Ethylene-rich diene polymers having polyvinylpyridine blocks and their use in engine lubricant compositions

Abstract

The present invention relates to a block polymer and an engine lubricant composition containing the block polymer and a mineral-based oil. The block polymer contains a first block and a second block. The first block is a copolymer of 1,3-butadiene and ethylene, contains more than 90 mol% of ethylene units, and the molar percentage is represented relative to the total number of constituent repeating units of the first block. The second block is a homopolymer of vinyl pyridine.

Description

Technical Field

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

Background Art

[0002] Engine oils, which are lubricating compositions containing mineral-based oils, are used in engines to minimize energy losses caused by friction within the engine under low-temperature conditions and to maintain a continuous film of lubricant on the lubricated parts of the engine under high-temperature conditions. In order not to break the lubricating film, it is important that the viscosity of the lubricating composition decreases as much as possible during operation under high-temperature conditions. Mineral-based oils represent the main constituent of lubricating compositions that are engine oils. The viscosity of mineral-based oils decreases with an increase in temperature and increases with a decrease in temperature. It follows that the viscosity of lubricating compositions containing mainly mineral-based oils also experiences fluctuations in its viscosity with temperature. To weaken the effect of an increase in temperature on the viscosity of lubricating compositions, it is known to add additives to mineral-based oils. These additives act to thicken the lubricating composition as the temperature increases in order to partially improve the drop in viscosity under high-temperature conditions. To counteract the decrease in the viscosity of mineral-based oils, they generally increase the high-temperature viscosity. These thickening additives are generally polymers. Two main families of polymers sold for this purpose are polymers having ester functional groups such as poly(meth)acrylates, and hydrocarbon-based polymers such as polyisobutylene, copolymers of ethylene and propylene, also known as OCP, hydrogenated copolymers of diene and styrene, and likewise hydrogenated polybutadiene.

Summary of the Invention

[0003] The applicant has discovered that a block polymer containing a polyvinylpyridine block and a block rich in ethylene, which is a copolymer of ethylene and 1,3-butadiene, effectively increases the viscosity of engine oil at high temperatures to the same extent as OCP. Therefore, a first subject of the present invention is a block polymer containing a first block and a second block, wherein the first block is a copolymer of 1,3-butadiene and ethylene, contains more than 90 mol% of ethylene units, and the molar percentage is represented relative to the total number of constituent repeating units of the first block, and the second block is a homopolymer of vinylpyridine. A second subject of the present invention is a lubricating composition comprising a mineral base oil and a block polymer according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0004] Any interval of values represented by the expression "between a and b" represents a range of values greater than "a" and less than "b" (in other words, the limits a and b are excluded), whereas any interval of values represented by the expression "a to b" means a range of values from "a" up to and including the maximum "b" (in other words, including the strict limits a and b). Unless otherwise indicated, the content of the units in the first block is expressed as a molar percentage relative to all of the constituent repeating units of the first block. The compounds referred to in this specification may be of fossil origin or may be bio-based. In the latter case, they can be produced, in whole or in part, from biomass or can be obtained from renewable starting materials produced, in whole or in part, from biomass. Similarly, the compounds referred to may be derived from the recycling of already used materials, i.e., they can be produced, in whole or in part, by a recycling process or, alternatively, they may be obtained from starting materials that themselves have been produced by a recycling process.

[0005] The expression "based on" used to define the constituent materials of a catalyst system (or catalyst composition) is understood to mean a mixture of these constituent materials, or the product of the reaction of some or all of these constituent materials with each other. An essential feature of the block polymer according to the present invention is that it contains two blocks. The first constituent block of the block polymer according to the present invention is a copolymer of ethylene and 1,3-butadiene. The constituent monomer units of the first block are those resulting from the copolymerization of ethylene and 1,3-butadiene. The ethylene units present in the first block represent more than 90 mol% of the total number of constituent repeating units of the first block. Preferably, the ethylene units present in the first block represent less than 97 mol% of the total number of constituent repeating units of the first block. As is known, the term "ethylene unit" means a unit containing a -(CH2-CH2)- sub-unit.

[0006] As is known, 1,3-butadiene can be inserted into the growing polymer chain by 1,4 or 1,2 insertion, respectively producing the formation of 1,3-butadiene units in the 1,4 configuration or 1,3-butadiene units in the 1,2 configuration. When the first block contains units of 1,3-butadiene in the 1,4 configuration, the 1,4-trans units preferably represent more than 50% of the units in the 1,4 configuration, more preferably more than 80% of the units in the 1,4 configuration. The first block may additionally contain 1,2-cyclohexanediyl sub-units, also referred to as 1,2-cyclohexanediyl units of formula (I).

