Radical emulsion polymerization process of a monomer mixture of 1,3-butadiene and (meth)acrylate.

Abstract

The present invention relates to a cold emulsion radical polymerization process for a monomer mixture of 1,3-butadiene and a (meth)acrylate containing 1,3-butadiene and an alkyl methacrylate, wherein the polymerization reaction is initiated by a redox system comprising an organic hydroperoxide and an iron(II) salt in the presence of a mercaptan as a transfer agent. The relative amounts of initiator, transfer agent, and monomers lead to a macrostructure characterized by a novel compromise between the number-average molar mass, Mn, and the dispersity, Δ. This compromise further improves the rolling resistance performance of a tire comprising a rubber composition including an elastomer prepared according to the process of the invention.

Description

Title of the invention: Process for radical polymerization in emulsion of a monomer mixture of 1,3-butadiene and (meth)acrylate.

[0001] The field of the present invention is that of cold emulsion radical polymerization processes of monomer mixture of 1,3-butadiene and a (meth)acrylate.

[0002] It is known from patent application WO 2016 / 001052 that the use in a tire tread compound of elastomers comprising more than 20 mole percent of monomer units of a methacrylic acid ester improves the wet grip performance of the tire while maintaining a good compromise between performance and rolling resistance. The elastomers described in this patent application WO 2016 / 001052 are prepared by hot emulsion radical polymerization (50°C). The hot emulsion radical polymerization of 1,3-butadiene has the disadvantage of producing macrogel and branched chains in the elastomer. 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.

[0003] The cold emulsion radical polymerization of a monomer mixture of styrene, 1,3-butadiene, and a carbonate-substituted alkyl methacrylate was described in WO 2018015646 Al to provide an elastomer that improves the reinforcement properties of a silica-reinforced rubber composition. The improved reinforcement of the rubber composition is attributed to the presence of the carbonate groups in the elastomer. Because the elastomer was synthesized by cold emulsion radical polymerization, its macrogel content is less than 0.3% and its branched-chain content is almost zero. Nevertheless, the molar mass distribution of the elastomer is relatively broad compared to its number-average molar mass.

[0004] There is therefore a need to provide an elastomer containing butadiene units and methacrylate units which does not have the aforementioned disadvantages of the elastomers mentioned above.

[0005] Continuing its research efforts to solve the problem posed, the Applicant discovered a new cold emulsion radical polymerization process for a monomer mixture of 1,3-butadiene and a (meth)acrylate containing 1,3-butadiene and an alkyl methacrylate. The process, which has two alternatives, leads to the synthesis of copolymers containing butadiene units and alkyl methacrylate units and exhibiting a macrostructure that allows them to further improve the rolling resistance performance of a tire. The macrostructure is characterized by a new compromise between the number-average molar mass, Mn, and the dispersity, D.

[0006] Thus the invention is a cold emulsion radical polymerization process of a monomer mixture of 1,3-butadiene and a (meth)acrylate containing 1,3-butadiene and an alkyl methacrylate, process in which the polymerization reaction is initiated by a redox system comprising an organic hydroperoxide and an iron (II) salt in the presence of a mercaptan as a transfer agent, the amounts of organic hydroperoxide and mercaptan satisfying 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 which is less than 10⁴ and 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 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. Detailed description

[0007] 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").

[0008] 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.

[0009] In the present invention, the term "tire" (in English, "tire") refers to 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.

[0010] All percentages are mass percentages unless otherwise stated.

[0011] The molar percentages relating to the composition of the copolymer according to the invention are calculated with respect to the total number of monomer units of the copolymer.

[0012] As is known, the term (meth)acrylate refers indifferently to an acrylate or a methacrylate.

