. Preferably, the 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 from 8 to 20 carbon atoms.

[0073] As conjugated dienes, which can be used in accordance with the invention, the following are particularly suitable:

[0074] 1,3-dienes such as 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-di(C1-C8 alkyl)-1,3-butadienes 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.

[0075] Preferably, the B' block comprises 1,3-diene units having 4 to 12 carbon atoms, more particularly, the B' block comprises 1,3-butadiene units.

[0076] Suitable vinylaromatic monomers include styrene, α-methyl styrene, ortho-meta-, para-methyl styrene, the commercial mixture "vinyl-toluene", para-tert-butyl styrene, methoxystyrenes, vinylmesitylene, divinylbenzene and vinylnaphthalene.

[0077] According to one embodiment of the invention, the elastomer block B' comprises styrene or α-methyl styrene units or both styrene units and α-methyl styrene units, preferably styrene units.

[0078] The B' block is preferably a random copolymer comprising 1,3-butadiene units and styrene units. More preferably, the B' block is a random copolymer of

[0079] 1.3-butadiene and styrene.

[0080] 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 the block B'.

[0081] Preferably for the invention, the 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 give the second thermoplastic elastomer good elastomeric properties and satisfactory mechanical strength, as well as the composition in accordance with the invention. The number-average molar mass of the block B' can be determined by size exclusion chromatography in a manner known to those skilled in the art using a calibration curve produced from polybutadienes standards.

[0082] The thermoplastic block "A'" or block A' 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.

[0083] 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 expressed here relative to polystyrene standards.

[0084] According to the invention, the thermoplastic blocks A' comprise predominantly in moles α-methylstyrene units in order to provide good thermal resistance to the thermoplastic elastomer, as well as to the composition in accordance with the invention. Each thermoplastic block A' preferably comprises more than 95 mol% of α-methylstyrene units.

[0085] When the thermoplastic blocks A' further comprise units of at least one other monomer, this may be vinylaromatic, preferably it is styrene. These units of another monomer may also be a conjugated diene.

[0086] According to a particularly preferred embodiment of the invention, the thermoplastic blocks A' are essentially composed of α-methylstyrene units, that is to say that the thermoplastic blocks A' do not comprise units of a monomer other than α-methylstyrene. Thus, better thermal resistance at higher temperatures of the thermoplastic elastomer is observed, as well as of the composition in accordance with the invention. For this reason, the thermoplastic blocks A' have a Tg which 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.

[0087] The minimum content of thermoplastic blocks A' in the second plastic elastomer may vary depending on the conditions of use of the composition in accordance with 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.

[0088] Advantageously, the second TPE is a triblock thermoplastic elastomer of formula A'-B'-A' in which the blocks A' each represent a poly(a-methyl styrene) thermoplastic block, the block B' is a random 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. 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.

[0089] According to one embodiment of the invention, the content of the first thermoplastic elastomer is within a range from 20 to 80 phr, preferably from 30 to 70 phr and the content of the second thermoplastic elastomer is within a range from 20 to 80 phr, preferably from 30 to 70 phr, and the total content of the first thermoplastic elastomer and the second thermoplastic elastomer is greater than or equal to 80 phr and less than or equal to 100 phr.

[0090] According to a particular embodiment, the composition further comprises one or more thermoplastic poly(a-methyl styrene) homopolymers.

[0091] According to a particular embodiment of the invention, the composition comprises a homopolymer of α-methylstyrene (poly(α-methyl styrene)) in a mass proportion ranging from 5 to 45% by mass relative to the total mass of the composition.

[0092] Synthesis

[0093] The thermoplastic elastomers useful for the purposes of the invention can be manufactured in a known manner according to various synthesis methods described in the prior art.

[0094] A first method of synthesis consists, for example, in anionically polymerizing α-methylstyrene in order to concomitantly form the two thermoplastic blocks in the presence of polydienyldilithium as a polymerization initiator. For example, WO8505116A1 and EP0014947A1 describe such methods which comprise the copolymerization of styrene and α-methylstyrene to generate the thermoplastic blocks. A triblock copolymer of the poly(α-methylstyrene-co-styrene)-b-polydiene-b-poly(α-methylstyrene-co-styrene) type is thus obtained. Similar methods of synthesis can be envisaged for manufacturing poly(α-methylstyrene)-b-polydiene-poly(α-methylstyrene) triblock polymers using polydienyllithium as a polymerization initiator. Such a method is for example described in FR3045615.

