WO2024175571A1

WO2024175571A1 - Functional copolymers of ethylene and 1,3-butadiene and use thereof in a lubricating composition for an engine

Info

Publication number: WO2024175571A1
Application number: PCT/EP2024/054240
Authority: WO
Inventors: Thibaut SOUCHARD; Julien Thuilliez; Robert NGO
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2023-02-23
Filing date: 2024-02-20
Publication date: 2024-08-29
Also published as: FR3146142A1

Abstract

A copolymer of ethylene and 1,3-butadiene which contains more than 90 mol % to less than 97 mol % of ethylene units and which carries, at one of its chain ends, a single monomer unit of a methacrylate. A copolymer of this kind can be used as a thickener in engine lubricant compositions.

Description

Functional ethylene-1,3-butadiene copolymers and their use in an engine lubricating composition

The field of the present invention is that of copolymers of ethylene and 1,3-butadiene for use in engine oils as additives to improve the performance of engine oils.

Engine oils, lubricating compositions containing mineral base oils, are used in an engine to minimize the energy losses caused by friction in the engine when cold and to maintain a continuous film of lubricant on the lubricated elements of the engine when hot. It is important that the viscosity of the lubricating composition decreases as little as possible during hot operation to avoid breakdown of the lubricating film. To ensure both these functions when cold and when hot, it is desirable to have a lubricating composition which has the smallest variation in viscosity with temperature. Since a high viscosity index ensures a lesser decrease in viscosity when the temperature increases, lubricating compositions having a high viscosity index are therefore sought.

Mineral base oils are a major constituent of lubricating compositions such as engine oils. The viscosity of a mineral base oil decreases with increasing temperature and increases with decreasing temperature. It follows that the viscosity of a lubricating composition containing predominantly a mineral base oil also varies with temperature.

To reduce this influence of temperature on the viscosity of a lubricating composition, it is known to add additives to a mineral base oil. These additives, called viscosity improvers or viscosity index improvers, have a role of selective thickening of the lubricating composition when the temperature increases to partially remedy the drop in viscosity noted when hot. They generally increase the viscosity at high temperature to counteract the decrease in viscosity of the mineral base oil without significantly increasing it at low temperature. Viscosity index improvers are generally polymers. The two main families of polymers marketed as viscosity index improvers are ester-functional polymers such as poly(meth)acrylates and hydrocarbon polymers such as polyisobutylenes, ethylene and propylene copolymers also called OCPs, hydrogenated diene and styrene copolymers, and hydrogenated polydienes. Nevertheless, there is still a need to further improve the viscosity index of lubricating compositions containing mineral base oil such as engine oils. The Applicant has discovered novel functional copolymers of ethylene and 1,3-butadiene which, when used as additives in a lubricating composition containing a base oil, make it possible to improve the viscosity index of the lubricating composition.

Thus, a first subject of the invention is a copolymer of ethylene and 1,3-butadiene which contains more than 90% to less than 97% by mole of ethylene units and which carries at one of its chain ends a single monomer unit of a methacrylate.

A second subject of the invention is a lubricating composition which comprises a mineral base oil and a copolymer of ethylene and 1,3-butadiene in accordance with the invention.

Detailed description

Any range of values denoted by the expression "between a and b" represents the domain of values greater than "a" and less than "b" (i.e. excluding the limits "a" and "b") while any range of values denoted by the expression "from a to b" means the domain of values from "a" to "b" (i.e. including the strict limits "a" and "b").

The compounds mentioned in the description may be of fossil or bio-sourced origin. In the latter case, they may be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. Similarly, the compounds mentioned may also come from the recycling of materials already used, i.e. they may be, partially or totally, derived from a recycling process, or obtained from raw materials themselves derived from a recycling process.

In the present invention, the molar ratios (expressed as a molar percentage) in a unit in the ethylene-1,3-butadiene copolymer according to the invention are calculated relative to the total number of moles of ethylene, butadiene and 1,2-cyclohexane units which are present in the copolymer. The number of moles of 1,2-cyclohexane units in the copolymer may be equal to 0 or different from 0.

The copolymer according to the invention has the essential characteristic of being a copolymer of ethylene and 1,3-butadiene, which implies that the monomer units of the copolymer are those resulting from the copolymerization of ethylene and 1,3-butadiene. The copolymer therefore contains ethylene units and butadiene units. In a known manner, an ethylene unit is a monomer unit with the unit -(CH2-CH2)-. In a known manner, a butadiene unit is a monomer unit with the unit -CH2-CH(CH=CH2)-, called a 1,2 unit, or a monomer unit with the unit -CH2-CH=CH-CH2-, called a 1,4 unit, depending on whether the 1,3-butadiene monomer is inserted into the polymer chain during the polymerization reaction by a 2,1 or 1,4 addition. In the copolymer according to the invention, the molar content of ethylene units is greater than 90% and less than 97%. Preferably, the molar content of ethylene units in the copolymer is from 92% to 95%. Preferably, the copolymer contains 1,2 units.

