Patent Description:
Commercial scale options for high-performance perfluoropolyether lubricants are limited to only a few main approaches that use anionic polymerization of hexafluoropropylene epoxide (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 <NUM>,<NUM>,<NUM>,<NUM>-tetrafluorooxetane and its further fluorination is also practiced, producing a -(CF<NUM>CF<NUM>CH<NUM>O)n-polymer that requires significant further fluorination to make a - (CF<NUM>CF<NUM>CF<NUM>O)n- polymer.

Commercial oils formed by anionic polymerization of HFPO (poly -CF(CF<NUM>)CF<NUM>O-), 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, low molecular weight of relatively viscous oils increases their volatility and may limit some of their application.

Commercial oils produced from TFE by photo-oxidation polymerization that contain -CF<NUM>CF<NUM>O- units (TFEO units) 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, but also contain difluoroformyl (-CF<NUM>O-) groups, and therefore decompose more rapidly in the presence of Lewis acids, metal halides, such as AlCl<NUM>, metal oxides, or metals, such as aluminum or iron, than other commercial perfluoropolyethers (PFPEs), such as poly -(CF(CF<NUM>)CF<NUM>O)n- (Krytox™ PFPE-K) or-(CF<NUM>CF<NUM>CF<NUM>O)n- (PFPE-D), which do not contain -CF<NUM>O- groups. Commercial oils containing -CF(CF<NUM>)CF<NUM>O- units, produced from HFP by photo-oxidation polymerization, and available under the trade name Fomblin® Y (Solvay Specialty Polymers, Milan, IT) also contain difluoroformyl (-CF<NUM>O-) groups that lower their stability compared to PFPE-K.

The end groups in Fomblin® M and Fomblin® Z oils are mostly CF<NUM>O-groups, which also lower their stability compared to the longer CF<NUM>CF<NUM>O-, CF<NUM>CF<NUM>CF<NUM>O-, and (CF<NUM>)<NUM>CFO- groups in the presence of metal halides and oxides [see, for example, <NPL>)]. Therefore, oils with a reduced amount of CF<NUM>O- end groups are desired to achieve higher stability. Oils that contain difluoroformyl (-CF<NUM>O-) 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, <NPL>)]. In addition, certain metals and metal oxides, such as aluminum oxide (Al<NUM>O<NUM>) and titanium oxide (TiO<NUM>), have a catalytic effect on the degradation of Fomblin® Y oils [<NPL>)].

<CIT>et al. , suggests perfluoropolyether oils from anionic polymerization of HFPO or both HFPO and TFEO in the presence of a cesium fluoride catalyst.

<CIT>, suggests copolymers containing -CF(CF<NUM>)CF<NUM>O- units and -CF<NUM>CF<NUM>O-units in addition to polymers containing -CF(CF<NUM>)CF<NUM>O- units and polymers containing -CF<NUM>CF<NUM>O- units having a viscosity within a certain range of values at <NUM>.

<CIT>, discloses fluorocarbon polyethers including copolymers including HFPO and TFEO and having a high TFEO content.

There is a need for lubricants that have a relatively small change in viscosity over a relatively wide temperature range corresponding to a high viscosity index (VI), a low pour point, a high stability against degradation at elevated temperatures in the presence of metals and metal oxides, which may be present on the surface of metals and metal alloys and act as Lewis acids, and a low volatility at elevated temperatures.

In an exemplary embodiment, a copolymer includes about <NUM> mol% to about <NUM> mol% of -CF<NUM>CF<NUM>O- units, about <NUM> mol% to about <NUM> mol% of -CF(CF<NUM>)CF<NUM>O- units, and about <NUM> mol% to about <NUM> mol% of one or more additional perfluoroalkyleneoxy units. The copolymer has a number average molecular weight (Mn) in the range of about <NUM>,<NUM> to about <NUM>,<NUM>, a viscosity index in the range of about <NUM> to about <NUM>, and an average TFEO run length of less than about <NUM>.

In another exemplary embodiment, a process of forming a perfluoroalkyl polyether copolymer includes feeding a gas stream containing tetrafluoroethylene oxide (TFEO) and hexafluoropropylene epoxide (HFPO) into a reactor containing a fluorinated solvent, an alkali metal fluoride salt, a polyethylene glycol) dialkyl ether, and either a short chain perfluoroalkyl polyether acid fluoride or a perfluoroalkyl acid fluoride, to form an acid fluoride-containing polymer. The TFEO and HFPO are fed in relative amounts such that the copolymer includes about <NUM> mol% to about <NUM> mol% of -CF<NUM>CF<NUM>O- units and about <NUM> mol% to about <NUM> mol% of -CF(CF<NUM>)CF<NUM>O- units. The process also includes hydrolyzing the acid fluoride-containing polymer with water or an aqueous solution of base to form a perfluoroalkyl polyether carboxylic acid or carboxylate salt. The process further includes distilling off the fluorinated solvent and treating the perfluoroalkyl polyether carboxylic acid or carboxylate salt with elemental fluorine to obtain the perfluoroalkyl polyether copolymer.