[0095] A second method of synthesis consists of anionically polymerizing α-methyl styrene in a first step. Then, in a second step, the diene monomer is polymerized on the living poly(α-methyl styrene) chains obtained. This gives a diblock poly(α-methylstyrene)-b-polydiene polymer whose dienyl end is living. 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 living polymer chains. Examples of coupling agents include dihalotin and dihalosilane, in particular dibutyltin dichloride or dimethyldichlorosilane, or dialkoxysilanes.The polymer resulting from the coupling step is a poly(a-methylstyrene)-b-polydiene-b-poly(a-methylstyrene) triblock.

[0096] Methods for implementing the second mode of synthesis are described, for example, in US4302559A. The synthesis of the block copolymer comprises a first step of polymerization of α-methyl styrene at low temperature in the presence of a first polar agent, called a polar activator, to form the poly(α-methyl styrene) block. In a second step, a first addition of a small amount of conjugated diene is carried out to add a living polydienyl block of a few units at the end of the chain of the poly(α-methyl styrene) block and thus avoid the depolymerization of α-methyl styrene, 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 inserting the residual α-methyl styrene in a random manner 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 static poly(butadiene-co-a-methyl styrene) copolymer.

[0097] Other processes implementing this second mode of synthesis of a poly(a-methylstyrene)-b-polydiene-b-poly(a-methylstyrene) triblock copolymer are described as making it possible to obtain a central diene elastomer block free of a-methylstyrene. For example, in document FR2243214, the process consists, in a first step, of homopolymerizing the a-methylstyrene in a concentrated medium at temperatures between 0°C and 40°C. At the end of this step, the conjugated diene and the solvent necessary for the synthesis of the poly(conjugated diene) block are added. At the end of this last polymerization step, the polymer obtained is coupled using a coupling agent. More recently, W02020070406A1 describes another process for the synthesis of a poly(a-methylstyrene)-b-polydiene-b-poly(a-methylstyrene) triblock copolymer whose central diene elastomer block is also free of a-methylstyrene.

[0098] The 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, in addition to the triblock ABA, (or triblock A'-B'-A') of other populations of macromolecules such as thermoplastic polymers having the microstructure of the block A (or A'), diene elastomers having the microstructure of the block B (or B') or diblock polymers of formula AB (or A'-B'), the blocks A, A', B and B' being as defined in the present application. Thus, within the scope of the invention, the person 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 triblock ABA and the triblock A'-B'-A' 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 comprise a thermoplastic polymer having the microstructure of the A block in the case of synthesis of the ABA triblock (or A' in the case of synthesis of the A'-B'-A' triblock).

[0099] Polymerization can be carried out using a continuous process or a batch process.

[0100] The polymer composition according to the invention may further comprise at least one component chosen from non-thermoplastic elastomers, reinforcing fillers chosen 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 comprising zinc monoxide and stearic acid, guanidine derivatives, extending oils, silica covering agents.

[0101] The present invention also relates to a finished or semi-finished product intended for the manufacture of tires comprising a polymer composition according to the invention.

[0102] Another subject 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.

[0103] EXAMPLES OF CARRYING OUT THE INVENTION

[0104] I. Tests and measurements

[0105] A - Measurement of the Mn of TPEs

[0106] 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) standards.

[0107] For these measurements, the TPE sample is first solubilized in stabilized tetrahydrofuran at a concentration of 1 g / L; then the solution is filtered with PTFE filters with a porosity of 0.45 μm before injection. The equipment used is a "WATERS alliance" chromatographic chain. 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 is used (set of three AGILENT columns). 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 chromatographic data is the "WATERS ALLIANCE" system.

[0108] 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.