Chemical formula

[0007] According to a particularly preferred embodiment of the present invention, the first block contains 1,2-cyclohexanediyl sub-units. Preferably, the molar content of 1,2-cyclohexanediyl sub-units in the first block is less than 10% of the total number of constitutional repeating units of the first block. More preferably, this varies from 1% to less than 10% of the total number of constitutional repeating units of the first block. According to a particularly preferred embodiment of the present invention, the first block is a statistical copolymer of ethylene and 1,3-butadiene. An essential feature of the second constituent block of the block polymer according to the present invention is that it is a homopolymer of vinylpyridine. The vinylpyridine whose monomer units constitute the second block is the vinylpyridine as defined in the described embodiments of the process according to the present invention. Preferably, the vinylpyridine is 4-vinylpyridine, 2-vinylpyridine, or a mixture thereof. More preferably, the vinylpyridine is 4-vinylpyridine.

[0008] The molar content of the vinylpyridine units present in the second block can be less than 1% or much greater than 1% of the total number of constitutional repeating units of the first block. This is preferably greater than 0.1% of the total number of constitutional repeating units of the first block. This is preferably less than 20% of the total number of constitutional repeating units of the first block. The block polymer according to the invention is preferably a diblock. When the block polymer is a diblock, it is typically of the formula A-B, where A represents the first block and B represents the second block. The block polymer according to the invention can be prepared by a subsequent polymerization process. This involves the polymerization of a monomer mixture of ethylene and 1,3-butadiene in the presence of a catalyst system to form the first block, followed by the homopolymerization of vinylpyridine to form the second block. The catalyst system is based on at least one metallocene of formula (I) and an organomagnesium compound P(Cp 1 Cp 2 )Nd(BH4) (1+y) Li y (THF) x (II) and is based on (Cp 1 and Cp 2 are selected from the group consisting of fluorenyl, cyclopentadienyl and indenyl groups, the groups being substituted or unsubstituted, P is a group bridging two groups Cp 1 and Cp 2 , the group ZR 1 R 2 represents, Z represents a silicon or carbon atom, and the same or different R 1 and R 2 each represent an alkyl group containing 1 to 20 carbon atoms, preferably methyl, y is an integer greater than or equal to 0, x is an integer or non-integer greater than or equal to 0)

[0009] In formula (II), the neodymium atoms are bonded to a ligand molecule consisting of two groups Cp 1 and Cp 2 which are linked together by a bridge P. Preferably, the symbol P represented by the term bridge corresponds to the formula ZR 1 R 2 where Z represents a silicon atom and the same or different R 1 and R 2 represent alkyl groups containing 1 to 20 carbon atoms. More preferably, the bridge P is of the formula SiR 1 R 2 where R 1 and R 2 are the same and as defined above. Even more preferably, P corresponds to the formula SiMe2. As substituted cyclopentadienyl, fluorenyl and indenyl groups, those substituted with an alkyl group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, or otherwise a trialkylsilyl group such as SiMe3 can be mentioned. When the ligand Cp 1 and Cp 2 are substituted, they are preferably substituted with a methyl group, a butyl group, notably a tert-butyl group, or a trimethylsilyl group. These groups are preferred regardless of the embodiment of the present invention. The choice of groups is also guided by the ease of access to the corresponding molecules which are substituted cyclopentadiene, fluorene and indene, since said molecules are commercially available or can be easily synthesized.

[0010] As substituted cyclopentadienyl groups, those substituted either at the 2 (or 5) position or at the 3 (or 4) position, in particular those substituted at the 2 position, more particularly the tetramethylcyclopentadienyl group can be mentioned. The 2 (or 5) position indicates the position of the carbon atom adjacent to the carbon atom to which the bridge P is attached, as represented in the following schematic diagram. Note that substitution at the 2 or 5 position is also referred to as substitution at the α position with respect to the bridge.

[0011] [Chemical formula] Examples of the substituted fluorenyl group include those substituted with an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms. The choice of the group is also guided by the ease of access to the corresponding molecule which is the substituted fluorene, since the fluorene is commercially available or can be easily synthesized.

[0012] Examples of the substituted fluorenyl group include those substituted at the 2, 7, 3 or 6 positions, and more particularly, 2,7 - di(tert - butyl)fluorenyl and 3,6 - di(tert - butyl)fluorenyl groups. The 2, 3, 6 and 7 positions respectively indicate the positions of the carbon atoms of the ring as shown in the following schematic diagram, and the 9 position corresponds to the carbon atom to which the bridging P is attached. [Chemical formula] Examples of the substituted indenyl group include those substituted at the 2 position, and more particularly, 2 - methylindenyl or 2 - phenylindenyl. The 2 position indicates the position of the carbon atom adjacent to the carbon atom to which the bridging P is attached as shown in the following schematic diagram. [Chemical formula] According to one embodiment of the present invention, Cp 1 and Cp 2 are different, one representing a cyclopentadienyl group and the other representing a fluorenyl group. This embodiment is particularly suitable for preparing a first block that does not contain any 1,2 - cyclohexanediyl sub - unit of formula (I).

