Polyalkyl (meth) acrylate polymers as high viscosity base fluids

Abstract

The present invention relates to poly alkyl (meth) acrylate polymers and methods of making these polymers. The invention also relates to a lubricating oil composition containing the polymer, and application of the polymer in the lubricating oil composition. The present invention relates to the use as a lubricant additive or as a synthetic base fluid in gear oil compositions, transmission oil compositions, hydraulic oil compositions, engine oil compositions, marine oil compositions, industrial lubricating oil compositions or in greases.

Description

Technical Field

[0001] This invention relates to poly(meth)acrylate alkyl ester polymers and methods for preparing these polymers. The invention also relates to lubricating oil compositions comprising the aforementioned polymers, and the use of said polymers as lubricant additives or synthetic base fluids to be added to lubricating oil compositions, preferably in gear oil compositions, transmission oil compositions, hydraulic oil compositions, engine oil compositions, marine oil compositions, industrial lubricating oil compositions, or in greases. Background Technology

[0002] This invention relates to the field of lubrication. A lubricant is a composition that reduces friction between surfaces. In addition to allowing freedom of movement between two surfaces and reducing mechanical wear, a lubricant can also inhibit surface corrosion and / or inhibit damage to the surface due to heat or oxidation. Examples of lubricant compositions include, but are not limited to, engine oils, transmission fluids, gear oils, industrial lubricants, greases, and metalworking fluids.

[0003] Lubricants typically contain a base fluid and a variable amount of additives. The terms "base oil," "base compound," or "base fluid" are generally used interchangeably. Here, "base fluid" is used as a general term.

[0004] High-viscosity base fluids are used to increase the viscosity index (VI) and thicken lubricant formulations with stringent shear stability requirements. A typical application is gear oils, which have very demanding requirements due to the high mechanical stress and wide temperature range during operation.

[0005] Depending on the intended use of the lubricant, various additives can be combined with the base fluid. Examples of lubricant additives include, but are not limited to, viscosity index improvers, thickeners, pour point depressants, oxidation inhibitors, corrosion inhibitors, dispersants, high-pressure additives, defoamers, and metal deactivators.

[0006] The most common thickener used in mineral oil-based industrial gear oils is bright stock. Bright stock is a product of technologically obsolete Group I base oil refineries, so its future supply is uncertain. Replacing it with an alternative thickener is difficult because typical polyolefin thickeners such as polyisobutylene (PIB), olefin copolymers (OCP), and polyalphaolefins (PAO) are highly nonpolar, leading to compatibility issues (LUBES'N'GREASES (2015) 4, pp. 52-60; LUBES'N'GREASES (2021) 11, pp. 24-29; LUBES'N'GREASES (2022) 4, pp. 35-38). Bright stock also has a limited viscosity, so higher ISO viscosity grades such as 680 or 1000 require stronger thickeners in combination with bright stock.

[0007] Alternatively, thickeners with higher polarity can be used. The advantage of these high-polarity base fluids is that they do not require the addition of non-polar, low-viscosity fluids, such as esters or highly alkylated naphthalenes, as compatibilizers for polar lubricant additives. Furthermore, high-polarity fluids generally do not cause coating and sealing problems compared to low-polarity fluids. Such high-polarity thickeners are, for example, copolymers of α-olefins with maleic esters (e.g., DE3223694), copolymers of α-olefins with acrylates (e.g., DE2243064 or EP4015604), copolymers of α-olefins with methacrylates (e.g., EP0471266), or terpolymers based on the aforementioned monomers (e.g., WO2020078770).

[0008] Alternatively, oil-compatible polyesters (e.g., WO0146350 or WO2022003087), polyvinyl ether (US20130165360), polyacrylates (e.g., EP4073210) or poly(meth)acrylates (PAMA) can be used.

[0009] More specifically, poly(meth)acrylate alkyl ester base fluids (PAMA base fluids) are primarily used as and designed as thickeners in synthetic or semi-synthetic formulations with very high performance, exhibiting performance parameters similar to those of polyalphaolefin base fluids (PAO base fluids). PAMA base fluids are typically used in the most demanding applications, such as wind turbine gear oils. Document US9,617,495 discloses poly(meth)acrylate alkyl esters for use in lubricants with high viscosity index and good anti-wear properties, particularly in wind turbine transmissions. To achieve this intended use, the poly(meth)acrylate alkyl ester polymer disclosed in US9,617,495 uses linear and branched (meth)acrylate C6-C containing 50 to 100% by weight. 15 Preparation of a monomer mixture of alkyl esters, wherein the monomers are based on (meth)acrylic acid C6-C. 15 The total weight percentage of branched (meth)acrylate alkyl esters is 5 to 80% by weight, preferably 10 to 65% by weight. All embodiments are based on a careful balance of linear and branched monomers to provide a high viscosity index (VI) while preventing crystallization at low temperatures. The transmission lubricant is described as containing at least 30% by weight of poly(meth)acrylate alkyl esters, which is a very high treatment rate. However, for less demanding applications, the high dosage of PAMA required to achieve viscosity measurement performance makes them less attractive compared to polyolefins such as PIB.

[0010] As is well known, monomers with aromatic or non-aromatic alicyclic side chains provide high glass transition temperature properties to the polymers they are incorporated into, and are therefore commonly used in polymers for optical components, resins, adhesives or coatings (Ullmann's Encyclopedia of Industrial Chemistry, 2013 edition, page 3, chapter "Polymethacrylates"; CN115894822A; WO2022033945A1).

[0011] JP2021017559 relates to copolymers prepared from mixtures of monomers having cyclic chains (Formulas 1 to 5) and branched (meth)acrylate monomers (Formula 6), and their use as additives in lubricating oil compositions. These lubricating oil additives are described to exhibit good properties in terms of thick oil film formation capability and wear resistance. The provided examples were prepared in Yubase 3 and 4 API Group III base oils having kinematic viscosities up to 4 mm² / s at 100°C, and the lubricating oil compositions all have a target kinematic viscosity of 5.4 mm² / s at 100°C. Due to their low viscosity, such thin gear oil formulations require additional measures to protect the surface from damage. One concept is to form a viscous film on the surface, as described in JP2021017559. These film-forming agents ideally have little effect on the bulk viscosity of the formulation to avoid unnecessary thickening, which limits the amount of additive or necessitates the use of a thinner base oil for the formulation.