According to a preferred embodiment of the invention, the copolymer also contains 1,2-cyclohexane units. The presence of these 6-membered saturated hydrocarbon cyclic units in the copolymer results from a very particular insertion of ethylene and 1,3-butadiene during their copolymerization, as is for example described in document WO 2007054224. A 1,2-cyclohexane unit corresponds to formula (I).

Preferably, the molar rate of 1,2-cyclohexane units in the copolymer is greater than 1%, preferably greater than or equal to 2%. Preferably, the molar rate of 1,2-cyclohexane units in the copolymer is less than 4%.

According to a preferred embodiment of the invention, the molar rate of 1,2-cyclohexane units in the copolymer is greater than 1% and less than 4%.

According to a particularly preferred embodiment of the invention, the molar rate of 1,2-cyclohexane units in the copolymer is greater than or equal to 2% and less than 4%.

Preferably, the molar rate of butadiene units in the copolymer is greater than 1%, preferably greater than or equal to 2%. According to any one of the embodiments of the invention, the molar rate of butadiene units in the copolymer is preferably less than 5%.

Preferably, more than 30 mol% of the butadiene units in the copolymer are 1,2 units. When the copolymer contains 1,4 units, preferably more than 50%, more preferably more than 80 mol% of the 1,4 units are of trans configuration. According to any one of the embodiments of the invention, the copolymer preferably contains 1,2 units and 1,4 units.

The copolymer according to the invention is a functional copolymer, since it also has the essential characteristic of carrying a functional group at one of its chain ends. The functional group consists of a monomer unit of a methacrylate. Typically, the methylene group CH2 of the -CH2-CHMe-COO- unit of the monomer unit of a methacrylate is engaged in a covalent bond with a carbon atom of the copolymer chain of ethylene and 1,3-butadiene. Preferably, the methacrylate is an alkyl methacrylate, in which case the functional group is of formula -CH2-CHMe-COOR, R being an alkyl. As alkyl methacrylate, mention may be made in particular of alkyl methacrylates whose alkyl contains 1 to 20 carbon atoms, more particularly alkyl methacrylates whose alkyl contains 1 to 8 carbon atoms. The alkyl methacrylate is advantageously methyl methacrylate.

Preferably, the copolymer according to the invention is a statistical copolymer.

Also preferably, the copolymer according to the invention has a crystallinity rate greater than 30% and less than 45%. More preferably, the crystallinity rate of the copolymer is greater than 35%. Even more preferably, the crystallinity rate of the copolymer is less than 43%.

Preferably, the copolymer has a number average molar mass, Mn, greater than 8000 g/mol, preferably greater than 10000 g/mol.

Preferably, the copolymer has a number average molar mass of less than 200,000 g/mol, preferably less than 150,000 g/mol, more preferably less than 130,000 g/mol, even more preferably less than 100,000 g/mol.

According to a particularly preferred embodiment of the invention, the copolymer in accordance with the invention has a number-average molar mass greater than 8000 g/mol and less than 130000 g/mol.

According to a particularly more preferred embodiment of the invention, the copolymer has a number-average molar mass greater than 10,000 g/mol and less than 100,000 g/mol.

The copolymer preferably has a dispersity D, equal to Mw/Mn (Mw being the weight average molar mass) greater than 1 and less than 5, preferably less than 4, more preferably less than 3. The values of Mn, Mw and D are measured by size exclusion chromatography analysis with a polystyrene calibration.

The copolymer preferably has a melting temperature greater than or equal to 97°C, more preferably a melting temperature greater than 97°C.

The copolymer according to the invention can be prepared by copolymerization of ethylene and 1,3-diene in the presence of a catalytic system, followed by a functionalization reaction of the copolymer chain end. The catalytic system comprises a metallocene of formula (II) and an organomagnesium P(Cp ¹ Cp ² )Nd(BH ₄ )(i ₊ y)-Ly-N _x (II)

Cp ¹ and Cp ² , identical or different, being chosen from the group consisting of substituted fluorenyl groups and the unsubstituted fluorenyl group of formula C11H2, P being a group bridging the two groups Cp ¹ and Cp ² and representing a group ZR ¹ R ² , Z representing a silicon or carbon atom, R ¹ and R ² , identical or different, each representing an alkyl group comprising from 1 to 20 carbon atoms, preferably a methyl, y, an integer, being equal to or greater than 0, x, an integer or not, being equal to or greater than 0,

L representing an alkali metal selected from the group consisting of lithium, sodium and potassium,

N representing a molecule of an ether, preferably diethyl ether or tetrahydrofuran.

