EP4423220A1

EP4423220A1 - Lubrication greases including copolymers of tetrafluoroethyene oxide and hexafluoropropylene oxide

Info

Publication number: EP4423220A1
Application number: EP22812917.7A
Authority: EP
Inventors: Alexander Borisovich Shtarov; Pelin HACARLIOGLU; Jon Lee Howell
Original assignee: Chemours Co FC LLC
Current assignee: Chemours Co FC LLC
Priority date: 2021-10-25
Filing date: 2022-10-24
Publication date: 2024-09-04
Also published as: CN118139951A; JP2024539995A; US20250002804A1; KR20240090772A; WO2023076178A1

Abstract

A grease includes a perfluoropolyether oil copolymer and a thickener mixed with the copolymer. The copolymer includes about 20 mol% to about 80 mol% of –CF2CF2O– units, about 20 mol% to about 80 mol% of –CF(CF3)CF2O– units, and about 0 mol% to about 45 mol% of one or more additional perfluoroalkyleneoxy units. The copolymer has a viscosity index in the range of about 120 to about 220. The copolymer has an average TFEO run length of less than about 6. A process of forming a grease includes mixing a perfluoropolyether oil copolymer with a thickener to form the grease.

Description

TITLE

LUBRICATION GREASES INCLUDING COPOLYMERS OF TETRAFLUOROETHYENE OXIDE AND HEXAFLUOROPROPYLENE OXIDE

FIELD OF THE INVENTION

[0001] The present invention relates to lubrication greases and more particularly to lubrication greases containing copolymers of tetrafluoroethylene oxide and hexafluoropropylene oxide and a thickener.

BACKGROUND OF THE INVENTION

[0002] Commercial scale options for high-performance perfluoropolyether lubricants are limited to only a few main approaches that use anionic polymerization of hexafluoropropylene oxide (HFPO) monomer at low temperatures or controlled photo-oxidation polymerization of tetrafluoroethylene (TFE) or hexafluoropropylene (HFP) or both. The preparation of partially-fluorinated polymers of 2,2,3, 3-tetrafluorooxetane and its further fluorination is also practiced, producing a -(CF2CF2CH2O)_n- polymer that requires significant further fluorination to make a -(CF2CF₂CF₂O)n- polymer.

[0003] Commercial oils formed by anionic polymerization of HFPO (poly -CF(CFS)CF2O-), available under the trade name Krytox™ (The Chemours Company FC, LLC, Wilmington, DE) (PFPE-K), have superior stability in the presence of metal halides and oxides; however, their viscosity changes significantly with a change in temperature (low viscosity index), and they have relatively higher pour points. Additionally, the low molecular weight of relatively viscous oils increases their volatility and may limit some of their application.

[0004] Commercial oils produced from TFE by photo-oxidation polymerization that contain tetrafluoroethylene oxide (TFEO) units of -CF2CF2O- and are available under the trade names Fomblin® M and Fomblin® Z (Solvay Specialty Polymers, Milan, IT), have a lower pour point and a higher viscosity index than other commercial perfluoropolyethers (PFPEs), such as poly -(CF(CF3)CF₂O)n- (Krytox™ PFPE-K) or - (CF₂CF₂CF₂O)_n- (PFPE-D), which do not contain -CF₂O- groups. The commercial oils containing -CF(CFs)CF₂O- units, produced from HFP by photo-oxidation polymerization, and available under the trade name Fomblin® Y (Solvay Specialty Polymers, Milan, IT) also contain difluoroformyl (-CF₂O-) groups, which lower their stability compared to PFPE-K and promote rapid decomposition in the presence of Lewis acids; metal halides, such as AlCh; metal oxides; or metals, such as aluminum or iron.