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.

Provided are exemplary lubricants with a high viscosity index (VI), a low pour point, a low volatility at high temperature, a high stability in the presence of metals, metal oxides, Lewis acids, or combinations thereof.

The provided polymers 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 <NUM>/<NUM> viscosity ratios and higher VI). When polymers of similar viscosity at <NUM> (International Standards Organization (ISO) viscosity grade (VG)) are compared, TFEO/HFPO copolymers containing <NUM>-<NUM> mol% of -CF(CF<NUM>)CF<NUM>O- units have a lower pour point than Fomblin® Y, - CF(CF<NUM>)CF<NUM>O-co-CF<NUM>O- lubricants, poly-HFPO Krytox™ lubricants, and poly-TFEO homopolymers.

As used herein, viscosity index (VI) is a unitless value for a subject polymer or copolymer oil based on its kinematic viscosities at <NUM> and <NUM> and calculated by the following formula: <MAT> where U is the subject oil's kinematic viscosity at <NUM> and L and H are values of kinematic viscosity at <NUM> for reference oils having a VI of <NUM> and a VI of <NUM>, respectively, and having the same kinematic viscosity at <NUM> as the subject oil, where values for L and H are found in ASTM D2270.

As used herein, ISO viscosity grade refers to the ISO VG that corresponds to the kinematic viscosity of oil at <NUM> reported in centistokes.

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.

As used herein, stability refers to the temperature at which <NUM>% weight loss is observed in the presence of <NUM>% aluminum oxide (neutral α-Al<NUM>O<NUM>), as Lewis acid, in a standard <NUM>/min ramp TGA test, with a higher temperature indicating a greater stability.

As used herein, volatility refers to % weight loss of the oil from room temperature to <NUM> observed in a standard <NUM>/min ramp TGA test, with a lower mass loss indicating a lower volatility.

As used herein, average TFEO run length refers to the average number of consecutive -CF<NUM>CF<NUM>O- units in a copolymer formed by the ring-opening of TFEO monomer.

TFEO has the following chemical structure:
<CHM>
which becomes a -CF<NUM>CF<NUM>O- perfluoroalkyleneoxy unit in the copolymer.

HFPO has the following chemical structure:
<CHM>
which becomes a -CF(CF<NUM>)CF<NUM>O- perfluoroalkyleneoxy unit in the copolymer.

In exemplary embodiments, the ratio of monomers in a gas stream is selected to improve and change the lubricant properties of the resulting copolymer. In exemplary embodiments, the copolymer has about <NUM> mol% to about <NUM> mol% of -CF<NUM>CF<NUM>O- units and about <NUM> mol% to about <NUM> mol% -CF(CF<NUM>)CF<NUM>O- units, alternatively about <NUM> mol% to about <NUM> mol% of -CF<NUM>CF<NUM>O- units and about <NUM> mol% to about <NUM> mol% of -CF(CF<NUM>)CF<NUM>O- units. In exemplary embodiments, the copolymer has at least about <NUM> mol% of -CF<NUM>CF<NUM>O- units, alternatively at least about <NUM> mol% of -CF<NUM>CF<NUM>O- units, alternatively at least about <NUM> mol% of -CF<NUM>CF<NUM>O- units, alternatively at least about <NUM> mol% of -CF<NUM>CF<NUM>O-units, alternatively at least about <NUM> mol% of -CF<NUM>CF<NUM>O- units, or any value, range, or sub-range therebetween. In exemplary embodiments, the copolymer has at least about <NUM> mol% of -CF(CF<NUM>)CF<NUM>O- units, alternatively at least about <NUM> mol% of -CF(CF<NUM>)CF<NUM>O- units, alternatively at least about <NUM> mol% of -CF(CF<NUM>)CF<NUM>O- units, alternatively at least about <NUM> mol% of -CF(CF<NUM>)CF<NUM>O- units, alternatively at least about <NUM> mol% of -CF(CF<NUM>)CF<NUM>O- units, alternatively at least about <NUM> mol% of -CF(CF<NUM>)CF<NUM>O- units, alternatively at least about <NUM> mol% of -CF(CF<NUM>)CF<NUM>O- units, alternatively at least about <NUM> mol% of - CF(CF<NUM>)CF<NUM>O- units, or any value, range, or sub-range therebetween.

