Branched polyalkylene glycol lubricants for use with hydro-fluorocarbon refrigerants

Abstract

Lubricant compositions for use with hydrofluorocarbon refrigerants, wherein the lubricant comprises: a) at least 50 wt% of a branched polyalkylene glycol having at least 3 chains; and b) wherein the lubricant has a kinematic viscosity at 40℃ of at least 50 mm2 / s.

Description

4823-01 1BRANCHED POLY ALKYLENE GLYCOL LUBRICANTS FOR USE WITH HYDROFLUOROCARBON REFRIGERANTS* * *FIELD OF ENDEAVOR

[0001] The field of endeavor pertains to branched polyalkylene glycol lubricants and their use with hydrofluorocarbon refrigerants in refrigeration and A / C compressors.BACKGROUND OF THE INVENTION

[0002] It is well known that viscosity is an important characteristic of a lubricant. In refrigeration and A / C applications, lubricant must also have the right miscibility properties for refrigerant being used. Often, the lubricant with the best viscosity profile for a particular application may not have the best miscibility properties. For example, the viscosity of a polyalkylene glycol lubricant may be increased by forming or selecting polyalkylene glycols with longer chains in the molecular structure, thereby increasing the viscosity and improving the lubricant’s ability to reduce wear in the compressor. As such, most polyethers are initiated with a diol or a mono-ol, resulting in single linear polymer chains and typically have kinematic viscosities greater than 100 mm2 / s at 40°C. These longer chained polyalkylene glycols, however, tend to have poor miscibility properties with fluorinated refrigerants, particularly refrigerants composed of short-chained molecules, such as difluoromethane (R-32). These long polymer chains offer high viscosity polyethers but they are not optimized for miscibility with R-32 and R-32 containing refrigerants. Shorter polymer chains have favorable miscibility characteristics with R-32 but short polymer chains produce low viscosity polyethers. Thus, there is a need for polyalkylene glycol lubricants that offer a higher viscosity profile while maintaining high miscibility with short-chained refrigerants.SUMMARY OF THE INVENTION

[0003] The inventors have surprisingly determined that lubricants comprising branched poylalkylene glycols having at least 3 chains in the molecule have good viscosity properties to reduce wear and are miscible with short-chained refrigerants. Accordingly, lubricants comprising at least 50 wt% of a branched poylalkylene glycol having at least 3 chains are disclosed. The lubricants have a kinematic viscosity at 40 °C of at least 50 mm2 / s.

[0004] In some embodiments, the polyalkylene glycol as at least 4 chains. In the same or different embodiments, each chain of the polyalkylene glycol may independently have 1 to 15 polyalkylene oxide repeat units.4823-01 2

[0005] The polyalkylene glycols disclosed herein may have the structure of formula (I):wherein n may be 0 or 1; R1may be H, a linear or branched C1-C12 (or Ci-Ce) hydro- carbyl group, or CH2O(C3H6O)WOR5; each of R2, R3, R4and R5may independently be H or a linear or branched C1-C12 (or Ci-Ce) hydrocarbyl group, or an acyl group having the formula -(C=O)Re where Re is a linear or branched hydrocarbyl group of 1 to 12 carbons; and each of w, x, y, and z may independently be an integer from 1 to 15. In some embodiments, the hydrocarbyl groups are alkyl groups.

[0006] In some embodiments, the polyalkylene glycol may be the reaction product of at least one hydrocarbyl polyol and at least one alkylene oxide. Suitable hydrocarbyl polyols are not overly limited and may include trimethylolpropane, dipentaerythritol, pentaerythritol, sorbitol, glycerol, mannitol, or mixtures thereof. Suitable alkylene oxides include, but are not limited to ethylene oxide, propylene oxide, butylene oxide, or mixtures thereof. In some embodiments, the at least one hydrocarbyl polyol may be trimethylolpropane and / or glycerol. In yet other embodiments, the at least one hydrocarbyl polyol may be trimethylolpropane. In the same or different embodiments, the at least one hydrocarbyl polyol may be glycerol.

[0007] In some embodiments, less than 70% mol% of the alkylene groups in the polyalkylene glycol may be derived from ethylene oxide. In the same or different embodiments, the alkylene groups in the polyalkylene glycol may be derived from propylene oxide and / or butylene oxide. In yet other embodiments, the alkylene groups in the polyalkylene glycol may be derived from propylene oxide. In some embodiments, the molar4823-01 3 ratio of the a) at least one hydrocarbyl polyol to the b) at least one alkylene oxide may be at least 1 :3 or at least 1 :4.