[0013] According to another embodiment of the present invention, Cp 1 and Cp 2 are the same and are selected from the group consisting of a substituted fluorenyl group and a fluorenyl group. Advantageously, Cp 1and Cp 2 each represents a substituted fluorenyl group or a fluorenyl group, preferably a fluorenyl group. The fluorenyl group has the formula C 13 H8. Preferably, the metallocene has the formula (IIa), (IIb), (IIc), (IId) or (IIe), in which the symbol Flu has the formula C 13 H8 fluorenyl group. [{Me2SiFlu2Nd(μ-BH4)2Li(THF)}2] (IIa) [Me2SiFlu2Nd(μ-BH4)2Li(THF)] (IIb) [Me2SiFlu2Nd(μ-BH4)(THF)] (IIc) [{Me2SiFlu2Nd(μ-BH4)(THF)}2] (IId) [Me2SiFlu2Nd(μ-BH4)] (IIe)

[0014] The organomagnesium compound used as a cocatalyst in the catalyst system is a compound having at least one C-Mg bond. Examples of the organomagnesium compound include diorganomagnesium compounds, particularly dialkylmagnesium compounds, and organomagnesium halides, particularly alkylmagnesium halides. The diorganomagnesium compound typically has the formula MgR 3 R 4 wherein R 3 and R 4 represent a carbon-based group. The term "carbon-based group" means a group containing one or more carbon atoms. Preferably, R 3 and R 4 contain 2 to 10 carbon atoms. More preferably, R 3 and R 4Each represents an alkyl. The organomagnesium compound is preferably a di-organomagnesium compound or a halogenated organomagnesium, advantageously a dialkylmagnesium compound, more preferably butylethylmagnesium or butyloctylmagnesium, and even more preferably butyloctylmagnesium.

[0015] The catalyst system can be customarily prepared by a process similar to that described in the patent applications of International Publication No. WO 2007 / 054224 or International Publication No. WO 2007 / 054223. For example, the organomagnesium compound and the metallocene are reacted in a hydrocarbon-based solvent, typically at a temperature in the range of 20°C to 80°C for a period of 5 to 60 minutes. The catalyst system is generally prepared in an aliphatic hydrocarbon-based solvent such as methylcyclohexane, or an aromatic hydrocarbon-based solvent such as toluene. Generally, after its synthesis, the catalyst system is used as such in the process for the synthesis of block polymers.

[0016] Alternatively, the catalyst system can be prepared by a process similar to that described in the patent application of International Publication No. WO 2017 / 093654 or in the patent application of International Publication No. WO 2018 / 020122. According to this alternative, the catalyst system further contains a preformed monomer selected from 1,3-diene, ethylene or a mixture of ethylene and 1,3-diene, in which case the catalyst system is based at least on a metallocene, an organomagnesium compound and a preformed monomer. To obtain the first reaction product, for example, the organomagnesium compound and the metallocene are reacted in a hydrocarbon-based solvent, typically at a temperature of 20 °C to 80 °C for 10 to 20 minutes, and then a preformed monomer selected from 1,3-diene, ethylene or a mixture of ethylene and 1,3-diene is reacted with this first reaction product at a temperature in the range of 40 °C to 90 °C for 1 hour to 12 hours. The preformed monomer is preferably 1,3-butadiene, or a mixture of ethylene and 1,3-butadiene. The catalyst system thus obtained can be used immediately in the process according to the invention or stored under an inert atmosphere, and then used in a polymerization process for preparing block polymers.

[0017] The metallocenes used to prepare the catalyst system can be in the form of crystalline or amorphous powders or, alternatively, in the form of single crystals. The metallocenes can be in monomeric or dimeric form, and these forms are determined by the method of preparing the metallocene, as described, for example, in patent applications WO 2007 / 054224 or WO 2007 / 054223. The metallocenes can be prepared conventionally by reaction in a suitable solvent, such as an ether, e.g., diethyl ether or tetrahydrofuran, or any other solvent known to those skilled in the art, of an alkali metal salt of the ligand and a rare earth metal borohydride, especially under inert and anhydrous conditions, by a process similar to that described in patent applications WO 2007 / 054224 or WO 2007 / 054223. After the reaction, the metallocene is separated from the reaction by-products by techniques known to those skilled in the art, such as filtration or precipitation from a second solvent. The metallocene is finally dried and isolated in solid form.

