Statistical copolymer elastomer of 1,3-butadiene and a (meth)acrylate.

Abstract

The present invention relates to a statistical copolymer elastomer of 1,3-butadiene and a (meth)acrylate having a 1,4-trans butadiene unit content greater than 70% by mole of the butadiene units of the copolymer, containing 30% to 70% mol of 1,3-butadiene, 0 to 5% mol of glycerol carbonate (meth)acrylate and at least 30% mol of an alkyl methacrylate, having a number-average molar mass, Mn, greater than 350,000 g / mol and less than 500,000 g / mol, a dispersity, Đ, such that the ratio between Mn and dispersity is greater than 150,000 g / mol, the molar percentages being calculated with respect to the total monomer units of the copolymer. The elastomer has a macrostructure characterized by a new compromise between Mn and dispersity, Δ. This compromise makes it possible to further improve the rolling resistance performance of a tire containing a rubber composition including the elastomer.

Description

Title of the invention: Statistical copolymer elastomer of 1,3-butadiene and a (meth)acrylate.

[0001] The field of the present invention is that of diene elastomers intended to be introduced into rubber compositions reinforced by a reinforcing filler, in particular used in the manufacture of tires for vehicles.

[0002] One of the requirements for a tire is to ensure optimal road grip, particularly on wet surfaces. One way to give the tire high grip on wet surfaces is to use a rubber compound in its tread that exhibits a high hysteresis potential.

[0003] But at the same time, the tire tread must also minimize its contribution to the tire's rolling resistance, that is, be as hysteretic as possible. Thus, the rubber composition of the tread must satisfy two conflicting requirements: it must exhibit maximum hysteresis potential to meet the grip requirement and the lowest possible hysteresis to meet the rolling resistance requirement.

[0004] Meeting both the requirement for grip, especially on wet surfaces, and rolling resistance remains a constant concern for tire manufacturers.

[0005] To improve the wet grip performance of a tire while maintaining a good compromise between performance and rolling resistance, it is known from patent application WO 2016 / 001052 to introduce elastomers comprising more than 20 mole percent of the monomer units of a methacrylic acid ester into the rubber compositions constituting the tire treads. The elastomers described in this patent application WO 2016 / 001052 are prepared by hot emulsion radical polymerization (50°C). It is known that the hot emulsion radical polymerization of a monomer mixture containing 1,3-butadiene produces an elastomer having a 1,4-trans unit content of less than 65 mole percent of the butadiene units of the elastomer, having macrogel and branched chains.However, the presence of macrogel and branched chains in an elastomer is known to decrease the rolling resistance performance of a tire whose tread contains such an elastomer.

[0006] Continuing its research efforts, the Applicant discovered a new elastomer containing butadiene units and alkyl methacrylate units without the aforementioned drawbacks. In addition to its composition, which already ensures good adhesion on wet ground of a tire due to its alkyl methacrylate content, the elastomer according to the invention has the particularity of presenting a macrostructure which allows it to further improve the rolling resistance performance of a tire.

[0007] Thus, a first object of the invention is a statistical copolymer of 1,3-butadiene and a (meth)acrylate having a 1,4-trans butadiene unit content greater than 70 mol% of the butadiene units of the copolymer and containing 30% to 70 mol% of 1,3-butadiene, 0 to 5 mol% of glycerol carbonate (meth)acrylate, and at least 30 mol% of an alkyl methacrylate, which copolymer is an elastomer having a number-average molar mass, Mn, greater than 350,000 g / mol and less than 500,000 g / mol, a dispersity, D, such that the ratio between the number-average molar mass and the dispersity is greater than 150,000 g / mol, the molar percentages being calculated with respect to the total monomer units of the copolymer.

[0008] A second object of the invention is a rubber composition which includes a reinforcing filler, a crosslinking system and a copolymer according to the invention.

[0009] Another object of the invention is a tire which includes a tread, which tire includes a rubber composition according to the invention, preferably in its tread. Detailed description

[0010] Any interval of values ​​designated by the expression "between a and b" represents the domain of values ​​greater than "a" and less than "b" (i.e. bounds "a" and "b" excluded) while any interval of values ​​designated by the expression "from a to b" means the domain of values ​​going from "a" to "b" (i.e. including the strict bounds "a" and "b").

[0011] The compounds mentioned in the description may be of fossil origin or bio-based. 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 used, that is to say, they may be partially or totally derived from a recycling process, or obtained from raw materials themselves derived from a recycling process.

[0012] In the present invention, the term "tire" (in English, "tire") means a pneumatic or non-pneumatic tire. A pneumatic tire typically comprises two beads intended to contact a rim, a crown consisting of at least one crown reinforcement and a tread, and two sidewalls, the tire being reinforced by a carcass reinforcement anchored in both Beading. A non-pneumatic tire, on the other hand, usually comprises a base, designed for example for mounting on a rigid rim, a crown reinforcement ensuring the connection with a tread, and a deformable structure, such as spokes, ribs, or dimples, this structure being arranged between the base and the crown. Such non-pneumatic tires do not necessarily include a sidewall. Non-pneumatic tires are described, for example, in documents WO 03 / 018332 and FR2898077. According to any one of the embodiments of the invention, the tire according to the invention is preferably a pneumatic tire.

[0013] All percentages are mass percentages unless otherwise indicated.

[0014] The abbreviation "pce" means parts by weight per hundred parts of elastomers present in the elastomer matrix. The elastomer matrix refers to all the elastomers present in the rubber composition.