[0008] The branched poylalkylene glycol lubricants disclosed herein may be used with or in a composition comprising at least one hydrofluorocarbon refrigerant. In some embodiments the at least one hydrofluorocarbon refrigerant is not perfluorinated. In the same or different embodiments, the at least one hydrofluorocarbon refrigerant may comprise difluoromethane (R-32) or refrigerant blends thereof. In other embodiments, the hydrofluorocarbon refrigerant may comprise difluoromethane (R-32) and at least one hydrofluoroolefin refrigerant.DETAILED DESCRIPTION OF THE INVENTION

[0009] Various preferred features and embodiments will be described below by way of non-limiting illustration. The technology disclosed herein provides lubricants for use in refrigeration systems that are miscible with hydrofluorocarbon refrigerants. The disclosed lubricant may comprise branched poylalkylene glycols having at least 3 chains in the molecule. The lubricants may also have good viscosity properties to reduce wear. Accordingly, lubricants comprising at least 50 wt% of a branched poylalkylene glycol having at least 3 chains are disclosed. The lubricants have a kinematic viscosity at 40 °C of at least 50 mm2 / s.Branched Polyalkylene glycol (PAG)

[0010] Suitable branched polyalkylene glycols (“PAGs”) are not overly limited and can include any PAG having 3 or more chains. In some embodiments, the polyalkylene glycol as at least 4 chains. In the same or different embodiments, each chain of the polyalkylene glycol may independently have 1 to 15 polyalkylene oxide repeat units.

[0011] The polyalkylene glycols disclosed herein may have the structure of formula (I):4823-01 4wherein n may be 0 or 1; R1may be H, a linear or branched C1-C12 (or Ci-Ce) hydro- carbyl group, or CH2O(C3H6O)WOR5; each of R2, R3, R4and R5may independently be H or a linear or branched C1-C12 (or Ci-Ce) hydrocarbyl group, or an acyl group having the formula -(C=O)Re where Re is a linear or branched hydrocarbyl group of 1 to 12 carbons; and each of w, x, y, and z may independently be an integer from 1 to 15. In some embodiments, the hydrocarbyl groups are alkyl groups.

[0012] As used herein, the term “hydrocarbyl” refers to a group having a carbon atom directly attached to the remainder of the molecule, where the group includes at least carbon and hydrogen atoms. If the hydrocarbyl group comprises more than one carbon atom, then those carbons need not necessarily be linked to each other. For example, at least two of the carbons may be linked via a suitable element or group. In various embodiments, the term “hydrocarbyl” refers to a group having a carbon atom directly attached to the remainder of the molecule, where the group consists of carbon, hydrogen, optionally one or more heteroatoms provided the heteroatoms do not alter the predominantly hydrocarbon nature of the substituent. The heteroatom may link at least two of the carbons in the hydrocarbyl group, and optionally no more than two non-hydrocarbon substituents. Suitable heteroatoms will be apparent to those skilled in the art and include, for instance, sulphur, nitrogen, oxygen, phosphorus and silicon. Where the hydrocarbyl contains heteroatoms, optionally, no more than two heteroatoms will be present for every ten carbon atoms in the hydrocarbyl group. Suitable non-hydrocarbon substituents will also be apparent to those skilled in the art and include, for instance, halo, hydroxy, alkoxy, mercapto, alkylmercapto, nitro, nitroso, and sulphoxy.4823-01 5

[0013] Examples of hydrocarbyls within the context of the present technology therefore include:

[0014] hydrocarbon groups selected from aliphatic (e.g. alkyl or alkenyl), alicyclic (e.g. cycloalkyl, cycloalkenyl, cycloalkadienyl), and aromatic groups;

[0015] substituted hydrocarbon groups, selected from hydrocarbon groups defined in (i) substituted with no more than two non-hydrocarbon substituents and / or one or more hydrocarbon substituents, the non-hydrocarbon substituents being selected from the group consisting of halo, hydroxy, alkoxy, mercapto, alkylmercapto, nitro, nitroso, and sulphoxy;

[0016] hetero-containing hydrocarbon groups, selected from hydrocarbon groups defined in (i) containing one or more heteroatom in the ring or chain, provided that the group has no more than two heteroatoms present for every ten carbon atoms in the group, the heteroatoms being selected from sulphur, nitrogen, oxygen, phosphorus and silicon. The hetero-containing hydrocarbon groups may be substituted with no more than two non-hydrocarbon substituents and / or one or more hydrocarbon substituents.

