Ester compounds

Abstract

An ester comprises a reaction product of a cyclic anhydride and a polyol. The ester may be a polymer with at least four monomer units. The cyclic anhydride may be succinic anhydride, maleic anhydride,

Description

Silicone compounds, such as polydimethylsiloxane, functionalised polydimethylsiloxanes, organosilicones, and related compounds are used widely in a range of applications and products. They may be provided in concentrate compositions, either for direct use or for later dilution priorto use. However, high concentrations of silicone compounds can cause concentrate compositions to be highly viscous and difficult to pour or pump. Furthermore, high concentrations of the silicone compound can cause concentrate compositions to be unstable when stored for extended periods of time, especially when the silicone compound is poorly soluble or poorly miscible with a diluent comprised in the concentrate composition. There are a number of disadvantages associated with the use of such silicone compounds, including their low biodegradability, which has led to environmental concerns. It is thus an object of the invention to provide an alternative to silicone compounds that can be used in a wide range of applications and uses. It is another object of the invention to provide alternatives to silicone compounds that are more biodegradable whilst having equal or improved properties. It is another object of the invention to improve the stability and / or flowability of concentrate compositions comprising such compounds. Summary of the Invention According to aspects of the present invention, there is provided an ester compound, method and concentrate composition as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and from the description which follows. The inventors have identified that certain ester compounds have properties that are at least comparable to those provided by known silicone compounds, whilst also being more biodegradable. According to a first aspect of the invention, there is provided an ester compound, wherein the ester compound is the reaction product of reactants comprising one or more first reactants and one or more second reactants, wherein the or each first reactant is a cyclic anhydride and the or each second reactant is a polyol. According to a second aspect of the invention, there is provided a concentrate composition comprising one or more ester compounds and optionally at least one solvent, wherein the concentrate composition comprises at least 20 wt% of the one or more ester compounds, and wherein the or each ester compound is the reaction product of reactants comprising one or more first reactants and one or more second reactants, wherein the or each first reactant is a cyclic anhydride and the or each second reactant is a polyol. According to a third aspect of the invention, there is provided a use of a surfactant to emulsify at least one ester compound in an aqueous concentrate composition, wherein the aqueous concentrate composition comprises at least 20 wt% of the one or more ester compounds, and wherein the ester compound is the reaction product of reactants comprising one or more first reactants and one or more second reactants, wherein the or each first reactant is a cyclic anhydride and the or each second reactant is a polyol. According to a fourth aspect of the invention, there is provided a method of emulsifying at least one ester compound in an aqueous composition to make an aqueous ester compound concentrate composition, wherein the aqueous ester compound concentrate composition comprises at least 20 wt% of the one or more ester compounds, the method comprising admixing a surfactant with the ester compound in an aqueous composition, wherein the ester compound is the reaction product of reactants comprising one or more first reactants and one or more second reactants, wherein the or each first reactant is a cyclic anhydride and the or each second reactant is a polyol. Other features of the invention will be apparent from the dependent claims, and from the description which follows. Features described in relation to the second, third and fourth aspects may have any of the suitable features and advantages described in relation to the first aspect. Detailed Description of the Invention Unless otherwise stated, the following terms used in the specification and claims have the meanings set out below. The terms “alkyl” and “alkylene” include both straight and branched chain alkyl and alkylene groups respectively unless otherwise stated. References to individual alkyl groups such as “propyl” are specific for the straight chain version only and references to individual branched chain alkyl groups such as “isopropyl” are specific for the branched chain version only. For example, “C3-30 alkyl” includes C6-24 alkyl, Ce-s alkyl, propyl, isopropyl and t-butyl. The term “alkenyl” includes both straight and branched chain alkenyl groups. References to individual alkenyl groups such as “propenyl” are specific for the straight chain version only and references to individual branched chain alkenyl groups such as “isopropenyl” are specific for the branched chain version only. For example, “C3-30 alkenyl” includes C6-24 alkenyl, Ce-s alkenyl, propenyl and isopropenyl. Herein C3-30 means a group having from 3 to 30 carbons atoms therein, for example having 3, 4, 5 etc up to 30 carbon atoms. The term "hydrocarbyl" is used in its ordinary sense, which is well-known to those skilled in the art. Specifically, it refers to a group having a carbon atom directly attached to the remainder of the molecule and having predominantly hydrocarbon character. As used in the specification and the appended claims, the singular forms "a", "an," and "the" include both singular and plural referents unless the context clearly dictates otherwise. Throughout this specification, the term “comprising” or “comprises” means including the component(s) specified but not to the exclusion of the presence of other components. The term “consisting essentially of’ or “consists essentially of’ means including the components specified but excluding other components except for components added for a purpose other than achieving the technical effect of the invention. The term “consisting of’ or “consists of’ means including the components specified but excluding other components. Whenever appropriate, depending upon the context, the use of the term “comprises” or “comprising” may also be taken to include the meaning “consists essentially of’ or “consisting essentially of’, and also may also be taken to include the meaning “consists of’ or “consisting of’. As used herein, unless otherwise expressly specified, all numbers such as those expressing values, ranges, amounts of percentages may be read as if prefaced by the word “about”, even if the term does not expressly appear. The recitation of numerical ranges by endpoints includes all integer numbers and, where appropriate, fractions subsumed within that range (e.g. 1 to 5 can include 1,2,3,4 when referring to, for example, a number of elements, and can also include 1.5, 2, 2.70 and 3.80, when referring to, for example, measurements). The recitation of end points also includes the end point values themselves (e.g. from 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges subsumed therein. The optional features set out herein may be used either individually or in combination with each other where appropriate and particularly in the combinations as set out in the accompanying claims. The optional features for each exemplary aspect of the invention, as set out herein are also applicable to any other aspects or exemplary aspects of the invention, where appropriate. In other words, the skilled person reading this specification should consider the optional features for each aspect or embodiment of the invention as interchangeable and combinable between different aspects of the invention. As used herein, the term "and / or," when used in a list of two or more items, means that any one of the listed items can be employed by itself or any combination of two or more of the listed items can be employed. For example, if a list is described as comprising group A, B, and / or C, the list can comprise A alone; B alone; C alone; A and B in combination; A and C in combination, B and C in combination; or A, B, and C in combination. The term “reactant” is used herein to refer to a compound comprising at least one reactive functional group. As reported herein, the number average molecular weight was determined by gel permeation chromatography using a polystyrene standard according to ASTM D6579-11 (“Standard Practice for Molecular Weight Averages and Molecular Weight Distribution of Hydrocarbon, Rosin and Terpene Resins by Size Exclusion Chromatography”. UV detector; 254 nm, solvent:unstabilised THF, retention time marker:toluene, sample concentration:2mg / ml). According to a first aspect of the invention, there is provided an ester compound, wherein the ester compound is the reaction product of reactants comprising one or more first reactants and one or more second reactants, wherein the or each first reactant is a cyclic anhydride and the or each second reactant is a polyol. Suitable features of the first aspect will now be described. The ester compound of the first aspect is the reaction product of reactants comprising one or more first reactants and one or more second reactants as defined herein. In other words, the ester compound may be obtainable or obtained by reacting reactants comprising one or more first reactants and one or more second reactants as defined herein.. The ester compound of the first aspect may be the reaction product of reactants consisting essentially of or consisting of one or more first reactants and one or more second reactants as defined herein. In other words, the ester compound may be obtainable or obtained by reacting reactants consisting essentially of or consisting of one or more first reactants and one or more second reactants as defined herein. The first and second reactants may be reacted in any suitable molar ratio to make the ester compound, as would be appreciated by a person skilled in the art. The first and second reactants may be reacted in a molar ratio of from 1:10 to 10:1, preferably from 1:6 to 6:1, for example from 1:3 to 3:1. Preferably, the first and second reactants may be reacted in a molar ratio of 1:1. Ratios refer to the total amounts of first reactants or second reactants if more than one first reactant or second reactant is present. The ester compound may be prepared by any suitable method, as would be known to persons skilled in the art. Suitably, the ester compound is not in a solid form. For example, the ester compound is preferably in the form of a liquid or gel, preferably a liquid. In some embodiments, the ester compound does not contain any nitrogen atoms. References herein to a reaction product of reactants comprising the first and second reactants are intended to refer to a product of the reaction of reactants comprising the first and second reactants conducted in any suitable manner. For example, the reaction may occur between the first and second reactants in the absence of other reactant(s) or may occur in the presence of other reactant(s). The or each of the one or more first reactants used to make the ester compound is a cyclic anhydride. Mixtures of two or more different first reactants (i.e. different cyclic anhydrides) may be used to make the ester compound. Any suitable cyclic anhydride may be used to make the ester compound, as would be understood by the person skilled in the art. By the term cyclic anhydride we mean a compound (or reactant) that comprises at least one anhydride group that is contained within a ring structure. For example, the ring structure that contains the anhydride group may comprise from 4 to 8 atoms, which atoms are typically carbon and oxygen. The ring structure that contains the anhydride group may be saturated or partially unsaturated (and is preferably saturated). The cyclic anhydride compound may typically comprise more than 8 atoms. For example, suitable cyclic anhydrides may include one or more of an anhydride of formula (I), of formula (II) and of formula (III): wherein in formula (I) R1 and R2 are each independently selected from hydrogen, an alkyl group and an alkenyl group, or R1 and R2 together with the carbon atoms to which they are attached represent an optionally substituted cyclic group; in formula (II) R3 and R4 are each independently selected from hydrogen, an alkyl group and an alkenyl group, or R3 and R4 together with the carbon atoms to which they are attached represent an optionally substituted cyclic group; and in formula (III) X is CR9R10, O, S, or NR11; R5, R6, R7, R8, R9, R10, and R11 are each independently selected from hydrogen, an alkyl group and an alkenyl group, and / or any of R5, R6, R7, R8, R9, R10, and R11 together with the atoms to which they are attached represent an optionally substituted cyclic group. Cyclic anhydrides of formula (I) are preferred. X may suitably be CR9R10, O, or S. Preferably, X is CR9R10. When any of R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, and R11 represents an alkyl group or an alkenyl group, the or each alkyl or alkenyl group may be branched or unbranched. The or each alkyl group may contain from 1 to 30 carbon atoms and the or each alkenyl group may contain from 2 to 30 carbon atoms. Preferably, the or each alkyl or alkenyl group may contain 6 or more carbon atoms. For example, the or each alkyl or alkenyl group may contain from 6 to 30, such as from 8 to 24, carbon atoms (i.e. may be a Ce-30, such as a Cs-24, alkyl or alkenyl group). When any of R1 and R2, or R3 and R4, orR5, R6, R7, R8, R9, and R10 represents an alkenyl group, the alkenyl group may be a branched alkenyl group, such as a tetrapropenyl group or a polyisobutenyl group. When any of R1 and R2, or R3 and R4, orR5, R6, R7, R8, R9, and R10 represents an alkenyl group, the alkenyl group may be a polyisobutenyl group. The polyisobutenyl group (when present) suitably has a number average molecular weight of from 100 to 2000, preferably from 100 to 1000, for example 260 or 550. The cyclic anhydride may be a polyisobutenyl succinic anhydride, for example wherein the polyisobutenyl group has a number average molecular weight of 260 or 550. When any of R1 and R2, or R3 and R4, orR5, R6, R7, R8, R9, and R10 represents an alkenyl group, the alkenyl group may be derived from a terminal olefin or an internal olefin. For example, the cyclic anhydride monomer may be an alkenyl substituted succinic anhydride prepared by the reaction of an alkene with maleic anhydride, wherein the alkene is a terminal olefin or an internal olefin. In some embodiments the alkenyl group may be derived from a terminal olefin. The term terminal olefin is used to refer to alkene compounds having a predominantly terminal double bond. Such compounds are also commonly described as terminal alkenes. Terminal double bonds terminate in a =CH2 group and may either be at the a-position or may be vinylidene groups. The terminal olefin is preferably an a-olefin. Examples of suitable terminal olefins include C15-18 terminal olefin and Cie terminal olefin. In some preferred embodiments the alkenyl group is derived from an internal olefin. The term internal olefin is used to refer to alkene compounds in which the alkene groups are predominantly not terminal. Examples of suitable internal olefins include C12 internal olefin, C15-18 internal olefin, C16 internal olefin and C18 internal olefin. The internal olefin is a p or higher olefin, such as a p-olefin. Internal olefins are sometimes known as isomerised olefins and may be prepared by isomerisation of an a-olefin. Typically, terminal olefins and internal olefins may be provided as a mixture of isomers. Suitably at least 70 mol%, such as at least 80 mol%, preferably at least 90 mol%, for example at least 95 mol% of the double bonds in terminal olefins are terminal double bonds. Suitably at least 70 mol%, such as at least 80 mol%, preferably at least 90 mol%, for example at least 95 mol% of the terminal double bonds in the terminal olefins are at the a-position (i.e. they are a-alkene groups). Suitably at least 70 mol%, such as at least 80 mol%, preferably at least 90 mol%, for example at least 95 mol% of the double bonds in internal olefins are non-terminal double bonds. Suitably, one of R1 and R2, R3 and R4, orR5, R6, R7, R8, R9, R10, and R11 may be an alkyl group or an alkenyl group (such as an alkenyl group derived from a terminal olefin or an internal olefin, preferably an internal olefin) and the other (or others) may be hydrogen. Examples of cyclic anhydride reactants of the formula (I), (II) or (III) wherein any of R1 and R2, R3 and R4, orR5, R6, R7, R8, R9, R10, and R11 represents hydrogen or a Ce-3o, such as a Cs-24, branched or unbranched alkyl or alkenyl group include succinic anhydride, dodecenyl succinic anhydride (such as (2-dodecen-1-yl)succinic anhydride or branched dodecenyl succinic anhydride), Cm alkenyl succinic anhydride, tetrapropenyl succinic anhydride, octadecenyl succinic anhydride, octenyl succinic anhydride, nonenyl succinic anhydride, C20-24 alkenyl succinic anhydride, C15-18 alkenyl succinic anhydride (such as C15-18 internal olefin-derived alkenyl succinic anhydride), C16 alkenyl succinic anhydride (such as C16 internal olefin-derived alkenyl succinic anhydride or C16 terminal olefin-derived alkenyl succinic anhydride), maleic anhydride and glutaric anhydride. The cyclic anhydride reactants of the formula (I), (II) or (III) wherein any of R1 and R2, R3 and R4, orR5, R6, R7, R8, R9, R10, and R11 represents hydrogen ora C6-30, such as a Cs-24, branched or unbranched alkyl or alkenyl group may be selected from succinic anhydride, dodecenyl succinic anhydride (such as (2-dodecen-1-yl)succinic anhydride), tetrapropenyl succinic anhydride, octadecenyl succinic anhydride, octenyl succinic anhydride, nonenyl succinic anhydride, C20-24 alkenyl succinic anhydride, maleic anhydride and glutaric anhydride. The cyclic anhydride reactants of the formula (I), (II) or (III) wherein any of R1 and R2, R3 and R4, orR5, R6, R7, R8, R9, R10, and R11 represents hydrogen ora C6-30, such as a Cs-24, branched or unbranched alkyl or alkenyl group may preferably be selected from dodecenyl succinic anhydride (such as (2-dodecen-1-yl)succinic anhydride), tetrapropenyl succinic anhydride, octadecenyl succinic anhydride, octenyl succinic anhydride, nonenyl succinic anhydride, C20-24 alkenyl succinic anhydride, and glutaric anhydride. The cyclic anhydride reactants are preferably selected from branched dodecenyl succinic anhydride, C14 alkenyl succinic anhydride, C15-18 alkenyl succinic anhydride (such as C15-18 internal olefin-derived alkenyl succinic anhydride), and C16 alkenyl succinic anhydride (such as Ci6 internal olefin-derived alkenyl succinic anhydride or Cie terminal olefin-derived alkenyl succinic anhydride). The cyclic anhydride reactants are further preferably selected from C15-18 alkenyl succinic anhydride (such as C15-18 internal olefin-derived alkenyl succinic anhydride) and C16 alkenyl succinic anhydride (such as C16 internal olefin-derived alkenyl