Method for preparing a star copolymer of a 1,3-diene and ethylene

Abstract

The invention relates to a method for preparing a star copolymer of a 1,3-diene and ethylene, the copolymer containing more than 50 mol% ethylene units, which method comprises the polymerization of a monomer mixture of a 1,3-diene and ethylene in the presence of a catalytic system based at least on a neodymocene borohydride metallocene and an organomagnesium co-catalyst, followed by the reaction of tin tetrachloride with the reaction product of the polymerization, and then by a chain termination reaction. The invention also relates to a star copolymer capable of being obtained by the method according to the invention.

Description

[0001] Process for preparing a star copolymer of 1,3-diene and ethylene

[0002] The field of the invention is that of processes for the synthesis of polymers rich in ethylene units and containing units of a 1,3-diene.

[0003] Diene polymers rich in ethylene units are known, for example, from patent applications WO 2007054223 and WO 2007054224. Such copolymers are intended, for example, for use in tire treads. The high molar content of ethylene units in these copolymers, exceeding 50%, makes them less susceptible to oxidation than the diene polymers traditionally used in rubber compositions, such as polybutadienes, polyisoprenes, and butadiene-styrene copolymers.

[0004] It has been observed that copolymers containing 1,3-diene units and more than 50 mole percent ethylene units tend to flow under their own weight. This cold flow is uncontrolled and can pose difficulties in the use of these copolymers, particularly during storage in bales or crates. To overcome this problem, patent application WO 2021 / 123592 proposed branching the copolymer chain during its growth in the polymerization reaction. There remains a need to provide alternative processes for preparing novel ethylene-rich copolymers containing 1,3-diene units with a reduced propensity to flow.

[0005] Continuing its efforts to address these flow problems in storage, the Applicant has developed a new process that leads to the preparation of star copolymers of 1,3-diene and ethylene, the copolymer containing more than 50% by mole of ethylene units.

[0006] Thus, a first object of the invention is a process for preparing a star copolymer of a 1,3-diene and ethylene, the copolymer containing more than 50% by mole of ethylene units, which process comprises the successive steps a), b) and c),

[0007] - step a) being the polymerization of a monomeric mixture of a 1,3-diene and ethylene in the presence of a catalytic system based on at least one metallocene of formula (la) and a co-catalyst, the co-catalyst being an organomagnesium compound, {P(Cp 1 )(Cp 2 )Nd(BH4)(i+ y) -L y -Nx} (the)

[0008] CP 1 and Cp 2, identical or different, being chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted,

[0009] P being a group bridging the two groups Cp 1 and Cp 2 and comprising a silicon or carbon atom,

[0010] Nd designating the neodymium atom,

[0011] L represents an alkali metal chosen from the group consisting of lithium, sodium, and potassium,

[0012] N representing a molecule of an ether,

[0013] 2023PAT00384WO x, an integer or not, being equal to or greater than 0, y, an integer, being equal to or greater than 0,

[0014] - step b) being the reaction of tin tetrachloride with the reaction product of the polymerization of step a),

[0015] - step c) being a chain termination reaction.

[0016] A second object of the invention is a star copolymer of 1,3-diene and ethylene, which copolymer contains more than 50 mole percent ethylene units and consists of copolymer chains linked together by a tin atom. The copolymer can be obtained by the process according to the invention.

[0017] Detailed description

[0018] Any range of values ​​designated by the expression "between a and b" represents the range of values ​​greater than "a" and less than "b" (i.e., bounds a and b excluded) while any range of values ​​designated by the expression "from a to b" means the range of values ​​from "a" to "b" (i.e., including the strict bounds a and b).

[0019] The compounds mentioned in the description can be of fossil origin or bio-based. In the latter case, they may be partially or entirely derived from biomass or obtained from renewable raw materials derived from biomass. Similarly, the compounds mentioned may also come from the recycling of previously used materials; that is, they may be partially or entirely produced through a recycling process, or obtained from raw materials themselves derived from a recycling process.

[0020] The expression "based on" used to define the constituents of the catalytic system means the mixture of these constituents, or the product of the reaction of some or all of these constituents with each other.

[0021] Step a) of the process according to the invention is a polymerization reaction of a monomer mixture of a 1,3-diene and ethylene which allows the preparation of copolymer chains of a 1,3-diene and ethylene, growing chains intended to react in the next step, step b), with a star-forming agent, tin tetrachloride.

[0022] The 1,3-diene in the monomer mixture of step a) is a single compound, that is, a single 1,3-diene, or a mixture of 1,3-dienes that differ from one another in their chemical structure. Suitable 1,3-dienes include those having from 4 to 20 carbon atoms, such as 1,3-butadiene, isoprene, myrcene, p-farnesene, and mixtures thereof. Preferably, the 1,3-diene is 1,3-butadiene, isoprene, myrcene, p-famesene, or mixtures thereof, particularly a mixture of at least two of these. More preferably, the 1,3-diene is 1,3-butadiene or a mixture of 1,3-dienes containing 1,3-butadiene, which is preferably a mixture of 1,3-butadiene and myrcene or a mixture of 1,3-butadiene and p-farnesene. Advantageously, the 1,3-diene in the monomer mixture is 1,3-butadiene.

