Polymer composition comprising a blend of thermoplastic elastomers

Abstract

This invention relates to a polymer composition comprising a first thermoplastic block elastomer of the formula A-B-A, wherein A is a thermoplastic block comprising, molarly, primarily α-methylstyrene units, and B is a diene elastomer block comprising, relative to the mass of, greater than 95% by mass of diene units; and a second thermoplastic block elastomer of the formula A'-B'-A', wherein A' is a thermoplastic block comprising, molarly, primarily α-methylstyrene units, and B' is a statistical copolymer elastomer block comprising diene units and vinyl aromatic units. This composition exhibits improved processability and maintained or even increased stiffness. The invention also relates to finished or semi-finished products comprising this composition, intended for use in the manufacture of tires or tire treads comprising this composition.

Description

Technical Field

[0001] This invention relates to a polymer composition comprising a thermoplastic elastomer based on diene units and units comprising aromatic moieties. Background Technology

[0002] In the field of tires for motor vehicles, the applicant has previously developed rubber compositions containing at least one thermoplastic elastomer. These tires offer a very good trade-off between grip and rolling resistance performance, while also exhibiting good road handling.

[0003] Thermoplastic elastomers (TPEs) are elastomers of great interest in many fields because they combine the properties of flexible elastomer blocks and rigid thermoplastic blocks. Furthermore, the association of the rigid thermoplastic blocks with each other gives the material the characteristics of a cross-linked elastomer. This is because the rigid nodules formed by the regions where the thermoplastic blocks associate with each other act as cross-linking nodes. Therefore, the material is rigid and does not flow. On the other hand, when the temperature rises above the glass transition temperature or melting point of the rigid blocks, the polymer becomes able to flow, thus enabling the material to be molded. When the temperature returns to a level below the operating temperature (Tg) of the thermoplastic blocks, the latter regains its rigidity. This distinctive characteristic of TPEs implies a very wide range of application potential.

[0004] The most common thermoplastic elastomers include styrene block copolymers, known as styrene TPEs. The glass transition temperature (Tg) of polystyrene blocks is approximately 80°C to 100°C, depending on the size of the polystyrene blocks. For some applications, the Tg value of polystyrene blocks is insufficient. In fact, this value makes it inconceivable to use these TPEs to manufacture certain articles specifically designed for use under conditions exceeding 100°C.

[0005] Copolymers containing poly(α-methylstyrene) blocks instead of polystyrene blocks have been proposed as other styrene TPEs because these copolymers exhibit superior heat resistance due to the high Tg of approximately 150°C–170°C in their rigid poly(α-methylstyrene) blocks. These thermoplastic elastomers are extensively described in the prior art, academic literature, and patent literature, such as WO2007112232A2 or FR2243214.

[0006] The applicant has previously developed compositions containing thermoplastic elastomers for tires (particularly tire treads), such as document WO2012152686 or more recent document WO2023202915A1, which describe a TPE matrix comprising a TPE triblock having a diene elastomer block and two thermoplastic blocks comprising α-methylstyrene units.

[0007] Tire manufacturers are constantly striving to improve tire tread performance, which must meet numerous technical requirements, particularly ensuring excellent road handling in motor vehicles. To improve road handling, it is known that the tread needs a certain level of rigidity.

[0008] Therefore, it is ideal for TPE compositions containing rigid blocks based on α-methylstyrene to possess good rigidity, especially in tire manufacturing. To this end, there has been a continuous search for improving the processability and moldability of such TPE compositions.

[0009] It is well known that the use of plasticizers in combination with TPEs (especially TPEs containing α-methylstyrene-based blocks) can improve their processability and moldability, as described in documents WO2012152686 or WO2015 / 113966. However, it is also generally believed that the use of plasticizers in TPE compositions reduces rigidity. Summary of the Invention

[0010] The objective of this invention is to improve the processability of thermoplastic block TPE rubber compositions containing α-methylstyrene units while increasing or at least maintaining the rigidity of the composition.

[0011] This objective was achieved as follows: the inventors discovered a specific rubber composition during their research that exhibits improved processability without compromising the rigidity of the composition. The rubber composition comprises a first block TPE and a second block TPE. The first block TPE comprises a diene flexible block and a thermoplastic rigid block, wherein the thermoplastic rigid block comprises α-methylstyrene units. The second block TPE comprises a flexible random copolymer block and a rigid thermoplastic block, wherein the flexible random copolymer block comprises diene-derived units (or portions) and vinyl aromatic-derived units (or portions), and the rigid thermoplastic block comprises α-methylstyrene units.

[0012] These significant performance improvements enable tires, including those with treads based on such TPE compositions, to achieve a very good balance between tire processability and road handling.

[0013] Therefore, the first subject of the present invention is a polymer composition comprising: - A first thermoplastic block elastomer of formula ABA, wherein A is a thermoplastic block that mainly comprises α-methylstyrene units on a molar basis, and B is a diene elastomer block that, based on the mass of the diene elastomer block, comprises more than 95% by mass of diene units. - A second thermoplastic block elastomer of formula A'-B'-A', wherein A' is a thermoplastic block that mainly comprises α-methylstyrene units on a molar basis, and B' is a random copolymer elastomer block that comprises diene units and vinyl aromatic units.

[0014] Another subject of the invention is finished or semi-finished products comprising polymer compositions according to the invention, said finished or semi-finished products intended for use in the manufacture of tires, particularly tire treads comprising such compositions.

[0015] Another subject of the invention is a tire, which contains a polymer composition according to the invention in all or part of its tread.

[0016] The content of this invention The subject matter of this invention (which will be described in more detail below) is at least one of the embodiments listed below: 1. A polymer composition comprising: - A first thermoplastic block elastomer of formula ABA, wherein A is a thermoplastic block that mainly comprises α-methylstyrene units on a molar basis, and B is a diene elastomer block that, based on the mass of the diene elastomer block, comprises more than 95% by mass of diene units. - A second thermoplastic block elastomer of formula A'-B'-A', wherein A' is a thermoplastic block that mainly comprises α-methylstyrene units on a molar basis, and B' is a random copolymer elastomer block that comprises diene units and vinyl aromatic units.

