Polymer compositions and use thereof

Abstract

A polymer composition comprising a fluorescent whitening or brightening agent with the structure of Formula I. Where A is O or -NH; X is S, O -NH or -NR3, Q is H or -C(O)AR2, R1 is H, alkyl, alken

Description

TECHNICAL FIELD The present invention concerns a polymeric composition incorporating a fluorescent whitening agent or optical brightener, and the use thereof. BACKGROUND Fluorescent whitening agents (FWAs) or optical brighteners are chemical compounds that absorb light in the ultraviolet and violet region of the electromagnetic spectrum and re-emit light in the blue region. FWAs or optical brighteners are used to enhance the appearance of different materials through their "whitening" effect, resulting from an increasing overall amount of blue light reflected that counterbalances the yellowish appearance and makes materials showing a brighter white colour. In the plastics industry, optical brighteners have been used for many years to improve the colour of various plastics and are able to mask inherent yellowness that occurs during plastic discolouration, or to impart unique and robust colour to speciality plastic products. FWAs or optical brighteners are effective in a variety of polymer substrates such as engineering plastics (e.g. polyesters, polycarbonate, polyamides, and acrylics), thermoplastic polyurethane, polyvinylchloride, styrene homo- and copolymers, polyolefins, adhesives, and other organic substrates. Although expensive, FWAs or optical brighteners can be used at low cost due to their effectiveness at low loading levels. Typically, these additives may be used at concentrations of about 5 to 400 parts per million (ppm). Pigmented polymers often require higher loadings of additive because colourants, such as titanium dioxide, compete with the brightener for the UV light needed to function. Two of the most commonly used optical brighteners in the plastics industry are derivatives of the bis-benzoxazole type. These include the bis-benzoxazolyl-stilbene, OBI (CAS 1533-45-5), and the bis-benzoxazolyl-thiophene, OB (CAS 7128-64-5). Another example of an industry standard FWA in the plastic and paper industry include BBU (CAS 16470-24-9). Examples of conventional FWAs or optical brighteners known in the art include: CN109438479A describes an ultraviolet absorber with a pyridone ester skeleton structure functionalised with flexible alkyl chains and water-soluble groups to change the water solubility and the dispersibility of the absorber inside polymers. The ultraviolet absorber is provided with a plurality of controllable sites, enabling the changing of the optical properties 5 to suit different requirements, making the absorber high in optical performance, degree of freedom, material performance, and wide in applicability. CN114507230A describes a bicyclic pyridone derivative as well as a synthesis method and application thereof. The bicyclic pyridone compounds can be synthesised from cheap and low- 10 toxicity citric acid, and therefore the production cost is low, and the synthesis is simple. The compounds can be used as an intermediate for further synthesis of bicyclic pyridone compounds, and the compound has good antibacterial activity and fluorescence characteristics. 15 CN113248787A describes a thiazolidinone-based bio-based plasticiser, which by virtue of a pyridone diacid, has the advantages of renewable raw materials, simple synthesis, low biotoxicity, and the like, which effectively reduces the production cost of the plasticiser, the environmental pressures and the safety risks in the use process, so that the bio-based 20 plasticiser disclosed is expected to replace traditional phthalate plasticisers. CN110003377A describes a polymer that has been modified with an ultraviolet absorber function, and a preparation method thereof. The document describes copolymerisation of monomers with different ultraviolet absorption properties to produce a polymer film that has very high visible light permeability, fluorescence, workability, excellent stability, and 25 outstanding ultraviolet shielding performance. The polymer finds applications in the fields of aviation, buildings, agriculture, and optical devices. WO2016164437 describes a sensing method comprising disposing a fluorophore in a biological environment, wherein the fluorophore comprises a dioxo-pyridine ring (DPR) or a 30 thiazolopyridine acid (TPA). The method further comprises exposing the