[0013] Since the monomer mixture to be polymerized contains 1,3-butadiene and a (meth)acrylate, including an alkyl methacrylate, the copolymers prepared according to the process of the invention are copolymers of 1,3-butadiene and an alkyl methacrylate, or copolymers of 1,3-butadiene, an alkyl methacrylate, and another (meth)acrylate. The term "another (meth)acrylate" means a methacrylate other than an alkyl methacrylate.

[0014] The process according to the invention is a cold emulsion radical polymerization process, because the production of free radicals useful for initiating the polymerization reaction takes place without thermal activation thanks to the presence of the redox system composed of the Fe(II) salt and the organic hydroperoxide.

[0015] The use of a redox system in a radical emulsion polymerization is well known for enabling cold polymerization, typically at around 5°C. In the process according to the invention, the polymerization reaction is carried out at a temperature between 0° and 10°C. The radical polymerization of 1,3-butadiene in a cold emulsion is known to produce copolymers with a macrogel content of less than 0.3% by mass of the copolymer and without branched chains. The radical polymerization of 1,3-butadiene in a cold emulsion is also known to promote the insertion of 1,3-butadiene in the form of 1,4-trans butadiene units, which then 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 typically contains 1,4-trans butadiene units which represent more than 70% by mole of the butadiene units of the copolymer.1,4-trans butadiene units refer to butadiene units that are inserted into the copolymer chain in the 1,4-trans form.

[0016] The polymerization reaction is therefore initiated by free radicals resulting from the transfer of electrons from Fe(II) to the organic hydroperoxide. The organic hydroperoxide is thus considered to be the initiator of the polymerization reaction. Suitable examples of organic hydroperoxides include tert-butyl hydroperoxide, cumene hydroperoxide, and p-menthane hydroperoxide. Preferably, cumene hydroperoxide is the organic hydroperoxide. The Fe(II) salt can be, for example, ferrous sulfate, iron(II) pyrophosphate, or their hydrates. The iron(II) salt is preferably ferrous sulfate or a ferrous sulfate hydrate, more preferably ferrous sulfate heptahydrate, FeSO4·7H2O. The iron(II) salt is generally used in an amount corresponding to the stoichiometry of the redox reaction, that is, an Fe(II) / initiator ratio (the number of moles of Fe(II) to the number of moles of initiator) equal to 1, or close to the stoichiometry, that is, an Fe(II) / initiator ratio ranging from 0.9 to 1.0.

[0017] 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. Preferably, the mercaptan is n-dodecyl mercaptan or tert-dodecyl mercaptan.

[0018] The process can be implemented according to two alternatives for obtaining copolymers having the macrostructure defined by their number-average molar mass and the ratio between their number-average molar mass and their dispersity. According to the first alternative, which corresponds to the conditions a) the ratio between the number of moles of organic hydroperoxide and the number of moles of monomers is less than 10⁴ and the ratio between the number of moles of mercaptan and the number of moles of organic hydroperoxide is greater than 2.

[0019] According to the second alternative which corresponds to conditions b), the ratio between the number of moles of organic hydroperoxide and the number of moles of monomers is greater than or equal to 9x10 4 and the ratio between the number of moles of mercaptan and the number of moles of organic hydroperoxide is less than 0.5.

[0020] Each of these conditions allows the production of copolymers having a specific macrostructure defined by both the number-average molar mass of the copolymer and a ratio between the number-average molar mass and the dispersity of the copolymer. The copolymers prepared according to the process of the invention have a number-average molar mass greater than 350,000 g / mol and less than 500,000 g / mol and a dispersity such that the ratio between the number-average molar mass and the dispersity is greater than 150,000 g / mol. These characteristics The macrostructure defines a compromise between the number-average molar mass and the dispersity that reduces the hysteresis of a rubber compound. Reducing the hysteresis of the rubber compound results in a reduction of the rolling resistance of a tire whose tread is made entirely or partially of a rubber compound comprising an elastomer prepared according to the process of the invention. The rolling resistance performance of a tire containing a rubber compound comprising an elastomer prepared according to the process of the invention will be reduced as the amount of elastomer in the elastomer matrix of the rubber compound increases.

