Polymers useful as fatigue life improvers for lubricants

Abstract

To provide a polymer to be used for a lubricant composition for improving fatigue resistance of metallic components in a change gear, an engine or a liquid pressure pump even when the lubricant composition has more excellent low viscosity for fuel economy, to provide a method for manufacturing the polymer, to provide a lubricant composition containing the polymer, and to provide a use of the polymer.SOLUTION: The polymer is a polyalkyl (meth) acrylate (PAMA) which is manufactured by using a monofunctional chain transfer agent (formula(II)) or a polyfunctional chain transfer agent (formula(III)), and has a polar functional group.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to polymers, methods for making such polymers, and lubricating oil compositions containing such polymers. The present invention also relates to the use of the polymers as fatigue life improvers in low viscosity lubricating oils, such as transmission fluids, gear oils, engine oils, or hydraulic oils, where fuel economy is desired. [Background technology]

[0002] The present invention relates to the field of lubrication. A lubricant is a composition that reduces friction between surfaces. In addition to allowing free movement between two surfaces and reducing the mechanical wear of the surfaces, a lubricant can also inhibit corrosion of the surfaces and / or inhibit thermal or oxidative damage to the surfaces. Examples of lubricating oil compositions include, but are not limited to, engine oils, transmission oils, gear oils, industrial lubricants, greases, and metalworking oils.

[0003] A typical lubricating oil composition comprises a base fluid and, optionally, one or more additives. Conventional base fluids are hydrocarbons, such as mineral oils. The terms base oil and base fluid are commonly used interchangeably. Here, base fluid is used as a general term.

[0004] A wide variety of additives may be combined with the base fluid depending on the intended use of the lubricant. Examples of lubricant additives include, but are not limited to, viscosity index improvers, thickeners, antioxidants, corrosion inhibitors, dispersants, extreme pressure additives, antifoam agents, and metal deactivators.

[0005] The greatest current challenge for lubricant manufacturers and original equipment manufacturers (OEMs) in the automotive industry is the ever-increasing fuel economy or fuel economy goal. Despite hardware changes, one approach is to reduce the oil viscosity of the lubricant, thus resulting in thinner lubricant films at high temperatures. The result of this trend is increased levels of damage, especially in transmissions and roller bearings.

[0006] The design of the transmission must ensure that all sliding and rolling contact points, i.e., the gears and roller bearings, are adequately lubricated during all stages of operation. Damage is the result of excessive local stresses and can occur in two ways on the metal surfaces of the transmission, especially on the gears and roller bearings: 1. Wear resulting from the sudden removal of material after friction versus surface wear resulting from continuous surface material removal or scuffing. 2. Fatigue, visible as gray staining (surface fatigue, micropitting) or craters (subsurface fatigue, pitting). This damage is caused by shear stresses in the metal lattice, which cause material to flake off or break off due to cracks that form 20-40µm or 100-500µm below the surface.

[0007] Gray staining (micropitting) begins 20-40 μm below the surface with tiny cracks in the metal lattice. The cracks propagate to the surface and lead to spalling of material visible as gray staining. In the case of transmissions, micropitting occurs preferentially in areas of sliding contact.

[0008] Crater formation is a fatigue damage that can be observed in all speed ranges. The damage begins with a crack in the metal lattice at a depth of 100-500 μm, which propagates to the surface and causes material fracture, resulting in a crater. In gears, the damage occurs preferentially in the center of the tooth flank, and in roller bearings on the raceway.

[0009] WO2009 / 019065 (WO2009 / 019065) describes polyalkyl(meth)acrylates (PAMAs) with polar and non-polar segments that have improved anti-fatigue properties. The polar polymer segments are composed of nitrogen-containing monomer units. WO2009 / 019065 teaches that a block structure, i.e., a concentration of polar groups at one end of the polymer, is superior to polymers with statistical or random distribution of the polar groups.

[0010] JP 2018-16798 describes the use of poly(alkylene glycol)-containing PAMA as a friction modifier. Fatigue behavior is not mentioned. The polymer is produced without any chain transfer agent.

[0011] EP 2514774 A1 and EP 2336206 A1 describe the use of poly(alkylene glycol)-containing PAMA polymers to improve the low-temperature properties of fuel oils. The polymers are produced without the use of any chain transfer agents, and it is noted that sulfur-containing chain transfer agents are particularly undesirable.

[0012] U.S. Patent No. 3,337,516 (US3,337,516A) describes the use of poly(alkylene glycol)-containing oil-soluble polymers as detergent and anti-wear additives in lubricating engine oils. The described structures solubilize fuel combustion by-products, thereby protecting against engine deposits and wear. Gear fatigue damage is not addressed.