[0023] 2023PAT00384WO The monomer mixture of step a) generally contains more than 50 mole percent of ethylene, the percentage being expressed relative to the total number of moles of monomers in the monomer mixture of step a).

[0024] The copolymerization of the monomer mixture can be carried out in accordance with patent applications WO 2007054223 A2 and WO 2007054224 A2 using a catalytic system composed of a metallocene and an organomagnesium compound.

[0025] In this application, a metallocene is defined as an organometallic complex in which the metal, in this case the neodymium atom, is bonded to a molecule called the ligand and consisting of two Cp groups. 1 and Cp 2 connected to each other by a bridge P. These groups Cp 1 and Cp 2 , identical or different, are chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, these groups being able to be substituted or unsubstituted.

[0026] According to the invention, the metallocene used as a basic constituent in the catalytic system corresponds to the formula (la)

[0027] {P(Cp 1 )(Cp 2 )Nd(BH4)(i +y )-Ly-N x} (there)

[0028] P being a group bridging the two groups Cp 1 and Cp 2 and comprising a silicon or carbon atom,

[0029] CP 1 and Cp 2 , identical or different, being chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted,

[0030] Nd designating the neodymium atom,

[0031] L represents an alkali metal chosen from the group consisting of lithium, sodium, and potassium,

[0032] N representing a molecule of an ether, x, an integer or not, being equal to or greater than 0, y, an integer, being equal to or greater than 0.

[0033] Any ether that has the ability to complex alkali metal is suitable as an ether, including diethyl ether, methyltetrahydrofuran, and tetrahydrofuran.

[0034] Examples of substituted cyclopentadienyl, fluorenyl, and indenyl groups include those substituted with alkyl radicals having 1 to 6 carbon atoms, aryl radicals having 6 to 12 carbon atoms, or trialkylsilyl radicals such as SiMes. The choice of radicals is also influenced by the availability of the corresponding molecules—the substituted cyclopentadienes, fluorenes, and indenes—because these are either commercially available or easily synthesized.

[0035] Examples of substituted fluorenyl groups include those substituted at positions 2, 7, 3, or 6, particularly 2,7-ditertiobutyl-fluorenyl and 3,6-ditertiobutyl-fluorenyl. Positions 2, 3, 6, and 7 respectively designate the positions of the carbon atoms in the rings, as shown in the diagram below, with position 9 corresponding to the atom of

[0036] 2023PAT00384WO

[0037] Examples of substituted cyclopentadienyl groups include those substituted at both position 2 (or 5) and position 3 (or 4), particularly those substituted at position 2, most notably the tetramethylcyclopentadienyl group. Position 2 (or 5) refers to the position of the carbon atom adjacent to the carbon atom to which the π-bridge is attached, as shown in the diagram below. It is worth noting that a substitution at position 2 or 5 is also referred to as an alpha-bridge substitution.

[0038] Examples of substituted indenyl groups include those substituted at position 2, particularly 2-methylindenyl and 2-phenylindenyl. Position 2 refers to the position of the carbon atom adjacent to the carbon atom to which the P-bridge is attached, as shown in the diagram below.

[0039] Preferably, Cp 1 and Cp 2 Whether identical or different, they are alpha-substituted cyclopentadienyls, substituted fluorenyls, substituted indenyls, or fluorenyls of formula C13H8 or indenyls of formula C9H7. More preferably, Cp 1 and Cp 2 The identical or different fluorenyl groups are chosen from the group consisting of substituted fluorenyl groups and the unsubstituted fluorenyl group of formula CBHS. Advantageously, Cp 1 and Cp 2are identical and each represents an unsubstituted fluorenyl group with the formula C13H8, represented by the symbol Flu.

[0040] Preferably, bridge P connecting the Cp groups 1 and Cp 2 is of formula ZRjR 2 , in which Z represents a silicon or carbon atom, R 1 and R 2 These, identical or different, each represent an alkyl group comprising 1 to 20 carbon atoms, preferably a methyl group. In the formula ZR'R 2 , Z advantageously represents a silicon atom, Si.

[0041] 2023PAT00384WO Very advantageously, R 1 and R 2 each represent a methyl group and Z represents a silicon atom.

[0042] Better still, the metallocene has the formula (1-1), (1-2), (1-3), (1-4) or (1-5) according to any one of the embodiments of the invention:

[0043] [Me2Si(Flu)2Nd(p-BH4)2Li(THF)] (1-1)

[0044] [{Me2SiFlu2Nd(p-BH4)2Li(THF)}2] (1-2)

[0045] [Me2SiFlu2Nd(p-BH4)(THF)] (1-3)

[0046] [{Me2SiFlu2Nd(p-BH4)(THF)}2] (1-4)

[0047] [Me2SiFlu2Nd(p-BH4)] (1-5) in which Flu represents the CBHS group.

[0048] The metallocene used in the synthesis of the catalytic system can be in the form of crystalline or non-crystalline powder, or as single crystals. The metallocene can be monomeric or dimeric, depending on the preparation method, as described in the patent application.