[0018] As with any synthesis carried out in the presence of an organometallic compound, the synthesis of the metallocene and of the catalyst system takes place under anhydrous conditions in an inert atmosphere. Typically, the reaction starts from an anhydrous solvent and compounds and is carried out under anhydrous nitrogen or argon. Those skilled in the art also adapt the polymerization conditions and the respective concentrations of the reagents (constituent substances of the catalyst system, monomers) according to the equipment (tools, reactors) used to carry out the polymerization. As is known to those skilled in the art, the polymerization and handling of the monomers, of the catalyst system and of the copolymerization solvent take place under anhydrous conditions and in an inert atmosphere. The polymerization solvent is typically an aliphatic or aromatic hydrocarbon-based solvent. The polymerization is preferably carried out continuously or discontinuously in solution, in a reactor, advantageously a stirred reactor. The polymerization solvent can be an aromatic or aliphatic hydrocarbon-based solvent. Examples of polymerization solvents include toluene and methylcyclohexane. Advantageously, the polymerization is carried out in solution in a hydrocarbon-based solvent such as methylcyclohexane. Those skilled in the art will adapt the polymerization conditions such as the polymerization temperature, the respective concentrations of the reagents, and the pressure in the reactor according to the composition of the monomer mixture, the polymerization reactor, and the desired micro-structure and macro-structure of the copolymer chain.

[0019] The first block is synthesized by copolymerization of ethylene and 1,3-butadiene. Ethylene and 1,3-butadiene can be introduced into a reactor containing a polymerization solvent and a catalyst system, or conversely, the catalyst system can be introduced into a reactor containing a polymerization solvent and the monomers ethylene and 1,3-butadiene. The polymerization temperature generally varies within the range of 30°C to 160°C, preferably 30°C to 120°C. During the synthesis of the first block, the temperature of the reaction medium is preferably kept constant during polymerization, and the total pressure in the reactor is also preferably kept constant. Preferably, the monomer mixture of ethylene and 1,3-butadiene is polymerized at a constant ethylene pressure. To achieve the desired macro-structure of the first block, those skilled in the art will adapt the polymerization conditions, in particular the molar ratio of the organomagnesium reagent to the metal Nd constituting the metallocene. The molar ratio can reach a value of 100, and it is known that a molar ratio of less than 10 is more convenient for obtaining a polymer with a high molar mass.

[0020] During the synthesis of the first block, ethylene and 1,3-butadiene can be continuously added to the polymerization reactor, in which case the polymerization reactor is a feed reactor. This embodiment is particularly most suitable for the synthesis of the first block which is a statistical copolymer. The synthesis of the first block is completed by interrupting the supply of the monomers, in particular by the pressure in the reactor preferably dropping to around 3 bar. The reaction medium at the end of the synthesis of the first block is preferably degassed by performing several degassings using an inert gas, for example nitrogen. The preparation of the block polymer follows the synthesis of the second block by subsequent homopolymerization of vinyl pyridine in the degassed reaction medium. Vinyl pyridine can be a mixture of vinyl pyridines or one of the isomers of vinyl pyridine, and the isomerism is determined by the substituted carbon of the aromatic ring of pyridine. Preferably, vinyl pyridine is 4-vinyl pyridine, 2-vinyl pyridine or a mixture thereof. More preferably, vinyl pyridine is 4-vinyl pyridine. As is the case with most commercially available vinyl pyridines, when vinyl pyridine is packaged in the presence of a stabilizer, it is typically used after removal of the stabilizer, which can be done in a well-known manner by distillation or by contact with alumina, for example, treatment in an alumina column.

[0021] Vinyl pyridine can be added to the reactor in pure form or diluted in a hydrocarbon-based solvent, preferably an aliphatic hydrocarbon-based solvent such as methylcyclohexane. Pure or diluted vinyl pyridine is introduced into the degassed reaction medium. The amount of vinyl pyridine introduced into the reaction mixture polymerized in the form of the second block is adjusted by those skilled in the art according to the desired content of the vinyl pyridine in block form in the block polymer. This can vary within a wide range, particularly from 0.01 to 25 g per 100 g of the first block formed, more specifically from 2 g to 25 g per 100 g of the block formed. The homopolymerization of vinyl pyridine is preferably carried out at the same temperature as that for the synthesis of the first block. The polymerization temperature for the synthesis of the second block generally varies within the range of 30 to 160 °C, preferably 30 to 120 °C. After the synthesis of the second block, typically, chromatographic analysis can be continued to monitor the consumption of vinyl pyridine. The synthesis of the second block is completed when the second block reaches the desired number average molar mass or when the conversion of the reaction for polymerizing vinyl pyridine reaches the desired conversion, for example, 100%.

[0022] The synthesis of the second block can be stopped by cooling the polymerization medium or by adding an alcohol, preferably an alcohol containing from 1 to 3 carbon atoms, such as ethanol. The block polymer 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 steam stripping. Preferably, the block polymers according to the invention that can be prepared by the process according to the invention are diblocks. The block polymer can be added to a mineral base oil to form a lubricating composition, which is another subject of the present invention. The constituent block polymers of the lubricating composition can be a mixture of block polymers as defined above, which are different from each other from the point of view of their respective compositions.

