Diesters of polyethylene oxide as lubricant base oils.

Abstract

Lubricating fluids comprising base oils utilizing carboxylic acid esters of carboxyl di-endcapped polyethylene glycols or mixtures thereof to enable the production of highly efficient fluids having ultra-low viscosity, high flash point, high viscosity index (VI), excellent low temperature properties (viscosity and pour point / freeze point) and low elastohydrodynamic (EHD) shear strength, and enhanced temperature properties for machines or machine elements operating in the elastohydrodynamic lubrication regime.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of and claims priority to U.S. patent application Ser. No. 63 / 266,475, entitled "Diesters of Polyethylene Oxide as Lubricant Base Oils," filed Jan. 6, 2021, the entirety of which is incorporated herein by reference.

[0002] Technical Field

[0002] The present teachings relate generally to lubricating fluids, and more specifically to a family of lubricating base oil technologies having ultra-low viscosity while maintaining a high flash point, high viscosity index (VI), excellent low temperature performance, and low elastohydrodynamic (EHD) shear strength. [Background technology]

[0003] background

[0003] Elastohydrodynamic machine elements are mechanical devices that operate with a thin film of fluid between nominally smooth, rolling, sliding, elastically deformable, non-matching surfaces in contact with one another. Fluids in elastohydrodynamic contact typically behave not as viscous fluids, but as elastic-plastic solids that have a yield strength or shear strength for normal rolling shear motion. Shear within the contact area occurs only when the two contacting surfaces have a difference in their relative velocity, which can be caused by the geometry of the contacting surfaces and their relative motion in the natural operation of the machine elements.

[0004]

[0004] The efficiency of this machine element depends primarily on the high stress shear strength of the fluid used to lubricate these highly stressed, elastically deformable, non-matching contact surfaces. The nature of the shear strength of the fluid under contact operating conditions can substantially affect its efficiency, depending on the degree of sliding motion between mating surfaces under elastohydrodynamic lubrication conditions. Thus, fluids with low elastohydrodynamic shear strength have lower fluid shear losses in rolling sliding motion or pure sliding motion in such contacts, allowing for better efficiency.

[0005]

[0005] U.S. Patent No. 9,879,198 describes low shear strength lubricating fluids composed of a mixture of carboxyl diester polytetramethylene ether glycols and closely related complex esters. Despite the low elastohydrodynamic shear strength of the lubricating fluids, they suffer from poor low temperature performance (e.g., pour point, freezing point), limiting applications where the fluid is exposed to temperatures below -7°C. The contents of U.S. Patent No. 9,879,198 are incorporated herein by reference in their entirety.

[0006]

[0006] Existing lubricating fluids also suffer from problems when exposed to large temperature fluctuations that can affect lubricating fluid life or gearbox life. Lubricating fluids should also have lower flammability / combustibility to reduce the risk of fire.

[0007]

[0007] Therefore, there is a need for improved lubricating fluids that address the above problems. Summary of the Invention

[0008] overview

[0008] The needs set forth herein, as well as further and other needs and advantages, are addressed by the present embodiments, the solutions and advantages of which are described below.

[0009]

[0009] An object of the present teachings is to provide a lubricant base oil having an ultra-low viscosity, high flash point, and high viscosity index (VI) while maintaining low elastohydrodynamic (EHD) shear strength and excellent low temperature performance.

[0010]

[0010] Another object of the present teachings is to provide a lubricant base oil that enables increased energy efficient lubrication in all applications where mechanical components may operate in a variety of temperature environments, including low operating temperatures, high operating temperatures and wide ranges of operating temperatures (e.g., automobiles, wind turbines, alternative energy).

[0011]

[0011] A further object of the present teachings is to provide for the production of highly efficient fluids having enhanced temperature characteristics for machines or machine elements operating in the elastohydrodynamic lubrication regime.

[0012]

[0012] It is a further object of the present teachings to provide base oil technology that supports the continued growth of alternative energy, particularly in the electric vehicle (EV) sector. Because EV transmission fluids must simultaneously act as coolants and lubricants, fluids properly formulated according to the present teachings provide increased energy efficiency and extended gearbox life over a wide range of operating temperatures.