[0049] WO 2007054224 A2 or WO 2007054223 A2. Metallocene can be prepared conventionally by a process analogous to that described in patent application WO 2007054224 A2 or WO 2007054223 A2, in particular by reacting, under inert and anhydrous conditions, the salt of an alkali metal of the ligand with a rare-earth borohydride, neodymium, in a suitable solvent, such as an ether, like diethyl ether or tetrahydrofuran, or any other solvent known to those skilled in the art. After the reaction, the metallocene is separated from the reaction byproducts by techniques known to those skilled in the art, such as filtration or precipitation in a second solvent. The metallocene is then dried and isolated in solid form.

[0050] The organomagnesium compound, another basic constituent of the catalytic system, is the co-catalyst of the catalytic system. Typically, the organomagnesium compound can be a diorganomagnesium compound or a halide of an organomagnesium compound. Preferably, the organomagnesium compound has the formula (lia) in which R 3 and R 4 , identical or different, represent a carbon group.

[0051] MgR 3 R 4 (lia)

[0052] A carbon group is defined as a group containing one or more carbon atoms. The carbon group can be a hydrocarbon group (hydrocarbyl group) or a heterohydrocarbon group, that is, a group containing one or more heteroatoms in addition to carbon and hydrogen atoms. Organomagnesium compounds with a heterohydrocarbon group are suitable for the compounds described as transfer agents in patent application WO2016092227 AL. The carbon group is represented by the symbols R 3 and R4 are preferentially hydrocarbon groups.

[0053] Carbon groups represented by R 3 and R 4 They can be aliphatic or aromatic. They can contain one or more heteroatoms such as an oxygen, nitrogen, silicon, or sulfur atom. Preferably, they are alkyl, phenyl, or aryl. They can contain 1 to 20 carbon atoms.

[0054] The alkyls represented R 3 and R 4 They can contain 2 to 10 carbon atoms and include ethyl, butyl, and octyl.

[0055] 2023PAT00384WO The aryls represented R 3 and R 4 can contain 7 to 20 carbon atoms and are notably a phenyl substituted by one or more alkyls such as methyl, ethyl, isopropyl.

[0056] R 3 and R 4are preferentially alkyls containing 2 to 10 carbon atoms, phenyls or aryls containing 7 to 20 carbon atoms.

[0057] According to a particular embodiment of the invention, R 3 comprises a benzene ring substituted by a magnesium atom, one of the carbon atoms of the benzene ring ortho to the carbon substituted by the magnesium atom being substituted by a methyl, ethyl, isopropyl, or ring-forming with its nearest neighbor carbon atom in the meta position, the other carbon atom of the benzene ring ortho being substituted by a methyl, ethyl, or isopropyl and R 4 is an alkyl group. According to this particular embodiment, R 3 is advantageously 1,3-dimethylphenyl, 1,3-diethylphenyl, mesityl, or 1,3,5-triethylphenyl and R 4 is advantageously ethyl, butyl, octyl.

[0058] According to another particular embodiment of the invention, R 3 and R 4 are alkyls containing 2 to 10 carbon atoms, including ethyl, butyl, octyl.

[0059] For example, the following are suitable organomagnesium compounds: butylethylmagnesium, butylloctylmagnesium, ethylmagnesium chloride, butylmagnesium chloride, ethylmagnesium bromide, butylmagnesium bromide, octylmagnesium chloride, octylmagnesium bromide, 1,3-dimethylphenylbutylmagnesium, 1,3-diethylphenylethylmagnesium, butylmesitylmagnesium, ethylmesitylmagnesium, 1,3-diethylphenylbutylmagnesium, 1,3-diethylphenylethylmagnesium, 1,3-diisopropylphenylbutylmagnesium, 1,3-disopropylphenylethylmagnesium, 1,3,5-triethylphenylbutylmagnesium, 1,3,5-triethylphenylethylmagnesium, 1,3,5-tri sopropylphenylbutylmagnesium, 1,3,5-trii sopropylphenylethylmagnesium.

[0060] The compounds with the formula (lia), Grignard reagents, are well known; some are even commercial products. For their synthesis, one can also refer, for example, to the collection of volumes in "Organic Synthesis".

[0061] Like all organomagnesium compounds, the organomagnesium compound constituting the catalytic system, particularly one with the formula (lia), can exist as a monomer or as a polymer. For example, the organomagnesium compound (lia) can exist as a monomer (R 3 -Mg-R 4 )i or in the form of a polymer entity (R 3 -Mg-R 4 ) p , p being an integer greater than 1, in particular a dimer (R 3 -Mg-R 4 )2.

[0062] Furthermore, whether in the form of a monomeric or polymer entity, the organomagnesium can also be presented as an entity coordinated to one or more molecules of a solvent, preferably an ether such as diethyl ether, tetrahydrofuran or methyltetrahydrofuran.

[0063] According to any one of the embodiments of the invention, the organomagnesium is preferably of formula (lia).

[0064] 2023PAT00384WO The amounts of co-catalyst and metallocene reacted are such that the ratio between the number of moles of Mg of the co-catalyst and the number of moles of the rare earth of the metallocene, neodymium, preferably goes from 0.5 to 200, more preferably from 1 to less than 20. The range of values ​​from 1 to less than 20 is in particular more favourable for obtaining copolymers of high molar masses.

