Copolymer of conjugated diene and ethylene

Abstract

The invention relates to copolymers of conjugated dienes and ethylene, said copolymers comprising ethylene units and 1,3-diene units, the proportion of ethylene units in the ethylene units and 1,3-diene units being between 50 and 95 mol%, the proportion of 1,3-diene units in the 1,3-diene units of the formula CH2=CR-CH=CH2 being more than 50 mol%, the symbol R representing a hydrocarbon chain containing from 3 to 20 carbon atoms. This copolymer has an improved compromise between the ethylene content, the stiffness and the crystallinity for use in tyres.

Description

[0001] This application is a divisional application of Chinese patent application No. 201980083280.8, filed on December 13, 2019, entitled "Copolymer of Conjugated Diene and Ethylene". Technical Field

[0002] The present invention pertains to copolymers of conjugated dienes and ethylene, said copolymers being rich in ethylene units and used as elastomers in tire rubber compositions. Background Technology

[0003] The most widely used diene elastomers in tire manufacturing are polybutadiene, polyisoprene (especially natural rubber), and copolymers of 1,3-butadiene and styrene. These elastomers share a high molar proportion of diene units (typically much greater than 50%), making them sensitive to oxidation (especially under the influence of ozone).

[0004] Conversely, the applicant has described elastomers with relatively few diene units, particularly to reduce their sensitivity to oxidation. For example, such elastomers are described in document WO 2007054223. These elastomers are copolymers of 1,3-butadiene and ethylene containing more than 50 mol% ethylene units. These elastomers are referred to as ethylene-rich diene elastomers.

[0005] Ethylene-rich copolymers of 1,3-butadiene and ethylene are crystalline, with crystallinity increasing with increasing ethylene content. The presence of crystalline portions in the copolymer can be problematic when used in rubber compositions. Since the melting of the crystalline portions of the copolymer leads to a decrease in stiffness, the stiffness of rubber compositions containing such copolymers and used in tires also decreases when the temperature reaches or exceeds the melting point of the crystalline portions (this can occur during repeated braking and acceleration phases of a tire). Therefore, this dependence of stiffness on temperature can lead to uncontrolled fluctuations in tire performance quality. Advantageously, diene polymers rich in ethylene units can be obtained, which reduce (and even eliminate) the crystallinity of the diene polymer.

[0006] In document WO 2007054224, the applicant has described ethylene-rich diene copolymers with reduced crystallinity. These copolymers are copolymers of 1,3-butadiene and ethylene, which also contain saturated six-membered cyclic hydrocarbon units. However, the introduction of these copolymers into rubber compositions may impart excessively high stiffness to the rubber composition. The high stiffness of the rubber composition is attributed to the equally high stiffness of the elastomer. The high stiffness of the rubber composition may cause problems because it itself may make the rubber composition unsuitable for certain applications. Summary of the Invention

[0007] In order to achieve the goal of synthesizing ethylene-rich diene elastomers, the applicant has discovered a novel polymer that can solve the above problems, in particular by proposing an improved trade-off between ethylene content, stiffness and crystallinity for use in tires.

[0008] Therefore, the first subject of the present invention is a copolymer (preferably an elastomer) of ethylene and a 1,3-diene of formula (I), said copolymer comprising ethylene units and 1,3-diene units, wherein the proportion of ethylene units in the ethylene units and 1,3-diene units is between 50 mol% and 95 mol%, and the 1,4-configured 1,3-diene units account for more than 50 mol% of the 1,3-diene units.

[0009] Equation (I): CH2=CR-CH=CH2

[0010] The symbol R represents a hydrocarbon chain with 3 to 20 carbon atoms.

[0011] Another subject of the present invention is a method for preparing copolymers according to the present invention.

[0012] The present invention also relates to rubber compositions comprising at least one copolymer according to the invention, a reinforcing filler, and a crosslinking system, wherein the copolymer is an elastomer.

[0013] The present invention also relates to tires comprising a rubber composition according to the present invention. Detailed Implementation

[0014] In this specification, any numerical interval expressed as "between a and b" represents a range of values ​​greater than "a" and less than "b" (i.e., excluding the limits a and b), while any numerical interval expressed as "from a to b" represents a range of values ​​extending from "a" to "b" (i.e., including the strict limits a and b).

[0015] Unless otherwise stated, the content of units obtained by inserting monomers into copolymers is expressed as a molar percentage relative to all monomer units of the copolymer.

[0016] The compounds mentioned in the specification may be of fossil or bio-based origin. In the case of bio-based origin, they may be partially or wholly derived from biomass or obtained from renewable starting materials derived from biomass. Particular attention is paid to monomers.

[0017] The 1,3-diene of formula (I) as defined above and used for the purposes of this invention is a substituted 1,3-diene that, when polymerized, can produce units of configurations 1 and 2 represented by formula (1), units of configurations 3 and 4 represented by formula (2), and units of configuration 1 and 4 (the trans form of which is represented by formula (3) below). 1,4-configured 1,3-diene units (whether cis or trans) can be represented by the molecular formula -(CH2-CR=CH-CH2)-.

