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

Abstract

The present invention relates to a statistical elastomer copolymer of 1,3-butadiene and of a (meth)acrylate, having a content of 1,4-trans butadiene units of greater than 70 mol% of the butadiene units in the copolymer, and containing from 30 mol% to 70 mol% of 1,3-butadiene, from 0 mol% to 5 mol% of glycerol carbonate (meth)acrylate, and at least 30 mol% of an alkyl methacrylate, having a number-average molar mass, Mn, of greater than 350 000 g / mol and less than 500 000 g / mol, a dispersity, Đ, such that the ratio of the Mn to the dispersity is greater than 150,000 g / mol, wherein the molar percentages are calculated relative to all of the monomer units in the copolymer. The elastomer has a macrostructure characterised by a novel trade-off between Mn and dispersity, Đ. This trade-off makes it possible to further improve the rolling resistance performance of a tyre comprising a rubber composition that comprises the elastomer.

Description

[0001] Statistical copolymer elastomer of 1,3-butadiene and a (meth)acrylate.

[0002] 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 vehicle tires.

[0003] One of the requirements for a tire is to ensure optimal grip on the road, especially on wet surfaces. One way to give the tire high wet grip is to use a rubber compound in its tread, which compound has a high hysteretic potential.

[0004] But at the same time the tire tread must also minimize its contribution to the tire's rolling resistance, i.e. be as hysteretic as possible. Thus, the rubber composition of the tread must satisfy two contradictory requirements, namely to have a maximum hysteresis potential to satisfy the grip requirement and to have as little hysteresis as possible to satisfy the rolling resistance requirement.

[0005] Meeting both the requirement for grip, particularly on wet ground, and rolling resistance remains a constant concern for tire manufacturers.

[0006] 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 mol% of the monomer units of a methacrylic acid ester into the rubber compositions constituting tire treads. The elastomers described in this patent application WO 2016 / 001052 are prepared by hot radical emulsion polymerization (50°C). It is known that hot radical emulsion polymerization of a monomer mixture containing 1,3-butadiene produces an elastomer having a content of 1,4-trans units less than 65 mol% 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 reduce the rolling resistance performance of a tire whose tread contains such an elastomer.

[0007] Continuing the research efforts, the Applicant discovered a new elastomer containing butadiene units and alkyl methacrylate units without having the disadvantages mentioned. In addition to its composition which already ensures good wet grip of a tire due to its alkyl methacrylate content, the elastomer in accordance with the invention has the particularity of having a macrostructure which allows it to further improve the rolling resistance performance of a tire.

[0008] Thus, a first subject of the invention is a random copolymer of 1,3-butadiene and a (meth)acrylate having a content of 1,4-trans butadiene units greater than 70 mol% of the butadiene units of the copolymer and containing from 30% to 70 mol% of 1,3-butadiene, from 0 to 5 mol% of glycerol carbonate (meth)acrylate and at least 30 mol% of an alkyl methacrylate, which copolymer is an elastomer which has a number-average molar mass, Mn, greater than 350,000 g / mol and less than 500,000 g / mol, a dispersity, £), 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 relative to the totality of the monomer units of the copolymer.

[0009] A second subject of the invention is a rubber composition which comprises a reinforcing filler, a crosslinking system and a copolymer in accordance with the invention.

[0010] Another subject of the invention is a tire which comprises a tread, which tire comprises a rubber composition in accordance with the invention, preferably in its tread.

[0011] Detailed description

[0012] 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., excluding the limits "a" and "b"), while any interval of values ​​designated by the expression "from a to b" means the domain of values ​​from "a" to "b" (i.e., including the strict limits "a" and "b").

[0013] The compounds mentioned in the description may be of fossil or bio-sourced origin. In the latter case, they may be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. Similarly, the compounds mentioned may also come from the recycling of materials already in use, 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.

[0014] In the present invention, the term "tyre" means a pneumatic or non-pneumatic tire. A pneumatic tire usually comprises two beads intended to come into contact with a rim, a crown composed of at least one crown reinforcement and a tread, two sidewalls, the tire being reinforced by a carcass reinforcement anchored in the two beads. A non-pneumatic tire, for its part, 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 cells, this structure being arranged between the base and the crown. Such non-pneumatic tires do not necessarily comprise 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 bandage.