[0065] According to a first embodiment, the catalytic system is prepared conventionally by a process analogous to that described in patent application WO 2007054224 A2 or WO 2007054223 A2. For example, the co-catalyst, in this case the organomagnesium compound, and the metallocene are reacted in a hydrocarbon solvent, typically at a temperature ranging from 20 to 80°C for a duration of 5 to 60 minutes. The catalytic system is generally prepared in a hydrocarbon solvent, either aliphatic such as methylcyclohexane or aromatic such as toluene, preferably in an aliphatic hydrocarbon solvent such as methylcyclohexane. Generally, after its synthesis, the catalytic system is used as is for step a).

[0066] According to a second embodiment, the catalytic system can be prepared by a process analogous to that described in patent application WO 2017093654 Al or in patent application WO 2018020122 Al, and it then contains a preforming monomer selected from 1,3-dienes, ethylene, and mixtures thereof, and is said to be of the preformed type. For example, the organomagnesium compound and the metallocene are typically reacted in a hydrocarbon solvent at a temperature of 20 to 80°C for 10 to 20 minutes to obtain a first reaction product. This first reaction product is then reacted with a preforming monomer at a temperature of 40 to 90°C for 1 to 12 hours. The preforming monomer is preferably used in a molar ratio (preforming monomer / metallocene metal) of 5 to 1000, preferably 10 to 500.Before its use in polymerization, the preformed catalytic system can be stored under an inert atmosphere, specifically at a temperature ranging from -20°C to room temperature (23°C). According to this second embodiment, the preformed catalytic system has as its basic constituent a preforming monomer selected from among 1,3-dienes, ethylene, and mixtures thereof. In other words, the so-called preformed catalytic system contains, in addition to the metallocene and the cocatalyst, a preforming monomer. The 1,3-diene used as the preforming monomer can be 1,3-butadiene, isoprene, or a 1,3-diene with the formula CH2=CR. 5 -CH=CH2, the symbol R 5 representing a hydrocarbon group having 3 to 20 carbon atoms, in particular myrcene or P-farnesene. The preforming monomer is preferentially a 1,3-diene, more preferably 1,3-butadiene.

[0067] The catalytic system typically occurs in a solvent which is preferentially the solvent in which it was prepared, and the concentration of rare earth metal, i.e. neodymium, of metallocene is then in a range preferably from 0.0001 to 0.2 mol / L more preferably from 0.001 to 0.03 mol / L.

[0068] As with any synthesis carried out in the presence of organometallic compounds, the synthesis of the metallocene, the synthesis of the organomagnesium compound, and the synthesis of the catalytic system take place

[0069] 2023PAT00384WO under anhydrous conditions in an inert atmosphere. Typically, reactions are carried out from solvents and anhydrous compounds under anhydrous nitrogen or argon.

[0070] The polymerization of the monomer mixture is carried out in a reactor, preferably in solution, either continuously or batchwise. The polymerization solvent is typically a hydrocarbon solvent, preferably aliphatic. Methylcyclohexane is a particularly suitable example of an aliphatic hydrocarbon solvent. The monomer mixture can be introduced into the reactor containing the polymerization solvent and the catalytic system, or conversely, the catalytic system can be introduced into the reactor containing the polymerization solvent and the monomer mixture. The monomer mixture and the catalytic system can be introduced simultaneously into the reactor containing the polymerization solvent, particularly in the case of continuous polymerization. Polymerization is typically carried out under anhydrous conditions and in the absence of oxygen, possibly with the addition of an inert gas.The polymerization temperature generally varies in a range of 40 to 150°C, preferably 40 to 120°C. A person skilled in the art adapts the polymerization conditions such as the polymerization temperature, the concentration of each of the reactants, the pressure in the reactor according to the composition of the monomer mixture, the polymerization reactor, and the desired microstructure and macrostructure of the copolymer chain.

[0071] Polymerization is preferably carried out at constant pressure in monomers. A continuous addition of each or one of the monomers can be made to the polymerization reactor, in which case the polymerization reactor is a fed reactor. This embodiment is particularly suitable for the statistical incorporation of monomers. Preferably, the polymerization in step a) is a statistical polymerization, resulting in the statistical incorporation of monomers from the monomer mixture used in step a).

[0072] Once the desired monomer conversion rate is achieved in the polymerization reaction of step a), step b is carried out.

[0073] Step b) of the process according to the invention involves reacting the reaction product of step a) with tin tetrachloride. Step b) is a star-linking reaction of the copolymer chains, one end of which reacts with tin tetrachloride. After deactivation of the reactive sites by a polymer chain termination reaction (step c), a copolymer of 1,3-diene and ethylene is obtained, containing copolymer chains linked together by a tin atom, in particular 3-branch star chains linked together by a tin atom, 4-branch star chains linked together by a tin atom, or a mixture thereof.

[0074] Preferably, step b) is carried out in an aliphatic hydrocarbon solvent, such as methylcyclohexane. Advantageously, it is carried out in the reaction mixture from step a). It is generally performed by adding tin tetrachloride to the reaction product of step a) in its reaction mixture under stirring. Steps a) and b) are advantageously carried out in an aliphatic hydrocarbon solvent.