[0013] Japanese Patent Publication No. 2006-307042 (JP2006-307042) describes the use of poly(alkylene glycol)-based lubricity improvers for fuel oils. No sulfur-containing chain transfer agents are used, and fatigue damage to gears and rollers is not mentioned in the patent publication. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] International Publication No. 2009 / 019065 [Patent Document 2] Japanese Patent Application Laid-Open No. 2018-16798 [Patent Document 3] European Patent Application Publication No. 2514774 [Patent Document 4] European Patent Application Publication No. 2336206 [Patent Document 5] U.S. Patent No. 3,337,516 [Patent Document 6] Japanese Patent Application Laid-Open No. 2006-307042 [Patent Document 7] International Publication No. 96 / 30421 [Patent Document 8] International Publication No. 97 / 47661 [Patent Document 9] WO 98 / 40415 [Patent Document 10] International Publication No. 98 / 01478 [Patent Document 11] International Publication No. 2004 / 083169 [Non-patent literature]

[0015] [Non-Patent Document 1] Ullmann's Encyclopedia of Industrial Chemistry, 6th edition [Non-patent document 2] J.-S. Wang, et al., J. Am. Chem. Soc, vol. 117, p. 5614-5615 (1995) [Non-patent document 3] Matyjaszewski, Macromolecules, vol. 28, p. 7901-7910 (1995) Summary of the Invention [Problem to be solved by the invention]

[0016] It was therefore an object of the present invention to provide polymers for use in lubricant compositions that improve the fatigue resistance of metal parts such as in transmissions, engines or hydraulic pumps, even when the lubricant composition has a low viscosity which is better for fuel economy. [Means for solving the problem]

[0017] It has surprisingly been found that polar functional polyalkyl(meth)acrylates (PAMAs) prepared using monofunctional chain transfer agents (formula (II)) or polyfunctional chain transfer agents (formula (III)) as defined in claim 1 exhibit improved fatigue resistance when used in lubricant compositions for transmissions, engines or hydraulic pumps compared to PAMAs prepared without the use of a chain transfer agent (CTA).

[0018] Thus, a first aspect of the present invention is a polymer as defined in claim 1 and its dependent claims.

[0019] A second aspect of the invention is a method for producing such a polymer.

[0020] A third aspect of the present invention is a lubricating oil composition comprising at least one polymer according to the present invention and at least one base fluid.

[0021] A fourth aspect of the invention is the use of such polymers in lubricating oil compositions to improve the fatigue resistance of metal gear or metal roller bearings. DETAILED DESCRIPTION OF THE INVENTION

[0022] Polymers of the Invention According to a first aspect of the present invention, there is provided a method for manufacturing a semiconductor device comprising: (a) Formula (I) [ka] [In the formula, R1, R2=H R3=H or CH3 X=O or NH R4O = independently alkyleneoxy groups having 2 to 4 carbon atoms R5=H or CH3 p=1 to 90, preferably 1 to 30, and even more preferably 1 to 23] one or more poly(alkylene glycol) (meth)acrylates of (b) optionally, one or more C1-C6 alkyl (meth)acrylates; (c) One or more C7-C 15 alkyl (meth)acrylate, (d) optionally, one or more C 16 ~C 30 Alkyl (meth)acrylate The present invention relates to a polyalkyl(meth)acrylate polymer obtainable by polymerizing a monomer composition comprising: wherein the polymer has a mass average molecular weight of 5000 to 30000 g / mol, and The polymer has the formula (II) [ka] [In the formula, R6 is H or CH3 、 R7 is a linear or branched alkyl group having 1 to 18 carbon atoms, or a group represented by formula (III) [ka]

[0032] The copolymer is prepared using one or more chain transfer agents.

[0023] According to a preferred embodiment of the present invention, the monomer composition for producing the polyalkyl(meth)acrylate polymer of the present invention contains, based on the total mass of the monomer composition: (a) 1 to 20% by mass of poly(alkylene glycol) (meth)acrylate monomer units of formula (I) (b) 0 to 5 mass% of one or more C1 to C6 alkyl (meth)acrylates, (c) One or more C7-C 15 Alkyl (meth)acrylate 80 to 99 mass %, (d) One or more types of C 16 ~C 30 Alkyl (meth)acrylate 0 to 20% by mass Includes.

[0024] According to a more preferred embodiment of the present invention, the monomer composition for producing the polyalkyl(meth)acrylate polymer of the present invention contains, based on the total mass of the monomer composition: (a) 2 to 12% by mass of poly(alkylene glycol) (meth)acrylate monomer units of formula (I) (b) 0.1 to 2 mass% of one or more C1 to C6 alkyl (meth)acrylates, (c) One or more C7-C 15 Alkyl (meth)acrylate 86 to 97.9 mass%, (d) One or more types of C 16 ~C 30 Alkyl (meth)acrylate 0 to 20% by mass Includes.