[0017] 2. The composition according to embodiment 1, wherein the thermoplastic blocks A and A' comprise greater than 95 mol% of α-methylstyrene units.

[0018] 3. The composition according to embodiment 1 or 2, wherein the thermoplastic blocks A and A' comprise styrene units.

[0019] 4. The composition according to embodiment 1 or 2, wherein the thermoplastic blocks A and A' are α-methylstyrene homopolymers.

[0020] 5. The composition according to any one of the foregoing embodiments, wherein the thermoplastic block A accounts for at least 10% by mass, preferably 10% to 45% by mass, more preferably 10% to 40% by mass, of the first thermoplastic elastomer; and the thermoplastic block A' accounts for at least 10% by mass, preferably 10% to 45% by mass, more preferably 10% to 40% by mass, of the second thermoplastic elastomer.

[0021] 6. The composition according to any one of the foregoing embodiments, wherein the elastomeric block B comprises 0% by mass to less than 5% by mass of one or more vinyl aromatic monomer units.

[0022] 7. The composition according to embodiment 6, wherein the vinyl aromatic monomer unit of block B is selected from styrene and α-methylstyrene.

[0023] 8. The composition according to any one of the foregoing embodiments, wherein the elastomeric block B comprises, by weight, a 1,3-butadiene unit.

[0024] 9. The composition according to any one of the foregoing embodiments, wherein the elastomeric block B is a polybutadiene (BR) block.

[0025] 10. The composition according to any one of the foregoing embodiments, wherein the first thermoplastic elastomer is a poly(α-methylstyrene)-polybutadiene-poly(α-methylstyrene) copolymer.

[0026] 11. The composition according to any one of the foregoing embodiments, wherein, relative to the mass of the block B', the elastomeric 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 vinyl aromatic units, wherein the vinyl aromatic units are preferably styrene units.

[0027] 12. The composition according to any one of the foregoing embodiments, wherein the elastomeric block B' comprises a 1,3-butadiene unit and a styrene unit.

[0028] 13. The composition according to any one of the foregoing embodiments, wherein the elastomeric block B' is a random copolymer of 1,3-butadiene and styrene.

[0029] 14. The composition according to any one of the foregoing embodiments, wherein the content of the first thermoplastic elastomer is in the range of 20 to 80 phr, preferably 30 to 70 phr, the content of the second thermoplastic elastomer is in the range of 20 to 80 phr, preferably 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.

[0030] 15. The composition according to any one of the foregoing embodiments, wherein the composition further comprises an α-methylstyrene homopolymer (poly(α-methylstyrene)) in a mass percentage ranging from 5% to 45% by mass relative to the total mass of the composition.

[0031] 16. The composition according to any one of the foregoing embodiments, comprising at least one component selected from: non-thermoplastic elastomers, reinforcing fillers, elastomer / filler coupling agents, non-reinforcing fillers, processing aids, stabilizers, plasticizers, pigments, antioxidants, anti-fatigue agents, anti-ozone waxes, adhesion promoters, reinforcing resins, crosslinking systems, crosslinking activators, guanidine derivatives, extender oils, silica covering agents, wherein the reinforcing filler is selected from carbon black and other organic and inorganic silica reinforcing fillers, particularly silica, and mixtures of these fillers, the crosslinking system is based on sulfur and / or peroxides and / or bismaleimide, and the crosslinking activator comprises zinc monoxide and stearic acid.

[0032] 17. A finished or semi-finished product intended for use in the manufacture of tires, comprising the composition according to any one of the foregoing embodiments.

[0033] 18. A tire comprising a tread, said tire including a composition according to any one of embodiments 1 to 16 in all or part of its tread.

[0034] definition In this document, unless otherwise expressly stated, all percentages (%) shown are mass percentages (%).

[0035] Furthermore, any numerical interval expressed as “between a and b” represents the range within the endpoints a and b (i.e., excluding the endpoints a and b), while any numerical interval expressed as “from a to b” refers to the range of values ​​extending from a to b (i.e., including the strict endpoints a and b).

[0036] In this specification, the terms "parts / 100 parts elastomer" or "phr" are intended to mean parts by mass of a component / 100 parts by mass of elastomer, that is, 100 parts by mass of the total mass of elastomers in the composition (whether they are thermoplastic or non-thermoplastic). Thus, for example, a component of 60 phr would mean 60 grams of that component / 100 grams of elastomer.

[0037] Poly(α-methylstyrene) is generally understood to refer to α-methylstyrene homopolymer.

[0038] In this specification, the designation "unit X" (or "part X") or "unit of monomer X" of a polymer should be understood as referring to a monomer unit polymerized from monomer X. Therefore, "α-methylstyrene unit" is a unit polymerized from α-methylstyrene monomer.

[0039] The carbon-containing compounds mentioned in the specification can be fossil-derived or bio-based. In the latter case, they can be partially or wholly produced from biomass, or obtained from renewable raw materials derived from biomass. Similarly, the mentioned compounds can also originate from the recycling of used materials, meaning they can be partially or wholly derived from recycling processes, or obtained from raw materials that themselves originate from recycling processes. This particularly applies to monomers, polymers, etc. Invention Details The polymer composition according to the present invention comprises a first thermoplastic elastomer and a second thermoplastic elastomer.

[0041] Both TPEs applicable to the purposes of this invention are triblock elastomers. The first has the formula ABA, wherein two rigid thermoplastic segments A comprise α-methylstyrene units and are connected by a flexible segment B composed of a diene elastomer. The second has the formula A'-B'-A', wherein two rigid thermoplastic segments A' comprise α-methylstyrene units and are connected by a flexible segment B' composed of a random copolymer elastomer comprising diene units and vinyl aromatic units.