[0075] 2023PAT00384WO Before adding tin tetrachloride, the reactor is preferably degassed and inert. Degassing the reactor removes residual gaseous monomers and also facilitates the addition of tin tetrachloride. Alternatively, tin tetrachloride can be injected into the reactor under pressure. Inertizing the reactor, for example with nitrogen, prevents the carbon-metal bonds present in the reaction medium, which are necessary for the star-forming reaction of the copolymer chains, from being deactivated. Tin tetrachloride can be added pure or diluted in a hydrocarbon solvent, preferably aliphatic such as methylcyclohexane or aromatic such as toluene. The tin tetrachloride is left in contact with the reaction product of step a) for the time required for the star-forming reaction.The star-forming reaction can typically be monitored by chromatographic analysis to track the consumption of the star-forming agent or by measuring the viscosity of the polymer solution. The star-forming reaction is preferably carried out at a temperature of 23 to 120 °C for 1 to 60 minutes with stirring. Step b) is preferably conducted with a molar ratio of tin tetrachloride to carbon-magnesium bonds per mole of cocatalyst in the catalytic system ranging from 0.01 to 1, preferably between 0.1 and 0.5.The ratio of the number of moles of tin tetrachloride to the number of carbon-magnesium bonds per mole of cocatalyst in the catalytic system can vary depending on the desired level of star polymer in the polymer obtained at the end of step c), the desired number of branches in the star copolymer, and, in the case of obtaining a mixture of star copolymers with different numbers of branches, their respective proportions. A ratio between 0.1 and 0.5 favors the highest levels of star formation. Advantageously, step b), the star formation reaction, is carried out with a ratio of the number of moles of tin tetrachloride to the number of carbon-magnesium bonds per mole of cocatalyst in the catalytic system between 0.1 and 0.5. Typically, in a diorganomagnesium compound such as butylloctylmagnesium (BOMAG), there are two carbon-magnesium bonds per mole of the magnesium compound.The ratio between the number of moles of tin tetrachloride and the number of carbon-magnesium bonds per mole of co-catalyst of the catalytic system therefore corresponds to the ratio between the number of moles of tin tetrachloride introduced into the reaction medium and the number of moles of carbon-magnesium bonds provided by the catalytic system.

[0076] Once the end of the chain has been modified, step b) is followed by step c).

[0077] Step c), the chain termination reaction, is typically a reaction that deactivates any remaining reactive sites in the reaction medium from step b). In step c), a chain termination agent is brought into contact with the reaction product from step b), usually in its reaction medium, for example, by adding the termination agent to the tissue reaction medium from step b) or by pouring the tissue reaction medium from step b) onto a solution containing the termination agent. The termination agent is usually in stoichiometric excess. The termination agent is typically a protic compound, a compound that contains a relatively acidic proton. Examples of termination agents include water, carboxylic acids (particularly C2-C18 fatty acids such as acetic acid and stearic acid), aliphatic or aromatic alcohols such as methanol, ethanol, and isopropanol, and phenolic antioxidants.

[0078] 2023PAT00384WO After reaction with a protic compound, the process yields a star copolymer. The copolymer prepared according to the process of the invention can be separated from the reaction medium of step c) by methods well known to those skilled in the art, for example, by evaporation of the solvent under reduced pressure or by steam stripping. The polymer prepared according to the process is a copolymer of 1,3-diene and ethylene and contains more than 50 mole percent ethylene. The copolymer contains copolymer chains linked together by a tin atom, in particular 3-branch star chains linked together by a tin atom, 4-branch star chains linked together by a tin atom, or a mixture thereof. In other words, the copolymer is preferably a 3-branch copolymer, a 4-branch copolymer, or a mixture thereof.The copolymer prepared according to the process of the invention may also contain copolymer chains devoid of tin atoms. Their presence may result from the deactivation of a portion of the growing copolymer chains obtained in step a).

[0079] The copolymer according to the invention, another object of the invention and obtainable by the process according to the invention, has as its essential characteristic that it is a copolymer of 1,3-diene and ethylene. The constituent units of the copolymer are those resulting from the polymerization of 1,3-diene and ethylene.

[0080] The copolymer also has the essential characteristic of containing more than 50 mole percent ethylene units. Preferably, the copolymer contains more than 60 mole percent ethylene units, and more preferably more than 65 mole percent ethylene units. Preferably, the copolymer contains less than 90 mole percent ethylene units, more preferably at most 85 mole percent ethylene units, and even more preferably at most 80 mole percent ethylene units. The percentages of ethylene units in the copolymer are expressed relative to the total number of units resulting from the polymerization of 1,3-diene and ethylene.

[0081] 1,3-diene is a single compound, that is, a single 1,3-diene, or a mixture of 1,3-dienes that differ from one another in their chemical structure. Those with 4 to 20 carbon atoms are suitable as 1,3-dienes.

[0082] Preferably, the 1,3-diene is 1,3-butadiene, isoprene, myrcene, p-famesene, or mixtures thereof, such as a mixture of at least two of them. The mixture of at least two of them is advantageously a mixture that contains 1,3-butadiene.

[0083] According to a particular embodiment of the invention, 1,3-diene is a mixture of 1,3-dienes which contains 1,3-butadiene.