[0013] These and other objects of the present teachings are directed to a compound of formula: [ka] (wherein R1 and R2 each independently comprise an alkyl group having 4 to 6 carbon atoms, and m is in the range of 2 to 12). The lubricating fluid is provided with a carboxyl diester of polyethylene glycol having an average molecular weight in the range of 240 g / mol to 500 g / mol. R1 and R2 each independently include, but are not limited to, linear alkyl groups. In an alternative embodiment, R1 and R2 each independently include, but are not limited to, branched alkyl groups. The lubricating fluid further comprises at least one additive selected from the group consisting of antioxidants, metal dispersants, non-metal dispersants, metal detergents, non-metal detergents, corrosion inhibitors, rust inhibitors, metal deactivators, metal wear inhibitors, non-metal wear inhibitors, phosphorus-containing antiwear agents, non-phosphorus-containing antiwear agents, sulfur-containing antiwear agents, non-sulfur-containing antiwear agents, metal extreme pressure additives, non-metal extreme pressure additives, phosphorus-containing extreme pressure additives, non-phosphorus-containing extreme pressure additives, sulfur-containing extreme pressure additives, non-sulfur-containing extreme pressure additives, anti-seizure agents, pour point depressants, wax modifiers, viscosity modifiers, seal compatibilizers, friction modifiers, lubricants, antifouling agents, colorants, antifoaming agents, demulsifiers, and combinations thereof. The lubricating fluid further comprises at least one lubricant base oil selected from the group consisting of mineral oils, polyalphaolefins, esters, polyalkylene glycols, ethylene-propylene oils, silicone oils, and combinations thereof.

[0014]

[0014] Other features and aspects of the present teachings will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate features according to embodiments of the present teachings. The summary is not intended to limit the scope of the present teachings, which is defined by the claims contained herein. [Brief description of the drawings]

[0015] BRIEF DESCRIPTION OF THE DRAWINGS [Figure 1]

[0015] An example of the shear strength of a monobranched carboxylic diester according to one embodiment is shown. [Diagram 2]

[0015] An example of the shear strength of a monobranched carboxylic diester according to one embodiment is shown. [Diagram 3]

[0016] 1 illustrates the shear strength of a monobranched carboxylic diester according to another embodiment. [Figure 4]

[0016] The shear strength of a monobranched carboxylic diester according to another embodiment is illustrated. [Diagram 5]

[0017] 1 illustrates the shear strength of a linear carboxylic diester according to an embodiment. [Figure 6]

[0017] The shear strength of a linear carboxylic diester according to one embodiment is illustrated. [Figure 7]

[0018] 1 illustrates an example of a method of using a lubricating fluid according to the present teachings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Detailed Description

[0019] The present teachings are described in more detail below with reference to the accompanying drawings, in which embodiments are shown. The following description illustrates the present teachings by way of example and is not intended to limit the principles of the present teachings.

[0017]

[0020] The present teachings are described in more or less specific terms with respect to structural features, however, it is to be understood that the present teachings are not limited to the specific features shown and described, since the articles and / or methods disclosed herein include preferred forms of carrying out the present teachings.

[0018]

[0021] In general, all terms used in the claims should be interpreted according to their ordinary meaning in the art, unless otherwise expressly defined herein. All references to a / an / the element, apparatus, component, means, step, etc. should be openly interpreted as referring to at least one instance of the element, apparatus, component, means, step, etc., unless otherwise indicated. Other than in the examples or unless otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein should be understood to be modified in all instances by the term "about."

[0019]

[0022] The present teachings provide formulated lubricant base oils with ultra-low viscosity, high flash point, high viscosity index (VI), low elastohydrodynamic shear strength and good low temperature performance to produce lubricating fluids with high energy efficiency and improved temperature properties suitable for elastohydrodynamic lubrication.