[0018]

[0019] As is well known, the ethylene unit is a unit of the -(CH2-CH2)- motif.

[0020] The copolymer according to the invention is a copolymer of ethylene and a 1,3-diene of formula (I), which means that the monomeric unit of the copolymer is a unit produced by the polymerization of ethylene and a 1,3-diene. Therefore, the copolymer comprises ethylene units and 1,3-diene units. The 1,3-diene used in the present invention is only one compound (i.e., only one 1,3-diene of formula (I)) or a mixture of 1,3-dienes of formula (I) (the 1,3-dienes in the mixture differ from each other in the group represented by the symbol R).

[0021] The essential characteristic of the copolymer according to the invention is that it contains between 50 mol% and 95 mol% ethylene units. In other words, the proportion of ethylene units in the ethylene and 1,3-diene units is between 50 mol% and 95 mol%. Preferably, in the copolymer according to the invention, the proportion of ethylene units in the ethylene and 1,3-diene units is at least 60 mol%. More preferably, the proportion of ethylene units in the ethylene and 1,3-diene units is at least 70 mol%. Preferably, in the copolymer according to the invention, the proportion of ethylene units in the ethylene and 1,3-diene units is at most 90 mol%.

[0022] According to a particular embodiment of the invention, the ethylene unit accounts for at most 85 moles of the ethylene unit and the 1,3-diene unit.

[0023] According to a preferred embodiment of the invention, in the copolymer according to the invention, the ethylene unit accounts for 60 mol% to 90 mol% of the ethylene unit and the 1,3-diene unit, and advantageously 70 mol% to 90 mol% of the ethylene unit and the 1,3-diene unit.

[0024] According to another specific embodiment of the invention, in the copolymer according to the invention, the ethylene unit accounts for 60 mol% to 85 mol% of the ethylene unit and the 1,3-diene unit, and advantageously 70 mol% to 85 mol% of the ethylene unit and the 1,3-diene unit.

[0025] Another essential feature of the copolymer according to the invention lies in its inclusion of 1,3-diene units of formula (I), said 1,3-diene units having a 1,4 configuration of greater than 50%. In other words, the 1,4-configured 1,3-diene units account for more than 50 mol% of the total 1,3-diene units. The remaining 1,3-diene units in the copolymer, up to 100 mol%, are formed wholly or partially from 1,2 or 3,4-configured 1,3-diene units. Preferably, the 1,4-configured 1,3-diene units account for more than 70 mol% of the total 1,3-diene units. Advantageously, more than half of the 1,4-configured 1,3-diene units are 1,4-trans-configured, meaning that the 1,4-trans-configured 1,3-diene units account for more than 50 mol% of the total 1,4-configured 1,3-diene units.

[0026] In the 1,3-diene of formula (I) claimed in this invention, the hydrocarbon chain represented by the symbol R can be straight or branched, in which case the symbol R represents a straight or branched chain. Preferably, the hydrocarbon chain is acyclic, in which case the symbol R represents an acyclic chain. In formula (I), the hydrocarbon chain represented by the symbol R can be saturated or unsaturated, in which case the symbol R represents a saturated or unsaturated chain. Preferably, the symbol R represents a hydrocarbon chain having 6 to 16 carbon atoms. More preferably, the symbol R represents an unsaturated acyclic chain. Even better, the symbol R represents an unsaturated and branched acyclic chain. Advantageously, the 1,3-diene is myrcene or β-farnesene.

[0027] According to a preferred embodiment of the present invention, the 1,3-diene is myrcene.

[0028] According to another preferred embodiment of the invention, the 1,3-diene is β-farnesene.

[0029] According to any embodiment of the present invention, the copolymer according to the present invention is preferably an elastomer.

[0030] The copolymers according to the invention can be prepared by a method comprising copolymerizing ethylene with 1,3-diene in the presence of a catalytic system, said catalytic system being based at least on a metallocene of formula (II) and an organomagnesium compound of formula (III).

[0031] Equation (II): P(Cp)(Flu)Nd(BH4) (1+y)- L y -N x

[0032] Formula (III): MgR 1 R 2

[0033] Cp represents the cyclopentadienyl group of formula C5H4, and Flu represents the C5H4 group. 13 The fluorenyl group of H8,

[0034] P represents the bridging groups Cp and Flu, and signifies ZR. 3 R 4 The group of the group, Z represents silicon or carbon atom, R 3 and R 4 They may be the same or different, and each represents an alkyl group containing 1 to 20 carbon atoms, preferably methyl.

[0035] y is an integer equal to or greater than 0.

[0036] x is an integer equal to or greater than 0, or a non-integer.

[0037] L indicates an alkali metal selected from lithium, sodium, and potassium.