[0012] WO2016188839 relates to additives for diesel engine fuels, wherein the additives are made of bicyclic (meth)acrylates (e.g., IBOMA) and C8-C 24 A copolymer prepared from (meth)acrylate and optionally at least one aromatic vinyl monomer and / or other olefinic unsaturated monomers. The copolymer has a weight-average molecular weight of more than 400,000 Daltons and at most 50,000,000 Daltons, and is used as an additive package for fuels.

[0013] There remains a need for highly shear-stable polymeric synthetic base fluid or lubricating oil polymeric additives that positively influence oil solubility and component solubility. Furthermore, this new polymer should be able to thicken oil to the desired viscosity even at low dosages. When used in lubricating oil compositions, the polymer should exhibit good viscosity measurement properties, including low-temperature and viscosity index properties, to mitigate the effect of viscosity changes with temperature. Summary of the Invention Invention Overview

[0015] Surprisingly, it has been found that poly(meth)acrylate alkyl ester polymers containing a certain amount of the alicyclic methacrylate monomer unit (a) as defined in claim 1 can meet the viscosity measurement performance targets of industrial gear oils at dosages close to those of simple, well-known polyolefins (e.g., ethylene-propylene copolymers or polyisobutylene) commonly used in the lubricant market. Furthermore, they possess the advantage of polar, high-viscosity base fluids, such as the compatibility of the additive with the base fluid, which allows for the complete or partial replacement of bright oils in formulations.

[0016] Therefore, the first aspect of the present invention is the poly(meth)acrylate alkyl polymer as defined in claim 1 and its dependent claims.

[0017] A second aspect of the invention is a method for preparing a poly(meth)acrylate alkyl polymer according to the invention.

[0018] A third aspect of the invention is a lubricating oil composition comprising at least one base oil and at least one poly(meth)acrylate alkyl polymer according to the invention.

[0019] A fourth aspect of the invention is a method for thickening a lubricating oil composition by adding a poly(meth)acrylate alkyl polymer according to the invention as a lubricant additive or a synthetic base fluid to the lubricating oil composition, preferably a gear oil composition, transmission oil composition, hydraulic oil composition, engine oil composition, marine oil composition, industrial lubricating oil composition, or grease. Invention Details

[0021] Polymers according to the present invention

[0022] This invention relates to a poly(meth)acrylate alkyl ester polymer, which can be obtained by polymerizing a monomer composition comprising the following monomers:

[0023] a) Based on the total weight of the monomer composition, at least 10% by weight of monomer a), which is selected from alkyl methacrylates of formula (I) or mixtures thereof.

[0024]

[0025] Where R 1 It is a substituted or unsubstituted alicyclic group.

[0026] b) Based on the total weight of the monomer composition, 0 to 90% by weight of monomer b), which is selected from alkyl methacrylates of formula (II) or mixtures thereof.

[0027]

[0028] Where R2 It is a branched alkyl group having 8 to 10 carbon atoms, and wherein, based on the total amount of methacrylate monomers (b) of formula (II), 80% to 100% by weight of R 2 The group is branched.

[0029] c) Based on the total weight of the monomer composition, 0 to 90% by weight of monomer c), which is selected from alkyl methacrylate monomers of formula (III) or mixtures thereof.

[0030]

[0031] Where R 3 It is a straight-chain or branched alkyl group having 11 to 30 carbon atoms.

[0032] Wherein, based on the total weight of the monomer composition, the total amount of monomers a), b), and c) is 90% by weight or more, and

[0033] The alkyl chain R of monomers a), b) and c) in the monomer composition thereof 1 R 2 and R 3 The average number of carbon atoms is 7 to 10.2.

[0034] The poly(meth)acrylate polymer described therein has a weight-average molecular weight of 5,000 to 30,000 g / mol according to DIN 55672-1.

[0035] In this invention, the term "alkyl methacrylate" refers to an ester of methacrylic acid, and the term "alkyl acrylate" refers to an ester of acrylic acid. The term "(meth)acrylate" refers to an ester of acrylic acid, an ester of methacrylic acid, or a mixture of an ester of acrylic acid and an ester of methacrylic acid.

[0036] Within the meaning of this invention, monomer composition refers to monomers used to prepare polymers according to the invention (excluding other reactants, such as initiators and chain transfer agents).

[0037] Within the meaning of this invention, the term "alkyl chain R of monomers a), b) and c) in a monomer composition" refers to... 1 R 2 and R 3 The "average carbon number" corresponds to the average carbon number of the alkyl chain of monomer a) and optionally monomer b) and / or monomer c) (when also present in the monomer composition).

[0038] According to a preferred aspect of the invention, the poly(meth)acrylate polymer has a strength of 3,000 to 50,000 mm at 100°C as per ASTM D445. 2The kinematic viscosity is 3,000 to 30,000 mm² / s according to ASTM D445 at 100°C. More preferably, the poly(meth)acrylate polymer has a kinematic viscosity of 3,000 to 30,000 mm² / s according to ASTM D445. 2 / s, and more preferably according to ASTM D445 at 100°C 5,000 to 20,000 mm 2 kinematic viscosity / s.

[0039] According to the present invention, the poly(meth)acrylate polymer comprises at least 10% by weight of monomer a) selected from alkyl methacrylates of formula (I) or mixtures thereof, wherein R 1 It is a substituted or unsubstituted alicyclic group. Preferably, based on the total weight of the monomer composition, the poly(meth)acrylate polymer contains 10% to 100% by weight of monomer a), more preferably at least 15% by weight of monomer a), more preferably 15% to 90% by weight, even more preferably 20% to 80% by weight, most preferably 24% to 70% by weight, and most preferably 30% to 70% by weight.

[0040] Preferably, monomer a) is selected from cyclohexyl methacrylate, isobornyl methacrylate, 3,3,5-trimethylcyclohexyl methacrylate, 4-tert-butylcyclohexyl methacrylate, cyclopentyl methacrylate, dicyclopentyl methacrylate, or mixtures thereof. More preferably, monomer a) is selected from cyclohexyl methacrylate, isobornyl methacrylate, 3,3,5-trimethylcyclohexyl methacrylate, dicyclopentyl methacrylate, or mixtures thereof.

[0041] According to the present invention, based on the total weight of the monomer composition, the monomer composition for preparing the poly(meth)acrylate polymer contains 0 to 90% by weight, preferably 0 to 85% by weight, more preferably 0 to 80% by weight, even more preferably 0 to 76% by weight, and most preferably 0 to 70% by weight of monomer b of formula (II).