The copolymer may also include up to about <NUM> mol% of one or more additional perfluoroalkyleneoxy units other than the -CF<NUM>CF<NUM>O- and -CF(CF<NUM>)CF<NUM>O- perfluoroalkyleneoxy units, alternatively about <NUM>% to about <NUM>%, alternatively about <NUM>% to about <NUM>%, alternatively about <NUM>% to about <NUM>%, alternatively about <NUM>% to about <NUM>%, alternatively about <NUM>% to about <NUM>%, alternatively up to about <NUM>%, alternatively up to about <NUM>%, alternatively up to about <NUM>%, alternatively up to about <NUM>%, or any value, range, or sub-range therebetween. In some embodiments, the additional perfluoroalkyleneoxy unit is (-CF<NUM>-CF<NUM>-CF<NUM>-O-). In some embodiments, (-CF<NUM>-CF<NUM>-CF<NUM>-O-) units are introduced by co-polymerization of TFEO, and optionally HFPO, with <NUM>,<NUM>,<NUM>,<NUM>-tetrafluorooxetane to make (-CH<NUM>-CF<NUM>-CF<NUM>-O-) containing polyfluorinated ether, followed by fluorination with elemental fluorine to form -CF<NUM>-CF<NUM>-CF<NUM>-O- containing polymers.

In exemplary embodiments, the copolymer has a number average molecular weight (Mn) in the range of about <NUM>,<NUM> Daltons (Da) to about <NUM>,<NUM> Da, alternatively about <NUM>,<NUM> Da to about <NUM>,<NUM> Da, alternatively about <NUM>,<NUM> Da to about <NUM>,<NUM> Da, or any value, range, or sub-range therebetween.

In exemplary embodiments, the copolymer has a viscosity index in the range of about <NUM> to about <NUM>, alternatively about <NUM> to about <NUM>, alternatively about <NUM> to about <NUM>, alternatively about <NUM> to about <NUM>, alternatively about <NUM> to about <NUM>, or any value, range, or sub-range therebetween.

In exemplary embodiments, the copolymer has an average TFEO run length of less than about <NUM>, alternatively less than about <NUM>, alternatively less than about <NUM>, alternatively less than about <NUM>, alternatively less than about <NUM>, or any value, range, or sub-range therebetween. A shorter average TFEO run length reduces the likelihood of crystallization of the copolymer upon cooling.

In exemplary embodiments, the copolymer has a pour point of about - <NUM> or less, alternatively about -<NUM> or less, alternatively about -<NUM> or less, alternatively about -<NUM> or less, or any value, range, or sub-range therebetween.

In exemplary embodiments, the end groups of the copolymer contain primarily CF<NUM>CF<NUM>CF<NUM>O- and CF<NUM>CF<NUM>O- end groups, thereby avoiding the high amount of CF<NUM>O- end groups typical for a perfluoropolyether containing -CF<NUM>-CF<NUM>-O- units made by photo-oxidation polymerization of TFE, and giving a lubricant with a high stability and low volatility.

In exemplary embodiments, about <NUM> mol% or less of the end groups are CF<NUM>O- end groups, alternatively about <NUM> mol% or less, alternatively about <NUM> mol% or less, alternatively about <NUM> mol% or less, or any value, range, or sub-range therebetween. In exemplary embodiments, about <NUM> mol% or more of the end groups are selected from CF<NUM>CF<NUM>CF<NUM>O-, (CF<NUM>)<NUM>CFO-, and CF<NUM>CF<NUM>O- end groups, alternatively about <NUM> mol% or more, alternatively about <NUM> mol% or more, alternatively about <NUM> mol% or more, or any value, range, or sub-range therebetween.

In exemplary embodiments, the stability of the copolymer is about <NUM> or greater, alternatively about <NUM> to about <NUM>, alternatively about <NUM> or greater, alternatively about <NUM> or greater, alternatively about <NUM> or greater, alternatively about <NUM> or greater, alternatively about <NUM> to about <NUM>, alternatively about <NUM> or greater, or any value, range, or sub-range therebetween.

In exemplary embodiments, the volatility of the copolymer at a useful temperature range is about <NUM>% or less, alternatively about <NUM>% to about <NUM>%, alternatively about <NUM>% or less, alternatively about <NUM>% or less, alternatively about <NUM>% or less, alternatively about <NUM>% to about <NUM>%, or any value, range, or sub-range therebetween.

In exemplary embodiments, the ISO viscosity grade of the copolymer is about <NUM> or greater, alternatively about <NUM> to about <NUM>, alternatively about <NUM> or greater, alternatively about <NUM> to about <NUM>, alternatively about <NUM> to about <NUM>, alternatively about <NUM> or greater, alternatively about <NUM> or greater, alternatively about <NUM> to about <NUM>, or any value, range, or sub-range therebetween.

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, CF<NUM>C(O)F or CF<NUM>CF<NUM>C(O)F, or a perfluoroalkyl ketone or its corresponding alkoxide, such as, for example, CF<NUM>CF<NUM>O-; CF<NUM>CF<NUM>CF<NUM>O-; (CF<NUM>)<NUM>CFO-, or CF<NUM>CF<NUM>CF<NUM>CF<NUM>O-; 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 -CF<NUM>CF<NUM>O- units and -CF(CF<NUM>)CF<NUM>O- 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 CF<NUM>O-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 <NUM>:<NUM> at the end of polymerization such that about <NUM> mol% or less of the end groups of the perfluoroalkyl polyether copolymer are CF<NUM>O- end groups. The method further includes working up the acid fluoride-containing polymer to form the copolymer.

