WO2014124698A1

WO2014124698A1 - Ester lubricant for oilfield- and other industrial lubricant applications

Info

Publication number: WO2014124698A1
Application number: PCT/EP2013/053214
Authority: WO
Inventors: Heinz Müller; Diana MÄKER; Nadja Herzog; Tanja LÜDTKE
Original assignee: Amril Ag
Priority date: 2013-02-18
Filing date: 2013-02-18
Publication date: 2014-08-21

Abstract

The present invention relates to a lubricant composition comprising an optionally cross- linked ester obtainable by reacting a polyol alkoxylate with a monocarboxylic acid. Further aspects of the invention relate to a tetraester obtainable by reacting a polyol alkoxylate with a monocarboxylic acid and uses of said composition and tetraester.

Description

ESTER LUBRICANT FOR OILFIELD- AND OTHER INDUSTRIAL LUBRICANT APPLICATIONS

BACKGROUND OF THE INVENTION

Lubricants with improved biodegradability are desirable for example for equipment used in certain resource industries, such as forestry, mining, petroleum exploration and production in particular wherever the lubricants themselves might come into contact with the environment. In one study carried out in 2002, it was found that up to 50 percent of the world's global lubricant production could be lost into the environment through emissions into the air such as engine oil exhaust, spillage, or dumping of used oil. Such a large percentage coupled with ecological concerns has led to resurgence in the use of biodegradable feedstocks.

Frequently, a lubricating oil whose base oil is PAO (polyalphaolefin) is used. Despite exhibiting excellent low-temperature properties the typical PAO lubricating oil, however, has poor biodegradability, so that an alternative thereto has been sought for.

For demanding applications, considerably high lubricity, improved biodegradability and low- temperature fluidity of the lubricant is desirable.

It was therefore an object of the invention to provide a lubricant composition which is less toxic, has excellent low-temperature properties and exhibits improved biodegradability.

SUMMARY OF THE INVENTION

The present invention provides a lubricant composition comprising an ester obtainable by reacting at least

(a) a polyol alkoxylate with

(b) a monocarboxylic acid

and wherein the ester is cross-linked or not cross-linked. Also provided is a tetraester obtainable by reacting

(a) a polyol alkoxylate with

(b) a monocarboxylic acid;

wherein said polyol alkoxylate and said monocarboxylic acid are as defined herein in the context of the lubricant composition.

One aspect of the invention relates to an ester with at least four ester groups obtainable by reacting

(a) a polyol alkoxylate with

(b) a monocarboxylic acid;

wherein said polyol alkoxylate and said monocarboxylic acid are as defined above for the lubricant composition of the invention. In this embodiment it is preferred that said ester has no free hydroxyl groups. A further aspect of the invention relates to the use of an ester of the invention as a lubricant, wherein the lubricant is preferably selected from the group consisting of engine oil, oil drilling fluid, hydraulic oil, compressor oil, gear oil, bearing oil, low temperature lubricant and turbine oil. DETAILED DESCRIPTION OF THE INVENTION

Before the present invention is described in detail below, it is to be understood that this invention is not limited to the particular methodology, protocols and reagents described herein as these may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention which will be limited only by the appended claims. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art.

In the following passages different aspects of the invention are defined in more detail. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous. Some documents are cited throughout the text of this specification. Each of the documents cited herein (including all patents, patent applications, scientific publications, manufacturer's specifications, instructions, DIN norms etc.), whether supra or infra, are hereby incorporated by reference in their entirety. Nothing herein is to be construed as an admission that the invention is not entitled to antedate such disclosure by virtue of prior invention.

In the following definitions of some chemical terms are provided. These terms will in each instance of its use in the remainder of the specification have the respectively defined meaning and preferred meanings. The term "alkyl" refers to a saturated straight or branched carbon chain. Preferably, an alkyl as used herein is a C1-C20 alkyl and more preferably is a C1-C10 alkyl, i.e. having 1 , 2, 3, 4, 5, 6, 7, 8, 9 or 10 carbon atoms, e.g. is selected from methyl, ethyl, propyl, z^'so-propyl, butyl, z^'so-butyl, tert- vXy\, pentyl or hexyl, heptyl, octyl, nonyl and decyl. Alkyl groups are optionally substituted. The term "alcohol" refers to a compound having one or more hydroxyl groups. For example a C8-C36 alkyl alcohol is a C8-C36 alkyl substituted with one or more hydroxyl groups. The term "polyol" refers to an alcohol having at least two hydroxyl groups.

The term "heteroalkyl" refers to a saturated straight or branched carbon chain. Preferably, the chain comprises from 1 to 9 carbon atoms, i.e. 1, 2, 3, 4, 5, 6, 7, 8, 9 e.g. methyl, ethyl, propyl, z^'so-propyl, butyl, z^'so-butyl, sec-butyl, tert-butyl, pentyl or hexyl, heptyl, octyl, nonyl which is interrupted one or more times, e.g. 1, 2, 3, 4, 5, with the same or different heteroatoms. Preferably the heteroatoms are selected from O, S, and N, e.g. -O-CH₃, -S-CH₃, -CH2-O-CH3, -CH₂-0-C₂H₅, -CH₂-S-CH₃, -CH₂-S-C₂H₅, -C₂H₄-0-CH₃, -C₂H₄-0- C₂H₅, -C₂H₄-S-CH₃, -C₂H₄-S-C₂H₅ etc. Heteroalkyl groups are optionally substituted. The terms "cycloalkyl" and "heterocycloalkyl", by themselves or in combination with other terms, represent, unless otherwise stated, cyclic versions of "alkyl" and "heteroalkyl", respectively, with preferably 3, 4, 5, 6, 7, 8, 9 or 10 atoms forming a ring, e.g. cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl etc. The terms "cycloalkyl" and "heterocycloalkyl" are also meant to include bicyclic, tricyclic and polycyclic versions thereof. If more than one cyclic ring is present such as in bicyclic, tricyclic and polycyclic versions, then these rings may also comprise one or more aryl- or heteroaryl ring. The term "heterocycloalkyl" preferably refers to a saturated ring having five members of which at least one member is a N, O or S atom and which optionally contains one additional O or one additional N; a saturated ring having six members of which at least one member is a N, O or S atom and which optionally contains one additional O or one additional N or two additional N atoms; or a saturated bicyclic ring having nine or ten members of which at least one member is a N, O or S atom and which optionally contains one, two or three additional N atoms. "Cycloalkyl" and "heterocycloalkyl" groups are optionally substituted. Additionally, for heterocycloalkyl, a heteroatom can occupy the position at which the heterocycle is attached to the remainder of the molecule. Preferred examples of cycloalkyl include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, spiro[3,3]heptyl, spiro[3,4]octyl, spiro[4,3]octyl, spiro[3,5]nonyl, spiro[5,3]nonyl, spiro[3,6]decyl, spiro[6,3]decyl, spiro[4,5]decyl, spiro[5,4]decyl, bicyclo[4.1.0]heptyl, bicyclo[3.2.0]heptyl, bicyclo[2.2.1]heptyl, bicyclo[2.2.2]octyl, bicyclo[5.1.0]octyl, bicyclo[4.2.0]octyl, octahydro-pentalenyl, octahydro-indenyl, decahydro-azulenyl, adamantly, or decahydro-naphthalenyl. Examples of heterocycloalkyl include 1 -(1,2,5, 6- tetrahydropyridyl), 1-piperidinyl, 2-piperidinyl, 3-piperidinyl, 4-morpholinyl, 3-morpholinyl, 1,8 diaza-spiro-[4,5] decyl, 1,7 diaza-spiro-[4,5] decyl, 1,6 diaza-spiro-[4,5] decyl, 2,8 diaza- spiro[4,5] decyl, 2,7 diaza-spiro[4,5] decyl, 2,6 diaza-spiro[4,5] decyl, 1,8 diaza-spiro-[5,4] decyl, 1,7 diaza-spiro-[5,4] decyl, 2,8 diaza-spiro-[5,4] decyl, 2,7 diaza-spiro[5,4] decyl, 3,8 diaza-spiro[5,4] decyl, 3,7 diaza-spiro[5,4] decyl, l-aza-7,1 l-dioxo-spiro[5,5] undecyl, 1,4- diazabicyclo[2.2.2]oct-2-yl, tetrahydrofuran-2-yl, tetrahydrofuran-3-yl, tetrahydrothien-2-yl, tetrahydrothien-3-yl, 1-piperazinyl, 2-piperazinyl, and the like.