[0084] According to another particularly preferred embodiment of the invention, the copolymer according to the invention contains ethylene units, 1,3-butadiene units, and cyclic units, 1,2-cyclohexane motifs. The 1,2-cyclohexane units have formula (I). The cyclic units result from a specific insertion of the ethylene and 1,3-butadiene monomers into the polymer chain, in addition to the conventional ethylene and 1,3-butadiene units, respectively -(CH2-CH2)-, (CH2-CH=CH-CH2)-, and (CH2-CH(C=CH2))-. The

[0085] 2023PAT00384WO mechanism of obtaining such a microstructure is for example described in the document Macromolecules 2009, 42, 3774-3779.

[0086] When the copolymer according to the invention contains 1,2-cyclohexane units, it preferably contains at most 15% by mol, the percentage being expressed relative to the total number of units resulting from the polymerization of 1,3-diene and ethylene. Such a copolymer can be prepared by the process according to the invention in which the metallocene of the catalytic system has as its ligand two fluorenyl groups, substituted or unsubstituted.

[0087] Preferably, the copolymer according to the invention is a copolymer of ethylene and 1,3-butadiene.

[0088] According to any one embodiment of the invention, the copolymer according to the invention is preferably a statistical copolymer. In other words, the monomer units constituting the copolymer chains (or arms) of the statistical copolymer according to the invention are statistically distributed within the copolymer chains. Such a copolymer can be prepared by the process according to the invention, in which the polymerization reaction is carried out at constant pressure in a reactor, and each or one of the monomers is continuously added to the reactor. Advantageously, the copolymer according to the invention is a statistical copolymer of ethylene and 1,3-butadiene.

[0089] The copolymer according to the invention also has the additional characteristic of being tin-linked. In other words, the copolymer chains constituting the copolymer according to the invention are linked together by a tin atom. The tin-linked copolymer according to the invention is preferably a 3-branch copolymer, a 4-branch copolymer, or mixtures thereof. In other words, it preferably consists of 3-branch tin-linked chains, 4-branch tin-linked chains, or a mixture thereof.

[0090] The aforementioned features of the present invention, as well as others, will be better understood upon reading the following description of the examples of embodiments of the invention, given by way of illustration.

[0091] 2023PAT00384WO Examples

[0092] Size exclusion chromatography (SEC): a) Principle of measurement:

[0093] 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.

[0094] Combined with three detectors (3D), a refractometer, a viscometer, and a 90° light scattering detector, SEC allows for the determination of the absolute molar mass distribution of a polymer. The various absolute molar masses, number average (Mn), weight average (Mw), and dispersity (ε) (Mw / Mn) can also be calculated. b) Polymer preparation:

[0095] Each sample is solubilized in tetrahydrofuran at a concentration of approximately 1 g / L. The solution is then filtered through a 0.45 µm pore size filter before injection. c) SEC 3D analysis:

[0096] To determine the number-average molar mass (Mn), and where applicable the weight-average molar mass (Mw) and the polydispersity index (Ip or also denoted D = Mw / Mn) of the polymers, the following method is used:

[0097] The number-average molar mass (Mn), weight-average molar mass (Mw), and polydispersity index of the polymer (hereafter referred to as the sample) are determined in absolute terms by triple-detection size exclusion chromatography (SEC). Triple-detection size exclusion chromatography has the advantage of directly measuring average molar masses without calibration.

[0098] To determine the average molar masses, a previously prepared and filtered 1 g / L tetrahydrofuran solution is injected into the chromatography system. The equipment used is a Wyatt chromatography system. The elution solvent is tetrahydrofuran containing 250 ppm of BHT (2,6-diter-butyl-4-hydroxytoluene), with a flow rate of 1 mL / min. 1The system temperature was 35°C and the analysis time 60 min. The columns used were a set of three AGILENT columns, commercially known as "PL GEL MIXED B LS". The injected volume of the sample solution was 100 pL. The detection system consisted of a Wyatt differential viscometer, commercially known as "VISCOSTAR II", a Wyatt differential refractometer, commercially known as "OPTILAB T-REX" with a wavelength of 658 nm, and a Wyatt multi-angle static light scattering detector, commercially known as "DAWN HELEOS 8+", also with a wavelength of 658 nm.

[0099] The data is acquired and processed using ASTRA software and the dn / dc of ethylene-based copolymers is considered to be 0.1000 by default.

[0100] Nuclear magnetic resonance (NMR):

[0101] Ethylene-1,3-butadiene copolymers are characterized by NMR spectroscopy 1 H, 13C. The NMR spectra are recorded on a Brüker Avance III 500 MHz spectrometer equipped with a 5 mm BBIz-grad "broadband" cryo-probe. The 'H' NMR experiment

[0102] 2023PAT00384WO quantitative, uses a simple 30° pulse sequence and a 5-second repetition delay between each acquisition. 64 to 256 accumulations are performed. The NMR experiment 13 Quantitative C uses a simple 30° pulse sequence with proton decoupling and a 10-second repetition delay between each acquisition. 1024 to 10240 accumulations are performed. Two-dimensional experiments are used to determine the structure of polymers. The determination of the microstructure of copolymers is defined in the literature, according to the article by Llauro et al., Macromolecules 2001, 34, 6304-6311.

[0103] Inherent viscosity:

[0104] The inherent viscosity at 25 °C of a 0.1 g / dL polymer solution in toluene is measured from a dry polymer solution.

