Ethylene-rich diethylene polymers with a polyvinylpyridine block and their use in engine lubricant compositions

Description

[0001] The field of the invention is that of block polymers containing an ethylene-rich diene block and a polyvinylpyridine block, intended for use in motor oils as additives to improve the performance of these oils at high temperature.

[0002] Engine oils, lubricating compounds containing mineral base oils, are used in engines to minimize energy losses due to friction during cold starts and to maintain a continuous film of lubricant on the engine's lubricated components during hot operation. It is important that the viscosity of the lubricant compound decreases as little as possible during hot operation to prevent the lubricant film from breaking down.

[0003] Mineral base oils are a major component of lubricating compositions such as engine oils. The viscosity of a mineral base oil decreases with increasing temperature and increases with decreasing temperature. Consequently, the viscosity of a lubricating composition containing primarily a mineral base oil also varies with temperature.

[0004] To mitigate the effect of temperature increases on the viscosity of a lubricating composition, it is common practice to add additives to a mineral base oil. These additives thicken the lubricating composition as the temperature rises, partially compensating for the drop in viscosity at high temperatures. They generally increase viscosity at high temperatures to counteract the decrease in viscosity of the mineral base oil. These thickening additives are usually polymers. The two main families of polymers commercially available for this purpose are ester polymers such as poly(meth)acrylates and hydrocarbon polymers such as polyisobutylenes, ethylene-propylene copolymers (also known as OCPs), hydrogenated diene-styrene copolymers, and hydrogenated polydienes.

[0005] The Applicant discovered that block polymers containing a polyvinylpyridine block and a block that is a copolymer of ethylene and 1,3-butadiene and is rich in ethylene increased the viscosity of high-temperature motor oils as effectively as OCPs.

[0006] Thus, a first object of the invention is a block polymer containing a first block and a second block, the first block being a copolymer of 1,3-butadiene and ethylene containing more than 90 mole percent of ethylene units, the mole percentage being expressed in relation to the total number of repeating units constituting the first block, the second block being a homopolymer of a vinylpyridine.

[0007] A second object of the invention is a lubricating composition comprising a mineral base oil and a block polymer according to the invention. Description :

[0008] 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).

[0009] Unless otherwise stated, unit rates in the first block are expressed as a mole percentage relative to the total number of repeating units constituting the first block.

[0010] 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.

[0011] The expression "based on" used to define the constituents of a catalytic system (or catalytic composition) means the mixture of these constituents, or the product of the reaction of some or all of these constituents with each other.

[0012] The block polymer according to the invention has as its essential characteristic that it contains two blocks.

[0013] The first building block of the block polymer according to the invention is a copolymer of ethylene and 1,3-butadiene. The monomer units constituting the first block are those resulting from the copolymerization of ethylene and 1,3-butadiene.

[0014] The ethylene units present in the first block represent more than 90% by mole of the total number of repeating units constituting the first block. Preferably, the ethylene units present in the first block represent less than 97% by mole of the total number of repeating units constituting the first block. An ethylene unit is understood to be a unit whose motif is -(CH₂-CH₂)-.

[0015] As is known, 1,3-butadiene can insert itself into a growing polymer chain by a 1,4 or 1,2 insertion to give rise respectively to the formation of 1,3-butadiene units in configuration 1,4 or 1,3-butadiene units in configuration 1,2. When the first block contains 1,3-butadiene units in the 1,4 configuration, the 1,4-trans units preferentially represent more than 50% of the units in configuration 1,4, more preferably more than 80% of the units in configuration 1,4.

[0016] The first block may also contain 1,2-cyclohexanediyl motifs, also called 1,2-cyclohexanediyl units of formula (I). The presence of these cyclic structures in the first block results from a very specific insertion of ethylene and 1,3-butadiene during their copolymerization. The mechanism for obtaining such a microstructure is described, for example, in Macromolecules 2009, 42, 3774-3779. The content of the 1,2-cyclohexanediyl motif in the first block can vary depending on the polymerization conditions for forming the first block, for example, depending on the respective ethylene and 1,3-butadiene contents in the polymerization medium, the pressure in the polymerization reactor, and the catalytic polymerization system, as described, for example, in WO 2021023924, WO 2017103543, and WO 2018104669.

[0017] According to a particularly preferred embodiment of the invention, the first block contains 1,2-cyclohexanediyl motifs. Preferably, the molar content of the 1,2-cyclohexanediyl motif in the first block is less than 10% of the total number of repeating units constituting the first block. More preferably, it ranges from 1% to less than 10% of the total number of repeating units constituting the first block.

[0018] According to a particularly preferred embodiment of the invention, the first block is a statistical copolymer of ethylene and 1,3-butadiene.