[0017] In some embodiments, the term “hydrocarbyl” refers to a group having a carbon atoms directly attached to the remainder of the molecule, where the group consists of carbon and hydrogen atoms.

[0018] In some embodiments, the polyalkylene glycol may be the reaction product of at least one hydrocarbyl polyol and at least one alkylene oxide. Suitable hydrocarbyl polyols are not overly limited and may include trimethylolpropane, dipentaerythritol, pentaerythritol, sorbitol, glycerol, mannitol, or mixtures thereof. Suitable alkylene oxides include, but are not limited to ethylene oxide, propylene oxide, butylene oxide, or mixtures thereof. In some embodiments, the at least one hydrocarbyl polyol may be trimethylolpropane and / or glycerol. In yet other embodiments, the at least one hydrocarbyl polyol may be trimethylolpropane. In the same or different embodiments, the at least one hydrocarbyl polyol may be glycerol. In some embodiments, the PAG may have at least four branches or at least six branches that is the reaction product of at least one hydrocarbyl polyol selected from dipentaerythritol, pentaerythritol, or mixtures thereof.

[0019] In some embodiments, less than 70% mol% of the alkylene groups in the polyalkylene glycol may be derived from ethylene oxide. In the same or different embodiments, the alkylene groups in the polyalkylene glycol may be derived from propylene oxide and / or butylene oxide. In yet other embodiments, the alkylene groups in the polyalkylene glycol may be derived from propylene oxide. In some embodiments, the molar4823-01 6 ratio of the a) at least one hydrocarbyl polyol to the b) at least one alkylene oxide may be at least 1 :3 or at least 1 :4.

[0020] The polyalkylene glycol may have a number average (Mn) molecular weight of 400 to 2000, or 400 to 1500, as measured by ESI-MS (Electrospray Ionization Mass Spectrometry). In one embodiment, the polyalkylene glycol may have a number average molecular weight of at 700 to 800. Commercially available branched polyalkylene glycols include Polyglycol PT 700 available from Dow and Rokopol V700 available from PCC.

[0021] In some embodiments, one or more of the PAG branches may have a capped terminal end, wherein the hydroxy group is replaced with an alkoxy group, that is the branch is capped with a hydrocarbyl (or alkyl) ether. The PAG branches may be single end-capped, wherein one of the branches is capped, double end-capped, wherein two of the branches are capped, triple end-capped wherein 3 branches are capped, etc. Suitable alkoxy groups include, but are not limited to, methyloxy, ethyloxy, propyloxy, and butyloxy. In the same or different embodiments, the PAG may have at least one branch that is capped with tetrahydrofurfuryl alcohol (THF).

[0022] In some embodiments, the PAG may be a branched, un-capped 700 to 800 Mnmolecular weight PAG having a propylene oxide backbone. In some embodiments, the PAG may be a branched PAG having a propylene oxide backbone wherein at least one of the branches is capped with a methyloxy group. In some embodiments, the PAG may be a branched PAG having a propylene oxide backbone wherein at least one of the branches is capped with a butyloxy group.

[0023] In some embodiments, the

[0024] In any embodiments, the lubricants disclosed herein may further include one or more performance additives. Suitable examples of performance additives include antiwear additives, antioxidants, defoamers, acid catchers, or mixtures thereof.

[0025] Accordingly, in any embodiment, the lubricant may have at least one one antiwear additives, typically, a phosphorus additive. Suitable phosphorus additives may be selected from phosphites, phosphonates, alkylphosphate esters, amine or ammonium phosphate salts.

[0026] Phosphorus esters include the reaction products of dihydrocarbon and trihydrocarbon phosphites, e.g., dibutyl phosphite, diheptyl phosphite, dicyclohexyl phosphite, pentylphenyl phosphite; dipentylphenyl phosphite, tridecyl phosphite, distearyl phosphite and polypropylene substituted phenol phosphites, amine salts of alkyl and dialkylphosphoric acids.4823-01 7

[0027] Amine phosphates may be amine salts of (i) monohydrocarbylphosphoric acid, (ii) dihydrocarbylphosphoric acid, (iii) hydroxy-substituted di-ester of phosphoric acid, or (iv) phosphorylated hydroxy-substituted di- or tri-ester of phosphoric acid. The amine salt of a sulfur-free phosphorus-containing compound may be salts of primary amines, secondary amines, tertiary amines, or mixtures thereof.