[0025] According to an even more preferred embodiment of the present invention, the monomer composition for producing the polyalkyl(meth)acrylate polymer of the present invention comprises, based on the total weight of the monomer composition: (a) 3 to 10% by mass of poly(alkylene glycol) (meth)acrylate monomer units of formula (I) (b) 0.1 to 2 mass% of one or more C1 to C6 alkyl (meth)acrylates, (c) One or more C7-C 15 Alkyl (meth)acrylate 88 to 96.9 mass%, (d) One or more types of C 16 ~C 30 Alkyl (meth)acrylate 0 to 20% by mass Includes.

[0026] Preferably, the amounts of the monomers a) to d) shown above for producing the polymer total 100% by weight, based on the total weight of the monomer composition.

[0027] According to the present invention, the polyalkyl(meth)acrylate polymer preferably has a weight average molecular weight of 5000 to 25000 g / mol, more preferably 8000 to 22000 g / mol, and even more preferably 10000 to 20000 g / mol.

[0028] The weight average molecular weight of the claimed polymers is determined by size exclusion chromatography (SEC) using polystyrene as the standard and THF as the eluent.

[0029] According to the present invention, the polyalkyl(meth)acrylate polymer preferably has a PDI of 1.5 to 3, more preferably 1.5 to 2.5, and even more preferably 1.6 to 2.0.

[0030] In a preferred embodiment of the present invention, the total amount of one or more chain transfer agents of formula (II) used to prepare the polyalkyl(meth)acrylate polymer of the present invention is from 1 to 10% by weight, preferably from 2 to 6% by weight, based on the total weight of the monomer composition.

[0031] In another preferred embodiment of the present invention, the chain transfer agent is selected from the group consisting of n-dodecyl mercaptan, t-dodecyl mercaptan, 1,3,5-tris(3-mercaptobutyloxyethyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, or a mixture thereof.

[0032] As noted above, in addition to monomer a) corresponding to one or more poly(alkylene glycol) (meth)acrylates of formula (I), the monomer composition for preparing the polymers according to the invention also comprises alkyl (meth)acrylate monomers b), c) and d).

[0033] The term alkyl (meth)acrylate includes alkyl methacrylate and alkyl acrylate, and mixtures thereof. These monomers are well known in the art. The alkyl group of the ester compound may be linear, cyclic, or branched. The monomers may be used individually or as a mixture of different alkyl (meth)acrylate monomers.

[0034] According to one embodiment of the present invention, the monomer units (b) derived from one or more alkyl (meth)acrylates are represented by formula (IV): [ka] wherein R is hydrogen or methyl; 1 means a linear, branched or cyclic alkyl group having 1 to 6 carbon atoms, preferably 1 to 5 carbon atoms, more preferably 1 to 3 carbon atoms].

[0035] Examples of monomers according to formula (IV) are, inter alia, (meth)acrylates derived from saturated alcohols, such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate and hexyl (meth)acrylate; cycloalkyl (meth)acrylates, such as cyclopentyl (meth)acrylate and cyclohexyl (meth)acrylate. Preferably, the polymer comprises units derived from methyl methacrylate.

[0036] According to another aspect of the present invention, the monomer units (c) derived from one or more alkyl (meth)acrylates are represented by the formula (V): [ka] wherein R is hydrogen or methyl; 2means a linear, branched or cyclic alkyl group having 7 to 15 carbon atoms].

[0037] Examples of component (V) are, inter alia, (meth)acrylates derived from saturated alcohols, such as 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, 2-tert-butylheptyl (meth)acrylate, n-octyl (meth)acrylate, 3-isopropylheptyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, 5-methylundecyl (meth)acrylate, n-dodecyl (meth)acrylate, 2-methyldodecyl (meth)acrylate. (meth)acrylates derived from unsaturated alcohols, such as oleyl (meth)acrylate; cycloalkyl (meth)acrylates, such as cyclohexyl (meth)acrylates having ring substituents, for example, tert-butylcyclohexyl (meth)acrylate and trimethylcyclohexyl (meth)acrylate, bornyl (meth)acrylate, and isobornyl (meth)acrylate.

[0038] Furthermore, according to another aspect of the present invention, the monomer unit (d) derived from one or more alkyl (meth)acrylates is represented by the formula (VI): [ka] wherein R is hydrogen or methyl; 3 means a linear, branched or cyclic alkyl group having 16 to 30 carbon atoms].

[0039] Examples of component (VI) are, inter alia, (meth)acrylates derived from saturated alcohols, such as hexadecyl (meth)acrylate, 2-methylhexadecyl (meth)acrylate, heptadecyl (meth)acrylate, 5-isopropylheptadecyl (meth)acrylate, 4-tert-butyloctadecyl (meth)acrylate, 5-ethyloctadecyl (meth)acrylate, 3-isopropyloctadecyl (meth)acrylate, ... Included are decyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, cetyl eicosyl (meth)acrylate, stearyl eicosyl (meth)acrylate, docosyl (meth)acrylate, cycloalkyl (meth)acrylates such as 2,4,5-tri-t-butyl-3-vinylcyclohexyl (meth)acrylate, 2,3,4,5-tetra-t-butylcyclohexyl (meth)acrylate.