succinic anhydride or C16 terminal olefin-derived alkenyl succinic anhydride). When any of R1 and R2, or R3 and R4, orR5, R6, R7, R8, R9, R10, and R11, together with the atoms to which they are attached represent an optionally substituted cyclic group, the cyclic group so formed may be mono or polycyclic (preferably mono or bicyclic) and may be aromatic or nonaromatic. Examples of aromatic groups that may be so formed include benzene and naphthalene. Examples of non-aromatic groups that may be so formed include cyclopentane, cyclohexane, and cyclooctane. Any of R5, R6, R7, R8, R9, R10, and R11 together with the atoms to which they are attached may represent an optionally substituted cyclic group. Any of R5, R6, R7, R8, R9, R10, and R11 not representing a cyclic group are independently selected from hydrogen, an alkyl group and an alkenyl group as described herein. Two, three, four, five, or six of R5, R6, R7, R8, R9, R10, and R11 together with the atoms to which they are attached may represent an optionally substituted cyclic group. Suitably at least R5 and R7, or R5 and R9, or R5 and R11, or R7 and R9, or R7 and R11, or R5, R7 and R9, or R5, R7 and R11 together with the atoms to which they are attached may represent an optionally substituted cyclic group. For the avoidance of doubt, when any of R5, R6, R7, R8, R9, and R10 together with the atoms to which they are attached represent an optionally substituted cyclic group, one or more of R5, R6, R7, R8, R9, and R10 may contribute to one or more double bonds (for example, aromaticity) in the cyclic group. For example, R8 and R10 may together form a carbon-carbon double bond, which may form part of an aromatic cyclic group. The optionally substituted cyclic group represented by R1 and R2, or R3 and R4, or any of R5, R6, R7, R8, R9, R10, and R11, together with the atoms to which they are attached (when present) may be optionally substituted with any suitable substituent(s), such as for example one or more substituents independently selected from alkyl (for example C1-30, preferably C1-24, such as C1-4 or Cs-24, alkyl), alkenyl (for example C2-30, preferably C2-24, such as C2-4 or Cs-24, alkenyl), alkoxy (for example C1-30, preferably C1-24, such as C1-4 or Cs-24, alkoxy), alkenyloxy (for example C2-30, preferably C2-24, such as C2-4 or Cs-24, alkenyloxy), carboxy, alkoxy-carbonyl (for example C1-30, preferably C1-24, such as C1-4 or Cs-24, alkoxy-carbonyl), alkenyloxy-carbonyl (for example C2-30, preferably C2-24, such as C2-4 or Cs-24, alkenyloxy-carbonyl), hydroxy, halo (for example chloro or fluoro), nitro and cyano groups. The optionally substituted cyclic group represented by R1 and R2, or R3 and R4, or any of R5, R6, R7, R8, R9, R10, and R11, together with the atoms to which they are attached (when present) may alternatively be substituted by groups which form a further cyclic anhydride group. An example of such a cyclic anhydride is pyromellitic dianhydride. However, in some embodiments the cyclic anhydride monomers of the formula (I), (II) or (III) contain a single (i.e. only one) anhydride group. In such embodiments, the optionally substituted cyclic group represented by R1 and R2, or R3 and R4, or any of R5, R6, R7, R8, R9, R10, and R11, together with the atoms to which they are attached (when present) may not be substituted by a further cyclic anhydride group. Examples of suitable cyclic anhydrides of formula (I) in which R1 and R2 together with the carbon atoms to which they are attached represent an optionally substituted cyclic group include optionally substituted 1,2-cyclohexanedicarboxylic anhydride and 1,3-cyclopentanedicarboxylic anhydride. 1,2-Cyclohexanedicarboxylic anhydride is preferred. Examples of suitable anhydrides of formula (II) in which R3 and R4 together with the carbon atoms to which they are attached represent an optionally substituted cyclic group include optionally substituted phthalic anhydride, pyromellitic dianhydride, 1,2-naphthalic anhydride and 2,3-naphthalic anhydride. Examples of a substituted phthalic anhydride may include 1,2,4-benzenetricarboxylic anhydride, and 6-((octadec-9-en-1-yloxy)carbonyl)-1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid. Examples of suitable anhydrides of formula (III) in which any of R5, R6, R7, R8, R9, R10, and R11 together with the carbon atoms to which they are attached represent an optionally substituted cyclic group include optionally substituted 1,8-naphthalic anhydride and homophthalic anhydride. Preferred cyclic anhydrides include one or more cyclic anhydrides of formula (I) wherein R1 and R2 are each independently selected from hydrogen and a Cs-3o, such as a Cs-24, alkyl or alkenyl group, or wherein R1 and R2 together with the carbon atoms to which they are attached represent an optionally substituted cyclic group; or of formula (II) wherein R3 and R4 are each independently selected from hydrogen and a Cs-3o, such as a Cs-24, alkyl or alkenyl group, or wherein R3 and R4 together with the carbon atoms to which they are attached represent an optionally substituted cyclic group; or of formula (III) wherein X is CR9R10, O, or S and R5, R6, R7, R8, R9, and R10 are each independently selected from hydrogen and a Cs-3o, such as a Cs-24, an alkyl group or alkenyl group, and / or wherein any of R5, R6, R7, R8, R9, and R10 together with the carbon atoms to which they are attached represent an optionally substituted cyclic group. More preferred cyclic anhydrides include one or more cyclic anhydrides of formula (I) wherein R1 and R2 are each independently selected from hydrogen and a Cs-3o, such as a Cs-24, alkenyl group, or wherein R1 and R2 together with the carbon atoms to which they are attached represent an optionally substituted cyclic group; or of formula (II) wherein R3 and R4 are both hydrogen, or wherein R3 and R4 together with the carbon atoms to which they are attached represent an optionally substituted cyclic group; or of formula (III) wherein X is CR9R10, O, or S and R5, R6, R7, R8, R9, and R10are each hydrogen, and / or wherein any of R5, R6, R7, R8, R9, and R10 together with the carbon atoms to which they are attached represent an optionally substituted cyclic group. Preferably, at least one of the first reactants is a cyclic anhydride of formula (I), (II) or (III) wherein at least one of R1 and R2, or at least one of R3 and R4, or at least one of R5, R6, R7, R8, R9, R10, and R11, is a Ce-30, such as a Cs-24, alkyl or alkenyl (more preferably alkenyl) group (such as an alkenyl group derived from a terminal olefin or an internal olefin, preferably an internal olefin). Preferably, at least one of the first reactants is a cyclic anhydride of formula (I), (II) or (III) wherein at least one of R1 and R2, or at least one of R3 and R4, or at least one of R5, R6, R7, R8, R9, R10, and R11, is a Ce-30, such as a Cs-24, alkyl or alkenyl (more preferably alkenyl) group (such as an alkenyl group derived from a terminal olefin or an internal olefin, preferably an internal olefin) and the other (or others) is (or are) hydrogen. For example, the cyclic anhydride may be an anhydride of formula (I) wherein R1 and R2 are both hydrogen (i.e. the cyclic anhydride may be succinic anhydride). For example, the cyclic anhydride may be an anhydride of formula (II) wherein R3 and R4 are both hydrogen (i.e. the cyclic anhydride may be maleic anhydride). For example, the cyclic anhydride may be an anhydride of formula (III) in which X is CR9R10 and R5, R6, R7, R8, R9, and R10 each represent hydrogen (i.e. the cyclic anhydride may be glutaric anhydride). For example, the cyclic anhydride may be an anhydride of formula (III) in which X is O and R5, R6, R7, and R8 each represent hydrogen (i.e. the cyclic anhydride may be diglycolic anhydride). For example, the cyclic anhydride may be an anhydride of formula (III) in which X is S and R5, R6, R7, and R8 each represent hydrogen (i.e. the cyclic anhydride may be thiodiglycolic anhydride). For example, the or each cyclic anhydride may be an anhydride of formula (I) wherein R1 and R2 are both hydrogen or wherein one of R1 and R2 is an alkyl or alkenyl group (such as an alkenyl group derived from a terminal olefin or an internal olefin, preferably an internal olefin) and the other of R1 and R2 is hydrogen. For example, the or each cyclic anhydride may be an anhydride of formula (I) wherein R1 and R2 are both hydrogen or wherein one of R1 and R2 is a C6-30, such as a Ca-24, alkyl or alkenyl (more preferably alkenyl) group (such as an alkenyl group derived from a terminal olefin or an internal olefin, preferably an internal olefin) and the other of R1 and R2 is hydrogen. Examples of such cyclic anhydride compounds include succinic anhydride, C20-24 alkenyl succinic anhydride, dodecenyl succinic anhydride (such as (2-dodecen-1-yl)succinic anhydride or branched dodecenyl succinic anhydride), nonenyl succinic anhydride, C14 alkenyl succinic anhydride, octadecenyl succinic anhydride, octenyl succinic anhydride, C15-18 alkenyl succinic anhydride (such as C15-18 internal olefin-derived alkenyl succinic anhydride), and C16 alkenyl succinic anhydride (such as C16 internal olefin-derived alkenyl succinic anhydride or C16 terminal olefin-derived alkenyl succinic anhydride). The cyclic anhydride compound may be selected from succinic anhydride, C20-24 alkenyl succinic anhydride, dodecenyl succinic anhydride (such as (2-dodecen-1-yl)succinic anhydride), nonenyl succinic anhydride, octadecenyl succinic anhydride and octenyl succinic anhydride. The cyclic anhydride compound is preferably selected from branched dodecenyl succinic anhydride, C14 alkenyl succinic anhydride, C15-18 alkenyl succinic anhydride (such as C15-18 internal olefin-derived alkenyl succinic anhydride), and C16 alkenyl succinic anhydride (such as C16 internal olefin-derived alkenyl succinic anhydride or C16 terminal olefin-derived alkenyl succinic anhydride). Preferably, the or each cyclic anhydride may be an anhydride of formula (I) wherein one of R1 and R2 is an alkenyl group, such as a C6-30 (preferably C8-24) alkenyl group (such as a C6-30 (preferably C8-24) alkenyl group derived from a terminal olefin or an internal olefin, preferably an internal olefin), and the other of R1 and R2 is hydrogen. Examples of such cyclic anhydride compounds include C20-24 alkenyl succinic anhydride, dodecenyl succinic anhydride (such as (2-dodecen-1-yl)succinic anhydride or branched dodecenyl succinic anhydride), nonenyl succinic anhydride, C14 alkenyl succinic anhydride, octadecenyl succinic anhydride, octenyl succinic anhydride, C15-18 alkenyl succinic anhydride (such as C15-18 internal olefin-derived alkenyl succinic anhydride), and C16 alkenyl succinic anhydride (such as C16 internal olefin-derived alkenyl succinic anhydride or C16 terminal olefin-derived alkenyl succinic anhydride). The cyclic anhydride compound may be selected from C20-24 alkenyl succinic anhydride, dodecenyl succinic anhydride (such as (2-dodecen-1-yl)succinic anhydride), nonenyl succinic anhydride, octadecenyl succinic anhydride and octenyl succinic anhydride. The cyclic anhydride compound is preferably selected from branched dodecenyl succinic anhydride, C14 alkenyl succinic anhydride, C15-18 alkenyl succinic anhydride (such as C15-18 internal olefin-derived alkenyl succinic anhydride), and C16 alkenyl succinic anhydride (such as C16 internal olefin-derived alkenyl succinic anhydride or C16 terminal olefin-derived alkenyl succinic anhydride). Preferably, the or each cyclic anhydride may be dodecenyl succinic anhydride, such as (2-dodecen-1-yl)succinic anhydride. The or each cyclic anhydride may be an anhydride of formula (I) wherein one of R1 and R2 is hydrogen and the other of R1 and R2 is a polyisobutenyl group, for example wherein the polyisobutenyl group suitably has a number average molecular weight of from 100 to 2000, preferably from 100 to 1000, for example 260 or 550. Preferably, the or each cyclic anhydride may be a cyclic anhydride of formula (I) or (II) wherein R1 and R2, or R3 and R4, together with the carbon atoms to which they are attached represent an optionally substituted cyclic group, wherein the cyclic group is an aromatic or a non-aromatic group and is mono or polycyclic. Preferably, the or each cyclic anhydride may be an anhydride of formula (I) wherein R1 and R2 together with the carbon atoms to which they are attached represent an optionally substituted cyclic group, wherein the cyclic group is a non-aromatic (for example saturated) mono or bicyclic group. More preferably, the or each cyclic anhydride may be a cyclic anhydride of formula (I) wherein R1 and R2 together with the carbon atoms to which they are attached represent an optionally substituted cyclic group, wherein the cyclic group is a non-aromatic (for example saturated) monocyclic group, such as a cyclohexane group. Preferably, the or each cyclic anhydride may be an anhydride of formula (II) wherein R3 and R4 together with the carbon atoms to which they are attached represent an optionally substituted cyclic group, wherein the cyclic group is an aromatic mono or bicyclic group, such as a benzene or naphthalene group. More preferably, the or each cyclic anhydride may be a cyclic anhydride of formula (II) wherein R3 and R4 together with the carbon atoms to which they are attached represent an optionally substituted cyclic group, wherein the cyclic group is an aromatic monocyclic group, such as a benzene group. Preferably, the or each cyclic anhydride may be an anhydride of formula (III) wherein X is CR9R10 and R5, R6, R7, R8, R9, and R10 together with the carbon atoms to which they are attached represent an optionally substituted cyclic group, wherein the cyclic group is an aromatic bicyclic group, such as a naphthalene group; or R7 and R8 are hydrogen and R5, R6, R9 and R10 together with the carbon atoms to which they are attached represent an optionally substituted cyclic group, wherein the cyclic group is an aromatic monocyclic group, such as a benzene group. More preferably, the or each cyclic anhydride may be an anhydride of formula (III) wherein X is CR9R10 and R5, R6, R7, R8, R9, and R10 together with the carbon atoms to which they are attached represent an optionally substituted cyclic group, wherein the cyclic group is an aromatic bicyclic group, such as a naphthalene group. When the cyclic anhydride is an anhydride of formula (I) wherein R1 and R2 together with the carbon atoms to which they are attached represent an optionally substituted cyclohexane group, the cyclic anhydride may be of the formula (IA): wherein n is an integer from 0 to 4 and each R12 (when present) is independently selected from alkyl (for example C1-30, preferably C1-24, such as C1-4, alkyl), alkenyl (for example C2-30, preferably C2-24, such as C2-4, alkenyl), alkoxy (for example C1-30, preferably C1-24, such as C1-4, alkoxy), alkenyloxy (for example C2-30, preferably C2-24, such as C2-4, alkenyloxy), carboxy, alkoxy-carbonyl (for example C1-30, preferably C1-24, such as C1-4, alkoxy-carbonyl), alkenyloxycarbonyl (for example C2-30, preferably C2-24, such as C2-4, alkenyloxy-carbonyl), hydroxy, halo (for example chloro or fluoro), nitro and cyano groups, or when n is 2 the two R12 groups may represent a further cyclic anhydride group (such as a further succinic anhydride group). In some embodiments, the cyclic anhydride of formula (IA) contains a single (i.e. only one) anhydride group. In such embodiments, two R12 groups may not represent a further cyclic anhydride group. Examples of suitable succinic anhydrides of formula (IA) include 1,2-cyclohexanedicarboxylic anhydride. When the cyclic anhydride is an anhydride of formula (II) wherein R3 and R4 together with the carbon atoms to which they are attached represent an optionally substituted benzene group, the cyclic anhydride may be of the formula (IIA): (I I A) wherein n’ is an integer from 0 to 4 and each R13 (when present) is independently selected from alkyl (for example C1-30, preferably C1-24, such as C1-4, alkyl), alkenyl (for example C2-30, preferably C2-24, such as C2-4, alkenyl), alkoxy (for example C1-30, preferably C1-24, such as C1-4, alkoxy), alkenyloxy (for example C2-30, preferably C2-24, such as C2-4, alkenyloxy), carboxy, alkoxy-carbonyl (for example C1-30, preferably C1-24, such as C1-4, alkoxy-carbonyl), alkenyloxycarbonyl (for example C2-30, preferably C2-24, such as C2-4, alkenyloxy-carbonyl), hydroxy, halo (for example chloro or fluoro), nitro and cyano groups, or when n’ is 2 the two R13 groups may represent a further cyclic anhydride group (such as a further succinic anhydride group). When R13 represents a alkoxy-carbonyl (for example C1-30, preferably Ca-24, alkoxy-carbonyl) or alkenyloxy-carbonyl (for example C2-30, preferably Ca-24, alkenyloxy-carbonyl), substituent, the alkoxy-carbonyl or alkenyloxy-carbonyl group may be of the formula -C(O)OR13 wherein R13 is a C1-30, preferably Ca-24, alkyl group or a C2-30, preferably Ca-24, alkenyl group. Suitably R13 may represent an oleyl group. Examples of suitable succinic anhydrides of formula (HA) include phthalic anhydride, pyromellitic dianhydride, 1,2,4-benzenetricarboxylic anhydride, 1,2-naphthalic anhydride and 2,3-naphthalic anhydride, and 6-((octadec-9-en-1-yloxy)carbonyl)-1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid. When the cyclic anhydride is an anhydride of formula (III) wherein X is CR9R10 and R5, R6, R7, R8, R9, and R10 together with the carbon atoms to which they are attached representan optionally substituted naphthalene group, the cyclic anhydride may be of the formula (IIIA): (IIIA) wherein each of m and m’ is independently an integer from 0 to 3 and each of R14 and R15 (when present) is independently selected from alkyl (for example C1-30, preferably C1-24, such as C1-4, alkyl), alkenyl (for example C2-30, preferably C2-24, such as C2-4, alkenyl), alkoxy (for example Ci-30, preferably C1-24, such as C1-4, alkoxy), alkenyloxy (for example C2-30, preferably C2-24, such as C2-4, alkenyloxy), carboxy, alkoxy-carbonyl (for example C1-30, preferably C1-24, such as C1-4, alkoxy-carbonyl), alkenyloxy-carbonyl (for example C2-30, preferably C2-24, such as C2-4, alkenyloxy-carbonyl), hydroxy, halo (for example chloro or fluoro), nitro and cyano groups. Examples of suitable succinic anhydrides of formula (IIIA) include 1,8-naphthalic anhydride. When the cyclic anhydride is an anhydride of formula (III) wherein X is CR9R10, R7 and R8 are hydrogen and R5, R6, R9 and R10 together with the carbon atoms to which they are attached represent an optionally substituted benzene group, the cyclic anhydride may be of the formula (IIIB): wherein m” is an integer from 0 to 4 and each R16 (when present) is independently selected from alkyl (for example C1-30, preferably C1-24, such as C1-4, alkyl), alkenyl (for example C2-30, preferably C2-24, such as C2-4, alkenyl), alkoxy (for example C1-30, preferably C1-24, such as C1-4, alkoxy), alkenyloxy (for example C2-30, preferably C2-24, such as C2-4, alkenyloxy), carboxy, alkoxy-carbonyl (for example C1-30, preferably C1-24, such as C1-4, alkoxy-carbonyl), alkenyloxycarbonyl (for example C2-30, preferably C2-24, such as C2-4, alkenyloxy-carbonyl), hydroxy, halo (for example chloro or fluoro), nitro and cyano groups. Examples of