[0015] All percentages are by mass unless otherwise stated.

[0016] The abbreviation "pce" means parts by weight per hundred parts of elastomers present in the elastomer matrix. The term "elastomer matrix" means all the elastomers present in the rubber composition. The molar percentages relating to the composition of the copolymer in accordance with the invention are calculated relative to all the monomer units of the copolymer, with the exception of the content of 1,4-trans butadiene units which is calculated conventionally relative to the butadiene units of the copolymer.

[0017] As is well known, the term (meth)acrylate refers indifferently to an acrylate or a methacrylate.

[0018] The random copolymer of 1,3-butadiene and a (meth)acrylate in accordance with the invention is an elastomer and has the characteristic of containing from 30% to 70% mol of 1,3-butadiene, from 0 to 5% mol of glycerol carbonate (meth)acrylate and at least 30% mol of an alkyl methacrylate.

[0019] Glycerol carbonate (meth)acrylate is preferably glycerol carbonate methacrylate, in particular due to its commercial availability.

[0020] Alkyl methacrylate means one or more alkyl methacrylates. When said alkyl methacrylate refers to several alkyl methacrylates, the molar percentage of said alkyl methacrylate relates to all of the alkyl methacrylates. Preferably, the content of said alkyl methacrylate is at least 40 mol%.

[0021] The alkyl of said alkyl methacrylate is preferably an alkyl containing from 2 to 10 carbon atoms, more preferably is n-butyl or 2-ethylhexyl. When said alkyl methacrylate designates several alkyl methacrylates, the alkyls 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.

[0022] According to one embodiment of the invention, (meth)acrylate denotes said alkyl methacrylate or several (meth)acrylates including said alkyl methacrylate.

[0023] 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.

[0024] 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.

[0025] Preferably, the 1,3-butadiene content in the copolymer varies in a range from 40% to 60% mol.

[0026] The contents of 1,3-butadiene and alkyl methacrylate useful for the purposes of the invention define a copolymer which makes it possible to improve the performance compromise between the rolling resistance and the wet grip of a tire. The tire sees its wet grip improve without deterioration of its rolling resistance, especially as the quantity of the copolymer in accordance with the invention increases in the elastomer matrix of the rubber composition constituting all or part of its tread.

[0027] A content of glycerol carbonate (meth)acrylate in the copolymer in accordance with the invention which is greater than 0%, in particular ranging from 2% to 3% mol, gives the possibility of crosslinking the copolymer by a crosslinking system which contains sulfur or by a crosslinking system which is free of sulfur and which contains one or more compounds reactive with respect to the carbonate functions.

[0028] Another essential characteristic of the copolymer according to the invention is its macrostructure which is defined both by 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 which makes it possible to reduce the hysteresis of a rubber composition. The reduction in the hysteresis of the rubber composition results in a reduction in the rolling resistance of a tire whose tread is made entirely or partly of a rubber composition comprising the copolymer.The rolling resistance performance of a tire containing a rubber composition comprising a copolymer according to the invention will be reduced as the amount of the copolymer in the elastomer matrix of the rubber composition increases. The higher the ratio between the number-average molar mass and the dispersity, the more the rolling resistance performance is improved.

[0029] The copolymer according to the invention is typically prepared by cold radical emulsion polymerization of a monomer mixture of 1,3-butadiene and a (meth)acrylate.

[0030] To initiate the radical polymerization reaction, an organic hydroperoxide is typically used as an initiator. Suitable initiators are, for example, tert-butyl hydroperoxide, cumene hydroperoxide, p-menthane hydroperoxide, preferably cumene hydroperoxide.