[0019] The second building block of the block polymer according to the invention is essentially characterized by being a homopolymer of a vinylpyridine. The vinylpyridine whose monomer units constitute the second block is a vinylpyridine as defined in the described embodiments of the process according to the invention. Preferably, the vinylpyridine is 4-vinylpyridine, 2-vinylpyridine, or a mixture thereof. More preferably, the vinylpyridine is 4-vinylpyridine.

[0020] The molar percentage of vinylpyridine units in the second block may be less than 1% or much greater than 1% of the total number of repeat units constituting the first block. Preferably, it is greater than 0.1% of the total number of repeat units constituting the first block. Preferably, it is less than 20% of the total number of repeat units constituting the first block.

[0021] The block polymer according to the invention is preferably a diblock. When the block polymer is a diblock, it typically has the formula AB, where A designates the first block and B the second block.

[0022] The block polymer according to the invention can be prepared by a subsequent polymerization process. It comprises the polymerization of a monomer mixture of ethylene and 1,3-butadiene in the presence of a catalytic system to form the first block, followed by the homopolymerization of a vinylpyridine to form the second block.

[0023] The catalytic system is based on at least a metallocene of formula (II) and an organomagnesium compound P(Cp 1< Cp 2< )Nd(BH 4 ) (1+y) Li y (THF) x (II) Cp 1< and Cp 2< 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 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.

[0024] In formula (II), the neodymium atom is bonded to a ligand molecule consisting of two groups, Cp1 and Cp2, linked by the P-bridge. Preferably, the symbol P, designated as the bridge, has the formula ZR1R2, where Z represents a silicon atom, and R1 and R2, which may be identical or different, represent an alkyl group comprising from 1 to 20 carbon atoms. More preferably, the P-bridge has the formula SiR1R2, where R1 and R2 are identical and as defined previously. Even more preferably, P has the formula SiMe2.

[0025] Examples of substituted cyclopentadienyl, fluorenyl, and indenyl groups include those substituted with alkyl groups having 1 to 6 carbon atoms, aryl groups having 6 to 12 carbon atoms, or trialkylsilyl groups such as SiMe3. When the Cp1 and Cp2 ligands are substituted, they are preferentially substituted with methyl groups, butyl groups (particularly tert-butyl groups), or trimethylsilyl groups. These groups are preferred regardless of the embodiment of the invention. The choice of groups is also guided by the accessibility of the corresponding molecules, namely the substituted cyclopentadienes, fluorenes, and indenes, because these are either commercially available or easily synthesized.

[0026] 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.

[0027] Examples of substituted fluorenyl groups include those substituted with alkyl groups having 1 to 6 carbon atoms or with aryl groups having 6 to 12 carbon atoms. The choice of groups is also influenced by the availability of the corresponding molecules, namely the substituted fluorenes, because these are either commercially available or easily synthesized.

[0028] Examples of substituted fluorenyl groups include those substituted at positions 2, 7, 3, or 6, particularly the 2,7-ditertiobutyl-fluorenyl and 3,6-ditertiobutyl-fluorenyl groups. 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 carbon atom to which the P-bridge is attached.

[0029] 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.

[0030] According to one embodiment of the invention, Cp 1< and Cp 2< are different, one representing a cyclopentadienyl group, the other a fluorenyl group. This embodiment is particularly suitable for preparing a first block that is devoid of a 1,2-cyclohexanediyl motif of formula (I).

[0031] According to another embodiment of the invention, Cp1 and Cp2 are identical and are selected from the group consisting of substituted fluorenyl groups and the fluorenyl group. Advantageously, Cp1 and Cp2 each represent a substituted fluorenyl group or a fluorenyl group, preferably a fluorenyl group. The fluorenyl group has the formula C13H8. Preferably, the metallocene has the formula (IIa), (IIb), (IIc), (IId), or (IIe), in which the symbol Flu represents the fluorenyl group of formula C13H8. [{Me 2 SiFlu 2 Nd(µ-BH 4 ) 2 Li(THF)} 2 ] (IIa) [Me 2 SiFlu 2 Nd(µ-BH 4 ) 2 Li(THF)] (IIb) [Me 2 SiFlu 2 Nd(µ-BH 4 )(THF)] (Ilc) [{Me 2 SiFlu 2 Nd(µ-BH 4 )(THF)} 2 ] (IId) [Me 2 SiFlu 2 Nd(µ-BH 4 )] (Ile)

[0032] The organomagnesium compound used in the catalytic system as a co-catalyst is a compound that contains at least one C-Mg bond. Examples of organomagnesium compounds include diorganomagnesium compounds, particularly dialkylmagnesium compounds, and organomagnesium halides, particularly alkylmagnesium halides. A diorganomagnesium compound typically has the formula MgR3<R4<, where R3< and R4<, whether identical or different, represent a carbon group. A carbon group is defined as a group containing one or more carbon atoms. Preferably, R3< and R4< contain 2 to 10 carbon atoms. Even more preferably, R3< and R4< each represent an alkyl group. The organomagnesium is preferably a diorganomagnesium or an organomagnesium halide, advantageously a dialkylmagnesium, better butylethylmagnesium or butyloctylmagnesium, even better butyloctylmagnesium.