[0042] Preferably, monomer b) of formula (II) is selected from 2-octyl methacrylate, isooctyl methacrylate, 2-ethylhexyl methacrylate, isononyl methacrylate, 2,6-dimethyl-4-heptyl methacrylate, 2-propylheptyl methacrylate, isodecanyl methacrylate, or mixtures thereof.

[0043] According to another preferred aspect of the invention, the monomer composition for preparing the poly(meth)acrylate polymer may further comprise a methacrylate monomer (c) of formula (III) having a straight-chain or branched alkyl chain with 11 to 30 carbon atoms, preferably a methacrylate monomer (c) having a straight-chain or branched alkyl chain with 11 to 15 carbon atoms, or a mixture thereof. The methacrylate (c) refers to an ester of methacrylic acid with a straight-chain or branched alcohol having 11 to 30 carbon atoms. The term "methacrylic acid with a straight-chain or branched alcohol having 11 to 30 carbon atoms" includes a single methacrylate of an alcohol with a specific length, as well as mixtures of methacrylates of alcohols with different lengths. The most preferred methacrylate (c) is lauryl methacrylate (having C... 12 -C 14 Alkyl methacrylates of straight-chain alkyl groups.

[0044] According to the present invention, based on the total weight of the monomer composition, the monomer composition for preparing the poly(meth)acrylate polymer comprises 0 to 90% by weight of monomer c) of formula (III), preferably 0 to 85% by weight, more preferably 0 to 80% by weight, even more preferably 0 to 76% by weight, and most preferably 0 to 70% by weight of monomer c).

[0045] According to the present invention, based on the total weight of the monomer composition, the monomer composition for preparing the poly(meth)acrylate polymer comprises 90% by weight or more monomers a), b), and c). This means that, based on the total weight of the monomer composition, the total amount of monomer a) and optionally b) and c) (since monomers b) and c) is optional according to the present invention) is at least 90% by weight in the monomer composition. In other words, based on the total weight of the monomer composition, the monomer composition for preparing the poly(meth)acrylate polymer comprises 90 to 100% by weight of monomers a), b), and c). Preferably, based on the total weight of the monomer composition, the total amount of monomers a), b), and c) in the monomer composition is 95% by weight or more. In other words, based on the total weight of the monomer composition, the monomer composition for preparing the poly(meth)acrylate polymer preferably comprises at least 95% by weight of monomers a), optionally b), and c) (since monomers b) and c) are optional according to the present invention). Preferably, based on the total weight of the monomer composition, the monomer composition for preparing the poly(meth)acrylate polymer preferably contains 95 to 100% by weight of monomers a), b) and c).

[0046] According to a preferred aspect of the invention, based on the total weight of the monomer composition, the monomer composition for preparing the poly(meth)acrylate polymer may further comprise monomer d), which is selected from alkyl (meth)acrylates having a straight-chain alkyl chain having 1 to 6 carbon atoms, alkyl acrylates having an alkyl chain having 8 to 18 carbon atoms, or mixtures thereof. Most preferably, monomer d) is selected from methyl methacrylate, methyl acrylate, butyl methacrylate, butyl acrylate, ethyl methacrylate, ethyl acrylate, 2-ethylhexyl acrylate, 2-propylheptyl acrylate, lauryl acrylate, isotridecyl acrylate, octadecyl acrylate, or mixtures thereof.

[0047] Preferably, based on the total weight of the monomer composition, the monomer composition for preparing the poly(meth)acrylate polymer contains 0 to 5% by weight, more preferably 0 to 3% by weight of monomer d).

[0048] According to a preferred aspect of the invention, based on the total weight of the monomer composition, the total amount of monomers a), b), c), and d) in the monomer composition for preparing the poly(meth)acrylate polymer is at least 95% by weight, more preferably 100% by weight. When the total amount of monomers a), b), c), and d) in the monomer composition for preparing the poly(meth)acrylate polymer is 100% by weight, it means that the monomer composition for preparing the poly(meth)acrylate polymer consists of monomer a) and optionally a mixture of monomers b), c), and d).

[0049] According to the present invention, the monomers present in the monomer composition are monomers a) and optionally b) and / or c) with alkyl chains R 1 R 2 and R 3 The average number of carbon atoms is 7 to 10.2, preferably 7 to 10, and more preferably 7.5 to 10.

[0050] According to the present invention, the poly(meth)acrylate polymer has a weight-average molecular weight of 5,000 to 30,000 g / mol, preferably 10,000 to 25,000 g / mol, and more preferably 12,000 to 20,000 g / mol, according to DIN 55672-1.

[0051] In this invention, the weight-average molecular weight (M) of the copolymer w ) or number-average molecular weight (M n The determination was performed by gel permeation chromatography (GPC) using PMMA calibration standards, according to DIN 55672-1, under the following measurement conditions:

[0052] Eluent: Tetrahydrofuran (THF)

[0053] Operating temperature: 35℃

[0054] Columns: The column group consists of four columns: two SDV 106 Å, one SDV 104 Å, and one SDV 103 Å (PSS Standards Service GmbH, Mainz, Germany), all with dimensions of 300 × 8 mm and an average particle size of 10 µm.

[0055] Flow rate: 1 mL / min

[0056] Injection volume: 100 μL

[0057] Instrument: Agilent 1100 series, consisting of an autosampler, pump, and column oven.

[0058] Detection device: A refractive index detector from the Agilent 1100 series.

[0059] Preferably, the polymers of the present invention have very low crosslinking degree and narrow molecular weight distribution, which further contributes to shear resistance. Low crosslinking degree and narrow molecular weight are reflected in the polydispersity index (PDI) of the poly(meth)acrylate polymers. Preferably, the polydispersity index (PDI) of the copolymers according to the present invention is in the range of 1.0 to 3.0, more preferably in the range of 1.5 to 2.8. The polydispersity index is defined as the ratio of weight-average molecular weight to number-average molecular weight (Mi). w / M n ).

[0060] According to the present invention, the poly(meth)acrylate alkyl ester polymer is an amorphous statistical polymer in which monomer units a) and optionally monomers b) and / or c) and / or d) are randomly and sometimes unevenly distributed in the polymer.

[0061] The method for preparing the poly(meth)acrylate polymer of the present invention

[0062] According to the present invention, the above polymer is prepared according to a method comprising the following steps:

[0063] i) Provide the monomer composition as described above; and

[0064] ii) Initiate free radical polymerization in the monomer composition.

