SYNTHETIC ESTER BASE STOCKS FOR LOW EMISSION LUBRICANTS

Abstract: A low emissions, high oxidative stability crankcase lubricating oil formulation which is prepared from a base stock which comprises at least one synthetic ester selected from the group consisting of: polyol esters, synthetic esters having between 5-35 % unconverted hydroxyl groups, based on the total amount of hydroxyl groups in the polyol, and synthetic esters combined with at least one additional functional group which is capable of increasing the polarity of the functionalized synthetic ester, wherein the base stock has an oxygen, nitrogen or halogen content of at least 15 wt.%, based on the total weight of the base stock; and a lubricant additive package.

Description: Title SYNTHETIC ESTER BASE STOCKS FOR LOW EMISSION LUBRICANTS Inventors R H Schlosberg W Weissman M Radosz, G D Dupre, R D Gray, . E Johnston, P E Godici, R S Pohzzotti, L Kaplan The present invention relates generally to a family of unique highly polarized svnthetic esters for use in crankcase lubricating oils or other systems where hydrocarbon fuel and lubncant emissions suppression (I e , reduction), and a high degree of resistance to oxidative attack is desired In particular, the lubricating oil comprises a family of unique synthetic ester base stocks which are sufficiently polar to ensure that hydrocarbon fuel components are onlv minimally soluble in the lubncating oil, therebv reducing the amount of fuel which can be trapped in oil film at engine shutdown and exhausted from an engine together with the lubncant especially dunng engine start-up BACKGROUND OF THE INVENTION Over the past 10 to 15 years there has been a concerted effort bv both engine manufacturers and petroleum suppliers to alleviate environmental concerns over engine exhaust emissions by substantially reducing the amount of hydrocarbon contained in such emissions In recent years, attention has been turned to the effect which certain engine lubncants have in reducing hydrocarbon emissions Recent studies have focused on the vaπous potential hvdrocarbon emission sources, e g engine crevices oil laver, deposits, incomplete combustion and liquid fuel in engine cylinders Each of these sources can produce a layer of hydrocarbons on the cylinder surface In an article by J Schramm and S C Sorenson, Journal of Chromatography, Vol 538, pp 1241 (1991), it was suggested that solubilitv characteristics ofthe lubncant influences the absorption of fuel molecules into the lubricant The fuel molecules absorbed within the lubncant are then released together with other engine exhaust emissions Lubricants in commercial use today are prepared from a vanety of natural and/or synthetic base stocks admixed with vaπous additive packages and solvents depending upon their intended application Typical base stocks include mineral oils, highly refined mineral oils, polv alpha olefins (PAO), polyalkylene glycols (PAG), phosphate esters, silicone oils, diesters and polyol esters The present inventors have discovered that a select group of synthetic ester base stocks are able to reduce the amount of hydrocarbons exhausted together with the emissions from crankcase engines or other engines where fuel and lubncant emission suppression is desirable The synthetic ester base stocks are those which form highly polarized lubricants in which fuel components are only minimally soluble, thereby reducing the amount of fuel which is dissolved and/or dispersed within the lubricant, thereby leading to a reduction of hydrocarbons in the exhaust gas The present inventors have also discovered that if the fuel is only minimally soluble within the lubricant, then a reduced amount of fuel is available for depositing within engine crevices or on the engine cylinder surface These highly polar synthetic ester base stocks result in lesser amounts of hydrocarbon being trapped within the lubricating oil film during the compression stroke Therefore, after combustion there will be less adsorbed hydrocarbon available for discharge out the exhaust system pnor to catalyst heat-up, thereby reducing the overall amount of hydrocarbon emission from a respective engine Since there are less light hydrocarbons dissolved within the lubncating oil due to the high polarity thereof, the lubricating oil composition itself will be less volatile which will also reduce the amount of lubricant exhausted from the engine as emissions In particular, the present inventors have discovered that highly polanzed synthetic ester lubricant base stocks having unreacted hydroxyl groups and an overall oxygen content of 15 wt % or greater are capable of suppressing fuel (e g , paraffin, olefin and aromatic hydrocarbons) and lubricant emissions from crankcase engines due to the fact that the fuel is only minimallv soluble within the lubncant base stock Contrary to current theories which believe that hydroxyl groups lower the oxidative stability ofthe resultant lubricant, the present inventors have also discovered that a select group of synthetic esters having a strongly polar end group such as a hvdroxyl group on the ester's carbon chain not only reduces the fuel solubility in the lubricant, but are thermally and oxidatively stable molecules which increase the number of drain intervals required over a set period of time, and decrease inlet valve deposit formation and combustion chamber deposit formation The present inventors have also determined that synthetic esters which are combined with at least one additional functional group that is capable of increasing the polaπtv ofthe functionalized synthetic ester and wherein the synthetic ester has an oxygen, nitrogen and/or halogen content of at least 15 wt %, based on the total weight ofthe synthetic ester are also capable of suppressing fuel and lubncant emissions Still further, the present inventors have discovered that polyol esters which have an oxvgen, nitrogen and/or halogen content of at least 15 wt %, based on the total weight ofthe polvol ester, are also capable of suppressing fuel and lubricant emission The present inv ention also provides many additional advantages which shall become apparent as described below SUMMARY OF THE INVENTION A low emissions lubricant for hydrocarbon engine operation which comprises a base stock that is capable of increasing the polanty ofthe lubncant such that hvdrocarbon fuel is only minimally soluble therein The lubricant preferably includes a lubricant additive package which is suitable for its intended use Preferably, the low emissions lubricant for use with hydrocarbon fuels according to the present invention includes a base stock which comprises at least one synthetic ester selected from the group consisting of (1) polyol esters having an oxygen, nitrogen or