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 -OCF<NUM>H, -OCF(CF<NUM>)H, and/or - OCF=CF<NUM> end groups. The process further includes treating the perfluoroalkyl polyether carboxylic acid or carboxylate salt, or above mixture containing -OCF<NUM>H, -OCF(CF<NUM>)H, and/or -OCF=CF<NUM> end groups with elemental fluorine to obtain the perfluoroalkyl polyether copolymer.

In exemplary embodiments, the reactor is an autoclave. In exemplary embodiments, the reaction occurs at a temperature in the range of about - <NUM> to about <NUM>, alternatively about -<NUM> to about -<NUM>, or any value, range, or sub-range therebetween, over a period of about <NUM> to about <NUM> hours.

In exemplary embodiments, the hydrolysis is with an aqueous sodium hydroxide solution to reach a pH in the range of <NUM> to <NUM>. In exemplary embodiments, the treatment is with <NUM>% elemental fluorine at a stepwise increasing temperature from <NUM> to <NUM>, alternatively from <NUM> to <NUM>, alternatively from <NUM> to <NUM>, alternatively from <NUM> to <NUM>, alternatively from <NUM> to <NUM>, or any range or sub-range therebetween.

Copolymers of the present invention may be used in any of a number of different applications, including, but not limited to, vacuum pump lubrication, automotive part lubrication, aviation part lubrication, and valve lubrication, including lubrication environments having a wide range of temperature and chemical conditions.

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

<NUM>F NMR spectra (<NUM>, Bruker Ascend <NUM>) were obtained for neat oils of the inventive examples or by dissolving the oils in Freon-<NUM> with C<NUM>D<NUM> capillary.

The average length of poly-TFEO segments in the inventive examples was calculated by dividing the sum of integration of the <NUM>F NMR peaks that correspond to the poly(-CF<NUM>CF<NUM>O-) segments (-<NUM> to -<NUM> ppm, several singlets, a), and the integration of the <NUM>F NMR peaks that correspond to the -CF<NUM>CF<NUM>O--F(CF<NUM>)CF<NUM>O- (-<NUM> to -<NUM> ppm, AB-system, b) at the end of the poly(-CF<NUM>CF<NUM>O-) segment neighboring the -CF(CF<NUM>)-group, divided by <NUM>, and by the integration of the <NUM>F NMR peaks that correspond to the TFEO-segment -CF<NUM>CF<NUM>O- neighboring the -CF(CF<NUM>)CF<NUM>O- group (-<NUM> to -<NUM> ppm, AB-system, b). In short, the average length of poly-TFEO segments was calculated as: (a + b) / 2b.

The overall percent of the CF<NUM>O- end groups in the fluorinated oil copolymer was calculated by dividing the sum of the integration of the <NUM>F NMR peaks that correspond to the poly- CF<NUM>O- groups (-<NUM> and -<NUM> ppm, singlets, a) divided by <NUM>, and divided by the sum of the integration of CF<NUM>O- divided by <NUM>, CF<NUM>CF<NUM>O- (-<NUM> and -<NUM> ppm, multiple singlets, b) divided by <NUM>, and CF<NUM>CF<NUM>CF<NUM>O- (-<NUM> and -<NUM> ppm, singlets, c) groups. In short, the mol% of CF<NUM>O- end groups was calculated as: (a /<NUM>) / (a/<NUM>+b/<NUM>+c).

The overall percent of the -CF(CF<NUM>)CF<NUM>O- groups in the fluorinated oil copolymer was calculated by dividing the sum of the integration of the <NUM>F NMR peaks that correspond to the -CF(CF<NUM>)CF<NUM>O- group (-<NUM> to -<NUM> ppm, multiplets, a), by the sum of integration of the <NUM>F NMR peaks that correspond to the -CF(CF<NUM>)CF<NUM>O- group (-<NUM> to -<NUM> ppm, multiplets, a), poly(-CF<NUM>CF<NUM>O-) segments (-<NUM> to -<NUM> ppm, several singlets, b) divided by <NUM>, and the integration of the <NUM>F NMR peaks that correspond to the -CF<NUM>CF<NUM>O-CF(CF<NUM>)CF<NUM>O- (-<NUM> to -<NUM> ppm, AB-system, c) at the end of poly(-CF<NUM>CF<NUM>O-) segment neighboring the -CF(CF<NUM>)-group divided by <NUM>. In short, the mol% of-CF(CF<NUM>)CF<NUM>O- units was calculated as: a / (a+b/<NUM>+c/<NUM>).