[0020] Base Oil

[0023] The present teachings utilize carboxylic acid esters of carboxyl di-endcapped polyethylene glycols or mixtures thereof to enable the production of highly efficient fluids with ultra-low viscosity, high flash points, high viscosity index (VI), excellent low temperature properties (viscosity and pour point / freeze point), low elastohydrodynamic (EHD) shear strength, and enhanced temperature properties for machines or machine elements operating in the elastohydrodynamic lubrication regime.

[0021]

[0024] The present teachings provide a lubricating base oil comprising a carboxyl diester of polyethylene glycol. In one embodiment, the carboxyl diester of polyethylene glycol has the formula (1): [ka] It has the structure:

[0022]

[0025] R1 and R2 may each independently comprise a linear alkyl group having from 4 to 6 carbon atoms. In yet another example, R1 and R2 may each contain a branched alkyl group having from 4 to 6 carbon atoms, and the amount of branched alkyl group in the combination of R1 and R2 is less than 10%, less than 5%, or less than 1% by weight of the total weight of the carboxyl diester of polyethylene glycol.

[0023]

[0026] In some examples, R1 and R2 may each independently be derived from a mixture of butyl carboxylic acid, pentane carboxylic acid, and hexane carboxylic acid. In some examples, R1 and R2 each independently are derived from butyl carboxylic acid. In some examples, R1 and R2 each independently are derived from pentane carboxylic acid. In some examples, R1 and R2 each independently are derived from hexane carboxylic acid.

[0024]

[0027] (CH2-CH2-O) means an ethylene oxide unit (EO unit). In some embodiments of formula (1), m ranges from 2 to 12, preferably from 2 to 7.

[0025]

[0028] The carboxyl diester of polyethylene glycol of formula (1) has an average molecular weight in the range of 240 g / mol to 500 g / mol. Base oils composed of low molecular weight carboxyl diesters of polyethylene oxide can provide lubricating fluids with very low viscosity, high flash point, high VI, low EHD shear strength and low freezing point (or pour point).

[0026]

[0029] Lubricating fluids comprising the carboxylic diester of polyethylene glycol of formula (1) have low viscosities, for example very low kinematic viscosities (eg, ≦3.8 cSt at 100° C.).

[0027]

[0030] Lubricating fluids containing the carboxylic diesters of polyethylene glycol of formula (1) also have high flash points (eg, ≧200° C.).

[0028]

[0031] Lubricating fluids containing the carboxylic diester of polyethylene glycol of formula (1) also have a high VI (eg, ≧150).

[0029]

[0032] Lubricating fluids containing the carboxylic diesters of polyethylene glycol of formula (1) have extremely low shear strength in elastohydrodynamic and rolling sliding contacts, thus enabling the production of fluids for use in elastohydrodynamic lubrication that have high energy efficiency due to low shear losses.

[0030]

[0033] Lubricating fluids containing the carboxyl diester of polyethylene glycol of formula (1) also have a very low freezing point that improves the low temperature performance of the lubricating fluid, and can therefore be used in all applications where mechanical elements may operate in low temperature environments (e.g., automobiles, wind turbines, alternative energy). In one embodiment, the lubricating fluids containing the carboxyl diester of polyethylene glycol of formula (1) have a freezing point ≦−25° C.

[0031] Characterization of base oils with and without additives

[0034] The lubricating fluids of the present teachings can be characterized by various standard tests known to those skilled in the art. The energy efficiency of a lubricating fluid can be affected by the viscosity of the lubricating fluid and the traction coefficient of the lubricating fluid. The viscosity of a lubricating fluid is closely related to its ability to reduce friction in contact between solid surfaces. The traction coefficient of a lubricating fluid is related to the energy loss at a particular load.

[0032]

[0035] The traction coefficient can be measured using a PCS Mini-Traction Machine (MTM) manufactured by PCS Instruments, Ltd., measuring at various sliding to rolling ratios (e.g., 0.1% to 200%), temperatures, and loads ranging from 20 N to 70 N or maximum Hertzian contact stresses of 0.5 GPa to 1.5 GPa.