[0033] The catalytic system can be prepared conventionally by a process analogous to that described in patent application WO 2007054224 A2 or WO 2007054223 A2. For example, the organomagnesium compound and the metallocene are typically reacted in a hydrocarbon solvent 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. Generally, after its synthesis, the catalytic system is used as is in the block polymer synthesis process.

[0034] Alternatively, the catalytic system can 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 preforming monomer selected from a 1,3-diene, ethylene or a mixture of ethylene and a 1,3-diene, in which case the catalytic system is based at least on the metallocene, the organomagnesium and the preforming monomer. For example, the organomagnesium and 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, then with this first reaction product the preforming monomer chosen from a 1,3-diene, ethylene or a mixture of ethylene and a 1,3-diene is reacted at a temperature of 40 to 90°C for 1h to 12h.The preforming monomer is preferably 1,3-butadiene or a mixture of ethylene and 1,3-butadiene. The catalytic system thus obtained can be used immediately in the process according to the invention or stored under an inert atmosphere before its use in the polymerization process to prepare the block polymer.

[0035] The metallocene used to prepare 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 method of preparation, as described in patent applications WO 2007054224 A2 and WO 2007054223 A2. The metallocene can be prepared conventionally by a process analogous to that described in patent applications WO 2007054224 A2 and WO 2007054223 A2, specifically by reacting, under inert and anhydrous conditions, the salt of an alkali metal of the ligand with a rare-earth borohydride 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 using 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.

[0036] 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 in an inert atmosphere. Typically, the reactions are conducted using solvents and anhydrous compounds under anhydrous nitrogen or argon.

[0037] A person skilled in the art also adapts the polymerization conditions and the concentrations of each of the reactants (components of the catalytic system, monomers) according to the equipment (tools, reactors) used to carry out the polymerization. As is known to those skilled in the art, polymerization, as well as the handling of the monomers, the catalytic system, and the copolymerization solvent(s), is performed under anhydrous conditions and in an inert atmosphere. Polymerization solvents are typically hydrocarbon, aliphatic, or aromatic solvents.

[0038] Polymerization is preferably carried out in solution, continuously or batchwise, in a reactor, advantageously in a stirred reactor. The polymerization solvent may be a hydrocarbon, aromatic, or aliphatic solvent. Examples of polymerization solvents include toluene and methylcyclohexane. Advantageously, polymerization is carried out in solution in a hydrocarbon solvent such as methylcyclohexane.

[0039] 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 reactor according to the composition of the monomer mixture, the polymerization reactor, the desired microstructure and macrostructure of the copolymer chain.

[0040] The synthesis of the first block is carried out by the copolymerization of ethylene and 1,3-butadiene. Ethylene and 1,3-butadiene 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 monomers, ethylene and 1,3-butadiene.

[0041] The polymerization temperature generally varies within a range of 30 to 160°C, preferably from 30 to 120°C. During the synthesis of the first block, the temperature of the reaction medium is advantageously kept constant during polymerization, and the total pressure in the reactor is also advantageously kept constant. Preferably, the polymerization of the ethylene monomer and 1,3-butadiene mixture is carried out at constant ethylene pressure.

[0042] To achieve the desired macrostructure of the first block, a person skilled in the art adjusts the polymerization conditions, particularly the molar ratio of the organomagnesium compound to the Nd metal that constitutes the metallocene. The molar ratio can reach a value of 100, although a molar ratio below 10 is more favorable for obtaining polymers with high molar masses.

[0043] During the synthesis of the first block, a continuous addition of ethylene and 1,3-butadiene 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 a first block that is a random copolymer.

[0044] The synthesis of the first block is completed by stopping the supply of monomers, notably by reducing the pressure in the reactor, preferably to approximately 3 bar. The reaction mixture following the synthesis of the first block is degassed, preferably by repeated degassing with an inert gas, such as nitrogen. The preparation of the block polymer continues with the synthesis of the second block by the subsequent homopolymerization of vinylpyridine in the degassed reaction mixture.