[0040] Further Monomers Preferably, the monomer composition further contains a further monomer (monomer (e)) in addition to the monomers (a) to (d).

[0041] Further monomers that can be used according to the invention are selected from the group consisting of styrene monomers having 8 to 17 carbon atoms, vinyl esters having 1 to 11 carbon atoms in the acyl group, vinyl ethers having 1 to 10 carbon atoms in the alcohol group, dispersing nitrogen-functionalized monomers, heterocyclic (meth)acrylates, heterocyclic vinyl compounds, monomers containing covalently bound phosphorus atoms, monomers with epoxy groups and monomers with halogens.

[0042] Suitable styrene monomers having 8 to 17 carbon atoms are selected from the group consisting of styrene, substituted styrenes having alkyl substituents in the side chain, such as α-methylstyrene and α-ethylstyrene, substituted styrenes having alkyl substituents on the ring, such as vinyltoluene and p-methylstyrene, halogenated styrenes, such as monochlorostyrenes, dichlorostyrenes, tribromostyrenes and tetrabromostyrenes, nitrostyrene; styrene being preferred.

[0043] Suitable vinyl esters having 1 to 11 carbon atoms in the acyl group are selected from the group consisting of vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate; preferably vinyl esters having 2 to 9, more preferably 2 to 5, carbon atoms in the acyl group, wherein the acyl group may be linear or branched.

[0044] Suitable vinyl ethers having 1 to 10 carbon atoms in the alcohol group are selected from the group consisting of vinyl methyl ether, vinyl ethyl ether, vinyl propyl ether, vinyl butyl ether; preferably vinyl ethers having 1 to 8, more preferably 1 to 4, carbon atoms in the alcohol group, wherein the alcohol group may be linear or branched.

[0045] Suitable monomers derived from dispersible nitrogen-functionalized monomers are selected from the group consisting of aminoalkyl(meth)acrylates, such as N,N-dimethylaminoethyl(meth)acrylate, N,N-dimethylaminopropyl(meth)acrylate, N,N-diethylaminopentyl(meth)acrylate, N,N-dibutylaminohexadecyl(meth)acrylate; aminoalkyl(meth)acrylamides, such as N,N-dimethylaminopropyl(meth)acrylamide.

[0046] Suitable heterocyclic (meth)acrylates are selected from the group consisting of 2-(1-imidazolyl)ethyl (meth)acrylate, 2-(4-morpholinyl)ethyl (meth)acrylate, 1-(2-methacryloyloxyethyl)-2-pyrrolidone, N-methacryloylmorpholine, N-methacryloyl-2-pyrrolidinone, N-(2-methacryloyloxyethyl)-2-pyrrolidinone, N-(3-methacryloyloxypropyl)-2-pyrrolidinone.

[0047] Suitable heterocyclic vinyl compounds are selected from the group consisting of 2-vinylpyridine, 4-vinylpyridine, 2-methyl-5-vinylpyridine, 3-ethyl-4-vinylpyridine, 2,3-dimethyl-5-vinylpyridine, vinylpyrimidine, vinylpiperidine, 9-vinylcarbazole, 3-vinylcarbazole, 4-vinylcarbazole, 1-vinylimidazole, 2-methyl-1-vinylimidazole, N-vinylpyrrolidone, N-vinylpyrrolidine, 3-vinylpyrrolidine, N-vinylcaprolactam, N-vinylbutyrolactam, vinyloxolane, vinylfuran, vinyloxazoles and hydrogenated vinyloxazoles.

[0048] Monomers containing a covalently bonded phosphorus atom include 2-(dimethylphosphato)propyl (meth)acrylate, 2-(ethylenephosphito)propyl (meth)acrylate, dimethylphosphinomethyl (meth)acrylate, dimethylphosphonoethyl (meth)acrylate, diethyl(meth)acryloylphosphonate, dipropyl(meth)acryloylphosphate, 2-(dibutylphosphono)ethyl (meth)acrylate, diethylphosphatoethyl (meth)acrylate, 2-(dimethylphosphato)-3-hydroxypropyl (meth)acrylate, 2-(ethylenephosphito)-3-hydroxypropyl (meth)acrylate. acrylate, 3-(meth)acryloyloxy-2-hydroxypropyl diethyl phosphonate, 3-(meth)acryloyloxy-2-hydroxypropyl dipropyl phosphonate, 3-(dimethyl phosphato)-2-hydroxypropyl (meth)acrylate, 3-(ethylene phosphito)-2-hydroxypropyl (meth)acrylate, 2-(meth)acryloyloxy-3-hydroxypropyl diethyl phosphonate, 2-(meth)acryloyloxy-3-hydroxypropyl dipropyl phosphonate and 2-(dibutyl phosphono)-3-hydroxypropyl (meth)acrylate.