[0005] The end groups in Fomblin® M and Fomblin® Z oils are mostly CF3O- groups, which also lowers their stability compared to the longer CF₃CF₂O-, CF₃CF₂CF₂O-, and (CF3)₂CFO- end groups in the presence of metal halides and oxides [see, for example, Kasai, “Perfluoropolyethers: Intramolecular Disproportionation”, Macromolecules, Vol. 25, pp. 6791- 6799 (1992)]. Therefore, oils with a reduced amount of CFsO- end groups are desired to achieve higher stability. Oils that contain difluoroformyl (-CF₂O-) groups, such as Fomblin® M, Fomblin® Z, and Fomblin® Y oils, also have a lower thermo-oxidative stability in the presence of metals [see, for example, Koch et al., “Thermo-Oxidative Behaviour of Perfluoropolyalkylethers”, Journal of Synthetic Lubrication, Vol. 12, pp. 191-204 (1995)]. In addition, certain metals and metal oxides, such as aluminum oxide (AI₂Os) and titanium oxide (TiO₂), have a catalytic effect on the degradation of Fomblin® Y oils [Sianesi et al., “Perfluoropolyethers: Their Physical Properties and Behavior at High and Low Temperatures”, Wear, Vol. 18, pp. 85-100 (1971)].

[0006] U.S. Patent No. 8,067,344, entitled “Lubricating grease composition” and issued November 29, 2011 to Shimura et al., suggests perfluoropolyether oils from anionic polymerization of HFPO, or both HFPO and TFEO, in the presence of a cesium fluoride catalyst.

[0007] U.S. Patent Application Publication No. 2005/0075250, entitled “Lubricating greases” by MaCcone et al. and published April 7, 2005, suggests copolymers containing -CF(CFs)CF₂O- units and -CF₂CF₂O- units in addition to polymers containing -CF(CFs)CF2O- units and polymers containing -CF2CF2O- units having a viscosity within a certain range of values at 20°C.

[0008] French Patent No. 1373014, issued September 25, 1964, discloses fluorocarbon polyethers including copolymers including HFPO and TFEO and having a high TFEO content.

[0009] There is a need for greases of inert PFPE oils having a relatively small change in viscosity over a wide temperature range, a low pour point, a low volatility, and a high thermal stability.

BRIEF DESCRIPTION OF THE INVENTION

[0010] In an exemplary embodiment, a grease includes a perfluoropolyether oil copolymer and a thickener mixed with the copolymer. The copolymer includes about 20 mol% to about 80 mol% of - CF2CF2O- units, about 20 mol% to about 80 mol% of -CF(CF3)CF2O- units, and about 0 mol% to about 45 mol% of one or more additional perfluoroalkyleneoxy units. The copolymer has a viscosity index in the range of about 120 to about 220. The copolymer has an average TFEO run length of less than about 6.

[0011] In another exemplary embodiment, a process of forming a grease includes mixing a perfluoropolyether oil copolymer with a thickener to form the grease. The copolymer includes about 20 mol% to about 80 mol% of -CF2CF2O- units, about 20 mol% to about 80 mol% of - CF(CF3)CF2O- units, and about 0 mol% to about 45 mol% of one or more additional perfluoroalkyleneoxy units. The copolymer has a viscosity index in the range of about 120 to about 220. The copolymer has an average TFEO run length of less than about 6.

[0012] Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiments, which illustrate, by way of example, the principles of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] Provided are exemplary greases of thickeners and inert PFPE oils having a relatively small change in viscosity over a wide temperature range, a low pour point, a low volatility, and a high thermal stability.

[0014] In exemplary embodiments, the PFPE oils have a relatively small change in viscosity over a wide temperature range, a low pour point, a low volatility, and a high thermal stability.

[0015] In greases, a low volatility of the PFPE oil is of particular importance, since any loss of oil during operating conditions increases the relative amount of thickener in the grease, potentially changing the physical properties of the grease.

[0016] In greases, the operating conditions generally make a high thermal stability of the PFPE oil less important, particularly for operation at low temperatures, than if the oil is used alone as a lubricant without a thickener.

[0017] In exemplary embodiments, the greases have lower torque values for lubricated ball bearings than greases of conventional PFPE oils of similar International Standards Organization (ISO) grade and/or have great weatherability.

[0018] In exemplary embodiments, the greases are useful in severe conditions, including, but not limited to, high temperatures, very low pressures coupled with very low temperatures, applications requiring low torque, environments containing aggressive chemicals and solvents, and/or environments containing oxygen or chloride.