[0033]

[0036] Viscosity, often referred to as viscous coefficient (DV), can be measured using kinematic viscosity (KV). Kinematic viscosity (KV) can be determined by ASTM D445-06 Standard Test Method for Kinematic Viscosity (and Calculation of Viscous Coefficient) of Transparent and Opaque Liquids. Kinematic viscosity can also be calculated from low shear rate viscous coefficient (DV) and density measurements using the formula: KV=DV / ρ, where ρ is density.

[0034]

[0037] Viscosity index (VI) is a unitless measurement of the change in viscosity of a lubricating fluid with a change in temperature. The higher the VI, the more stable the viscosity remains with temperature fluctuations. Viscosity index can be determined from the kinematic viscosity at 40°C and 100°C according to the standard practice of ASTM D2270-04 Viscosity Index Calculation.

[0035]

[0038] Flash point is the minimum temperature at which the vapor of a lubricating fluid ignites when an ignition source is applied. Flash point can be determined by various methods and standards (see, for example, CEN / TR15138 Flash Point Testing Guide and ISO TR29662 Flash Point Testing Guidance), and measurements can vary with different equipment and test protocols, including temperature ramp rates, sample equilibration times, sample volumes, sample agitation, etc. Two basic methods for measuring flash point are open cup and closed cup. In an open cup device, the sample is placed in an open cup and an ignition source is placed. In a closed cup device, the sample is placed in a cup sealed with a lid and an ignition source can be introduced. EXAMPLES

[0036]

[0039] Table 1 below shows some examples of lubricating fluids of the present teachings in terms of DV, KV, VI, flash point, and freezing point (or pour point).

[0037]

[0040] [Table 1]

[0038]

[0041] Note: DEG means diethylene glycol, a polyethylene glycol with 2 EO units. TTEG means tetraethylene glycol, a polyethylene glycol with 4 EO units. PEG200 means polyethylene glycol with a nominal average molecular weight of 200 Daltons. PEG300 means polyethylene glycol with a nominal average molecular weight of 300 Daltons. To calculate VI, the KV at 100°C must be 2.0 cSt or greater.

[0039]

[0042] Table 2 below shows some examples of simple diesters of PEG300 of linear and monobranched carboxylic acids in the measurements of KV, VI, density, DV, freezing point (or pour point) and flash point (or Cleveland CC flash point). The first sample "1" refers to isovaleryl PEG300 diester (alpha-methyl branched). The second sample "2" refers to 2-ethylhexyl PEG300 diester (alpha-ethyl branched). The third sample "3" refers to n-hexyl PEG300 diester (linear and unbranched).

[0040]

[0043] [Table 2]

[0041]

[0044] As shown by the results in Table 2, the linear n-hexyl PEG fluid Sample 3 exhibited lower KV, higher VI, improved low temperature viscosity, lower freezing point and higher flash point even though it had a lower viscosity compared to the monobranched samples (i.e., Samples 1 and 2).

[0042]

[0045] It may be expected that some of the above property differences between the linear and branched samples can be attributed to structure-property relationships in lubricant base oils. However, the lower freezing point of the linear PEG diester is an unexpected result, because typically, in lubricant base oils, branching generally reduces the freezing point or pour point. In addition, the higher flash point of the linear PEG diester is an unexpected result, because all three samples have similar molecular weights. Thus, the lack of branching in sample 3 is likely to contribute to the unexpected relatively high flash point.

[0043]

[0046] Referring to Figures 1-6, the shear strength of each of the three samples is shown at various temperatures, pressures, and shear rates. Figures 1 and 2 show the maximum traction coefficient of Sample 1 at various temperatures and pressures when shear rates of 1 m / s (meters per second) and 3 m / s are applied, respectively. Figures 3 and 4 show the maximum traction coefficient of Sample 2 at various temperatures and pressures when shear rates of 1 m / s (meters per second) and 3 m / s are applied, respectively. Figures 5 and 6 show the maximum traction coefficient of Sample 3 at various temperatures and pressures when shear rates of 1 m / s (meters per second) and 3 m / s are applied, respectively. Each of the above tests was carried out at temperatures of 40°C to 120°C and pressures of 0.8 GPa (gigapascals) to 1.2 GPa.