[0015] The molar percentages relating to the composition of the copolymer according to the invention are calculated with respect to the total monomer units of the copolymer, with the exception of the rate of 1,4-trans butadiene units which is conventionally calculated with respect to the butadiene units of the copolymer.

[0016] As is known, the term (meth)acrylate refers indifferently to an acrylate or a methacrylate.

[0017] The statistical copolymer of 1,3-butadiene and a (meth)acrylate according to the invention is an elastomer and is characterized by containing 30% to 70% molar of 1,3-butadiene, 0 to 5% molar of glycerol carbonate (meth)acrylate and at least 30% molar of an alkyl methacrylate.

[0018] Glycerol carbonate (meth)acrylate is preferably methacrylate of glycerol carbonate, particularly due to its commercial availability.

[0019] Preferably, the content of said alkyl methacrylate is at least 40 mol%.

[0020] The alkyl group of said alkyl methacrylate is preferably an alkyl group containing from 2 to 10 carbon atoms, most preferably n-butyl or 2-ethylhexyl. When said alkyl methacrylate refers to several alkyl methacrylates, the alkyl groups of the methacrylates differ from one another by the length of the alkyl chain and preferably contain from 2 to 10 carbon atoms. Advantageously, the alkyl methacrylate is n-butyl methacrylate.

[0021] According to one embodiment of the invention, (meth)acrylate refers to said alkyl methacrylate or several (meth)acrylates including said alkyl methacrylate.

[0022] According to a preferred embodiment of the invention, the copolymer is a copolymer of 1,3-butadiene and said alkyl methacrylate, in particular a copolymer of 1,3-butadiene and n-butyl methacrylate or a copolymer of 1,3-butadiene and 2-ethylhexyl methacrylate, preferably a copolymer of 1,3-butadiene and n-butyl methacrylate.

[0023] According to another preferred embodiment of the invention, the copolymer is a copolymer of 1,3-butadiene, said alkyl methacrylate, and glycerol carbonate (meth)acrylate, the glycerol carbonate (meth)acrylate preferably being glycerol carbonate methacrylate. According to this other preferred embodiment of the invention, the copolymer is a copolymer of 1,3-butadiene, n-butyl methacrylate, and glycerol carbonate methacrylate.

[0024] Preferably, the 1,3-butadiene content in the copolymer varies in a range from 40% to 60% molar.

[0025] The 1,3-butadiene and alkyl methacrylate contents relevant to the needs of the invention define a copolymer that improves the performance trade-off between rolling resistance and wet grip of a tire. The tire's wet grip improves without compromising its rolling resistance, as the amount of the copolymer according to the invention increases in the elastomer matrix of the rubber compound constituting all or part of its tread.

[0026] A content of glycerol carbonate (meth)acrylate in the copolymer according to the invention which is greater than 0%, in particular ranging from 2% to 3% molar, gives the possibility of crosslinking the copolymer by a crosslinking system which contains sulfur or by a crosslinking system which is devoid of sulfur and which contains one or more compounds reactive with respect to carbonate functions.

[0027] Another essential characteristic of the copolymer according to the invention is its macrostructure, which is defined by both its number-average molar mass and its dispersity. The number-average molar mass of the copolymer according to the invention is greater than 350,000 g / mol and less than 500,000 g / mol; its dispersity is such that the ratio between the number-average molar mass and the dispersity is greater than 150,000 g / mol. These characteristics relating to the macrostructure define a compromise between the number-average molar mass and the dispersity that makes it possible to reduce the hysteresis of a rubber composition. The reduction of the hysteresis of the rubber composition results in a reduction of the rolling resistance of a tire whose tread is made up, in whole or in part, of a rubber composition comprising the copolymer.The rolling resistance performance of a tire containing a rubber compound including a copolymer according to the invention will be reduced as the amount of copolymer in the elastomer matrix of the rubber compound increases. The higher the ratio between the number-average molar mass and the dispersity, the better the rolling resistance performance.

[0028] The copolymer according to the invention is typically prepared by polymerization radical in cold emulsion of a monomer mixture of 1,3-butadiene and a (meth)acrylate.

[0029] To initiate the radical polymerization reaction, an organic hydroperoxide is typically used as an initiator. Suitable examples include tert-butyl hydroperoxide, cumene hydroperoxide, p-menthane hydroperoxide, and preferably cumene hydroperoxide.

[0030] The compounds mentioned above are used in redox systems in which transition metal salts, particularly an iron(II) salt such as ferrous sulfate or iron(II) pyrophosphate, are involved. The transition metal salt is generally used in an amount corresponding to the stoichiometry of the redox reaction, i.e., an Fe(II) / initiator ratio of 1 mole of Fe(II) to 1 mole of initiator, or close to the stoichiometry, i.e., an Fe(II) / initiator ratio ranging from 0.9 to 1.0. The use of a redox system in emulsion radical polymerization is well known for enabling cold polymerization, typically at around 5°C. These cold polymerization conditions lead to the obtaining of copolymers practically without macrogel (macrogel content less than 0.3% by mass of the copolymer mass) and without branched chains.These cold polymerization conditions lead to the insertion of 1,3-butadiene in the form of 1,4-trans butadiene units, which represent at least 70% by mole of the butadiene units in the copolymer, compared to less than 65% for polymerization at 50°C. The copolymer according to the invention contains 1,4-trans butadiene units that represent more than 70% by mole of the butadiene units in the copolymer. The 1,4-trans butadiene units refer to the butadiene units that are inserted into the copolymer chain in the 1,4-trans form.