[0038] N represents an ether molecule, preferably diethyl ether or tetrahydrofuran.

[0039] R 1 and R 2 They can be the same or different, and represent carbon-based.

[0040] The catalytic system can be conventionally prepared by a method similar to that described in application WO 2007054223. For example, organomagnesia compounds and metallocenes are typically reacted in a hydrocarbon solvent at a temperature ranging from 20°C to 80°C for a period of time (between 5 and 60 minutes). The catalytic system is typically prepared in an aliphatic hydrocarbon solvent (e.g., methylcyclohexane) or an aromatic hydrocarbon solvent (e.g., toluene). Generally, after synthesis, the catalytic system is used in this form in methods for synthesizing copolymers according to the invention.

[0041] Metallocenes used to prepare catalytic systems can be in the form of crystalline or amorphous powders, or in single-crystal form. Metallocenes can be provided in monomeric or dimer form, depending on the method of preparation, as described, for example, in application WO 2007054224. Metallocenes can be conventionally prepared by methods similar to those described in application WO 2007054223, particularly under inert and anhydrous conditions by reacting an alkali metal salt of a ligand with a rare earth metal borohydride in a suitable solvent (e.g., an ether (e.g., diethyl ether or tetrahydrofuran) or any other solvent known to those skilled in the art). Following the reaction, the metallocene is separated from the reaction byproducts using techniques known to those skilled in the art (e.g., filtration or precipitation in a second solvent). Finally, the metallocene is dried and separated in solid form.

[0042] Any synthesis, such as that in the presence of organometallic compounds, metallocene synthesis, and synthesis of catalytic systems, is carried out under anhydrous conditions in an inert atmosphere. Typically, the reaction begins with anhydrous solvents and compounds in anhydrous nitrogen or argon.

[0043] Preferably, the metallocene is of formula (IIa), (IIb), (IIc), (IId), or (IIe), wherein the symbol Flu represents formula C. 13 The fluorenyl group of H8, and the cyclopentadienyl group of the symbol Cp (represented by formula C5H4).

[0044] Formula (IIa): [{Me2SiCpFluNd(μ-BH4)2Li(THF)}2]

[0045] Formula (IIb): [Me2SiCpFluNd(μ-BH4)2Li(THF)]

[0046] Formula (IIC): [Me2SiCpFluNd(μ-BH4)(THF)]

[0047] Formula (IId): [{Me2SiCpFluNd(μ-BH4)(THF)}2]

[0048] Formula (IIe): [Me2SiCpFluNd(μ-BH4)]

[0049] The organomagnesium compound used in this invention is of the formula MgR 1 R 2 , where R 1 and R 2 They can be the same or different, and both represent carbonyl groups. Carbonyl is understood to mean a group containing one or more carbon atoms. Preferably, R 1 and R 2 It contains 2 to 10 carbon atoms.

[0050] According to a preferred embodiment of the present invention, R 1 and R 2 Each refers to an alkyl group, preferably an alkyl group containing 2 to 10 carbon atoms. The organomagnesium compound is advantageously a dialkylmagnesium compound, more preferably butylethylmagnesium or butyloctylmagnesium, and even more preferably butyloctylmagnesium.

[0051] According to any embodiment of the invention, the molar ratio of the organomagnesia compound to the metal Nd constituting the metallocene is preferably in the range of 1 to 100, more preferably greater than or equal to 1 and less than 10. The numerical range of 1 to less than 10 is particularly advantageous for obtaining copolymers with high molar mass.

[0052] Those skilled in the art can also adjust the polymerization conditions and the concentration of each reactant (component of the catalytic system, monomer) according to the equipment (apparatus, reactor) used to carry out the polymerization and various chemical reactions. As is known to those skilled in the art, the copolymerization, as well as the operation of the monomer, catalytic system, and polymerization solvent, is carried out under anhydrous conditions and an inert atmosphere. The polymerization solvent is typically an aliphatic hydrocarbon solvent or an aromatic hydrocarbon solvent.

[0053] Polymerization is preferably carried out continuously or in batches in solution. The polymerization solvent can be an aromatic hydrocarbon solvent or an aliphatic hydrocarbon solvent. Examples of polymerization solvents include toluene and methylcyclohexane. The monomer can be introduced into a reactor containing the polymerization solvent and a catalytic system, or conversely, the catalytic system can be introduced into a reactor containing the polymerization solvent and the monomer. Copolymerization is typically carried out under anhydrous conditions in the absence of oxygen and in the optional presence of an inert gas. The polymerization temperature is typically varied within the range of 30°C to 150°C, preferably from 30°C to 120°C. Preferably, copolymerization is carried out under constant ethylene pressure.

[0054] Polymerization can be terminated by cooling the polymerization medium. The polymer can be recovered using conventional techniques known to those skilled in the art, such as precipitation, solvent evaporation under reduced pressure, or steam stripping.