In formula (II), the neodymium atom is linked to a ligand molecule consisting of the two groups Cp ¹ and Cp ² linked together by the bridge P. Preferably, the symbol P, designated as a bridge, corresponds to the formula ZR ¹ R ² , Z representing a silicon atom, R ¹ and R ² , identical or different, representing an alkyl group comprising from 1 to 20 carbon atoms. More preferably, the bridge P is of formula SiR ¹ R ² , R ¹ and R ² , being identical and as defined above. Even more preferably, P corresponds to the formula SilX/le2-

As substituted fluorenyl groups, mention may be made of those substituted by alkyl radicals having 1 to 6 carbon atoms or by aryl radicals having 6 to 12 carbon atoms. The choice of radicals is also guided by the accessibility of the corresponding molecules that are the substituted fluorenes, because the latter are commercially available or easily synthesized.

As substituted fluorenyl groups, mention may be made more particularly of the 2,7-di-tert-butyl-fluorenyl and 3,6-di-tert-butyl-fluorenyl groups. Positions 2, 3, 6 and 7 respectively designate the position of the carbon atoms of the rings as shown in the diagram below, position 9 corresponding to the carbon atom to which the P bridge is attached.

Preferably, Cp ¹ and Cp ² are identical. Advantageously, in formula (II) Cp ¹ and Cp ² each represent the fluorenyl group. The fluorenyl group is of formula C11HS. Preferably, the metallocene is of formula (Ha), (llb), (Ile), (I Id) or (Ile) in which the symbol Flu has the fluorenyl group of formula C11HS.

[{Me ₂ SiFlu ₂ Nd(p-BH4)2Li(THF)}2] (Ha)

[Me ₂ SiFlu ₂ Nd(p-BH ₄ ) ₂ Li(THF)] (llb) [Me ₂ SiFlu ₂ Nd(p-BH ₄ )(THF)] (Ile)

[{Me ₂ SiFlu2Nd(n-BH4)(THF)} ₂ ] (lid)

[Me ₂ SiFlu ₂ Nd(p-BH ₄ )] (He)

The organomagnesium used in the catalytic system as a co-catalyst is a compound that has at least one C-Mg bond. As organomagnesium compounds, mention may be made of diorganomagnesiums, in particular dialkylmagnesiums and organomagnesium halides, in particular alkylmagnesium halides. A diorganomagnesium is typically of formula MgR ³ R ⁴ in which R ³ and R ⁴ , identical or different, represent a carbon group. A carbon group is understood to mean a group that contains one or more carbon atoms. Preferably, R ³ and R ⁴ contain 2 to 10 carbon atoms. More preferably, R ³ and R ⁴ each represent an alkyl. The organomagnesium is advantageously a dialkylmagnesium, better still butylethylmagnesium or butyloctylmagnesium, even better still butyloctylmagnesium.

The catalytic system can be prepared in a traditional manner by a process similar to that described in patent application WO 2007054224. For example, the organomagnesium and the metallocene are reacted in a hydrocarbon solvent, typically at a temperature ranging from 20 to 80°C for a period of between 5 and 60 minutes. The catalytic system is generally prepared in a hydrocarbon solvent, aliphatic such as methylcyclohexane or aromatic such as toluene.

The metallocene used to prepare the catalytic system may be in the form of a crystallized or non-crystalized powder, or in the form of single crystals. The metallocene may be in a monomeric or dimeric form, these forms depending on the method of preparation of the metallocene, as for example described in patent application WO 2007054224. The metallocene may be prepared in a traditional manner by a process analogous to that described in patent application WO 2007054224, in particular by reaction under inert and anhydrous conditions of the salt of an alkali metal of the ligand with a rare earth borohydride in a suitable solvent, such as an ether, such as diethyl ether or tetrahydrofuran or any other solvent known to those skilled in the art. After reaction, the metallocene is separated from the reaction by-products by techniques known to those skilled in the art, such as filtration or precipitation in a second solvent. The metallocene is finally dried and isolated in solid form.

The person skilled in the art adapts the molar ratio of the organomagnesium to the Nd metal constituting the metallocene according to the desired molar mass of the copolymer. The molar ratio can reach the value of 100, knowing that a molar ratio of less than 10 is more favorable for obtaining polymers with high molar masses.

As with any synthesis carried out in the presence of organometallic compounds, the synthesis of the metallocene and that of the catalytic system take place under anhydrous conditions under an inert atmosphere. Typically, the reactions are carried out using solvents and anhydrous compounds under anhydrous nitrogen or argon. In particular, the solvents are generally purified, for example in a known manner by distillation, by treatment on alumina columns, by bubbling an inert gas such as nitrogen or argon or by treatment with an organometallic compound such as an organolithium, an organomagnesium or an organoaluminum.

The catalytic system is generally introduced into the reactor containing the polymerization solvent and the monomers.