[0031] Also known to prevent possible degradation of the initiator by stabilizing the pH of the emulsion, a buffer is used. Phosphate buffers such as tetrasodium pyrophosphate are an example.

[0032] In a manner also known to control the gel rate and macrostructure of the copolymer, a transfer agent is introduced into the polymerization medium, and the conversion of the monomers is typically limited to less than 75%, preferably less than 60%. Examples of transfer agents include mercaptans with chain lengths of 10 to 14 carbon atoms, such as n-dodecyl mercaptan and tert-dodecyl mercaptan.

[0033] To obtain the copolymers according to the invention, the quantities of organic hydroperoxide and mercaptan satisfy conditions a) or conditions b): conditions a) being defined by a ratio between the number of moles of organic hydroperoxide and the number of moles of monomers in the mixture monomer which is less than 10⁴ and a ratio of the number of moles of mercaptan to the number of moles of organic hydroperoxide which is greater than 2, conditions b) being defined by a ratio of the number of moles of organic hydroperoxide to the number of moles of monomers in the monomer mixture which is greater than or equal to 9x10⁴ and a ratio of the number of moles of mercaptan to the number of moles of organic hydroperoxide which is less than 0.5.

[0034] Preferably, conditions a) are that the ratio between the number of moles of organic hydroperoxide and the number of moles of monomers in the monomer mixture is preferably greater than 5x105 and the ratio between the number of moles of mercaptan and the number of moles of organic hydroperoxide is preferably less than 4.

[0035] Preferably, conditions b) are that the ratio between the number of moles of organic hydroperoxide and the number of moles of monomers in the monomer mixture is preferably less than 5x103 and the ratio between the number of moles of mercaptan and the number of moles of organic hydroperoxide is preferably greater than 0.1.

[0036] Surfactants are also used in a known manner to stabilize the aqueous emulsion. The surfactant(s) used may be chosen from among nonionic, anionic, or cationic surfactants, preferably from among anionic or cationic surfactants. Anionic surfactants include, in particular, all anionic surfactants comprising at least one alkyl group having from 6 to 40 carbon atoms (hereinafter referred to as C6-C40 alkyl) or at least one aromatic ring substituted by a C6-C40 alkyl group, and at least one anionic group chosen from among sulfates, sulfonates, phosphates, phosphonates, and carboxylates.Preferably, the anionic surfactant(s) comprising at least one C6-C40 alkyl group or at least one aromatic ring substituted with a C6-C40 alkyl group are selected from sodium stearate, sodium lauryl sulfate, sodium lauryl ether sulfate, dehydrogenated resin acids and their alkali metal salts, sodium dodecylbenzene sulfonates, and mixtures thereof. Cationic surfactants include, in particular, all cationic surfactants comprising at least one C6-C40 alkyl group or at least one aromatic ring substituted with a C6-C40 alkyl group, and at least one cationic group selected from ammonium and pyridium. Preferably, the cationic surfactant(s) are chosen from alkyltrimethylammonium salts such as trimethyldecylammonium chloride or bromide and benzalkonium salts and mixtures of these compounds.Preferably, the surfactant(s) to be used are chosen from trimethyldecylammonium chloride, sodium dodecyl sulfate and the . Sodium stearate. The surfactant is typically used at a concentration that is higher than its critical micellar concentration (cmc), typically 2 to 5 times its cmc.

[0037] The monomers to be polymerized, in this case the monomer mixture of 1,3-butadiene and a (meth)acrylate containing 1,3-butadiene and an alkyl methacrylate, are introduced into a reactor containing an aqueous phase containing the surfactant. The total concentration of monomers introduced is typically between 5% and 35% by weight relative to the total weight of monomers introduced and water.

[0038] Preferably, the monomer mixture contains 30% to 70% mol of 1,3-butadiene, 0% to 5% mol of glycerol (meth)acrylate carbonate, and at least 30% mol of an alkyl methacrylate. More preferably, the monomer mixture is a mixture of 30% to 70% mol of 1,3-butadiene, 0% to 5% mol of glycerol (meth)acrylate carbonate, and at least 30% mol of an alkyl methacrylate, in which case the synthesized copolymer is a copolymer of 1,3-butadiene and alkyl methacrylate or a terpolymer of 1,3-butadiene, glycerol (meth)acrylate carbonate, and alkyl methacrylate. Even more preferably, the monomer mixture is a mixture of 30% to 70 mol% 1,3-butadiene and 70% to 30 mol% alkyl methacrylate, in which case the synthesized copolymer is a copolymer of 1,3-butadiene and alkyl methacrylate. Advantageously, the alkyl methacrylate is n-butyl methacrylate.

[0039] As is known, polymerization is generally carried out in an oxygen-free reactor at a polymerization temperature around 5°C, for example between 0°C and 10°C, advantageously at 5°C. Polymerization can be carried out continuously or discontinuously (the so-called "batch" process), possibly using a semi-fed "batch" process where monomers are fed during the polymerization reaction, particularly throughout the entire polymerization reaction. The continuous process and the "batch" process are particularly preferred for obtaining a statistical copolymer.

[0040] In order to stop the polymerization reaction at the correct conversion point, a reducing agent, the stopper, is typically introduced in a known manner. Examples include the phenol family, such as hydroquinone and resorcinol, and hydroxylamines such as N,N-diethylhydroxylamine. Preferably, the stopper is used in excess of the initiator introduced into the polymerization medium, typically with a ratio of more than 1 moles of stopper to more than 1 moles of initiator, preferably ranging from 2 to 5.