[0055] According to any embodiment of the invention, the introduction of 1,3-diene and ethylene into the growing polymer chain is preferably random. The copolymers according to the invention are advantageously random copolymers.

[0056] The copolymers according to the invention (especially when they are elastomers) can be used in rubber compositions.

[0057] The rubber composition (another subject of the invention) is characterized in that it comprises at least one elastomer, reinforcing filler and crosslinking system according to the invention.

[0058] The crosslinking system can be based on sulfur, sulfur donors, peroxides, bismaleimide, or mixtures thereof. The crosslinking system is preferably a vulcanization system, i.e., a system based on sulfur (or sulfur donors) and a primary vulcanization accelerator. Various known secondary vulcanization accelerators or vulcanization activators (e.g., zinc oxide, stearic acid or equivalent compounds, or guanidine derivatives (especially diphenylguanidine)) or known vulcanization retarders can be added to this basic vulcanization system.

[0059] The reinforcing fillers used in the present invention can include any type of "reinforcing" filler known for its ability to enhance the ability of rubber compositions used in the manufacture of tires, such as organic fillers (e.g., carbon black), reinforcing inorganic fillers (e.g., silica combined with a coupling agent in a known manner), or mixtures of both. Such reinforcing fillers typically consist of nanoparticles with an average (by weight) size of less than one micrometer, typically less than 500 nm, most typically between 20 nm and 200 nm, and particularly and more preferably between 20 nm and 150 nm. Those skilled in the art can adjust the content of the reinforcing filler according to the intended use of the rubber composition.

[0060] The rubber composition may additionally include other additives known for use in tire rubber compositions, such as plasticizers, anti-ozone agents, or antioxidants.

[0061] The rubber compositions according to the invention are typically manufactured in a suitable mixer using two consecutive preparation stages known to those skilled in the art: a first stage (“non-production” stage) of thermomechanical processing or kneading at high temperatures, with a maximum temperature between 130°C and 200°C, followed by a second stage (“production” stage) of mechanical processing at low temperatures, typically below 110°C (e.g., between 40°C and 100°C), during which the crosslinking system is added.

[0062] The rubber composition according to the invention can be in an unprocessed state (before crosslinking or vulcanization) or a cured state (after crosslinking or vulcanization), and can be used in tire semi-finished products.

[0063] Tires (another subject of the invention) comprise rubber compositions according to the invention as defined in any embodiment of the invention.

[0064] In summary, the present invention can be implemented according to any one of the following modes 1 to 23:

[0065] Pattern 1: A copolymer of ethylene and a 1,3-diene of formula (I), said copolymer comprising ethylene units and 1,3-diene units, wherein the proportion of ethylene units in the total ethylene and 1,3-diene units is between 50 mol% and 95 mol%, and the 1,4-configured 1,3-diene units constitute more than 50 mol% of the 1,3-diene units.

[0066] Equation (I): CH2=CR-CH=CH2

[0067] The symbol R represents a hydrocarbon chain with 3 to 20 carbon atoms.

[0068] Mode 2: The copolymer according to Mode 1, wherein the ethylene unit accounts for at least 60 moles of the ethylene unit and the 1,3-diene unit.

[0069] Mode 3: A copolymer according to Mode 1 or Mode 2, wherein the ethylene unit accounts for at least 70 moles of the ethylene unit and the 1,3-diene unit.

[0070] Mode 4: A copolymer according to any one of Modes 1 to 3, wherein the ethylene unit accounts for at most 90 moles of the ethylene unit and the 1,3-diene unit.

[0071] Mode 5: A copolymer according to any one of Modes 1 to 4, wherein the ethylene unit accounts for at most 85 moles of the ethylene unit and the 1,3-diene unit.

[0072] Mode 6: A copolymer according to any one of Modes 1 to 5, wherein the 1,4-configured 1,3-diene units account for more than 70 mol% of the 1,3-diene units.

[0073] Pattern 7: A copolymer according to any one of Patterns 1 to 6, wherein more than half of the 1,4-diene units are in the 1,4-trans configuration.

[0074] Pattern 8: A copolymer according to any one of Patterns 1 to 7, wherein the symbol R represents a hydrocarbon chain having 6 to 16 carbon atoms.

[0075] Pattern 9: A copolymer according to any one of Patterns 1 to 8, wherein the symbol R represents a non-cyclic chain.

[0076] Pattern 10: A copolymer according to any one of Patterns 1 to 9, wherein the symbol R represents a straight chain or a branched chain.

[0077] Pattern 11: A copolymer according to any one of Patterns 1 to 10, wherein the symbol R represents a saturated chain or an unsaturated chain.

[0078] Pattern 12: A copolymer according to any one of Patterns 1 to 11, wherein R represents an unsaturated noncyclic chain.

[0079] Pattern 13: A copolymer according to any one of Patterns 1 to 12, wherein the 1,3-diene is myrcene or β-farnesene.