[0065] Alkyl poly(meth)acrylates can preferably be obtained by free radical polymerization. Therefore, the weight proportion of the respective repeating units in these polymers is calculated from the weight proportion of the respective monomers used to prepare the polymer.

[0066] The preparation of poly(meth)acrylates from the above compositions is known per se. For example, these polymers can be obtained, in particular, by free radical polymerization and related methods such as ATRP (atom transfer radical polymerization) or RAFT (reversible addition schisis chain transfer).

[0067] A review of these methods is given in K. Matyjaszewski, TP Davis, Handbook of Radical Polymerization, Wiley Interscience, Hoboken 2002, with further specific references, which are explicitly referenced for the purposes of this disclosure.

[0068] The free radical polymerization of olefinic unsaturated compounds can be achieved in ways known per se. Conventional free radical polymerization is described in particular in Ullmann's Encyclopedia of Industrial Chemistry, sixth edition.

[0069] In this invention, polymerization is initiated using at least one polymerization initiator for free radical polymerization. These include azo initiators widely known in the art, such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylpentanonitrile), and 1,1-azobiscyclohexanecarboxynitrile, organic peroxides such as dicumyl peroxide, diacyl peroxides such as dilauroyl peroxide, peroxydicarbonates such as diisopropyl peroxydicarbonate, peresters such as tert-butyl peroxy-2-ethylhexanoate, etc.

[0070] According to the present invention, a polymerization initiator with a half-life of 1 hour is particularly preferred at temperatures ranging from 25°C to 200°C, preferably from 50°C to 150°C, and especially from 50°C to 100°C. A particularly preferred polymerization initiator is a peroxide-type polymerization initiator, more preferably tert-butyl peroxy-2-ethylhexanoate.

[0071] In a preferred method, the at least one polymerization initiator for free radical polymerization is preferably added in one step, more preferably in multiple addition steps, even more preferably in at least two addition steps, and most preferably in three addition steps. The polymerization initiator can preferably be added all at once in each addition step. More preferably, the polymerization initiator can be metered in each addition step, and even more preferably metered continuously, particularly at a constant metering rate.

[0072] The polymerization initiator may be added in each step in undiluted or diluted form, preferably dissolved in a solvent, especially in the form of a 10% to 50% solution of at least one mineral oil, polyalphaolefin and / or feed monomer, more preferably in monomer a), monomer b), monomer c), monomer d) or mixtures thereof.

[0073] For the purposes of this invention, it has been found particularly suitable to add the polymerization initiator in all three steps, in which case the amount of initiator added in the third step is greater than the amount of initiator added in the first and second steps. More preferably, based on the total weight of the polymerization initiator added in the second step, the amount of polymerization initiator added in the third step is greater than the amount added in the second step. More preferably, based on the total weight of the polymerization initiator added in the second step, the amount of polymerization initiator added in the third step is at least 120% by weight, more preferably from 120% by weight to 1000% by weight, and most preferably from 150% by weight to 500% by weight.

[0074] In the third step, the polymerization initiator is suitably added all at once. Alternatively, it is also preferable to add the polymerization initiator metered in the third step, preferably continuously metered, especially at a constant metering rate. In a very particularly preferred embodiment of the invention, the polymerization initiator is metered continuously in the first, second, and third steps, advantageously at a constant metering rate in each case, with the average metering rate of the third step preferably greater than that of the second step, and the average metering rate of the second step preferably greater than that of the first step. The ratio of the average metering rate of the third step to the average metering rate of the second step is preferably greater than 1.2:1, preferably in the range of 1.2:1 to 10:1, more preferably greater than 1.5:1, even more preferably greater than 2:1, and especially greater than 3:1.

[0075] The third step is preferably started when 0.01 to 50% by weight, more preferably 10 to 40% by weight, and even more preferably 15 to 35% by weight of the total amount of polymerization initiator added in the second step has been consumed.

[0076] The method detailed above enables rapid and highly efficient polymerization of olefinic unsaturated compounds, yielding polymers with relatively low residual monomer content. Nevertheless, it has been found highly advantageous to provide further initiation near the end of the reaction to further reduce the residual monomer content of the reaction mixture. Preferably, at least 75% by weight, suitably at least 90% by weight, of the total amount of polymerization initiator added during the final step is provided for further initiation, especially when at least 95% by weight has been consumed. Preferably, an additional 5% to 100% by weight of polymerization initiator is added, based on the total amount of polymerization initiator previously added.

[0077] Based on the total weight of the monomers (i.e., the total weight of the monomer composition), the total amount of the initiator is preferably in the range of 0.5 to 1% by weight, more preferably in the range of 0.6 to 0.8% by weight.

[0078] This method can be carried out with or without a chain transfer agent. The chain transfer agent used can be a typical class of substances described for free radical polymerization as known to those skilled in the art.

[0079] Sulfur-free chain transfer agents include, for example, and this is not intended to be limiting, dimeric α-methylstyrene (2,4-diphenyl-4-methyl-1-pentene), enol ethers of aliphatic and / or alicyclic aldehydes, terpenes, β-terpinene, terpinene oil, 1,4-cyclohexadiene, 1,4-dihydronaphthalene, 1,4,5,8-tetrahydronaphthalene, 2,5-dihydrofuran, 2,5-dimethylfuran and / or 3,6-dihydro-2H-pyran, with dimeric α-methylstyrene being preferred.

[0080] The sulfur-containing chain transfer agent used is preferably a mercapto compound, a dialkyl sulfide, a dialkyl disulfide, and / or a diaryl sulfide. Examples of chain transfer agents include: di-n-butyl sulfide, di-n-octyl sulfide, diphenyl sulfide, thiodiglycol, ethyl thioethanol, diisopropyl disulfide, di-n-butyl disulfide, di-n-hexyl disulfide, diacetyl disulfide, diethanol sulfide, di-tert-butyl trisulfide, and dimethyl sulfoxide. The compounds preferably used as chain transfer agents are mercapto compounds, dialkyl sulfides, dialkyl disulfides, and / or diaryl sulfides. Examples of these compounds are ethyl mercaptoacetate, 2-ethylhexyl mercaptoacetate, pentaerythritol tetramercaptoacetate, cysteine, 2-mercaptoethanol, 1,3-mercaptopropanol, 3-mercaptoprop-1,2-diol, 1,4-mercaptobutanol, mercaptoacetic acid, 3-mercaptopropionic acid, thioglycolic acid, mercaptosuccinic acid, thioglycerol, thioacetic acid, thiourea, and alkyl thiols, such as n-butylthiol, n-hexylthiol, tert-dodecylthiol, or n-dodecylthiol. Particularly preferred polymerization modifiers are mercapto alcohols and mercaptocarboxylic acids. In the context of this invention, n-dodecylthiol and tert-dodecylthiol are very particularly preferred as chain transfer agents.