[0028] Amine phosphate salts may be derived from mono- or di- hydrocarbyl phosphoric acid (typically alkyl phosphoric acid), or mixtures thereof. The alkyl of the mono- or di- hydrocarbyl phosphoric acid may comprise linear or branched alkyl groups of 3 to 36 carbon atoms. The hydrocarbyl group of the linear or branched hydro- carbylphosphoric acid may contain 4 to 30, or 8 to 20 carbon atoms. Examples of a suitable hydrocarbyl group of the hydrocarbyl phosphoric acid may include isopropyl, n-bu- tyl, sec-butyl, amyl, 4-methyl-2-pentyl (i.e. methylamyl), n-hexyl, n-heptyl, n-octyl, isooctyl, 2-ethylhexyl, nonyl, 2-propylheptyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, oleyl, or combinations thereof. In one embodiment, the phosphate is a mixture of mono- and di- (2-ethyl)hexylphosphate.

[0029] Examples of suitable primary amines include ethylamine, propylamine, butylamine, 2-ethylhexylamine, octylamine, and dodecylamine, as well as such fatty amines as n-octylamine, n-decylamine, n-dodecylamine, n-tetradecylamine, n-hexadecylamine, n-octadecylamine and oleyamine. Other useful fatty amines include commercially available fatty amines such as “Armeen®” amines (products available from Akzo Chemicals, Chicago, Ill.), such as Armeen C, Armeen O, Armeen O L, Armeen T, Armeen H T, Armeen S and Armeen S D, wherein the letter designation relates to the fatty group, such as coco, oleyl, tallow, or stearyl groups.

[0030] In some embodiments, the at least one phosphorous additive may comprise a phosphate, phosphite, phosphonate, or mixtures thereof. In some embodiments, the at least one phosphorous additive may comprise an aryl phosphate or an aryl phosphate in combination with an alkenyl phosphite. Suitable phosphorous additives include, but are not limited to, Ci6 - Cis alkenyl phosphite, butylated triphenyl phosphate, tri cresyl phosphate, dimethyl octadecyl phosphonate, or mixtures thereof. In some embodiments, the refrigeration lubricant may comprise Ci6 - Cis alkenyl phosphite and butylated triphenyl phosphate.

[0031] Accordingly, in some embodiments, the lubricants may comprise, alkenyl phosphite, butylated triphenyl phosphate, tricresyl phosphate, dimethyl octadecyl phosphonate, or combinations thereof. If present, the at least one phosphorous additive may4823-01 8 be present at 0.1 to 4 wt% (or 0.1 to 3 wt%, or 0.2 to 1 wt%, or 0.3 to 0.6 wt%), based on a total weight of the lubricant.

[0032] The antioxidants suitable for use in lubricants are not overly limited. Suitable antioxidants include butylated hydroxytoluene (BHT), butylatedhydroxyanisole (BHA), phenyl-a-naphthylamine (PANA), octyl ated / butylated diphenylamine, high molecular weight phenolic antioxidants, hindered bis-phenolic antioxidant, di-alpha-tocopherol, di- tertiary butyl phenol.

[0033] In some embodiments, the antioxidant includes one or more of:(i) Hexamethylene bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate), CAS registration number 35074-77-2, available commercially from BASF;(ii) N-phenylbenzenamine, reaction products with 2,4,4- trimethylpentene, CAS registration number 68411-46-1, available commercially from BASF;(iii) Phenyl-a-and / or phenyl-b-naphthylamine, for example N-phenyl-ar-(l, 1,3,3- tetram ethylbutyl)- 1 -naphthal enamine, available commercially from BASF;(iv) Tetrakis[methylene(3,5-di- / c / 7-butyl-4-hydroxyhydrocinnamate)] methane, CAS registration number 6683-19-8;(v) Thiodiethylenebis (3,5-di- / er / -butyl-4-hydroxyhydrocinnamate), CAS registration number 41484-35-9, which is also listed as thiodiethylenebis (3,5-di- tert-butyl-4-hydroxy-hydro-cinnamate) in 21 C.F.R. §178.3570;(vi) Butylated hydroxytoluene (BHT);(vii) Butylated hydroxyanisole (BHA);(viii) Bis(4-(l,l,3,3-tetramethylbutyl)phenyl)amine, available commercially from BASF; and(ix) Benzenepropanoic acid, 3,5-bis(l,l-dimethylethyl)-4-hydroxy-, thiodi-2,1- ethanediyl ester, available commercially from BASF.