The term "alicyclic system" refers to mono, bicyclic, tricyclic or polycyclic version of a cycloalkyl or heterocycloalkyl comprising at least one double and/or triple bond. However, an alicyclic system is not aromatic or heteroaromatic, i.e. does not have a system of conjugated double bonds/free electron pairs. Thus, the number of double and/or triple bonds maximally allowed in an alicyclic system is determined by the number of ring atoms, e.g. in a ring system with up to 5 ring atoms an alicyclic system comprises up to one double bond, in a ring system with 6 ring atoms the alicyclic system comprises up to two double bonds. Thus, the "cycloalkenyl" as defined below is a preferred embodiment of an alicyclic ring system. Alicyclic systems are optionally substituted. The term "aryl" preferably refers to an aromatic monocyclic ring containing 6 carbon atoms, an aromatic bicyclic ring system containing 10 carbon atoms or an aromatic tricyclic ring system containing 14 carbon atoms. Examples are phenyl, naphtyl or anthracenyl. The aryl group is optionally substituted. The term "aralkyl" refers to an alkyl moiety, which is substituted by aryl, wherein alkyl and aryl have the meaning as outlined above. An example is the benzyl radical. Preferably, in this context the alkyl chain comprises from 1 to 8 carbon atoms, i.e. 1, 2, 3, 4, 5, 6, 7, or 8, e.g. methyl, ethyl methyl, ethyl, propyl, z^'so-propyl, butyl, z^'so-butyl, sec-butenyl, tert-butyl, pentyl or hexyl, pentyl, octyl. The aralkyl group is optionally substituted at the alkyl and/or aryl part of the group.

The term "heteroaryl" preferably refers to a five or six-membered aromatic monocyclic ring wherein at least one of the carbon atoms are replaced by 1, 2, 3, or 4 (for the five membered ring) or 1, 2, 3, 4, or 5 (for the six membered ring) of the same or different heteroatoms, preferably selected from O, N and S; an aromatic bicyclic ring system wherein 1, 2, 3, 4, 5, or 6 carbon atoms of the 8, 9, 10, 11 or 12 carbon atoms have been replaced with the same or different heteroatoms, preferably selected from O, N and S; or an aromatic tricyclic ring system wherein 1, 2, 3, 4, 5, or 6 carbon atoms of the 13, 14, 15, or 16 carbon atoms have been replaced with the same or different heteroatoms, preferably selected from O, N and S. Examples are oxazolyl, isoxazolyl, 1,2,5-oxadiazolyl, 1,2,3-oxadiazolyl, pyrrolyl, imidazolyl, pyrazolyl, 1,2,3-triazolyl, thiazolyl, isothiazolyl, 1,2,3,-thiadiazolyl, 1,2,5- thiadiazolyl, pyridinyl, pyrimidinyl, pyrazinyl, 1,2,3-triazinyl, 1,2,4-triazinyl, 1,3,5-triazinyl, 1-benzofuranyl, 2-benzofuranyl, indolyl, isoindolyl, benzothiophenyl, 2-benzothiophenyl, 1H- indazolyl, benzimidazolyl, benzoxazolyl, indoxazinyl, 2,1-benzisoxazoyl, benzothiazolyl, 1,2- benzisothiazolyl, 2,1-benzisothiazolyl, benzotriazolyl, quinolinyl, isoquinolinyl, quinoxalinyl, quinazolinyl, 1,2,3-benzotriazinyl, or 1,2,4-benzotriazinyl.

The term "heteroaralkyl" refers to an alkyl moiety, which is substituted by heteroaryl, wherein alkyl and heteroaryl have the meaning as outlined above. An example is the 2- alklypyridinyl, 3-alkylpyridinyl, or 2-methylpyridinyl. Preferably, in this context the alkyl chain comprises from 1 to 8 carbon atoms, i.e. 1, 2, 3, 4, 5, 6, 7, or 8, e.g. methyl, ethyl methyl, ethyl, propyl, z^'so-propyl, butyl, z^'so-butyl, sec-butenyl, tert-butyl, pentyl or hexyl, pentyl, octyl. The heteroaralkyl group is optionally substituted at the alkyl and/or heteroaryl part of the group.