[0021] Under conditions a), preferably the ratio between the number of moles of organic hydroperoxide and the number of moles of monomers 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.

[0022] Under conditions b), preferably the ratio between the number of moles of organic hydroperoxide and the number of moles of monomers 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.

[0023] The monomer mixture preferably contains 30% to 70% mol of 1,3-butadiene, 0 to 5% mol of (meth)acrylate glycerol carbonate and at least 30% mol of an alkyl methacrylate.

[0024] According to a first embodiment of the invention, the monomer mixture is a mixture of 30% to 70% molar of 1,3-butadiene, 0 to 5% molar of (meth)acrylate glycerol carbonate and at least 30% molar of an alkyl methacrylate.

[0025] According to a second embodiment of the invention, the monomer mixture is a mixture of 30% to 70% molar of 1,3-butadiene and 70% to 30% molar of an alkyl methacrylate.

[0026] According to a third embodiment of the invention, the monomer mixture is a mixture of 30% to 70% molar of 1,3-butadiene, 1% to 5% molar of glycerol carbonate (meth)acrylate and at least 30% molar of an alkyl methacrylate.

[0027] The constituent monomer units of the copolymer prepared according to the first embodiment are butadiene units, alkyl methacrylate units, and glycerol carbonate (meth)acrylate units when the monomer mixture contains more than 0 mol% of glycerol carbonate (meth)acrylate; the constituent monomer units of the copolymer prepared according to the second embodiment are butadiene units and alkyl methacrylate units; the constituent monomer units of the copolymer prepared according to the third embodiment are butadiene units, alkyl methacrylate units, and (meth)acrylate units of glycerol carbonate.

[0028] The molar compositions of the monomer mixture defined in the first embodiment as well as in the second and third embodiments are favorable for obtaining a copolymer having elastomeric properties giving a tire good adhesion performance on wet ground when used in a rubber composition of a tire tread.

[0029] In the process according to the invention, whether implemented according to the first alternative or the second alternative, preferably the alkyl of the alkyl methacrylate contains from 2 to 10 carbon atoms, more preferably the alkyl of the alkyl methacrylate contains from 4 to 10 carbon atoms, even more preferably the alkyl of the alkyl methacrylate is n-butyl.

[0030] Surfactants are also used in a known manner to stabilize the aqueous emulsion. The surfactant(s) usable in the process according to the invention may be chosen from nonionic, anionic, or cationic surfactants, preferably from 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 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 trimethyldecy-lammonium chloride or bromide and benzalkonium salts and mixtures of these compounds.Preferably, the surfactant(s) usable in the process according to the invention are chosen from trimethoprim-ammonium chloride, sodium dodecyl sulfate, and sodium stearate. The surfactant is typically used at a concentration that is higher than its critical micellar concentration (eme), typically 2 to 10 times its CMC.

[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] 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 preferably between 5% and 35% by weight relative to the total weight of monomers introduced and water.

[0033] As is known, polymerization is typically carried out in an oxygen-free reactor. Polymerization can be performed 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 and "batch" processes are especially preferred for obtaining a statistically significant copolymer without compositional drift, as compositional drift results in a copolymer exhibiting a compositional gradient.

[0034] 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 relative to the initiator introduced into the polymerization medium; typically, the ratio of the number of moles of stopper to the number of moles of initiator introduced into the polymerization medium is greater than 1 and less than 10, preferably ranging from 2 to 5.

[0035] Once synthesized, the copolymer 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.

[0036] To recover the copolymer in the latex phase and without residual monomers, it is preferable to carry out a devolatilization step of the residual monomers present in the latex, generally by steam distillation (stripping). To recover the copolymer in solid form, it is necessary to add an emulsion destabilization step, with or without a prior stripping step, and a coagulum drying step. The emulsion can be destabilized by the addition of 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. The latex can also be coagulated 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 usually washed with water.