[0031] The above-mentioned compounds are used in redox systems, in which transition metal salts, especially 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 between the number of moles of Fe(II) and the number of moles of initiator equal to 1, 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 a radical emulsion polymerization is well known for being able to polymerize cold, typically around 5°C. These cold polymerization conditions lead to the production of copolymers with practically no macrogel (macrogel content less than 0.3% by mass of the copolymer mass) and without branched chains.These cold polymerization conditions lead to an insertion of 1,3-butadiene in the form of 1,4-trans butadiene units which represent at least 70 mol% of the butadiene units of the copolymer, compared to less than 65% for polymerization at 50°C. The copolymer according to the invention contains 1,4-trans butadiene units which represent more than 70 mol% of the butadiene units of the copolymer. 1,4-trans butadiene units designate the butadiene units which are inserted into the copolymer chain in the 1,4-trans form.

[0032] Also known to avoid possible degradation of the initiator by stabilizing the pH of the emulsion, a buffer is used. Examples include phosphate buffers such as tetrasodium pyrophosphate.

[0033] Also known to control the gel rate and the macrostructure of the copolymer, a transfer agent is introduced into the polymerization medium and the conversion of the monomers is typically limited to a conversion of less than 75%, preferably less than 60%. As transfer agents, mention may be made of mercaptans with a chain length of 10 to 14 carbon atoms such as n-dodecyl mercaptan, tert-dodecyl mercaptan.

[0034] To obtain the copolymers in accordance with the invention, the quantities of organic hydroperoxide and mercaptan fulfill 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 monomer mixture which is less than 10' 4and a ratio between the number of moles of mercaptan and the number of moles of organic hydroperoxide which is greater than 2, conditions b) being defined by a ratio between the number of moles of organic hydroperoxide and the number of moles of monomers in the monomer mixture which is greater than or equal to 9xl0 -4 and a ratio between the number of moles of mercaptan and the number of moles of organic hydroperoxide which is less than 0.5.

[0035] 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 5xl0 -5 and the ratio between the number of moles of mercaptan and the number of moles of organic hydroperoxide is preferably less than 4.

[0036] 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 5xl0 -3 and the ratio between the number of moles of mercaptan and the number of moles of organic hydroperoxide is preferably greater than 0.1.

[0037] To stabilize the aqueous emulsion, surfactants are also used in a known manner. The surfactant(s) that can be used may be chosen from nonionic, anionic or cationic surfactants, preferably from anionic or cationic surfactants. As anionic surfactants, mention may in particular be made of 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 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 by a C6-C40 alkyl group are chosen from sodium stearate, sodium lauryl sulfate, sodium lauryl ether sulfate, dehydrogenated resin acids and their alkali metal salts and sodium dodecylbenzene sulfonates and mixtures of these compounds. As cationic surfactants, mention may in particular be made of all cationic surfactants comprising at least one C6-C40 alkyl group or at least one aromatic ring substituted by a C6-C40 alkyl group, and at least one cationic group chosen from ammoniums and pyridiums. 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 said surfactant(s) which can be used are chosen from trimethyldecylammonium chloride, sodium dodecyl sulfate and sodium stearate. The surfactant is typically used at a concentration which is higher than its critical micelle concentration (cmc), typically 2 to 5 times its cmc.

[0038] The monomers to be polymerized, in this case the monomer mixture of 1,3-butadiene and a (meth)acrylate which contains 1,3-butadiene and an alkyl methacrylate, are introduced into a reactor which contains 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.

[0039] Preferably, the monomer mixture contains 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. More preferably, the monomer mixture is a mixture of 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, in which case the synthesized copolymer is a copolymer of 1,3-butadiene and alkyl methacrylate or a terpolymer of 1,3-butadiene, glycerol carbonate (meth)acrylate and alkyl methacrylate. Even more preferably, the monomer mixture is a mixture of 30% to 70% mol of 1,3-butadiene and 70% to 30% mol of an 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.

[0040] In a known manner, the polymerization is generally carried out in an oxygen-free reactor at a polymerization temperature of around 5°C, for example between 0°C and 10°C, advantageously at 5°C. The polymerization can be carried out continuously or discontinuously (called a “batch” process), possibly a semi-fed “batch” process when a monomer feed is carried out during the polymerization reaction, in particular throughout the polymerization reaction. The continuous process and the “batch” process are particularly preferred for obtaining a random copolymer.