The terms "alkenyl" and "cycloalkenyl" refer to olefmic unsaturated carbon atoms containing chains or rings with one or more double bonds. Examples are propenyl and cyclohexenyl. Preferably, the alkenyl chain comprises from 2 to 8 carbon atoms, i.e. 2, 3, 4, 5, 6, 7, or 8, e.g. ethenyl, 1 -propenyl, 2-propenyl, z^'so-propenyl, 1-butenyl, 2-butenyl, 3-butenyl, z^'so-butenyl, sec-butenyl, 1-pentenyl, 2-pentenyl, 3-pentenyl, 4-pentenyl, hexenyl, heptenyl, octenyl. The term also comprises CH₂, i.e. methenyl, if the substituent is directly bonded via the double bond. Preferably the cycloalkenyl ring comprises from 3 to 14 carbon atoms, i.e. 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 or 14, e.g. cyclopropenyl, cyclobutenyl, cyclopentenyl, cyclohexenyl, cyclo heptenyl, cyclooctyl, cyclononenyl, cyclodecenyl, spiro[3,3]heptenyl, spiro[3,4]octenyl, spiro[4,3]octenyl, spiro[3,5]nonenyl, spiro[5,3]nonenyl, spiro[3,6]decenyl, spiro[6,3]decenyl, spiro[4,5]decenyl, spiro[5,4]decenyl, bicyclo[4.1.0]heptenyl, bicyclo[3.2.0]heptenyl, bicyclo[2.2.1]heptenyl, bicyclo[2.2.2]octenyl, bicyclo[5.1.0]octenyl, bicyclo[4.2.0]octenyl, hexahydro-pentalenyl, hexahydro-indenyl, octahydro-azulenyl, or o ctahydro -naphthaleny 1.

The term "alkynyl" refers to unsaturated carbon atoms containing chains or rings with one or more triple bonds. An example is the propargyl radical. Preferably, the alkynyl chain comprises from 2 to 8 carbon atoms, i.e. 2, 3, 4, 5, 6, 7, or 8, e.g. ethynyl, 1-propynyl, 2- propynyl, 1-butynyl, 2-butynyl, 3-butynyl, 1-pentynyl, 2-pentynyl, 3-pentynyl, 4-pentynyl, hexynyl, pentynyl, octynyl.

As defined herein a polyol alkoxylate is preferably any compound comprising an alkoxylated polyol.

As used herein "dimer acid", or "dimerized fatty acid" refers to dicarboxylic acids prepared by dimerizing unsaturated fatty acids obtained from tall oil, usually on clay catalysts. A preferred dimmer acid is a dimer of a C8-C32 carboxylic acid and most preferably a dimer of oleic acid.

The term "optionally substituted" in each instance if not further specified refers to between 1 and 10 substituents, e.g. 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 substituents which are in each instance independently selected from the group consisting of halogen, in particular F, CI, Br or I; -NO₂, -CN, -OR^*, -NR'R", -(CO)OR', -(CO)OR'", -(CO)NR'R", -NR'COR" ", -NR'COR', -NR"CONR'R", -NR"S0₂A, -COR' "; -S0₂NR'R", -OOCR' ", -CR" 'R" "OH, -R"'OH, and -E;

R' and R' ' is each independently selected from the group consisting of hydrogen, alkyl, alkenyl, alkynyl, -OE, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, and aralkyl or together form a heteroaryl, or heterocycloalkyl; optionally substituted;

R' " and R" " is each independently selected from the group consisting of alkyl, alkenyl, alkynyl, cycloalkyl, heterocycloalkyl, alkoxy, aryl, aralkyl, heteroaryl, and -NR'R";

E is selected from the group consisting of alkyl, alkenyl, cycloalkyl, alkoxy, alkoxyalkyl, heterocycloalkyl, an alicyclic system, aryl and heteroaryl; optionally substituted;

If two or more radicals can be selected independently from each other, then the term "independently" means that the radicals may be the same or may be different.

The present invention provides novel lubricants. It was unexpectedly found that the lubricant composition and tetraester of the invention has good lubricating properties, a low pour point, is less toxic and exhibits improved biodegradability.

Thus, in a first aspect the invention provides a lubricant composition comprising an ester obtainable by reacting at least

(a) a polyol alkoxylate with

(b) a monocarboxylic acid

and wherein the ester is cross-linked or not cross-linked.

The esters of the invention can be obtained utilizing conventional esterification procedures. This generally involves reacting a molar excess of the carboxylic acid with the polyol alkoxylate at an elevated temperature while removing water. The reaction may be carried out by refluxing the reactants in an azeotroping solvent, such as toluene or xylene, to facilitate removal of water. Preferably, however, the reaction is carried out in the absence of solvents. Esterification catalysts may be used but are not necessary for the reaction. At the completion of the reaction the excess acid and (if present) any solvent can be separated from the ester by vacuum stripping or distillation. The ester product thus produced may be utilized as such or it may be alkali refined or otherwise treated to reduce the acid number, remove catalyst residue, reduce the ash content, etc. For the purpose of this invention preferably essentially all of the hydroxyl groups are reacted and the resulting ester products have hydroxyl values (mg KOH/g) less than 10. In one embodiment, said ester is a full ester which means that during ester synthesis preferably all free hydroxyl groups of the alcohol reactant are reacted with a monocarboxylic acid such that no free hydroxyl groups remain on the polyol part of the full ester after the reaction. Optional cross-linking of the ester can be achieved for example, by further adding a polycarboxylic acid such as a dicarboxylic acid into the reaction mixture. Thus, in a preferred embodiment, said ester of the invention is obtainable by reacting (a) a polyol alkoxylate, (b) a monocarboxylic acid and (c) a polycarboxylic acid wherein said polycarboxylic acid is e.g. a dicarboxylic acid. Useful dicarboxylic acids are preferably selected from the group consisting of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, dimer acid, and sebacic acid. The molar ratio between said mono- and said polycarboxylic acid during synthesis can for example be 10: 1.

In a preferred embodiment the ester is obtainable by reacting

(a) a polyol alkoxylate with

(b) said monocarboxylic acid,

wherein the ester is not cross-linked.

If the ester is not cross-linked this means that the reaction mixture comprises less than 0.05 wt% (based on the weight of the reaction mixture) of a polycarboxylic acid and that most preferably the reaction mixture comprises no polycarboxylic acid. In embodiments where the ester is cross-linked the reaction preferably comprises not more than 10 wt% (based on the weight of the reaction mixture) of a polycarboxylic acid. Most preferably, the ester of the invention is not cross linked. In a preferred embodiment of the lubricant composition said polyol alkoxylate in (a) is obtainable by alkoxylation of a polyol that is a branched or unbrached C4-C40 alkane polyol. In one embodiment said polyol is a branched or unbrached C5-C40 alkane polyol. Most preferably, said alkane polyol is a branched C5-C10 polyol. In a further preferred embodiment, said polyol comprises at least three hydroxyl groups. In one particularly preferred embodiment said polyol is selected from the group consisting of diglycerol, triglycerol, trimethylol ethane, trimethylol propane, trimethylol butane, trimethylol pentane, trimethylol hexane, trimethylol heptane, pentaerythritol, di(pentaerythritol), tri(pentaerythritol), tetra(pentaerythritol), penta(pentaerythritol), dimethylolpropane, dimerdiol, trimertriol and neopentyl glycol.