[0080] Pattern 14: A copolymer according to any one of Patterns 1 to 13, wherein the copolymer is a random copolymer.

[0081] Pattern 15: A copolymer according to any one of Patterns 1 to 14, wherein the copolymer is an elastomer.

[0082] Mode 16: A method for preparing a copolymer defined in any one of Modes 1 to 15, said method comprising polymerizing ethylene and 1,3-diene in the presence of a catalytic system, said catalytic system being based at least on a metallocene of formula (II) and an organomagnesium compound of formula (III).

[0083] Equation (II): P(Cp)(Flu)Nd(BH4) (1+y)- L y -N x

[0084] Formula (III): MgR 1 R 2

[0085] Cp represents the cyclopentadienyl group of formula C5H4, and Flu represents the C5H4 group. 13 The fluorenyl group of H8,

[0086] P represents the bridging groups Cp and Flu, and signifies ZR. 3 R 4 The group of the group, Z represents silicon or carbon atom, R 3 and R 4 They may be the same or different, and each represents an alkyl group containing 1 to 20 carbon atoms, preferably methyl.

[0087] y is an integer equal to or greater than 0.

[0088] x is an integer equal to or greater than 0, or a non-integer.

[0089] L indicates an alkali metal selected from lithium, sodium, and potassium.

[0090] N represents an ether molecule, preferably diethyl ether or tetrahydrofuran.

[0091] R 1 and R 2 They can be the same or different, and represent carbon-based.

[0092] Mode 17: The method according to Mode 16, wherein the metallocene is of formula (IIa), (IIb), (IIc), (IId), or (IIe).

[0093] Formula (IIa): [{Me2SiCpFluNd(μ-BH4)2Li(THF)}2]

[0094] Formula (IIb): [Me2SCpiFluNd(μ-BH4)2Li(THF)]

[0095] Formula (IIC): [Me2SiCpFluNd(μ-BH4)(THF)]

[0096] Formula (IId): [{Me2SiCpFluNd(μ-BH4)(THF)}2]

[0097] Formula (IIe)[Me2SiCpFluNd(μ-BH4)]

[0098] Cp represents the cyclopentadienyl group of formula C5H4, and Flu represents the C5H4 group. 13 The fluorene group of H8.

[0099] Mode 18: The method according to any one of Modes 16 and 17, wherein R 1 and R 2 It contains 2 to 10 carbon atoms.

[0100] Mode 19: The method according to any one of Modes 16 to 18, wherein R 1 and R 2 Each represents an alkyl group.

[0101] Mode 20: The method according to Mode 19, wherein R 1 and R 2 Each represents an alkyl group containing 2 to 10 carbon atoms.

[0102] Mode 21: The method according to any one of Modes 16 to 20, wherein the organomagnesium compound is a dialkylmagnesium compound, preferably butylethylmagnesium or butyloctylmagnesium, more preferably butyloctylmagnesium.

[0103] Pattern 22: A rubber composition comprising at least one copolymer, reinforcing filler, and crosslinking system as defined in Pattern 15.

[0104] Mode 23: Tire, the tire comprising a rubber composition defined according to Mode 22.

[0105] The above and other features of the invention will become clearer from the following description of several embodiments of the invention given as a non-limiting description.

[0106] Example

[0107] 1) Polymer synthesis:

[0108] In the synthesis of the copolymer according to the present invention, the 1,3-diene used is myrcene or β-farnesene, and in the 1,3-diene of formula (I), R is a hydrocarbon group having 6 atoms and 11 carbon atoms respectively and having the following formula:

[0109] In myrcene, R corresponds to the formula CH2-CH2-CH=CMe2;

[0110] In β-farnesene, R corresponds to the formula CH2-CH2-CH=CMe-CH2-CH2-CH=CMe2.

[0111] All reactants were commercially available, except for metallocene [{Me₂SiFlu₂Nd(μ-BH₄)₂Li(THF)}] and [Me₂SiCpFluNd(μ-BH₄)₂Li(THF)] (prepared according to the steps described in applications WO 2007054224 and WO 2007054223).

[0112] Butyloctylmagnesium BOMAG (20% heptane, C = 0.88 mol / L) -1 The ethylene (N35 grade) was obtained from Chemtura and stored in Schlenk tubes under an inert atmosphere. No purification was required for use. Myrcene (purity ≥95%) was obtained from Sigma-Aldrich. β-farnesene (purity: 90-95%) was obtained from 1717 CheMall.