[0109] The calculated number-average molar masses are relative to a calibration curve produced from commercial standard polystyrenes "PSS-pskitlh-3" in the case of thermoplastic polymers comprising a-methyl styrene units alone.

[0110] The calculated number-average molar masses are relative to a calibration curve produced from commercial standard polybutadienes "PSS-bdfkit" in the case of products comprising diblock and / or triblock thermoplastic elastomers containing butadiene units.

[0111] In the case of products resulting from the synthesis of thermoplastic block elastomers (thermoplastic block comprising a-methyl styrene units — b — polydiene — b — thermoplastic block comprising a-methyl styrene units) containing less than 10% by mass of thermoplastic polymer comprising poly (a-methyl styrene) units, the distribution of the different species of the product is carried out 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 of the chromatogram.

[0112] In the case of products containing more than 10% by mass of thermoplastic polymer comprising poly(a-methyl styrene) 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 producing a calibration line by metered addition of thermoplastic polymer comprising poly(a-methyl styrene) units, in a manner known to those skilled in the art.

[0113] B - Differential scanning calorimetry (DSC) of TPEs

[0114] The characterization of the Tg of the elastomer block and the thermoplastic blocks is carried out by a DSC measurement using a DSC1 device from Mettler Toledo. The device is operated under a helium atmosphere. A sample of 10 to 20 mg of thermoplastic elastomer is placed in a crucible conventionally used by those skilled in the art to carry out Tg measurements.

[0115] The sample is first placed in an isothermal state at +25°C for 2 minutes and then cooled to -150°C at a rate of 50°C per minute. An isothermal state is then applied at -150°C for 10 minutes. An initial heating 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 device. The sample is then kept in an isothermal state at -150°C for 15 minutes. The second heating then begins from -150°C to +10°C at a speed of 20°C per minute (Tg measurement range of the elastomer part of the TPE) and continues from +10°C to +250°C at a speed of 50°C per minute (Tg measurement range of the thermoplastic blocks). In this measurement only the second heating is used.

[0116] C - Proton Nuclear Magnetic Resonance (NMR

[0117] The determinations of the levels of the different monomer units within T thermoplastic elastomer are carried out by NMR analysis. The spectra are acquired on a 500MHz BRUKER spectrometer equipped with a "Broad Band" BBIz-grad 5mm probe. The quantitative 'H NMR experiment uses a simple 30° pulse sequence and a repetition delay of 5 seconds between each acquisition. The samples are solubilized in CDCh. The integration zones considered for quantification are the spectral signature zones of the monomer units known to those skilled in the art.

[0118] D- RPA (Rubber Process Analyzer) viscosity measurement

[0119] The method for measuring G' and G” uses an RPA type oscillating disc rheology apparatus, such as the 2000 LV device (Oscillating Disc Rheometer) supplied by Alpha Technologies®, equipped with the standard 200 in. Ibs (22.6 dNm) viscosity sensor. The RPA machine allows torsional stress to be applied to a material sample enclosed in a chamber (or enclosure) with biconical walls. To measure G' (T) (elastic shear modulus), a material sample of approximately 30 mm in diameter and a mass of approximately 5 g is placed in the RPA enclosure or chamber (a total volume of 5 cm 3 is considered optimal; the quantity is sufficient when a small amount of sample escapes from each side of the enclosure and is visible at the end of the test). At the end of this operation, the sample is perfectly molded in the closed enclosure of the RPA.

[0120] A shaping operation is carried out by applying a temperature of 180°C to the sample enclosed in the RPA enclosure for a period of 40 minutes with a deformation of 2.8% peak-peak at 1.7 Hz.

[0121] At the end of this operation, the sample is perfectly molded in the closed enclosure of the RPA. The sample is then cooled to 40°C directly in the RPA enclosure. It is then possible to start measuring the value of G' at 5% peak-peak strain and 10 Hz in a temperature range varying from 40 to 200°C (ramp: 3°C / min).

[0122] 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.

[0123] The shaping and measuring steps of G' are done without intervention, by programming the RPA machine.

[0124] 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.