[0081] In one particular aspect of the invention, a mixture of chain transfer agents may be used, preferably including sulfur-containing chain transfer agents (such as the aforementioned thiols derivatives) and sulfur-free chain transfer agents (such as terpinene, terpinene and their derivatives), as well as suitable transition metal complexes. More preferably, the chain transfer agent is selected from n-dodecyl mercaptan, tert-dodecyl mercaptan, terpinene or mixtures thereof.

[0082] Based on the total weight of the monomers used in the polymerization (i.e., the total weight of the monomer composition), the chain transfer agent is preferably used in an amount of 0.05 to 10% by weight, especially 1 to 6% by weight, more preferably 2 to 4.5% by weight.

[0083] Further information can be found in the professional literature, especially in publications such as H. Rausch-Puntigam, T. Völker “Acryl- und Methacrylverbindungen” [Acrylic and Methacrylic Compounds] Springer, Heidelberg, 1967; Houben-Weyl “Methoden der organischenChemie” [Organic Chemical Methods] Vol. XIV / 1, p. 66 and subsequent pages, Georg Thieme, Heidelberg, 1961; and Kirk-Othmer “Encyclopedia of Chemical Technology”, Vol. 1, p. 296 and subsequent pages, J. Wiley, New York, 1978.

[0084] Of particular interest are methods in which the majority of the monomer is initially charged and the polymerization initiator is added in multiple steps during the polymerization time, as explained above. Preferably, at least 50% by weight of the monomer can be initially charged into the reactor, especially at least 60% by weight, more preferably at least 80% by weight, and most preferably at least 90% by weight. Subsequently, the aforementioned initiator can be added at the polymerization temperature. The chain transfer agent can be initially charged or added together with the initiator, with the chain transfer agent initially charged in the preferred method. Particularly preferred here is the method in which at least 50% by weight of the total weight of the chain transfer agent is initially charged into the reactor, especially at least 60% by weight, more preferably at least 80% by weight, and most preferably at least 90% by weight.

[0085] The polymerization can be carried out under standard pressure, reduced pressure, or increased pressure. The polymerization temperature is not critical. However, it is generally within the range of 20 to 200°C, preferably 20 to 180°C, and more preferably 60 to 150°C. In the case of free radical polymerization, a higher polymerization temperature may be preferred; for example, in the case of stepwise addition of the initiator, the polymerization temperature may preferably be within the range of 20 to 180°C, more preferably 60 to 150°C. Particularly preferred here is a method in which the polymerization is carried out at a temperature 0 to 30°C higher than the reaction temperature (where the half-life of the initiator is 30 minutes).

[0086] The polymerization can be carried out with or without a solvent. The term "solvent" should be interpreted broadly here. Solvents to be used include hydrocarbon solvents, such as aromatic solvents like toluene, benzene, and xylene, and saturated hydrocarbons such as cyclohexane, heptane, octane, nonane, decane, and dodecane, which may also be present in branched form. These solvents can be used alone or as mixtures. Particularly preferred solvents are mineral oils, natural oils, and synthetic oils, and mixtures thereof.

[0087] In a preferred embodiment, the proportion of solvent can be kept low. A preferred embodiment of the method according to the invention is characterized in that, after polymerization, it is not necessary to remove the solvent from the composition, for example, by distillation, to obtain a usable polymer mixture. Therefore, based on the total weight of the monomer composition, the total amount of solvent used for the polymerization reaction is preferably in the range of 0 to 70% by weight, more preferably 0 to 50% by weight, and even more preferably 0 to 40% by weight.

[0088] The measures detailed above, particularly the stepwise addition of the initiator to a reactor containing a relatively large amount of monomer, offer surprising advantages. One particularly significant advantage is that the reaction can be carried out without any significant amount of solvent. This allows the reaction to proceed very inexpensively. Surprisingly, and more specifically, it allows for the attainment of a very narrow molecular weight distribution at low polydispersity indices without the need for expensive methods such as ATRP. Furthermore, reaction time and initiator consumption can be minimized.

[0089] Lubricating oil composition

[0090] As indicated above, the present invention also relates to a lubricating oil composition comprising at least one base oil and at least one poly(meth)acrylate polymer as defined in the present invention.

[0091] Base oils correspond to lubricant base oils, namely mineral oils, synthetic oils or natural oils, animal oils or vegetable oils, which are suitable for their use / selected according to the intended use.

[0092] Base oils used to formulate lubricating oil compositions according to the present invention include, for example, conventional base oils selected from the API (American Petroleum Institute) base oil categories known as Group I, Group II, Group III, Group IV, and Group V. Group I and Group II base oils are mineral oil materials (e.g., alkane oils and cycloalkane oils) with a viscosity index (or VI) of less than 120. A further distinction between Group I and Group II is that Group II contains more than 90% saturated material, while Group I contains less than 90% saturated material (i.e., more than 10% unsaturated material). Group III is considered to be the highest level of mineral base oil having a VI of greater than or equal to 120 and a saturation level of greater than or equal to 90%. Group IV base oils are polyalphaolefins (PAOs). Group V base oils are esters and any other base oils not included in Groups I through IV. These base oils can be used alone or as mixtures.

[0093] Preferably, the base oil included in the lubricating oil composition of the present invention is selected from the mineral oil group consisting of API Group I base oils, API Group II base oils, API Group III base oils, or mixtures thereof. Most preferably, the lubricant composition comprises API Group I base oils, API Group II base oils, or mixtures thereof.

[0094] According to a preferred embodiment of the invention, the lubricating oil composition comprises at least one component with a kinematic viscosity of 6 mmHg at 100°C according to ASTM D445. 2 / s or higher of base oils selected from API Group I base oils, API Group II base oils or mixtures thereof, and at least one poly(meth)acrylate polymer as defined in this invention.

[0095] Preferably, based on the total weight of the lubricating oil composition, the lubricating oil composition contains 5 to 50% by weight, more preferably 5 to 40% by weight, and even more preferably 5 to 25% by weight of the poly(meth)acrylate polymer according to the invention.

[0096] Preferably, based on the total weight of the lubricating oil composition, the lubricating oil composition according to the invention comprises 50 to 95% by weight, more preferably 60 to 95% by weight, and even more preferably 75 to 95% by weight of base oil.