[0019] The provided PFPE oils are copolymers of tetrafluoroethylene oxide (TFEO) and hexafluoropropylene oxide (HFPO) that offer high thermal and chemical stability, low volatility, and improved viscosity change (e.g., lower 40°C/100°C viscosity ratios and higher viscosity indexes). When polymers of similar viscosity at 40°C (ISO viscosity grade (VG)) are compared, TFEO/HFPO copolymers containing 20-80 mol% of - CF(CFS)CF20- units have a lower pour point than Fomblin® Y, - CF(CF3)CF2O-CO-CF2O- lubricants, poly-HFPO Krytox™ lubricants, and poly-TFEO homopolymers.

[0020] As used herein, viscosity index (VI) is a unitless value for a subject polymer or copolymer oil based on its kinematic viscosities at 40°C and 100°C and calculated by the following formula: where U is the subject oil’s kinematic viscosity at 40°C and L and H are values of kinematic viscosity at 40°C for reference oils having a VI of 0 and a VI of 100, respectively, and having the same kinematic viscosity at 100°C as the subject oil, where values for L and H are found in ASTM D2270.

[0021] As used herein, ISO viscosity grade refers to the ISO VG that corresponds to the kinematic viscosity of oil at 40°C reported in centistokes.

[0022] As used herein, pour point refers to the temperature, below which the polymer or copolymer loses its ability to be poured down from a beaker, following the American Society for Testing and Materials (ASTM) D97 standard test method.

[0023] As used herein, stability refers to the temperature at which 50% weight loss is observed in the presence of 2% aluminum oxide (neutral 0C-AI2O3), as Lewis acid, in a standard 10°C/min ramp TGA test, with a higher temperature indicating a greater stability.

[0024] As used herein, volatility refers to % weight loss of the oil from room temperature to 300°C observed in a standard 10°C/min ramp TGA test, with a lower mass loss indicating a lower volatility. [0025] As used herein, average TFEO run length refers to the average number of consecutive -CF2CF2O- units in a copolymer formed by the ring-opening of TFEO monomer.

[0026] TFEO has the following chemical structure: which becomes a -CF2CF2O- perfluoroalkyleneoxy unit in the copolymer.

HFPO has the following chemical structure: which becomes a -CF(CF3)CF2O- perfluoroalkyleneoxy unit in the copolymer.

[0027] The PFPE oil copolymer contains randomly distributed HFPO and TFEO repeat units. In exemplary embodiments, the PFPE oil copolymer has the following chemical formula:

CF3(CF₂)zO-[CF(CF3)CF2O]x(CF2CF2O)y-CF₂R¹ (3) where R¹ is -F or -CFs, z is 1-2, and x and y are independently 0-30, such as, for example, 1-30, 2-30, 3-30, 5-30, 5-25, 5-20, 10-20, or any value, range, or sub-range therebetween.

[0028] In exemplary embodiments, the ratio of monomers in the gas stream is selected to improve and change the lubricant properties of the resulting copolymer. In exemplary embodiments, the copolymer has about 20 mol% to about 80 mol% of -CF2CF2O- units and about 20 mol% to about 80 mol% -CF(CFs)CF2O- units, alternatively about 20 mol% to about 75 mol% of -CF2CF2O- units and about 25 mol% to about 80 mol% of -CF(CFs)CF2O- units. In exemplary embodiments, the copolymer has at least about 20 mol% of -CF2CF2O- units, alternatively at least about 25 mol% of -CF2CF2O- units, alternatively at least about 30 mol% of -CF2CF2O- units, alternatively at least about 35 mol% of -CF2CF2O- units, alternatively at least about 40 mol% of -CF2CF2O- units, or any value, range, or sub-range therebetween. In exemplary embodiments, the copolymer has at least about 20 mol% of -CF(CFs)CF2O- units, alternatively at least about 25 mol% of -CF(CFs)CF2O- units, alternatively at least about 30 mol% of -CF(CFs)CF2O- units, alternatively at least about 35 mol% of -CF(CFs)CF2O- units, alternatively at least about 40 mol% of -CF(CFs)CF2O- units, alternatively at least about 45 mol% of -CF(CFS)CF2O- units, alternatively at least about 50 mol% of -CF(CFS)CF2O- units, alternatively at least about 55 mol% of -CF(CFS)CF2O- units, or any value, range, or sub-range therebetween.