[0049] Suitable monomers having an epoxy group include, for example, glycidyl (meth)acrylate and glycidyl (meth)allyl ether.

[0050] Suitable halogen-containing monomers include, for example, vinyl chloride, vinyl bromide, vinylidene chloride, (meth)allyl chloride, and halogenated styrenes (eg, dichlorostyrene).

[0051] Preferably, the monomer composition contains 0 to 5 mass %, more preferably 0.1 to 3 mass %, and even more preferably 0.2 to 3 mass % of monomer (e) relative to the total mass of the monomer composition.

[0052] Preferably, the amounts of the monomers a) to e) shown above for producing the polymer total 100% by weight, based on the total weight of the monomer composition.

[0053] Methods of the Invention According to another aspect, the present invention also relates to a method for producing a polyalkyl(meth)acrylate polymer as defined above, said method comprising the following steps: (i) providing a monomer composition as defined in claim 1 and its dependent claims; (ii) initiating radical polymerization of the monomer composition to obtain a random copolymer. Includes.

[0054] Standard free radical polymerization is described in detail, inter alia, in Ullmann's Encyclopedia of Industrial Chemistry, 6th Edition. According to the present invention, chain transfer agents of formula (II) as defined in claim 1 are used for this purpose.

[0055] The ATRP process itself is known. It is considered a "living" free radical polymerization, although the description of its mechanism is not intended to be limiting. In these processes, a transition metal compound is reacted with a compound having a transferable atomic group. This involves the transfer of the transferable atomic group to the transition metal compound, resulting in the oxidation of the metal. This reaction forms a free radical that adds to the ethylene group. However, the transfer of the atomic group to the transition metal compound is reversible, so that the atomic group is transferred back to the growing polymer chain, resulting in the formation of a controlled polymerization system. Accordingly, it is possible to control the formation, molecular weight, and molecular weight distribution of the polymer.

[0056] This ATRP reaction procedure is described, for example, in J.-S. Wang, et al., J. Am. Chem. Soc, vol. 117, pp. 5614-5615 (1995), and Matyjaszewski, Macromolecules, vol. 28, pp. 7901-7910 (1995). In addition, the following patent application publications disclose variations of the above-described ATRP: International Publication No. 96 / 30421 (WO 96 / 30421), International Publication No. 97 / 47661 (WO 97 / 47661), International Publication No. 97 / 18247 (WO 97 / 18247), International Publication No. 98 / 40415 (WO 98 / 40415) and International Publication No. 99 / 10387 (WO 99 / 10387).In addition, the polymer of the present invention can also be obtained, for example, by the RAFT method.This method is described in detail, for example, in International Publication No. 98 / 01478 (WO 98 / 01478) and International Publication No. 2004 / 083169 (WO 2004 / 083169).

[0057] The polymerization can be carried out under normal, reduced, or elevated pressure. The polymerization temperature is also not critical. However, the polymerization temperature is generally within the range of -20 to 200°C, preferably 50 to 150°C, and more preferably 80 to 130°C.

[0058] According to the present invention, polymerization step (ii) comprises the addition of a chain transfer agent of formula (II) as defined in claim 1. The chain transfer agent is selected from the group consisting of oil-soluble mercaptans, such as n-dodecyl mercaptan, tert-dodecyl mercaptan, 1,3,5-tris(3-mercaptobutyloxyethyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 2-mercaptoethanol, or mixtures thereof; chain transfer agents from the terpene class, such as terpinolene. Particularly preferred is the addition of n-dodecyl mercaptan, tert-dodecyl mercaptan, 1,3,5-tris(3-mercaptobutyloxyethyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, or mixtures thereof.

[0059] According to the present invention, the total amount of one or more chain transfer agents of formula (II) is preferably 1 to 10% by mass, more preferably 2 to 6% by mass, based on the total mass of the monomer composition.

[0060] The polymerization step (ii) of the process can be carried out in the absence or presence of a radical initiator. Preferably, step (ii) is carried out without any radical initiator.

[0061] When a radical initiator is used, suitable radical initiators are, for example, azo initiators such as dimethyl 2,2'-azobis(2-methylpropionate), azobis-isobutyronitrile (AIBN), 2,2'-azobis(2-methylbutyronitrile) (AMBN) and 1,1-azobiscyclohexanecarbonitrile; and peroxy compounds such as methyl ethyl ketone peroxide, acetylacetone peroxide, dilauryl peroxide, tert-butyl per-2-ethylhexanoate, ketone peroxide, tert-butyl peroctoate.

[0062] The total reaction time of the radical polymerization is preferably 2 to 10 hours, more preferably 3 to 9 hours.