halogen content of at least 15 wt %, based on the total weight ofthe base stock, (2) synthetic esters having between 5-50% unconverted hydroxyl groups, based on the total amount of hydroxyl groups in the polyol, and an oxygen, nitrogen or halogen content of at least 15 wt %, based on the total weight ofthe base stock, and (3) synthetic esters combined with at least one additional functional group which is capable of further increasing the polanty ofthe functionalized synthetic ester and having an oxygen, nitrogen or halogen content of at least 15 wt %. based on the total weight of the base stock One particularly preferred synthetic ester is an ester having between 5-50% unconverted hydroxyl groups which is formed from the reaction product of a branched or linear alcohol having the general formula R(OH) n , wherein R is an aliphatic or cvclo-aliphatic group having from about 2 to 20 carbon atoms and n is at least 2, and at least one branched mono-carboxylic acid which has a carbon number in the range between about C> to C ., wherein the synthetic ester composition has between 5-50% unconverted hydroxyl groups, based on the total amount of hvdroxyl groups in the branched or linear alcohol Functional groups which are capable of increasing the polarity ofthe synthetic ester include ketones, aromatics, halogens, hydroxyl, acids, amides, ethers, alcohols, olefinic groups, etc The low emissions lubricant formed using the particular synthetic ester base stocks ofthe present invention exhibit the following properties: (1) a solubility of the hydrocarbon fuels in the lubricant of less than 5% at 1 bar; (2) a base stock having a metals content of less than 10 ppm; and (3) a base stock having a total acid number of less than 0 05 milligrams KOH per gram ofthe base stock. When used as a crankcase lubricating oil the synthetic ester base stock is preferably admixed with a lubricant additive package which comprises at least one additive selected from the group consisting of: ashless dispersants, metal detergents, corrosion inhibitors, metal dihydrocarbyl dithiophosphates. anti- oxidants, pour point depressants, anti-foaming agents, anti-wear agents, friction modifiers, and viscosity modifiers. Typically, in an amount of about 80-99% by weight ofthe base stock and about I to 20% by weight the additive package. It is preferable to admix selected viscosity index additives with the base stocks ofthe present invention to improve the viscosity index, while maintaining the limited solubility o the base stock in hydrocarbon fuels. It is also conceivable that dispersive additives can be admixed with synthetic ester base stocks having unconverted hydroxyl groups in order to localize the resulting lubricant, i.e., at the fuel-air/lube and fuel-wall/lube interfaces Still other lubricants can be formed by blending the unique synthetic ester base stocks of the present invention with at least one additional base stock selected from the group consisting of mineral oils, highly refined mineral oils, poly alpha olefins, polybutenes, polyalkylene glycols, phosphate esters, silicone oils, diesters, polyisobutylenes, ethylene and butene copolymers, and other polyol esters. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides a method for substantially reducing or eliminating the amount of hydrocarbon layer absorbed on the various surfaces of a passenger car gas or diesel engine, i e , engine crevices or cylinder surfaces. The reduction in hydrocarbon and carbon monoxide emissions from such engines is accomplished by forming a crankcase engine lubricant from a base stock which comprises a highly polar synthetic ester having an oxygen, nitrogen or halogen content of 15 wt.% or greater, whereby the hydrocarbon component is only minimally soluble within the lubricant film disposed on the various surfaces of a passenger car gas or diesel engine, i e , engine crevices or cylinder surfaces The synthetic ester base stock according to the present invention can include any ( 1 ) polyol ester having an oxygen, nitrogen or halogen content of at least 15 wt %, based on the total weight ofthe base stock; (2) synthetic ester having between 5-50% unconverted hydroxyl groups, based on the total amount of hydroxyl groups in the polyol and an oxygen, nitrogen or halogen content of at least 15 wt %, based on the total weight ofthe base stock; and (3) synthetic ester combined with at least one additional functional group which is capable of further increasing the polarity of the functionalized synthetic ester and an oxygen, nitrogen or halogen content of at least 15 wt %, based on the total weight ofthe base stock. Each ofthe above listed synthetic ester base stocks provide low solubility for hydrocarbon species, e g., paraffins, olefins or aromatics. It is of particular importance that any ofthe selected synthetic ester base stocks which are used to form a low emissions lubricant exhibit a high degree of polarity with respect to the hydrocarbon fuels. The low emissions lubricant formed using the particular synthetic ester base stocks ofthe present invention exhibit the foliowing properties: (1) a solubility of the hydrocarbon fuels in the lubricant of less than 5% at 1 bar; (2) a base stock having a metals content of less than 10 ppm, and (3) a base stock having a total acid number of less than 0 05 milligrams KOH per gram of the base stock Highly polar synthetic polyol esters are typically formed by reacting a polyhydric alcohol with either a branch acid, linear acid or mixture thereof The esterification reaction is preferably conducted, with or without a catalyst, at a temperature in the range between about 140 to 250°C and a pressure in the range between about 30 mm Hg to 760 mm Hg (3 999 to 101 308 kPa) for about 0 1 to 12 hours, preferably 2 to 8 hours The stoichiometry in the reactor is variable, with the capabilitv of vacuum stripping excess reagent to generate the preferred final composition If the esterification reaction is conducted under catalytic conditions, then the preferred esterification catalysts are titanium, zirconium and tin catalysts such as titanium, zirconium and tin alcoholates, carboxylates and chelates Selected acid catalysts mav also be used in this esterification process See U S Patent Nos 5,324,853 (Jones et al ), which issued on June 28, 1994, and 3,056,818 (Werber), which issued on October 2, 1962, both of which are incorporated herein by reference ALCOHOLS Among the alcohols which can be reacted with either the branched acid or branched and linear acid mixture are. by way of example, polyols (l e . polyhydroxvl compounds) represented by the general formula R(OH) n wherein R is any aliphatic or cyclo-aliphatic hydrocarbyl group (preferably an alkyl) and n is at least 2 The