[0042] The number-average molar mass (denoted as Mn) of the TPE of the present invention is preferably between 30,000 and 500,000 g / mol, more preferably between 40,000 and 400,000 g / mol. Below these minimum values, the cohesive strength between the chains of the TPE may be affected; furthermore, increased operating temperature may affect mechanical properties, particularly fracture properties. Furthermore, excessively high mass Mn is detrimental to processing. Therefore, values ​​in the range of 50,000 to 300,000 g / mol have been found to be particularly suitable, especially for TPEs used in tire compositions. Mn in the range of 80,000 to 150,000 g / mol is more preferred.

[0043] For TPE, 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 generated from polybutadiene (PB) standards.

[0044] The polydispersity index (PI) of TPE (Note: PI = Mw / Mn, where Mw is the weight-average molar mass and Mn is the number-average molar mass) is preferably less than 3, more preferably less than 2, and even more preferably less than 1.5.

[0045] As is well known, TPE has two glass transition temperature (Tg) peaks, with the lowest temperature corresponding to the elastomeric portion of TPE and the highest temperature corresponding to the thermoplastic portion of TPE.

[0046] I - First thermoplastic elastomer The first thermoplastic elastomer used in this invention is a block copolymer of the formula ABA, wherein A is a thermoplastic block that mainly comprises α-methylstyrene units on a molar basis, and B is a diene elastomer block that comprises diene units in an amount greater than 95% by mass relative to the diene elastomer block.

[0047] Diene elastomer block "B" or block B For the purposes of this invention, block B of the first TPE is a diene elastomer. A diene elastomer should be understood as an elastomer (i.e., a homopolymer or copolymer) at least partially derived from a diene monomer (a monomer containing two conjugated or non-conjugated carbon-carbon double bonds). The Tg of block B is typically below 0°C, very preferably below -10°C. Tg values ​​above these values ​​may degrade the performance of the composition during use at extremely low temperatures. It is also preferable that the Tg of the elastomeric block of the TPE is greater than -100°C. An essential characteristic of block B is that it predominantly comprises diene units (by mass). In other words, the diene units of block B constitute the highest weight fraction of the constituent units of block B.

[0048] Preferably, block B is any homopolymer obtained by polymerization of conjugated diene monomers having 4 to 15 carbon atoms, or a copolymer obtained by copolymerization of one or more conjugated dienes having 4 to 15 carbon atoms, or optionally a copolymer obtained by copolymerization of one or more vinyl aromatic monomers having 8 to 20 carbon atoms.

[0049] The following are particularly suitable as conjugated dienes that can be used according to the present invention: 1,3-dienes, such as 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene); 2,3-di(C1-C5 alkyl)-1,3-butadiene, such as 2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene or 2-methyl-3-isopropyl-1,3-butadiene, phenyl-1,3-butadiene and 1,3-pentadiene.

[0050] More preferably, block B comprises a monomeric unit of a 1,3-diene having 4 to 12 carbon atoms. Even more preferably, block B comprises a 1,3-butadiene unit.

[0051] Block B is preferably a copolymer of polybutadiene (BR) or 1,3-butadiene, particularly a copolymer of 1,3-butadiene and a vinyl aromatic monomer.

[0052] The following are particularly suitable as vinyl aromatic monomers: styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene or p-methylstyrene, commercial mixtures of "vinyltoluene", p-(tert-butyl)styrene, methoxystyrene, vinyltrimethylbenzene, divinylbenzene and vinylnaphthalene. The vinyl aromatic monomer is preferably styrene or α-methylstyrene, more preferably α-methylstyrene.

[0053] According to a particularly preferred embodiment of the invention, the elastomeric block B mainly comprises 1,3-butadiene units by weight, and block B is preferably a polybutadiene block.

[0054] According to one embodiment of the invention, the elastomeric block B comprises 0% to less than 5% by mass of one or more vinyl aromatic monomer units. According to this preferred embodiment of the invention, the vinyl aromatic monomer units of the elastomeric block B are advantageously selected from styrene and α-methylstyrene, more advantageously α-methylstyrene.

[0055] Preferably, the number-average molar mass (“Mn”) of the elastomeric block B is at least 25,000 g / mol, more preferably at least 35,000 g / mol and at most 350,000 g / mol, and more preferably at most 250,000 g / mol, thereby giving the thermoplastic elastomer good elastic properties and satisfactory mechanical strength. The number-average molar mass of the elastomeric 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 generated from a polybutadiene standard.

[0056] Thermoplastic block "A" or block A A first thermoplastic elastomer that can be used for the purposes of this invention comprises two terminal thermoplastic blocks (or rigid blocks) containing α-methylstyrene units.

[0057] Preferably, the number-average molar mass (“Mn”) of each thermoplastic block A is at least 5,000 g / mol, more preferably at least 7,000 g / mol and at most 100,000 g / mol, more preferably at most 50,000 g / mol. The number-average molar mass of thermoplastic block A can be determined by size exclusion chromatography in a manner known to those skilled in the art, and is expressed herein relative to a polystyrene standard.

[0058] According to the present invention, thermoplastic block A mainly comprises α-methylstyrene units (in molar terms), thereby imparting good heat resistance to the thermoplastic elastomer and composition according to the present invention. In other words, the α-methylstyrene units of block A constitute the maximum molar fraction of the constituent units of block A. Thermoplastic block A preferably comprises more than 95 mol% α-methylstyrene units, this percentage being expressed relative to the total constituent monomer units of block A.

[0059] When thermoplastic block A further comprises units derived from at least one other monomer, said at least one other monomer may be a vinyl aromatic monomer, preferably styrene. These units derived from other monomers may also be conjugated dienes.