The number average molecular weight (Mn) value was determined by <NUM>F NMR by taking into account the weight and number of repeat units from integration of all -CF<NUM>CF<NUM>O- (-<NUM> to -<NUM> ppm, several singlets, and -<NUM> to -<NUM> ppm, AB-system), and -CF(CF<NUM>)CF<NUM>O- (-<NUM> to -<NUM> ppm, multiplets) per number of end groups: CF<NUM>O- (-<NUM> and -<NUM> ppm, singlets), CF<NUM>CF<NUM>O- (CF<NUM>CF<NUM>O-, -<NUM> and -<NUM> ppm, multiple singlets), and CF<NUM>CF<NUM>CF<NUM>O- (CF<NUM>CF<NUM>CF<NUM>O-, -<NUM> and -<NUM> ppm, singlets).

Kinematic viscosities were measured using Gravity Flow U-shaped Glass Tube Capillary Viscometer (ASTM D445-<NUM>) at temperatures of <NUM> and <NUM> and reported in centistokes (cSt). The ISO VG value corresponds to the oil kinematic viscosity measured at <NUM> and reported in centistokes (cSt).

To determine stability, the test oil with <NUM>% aluminum oxide (neutral α-Al<NUM>O<NUM>), as Lewis acid, was loaded onto a tared <NUM>-µg platinum pan in a TA Instruments (New Castle, DE) Q500 TGA and the temperature was ramped linearly from ambient conditions to <NUM> at <NUM>/minute under an air or nitrogen atmosphere with a <NUM>/minute flow rate. Weight and temperature data was collected at a rate of <NUM> seconds/point. The stability is reported as the temperature at which <NUM>% weight loss of the test oil in the TGA occurs.

To determine volatility, the test oil was subjected to a standard <NUM>/minute ramp thermogravimetric analyzer (TGA) test under an air or nitrogen atmosphere with a <NUM>/minute flow rate. Weight and temperature data was collected at a rate of <NUM> seconds/point. The volatility is reported as weight loss % of the copolymer when the temperature reaches <NUM>.

A dry <NUM>-gal Hastelloy-C autoclave was charged with <NUM> of F[CF(CF<NUM>)CF<NUM>O]a-CF(CF<NUM>)C(O)F, where a has an average value of about <NUM>, <NUM> of cesium fluoride (CsF), <NUM> of tetraglyme (CH<NUM>O(CH<NUM>CH<NUM>O)<NUM>CH<NUM>), and <NUM> of perfluorobutyl methyl ether (HFE-<NUM>; <NUM> Company, Maplewood, MN) as a fluorinated solvent, agitated, and cooled to a temperature in the range of -<NUM> to -<NUM>.

A gas stream containing TFEO and HFPO was fed into the reactor over the period of <NUM>. The copolymer poly(hexafluoropropylene oxide-co-tetrafluoroethylene oxide) acid fluoride, having an Mn of about <NUM>, was obtained.

The solvent was distilled off and the distillation residue was treated with <NUM>% NaOH solution to reach a pH of <NUM>. A solution of the polymer in Vertrel™ XF solvent (<NUM>,<NUM>-dihydrodecafluoropentane, Miller-Stephenson Chemical Co. , Danbury, CT) was washed with water and methanol. The Vertrel™ XF solvent and a light product cut was distilled off under vacuum, and the tetraglyme removed by phase separation. The obtained ether copolymer mixture, R<NUM>[[CF(CF<NUM>)CF<NUM>O]n-[CF<NUM>CF<NUM>O]m]x-R<NUM>, where R<NUM> is F[CF(CF<NUM>)CF<NUM>O]a-CF(CF<NUM>)CF<NUM>O-, CF<NUM>CF<NUM>CF<NUM>O-, or CF<NUM>CF<NUM>O-, R<NUM> is CF(CF<NUM>)COOH or -CF=CF<NUM>, n has an average value of about <NUM>, and m has average value of about <NUM>, having an Mn of about <NUM>,<NUM>, was treated with <NUM>% elemental fluorine at a stepwise increasing temperature from <NUM> to <NUM> to obtain the perfluorinated copolymer product, F[CF(CF<NUM>)CF<NUM>O]n-[CF<NUM>CF<NUM>O]m-CF<NUM>CF<NUM>, R<NUM>[[CF(CF<NUM>)CF<NUM>O]n-[CF<NUM>CF<NUM>O]m]x-R<NUM>, where R<NUM> is F[CF(CF<NUM>)CF<NUM>O]a-CF(CF<NUM>)CF<NUM>O-, CF<NUM>CF<NUM>CF<NUM>O-, or CF<NUM>CF<NUM>O-, R<NUM> is CF<NUM>CF<NUM> or -CF<NUM>), n has an average value of about <NUM>, and m has an average value of about <NUM>, having an Mn of about <NUM>,<NUM>, which was separated by vacuum distillation into different fractions, including Inventive Example <NUM>, Inventive Example <NUM>, and Inventive Example <NUM>. Values for certain properties of Inventive Example <NUM>, Inventive Example <NUM>, and Inventive Example <NUM> are shown in Table <NUM>.