[0044]

[0047] As can be seen, the elastohydrodynamic (EHD) shear strength of the linear diester (i.e., Figures 5 and 6 corresponding to Sample 3) is similar to that of the branched diester (i.e., Figures 1 and 2 corresponding to Sample 1 and Figures 3 and 4 corresponding to Sample 2). Although the linear diester exhibits slightly lower EHD shear strength compared to the branched diester, the linear diester exhibits overall improved performance compared to the branched diester as shown in Table 2 above. Thus, the linear diester can provide similar EHD shear strength while providing advantages such as improved performance in colder conditions. This may be due to the fact that the component of PEG, which is a long chain of chained ethylene oxide in the backbone of the molecule, constitutes the majority of the molecular structure. Thus, the long chain of chained ethylene oxide may dominate many properties of the sample, including EHD shear strength.

[0045]

[0048] Various embodiments of the lubricating fluids according to the present teachings may further include at least one additive which, in some embodiments, may be selected from the group consisting of dispersants, detergents, defoamers, antioxidants, rust inhibitors, friction modifiers, corrosion inhibitors, extreme pressure additives, antiwear agents, pour point depressants, and combinations thereof.

[0046]

[0049] Dispersants according to the present teachings (including ashless dispersants) can include, for example, one or more of those based on polybutenyl succinimides, polybutenyl succinamides, benzylamines, succinate esters, succinate ester-amides, or boron derivatives thereof. Ashless dispersants can typically be present at 0.05% to 7% by weight of the total weight of the lubricating fluid.

[0047]

[0050] Detergents (including metal detergents) according to the present teachings include, for example, one or more of sulfonates, phenates, salicylates, and those containing calcium phosphates, magnesium phosphates, barium phosphates, etc. It may optionally be selected from overbased salts, basic salts, neutral salts, various acid numbers, etc. Metal detergents may optionally be included at 0.05 wt % to 5 wt % of the total weight of the lubricating fluid.

[0048]

[0051] Defoamers according to the present teachings may include, for example, one or more of polydimethylsilicone, trifluoropropylmethylsilicone, colloidal silica, polyalkyl acrylates, polyalkyl methacrylates, alcohol ethoxy / propoxylates, fatty acid ethoxy / propoxylates, and sorbitan partial fatty acid esters. Defoamers may typically be included at 10-100 mg / L.

[0049]

[0052] Antioxidants according to the present teachings include, for example, one or more of amine-based antioxidants such as alkylated diphenylamines, phenyl-α-naphthylamines, and alkylated phenyl-x-naphthylamines, phenol-based antioxidants such as 2,6-di-t-butylphenol, 4,4′-methylenebis-(2,6-di-t-butylphenol) and isooctyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, and / or sulfur-based antioxidants such as dilauryl-3,3′-dithiopropionate and zinc dithiophosphate. Antioxidants can typically be present at 0.05% to 5% by weight of the total weight of the lubricating fluid.

[0050]

[0053] Rust inhibitors according to the present teachings may include, for example, one or more of fatty acids, alkenyl succinic acid half esters, fatty acid soaps, alkyl sulfonates, polyhydric alcohol / fatty acid esters, fatty acid amines, oxidized paraffins, and alkyl polyoxyethylene ethers. The rust inhibitors may typically be present in an amount of 0% to 37% by weight of the total weight of the lubricating fluid.

[0051]

[0054] Friction modifiers according to the present teachings include, for example, one or more of organomolybdenum compounds, higher alcohols such as oleyl alcohol and stearyl alcohol, fatty acids such as oleic acid and stearic acid, esters such as oleyl glycerol ester, steryl glycerol ester and lauryl glycerol ester, amides such as laurylamide, oleylamide and stearylamide, amines such as laurylamine, oleylamine, stearylamine and alkyldiethanolamines and ethers such as lauryl glycerol ether and oleyl glycerol ether, fats and oils, amines, sulfurized esters, phosphate esters, acid phosphate esters, acid phosphites and amine salts of phosphate esters. Friction modifiers can typically be included at 0.05% to 5% by weight of the total weight of the lubricating fluid.