[0034] In one embodiment, the lubricants may comprise antioxidants that are alkylated ester phenols, alkaryl amines, ditertbutyl cresol, or combinations thereof. The antioxidants may be present in the lubricants from 0.02 wt% to 1 wt% or 2 wt%, or from 0.05 wt% to 1 wt%, or 0.1 to 0.5 wt%, or 0.1 to 0.3 wt%, based on a total weight of the lubricant. These various ranges are typically applied to all of the antioxidants present in the overall composition. However, in some embodiments, these ranges may also be applied to individual antioxidants.

[0035] In yet other embodiments, the refrigeration lubricant may further comprise at at least one other additive that is a defoamer, an acid scavenger, or combinations thereof.4823-01 9

[0036] Defoamers include polysiloxanes, copolymers of ethyl acrylate and 2-ethylhex- ylacrylate and optionally vinyl acetate as well as demulsifiers including fluorinated polysiloxanes, trialkyl phosphates, polyethylene glycols, polyethylene oxides, polypropylene oxides and (ethylene oxi de-propylene oxide) polymers. The disclosed technology may also be used with a silicone-containing antifoam agent in combination with a Cs - C17 alcohol. In yet other embodiments, the additional antifoams may include organic silicones such as polydimethyl siloxane, polyethylsiloxane, polydiethylsiloxane, polyacrylates and polymethacrylates, trimethyl-trifluoro-propylmethyl siloxane and the like. In one embodiment, the defoamer may be polydimethyl siloxane.

[0037] Acid scavengers can include alkoxides having an alkyl group of from about 1 to about 12 carbon atoms, or 1 to 10 carbon atoms or 1 to 4 or 6 or 8 carbon atoms. The carbons can be straight chain or branched, saturated or unsaturated. Example alkoxides include methoxides, ethoxides, isopropoxides, and tert-butoxides. In one embodiment, the acid scavengers include epoxides. The metal passivator may be present in the lubricants 0.009 to 0.5 wt%, based on a total weight of the lubricant composition. In some embodiments, the metal passivator may be present 0.01 to 0.5 wt% or 0.02 to 0.3 wt%, or 0.05 to 0.25 wt%, or even 0.02 to 0.07 wt%, based on a total weight of the lubricant.

[0038] The branched poylalkylene glycol lubricants disclosed herein may be used with or in a composition comprising at least one hydrofluorocarbon refrigerant. In some embodiments the at least one hydrofluorocarbon refrigerant is not perfluorinated. Exemplary hydrofluorocarbons (“HFC”) include trifluorom ethane (R-23), difluorom ethane (R-32), pentafluoroethane (R-125), 1,1, 1,2-tetrafluoroethane (R-134a), 1,1,1-trifluoroethane (R- 143a), 1, 1 -difluoroethane (R- 152a), 1,2-difluoroethane, 1,1, 1,2, 3, 3, 3 -heptafluoropropane (R-227ea), 1, 1,1,3,3,3-hexafluroropropane (R-236fa), and 1,1, 1,3, 3 -pentafluoropropane (R-245fa).

[0039] In the same or different embodiments, the at least one hydrofluorocarbon refrigerant may comprise difluoromethane (R-32) or refrigerant blends thereof. In other embodiments, the hydrofluorocarbon refrigerant may comprise difluoromethane (R-32) and at least one hydrofluoroolefin refrigerant. Exemplary hydrochlorofluoroolefins (“HCFO”) include, but are not limited to, cis-2,3,3,3-tetrafluoro-l-chloro-l-propene (R-1224yd(Z)), trans-2, 3 , 3 ,3 -tetrafluoro- 1 -chloro- 1 -propene, trans- 1 -chi oro-3 ,3,3 -trifluoro- 1 -propene (R-1233zd(E)), cis-l-chloro-3,3,3-trifluoro-l-propene, 2-chloro-3,3,3 trifluoropropene,4823-01 101,1, di chi oro-3, 3, 3 trifluoropropene, 1,2 dichloro-3,3,3 trifluoropropene (E), and 1,2 di- chloro-3,3,3 trifluoropropene (Z).