[0045] Vinylpyridine can be a mixture of vinylpyridines or one of the isomers of vinylpyridine, the isomerism being determined by the substituted carbon of the pyridine aromatic ring. Preferably, vinylpyridine is 4-vinylpyridine, 2-vinylpyridine, or a mixture thereof. Even more preferably, vinylpyridine is 4-vinylpyridine. When vinylpyridine is conditioned in the presence of a stabilizer, as is the case for most commercial vinylpyridines, it is typically used after removal of the stabilizer, which can be carried out in a well-known manner by distillation or by contact with alumina, for example, by treatment on alumina columns.

[0046] Vinylpyridine can be added to the reactor pure or diluted in a hydrocarbon solvent, preferably aliphatic such as methylcyclohexane. The vinylpyridine, pure or diluted, is introduced into the degassed reaction medium. The amount of vinylpyridine introduced into the reaction medium to be polymerized to form the second block is adjusted by those skilled in the art according to the desired percentage of vinylpyridine in block form within the block polymer. It can vary widely, particularly from 0.01 to 25 g per 100 g of the first block formed, and more specifically from 2 to 25 g per 100 g of the first block formed. The homopolymerization of vinylpyridine is preferably carried out at the same temperature as the synthesis of the first block. The polymerization temperature for the synthesis of the second block generally varies in the range of 30 to 160°C, preferably from 30 to 120°C.The synthesis of the second block can typically be monitored by chromatographic analysis to track vinylpyridine consumption. The synthesis of the second block is complete when the second block reaches the desired number-average molar mass or when the conversion of the vinylpyridine polymerization reaction reaches the desired level, for example, 100%.

[0047] The synthesis of the second block can be stopped by cooling the polymerization medium or by adding an alcohol, preferably one containing 1 to 3 carbon atoms, such as ethanol. The block polymer can be recovered using conventional techniques known to those skilled in the art, such as precipitation, evaporation of the solvent under reduced pressure, or steam stripping.

[0048] Preferably, the block polymer according to the invention that can be prepared by the process according to the invention is a diblock.

[0049] The block polymer can be added to a mineral base oil to form a lubricating composition, which is another object of the invention. The block polymer constituting the lubricating composition can be a mixture of block polymers as defined above, differing from one another in their respective compositions.

[0050] Suitable mineral base oils include Group I, Group II, and Group III base oils, and their blends. Groups I through III are defined in a well-known manner by the American Petroleum Institute (API) in its publication "API No. 1509 Engine Oil Licensing and Certification System, Appendix E, 14th Edition" of December 1996. Mineral base oils are typically obtained by atmospheric and vacuum distillation of crude oil, possibly followed by refining operations.

[0051] The proportion of block polymer added to the mineral base oil is adjusted by a person skilled in the art according to the nature of the mineral base oil, the characteristics of the block polymer, and, of course, the intended use of the lubricant. The mass percentage of the block polymer in the lubricant composition, or of the mixture of block polymers in the lubricant composition, can be up to 5% by weight of the lubricant composition, for example, from 0.01 to 5% by weight of the lubricant composition, preferably from 0.05 to 2% by weight of the lubricant composition. Preferably, the mineral base oil is a Group I base oil.

[0052] The mixture formed by the base oil and the block polymer constitutes a lubricating composition which may also contain other additives traditionally used in motor oil such as detergents and dispersants, antioxidants, compounds with an action against the formation of rust, foam, gel.

[0053] The lubricating composition according to the invention exhibits high-temperature thickening properties similar to motor oils containing traditionally used viscosity improvers such as ethylene and propylene copolymers.

[0054] In summary, the invention is advantageously implemented according to any one of the following embodiments 1 to 14: Mode 1: Block polymer containing a first block and a second block, the first block being a copolymer of 1,3-butadiene and ethylene containing more than 90 mole percent of ethylene units, the mole percent being expressed relative to the total number of repeating units constituting the first block, the second block being a homopolymer of a vinylpyridine. Mode 2: Block polymer according to mode 1 in which the first block is a random copolymer of ethylene and 1,3-butadiene. Mode 3: Block polymer according to any one of modes 1 to 2 in which the block polymer is a diblock. Mode 4: Block polymer according to any one of modes 1 to 3 in which the ethylene units present in the first block represent less than 97 mole percent of the total number of repeating units constituting the first block. Mode 5: Block polymer according to any one of modes 1 to 4 in which the first block contains 1,2-cyclohexanediyl motifs.Mode 6: Block polymer according to mode 5 in which the molar content of the 1,2-cyclohexanediyl motif in the first block is less than 10% of the total number of repeating units in the first block. Mode 7: Block polymer according to mode 5 or 6 in which the molar content of the 1,2-cyclohexanediyl motif in the first block ranges from 1% to less than 10% of the total number of repeating units in the first block. Mode 8: Block polymer according to any one of modes 1 through 7 in which the vinylpyridine is 4-vinylpyridine, 2-vinylpyridine, or a mixture thereof. Mode 9: Block polymer according to any one of modes 1 through 8 in which the molar content of vinylpyridine units in the second block is greater than 0.1% of the total number of repeating units in the first block.Mode 10: A block polymer according to any one of modes 1 to 9, wherein the molar percentage of vinylpyridine units in the second block is less than 20% of the total number of repeating units constituting the first block. Mode 11: A lubricating composition comprising a mineral base oil and a block polymer defined in any one of modes 1 to 10. Mode 12: A lubricating composition according to mode 11, wherein the mass percentage of the block polymer ranges from 0.01 to 5% by weight of the lubricating composition. Mode 13: A lubricating composition according to mode 11 or 12, wherein the mass percentage of the block polymer ranges from 0.05 to 2% by weight of the lubricating composition. Mode 14: A lubricating composition according to any one of modes 11 to 13, wherein the mineral base oil is a Group I base oil. Examples Determination of the microstructure of polymers:

[0055] High-resolution polymer NMR spectroscopy was performed on a Bruker 600 Avance III HD spectrometer operating at 600 MHz, equipped with a CP2.1 BBO 600S3 proton probe. Acquisitions were made at 368 K. Orthodichlorobenzene (o-DCB) was used as the solvent. Samples were analyzed at a concentration of approximately 1 wt% for proton NMR (1<H NMR). Chemical shifts were determined relative to the orthodichlorobenzene proton signal, fixed 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); d1: 10 s; 90° pulse “hard” 1 < H P1 = 13 µs and 16 W and 13 < C P2 = 26 µs and 84 W; Gradient: SMSQ10.100.

[0056] The assignment of the characteristic signals of the first block is defined in the literature, according to the article by Llauro et al., Macromolecules 2001, 34, 6304-6311.

[0057] The allocation of the characteristic signals of the second block is defined as follows: δ1 < H = 8.29 ppm (=CH-N=CH-); δ1 < H = 6.34 ppm (=C H -C(CH2)=C H -); δ 13< C = 150ppm (=CH-N=CH-); δ 13< C = 6.34ppm (= C HC(CH2) = C H-) DOSY (diffusion-ordered spectroscopy) NMR analysis of block polymers :

[0058] The DOSY experiment, an NMR method, allows for the analysis of complex mixtures and the detection of trace elements. The aim of this experiment is to demonstrate that the block polymer constitutes the majority of the sample and that the presence of homopolymer is very low or absent.

[0059] DOSY NMR analysis allows the separation of species present, particularly polymer matrices, by analyzing their diffusion coefficient in solution. The principle of the technique is as follows: The DOSY experiment consists of recording proton spectra while varying the applied gradient strength (G) and thus the diffusion strength. A linear increase in the gradient intensity will lead to an exponential decrease in the NMR signal intensity. The DOSY experiment will produce a two-dimensional map. The second dimension, F2, of the DOSY map corresponds, after processing by the Fourier transform, to the 1H dimension. The first dimension, F1, corresponds to the decay of the NMR signal as a function of the applied gradient strength. After processing the F2 dimension, the diffusion coefficient is extracted from equation (1), and a DOSY map is obtained. I = I 0 . exp − Dγ 2 G 2 δ 2 Δ − δ / 3 where I is the observed intensity, I0 the reference intensity, D the diffusion coefficient, γ the gyromagnetic ratio of the observed nucleus, G the gradient strength, δ the gradient length and Δ the diffusion time.

[0060] If the two matrices have the same diffusion coefficient, this means that the two matrices have the same hydrodynamic radius and are therefore grafted. Conversely, if the two matrices have different diffusion coefficients, this means that they are free from each other.

[0061] The equation that describes the diffusion coefficient is as follows: D = k B T 6 πηr S where kB is the Boltzmann constant, T the temperature, η the viscosity of the liquid in which the molecule is located, and rs the hydrodynamic radius of the molecule (in this case, the matrix or polymer). The experiment was conducted on samples of poly(butadiene-b-poly(ethylene-co-butadiene) synthesized according to the process of the invention.

[0062] Recording two 1D 1H NMR spectra with a scattering filter, one with a magnetic field gradient set at 90% of the maximum power of the gradient amplifier and the other at 1% of this value, allows, by comparison with the 1H NMR spectrum, observation of the signal loss due to spatial scattering of molecules and magnetization relaxation. The signal loss due to scattering is then attributed to "small molecules" not bound to the polymer matrix (reagents, antioxidants, solvents, etc.). Determination of the macrostructure of polymers :

[0063] Size Exclusion Chromatography (SEC) is used. 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 eluting first. While not an absolute method, SEC allows for the determination of the molar mass distribution of a polymer. Using commercial standard products, the various number-average (Mn) and weight-average (Mw) molar masses can be determined, and the dispersity (D = Mw / Mn) can be calculated using a Moore calibration.