hydrocarbyl group may contain from about 2 to about 20 or more carbon atoms, and the hydrocarbyl group may also contain substituents such as chlorine, nitrogen and/or oxvgen atoms The polyhydroxyl compounds generally mav contain one or more oxyalkylene groups and, thus, the polyhydroxyl compounds include compounds such as polyetherpolyols. The number of carbon atoms (i.e., carbon number, wherein the term carbon number as used throughout this application refers to the total number of carbon atoms in either the acid or alcohol as the case may be) and number of hydroxy groups (i.e., hydroxyl number) contained in the polyhydroxyl compound used to form the carboxylic esters may vary over a wide range The following alcohols are particularly useful as polyols: neopentyl glycol, 2,2-dimethylol butane, trimethylol ethane, trimethylol propane, trimethylol butane, mono-pentaerythritol, technical grade pentaerythritol, di-pentaerythritol. tri- pentaerythritol. ethylene glycol, propylene glycol and polyalkylene glycols (e.g., polyethylene glycols, polypropylene glycols, 1 ,4-butanediol, sorbitol and the like, 2-methylpropanediol, polybutylene glycols, etc., and blends thereof such as a polymerized mixture of ethylene glycol and propylene glycol). The most preferred alcohols are technical grade (e.g., approximately 88% mono-, 10% di- and 1-2% tri-pentaerythritol) pentaerythritol, monopentaerythritol, di-pentaerythritol, neopentyl glycol, trimethylol propane, and 1,4-butanediol. Any other alcohols suitable for making synthetic ester base stocks having the properties described above are also contemplated hereunder. See U.S. Patent No. 5,324,853 (Jones et al ), which issued on June 28, 1994, for a partial listing of other such alcohols. ACIDS Carboxylic acids which undergo esterification can be aliphatic, cyclo¬ aliphatic or aromatic, they can be substituted or unsubstituted, saturated or unsaturated. linear or branched, or they can be blends of acids. Among the preferred branched acids are mono-carboxylic acids which have a carbon number in the range between about C5 to C !? , more preferably about Cβ to C )0 . The mono- carboxylic acid is preferably at least one acid selected from the group consisting of: 2,2- dimeth l propionic acid (neopentanoic acid), neoheptanoic acid, neooctanoic acid, neononanoic acid, neodecanoic acid, 2-methyl pentanoic acid, 2-ethyl hexanoic acid (2EH), 3,5,5-tπmethvl hexanoic acid (TMH), isoheptanoic acid, isooctanoic acid, isononanoic acid and isodecanoic acid One especiallv preferred branched acid is 3,5,5-tπmethyl hexanoic acid The term "neo" as used herein refers to a trialkyl acetic acid I e , an acid which is tnply substituted at the alpha carbon with alkyl groups These alkvl groups are equal to or greater than CH 3 as shown in the general structure set forth herebelow Ri O I l l R 2 - C- C -OH R 3 ^ Alpha Carbon wherein R t R 2 , and R, are greater than or equal to CH< and not equal to hydrogen 3,5 ^-trimethyl hexanoic acid has the structure set forth herebelow CH 3 CH 3 O I I 3 I I CH3-C-CH2-CH-CH2-C-OH CH 3 The preferred mono- and /or di-carboxyhc linear acids are any linear saturated alkvl carboxylic acid having a carbon number in the range between about C to C , preferably C 2 to C Some examples of linear acids include acetic, propionic, pentanoic, heptanoic, octanoic, nonanoic, and decanoic acids Selected diacids include any C 2 to Cι 2 diacids e g , adipic, azelaic, sebacic and dodecanedioic acids A partial listing of acids used in the estenfication process are set forth in U S Patent No 5,324,8^3 (Jones et al ), which issued on June 28, 1994. and w hich is incorporated herein A preferred highly polar synthetic ester composition ofthe present invention is one which contains unconverted hvdroxyl groups Such an ester is typically formed by reacting a polyhvdroxyl compound with at least one branched acid In the polyol ester composition the polyol is preferably present in an excess of about 5 to 35 equivalent percent or more for the amount of acid used The composition ofthe feed polvol is adiusted so as to provide the desired composition ofthe product ester See U S Patent Application, Serial No 08/403,366 (Schlosberg et al ) which was filed on March 14 1995, and which is incorporated herein by reference Alternatively, linear acids can be admixed with the branched acids in a ratio of between about 1 99 to 80 20 and thereafter reacted with the branched or linear alcohol as set forth immediately above However, the same molar excess of alcohol used in the all branched case is also required in the mixed acids case such that the synthetic ester composition formed by reacting the alcohol and the mixed acids still has between about 5-35% unconverted hydroxyl groups, based on the total amount of hydroxyl groups in the alcohol The process of synthesizing polyol ester compositions having significant unconverted hydroxyl groups according to the present invention typically follows the equation below R(OH π + R COOH → R(OH), + R(OOCR ), + R(OOCR ) n ,OH -r R(OOCR )„ ;(OH) 2 + R(OOCR') n ι (OH), (Eq 1) wherein n is an integer having a value of at least 2, R is any aliphatic or cyclo- aliphatic hvdrocarbyl group containing from about 2 to about 20 or more carbon atoms and optionallv substituents such as chlorine, nitrogen and/or oxygen atoms, and R' is anv branched aliphatic hydrocarbyl group having a carbon number in the range between about G to C| 2 , more preferably about Cβ to Co, wherein methyl or ethyl branches are preferred and (l) is an integer having a value of between about 0 to n The reaction product also comprises at least one linear acid This linear acid being present in an amount of between about 1 to 80 wt % based on the total amount ofthe branched mono-carboxylic acid The linear acid is any linear saturated alkyl carboxvlic acid having a carbon number in the range between about C to Cι 2 Selected synthetic esters having between 5-35% unconverted hydroxyl groups exhibit between about 20 to 200 % higher thermal/oxidative stability as measured bv high pressure differential scanning calorimetry versus a fullv esterified composition formed from the branched or linear alcohol and the branched mono¬ carboxylic acid which have less than 10% unconverted hydroxyl groups, based on the total amount of hydroxyl groups in the branched or linear alcohol These synthetic ester compositions have a hydroxyl number which is at least 20 milligrams of KOH per gram of sample The preferred branched acids used to make synthetic esters having between 5-35% unconverted hvdroxyl groups are any mono-carboxylic acid which have a carbon number in the range between about C- to Cm For example, 2,2-dιmethyl propionic acid, neoheptanoic acid, neooctanoic acid, neononanoic