[0029] In some embodiments, the copolymer has about 55 mol% or more of -CF2CF2O- units and -CF(CFs)CF2O- units, in combination, such as, for example, about 60 mol% or more, about 65 mol% or more, about 70 mol% or more, about 75 mol% or more, about 80 mol% or more, about 85 mol% or more, about 90 mol% or more, about 95 mol% or more, about 99 mol% or more, essentially 100 mol%, or any value, range, or sub-range therebetween.

[0030] The copolymer may also include up to about 45 mol% of one or more additional perfluoroalkyleneoxy units other than the -CF2CF2O- and -CF(CFS)CF2O- perfluoroalkyleneoxy units, alternatively about 5% to about 45%, alternatively about 5% to about 35%, alternatively about 5% to about 25%, alternatively about 5% to about 10%, alternatively about 10% to about 40%, alternatively up to about 5%, alternatively up to about 10%, alternatively up to about 25%, alternatively up to about 35%, or any value, range, or sub-range therebetween. In some embodiments, the additional perfluoroalkyleneoxy unit is (-CF2-CF2-CF2-O-). In some embodiments, (-CF2-CF2-CF2-O-) units are introduced by co-polymerization of TFEO, and optionally HFPO, with 2,2,3,3-tetrafluorooxetane to make (-CH2-CF2- CF2-O-) containing polyfluorinated ether, followed by fluorination with elemental fluorine to form -CF2-CF2-CF2-O- containing polymers.

[0031] In exemplary embodiments, the copolymer has a number average molecular weight (M_n), as determined by ¹⁹F NMR, in the range of about 1 ,500 Daltons (Da) to about 20,000 Da, alternatively about 3,500 Da to about 13,000 Da, alternatively about 2,500 Da to about 10,000 Da, or any value, range, or sub-range therebetween.

[0032] In exemplary embodiments, the copolymer has a viscosity index in the range of about 100 to about 220, alternatively about 120 to about 220, alternatively about 135 to about 200, alternatively about 100 to about 210, alternatively about 150 to about 220, alternatively about 150 to about 200, or any value, range, or sub-range therebetween.

[0033] In exemplary embodiments, the copolymer has an average TFEO run length of less than about 6, alternatively less than about 5.5, alternatively less than about 5, alternatively less than about 4.5, alternatively less than about 4, or any value, range, or sub-range therebetween. A shorter average TFEO run length reduces the likelihood of crystallization of the copolymer upon cooling.

[0034] In exemplary embodiments, the copolymer has a pour point of about -20°C or less, alternatively about -30°C or less, alternatively about - 40°C or less, alternatively about -50°C or less, or any value, range, or subrange therebetween.

[0035] In exemplary embodiments, the end groups of the copolymer contain primarily CF3CF2CF2O- and CF3CF2O- end groups, thereby avoiding the high amount of CF3O- end groups typical for a perfluoropolyether containing -CF2CF2-O- units made by photo-oxidation polymerization of TFE, and giving a lubricant with a high stability and low volatility.

[0036] In exemplary embodiments, about 31 mol% or less of the end groups are CF3O- end groups, alternatively about 16 mol% or less, alternatively about 10 mol% or less, alternatively about 5 mol% or less, or any value, range, or sub-range therebetween. In exemplary embodiments, about 69 mol% or more of the end groups are selected from CF3CF2CF2O-, (CF₃)₂CFO-, and CF3CF2O- end groups, alternatively about 84 mol% or more, alternatively about 90 mol% or more, alternatively about 95 mol% or more, or any value, range, or sub-range therebetween.

[0037] In exemplary embodiments, the stability of the copolymer is about 250°C or greater, alternatively about 250°C to about 450°C, alternatively about 275°C or greater, alternatively about 300°C or greater, alternatively about 325°C or greater, alternatively about 350°C or greater, alternatively about 350°C to about 450°C, alternatively about 375°C or greater, or any value, range, or sub-range therebetween.

[0038] In exemplary embodiments, the volatility of the copolymer at a useful temperature range is about 5% or less, alternatively about 1 % to about 5%, alternatively about 4% or less, alternatively about 3% or less, alternatively about 2% or less, alternatively about 1 % to about 2%, or any value, range, or sub-range therebetween.