The catalytic system can be prepared in a traditional manner by a process similar to that described in patent application WO 2007054224. For example, the organomagnesium and the metallocene are reacted in a hydrocarbon solvent, typically at a temperature ranging from 20 to 80°C for a period of between 5 and 60 minutes. The catalytic system is generally prepared in a hydrocarbon solvent, aliphatic such as methylcyclohexane or aromatic such as toluene. Generally, after its synthesis, the catalytic system is used as is in the process for synthesizing the copolymer in accordance with the invention.

Alternatively, the catalytic system may be prepared by a process analogous to that described in patent application WO 2017093654 A1 or in patent application WO 2018020122 A1. According to this alternative, the catalytic system further contains a preformation monomer selected from a conjugated diene, ethylene or a mixture of ethylene and a conjugated diene, in which case the catalytic system is based on at least the metallocene, the organomagnesium and the preformation monomer. For example, the organomagnesium and the metallocene are reacted in a hydrocarbon solvent, typically at a temperature of 20 to 80°C for 10 to 20 minutes to obtain a first reaction product, then with this first reaction product, the preformation monomer chosen from a conjugated diene, ethylene or a mixture of ethylene and a conjugated diene is reacted at a temperature of 40 to 90°C for 1 hour to 12 hours. The catalytic system thus obtained can be used immediately after its synthesis in the process for synthesizing the copolymer according to the invention or can be stored under an inert atmosphere, in particular at a temperature of -20°C to room temperature (23°C), before its use in the process for synthesizing the copolymer according to the invention.

The person skilled in the art also adapts the polymerization conditions and the concentrations of each of the reactants (constituents of the catalytic system, monomers) according to the equipment (tools, reactors) used to conduct the polymerization and the various chemical reactions. As is known to the person skilled in the art, the copolymerization as well as the handling of the monomers, the catalytic system and the polymerization solvent(s) are carried out under anhydrous conditions and under an inert atmosphere.

The polymerization is preferably carried out in solution, in a continuous, semi-continuous or batch process. The polymerization solvent may be a hydrocarbon, aromatic solvent or aliphatic. Examples of polymerization solvents include toluene and methylcyclohexane. The monomers may be introduced into the reactor containing the polymerization solvent and the catalytic system or, conversely, the catalytic system may be introduced into the reactor containing the polymerization solvent and the monomers. The monomers and the catalytic system may be introduced simultaneously into the reactor containing the polymerization solvent, in particular in the case of continuous polymerization. The polymerization is typically carried out under anhydrous conditions and in the absence of oxygen, in the optional presence of an inert gas. The polymerization temperature generally varies in a range from 25 to 120°C, preferably 30 to 100°C. The 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 polymerization reactor according to the composition of the monomer mixture, the polymerization reactor, the desired microstructure and macrostructure of the copolymer chain.

The polymerization is preferably carried out at constant pressure in monomers. A continuous addition of each of the monomers or one of them can be carried out in the polymerization reactor, in which case the polymerization reactor is a fed reactor. This embodiment is particularly suitable for the synthesis of statistical copolymers.

When the desired monomer conversion rate is reached, the functionalization reaction of the copolymer chain end is carried out. The functionalization reaction consists in bringing together a functionalization agent, methacrylate, with the reaction product of the polymerization, preferably with stirring, to introduce a single methacrylate monomer unit at one of the ends of the copolymer chain without there being any subsequent polymerization of the methacrylate.

Before adding the methacrylate, the reactor is preferably degassed and inerted. Degassing the reactor makes it possible to eliminate the gaseous residual monomers and also facilitates the addition of the methacrylate to the reactor. Inerting the reactor, for example with nitrogen, makes it possible not to deactivate the carbon-metal bonds present in the reaction medium and necessary for the functionalization reaction of the copolymer. The methacrylate can be added pure or diluted in a hydrocarbon solvent, preferably aliphatic such as methylcyclohexane. The methacrylate is left in contact with the reaction product of step a) for the time necessary for the functionalization reaction of the chain end of the copolymer. The functionalization reaction can typically be monitored by chromatographic analysis to monitor the consumption of the methacrylate. The functionalization reaction is preferably carried out at a temperature ranging from 23 to 120 °C, for 1 to 60 minutes with stirring. The functionalization reaction is preferably carried out with a molar excess of methacrylate relative to the number of moles of neodymium and magnesium. To obtain a quasi-quantitative functionalization, the molar ratio between the number of moles of methacrylate and the number of moles of neodymium and magnesium is preferably greater than 2, in particular greater than 5, more particularly between 10 and 50.