[0063] The lubricating oil composition of the present invention As indicated above, the present invention also relates to lubricating oil compositions comprising one or more base fluids and one or more polymers according to the present invention.

[0064] The base fluids correspond to lubricant base fluids, mineral, synthetic or natural, animal or vegetable oils, selected according to their adapted / intended use.

[0065] Base fluids used to formulate lubricating oil compositions according to the present invention include conventional base stocks selected from the API (American Petroleum Institute) base stock categories known as Group I, Group II, Group III, Group IV, and Group V. Group I and II base stocks are mineral oil materials (e.g., paraffinic and naphthenic oils) having a viscosity index (or VI) of less than 120. Group I is further distinguished from Group II in that the latter contains 90% or more saturates and the former contains less than 90% saturates (i.e., 10% or more unsaturates). Group III is considered the highest level of mineral base oil, with a VI of 120 or more and a saturates level of 90% or more. Preferably, the base fluids included in the lubricating oil compositions of the present invention are selected from the group consisting of API Group II and III base fluids. Most preferably, the lubricating oil compositions comprise API Group III base fluids. Group IV base fluids are poly-alpha-olefins (PAOs). Group V base fluids are esters and all other base fluids not included in Groups I-IV base fluids. These base fluids can be used individually or in mixtures.

[0066] In a preferred embodiment of the present invention, the lubricating oil composition comprises 0.05 to 10 mass %, preferably 0.1 to 8 mass %, more preferably 0.5 to 6 mass %, even more preferably 1 to 5 mass %, and most preferably 2 to 4 mass %, of at least one polymer according to the present invention, relative to the total mass of the lubricating oil composition.

[0067] All of the properties and preferences set forth above for the polymers, base fluids and methods of the present invention apply to the lubricating oil compositions.

[0068] Further additives The lubricating oil composition according to the present invention may further comprise any other additional additives suitable for use in the formulation, including viscosity index improvers, pour point depressants, dispersants, demulsifiers, antifoam agents, lubricity additives, friction modifiers, antioxidants, detergents, dyes, corrosion inhibitors and / or odorants.

[0069] Use of the polymers according to the invention as fatigue life improvers The present invention also relates to the use of a polyalkyl(meth)acrylate polymer as defined above as an additive in a lubricating oil composition for improving the fatigue resistance of metal gears or metal roller bearings.

[0070] According to one aspect of the present invention, the lubricating oil composition is a transmission fluid, gear oil, engine oil or hydraulic oil, more specifically an automatic transmission fluid, manual transmission fluid, continuously variable transmission fluid, dual clutch transmission fluid, hybrid specific transmission fluid, gear oil formulation, industrial gear oil formulation, axle oil, engine oil formulation or hydraulic fluid.

[0071] Experimental section The present invention will be further described in detail below with reference to examples and comparative examples, which are not intended to limit the scope of the present invention in any way.

[0072] Definitions and Abbreviations The term "C12-15 alkyl (meth)acrylate" refers to an ester of (meth)acrylic acid and a linear or branched alcohol having 12 to 15 carbon atoms. The term encompasses individual (meth)acrylic acid esters with alcohols of a particular length, as well as mixtures of (meth)acrylic acid esters with alcohols of different lengths. ATF automatic transmission fluid C1AMA C1-Alkyl methacrylate = Methyl methacrylate (MMA) C 12 / 15 AMA C 12 / 15 Alkyl methacrylate (60% iso compound) CTA Chain Transfer Agent CTA (II) where R7 = (III) 1,3,5-tris(3-mercaptobutyloxyethyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (CTA of formula (II) where R7 corresponds to formula (III)) DI Dispersant-Inhibitor DDM Dodecyl mercaptan HEMA 2-hydroxyethyl methacrylate Initiator: Dimethyl 2,2'-azobis(2-methylpropionate) IPA Isopropyl Alcohol KV 40 Kinematic viscosity at 40°C, measured according to ASTM D445 KV 100 Kinematic viscosity at 100°C, measured according to ASTM D445 Monomer (a) Methoxypolyethylene glycol methacrylate where p=23 M n number average molecular weight MPR Micropitting Test Equipment M w mass average molecular weight OEM Original Equipment Manufacturer PAMA Polyalkyl(meth)acrylate PDI polydispersity index, M w / M n The molecular weight distribution calculated by t-BPO tert-butyl peroxide t-DDM tert-dodecyl mercaptan VI Viscosity Index, measured according to ASTM D2270 Yubase 3 2.9cSt KV 100 SK Lubricants Group III base oils Yubase 4 4.2cSt KV 100 SK Lubricants Group III base oils

[0073] Test Method The polymers of the present invention and comparative examples are characterized in terms of their molecular weight and PDI.The molecular weight of the polymer is determined by size exclusion chromatography (SEC) using commercially available polystyrene (PSt) standard.The determination is carried out by size exclusion chromatography using THF as eluent (flow rate: 1 mL / min; injection volume: 100 μL).