[0113] 1.1-Ethylene-1,3-Butadiene copolymer: not according to Example 1 of the present invention

[0114] The polymer is synthesized according to the following steps:

[0115] The co-catalyst butyloctylmagnesium (BOMAG) and subsequently the metallocene [Me₂SiCpFluNd(μ-BH₄)₂Li(THF)] were added to a 500 ml glass reactor containing 300 ml of toluene. Alkylation was carried out for 10 minutes at a reaction temperature of 20 °C. The amounts of each component in the catalytic system are shown in Table 1. Subsequently, monomers, ethylene (Eth) and 1,3-butadiene (Bde), were added in various proportions shown in Table 1 as a gaseous mixture. Polymerization was carried out at 80 °C under a constant ethylene pressure of 4 bar. The polymerization was terminated by cooling, reactor degassing, and the addition of 10 ml of ethanol. An antioxidant was added to the polymer solution. The copolymer was recovered by drying to constant weight in a vacuum oven. The microstructure and properties of the polymer are shown in Table 2.

[0116] 1.2-Ethylene-1,3-Butadiene copolymer: not according to Example 2 of the present invention

[0117] The polymer is synthesized according to the following steps:

[0118] The co-catalyst butyloctylmagnesium (BOMAG) and subsequently the metallocene [Me₂Si(Flu)₂Nd(μ-BH₄)₂Li(THF)] were added to a 500 mL glass reactor containing 300 mL of methylcyclohexane. Alkylation was carried out for 10 minutes at a reaction temperature of 20 °C. The amounts of each component in the catalytic system are shown in Table 1. Subsequently, monomers, ethylene (Eth) and 1,3-butadiene (Bde), were added in various proportions shown in Table 1 as a gaseous mixture. Polymerization was carried out at 80 °C under a constant ethylene pressure of 4 bar. The polymerization was terminated by cooling, degassing the reactor, and adding 10 mL of ethanol. An antioxidant was added to the polymer solution. The copolymer was recovered by drying to constant weight in a vacuum oven. The microstructure and properties of the polymer are shown in Table 2.

[0119] 1,3-Ethylene-Myrcene copolymer: according to Examples 3 to 5 of the present invention

[0120] The polymer is synthesized according to the following steps:

[0121] In a reactor containing methylcyclohexane, ethylene, and myrcene in proportions shown in Table 3 at 80°C, butyloctylmagnesium (BOMAG) was added to neutralize impurities in the reactor, followed by the addition of a catalyst system (see Table 3). The reaction temperature was then adjusted to 80°C, and polymerization began. The polymerization was carried out at a constant pressure of 8 bar. Throughout the polymerization process, ethylene and myrcene were fed into the reactor in proportions defined in Table 3. The polymerization was terminated by cooling, reactor degassing, and the addition of ethanol. An antioxidant was added to the polymer solution. The copolymer was recovered by drying to constant weight in an oven under vacuum. The catalyst system was a pre-formed catalyst system. It was prepared in methylcyclohexane from metallocene [Me₂SiCpFluNd(μ-BH₄)₂Li(THF)], the co-catalyst butyloctylmagnesium (BOMAG), and the pre-formed monomer 1,3-butadiene in the amounts shown in Table 3. It was prepared according to the preparation method in Section II of patent application WO 2018100279 A1.

[0122] Table 4 shows the microstructure and properties of the polymers.

[0123] 1,4-Ethylene and β-farnesene copolymer: according to Examples 6 and 7 of the present invention

[0124] The polymer is synthesized according to the following steps:

[0125] The co-catalyst butyloctylmagnesium (BOMAG) and subsequently the metallocene [Me₂SiCpFluNd(μ-BH₄)₂Li(THF)] were added to a 500 mL glass reactor containing 300 mL of methylcyclohexane. Alkylation was carried out for 10 minutes at a reaction temperature of 20 °C. The amounts of each component in the catalytic system are shown in Table 5. Subsequently, 70% of the β-farnesene feedstock was added to the reactor before the injection of gaseous ethylene, with the remaining 30% introduced into a reactor at 65% conversion. Polymerization was carried out at 80 °C under a constant ethylene pressure of 4 bar. The polymerization was terminated by cooling, reactor degassing, and the addition of 10 mL of ethanol. An antioxidant was added to the polymer solution. The copolymer was recovered by drying to constant weight in an oven under vacuum. The microstructure and properties of the polymer are shown in Table 6.

[0126] 2) Determination of polymer microstructure:

[0127] The copolymers of ethylene and 1,3-myrcene, as well as the copolymers of ethylene and β-farnesene, were characterized by nuclear magnetic resonance (NMR) spectroscopy and their microstructure was measured.

[0128] Spectrometer: For these measurements, a Bruker Avance III HD 400MHz spectrometer equipped with a Bruker cryogenic-BBFO z-class 5mm probe was used.

[0129] Experiment: Recording radio frequency pulses with a tilt angle of 30° 1 Experiment H was repeated 128 times with a cycle delay of 5 seconds. HSQC (heteronuclear single-quantum coherence) and HMBC (heteronuclear multi-bond correlation) were recorded. 1 H- 13 The C NMR experiments were repeated 128 times with an increment of 128. The experiments were conducted at 25°C.

[0130] Sample preparation: Dissolve 25 mg of sample in 1 ml of deuterated chloroform (CDCl3).