[0023] Suitable mineral base oils can include Group I base oils, Group II base oils and Group III base oils, and mixtures thereof. Groups I to III are defined, as is known, by the American Petroleum Institute (API) in its publication “API N°1509 Engine Oil Licensing and Certification System, Appendix E, 14th Edition”, December 1996. Mineral base oils are typically obtained by atmospheric and vacuum distillation of crude oil, and may be followed by refining operations. The content of the block polymer added to the mineral base oil is adjusted by those skilled in the art according to the properties of the mineral base oil, according to the characteristics of the block polymer and, of course, according to the use of the lubricating composition. The mass content of the block polymer or of the mixture of block polymers in the lubricating composition can range from 0.01% to 5% by mass of the lubricating composition, for example, preferably from 0.05% to 2% by mass of the lubricating composition. Preferably, the mineral base oil is a Group I base oil.

[0024] A mixture formed by a base oil and a block polymer constitutes a lubricating composition, which can further contain other additives conventionally used in engine oils, such as detergents and dispersants, antioxidants, compounds having an action against rust, foam, and ice formation. The lubricating composition according to the present invention has high-temperature thickening characteristics, like an engine oil containing a viscosity improver conventionally used, such as a copolymer of ethylene and propylene. In summary, the present invention is advantageously implemented according to any one of the following Embodiments 1 to 14. Embodiment 1: A block polymer containing a first block and a second block, wherein the first block is a copolymer of 1,3-butadiene and ethylene, contains more than 90 mol% of ethylene units, and the molar percentage is represented relative to the total number of constitutional repeating units of the first block, and the second block is a homopolymer of vinyl pyridine. Embodiment 2: The block polymer according to Embodiment 1, wherein the first block is a statistical copolymer of ethylene and 1,3-butadiene. Embodiment 3: The block polymer according to Embodiment 1 or 2, wherein the block polymer is a diblock.

[0025] Embodiment 4: The block polymer according to any one of Embodiments 1 to 3, wherein the ethylene units present in the first block represent less than 97 mol% of the total number of constitutional repeating units of the first block. Embodiment 5: The block polymer according to any one of Embodiments 1 to 4, wherein the first block contains 1,2-cyclohexanediyl sub-units. Embodiment 6: The block polymer according to Embodiment 5, wherein the molar content of 1,2-cyclohexanediyl sub-units in the first block is less than 10% of the total number of constitutional repeating units of the first block. Embodiment 7: The block polymer according to Embodiment 5 or 6, wherein the molar content of 1,2-cyclohexanediyl sub-units in the first block varies from 1% to less than 10% of the total number of constitutional repeating units of the first block. Embodiment 8: A block polymer according to any one of Embodiments 1 to 7, wherein the vinyl pyridine is 4-vinyl pyridine, 2-vinyl pyridine, or a mixture thereof.

[0026] Embodiment 9: A block polymer according to any one of Embodiments 1 to 8, wherein the molar content of vinyl pyridine units present in the second block is greater than 0.1% of the total number of constitutional repeating units of the first block. Embodiment 10: A block polymer according to any one of Embodiments 1 to 9, wherein the molar content of vinyl pyridine units in the second block is less than 20% of the total number of constitutional repeating units of the first block. Embodiment 11: A lubricating composition comprising a mineral base oil and a block polymer as defined in any one of Embodiments 1 to 10. Embodiment 12: A lubricating composition according to Embodiment 11, wherein the content by mass of the block polymer varies from 0.01% to 5% by mass of the lubricating composition. Embodiment 13: A lubricating composition according to Embodiment 11 or 12, wherein the content by mass of the block polymer varies from 0.05% to 2% by mass of the lubricating composition. Embodiment 14: A lubricating composition according to any one of Embodiments 11 to 13, wherein the mineral base oil is a Group I base oil.

Examples

[0027] Determination of the Microstructure of the Polymer: High-resolution NMR spectroscopy of the polymer was performed on a Bruker 600 Avance III HD spectrometer operating at 600 MHz equipped with a CP2.1 BBO 600S3 proton probe. Acquisition was carried out at 368 K. Ortho-dichlorobenzene (o-DCB) was used as the solvent. Proton NMR ( 1The sample was analyzed at a concentration of approximately 1% by mass for 1H NMR analysis. The chemical shift was determined relative to the proton signal of ortho-dichlorobenzene set at 7.2 ppm. The 2D analysis was carried out using the following sequence: HSQC: pulse program; hsqcetgpsi2 “HSQC with gradient”; SW1: 180 ppm ( 13 C); SW2: 12 ppm ( 1 H); d1: 10 s; 90° “hard” pulse 1 1H P1 = 13 μs and 16 W and 13 13C P2 = 26 μs and 84 W; gradient: SMSQ10.100.