[0041] Once synthesized, the copolymer according to the invention can be in either the latex state or the solid state, for example to be mixed with a reinforcing filler in order to prepare a masterbatch.

[0042] To recover the copolymer in latex phase and without residual monomers, it is preferable to perform a devolatilization step of these monomers, most commonly by steam distillation (stripping). To recover the copolymer in solid form, it is necessary to add a destabilization step of the emulsion, with or without a prior stripping step, and a drying step of the coagulum.

[0043] The emulsion can be destabilized by adding a third substance, for example an inorganic salt such as calcium, magnesium, potassium, or sodium chloride, sodium, magnesium, or sodium sulfate, or an organic salt such as magnesium or calcium acetate. Coagulation of the latex can also be achieved by adding a solvent selected from ketones and alcohols, including acetone, methanol, isopropanol, n-butanol, and ethanol. The coagulum is then generally washed with water.

[0044] The copolymer synthesis process according to the invention may further include a step of drying the copolymer after it has coagulated. Preferably, the copolymer can be dried under vacuum or at atmospheric pressure with nitrogen purging. Drying temperatures can range from ambient temperature (25°C) to 130°C, preferably from ambient temperature to 100°C, and even more preferably from ambient temperature to 70°C. Drying times are typically between 10 and 72 hours, preferably between 16 and 50 hours.

[0045] The rubber composition, another object of the invention, which contains the copolymer according to the invention, may contain, in addition to the copolymer according to the invention, other elastomers. Suitable other elastomers include, in particular, those commonly used in rubber compositions for the manufacture of tires, such as polyisoprenes, polybutadienes, isoprene copolymers, and butadiene copolymers such as butadiene-styrene copolymers.

[0046] According to any one embodiment of the invention, the percentage of the copolymer according to the invention in the rubber composition is preferably greater than 50 parts per cent, more preferably greater than 80 parts per cent, and even more preferably equal to 100 parts per cent. The rubber composition may contain one or more copolymers according to the invention that differ from one another in their composition or macrostructure. In the latter case, the indicated preferential percentages of the copolymer according to the invention in the rubber composition apply to all the copolymers according to the invention.

[0047] The rubber composition according to the invention is characterized by containing a crosslinking system.

[0048] According to one embodiment of the invention, the crosslinking system is a vulcanization system, that is to say, a sulfur-based system (or a sulfur-donating agent). sulfur) and a primary vulcanization accelerator. To this basic vulcanization system are added, incorporated during the first non-productive phase and / or during the productive phase as described later, various known secondary accelerators or vulcanization activators such as zinc oxide, stearic acid or equivalent compounds, guanidine derivatives (in particular diphenylguanidine), or known vulcanization retarders. Examples of vulcanization accelerators (primary or secondary) include any compound capable of acting as a vulcanization accelerator for diene elastomers in the presence of sulfur, notably thiazole-type accelerators and their derivatives, sulfenamide, thiuram, dithiocarbamate, dithiophosphate, thiourea, and xanthate-type accelerators. Sulfur is used at a preferential rate of between 0.5 and 12 pc, particularly between 1 and 10 pc.The primary vulcanization accelerator is used in the rubber compound at a preferential rate of between 0.5 and 10 parts per annum, more preferably between 0.5 and 5 parts per annum.

[0049] According to another embodiment applicable when the glycerol carbonate (meth)acrylate content in the copolymer is greater than 0 mol%, the crosslinking system consists of one or more compounds having at least two reactive groups with respect to the carbonate functional group. The amount of crosslinking system introduced into the rubber composition is indexed to the number of moles of reactive groups of this compound relative to the number of carbonate functional groups in the elastomeric matrix. The amount of this compound introduced into the rubber composition preferably varies from 0.05 to 5, and more preferably from 0.05 to 2 mol equivalents of reactive groups of this compound per mole of carbonate functional group in the elastomeric matrix.

[0050] In choosing the compound belonging to the crosslinking system having at least two reactive groups with respect to the carbonate functional group, reference may be made to the article "Reactive Applications of Cyclic Alkylene Carbonates" by John H. Clements in Industrial & Engineering Chemistry Research 2003 42, 4, 663-674. The article presents the reactive functional groups with carbonates, including acids, alcohols, and amines. In this regard, one can cite polyacids, in particular diacids, or their dehydrated form, namely anhydrides, and polyamines, in particular diamines. For example, commercially available polyacids useful for the purposes of the invention include oxalic acid, succinic acid, adipic acid, sebacic acid, dodecanedioic acid, terephthalic acid, trimesic acid and 3,4-bis(carboxymethyl)cyclopentanecarboxylic acid.Examples of polyamines include 1,6-diaminohexane, 1,8-diaminooctane and the "Jeffamines" family from Huntsman, in which a person skilled in the art will be able to choose the most appropriate polyamine in relation to the expected properties of the composition. cross-linked rubber.

[0051] Preferably, the crosslinking system is a vulcanization system.

[0052] The tread rubber composition according to the invention comprises any type of so-called reinforcing filler, known for its ability to reinforce a rubber composition usable for the manufacture of tires, for example an organic reinforcing filler such as carbon black, an inorganic reinforcing filler such as silica, or a mixture of these two types of filler.