[0039] In exemplary embodiments, the ISO viscosity grade of the copolymer is about 20 or greater, alternatively about 20 to about 170, alternatively about 25 or greater, alternatively about 25 to about 170, alternatively about 25 to about 110, alternatively about 50 or greater, alternatively about 95 or greater, alternatively about 95 to about 170, or any value, range, or sub-range therebetween.

[0040] In exemplary embodiments, the copolymer is formed by a process that includes feeding a gas stream containing TFEO and HFPO into a reactor containing a fluorinated solvent, an alkali metal fluoride salt, a polyethylene glycol) dialkyl ether, a short chain perfluoroalkyl polyether acid fluoride, a perfluoroalkyl acid fluoride, such as, for example, CF₃C(O)F or CFSCF2C(O)F, or a perfluoroalkyl ketone or its corresponding alkoxide, such as, for example, CF3CF2O; CF3CF2CF2O; (CFs CFO; or CF3CF2CF2CF2O; to form an acid fluoride-containing polymer. The TFEO and HFPO may be provided in relative amounts in the gas stream such that the copolymer includes any of the relative amounts -CF2CF2O- units and -CF(CFS)CF2O- units disclosed herein. Maintaining the TFEO and HFPO ratio relatively constant during the polymerization provides a consistent co-polymer composition. To reduce the percentage of CF3O- end groups, the relative amount of HFPO may be increased at the end of polymerization. In an exemplary embodiment, the gas stream is adjusted to contain a mole ratio of HFPO:TFEO of at least 4:1 at the end of polymerization such that about 5 mol% or less of the end groups of the perfluoroalkyl polyether copolymer are CF3O- end groups. The method further includes working up the acid fluoride-containing polymer to form the copolymer.

[0041] In exemplary embodiments, the work-up includes hydrolyzing the acid fluoride-containing polymer or a solution of the acid fluoride- containing polymer in a fluorinated solvent with water or an aqueous solution of base to form a perfluoroalkyl polyether carboxylic acid or carboxylate salt. Appropriate fluorinated solvents may include, but are not limited to, a partially fluorinated ether, such as, for example, perfluorobutyl methyl ether. The work-up further includes distilling off the fluorinated solvent with heating that may convert the polyether carboxylic acid or carboxylate salt partially or completely to the polyether with -OCF2H, - OCF(CFs)H, and/or -OCF=CF2 end groups. The process further includes treating the perfluoroalkyl polyether carboxylic acid or carboxylate salt, or above mixture containing -OCF2H, -OCF(CFs)H, and/or -OCF=CF2 end groups with elemental fluorine to obtain the perfluoroalkyl polyether copolymer.

[0042] In exemplary embodiments, the reactor is an autoclave. In exemplary embodiments, the reaction occurs at a temperature in the range of about -35°C to about 30°C, alternatively about -25°C to about - 15°C, or any value, range, or sub-range therebetween, over a period of about 14 to about 18 hours. [0043] In exemplary embodiments, the hydrolysis is with an aqueous sodium hydroxide solution to reach a pH in the range of about 1 to 4. In exemplary embodiments, the treatment is with 25% elemental fluorine at a stepwise increasing temperature from about 20°C to about 150°C, alternatively from about 25°C to about 150°C, alternatively from about 80°C to about 150°C, alternatively from about 20°C to about 80°C, alternatively from about 25°C to about 80°C, or any range or sub-range therebetween.

[0044] In some embodiments, the resulting PFPE oil copolymer has a low volatility such that the temperature at which 5 wt% loss is observed is at least about 200°C, alternatively at least about 250°C, alternatively at least about 300°C, or any value, range, or sub-range therebetween. In some embodiments, the PFPE oil copolymer has a low volatility such that the temperature at which 50 wt% loss is observed is at least about 300°C, alternatively at least about 350°C, alternatively at least about 400°C, or any value, range, or sub-range therebetween.