[0131] Sample calibration: relative to solvent (CHCl3) at δ 1H =7.2ppm and δ 13C Protonated impurity calibration at 77 ppm 1 H and 13 The axis of C chemical shift.

[0132] Spectral identification of copolymers of ethylene and 1,3-myrcene (see Formula 1):

[0133] In representative formula 1, symbols R1 and R2 denote the attachment sites of the unit to the polymer chain. In representative formula 1, the signals of the insertion forms of 1,3-dienes A, B, and C were observed on different recorded spectra. According to S. Georges et al. (S. Georges, M. Bria, P. Zinck, and M. Visseaux, Polymer, 55 (2014), 3869-3878), the characteristic signal of the -CH= group at the 8” position of form C... 1 H and 13 C chemical shift and characteristic signal of the -CH= group at position 3. 1 H and 13 The chemical shifts are the same.

[0134] Table 7 shows the chemical shifts of the characteristic signals of units A, B, and C. Units A, B, and C correspond to the 3,4 configuration, 1,2 configuration, and trans-1,4 configuration units, respectively.

[0135] Using Topspin software for 1D 1 Quantization is performed by integrating the H NMR spectrum.

[0136] The integrated signals of different primitives are:

[0137] Ethylene: The signal at 1.2 ppm corresponding to 4 protons.

[0138] Total myrcene: signal at position 1 corresponding to 6 protons (1.59 ppm).

[0139] Form A: Signal at position 7 corresponding to 2 protons (4.67 ppm).

[0140] Form B: The signal corresponding to the 8' position of one proton (5.54 ppm).

[0141] The quantification of microstructure is carried out as a mole percentage (mol%) as shown below: mol% of the element = mol% of the element 1 H integral * 100 / Σ (for each primitive) 1 H-integral).

[0142] Spectral identification of copolymers of ethylene and β-farnesene (see chemical formula 2):

[0143] In representative formula 2, symbols R1 and R2 denote the attachment points of the unit to the polymer chain. In representative formula 2, the signals of the inserted forms of farnesene A and B were observed on different recorded spectra. The 1H and 13C chemical shifts of the characteristic signal of the -CH= group at position 11" of form C are the same as those of the characteristic signals of the -CH= groups at positions 3 and 7. Table 8 shows the chemical shifts of the characteristic signals of units A, B, and C. Units A, B, and C (formula 2) correspond to the 3,4 configuration unit, the 1,2 configuration unit, and the trans-1,4 configuration unit, respectively.

[0144] Using Topspin software for 1D 1 Quantization is performed by integrating the H NMR spectrum.

[0145] The integrated signals of different primitives are:

[0146] Ethylene: the signal of 4-proton -CH2-CH2- (at 1.19 ppm),

[0147] Total farnesene: The signal of the 9 protons attributed to the groups at positions 1 and 13; this signal is common to all insertion forms of farnesene.

[0148] Form A: This form is unique to the signal at position 14 of the two protons.

[0149] Form B: This form is unique to the signal at position 11 of a single proton.

[0150] The proportion of form C cannot be obtained directly, but it can be calculated from the signals of groups belonging to positions 3, 7, and 11".

[0151] The quantification of microstructure is carried out as a mole percentage (mol%) as shown below: mol% of unit cell = mol% of unit cell 1 H integral × 100 / Σ (for each unit) 1 H-integral).

[0152] 3) Measurement of polymer stiffness (unprocessed state):

[0153] Measurements were performed in shear mode using cylindrical specimens with controlled geometries (thickness between 1.5 mm and 3 mm, and diameter between 22 mm and 28 mm) on an Anton Paar MCR301 rheometer. The specimens were subjected to sinusoidal shear stress at a fixed temperature (corresponding to the endpoint of the glass transition of the elastomer under temperature scanning at 10 Hz) at frequencies ranging from 0.01 Hz to 100 Hz. Following the method described in C. Liu, J. He, E. van Ruymbeke, R. Keunings, and C. Bailly's *Evaluation of different methods for the determination of the plateau modulus and the entanglement molecular weight* (Polymer, 47 (2006), 4461-4479), the stiffness value chosen as the stiffness of the sample's rubber platform was the value of the shear modulus G' at the frequency at which the loss modulus G' reaches its minimum.

[0154] 4) Determination of polymer crystallinity:

[0155] The temperature, enthalpy of fusion, and crystallinity of the polymers used were determined by differential scanning calorimetry (DSC) according to standard ISO 11357-3:2011. The reference enthalpy for polyethylene is 277.1 J / g (according to Handbook of Polymer, 4th edition, J. Brandrup, E. Himmergut, and E. A. Grulke, 1999).

[0156] 5) Results:

[0157] In Example 1 (Control), the diene copolymer synthesized by polymerization of ethylene and 1,3-butadiene in the presence of metallocene [Me2SiCpFluNd(μ-BH4)2Li(THF)] was rich in ethylene and had a high crystallinity (31%), which made it unsuitable for certain applications.