suitable succinic anhydrides of formula (IIIB) include homophthalic anhydride. Suitably, the or each cyclic anhydride may be selected from one or more of succinic anhydride, maleic anhydride, glutaric anhydride, a C6-30 alkenyl succinic anhydride such as C20-24 alkenyl succinic anhydride, dodecenyl succinic anhydride (such as (2-dodecen-1-yl)succinic anhydride or branched dodecenyl succinic anhydride), nonenyl succinic anhydride, C14 alkenyl succinic anhydride, octadecenyl succinic anhydride, octenyl succinic anhydride, octadecyl succinic anhydride, octyl succinic anhydride, C15-18 alkenyl succinic anhydride (such as C15-18 internal olefin-derived alkenyl succinic anhydride), C16 alkenyl succinic anhydride (such as C16 internal olefin-derived alkenyl succinic anhydride or C16 terminal olefin-derived alkenyl succinic anhydride), a branched alkenyl succinic anhydride such as tetrapropenyl succinic anhydride or polyisobutenyl succinic anhydride, phthalic anhydride, pyromellitic dianhydride, 1,2,4-benzenetricarboxylic anhydride, 1,2-cyclohexanedicarboxylic anhydride, 1,2-naphthalic anhydride, 2,3-naphthalic anhydride, 1,8-naphthalic anhydride and homophthalic anhydride. Suitably, the or each cyclic anhydride may be selected from one or more of succinic anhydride, maleic anhydride, glutaric anhydride, a Ce-30 alkenyl succinic anhydride such as C20-24 alkenyl succinic anhydride, dodecenyl succinic anhydride (such as (2-dodecen-1-yl)succinic anhydride), nonenyl succinic anhydride, octadecenyl succinic anhydride, octenyl succinic anhydride, octadecyl succinic anhydride, or octyl succinic anhydride, a branched alkenyl succinic anhydride such as tetrapropenyl succinic anhydride or polyisobutenyl succinic anhydride, phthalic anhydride, pyromellitic dianhydride, 1,2,4-benzenetricarboxylic anhydride, 1,2-cyclohexanedicarboxylic anhydride, 1,2-naphthalic anhydride, 2,3-naphthalic anhydride, 1,8-naphthalic anhydride and homophthalic anhydride. Suitably, the or each cyclic anhydride may be selected from one or more of a C6-30 alkenyl succinic anhydride such as C20-24 alkenyl succinic anhydride, dodecenyl succinic anhydride (such as (2-dodecen-1-yl)succinic anhydride), nonenyl succinic anhydride, octadecenyl succinic anhydride, octenyl succinic anhydride, octadecyl succinic anhydride, or octyl succinic anhydride, a branched alkenyl succinic anhydride such as tetrapropenyl succinic anhydride or polyisobutenyl succinic anhydride, phthalic anhydride, pyromellitic dianhydride, 1,2,4-benzenetricarboxylic anhydride, 1,2-cyclohexanedicarboxylic anhydride, 1,2-naphthalic anhydride, 2,3-naphthalic anhydride, 1,8-naphthalic anhydride and homophthalic anhydride. Suitably, the or each cyclic anhydride may be selected from one or more of succinic anhydride, maleic anhydride, glutaric anhydride, a C6-30 alkenyl succinic anhydride such as C20-24 alkenyl succinic anhydride, dodecenyl succinic anhydride (such as (2-dodecen-1-yl)succinic anhydride), nonenyl succinic anhydride, octadecenyl succinic anhydride, octenyl succinic anhydride, octadecyl succinic anhydride, or octyl succinic anhydride, and a branched alkenyl succinic anhydride such as tetrapropenyl succinic anhydride or polyisobutenyl succinic anhydride. Suitably, the or each cyclic anhydride may be selected from one or more of phthalic anhydride, pyromellitic dianhydride, 1,2,4-benzenetricarboxylic anhydride, 1,2-cyclohexanedicarboxylic anhydride, 1,2-naphthalic anhydride, 2,3-naphthalic anhydride, 1,8-naphthalic anhydride and homophthalic anhydride. More suitably, the or each cyclic anhydride may be selected from one or more of succinic anhydride, maleic anhydride, C20-24 alkenyl succinic anhydride, dodecenyl succinic anhydride (such as (2-dodecen-1-yl)succinic anhydride), nonenyl succinic anhydride, octadecenyl succinic anhydride, octenyl succinic anhydride, phthalic anhydride, pyromellitic dianhydride, 1,2,4-benzenetricarboxylic anhydride, 1,2-cyclohexanedicarboxylic anhydride, 1,2-naphthalic anhydride, 2,3-naphthalic anhydride, 1,8-naphthalic anhydride, homophthalic anhydride and glutaric anhydride. More suitably, the or each cyclic anhydride may be selected from one or more of succinic anhydride, maleic anhydride, C20-24 alkenyl succinic anhydride, dodecenyl succinic anhydride (such as (2-dodecen-1-yl)succinic anhydride), nonenyl succinic anhydride, octadecenyl succinic anhydride, octenyl succinic anhydride, and glutaric anhydride. More suitably, the or each cyclic anhydride may be selected from one or more of C20-24 alkenyl succinic anhydride, dodecenyl succinic anhydride (such as (2-dodecen-1-yl)succinic anhydride), nonenyl succinic anhydride, octadecenyl succinic anhydride, octenyl succinic anhydride, and glutaric anhydride. Preferably, the or each cyclic anhydride may be selected from one or more of succinic anhydride, maleic anhydride, C20-24 alkenyl succinic anhydride, dodecenyl succinic anhydride (such as (2-dodecen-1-yl)succinic anhydride), nonenyl succinic anhydride, octadecenyl succinic anhydride, octenyl succinic anhydride, phthalic anhydride, pyromellitic dianhydride, 1,2,4-benzenetricarboxylic anhydride, 1,2-cyclohexanedicarboxylic anhydride and 1,8-naphthalic anhydride. Preferably, the or each cyclic anhydride may be selected from one or more of succinic anhydride, maleic anhydride, C20-24 alkenyl succinic anhydride, dodecenyl succinic anhydride (such as (2-dodecen-1-yl)succinic anhydride), nonenyl succinic anhydride, octadecenyl succinic anhydride, and octenyl succinic anhydride. Preferably, the or each cyclic anhydride may be selected from one or more of C20-24 alkenyl succinic anhydride, dodecenyl succinic anhydride (such as (2-dodecen-1-yl)succinic anhydride), nonenyl succinic anhydride, octadecenyl succinic anhydride, and octenyl succinic anhydride. Preferably, the or each cyclic anhydride may be selected from one or more of phthalic anhydride, pyromellitic dianhydride, 1,2,4-benzenetricarboxylic anhydride, 1,2-cyclohexanedicarboxylic anhydride and 1,8-naphthalic anhydride. Preferably, the or each cyclic anhydride may be selected from one or more of branched dodecenyl succinic anhydride, C14 alkenyl succinic anhydride, C15-18 alkenyl succinic anhydride (such as C15-18 internal olefin-derived alkenyl succinic anhydride), and C16 alkenyl succinic anhydride (such as C16 internal olefin-derived alkenyl succinic anhydride or C16 terminal olefinderived alkenyl succinic anhydride). Preferably, the or each cyclic anhydride may be selected from one or more of C15-18 alkenyl succinic anhydride (such as C15-18 internal olefin-derived alkenyl succinic anhydride) and C16 alkenyl succinic anhydride (such as Ci6 internal olefin-derived alkenyl succinic anhydride or Ci6 terminal olefin-derived alkenyl succinic anhydride). The cyclic anhydride compounds discussed herein may be commercially available or may be prepared using procedures well known in the art. For example, alkenyl substituted succinic anhydrides are typically prepared by the reaction of an alkene with maleic anhydride. Preferably, the or each cyclic anhydride may be independently selected from a Ce-30 alkyl or alkenyl substituted succinic anhydride, phthalic anhydride and pyromellitic dianhydride. Preferably, the or each cyclic anhydride may be independently selected from a Ce-30 alkyl or alkenyl substituted succinic anhydride. Preferably, the or each cyclic anhydride may be independently selected from a C6-30 alkenyl substituted succinic anhydride wherein the alkenyl group is derived from a terminal olefin or an internal olefin, preferably an internal olefin. Preferably, the or each cyclic anhydride may be independently selected from (2-dodecen-1-yl)succinic anhydride, branched dodecenyl succinic anhydride, Cm alkenyl succinic anhydride, nonenyl succinic anhydride, octadecenyl succinic anhydride, C15-18 alkenyl succinic anhydride (such as C15-18 internal olefin-derived alkenyl succinic anhydride), C16 alkenyl succinic anhydride (such as C16 internal olefin-derived alkenyl succinic anhydride or C16 terminal olefin-derived alkenyl succinic anhydride), tetrapropenyl succinic anhydride, phthalic anhydride and pyromellitic dianhydride. Preferably, the or each cyclic anhydride may be independently selected from (2-dodecen-1-yl)succinic anhydride, nonenyl succinic anhydride, octadecenyl succinic anhydride, phthalic anhydride and pyromellitic dianhydride. Preferably, the or each cyclic anhydride may be independently selected from (2-dodecen-1-yl)succinic anhydride, nonenyl succinic anhydride, and octadecenyl succinic anhydride. Preferably, the or each cyclic anhydride may be independently selected from phthalic anhydride and pyromellitic dianhydride. The cyclic anhydride compounds discussed herein may be commercially available or may be prepared using procedures well known in the art. The or each of the one or more second reactants used to make the ester compound is a polyol. Mixtures of two or more different second reactants (i.e. different polyols) may be used to make the ester compound. Any suitable polyol may be used to make the ester compound, as would be understood by the person skilled in the art. The term polyol is used to refer to any compound including two or more hydroxy (OH) functional groups. In some embodiments the or each polyol may comprise carbon, hydrogen and oxygen atoms, and optionally additionally nitrogen atoms. In other embodiments, the or each polyol may consist essentially of or consist of carbon, hydrogen and oxygen atoms. Suitable polyols for preparing the ester compound may be compounds having from 2 to 10, preferably from 2 to 6, more preferably 2 or 3, hydroxy groups. In some embodiments the polyol may have only two hydroxy groups (i.e. the polyol may be a diol). Suitable polyols may include one or more of a polyol of formula (IV): H-(OR17)P-OH (IV) wherein each R17 is independently an optionally substituted hydrocarbylene group and p is an integer of at least 1. When p is an integer of greater than 1, the polyol of formula (IV) may comprise groups R17 that are all the same or may comprise groups R17that are different. Suitably, each R17 in the formula (IV) may be the same. Preferably p is an integer from 1 to 140, such as from 1 to 110, from 1 to 40 or from 1 to 10. For example, suitable polyols may include one or more of a polyol of formula (IVA): H-(OR18)q-OH (IVA) wherein each R18 is independently an optionally substituted alkylene group and q is an integer of at least 1. When q is an integer of greater than 1, the polyol of formula (IV) may comprise groups R18 that are all the same or may comprise groups R18 that are different. Suitably, each R18 in the formula (IVA) is the same. Preferably q is an integer from 1 to 140, such as from 1 to 110, from 1 to 40 or from 1 to 10. When the polyol of formula (IV) or (IVA) contains a substituted hydrocarbylene or alkylene group, any suitable substituent may be present, such as for example a carboxy or amido substituent. The polyol of formula (IVA) may have more than 2 hydroxy groups and the group R18 may be a hydroxy substituted alkylene group. Each hydroxy substituted alkylene group R18 may have 1,2 or more hydroxy groups. Each hydroxy substituted alkylene group R18 may preferably have 1 hydroxy group. The polyol of formula (IVA) may have 2 hydroxy groups and the group R18 may be an optionally substituted alkylene group wherein the optional substituent is not hydroxy. The polyol of formula (IV) or of formula (IVA) may be a sugar derived compound in which R17 or R18 includes one or more hydroxy residues. The or each R17 or R18 may represent a cyclic alkylene unit. One or more heteroatoms (for example oxygen atoms) may be present in the cyclic alkylene unit. For example the unit may contain an ether linkage. Suitably the or each R17 or R18 may be one or more saccharide units or may be substituted with one or more saccharide units. Suitably the or each R17 or R18 may be an unsubstituted alkylene group. Preferably the or each R17 or R18 is an optionally substituted alkylene group having from 1 to 50, such as from 1 to 40, preferably from 1 to 30, more preferably from 1 to 20, suitably from 1 to 12 or from 1 to 10, for example from 2 to 6, carbon atoms. Preferably the or each R17 or R18 is an unsubstituted alkylene group having from 1 to 50, preferably from 1 to 20, more preferably from 1 to 12 or from 1 to 10, suitably from 2 to 6 carbon atoms. Each R17 or R18 may be straight chained or branched. Suitably the or each R17orR18 may be an ethylene, propylene, butylene, pentylene, hexylene or dodecylene group. When R17 or R18 has more than 2 carbon atoms any isomer may be present. Preferably R17 or R18 is an ethylene or a propylene group, most preferably an ethylene group. When q is 1, R18 may be a group of formula (CH2)x wherein x is from 2 to 12, preferably from 3 to 12. Suitably when q is 1, R18 may be a straight chain or branched optionally substituted alkylene group and the polyol may be selected from ethylene glycol, propylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,6-hexanediol, 1,12-dodecanediol, trimethylolpropane, 2-ethyl-1,3,-hexanediol, 2,2-diethyl-1,3-propanediol, 2,2-bis(hydroxymethyl)propionic acid, pentaerythritol, sorbitol, xylitol, glycerol and neopentyl glycol. In some embodiments, the polyol may be selected from ethylene glycol, propylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,6-hexanediol, 1,12-dodecanediol, trimethylolpropane, 2-ethyl-1,3,-hexanediol, 2,2-diethyl-1,3-propanediol, 2,2-bis(hydroxymethyl)propionic acid, pentaerythritol, sorbitol, xylitol, and neopentyl glycol. Suitably when q is 1, R18 may be a straight chain or branched alkylene group having from 2 to 12, preferably from 3 to 12, carbon atoms. Suitable compounds of this type include ethylene glycol, propylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,6-hexanediol, 1,12-dodecanediol, trimethylolpropane, 2-ethyl-1,3,-hexanediol, 2,2-diethyl-1,3-propanediol, pentaerythritol and neopentyl glycol. Suitably when q is 1, R18 may be a branched alkylene group having from 2 to 12, preferably from 3 to 12, carbon atoms. Suitable compounds of this type include propylene glycol, 1,2-butanediol, 1,3-butanediol, trimethylolpropane, 2-ethyl-1,3,-hexanediol, 2,2-diethyl-1,3-propanediol, pentaerythritol and neopentyl glycol. Suitably when q is 2 or more, the or each R18 may be a straight chain or branched alkylene group and the polyol may, for example, be selected from diglycerol, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol and polypropylene glycol. Suitably when q is 2 or more, the or each R18 may be a straight chain or branched alkylene group having from 2 to 4, preferably 2 or 3, carbon atoms. Suitable compounds of this type include diethylene glycol, triethylene glycol, di propylene glycol, tripropylene glycol, polyethylene glycol (PEG), for example having a number average molecular weight of from 150 to 6000, and polypropylene glycol (PPG), for example having a number average molecular weight of from 400 to 2000. Suitable polyols may include one or more of PEG 6000, PEG 1500, PEG 1000, PEG 600, PEG 400, PEG 200, PPG 2000, PPG 1000 and PPG 425. The or each R17 or R18 may comprise a mixture of isomers. For example when R17 or R18 is propylene, the polyol may include moieties -CH2CH(CH3)- and -CH(CH3)CH2- in any order within the chain. R17 or R18 may comprise a mixture of different groups for example ethylene, propylene or butylene units. The or each R18 may be an ethylene, propylene or butylene group. For example, the or each R18 may be an n-propylene or n-butylene group or an isopropylene or isobutylene group. For example the or each R18 may be -CH2CH2-, -CH2CH(CH3)-, - CH(CH3)CH2-, CH2CH2CH2-, -CH2C(CH3)2-, -CH2CH2CH2CH2-, -CH(CH3)CH(CH3)- or-CH2CH(CH2CH3)-. Preferably R18 is selected from -CH2CH2-, -CH2CH2CH2-, -CH(CH3)CH2- or -CH2CH(OH)CH2, more preferably from -CH2CH2-, and-CH2CH2CH2-. Suitably the polyol of formula (IV) or (IVA) may be a sugar derived alcohol, for example, glucose, fructose, trehalose, sucrose, lactose, maltose or sorbitol, preferably sorbitol. Suitably the polyol of formula (IV) may be selected from one or more of 1,12-dodecanediol, 1,6-hexanediol, trimethylolpropane, neopentyl glycol, polyethylene glycol (such as PEG 6000, PEG 1500, PEG 1000, PEG 600, PEG 400, PEG 200), polypropylene glycol (such as PPG 2000, PPG 1000, PPG 425), sorbitol, trimethylolpropane and xylitol. Suitably, the polyol, for example of formula (IV), may be an ester of glycerol (also known as a glyceride) and a hydroxycarboxylic acid. The ester of glycerol may be a mono-, di- or triglyceride, suitably a tri-glyceride. Suitably, the hydroxycarboxylic acid comprises one or more hydroxyl groups and one or more carboxylic acid groups. The hydroxycarboxylic acid may be a monocarboxylic acid comprising one or more hydroxyl groups. The hydroxycarboxylic acid may be of the formula R19COOH, wherein R19 is a hydroxylsubstituted hydrocarbyl group. R19is suitably a hydroxy-substituted alkyl, alkenyl or alkaryl group, preferably a hydroxy-substituted alkyl or alkenyl group. R19 suitably comprises from 1 to 25 carbon atoms, preferably from 1 to 20 carbon atoms, more preferably from 1 to 17 carbon atoms. Suitably, the hydroxycarboxylic acid may be selected from glycolic acid, lactic acid, hydroxy butyric acid, hydroxyvaleric acid, hydroxycaproic acid, hydroxystearic acid (preferably 12-hydroxystearic acid), 2,2-bis(hydroxymethyl)propionic acid, mandelic acid or ricinoleic acid. Preferably, the hydroxycarboxylic acid or the cyclic ester thereof may be selected from glycolic acid, mandelic acid, ricinoleic acid, malic acid, tartaric acid or citric acid. More preferably, the hydroxycarboxylic acid or the cyclic ester thereof is ricinoleic acid. Preferably, when the polyol is an ester of glycerol, the polyol may be a mono-, di- or tri-glyceride of ricinoleic acid. Most preferably, when the polyol is an ester of glycerol, the polyol may be a tri-glyceride of ricinoleic acid, such as castor oil. Suitable polyols may include one or more of an alkoxylated polyol of formula (IV) or (IVA). These polyols may be the reaction product of a polyol of formula (IV) or (IVA) and one or more alkylene oxides, such as ethylene oxide or propylene oxide. Such alkoxylated polyols may include polyoxyethylene (80) sorbitan monooleate (also known as Tween® 80) and 2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate. Preferably, the or each polyol may be independently selected from castor oil, 1,6-hexanediol, sorbitol, neopentyl glycol and a polyalkylene glycol (such as PEG 200). When the or each polyol comprises carbon, hydrogen, oxygen and nitrogen atoms, the or each polyol may comprise two or more (such as 2 or 3) hydroxy groups and one or more (suitably one) amine groups. The amine groups may suitably be secondary or tertiary amines. Preferably the amine groups are tertiary amines. These polyols may be referred to herein as nitrogen containing polyols. For example, suitable nitrogen containing polyols may include one or more of a polyol of formula (V) or a derivative thereof: NR20R21R22 (V) wherein R20, R21 and R22 are each independently selected from hydrogen, hydroxyalkyl and hydrocarbyl, provided that at least two of R20, R21 and R22 represents a hydroxyalkyl group. Preferably, the at least two of R20, R21 