acid, neodecanoic acid, 2-methyl pentanoic acid, 2-ethyl hexanoic acid, 3,5,5-tnmethyl hexanoic acid, isoheptanoic acid, isooctanoic acid, isononanoic acid and isodecanoic acid The preferred linear acids are any linear saturated alkvl carboxylic acid having a carbon number in the range between about C to C7 For example, acetic acid, propionic acid, pentanoic acid, heptanoic acid, octanoic acid, nonanoic acid, and decanoic acid Alternatively, the linear acid can be a diacid, e g , adipic acid, azelaic acid sebacic acid and dodecanedioic acid The preferred branched or linear alcohols are selected from the group consisting of neopentvl glycol, 2,2-dιmethylol butane, tπmethylol ethane, trimethylol propane, tπmethvlol butane, mono-pentaerythπtol, technical grade pentaerythritol, di-pentaerythπtol, tπ-pentaervthπtol. ethylene glycol propylene glycol, polvalkvlene glvcols 1 ,4-butanedιol. sorbitol, and 2-methylpropanedιol Additionally, synthetic esters that are combined with additional functional groups such as ketones, aromatics, halogens, hydroxyl, esters, acids, amides, ethers, alcohols, olefinic groups, etc to provide increased polanty and low solubilitv for hvdrocarbon species are also contemplated by the present invention The synthetic ester base stocks according to the present invention can be used in the formulation of various lubncants, such as, crankcase engine oils (l e , passenger car motor oils, heavy duty diesel motor oils, and passenger car diesel oils) and other engine lubrication applications The lubπcating oils contemplated for use with the synthetic ester base stocks ofthe present invention include both synthetic hvdrocarbon oils of lubπcating viscosity and blends thereof with at least one additional base stock selected from the group consisting of mineral oils, highly refined mineral oils, poly alpha olefins, polyalkylene glycols, phosphate esters, silicone oils diesters, polyisobutylenes and other polyol esters The svnthetic hydrocarbon oils include long chain alkanes such as cetanes and olefin polymers such as oligomers of isobutylene, hexene, octene, decene, dodecene, and copolymers of ethylene and butene, etc Still other synthetic oils include ( 1 ) fully esterified ester oils, with no free hydroxyls, such as pentaerythπtol esters of monocarboxylic acids having 2 to 20 carbon atoms, tnmethylol propane esters of monocarboxv c acids having 2 to 20 carbon atoms, (2) polyacetals and (3) siloxane fluids Especially useful among the synthetic esters are those made from polvcarboxv lie acids and monohydric alcohols More preferred are the ester fluids made by fullv esteπfying pentaerythritol, or mixtures thereof with di- and tπ- pentaerythritol, with an aliphatic monocarboxylic acid containing from 1 to 20 carbon atoms, or mixtures of such acids The formulated lubricant according to the present invention preferably comprises about 80-99% by weight of at least one polyol ester composition ofthe present invention, about 1 to 20% by weight lubricant additive package CRANKCASE LUBRICATING OILS Synthetic ester base stocks having an oxygen, nitrogen or halogen (e.g., fluorine, chlorine or bromine) content of at least 15 wt %, based on the total weight ofthe base stock, can be used in the formulation of crankcase lubricating oils (i.e., passenger car motor oils, heavy duty diesel motor oils, and passenger car diesel oils) for spark-ignited and compression-ignited engines. The additives listed below are typically used in such amounts so as to provide their normal attendant functions. Typical amounts for individual components are also set forth below. All the values listed are stated as mass percent active ingredient. ADDITIVE MASS % MASS % (Broad) (Preferred) Ashless Dispersant 0 1 - 20 I - 8 Metal detergents 0 1 - 15 0 2 - 9 Corrosion Inhibitor 0 - 5 0 - 1 5 Metal dihvdrocarbvl dithiophosphate 0 1 - 6 0 1 - 4 Supplemental anti-oxidant 0 -5 0 01 - 1 5 Pour Point Depressant 0 01 - 5 0 01- 1.5 Anti-Foaming Agent 0 - 5 0 001-0 15 Supplemental Anti-wear Agents 0 - 0 5 0 - 0 2 Friction Modifier 0 - 5 0 - 1 5 Viscositv Modifier 0 01- 6 0 - 4 Synthetic Ester Base stock Balance Balance The individual additives may be incorporated into a base stock in any convenient way Thus, each ofthe components can be added directly to the base stock by dispersing or dissolving it in the base stock at the desired level of concentration Such blending mav occur at ambient temperature or at an elevated temperature Preferably, all the additives except for the viscosity modifier and the pour point depressant are blended into a concentrate or additive package described herein as the additive package, that is subsequently blended into base stock to make finished lubricant Use of such concentrates is conventional The concentrate will typically be formulated to contain the additive(s) in proper amounts to provide the desired concentration in the final formulation when the concentrate is combined with a predetermined amount of base lubncant The concentrate is preferably made in accordance with the method descπbed in U S Patent No 4,938,880, which is incoφorated herein by reference That patent describes making a pre-mix of ashless dispersant and metal detergents that is pre-blended at a temperature of at least about 100°C Thereafter, the pre¬ mix is cooled to at least 85°C and the additional components are added The final crankcase lubricating oil formulation may employ from 2 to 15 mass % and preferably 5 to 10 mass %, typically about 7 to 8 mass % ofthe concentrate or additive package with the remainder being base stock The ashless dispersant comprises an oil soluble polymeric hydrocarbon backbone having functional groups that are capable of associating with particles to be dispersed Typicallv, the dispersants comprise amine, alcohol, amide, or ester polar moieties attached to the polymer backbone often via a bridging group The ashless dispersant may be, for example, selected from oil soluble salts, esters, amino-esters. amides, imides. and oxazoiines of long chain hydrocarbon substituted mono and dicarboxylic acids or their anhvdπdes, thiocarboxylate derivatives of long chain hydrocarbons, long chain aliphatic hydrocarbons having a polyamine attached directly thereto, and Mannich condensation products formed by condensing a long chain substituted phenol with formaldehyde and polyalkylene polyamine The viscositv modifier (VM) functions to impart high and low temperature operability to a lubricating oil The VM used may have that sole function, or may be multifunctional Multifunctional viscosity modifiers that also function as dispersants are also known Suitable viscosity modifiers are polyisobutylene, copolymers of ethylene and propylene and higher alpha-olefins, polvmethacrylates, polyalkylmethacrylates, methacrylate