[0074] The additive compositions containing the polymers according to the present invention and comparative examples were evaluated for their viscosity index (VI) according to ASTM D 2270, viscosity at 40°C (KV) according to ASTM D 445 40 ) and 100℃(KV 100 The viscosity was characterized in terms of kinematic viscosity at 1000 kJ / s.

[0075] synthesis Several polymers were synthesized to demonstrate their effectiveness in lubricating oils as anti-fatigue life enhancers. Detailed composition information can be found in Table 1. The molecular weights M of the synthesized polymers n and M w and PDI were also measured and can be found in Table 1.

[0076] Process 1 (Examples 2, 3 and 4) A four-necked glass round-bottom flask equipped with a condenser, stirrer, and thermocouple was charged with a monomer mixture consisting of the monomers, CTA, and solvents listed in Table 1. The monomer mixture was heated to 110°C for 30 minutes under a nitrogen gas atmosphere. 2 wt. % of the total initiator was added to the flask over 60 minutes. Then 25 wt. % of the total initiator feed mixture was added to the flask over 60 minutes. Then the remaining initiator feed mixture was added to the flask over 60 minutes. At 60 and 120 minutes after the end of the feed, 0.19 g of tBPO was added to the flask. The reaction mixture was held at 110° C. for 180 minutes, and then the toluene was removed under vacuum at 120° C. to give Examples 2, 3, and 4.

[0077] Process 2 (Comparative Example 1) A four-necked glass round-bottom flask equipped with a condenser, stirrer, and thermocouple was charged with the isopropyl alcohol shown in Comparative Example 1 in Table 1 and heated to 80°C for 30 minutes under a nitrogen gas atmosphere. A monomer mixture consisting of monomers and initiator was fed to the flask over 180 minutes. 60 minutes after the end of the feed, the isopropyl alcohol was removed under vacuum at 80°C to yield Comparative Example 1.

[0078] Table 1 : Compositions of Examples and Comparative Examples. [Table 1] * The amounts of initiator, CTA, toluene and IPA are calculated relative to the total monomer amount. ** SEC with polystyrene calibration.

[0079] Evaluation of fatigue life improvers Lubricant Formulations To compare the fatigue performance of the polymers according to the invention, a formulation was prepared with a treat rate of 3 wt. % of the polymer according to the invention, 7.25 wt. % of the ATF DI package, and a KV of 4.4 cSt. 100 The two base fluids were adjusted to KV 100 was used to adjust to that level (Yubase 3 and Yubase 4). A summary of all formulations and viscosity properties can be found in Table 2.

[0080] Table 2 : Overview of formulations used to determine fatigue resistance properties. [Table 2]

[0081] Determination of fatigue resistance: The fatigue resistance measurements were made using a PCS Instruments Micropitting Tester (MPR), which consists of a roller specimen surrounded by three rings.

[0082] The instrument is operated by an on-board processor that allows for the setting up of speed, load, temperature and slip rate. The test chamber is filled with 150 mL of oil.

[0083] The test specimens, i.e. the roller and the ring, are made of SAE 52100 bearing steel with average roughnesses of 0.2 and 0.4 μm, respectively, which allows for the rapid formation of surface fatigue on the roller test specimens.

[0084] An accelerometer is placed on top of the test chamber and records vibrations throughout the test. The formation of surface fatigue can then be translated into an increase in vibration.

[0085] The test conditions are listed in Table 3 below: Table 3 : Description of the protocol for assessing the fatigue resistance. [Table 3]

[0086] The vibrations are recorded for the entire duration of the test.

[0087] A quantifiable result that can express the fatigue resistance as a number is obtained as follows: Integrate the curve of vibration values ​​within the test period using the trapezoidal rule. The integrated area corresponds to the "total damage" over the entire test period. The smaller the area, the greater the fatigue resistance effect of the tested product.

[0088] The determined areas and the fatigue resistance calculated therefrom as percentages relative to the reference oil are summarized in Table 4: Table 4 :Quantitative assessment of fatigue reduction. [Table 4]

[0089] Table 4 shows that the total area under the oscillation curve is much lower for Examples 2, 3, and 4 compared to Comparative Example 1. This means that the polymers of Examples 2, 3, and 4, which were produced using the monomer composition in combination with the chain transfer agent defined by the present invention, exhibit the best performance in fatigue resistance. This is also shown in the percentage improvement in fatigue resistance compared to Comparative Example 1, which uses HEMA and no chain transfer agent, i.e., a 32.2-59.2% improvement in fatigue resistance.

[0090] Examples 2 and 3 show that the combination of HEMA and the chain transfer agent of formula (II) as defined in claim 1 results in an improvement in fatigue resistance, i.e., 32.2 and 44.6%, respectively. The combination of the monomer of formula (I) and the chain transfer agent of formula (II) as defined in claim 1 also has better fatigue resistance than Comparative Example 1.