[0105] The inherent viscosity is determined by measuring the flow time t of the polymer solution and the flow time to of the toluene in a capillary tube. In an Ubbelhode tube (capillary diameter 0.46 mm, capacity 18 to 22 mL), placed in a bath thermostated at 25°C ± 0.1 °C, the flow time of the toluene and that of the 0.1 g / dL polymer solution are measured.

[0106] The inherent viscosity is obtained by the following relation: r|inh = [ln (t / to)] / C with:

[0107] C: concentration of the polymer toluene solution in g / dL; t: flow time of the polymer toluene solution in seconds; to: flow time of toluene in seconds; r|inh: inherent viscosity expressed in dl / g.

[0108] Cold-flow:

[0109] The cold flow CF 100(1 ±6) is derived from the following measurement method:

[0110] This involves measuring the weight of extruded rubber through a calibrated die over a given time (6 hours), under fixed conditions (at 100°C). The die has a diameter of 6.35 mm and a thickness of 0.5 mm.

[0111] The cold-flow apparatus is a cylindrical cup with a hole in the bottom. Approximately 40g ± 4g of gum, previously prepared as a pellet (2 cm thick and 52 mm in diameter), is placed in this device. A calibrated 1 kg (± 5 g) piston is positioned on top of the gum pellet. The entire assembly is then placed in an oven, thermally stabilized at 100°C ± 0.5°C.

[0112] During the first hour in the oven, the measurement conditions are not stable. After one hour, the extruded product is therefore cut out and discarded.

[0113] The measurement then lasts 6 hours ± 5 minutes, during which the product is left in an oven. At the end of the 6 hours, the sample of extruded product must be retrieved by cutting it flush with the surface of the base. The result of the test is the weight of the gum in grams.

[0114] Determination of the glass transition temperature of copolymers:

[0115] The glass transition temperature (Tg) and the glass transition width AT are measured using a Differential Scanning Calorimeter (DSC) according to ASTM D3418 (1999).

[0116] 2023PAT00384WO Preparation of copolymers:

[0117] The metallocene [{Me2SiFlu2Nd(p-BH4)2Li(THF)}]2 is prepared according to the procedure described in patent application WO 2007054224.

[0118] Butylloctylmagnesium BOMAG (20% in heptane, at 0.88 mol / L) 1) comes from Chemtura and is stored in a Schlenk tube under an inert atmosphere.

[0119] The ethylene, of N35 grade, comes from the company Air Liquide and is used without prior purification.

[0120] 1,3-Butadiene is purified over alumina guards.

[0121] Tin tetrachloride is marketed by Fox Chemicals.

[0122] The methylcyclohexane (MCH) solvent from BioSolve is dried and purified on an alumina column in a solvent fountain from mBraun and used under an inert atmosphere.

[0123] All reactions are carried out under an inert atmosphere.

[0124] Example 1: Preparation of an ethylene and 1,3-butadiene copolymer EBR1 not according to the invention:

[0125] In a 70 L reactor containing methylcyclohexane (64 L), ethylene, and 1,3-butadiene at a butadiene / ethylene (btd / eth) mass ratio of 0.76, BOMAG butylclotylmagnesium is added in the amounts indicated in Table 1, followed by the catalytic system (0.006 mol). At this point, the reaction temperature is regulated to 80°C, and the polymerization reaction begins. The polymerization reaction proceeds at a constant pressure of 8 bar. The reactor is fed with ethylene and 1,3-butadiene at a butadiene / ethylene mass ratio of 0.76 throughout the polymerization process. The polymerization reaction is stopped by cooling, degassing the reactor, and adding ethanol. An antioxidant is added to the polymer solution. The copolymer is recovered after steam stripping and drying to a constant mass.

[0126] The weighed mass allows the average catalytic activity of the catalytic system to be determined, expressed in kilograms of polymer synthesized per mole of neodymium metal per hour (kg / mol.h).

[0127] Example 2: Preparation of an ethylene and 1,3-butadiene copolymer EBR2 according to the invention:

[0128] In a 70 L reactor containing methylcyclohexane (64 L), ethylene, and 1,3-butadiene at a butadiene / ethylene (btd / eth) mass ratio of 0.76, BOMAG butylmagnesium is added in the proportions indicated in Table 1, followed by the catalytic system (0.006 mol). At this point, the reaction temperature is regulated to 80°C, and the polymerization reaction begins. The polymerization reaction proceeds at a constant pressure of 8 bar. The reactor is fed with ethylene and 1,3-butadiene at a butadiene / ethylene mass ratio of 0.76 throughout the polymerization process. After polymerization, the monomer injection is stopped, and a 71 g / L SnCl solution in methylcyclohexane is introduced into the polymerization medium, which is then stirred for 15 minutes. After the reaction, the reaction mixture is cooled and ethanol is injected, followed by an antioxidant. The copolymer is then recovered.

[0129] 2023PAT00384WO steam stripping and drying to constant mass.

[0130] The weighed mass allows the average catalytic activity of the catalytic system to be determined, expressed in kilograms of polymer synthesized per mole of neodymium metal per hour (kg / mol.h).