[0041] In order to stop the polymerization reaction at the correct conversion, in a known manner, a reducing agent, the stopper, is typically introduced. For example, mention may be made of the family of phenols such as hydroquinone, resorcinol, hydroxylamines such as N, N-diethylhydroxylamine. Preferably, the stopper is generally used in excess relative to the initiator introduced into the polymerization medium, typically the ratio between the number of moles of stopper and the number of moles of initiator introduced into the polymerization medium being greater than 1 and less than 10, preferably ranging from 2 to 5.

[0042] Once synthesized, the copolymer in accordance with the invention can be in either latex or solid form, for example to be mixed with a reinforcing filler in order to prepare a masterbatch.

[0043] To recover the copolymer in latex phase and without residual monomers, it is preferable to carry out a step of devolatilization of these monomers, most generally by steam distillation (stripping). To recover the copolymer in solid form, it is necessary to add a step of destabilization of the emulsion with or without a prior stripping step and a step of drying the coagulum.

[0044] Destabilization of the emulsion can be achieved by the addition of a third body, 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 the addition of a solvent chosen from ketones and alcohols and in particular acetone, methanol, isopropanol, n-butanol and ethanol. The coagulum is then generally washed with water.

[0045] The process for synthesizing the copolymer according to the invention may further comprise a step of drying the copolymer, once coagulated. Preferably, the copolymer may be dried under vacuum or at atmospheric pressure under nitrogen scavenging. The drying temperatures may vary from room temperature (25°C) to 130°C, preferably from room temperature to 100°C, and even more preferably from room temperature to 70°C. The drying times are typically between 10 h and 72 h, preferably between 16 h and 50 h.

[0046] The rubber composition, another subject 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, the elastomers usually used in rubber compositions intended for the manufacture of tires, such as polyisoprenes, polybutadienes, isoprene copolymers, butadiene copolymers such as butadiene and styrene copolymers.

[0047] According to any one of the embodiments of the invention, the content of the copolymer in accordance with the invention in the rubber composition is preferably greater than 50 phr, more preferably greater than 80 phr, even more preferably equal to 100 phr. The rubber composition may contain one or more copolymers in accordance with the invention which differ from one another by their composition or their macrostructure. In the latter case, the indicated preferential contents of copolymer in accordance with the invention in the rubber composition apply to all of the copolymers in accordance with the invention.

[0048] The rubber composition in accordance with the invention has the characteristic of containing a crosslinking system.

[0049] According to one embodiment of the invention, the crosslinking system is a vulcanization system, i.e. a system based on sulfur (or a sulfur-donating agent) and a primary vulcanization accelerator. Added to this basic vulcanization system are, 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 even known vulcanization retarders.As a (primary or secondary) vulcanization accelerator, any compound capable of acting as a vulcanization accelerator for diene elastomers in the presence of sulfur may be mentioned, in particular accelerators of the thiazole type and their derivatives, accelerators of the sulfenamide, thiuram, dithiocarbamate, dithiophosphate, thiourea and xanthate types. Sulfur is used at a preferential rate of between 0.5 and 12 pce, in particular between 1 and 10 pce. The primary vulcanization accelerator is used in the rubber composition at a preferential rate of between 0.5 and 10 pce, more preferably between 0.5 and 5 pce.

[0050] According to another embodiment applicable when the content of glycerol carbonate (meth)acrylate in the copolymer is greater than 0 mol%, the crosslinking system consists of one or more compounds having at least two groups reactive with respect to the carbonate function. The quantity 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 functions in the elastomer matrix. The quantity of this compound introduced into the rubber composition preferably varies from 0.05 to 5, more preferably from 0.05 to 2 molar equivalents of reactive groups of this compound for one mole of carbonate function in the elastomer matrix.

[0051] In the choice of the compound belonging to the crosslinking system having at least two groups reactive with respect to the carbonate function, one can refer 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 functions with carbonates, in particular acids, alcohols and amines. In this respect, one can cite polyacids, in particular diacids, or their dehydrated form, namely anhydrides, polyamines, in particular diamines. For example, as commercially available polyacids useful for the purposes of the invention, mention may be made of oxalic acid, succinic acid, adipic acid, sebacic acid, dodecanedioic acid, terephthalic acid, trimesic acid and 3,4-bis(carboxymethyl)cyclopentanecarboxylic acid.Examples of polyamines that may be mentioned include 1,6-diaminohexane, 1,8-diaminooctane and the “Jeffamines” family from Huntsman, from which a person skilled in the art will be able to choose the most appropriate polyamine in relation to the expected properties of the crosslinked rubber composition.