[0037] The process may further include a step of drying the copolymer after it has coagulated. The copolymer may be dried under vacuum or at atmospheric pressure with nitrogen purging. Drying temperatures may vary 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 h and 72 h, preferably between 16 h and 50 h.

[0038] 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

[0039] Determination of the glass transition temperature:

[0040] The glass transition temperatures Tg and glass transition widths AT of the copolymers are measured using a differential scanning calorimeter according to ASTM D3418-08. Size exclusion chromatography (SEC):

[0041] 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 the WATERS EMPOWER system. The calculated average molar masses are relative to a calibration curve created using standard polystyrenes. thank you “PSS READY CAL-KIT”. Dynamic properties:

[0042] The dynamic properties are measured on a viscoanalyzer (Metravib VA4000), according to ASTM D 5992-96. The response of a vulcanized composition sample (cylindrical specimen 4 mm thick and 400 mm2 in cross-section) is recorded, 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.

[0043] 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.

[0044] Synthesis of copolymers:

[0045] The copolymers of examples 1 to 30 are prepared according to the following protocol:

[0046] 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 0.1 mol / L tert-dodecyl mercaptan (RSH) solution in alkyl methacrylate - Preparation of a solution of N,N-diethylhydroxylamine (stopper) in water at approximately 0.05 mol / L in water.

[0047] 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.

[0048] 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, let it stir for 10 to 15 minutes until the emulsion forms, then inject the initiator, the cumene hydroperoxide solution. The end of the initiator addition marks the start of polymerization (i.e., t=0 min).

[0049] 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 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 acetone / methanol to 1 volume of reaction medium. The coagulum is dried under partial vacuum and nitrogen purging for 48 h at 40°C.

[0050] The synthesis conditions for the copolymers of Examples 1 and 2 are shown in Table 1. In the table, the abbreviation "eq." stands for molar equivalent. By convention, the quantities of water and surfactant are given as parts by mass per hundred parts of the monomer mixture. The quantity of cumene hydroperoxide (initiator) is given as a molar percentage relative to the total quantity of starting monomers; the quantities of RSH, iron complex, and stopper are given as molar equivalents relative to the quantity of initiator. The composition of the starting monomer filler is given as a molar percentage calculated on the total number of moles of monomers composing the starting monomer filler, the starting monomer filler constituting the monomer mixture to be polymerized. Example 1 does not conform to the invention, since the polymerization conditions are those described in document WO 2018015646 A1, the ratio of the number of moles of organic hydroperoxide to the number of moles of monomers being 7.4 x 10⁴ and the ratio of the number of moles of mercaptan to the number of moles of organic hydroperoxide being 0.71. Example 2 conforms to the invention, since the ratio of the number of moles of organic hydroperoxide to the number of moles of monomers being 9 x 10³ is less than 10⁴ and the ratio of the number of moles of mercaptan to the number of moles of organic hydroperoxide being 2.8 is greater than 2.

[0051] The results of examples 1 and 2 are shown in Table 1. The copolymer in Example 2 has a Mn value of approximately 430,000 and a Mn / D ratio of about 166,000 g / mol, whereas the copolymer in Example 1 has a Mn value of only 158,000 and a Mn / D ratio of about 41,000 g / mol. It is clear that the copolymer in Example 1 has a molar mass distribution that is broadly... given its number-average molar mass, compared to the copolymer in example 2.