Once the chain end has been modified, the reactive sites still present in the reaction medium are deactivated. Typically, a chain terminating agent is brought into contact with the reaction product of step b), generally in its reaction medium, for example by adding the terminating agent to the reaction medium at the end of the functionalization reaction or vice versa. The terminating agent is generally in stoichiometric excess relative to the number of moles of neodymium and magnesium. The terminating agent is typically a protic compound, a compound that has a relatively acidic proton. As terminating agents, mention may be made of water, carboxylic acids, in particular C2-C18 fatty acids such as acetic acid, stearic acid, aliphatic or aromatic alcohols, such as methanol, ethanol, isopropanol, phenolic antioxidants.

The functional copolymer can be recovered according to conventional techniques known to those skilled in the art, for example by precipitation, by evaporation of the solvent under reduced pressure or by stripping with water vapor.

The functional copolymer is advantageously used as an additive to a lubricating composition.

The functional copolymer is typically added to a mineral base oil to form a lubricating composition, another subject of the invention. Suitable mineral base oils include Group I base oils, Group II base oils, and Group III base oils, and mixtures thereof. Groups I to III are defined in a manner known from the American Petroleum Institute (API) in its publication API No. 1509 Engine Oil Licensing and Certification System, Appendix E, 14th Edition, dated December 1996. Mineral base oils are typically obtained by atmospheric and vacuum distillation of crude oil, optionally followed by refining operations. Preferably, the mineral base oil is a Group I base oil.

The rate of the functional copolymer added to the mineral base oil is adjusted by a person skilled in the art according to the nature of the mineral base oil, according to the characteristics of the functional copolymer such as its ethylene unit content, its crystallinity rate, its 1,2-cyclohexane unit content, its number-average molar mass, and of course according to the use of the lubricating composition. The mass rate of the functional copolymer in the lubricating composition or of the mixture of functional copolymers in the lubricating composition can be up to 5% by weight of the lubricating composition, for example from 0.01 to 5% by weight of the lubricating composition, preferably from 0.05 to 2% by weight of the lubricating composition. The functional copolymer which constitutes the lubricating composition can be a mixture of copolymers as defined above which are differentiate from each other by their crystallinity rate, their microstructure, their macrostructure.

The lubricating composition may also contain other additives traditionally used in an engine oil such as detergents and dispersants, antioxidants, compounds having an action against the formation of rust, foam, gel.

The lubricating composition according to the invention has selective thickening properties as a function of temperature like engine oils containing viscosity improvers traditionally used such as ethylene and propylene copolymers. The lubricating compositions according to the invention may prove to be even more efficient with respect to their temperature selectivity than lubricating compositions containing ethylene and propylene copolymers generally containing at most 50 mol% of ethylene units, typically used as thickening additives for base oils. The lubricating compositions are also more efficient than those containing polymethacrylates. Indeed, a viscosity index at least as high, or even higher, is obtained by mixing a mineral base oil with a functional copolymer according to the invention rather than with an ethylene and propylene copolymer or a polymethacrylate.

Preferably, the lubricating composition according to the invention is an engine oil.

In summary, the invention is advantageously implemented according to any one of the following embodiments 1 to 21:

1. Copolymer of ethylene and 1,3-butadiene which contains more than 90% to less than 97% by mole of ethylene units and which carries at one of its chain ends a single monomer unit of a methacrylate.

2. Copolymer according to mode 1 in which the molar rate of ethylene units in the copolymer is from 92% to 95%.

3. Copolymer according to mode 1 or 2 in which the methacrylate is an alkyl methacrylate.

4. Copolymer according to any one of modes 1 to 3 in which the methacrylate is methyl methacrylate.

5. A copolymer according to any one of methods 1 to 4, which copolymer has a degree of crystallinity greater than 30% and less than 45%.

6. Copolymer according to any one of modes 1 to 5, which copolymer has a degree of crystallinity greater than 35%.

7. Copolymer according to any one of modes 1 to 6, which copolymer is a random copolymer. 8. Copolymer according to any one of modes 1 to 7, which copolymer contains 1,2-cyclohexane units, cyclic units of formula (I).

CH - CH

/ \ (0

9. Copolymer according to any one of methods 1 to 8 in which the molar rate of 1,2-cyclohexane units is greater than 1%, preferably greater than or equal to 2%.

10. Copolymer according to any one of methods 1 to 9 in which the molar rate of 1,2-cyclohexane units is less than 4%.

11. Copolymer according to any one of methods 1 to 10 in which the molar rate in butadiene units is greater than 1%, preferably greater than or equal to 2%.

12. Copolymer according to any one of methods 1 to 11 in which the molar rate in butadiene units is less than 5%.

13. Copolymer according to any one of methods 1 to 12, which copolymer has a number average molar mass greater than 8000 g/mol, preferably greater than 10000 g/mol.

14. Copolymer according to any one of methods 1 to 13, which copolymer has a number average molar mass of less than 200,000 g/mol, preferably less than 150,000 g/mol, more preferably less than 130,000 g/mol, even more preferably less than 100,000 g/mol.