[0053] Such a reinforcing charge typically consists of nanoparticles whose average size (by mass) is less than one micrometer, generally less than 500 nm, most often between 20 and 200 nm, in particular and more preferably between 20 and 150 nm.

[0054] All carbon blacks are suitable as carbon blacks, including those conventionally used in tire treads. Among these, particularly the reinforcing carbon blacks of the 100, 200, and 300 series (ASTM grades), such as NI 15, N134, N234, N326, N330, N339, N347, and N375, are suitable. These carbon blacks can be used in isolation, as commercially available, or in any other form, for example, as a carrier for certain rubberizing additives used.

[0055] By "reinforcing inorganic filler", herein should be understood any inorganic or mineral filler, whatever its color and origin (natural or synthetic), also called "white" filler, "light" filler or even "non-black" filler as opposed to carbon black, capable of reinforcing by itself, without any other means than an intermediate coupling agent, a rubber composition intended for the manufacture of pneumatic tires, in other words, capable of replacing, in its reinforcing function, a conventional carbon black of pneumatic grade; such a filler is generally characterized, in a known way, by the presence of hydroxyl groups (OH) on its surface.

[0056] The silica used can be any reinforcing silica known to those skilled in the art, in particular any precipitated or pyrogenated silica having a BET surface area and a CTAB specific surface area both less than 450 m2 / g.

[0057] The physical state in which the silica is presented is irrelevant, whether it is in the form of powder, microbeads, granules, or spheres. Of course, the term "reinforcing inorganic filler" also refers to mixtures of different silicas, in particular highly dispersible silicas such as those described above.

[0058] Those skilled in the art will understand that, as an equivalent filler to the silica described in this paragraph, a reinforcing filler of another nature, in particular an organic one such as carbon black, could be used, provided that this filler The reinforcing compound would be coated with an inorganic layer such as silica, or would have functional sites on its surface, particularly hydroxyl sites, requiring the use of a coupling agent to establish the bond between the filler and the copolymer. Examples include carbon blacks for tires, such as those described in patent documents WO 96 / 37547 and WO 99 / 28380.

[0059] Preferably, the reinforcing filler content is between 40 and 200 parts per annum (ppm). Below 40 ppm, the reinforcement of the rubber compound is insufficient to provide an adequate level of cohesion or wear resistance. More preferably, the reinforcing filler content is at least 50 ppm. Above 200 ppm, there is a risk of increased hysteresis and therefore increased rolling resistance of the tires. For this reason, the reinforcing filler content is advantageously in the range of 50 to less than 200 ppm, and preferably from 50 to 160 ppm. These preferred ranges of reinforcing filler content can be applied to any of the embodiments of the invention.

[0060] Preferably, the reinforcing filler comprises silica. More preferably, the reinforcing filler comprises more than 50% by mass of silica.

[0061] When silica represents more than 50% by mass of the reinforcing filler, carbon black is preferably used at a rate of less than 20%, more preferably less than 10% (for example, between 0.5 and 20%, particularly between 2 and 10%), and even more preferably less than 5%. Within the indicated ranges, the coloring (black pigmenting agent) and anti-UV properties of carbon black are beneficial, without compromising the typical performance provided by the inorganic reinforcing filler, namely silica.

[0062] To couple silica to the elastomeric matrix, particularly when silica constitutes more than 50% by weight of the reinforcing filler in the rubber composition, a coupling agent (or bonding agent) is generally and in a well-known manner. More precisely, a coupling agent is understood to be an agent capable of establishing a sufficient chemical and / or physical bond between the silica and the elastomeric matrix, while also facilitating the dispersion of the silica within the elastomeric matrix.

[0063] This at least bifunctional agent is intended to ensure sufficient chemical and / or physical connection between the silica (surface of its particles) and the elastomeric matrix. Organosilanes are used in particular, notably polysulfurized alkoxysilanes or mercaptosilanes, or polyorganosiloxanes bearing functional groups capable of binding physically and / or chemically to the inorganic filler and functional groups capable of binding physically and / or chemically to the matrix. elastomer, for example via a sulfur atom. Silica / elastomer bonding agents, in particular, have been described in a large number of documents, the best known being bifunctional alkoxysilanes such as polysulfide alkoxysilanes. Polysulfide silanes, described as "symmetric" or "asymmetric" depending on their specific structure, are used, for example, as described in applications WO03 / 002648 (or US 2005 / 016651) and WO03 / 002649 (or US 2005 / 016650).

[0064] As a coupling agent other than polysulfurized alkoxysilane, mention shall be made in particular of bifunctional POSS (polyorganosiloxanes) or polysulfurized hydroxysilanes as described in patent applications WO 02 / 30939 (or US 6,774,255) and WO 02 / 31041 (or US 2004 / 051210), or silanes or POSS bearing azo-dicarbonyl functional groups, as described for example in patent applications WO 2006 / 125532, WO 2006 / 125533, WO 2006 / 125534.

[0065] The coupling agent content, whether a single compound or a mixture of compounds, is advantageously less than 20 parts per cent (ppm), it being understood that it is generally desirable to use as little as possible. Typically, the coupling agent content is from 0.5% to 15% by weight relative to the amount of silica. Its content is preferably between 0.5% and 12 ppm, more preferably in the range of 3% to 10 ppm. This content is easily adjusted by those skilled in the art according to the amount of silica used in the composition.