[0131] The catalytic system used in the preparation of EBR1 and EBR2 is prepared according to the following procedure:

[0132] In a reactor containing 100 mL of methylcyclohexane (MCH) hydrocarbon solvent, the co-catalyst butylctylmagnesium (BOMAG) is added with a molar ratio Mg / Nd = 2.2, then butadiene with a molar ratio butadiene / Nd = 90. Metallocene [Me2Si(Flu)2Nd(p-BH4)2Li(THF)] is then added to the reaction medium (0.71 mmol).

[0133] The pre-formation takes place at a temperature of 80°C for 5 hours.

[0134] The copolymers are analyzed by SEC 3D, NMR, DSC.

[0135] The copolymerization and star-forming reaction conditions specific to each example, including the ratio between the number of moles of tin tetrachloride introduced into the reaction medium and the number of carbon-magnesium bonds provided by the catalytic system, are shown in Table 1, and the characteristics of the synthesized copolymers are shown in Table 2. The SEC 3D method was used to determine the number-average molar masses and the ethylene content determined by NMR and expressed as a molar percentage relative to all the monomer units of the copolymer.

[0136] The viscosity values ​​measured using an Ostwald viscometer and reported in Table 1 show that the EBR2 copolymer synthesized according to the process of the invention (Example 2) has a higher viscosity than the EBR1 copolymer of Example 1, which is not in accordance with the invention (Example 1), and indicate that the reaction with tin tetrachloride leads to the formation of star copolymers. The increase in number-average molar masses, reported in Table 2, observed between Example 2 and Example 1 confirms the formation of star chains, particularly four-branch chains, since the average molar masses increased by a factor of approximately 4. The observed increases in viscosity reflect a change in the rheological properties of the copolymer of Example 2 compared to the non-star copolymer of Example 1. The star copolymer has a lower propensity to flow, which is also confirmed by cold-flow measurements.

[0137] Finally, as reported in Table 2, the DSC analysis results indicate that each copolymer exhibits a single Tg value, as well as a relatively low AT value (less than 6°C). These data demonstrate the formation of statistically significant copolymers.

[0138] Table 1: 2023PAT00384WO

[0139] Table 2:

[0140] 2023PAT00384WO

Claims

Claims: A process for preparing a star copolymer of a 1,3-diene and ethylene, the copolymer containing more than 50 mole percent of ethylene units, which process comprises successive steps a), b) and c), - step a) being the polymerization of a monomeric mixture of a 1,3-diene and ethylene in the presence of a catalytic system based on at least one metallocene of formula (la) and a co-catalyst, the co-catalyst being an organomagnesium compound, {P(Cp 1 )(Cp 2 )Nd(BH4)(i +y )-Ly-N x} (there) CP 1 and Cp 2 , identical or different, being chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted, P being a group bridging the two groups Cp 1 and Cp 2 and comprising a silicon or carbon atom, Nd designating the neodymium atom, L represents an alkali metal chosen from the group consisting of lithium, sodium, and potassium, N representing a molecule of an ether, x, an integer or not, being equal to or greater than 0, y, an integer, being equal to or greater than 0, - step b) being the reaction of tin tetrachloride with the reaction product of the polymerization of step a), - step c) being a chain-terminating reaction. A process according to claim 1, wherein step b) is carried out with a molar ratio of the number of moles of tin tetrachloride to the number of moles of carbon-magnesium bonds per mole of co-catalyst of the catalytic system ranging from 0.01 to 1, preferably from 0.1 to 0.

5. A process according to any one of claims 1 to 2, wherein the 1,3-diene of the monomer mixture is 1,3-butadiene. A process according to any one of claims 1 to 3, wherein the catalytic system contains a preforming monomer selected from 1,3-dienes, ethylene, and mixtures thereof. A process according to claim 4, wherein the preforming monomer is a 1,3-diene. A process according to claim 4 or 5, wherein the preforming monomer is 1,3-butadiene. A method according to any one of claims 1 to 6, wherein Cp 1 and Cp 2are identical and each represents an unsubstituted fluorenyl group of formula CBHS. A method according to any one of claims 1 to 7, wherein the bridge P connects the Cp groups 1 and Cp 2 is of formula ZR. 1 R. 2 , in which Z represents a silicon or carbon atom, R 1 and R 2 , identical or different, each represent an alkyl group comprising from 1 to 20 carbon atoms, preferably a methyl. 2023PAT00384WO 9. Method according to claim 8, wherein R 1 and R 2 each represent a methyl group and Z represents a silicon atom.

10. A process according to any one of claims 1 to 9, wherein steps a) and b) are carried out in an aliphatic hydrocarbon solvent.

11. A star copolymer of 1,3-diene and ethylene, wherein the copolymer contains more than 50 mole percent ethylene units and consists of copolymer chains linked together by a tin atom.

12. Copolymer according to claim 11, wherein the copolymer is a 3-branch copolymer, a 4-branch copolymer, or a mixture thereof.

13. Copolymer according to claim 11 or 12, wherein the copolymer is a statistical copolymer. 14 Star copolymer according to any one of claims 11 to 13, wherein the 1,3-diene is 1,3-butadiene, isoprene, myrcene, P-famesene or mixtures thereof. 15 Star copolymer according to any one of claims 11 to 14, which copolymer is a copolymer of ethylene and 1,3-butadiene. 2023PAT00384WO

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