and R22 that represent a hydroxyalkyl group are the same. For example, in the compounds of formula (V), R20 and R21 may each represent hydroxyalkyl and R22 may represent hydrogen, hydroxyalkyl or hydrocarbyl. In the formula (V), the hydroxyalkyl group may contain from 1 to 8, such as from 1 to 4, such as 2 or 3, carbon atoms. For example, each hydroxyalkyl group may be hydroxyethyl or hydroxypropyl, particularly hydroxyethyl. In the formula (V), the hydrocarbyl group (when present) may represent any suitable such group, such as an alkyl group, for example an alkyl group containing from 1 to 10, such as from 1 to 6 or from 1 to 4, carbon atoms. Thus, the hydrocarbyl group may represent a methyl, ethyl, propyl or butyl group (especially butyl or methyl). For example, in the compounds of formula (V), R20 and R21 may each represent hydroxyalkyl and R22 may represent hydrogen, hydroxyalkyl or hydrocarbyl (especially hydrogen or hydrocarbyl, more especially hydrocarbyl). In some embodiments, the R20 and R21 may each represent hydroxyalkyl and R22 may represent hydroxyalkyl or hydrocarbyl. Preferably in the compounds of formula (V), R20 and R21 both represent hydroxyethyl and R22 represents hydrogen or hydrocarbyl, such as a hydrocarbyl group containing from 1 to 6, or from 1 to 4, carbon atoms. Preferably in the compounds of formula (V), R20 and R21 both represent hydroxyethyl and R22 represents hydrogen or an alkyl group containing from 1 to 6, or from 1 to 4, carbon atoms (especially methyl). Examples of suitable nitrogen containing polyols include N-methyl diethanolamine, N-butyl diethanolamine, triethanolamine and diethanolamine, and derivatives thereof. The or each nitrogen containing polyol may be independently selected from N-methyl diethanolamine, N-butyl diethanolamine, and triethanolamine, and derivatives thereof. The or each nitrogen containing polyol may be independently selected from N-methyl diethanolamine, N-butyl diethanolamine, and triethanolamine. References herein to nitrogen containing polyols include derivatives thereof, such as a corresponding quaternary compound. Thus, as example of a suitable derivative of a nitrogen containing polyol is tris(2-hydroxyalkyl)methylammonium compound, for example tris(2-hydroxyethyl)methylammonium methylsulfate, which is a quaternary ammonium salt of triethanolamine. In some preferred embodiments, the nitrogen containing polyols are not derivatised, for example they are not quaternary ammonium salts. Preferably, the or each nitrogen containing polyol may be independently selected from N-butyl diethanolamine, diethanolamine and N-methyl diethanolamine, and derivatives (for example quaternary ammonium salts) thereof. Preferably, the or each nitrogen containing polyol may be independently selected from N-butyl diethanolamine and N-methyl diethanolamine, and derivatives (for example quaternary ammonium salts) thereof. Further examples of suitable nitrogen containing polyols include those formed by reaction of a hydroxy substituted cyclic ester or cyclic carbonate, such as glycerol carbonate or gluconolactone, with a suitable primary or secondary amine compound, such as ethanolamine, dipropylamine, hexylamine, dodecylamine, phenethylamine, dipropylamine, ethylenediamine, or a polyether polyamine. Suitable polyether amines may include polyether monoamines (such as for example Jeffamine M-1000) and polyether polyamines (such as for example Jeffamine ED-600). As the skilled person would appreciate, the reaction of a hydroxy substituted cyclic ester or cyclic carbonate with a suitable primary or secondary amine compound will result in a ring opening reaction to form a compound such as a N-carbamoyl polyol or an amido polyol. The or each polyol may be selected from one or more polyol of the formula (IV) or (IVA) as defined herein (including an ester of glycerol and a hydroxycarboxylic acid (such as castor oil)), one or more of an alkoxylated polyol of formula (IV) or (IVA) as defined herein, one or more nitrogen containing polyol as defined herein (including compounds of the formula (V)) and one or more polyol formed by reaction of a hydroxy substituted cyclic ester or cyclic carbonate with a suitable primary or secondary amine compound. Preferably, the or each polyol may be selected from one or more polyol of the formula (IV) or (IVA) as defined herein (including an ester of glycerol and a hydroxycarboxylic acid (such as castor oil)), one or more of an alkoxylated polyol of formula (IV) or (IVA) as defined herein, one or more nitrogen containing polyol of the formula (V) as defined herein and one or more polyol formed by reaction of a hydroxy substituted cyclic ester or cyclic carbonate with a suitable primary or secondary amine compound. More preferably, the or each polyol may be selected from one or more polyol of the formula (IV) or (IVA) as defined herein (such as an ester of glycerol and a hydroxycarboxylic acid , for example castor oil), and one or more nitrogen containing polyol of the formula (V) as defined herein. In one embodiment, the or each polyol may be selected from one or more polyol of the formula (IV) or (IVA) as defined herein, such as an ester of glycerol and a hydroxycarboxylic acid (for example castor oil). In another embodiment, the or each polyol may be selected from one or more of an alkoxylated polyol of formula (IV) or (IVA) as defined herein. In one embodiment, the or each polyol may be selected from one or more polyol of the formula (IV) or (IVA) as defined herein, such as an ester of glycerol and a hydroxycarboxylic acid (for example castor oil) and from one or more of an alkoxylated polyol of formula (IV) or (IVA) as defined herein. In another embodiment, the or each polyol may be selected from one or more nitrogen containing polyol as defined herein (including compounds of the formula (V)). In another embodiment, the or each polyol may be selected from one or more polyol formed by reaction of a hydroxy substituted cyclic ester or cyclic carbonate with a suitable primary or secondary amine compound. In one embodiment, the ester compound may be the reaction product of reactants comprising one (i.e. a single) cyclic anhydride and one (i.e. a single) polyol. In other embodiments, the ester compound may be the reaction product of reactants comprising two different cyclic anhydrides and one (i.e. a single) polyol, or the ester compound may be the reaction product of reactants comprising one (i.e. a single) cyclic anhydride and two different polyols. The combined amount of the one or more first reactants and the one or more second reactants may be at least 50 mol%, suitably at least 75 mol%, preferably at least 90 mol%, for example at least 95 wt% of the reactants that are reacted to obtain the ester compound. In one embodiment, the ester compound may be the reaction product of reactants consisting essentially of or consisting of one (i.e. a single) cyclic anhydride and one (i.e. a single) polyol. In other embodiments, the ester compound may be the reaction product of reactants consisting essentially of or consisting of two different cyclic anhydrides and one (i.e. a single) polyol , or the ester compound may be the reaction product of reactants consisting essentially of or consisting of one (i.e. a single) cyclic anhydride and two different polyols. The ester compound for use herein may be the reaction product of reactants comprising the one or more first reactants and one or more second reactants as disclosed herein and additionally one or more third reactants. In other words, the ester compound may be the reaction product of reactants comprising one or more first reactants as disclosed herein, one or more second reactants as disclosed herein and one or more third reactants. The one or more third reactants may for example act as end capping groups and / or may introduce additional functional groups to the ester compounds. The one or more third reactants may be selected to impart the desired groups and / or properties to the ester compound by the person skilled in the art. The combined amount of the one or more first reactants, the one or more second reactants, and the one or more third reactants may be at least 50 mol%, suitably at least 75 mol%, preferably at least 90 mol%, for example at least 95 wt% of the reactants that are reacted to obtain the ester compound. The ester compound for use herein may be the reaction product of reactants consisting essentially of or consisting of the one or more first reactants and one or more second reactants as disclosed herein and additionally one or more third reactants. In other words, the ester compound may be the reaction product of reactants consisting essentially of or consisting one or more first reactants as disclosed herein, one or more second reactants as disclosed herein and one or more third reactants. The ester compound for use herein is suitably the reaction product of no more than four different reactants. Preferably, the ester compound is the reaction product of no more than three different reactants. For example, the ester compound may be the reaction product of one first reactant, one second reactant, and one third reactant, or the reaction product of two different first reactants and one second reactant as disclosed herein. In some preferred embodiments, the ester compound is the reaction product of only two different reactants, i.e. one first reactant and one second reactant as disclosed herein (and no further reactants). Examples of suitable third reactants include one or more of the following: (i) polycarboxylic acids or reactive equivalents thereof; (ii) monocarboxylic acids or esters thereof; (iii) hydroxycarboxylic acids or cyclic esters thereof; (iv) epoxide compounds; (v) polyfunctional reactants having a reactive amino group; (vi) monoalcohols; and (vii) monofunctional reactants having a reactive amino group. The third reactant may be (i) a polycarboxylic acid or a reactive equivalent thereof. Suitable polycarboxylic acids comprise two or more carboxylic acid groups, such as two or three carboxylic acid groups. Preferred polycarboxylic acids are dicarboxylic acids. The polycarboxylic acid may be aliphatic or aromatic. The aliphatic polycarboxylic acid may be cycloaliphatic. The aliphatic polycarboxylic acid may be saturated or unsaturated. By the term “unsaturated” we mean that the polycarboxylic acid comprises one or more carbon-carbon double bonds. The polycarboxylic acid may comprise one or more heteroatoms other than in the carboxylic acid groups. By the term “heteroatoms” we mean atoms other than carbon or hydrogen, such as oxygen, nitrogen and sulfur atoms. For example, the polycarboxylic acid may comprise one or more moieties selected from hydroxy groups, amino groups, ether groups, and / or thioether groups. Reactive equivalents of polycarboxylic acids may be used. By the term “reactive equivalent”, we mean a compound that results in the same reaction product as the corresponding polycarboxylic acid. Suitable reactive equivalents include acid chlorides and esters of the polycarboxylic acids described herein. Examples of suitable polycarboxylic acids or reactive equivalents thereof include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, maleic acid, fumaric acid, malic acid, tartaric acid, citric acid, C20-24 alkenyl succinic acid, dodecenyl succinic acid (such as (2- dodecen-1-yl)succinic acid), nonenyl succinic acid, octadecenyl succinic acid, octenyl succinic acid, polyisobutenylsuccinic acid, itaconic acid, 1,2-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, phthalic acid, isophthalic acid, terephthalic acid, homophthalic acid, 1,2,4-benzenetricarboxylic acid, pyromellitic acid, 1,2-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, diglycolic acid, thiodiglycolic acid, 3,3’-thiodipropanoic acid, iminodiacetic acid, poly(ethylene glycol)bis(carboxymethyl) ether, a dimer acid, and acid chlorides and esters thereof. Preferably, the polycarboxylic acid is selected from pimelic acid, suberic acid, sebacic acid, dodecanedioic acid, citric acid, diglycolic acid, thiodiglycolic acid, poly(ethylene glycol)bis(carboxymethyl) ether, or a hydrogenated dimer acid. The third reactant may be (ii) a monocarboxylic acid or an ester thereof. Suitable monocarboxylic acids may be aliphatic or aromatic. The aliphatic monocarboxylic acid may be cycloaliphatic. The aliphatic monocarboxylic acid may be saturated or unsaturated. The monocarboxylic acid may contain from 2 to 40 carbon atoms, suitably from 4 to 30 carbon atoms, preferably from 6 to 20 carbon atoms, for example from 8 to 18 carbon atoms. The monocarboxylic acid may be a fatty acid. Examples of suitable monocarboxylic acids or esters thereof include hexanoic acid, octanoic acid, decanoic acid, lauric acid, myristic acid, myristoleic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, linolelaidic acid, arachidic acid, arachidonic acid, behenic acid, erucic acid, and esters (preferably methyl esters) thereof. Preferably, the monocarboxylic acid is selected from propionic acid, hexanoic acid, lauric acid, stearic acid, oleic acid, or erucic acid. The third reactant may be (iii) a hydroxycarboxylic acid or a cyclic ester thereof. Suitable hydroxycarboxylic acids comprise one or more hydroxy groups and one or more carboxylic acid groups. The hydroxycarboxylic acid may be a monocarboxylic acid comprising one or more hydroxy groups. By the term “cyclic ester” of a hydroxycarboxylic acid we mean a compound comprising a cyclic group, wherein the cyclic group comprises one or more ester groups. The ester may be a cyclic monoester or a cyclic diester. The cyclic ester may correspond to a single cyclised molecule of the hydroxycarboxylic acid. This may, for example, be formed by an intramolecular reaction between the hydroxy group and the carboxylic acid group on one molecule of the hydroxycarboxylic acid. Alternatively, the cyclic ester may correspond to a cyclic dimer of a hydroxycarboxylic acid. This may, for example, be formed by an intermolecular reaction between the hydroxy groups and the carboxylic acid groups on two molecules of the hydroxycarboxylic acid. Examples of suitable hydroxycarboxylic acids or cyclic esters thereof include glycolic acid, lactic acid, hydroxy butyric acid, hydroxyvaleric acid, hydroxycaproic acid, hydroxystearic acid (preferably 12-hydroxystearic acid), dihydroxystearic acid, 2,2-bis(hydroxymethyl)propionic acid, mandelic acid, ricinoleic acid, malic acid, tartaric acid, citric acid, y-butyrolactone, 6-valerolactone, s-caprolactone, menthide, D-lactide, L-lactide, or DL-lactide. Preferably, the hydroxycarboxylic acid is selected from ricinoleic acid or citric acid. The third reactant may be (iv) an epoxide compound. Suitable epoxide compounds may comprise one or more than one epoxide group. For example, suitable epoxide compounds may comprise two epoxide groups. Examples of suitable epoxide compounds include 1,2-epoxydodecane, ethyl glycidyl ether, isopropylglycidyl ether, 2-ethylhexyl glycidyl ether, octyl glycidyl ether, nonyl glycidyl ether, decyl glycidyl ether, butyl glycidyl ether (such as n-butyl glycidyl ether), 1,2-epoxyhexane, epichlorohydrin, glycidyltrimethylammonium chloride, cyclopentene oxide, cyclohexene oxide, poly(ethylene glycol) diglycidyl ether, poly(propylene glycol) diglycidyl ether and poly(butylene glycol) diglycidyl ether. The third reactant may be (v) a polyfunctional reactant having a reactive amino group. By the term “polyfunctional reactant” we mean a reactant with at least two reactive groups. By the term “reactive group” we mean a group that reacts with the first reactant and / or the second reactant. At least one of the reactive groups is a reactive amino group. The other reactive groups in the polyfunctional reactant may be reactive amino groups, or may be reactive groups other than amino groups, such as hydroxy groups or carboxyl groups. Reactive amino groups are suitably primary amino groups or secondary amino groups. The polyfunctional reactant may comprise at least one reactive amino group and at least one hydroxy group. The polyfunctional reactant may be an alkanolamine or an alkoxylated alkanolamine. The polyfunctional reactant may comprise at least two reactive amino groups. The polyfunctional reactant may be an aliphatic diamine, a polyether diamine, ora polyalkylene polyamine. The polyfunctional reactant may comprise at least one reactive amino group and at least one carboxyl group. The polyfunctional reactant may be an amino acid, such as a naturally occurring amino acid. Examples of suitable polyfunctional reactants having at least one reactive amino group include ethanolamine, diethanolamine, ethylene diamine, coco propylene diamine, diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), a polyether diamine (preferably Jeffamine ED-600, Jeffamine ED-900, or Jeffamine ED-2003 which are commercially available), alanine, arginine, asparagine, aspartate, cysteine, glutamine, glutamate, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, and valine. The third reactant may be (vi) a monoalcohol. Suitable monoalcohols may be aliphatic or aromatic. The aliphatic monoalcohol may be cycloaliphatic. The aliphatic monoalcohol may be saturated or unsaturated. The monoalcohol may contain from 2 to 40 carbon atoms, suitably from 4 to 30 carbon atoms, preferably from 6 to 20 carbon atoms, for example from 8 to 18 carbon atoms. The monoalcohol may be a fatty alcohol. Examples of suitable monoalcohols include hexanol, octanol, 2-ethylhexanol, decanol, dodecanol alcohol, myristyl alcohol, myristoleyl alcohol, palmityl alcohol, palmitoleyl alcohol, stearyl alcohol, oleyl alcohol, elaidyl alcohol, linoleyl alcohol, linolelaidyl alcohol, arachidyl alcohol, arachidonyl alcohol, behenyl alcohol, erucyl alcohol, benzyl alcohol, and choline chloride. Preferably, the monoalcohol is hexanol or oleyl alcohol. The third reactant may be (vii) a monofunctional reactant having a reactive amino group. Suitable monofunctional reactants having a reactive amino group have one reactive amino group and no other reactive groups. The monofunctional reactant may contain other functional groups that are not reactive groups, such as tertiary amino groups or ether groups. The monofunctional reactant may be an aliphatic monoamine (such as a fatty alkyl amine), an N,N-dialkylaminoalkylamine, ora polyether monoamine. The polyether monoamine suitably comprises a polyether backbone selected from polyethylene glycol (PEG), polypropylene glycol (PPG), or a copolymer of polyethylene glycol (PEG) and polypropylene glycol (PPG). The copolymer of PEG and PPG may be a block copolymer or a random copolymer. The polyether backbone is suitably capped at one end with the reactive amino group, and capped at the other end with an alkyl group (preferably a methyl group). The polyether monoamine suitably has a molecular weight of from 150 to 6000, preferably from 400 to 3000, for example from 600 to 2000. The polyether monoamine may have a weight average molecular weight of from 150 to 6000, preferably from 400 to 3000, for example from 600 to 2000. Examples of suitable monofunctional reactants having a reactive amino group include propylamine, dipropylamine, butylamine, hexylamine, octylamine, decylamine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine, tallow