[0052] Preferably, the crosslinking system is a vulcanization system.

[0053] The rubber composition of the tread 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 a reinforcing organic filler such as carbon black, a reinforcing inorganic filler such as silica, or a mixture of these two types of filler.

[0054] Such a reinforcing filler 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.

[0055] Suitable carbon blacks are all carbon blacks, including those conventionally used in tire treads. Among these, the reinforcing carbon blacks of the 100, 200, and 300 series (ASTM grades), such as blacks N115, N134, N234, N326, N330, N339, N347, and N375, are particularly suitable. These carbon blacks can be used in their isolated form, as commercially available, or in any other form, for example as a carrier for some of the rubber additives used.

[0056] By "reinforcing inorganic filler" is meant here 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 on its own, 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 pneumatic grade carbon black; such a filler is generally characterized, in a known manner, by the presence of hydroxyl groups (OH) on its surface.

[0057] The silica used may be any reinforcing silica known to those skilled in the art, in particular any precipitated or pyrogenic silica having a BET surface area and a CTAB specific surface area both less than 450 m 2 / g.

[0058] The physical state in which the silica is presented is indifferent, whether in the form of powder, microbeads, granules, or even beads. Of course, reinforcing inorganic fillers also include mixtures of different silicas, in particular highly dispersible silicas as described above.

[0059] A person skilled in the art will understand that, as a filler equivalent to the silica described in this paragraph, a reinforcing filler of another nature, in particular organic such as carbon black, could be used, provided that this reinforcing filler is covered with an inorganic layer such as silica, or else comprises functional sites on its surface, in particular hydroxyl sites, requiring the use of a coupling agent to establish the bond between the filler and the copolymer. By way of example, mention may be made, for example, of carbon blacks for tires as described, for example, in patent documents WO 96 / 37547, WO 99 / 28380.

[0060] Preferably, the reinforcing filler content is between 40 and 200 phr. Below 40 phr, the reinforcement of the rubber composition is insufficient to provide an adequate level of cohesion or wear resistance of the rubber composition. More preferably, the reinforcing filler content is at least 50 phr. Above 200 phr, there is a risk of increasing the hysteresis and therefore the rolling resistance of the tires. For this reason, the reinforcing filler content is advantageously in a range from 50 to less than 200 phr, better still from 50 to 160 phr. These preferred ranges of the reinforcing filler content can apply to any of the embodiments of the invention.

[0061] Preferably, the reinforcing filler comprises a silica. More preferably, the reinforcing filler comprises more than 50% by mass of a silica.

[0062] When silica represents more than 50% by mass of the reinforcing filler, carbon black is preferably used at a rate of less than 20 phr, more preferably less than 10 phr (for example between 0.5 and 20 phr, in particular between 2 and 10 phr), even more preferably less than 5 phr. In the indicated ranges, the coloring (black pigmenting agent) and anti-UV properties of carbon blacks are benefited from, without otherwise penalizing the typical performances provided by the reinforcing inorganic filler that is silica.

[0063] To couple the silica to the elastomer matrix, in particular in the case where the silica constitutes more than 50% by weight of the reinforcing filler of the rubber composition, a coupling agent (or bonding agent) is generally used in a well-known manner. By coupling agent, we mean more precisely an agent capable of establishing a sufficient bond of a chemical and / or physical nature between the silica and the elastomer matrix, while facilitating the dispersion of the silica within the elastomer matrix.

[0064] This at least bifunctional agent is intended to ensure a sufficient connection, of a chemical and / or physical nature, between the silica (surface of its particles) and the elastomer matrix. In particular, organosilanes are used, in particular polysulfurized alkoxysilanes or mercaptosilanes, or polyorganosiloxanes carrying functions capable of physically and / or chemically bonding to the inorganic filler and functions capable of physically and / or chemically bonding to the elastomer matrix, 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 polysulfurized alkoxysilanes.In particular, polysulfurized silanes are used, called "symmetrical" or "asymmetrical" depending on their particular structure, as described for example in applications W003 / 002648 (or US 2005 / 016651) and W003 / 002649 (or US 2005 / 016650).