copolymers, copolymers of an unsaturated dicarboxylic acid and a vinyl compound, inter polymers of styrene and acrylic esters, and partially hydrogenated copolymers of styrene/ isoprene, styrene/butadiene, and isoprene/butadiene, as well as the partially hydrogenated homopolymers of butadiene and isoprene and isoprene/divinylbenzene Metal-containing or ash-formmg detergents function both as detergents to reduce or remove deposits and as acid neutrahzers or rust inhibitors, thereby reducing wear and corrosion and extending engine life Detergents generally comprise a polar head with a long hydrophobic tail, with the polar head compnsing a metal salt of an acidic organic compound The salts may contain a substantially stoichiometric amount ofthe metal in which case they are usually described as normal or neutral salts and would typically have a total base number or TBN (as may be measured by ASTM D2896) of from 0 to 80 It is possible to include large amounts of a metal base by reacting an excess of a metal compound such as an oxide or hvdroxide with an acidic gas such as carbon dioxide The resulting overbased detergent comprises neutralized detergent as the outer layer of a metal base (e g carbonate) micelle Such overbased detergents may have a TBN of 150 or greater, and typicallv of from 250 to 450 or more Detergents that may be used include oil-soluble neutral and overbased sulfonates, phenates, sulfurized phenates, thiophosphonates, salicylates and naphthenates and other oil-soluble carboxylates of a metal, particularlv the alkali or alkaline earth metals, e g , sodium, potassium lithium, calcium, and magnesium The most commonly used metals are calcium and magnesium, which mav both be present in detergents used in a lubncant, and mixtures of calcium and/or magnesium with sodium Particularly convenient metal detergents are neutral and overbased calcium sulfonates having TBN of from 20 to 450 TBN, and neutral and overbased calcium phenates and sulfurized phenates having TBN of from 50 to 450 Dihvdrocarbyl dithiophosphate metal salts are frequently used as anti-wear and antioxidant agents The metal may be an alkali or alkaline earth metal, or aluminum, lead, tin, molybdenum, manganese, nickel or copper The zinc salts are most commonly used in lubricating oil in amounts of 0 1 to 10, preferably 0 2 to 2 wt %, based upon the total weight ofthe lubricating oil composition They may be prepared in accordance with known techniques by first forming a dihvdrocarbyl dithiophosphoπc acid (DDPA), usually by reaction of one or more alcohol or a phenol with P 2 S 5 and then neutralizing the formed DDPA with a zinc compound For example a dithiophosphoπc acid may be made by reacting mixtures of primary and secondary alcohols Alternatively, multiple dithiophosphoπc acids can be prepared where the hydrocarbyl groups on one are entirely secondary in character and the hydrocarbyl groups on the others are entirely pnmary in character To make the zinc salt any basic or neutral zinc compound could be used but the oxides, hydroxides and carbonates are most generally employed Commercial additives frequently contain an excess of zinc due to use of an excess ofthe basic zinc compound in the neutralization reaction Oxidation inhibitors or antioxidants reduce the tendency of base stocks to deteriorate in service which deterioration can be evidenced by the products of oxidation such as sludge and varnish-like deposits on the metal surfaces and by viscosity growth Such oxidation inhibitors include hindered phenols, alkaline earth metal salts of alkylphenolthioesters having preferably Cs to C 12 alkyl side chains, calcium nonylphenol sulfide, ashless oil soluble phenates and sulfurized phenates, phosphosulfurized or sulfurized hydrocarbons, phosphorous esters, metal thiocarbamates, oil soluble copper compounds as described in US 4,867,890, and molybdenum containing compounds Friction modifiers may be included to improve fuel economy Oil-soluble alkoxylated mono- and diamines are well known to improve boundary layer lubrication The amines may be used as such or in the form of an adduct or reaction product with a boron compound such as a boric oxide, boron halide, metaborate. boric acid or a mono-, di- or trialkyl borate. Other friction modifiers are known. Among these are esters formed by reacting carboxylic acids and anhydrides with alkanols Other conventional friction modifiers generally consist of a polar terminal group (e.g. carboxyl or hydroxyl) covalently bonded to an oleophillic hydrocarbon chain Esters of carboxylic acids and anhydrides with alkanols are described in US 4,702,850 Examples of other conventional friction modifiers are described by M. Belzer in the "Journal of Tribology" ( 1992), Vol 1 14, pp. 675-682 and M. Belzer and S Jahanmir in "Lubrication Science" ( 1988), Vol l , pp 3-26. Rust inhibitors selected from the group consisting of nonionic polyoxyalkylene polyols and esters thereof, polyoxyalkylene phenols, and anionic alkyl sulfonic acids mav be used. Copper and lead beaπng corrosion inhibitors may be used, but are typically not required with the formulation of the present invention Typically such compounds are the thiadiazole polysulfides containing from 5 to 50 carbon atoms, their derivatives and polymers thereof Derivatives of 1,3,4 thiadiazoles such as those described in U S Pat Nos 2 719, 125, 2,719, 126, and 3,087,932 are typical Other similar materials are described in U S Pat Nos 3,821,236, 3,904,537, 4,097,387, 4.107,059 4, 136,043, 4 188,299, and 4, 193,882 Other additives are the thio and polythio sulfenamides of thiadiazoles such as those described in UK Patent Specification No 1 ,560,830 Benzotriazoles derivatives also fall withm this class of additives When these compounds are included in the lubncating composition thev are preferably present in an amount not exceeding 0 2 wt % active ingredient A small amount of a demulsifving component may be used A preferred demulsifymg component is described in EP 330,522 It is obtained bv reacting an alkylene oxide with an adduct obtained by reacting a bis-epoxide with a polyhydric alcohol The demulsifier should be used at a level not exceeding 0 1 mass % active ingredient λ treat rate of 0 001 to 0 05 mass % active ingredient is convenient Pour point depressants, otherwise known as lube oil flow improvers, lower the minimum temperature at which the fluid will flow or can be poured Such additives are well known Typical of those additives which improve the low temperature fluidity of the fluid are C« to Cm dialkyl fumarate/vinyl acetate copolymers and polyalkylmethacrylates Foam control can be provided by many compounds including an antifoamant ofthe polvsiloxane type for example, silicone oil