[0064] Polymer preparationNo special treatment is required for the polymer sample prior to 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 used is equipped with an inline filtration system.

[0065] SEC Analysis: High-temperature size exclusion chromatography (HTEC) is used. The instrument is a GPC-IR chromatograph equipped with an IR-6 infrared detector from Polymer Char. Detection is performed by the IR detector on the vibrational bands of the CH2 and CH3 groups. A set of three commercially available Mixed BN-LS reference columns from Polymer Char is used. The elution solvent is 1,2,4-trichlorobenzene containing 300 ppm BHT. The flow rate is 1 mL / min, the system temperature is 160°C, and the analysis time is 90 minutes.

[0066] The injected volume of the polymer sample solution is 200 µl. The chromatographic data processing software is the "GPC-one" system from "Polymer Char".

[0067] The average molar masses are determined from a calibration curve made from commercial standard polystyrenes "PSS READY CAL-KIT". Determination of the degree of crystallinity of polymers, their melting point and their glass transition temperature:

[0068] The degree of crystallinity, melting point, and glass transition temperature are determined by differential scanning calorimetry (DSC). The analyses are performed on a NETZSCH DSC 214 Polyma DSC instrument calibrated with indium. This instrument has a temperature range of -150 to 700 °C. A computer integrated into the DSC controls the instrument using Netzsch's Proteus software. The sample (approximately 10 mg) is weighed and sealed in a 40 µL aluminum crucible. The crucible is pierced with a fine needle just before measurement.The samples are analyzed under helium at 40 mL / min following a dynamic method comprising 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 minutes; Step 7: heating from -150°C to 200°C at 20°C / min.

[0069] The first four steps erase the sample's thermal history. Measurements of the glass transition temperature (Tg) and melting temperature (Tf) are taken on the seventh step. This seventh step is also retained to obtain information on the sample's crystallization and determine the degree of crystallinity. The Tg and Tf values ​​are determined by applying data reprocessing in the "Proteus" software from Netzsch. The degree of crystallinity is determined using ISO 11357-3:2011 for measuring the melting and crystallization temperatures and enthalpies of the polymers used by differential scanning calorimetry (DSC). The reference enthalpy of polyethylene is 293 J / g (source: B. Wunderlich, Thermal Analysis, Academic Press, 1990, p. 281). Polymer synthesis :

[0070] All reagents are commercially obtained except for metallocene [{Me 2 SiFlu 2 Nd(µ-BH 4 ) 2 Li(THF)}] which is prepared according to the procedure described in patent applications WO 2007054224.

[0071] Butylloctylmagnesium BOMAG (20% by mass in heptane, C = 0.88 mol L⁻¹) is sourced from Lanxess and stored in a metal cylinder under an inert atmosphere. N35 grade ethylene is sourced from Air Liquide and used without prior purification. 1,3-Butadiene is purified using alumina guards. Methylcyclohexane solvent from BioSolve is dried and purified on an alumina column in a solvent fountain from mBraun and used under an inert atmosphere. All reactions are carried out under an inert atmosphere. Purification of 4-vinylpyridine:

[0072] Purified 4-vinylpyridine is prepared according to the following procedure: 100 mL of 4-vinylpyridine (Sigma-Aldrich, 95% purity, containing 100 ppm hydroquinone) is placed in a Steinie bottle. 30 g of alumina is introduced into the bottle. The bottle is then capped and shaken for 60 minutes at room temperature (23°C), protected from light. Preparation of a 4-vinylpyridine solution in methylcyclohexane :

[0073] Before any use in preparing solutions, methylcyclohexane (MCH) is purified by passing through alumina guards.

[0074] A first solution of 4-vinylpyridine in MCH, solution A, is prepared by introducing 0.26 mL of purified 4-vinylpyridine into 20 mL of MCH contained in a 250 mL Steinie bottle capped and pressurized with nitrogen.

[0075] A second 4-vinylpyridine in MCH solution, solution B, is prepared by introducing 0.65 mL of purified 4-vinylpyridine into 20 mL of MCH contained in a capped 250 mL Steinie bottle pressurized with nitrogen.

[0076] The bottles containing solutions A and B respectively are pressurized to 3 bars of nitrogen. Example 1: Preparation of a block polymer according to the invention :

[0077] 30.4 mg (47.5 µmol) of the metallocene Me 2 Si(C 13 H 8 ) 2 Nd(BH 4 ) 2 Li.THF are weighed into a 250 mL Steinie bottle in a glove box.