Inventive Examples <NUM>-<NUM> all have a high viscosity index, a low TFEO run length, and a low CF<NUM>O- end group content. Inventive Example <NUM> has a low pour point. Pour point was not determined for Inventive Example <NUM> and Inventive Example <NUM>.

A dry <NUM>-gal Hastelloy-C autoclave was charged with <NUM> of F[CF(CF<NUM>)CF<NUM>O]<NUM>-CF(CF<NUM>)C(O)F, <NUM> of CsF, <NUM> of tetraglyme (CH<NUM>O(CH<NUM>CH<NUM>O)<NUM>CH<NUM>), and <NUM> of perfluorobutyl methyl ether (HFE-<NUM>) as a fluorinated solvent, agitated, and cooled to a temperature in the range of -<NUM> to -<NUM>.

A gas stream containing TFEO and HFPO was fed into the reactor over the period of <NUM>. The copolymer poly(hexafluoropropylene oxide) (tetrafluoroethylene oxide) acid fluoride was obtained, where the acid fluoride end groups were -CF(CF<NUM>)C(O)F or -CF<NUM>C(O)F.

The solvent was distilled off and the distillation residue was treated with <NUM>% NaOH solution to reach a pH in the range of <NUM> to <NUM>. A solution of the polymer in Vertrel™ XF solvent was washed with water and methanol. The Vertrel™ XF solvent and a light product cut was distilled off under vacuum, and the tetraglyme removed by phase separation. The obtained acid copolymer was treated with <NUM>% elemental fluorine at a stepwise increasing temperature from <NUM> to <NUM> to obtain the perfluorinated copolymer product, where the end group was -OCF<NUM>CF<NUM> or -OCF<NUM>, which was separated by vacuum distillation into different fractions, including Inventive Example <NUM> and Inventive Example <NUM>. Values for certain properties of Inventive Example <NUM> and Inventive Example <NUM> are shown in Table <NUM>.

Inventive Examples <NUM>-<NUM> both have a high viscosity index, a low TFEO run length, and a low CF<NUM>O- end group content. Inventive Example <NUM> has a low pour point. Pour point was not determined for Inventive Example <NUM>.

A gas stream containing TFEO and HFPO was fed into the reactor over the period of about <NUM>. The copolymer poly(hexafluoropropylene oxide) (tetrafluoroethylene oxide) acid fluoride was obtained, where the end groups were -CF(CF<NUM>)C(O)F or -CF<NUM>C(O)F, with an Mn of about <NUM>, as determined by <NUM>F NMR analysis.

The solvent was distilled off and the distillation residue was diluted with Vertrel™ XF and treated with a <NUM>% NaOH aqueous solution to reach a pH in the range of <NUM> to <NUM> and phase-separated. A solution of the polymer in Vertrel™ XF solvent was washed with water and methanol. The Vertrel™ XF solvent and a light product cut was distilled off under vacuum while gradually increasing the temperature from <NUM> to <NUM>. After cooling the remaining solution to room temperature, a small tetraglyme top phase removed by phase separation. The obtained copolymer having end groups of -OCF(CF<NUM>)COOH (about <NUM> mol%), -OCF<NUM>COOH (about <NUM> mol%), and -OCF<NUM>H (about <NUM>%), based on proton nuclear magnetic resonance (<NUM>H-NMR) spectroscopy, was treated with flow of <NUM>% elemental fluorine at a stepwise increasing temperature from <NUM> to <NUM> over a period of <NUM> to obtain the perfluorinated copolymer product, where the end groups were -OCF<NUM>CF<NUM> (about <NUM> mol%) or -OCF<NUM> (about <NUM> mol%), which was separated by vacuum distillation into different fractions, including Inventive Example <NUM>, Inventive Example <NUM>, Inventive Example <NUM>, Inventive Example <NUM>, and Inventive Example <NUM>. Values for certain properties of Inventive Example <NUM>, Inventive Example <NUM>, Inventive Example <NUM>, Inventive Example <NUM>, and Inventive Example <NUM> are shown in Table <NUM>.

Inventive Examples <NUM>-<NUM> all have a high viscosity index, a low TFEO run length, and a low CF<NUM>O- end group content. Inventive Examples <NUM>-<NUM> all have a low pour point.

A gas stream containing TFEO and HFPO was fed into the reactor over the period of about <NUM>. The copolymer poly(hexafluoropropylene oxide) (tetrafluoroethylene oxide) acid fluoride was obtained, containing the end groups -CF(CF<NUM>)C(O)F or -CF<NUM>C(O)F.