or polydimethyl siloxane Some ofthe above-mentioned additives can provide a multiplicity of effects, thus for example, a single additive may act as a dispersant-oxidation inhibitor This approach is well know n and does not require further elaboration EXAMPLE 1 For comparativ e purposes. Table 1 below demonstrates the Federal Test Procedure (FTP) emissions reduction for hydrocarbon (HC), I e , -3 9%, and carbon monoxide (CO) I e , -6 0% when a svnthetic polyol ester having an oxygen content of 20 wt %, based on the total weight ofthe base stock (I e , the polyol ester is formed from the reaction product of pentaerythntol and an oxooctanoic acid, l e , a mixture of branched C« acids which are formed from the hydroformvlation of a mixture of C 7 olefins) is compared agamst a mineral oil base stock of similar kinematic viscosity, typical of that contained in an SAE 30 grade motor oil Table 1 % Difference in FTP Emissions Pol vol Ester vs Mineral Oil Significant Level [%] HC -3 9 (85) CO -6 0 (78) NO, +6 4 (85) EXAMPLE 2 The data set forth below in Table 2 support the proposition that solubilities in highly polar lubricants such as those covered by the present invention are reduced versus that in mineral oil lubricants The solubility of the vaπous lubncants obtained at 150°C by gas chromatography Table 2 Wt % at 1 bar Lubncant Molecular Wt nC,nH;; p-Xvlene MTBE Mineral Oil " !85 7 9 3 0 0 3 TPE-BrC 9 /α " ci 707 4 3 2 4 0 3 PPG "" 1000 3 5 2 5 0 3 * The Mineral Oil is a low sulfur neutralized saturated, linear hvdrocarbon mineral oil having between 14 to 34 carbon atoms (less than 3 wt % oxvgen. mtrogen and/or halogen content) ** TPE-BrC /Cy is a technical grade pent.iervthntol ester of ca 75% BrC 9 (3,5.5-tπmethvl hexanoic acid ) and ca 25% BrCs <o\ooctanoιc acid) (18 8 wi % oxvgen nitrogen and/or halogen content) *** PPG is polvpropvlene glvcol (27 8 wi % oxv gen mtrogen and/or halogen content) When normalized, l e . adjusted by assuming a Flory Huggins relationship could be applied, to comparable molecular weights, there still is benefit seen for the highly polar lubricants verses conventional mineral oil-based lubncants as shown in Table 3 below Table 3 Calc for Mol Wt % at 1 bar Lubπcani Wt = Mm Oil nC,nH; 2 p-Xvlene MTBE Mineral Oil 385 7 9 3 0 0 3 TPE-BrC 9 /C< 385 5 3 3 0 0 3 PPG "" 385 4 8 3 4 0 3 * The Mineπil Oil is a low sulfur neutrali ed, saturated, linear hvdrocarbon mineral oil having between 14 to 34 carbon atoms (less than 3 wt % oxvgen. mtrogen and/or halogen content) ** TPE-BrC /C is a technical grade pentaervthπtol ester of ca 75% BrC 9 (3.5.5-tπmethvl hexanoic acid) and ca 25% BrC* (oxooctanoic acid) (18 8 wt % oxvgen mtrogen and/or halogen content) *** PPG is polvpropvlene glvcol (27 8 wi % oxvgen mtrogen and/or halogen content) This example demonstrates that the more polar the lubricant, the less solubility the lubricant is in the hydrocarbon fuel which results in a reduction in the amount of fuel which is exhausted from a crankcase engine together with the lubncant EXAMPLE 3 Solubility data for gasoline components in alternative lubricants at 150°C by gas chromatography is set forth below in Table 4 wherein a deliberately highly polar comparative base stock showed further reduction in fuel solubility Table 4 Wt. % at 1 bar Lubncant Molecular Wt π ιπH. ; p-Xylene MTBE Mineral Oil 385 7 9 3 0 0 3 TPE-BrCyC, " ca 707 4 3 2 4 0 3 TPE-BrC 9 w/ un¬ 500 3 7 2 4 0 3 converted OH """ * The Mineral Oil is a low sulfur, neutralized, saturated, linear hydrocarbon mineral oil having between 14 to 34 carbon atoms, (less than 3 wt.% oxygen, nitrogen and/or halogen content) ** TPE-BrC /C, is a technical grade peniaerythπtol ester of ca 75% BrC 9 (3,5.5-tnmethyl hexanoic acid) and ca 25%. BrC κ (o.xooctanoic acid). (18.8 wt.% oxygen, mtrogen and/or halogen content) *** TPE-BrC ! with unconverted OH is a technical grade pentaerythritol ester of ca 100% BrC 9 (3.5.5-tπmetln 1 hexanoic acid) having 30% unconverted hydroxy groups disposed about the carbon chain of the ester (20 1 wi % oxvgen. nitrogen and/or halogen content). When normalized (i.e , adjusted by assuming a Flory Huggins relationship could be applied) to comparable molecular weights, there is benefit seen for the polar synthetic ester lubricants versus conventional ester- and mineral oil-based lubricants as shown in Table 5 below Table 5 Wt. % at l bar Lubncant Molecular Wt nCιnH :: p-Xylene MTBE Mineral Oil 385 7 9 3 0 0 3 between 14 io 34 carbon moms ( less than 3 * M % oxv gen. nitrogen and/or halogen content) ** TPE-BrC - C is a technical grade pcnt.icrytliπtoi ester of ca. 75%, BrCo (3.5.5-lπmethvl hexanoic acid i and ca. 25%. BrC< (o.xooctanoic acid ) ( 18 8 wt % oxv gen. nitrogen and/or halogen content) *** TPE-BrC , w uh uncom crted OH is a technical grade pentaerythritol ester of ca ! 00%> BrC 9 l hexanoic acid) having .30%. unconverted hydroxy groups disposed about the carbon chain of the ester ( 20 I wt %. oxygen, nitrogen and/or halogen content) The above examples demonstrate that the lubricant composition has a drastic effect on the hydrocarbon fuel solubility in the lubricant and in subsequent engine emission hydrocarbon levels Furthermore, these examples demonstrate that highly polar polyol ester lubricants (i e , those containing sufficiently high (15 wt % or greater) oxygen, nitrogen and/or halogen content) have reduced capability for solubilizing paraffin and aromatic fuel components, thus reducing hydrocarbon exhaust emissions from a crankcase engine The examples further demonstrate that a strongly polar end group such as an unconverted hydroxyl group on the lubricant further reduces the fuel solubilitv in the lubricant It is also extremely desirable in crankcase lubricant applications to provide a lubricant product which is thermally/oxidatively stable. One means of measuring relative thermal/oxidative stability in lubricants is via high pressure differential scanning calorimetry (HPDSC) In this test, the sample is heated to a fixed temperature and held there under a pressure of air (or oxygen) and the time to onset of decomposition is measured The longer the time to decomposition, the more stable the sample In all cases described hereafter, the conditions are as follows unless specifically noted otherwise 220°C, 3 445 MPa (500 psi) air (i.e., 0 689 MPa ( 100 psi) oxygen and 2 " 56 MPa (400 psi) nitrogen), and the addition of 0 5 wt % dioctvl diphenyl amine i Vanlube-81 ® ) as an antioxidant EXAMPLE 4 The data set forth below in Table 6 indicate that there is considerable room for improving the thermal/oxidative performance of polyol esters as measured by the HPDSC test In particular, it should be noted that esters of 3, 5, 5 -trimethyl hexanoic acid and 2,2-dιmethylpropιonιc