[0052]

[0055] Extreme pressure additives according to the present teachings include, for example, one or more organic sulfur, phosphorus, or chlorine compounds (including sulfur-phosphorus and sulfur-phosphorus-boron compounds) that chemically react with metal surfaces under high pressure conditions.

[0053]

[0056] Antiwear agents according to the present teachings can include, for example, one or more of zinc dithiophosphate, zinc dialkyldithiophosphate, tricresyl phosphate, halocarbons (chlorinated paraffins), glycerol monooleate, and stearic acid.

[0054]

[0057] Corrosion inhibitors according to the present teachings include, for example, zinc dithiophosphate.

[0055]

[0058] Pour point depressants according to the present teachings can include, for example, one or more of ethylene / vinyl acetate copolymers, condensates of chlorinated paraffins and naphthalenes, condensates of chlorinated paraffins and phenols, polymethacrylates, polyalkylstyrenes, etc. Pour point depressants can typically be present at 0.1 wt % to 10 wt % of the total weight of the lubricating fluid.

[0056]

[0059] Additionally, in accordance with the present teachings, a solubilizer (ie, co-solvent) may be included that is typically used to dissolve polar additives in less polar or non-polar base oils.

[0057]

[0060] The total content of additives in the lubricating fluid composition of the present teachings is not limited, however, one or more additives (including the solubilizing agents described above) can be present in an amount of 1 wt % to 30 wt % of the total weight of the lubricating fluid, preferably 2 wt % to 15 wt % of the total weight of the lubricating fluid.

[0058]

[0061] 7, a lubricating fluid 70 according to the present teachings is applied and used between two machine components 711, 712 of a machine 700, such as a motor or engine. The lubricating fluid 710 has improved temperature performance and high energy efficiency and enables the machine components 711, 712 to operate in an elastohydrodynamic lubrication regime. Thus, the present teachings provide a machine including two components and a lubricating fluid applied between the two components. The present teachings also provide a process of using the lubricating fluid, including applying the lubricating fluid between two components of the machine.

[0059]

[0062] Lubricating fluids according to the present teachings may include at least one additive selected from the group consisting of antioxidants, metal dispersants, non-metal dispersants, metal detergents, non-metal detergents, corrosion inhibitors, rust inhibitors, metal deactivators, metal wear inhibitors, non-metal wear inhibitors, phosphorus-containing antiwear agents, non-phosphorus-containing antiwear agents, sulfur-containing antiwear agents, non-sulfur-containing antiwear agents, metal extreme pressure additives, non-metal extreme pressure additives, phosphorus-containing extreme pressure additives, non-phosphorus-containing extreme pressure additives, sulfur-containing extreme pressure additives, non-sulfur-containing extreme pressure additives, anti-seizure agents, pour point depressants, wax modifiers, viscosity modifiers, seal compatibilizers, friction modifiers, lubricants, antifouling agents, color developers, antifoam agents, demulsifiers, and combinations thereof.

[0060]

[0063] The lubricating fluids of the present teachings may further comprise one or more other lubricant base oils, at least one of which is selected from the group consisting of mineral oils (i.e., Group I, II, II+, III, III+), polyalphaolefins (PAO) (Group IV), esters (Group V), polyalkylene glycols (PAG), ethylene-propylene oils, silicone oils, and any other lubricating base oils used in lubricant and grease formulations.

[0061]

[0064] Although the present teachings have been described above with respect to specific embodiments, it should be understood that the present teachings are not limited to those disclosed embodiments. Many modifications and other embodiments will occur to those skilled in the art to which the present invention pertains. They are intended to be and are encompassed by both the present disclosure and the appended claims. For example, in some instances, one or more features disclosed in connection with one embodiment may be used alone or in combination with one or more features of one or more other embodiments. It is intended that the scope of the present teachings should be determined by the proper interpretation and understanding of any claims and their legal equivalents, as understood by those skilled in the art based on the disclosure of this specification and the accompanying drawings.