Preferably, the composition of the invention does not comprise a phosphate ester. It is further preferred that said alkoxylate is a C3-C10 alkoxylate and preferably propoxylate.

In one preferred embodiment, said polyol alkoxylate in (a) is alkoxylated pentaerythritol which in an even more preferred embodiment has the following structure:

wherein

R¹, R², R³ and R⁴ are each independently selected from the group consisting of C3-C8 alkyl (e.g. C3-, C4-, C5-, C6-, CI- or C8-alkyl) and C3-C8 alkenyl (e.g. C3-, C4-, C5-, C6-, CI- or C8-alkenyl), optionally substituted; and

a+b+c+d is an integer number between 1 and 30, preferably between 4 and 10 (e.g. 4, 5, 6, 7, 8, 9 or 10) and most preferably 5.

In a further preferred embodiment said polyol alkoxylate in (a) has the following structure:

wherein a+b+c+d = an integer number between 1 and 30, preferably between 4 and 10 (e.g. 4, 5, 6, 7, 8, 9 or 10) and most preferably 5.

Also preferred is a lubricant composition of the invention, wherein said monocarboxylic acid in (b) is a branched or unbranched, saturated or unsaturated C6-C22 monocarboxylic acid. Most preferably the monocarboxylic acid is unbranched and aliphatic. For example, a saturated C8-C10 monocarboxylic acid (e.g. octanoic acid, nonanoic acid or decanoic acid) or an unsaturated C16-C18 monocarboxylic acid (e.g. palmitoleic acid, sapienic acid, oleic acid or elaidic acid) can be used to prepare the ester of the invention. Preferably said monocarboxylic acid is aliphatic. Most preferably said monocarboxylic acid is selected from the group consisting of hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, icosanoic acid, myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linoelaidic acid, a-linolenic acid, arachidonic acid, eicosapentaenoic acid, erucic acid, docosahexaenoic acid, hydroxy stearic acid, ricinoleic acid, iso stearic acid, isononanoic acid, isotridecanoic acid and mixtures thereof.

Preferably, said ester is an alkoxylated pentaerythritol saturated or unsaturated C6-C22 monocarboxylic acid tetraester and even more preferably it is an alkoxylated pentaerythritol saturated or unsaturated C8-C18 monocarboxylic acid tetraester. For example, a saturated C8- CIO monocarboxylic acid (e.g. octanoic acid, nonanoic acid or decanoic acid) or an unsaturated C16-C18 monocarboxylic acid (e.g. palmitoleic acid, sapienic acid, oleic acid or elaidic acid) can be used to prepare the tetraester of the invention. In a further preferred embodiment said ester is an alkoxylated pentaerythritol monocarboxylic acid tetraester wherein said monocarboxylic acid is preferably selected from the group consisting of hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, icosanoic acid, myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linoelaidic acid, a-linolenic acid, arachidonic acid, eicosapentaenoic acid, erucic acid, docosahexaenoic acid, hydroxy stearic acid, ricinoleic acid, iso stearic acid, isononanoic acid, isotridecanoic acid and mixtures thereof. Preferably said monocarboxylic acid is aliphatic.

In a preferred lubricant composition according to the invention said monocarboxylic acid in (b) is unsaturated.

As it has been unexpectedly found that the ester of the invention which is based on said alkoxylated polyol has a desired low pour point, a further preferred embodiment of the invention relates to a lubricant composition of the invention, wherein said ester has a pour point as measured by DIN ISO 3016(10/82) which is lower than the pour point as measured by DIN ISO 3016(10/82) of an ester produced by reacting said polyol with said monocarboxylic acid whereby said polyol is however not alkoxylated and/or wherein said ester has a biological degradability of greater than 66,5% after 28 days according to the manometric respirometric test defined in OECD 301 F. Thus, it is preferred that the ester according to the invention has a pour point as measured by DIN ISO 3016(10/82) which is lower than the pour point as measured by DIN ISO 3016(10/82) for the same ester which however is based on a non-propoxylated polyol. More preferably the ester of the invention has a biological degradability of greater than 67%, 68%, 69%, 70%, 71%, 72%, 73% or greater than 74% after 28 days according to the manometric respirometric test defined in OECD 301 F.

In a particularly preferred embodiment, said ester has an improved pour point as measured by DIN ISO 3016(10/82) e.g. a pour point of below -35°C and more preferably below -36°C, - 37°C, -38°C, -39°C, -40°C, -4FC, -42°C, -50°C or below -60°C.

In one embodiment the polyol alkoxylate in (a) has a hydroxyl number of between 500 and 600 as measured according to DIN 53240-2.

Also preferred is a lubricant composition according to the invention, wherein said lubricant composition further comprises a lubricant additive that is different from said ester and that is selected from the group consisting of a further lubricant, a viscosity modifier, a friction modifier, an ashless detergent, a cloud point depressant, a pour point depressant, a demulsifier, a flow improver, an anti-static agent, an ashless antioxidant, an antifoam agent, a corrosion inhibitor, an antiwear agent, a seal swell agent, a lubricity aid, an antimisting agent, an organic solvent, a gel-breaking surfactant and mixtures thereof.

In this context, the mentioned viscosity modifier is preferably selected from the group consisting of hydrogenated copolymers of styrene-butadiene, ethylene-propylene copolymers, polyisobutenes, hydrogenated styrene-isoprene polymers, hydrogenated isoprene polymers, polymethacrylates, polyacrylates, polyalkyl styrenes, alkenyl aryl conjugated diene copolymers, polyolefms, esters of maleic anhydride-styrene copolymers, functionalized polyolefms, ethylene-propylene copolymers functionalized with the reaction product of maleic anhydride and an amine, polymethacrylate functionalized with an amine, styrene- maleic anhydride copolymers reacted with an amine, polymethacrylate polymers, esterified polymers, esterified polymers of a vinyl aromatic monomer and an unsaturated carboxylic acid or derivative thereof, olefin copolymers, ethylene-propylene copolymer, polyisobutylene or mixtures thereof. A gel breaking surfactant is preferably selected from the group consisting of glycerol monooleate, tall oil fatty acid, linoleic and stearic acids and derivatives thereof, non-ionic surfactants, and mixtures thereof.