[0158] In Example 2 (not according to the invention), an ethylene-rich diene copolymer synthesized in the presence of metallocene [Me₂Si(Flu)₂Nd(μ-BH₄)₂Li(THF)] has cyclic units. Although it contains an ethylene content comparable to the control, it is amorphous. However, it has relatively high stiffness, which makes it unsuitable for certain applications.

[0159] Using myrcene instead of 1,3-butadiene yields copolymers with lower crystallinity, even at extremely high ethylene contents. Indeed, in Example 3, although the copolymer has a higher ethylene content (77%) than Examples 1 and 2 (73% and 71%, respectively), its crystallinity is close to 0%, and its stiffness in the unprocessed state is much lower than that of Examples 1 and 2.

[0160] Using β-farnesene instead of myrcene can yield copolymers with the same stiffness as copolymers of ethylene and myrcene, but in the case of β-farnesene, this result is obtained at higher ethylene contents. In fact, the ethylene unit content of Examples 6 and 7 is higher than that of Examples 4 and 5, while the crystallinity and stiffness in the unprocessed state are almost the same.

[0161] In summary, using 1,3-dienes (e.g., myrcene or β-farnesene) of the formula CH2=CR-CH=CH2 (where R represents a hydrocarbon chain with 3 to 20 carbon atoms) instead of 1,3-butadiene can synthesize ethylene-rich diene polymers with an improved trade-off between ethylene content, crystallinity, and stiffness, and can broaden the application range of ethylene-rich diene copolymers in rubber compositions.

[0162] [Chemical Formula 1]

[0163]

[0164] [Chemical Formula 2]

[0165]

[0166] Table 1

[0167]

[0168] Table 2

[0169]

[0170] Table 3

[0171]

[0172] Table 4

[0173]

[0174] Table 5

[0175]

[0176] Table 6

[0177]

[0178] Table 7: Ethylene-Myrcene Copolymers 1 H and 13 C signal attribution

[0179]

[0180] Table 8: Ethylene-β-farnesene copolymers 1 H and 13 C signal attribution

[0181]

Claims

1. A method for preparing a copolymer of ethylene and myrcene, said copolymer comprising ethylene units and myrcene units, wherein the proportion of ethylene units in the total ethylene and myrcene units is between 50 mol% and 95 mol%, and 1,4-configured myrcene units constitute more than 50 mol% of the myrcene units. The method includes polymerizing ethylene and myrcene in the presence of a catalytic system, said catalytic system being based at least on metallocene compounds of formula II and organomagnesium compounds of formula III. Formula II: P(Cp)(Flu)Nd(BH4) (1+y)- L y -N x Formula III: MgR 1 R 2 Cp represents the cyclopentadienyl group of formula C5H4, and Flu represents the C5H4 group. 13 The fluorenyl group of H8, P represents the bridging groups Cp and Flu, and signifies ZR. 3 R 4 The group of the group, Z represents silicon or carbon atom, R 3 and R 4 They may be the same or different, and each represents an alkyl group containing 1 to 20 carbon atoms. y is an integer equal to or greater than 0. x is an integer equal to or greater than 0, or a non-integer. L indicates an alkali metal selected from lithium, sodium, and potassium. N represents an ether molecule. R 1 and R 2 They can be the same or different, and represent carbon-based.

2. The method for preparing the copolymer of ethylene and myrcene according to claim 1, wherein, R 3 and R 4 Each represents a methyl group.

3. The method for preparing the copolymer of ethylene and myrcene according to claim 1, wherein, Metallocenes are of formulas IIa, IIb, IIc, IId, or IIe. Formula IIa: [{Me2SiCpFluNd(µ-BH4)2Li(THF)}2] Formula IIb: [Me2SCpiFluNd(µ-BH4)2Li(THF)] Formula IIc: [Me2SiCpFluNd(µ-BH4)(THF)] Formula IId: [{Me2SiCpFluNd(µ-BH4)(THF)}2] Formula IIe: [Me2SiCpFluNd(µ-BH4)] Cp represents the cyclopentadienyl group of formula C5H4, and Flu represents the C5H4 group. 13 The fluorene group of H8.

4. The method for preparing the copolymer of ethylene and myrcene according to claim 1, wherein, R 1 and R 2 Each represents an alkyl group.

5. The method for preparing a copolymer of ethylene and myrcene according to claim 4, wherein, R 1 and R 2 Each represents an alkyl group containing 2 to 10 carbon atoms.

6. The method for preparing a copolymer of ethylene and myrcene according to claim 1, wherein, The organomagnesium compound is butyl ethyl magnesium or butyl octyl magnesium.

7. The method for preparing a copolymer of ethylene and myrcene according to claim 1, wherein, The organomagnesium compound is butyloctylmagnesium.

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