[0045] In exemplary embodiments, the resulting PFPE oil copolymer is combined with one or more thickeners to form a grease. In some embodiments, the PFPE oil and the thickener, in combination, make up at least about 95 wt% of the grease, such as, for example, at least about 96 wt%, at least about 97 wt%, at least about 98 wt%, at least about 99 wt%, at least about 99.5 wt%, or any value, range, or sub-range therebetween.

[0046] In exemplary embodiments, the thickener is in the form of particles that are chemically inert or substantially chemically inert. In exemplary embodiments, the thickener is polytetrafluoroethylene (PTFE), talc, silica (SiC ), fluorinated ethylene propylene (FEP), perfluoroalkoxy alkane (PFA), clay, graphite, surface-treated silica, boron nitride, calcium carbonate, or a combination thereof.

[0047] In exemplary embodiments, the amount of the thickener in the grease is in the range of about 1 wt% to about 50 wt%, alternatively about 1 wt% to about 35 wt%, alternatively about 10 wt% to about 50 wt%, alternatively about 15 wt% to about 35 wt%, alternatively about 15 wt% to about 25 wt%, alternatively about 20 wt% to about 22 wt%, or any value, range, or sub-range therebetween.

[0048] In exemplary embodiments, the thickener is added in the form of a powder. In some embodiments, the powder is a micropowder. In some embodiments, the thickener is added by milling the oil with the thickener.

[0049] In exemplary embodiments, the thickener particles have a surface area in the range of about 2 m²/g to about 35 m²/g, alternatively about 7 m²/g to about 25 m²/g, alternatively about 10 m²/g to about 20 m²/g, or any value, range, or sub-range therebetween.

[0050] In exemplary embodiments, the thickener particles have an average particle size in the range of about 30 nm to about 300 nm, alternatively about 50 nm to about 250 nm, or any value, range, or subrange therebetween. The average particle size refers to the average primary particle size. When the thickener is PTFE, the PTFE preferably has a number average molecular weight M_n, as determined based on a total number of endgroups on the PTFE per 10⁶ CF2 groups as determined by Fourier- transform infrared (FTIR) spectroscopy, of at least about 10,000 Da, alternatively about 10,000 to about 10,000,000 Da, alternatively at least 100,000 Da, alternatively at least 1 ,000,000 Da, or any value, range, or sub-range therebetween.

[0051] In some embodiments, the grease has a starting torque at -40 °C of less than 1500 g-cm, alternatively less than 1100 g-cm, alternatively less than 1000 g-cm, or any value, range, or sub-range therebetween. In some embodiments, the grease has a running torque at -40 °C of less than 500 g-cm, alternatively less than 450 g-cm, alternatively less than 250 g-cm, or any value, range, or sub-range therebetween.

[0052] In some embodiments, the grease also includes one or more additives. In some embodiments, the additives provide a specific benefit or property, such as, for example, anti-wear or anti-rust. Appropriate additives may include, but are not limited to, molybdenum disulfide (moly disulfide), sodium nitrite, polyfluoropolyoxa-alkyl aryl phosphate esters, organic molybdenum compounds, or tungsten disulfide.

[0053] The greases disclosed herein may have nonflammability and high stability in oxygen environments, low vapor pressure, chemical inertness, high temperature stability, insolubility to many chemicals, good lubricity and resistance to oxidation, the ability to withstand constant temperatures up to about 550°F (about 288°C) and intermittent temperatures up to about 800°F (about 427°C), and/or an ability to remain fluid at very low temperatures, making them useful in any of a number of different applications, including, but not limited to, valve and O-ring lubrication in oxygen service, aircraft instrument bearing lubrication, seal lubrication in reactive chemical environments, life bearing seals, such as in electric motors, high-temperature grease applications, low-temperature grease applications, automotive applications, turbine applications, and/or aerospace applications.

EXAMPLES

[0054] The invention is illustrated in the following examples which do not limit the scope of the invention as described in the claims.

Compositions

[0055] Three inventive example compositions were formed and tested. The oil of the first inventive example (IE1 ) was about 44 mol% HFPO and about 56 mol% TFEO. The oil of the second inventive example (IE2) was about 34 mol% HFPO and about 66 mol% TFEO. The oil of the third inventive example (IE3) was about 43 mol% HFPO and about 57 mol% TFEO.