[0066] The rubber composition according to the invention may also contain coupling activators, silica coating agents or more generally processing aids capable, in a known manner, through an improvement in the dispersion of the filler in the elastomer matrix and a reduction in the viscosity of the rubber composition, of improving its processing ability in the raw state, these agents being for example hydrolyzable silanes such as alkylalkoxysilanes, polyols, polyethers, primary, secondary or tertiary amines, hydroxylated or hydrolyzable polyorganosiloxanes.

[0067] The rubber composition according to the invention may also include all or part of the usual additives commonly used in rubber compositions for the manufacture of tires, such as plasticizers, pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, antioxidants, anti-fatigue agents and mixtures of such compounds.

[0068] The rubber composition according to the invention can be manufactured in suitable mixers, generally using two successive preparation phases well known to those skilled in the art: a first working or thermomechanical mixing phase (the so-called "non-productive" phase) at high temperature, up to a maximum temperature between 110°C and 190°C, preferably between 120°C and 180°C, followed by a second mechanical working phase (the so-called "productive" phase) down to a lower temperature, typically below 110°C, for example between 40°C and 100°C, a finishing phase during which the crosslinking system is incorporated.

[0069] The rubber composition according to the invention can be prepared according to a process which comprises the following steps: - thermomechanically knead the elastomer matrix, the reinforcing filler, where applicable the coupling agent, where applicable the plasticizing system, and the other additives of the rubber composition with the exception of the crosslinking system, until a maximum temperature of between 110°C and 190°C is reached; - cool the assembly to a temperature below 100°C; - then incorporate the crosslinking system; - knead everything until a maximum temperature below 110°C to obtain a rubber composition.

[0070] After incorporating all the ingredients of the rubber composition, the resulting final composition is then calendered, for example in the form of a sheet or plate, particularly for laboratory characterization, or extruded, for example to form a rubber profile used as a rubber component, particularly in tire manufacturing. The rubber composition according to the invention can be used in calendered form in a tire. The calendered or extruded product formed from the rubber composition constitutes, in whole or in part, a semi-finished product, in particular a tire.

[0071] Thus, according to a particular embodiment of the invention, the rubber composition according to the invention, which can be either in the raw state (before crosslinking or vulcanization) or in the cured state (after crosslinking or vulcanization), is in a tire, for example in a tire tread.

[0072] Crosslinking (or curing), where applicable vulcanization, is carried out in a known manner at a temperature generally between 130°C and 200°C, for a sufficient time which can vary for example between 5 and 120 min depending in particular on the curing temperature, the crosslinking system adopted and the crosslinking kinetics of the composition considered.

[0073] The rubber compound may constitute all or part of a semi-finished tire article, such as a tire tread. The semi-finished article may be manufactured according to the process described above, which includes an additional step of calendering or extruding the rubber compound.

[0074] The tire according to the invention comprises a rubber composition in accordance with the invention. The rubber composition preferably constitutes all or part of the tire tread. The tire is both in its raw state (i.e., before curing) and in its cured state (i.e., after cross-linking or vulcanization).

[0075] The aforementioned features of the present invention, as well as others, will be better understood upon reading the following description of examples of embodiments of the invention, given by way of illustration and not limitation. Examples

[0076] Determination of the glass transition temperature:

[0077] The glass transition temperatures Tg and glass transition widths AT of the polymers are measured using a Differential Scanning Calorimeter ("Differential Scanning Calorimeter") according to ASTM D3418-08. Size exclusion chromatography (SEC):

[0078] Size Exclusion Chromatography (SEC) separates macromolecules in solution according to their size using columns filled with a porous gel. The macromolecules are separated according to their hydrodynamic volume, with the largest being eluted first. While not an absolute method, SEC allows for the determination of the molar mass distribution of a polymer. Using commercial standard products, the various number-average (Mn) and weight-average (Mw) molar masses can be determined, and the polymolecularity or dispersity index (D = Mw / Mn, also denoted Ip) can be calculated using a Moore calibration. No special treatment of the polymer sample is required before analysis. It is simply solubilized in a tetrahydrofuran solution at a concentration of approximately 1 g / L. Then, the solution is filtered through a 0.45 pm porosity filter before injection. The equipment used is a WATERS alliance e2695 chromatograph. The elution solvent is tetrahydrofuran. The flow rate is 1 mL / min, the system temperature is 35°C, and the analysis time is 35 min. A set of three Agilent MIXED-B-LS columns is used in series. The injected volume of the polymer sample solution is 100 pL. The detector is a WATERS 2410 differential refractometer, and the chromatographic data processing software is WATERS EMPOWER. The calculated average molar masses are relative to a calibration curve created using commercial polystyrene standards from PSS READY CAL-KIT. Dynamic properties:

[0079] The dynamic properties are measured on a viscoanalyzer (Metravib VA4000), according to ASTM D 5992-96. The response of a sample of vulcanized position (cylindrical specimen 4 mm thick and 400 mm2 in cross-section), subjected to sinusoidal loading in simple alternating shear, at a frequency of 10Hz, under normal temperature conditions (23°C) according to ASTM D 1349-99.