[0078] 296 mL of MCH are introduced into a 750 mL Steinie bottle. The bottle is placed under an inert atmosphere by bubbling with nitrogen for 10 minutes. 4.57 mL (499 µmol, Mg / Nd = 10.5) of a 0.11 mol / L butylctylmagnesium solution in MCH are introduced into the 750 mL bottle containing the MCH to form solution C.

[0079] A monomeric mixture of ethylene and 1,3-butadiene containing 92 mol% ethylene and 8 mol% 1,3-butadiene is also prepared by injecting first 0.48 bar of 1,3-butadiene into a ballast, followed by 5.52 bar of ethylene to complete the gas mixture. This yields 6 bar absolute pressure from a mixture containing 92 mol% ethylene and 8 mol% 1,3-butadiene (ethylene / butadiene mixture: 92 / 8).

[0080] The ballast is connected to a polymerization reactor.

[0081] Approximately one third of solution C is transferred into the 250 mL bottle containing the metallocene via a cannula to activate the metallocene and form the catalytic system.

[0082] Half of solution C is introduced into the stirred reactor (at 400 rpm) and heated to 77°C, the reactor having been previously placed under an inert atmosphere. The contents of the 250 mL bottle containing the catalytic system are introduced into the reactor. The remainder of solution C is then transferred to the reactor. The reactor is degassed under vacuum until gas bubbles form, then pressurized to 3 bar with the ethylene / butadiene mixture: 92 / 8.

[0083] When the ballast pressure shows a pressure drop corresponding to 12.7 g of monomers, the reactor is degassed with 3 vent / nitrogen cycles.

[0084] Solution A containing 4-vinylpuridine is introduced into the reactor. Stirring is maintained for 1 hour, then the heating is switched off and stirring stopped.

[0085] The reactor is disassembled, the polymerization medium is deactivated with 2 mL of ethanol to stop the polymerization reaction, then transferred into an aluminum tray and dried under vacuum at 60°C in an oven for 24 h. The recovered polymer is white and opaque.

[0086] After 24 hours, the dry polymer is recovered for analysis. The block polymer is a diblock containing a first block of a random copolymer of ethylene and 1,3-butadiene and a second block of poly(4-vinylpyridine).

[0087] The first block of the block polymer contains 91 mole percent of ethylene units, 6 mole percent of 1,2-cyclohexanediyl units, 1 mole percent of 1,3-butadiene units in the 1,2 configuration, and 2 mole percent of 1,3-butadiene units in the 1,4 configuration, predominantly 1,4-trans. The second poly(4-vinylpyridine) block represents 0.5 mole percent of the total number of ethylene units, 1,2-cyclohexanediyl units, 1,3-butadiene units in the 1,2 configuration, and 1,3-butadiene units in the 1,4-trans configuration.

[0088] DOSY NMR shows a diffusion coefficient corresponding to the EBR-b-PVP block polymer. The block polymer, analyzed by SEC / HT, has a number-average molar mass of 12500 g / mol and a dispersity index of 1.88. Example 2: Preparation of a block polymer according to the invention :

[0089] A block polymer is prepared according to the same procedure as in Example 1, except that solution A is replaced by solution B. The first block of the block polymer contains 92 mol% ethylene units, 5 mol% 1,2-cyclohexanediyl units, 1 mol% 1,3-butadiene units in the 1,2 configuration, and 2 mol% 1,3-butadiene units in the 1,4 configuration, predominantly 1,4-trans. The molar percentage of 4-vinylpyridine units is 1.4 mol% of the total number of ethylene units, 1,2-cyclohexanediyl units, 1,3-butadiene units in the 1,2 configuration, and 1,3-butadiene units in the 1,4 configuration, predominantly 1,4-trans.

[0090] The block polymer, analyzed by SEC / HT, has a number-average molar mass of 12000 g / mol and a dispersity index of 1.9.

[0091] The weighed mass of block polymer allows the determination of the average catalytic activity of the catalytic system, expressed in kilograms of polymer synthesized per mole of neodymium metal per hour (kg / mol.h). The catalytic activity is 214 kg.mol / h.

[0092] The Tg of the polyvinylpyridine block is 160°C. The crystallinity of the block polymer is 36.8%. Example 3: Preparation of a statistical ethylene-1,3-butadiene copolymer, not according to the invention:

[0093] A polymer is prepared using the same procedure as in Examples 1 and 2, except that no vinylpyridine solution is added after the copolymerization of ethylene and 1,3-butadiene. When the ballast pressure drops to a level corresponding to 12.7 g of monomers, the reactor is degassed with three vent / nitrogen cycles and the mixture is stopped with 2 mL of ethanol.

[0094] The polymer solution is then dried in a vacuum oven at 60°C and under nitrogen purging for 24 hours.