alkyl amine, benzylamine, phenethylamine, 3-dimethylaminopropylamine (DMAPA), or Jeffamine M-1000 (which is commercially available). Preferably, the monofunctional reactant having a reactive amino group is selected from dodecylamine, N,N-dimethylaminopropylamine (DMAPA), or Jeffamine M-1000. The ester compounds may be prepared from the first, second and optionally third reactants by any suitable method, as would be known to the person skilled in the art. The esterification reaction will typically be conducted in the presence of a suitable esterification catalyst, such as tin(ll) ethylhexanoate, tin(ll) oxalate, p-toluenesulfonic acid, methanesulfonic acid, or sulfuric acid. Another suitable catalyst system comprises 1,8-diazabicyclo(5.4.0)undec-7-ene and dicyclohexylurea. The esterification reaction may be carried out for any suitable length of time, such as at least 1 hour, preferably at least 3 hours, for example at least 5 hours. The esterification reaction may be carried out at any suitable temperature, such as from 50 to 300°C, preferably from 100 to 200°C. References herein to a reactant are intended to refer to the compounds that react to form the ester compound and are not intended to include a catalyst used in the reaction. Suitable molar ratios of the first, second and optional third reactants may be used to prepare the ester compounds. Suitably, the ester compound is not further reacted after the reaction of the reactants. When the third reactant is used, the molar ratio of the first reactant to the sum of the second and third reactants is suitably from 1:1 to 1:5, such as from 1:1 to 1:3. Suitably, the ester compound may be the reaction product of reactants consisting essentially of or consisting of one or more first reactants, one or more second reactants, and optionally one or more third reactants, wherein the or each first reactant is a cyclic anhydride; the or each second reactant is a polyol, wherein at least one of the one or more second reactants is a nitrogen containing polyol and / or a polyol of formula (IVA): H-(OR18)q-OH (IVA) wherein each R18 is independently an optionally substituted alkylene group wherein the optional substituent is not hydroxy and q is an integer of at least 1; and the or each third reactant is selected from: (viii) polycarboxylic acids or reactive equivalents thereof; (ix) monocarboxylic acids or esters thereof; (x) hydroxycarboxylic acids or cyclic esters thereof; (xi) epoxide compounds; (xii) polyfunctional reactants having a reactive amino group; (xiii) monoalcohols; and (xiv) monofunctional reactants having a reactive amino group. Suitably, the ester compound may be the reaction product of reactants consisting essentially of or consisting of one or more first reactants, one or more second reactants, and optionally one or more third reactants, wherein the or each first reactant is a cyclic anhydride; the or each second reactant is a polyol, wherein at least one of the one or more second reactants is selected from ethylene glycol, propylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,6-hexanediol, 1,12-dodecanediol, 2-ethyl-1,3,-hexanediol, 2,2-diethyl-1,3-propanediol, 2,2-bis(hydroxymethyl)propionic acid, neopentyl glycol, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol, polypropylene glycol, 2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate, N-methyl diethanolamine, N-butyl diethanolamine, diethanolamine, or derivatives (for example quaternary ammonium salts) of N-methyl diethanolamine or N-butyl diethanolamine; and the or each third reactant is selected from: (i) polycarboxylic acids or reactive equivalents thereof; (ii) monocarboxylic acids or esters thereof; (iii) hydroxycarboxylic acids or cyclic esters thereof; (iv) epoxide compounds; (v) polyfunctional reactants having a reactive amino group; (vi) monoalcohols; and (vii) monofunctional reactants having a reactive amino group. Suitably, the ester compound may be the reaction product of reactants consisting essentially of or consisting of one or more first reactants, one or more second reactants, and optionally one or more third reactants, wherein the or each first reactant is a cyclic anhydride; the or each second reactant is a polyol; and the or each third reactant is selected from: (i) polycarboxylic acids or reactive equivalents thereof; (ii) aliphatic monocarboxylic acids or esters thereof; (iii) hydroxycarboxylic acids or cyclic esters thereof; (iv) epoxide compounds; (v) polyfunctional reactants having a reactive amino group; (vi) monoalcohols; and (vii) monofunctional reactants having a reactive amino group. Suitably, the ester compound may be the reaction product of reactants consisting essentially of or consisting of one or more first reactants, one or more second reactants, and optionally one or more third reactants, wherein the or each first reactant is a cyclic anhydride; the or each second reactant is a polyol; and the or each third reactant is selected from: (i) polycarboxylic acids or reactive equivalents thereof; (ii) hydroxycarboxylic acids or cyclic esters thereof; (iii) epoxide compounds; (iv) polyfunctional reactants having a reactive amino group; (v) monoalcohols; and (vi) monofunctional reactants having a reactive amino group. Suitably, the ester compound may be the reaction product of reactants consisting essentially of or consisting of one or more first reactants, one or more second reactants, and optionally one or more third reactants, wherein the or each first reactant is a cyclic anhydride; the or each second reactant is a polyol; and the or each third reactant is selected from: (i) polycarboxylic acids or reactive equivalents thereof; (ii) monocarboxylic acids or esters thereof; (iii) hydroxycarboxylic acids or cyclic esters thereof; (iv) epoxide compounds; (v) polyfunctional reactants having a reactive amino group selected from ethanolamine, diethanolamine, ethylene diamine, coco propylene diamine, diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), a polyether diamine (preferably Jeffamine ED-600, Jeffamine ED-900, or Jeffamine ED-2003 which are commercially available), alanine, arginine, asparagine, aspartate, cysteine, glutamine, glutamate, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, or valine; (vi) monoalcohols; and (vii) monofunctional reactants having a reactive amino group selected from propylamine, dipropylamine, butylamine, hexylamine, octylamine, decylamine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine, tallow alkyl amine, benzylamine, phenethylamine, 3-dimethylaminopropylamine (DMAPA), or Jeffamine M-1000. Suitably, the ester compound may be the reaction product of reactants consisting essentially of or consisting of one or more first reactants, one or more second reactants, and optionally one or more third reactants, wherein the or each first reactant is a cyclic anhydride; the or each second reactant is a polyol; and the or each third reactant is selected from: (i) polycarboxylic acids or reactive equivalents thereof; (ii) monocarboxylic acids or esters thereof; (iii) hydroxycarboxylic acids or cyclic esters thereof; (iv) epoxide compounds; and (v) monoalcohols. Suitably, the or each third reactant (when present) is a monocarboxylic acid or an ester thereof selected from hexanoic acid, octanoic acid, decanoic acid, lauric acid, myristic acid, myristoleic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, linolelaidic acid, arachidic acid, arachidonic acid, behenic acid, erucic acid, and esters (preferably methyl esters) thereof; and the second and third reactants are reacted in a molar ratio of from 1:2 to 2:1, such as from 1:2 to 1:1, preferably 1:1 or 1:1.5. Suitably, the or each third reactant (when present) is a fatty acid and the second and third reactants are reacted in a molar ratio of from 1:2 to 2:1, such as from 1:2 to 1:1, preferably 1:1 or 1:1.5. Ratios refer to the total amounts of second reactants or third reactants if more than one second reactant or third reactant is present. Suitably, at least one of the first reactants may be a cyclic anhydride of formula (I) wherein at least one of R1 and R2 is a Ce-30, such as a Cs-24, alkyl or alkenyl (more preferably alkenyl) group (such as an alkenyl group derived from a terminal olefin or an internal olefin, preferably an internal olefin) and at least one of the second reactants may be castor oil. Suitably, at least one of the first reactants may be a cyclic anhydride of formula (I) wherein R1 is hydrogen and R2 is a Ce-3o, such as a Cs-24, alkyl or alkenyl (more preferably alkenyl) group (such as an alkenyl group derived from a terminal olefin or an internal olefin, preferably an internal olefin) and at least one of the second reactants may be castor oil. In some embodiments, the second reactants may comprise in addition to castor oil a polyalkylene glycol (such as PEG 200). Suitably, the first reactant may be a cyclic anhydride of formula (I) wherein R1 is hydrogen and R2 is a Ce-30, such as a Cs-24, alkyl or alkenyl (more preferably alkenyl) group (such as an alkenyl group derived from a terminal olefin or an internal olefin, preferably an internal olefin) and the second reactant may be castor oil. Suitably, the or each first reactant may be selected from maleic anhydride, succinic anhydride, nonenyl succinic anhydride, dodecenyl succinic anhydride (such as (2-dodecen-1-yl)succinic anhydride or branched dodecenyl succinic anhydride), tetrapropenyl succinic anhydride, Cm alkenyl succinic anhydride, C15-18 alkenyl succinic anhydride (such as C15-18 internal olefinderived alkenyl succinic anhydride), and C16 alkenyl succinic anhydride (such as C16 internal olefin-derived alkenyl succinic anhydride or C16 terminal olefin-derived alkenyl succinic anhydride) and the or each second reactant may be selected from castor oil and PEG 200 (preferably at least castor oil). Suitably, the or each first reactant may be selected from maleic anhydride, succinic anhydride, nonenyl succinic anhydride, C15-18 alkenyl succinic anhydride (such as C15-18 internal olefinderived alkenyl succinic anhydride), and C16 alkenyl succinic anhydride (such as C16 internal olefin-derived alkenyl succinic anhydride or C16 terminal olefin-derived alkenyl succinic anhydride) and the or each second reactant may be selected from castor oil and PEG 200 (preferably at least castor oil). Suitably, the or each first reactant may be selected from succinic anhydride, dodecenyl succinic anhydride (such as (2-dodecen-1-yl)succinic anhydride or branched dodecenyl succinic anhydride), and Cm alkenyl succinic anhydride and the or each second reactant may be selected from castor oil and PEG 200 (preferably at least castor oil). Suitably, the or each first reactant may be selected from C15-18 alkenyl succinic anhydride (such as C15-18 internal olefin-derived alkenyl succinic anhydride) and C16 alkenyl succinic anhydride (such as C16 internal olefin-derived alkenyl succinic anhydride or C16 terminal olefin-derived alkenyl succinic anhydride) and the or each second reactant may be selected from castor oil and PEG 200 (preferably at least castor oil). Suitably, the first reactant may be dodecenyl succinic anhydride and the second reactant may be castor oil. The dodecenyl succinic anhydride and the castor oil may be reacted in a molar ratio of from 10:1 to 1:10, such as from 2:1 to 1:2, preferably from 1.5:1 to 1:1.5. More preferably, the dodecenyl succinic anhydride and the castor oil may be reacted in a 1:1 molar ratio. Suitably, the first reactant may be selected from succinic anhydride, maleic anhydride, glutaric anhydride, C20-24 alkenyl succinic anhydride, nonenyl succinic anhydride, C14 alkenyl succinic anhydride, octadecenyl succinic anhydride, octenyl succinic anhydride, octadecyl succinic anhydride, octyl succinic anhydride, C15-18 alkenyl succinic anhydride (such as C15-18 internal olefin-derived alkenyl succinic anhydride), C16 alkenyl succinic anhydride (such as C16 internal olefin-derived alkenyl succinic anhydride or C16 terminal olefin-derived alkenyl succinic anhydride), a branched alkenyl succinic anhydride such as tetrapropenyl succinic anhydride or polyisobutenyl succinic anhydride, phthalic anhydride, pyromellitic dianhydride, 1,2,4-benzenetricarboxylic anhydride, 1,2-cyclohexanedicarboxylic anhydride, 1,2-naphthalic anhydride, 2,3-naphthalic anhydride, 1,8-naphthalic anhydride or homophthalic anhydride and the second reactant may be castor oil. The first reactant and second reactant may be reacted in a molar ratio of from 1:1.2 to 1.2:1, preferably in a 1:1 molar ratio. Suitably, the first reactant may be selected from succinic anhydride, maleic anhydride, glutaric anhydride, C20-24 alkenyl succinic anhydride, nonenyl succinic anhydride, octadecenyl succinic anhydride, octenyl succinic anhydride, octadecyl succinic anhydride, octyl succinic anhydride, a branched alkenyl succinic anhydride such as tetrapropenyl succinic anhydride or polyisobutenyl succinic anhydride, phthalic anhydride, pyromellitic dianhydride, 1,2,4-benzenetricarboxylic anhydride, 1,2-cyclohexanedicarboxylic anhydride, 1,2-naphthalic anhydride, 2,3-naphthalic anhydride, 1,8-naphthalic anhydride or homophthalic anhydride and the second reactant may be castor oil. The first reactant and second reactant may be reacted in a 1:1 molar ratio. Suitably, the first reactant may be selected from C20-24 alkenyl succinic anhydride, nonenyl succinic anhydride, octadecenyl succinic anhydride, octenyl succinic anhydride, octadecyl succinic anhydride, or octyl succinic anhydride and the second reactant may be castor oil. The first reactant and second reactant may be reacted in a 1:1 molar ratio. Suitably, at least one of the first reactants may be a cyclic anhydride of formula (I) wherein R1 and R2 are independently hydrogen ora C6-30, such as a Cs-24, alkyl or alkenyl (more preferably alkenyl) group (such as a C6-30, preferably Cs-24, alkenyl group derived from a terminal olefin or an internal olefin, preferably an internal olefin), or at least one of the first reactants may be a cyclic anhydride of formula (II) wherein R3 and R4 together with the carbon atoms to which they are attached represent an optionally substituted cyclic group; and at least one of the second reactants may be selected from N-methyl diethanolamine, N-butyl diethanolamine, castor oil, tris(2-hydroxyethyl)methyl ammonium methylsulfate, PEG 200, 1,6-hexanediol, or sorbitol. Suitably, at least one of the first reactants may be a cyclic anhydride of formula (I) wherein least one of R1 and R2 is a C6-30, such as a Cs-24, alkyl or alkenyl (more preferably alkenyl) group (such as a C6-30, preferably Cs-24, alkenyl group derived from a terminal olefin or an internal olefin, preferably an internal olefin), or at least one of the first reactants may be a cyclic anhydride of formula (II) wherein R3 and R4 together with the carbon atoms to which they are attached represent an optionally substituted cyclic group; and at least one of the second reactants may be selected from N-methyl diethanolamine, N-butyl diethanolamine, castor oil, tris(2-hydroxyethyl)methyl ammonium methylsulfate, PEG 200, 1,6-hexanediol, or sorbitol. Suitably, at least one of the first reactants may be a cyclic anhydride of formula (I) wherein least one of R1 and R2 is a C6-30, such as a Cs-24, alkyl or alkenyl (more preferably alkenyl) group (such as a C6-30, preferably Cs-24, alkenyl group derived from a terminal olefin or an internal olefin, preferably an internal olefin); and at least one of the second reactants may be selected from N-methyl diethanolamine, N-butyl diethanolamine, castor oil, tris(2-hydroxyethyl)methyl ammonium methylsulfate, PEG 200, 1,6-hexanediol, or sorbitol. Suitably, the ester compound may be the reaction product of reactants comprising, consisting essentially of, or consisting of one or more first reactants and one or more second reactants, wherein the or each first reactant is a cyclic anhydride of formula (I) wherein R1 and R2 are independently hydrogen ora C6-30, such as a Cs-24, alkyl or alkenyl (more preferably alkenyl) group, or a cyclic anhydride of formula (II) wherein R3 and R4 are each independently selected from hydrogen, an alkyl group and an alkenyl group, orR3 and R4 together with the carbon atoms to which they are attached represent an optionally substituted cyclic group; and the or each second reactant is selected from a polyol of formula (IVA): H-(OR18)q-OH (IVA) wherein each R18 is independently an unsubstituted alkylene group and q is an integer of at least 1, a polyol of formula (V): NR20R21R22 (V) wherein R20 and R21 each represent a hydroxyalkyl group and R22 represents a hydrocarbyl group; and castor oil. The molar ratio of one or more first reactants and the one or more second reactants is suitably from 1.2:1 to 1:1.2. Preferably the molar ratio is 1:1. Suitably, the ester compound may be the reaction product of reactants comprising, consisting essentially of, or consisting of a first reactant, one or more second reactants, and optionally a third reactant, wherein the first reactant is selected from succinic anhydride, dodecenyl succinic anhydride, Cm alkenyl succinic anhydride, octadecenyl succinic anhydride, or pyromellitic dianhydride; the one or more second reactants are selected from N-methyl diethanolamine, N-butyl diethanolamine, castor oil, tris(2-hydroxyethyl)methyl ammonium methylsulfate, PEG 200, 1,6-hexanediol, or sorbitol; and the third reactant is oleyl alcohol. The molar ratio of the first reactant and the one or more second reactants is preferably 1:1. When the third reactant is used, the molar ratio of the first, second and third reactants is suitably 1:1:1.5. Suitably, the ester compound may be the reaction product of reactants comprising a first reactant, one or more second reactants, and optionally a third reactant, wherein the first reactant is selected from dodecenyl succinic anhydride, octadecenyl succinic anhydride, or pyromellitic dianhydride; the one or more second reactants are selected from N-methyl diethanolamine, N-butyl diethanolamine, castor oil, tris(2-hydroxyethyl)methyl ammonium methylsulfate, PEG 200, 1,6-hexanediol, or sorbitol; and the third reactant is oleyl alcohol. The molar ratio of the first reactant and the one or more second reactants is preferably 1:1. When the third reactant is used, the molar ratio of the first, second and third reactants is suitably 1:1:1.5. Suitably, the ester compound may be the reaction product of reactants consisting essentially of or consisting of a first reactant, one or more second reactants, and optionally a third reactant, wherein the first reactant is selected from dodecenyl succinic anhydride, octadecenyl succinic anhydride, or pyromellitic dianhydride; the one or more second reactants are selected from N-methyl diethanolamine, N-butyl diethanolamine, castor oil, tris(2-hydroxyethyl)methyl ammonium methylsulfate, PEG 200, 1,6-hexanediol, or sorbitol; and the third reactant is oleyl alcohol. The molar ratio of the first reactant and the one or more second reactants is preferably 1:1. When the third reactant is used, the molar ratio of the first reactant, second and third reactants is suitably 1:1:1.5. Suitably, the ester compound may be the reaction product