[0125] E- Measurement of the complex dynamic shear modulus

[0126] Dynamic properties (after forming): Tensile test

[0127] 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 sample of crosslinked composition (cylindrical specimen 4 mm thick and 400 mm long) is recorded. 2of section), subjected to sinusoidal stress in alternating simple shear, at a frequency of 10 Hz, under defined temperature conditions, for example at 23°C according to standard ASTM D 1349-99, or depending on the case at a different temperature. A strain amplitude sweep is carried out 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.

[0128] It is recalled that, in a manner well known to those skilled in the art, the value of G* 10% at 23°C is representative of the rigidity of the material: the lower G* 10% at 23°C, the lower the rigidity.

[0129] II. Synthesis of polymers and preparation of polymer compositions

[0130] In the following tests we will adopt the following name: poly(a-methyl styrene) = PAMS

[0131] A - Synthesis of a first TPE, triblock polymer poly(a-methylstyrene)-b-polybutadiene-b-poly(a-methylstyrene) or TPE1

[0132] In an 80 L jacketed reactor, 2.0 L of cyclohexane, 0.106 L of tetrahydrofuran and 5 kg of α-methylstyrene were successively introduced under constant nitrogen flow. All products were previously purified and / or dried.

[0133] After the temperature has been brought to 17°C, 0.125 mol of sec-butyllithium is introduced into the reactor in the form of 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.

[0134] After 33 minutes of polymerization at 17°C, the measured AMS conversion is 32%, 0.675 kg of 1,3-butadiene is introduced, then the reaction mixture is diluted with 23 L of cyclohexane. 3.9 kg of 1,3-butadiene is then introduced and the temperature is raised to 40°C. The temperature is maintained at a maximum temperature of 42°C. The polymerization lasts 102 minutes. The measured 1,3-butadiene conversion is 92%. After the polymerization, 0.06 mole of dimethyldichlorosilane is added with constant stirring. The reaction medium is maintained at 40°C for 30 minutes.

[0135] A Tissue of this coupling step a triblock polymer poly(a-methylstyrene)-b-polybutadiene-b-poly(a-methylstyrene) is synthesized. 0.2 pce of an antioxidant, Irganox 1520L® (from BASF), is then added. The anti-oxidized polymer is separated from the solvent by steam stripping, then the polymer is dried in a vacuum oven under nitrogen flushing at 60°C.

[0136] The Tg DSC of the flexible polybutadiene block -49°C (AT, glass transition width, being equal to 9°C). Bl - Synthesis of a first second TPE, triblock polymer poly(a-methylstyrene)-b-poly(butadiene-co-styrene)-b-poly(a-methylstyrene) (or TPE2-1)

[0137] In an 80 L jacketed reactor, 2.1 L of cyclohexane, 0.106 L of tetrahydrofuran and 5 kg of α-methylstyrene were successively introduced under constant nitrogen flow. All products were previously purified and / or dried.

[0138] After the temperature has been brought to 17°C, 0.125 mol of sec-butyllithium is introduced into the reactor in the form of 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.

[0139] After 50 minutes of polymerization of T a-methyl styrene, the measured conversion of AMS is 50%), 0.42 kg of 1,3-butadiene and 0.26 kg of styrene are introduced, then 39 L of cyclohexane are added to the reaction mixture. Then 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 temperature of 42°C. The polymerization lasts 145 minutes. The measured conversion is 74%.

[0140] After polymerization, 0.06 mole of dimethyldichlorosilane is added with constant stirring. The reaction medium is maintained at 40°C for 30 minutes.

[0141] At the end of this coupling step, a triblock polymer poly(a-methylstyrene)-b-butadiene-styrene-b-poly(a-methylstyrene) is synthesized. 0.2 pce of an antioxidant, Irganox 1520L® (from BASF), is added. The anti-oxidized polymer is separated from the solvent by steam stripping, then the polymer is dried in a vacuum oven under nitrogen sparging at 60°C.

[0142] The DSC Tg of the flexible poly(butadiene-co-styrene) block -38°C (AT, glass transition width, being equal to 9°C).