[0095] 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 per hour (kg / mol.h). The catalytic activity is 191 kg / mol.h.

[0096] SEC HT analysis of the copolymer shows a unimodal molecular distribution, and a Mn of 11,800 g / mol with a dispersity of 1.87.

[0097] The ethylene and 1,3-butadiene copolymer contains 91 mole percent of ethylene units, 6 mole percent of 1,2-cyclohexanediyl units, 1 mole percent of 1,3-butadiene units in the 1,2 configuration and 2 mole percent of 1,3-butadiene units in the 1,4 configuration.

[0098] The Tg of the ethylene-1,3-butadiene copolymer is at -21°C. The DSC thermogram shows an endothermic phenomenon at the transition temperature (-21°C) identical to that of example 1 and example 2.

[0099] Example 3 is a control example, since it corresponds to the synthesis of the first block of examples 1 and 2. Preparation of lubricating compositions containing a 600 base oil :

[0100] Lubricating compositions C0, C1, and C2 are prepared according to the following procedure: 1 g of polymer is introduced into a 250 mL Steinie bottle containing 200 g of a CORE™< 600 Group I mineral base oil. The Steinie bottle is capped and shaken in a water bath at 90°C for 12 hours. The viscosity of the resulting mixture is measured at 100°C. For composition C1, the polymer is the block polymer from Example 1; for composition C2, the polymer is the block polymer from Example 2; for composition C0, the polymer is an OCP polymer marketed by Lubrizol under the reference "7077", a copolymer of ethylene and propylene with approximately 50 mol% ethylene.Composition C0, containing a 600 base oil, is a reference composition, as it contains a copolymer not conforming to the invention, namely Lubrizol's "7077" copolymer, an additive commonly used in motor oils as a high-temperature (100°C) thickening agent. The "CORE™ < 600" base oil marketed by Exxon is a Group I mineral base oil and is commonly used as a base oil in motor oils.

[0101] The kinematic viscosity at 100°C of the lubricating compositions is measured according to ASTM 445-21. The viscosity results presented on a base of 100 relative to a control are shown in Table 1. The control consists of the same base oil that is used in the lubricating compositions. Table 1 Lubricant composition T1 C0 C1 C2 Base oil 600 600 600 600 Polymer - OCP Example 1 Example 2 Viscosity at 100°C 100 103 108 109

[0102] It is observed that the lubricating composition containing a block polymer according to the invention (C1; C2) has a viscosity at 100°C that is higher than that of the base oil it contains (T1). The viscosities of the lubricating compositions C1 and C2 are higher than that of the reference composition C0. This result is obtained even though the copolymers according to the invention have a number-average molar mass much lower than that of the OCP copolymer. Surprisingly, as a high-temperature thickening agent for mineral base oils, the block polymers according to the invention prove to be as effective as an OCP copolymer.

Claims

1. Block polymer containing a first block and a second block, the first block being a copolymer of 1,3-butadiene and ethylene, containing more than 90 mol% of ethylene units, the molar percentage being expressed relative to the total number of constituent repeat units of the first block, the second block being a homopolymer of a vinylpyridine.

2. Block polymer according to Claim 1, wherein the first block is a statistical copolymer of ethylene and 1,3-butadiene.

3. Block polymer according to either one of Claims 1 to 2, which block polymer is a diblock.

4. Block polymer according to any one of Claims 1 to 3, wherein the ethylene units present in the first block represent less than 97 mol% of the total number of constituent repeat units of the first block.

5. Block polymer according to any one of Claims 1 to 4, wherein the first block contains 1,2-cyclohexanediyl subunits.

6. Block polymer according to Claim 5, wherein the molar content of 1,2-cyclohexanediyl subunits in the first block is less than 10% of the total number of constituent repeat units of the first block.

7. Block polymer according to Claim 5 or 6, wherein the molar content of 1,2-cyclohexanediyl subunits in the first block varies from 1% to less than 10% of the total number of constituent repeat units of the first block.

8. Block polymer according to any one of Claims 1 to 7, wherein the vinylpyridine is 4-vinylpyridine, 2-vinylpyridine or the mixture thereof.

9. Block polymer according to any one of Claims 1 to 8, wherein the molar content of vinylpyridine units present in the second block is greater than 0.1% of the total number of constituent repeat units of the first block.

10. Block polymer according to any one of Claims 1 to 9, wherein the molar content of vinylpyridine units in the second block is less than 20% of the total number of constituent repeat units of the first block.

11. Lubricating composition comprising a mineral base oil and a block polymer as defined in any one of Claims 1 to 10.

12. Lubricating composition according to Claim 11, wherein the mineral base oil is a group I base oil.