of reactants comprising, consisting essentially of, or consisting of a first reactant and one or more second reactants, wherein the first reactant is selected from succinic anhydride, dodecenyl succinic anhydride, or Cm alkenyl succinic anhydride; and the one or more second reactants are selected from N-methyl diethanolamine, castor oil, or PEG 200. The molar ratio of the first reactant and the one or more second reactants is suitably from 1.2:1 to 1:1.2. The molar ratio of the first reactant and the one or more second reactants is preferably 1:1. Preferably, the ester compound is the reaction product of reactants comprising: (i) dodecenyl succinic anhydride and N-methyl diethanolamine, preferably in a molar ratio of 1:1; (ii) dodecenyl succinic anhydride, castor oil, and tris(2-hydroxyethyl)methyl ammonium methylsulfate, preferably in a molar ratio of 1:0.6:0.4; (iii) dodecenyl succinic anhydride and N-butyl diethanolamine, preferably in a molar ratio of 1:1; (iv) octadecenyl succinic anhydride and N-butyl diethanolamine, preferably in a molar ratio of 1:1; (v) dodecenyl succinic anhydride, N-methyl diethanolamine, and castor oil, preferably in a molar ratio of 1:0.5:0.5; (vi) dodecenyl succinic anhydride and castor oil, preferably in a molar ratio of 1:1; (vii) dodecenyl succinic anhydride, N-butyl diethanolamine, and PEG 200, preferably in a molar ratio of 1:0.5:0.5; (viii) pyromellitic dianhydride, PEG 200 and oleyl alcohol, preferably in a molar ratio of 1:1:1.5; (ix) dodecenyl succinic anhydride, N-butyl diethanolamine, and 1,6-hexanediol, preferably in a molar ratio of 1:0.8:0.2; (x) octadecenyl succinic anhydride and N-methyl diethanolamine, preferably in a molar ratio of 1:1; or (xi) dodecenyl succinic anhydride, sorbitol, and 1,6-hexanediol, preferably in a molar ratio of 1:0.2:0.8. Preferably, the ester compound is the reaction product of reactants consisting essentially of or consisting of: (i) dodecenyl succinic anhydride and N-methyl diethanolamine, preferably in a molar ratio of 1:1; (ii) dodecenyl succinic anhydride, castor oil, and tris(2-hydroxyethyl)methyl ammonium methylsulfate, preferably in a molar ratio of 1:0.6:0.4; (iii) dodecenyl succinic anhydride and N-butyl diethanolamine, preferably in a molar ratio of 1:1; (iv) octadecenyl succinic anhydride and N-butyl diethanolamine, preferably in a molar ratio of 1:1; (v) dodecenyl succinic anhydride, N-methyl diethanolamine, and castor oil, preferably in a molar ratio of 1:0.5:0.5; (vi) dodecenyl succinic anhydride and castor oil, preferably in a molar ratio of 1:1; (vii) dodecenyl succinic anhydride, N-butyl diethanolamine, and PEG 200, preferably in a molar ratio of 1:0.5:0.5; (viii) pyromellitic dianhydride, PEG 200 and oleyl alcohol, preferably in a molar ratio of 1:1:1.5; (ix) dodecenyl succinic anhydride, N-butyl diethanolamine, and 1,6-hexanediol, preferably in a molar ratio of 1:0.8:0.2; (x) octadecenyl succinic anhydride and N-methyl diethanolamine, preferably in a molar ratio of 1:1; or (xi) dodecenyl succinic anhydride, sorbitol, and 1,6-hexanediol, preferably in a molar ratio of 1:0.2:0.8. Preferably, the ester compound is the reaction product of reactants comprising: (i) dodecenyl succinic anhydride and N-methyl diethanolamine, preferably in a molar ratio of 1:1; (ii) dodecenyl succinic anhydride and castor oil, preferably in a molar ratio of 1:1; (iii) succinic anhydride and castor oil, preferably in a molar ratio of 1:1; (iv) succinic anhydride, castor oil, and PEG 200, preferably in a molar ratio of 1:0.8:0.2; or (v) Cm alkenyl succinic anhydride and castor oil, preferably in a molar ratio of 1:1. Preferably, the ester compound is the reaction product of reactants consisting essentially of or consisting of: (i) dodecenyl succinic anhydride and N-methyl diethanolamine, preferably in a molar ratio of 1:1; (ii) dodecenyl succinic anhydride and castor oil, preferably in a molar ratio of 1:1; (iii) succinic anhydride and castor oil, preferably in a molar ratio of 1:1; (iv) succinic anhydride, castor oil, and PEG 200, preferably in a molar ratio of 1:0.8:0.2; or (v) Cm alkenyl succinic anhydride and castor oil, preferably in a molar ratio of 1:1. Preferably, the ester compound is the reaction product of reactants comprising: (i) Cm alkenyl succinic anhydride and castor oil, preferably in a molar ratio of 1:1; (ii) Ci6 internal olefin-derived alkenyl succinic anhydride and castor oil, preferably in a molar ratio of 1:1; (iii) tetrapropenyl succinic anhydride, Ci6 internal olefin-derived alkenyl succinic anhydride, and castor oil, preferably in a molar ratio of 0.5:0.5:1; (iv) Ci6 internal olefin-derived alkenyl succinic anhydride, Ci6 terminal olefin-derived alkenyl succinic anhydride, and castor oil, preferably in a molar ratio of 0.5:0.5:1; (v) tetrapropenyl succinic anhydride, maleic anhydride, and castor oil, preferably in a molar ratio of 0.5:0.5:1; or (vi) tetrapropenyl succinic anhydride, castor oil, and PEG 200, preferably in a molar ratio of 1:0.8:0.2. Preferably, the ester compound is the reaction product of reactants consisting essentially of or consisting of: (i) Cm alkenyl succinic anhydride and castor oil, preferably in a molar ratio of 1:1; (ii) Ci6 internal olefin-derived alkenyl succinic anhydride and castor oil, preferably in a molar ratio of 1:1; (iii) tetrapropenyl succinic anhydride, Ci6 internal olefin-derived alkenyl succinic anhydride, and castor oil, preferably in a molar ratio of 0.5:0.5:1; (iv) Ci6 internal olefin-derived alkenyl succinic anhydride, Ci6 terminal olefin-derived alkenyl succinic anhydride, and castor oil, preferably in a molar ratio of 0.5:0.5:1; (v) tetrapropenyl succinic anhydride, maleic anhydride, and castor oil, preferably in a molar ratio of 0.5:0.5:1; or (vi) tetrapropenyl succinic anhydride, castor oil, and PEG 200, preferably in a molar ratio of 1:0.8:0.2. Preferably, the ester compound is the reaction product of reactants comprising, or of reactants consisting essentially of or consisting of, dodecenyl succinic anhydride and castor oil, preferably in a molar ratio of 1:1, and wherein the ester compound has a number average molecular weight of from 2,000 to 3,000 Daltons and / or a polydispersity index of from 1 to 4, such as from 1.1 to 2, preferably from 1.5 to 1.6. The ester compound may be a polymer. The reactants used to prepare the ester compound may be monomers. The first reactant may be a first monomer, the second reactant may be a second monomer, and the third reactant (when present) may be a third monomer. Thus, the ester compound may be a polymer comprising, consisting essentially of, or consisting of repeat units derived from the one or more first reactants, repeat units derived from the one or more second reactants, and optionally repeat units derived from one or more third reactants as defined herein. Typically, the polymer is a polyester. The polymer may be a random copolymer or a block copolymer, in particular when there is more than one first reactant or more than one second reactant. Preferably, the polymer is a random copolymer. The polymer formed from the first, second and optional third reactants may comprise a suitable number of total monomer units (i.e. repeat units). For example, the polymer may comprise at least 4 monomer units. In other words, the polymer may comprise a total of at least 4 monomer units including the first, second and optional third monomers. Suitably, the polymer may comprise from 4 to 50 monomer units, preferably from 4 to 30 monomer units. Suitably, the polymer herein that is the reaction product of monomers comprising one or more first monomers and one or more second monomers is substantially free or free of cross-linking. Suitably, the ester compound has a number average molecular weight of from 1,000 to 150,000 Daltons, preferably from 1,000 to 15,000 Daltons (for example from 2,000 to 7,000 or from 2,000 to 3,000 Daltons). Suitably, the ester compound has a polydispersity index of from 1 to 4, such as from 1.1 to 2, preferably from 1.5 to 1.6. The polydispersity index of an ester compound is given by the ratio of Mwto Mn (Mw / Mn), wherein Mw is the weight-average molecular weight and Mn is the number average molecular weight. Preferably, the ester compound is substantially free of silicon atoms. By substantially free of silicon atoms we mean that the ester compound contains less than 1 wt% of silicon in the ester compound, preferably less than 0.5 wt% of silicon in the ester compound. More preferably, the ester compound is free of silicon atoms, by which we mean that it is not possible to detect silicon in the ester compound. Suitable methods of measuring the amount of silicon in an ester compound are well known to those skilled in art and include elemental analysis and inductively coupled plasma (ICP) spectroscopy. Preferably, the ester compound is substantially free of fluorine atoms. The ester compound may be substantially free of halogen atoms. By substantially free of fluorine or halogen atoms we mean that the ester compound contains less than 1 wt% of fluorine or halogen in the ester compound, preferably less than 0.5 wt% of fluorine or halogen in the ester compound. More preferably, the ester compound is free of fluorine atoms. The ester compound may be free of halogen atoms. By free of fluorine or halogen atoms we mean that it is not possible to detect fluorine or halogen in the ester compound. Suitable methods of measuring the amount of fluorine or halogen in a compound are well known to those skilled in art and include elemental analysis and inductively coupled plasma (ICP) spectroscopy. Preferably, the ester compound is substantially free of quaternary ammonium moieties. By substantially free of quaternary ammonium moieties we mean that the ester compound contains less than 1 wt% of quaternary nitrogen atoms in the ester compound, preferably less than 0.5 wt% of quaternary nitrogen atoms in the ester compound. More preferably, the ester compound is free of quaternary ammonium moieties, by which we mean that it is not possible to detect quaternary ammonium moieties in the ester compound. When the ester compound is the reaction product of reactants comprising, or of reactants consisting essentially of or consisting of, dodecenyl succinic anhydride and castor oil (preferably in a molar ratio of 1:1), the ester compound may comprise, or consist essentially of or consist of, one or more moieties of the formula (VI) or an isomer thereof: o o (VI) According to a second aspect of the invention, there is provided a concentrate composition comprising one or more ester compounds and optionally at least one solvent, wherein the concentrate composition comprises at least 20 wt% of the one or more ester compounds, and wherein the or each ester compound is the reaction product of reactants comprising one or more first reactants and one or more second reactants, wherein the or each first reactant is a cyclic anhydride and the or each second reactant is a polyol. The concentrate composition may comprise at least 30 wt%, at least 40 wt%, at least 50 wt%, at least 60 wt%, at least 70 wt%, or at least 80 wt% of the one or more ester compounds based on the total weight of the concentrate composition. The concentrate composition additionally may comprise 99 wt% or less, such as 95 wt% or less, for example 90 wt% or less of the one or more ester compounds based on the total weight of the concentrate composition. The concentrate composition may comprise from 20 to 99 wt%, preferably from 20 to 95 wt%, for example from 50 to 90 wt%, of the one or more ester compounds based on the total weight of the concentrate composition. References herein to the amount of ester compound in the concentrate composition are intended to refer to the total of the or each ester compound as defined herein that is included in the composition, i.e. based on the total weight of the concentrate composition. Suitably, the concentrate composition may be stable for at least 1 week, preferably at least 4 weeks, most preferably at least 8 weeks under ambient conditions (for example, at atmospheric pressure and at a temperature of 20°C). The stability of the concentrate composition may be determined visually. Suitably, the concentrate composition is unstable when it shows creaming, sedimentation, separation, ora combination thereof. Suitably, the concentrate composition may comprise at least 20 wt%, such as at least 30 wt%, at least 40 wt%, at least 50 wt%, at least 60 wt%, at least 70 wt%, or at least 80 wt% of the one or more ester compounds and the concentrate composition may be stable for at least 1 week, preferably at least 4 weeks or at least 8 weeks, most preferably at least 3, 6, 12 or 24 months, under ambient conditions. Suitably, the concentrate composition may be flowable. The meaning of a “flowable” composition is well known to those skilled in the art. Typically, flowable compositions are pourable from a container at 20°C. Flowable compositions may be poured without needing to heat the composition above 20°C or manually scraping the composition. Suitably, the concentrate composition may have a viscosity of 7,000 cP or less, preferably 3,500 cP or less at 20°C. Suitably, the concentrate composition may comprise at least 20 wt%, such as at least 30 wt%, at least 40 wt%, at least 50 wt%, at least 60 wt%, at least 70 wt%, or at least 80 wt% of the ester compound and the concentrate composition may be flowable. Suitably the concentrate composition of the second aspect is substantially free of silicon atoms. By substantially free of silicon atoms we mean that the composition contains less than 1 wt%, preferably less than 0.5 wt%, of silicon in the composition. More preferably, the composition is free of silicon atoms, by which we mean that it is not possible to detect silicon in the composition. Suitable methods of measuring the amount of silicon in a composition are well known to those skilled in art and include elemental analysis and inductively coupled plasma (ICP) spectroscopy. The ester compound referred to in relation to the second aspect may comprise the reaction product of reactants comprising one or more first reactants, one or more second reactants and optionally one or more third reactants as defined herein. The ester compound referred to in relation to the second aspect may be the reaction product of reactants consisting essentially of or consisting of one or more first reactants, one or more second reactants and optionally one or more third reactants as defined herein. Features of the ester compound, and of the first and second reactants (and the third reactants when present), in relation to the second aspect of the invention are as set out herein in relation to the first aspect of the invention. The concentrate composition of the second aspect may optionally comprise any suitable solvent, such as for example a polar solvent, such as a polar protic solvent. Preferably, the concentrate composition comprises at least one solvent. The solvent may be an aqueous solvent. Thus, the concentrate composition may be an aqueous composition. The term “aqueous solvent” herein is considered to mean water or mixtures of water and at least one water miscible solvent. Water miscible solvents may include alcohols and substantially water-miscible organic solvents. Preferably the aqueous solvent is water. When the solvent is an aqueous solvent, the concentrate composition may be in the form of an emulsion. The solvent may be a non-aqueous solvent. The non-aqueous solvent suitably comprises an organic solvent, such as an alcohol. The non-aqueous solvent preferably does not comprise any surfactant. Suitable such alcohols for use in the solvent include monohydric alcohols, polyhydric alcohols, alkoxy alcohols and aryloxy alcohol. Suitable alcohols are monohydric alcohols, polyhydric alcohols and alkoxy alcohols. Preferred alcohols are miscible with water. Suitable simple monohydric alcohols include methanol, ethanol, isopropanol and butanol. The solvent may comprise a polyhydric alcohol or an alkoxyalcohol. Suitable alkoxy alcohols include diethylene glycol monobutyl ether, 3-methoxy-3-methyl-1-butanol and 2-butoxyethanol. Suitable aryloxy alcohols include 2-phenoxyethanol. Suitable polyhydric alcohols include glycerol, ethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol and 2-methylpentanediol. Suitable polyhydric alcohols include glycerol, ethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol and polypropylene glycol. Preferably, the non-aqueous solvent comprises a monohydric alcohol such as isopropanol. The concentrate composition may comprise at least 20 wt%, at least 30 wt%, at least 40 wt%, at least 50 wt%, at least 60 wt% or at least 70 wt% of the at least one solvent (when present) based on the total weight of the concentrate composition. The concentrate composition additionally may comprise 80 wt% or less, such as 70 wt% or less, of the at least one solvent (when present) based on the total weight of the concentrate composition. The concentrate composition may comprise from 20 to 80 wt%, preferably from 20 to 75 wt%, such as from 50 to 80 wt% or from 50 to 75 wt%, of the at least one solvent (when present) based on the total weight of the concentrate composition. The concentrate composition of the second aspect may additionally comprise one or more surfactants (in particular when the solvent is an aqueous solvent). Preferably, the concentrate composition of the second aspect comprises one or more surfactants (in particular when the solvent is an aqueous solvent). Any suitable surfactant(s) may be included, such as for example one or more surfactants selected from anionic surfactants, cationic surfactants, non-ionic surfactants, and amphoteric or zwitterionic surfactants. One or more non-ionic surfactant(s) and / or amphoteric or zwitterionic surfactant(s) are preferred. The concentrate composition may comprise an anionic surfactant. Suitable anionic surfactants may include sulfate surfactants (such as mono- or di-alkyl sulfates or alkyl ether sulfates), sulfonate surfactants, alkyl ether carboxylate surfactants, sarcosinate surfactants, phosphate surfactants, succinate surfactants, sulfosuccinate surfactants, sulfoacetate surfactants, isethionate surfactants, taurate surfactants, amino acid surfactants such as glutamates and glycinates, lactylate surfactants, and fatty acid salts. Particularly exemplary salts of the above, where applicable, are the sodium, potassium, ammonium, magnesium and triethanolamine salts. The concentrate composition may comprise a cationic surfactant. The cationic surfactant may be an ammonium salt such as an alkyl trimethyl ammonium salt, a dialkyl dimethyl ammonium salt, an alkyl-(N-hydroxyethyl)-dimethyl ammonium salt, or an alkyldimethylbenzylammonium salt (i.e. a benzalkonium salt). The salt may be a halide, hydroxide, sulfate, hydrogensulfate, phosphate, or carboxylate salt. The salt is suitably a halide salt, such as a fluoride, chloride, or bromide salt. The salt may be a carboxylate salt, such as formate or acetate salt. Preferably, the salt is chloride. The concentrate composition may comprise a non-ionic surfactant. Suitable non-ionic surfactants for use herein include castor oil, alcohol alkoxylates (such as alcohol ethoxylates, alcohol