[0060] According to a particularly preferred embodiment of the invention, thermoplastic block A is primarily composed of α-methylstyrene units, meaning that thermoplastic block A does not contain units derived from monomers other than α-methylstyrene. Therefore, the thermoplastic elastomer and compositions comprising it are observed to exhibit better heat resistance at higher temperatures. Consequently, the Tg of thermoplastic block A is preferably greater than or equal to 100°C, more preferably at least 120°C, even more preferably at most 200°C, advantageously within the range of 100°C to 200°C, preferably 120°C to 180°C.

[0061] The minimum content of thermoplastic block A in the first thermoplastic elastomer may vary depending on the conditions of use of the composition according to the invention and may be adjusted by those skilled in the art. Preferably, the two thermoplastic blocks A account for at least 10% by mass of the first thermoplastic elastomer, more preferably 10% to 45% by mass, and more preferably 10% to 40% by mass.

[0062] In the context of this invention, the polymer composition may comprise one or more first thermoplastic elastomers of the formula ABA. If multiple first thermoplastic elastomers are present, they are distinguished by their macroscopic or microscopic structures.

[0063] Advantageously, the first TPE is a triblock thermoplastic elastomer of the formula ABA, wherein block A represents a poly(α-methylstyrene) thermoplastic block, block B is a diene elastomer block, block B is particularly a homopolymer or copolymer of 1,3-diene, the 1,3-diene being as defined above, particularly 1,3-butadiene, preferably 1,3-butadiene.

[0064] II - Second thermoplastic elastomer The second thermoplastic elastomer used to implement the present invention is a block copolymer of the formula A'-B'-A', wherein A' is a thermoplastic block that mainly comprises α-methylstyrene units on a molar basis, and B' is a random copolymer elastomer block comprising diene units and vinyl aromatic units, particularly a random copolymer elastomer block (1,3-diene-co-vinyl aromatic comonomer).

[0065] Diene elastomer block "B'" or block B' The second TPE used for the purposes of this invention can be any random copolymer known to those skilled in the art that comprises diene units and vinyl aromatic units (especially styrene units). Its Tg is typically below 0°C, very preferably below -10°C. Tg values ​​above these values ​​may degrade the performance quality of the compositions according to the invention during use at extremely low temperatures. It is also preferred that the Tg of block B' is greater than -100°C.

[0066] The expression “random copolymer elastomer formed of diene unit and styrene unit” (or elastomer block “B’)” should be understood as referring to a random copolymer elastomer derived at least in part from diene monomers (monomers with two conjugated or non-conjugated carbon-carbon double bonds) and at least in part from vinyl aromatic monomers (monomers of the formula Ar-CH=CH2 or Ar-CMe=CH2, where the symbol Ar represents aryl).

[0067] Preferably, block B' is an elastomer obtained by random copolymerization of one or more conjugated dienes having 4 to 15 carbon atoms with one or more vinyl aromatic monomers having 8 to 20 carbon atoms.

[0068] The following are particularly suitable as conjugated dienes that can be used according to the present invention: 1,3-dienes, such as 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene); 2,3-di(C1-C5 alkyl)-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.

[0069] Preferably, block B' comprises a 1,3-diene unit having 4 to 12 carbon atoms; more specifically, block B' comprises a 1,3-butadiene unit.

[0070] The following are particularly suitable as vinyl aromatic monomers: styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene or p-methylstyrene, "vinyltoluene" commercial mixtures, p-(tert-butyl)styrene, methoxystyrene, vinyltrimethylbenzene, divinylbenzene and vinylnaphthalene.

[0071] According to one embodiment of the invention, the elastomeric block B' comprises a styrene unit or an α-methylstyrene unit, or both a styrene unit and an α-methylstyrene unit, preferably a styrene unit.

[0072] Block B' is preferably a random copolymer comprising 1,3-butadiene units and styrene units. More preferably, block B' is a random copolymer of 1,3-butadiene and styrene.

[0073] According to one embodiment of the invention, the elastomeric block B' advantageously contains more than 5% by mass and less than 45% by mass, preferably more than 10% by mass and less than 40% by mass, styrene relative to the mass of the block B'.

[0074] Preferably, in this invention, the number-average molar mass (“Mn”) of block B’ is 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, thereby imparting good elastic properties and satisfactory mechanical strength to the second thermoplastic elastomer and 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 generated from a polybutadiene standard.

[0075] Thermoplastic block "A'" or block A' The second triblock thermoplastic elastomer A'-B'-A' according to the present invention comprises two terminal thermoplastic or rigid blocks, wherein block A' comprises α-methylstyrene units.

[0076] Preferably, the number-average molar mass (“Mn”) of each thermoplastic block A’ is at least 5,000 g / mol, more preferably at least 7,000 g / mol, and at most 100,000 g / mol, more preferably at most 50,000 g / mol. The number-average molar mass of block A’ can be determined by size exclusion chromatography in a manner known to those skilled in the art, and is expressed herein relative to a polystyrene standard.

[0077] According to the present invention, the thermoplastic block A' mainly comprises (in molar) α-methylstyrene units, thereby imparting good heat resistance to the thermoplastic elastomer and composition according to the present invention. Each thermoplastic block A' preferably comprises more than 95 mol% α-methylstyrene units.

[0078] When the thermoplastic block A' further comprises units of at least one other monomer, the monomer may be a vinyl aromatic monomer; preferably styrene. These units of the other monomer may also be conjugated dienes.

[0079] According to a particularly preferred embodiment of the invention, the thermoplastic block A' is primarily composed of α-methylstyrene units, meaning that the thermoplastic block A' does not contain units derived from monomers other than α-methylstyrene. Therefore, the thermoplastic elastomer and composition according to the invention are observed to have better heat resistance at higher temperatures. Consequently, the Tg of the thermoplastic block A' is preferably greater than or equal to 100°C, more preferably at least 120°C, and even more preferably at most 200°C, advantageously within the range of 100°C to 200°C, preferably 120°C to 180°C.