[0091] The polymers of the present invention enable efficient protection of metal gears or metal roller bearings from fatigue damage, which is achieved by lubricating oil compositions with a low KV of 4.4 cSt, which is difficult to achieve. 100 It is even possible for the

Claims

1. (x) one or more base fluids; and (y) 1 to 5 wt. % of one or more polyalkyl(meth)acrylate polymers, based on the total weight of the lubricating oil composition. A lubricating oil composition for improving the fatigue resistance of metal gears or metal roller bearings, comprising: The polyalkyl(meth)acrylate polymer is (a) Formula (I) 【Chemistry 1】 [In the formula, R １ , R ２ is H, R ３ is H or CH ３ and X is O or NH; R ４ each O is independently an alkyleneoxy group having 2 to 4 carbon atoms; R ５ is CH ３ and p is 1 to 30. 2 to 12% by mass of one or more poly(alkylene glycol) (meth)acrylates, (b) one or more C １ ~C ６ Alkyl (meth)acrylate 0.1 to 2 mass%, (c) one or more C ７ ~C １５ Alkyl (meth)acrylate 86 to 97.9% by mass, It is obtained by polymerizing a monomer composition comprising The polyalkyl(meth)acrylate polymer has a weight average molecular weight of 5,000 to 30,000 g / mol, and The polyalkyl(meth)acrylate polymer has the formula (II): 【Chemistry 2】 [In the formula, R ６ is H or CH ３ and R ７ is a linear or branched alkyl group having 1 to 18 carbon atoms, or a group of formula (III): 【Transformation 3】 and the structure wherein the total amount of the one or more chain transfer agents of formula (II) is 1 to 10 mass % based on the total mass of the monomer composition.

2. The monomer composition contains, relative to the total mass of the monomer composition, (a) 3 to 10% by mass of a poly(alkylene glycol) (meth)acrylate of formula (I): (b) one or more C １ ~C ６ Alkyl (meth)acrylate 0.1 to 2 mass%, (c) one or more C ７ ~C １５ Alkyl (meth)acrylate 88 to 96.9% by mass, The lubricating oil composition of claim 1, comprising:

3. 3. The lubricating oil composition of claim 1, wherein the polyalkyl(meth)acrylate polymer has a weight average molecular weight of 5,000 to 25,000 g / mol.

4. The lubricating oil composition of any one of claims 1 to 3, wherein the polyalkyl(meth)acrylate polymer has a PDI of 1.5 to 3.

5. The lubricating oil composition of any one of claims 1 to 4, wherein the chain transfer agent is selected from the group consisting of n-dodecyl mercaptan, t-dodecyl mercaptan, 1,3,5-tris(3-mercaptobutyloxyethyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, or mixtures thereof.

6. 6. The lubricating oil composition of claim 5, wherein the lubricating oil composition further comprises at least one additive selected from the group consisting of a viscosity index improver, a pour point depressant, a dispersant, a detergent, an antifoam agent, a corrosion inhibitor, an antioxidant, an antiwear additive, an extreme pressure additive, or a friction modifier.

7. 1. Use of a polyalkyl(meth)acrylate polymer as an additive in a lubricating oil composition for improving the fatigue resistance of metal gears or metal roller bearings, wherein the polyalkyl(meth)acrylate polymer is present in an amount of: (a) Formula (I) 【Chemistry 4】 [In the formula, R １ , R ２ is H, R ３ is H or CH ３ and X is O or NH; R ４ each O is independently an alkyleneoxy group having 2 to 4 carbon atoms; R ５ is CH ３ and p is 1 to 30. 2 to 12% by mass of one or more poly(alkylene glycol) (meth)acrylates, (b) one or more C １ ~C ６ Alkyl (meth)acrylate 0.1 to 2 mass%, (c) one or more C ７ ~C １５ Alkyl (meth)acrylate 86 to 97.9% by mass, It is obtained by polymerizing a monomer composition comprising The polyalkyl(meth)acrylate polymer has a weight average molecular weight of 5,000 to 30,000 g / mol, and The polyalkyl(meth)acrylate polymer has the formula (II): 【Transformation 5】 [In the formula, R ６ is H or CH ３ and R ７ is a linear or branched alkyl group having 1 to 18 carbon atoms, or a group of formula (III): 【Transformation 6】 and the structure wherein the total amount of the one or more chain transfer agents of formula (II) is 1 to 10 mass %, based on the total mass of the monomer composition, and the lubricating oil composition comprises 1 to 5 mass % of the polyalkyl(meth)acrylate polymer, based on the total mass of the lubricating oil composition.

8. 8. The use according to claim 7, wherein the lubricating oil composition is a transmission fluid, gear oil, engine oil or hydraulic oil.

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