biological environment to electromagnetic radiation having a wavelength corresponding to an excitation wavelength of the fluorophore, detecting light emitted by the fluorophore, and correlating the light emitted by the fluorophore to a presence or absence of an analyte within the biological environment in an amount above a minimum detection threshold. The conventional FWAs or optical brighteners used in the plastics industry have several disadvantages, which include that they are conventionally manufactured from fossil fuels; they are typically non-biodegradable; and that they are typically toxic in the aquatic environment. Our co-pending international application, PCT / EP2024 / 056098 (published as WO / 2024 / 184492) discloses biodegradable fluorescent whitening agents for use in laundry applications based on pyridone derivatives, which have fewer environmental drawbacks. The present invention seeks to overcome these disadvantages and provide improved FWAs or optical brighteners for plastic applications with comparable functionality, but with fewer environmental drawbacks. SUMMARY OF THE INVENTION According to a first aspect of the invention there is provided a polymeric composition incorporating a compound of structure (I) as a fluorescent whitening agent or optical brightener, having the structure: wherein: A is O, or -NH; XisS, O, -NH, or-NR3; Qis H or-C(O)AR2; R1 is H, alkyl, alkenyl, polyalkylene glycol, or alkoxy-polyalkylene glycol; R2 is H, alkyl, alkenyl, polyalkylene glycol, or alkoxy-polyalkylene glycol; R3 is alkyl, alkenyl, polyalkylene glycol or alkoxy-polyalkylene glycol; and wherein R1, R2 and / or R3 are different from or the same as each other, and wherein, when R1 and / or R2 is a linear alkyl, it is a C7-C34 alkyl, and when R1 and / or R2 is a branched alkyl, it is a C1-C34 alkyl. In preferred embodiments, A is O. In preferred embodiments, when R1, R2 and / or R3 is alkyl, they may be a linear or branched alkyl. In some embodiments R1 and / or R2 may be a linear C7-C34 alkyl. In some embodiments R1 and / or R2 may be a branched C1-C34 alkyl. In some embodiments, when R1, R2 and / or R3 represents a linear or branched alkyl, R1, R2 and / or R3 may be preferably selected from heptyl, octyl, 2-ethylhexyl, 1,1-dimethylpropyl, 1,3,3-trimethylpropyl, 2,5-dimethylhexyl, isopropyl, 3-methylpentan-2-yl, 3-methylpentan-3-yl or tertbutyl. In embodiments when R1, R2 and / or R3 is alkenyl, it may be a linear or branched alkenyl, and may be a C2-C30 alkenyl, such as for example, (Z)-9-octadecen-yl or (Z)-13-tetracosen-yl. In embodiments when R1, R2 and / or R3 is polyalkylene glycol, it may be selected from, for example, polyethylene glycol (PEG), polypropylene glycol (PPG), or polybutylene glycol (PBG). In embodiments when R1, R2 and / or R3 is a polyalkylene glycol (such as PEG, for example), it may have from 2 to 1000 repeat units. More preferably, it has 2 to 20 repeat units. Still more preferably, it has 8 to 12 repeat units. Most preferably, it has 3 repeat units. In embodiments when R1, R2 and / or R3 is alkoxy-polyalkylene glycol, it may be methyloxy-polyethylene glycol (MeO-PEG), ethoxy-polyethylene glycol (EtO-PEG), or methyloxy-polypropylene glycol (MeO-PPG). In embodiments when R1, R2 and / or R3 is an alkoxy-polyalkylene glycol (such as MeO-PEG, for example), it may have from 2 to 1000 repeat units. More preferably, it has 2 to 20 repeat units. Still more preferably, it has 8 to 12 repeat units. Most preferably, it has 3 repeat units. Advantageously, as R1, R2 and / or R3 can be the same as or different from each other, the compound may be balanced with respect to its compatibility with the polymeric composition, which enables enhancement of the composition for a particular plastic application. The polymer composition may comprise a multiplicity of different FWA or optical brightener compounds, which may preferably be according to structure (I). In most preferred examples, the polymer composition may comprise a multiplicity of different FWA or optical brightener compounds, and all of the compounds may be according to structure (I). For example, the composition may comprise at least one, at least two, at least three, or at least four different FWA or optical brightener compounds according to the invention. The polymer composition may comprise further additives and components to alter and / or control the properties of the composition. The FWA or optical brightener compounds contained within