Ashless antioxidants preferably include alkyl-substituted phenols such as 2,6-di-tertiary butyl- 4-methyl phenol, phenate sulfides, phosphosulfurized terpenes, sulfurized esters, aromatic amines, diphenyl amines, alkylated diphenyl amines and hindered phenols, bis-nonylated diphenylamine, nonyl diphenylamine, octyl diphenylamine, bis-octylated diphenylamine, bis- decylated diphenylamine, decyl diphenylamine and mixtures thereof. Hindered phenols include but are not limited to 2,6-di-tert-butylphenol, 4-methyl-2,6-di-tert-butylphenol, 4- ethyl-2,6-di-tert-butylphenol, 4-propyl-2,6-di-tert-butyl phenol, 4-butyl-2,6-di-tert- butylphenol 2,6-di-tert-butylphenol, 4-pentyl-2-6-di-tert-butylphenol, 4-hexyl-2,6-di-tert- butylphenol, 4-heptyl-2,6-di-tert-butylphenol, 4-(2-ethylhexyl)-2,6-di-tert-butylphenol, 4- octyl-2,6-di-tert-butylphenol, 4-nonyl-2,6-di-tert-butylphenol, 4-decyl-2,6-di-tert-butylphenol, 4-undecyl-2,6-di-tert-butylphenol, 4-dodecyl-2,6-di-tert-butylphenol, 4-tridecyl-2,6-di-tert- butylphenol, 4-tetradecyl-2,6-di-tert-butylphenol, methylene-bridged sterically hindered phenols include but are not limited to 4,4-methylenebis(6-tert-butyl-o-cresol), 4,4- methylenebis(2-tert-amyl-o-cresol), 2,2-methylenebis(4-methyl-6-tert-butylphenol), 4,4- methylene-bis(2,6-di-tertbutylphenol) and mixtures thereof. Another example of an ashless antioxidant is a hindered, ester-substituted phenol, which can be prepared by heating a 2,6- dialkylphenol with an acrylate ester under based conditions, such as aqueous KOH. Ashless antioxidants may be used alone or in combination. The antioxidants are typically present in the range of about 0 wt % to about 95 wt %, in one embodiment in the range from about 0.01 wt % to 95 wt % and in another embodiment in the range from about 1 wt % to about 70 wt % and in another embodiment in the range from about 5 wt % to about 60 wt % based on the total weight of the lubricant composition.

The extreme pressure/anti-wear agents include a sulfur or chlorosulphur extreme pressure (EP) agent, a chlorinated hydrocarbon EP agent, or a phosphorus EP agent, or mixtures thereof. Examples of such EP agents are amine salts of phosphorus acid, chlorinated wax, organic sulfides and polysulfides, such as benzyldisulfide, bis-(chlorobenzyl) disulfide, dibutyl tetrasulfide, sulfurized sperm oil, sulfurized methyl ester of oleic acid sulfurized alkylphenol, sulfurized dipentene, sulfurized terpene, and sulfurized Diels-Alder adducts; phosphosulfurized hydrocarbons, such as the reaction product of phosphorus sulfide with turpentine or methyl oleate, phosphorus esters such as the dihydrocarbon and trihydrocarbon phosphate, i.e., dibutyl phosphate, diheptyl phosphate, dicyclohexyl phosphate, pentylphenyl phosphate; dipentylphenyl phosphate, tridecyl phosphate, distearyl phosphate and polypropylene substituted phenol phosphate, metal thiocarbamates, such as zinc dioctyldithiocarbamate and barium heptylphenol diacid, such as zinc dicyclohexyl phosphorodithioate and the zinc salts of a phosphorodithioic acid combination may be used and mixtures thereof. In one embodiment the antiwear agent/extreme pressure agent comprises an amine salt of a phosphorus ester acid. The amine salt of a phosphorus ester acid includes phosphoric acid esters and salts thereof; dialkyldithiophosphoric acid esters and salts thereof; phosphites; and phosphorus-containing carboxylic esters, ethers, and amides; and mixtures thereof. In one embodiment the phosphorus compound further comprises a sulfur atom in the molecule. In one embodiment the amine salt of the phosphorus compound is ashless, i.e., metal-free (prior to being mixed with other components). The amines which may be suitable for use as the amine salt include primary amines, secondary amines, tertiary amines, and mixtures thereof.

Antifoam agents include organic silicones such as poly dimethyl siloxane, poly ethyl siloxane, polydiethyl siloxane, polyacrylates and polymethacrylates, trimethyl-triflouro-propylmethyl siloxane and the like. An antifoam agent may be used in the range of about 0 wt % to about 20 wt %, in one embodiment in the range of about 0.02 wt % to about 10 wt % and in another embodiment in the range of 0.05 wt % to about 2.5 wt % based on the weight of the lubricant composition.