[0097] All the preferred aspects of the polymer, base oil, and quantity listed above apply to this lubricant composition.

[0098] The lubricating oil composition according to the invention may also contain any other additional additives suitable for the formulation. These additives include additional viscosity index improvers, pour point depressants, dispersants, demulsifiers, defoamers, lubricating additives, friction improvers, antioxidants, detergents, dyes, corrosion inhibitors, and / or odorants.

[0099] According to a preferred aspect of the invention, the total content of poly(meth)acrylate and base oil in the lubricant composition is 90% by weight or more, or 95% by weight or more, based on the total weight of the lubricant composition.

[0100] Application of the poly(meth)acrylate polymer of the present invention

[0101] The present invention also relates to the use of the poly(meth)acrylate alkyl polymer according to the invention as defined herein as a lubricant additive or a synthetic base fluid, which is carried out by adding the poly(meth)acrylate alkyl polymer to a lubricating oil composition.

[0102] Preferably, the lubricating oil composition is a gear oil composition, a transmission oil composition, a hydraulic oil composition, an engine oil composition, a marine oil composition, an industrial lubricating oil composition, or a grease.

[0103] The present invention also relates to a method for thickening a lubricating oil composition by adding a poly(meth)acrylate alkyl polymer according to the invention as a lubricant additive or a synthetic base fluid to the lubricating oil composition.

[0104] Therefore, the present invention relates to a method for optimizing the rheological properties of a lubricating oil composition by adding a poly(meth)acrylate alkyl polymer according to the present invention as a lubricant additive or a synthetic base fluid to the lubricating oil composition.

[0105] In the experimental section, examples demonstrate that even at low dosages, the poly(meth)acrylate alkyl polymer according to the invention provides excellent thickening effects when added to lubricating oil compositions while maintaining good shear stability. Furthermore, when used in lubricating oil compositions, this polymer exhibits good viscosity measurement properties, including low-temperature and viscosity index properties, effectively reducing viscosity variations with temperature. This polymeric additive also has a positive impact on component solubility due to its chemical structure.

[0106] Experimental Section

[0107] The invention is further illustrated in detail below with reference to embodiments and comparative examples, but is not intended to limit the scope of the invention. All percentages given in the table below with respect to monomers or base fluids are weight percentages (wt%).

[0108] Abbreviation

[0109] AP / E Core TM 2500 KV100 from ExxonMobil is a base material with a flow rate of ~31.5 mm² / s.

[0110] Average C#: Average number of carbon atoms in the alkyl groups of monomers a), b), and c).

[0111] BV Bulk Viscosity

[0112] BV100 bulk viscosity at 100°C according to ASTM D445

[0113] Chevron 600R uses Group II base oil with a KV100 of 12 mm² / s from Chevron.

[0114] CHMA cyclohexyl methacrylate

[0115] cSt corresponds to centistokes per second in SI units of mm² / s.

[0116] cP corresponds to mPa in SI units. . s centipoise

[0117] DDM dodecyl mercaptan

[0118] EHA 2-Ethylhexyl Acrylate

[0119] EHMA 2-Ethylhexyl Methacrylate

[0120] HiTEC ® 307 is available in additive packages from Afton Chemical.

[0121] IBOMA isobornyl methacrylate

[0122] Ini initiator

[0123] IDMA isodecyl methacrylate (89.9% by weight C) 10 Alkyl chain; the proportion of branched alkyl chain is 98% by weight)

[0124] ISO (International Organization for Standardization)

[0125] KRL's tapered roller bearing shear stability test according to CEC L-45-A-99

[0126] KV kinematic viscosity as measured by ASTM D445

[0127] KV40 kinematic viscosity measured at 40°C according to ASTM D445.

[0128] KV100 kinematic viscosity measured at 100°C according to ASTM D445.

[0129] LIMA is an alkyl methacrylate with 12 to 15 carbon atoms in the alkyl side chain (based on LIAL 125 alcohol available from Sasol; branched alkyl chain percentage is 60% by weight).

[0130] LMA lauryl methacrylate (73% by weight C) 12 27% by weight C 14 (All are straight links)

[0131] MMA (methyl methacrylate)

[0132] M n Number average molecular weight

[0133] M w weight average molecular weight

[0134] nm not measured

[0135] PDI (Polydispersity Index)

[0136] PHMA (Propylheptyl Methacrylate)

[0137] PP Pour Point

[0138] PPD (Pour Point Depressant)

[0139] Shear loss of SL40 measured at 40°C after running at KRL (for 20 hours at 60°C)

[0140] TDDM tert-dodecyl mercaptan

[0141] TMCHMA Trimethylcyclohexyl methacrylate

[0142] VG viscosity grade

[0143] VI Viscosity Index

[0144] VPL 1-325 Evonik VISCOPLEX ® 1-325, Pour Point Depressant for Alkyl Polymethacrylate

[0145] Test methods

[0146] KV ASTM D445

[0147] VI ASTM D2270

[0148] KRL CEC L-45-A-99

[0149] PP ASTM D5950

[0150] Example

[0151] Procedure A for preparing the polymer in Example 1

[0152] Initially, monomers as defined in Table 1 were loaded into a round-bottom flask equipped with a glass stirrer, nitrogen inlet, thermometer, and reflux condenser. For Example Ex.1 of the present invention, 344.3 g of EHMA, 100.0 g of LMA, and 50.0 g of CHMA were loaded into the flask together with 10.00 g (2.0 wt% relative to the total monomers) of dodecyl mercaptan (DDM) and 5.20 g (1.04 wt% relative to the total monomers) of tert-dodecyl mercaptan (TDDM). The mixture was heated to 110°C while stirring and bubbling with nitrogen to inert it. Subsequently, 3.25 g of tert-butyl peroxy-2-ethylhexanoate (0.65 wt% relative to the total monomers) was dissolved in 5.70 g of EHMA. The initiator solution was metered in over 3 hours, with 5 wt% added in the first hour, 25 wt% added in the second hour, and 70 wt% added in the third hour. After the feeding was completed, the mixture was stirred for another hour.

[0153] Embodiments Ex.2 to Ex.10 and Ex.21 to Ex.23 of the present invention, and Comparative Example Ex.1 Ex.2 Ex.4 and Ex.7 Up to Ex.11 Prepared in the same manner as in Example 1 of the present invention, except that the amount of reactants and / or other reaction conditions are changed as listed in Table 1.