the polymer compositions of the invention are advantageous over current industry standards as they provide comparable fluorescence using a smaller compound, with a lower molecular weight. The compounds therefore provide improved visual appeal, perceived quality and shelf impact on plastics products made from the polymer compositions. Additionally, further functionalisation of the compound formulae to modulate application performance may be readily achieved, with little effect on the overall fluorescent behaviour of the fluorescent whitening agent or optical brightener. The FWA or optical brightener compounds described in the present invention have a further advantage over current standards, as a similar fluorescence performance can be achieved with a much smaller molecular weight, which in turn can lead to a lower loading of the FWA or optical brightener in the final application. Lower loadings can mitigate any potential adverse effects associated with the compound. According to a second aspect of the invention there is provided a method of synthesising the compound of structure (I) provided within the polymer composition according to the first aspect of the invention. In embodiments, the method may comprise: (i) condensation of an acid with an amine to form fluorescent core comprising a carboxylic acid group; and / or (ii) functionalisation of a carboxylic acid group on a fluorescent core by esterification or amidation. In preferred embodiments, the compound may be synthesised from readily available and biorenewable starting materials, such as for example, citric acid. In some embodiments, the method of synthesis may be water-based or use green chemistry methods. Advantageously, the method of synthesis for the compound provided within the polymer composition according to the first aspect of the invention have a lower environmental impact than those known in the art and are easily scalable for industrial production methods. According to a third aspect of the invention there is provided a use of the polymeric composition according to the first aspect of the invention. In one embodiment, the polymeric composition may be used as a masterbatch for plastic production. In preferred embodiments, the polymeric composition may be used within plastic products, such as, but not limited to, plastic films or packaging. According to a fourth aspect of the invention there is provided a plastic product comprising a fluorescent whitening agent or optical brightener according to the first aspect of the invention. The product may be a masterbatch for use in plastic production, or the final plastic product itself. In preferred embodiments, the plastic product may comprise a low loading of the FWA or optical brightener. Any feature discussed in reference to one of the aspects of the present invention applies equally to all of the other aspects discussed herein. DETAILED DESCRIPTION Fluorescent whitening agents (also referred to as FWAs) and optical brighteners, are additives widely used in the plastics industry to enhance the whiteness, brightness, and visual appeal of various polymer products. FWAs are compounds that absorb invisible ultraviolet (UV) light and re-emit it as visible blue light (wavelength 400 - 500 nm), making plastics look whiter and brighter. This effect compensates for the natural yellowish cast of many polymers, improving both perceived whiteness and lightness. Current industry standard FWAs and optical brighteners, including OB and OB-1, have large conjugated aromatic systems of high molecular mass, which have limited capability to be oxidised or hydrolysed, making them less biodegradable. As a result, current industry standard FWAs are raising environmental concern as they are not only detected as pollutants in urban wastewaters (Marine Pollution Bulletin, 2022, 178, 113559) but also in indoor environments (Environ. Sci. Technol., 2022, 56, 10131-10140). With a rise in plastic pollution worldwide, it is key that FWAs and optical brighteners used in polymer compositions are environmentally friendly and able to degrade at a faster rate to prevent accumulation in the environment. Thus, an environmentally friendly FWA or optical brightener is one that has lower impact on the environment, starting from the manufacturing stage, being not derived from the oil industry, but from renewable sources, up to the usage and end-of-life stage of the final products incorporating the FWA or optical brighteners, given their