[0143] B-2- Synthesis of a second TPE, triblock polymer poly(a-methylstyrene)-b-poly(butadiene-co-styrene)-b-poly(a-methylstyrene) (or TPE2-2)

[0144] In an 80 L reactor equipped with a double jacket, 2.6 L of cyclohexane, 0.028 L of tetrahydrofuran and 2 kg of alphamethylstyrene were successively introduced under constant nitrogen scavenging. All products were previously purified and / or dried.

[0145] 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. After 40 minutes of polymerization, the measured conversion is 34%, 0.567 kg of 1,3-butadiene and 0.24 kg of styrene are introduced, after which the reaction mixture is diluted with 43.6 L of cyclohexane. 3.8 kg of 1,3-butadiene and 1.6 kg of styrene are then introduced and the temperature is raised to 40°C. The temperature is maintained at a maximum temperature of 42°C. The polymerization lasts 85 minutes. The measured conversion is 68%.

[0146] After polymerization, 0.072 moles of dimethyldichlorosilane are added with constant stirring. The reaction medium is maintained at 40°C for 30 minutes.

[0147] At the end of this coupling step, a poly(a-methylstyrene)-b-butadiene-styrene-b-poly(a-methyl styrene) triblock polymer is synthesized. 0.2 pce of an antioxidant, Irganox 1520L® (from BASF), is added. The anti-oxidized polymer is separated from the solvent by a steam stripping operation, then the polymer is dried in a vacuum oven under nitrogen flushing at 60°C.

[0148] The DSC Tg of the flexible poly(butadiene-co-styrene) block -48°C (AT, glass transition width, being equal to 9°C).

[0149] C - Preparation of polymer compositions

[0150] For each composition, the TPE polymers are placed in a container with toluene in the proportions of 10% by volume of polymer in toluene, and stirred for a period of 24 hours at room temperature. The solution is then placed for drying under a hood at room temperature for a period of 24 to 36 hours, then in a vacuum oven at 60°C for 24 hours. The film obtained is shaped by pressing at a temperature of 180°C for 10 minutes in order to obtain the test specimens necessary for the characterizations.

[0151] Table 1 summarizes the components of the polymer compositions, their characteristics and respective rates in pce.

[0152] [Table 1] AT = glass transition width

[0153] Tables 2 and 3 show the characteristics of the TPEs used in the examples.

[0154] [Table 2] [Table 3]

[0155] P AMS = poly(a-methyl styrene)

[0156] % STY = mass percentage of Styrene units

[0157] % PB 1.2 = mass percentage of butadiene units in the form of 1.2 unit - % PB 1.4 = mass percentage of butadiene units in the form of 1.4 unit

[0158] % AMS = mass percentage of a-methyl styrene units

[0159] Mp = peak mass

[0160] % mass = mass percentage.

[0161] D - Results Table 4 shows the results of the different polymer compositions, M1 to M5. [Table 4]

[0162] The results are presented on a base of 100 compared to the control Ml. Compared to the composition

[0163] Ml which comprises TPE1 only, compositions M2 to M5 according to the invention have a lower viscosity and a higher rigidity.

Claims

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

2. Composition according to claim 1 in which the thermoplastic blocks A and A' comprise more than 95 mol% of α-methylstyrene units.

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

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

5. Composition according to any one of the preceding claims 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, more preferably 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, more preferably from 10% to 40% by mass.

6. Composition according to any one of the preceding claims in which 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 in which the elastomer block B mainly comprises 1,3-butadiene units, preferably the block B is a polybutadiene block (BR).

8. 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 the block B'.

9. Composition according to any one of the preceding claims 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 styrene relative to the mass of the block B'.

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

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

12. Composition according to any one of the preceding claims in which the content of the first thermoplastic elastomer is within a range from 20 to 80 phr, preferably from 30 to 70 phr, the content of the second thermoplastic elastomer is within a range from 20 to 80 phr, preferably from 30 to 70 phr, and the total content of the first thermoplastic elastomer and the second thermoplastic elastomer is greater than or equal to 80 phr.

13. Composition according to any one of the preceding claims, which composition further comprises an α-methylstyrene homopolymer in a mass proportion ranging 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.

Images