[0065] As coupling agent other than polysulfurized alkoxysilane, mention will be made in particular of bifunctional POSS (polyorganosiloxanes) or hydroxysilane polysulfides 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 carrying azodicarbonyl functional groups, as described for example in patent applications WO 2006 / 125532, WO 2006 / 125533, WO 2006 / 125534.

[0066] The content of coupling agent, whether a single compound or a mixture of compounds, is advantageously less than 20 phr, it being understood that it is generally desirable to use as little as possible. Typically the level of coupling agent represents from 0.5% to 15% by weight relative to the quantity of silica. Its level is preferably between 0.5 and 12 phr, more preferably within a range of 3 to 10 phr. This level is easily adjusted by a person skilled in the art according to the level of silica used in the composition.

[0067] The rubber composition in accordance with the invention may also contain coupling activators, silica covering agents or more generally processing aids capable, in a known manner, thanks to 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 processability 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.

[0068] The rubber composition in accordance with the invention may also comprise all or part of the usual additives normally used in rubber compositions intended for the manufacture of tires, such as, for example, plasticizers, pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, antioxidants, anti-fatigue agents and mixtures of such compounds.

[0069] The rubber composition in accordance with the invention can be manufactured in suitable mixers, generally using two successive preparation phases well known to those skilled in the art: a first thermomechanical working or kneading phase (so-called "non-productive" phase) at high temperature, up to a maximum temperature of between 110°C and 190°C, preferably between 120°C and 180°C, followed by a second mechanical working phase (so-called "productive" phase) down to a lower temperature, typically below 110°C, for example between 40°C and 100°C, finishing phase during which the crosslinking system is incorporated.

[0070] The rubber composition in accordance with the invention can be prepared according to a process which comprises the following steps:

[0071] - thermomechanically kneading 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;

[0072] - cool the assembly to a temperature below 100°C;

[0073] - then incorporate the crosslinking system;

[0074] - knead everything to a maximum temperature below 110°C to obtain a rubber composition.

[0075] After incorporating all the ingredients of the rubber composition, the final composition thus obtained is then calendered, for example in the form of a sheet or plate, in particular for characterization in the laboratory, or extruded, to form for example a rubber profile used as a rubber component, in particular for making the tire. The rubber composition according to the invention can be used in the form of calendering in a tire. The calendering or the extrudate formed from the rubber composition constitutes in whole or in part a semi-finished product, in particular a tire.

[0076] Thus, according to a particular embodiment of the invention, the rubber composition in accordance with the invention, which may be either in the raw state (before crosslinking or vulcanization), or in the cooked state (after crosslinking or vulcanization), is in a tire, for example in a tire tread.

[0077] Crosslinking (or curing), and where appropriate vulcanization, is carried out in a known manner at a temperature generally between 130°C and 200°C, for a sufficient time which may 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 in question.

[0078] The rubber composition may constitute all or part of a semi-finished article for a tire, 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 composition.

[0079] The tire according to the invention comprises a rubber composition according to the invention. The rubber composition preferably constitutes all or part of the tread of the tire. The tire is both in the raw state (i.e., before curing) and in the cured state (i.e., after crosslinking or vulcanization).

[0080] The above-mentioned characteristics of the present invention, as well as others, will be better understood upon reading the following description of the exemplary embodiments of the invention, given for illustrative and non-limiting purposes.

[0081] Examples

[0082] Determination of the glass transition temperature:

[0083] The glass transition temperatures Tg and glass transition widths AT of the polymers are measured using a differential scanning calorimeter according to ASTM D3418-08. ie exclusion ue

[0084] 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. Although not an absolute method, SEC allows us to understand 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 polydispersity index or dispersity (£) = Mw / Mn, also noted Ip) calculated using a so-called MOORE calibration. There is no special treatment of the polymer sample 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.