[0154] Procedure B for preparing the polymer in Example 11

[0155] For Ex.11, 192.0 g of IDMA and 48.0 g of IBOMA were loaded into a flask along with 58.2 g of Chevron 600R, 4.56 g (1.9 wt% of total monomers) of DDM, and 3.36 g (1.4 wt% of total monomers) of TDDM. The mixture was heated to 110 °C while stirring and bubbling with nitrogen to inertize it. Subsequently, 0.6 g of tert-butyl peroxy-2-ethylhexanoate (0.25 wt% of total monomers) was dissolved in 1.8 g of Chevron 600R. The initiator solution was metered over 3 hours, with 5 wt% added in the first hour, 25 wt% in the second hour, and 70 wt% in the third hour. After the feed was completed, the mixture was stirred for another hour, and then the initiator booster shot (0.48 g of tert-butyl peroxy-2-ethylhexanoate, 0.20 wt% of total monomers) was added. After 3 hours, a second initiator additive (0.48 g of tert-butyl peroxy-2-ethylhexanoate, 0.20% by weight relative to the total monomer content) was added. The mixture was then stirred for another 2 hours.

[0156] Embodiments Ex.12 to Ex.20 and Comparative Example Ex.3 of this invention. Ex.5 and Ex.6 Prepared in a manner similar to that of Example 11 of the present invention, except that the amounts of reactants and / or other reaction conditions are changed as listed in Table 1. For Ex.18 to Ex.20, the initiator is dissolved in the monomer instead of in the oil, and dilution with oil is performed after polymerization.

[0157] Details of the polymer compositions and basic properties of the polymers prepared according to procedures A and B described above are provided in Tables 1 and 2. The majority amount of monomer is always loaded into the flask first. A solution of initiator in the remaining monomer or oil is then fed at 110°C for a set time period. For copolymers using a monomer mixture, all monomers are mixed and loaded into the reactor before the initiator is fed. The amount of chain transfer agent is adjusted as listed in Table 1 to control the molecular weight of the polymer. All polymers are synthesized using 0.65% by weight of initiator relative to the total monomer amount.

[0158] In this invention, the bulk viscosity (BV) of the polymer (the product obtained from the polymerization reaction) corresponds to the kinematic viscosity (KV) of the resulting polymer, measured according to ASTM D445. Therefore, the bulk viscosity (BV100) of the polymer shown in Table 2 below is measured as the kinematic viscosity at 100°C according to ASTM D445. For Examples Ex.11 to Ex.23 of this invention, the polymer is diluted in Chevron 600R oil to simplify polymer handling. Therefore, the bulk viscosity corresponds to the KV100 of the polymer diluted in oil.

[0159] The thickening effect of each polymer in the oil was tested by blending 30% by weight of the polymer into 70% by weight of Chevron 600R base oil (Group II base oil). The kinematic viscosity at 100°C and 40°C was measured according to ASTM D445 and the results are listed in Table 2.

[0160] Then, formulations containing the polymers of the present invention and comparative polymers, as shown in Table 2, were prepared. The composition and properties of the formulations, such as viscosity index, kinematic viscosity, PP, and shear loss, are shown in Tables 3.1 and 3.2, Tables 4 and 5. Formulations were prepared in API Group II base oils with a target KV40 of 320 mm² / s. Examples according to the present invention are listed in Table 3, and comparative examples are listed in Table 4. Table 5 lists formulations for use in API Group II base oils and bright oils (AP / E Core). TM The formulations of the present invention, which target a KV40 of 460 mm² / s in a mixture of 2500, are used in the examples and comparative formulations of the present invention.

[0161] Table 1: Composition of the reaction mixture used to prepare the polymers of the embodiments and comparative examples of the present invention

[0162]

[0163] The polymer was diluted with Group II base oil, relative to the total monomer content of Chevron 600R (in weight %).

[0164] The polymer composition also contains a small amount of MMA (0.21% by weight relative to the total weight of the monomers).

[0165] Table 2: Polymer properties of the embodiments and comparative examples of the present invention

[0166]

[0167] Examples 11 to 23 of this invention have been diluted in Group II base oils (see Table 1).

[0168] "nm" refers to "not measured".

[0169] Table 3.1 The lubricant formulation with approximately 320 mm² / s KV40 according to embodiments of the present invention is used.

[0170]

[0171] Pure polymer dosage (add oil dilution to the total amount of Chevron 600R).

[0172] Table 3.2 : Lubricant formulation with approximately 320 mm² / s KV40 using embodiments of the present invention (continued)

[0173]

[0174] Pure polymer dosage (add oil dilution to the total amount of Chevron 600R).

[0175] Table 4 A comparative lubricant formulation with a KV40 of approximately 320 mm² / s was used.

[0176]

[0177] Table 5 Lubricant formulations with a KV40 of approximately 460 mm² / s were prepared using the present invention and comparative polymer examples.

[0178]

[0179] Pure polymer dosage (add oil dilution to the total amount of Chevron 600R).

[0180] As shown in Table 2 above, unlike the comparative polymers, the polymers according to the invention have very high BV100 values ​​(Ex.1 to Ex.4). This is also reflected in the comparison of thickening in Group II base oils at 30% by weight for each polymer listed in Table 2. The KV40 value is most relevant to thickening power, as viscosity at 40°C defines the ISO class of the fluid. All embodiments of the invention have higher KV40 values ​​than the comparative examples. In particular, embodiments of the invention with a large amount of cyclic comonomers (≥ 50% by weight), such as Ex.10, Ex.14, Ex.15, and Ex.17, exhibited the highest thickening in the example formulations, with KV40 values ​​exceeding 1000 mm² / s.

[0181] When comparing Ex.1 and Ex.7 according to the present invention. Or according to Ex.3 and Ex.8 of the present invention. At that time, the effect of cyclic monomers on thickening power could be observed, where even replacing 10% by weight of EHMA, which already provides high thickening power, with CHMA showed a good increase in the KV40 value. This is similar to the comparison of IDMA / CHMA combinations in Ex.3. Ex.10 When comparing Ex. 7 with Ex. 11 through Ex. 15 for IDMA / IBOMA combinations, this effect is observed to be related to the content of cyclic monomers. Larger side chains allow for the incorporation of more cyclic monomers into the polymer while maintaining solubility in oil (e.g., Ex. 17 with 100% TMCHMA). These results confirm the importance of the alkyl chains R of monomers a), b), and c) in the monomer compositions used to prepare the polymer. 1 R 2 and R 3 The average carbon number must be higher than 7 to maintain solubility in common base oil systems.