low toxicity towards humans and aquatic environment, and / or improved biodegradability. As demonstrated by the chemical structures of the current industry standards, this typically requires elongated aromatic systems based predominantly on carbon and hydrogen, which have high molecular weights, and are frequently derived from crude oil sources. In contrast, compounds based on pyridone and derivative thereof are known to achieve similar n-electron counts and also emit visible blue light in the 420 - 470 nm range, whilst also being bio-derivable. These derivatives, which have substantially lower molecular weights, achieve this effect through the incorporation of heteroatoms, such as nitrogen and oxygen. Therefore, the pyridone and its derivatives of the invention can be synthesised through cheap and low-toxicity citric acid, the production cost is low, and the synthesis process is simple. Polymeric Compositions and Formulations According to the invention, the FWA or optical brightener compounds are provided in a polymer composition. The polymer composition may comprise a polymer selected from at least one of, but not limited to, PU, TPU, PLA, PHA, PEF, PBT, HDPE, LDPE, PP, PVC, PC, PET, PA, PEEK, PEI, PEK, PPS, ABS, or Acrylics. In preferred embodiments, the polymer is selected from TPU, PLA, PHA, PEF, PBT, HDPE, LDPE, PP, PVC, PC, PET, PA, ABS. Alternatively, the polymer composition may comprise elastomers selected from at least one of natural rubber, SBR, BR, isoprene rubber, butyl rubber, EPDM, NBR, or chloroprene. In some particularly advantageous embodiments, the polymer composition may comprise a renewable bioplastic, such as at least one of PEF, PC, PET, PBT, or PPS. Advantageously, the polymer compositions according to polyethylene furanoate (PEF) is a popular biobased polymer, and this next-generation material can replace oil-based polymers. For example, PEF is renewable, non-toxic, and recyclable, and it has similar properties to traditional plastics. In embodiments of the invention, the polymer composition may further comprise additional components, making it adaptable to the application. The final formulation of the polymeric composition may comprise the resin or polymer in an amount from about 80% to about 99% w / w, from about 85% to about 99% w / w, from about 90% to about 98% w / w, from about 95% to about 98% w / w of the formulation. Alternatively, the formulation may comprise the resin or polymer in amount of about 85% w / w, about 90% w / w, about 92% w / w, about 94% w / w, about 96% w / w, about 98% w / w, or about 99% w / w. The remaining amount of the final formulation comprises the FWA or optical brightener compound and may further comprise additional additives. The final formulation of the polymeric composition may comprise at least one of, but not limited to, the following additives; pigments or dyes, flow agents, mould release agents, plasticisers, antioxidants, and / or UV stabilisers. In more specific applications, the final formulation may further comprise specialised additives to tailor the formulation to specific applications. Additionally, the final formulation may be mixed with fillers to improve mechanical properties, chemical and physical stability, barrier properties, electrical and thermal conductivity. The addition of additives and / or fillers may be advantageously used to alter the performance properties of the formulation, and tailor the formulation for a particular application. The additives may be selected from at least one of, but not limited to, antioxidants, antiozonants, antiscratch, anti-static, foaming agents, flame retardants, lubricants, waxes, compatibilisers, nucleating agents, plasticisers, processing aids, release agents, peptisers, thickeners, or pigments. The fillers may be selected from at least one of, but not limited to, glass fibres, ceramic fillers, carbon black, nanoparticles, conductive fillers, and / or titanium dioxide. The final formulation may be achieved by preparing a masterbatch in which the FWA or optical brightener is at a low concentration. The masterbatch may then be further diluted to achieve the final loading. As used herein the term "masterbatch" refers to a concentrated mixture of additives or pigments, such as FWAs or optical brighteners, which are blended and extruded with a carrier matrix, such as polymer or resin, to add to a final plastic product. The additives can be used to colour the product or give it other properties, such