[0085] The apparatus 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 MIXED-B-LS columns from Agilent 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 the "WATERS EMPOWER" system. The calculated average molar masses are relative to a calibration curve produced from commercial standard polystyrenes "PSS READY CAL-KIT".

[0086] The dynamic properties are measured on a viscoanalyzer (Metravib VA4000), according to the ASTM D 5992-96 standard. The response of a sample of vulcanized composition (cylindrical specimen 4 mm thick and 400 mm2 in cross-section), subjected to sinusoidal stress in alternating simple shear, at a frequency of 10 Hz, under normal temperature conditions (23°C) according to the ASTM D 1349-99 standard, is recorded.

[0087] A strain amplitude sweep is carried out 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.

[0088] Synthesis of elastomers:

[0089] The elastomers of examples 1 to 6 are prepared according to the following protocol:

[0090] Preparing the following charges in advance:

[0091] We weigh approximately exactly the quantity of solutes to prepare the solutions at an exactly known concentration which is close to a target concentration whose value is given below and introduced by the term "approximately".

[0092] - 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 to 60°C for 45 minutes while stirring regularly

[0093] - Preparation of a solution of cumene hydroperoxide (initiator) in alkyl methacrylate at approximately 0.04 mol / L - Preparation of a solution of tert-dodecylmercaptan (RSH) in alkyl methacrylate at approximately 0.1 mol / L

[0094] - Preparation of a solution of N,N-diethylhydroxylamine (stopper) in water at approximately 0.05 mol / L in water.

[0095] Sodium dodecyl sulfate (SDS), iron sulfate, cumene hydroperoxide, sodium pyrophosphate (Sodium pyrophosphate tetrabasic), potassium persulfate, terdodecyl mercaptan, N,N-diethylhydroxylamine, n-butyl methacrylate (BuMA), 2-ethylhexyl methacrylate (EHMA) are commercially available from Aldrich. 4-(Hydroxymethyl)-1,3-dioxolan-2-one methacrylate (CCMA) is from Specific Polymers. 1,3-butadiene (btd) and alkyl methacrylates are purified by passage through an alumina guard and nitrogen sparging.

[0096] A stirred reactor is charged according to the following operations: introduce the bubbled water for 45 minutes at 25°C then the sodium dodecyl sulfate (surfactant, TA) under nitrogen at 25°C followed by a nitrogen flush of 10 min 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 rest of the monomer charge with the exception of 1,3-butadiene, under nitrogen let the reactor cool to 5°C, then inject the Na2FeP2O7 solution, then inject the 1,3-butadiene, leave to stir for 10 to 15 minutes while the emulsion forms then inject the initiator, the cumene hydroperoxide solution.

[0097] The end of the addition of the initiator marks the start of polymerization (i.e. t=0 min).

[0098] Stirring 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 solution N,N-diethylhydroxylamine (stopper). The latex is then coagulated by adding a mixture of acetone and methanol (acetone / methanol: 50 / 50 by volume) at a rate of 3 volumes of the acetone / methanol mixture for one volume of reaction medium. The coagulum is dried under partial vacuum and nitrogen flushing for 48 h at 40°C.

[0099] The conditions for synthesizing the elastomers of Examples 1 to 6 are shown in Table 1; conventionally, the quantity of water and that of the surfactant are given in part by mass per hundred parts of monomer mixture; the quantity of iron sulfate being 0.90 molar equivalents relative 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 relative 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 as molar equivalents 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 making up the starting monomer charge, the starting monomer charge constituting the monomer mixture to be polymerized.

[0100] Table 1:

[0101] The number-average molar mass values ​​(Mn), dispersity (£>), molar composition of the elastomers of Examples 1 to 6 are shown in Table 2, as well as the value of the Mn / D ratio. The synthesized copolymers are all statistical: they all have an AT lower than 10°C. Each of the synthesized copolymers has a content of 1,4-trans butadiene units greater than 70 mol% of the butadiene units of the copolymer. The determination of the molar composition of the elastomers is carried out by 1H NMR analysis. The spectra are acquired on a BRUKER Avance 500 MHz spectrometer equipped with a BBFO z-grad 5 mm "broadband" cryoprobe for soluble samples and a HRMAS 4 mm z-grad probe 1 H / 13C. The quantitative 1H NMR experiment uses a single 30° pulse sequence and a 5-second repetition delay between each acquisition. Samples are solubilized or swollen in deuterated chloroform. Chemical shifts are calibrated relative to the protonated impurity of chloroform (6 ppm 1 H at 7.2 ppm).