15. A copolymer according to any one of methods 1 to 14, which copolymer has a number average molar mass greater than 8000 g/mol and less than 130,000 g/mol.

16. A copolymer according to any one of methods 1 to 15, which copolymer has a number average molar mass greater than 10000 g/mol and less than 100000 g/mol.

17. A copolymer according to any one of methods 1 to 16, which copolymer has a melting temperature greater than or equal to 97°C.

18. A lubricating composition which comprises a mineral base oil and a copolymer of ethylene and 1,3-butadiene defined in any one of embodiments 1 to 17.

19. Lubricating composition according to mode 18 in which the mineral base oil is a Group I oil, a Group II oil or a Group III oil.

20. Lubricating composition according to mode 18 or 19, which composition is an engine oil.

21. Lubricating composition according to any one of methods 18 to 20 in which the mass content of the copolymer of ethylene and 1,3-butadiene varies in a range from 0.01 to 5% by weight of the lubricating composition. The above-mentioned characteristics of the present invention, as well as others, will be better understood upon reading the following description of the exemplary embodiments of the invention, given for illustrative and non-limiting purposes.

Example

Determination of the microstructure of polymers:

High-resolution NMR spectroscopy of polymers was performed on a Bruker 600 Avance III HD spectrometer operating at 600 MHz equipped with a CP2.1 BBO 600S3 probe for the proton. Acquisitions were made at 368 K. Orthodichlorobenzene (o-DCB) was used as solvent. Samples were analyzed at a concentration of approximately 1% by mass for proton NMR ( ¹ H NMR) analyses. Chemical shifts were determined relative to the proton signal of orthodichlorobenzene set at 7.2 ppm. A 2D analysis was performed using the following sequence: HSQC: Pulse program; hsqcetgpsi2 “HSQC with gradients”; SW1: 180 ppm ( ¹³ C) SW2: 12 ppm ( ¹ H); dl: 10 s; 90° “hard” impulse ^T H PI = 13 ps and 16 W and ¹³ C P2 = 26 ps and 84 W; Gradient: SMSQ10.100.

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.

Determination of the macrostructure of polymers:

Size Exclusion Chromatography is used. It is recalled that SEC allows the separation of macromolecules in solution according to their size through columns filled with a porous gel. The macromolecules are separated according to their hydrodynamic volume, the largest being eluted first. Without being an absolute method, SEC allows the understanding of the distribution of molar masses of a polymer. From commercial standard products, the different number-average (Mn) and weight-average (Mw) molar masses can be determined and the dispersity (£) = Mw/Mn) calculated via a so-called MOORE calibration.

There is no special treatment of the polymer sample before analysis. It is simply solubilized in 1,2,4-trichlorobenzene containing 300 ppm of BHT ("butylated hydroxytoluene"), at a concentration of approximately 1 g/l. The solution is stirred for 2 hours at 160°C before injection; the chromatograph device used is equipped with an in-line filtration system.

High temperature size exclusion chromatography or

SEC-HT. The apparatus used is a “GPC-IR” chromatograph equipped with an “IR-6” infrared detector from “Polymer Char”. Detection is carried out by the IR detector on the vibration bands of the CH2 and CH3 groups. A set of 3 columns of commercial reference “Mixed BN-LS” from “Polymer Char” is used. The elution solvent is 1,2,4-trichlorobenzene containing 300 ppm of BHT. The flow rate is lmL/min, the system temperature is 160°C and the analysis time is 90 minutes (min). The injected volume of the polymer sample solution is 200 μl. The software for exploiting the chromatographic data is the “GPC-one” system from “Polymer Char”.

The average molar masses are determined from a calibration curve produced using commercial standard polystyrenes “PSS READY CAL-KIT”.

Determination of the glass transition temperature, the crystallinity rate of polymers and their melting point:

The crystallinity rate and melting point are determined by differential scanning calorimetry (DSC). The analyses are carried out on a DSC device "NETZSCH DSC 214 Polyma" calibrated with indium. This device has a temperature range of -150 to 700 °C. A computer integrated into the DSC controls the device using the Netzsch Proteus software. The sample (approximately 10 mg) is weighed and sealed in a 40 pL aluminum crucible. The crucible is pierced with a fine needle just before the measurement. The samples are analyzed under helium at 40 mL/min using a dynamic method with 7 temperature steps:

Step 1: cooling from 25°C to -150°C at 50°C/min; Step 2: isothermal at -150°C for 5 min; Step 3: heating from -150°C to 200°C at 20°C/min; Step 4: isothermal at 200°C for 5 min; Step 5: cooling from 200°C to -150°C at 20°C/min; Step 6: isothermal at -150°C for 5 min; Step 7: heating from -150°C to 200°C at 20°C/min.

The first four steps are used to erase the thermal history of the sample. The glass transition temperature (Tg) and melting temperature (Tf) measurements are made on the ^7th step. The ^7th step is also kept to obtain information on the crystallization of the sample and to determine the crystallinity rate.