propoxylates, and ethylene oxide / propylene oxide copolymer derived surfactants), aliphatic esters, aromatic esters, sugar esters (such as sorbitan esters), alkyl (poly)glycosides, fatty acid alkoxylates (such as fatty acid ethoxylates and fatty acid propoxylates), or polyethylene glycol esters (including partial esters), glycerol esters (including glycerol partial esters and glycerol triesters), fatty alcohols (such as cetearyl alcohol, lauryl alcohol, stearyl alcohol, behenyl alcohol), alkanolamides, fatty amine alkoxylates (such as fatty amine ethoxylates and fatty amine propoxylates), and polyglyceryl fatty acid esters. Suitable non-ionic surfactants for use herein include castor oil, alcohol alkoxylates (such as alcohol ethoxylates, alcohol propoxylates, and ethylene oxide / propylene oxide copolymer derived surfactants), aliphatic esters, aromatic esters, sugar esters (such as sorbitan esters), alkyl (poly)glycosides, fatty acid alkoxylates (such as fatty acid ethoxylates and fatty acid propoxylates), or polyethylene glycol esters (including partial esters), glycerol esters (including glycerol partial esters and glycerol triesters), fatty alcohols (such as cetearyl alcohol, lauryl alcohol, stearyl alcohol, behenyl alcohol), and alkanolamides. Preferably, the non-ionic surfactant may be selected from one or more of a sugar ester (such as a sorbitan ester) and a fatty amine alkoxylate (such as a fatty amine ethoxylate or fatty amine propoxylate). Suitable sugar esters may include alkoxylated (such as ethoxylated) sugar esters. For example, the sugar ester may comprise an alkoxylated (such as ethoxylated) sugar ester of a fatty acid, such as oleic acid. An example of a preferred sugar ester surfactant is Tween® 80. Suitable fatty amine alkoxylates may include fatty amine ethoxylates and fatty amine propoxylates. Fatty amine ethoxylates are preferred. The fatty amine alkoxylates may be based on any suitable fatty alcohol. Examples of preferred fatty amine alkoxylates include fatty amine ethoxylates such as Empilan® AMT 11, which is a fatty amine ethoxylate containing 11 moles of ethylene oxide, and Ethomeen® C22. The concentrate composition may comprise an amphoteric or zwitterionic surfactant. The amphoteric or zwitterionic surfactant may be selected from betaines (such as alkyl betaines and alkylamidopropyl betaines), amphoacetates, diamphoacetates, and amine oxides (such as alkylamine oxides and alkylamidopropyl amine oxides). Suitable amphoteric or zwitterionic surfactants include lauryl betaine, cocamidopropyl betaine, sodium lauroamphoacetate, sodium cocoamphoacetate, disodium cocoamphodiacetate, lauramine oxide, C12-18 alkyldimethylamine oxide, myristamine oxide, and cocamidopropyl amine oxide. The one or more surfactants may be selected from a fatty alkyl amphoacetate (for example cocoyl amphoacetate, lauryl amphoacetate), an alkyl (poly)glycoside (for example lauryl glycoside), an acyl glycinate (for example cocoyl glycinate), a sulfosuccinate, an amphodiacetate and a fatty alcohol ether carboxylate (for example C8-12 alkyl ether (6-11 moles EO) carboxylate). Fatty alkyl amphoacetates, such as lauryl amphoacetate (especially sodium lauroamphoacetate) are preferred. Preferably, the one or more surfactants are independently selected from one or more of a fatty alkyl amphoacetate, a sugar ester (such as a sorbitan ester) and a fatty amine alkoxylate (such as a fatty amine ethoxylate or fatty amine propoxylate). The concentrate composition may comprise at least 1 wt%, at least 3 wt%, at least 5 wt%, of the one or more surfactants (when present) based on the total weight of the concentrate composition. The concentrate composition additionally may comprise 15 wt% or less, such as 10 wt% or less, of the one or more surfactants (when present) based on the total weight of the concentrate composition. The concentrate composition may comprise from 1 to 15 wt%, preferably from 3 to 10 wt% of the one or more surfactants (when present) based on the total weight of the concentrate composition. The concentrate composition of the second aspect may comprise the one or more surfactants in an amount of from 1 to 100 wt%, suitably from 5 to 50 wt%, preferably from 5 to 25 wt% or from 10 to 25 wt% based on the total weight of the one or more ester compounds. When the concentrate composition comprises the one or more ester compounds, the at least one solvent and the one or more surfactants, the composition may comprise: (i) from 20 to 60 wt% of the one or more ester compounds; (ii) from 35 to 60 wt% of the at least one solvent; and (iii) from 1 to 15 wt% of the one or more surfactants; based on the total weight of the concentrate composition. When the concentrate composition comprises the one or more ester compounds, the at least one solvent and the one or more surfactants, the composition may comprise: (i) from 20 to 45 wt% of the one or more ester compounds; (ii) from 50 to 75 wt% of the at least one solvent; and (iii) from 1 to 15 wt% of the one or more surfactants; based on the total weight of the concentrate composition. When the concentrate composition comprises the one or more ester compounds, the at least one solvent and the one or more surfactants, the composition may comprise: (i) from 20 to 40 wt% of the one or more ester compounds; (ii) from 50 to 75 wt% of the at least one solvent; and (iii) from 3 to 10 wt% of the one or more surfactants; based on the total weight of the concentrate composition. According to a third aspect of the invention, there is provided a use of a surfactant to emulsify at least one ester compound in an aqueous concentrate composition, wherein the aqueous concentrate composition comprises at least 20 wt% of the one or more ester compounds, and wherein the ester compound is the reaction product of reactants comprising one or more first reactants and one or more second reactants, wherein the or each first reactant is a cyclic anhydride and the or each second reactant is polyol. The ester compound referred to in relation to the third aspect may comprise the reaction product of reactants comprising one or more first reactants, one or more second reactants and optionally one or more third reactants as defined herein. The ester compound referred to in relation to the third aspect may be the reaction product of reactants consisting essentially of or consisting of one or more first reactants, one or more second reactants and optionally one or more third reactants as defined herein. Features of the ester compound, and of the first and second reactants (and the third reactants when present), in relation to the third aspect of the invention are as set out herein in relation to the first aspect of the invention. Features of the surfactant in relation to the third aspect of the invention are as set out herein in relation to the second aspect of the invention. According to a fourth aspect of the invention, there is provided a method of emulsifying at least one ester compound in an aqueous composition to make an aqueous ester compound concentrate composition, wherein the aqueous ester compound concentrate composition comprises at least 20 wt% of the one or more ester compounds, the method comprising admixing a surfactant with the ester compound in an aqueous composition, wherein the ester compound is the reaction product of reactants comprising one or more first reactants and one or more second reactants, wherein the or each first reactant is a cyclic anhydride and the or each second reactant is a polyol. The ester compound referred to in relation to the fourth aspect may comprise the reaction product of reactants comprising one or more first reactants, one or more second reactants and optionally one or more third reactants as defined herein. The ester compound referred to in relation to the fourth aspect may be the reaction product of reactants consisting essentially of or consisting of one or more first reactants, one or more second reactants and optionally one or more third reactants as defined herein. Features of the ester compound, and of the first and second reactants (and the third reactants when present), in relation to the fourth aspect of the invention are as set out herein in relation to the first aspect of the invention. Features of the surfactant in relation to the fourth aspect of the invention are as set out herein in relation to the second aspect of the invention. Examples The invention will now be further described with reference to the following non-limiting examples. Example 1 - synthesis of polyol reactant from gluconolactone and amine Gluconolactone and an amine (1 eq) were combined in methanol (100 mL, for 70 mmol of gluconolactone) and heated at 65°C for 2 hours. The reaction mass was concentrated in vacuo to provide a polyol, which was used in subsequent reactions without further purification. In cases where a diamine was used (for example ethylenediamine or Jeffamine ED-600) the mole equivalents of diamine were reduced (0.5 eq). Example 2 - synthesis of polyol reactant from glycerol carbonate and amine Glycerol carbonate and an amine (1 eq) were combined and heated at 70°C for two hours. The reaction mass was cooled to provide a polyol, which was used in subsequent reactions without further purification. In cases where a diamine was used (for example ethylenediamine or Jeffamine ED-600) the mole equivalents of diamine were reduced (0.5 eq). Example 3 - general method for synthesis of ester compounds The cyclic anhydride reactant(s) were combined with the polyol(s) and optional further third reactants. Tin(ll) ethylhexanoate (0.5 wt% relative to the total weight of reactants) was added. The reaction mass was heated at 160°C for 6 hours. The resulting ester compound was decanted from the reaction flask, and no further purification was carried out. Ester compounds 1 to 85 were prepared according to Example 3, using the reactants and reaction stoichiometries as set out in Table 1. Table 1 Ester compounds Cyclic anhydride 1 Cyclic anhydride 2 (when present) Polyol 1 Polyol 2 (when present) Further reactant (when present) Molar ratio of reactants 1 Dodecenyl succinic anhydride N-methyl diethanolamine 1:1 2 Dodecenyl succinic anhydride Castor oil Tris(2-hydroxy ethyl)methyl ammonium methylsulfate 1:0.6:0.4 3 Dodecenyl succinic anhydride N-butyl diethanolamine 1:1 4 Octadecenyl succinic anhydride N-butyl diethanolamine 1:1 5 Dodecenyl succinic anhydride N-Methyl diethanolamine Castor oil 1:0.5:0.5 6 Dodecenyl succinic anhydride Castor oil 1:1 7 Dodecenyl succinic anhydride N-butyl diethanolamine PEG 200 1:0.5:0.5 8 Pyromellitic dianhydride PEG 200 Oleyl alcohol 1:1:1.5 9 Dodecenyl succinic anhydride N-butyl diethanolamine 1,6-Hexanediol 1:0.8:0.2 10 Octadecenyl succinic anhydride N-methyl diethanolamine 1:1 11 Dodecenyl succinic anhydride Sorbitol 1,6-Hexanediol 1:0.2:0.8 12 Dodecenyl succinic anhydride 1,12-Dodecanediol 1:1 13 Phthalic anhydride PPG 2000 1:1 14 Dodecenyl succinic anhydride N-butyl diethanolamine 1,6-Hexanediol 1:0.5:0.5 15 Dodecenyl succinic anhydride N-butyl diethanolamine PEG 400 1:0.5:0.5 16 Dodecenyl succinic anhydride N-butyl diethanolamine Neopentyl glycol 1:0.5:0.5 17 Maleic anhydride Castor oil 1:1 18 Dodecenyl succinic anhydride N-butyl diethanolamine PPG 2000 1:0.5:0.5 19 Dodecenyl succinic anhydride Trimethylol propane 1:1 20 C20-24ASA PEG 6000 1:1 21 Dodecenyl succinic anhydride N-butyl diethanolamine PEG 1000 1:0.5:0.5 22 C20-24ASA PEG 1000 Citric acid 1:0.9:0.1 23 Dodecenyl succinic anhydride N-butyl diethanolamine Diglycolic acid 1:0.5:0.5 24 Succinic anhydride Sucrose 1:0.5 25 Pyromellitic dianhydride PEG 200 Oleyl alcohol 1:1:2 26 Dodecenyl succinic anhydride N-butyl diethanolamine PPG 1000 1:0.5:0.5 27 Octenyl succinic anhydride Castor oil 1:1 28 Nonenyl succinic anhydride 1,6-Hexanediol 1:1 29 Dodecenyl succinic anhydride N-butyl diethanolamine Oleyl alcohol 1:0.9:0.1 30 Dodecenyl succinic anhydride N-butyl diethanolamine PEG 600 1:0.5:0.5 31 C20-24ASA PEG 1000 1:1 32 Dodecenyl succinic anhydride Trimethylol propane Erucic acid 1:1:1 33 Nonenyl succinic anhydride Castor oil 1:1 34 C20-24ASA Reaction product of gluconolactone and dodecylamine, prepared according to Ex 1 1:1 35 Dodecenyl succinic anhydride N-butyl diethanolamine PPG 2000 1:0.9:0.1 36 C20-24ASA PEG 1500 1:1 37 Pyromellitic dianhydride PEG 1000 Oleyl alcohol 1:1:1 38 Octadecenyl succinic anhydride 2,4,7,9-Tetramethyl-5-decyne- 4,7-diol ethoxylate 1:1 39 Phthalic anhydride Trimethylol propane Erucic acid 1:1:1 40 Nonenyl succinic anhydride Neopentyl glycol 1:1 41 C20-24ASA Succinic anhydride Neopentyl glycol 0.25:0.75:1 42 C20-24ASA 2,4,7,9-Tetramethyl-5-decyne- 4,7-diol ethoxylate 1:1 43 Dodecenyl succinic anhydride N-butyl diethanolamine 1,2-Propanediol 1:0.5:0.5 44 Pyromellitic dianhydride PEG 300 Oleyl alcohol 1:1:1.5 45 Dodecenyl succinic anhydride N-butyl diethanolamine Jeffamine M- 1000 1:0.9:0.1 46 Dodecenyl succinic anhydride N-butyl diethanolamine Duomeen CD 1:0.9:0.1 47 Nonenyl succinic anhydride PEG 6000 1:1 48 C20-24ASA PEG 1000 Citric acid 0.5:1:0.5 49 Nonenyl succinic anhydride PEG 200 1:1 50 Pyromellitic dianhydride PPG 425 Oleyl alcohol 1:1:1.5 51 Nonenyl succinic anhydride 1,12-Dodecanediol 1:1 52 Dodecenyl succinic anhydride Xylitol 1,6-Hexanediol 1:0.25:0.75 53 Dodecenyl succinic anhydride N-butyl diethanolamine PPG 425 1:0.5:0.5 54 1,2-Cyclohexane-dicarboxylic anhydride PPG 2000 1:1 55 Octadecenyl succinic anhydride Neopentyl glycol 1:1 56 Dodecenyl succinic anhydride N-butyl diethanolamine 3-Dimethyl-amino propylamine 1:0.9:0.1 57 C20-24ASA PPG 425 1:1 58 Phthalic anhydride PEG 200 1:1 59 Dodecenyl succinic anhydride Castor oil PEG 200 1:0.75:0.25 60 Dodecenyl succinic anhydride N-butyl diethanolamine Trimethylolpropane 1:0.9:0.1 61 Dodecenyl succinic anhydride N-butyl diethanolamine Oleic acid 0.9:1:0.1 62 Dodecenyl succinic anhydride N-butyl diethanolamine Castor oil 1:0.9:0.1 63 Pyromellitic dianhydride PPG 425 Oleyl alcohol 1:1:2 64 Dodecenyl succinic anhydride N-butyl diethanolamine 2-Ethyl-1,3-hexanediol 1:0.5:0.5 65 Dodecenyl succinic anhydride PPG 2000 1:1 66 Dodecenyl succinic anhydride N-butyl diethanolamine PEG 600 1:0.2:0.8 67 Nonenyl succinic anhydride Trimethylol propane Erucic acid 1:1:1 68 Dodecenyl succinic anhydride Succinic anhydride Neopentyl glycol 0.1:0.9:1 69 C20-24ASA Reaction product of glycerol carbonate and Jeffamine M- 1000, prepared according to Ex 2 1:1 70 C20-24ASA 1,12-Dodecanediol 1:1 71 Phthalic anhydride N-methyl diethanolamine 1:1 72 Octadecenyl succinic anhydride Diethanolamine 1:1 73 Pyromellitic dianhydride PEG 400 Oleyl alcohol 1:1:1.5 74 C20-24ASA Succinic anhydride Tris(2-hydroxy ethyl)methyl ammonium methylsulfate 0.25:0.75:1 75 C20-24ASA Trimethylol propane Erucic acid 1:1:1 76 Dodecenyl succinic anhydride Tris(2-hydroxy ethyl)methyl ammonium methylsulfate 1:1 77 Dodecenyl succinic anhydride Sorbitol 1,6-Hexanediol 1:0.25:0.75 78 Succinic anhydride Castor oil 1:1 79 Succinic anhydride Castor oil PEG 200 1:0.8:0.2 80 C14 alkenylsuccinic anhydride Castor oil 1:1 81 C16 IO ASA Castor oil 1:1 82 Tetrapropenyl succinic anhydride C16 IO ASA Castor oil 0.5:0.5:1 83 C16 IO ASA C16 TO ASA Castor oil 0.5:0.5:1 84 Tetrapropenyl succinic anhydride Maleic anhydride Castor oil 0.5:0.5:1 85 Tetrapropenyl succinic anhydride Castor oil PEG 200 1:0.8:0.2 Table 2 - abbreviations and chemical names PEG Poly(ethylene glycol) PPG Poly(propylene glycol) Duomeen CD N-cocoyl propylene diamine, commercially available from Nouryon Specialty Chemicals (Amsterdam, Netherlands) Jeffamine M-1000 Polyether monoamine comprising ethylene oxide and propylene oxide derived repeat units and having Mn ~ 1,000. Commercially available from Huntsman Corporation (Texas, United States) C20-24 ASA Commercially available alkenyl succinic anhydride including a mixture of C20 to C24 alkenyl groups C16 IO ASA C16 internal olefin-derived alkenyl succinic anhydride: a substituted succinic anhydride obtained by the reaction of maleic anhydride and a C16 internal olefin C16TO ASA C16 terminal olefin-derived alkenyl succinic anhydride: a substituted succinic anhydride obtained by the reaction of maleic anhydride and a C16 terminal olefin Example 4 - preparation of a concentrated composition using ester compound 6 Ester compound 6 was treated with an additive (up to 20 wt%) and homogenized thoroughly. The composition was allowed to stand for 24 hours at 20°C before visually observing and measuring the dynamic viscosity (cP). Dynamic viscosity was measured using an Anton Paar Stabinger SVM 301 viscometer. The results are shown in Table 3. Table 3 Proportion of ester compound 6 (wt%) Additive Proportion of additive (wt%) Dynamic viscosity @ 20°C (cP) Visual observation 100 None 7,046 Homogenous 90 Tween 80 10 5,060 Homogenous 80 Tween 80 20 3,889 Homogenous 80 Castor oil 20 4,732 Homogenous 90 Isopropanol 10 1,452 Homogenous 80 Isopropanol 20 760 Homogenous 80 Water 20 Not measurable Immiscible layers Tween 80 is an ethoxylated sorbitan ester based on a natural fatty acid (oleic acid) commercially available from Croda International Plc (Goole, UK). Example 5 - preparation of a concentrated aqueous emulsion using ester compound 6 A composition was prepared according to Table 4. Table 4 Component Proportion (wt%) Ester compound 6 20 Lauryl amphoacetate 6 Water 74 Total 100 After thorough mixing, an opaque emulsion was obtained. The composition was stored at 20°C and periodically observed over 8 weeks. The appearance of the composition was unchanged during this time period. Example 6 - Preparation of further concentrated aqueous emulsions. An ester compound (20 wt%), surfactant (5 wt% active unless otherwise indicated in table 5) and deionized water (balance, i.e. 75 wt% when surfactant is 5 wt%) were combined with a vortex mixer. The resulting mixture was left to stand at ambient temperature and the emulsion quality overtime was observed. The results are shown in Table 5. If the resulting mixture formed a stable emulsion, this is entered as “Stable”. If recorded as “Stable”, the stability time indicates the last time-point which was assessed. Table 5 Ester compound Surfactant Amount of surfactant (wt% active) Result Stability time 6 Sodium Lauroamphoacetate 5 Stable 8 weeks 6 Tallow amine ethoxylate (11 EO) 4 Stable 4 weeks 6 Tallow amine ethoxylate (11 EO) 6 Stable 3 months 6 Cocoyl amine ethoxylate (12 EO) 5 Stable 3 months 1 Tallow amine ethoxylate (11 EO) 5 Stable 10 days 78 Sodium Lauroamphoacetate 5 Stable 4 months 78 Tallow amine ethoxylate (11 EO) 5 Stable 3 months 78 Cocoyl amine ethoxylate (12 EO) 5 Stable 2 months 79 Sodium Lauroamphoacetate 5 Stable 4 months 80 Sodium Lauroamphoacetate 5 Stable 4 months Unless otherwise stated herein, the reference to “liquid”, “gel” and “solid” refer to a state at 25 °C and standard pressure (101,325 Pa). Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. All of the features disclosed in this specification (including any accompanying claims, and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. An ester compound, wherein the ester compound is the reaction product of reactants comprising one or more first reactants and one or more second reactants, wherein the or each first reactant is a cyclic anhydride and the or each second reactant is a polyol.