[0080] The minimum content of thermoplastic block A' in the second thermoplastic elastomer may vary depending on the conditions of use of the composition according to the invention and may be adjusted by those skilled in the art. Preferably, thermoplastic block A' accounts for at least 10% by mass of the thermoplastic elastomer, more preferably from 10% to 45% by mass, and even more preferably from 10% to 40% by mass.

[0081] Advantageously, the second TPE is a triblock thermoplastic elastomer of the formula A'-B'-A', wherein each block A' represents a poly(α-methylstyrene) thermoplastic block, and block B' is a random copolymer elastomer block of 1,3-diene and vinyl aromatic monomers, wherein the 1,3-diene is as defined above, and the 1,3-butadiene and the vinyl aromatic monomers are preferably as defined above, and preferably styrene.

[0082] In the context of this invention, the polymer composition may comprise one or more second thermoplastic elastomers A'-B'-A'. If multiple second thermoplastic elastomers are present, they are distinguished by their macroscopic or microscopic structures.

[0083] According to one embodiment of the present invention, the content of the first thermoplastic elastomer is in the range of 20 to 80 phr, preferably 30 to 70 phr; the content of the second thermoplastic elastomer is in the range of 20 to 80 phr, preferably 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.

[0084] According to a particular embodiment, the composition further comprises one or more thermoplastic poly(α-methylstyrene) homopolymers.

[0085] According to a specific embodiment of the invention, the composition comprises an α-methylstyrene homopolymer (poly(α-methylstyrene)) in a mass percentage ranging from 5% to 45% by mass relative to the total mass of the composition.

[0086] synthesis The thermoplastic elastomers used for the purposes of this invention can be prepared in a known manner according to various synthesis methods described in the prior art.

[0087] For example, one synthetic method involves anionic polymerization of α-methylstyrene in the presence of polydiene dilithium as a polymerization initiator to simultaneously form two thermoplastic blocks. Such methods are described, for example, in WO8505116A1 and EP0014947A1, which involve copolymerization of styrene and α-methylstyrene to generate thermoplastic blocks. This yields a poly(α-methylstyrene-co-styrene)-block-polydiene-block-poly(α-methylstyrene-co-styrene) triblock copolymer. Using lithium diene as a polymerization initiator, similar synthetic methods can be envisioned to produce poly(α-methylstyrene)-block-polydiene-poly(α-methylstyrene) triblock polymers. This process is described, for example, in FR3045615.

[0088] The second synthetic method involves anionic polymerization of α-methylstyrene in a first step. Then, in a second step, a diene monomer is polymerized onto the resulting active poly(α-methylstyrene) chain. This yields a poly(α-methylstyrene)-block-polydiene diblock polymer with active diene ends. To obtain a triblock thermoplastic elastomer, a coupling agent is added at this stage to couple the diene blocks of the chain. This step is carried out in a manner known per se. The coupling agent typically contains silicon or tin atoms, which are replaced by two groups that react with the carbanion ends of the active polymer chain. Examples of coupling agents that may be mentioned include dihalotin compounds and dihalosilane compounds, particularly dibutyltin dichloride or dimethyldichlorosilane, or dialkoxysilane. The polymer obtained from the coupling step is a poly(α-methylstyrene)-block-polydiene-block-poly(α-methylstyrene) triblock.

[0089] For example, US4302559A describes a process for implementing the second synthetic method. The synthesis of the block copolymer includes a first step in which α-methylstyrene is polymerized at low temperature in the presence of a first polar agent (called a polar activator) to form poly(α-methylstyrene) blocks. In a second step, a small amount of conjugated diene is initially added to add several active polydiene blocks to the chain ends of the poly(α-methylstyrene) blocks, thereby preventing the depolymerization of α-methylstyrene. A second addition of conjugated diene is then performed in the presence of another polar agent (called a polar activator) to allow the formation of a second block through subsequent polymerization of the conjugated diene, while the remaining α-methylstyrene is randomly inserted into the polymer chain. To obtain a triblock copolymer, a coupling agent is used to couple the polymer produced by the final polymerization step. According to this synthetic method, the central diene elastomer block of the triblock copolymer is a random poly(butadiene-copolymer-α-methylstyrene) copolymer.

[0090] Other methods employing this second method for synthesizing poly(α-methylstyrene)-block-polydiene-block-poly(α-methylstyrene) triblock copolymers have been described as capable of obtaining α-methylstyrene-free central diene elastomer blocks. For example, in document FR2243214, this method involves homopolymerizing α-methylstyrene in a concentrated medium at a temperature between 0°C and 40°C in a first step. At the end of this step, the conjugated diene and solvent necessary for synthesizing the poly(conjugated diene) block are added. At the end of this final polymerization step, the resulting polymer is coupled using a coupling agent. More recently, WO2020070406A1 describes another method for synthesizing poly(α-methylstyrene)-block-polydiene-block-poly(α-methylstyrene) triblock copolymers whose central diene elastomer blocks also do not contain α-methylstyrene.

[0091] Those skilled in the art will understand that, depending on the method and conditions for synthesizing the thermoplastic elastomer, the resulting product may include, in addition to triblock ABA (or triblock A'-B'-A'), other macromolecular groups, such as thermoplastic polymers having a microstructure of block A (or A'), diene elastomers having a microstructure of block B (or B'), or diblock polymers of formula AB (or A'-B'), wherein blocks A, A', B, and B' are as defined in this application. Therefore, in the context of this invention, those skilled in the art will understand that when the triblock elastomer is not separated after synthesis, the synthesized product may contain all of these groups. The products synthesized from triblock ABA and triblock A'-B'-A' may each contain up to 20% by mass of a diblock polymer of formula AB and a diblock polymer of formula A'-B'. Similarly, in the case of synthesizing triblock ABA, the resulting product may contain a thermoplastic polymer with a microstructure of block A, or in the case of synthesizing triblock A'-B'-A', the resulting product may contain a thermoplastic polymer with a microstructure of block A'.

[0092] Polymerization can be carried out using either continuous or intermittent processes (batch processing).