The viscosity modifier provides both viscosity improving properties and dispersant properties. Examples of dispersant-viscosity modifiers include vinyl pyridine, N-vinyl pyrrolidone and Ν,Ν'-dimethylaminoethyl methacrylate are examples of nitrogen-containing monomers and the like. Polyacrylates obtained from the polymerization or copolymerization of one or more alkyl acrylates also are useful as viscosity modifiers. Functionalized polymers can also be used as viscosity modifiers. Among the common classes of such polymers are olefin copolymers and acrylate or methacrylate copolymers. Functionalized olefin copolymers can be, for instance, interpolymers of ethylene and propylene which are grafted with an active monomer such as maleic anhydride and then derivatized with an alcohol or an amine. Other such copolymers are copolymers of ethylene and propylene which are reacted or grafted with nitrogen compounds. Derivatives of polyacrylate esters are well known as dispersant viscosity index modifiers additives. Dispersant acrylate or polymethacrylate viscosity modifiers such as Acryloid(TM) 985 or Viscoplex(TM) 6-054, from RohMax, are particularly useful. Solid, oil- soluble polymers such as the PIB (polyisobutylene), methacrylate, polyalkystyrene, ethylene/propylene and ethylene/propylene/ 1 ,4-hexadiene polymers and maleic anhydride- styrene interpolymer and derivatives thereof, can also be used as viscosity index improvers. The viscosity modifiers are known and commercially available. The viscosity modifiers are preferably present in the range of about 0 wt % to 80 wt %, in one embodiment in the range from about 0.25 wt % to about 50 wt % and in another embodiment in the range from about 0.5 wt % to about 10 wt % based on the total weight of the lubricant composition. A suitable friction modifier may preferably be an organo-molybdenum compound, including molybdenum dithiocarbamate. In one embodiment, the friction modifier is a phosphate ester or salt including a monohydrocarbyl, dihydrocarbyl or a trihydrocarbyl phosphate, wherein each hydrocarbyl group is saturated. Each hydrocarbyl group may contain from about 8 to about 30, or from about 12 up to about 28, or from about 14 up to about 24, or from about 14 up to about 18 carbons atoms. In another preferred embodiment, the hydrocarbyl groups are alkyl groups. Examples of hydrocarbyl groups include tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl groups and mixtures thereof. If the friction modifier is a phosphate salt, the phosphate salt may for example be prepared by reacting an acidic phosphate ester with an amine compound or a metallic base to form an amine or a metal salt. The amines may be monoamines or polyamines. In one embodiment, the friction modifier is a phosphite and may be a monohydrocarbyl, dihydrocarbyl or a trihydrocarbyl phosphite, wherein each hydrocarbyl group is saturated. In several embodiments each hydrocarbyl group may independently contain from about 8 to about 30, or from about 12 up to about 28, or from about 14 up to about 24, or from about 14 up to about 18 carbons atoms. In one embodiment, the hydrocarbyl groups are alkyl groups. Examples of hydrocarbyl groups include tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl groups and mixtures thereof. In one embodiment, the friction modifier is a fatty imidazoline comprising fatty substituents containing from 8 to about 30, or from about 12 to about 24 carbon atoms. A suitable fatty imidazoline includes those described in U.S. Pat. No. 6,482,777. The friction modifiers can be used alone or in combination. The friction reducing agents are preferably present in the range of about 0 wt % to 60 wt %, or from about 0.25 wt % to about 40 wt %, or from about 0.5 wt % to about 10 wt % based on the total weight of the lubricant composition. Said anti-misting agents include very high (>=100,000 Mn) polyolefms such as 1.5 Mn polyisobutylene (for example the material of the trades name Vistanex(R)), or polymers containing 2-(N-acrylamido), 2-methyl propane sulfonic acid (also known as AMPS(R)) or derivatives thereof. The anti-misting agents can be used alone or in combination. The anti- misting agents are present in the range of about 0 wt % to 10 wt %, or from about 0.25 wt % to about 10 wt %, or from about 0.5 wt % to about 2.5 wt % based on the total weight of the lubricant composition.

The corrosion inhibitors that can be used according to the invention include alkylated succinic acids and anhydrides derivatives thereof, organo phosphonates and the like. The corrosion inhibitors may be used alone or in combination. The rust inhibitors are present in the range of about 0 wt % to about 20 wt %, and in one embodiment in the range from about 0.0005 wt % to about 10 wt % and in another embodiment in the range from about 0.0025 wt % to about 2.5 wt % based on the total weight of the lubricant composition. Ashless metal deactivators include derivatives of benzotriazoles such as tolyltriazole, N,N- bis(heptyl)-ar-methyl- 1 H-benzotriazo le- 1 -methanamine, N,N-bis(nonyl)-ar-methyl- 1 H-

Benzotriazole- 1 -methanamine, N,N-bis(decyl)ar-methyl- 1 H-Benzotriazole- 1 -methanamine, N,N-(undecyl)ar-methyl- 1 H-benzotriazo le- 1 -methanamine, N,N-bis(dodecyl)ar-methyl- 1 H- Benzotriazole- 1 -methanamine N,N-bis(2-ethylhexyl)-ar-methyl- 1 H-Benzotriazole- 1 - methanamine and mixtures thereof. In one embodiment the metal deactivator is N,N-bis(l- ethylhexyl)ar-methyl-lH-benzotriazole-l -methanamine; 1,2,4-triazoles, benzimidazoles, 2- alkyldithiobenzimidazoles; 2-alkyldithiobenzothiazoles; 2-N,N-dialkyldithio- carbamoyl)benzothiazoles; 2,5-bis(alkyl-dithio)-l,3,4-thiadiazoles such as 2,5-bis(tert- octyldithio)-l,3,4-thiadiazole 2,5-bis(tert-nonyldithio)-l,3,4-thiadiazole, 2,5-bis(tert- decyldithio)-l,3,4-thiadiazole, 2,5-bis(tert-undecyldithio)-l,3,4-thiadiazole, 2,5-bis(tert- dodecyldithio)-l,3,4-thiadiazole, 2,5-bis(tert-tridecyldithio)-l,3,4-thiadiazole, 2,5-bis(tert- tetradecyldithio)-l,3,4-thiadiazole, 2,5-bis(tert-octadecyldithio)-l,3,4-thiadiazole, 2,5-bis(tert- nonadecyldithio)-l,3,4-thiadiazole, 2,5-bis(tert-eicosyldithio)-l,3,4-thiadiazole and mixtures thereof; 2,5-bis(N,N-dialkyldithiocarbamoyl)- 1 ,3 ,4-thiadiazoles; 2-alkydithio-5-mercapto thiadiazoles; and the like. The ashless metal deactivators may be used alone or in combination. The ashless metal deactivators are preferably present in the range of about 0 wt % to about 50 wt %, or from about 0.0005 wt % to about 25 wt %, or from about 0.0025 wt % to about 10 wt % based on the total weight of the lubricant composition.

Demulsifiers usable in a lubricant composition of the invention include polyethylene and polypropylene oxide copolymers and the like. The demulsifiers may be used alone or in combination. The demulsifiers are preferably present in the range of about 0 wt % to about 20 wt %, or from about 0.0005 wt % to about 10 wt %, or from about 0.0025 wt % to about 2.5 wt % based on the total weight of the lubricant composition.

Said lubricity aids include glycerol mono oleate, sorbitan mono oleate and the like. The lubricity aids may be used alone or in combination. The lubricity aids are preferably present in the range of about 0 wt % to about 50 wt %, or from about 0.0005 wt % to about 25 wt %, or from about 0.0025 wt % to about 10 wt % based on the total weight of the lubricant composition.

The flow improvers mentioned in the context of the lubricant composition of the invention include ethylene vinyl acetate copolymers and the like. The flow improvers may be used alone or in combination. The flow improvers are preferably present in the range of about 0 wt % to about 50 wt %, or from about 0.0005 wt % to about 25 wt %, or from about 0.0025 wt % to about 5 wt % based on the total weight of the lubricant composition.