as 'whiteness'. Masterbatches are a common means used in polymer processing to incorporate such additives into a polymer resin. The typical alternative to using a masterbatch is to compound the plastic from raw undiluted additives. In some embodiments, the FWA or optical brightener is at a concentration of between about 0% and about 50% w / w, about 5% and about 40% w / w, about 7.5% and about 30% w / w, about 10% and about 20% w / w, or about 10% and about 15% w / w in the plastic matrix masterbatch or polymeric composition. In some embodiments, the FWA or optical brightener is at a concentration of less than about 50% w / w, less than about 40% w / w, less than about 30% w / w, less than about 20% w / w, less than about 15% w / w, less than about 10% w / w, less than about 7.5% w / w, or less than about 5% w / w in the plastic matrix masterbatch or polymeric composition. In most preferred embodiments, the concentration of the FWA or optical brightener is about 10% w / w in the plastic matrix masterbatch or polymeric composition. The resultant masterbatch is the concentrated mixture, which may be extruded, cooled, and formed into granules, powders, or other suitable masterbatch vehicles. The carrier material of the masterbatch may be a specific polymer that is identical to or compatible with the base polymer for producing the plastic product. For example, polymers such as EVA or LDPE can be used as carriers for polyolefins and nylon, while polystyrene can be used for ABS, SAN, and polycarbonates. When a carrier other than the base plastic is used, this carrier material may modify the resulting plastic's properties. Typically, the ratio of masterbatch to base polymer may be selected from about 0% to about 15% w / w, from about 0% to about 10%, from about 1% to about 10%, from about 1% to about 5%, or from about 1% to about 4%. In some instances, a multiplicity of masterbatches may be used together. Advantageously the dilutive nature of masterbatches, compared to raw additives, allows for higher accuracy in dosing small amounts of expensive additives. The use of granular solid masterbatches reduces problems with dust typically inherent to the use of finer-grained solid additives. Solid masterbatches have longer shelf lives than solutions in solvents, which evaporate over time. The resultant plastic product may therefore comprise a low loading of the FWA or optical brightener. In embodiments of the invention, the loading of the FWA or optical brightener in the resultant plastic product may be from about 50 ppm to about 500 ppm, from about 60 ppm to about 400 ppm, from about 70 ppm to about 300 ppm, from about 80 ppm to about 200 ppm, or from about 90 ppm to about 150 ppm. In embodiments of the invention, the loading of the fluorescent whitening agent or optical brightener in the resultant plastic product may be less than about 500 ppm, less than about 400 ppm, less than about 300 ppm, less than about 200 ppm, less than about 100 ppm, or less than about 50 ppm. In preferred embodiments, the loading of the fluorescent whitening agent or optical brightener in the desired plastic product may be about 100 ppm. Typically, pigmented polymers and / or polymer compositions require higher loadings of brightener because colourants, such as titanium dioxide, compete with the brightener for the UV light needed in order to function. In such embodiments, the loading of the fluorescent whitening agent or optical brightener in the desired plastic product may be higher, for example, about 150 ppm, about 200 ppm, about 250 ppm, about 300 ppm, or about 350 ppm. The loading of the fluorescent whitening agent or optical brightener is low, and advantageously this has the effect that in coloured plastic products, the loading of pigment may be reduced, whilst also obtaining the same or comparable intensity of colour. Masterbatches are commonly used in the following areas: plastics and packaging industry, automotive industry, textile industry, agricultural film production, construction and building materials, medical devices, electronics, furniture manufacturing, and / or food packaging. Chemical Structure of Fluorescent Whitening Agents According to the invention, the FWA or optical brightener is of structure (I): (I) wherein: A is O, or -NH; XisS, O, -NH, or-NR3; Qis H or-C(O)AR2; R1 is H, alkyl, alkenyl, polyalkylene glycol, or alkoxy-polyalkylene glycol; R2 is H, alkyl, alkenyl, polyalkylene glycol, or alkoxy-polyalkylene glycol; R3 