[0080] A strain amplitude sweep is performed from 0.1% to 100% (forward cycle), then from 100% to 0.1% (return cycle). The result used is the loss factor measured on the return cycle, tanô at 10% strain. Synthesis of elastomers:

[0081] The elastomers of examples 1 to 6 are prepared according to the following protocol:

[0082] Preparing the following charges in advance: We weigh approximately exactly the quantity of solutes to prepare the solutions to an exactly known concentration which is close to a target concentration whose value is given below and introduced by the term "approximately". - Suspension in water of Na2FeP2O7 (iron complex) at approximately 0.015 mol / L: FeSO4, 7H2O and Na4P2O7 are diluted in bubbled water, then the mixture is heated at 60°C for 45 minutes with regular stirring - Preparation of a cumene hydroperoxide solution (initiator) in alkyl methacrylate at approximately 0.04 mol / L -Preparation of a tert-dodecyl mercaptan (RSH) solution in alkyl methacrylate at approximately 0.1 mol / L - Preparation of a solution of N,N-diethylhydroxylamine (stopper) in water at approximately 0.05 mol / L in water.

[0083] Sodium dodecyl sulfate (SDS), iron sulfate, cumene hydroperoxide, sodium pyrophosphate (tetrabasic sodium pyrophosphate), potassium persulfate, terdodecyl mercaptan, N,N-diethylhydroxylamine, n-butyl methacrylate (BuMA), and 2-ethylhexyl methacrylate (EHMA) are marketed by Aldrich. 4-(hydroxymethyl)-1,3-dioxolan-2-one methacrylate (CCMA) is sourced from Specify Polymers. 1,3-Butadiene (btd) and the alkyl methacrylates are purified by passing through an alumina guard and bubbling with nitrogen.

[0084] A stirred reactor is loaded according to the following operations: bubbling water for 45 minutes at 25°C, then sodium dodecyl sulfate (surfactant, TA) under nitrogen at 25°C, followed by a 10-minute nitrogen purge. inject the RSH solution at 25°C under nitrogen cool the reactor to reach 5°C When the reactor reaches approximately 12°C, inject the remainder of the monomer feedstock, with the exception of 1,3-butadiene, under nitrogen. Allow the reactor to cool to 5°C, then inject the Na2FeP2O7 solution. Then inject the 1,3-butadiene and let it stir for 10 to 15 minutes until the emulsion forms. then inject the priming agent, the cumene hydroperoxide solution. The end of the addition of the initiator marks the beginning of polymerization (i.e., t=0 min).

[0085] Agitation is maintained at 5°C. To stop the polymerization reaction, the latex is transferred by residual pressure of the monomers into another reactor containing the aqueous N,N-diethylhydroxylamine solution (stopper). The latex is then coagulated by adding a mixture of acetone and methanol (acetone / methanol: 50 / 50 by volume) at a ratio of 3 volumes of the acetone / methanol mixture to 1 volume of reaction medium. The coagulum is dried under partial vacuum and nitrogen purging for 48 h at 40°C.

[0086] The synthesis conditions for the elastomers of examples 1 to 6 are shown in Table 1; conventionally, the quantity of water and that of the surfactant are given partly by mass per hundred parts of monomer mixture; the quantity of iron sulfate being 0.90 molar equivalents compared to the quantity of initiator; the quantity of sodium pyrophosphate being 0.89 molar equivalents relative to the quantity of initiator; the quantity of stopper (N,N-diethylhydroxylamine) being 3 molar equivalents compared to the quantity of initiator; the quantity of cumene hydroperoxide (initiator) being given as a molar percentage relative to the total quantity of starting monomers; the quantities of RSH, iron complex, stopper being given in molar equivalent relative to the quantity of initiator; the composition of the starting monomer charge is given as a molar percentage calculated on the total number of moles of monomers composing the starting monomer charge, the starting monomer charge constituting the monomer mixture to be polymerized. Example Primer r RSH TA S / M Btd BuMA EHM A CCMA TA poly (min) Conv. (%) 1 0.074 0.71 2.4 2.4 54 46 0 0 270 70 2 0.074 0.71 2.4 2.4 56 0 44 0 410 57 3 0.074 0.71 2.4 2.4 55 42 0 3 180 62 4 0.009 2.8 4.8 4.8 56 44 0 0 412 60 5 0.009 2.8 4.8 4.8 58 0 42 0 355 42 6 0.009 2.8 2.4 4.8 55 43 0 2 375 43

[0087] Table 1:

[0088] The number-average molar mass values ​​(Mn), dispersity (μ), and molar composition of the elastomers in Examples 1 to 6 are shown in Table 2, along with the Mn / D ratio. The synthesized copolymers are all statistically stable: they all exhibit a melting point (AT) below 10°C. Each of the synthesized copolymers has a 1,4-trans butadiene unit content greater than 70% by mole of the butadiene units in the copolymer. Example btd BuMA EHM A CCMA Mn (g / mol) D Mn / f) (g / mol) Elastomer 1 54 46 0 0 198533 2.4 82722 El 2 56 0 44 0 238210 2.4 99254 E2 3 56 42 0 2 173218 2.5 69287 E3 4 56 44 0 0 449355 2.3 195371 E4 5 58 0 42 0 445744 2.4 185726 E5 6 55 43 0 2 404306 2.5 161722 E6

[0089] Table 2:

[0090] Preparation of rubber compositions:

[0091] To prepare the compositions, the following procedure is used: In an internal mixer (final fill level approximately 70% by volume), with an initial tank temperature of around 100°C, telastomer, reinforcing filler, and other additives are successively introduced. A thermomechanical process (non-productive phase) is then carried out in a single stage (total mixing time approximately 5 minutes) until a maximum "fall" temperature of 140 to 165°C, depending on the composition, is reached. The resulting mixture is then collected, cooled, and the vulcanization system is added to an external mixer for a second mechanical processing stage at approximately 40°C.