[0093] The polymer composition according to the invention may further comprise at least one component selected from: non-thermoplastic elastomers, reinforcing fillers, elastomer / filler coupling agents, non-reinforcing fillers, processing aids, stabilizers, plasticizers, pigments, antioxidants, anti-fatigue agents, anti-ozone waxes, adhesion promoters, reinforcing resins, crosslinking systems, crosslinking activators, guanidine derivatives, extender oils, and silica covering agents, wherein the reinforcing fillers are selected from carbon black and other organic and inorganic silica reinforcing fillers, particularly silica, and mixtures of these fillers, the crosslinking system is based on sulfur and / or peroxides and / or bismaleimide, and the crosslinking activator comprises zinc monoxide and stearic acid.

[0094] The present invention also relates to a finished or semi-finished product intended for use in the manufacture of tires, the finished or semi-finished product comprising a polymer composition according to the present invention.

[0095] Another subject of the invention is a tire comprising a tread in which a polymer composition according to the invention is included in all or part of its tread. Detailed Implementation

[0096] I. Testing and Measurement Measurement of Mn in A-TPE The macroscopic structure of TPE (Mw, Mn, PI) was determined by size exclusion chromatography (SEC) based on standard ISO 16014. 使用尺寸排阻色谱法测定聚合物的平均分子量和分子量分布 using size exclusion chromatography ), ASTM D5296 ( 分子量 高性能尺寸排阻色谱法测定聚苯乙烯的平均值和分子量分布 size exclusion chromatography The determination was performed using DIN 55672 (size exclusion chromatography).

[0097] For these measurements, the TPE sample was pre-dissolved in tetrahydrofuran at a stable concentration of 1 g / L, and then filtered through a PTFE filter with a porosity of 0.45 μm before injection. Waters Alliance chromatography lines were used. Tetrahydrofuran was used as the elution solvent, the flow rate was 1 mL / min, the system temperature was 35 °C, and the analysis time was 40 min. A set of three Agilent "Polypore" columns (consisting of divinylbenzene polystyrene gel with controlled porosity) was used. The injection volume of the polymer sample solution was 100 μL. The detector was a Waters 2410 differential refractometer, also kept at a constant temperature of 35 °C, and the associated software for processing the chromatographic data was the Waters Alliance system.

[0098] Polymer chains are separated based on the volume they occupy when dissolved in the solvent: the larger the volume, the less contact they have with the pores of the column, and the shorter the elution time.

[0099] For thermoplastic polymers containing only α-methylstyrene units, the calculated number-average molar mass is relative to the calibration curve generated from the commercial “PSS-pskit1h-3” polystyrene standard.

[0100] For products containing diblock and / or triblock thermoplastic elastomers with butadiene units, the calculated number-average molar mass is relative to a calibration curve generated from a commercially available "PSS-bdfkit" polybutadiene standard.

[0101] For products containing less than 10% by mass of a thermoplastic polymer (containing poly(α-methylstyrene) units), said products are synthesized from block thermoplastic elastomers (thermoplastic blocks-block-polydiene-block-thermoplastic blocks containing α-methylstyrene units), the distribution of different components in the product is obtained by integrating the RI signals of the SEC chromatogram. The mass proportion of each component is related to the integral of all RI signals in the chromatogram.

[0102] For products containing more than 10% by mass of thermoplastic polymer (containing poly(α-methylstyrene) units), the distribution of different components in the product is obtained by integrating the RI signal of the SEC chromatogram, while the RI response value is adjusted by using a specific increment of the refractive index dn / dc of each component, or by quantitatively adding thermoplastic polymer containing poly(α-methylstyrene) units, in a manner known to those skilled in the art, to generate a calibration line.

[0103] Differential scanning calorimetry (DSC) analysis of B-TPE The Tg values ​​of the elastomeric and thermoplastic blocks were characterized by DSC measurements using a DSC1 instrument from Mettler Toledo. The instrument was operated under a helium atmosphere. Samples of thermoplastic elastomer ranging from 10 to 20 milligrams were placed in crucibles commonly used by those skilled in the art for Tg measurements.

[0104] First, the sample was placed at a constant temperature of +25°C for 2 minutes, then cooled to -150°C at a rate of 50°C / min. It was then held at -150°C for 10 minutes. The first heating was then initiated, increasing the temperature from -150°C to +10°C at a rate of 20°C / min, and then continuing to increase it from 10°C to 250°C at a rate of 50°C / min. The sample was then quenched at the maximum rate allowed by the instrument to reach -150°C. The sample was then held at a constant temperature of -150°C for 15 minutes. The second heating was then initiated, increasing the temperature from -150°C to +10°C at a rate of 20°C / min (the range used for measuring the Tg of the elastomeric portion of TPE), and then continuing to increase it from +10°C to +250°C at a rate of 50°C / min (the range used for measuring the Tg of the thermoplastic block). This measurement used only the second heating operation.

[0105] C-proton nuclear magnetic resonance (C-proton nuclear magnetic resonance) 1 1H NMR) The content of various monomer units in thermoplastic elastomers was determined by NMR analysis. Spectra were acquired using a Bruker 500 MHz spectrometer equipped with a 5 mm BBIZ-class "broadband" probe. Quantitative analysis was performed. 1 The 1H NMR experiments used a 30° single-pulse sequence with a 5-second repetition time between each acquisition. The sample was dissolved in CDCl3. The integration region used for quantification is considered to be the spectral characteristic region of the monomeric unit known to those skilled in the art.

[0106] D-RPA ( Rubber Processing Analyzer Viscosity measurement The measurements of G' and G'' were performed using an RPA (Rotating Disk Rheometer), such as the Alpha Technologies® 2000 Lv instrument, equipped with a standard 200 in.lbs (22.6 dNm) viscosity sensor. The RPA device allows for torsional pressure to be applied to material samples encapsulated in a chamber with biconical walls.