[0052] Table 1: Reagents Example 1 Example 2 Water 240 480 Sodium dodecyl sulfate 3 3 Tert-dodecylmercaptan 0.71 eq / initiator 2.8 eq / initiator CCMA 2% molar 2% molar 1,3-butadiene 48% molar 48% molar BuMA 50% molar 50% molar Cumene hydroperoxide 0.074% molar / monomers 0.009% molar / monomers Iron complex: Iron (II) sulfate heptahydrate Tetrabasic sodium pyrophosphate 0.90 eq / initiator 0.89 eq / initiator 0.90 eq / initiator 0.89 eq / initiator N,N-diethylhydroxylamine 3 eq / initiator 3 eq / initiator Conversion 56% 56% Mn (g / mol) (eq PS) 158775 430978 D 3.86 2.59 Mn / D (eq PS) 41133 166400

[0053] The syntheses of the copolymers of examples 3 to 23 are carried out under the conditions described in Table 2, the quantity of stopper (N,N-diethylhydroxylamine) being 3 equivalents in relation to the quantity of initiator. In examples 3 to 9 and 15 to 16, the molar composition of the monomer mixture is 1,3-butadiene / BuMA / CCMA: 50 / 50 / 0: the elastomers prepared are copolymers of 1,3-butadiene and BuMA. In examples 10 to 14 and 17 to 23, the molar composition of the monomer mixture is 1,3-butadiene / BuMA / CCMA: 48 / 50 / 2: the elastomers prepared are ter-polymers of 1,3-butadiene, BuMA and CCMA. In Table 2, S / M is the ratio between the mass of water and the mass of monomers. of starting, Tpoiy the polymerization reaction time, Conv. the conversion of the polymerization reaction, the quantity of initiator is given as a molar percentage relative to the total quantity of starting monomers, the quantity of RSH is given as a molar equivalent relative to the quantity of initiator, the quantity of surfactant (TA) is given by the ratio between the concentration of the surfactant in the polymerization medium and its critical micellar concentration (CMC which is 0.0082 mol / L).

[0054] The results of examples 3 to 23 are shown in Table 2.

[0055] Table 2: Example Amor ceur RSH TA S / MTA poly (min) Conv. (%) Mn (g / mol) D Mn / f) (g / mol) 3 0.074 0.2 2.4 2.4 335 61.0 324662 3.4 95500 4 0.074 0.2 9.6 2.4 125 66.0 281022 4.0 70260 5 0.074 0.2 2.4 4.8 188 63.0 323631 3.4 95190 6 0.074 0.2 9.6 4.8 70 69.0 275723 3.5 78780 7 0.074 2.8 2.4 2.4 254 59.0 75557 2.1 36000 8 0.074 2.8 9.6 2.4 117 61.0 89237 2.1 42500 9 0.074 2.8 9.6 2.4 131 69.0 91052 2.1 43400 10 0.074 2.8 2.4 4.8 164 54.0 74318 2.0 37200 11 0.074 2.8 9.6 4.8 60 63.9 69641 2.0 34900 12 0.09 0.2 9.6 2.4 158 54.0 594756 3.2 185900 13 0.09 0.2 2.4 4.8 260 53.0 599241 3.1 193400 14 0.09 0.2 9.6 4.8 100 57.0 693980 3.7 187600 15 0.09 2.8 2.4 2.4 360 42.0 349255 3.2 109150 16 0.09 2.8 9.6 2.4 199 62.0 247610 4.6 53900 17 0.09 2.8 2.4 4.8 277 45.0 388755 2.9 134053 18 0.09 2.8 9.6 4.8 100 51.0 259497 2.9 89500 19 0.09 2.8 9.6 4.8 125 67.0 255314 3.0 85200 20 0.09 2.8 9.6 4.8 199 96.0 271617 3.2 84900 21 0.009 2.8 2.4 2.4 404 53.0 555199 2.8 198300 22 0.009 2.8 2.4 4.8 255 56.0 430978 2.6 165800 23 0.009 0.2 2.4 2.4 390 64.0 514540 3.7 139100