The solution was treated with a <NUM>% NaOH aqueous solution to reach a pH in the range of <NUM> to <NUM> and then phase-separated. The polymer solution was washed with water. The solvent and a light product cut was distilled off under vacuum while gradually increasing the temperature from <NUM> to <NUM>, and the remaining solution was cooled to room temperature. The obtained copolymer, having end groups of -OCF(CF<NUM>)COOH (about <NUM> mol%) or -OCF<NUM>COOH (about <NUM> mol% in combination), or -OCF(CF<NUM>)H (about <NUM>%), based on <NUM>H-NMR spectroscopy and an Mn of about <NUM>, was treated with <NUM>% elemental fluorine at a stepwise increasing temperature from <NUM> to <NUM> over a period of <NUM> in a shaker tube to obtain the perfluorinated copolymer product having end groups of -OCF<NUM>CF<NUM> (about <NUM> mol%) or -OCF<NUM> (about <NUM> mol%), which was separated by vacuum distillation into different fractions, including Inventive Example <NUM> and Inventive Example <NUM>. Values for certain properties of Inventive Example <NUM> and Inventive Example <NUM> are shown in Table <NUM>.

Inventive Examples <NUM> and <NUM> both have a high viscosity index, a low TFEO run length, and a low CF<NUM>O- end group content. Pour point was not determined for Inventive Examples <NUM> and <NUM>.

Inventive Examples <NUM>-<NUM> were prepared in separate batches following the procedure of the Example <NUM> with different TFEO /HFPO feed ratios while maintaining a stable feed ratio during the polymerization. Values for certain properties of Inventive Example <NUM> and Inventive Example <NUM> are shown in Table <NUM>.

The stability of the oil in the presence of a Lewis acid represented by aluminum oxide was determined as the temperature at which a weight loss of <NUM>% was observed in a standard <NUM>/min ramp thermogravimetric analyzer TGA test determined under nitrogen in the presence of <NUM>% aluminum oxide (neutral α-Al<NUM>O<NUM>). For Inventive Example <NUM> (MW = <NUM>, ISO VG= <NUM>), the stability (<NUM>% weight loss temperature in the presence of <NUM>% neutral α-Al<NUM>O<NUM>) was <NUM>. <NUM>% weight loss temperature in the standard <NUM>/min ramp TGA test of the Inventive Example <NUM> copolymer without aluminum oxide was also <NUM>. For Comparative Example <NUM> (Fomblin® M15, MW = <NUM>, ISO-<NUM>) the stability (<NUM>% weight loss temperature) for the standard <NUM>/min ramp TGA test in the presence of <NUM>% neutral α-Al<NUM>O<NUM>, was <NUM>, compared with <NUM>% weight loss temperature of <NUM> when it was tested without aluminum oxide.

The volatility of ISO VG= <NUM> oil of Inventive Example <NUM> measured as TGA % weight loss at <NUM> was measured to be <NUM>%, compared to the <NUM>% for ISO VG= <NUM> oil of Comparative Example <NUM>, and <NUM>% for Comparative Example <NUM> (ISO VG= <NUM>).

A dry <NUM>-gal Hastelloy-C autoclave was charged with <NUM> of F[CF(CF<NUM>)CF<NUM>O]<NUM>-CF(CF<NUM>)C(O)F, <NUM> of CsF, <NUM> of tetraglyme (CH<NUM>O(CH<NUM>CH<NUM>O)<NUM>CH<NUM>), and <NUM> of perfluorobutyl methyl ether (HFE-<NUM>) as a fluorinated solvent, agitated, and cooled to a temperature in the range of <NUM> to <NUM>.

A gas stream containing TFEO and <NUM>,<NUM>,<NUM>,<NUM>-tetrafluoro oxetane (cyclo-CH<NUM>CF<NUM>CF<NUM>O) was fed into the reactor over the period of about <NUM>. The copolymer poly(hexafluoropropylene oxide) (tetrafluoroethylene oxide) (tetrafluoro oxetane) acid fluoride solution, where the end groups were -OCH<NUM>CF<NUM>C(O)F or-OCF<NUM>C(O)F, was obtained.