[0040] The amount of each chemical component described is presented exclusive of any solvent or diluent oil, which may be customarily present in the commercial material, that is, on an active chemical basis, unless otherwise indicated. However, unless otherwise indicated, each chemical or composition referred to herein should be interpreted as being a commercial grade material which may contain the isomers, by-products, derivatives, and other such materials which are normally understood to be present in the commercial grade.

[0041] It is known that some of the materials described above may interact in the final formulation, so that the components of the final formulation may be different from those that are initially added. For instance, metal ions (of, e.g., a detergent) can migrate to other acidic or anionic sites of other molecules. The products formed thereby, including the products formed upon employing the composition of the present invention in its intended use, may not be susceptible of easy description. Nevertheless, all such modifications and reaction products are included within the scope of the present invention; the present invention encompasses the composition prepared by admixing the components described above.

[0042] The present methods, systems and compositions are thus adaptable for use in connection with a wide variety of heat transfer systems in general and refrigeration systems in particular, such as air-conditioning (including both stationary and mobile air conditioning systems), refrigeration, heat-pump systems, and the like.

[0043] As used herein, the term “refrigeration system” refers generally to any system or apparatus, or any part or portion of such a system or apparatus, which employs a refrigerant to provide cooling and / or heating. Such refrigeration systems include, for example, air conditioners, electric refrigerators, chillers, heat pumps, and the like.

[0044] The invention herein is useful for use in refrigeration or air conditioning compressors operating on hydrofluorocarbon refrigerants, which may be better understood with reference to the following examples.EXAMPLES

[0045] The lubricants disclosed herein may be used with any branched poylalkylene glycol having at least 3 chains. Suitable branched polyalkylene glycols are not overly limited and include any poylalkylene glycol that is branched or having at least 3 chains. The glycols may be selected by choosing a glycol having a kinematic viscosity suitable4823-01 11 for compressor applications. Suitable branched poylalkylene glycols include the Polyglycol PT series available from Dow.

[0046] Suitable branched polyalkylene glycols may be capped or uncapped PAGs, i.e. the PAGs may have caps on one or more of the branches. The PAGs may be capped as described in the preparatory example below.PREPARATORY EXAMPLE

[0047] A 700-molecular weight (Mn) polyalkylene glycol, for example PT700 available from Dow, may be capped using reagents in a molar ratio of PT700 / meI (methylio- dide) / CSL (caustic solution of 50% sodium hydroxide) of 1 :~4: 16. The reagents are added to a 4-neck flanged reaction vessel with N2 purge. The vessel is equipped with a thermocouple and reflux condenser. The polyglycol (430 g.) is added to the CSL (786 g.). The reagents are stirred at 520 rpm until good emulsion with light amber color is obtained. Then Mel (349 g.) is added to the emulsion and the mixture is heated and maintained at 45°C for 40 minutes.

[0048] Additional Mel (50 g) is added with stirring and allowed to react until the mixture turns clear and the reaction is complete (about 3 hours). The completeness is measured by taking samples and adding ethyl acetate and then brine. The organic portion is dried and analyzed using IR spectroscopy to ensure reaction is complete (OH peaks are no longer visible).

[0049] Once the reaction is complete, the capped PAG is then subjected to a 5% sodium bicarbonate wash while stirring and with 10% sodium thiosulfate and ethyl acetate. The resulting layers are separated and the organic layer is retained and dried over magnesium sulfate. The resulting material is a branched PAG wherein one or more of the PAG branches are capped with a methyl group.

[0050] As described above, the miscibility of PAGs with fluorinated refrigerants decreases as the PAG viscosity increases. The miscibility of a branched, un-capped 700- molecular weight (Mn) PAG having a propylene oxide backbone in a fluorinated refrigerant (R-454B) was tested (Table 1, Example 9). The branched PAG’s miscibility was compared to linear, butyloxy-single end-capped PAGs having a propylene oxide backbone of varying viscosities ranging from about 10 to about 100 mm2 / s at 40 °C (Examples 1-7). An additional liener, butyloxy-single end-capped PAG having an ethylene oxide propylene oxide (50 / 50) backbone and having a kinematic viscosity of about 100 mm2 / s at 40 °C was also tested (Example 8).4823-01 12