The Tg and Tf values are determined by applying the data reprocessing of the software "Proteus" from "Netzsch". The Tg value is measured according to the tangent method as described in the ASTM-3418 standard and corresponds to the point designated under the well-known name "mid-point". The melting temperature (Tf) corresponds to the tip of the melting peak. The degree of crystallinity is determined using the ISO 11357-3: 2011 standard for measuring the temperature and enthalpy of melting and crystallization of polymers used by differential scanning calorimetry (DSC). The reference enthalpy of polyethylene is 293 J/g (source: B. Wunderlich, Thermal analysis, Academie Press, 1990, 281).

Determination of the viscosity of lubricating compositions:

Viscosity index results are presented on a 100 basis relative to a control. Unless otherwise stated, the control consists of the same base oil that is used in the lubricating compositions. Viscosity index is measured according to ASTM D2270.

Preparation of the co

ethylene and 1,3-butadiene:

and Poly2

The copolymers are prepared by a semi-continuous process, i.e. a so-called process "fed batch". In an 80 L reactor containing methylcyclohexane (60 L) and heated to 100°C, ethylene and 1,3-butadiene are introduced according to a mass ratio given in Table 1 until 6 bars of pressure are reached in the reactor maintained at 100°C. A solution of butyloctylmagnesium (BOMAG) at 0.88 mol/L in methylcyclohexane is injected into the reactor, then the catalytic system (2.66 mmol equivalent of Nd, or 1.7 g of catalytic system). The reaction temperature is regulated at a temperature of 100°C, the pressure in the reactor increases to 8 bars and the polymerization reaction starts. The polymerization reaction takes place at a constant pressure of 8 bars. The reactor is fed throughout the polymerization reaction with ethylene and 1,3-butadiene according to the given mass ratio of ethylene and 1,3-butadiene. The conditions for each of the polymer syntheses are shown in Table 1, in particular the mass ratio of ethylene and 1,3-butadiene and the amount of BOMAG solution.

The catalytic system is a preformed catalytic system. It is prepared in methylcyclohexane from a metallocene, [Me2Si(Flu)2Nd(p-BH4)2Li(TH F)] at 0.0065 mol/L, a co-catalyst, butyloctylmagnesium (BOMAG) whose BOMAG/Nd molar ratio is equal to 2.2, and a preformed monomer, 1,3-butadiene whose 1,3-butadiene/Nd molar ratio is equal to 90. The medium is heated to 80°C for a period of 5 hours. It is prepared according to a preparation method in accordance with paragraph 11.1 of patent application WO 2017093654 A1.

All reagents are obtained commercially except the metallocene of formula [{Me2SiFlu2Nd(p-BH4)2Li(THF)}2] which can be prepared according to the procedure described in WO 2007054224. BOMAG butyloctylmagnesium (20% by mass in heptane, C = 0.88 mol L ^-1 ) comes from Lanxess and is stored in a metal cylinder under an inert atmosphere. Ethylene, of N35 quality, comes from Air Liquide and is used without prior purification. 1,3-butadiene is purified on alumina guards. The methylcyclohexane solvent from BioSolve is dried and purified on an alumina column in a solvent fountain from mBraun and used in an inert atmosphere. All reactions are carried out in an inert atmosphere.

The conversion of the polymerization reaction is measured by dry extract, and when the mass of 6 kg of polymer is reached, the injection of monomers into the reactor is stopped. It is then carried out according to procedure 1 or according to procedure 2.

Procedure 1: For the synthesis of the non-functional polymer Poly2, 122 mL of ethanol at 1 mol/L in methylcyclohexane are injected to stop the polymerization reaction. 226 mL of an antioxidant, Irganox 1520L at 218 g/L in methylcyclohexane are injected into the reactor. The contents of the reactor are transferred to another reactor called a "stripping reactor" to remove the solvent by steam distillation while maintaining a temperature of 100°C. The copolymer is recovered, then dried for 48 hours in an oven at 60°C under vacuum and nitrogen flushing. Procedure 2: For the synthesis of the functional polymer Polyl, 677.1 mL of methyl methacrylate are injected. The contact time between the copolymer and the methyl methacrylate is 15 minutes at 80°C. After 15 minutes, 216 mL of ethanol at 1 mol/L in methylcyclohexane are injected. 220 mL of an antioxidant, Irganox 1520L at 218 g/L in methylcyclohexane, are injected into the reactor. The contents of the reactor are transferred to another reactor called a "stripping reactor" to remove the solvent by steam distillation while maintaining a temperature of 100°C. The copolymer is recovered, then dried for 48 hours in an oven at 60°C under vacuum and nitrogen flushing.