[0107] To measure G'(T) (shear modulus), a material sample with a diameter of approximately 30 mm and a mass of approximately 5 g is placed in the chamber of the RPA (a total volume of 5 cubic centimeters is considered optimal; the amount is sufficient when a small amount of sample leaks from each side of the chamber and is visible at the end of the test). At the end of the operation, the sample is completely molded in the closed chamber of the RPA.

[0108] The molding operation was performed by applying a temperature of 180°C to the sample enclosed in the RPA chamber for 40 minutes at a peak-to-peak strain of 2.8% at 1.7 Hz.

[0109] At the end of this operation, the sample is fully molded in the closed chamber of the RPA. The sample is then cooled to 40°C directly in the RPA chamber. The G' value can then be measured in the temperature range of 40 to 200°C at 5% peak-to-peak strain and 10 Hz (ramp: 3°C / min).

[0110] A curve of G' versus temperature is obtained, and the G' modulus of the composition at 190°C can be obtained from the curve.

[0111] By programming the RPA equipment, the forming and G' measurement steps can be performed without intervention.

[0112] To recap, as is well known to those skilled in the art, the RPA value at 190°C represents the processability of the material: the lower the viscosity at 190°C, the easier the material is to mold.

[0113] E - Measurement of complex dynamic shear modulus Dynamic performance (post-molding): Tensile test The dynamic properties G* (10%) at 23°C were measured using a viscosity analyzer (Metravib VA4000) according to standard ASTM D 5992-96. The responses of cross-linked composition samples (cylindrical specimens with a thickness of 4 mm and a cross-sectional area of ​​400 mm²) subjected to simple alternating sinusoidal shear stress at a frequency of 10 Hz were recorded according to standard ASTM D 1349-99 under defined temperature conditions (e.g., at 23°C), or at different temperatures depending on the specific circumstances. Strain amplitude scans were performed from 0.1% to 50% (outward cycle) and then from 50% to 1% (backward cycle). The results used were correlated with the complex dynamic shear modulus G*. For the backward cycle, the values ​​of the complex dynamic shear modulus G* (10%) at 23°C and 10% strain are shown.

[0114] To recap, as is well known to those skilled in the art, the value of G*10% at 23°C represents the rigidity of a material: the lower the G*10% at 23°C, the greater the reduction in rigidity.

[0115] II. Polymer Synthesis and Preparation of Polymer Compositions In the following tests, the following names will be used: Poly(α-methylstyrene) = PAMS A - Synthesize the first TPE, namely, poly(α-methylstyrene)-block-polybutadiene-block-poly(α-methylstyrene) triblock polymer or TPE1. Under continuous nitrogen purging, 2.0 L of cyclohexane, 0.106 L of tetrahydrofuran, and 5 kg of α-methylstyrene were sequentially introduced into an 80 L jacketed reactor. All products were pre-purified and / or dried.

[0116] After the temperature is raised to 17°C, 0.125 mol of sec-butyllithium (in the form of a 0.13 mol / L cyclohexane solution) is introduced into the reactor. The molar ratio of activator (also known as a polar agent, tetrahydrofuran in this example) to initiator (sec-butyllithium in this example) is 2.3.

[0117] After polymerization at 17°C for 33 minutes, the AMS conversion was measured to be 32%. 0.675 kg of 1,3-butadiene was introduced, and the reaction mixture was diluted with 23 L of cyclohexane. Then, 3.9 kg of 1,3-butadiene was introduced, and the temperature was raised to 40°C. The temperature was maintained at a maximum of 42°C. Polymerization continued for 102 minutes. The 1,3-butadiene conversion was measured to be 92%. After polymerization, 0.06 mol of dimethyldichlorosilane was added under continuous stirring. The reaction medium was maintained at 40°C for 30 minutes.

[0118] At the end of this coupling step, a poly(α-methylstyrene)-block-polybutadiene-block-poly(α-methylstyrene) triblock polymer was synthesized. Then, 0.2 phr of the antioxidant Irganox 1520L® (obtained from BASF) was added. The antioxidant-protected polymer was separated from the solvent by steam entrainment (or steam stripping), and then dried in a vacuum oven at 60°C under nitrogen purging.

[0119] The Tg DSC of the flexible polybutadiene block is -49℃ (ΔT, glass transition width, equal to 9℃).

[0120] B-1 - Synthesize the first type of second TPE, namely, poly(α-methylstyrene)-block-poly(butadiene-co-styrene)-block-poly(α-methylstyrene) triblock polymer (or TPE2-1). Under continuous nitrogen purging, 2.1 L of cyclohexane, 0.106 L of tetrahydrofuran, and 5 kg of α-methylstyrene were sequentially introduced into an 80 L jacketed reactor. All products were pre-purified and / or dried.

[0121] After the temperature is raised to 17°C, 0.125 mol of sec-butyllithium (in the form of a 0.13 mol / L cyclohexane solution) is introduced into the reactor. The molar ratio of activator (tetrahydrofuran in this example) to initiator (sec-butyllithium in this example) is 2.3.

[0122] After 50 minutes of polymerization of α-methylstyrene, the AMS conversion was measured to be 50%. 0.42 kg of 1,3-butadiene and 0.26 kg of styrene were introduced, followed by the addition of 39 L of cyclohexane to the reaction mixture. Subsequently, 3.2 kg of 1,3-butadiene and 1.9 kg of styrene were introduced, and the temperature was raised to 40 °C. The temperature was maintained at a maximum of 42 °C. Polymerization continued for 145 minutes. The measured conversion was 74%.

[0123] After polymerization, 0.06 mol of dimethyldichlorosilane was added under continuous stirring. The reaction medium was maintained at 40°C for 30 minutes.

[0124] At the end of this coupling step, a poly(α-methylstyrene)-block-butadiene-styrene-block-poly(α-methylstyrene) triblock polymer was synthesized. 0.2 phr of the antioxidant Irganox 1520L® (obtained from BASF) was added. The antioxidant-protected polymer was separated from the solvent by steam stripping, and then dried in a vacuum oven at 60°C under nitrogen purging.