[0028] The attributes of the signal characteristics of the first block are defined in the literature according to the paper Llauro et al., Macromolecules, 2001, 34, 6304 - 6311. The attributes of the signal characteristics of the second block are defined as follows: δ 1 1H = 8.29 ppm (=CH-N=CH-); δ 1 1H = 6.34 ppm (=CH-C(CH2)=CH-); δ 13 13C = 150 ppm (=CH-N=CH-); δ 13 13C = 6.34 ppm (=CH-C(CH2)=CH-) DOSY NMR (Diffusion Ordered Spectroscopy) analysis of the block polymer: The DOSY experiment, which is an NMR method, enables the analysis of complex mixtures and the detection of traces. The aim of this experiment is to show that the block polymer represents the majority of the sample and that the presence of homopolymers is very low or absent.

[0029] DOSY NMR analysis makes it possible to separate the species present, notably the polymer matrix, by analyzing their solution diffusion coefficients. The principle of the technique is as follows: The DOSY experiment consists of recording the proton spectrum while varying the gradient force G applied and thus the diffusion force. A linear increase in the gradient intensity results in an exponential decrease in the intensity of the NMR signal. The DOSY experiment generates a two-dimensional map. The second dimension F2 of DOSY corresponds to the 1H dimension after Fourier transformation. The first dimension F1 corresponds to the decrease in the NMR signal as a function of the applied gradient force. After processing the dimension F2, the diffusion coefficient is extracted using equation (1), and a DOSY map is obtained. I = I0.exp(-Dγ 2 G 2 δ 2 (Δ - δ / 3)) (1) Where I is the observed intensity, I0 is the reference intensity, D is the diffusion coefficient, γ is the magnetic gyromagnetic ratio of the observed nucleus, G is the gradient force, δ is the gradient length, and Δ is the diffusion time. If two matrices have the same diffusion coefficient, this means that the two matrices have the same hydrodynamic radius and are thus grafted. On the other hand, if two matrices have two different diffusion coefficients, this means that they are free with respect to each other.

[0030] The equation describing the diffusion coefficient is as follows:

Number

[0031] Determination of the macrostructure of the polymer: Size exclusion chromatography is used. It will be recalled that SEC enables the separation of macromolecules in solution according to their size through a column packed with a porous gel. Macromolecules are separated according to their hydrodynamic volume, and the most bulky ones are eluted first. Although not an absolute method, SEC enables the understanding of the molar mass distribution of the polymer. Various number-average molar masses (Mn) and mass-average molar masses (Mw) can be determined from commercially available standards, and the dispersity (D = Mw / Mn) can be calculated by "Moore" calibration. Preparation of the polymer: There is no special treatment of the polymer sample before analysis. It is simply dissolved in 1,2,4-trichlorobenzene containing 300 ppm of BHT (butylated hydroxytoluene) at a concentration of approximately 1 g / l. The solution is stirred at 160 °C for 2 hours before injection, and the chromatographic device used is equipped with an in-line filtration system.

[0032] SEC analysis: High-temperature size exclusion chromatography or HT-SEC is used. The device used is a GPC-IR chromatograph equipped with an IR-6 infrared detector manufactured by Polymer Char. Detection is performed by the IR detector for the vibration bands of CH2 and CH3 groups. A set of three "mixed BN-LS", which are commercially available reference columns manufactured by Polymer Char, is used. The elution solvent is 1,2,4-trichlorobenzene containing 300 ppm of BHT, the flow rate is 1 ml / min, the temperature of the system is 160 °C, and the analysis time is 90 minutes (min). The injection volume of the polymer sample solution is 200 μl. The software for utilizing the chromatographic data is the GPC-One system manufactured by Polymer Char. The average molar mass is determined from a calibration curve generated from commercially available polystyrene standards of the PSS Ready Cal kit.

[0033] Determination of the crystallinity, melting points and glass transition temperatures of the polymers: The crystallinity, melting point and glass transition temperature are determined by differential scanning calorimetry (DSC). The analysis is performed on a Netzsch DSC 214 Polyma DSC device calibrated with indium. This device has a temperature range extending from -150 °C to 700 °C. A computer integrated with the DSC controls the device using Proteus software from Netzsch. A sample (approx. 10 mg) is weighed and sealed in a 40 μl aluminum crucible. Immediately before the measurement, the crucible is pierced with a fine needle. The sample is analyzed under helium at 40 ml / min according to a mechanical method involving seven temperature steps: Step 1: Cool from 25 °C to -150 °C at 50 °C / min; Step 2: Isothermal at -150 °C for 5 minutes; Step 3: Heat from -150 °C to 200 °C at 20 °C / min; Step 4: Isothermal at 200 °C for 5 minutes; Step 5: Cool from 200 °C to -150 °C at 20 °C / min; Step 6: Isothermal at -150 °C for 5 minutes; Step 7: Heat from -150 °C to 200 °C at 20 °C / min. The first four steps make it possible to erase the thermal history of the sample. The measurement of the glass transition temperature (Tg) and melting point (Tm) is performed in the seventh step. The seventh step is also retained to obtain information on the crystallization of the sample and to determine the crystallinity. The Tg and Tm values are determined by applying data reprocessing of the Proteus software from Netzsch. The crystallinity is determined by using ISO 11357-3:2011, a standard for measuring the temperature and enthalpy of fusion and crystallization 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, 281).