[0056] Two comparative example compositions were formed and tested for comparison to the inventive examples. The oil of the first comparative example (CE1) was commercially available Krytox™ VPF 1531 oil (The Chemours Company, Wilmington, DE), a homopolymer of HFPO. The oil of the second comparative example (CE2) was commercially available Krytox™ 143AA oil (The Chemours Company FC, LLC), a PFPE-based oil.

[0057] The oils were tested for viscosity, volatility, and molecular weight prior to addition of the thickener.

[0058] For each oil, a grease containing 79 wt% oil and 21 wt% PTFE powder as a thickener was made by milling the oil with the PTFE powder. The PTFE powder had an aggregate particle size D50 of 6.7 pm and a surface area of 24.4 m²/g (The Chemours Company, Wilmington, DE). The greases were tested for torque, wear, penetration, and separation.

Test Methods

Determination of the oil kinematic viscosity

[0059] Kinematic viscosities were measured using a Gravity Flow U- shaped Glass Tube Capillary Viscometer (ASTM D445-97) at temperatures of 40°C, 100°C, and -40°C and reported in centistokes (cSt). Viscosity indexes were calculated from the measured viscosities. The resulting values are shown in Table 1.

Determination of volatility

[0060] To determine volatility, the test oil was subjected to a standard 10°C/minute ramp therm ogravimetric analyzer (TGA) test under an air or nitrogen atmosphere with a 60 mL/minute flow rate. Weight and temperature data was collected at a rate of 0.50 seconds/point. The volatility is reported as the temperatures at which 5 wt% and 50 wt% loss is observed. The resulting values are shown in Table 1.

Determination of molecular weight

[0061] ¹⁹F NMR spectra (376.5 MHz, Bruker Ascend 400) were obtained for neat oils of the inventive examples or by dissolving the oils in Freon-113 with CeDe capillary. [0062] The number average molecular weight (M_n) value was determined by ¹⁹F NMR by taking into account the weight and number of repeat units from integration of all -CF2CF2O- (-90.0 to -91 .5 ppm, several singlets, and -86.7 to -88.7 ppm, AB-system), and -CF(CFs)CF2O- (-145 to -146.5 ppm, multiplets) per number of end groups: CF3O- (-56.0 and -58.1 ppm, singlets), CF3CF2O- (CF3CF2O-, -89.3 and -89.5 ppm, multiple singlets), and CF3CF2CF2O- (CF3CF2CF2O-, -131.8 and -132.3 ppm, singlets).

[0063] The number average molecular weight (M_n) value for the comparative examples was the reported value for the commercial products.

[0064] The resulting values are shown in Table 1 .

Determination of torque

[0065] To determine torque, the greases were subjected to a low- temperature ball bearing torque tests following the methods of ASTM D1478 (ASTM International, West Conshohocken, PA). The starting torque and the running torque at -40°C are reported in Table 2.

Determination of wear

[0066] An average 4-ball wear scar for each grease was determined following the method of ASTM D2266 at the conditions of 75°C, 1200 rpm, and 40 kgf for 60 minutes. Table 2 shows the average of two runs for each grease.

Determination of penetration

[0067] To determine penetration, the greases were subjected to one- quarter scale cone penetration of lubricating grease tests following the methods of ASTM D1403. The resulting grease penetration distances after 0, 4, 7, 12, and 13 days are shown in Table 2. Determination of separation

[0068] To determine oil separation, the greases were subject to oil separation tests following the methods of ASTM D6184. The test measured the bleeding of the oil from the grease under static conditions for 30 hours at an elevated temperature through a wire cone, simulating operational oil losses. Table 2 shows the weight loss percentages as measured at temperatures of 99°C and 204°C.

Results

[0069] Certain properties of the oils of the inventive and comparative examples are shown in Table. 1.

Table 1 : Oil Properties

[0070] Although the oils of IE1 and IE3 had a more similar HFPO:TFEO ratio, the oils of IE1 and IE2 had a more similar molecular weight, resulting in viscosities and volatilities that were more similar to each other.

[0071] The inventive oils had similar viscosities to the comparative oils at 40°C and 100°C and were generally less volatile than the comparative oils. The inventive oils had viscosities between those of the comparative oils at -40°C.