Said cloud point depressants include alkylphenols and derivatives thereof, ethylene vinyl acetate copolymers and the like. The cloud point depressants may be used alone or in combination. The cloud point depressants are preferably present in the range of about 0 wt % to about 50 wt %, or from about 0.0005 wt % to about 25 wt %, or from about 0.0025% to about 5 wt % based on the total weight of the lubricant composition. The pour point depressants include alkylphenols and derivatives thereof, ethylene vinyl acetate copolymers and the like. The pour point depressant may be used alone or in combination. The pour point depressant are for example present in the range of about 0 wt % to about 50 wt %, or from about 0.0005 wt % to about 25 wt %, or from about 0.0025 wt % to about 5 wt % based on the total weight of the lubricant composition.

The seal swell agents include organo sulfur compounds such as thiophene, 3- (decyloxy)tetrahydro- 1,1 -dioxide, phthalates and the like. The seal swell agents may be used alone or in combination. The seal swell agents are for example present in the range of about 0 wt % to about 50 wt %, or from about 0.0005 wt % to about 25 wt %, or from about 0.0025 wt % to about 5 wt % based on the total weight of the lubricant composition.

If the lubricant composition according to the invention comprises in a preferred embodiment a further lubricant, then said further lubricant may be selected from the group consisting of an ester, canola oil, castor oil, palm oil, sunflower seed oil, rapeseed oil, Tall oil, lanolin, polyalpha-olefin (PAO), polyalkylene glycol (PAG), a phosphate ester, an alkylated naphthalene (AN), a silicate ester, an ionic fluid and a lubricant with a pour point as measured by DIN ISO 3016(10/82) of below 0°C.

In a second aspect the invention provides an ester with at least four (and preferably between 4 and 6) ester groups obtainable by reacting

(a) a polyol alkoxylate with

(b) a monocarboxylic acid;

wherein said polyol alkoxylate and said monocarboxylic acid are as defined above for the lubricant composition of the invention. Said ester with at least four ester groups is not cross- linked. Preferably said tertraester is obtainable by reacting (a) a polyol comprising at least four hydroxyl groups with (b) a C8-C20 monocarboxylic acid and preferably with Oleic acid, whereby said polyol is alkoxylated with at least 5 propoxyl groups. In one embodiment said ester with at least four ester groups is based on a polyol alkoxylate having the following structure:

wherein a+b+c+d = between 4 and 10 (e.g. 4, 5, 6, 7, 8, 9 or 10) and most preferably 5.

In a further preferred embodiment the ester with at least four ester groups of the invention is obtainable by reacting (a) a polyol comprising at least four hydroxyl groups with (b) a saturated C8-C10 monocarboxylic acid (e.g. octanoic acid, nonanoic acid or decanoic acid) or with an unsaturated C16-C18 monocarboxylic acid (e.g. palmitoleic acid, sapienic acid, oleic acid or elaidic acid). Most preferably said polyol has the structure shown above.

In a further aspect the invention provides a tetraester obtainable by reacting

(a) a polyol alkoxylate with

(b) a monocarboxylic acid;

wherein said polyol alkoxylate and said monocarboxylic acid are as defined above for the lubricant composition of the invention. Said tetraester is not cross-linked.

Preferably said tertraester is obtainable by reacting (a) a polyol comprising at least four hydroxyl groups with (b) a C8-C20 monocarboxylic acid and preferably with Oleic acid, whereby said polyol is alkoxylated with at least 5 propoxyl groups. In one embodiment said tetraester is based on a olyol alkoxylate having the following structure:

In a further preferred embodiment the tetraester of the invention is obtainable by reacting (a) a polyol comprising at least four hydroxyl groups with (b) a saturated C8-C10 monocarboxylic acid (e.g. octanoic acid, nonanoic acid or decanoic acid) or with an unsaturated C16-C18 monocarboxylic acid (e.g. palmitoleic acid, sapienic acid, oleic acid or elaidic acid). Most preferably said polyol has the structure shown above.

A further aspect of the invention concerns the use of an ester according to the invention as defined herein as a lubricant, wherein the lubricant is preferably selected from the group consisting of engine oil, oil drilling fluid, hydraulic oil, compressor oil, gear oil, bearing oil, low temperature lubricant and turbine oil. Preferably the inventive ester and/or lubricant composition is used as low temperature lubricant for working temperatures of below 10°C, preferably of below 0°C and most preferably of below -30°C. Most preferably the ester is a tetraester of the invention as defined herein for lubrication at below 10°C, preferably of below 0°C and most preferably of below -30°C. In the aforementioned embodiment the polyol on which the tertraester is based can have the following structure:

In one aspect the invention concerns a lubricated item covered at least partially with the ester of the invention, wherein said lubricated item is selected from the group consisting of a ball bearing, a drill pipe, a drill bit and a gear mechanism (e.g. a step-up gear), an internal combustion engine, a gas engine, a stationary engine, a diesel engine, a marine diesel engine, a generator, a hydraulic system, a transmission system (e.g. automatic or manual transmission system), a differential, a gear box, an axle, a pump and a suspension system.

In a preferred embodiment of the ester and the composition of the invention said ester and said composition have a low toxicity of EC50 > 1000 as measured after 72 h according to DIN EN ISO 10253:2006.

Various modifications and variations of the invention will be apparent to those skilled in the art without departing from the scope of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. The following examples are merely illustrative of the present invention and should not be construed to limit the scope of the invention as indicated by the appended claims in any way. EXAMPLES

Example 1: Production of esters

All esters shown in the table below can be prepared as follows:

As polyol either pentaerythritol or propoxylated pentaerythritol was used. The propoxylated pentaerythritol used in the examples below ("Pentaerythritol + 5 PO") can be made by reacting about 5 equivalents of propylene oxide with 1 equivalent of pentaerythritol in the presence of a potassium catalyst. Upon completion of the reaction the potassium catalyst can be removed e.g. by treatment with magnesium silicate as is known in the art.

To prepare the ester, the polyol (either propoxylated or not as mentioned) is combined with a molar excess of the respective carboxylic acid (e.g. saturated C 8-10 monocarboxylic acid or oleic acid) and tin (II) oxalate as catalyst. The mixture is initially stirred at room temperature then heated under vacuum (10 torr) at about 220 - 230°C with nitrogen sparging until conversion of the acid has occurred. Remaining unreacted carboxylic acid is removed by distillation. Optionally, the catalyst can be removed by washing the reaction product five times with an equal volume of water, heating the washed product with magnesium silicate (5% by weight) for 2 hours at 90°C, and filtering. The filtered product can further be steam stripped e.g. under 10 mm Hg pressure until the residual acidity is less than 1 mg KOH/gram.