[0092] The rubber compositions are given in Table 3. The quantities are expressed in parts per 100 parts by weight of elastomer.

[0093] Table 3: Composition Cl C4 C2 C5 C3 C6 Elastomer El 100 Elastomer E4 100 Elastomer E2 100 Elastomer E5 100 Elastomer E3 100 Elastomer E6 100 Silica (1) 91 91 91 91 86 86 Plasticizer (2) 33 33 33 33 31 31 Resin (3) 6 6 6 6 Coupling agent (4) 9.1 9.1 9.1 9.11 8.9 8.9 DPG (5) 1.5 1.5 1.5 1.5 1.5 1.5 Antioxidant (6) 1.9 1.9 1.9 1.9 1.9 1.9 ZnO (7) 3.0 3.0 3.0 3.0 3.0 3.0 Stearic acid (8) 2.0 2.0 2.0 2.0 2.0 2.0 Sulfur 1.5 1.5 1.5 1.5 1.5 1.5 Sulfenamide (9) 1.5 1.5 1.5 1.5 1.5 1.5 1.5

[0094] (1) Silica “Zeosil 1165 MP” from the company Rhodia (type HDS)

[0095] (2) Tris(2-ethylhexyl)phosphate

[0096] (3) Polylimonene resin "Dercolyte L120" from the company DRT

[0097] (4) TESPT (“Si69” from the company Degussa)

[0098] (5) Diphenylguanidine (“Perkacit” DPG from Flexsys)

[0099] (6) N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, from Flexsys

[0100] (7) Industrial grade zinc oxide from Umicore

[0101] (8) Stearine “Pristerene 4931” from the company Uniqema

[0102] (9) N-cyclohexyl-2-benzothiazyl sulfenamide “Santicure CBS” of the company Flexys

[0103] The compositions thus obtained are then calendered either in the form of plates (2 to 3 mm thick) or thin sheets of rubber for the measurement of their physical or mechanical properties. The calendered compositions are then baked under pressure for 40 min at 160°C, and then characterized.

[0104] The results of the characterizations of the rubber compositions are shown in Table 4.

[0105] Table 4: Composition Cl C4 C2 C5 C3 C6 tanô 10% 0.380 0.350 0.410 0.360 0.372 0.335 Base 100 100 92 100 88 100 90

[0106] Elastomers E4 to E6 have a number-average molar mass greater than 350,000 g / mol and less than 500,000 g / mol and a Mn / λ ratio greater than 150,000 g / mol, and are therefore elastomers according to the invention, unlike elastomers E1 to E3. Elastomers E4 to E6 give the rubber composition lower hysteretic properties compared to elastomers E1 to E3. This result is attributed to the compromise between the number-average molar mass and the dispersity, which is reflected in a Mn / λ ratio greater than 150,000 g / mol. In other words, although E4 to E6 elastomers are composed of much longer chains than El to E3 elastomers, the chains constituting E4 to E6 elastomers exhibit a chain length homogeneity comparable to the chains of El to E3 elastomers.It is observed that the higher the Mn / μ ratio, the lower the tan α 10% values, suggesting an improvement in the rolling resistance of a tire whose tread contains an elastomer according to the invention in its rubber composition. It is also observed that the presence of carbonate groups in copolymers, whether conforming to the invention or not, contributes to lowering the tan α 10% values.

Claims

Demands

1. A statistical copolymer of 1,3-butadiene and a (meth)acrylate having a 1,4-trans butadiene unit content greater than 70 mol% of the butadiene units of the copolymer and containing 30% to 70 mol% of 1,3-butadiene, 0 to 5 mol% of glycerol carbonate (meth)acrylate and at least 30 mol% of an alkyl methacrylate, which copolymer is an elastomer having a number-average molar mass, Mn, greater than 350,000 g / mol and less than 500,000 g / mol, a dispersity, D, such that the ratio between the number-average molar mass and the dispersity is greater than 150,000 g / mol, the molar percentages being calculated with respect to the total monomer units of the copolymer.

2. Copolymer according to claim 1 in which the 1,3-butadiene content varies in a range from 40% to 60% molar.

3. Copolymer according to any one of claims 1 to 2 wherein the content of said alkyl methacrylate is at least 40 mol%.

4. Copolymer according to any one of claims 1 to 3, wherein (meth)acrylate means said alkyl methacrylate or several (meth)acrylates of which said alkyl methacrylate.

5. Copolymer according to any one of claims 1 to 4, wherein the copolymer is a copolymer of 1,3-butadiene and said alkyl methacrylate or a copolymer of 1,3-butadiene, said alkyl methacrylate and glycerol carbonate (meth)acrylate.

6. Copolymer according to any one of claims 1 to 5 wherein the (meth)acrylate of glycerol carbonate is the methacrylate of glycerol carbonate.

7. Copolymer according to any one of claims 1 to 6 wherein the alkyl of said alkyl methacrylate is an alkyl containing from 2 to 10 carbon atoms.

8. Copolymer according to any one of claims 1 to 7 wherein the alkyl of said alkyl methacrylate is n-butyl or 2-ethylhexyl.

9. Rubber composition comprising a reinforcing filler, a crosslinking system and a copolymer as defined in any one of claims 1 to 8.

10. Rubber composition according to claim 9 wherein the reinforcing filler comprises more than 50% by mass of a silica.

11. A tire that includes a tread, which pneumatic includes a rubber composition defined in any one of claims 9 to 10.

12. Tire according to claim 11, wherein the rubber composition constitutes all or part of the tread.