2. The ester compound according to claim 1, wherein the ester compound is a polymer.

3. The ester compound according to claim 2, wherein the polymer comprises at least 4 monomer units.

4. The ester compound according to any preceding claim, wherein the or each cyclic anhydride is one or more of an anhydride of formula (I), of formula (II) or of formula (III):wherein in formula (I) R1 and R2 are each independently selected from hydrogen, an alkyl group and an alkenyl group, or R1 and R2 together with the carbon atoms to which they are attached represent an optionally substituted cyclic group;in formula (II) R3 and R4 are each independently selected from hydrogen, an alkyl group and an alkenyl group, or R3 and R4 together with the carbon atoms to which they are attached represent an optionally substituted cyclic group; andin formula (III) X is CR9R10, O, S, or NR11; R5, R6, R7, R8, R9, R10, and R11 are each independently selected from hydrogen, an alkyl group and an alkenyl group, and / or any of R5, R6, R7, R8, R9, R10, and R11 together with the atoms to which they are attached represent an optionally substituted cyclic group.

5. The ester compound according to claim 4, wherein the or each first reactant is a cyclic anhydride selected from one or more of succinic anhydride, maleic anhydride, glutaric anhydride, a Ce-30 alkenyl succinic anhydride such as C20-24 alkenyl succinic anhydride, dodecenyl succinic anhydride (such as (2-dodecen-1-yl)succinic anhydride), nonenyl succinic anhydride, octadecenyl succinic anhydride, octenyl succinic anhydride, octadecyl succinicanhydride, or octyl succinic anhydride, a branched alkenyl succinic anhydride such as tetrapropenyl succinic anhydride or polyisobutenyl succinic anhydride, phthalic anhydride, pyromellitic dianhydride, 1,2,4-benzenetricarboxylic anhydride, 1,2-cyclohexanedicarboxylic anhydride, 1,2-naphthalic anhydride, 2,3-naphthalic anhydride, 1,8-naphthalic anhydride and homophthalic anhydride.

6. The ester compound according to claim 4 or 5, wherein the or each first reactant is a cyclic anhydride selected from one or more of succinic anhydride, maleic anhydride, C20-24 alkenyl succinic anhydride, dodecenyl succinic anhydride (such as (2-dodecen-1-yl)succinic anhydride), nonenyl succinic anhydride, octadecenyl succinic anhydride, octenyl succinic anhydride, phthalic anhydride, pyromellitic dianhydride, 1,2,4-benzenetricarboxylic anhydride, 1,2-cyclohexanedicarboxylic anhydride and 1,8-naphthalic anhydride.

7. The ester compound according to any preceding claim, wherein the or each second reactant is a polyol having from 2 to 10, preferably from 2 to 6, more preferably 2 or 3, hydroxy groups.

8. The ester compound according to claim 7, wherein the or each polyol is selected from one or more polyol of the formula (IV), one or more of an alkoxylated polyol of formula (IV), one or more nitrogen containing polyol, and one or more polyol formed by reaction of a hydroxy substituted cyclic ester or cyclic carbonate with a suitable primary or secondary amine compound, wherein the polyol of formula (IV) is of the formula H-(OR17)P-OH, wherein each R17 is independently an optionally substituted hydrocarbylene group and p is an integer of at least 1.

9. The ester compound according to claim 7 or 8, wherein the or each second reactant is a polyol independently selected from castor oil, 1,6-hexanediol, sorbitol, neopentyl glycol and a polyalkylene glycol (such as PEG 200).

10. The ester compound according to any preceding claim, wherein the ester compound has a number average molecular weight of from 1,000 to 150,000 Daltons, preferably from 1,000 to 15,000 Daltons (for example from 2,000 to 7,000 Daltons).

11. The ester compound according to any preceding claim, wherein the ester compound is the reaction product of reactants comprising, or of reactants consisting essentially of or consisting of, dodecenyl succinic anhydride and castor oil, preferably in a molar ratio of 1:1, and wherein the ester compound has a number average molecular weight of from 2,000 to 3,000 Daltons and / or a polydispersity index of from 1 to 4, such as from 1.1 to 2, preferably from 1.5 to 1.6.

12. The ester compound according to any preceding claim, wherein the ester compound is substantially free of silicon atoms.

13. A concentrate composition comprising one or more ester compounds and optionally at least one solvent, wherein the concentrate composition comprises at least 20 wt% of the one or more ester compounds, and wherein the or each ester compound is the reaction product of reactants comprising one or more first reactants and one or more second reactants, wherein the or each first reactant is a cyclic anhydride and the or each second reactant is a polyol.

14. The concentrate composition according to claim 13, wherein the composition comprises at least 30 wt%, at least 40 wt%, at least 50 wt%, at least 60 wt%, at least 70 wt%, or at least 80 wt% of one or more ester compounds.

15. The concentrate composition according to claim 13 or 14, wherein the composition additionally comprises one or more surfactants.

16. The concentrate composition according to claim 15, wherein the one or more surfactants are independently selected from anionic surfactants, cationic surfactants, non-ionic surfactants, and amphoteric or zwitterionic surfactants (preferably non-ionic surfactants and / or amphoteric or zwitterionic surfactants).

17. The concentrate composition according to claim 16, wherein the one or more surfactants are independently selected from one or more of a fatty alkyl amphoacetate, a sugar ester (such as a sorbitan ester) and a fatty amine alkoxylate (such as a fatty amine ethoxylate or fatty amine propoxylate).

18. The concentrate composition according to any of claims 13 to 17, wherein the concentrate composition is stable for at least 3, 6, 12 or 24 months under ambient conditions.

19. The concentrate composition according to any of claims 13 to 18, wherein the concentrate composition is flowable.

20. The concentrate composition according to claim 19, wherein the concentrate composition has a viscosity of 7,000 cP or less, preferably 3,500 cP or less at 20°C.A