acid (1 e , neopentanoic (neo-r 5 )) are particularly stable under the HPDSC test Table 6 HPDSC Sample Decomposition Number Ester Time, Min 1 TMP/n-C 9 14 2 2 TechPE/n-C, 14 7 TMP/TMH 1 19 4 TechPE/TMH 148 5 MPE/TMH 143 6 TMP/n-C 5 51 9 7 50% TMP/TMH and 50% TMP/n-C- 65 7 8 MPE/TMH/neo-C, 168 n-Cg is a linear normal C 9 acid TechPE is technical grade pentaerythritol (1 e , 88% mono-, 10% di- and 1- 2% tn- pentaerythπtol) MPE is mono-pentaervthπtol n-C< is a linear normal C 5 acid TMH is 3,5 5-tπmethvl hexanoic acid neo-C- is 2 2-dιmethvl propionic acid A polvol ester having uncon erted hydroxyl groups disposed thereon was formed using technical grade pentaervthπtol and 3,5,5-tπmethvl hexanoic acid (Sample 10) by mixing about 225 % molar equivalents of 3,5,5-trimethyl hexanoic acid with each mole of technical grade pentaerythritol. This was compared in Table 7 below with a conventional polyol ester formed from technical grade pentaerythritol and 3, 5.5 -trimethyl hexanoic acid (Sample 9) prepared using an excess of 3.5.5-trimethyl hexanoic acid Table 7 HPDSC Sample Decomposition Number Ester Time, Min. 9 TechPE/TMH 148 10 TechPE/TMH w/ 25% Unconverted OH 468 TechPE is technical grade pentaerythritol (i e , about 88% mono-, 10% di- and 1 - 2% tri- pentaerythritol) TMH is 3,5.5-trimethyI hexanoic acid The data set forth above in Tables 6 and 7 support the discovery by the present inventors that certain compositions of polyol esters which contain at least 5 mole % unconverted hvdroxyl (OH) groups have surprisingly enhanced thermal/oxidative stability as measured by high pressure differential scanning calorimetry (HPDSC) versus conventional polyol and non-polyol esters EXAMPLE 5 Certain polyol esters containing at least 5 mole % unconverted hydroxyl groups show dramatic enhancements in thermal/oxidative performance in the HPDSC test when compared to polyol esters of trimethylol propane and a linear acid (7810) These esters contain specific types of branching and the enhancement is seen for both trimethylol propane (TMP) and pentaerythritol (both mono grade and technical grade) esters. Table 8 below summarizes the results Table 8 HPDSC Sample Hydroxyl Decomposition Number Ester No Time, Min 1 TMP/2EH 20 30 1 2 TMP/2EH 64.0 225.3 3 TMP/2EH 75 0 125.3 4 MPE/2EH 12.1 24 4 5 MPE/2EH 63 8 183 5 6 TechPE/2EH 3 6 17 5 7 TechPE/TMH <10 148 8 TechPE/TMH 86 268 9 TechPE/TMH 68.5 364 10 TechPE/TMH >50 468 1 1 TMP/7810 0.2 26 1 12 TMP/7810 25.7 21 3 13 TMP/7810 26.8 22.9 14 TMP/7810 43 5 21 3 15 TMP/7810 73 8 26 5 Hydroxyl lx umber is measured in mg KOH/gram sample using a conventional near infrared technique. 2EH is 2-ethyl hexanoic acid TechPE is technical grade pentaerythritol (i e , 88% mono-, 10% di- and 1- 2% tri- pentaerythritol) MPE is mono-pentaerythritol TMH is 3,5 5-trimethyl hexanoic acid TMP is trimethylol propane 7810 is a blend of 37 mole % of a n-C 7 acid and 63 mole % of a mixture of 3-5 mole % n-Cβ acid, 48-58 mole % n-C* acid, 36-42 mole % n-Cm acid, and 0.5- 1 0 mole % n-C 12 acid The results set forth above in Table 8 demonstrate that when all ofthe initially added antioxidant (Vanlube©-81 ) is consumed, the ester radicals are not healed and true decomposition occurs rapidly as shown in sample numbers 1, 4 and 6 which have small amounts of unconverted hydroxyl groups, as well in the polyol esters formed from linear acids regardless of amount of unconverted hydroxyl groups present (see samples numbers 1 1-15) With certain branched esters such as sample numbers 2, 3, and 6-10 above, the unconverted hydroxyl group (i e., the only molecular change from the full ester) is capable of transferring its hydrogen to the first formed radical so as to created a more stable radical, thereby acting as an additional antioxidant With the linear acid esters set forth above in sample numbers 1 1 - 15, the internal radical generated from transfer of a hydrogen from an unconverted hydroxyl group is not significantly more stable than the initially formed carbon radical, thereby yielding essentially no change in decomposition time EXAMPLE 6 The data set forth below in Table 9 demonstrate that polyol ester compositions having unconverted hvdroxyl groups which are formed from polyols and branched acids in accordance with the present invention exhibit internal antioxidant properties Table 9 HPDSC Sample Hydroxyl Decomposition Number Ester Number Time. Min TechPE/TMH greater than 50 468 with 0 5%. V-81 TechPE/TMH greater than 50 58 3 with no V-81 3 TcchPE L less than 5 16 9 wιth 0 5% V-81 4 Tech PE/TMH less than 5 148 with 0 5%> V-81 5 Tech PE/TMH less than 5 3 14 with no V-81 V-81 is diocrv I diphenvl amine TechPE is technical grade pentaervthntol ( I e 88%. mono- 10%> di- and l-2%> tπ- pentncrvthntol) TMH is 3.5 5-ιrιmethvl hexanoic acid L9 is blend ol 62-70 mole "Λ, linear C 9 acid and 30-38 mole % branched C 9 acid The results in Table 9 above demonstrate that polyol esters with unconverted hydroxyl groups (I e sample numbers 1 and 2) greatly enhance the oxidative induction time of the lubricant formulation versus conventional polyol esters which do not have any significant amount of free or unconverted hydroxyl groups Moreover, combining these unique polyol esters with an antioxidant such as V-81 significantly extends the time required for decomposition (see sample no 1 ) Although the time for decomposition was reduced when this polyol ester did not include any added antioxidant, it still took approximately 3'/- times longer to decompose versus a conventional C<> acid polyol ester which had an antioxidant additive (I e , 58 3 minutes (sample 2) versus 16 9 minutes (sample 3)) Furthermore. Samples 4 and 5 demonstrate that decomposition ofthe polyol ester compositions having a hydroxyl number less than 5 occurs much more rapidly compared to polyol ester compositions ofthe same acid and polyol having a hydroxyl number greater than 50 (e g , Samples 1 and 2) regardless of whether or not an antioxidant is admixed with the respective polyol ester composition This clearly demonstrates that synthesizing a polyol ester composition having unconverted hydroxyl groups disposed about the carbon chain ofthe polyol ester provide enhanced thermal/oxidative stability to the resultant product, as measured by HPDSC Finally, a comparison of Sample Nos 2 and 5, wherein no antioxidant was used, clearly establishes the antioxidant properties ofthe polyol ester of technical grade pentaervthntol and 3,5,5-tπmethyl hexanoic acid having substantial amounts of unconverted hydroxyl groups bonded thereto That is, the sample with unconverted hydroxyl groups exhibited an HPDSC of 58.3 minutes versus the same polyol ester with little or no unconverted hydroxyl groups which exhibited an HPDSC of 3.14 minutes.