[0034] Synthesis of Polymer: All reagents are commercially available, except for the metallocene [{Me2SiFlu2Nd(μ - BH4)2Li(THF)}] prepared according to the procedure described in the patent application WO 2007 / 054224. Butyloctylmagnesium BOMAG (20 wt% in heptane, C = 0.88 mol·l -1 ) is created by Lanxess and stored in a metal cylinder under an inert atmosphere. Grade N35 ethylene is obtained from Air Liquide and used without prior purification. 1,3 - Butadiene is purified through an alumina guard tube. The methylcyclohexane solvent created by BioSolve is dried and purified over an alumina column in a solvent purifier created by mBraun and used in an inert atmosphere. All reactions are carried out in an inert atmosphere.

[0035] Purification of 4 - Vinylpyridine: The purified 4 - vinylpyridine is prepared according to the following procedure: 100 ml of 4 - vinylpyridine (Sigma - Aldrich, purity 95%, containing 100 ppm hydroquinone) is placed in a Schlenk bottle. 30 g of alumina is introduced into the bottle. The bottle is then capped and stirred at ambient temperature (23 °C) for 60 minutes in the dark.

[0036] Preparation of a solution of 4 - vinylpyridine in methylcyclohexane: Before use for preparing the solution, methylcyclohexane (MCH) is purified by passing it through an alumina guard tube. Solution A, the first solution of 4 - vinylpyridine in MCH, is prepared by introducing 0.26 ml of the purified 4 - vinylpyridine into 20 ml of MCH contained in a 250 - ml Schlenk bottle with a cap under nitrogen pressure. A second solution of 4-vinylpyridine in MCH, solution B, is prepared by introducing 0.65 ml of purified 4-vinylpyridine into 20 ml of MCH contained in a 250 ml stainless steel bottle with a lid under nitrogen pressure. The bottles containing solutions A and B are pressurized with 3 bar of nitrogen.

[0037] (Example 1) Preparation of block polymers according to the invention: 30.4 mg (47.5 μmol) of metallocene Me2Si(C 13 H8)2Nd(BH4)2Li.THF is weighed in a 250 ml stainless steel bottle in a glove box. 296 ml of MCH is introduced into a 750 ml stainless steel bottle. The bottle is placed under an inert atmosphere by nitrogen bubbling for 10 minutes. To form solution C, a solution of 4.57 ml (499 μmol, Mg / Nd = 10.5) of butyloctylmagnesium at 0.11 mol / l in MCH is introduced into the 750 ml bottle containing MCH. To replenish the gaseous mixture, a mixture of ethylene monomer 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 and then 5.52 bar of ethylene into the ballast. A 6 bar absolute mixture containing 92 mol% ethylene and 8 mol% 1,3-butadiene is obtained (ethylene / butadiene mixture: 92 / 8). The ballast is connected to the polymerization reactor. To activate the metallocene and form the catalyst system, approximately one-third of solution C is transferred by cannula to the 250 ml bottle containing the metallocene. Half of solution C is introduced into the reactor with stirring (at 400 rpm) and brought to 77 °C, but the reactor is placed under an inert atmosphere beforehand. The contents of the 250 ml bottle containing the catalyst system are introduced into the reactor. Then the remainder of solution C is transferred to the reactor. The reactor is degassed under vacuum until bubbles are formed and then pressurized to 3 bar with the ethylene / butadiene mixture: 92 / 8. When the pressure drop corresponding to the monomer with a ballast pressure of 12.7 g is recorded, the reactor is degassed using three evacuation / nitrogen cycles. Solution A containing 4-vinylpyridine is introduced into the reactor. Stirring is maintained for 1 hour, then the heating switch is turned off and stirring is stopped. The reactor is disassembled, and the polymerization medium is deactivated with 2 ml of ethanol to stop the polymerization reaction. Then, it is transferred to an aluminum tray and dried in an oven at 60 °C under vacuum for 24 hours. The recovered polymer is white and opaque. After 24 hours, the dry polymer is recovered for analysis. The block polymer is a diblock containing a first block of a statistical copolymer of ethylene and 1,3-butadiene and a second block of poly(4-vinylpyridine).

[0038] The first block of the block polymer contains 91 mol% ethylene units, 6 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, mainly in the 1,4-trans configuration. The second block of poly(4-vinylpyridine) represents 0.5 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-trans configuration. DOSY NMR analysis shows the diffusion coefficient corresponding to the block polymer EBR-b-PVP. The block polymer analyzed by HT-SEC has a number average molar mass of 12500 g / mol and a dispersity index of 1.88.