[0072] Certain properties of the greases of the inventive and comparative examples are shown in Table. 2. Table 2: Grease Properties

N/D = not determined

[0073] Table 2 shows that the inventive greases have good penetration and low oil separation.

[0074] One advantage of the inventive examples is a reduction in the low temperature torque measured at -40°C, which is not achieved by the poly-HFPO oil-based grease of CE1 . Also, the volatility demonstrated by TGA of the oil components of the inventive greases is substantially lower than that of similar ISO-grade (40°C viscosity) poly-HFPO oil components of greases such as CE1 . Further, the viscosity index of the oil components of the inventive greases is substantially higher than that of similar ISO- grade (40°C viscosity) poly-HFPO oil components of greases such as CE1. These properties extend the useful temperature range of the grease at both low and high temperature ranges.

[0075] All above-mentioned references are hereby incorporated by reference herein. [0076] While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made, and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

CLAIMS What is claimed is:

1 . A grease comprising: a perfluoropolyether oil copolymer comprising: about 20 mol% to about 80 mol% of -CF2CF2O- units; about 20 mol% to about 80 mol% of -CF(CF3)CF2O- units; and about 0 mol% to about 45 mol% of one or more additional perfluoroalkyleneoxy units; said copolymer having a viscosity index in the range of about 120 to about 220; and said copolymer having an average TFEO run length of less than about 6; and a thickener mixed with the copolymer.

2. The grease of claim 1 , wherein the copolymer has a number average molecular weight in the range of about 1 ,500 to about 20,000 Da.

3. The grease of claim 2, wherein the number average molecular weight is in the range about 3,500 to about 13,000 Da.

4 The grease of any of the preceding claims, wherein the one or more additional perfluoroalkyleneoxy units comprises -CF2CF2CF2O- units.

5. The grease of any of the preceding claims, wherein the ISO viscosity grade of the copolymer is above about 25.

6. The grease of any of the preceding claims, wherein the viscosity index is in the range of about 150 to about 220.

7. The grease of any of the preceding claims, wherein the average TFEO run length is less than about 4.5.

8. The grease of any of the preceding claims, wherein the copolymer has a pour point of about -20°C or less. The grease of claim 8, wherein the pour point is about -50°C or less. The grease of any of the preceding claims, wherein the thickener is selected from the group consisting of polytetrafluoroethylene, talc, silica, fluorinated ethylene propylene, perfluoroalkoxy alkane, clay, graphite, surface-treated silica, boron nitride, calcium carbonate, and combinations thereof. The grease of any of the preceding claims, wherein the thickener is present in the grease in an amount in the range of about 1 % to about 50% by weight of the grease. The grease of any of the preceding claims, wherein the thickener comprises particles having a surface area in the range of about 2 to about 35 m²/g. The grease of any of the preceding claims, wherein the thickener comprises particles having an average particle size in the range of 30 nm to 300 nm. The grease of any of the preceding claims, wherein the grease has a starting torque at -40°C of less than 1100 g-cm. The grease of any of the preceding claims, wherein the grease has a running torque at -40°C of less than 450 g-cm. A process of forming a grease, the process comprising: mixing a perfluoropolyether oil copolymer with a thickener to form the grease, wherein the perfluoropolyether oil copolymer comprises: about 20 mol% to about 80 mol% of -CF2CF2O- units; about 20 mol% to about 80 mol% of -CF(CF3)CF2O- units; and about 0 mol% to about 45 mol% of one or more additional perfluoroalkyleneoxy units; said copolymer having a viscosity index in the range of about 120 to about 220; and said copolymer having an average TFEO run length of less than about 6. The process of claim 16, wherein the mixing comprises milling the perfluoropolyether oil copolymer with the thickener. The process of claims 16 or 17, wherein the thickener is selected from the group consisting of polytetrafluoroethylene, talc, silica, fluorinated ethylene propylene, perfluoroalkoxy alkane, clay, graphite, surface-treated silica, boron nitride, calcium carbonate, and combinations thereof. The process of any of claims 16 through 18, wherein the grease has a starting torque at -40°C of less than 1100 g-cm. The process of any of claims 16 through 19, wherein the grease has a running torque at -40°C of less than 450 g-cm.