[0125] The Tg DSC of the flexible poly(butadiene-co-styrene) block is -38℃ (ΔT, glass transition width, equal to 9℃).

[0126] B-2 - Synthesize the second type of TPE, namely, poly(α-methylstyrene)-block-poly(butadiene-co-styrene)-block-poly(α-methylstyrene) triblock polymer (or TPE2-2). Under continuous nitrogen purging, 2.6 L of cyclohexane, 0.028 L of tetrahydrofuran, and 2 kg of α-methylstyrene were sequentially introduced into an 80 L jacketed reactor. All products were pre-purified and / or dried.

[0127] After the temperature was raised to 17°C, 0.15 mol of sec-butyllithium (in the form of 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.

[0128] After 40 minutes of polymerization, the conversion rate was measured to be 34%. 0.567 kg of 1,3-butadiene and 0.24 kg of styrene were then introduced, followed by dilution of the reaction mixture with 43.6 L of cyclohexane. Subsequently, 3.8 kg of 1,3-butadiene and 1.6 kg of styrene were introduced, and the temperature was raised to 40 °C. The temperature was maintained at a maximum of 42 °C. Polymerization continued for 85 minutes. The measured conversion rate was 68%.

[0129] After polymerization, 0.072 mol of dimethyldichlorosilane was added under continuous stirring. The reaction medium was maintained at 40°C for 30 minutes.

[0130] At the end of this coupling step, a poly(α-methylstyrene)-block-butadiene-styrene-block-poly(α-methylstyrene) triblock polymer was synthesized. 0.2 phr of the antioxidant Irganox 1520L® (obtained from BASF) was added. The antioxidant-protected polymer was separated from the solvent by steam stripping, and then dried in a vacuum oven at 60°C under nitrogen purging.

[0131] The Tg DSC of the flexible poly(butadiene-co-styrene) block is -48℃ (ΔT, glass transition width, equal to 9℃).

[0132] Preparation of C-polymer compositions For each composition, the TPE polymer was placed in a container filled with toluene at a volume ratio of 10% and stirred at ambient temperature for 24 hours. The solution was then dried at ambient temperature in a fume hood for 24 to 36 hours, followed by drying in a vacuum oven at 60°C for 24 hours. The resulting film was then pressed at 180°C for 10 minutes to obtain the sample required for characterization.

[0133] Table 1 summarizes the components of the polymer composition, their respective properties, and phr content.

[0134] [Table 1] ΔT = Glass transition width Tables 2 and 3 show the characteristics of the TPE used in the examples.

[0135] [Table 2] [Table 3] AMS = α-methylstyrene PAMS = Poly(α-methylstyrene) % STY = percentage of styrene units by mass % 1,2-PB=1,2-unit form, mass percentage of butadiene units % Mass percentage of butadiene units in 1,4-PB=1,4-unit form % AMS = mass percentage of α-methylstyrene units Mp = Peak mass Quality% = Percentage of mass.

[0136] D - Result Table 4 shows the results for various polymer compositions M1 to M5.

[0137] [Table 4] The results are given on a base of 100 relative to control M1. Compositions M2 to M5 according to the invention exhibit lower viscosity and higher rigidity compared to composition M1, which contains only TPE1.

Claims

1. A polymer composition comprising: - a first thermoplastic block elastomer of the formula A-B-A, wherein, A represents a thermoplastic block, which primarily comprises α-methylstyrene units on a molar basis; B represents a diene elastomer block, which, based on its mass, comprises more than 95% by mass of diene units. - A second thermoplastic block elastomer of formula A'-B'-A', wherein A' is a thermoplastic block that mainly comprises α-methylstyrene units on a molar basis, and B' is a random copolymer elastomer block that comprises diene units and vinyl aromatic units.

2. The composition of claim 1, wherein, The thermoplastic blocks A and A' contain more than 95 mol% α-methylstyrene units.

3. The composition according to claim 1 or 2, wherein, The thermoplastic blocks A and A' contain styrene units.

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

5. The composition according to any one of the preceding claims, wherein, The thermoplastic block A accounts for at least 10% of the mass of the first thermoplastic elastomer, preferably 10% to 45% of the mass, more preferably 10% to 40% of the mass; the thermoplastic block A' accounts for at least 10% of the mass of the second thermoplastic elastomer, preferably 10% to 45% of the mass, more preferably 10% to 40% of the mass.

6. The composition according to any one of the preceding claims, wherein, The elastomer block B comprises 0% to less than 5% by mass of one or more vinyl aromatic monomer units.

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

8. The composition according to any one of the preceding claims, wherein, Relative to the mass of the block B', the elastomeric block B' contains more than 5% by mass and less than 45% by mass, preferably more than 10% by mass and less than 40% by mass, vinyl aromatic units.

9. The composition according to any one of the preceding claims, wherein, The elastomeric block B' contains more than 5% by mass and less than 45% by mass, preferably more than 10% by mass and less than 40% by mass, of styrene relative to the mass of the block B'.

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

11. The composition according to any one of the preceding claims, wherein, The elastomeric block B' is a random copolymer of 1,3-butadiene and styrene.

12. The composition according to any one of the preceding claims, wherein, The content of the first thermoplastic elastomer is in the range of 20 phr to 80 phr, preferably 30 phr to 70 phr, and the content of the second thermoplastic elastomer is in the range of 20 phr to 80 phr, preferably 30 phr 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. The composition according to any one of the preceding claims, wherein the composition further comprises an α-methylstyrene homopolymer, wherein the mass percentage of the α-methylstyrene homopolymer is in the range of 5% by mass to 45% by mass relative to the total mass of the composition.

14. A finished or semi-finished product intended for use in the manufacture of tires, comprising the composition according to any one of the preceding claims.

15. A tire comprising a tread, said tire comprising, in whole or in part, the composition according to any one of claims 1 to 13.

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