Claims

1. formula 【Chemistry 1】 wherein R1 and R2 each independently comprise an alkyl group, each alkyl group having 4 to 6 carbon atoms, and m ranges from 2 to 12. A lubricating fluid comprising a carboxyl diester of polyethylene glycol having the formula: The lubricating fluid comprises a carboxyl diester having an average molecular weight in the range of 240 g / mole to 500 g / mole.

2. 2. The lubricating fluid of claim 1, wherein R1 and R2 each comprise a linear alkyl group.

3. 2. The lubricating fluid of claim 1, wherein R1 and R2 each comprise a branched alkyl group.

4. 4. The lubricating fluid of claim 3, wherein R1 and R2 each comprise an alpha-methyl group.

5. 4. The lubricating fluid of claim 3, wherein R1 and R2 each comprise an alpha-ethyl group.

6. 2. The lubricating fluid of claim 1, wherein R1 and R2 are each independently derived from at least one of butyl carboxylic acid, pentane carboxylic acid, hexane carboxylic acid, or a mixture of butyl carboxylic acid, pentane carboxylic acid, and hexane carboxylic acid.

7. 10. The lubricating fluid of claim 1 having a flash point, measured in a closed cup, of at least 200°C.

8. 2. The lubricating fluid of claim 1 having a kinematic viscosity at 100° C. of up to 3.8 cSt.

9. 10. The lubricating fluid of claim 1 having a viscosity index of at least 150.

10. 2. The lubricating fluid of claim 1 having a freezing point of at most -24°C.

11. 10. The lubricating fluid of claim 1, further comprising at least one additive selected from the group consisting of antioxidants, metal dispersants, non-metal dispersants, metal detergents, non-metal detergents, corrosion inhibitors, rust inhibitors, metal deactivators, metal wear inhibitors, non-metal wear inhibitors, phosphorus-containing antiwear agents, non-phosphorus-containing antiwear agents, sulfur-containing antiwear agents, non-sulfur-containing antiwear agents, metal extreme pressure additives, non-metal extreme pressure additives, phosphorus-containing extreme pressure additives, non-phosphorus-containing extreme pressure additives, sulfur-containing extreme pressure additives, non-sulfur-containing extreme pressure additives, anti-seizure agents, pour point depressants, wax modifiers, viscosity modifiers, seal compatibilizers, friction modifiers, lubricants, antifouling agents, color developers, antifoam agents, demulsifiers, and combinations thereof.

12. 10. The lubricating fluid of claim 1, further comprising at least one lubricant base oil selected from the group consisting of mineral oils, polyalphaolefins, esters, polyalkylene glycols, ethylene-propylene oils, silicone oils, and combinations thereof.

13. Two mechanical parts that interact with each other; and a lubricating fluid applied between the two parts, The lubricating fluid has the formula 【Chemistry 2】 wherein R1 and R2 each independently comprise an alkyl group, each alkyl group having 4 to 6 carbon atoms, and m ranges from 2 to 12. The carboxyl diester of polyethylene glycol having the formula: The carboxyl diester has an average molecular weight in the range of 240 g / mol to 500 g / mol.

14. 10. The machine of claim 9, wherein the machine components operate in an elastohydrodynamic lubrication regime.

15. A process for lubricating a machine comprising the steps of: 【Chemistry 3】 wherein R1 and R2 each independently comprise an alkyl group, each alkyl group having 4 to 6 carbon atoms, and m ranges from 2 to 12. A lubricating fluid comprising a carboxyl diester of polyethylene glycol having the formula: a lubricating fluid, wherein the carboxylic diester has an average molecular weight in the range of 240 g / mole to 500 g / mole; applying said lubricating fluid to an area between two mechanical parts of said machine; A process including.

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