[0056] Examples 12 to 14 and 21 to 22 are examples in accordance with the invention, since the synthesis process complies with conditions a) or conditions b), conditions a) being that the ratio between the number of moles of organic hydroperoxide and the number of moles of monomers is less than 10⁴ and the ratio between the number of moles of mercaptan and the number of moles of organic hydroperoxide is greater than 2, conditions b) being that the ratio between the number of moles of organic hydroperoxide and the number of moles of monomers is greater than or equal to 9 x 10⁴ and the ratio between the number of moles of mercaptan and the number of moles of organic hydroperoxide is less than 0.5. The other examples 3 to 11, 15 to 20 and 23 are not in accordance with the invention.Only the process according to the invention allows the obtaining of copolymers with the desired macrostructure, that is to say defined by an average number molar mass greater than 350,000 g / mol and less than 500,000 g / mol and a Mn / £ ratio > 150,000 g / mol.

[0057] Examples 24 to 29:

[0058] The syntheses of the copolymers in Examples 24 to 29 are carried out under the conditions described in Table 3, the amount of stopper (N,N-diethylhydroxylamine) being 3 equivalents relative to the amount of initiator. In Table 3, S / M is the ratio between the mass of water and the mass of starting monomers, Tpoiy is the polymerization reaction time, Conv is the conversion of the polymerization reaction, the amount of initiator is given as a molar percentage relative to the total amount of starting monomers, the amount of RSH is given as a molar equivalent relative to the amount of initiator, and the amount of TA is given by the ratio between the surfactant concentration in the polymerization medium and its critical micelle concentration (CMC, which is 0.0082 mol / L). The composition of the starting monomer filler is given as a molar percentage calculated on the total number of moles of monomers composing the starting monomer filler.

[0059] Table 3: Example Primer RSH TA S / M Btd BuM A EHM A CCM A Tpoly (min) Conv. (%) 24 0.074 0.71 2.4 2.4 54 46 0 0 270 70 25 0.074 0.71 2.4 2.4 56 0 44 0 410 57 26 0.074 0.71 2.4 2.4 55 42 0 3 180 62 27 0.009 2.8 4.8 4.8 56 44 0 0 412 60 28 0.009 2.8 4.8 4.8 58 0 42 0 355 42 29 0.009 2.8 2.4 4.8 55 43 0 2 375 43

[0060] The number-average molar mass values ​​(Mn), dispersity (μ), and molar composition of the elastomers in Examples 24 to 29 are shown in Table 4, as well as the Mn / D ratio value. The synthesized copolymers are all elastomers and statistical (AT less than 10°C).

[0061] Table 4: Example btd BuMA EHM A CCMA D Mn (g / mol) Mn / f) (g / mol) Elastomer 24 54 46 0 0 2.4 198533 83000 El 25 56 0 44 0 2.4 238210 99300 E2 26 56 42 0 2 2.5 173218 69300 E3 27 56 44 0 0 2.3 449355 195400 E4 28 58 0 42 0 2.4 445744 185800 E5 29 55 43 0 2 2.5 404306 161800 E6

[0062] Preparation of rubber compositions:

[0063] To prepare the rubber compositions, the following procedure is used: The elastomer, reinforcing filler, and other additives are successively introduced into an internal mixer (final filling level approximately 70% by volume), the initial tank temperature of which is approximately 100°C. A thermomechanical process (non-productive phase) is then carried out in a single step (total mixing time approximately 5 minutes) until a maximum "drop" temperature of 140 to 165°C, depending on the composition, is reached. The resulting mixture is then collected, cooled, and the vulcanizing system is added to an external mixer to perform a second mechanical processing phase at approximately 40°C.

[0064] The rubber compositions are given in Table 5. The quantities are expressed in parts per 100 parts by weight of elastomer.