The weighed mass of copolymer allows the determination of the average catalytic activity of the catalytic system expressed in kilograms of polymer synthesized per mole of neodymium metal and per hour (kg/mol.h).

The macrostructure characteristics of the polymers are given in Table 1, the microstructure characteristics as well as the melting temperature and the degree of crystallinity in Table 2. The rate of the units is expressed as a molar percentage calculated relative to the total number of moles of ethylene, butadiene and 1,2-cyclohexane units (designated in Table 2 as "cycle"). The two copolymers Polyl and Poly2 are statistical: they have a single Tg, measured at -53°C.

Table 1

Table 2:

Preparation of lubricating compositions:

The lubricating compositions are prepared according to the following procedure:

In a 250 mL Steinie bottle containing 200 g of a base oil are introduced 0.5 g or 1.5 g of polymer to prepare compositions containing respectively 0.25% or 0.75% of polymer. The Steinie bottle is capped and stirred in a thermostatic bath at 90°C for 12 hours. The viscosity of the resulting mixture is measured at 100°C. The polymers are the polymers Poly 1 and Poly 2 as well as an OCP polymer marketed by the company Lubrizol under the reference "7077", a copolymer of ethylene and propylene with approximately 50 mol% ethylene with a crystallinity rate of 2.3% and an Mn of 79200 g/mol, and a polymethacrylate marketed by the company Lubrizol under the reference "7775" with an Mn of 16700 g/mol. In some compositions, a mixture of additives for gearbox oil is also added, which is marketed by the company Lubrizol under the name "Anglamol 6043".

The formulation of the lubricating compositions is shown in Tables 3, 4 and 5, the contents indicated being expressed as a mass percentage relative to the quantity of the lubricating composition.

CORE™ 100 base oil is a Group I mineral base oil marketed by Exxon and is commonly used as a base oil in motor oils. It has a viscosity index of 96.

CORE™ 600 base oil is a Group I mineral base oil marketed by Exxon and is commonly used as a base oil in motor oils. It has a viscosity index of 96.

CORE™ 50 Base Oil is a Group II mineral base oil marketed by Exxon Corporation and is commonly used as a base oil in engine oils.

Compositions C2, C3, C8 to C10 all contain a functional copolymer according to the invention and a mineral base oil and are lubricating compositions in accordance with the invention. Compositions T1, T2 and T3 are their respective control compositions. Compositions C1, C5 to C7 which contain a mineral base oil and a commercial viscosity modifier which is not according to the invention are reference lubricating compositions.

Composition C4 is a lubricating composition which is not in accordance with the invention, since the viscosity modifier is a non-functional copolymer of ethylene and 1,3-butadiene.

The viscosity index values of the lubricating compositions are given in Tables 3 to 5.

Table 3

Table 4

Table 5

It is observed that the lubricating compositions according to the invention have a viscosity index higher than that of their respective control composition. It is also noted that the functional copolymers according to the invention prove to be more effective than the commercial polymers, even if they are used at lower contents. Finally, the comparison with composition C4 shows that the functional copolymer (Polyl) according to the invention proves to be more effective than its non-functional counterpart (Poly2) as a viscosity modifier, even though Polyl has a slightly lower number-average molar mass.

Claims

2. Copolymer according to claim 1 in which the methacrylate is an alkyl methacrylate.

3. Copolymer according to claim 1 or 2 in which the methacrylate is methyl methacrylate.

4. Copolymer according to any one of claims 1 to 3, which copolymer has a crystallinity rate greater than 30% and less than 45%.

5. Copolymer according to any one of claims 1 to 4, which copolymer has a crystallinity rate greater than 35%.

6. Copolymer according to any one of claims 1 to 5, which copolymer is a random copolymer.

7. Copolymer according to any one of claims 1 to 6, which copolymer contains 1,2-cyclohexane units, cyclic units of formula (I), preferably at a molar rate greater than 1%, more preferably at a molar rate greater than or equal to 2%.

CH - CH

/ \ (0

8. Copolymer according to any one of claims 1 to 7, which copolymer has a number average molar mass greater than 8000 g/mol, preferably greater than 10000 g/mol.

9. Copolymer according to any one of claims 1 to 8, which copolymer has a number average molar mass of less than 200,000 g/mol, preferably less than 150,000 g/mol, more preferably less than 130,000 g/mol, even more preferably less than 100,000 g/mol.

10. A lubricating composition which comprises a mineral base oil and a copolymer of ethylene and 1,3-butadiene defined in any one of claims 1 to 9.

11. A lubricating composition according to claim 10 wherein the mineral base oil is a Group I oil, a Group II oil or a Group III oil.

12. A lubricating composition according to any one of claims 10 to 11, which composition is an engine oil.

13. Lubricating composition according to any one of claims 10 to 12 in which the mass content of the copolymer of ethylene and 1,3-butadiene varies in a range from 0.01 to 5% by weight of the lubricating composition.