[0051] Miscibility is measured using ASHRAE Standard 218 - Method of Test for Lubricant and Refrigerant Miscibility Determination. For the miscibility test, a known amount of lubricant (5 wt%) and refrigerant (95 wt%) is placed in a glass tube. The glass tube is then sealed to maintain constant refrigerant gas mass with the lubricant and ob- serving the phase behavior at different temperature increments. Miscibility tubes are heated and / or cooled over a range of temperatures and phase change is monitored. Phases will be recorded as one of the following: IP is One-Phase Clear - the lubricant and refrigerant are in one phase that is visually clear; HZ is Translucent / Hazy - the lubricant / refrig- erant is still one phase, but solution is visually iridescent, or translucent; CL is Cloudy / Milky - the lubricant / refrigerant mixture appears thick, white, or milky, but no distinct phase separation is visible; 2P is Two-Phase Separation - lubricant and refrigerant can be clearly distinguished as two separate phases. Generally, miscibility ratings of IP or HZ will be acceptable in most applications, whereas miscibility ratings of CL or 2P will be unacceptable.4823-01 13

[0052] The miscibility results of the examples are shown in Table 1 below.Table 11 = linear, butyloxy-single end-capped PAG having a propylene oxide backbone 2 = linear, butyloxy-single end-capped PAG having an ethylene oxide propylene oxide (50 / 50) backbone3 = branched, un-capped 700 molecular weight PAG having a propylene oxide backbone4823-01 14

[0053] As shown in Table 1, the linear PAG’s miscibility with the refrigerant are generally acceptable at lower kinematic viscosities. As viscosities greater than 50, however, only the branched PAG has an acceptable miscibility with the refrigerant.

[0054] The branched PAG’s miscibility was also compared to polyol ester (POE) based lubricants. The comparative tests are shown in Table 2 below.Table 24823-01 153 = branched, un-capped 700 molecular weight PAG having a propylene oxide backbone4 = blend of POEs prepared from polyols and carboxylic acids5 = POE / PAG 50 / 50 blend, PAG is a linear, methyloxy-single end-capped PAG having a propylene oxide backbone

[0055] As shown in Table 2, the branched PAG is more miscible in the refrigerant than POE based lubricant, or even blends of POE lubricants with PAG lubricants.

[0056] Each of the documents referred to above is incorporated herein by reference, including any prior applications, whether or not specifically listed above, from which priority is claimed. The mention of any document is not an admission that such document qualifies as prior art or constitutes the general knowledge of the skilled person in any jurisdiction. Except in the Examples, or where otherwise explicitly indicated, all numerical quantities in this description specifying amounts of materials, reaction conditions, molecular weights, number of carbon atoms, and the like, are to be understood as modified by the word “about”. It is to be understood that the upper and lower amount, range, and ratio limits set forth herein may be independently combined. Similarly, the ranges and amounts for each element of the invention can be used together with ranges or amounts for any of the other elements.

[0057] As used herein, the transitional term “comprising,” which is synonymous with “including,” “containing,” or “characterized by,” is inclusive or open-ended and does not exclude additional, un-recited elements or method steps. However, in each recitation of “comprising” herein, it is intended that the term also encompass, as alternative embodiments, the phrases “consisting essentially of’ and “consisting of,” where “consisting of’ excludes any element or step not specified and “consisting essentially of’ permits the inclusion of additional un-recited elements or steps that do not materially affect the basic and novel characteristics of the composition or method under consideration.

[0058] While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. In this regard, the scope of the invention is to be limited only by the following claims.

Claims

4823-01 16What is claimed is:

1. A lubricant for use with hydrofluorocarbon refrigerants, wherein the lubricant comprises: a) at least 50 wt% (or at least 60, or at least 65, or at least 70, or at least 97 wt%, or 69 to 99.9 wt%, or 100 wt%) of a branched poylalkylene glycol having at least 3 chains; and b) wherein the lubricant has a kinematic viscosity at 40 °C of at least 50 mm2 / s (or at least 60 or at least 80 mm2 / s or at least 90 to 100 mm2 / s).