The copolymer solution was treated with <NUM>% NaOH aqueous solution to reach a pH in the range of <NUM> to <NUM>, then phase-separated, and then washed with water. The solvent and a light product cut was distilled off under vacuum while gradually increasing the temperature from <NUM> to <NUM>. The obtained copolymer, F[CF(CF<NUM>)CF<NUM>O]<NUM>-[CF<NUM>CF<NUM>O]m-[CH<NUM>CF<NUM>CF<NUM>O]n-Y, where m/n = <NUM>, and Y was -CH<NUM>CF<NUM>COOH (<NUM> mol%) or -CF<NUM>COOH (<NUM> mol%), based on <NUM>F-NMR spectroscopy, and having an Mn of about <NUM>, was treated with <NUM>% elemental fluorine, while gradually increasing the temperature from <NUM> to <NUM> over a period of <NUM> in a shaker tube, to obtain, after removal of volatile components in vacuum, the perfluorinated copolymer product F[CF(CF<NUM>)CF<NUM>O]<NUM>-[CF<NUM>CF<NUM>O]m-[CF<NUM>CF<NUM>CF<NUM>O]n-Z, where the overall content of polymer units was -[CF(CF<NUM>)CF<NUM>O]- about <NUM> mol%, -[CF<NUM>CF<NUM>O]- about <NUM> mol%, -[CF<NUM>CF<NUM>CF<NUM>O]- about <NUM> mol%, TFEO run length about <NUM>, and Z was -CF<NUM>CF<NUM> (about <NUM> mol%) or -CF<NUM> (about <NUM> mol%), as an opaque oil (<NUM>), with overall content of end-groups -OCF<NUM>CF<NUM>CF<NUM> (about <NUM> mol%), -OCF<NUM>CF<NUM> (about <NUM> mol%), and -OCF<NUM> (about <NUM> mol%).

Certain TFEO polymers and HFPO polymers and one copolymer of TFEO and HFPO with a low fraction of -CF(CF<NUM>)CF<NUM>O- units were evaluated as comparative examples.

Values of certain properties of Comparative Example <NUM>, a copolymer of TFEO and HFPO having a low fraction of -CF(CF<NUM>)CF<NUM>O- units, are shown in Table <NUM>.

Comparative Example <NUM> has a high TFEO run length and a low HFPO content, which results in a high pour point temperature of the long poly-TFEO regions.

Values of certain properties of TFEO and HFPO polymers are shown in Table <NUM>. Comparative Example <NUM> is Krytox™ VPF <NUM> oil (The Chemours Company FC, LLC), a commercial homopolymer of HFPO. Comparative Example <NUM> is Krytox™ GPL <NUM> oil (The Chemours Company FC, LLC), a commercial homopolymer of HFPO. Comparative Example <NUM> is Krytox™ GPL <NUM> oil (The Chemours Company FC, LLC), a commercial homopolymer of HFPO. Comparative Example <NUM> is Fomblin® Y25 fluid (Solvay Specialty Polymers, Milan, IT), which is an HFP oxidation polymer. Comparative Example <NUM> is a TFEO homopolymer. Comparative Example <NUM> is Fomblin® M15 fluid (Solvay Specialty Polymers, Milan, IT), which is a TFE oxidation polymer.

The viscosity index (VI) for the obtained TFEO/HFPO F[CF(CF<NUM>)CF<NUM>O]n-[CF<NUM>CF<NUM>O]m-CF<NUM>CF<NUM> copolymer oils of the inventive examples was higher than for the HFPO homopolymers, which have a similar viscosity at <NUM> (ISO VG), which is exemplified in Inventive Examples <NUM>, <NUM>, <NUM>, <NUM> (VI = <NUM>-<NUM>, ISO VG = <NUM>-<NUM>), versus HFPO homopolymers and -CF(CF<NUM>)CF<NUM>O-/-CF<NUM>O- in Comparative Examples <NUM> and <NUM> (VI = <NUM>-<NUM>, ISO VG = <NUM>-<NUM>), and Inventive Example <NUM> (VI = <NUM>, ISO VG = <NUM>) as compared with the HFPO homopolymer of Comparative Example <NUM> (VI = <NUM>, ISO VG = <NUM>).

The pour points of Inventive Examples <NUM>, <NUM>, <NUM>, <NUM> were in the range of -<NUM> to -<NUM>, which is lower than for the comparative examples of HFPO-containing oils of a similar ISO VG (<NUM>-<NUM> cSt), such as the HFPO homopolymer of Comparative Example <NUM>, or the Fomblin® Y -CF(CF<NUM>)CF<NUM>O/-CF<NUM>O- copolymer of Comparative Example <NUM>. The pour point of Inventive Example <NUM> was -<NUM>, which is lower than for the HFPO homopolymer of Comparative Example <NUM>, where both oils have similar viscosities at <NUM>.

Comparative Examples <NUM> and <NUM> have a low stability, and Comparative Example <NUM> has a high pour point.

All above-mentioned references are hereby incorporated by reference herein.

Claim 1:
A copolymer comprising:
about <NUM> mol% to about <NUM> mol% of -CF<NUM>CF<NUM>O- units;
about <NUM> mol% to about <NUM> mol% of -CF(CF<NUM>)CF<NUM>O- units; and
about <NUM> mol% to about <NUM> mol% of one or more additional perfluoroalkyleneoxy units;
said copolymer having a number average molecular weight in the range of about <NUM>,<NUM> to about <NUM>,<NUM>, determined as defined in the description;
said copolymer having an average TFEO (tetrafluoroethylene oxide) run length of less than about <NUM>, determined as described in the description, wherein the average TFEO run length refers to the average number of consecutive -CF<NUM>CF<NUM>O- units in a copolymer formed by the ring-opening of TFEO monomer.