[0182] As shown in Tables 3.1 and 3.2 above, the comparative examples shown in Table 4 (for F-1) are as follows. To F-3 Ex.1 2 6 Compared to other formulations, KV40 containing the polymer according to the invention provides a dosage reduction of at least 1.9% to 20.8% by weight for a 320 mm² / s formulation. The dosage can be further reduced by using polymers containing higher amounts of cyclic monomers a). Using the polymer according to the invention, low dosage is achieved while meeting the viscosity measurement performance required in industry (Lubricants and Industrial Oils Industry Standard ISO 12925-1:2018). Advantageously, a small shear loss of less than 5% at 40°C is observed.

[0183] As shown in Table 5, similar observations were obtained for formulations with higher KV40, such as 460 mm² / s, in Group I+II base oil blends. (Comparative Example Ex.1) Ex.3 Ex.6 (F-4) To F-6 Compared to the previous embodiments, Ex.6, Ex.8 and Ex.18 of the present invention have lower dosages (F-15 to F-17).

[0184] In summary, comparative examples based on polymers containing little or no cyclic monomer units exhibit poor thickening efficiency and cannot reduce the dosage to the same level as the polymer examples according to the present invention. Therefore, experimental data confirm that the poly(meth)acrylate alkyl polymers as defined in claim 1, prepared with monomer compositions containing sufficient amounts of cyclic methacrylate monomer a), are crucial for achieving very high thickening and dosage advantages while maintaining good viscosity measurement performance. This effect is even stronger for PAMA-based fluids that do not contain cyclic comonomers, even if they contain significant amounts of branched methacrylates.

Claims

1. A poly(meth)acrylate alkyl ester polymer, which can be obtained by polymerizing a monomer composition comprising the following monomers: a) Based on the total weight of the monomer composition, at least 10% by weight of monomer a), which is selected from alkyl methacrylates of formula (I) or mixtures thereof. Where R 1 It is a substituted or unsubstituted alicyclic group. b) Based on the total weight of the monomer composition, 0 to 90% by weight of monomer b), which is selected from alkyl methacrylates of formula (II) or mixtures thereof. Where R 2 It is a branched alkyl group having 8 to 10 carbon atoms, and wherein, based on the total amount of methacrylate monomers (b) of formula (II), 80% to 100% by weight of R 2 The group is branched. c) Based on the total weight of the monomer composition, 0 to 90% by weight of monomer c), which is selected from alkyl methacrylate monomers of formula (III) or mixtures thereof. Where R 3 It is a straight-chain or branched alkyl group having 11 to 30 carbon atoms. Wherein, based on the total weight of the monomer composition, the total amount of monomers a), b), and c) is 90% by weight or more, and The alkyl chain R of monomers a), b) and c) in the monomer composition thereof 1 R 2 and R 3 The average number of carbon atoms is 7 to 10.

2. The poly(meth)acrylate polymer described therein has a weight-average molecular weight of 5,000 to 30,000 g / mol according to DIN 55672-1.

2. The poly(meth)acrylate alkyl ester polymer according to the preceding claims, wherein the monomer a) is selected from cyclohexyl methacrylate, isobornyl methacrylate, 3,3,5-trimethylcyclohexyl methacrylate, 4-tert-butylcyclohexyl methacrylate, cyclopentyl methacrylate, dicyclopentyl methacrylate, or mixtures thereof.

3. The poly(meth)acrylate alkyl polymer according to any one of the preceding claims, wherein the monomer b) is selected from 2-octyl methacrylate, isooctyl methacrylate, 2-ethylhexyl methacrylate, isononyl methacrylate, 2,6-dimethyl-4-heptyl methacrylate, 2-propylheptyl methacrylate, isodecanyl methacrylate, or mixtures thereof.

4. The poly(meth)acrylate alkyl polymer according to any one of the preceding claims, wherein the monomer c) is a methacrylate alkyl monomer of formula (III) having a straight-chain or branched alkyl chain having 11 to 15 carbon atoms or a mixture thereof.

5. The poly(meth)acrylate polymer according to any one of the preceding claims, wherein the monomer composition comprises at least 15% by weight of monomer a) based on the total weight of the monomer composition.

6. The poly(meth)acrylate polymer according to any one of the preceding claims, wherein the monomer composition comprises 0 to 85% by weight of monomer b, based on the total weight of the monomer composition.

7. The poly(meth)acrylate polymer according to any one of the preceding claims, wherein the monomer composition comprises 0 to 70% by weight of monomer c, based on the total weight of the monomer composition.

8. The poly(meth)acrylate polymer according to any one of the preceding claims, wherein the total amount of monomers a), b) and c) in the monomer composition is 95% by weight or more based on the total weight of the monomer composition.

9. The poly(meth)acrylate polymer according to any one of the preceding claims, wherein the alkyl chains of monomers a), b) and c) are R 1 R 2 and R 3 The average number of carbon atoms is 7 to 10.

10. The poly(meth)acrylate alkyl polymer according to any one of the preceding claims, wherein, based on the total weight of the monomer composition, the monomer composition further comprises monomer d), which is selected from alkyl (meth)acrylates having a straight-chain alkyl chain having 1 to 6 carbon atoms, alkyl acrylates having an alkyl chain having 8 to 18 carbon atoms, or mixtures thereof.

11. The poly(meth)acrylate polymer according to any one of the preceding claims, wherein the poly(meth)acrylate polymer has a weight-average molecular weight of 10,000 to 25,000 g / mol, preferably 12,000 to 20,000 g / mol, according to DIN 55672-1.

12. The poly(meth)acrylate polymer according to any one of the preceding claims, wherein the total amount of monomers a), b), c) and d) in the monomer composition is 100 by weight based on the total weight of the monomer composition.

13. A method for preparing a poly(meth)acrylate polymer according to any one of claims 1 to 12, wherein the method comprises the following steps: i) Providing a monomer composition according to any one of claims 1 to 10 and 12; ii) Initiate free radical polymerization in the monomer composition to obtain the poly(meth)acrylate polymer.

14. A lubricating oil composition comprising one or more base oils and at least one poly(meth)acrylate polymer according to any one of claims 1 to 12.

15. A method for thickening a lubricating oil composition, which is achieved by adding the poly(meth)acrylate polymer according to any one of claims 1 to 12 as a lubricant additive or a synthetic base fluid to the lubricating oil composition.

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