2. The lubricant of claim 1, wherein the polyalkylene glycol as at least 4 chains.

3. The lubricant of claim 1 or 2, wherein each chain independently has 1 to 15 polyalkylene oxide repeat units.

4. The lubricant of any one of claims 1 to 3, wherein the polyalkylene glycol has the structure of formula (I):wherein n may be 0 or 1; R1may be H, a linear or branched C1-C12 (or Ci-Ce) hydrocarbyl group, or CH2O(C3H6O)WOR5; each of R2, R3, R4and R5may independently be H or a linear or branched C1-C12 (or Ci-Ce) hydrocarbyl group, or an acyl group having the formula -(C=O)Re where Re is a linear or branched hydrocarbyl group of 1 to 12 carbons; and each of w, x, y, and z may independently be an integer from 1 to 15.4823-01 175. The lubricant of any one of claims 1 to 4, wherein the hydrocarbyl groups are alkyl groups.

6. The lubricant of any one of claims 1 to 5, wherein the polyalkylene glycol is the reaction product of: a) at least one hydrocarbyl polyol selected from trimethylolpropane, dipentaerythritol, pentaerythritol, sorbitol, glycerol, mannitol, or mixtures thereof; and b) at least one alkylene oxide selected from ethylene oxide, propylene oxide, butylene oxide, or mixtures thereof.

7. The lubricant of claim 6, wherein the at least one hydrocarbyl polyol is trimethylolpropane and / or glycerol.

8. The lubricant of claim 6, wherein the at least one hydrocarbyl polyol is trimethylolpropane.

9. The lubricant of claim 6, wherein the at least one hydrocarbyl polyol is glycerol.

10. The lubricant of any one of claims 6 to 9, wherein less than 70% (or less than 60%, 50%, 40%, 30%, 20%, 10%, or less than 1%) mol% of the alkylene groups in the polyalkylene glycol are derived from ethylene oxide.

11. The lubricant of any one of claims 6 to 10, wherein the alkylene groups in the polyalkylene glycol are derived from propylene oxide and / or butylene oxide.

12. The lubricant of any one of claims 6 to 11, wherein the alkylene groups in the polyalkylene glycol are derived from propylene oxide.

13. The lubricant of any one of claims 6 to 12, wherein the molar ratio of the a) at least one hydrocarbyl polyol to the b) at least one alkylene oxide is at least 1 :3 or at least 1:4.

14. The lubricant of any one of claims 1 to 13, wherein the polyalkylene glycol has a number average (Mn) molecular weight of 400 to 2000 (or 400 to 1500, or 700 to 800).

15. A composition comprising: a) the lubricant of any one of claims 1 to 14; and b) at least one hydrofluorocarbon refrigerant.4823-01 1816. The composition of claim 15, wherein the at least one hydrofluorocarbon refrigerant is not perfluorinated.

17. The composition of claim 15 or 16, wherein the at least one hydrofluorocarbon refrigerant comprises difluoromethane (R-32) or refrigerant blends thereof.

18. The composition of any one of claims 15 to 17, wherein the hydrofluorocarbon refrigerant comprises difluoromethane (R-32) and at least one hydrofluoroolefin refrigerant.

19. A refrigeration system charged with: a) the lubricant of any one of claims 1 to 14; and b) at least one hydrofluorocarbon refrigerant.

20. A method of improving the miscibility of a poylalkylene glycol lubricant with hydrofluorocarbon refrigerants, the method comprising: a) preparing a polyalkylene glycol lubricant having at least 50 wt% (or at least 60, or at least 65, or at least 70, or at least 97 wt%, or 69 to 99.9 wt%, or 100 wt%) of a branched poylalkylene glycol having at least 3 chains; and b) wherein the polyalkylene glycol lubricant has a kinematic viscosity at 40 °C of at least 50 mm2 / s (or at least 60 or at least 80 mm2 / s or at least 90 to 100 mm2 / s).

21. The method of claim 20, wherein the miscibility of the polyalkylene glycol lubricant with hydrofluorocarbon refrigerants is improved as compared to a polyalkylene glycol lubricant prepared from a linear polyalkylene glycol lubricant having a kinematic viscosity at 40 °C of at least 50 mm2 / s (or at least 60 or at least 80 mm2 / s or at least 100 mm2 / s).

22. The use of a branched poylalkylene glycol having at least 3 chains to improve the miscibility of a lubricant having a kinematic viscosity at 40 °C of at least 50 mm2 / s (or at least 60 or at least 80 mm2 / s or at least 100 mm2 / s) with hydrofluorocarbon refrigerants.

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