[0065] Table 5: 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

[0066] (1) Silica “Zeosil 1165 MP” from the company Rhodia (type HDS)

[0067] (2) Tris(2-ethylhexyl)phosphate

[0068] (3) Polylimonene resin "Dercolyte L120" from the company DRT

[0069] (4) TESPT (“Si69” from the company Degussa)

[0070] (5) Diphenylguanidine (“Perkacit” DPG from Flexsys)

[0071] (6) N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, from Flexsys

[0072] (7) Industrial grade zinc oxide from Umicore

[0073] (8) Stearine “Pristerene 4931” from the company Uniqema

[0074] (9) N-cyclohexyl-2-benzothiazyl sulfenamide “Santicure CBS” of the company Flexys

[0075] 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 30 min at 150°C, and then characterized.

[0076] The results of the characterizations of the rubber compositions are shown in Table 6.

[0077] Table 6: 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

[0078] 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 prepared according to a process according to the invention, unlike elastomers E1 to E3. Elastomers E4 to E6 impart lower hysteretic properties to the rubber composition compared to elastomers E1 to E3. This result is attributed to the greater chain length homogeneity of elastomers E4 to E6. Indeed, elastomers E4 to E6 exhibit the best compromise between number-average molar mass and 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, 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 / £> ratio, the lower the tanô 10% values, which suggests an improvement in the rolling resistance of a tire whose tread contains an elastomer according to the invention in its rubber composition.

Claims

Demands

1. A cold emulsion radical polymerization process of a monomer mixture of 1,3-butadiene and a (meth)acrylate containing 1,3-butadiene and an alkyl methacrylate, wherein the polymerization reaction is initiated by a redox system comprising an organic hydroperoxide and an iron(II) salt in the presence of a mercaptan as a transfer agent, the amounts of organic hydroperoxide and mercaptan satisfying conditions a) or conditions b): conditions a) being defined by a ratio of the number of moles of organic hydroperoxide to the number of moles of monomers that is less than 10⁴ and a ratio of the number of moles of mercaptan to the number of moles of organic hydroperoxide that 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 which is greater than or equal to 9x10⁴ and a ratio between the number of moles of mercaptan and the number of moles of organic hydroperoxide which is less than 0.

5.

2. A process according to claim 1 wherein under conditions a) the ratio of the number of moles of organic hydroperoxide to the number of moles of monomers is greater than 5x105 and the ratio of the number of moles of mercaptan to the number of moles of organic hydroperoxide is less than 4.

3. A process according to claim 1 or 2 wherein under conditions b) the ratio of the number of moles of organic hydroperoxide to the number of moles of monomers is less than 5x103 and the ratio of the number of moles of mercaptan to the number of moles of organic hydroperoxide is greater than 0.

1.

4. A process according to any one of claims 1 to 3 wherein 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.

5. A process according to any one of claims 1 to 4 wherein 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.

6. A method according to any one of claims 1 to 5 wherein the

7.

8.

9.

10.

11.

12.

13.

14. monomer mixture is a mixture of 30% to 70% molar of 1,3-butadiene and 70% to 30% molar of an alkyl methacrylate. A process according to any one of claims 1 to 5 wherein the monomer mixture is a mixture of 30% to 70 mol% of 1,3-butadiene, 1% to 5 mol% of glycerol carbonate (meth)acrylate and at least 30 mol% of an alkyl methacrylate. A process according to any one of claims 1 to 7, wherein the alkyl group of the alkyl methacrylate contains from 2 to 10 carbon atoms. A process according to any one of claims 1 to 8, wherein the alkyl group of the alkyl methacrylate contains from 4 to 10 carbon atoms. A process according to any one of claims 1 to 9, wherein the alkyl group of the alkyl methacrylate is n-butyl. A process according to any one of claims 1 to 10 in which the polymerization reaction is carried out at a temperature between 0° and 10°C. A process according to any one of claims 1 to 11 wherein the organic hydroperoxide is cumene hydroperoxide. A process according to any one of claims 1 to 12 wherein the iron(II) salt is ferrous sulfate or a ferrous sulfate hydrate. A process according to any one of claims 1 to 13 wherein the mercaptan is n-dodecyl mercaptan or tert-dodecyl mercaptan.