[0039] (Example 2) Preparation of the block polymer according to the present invention: The block polymer is prepared according to the same procedure as in Example 1, and the only difference is 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, mainly in the 1,4-trans configuration. The molar content 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, mainly in the 1,4-trans configuration.

[0040] The block polymer analyzed by HT-SEC has a number average molar mass of 12,000 g / mol and a dispersity index of 1.9. The weighed mass of the block polymer makes it possible to determine the average catalytic activity of the catalyst system, expressed in kilograms of polymer synthesized per mole of neodymium metal and per hour (kg / mol·h). The catalytic activity is 214 kg·mol / h. The Tg of the polyvinylpyridine block is 160 °C. The crystallinity of the block polymer is 36.8%.

[0041] (Example 3) Preparation of a statistical ethylene-1,3-butadiene copolymer not according to the present invention: The polymer is prepared according to the same procedure as in Examples 1 and 2, except that the vinylpyridine solution is not added after the copolymerization of ethylene and 1,3-butadiene. When the pressure drop corresponding to 12.7 g of monomer is recorded for the ballast pressure, the reactor is degassed using three evacuation / nitrogen cycles and the mixing is stopped with 2 ml of ethanol. The polymer solution is then dried in an oven under vacuum at 60 °C for 24 hours under nitrogen flushing. The weighed mass of the copolymer makes it possible to determine the average catalytic activity of the catalyst system, expressed in kilograms of polymer synthesized per mole of neodymium metal and per hour (kg / mol·h). The catalytic activity is 191 kg / mol·h. HT-SEC analysis of the copolymer shows a unimodal molecular distribution and an Mn of 11,800 g / mol with a dispersity of 1.87. The copolymer of ethylene and 1,3-butadiene contains 91 mol% ethylene units, 6 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. The Tg of the copolymer of ethylene and 1,3-butadiene is -21 °C. The DSC thermogram shows an endothermic phenomenon when passing through the same transition temperature (-21 °C) as those of Example 1 and Example 2. Example 3 is a control example since it corresponds to the synthesis of the first block of Examples 1 and 2.

[0042] Preparation of a lubricating composition containing base oil 600: Lubricating compositions C0, C1, and C2 are prepared according to the following procedure: 1 g of the polymer is introduced into a 250 ml stainless steel bottle containing 200 g of CORE™ 600 Group I mineral base oil. The stainless steel bottle is capped and stirred in a thermostatic bath controlled 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 of Example 1; for composition C2, the polymer is the block polymer of Example 2; for composition C0, the polymer is an OCP sold under the reference name 7077 by Lubrizol, which is a copolymer of ethylene and propylene containing approximately 50 mol% ethylene. Composition C0 containing base oil 600 is a reference composition since it contains a copolymer from Lubrizol, copolymer 7077, an additive commonly used as a high-temperature (100 °C) thickener in engine oils. Base oil Core™ 600 sold by Exxon is a Group I mineral base oil and is commonly used as a base oil in engine oils. The kinematic viscosity of the lubricating composition at 100 °C is measured according to standard ASTM 445-21. The viscosity results are presented in Table 1, expressed relatively to the control with a reference of 100. The control consists of the same base oil used in the lubricating composition.

[0043]

Table 1

[0044] It is observed that the lubricating composition containing the block polymer (C1; C2) according to the present invention has a higher viscosity at 100 °C than that of the base oil containing (T1). The viscosities of lubricating compositions C1 and C2 are higher than those of the reference composition C0. This result is obtained even if the copolymer according to the present invention has a much lower number average molar mass than that of the OCP copolymer. Surprisingly, the block polymer according to the present invention has been found to be effective as an OCP copolymer as a high-temperature thickener for mineral base oils.

Claims

1. A block polymer comprising a first block and a second block, wherein the first block is a copolymer of 1,3-butadiene and ethylene, containing more than 90 mol% and less than 97 mol% of the total number of repeating units of the first block, the mole percentage being expressed relative to the total number of repeating units of the first block, and the second block is a homopolymer of vinylpyridine.

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

3. The block polymer according to claim 1, wherein the block polymer is a diblock.

4. The block polymer according to claim 1, wherein the first block contains a 1,2-cyclohexanediyl subunit.

5. The block polymer according to claim 4, wherein the molar content of 1,2-cyclohexanediyl subunits in the first block is less than 10% of the total number of constituent repeating units in the first block.

6. The block polymer according to claim 4, 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 repeating units constituting the first block.

7. The block polymer according to claim 1, wherein vinylpyridine is 4-vinylpyridine, 2-vinylpyridine, or a mixture thereof.

8. The block polymer according to claim 1, wherein the molar content of vinylpyridine units present in the second block is greater than 0.1% of the total number of constituent repeating units in the first block and less than 20% of the total number of constituent repeating units in the first block.

9. A lubricating composition comprising a mineral-based oil and a block polymer according to any one of claims 1 to 8.

10. The lubricating composition according to claim 9, wherein the mineral base oil is a group I base oil.