[0102] Table 2:

[0103] Preparation of rubber compositions:

[0104] To prepare the compositions, proceed as follows:

[0105] The elastomer, the reinforcing filler and the other additives are successively introduced into an internal mixer (final filling rate approximately 70% by volume), whose initial tank temperature is approximately 100°C. Thermomechanical work is then carried out (non-productive phase) in one step (total mixing time equal to approximately 5 min), until a maximum "fall" temperature ranging from 140 to 165°C is reached depending on the compositions. The mixture thus obtained is recovered, cooled and then the vulcanization system is added to an external mixer to carry out a second phase of mechanical work at approximately 40°C.

[0106] The rubber compositions are given in Table 3. The quantities are expressed in parts per 100 parts by weight of elastomer.

[0107] Table 3:

[0108] (1) Silica “Zeosil 1165 MP” from Rhodia (HDS type)

[0109] (2) Tris(2-ethylhexyl)phosphate

[0110] (3) Polylimonene resin "Dercolyte L120" from DRT company

[0111] (4) TESPT (“Si69” from the company Degussa)

[0112] (5) Diphenylguanidine (“Perkacit” DPG from Flexsys)

[0113] (6) N-(l,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, from Flexsys

[0114] (7) Industrial grade zinc oxide from Umicore

[0115] (8) Stearin “Pristerene 4931” from Uniqema company

[0116] (9) N-cyclohexyl-2-benzothiazyl sulfenamide “Santocure CBS” from Flexys The compositions thus obtained are then calendered either in the form of plates (thickness of 2 to 3 mm) or thin sheets of rubber for the measurement of their physical or mechanical properties. The calendered compositions are then cooked under pressure for 40 min at 160°C, then characterized.

[0117] The results of the characterizations of the rubber compositions are shown in Table 4.

[0118] Table 4:

[0119] 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 / D ratio > 150,000 g / mol and are therefore elastomers in accordance with 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 results in an Mn / D ratio greater than 150,000 g / mol. In other words, although elastomers E4 to E6 are composed of much longer chains than elastomers E1 to E3, the constituent chains of elastomers E4 to E6 exhibit a chain length homogeneity comparable to the chains of elastomers E1 to E3.It is observed that the higher the Mn / D ratio, the lower the tanô 10% values, which indicates an improvement in the rolling resistance of a tire whose tread contains an elastomer in accordance with the invention in its rubber composition. It is also observed that the presence of carbonate functions in the copolymers, whether compliant or not, contributes to reducing the tanô 10% values.

Claims

Claims 1. A random copolymer of 1,3-butadiene and a (meth)acrylate having a content of 1,4-trans butadiene units greater than 70 mol% of the butadiene units of the copolymer and containing from 30% to 70 mol% of 1,3-butadiene, from 0 to 5 mol% of glycerol carbonate (meth)acrylate and at least 30 mol% of an alkyl methacrylate, which copolymer is an elastomer which has a number average molar mass, Mn, greater than 350,000 g / mol and less than 500,000 g / mol, a dispersity, £), 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 relative 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% mol.

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

4. Copolymer according to any one of claims 1 to 3, in which the (meth)acrylate denotes said alkyl methacrylate or several (meth)acrylates including said alkyl methacrylate.

5. Copolymer according to any one of claims 1 to 4, which 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 in which the glycerol carbonate (meth)acrylate is glycerol carbonate methacrylate.

7. Copolymer according to any one of claims 1 to 6 in which 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 in which the alkyl of said alkyl methacrylate is n-butyl or 2-ethylhexyl.

9. A rubber composition which comprises a reinforcing filler, a crosslinking system and a copolymer defined in any one of claims 1 to 8.

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

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

12. A tire according to claim 11, in which the rubber composition constitutes all or part of the tread.

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