Example 2: Testing Biological Degradability

The biodegradation rate was measured using a manometric respirometry test according to OECD-Guideline 301 F adopted 17.07.92. The test was performed at a temperature of 22 ± 2 °C under aerobic conditions in closed bottles with automatic data registration. Respirometric BOD-determination is carried out with C02-absorption on soda lime. For the puropose of the data outlined in the following, bio degradability is expressed as the percentage oxygen uptake (corrected for blank uptake) of the Chemical Oxygen Demand (COD). Example 3: Determining Pour Point and Lubricant Quality

The pour point of a liquid is the lowest temperature at which it becomes semi solid and loses its flow characteristics. It was determined according to DIN ISO 3016(10/82). Lubricant quality is preferably determined using a testing under boundary lubricating conditions with the Brugger lubricant tester according to DIN 51347-1 at room temperature (20°C).

Example 4: Analyzing Lubricants

The compounds were prepared and analyzed as described above. The results are summarized in the following tables:

Comparison: Polyolester versus propoxylated polyolester

"PO" indicates the number of propoxyl groups on the pentaerythritol. Thus, the inventive esters shown above are based on pentaerythritol comprising on average five propoxyl groups.

"Skeletonema costatum" refers to water quality measured after adding the indicated amount of the ester. The water quality is measured by determining marine algal growth inhibition according to DIN EN ISO 10253:2006. A value of above 1000 indicates a sufficiently low toxicity. According to the above outlined results the alkoxylated polyol ester shows unexpected and enhanced lubrication properties and improved cold temperature behaviors. Furthermore it was surprising that despite the presence of propoxyl groups, the compound showed no disadvantages in toxicity and an improved biodegradability.

Claims

Lubricant composition comprising an ester obtainable by reacting at least

(a) a polyol alkoxylate with

(b) a monocarboxylic acid

and wherein the ester is cross-linked or not cross-linked.

Lubricant composition according to claim 1 wherein the ester is cross-linked and wherein the reaction further comprises

(c) a polycarboxylic acid.

Lubricant composition according to claim 1 or 2, wherein in (a) said polyol alkoxylate is obtainable by alkoxylation of a polyol that is a branched or unbrached C4-C40 alkane polyol.

Lubricant composition according to claim 3, wherein said polyol comprises at least three hydroxyl groups.

Lubricant composition according to any of claims 1-4, wherein said polyol is selected from the group consisting of diglycerol, triglycerol, trimethylol ethane, trimethylol propane, trimethylol butane, trimethylol pentane, trimethylol hexane, trimethylol heptane, pentaerythritol, di(pentaerythritol), tri(pentaerythritol), tetra(pentaerythritol), penta(pentaerythritol), dimethylolpropane, dimerdiol, trimertriol and neopentyl glycol.

Lubricant composition according to any of claims 1-5, wherein said alkoxylate is a C3-C10 alkoxylate and preferably propoxylate.

Lubricant composition according to any of claims 1-6, wherein said polyol alkoxylate in (a) is alkoxylated pentaerythritol.

8. Lubricant composition according to claim 7, wherein said polyol alkoxylate in (a) has the following structure:

wherein

R¹, R², R³ and R⁴ are each independently selected from the group consisting of a C3-

C8 alkyl and a C3-C8 alkenyl, optionally substituted; and

a+b+c+d is an integer number between 1 and 30, preferably between 4 and 10.

9. Lubricant composition according to claim 8, wherein said polyol alkoxylate in (a) has the following structure:

wherein a+b+c+d = an integer number between 1 and 30, preferably between 4 and 10.

10. Lubricant composition according to any of claims 1-9, wherein said monocarboxylic acid in (b) is a branched or unbranched, saturated or unsaturated C6-C22

monocarboxylic acid and preferably a monocarboxylic acid selected from the group consisting of hexanoic acid heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, icosanoic acid, myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linoelaidic acid, a-linolenic acid, arachidonic acid, eicosapentaenoic acid, erucic acid, docosahexaenoic acid, hydroxy stearic acid, ricinoleic acid, iso stearic acid, isononanoic acid, isotridecanoic acid and mixtures thereof.

11. Lubricant composition according to claim 10, wherein said ester is an alkoxylated pentaerythritol saturated or unsaturated C6-C22 monocarboxylic acid tetraester.

12. Lubricant composition according to any of claims 1-11, wherein said monocarboxylic acid in (b) is an unsaturated C16-C18 monocarboxylic acid or a saturated C8-C10 monocarboxylic acid.

13 Lubricant composition according to any of claims 1-12, wherein said ester has a pour point as measured by DIN ISO 3016(10/82) which is lower than the pour point as measured by DIN ISO 3016(10/82) of an ester produced by reacting said polyol with said monocarboxylic acid whereby said polyol is not alkoxylated

and/or wherein said ester has a biological degradability of greater than 65,5% after 28 days according to the mano metric respirometric test defined in OECD 301 F.

14. Lubricant composition according to any of claims 1-13, wherein said lubricant

composition further comprises a lubricant additive that is different from said ester and that is selected from the group consisting of a further lubricant, a viscosity modifier, a friction modifier, an ashless detergent, a cloud point depressant, a pour point depressant, a demulsifier, a flow improver, an anti-static agent, an ashless antioxidant, an antifoam agent, a corrosion inhibitor, an antiwear agent, a seal swell agent, a lubricity aid, an antimisting agent, an organic solvent, a gel-breaking surfactant and mixtures thereof.

15. Lubricant composition according to claim 14, wherein said further lubricant is selected from the group consisting of an ester, canola oil, castor oil, palm oil, sunflower seed oil, rapeseed oil, Tall oil, lanolin, polyalpha-olefm (PAO), polyalkylene glycol (PAG), a phosphate ester, an alkylated naphthalene (AN), a silicate ester, an ionic fluid and a lubricant with a pour point as measured by DIN ISO 3016(10/82) of below 0°C.

16. Ester with at least four ester groups obtainable by reacting

(a) a polyol alkoxylate with

(b) a monocarboxylic acid;

wherein said polyol alkoxylate and said monocarboxylic acid are as defined in claims 3-15. Use of an ester as defined in any of claims 1-16 as a lubricant, wherein the lubricant is preferably selected from the group consisting of engine oil, oil drilling fluid, hydraulic oil, compressor oil, gear oil, bearing oil, low temperature lubricant and turbine oil.