Claims: CLAIMS: We Claim 1 A low emissions lubricant for use with hydrocarbon fuels, said lubncant comprising a base stock which compnses at least one synthetic ester selected from the group consisting of (1) polyol esters having an oxygen, nitrogen or halogen content of at least 15 wt % based on the total weight of said base stock, (2) svnthetic esters having between 5-50% unconverted hydroxyl groups, based on the total amount of hydroxyl groups in said synthetic ester, and an oxygen, nitrogen or halogen content of at least 15 wt %, based on the total weight of said base stock, and (3) synthetic esters combined with at least one additional functional group which is capable of further increasing the polarity ofthe functionalized synthetic ester and having an oxygen, nitrogen or halogen content of at least 15 wt %, based on the total weight of said base stock, and an additive package 2 The low emissions lubncant according to claim 1 wherein said base stock has an oxygen, nitrogen and/or halogen content in the range of about 16 to 30 wt %, based on the total weight of said base stock 3 The low emissions lubncant according to claim 1 wherein said synthetic ester having between 5-35% unconverted hydroxyl groups is formed from the reaction product of a branched or linear alcohol having the general formula R(OH) n , wherein R is an aliphatic or cvclo-aliphatic group having from about 2 to 20 carbon atoms and n is at least 2 and at least one branched mono-carboxylic acid which has a carbon number in the range between about C5 to Cι 3 , wherein said synthetic ester composition has between 5-35% unconverted hydroxyl groups, based on the total amount of hydroxvl groups in said branched or linear alcohol 4 The low emissions lubricant according to claim 3 wherein between about 50 to 90% ofthe hydroxyl groups from said branched or linear alcohol are converted upon the estenfication of said branched or linear alcohol with said branched mono-carboxvhc acid 5 The low emissions lubricant according to claim 1 wherein said functional group which is capable of increasing the polanty of said synthetic ester is selected from the group consisting of ketones, aromatics, halogens, hydroxyl, acids, amides ethers, alcohols, and olefinic groups 6 The low emissions lubncant according to claim 1 wherein said synthetic ester is a polyol ester 7 The low emissions lubncant according to claim 1 wherein the solubility of said hydrocarbon fuels in said lubncant is less than 5% at 1 bar 8 The low emissions lubncant according to claim 1 wherein said base stock has a metals content of less than 10 ppm 9 The low emissions lubricant according to claim 1 wherein said base stock has a total acid number of less than 0 05 milligrams KOH per gram of said base stock 10 The low emissions lubricant according to claim 1 wherein said additive package comprises at least one additive selected from the group consisting of viscositv index improvers, corrosion inhibitors, oxidation inhibitors, dispersants, lube oil flow improvers, detergents and rust inhibitors, pour point depressants, anti- foaming agents, anti-wear agents, seal swellants, friction modifiers, extreme pressure agents, color stabilizers, demulsifiers, wetting agents, water loss improving agents, bactericides, drill bit lubricants, thickeners or gellants, anti- emulsifying agents, metal deactivators, coupling agents, surfactants, and additive solubilizers 1 1 The low emissions lubncant according to claim 1 wherein said base stock is blended with at least one additional base stock selected from the group consisting of mineral oils, highly refined mineral oils, poly alpha olefins, polybutenes, polyalkylene glycols, phosphate esters, silicone oils, diesters, polyisobutylenes, ethyl ene butene copolymers, and other polyol esters 12 A low emissions crankcase lubricating oil formulation which is prepared from a base stock which compπses at least one synthetic ester selected from the group consisting of ( 1 ) polyol esters having an oxygen, nitrogen or halogen content of at least 15 wt %, based on the total weight of said base stock, (2) synthetic esters having between 5-50% unconverted hydroxyl groups, based on the total amount of hydroxyl groups in said synthetic ester, and an oxygen, nitrogen or halogen content of at least 15 wt %, based on the total weight of said base stock, and (3) synthetic esters combined with at least one additional functional group which is capable of further increasing the polarity ofthe functionalized synthetic ester and having an oxygen nitrogen or halogen content of at least 15 wt %. based on the total weight of said base stock, and a lubricant additive package 13 The formulation according to claim 12 wherein said base stock has an oxygen, nitrogen and/or halogen content in the range of about 16 to 30 wt %, based on the total weight of said base stock 14 The formulation according to claim 12 wherein said additive package comprises at least one additive selected from the group consisting of ashless dispersants, metal detergents, corrosion inhibitors, metal dihydrocarbyl dithiophosphates, anti-oxidants, pour point depressants, anti-foaming agents, anti- wear agents friction modifiers, and viscosity modifiers 15 The formulation according to claim 12 wherein the solubility of said hydrocarbon fuels in said formulation is less than 5% at 1 bar 16 The formulation according to claim 12 wherein said base stock has a metals content of less than 10 ppm 17 The formulation according to claim 12 wherein said base stock has a total acid number of less than 0 05 milligrams KOH per gram of said base stock 18 The formulation according to claim 12 wherein said base stock is blended with at least one additional base stock selected from the group consisting of mineral oils, highly refined mineral oils, poly alpha olefins, polybutenes, polyalkylene glycols, phosphate esters, silicone oils, diesters, polyisobutylenes, ethylene/butene copolvmers, and other polyol esters 19 A lubncant base stock which comprises at least one synthetic ester selected from the group consisting of polyol esters, synthetic esters having between 5- 5% unconverted hydroxyl groups, based on the total amount of hydroxyl groups in the polyol, and synthetic esters combined with at least one additional functional group which is capable of increasing the polarity ofthe functionalized synthetic ester, wherein said base stock has an oxygen, nitrogen and/or halogen content of at least 15 wt %, based on the total weight of said base stock 20 The base stock according to claim 19 wherein said base stock has an oxygen, nitrogen and/or halogen content in the range of about 16 to 30 wt.%, based on the total wemht of said base stock 21 The base stock according to claim 19 wherein said synthetic ester having between 5-35% unconverted hydroxyl groups is formed from the reaction product of a branched or linear alcohol having the general formula R(OH)„, wherein R is an aliphatic or cyclo-aliphatic group having from about 2 to 20 carbon atoms and n is at least 2, and at least one branched mono-carboxylic acid which has a carbon number in the range between about C 5 to Cπ, wherein said synthetic ester composition has between 5-35% unconverted hydroxyl groups, based on the total amount of hydroxyl groups m said branched or linear alcohol 22 The base stock according to claim 21 wherein between about 50 to 95% ofthe hydroxyl groups from said branched or linear alcohol are converted upon the esterification of said branched or linear alcohol with said branched mono- carboxvlic acid 23 The base stock according to claim 19 wherein said functional group which is capable of increasing the polanty of said synthetic ester is selected from the group consisting of ketones, aromatics, halogens, hydroxyl, acids, amides, ethers, alcohols, olefinic groups 24 The base stock according to claim 23 wherein said synthetic ester is a polyol ester 25 The base stock according to claim 19 wherein said base stock has a metals content of less than 10 ppm 26 The base stock according to claim 19 wherein said base stock has a total acid number of less than 0 05 milligrams KOH per gram of said base stock

Inventors: DUPRE GERALD DENNIS, GODICI PATRICK EDWARD, GRAY RALPH D JR, JOHNSTON JOHN ERIC, KAPLAN L, POLIZZOTTI RICHARD S, RADOSZ MARK, SCHLOSBERG RICHARD HENRY, WEISSMAN WALTER, DUPRE, GERALD, DENNIS, GODICI, PATRICK, EDWARD, GRAY, RALPH, D., JR., JOHNSTON, JOHN, ERIC, KAPLAN, L., POLIZZOTTI, RICHARD, S., RADOSZ, MARK, SCHLOSBERG, RICHARD, HENRY, WEISSMAN, WALTER
Applicants: EXXON CHEMICAL PATENTS INC, EXXON CHEMICAL PATENTS INC.
Application year: 1996
Main classification: C10M105
IPC codes: C10M105, C10M169, C10N40