is alkyl, alkenyl, polyalkylene glycol or alkoxy-polyalkylene glycol; and wherein R1, R2 and / or R3 are different from or the same as each other, and wherein, when R1 and / or R2 is a linear alkyl, it is a C7-C34 alkyl, and when R1 and / or R2 is a branched alkyl, it is a C1-C34 alkyl. As used herein, the term "alkyl" refers to a linear or branched hydrocarbon chain group consisting solely of carbon and hydrogen atoms, containing no unsaturation, and having the specified number of carbon atoms, which is attached to the rest of the molecule by a single bond. In embodiments of the invention, an alkyl group is preferably a "C1-34 alkyl group", that is an alkyl group that is a linear or branched chain with 1 to 34 carbons. The alkyl group therefore has 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, T1, 28, 29, 30, 31, 32, 33, or 34 carbon atoms. Preferably, when a linear alkyl, it is a C7-C34 alkyl, and when a branched alkyl, it is a C1-C34 alkyl. Specifically, examples of "C1-34 alkyl group" include, but are not limited to, methyl group, ethyl group, n-propyl group, iso-propyl group, n-butyl group, iso-butyl group, sec-butyl group, tert-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, n-nonadecyl group, n-eicosyl group, 1,1-dimethylpropyl group, 1,2-dimethylpropyl group, 2,2-dimethylpropyl group, 1-ethylpropyl group, n-hexyl group, 1-ethyl-2-methylpropyl group, 1,1,2-trimethylpropyl group, 1-ethylbutyl group, 1-methylbutyl group, 2-methylbutyl group, 1,1-dimethylbutyl group, 1,2-dimethylbutyl group, 2,2-dimethylbutyl group, 1,3-dimethylbutyl group, 2,3-dimethylbutyl group, 2-ethylbutyl group, 2-methylpentyl group, 3-methylpentyl group and the like. As used herein, the term "alkenyl" refers to a linear or branched hydrocarbon chain group consisting solely of carbon and hydrogen atoms, containing one or more carbon-carbon double bonds, and having the specified number of carbon atoms, which is attached to the rest of the molecule by a single bond. Alkenyl groups are preferably "C2-30 alkenyl", more preferably "C2-20 alkenyl", even more preferably "C2-15 alkenyl", even more preferably "C2-10alkenyl", even more preferably "C2-8 alkenyl", most preferably "C2-6alkenyl" groups, respectively. As used herein, the term "polyalkylene glycol" refers to an oligomer or polymer formed of repeating units of an alkylene glycol. The structure of polyalkylene glycol is commonly expressed as -(O-Z)n-OH, where Z is the alkylene group and n is the number of repeating units. As used herein, the term "alkoxy polyalkylene glycol" refers to a polyalkylene that is terminated at one end by an alkoxy group. The structure of an alkoxy polyalkylene glycol is commonly expressed as -(O-Z)n-OY, where Z is the alkylene group, Y is an alkyl group, and n is the number of repeating units. As used herein, the term "PEG" refers to polyethylene glycol, an oligomer or polymer formed of repeating units of ethylene glycol. The structure of PEG is commonly expressed as -(O-CH2-CH2)n-OH, where n is the number of repeating units. PEG groups can vary in size and molecular weight, resulting in different physical properties. In embodiments of the invention, it will be understood that the PEG group would be bonded to A by an alkyl group, for example -CH2-CH2-(O-CH2-CH2)n-OH. As used herein, the term "MeO-PEG" refers to a polyethylene glycol that is terminated with a methyl group. The structure of MeO-PEG is expressed as -(O-CH2-CH2)n-OCH3, where n is the number of repeating units. In embodiments of the invention, it will be understood that the MeO-PEG group would be bonded to A by an alkyl group, for example -CH2-CH2-(O-CH2-CH2)n-OCH3. The side groups may be selected to compatibilise the FWA or optical brighteners with a target polymer of interest. The core is the component that predominantly provides the fluorescence properties, and the side groups, which may be saturated (i.e. comprise no double bonds) or unsaturated (i.e. comprise double bonds), or linear or branched, are selected to compatibilise the compound with a particular polymer. In different polymers, different R1 and / or R2 side-groups are preferred. Table 1 below, shows the 5 different preferred R1 and / or R2 groups for a FWA or optical brightener of structure (I), according to the polymer component of the polymeric composition. Table 1: Preferred Polymer-Compound Combinations Polymer Component R1 and / or R2 Linear Alkyl Branched Alkyl Acrylonitrile Butadiene Styrene (ABS) C7-C18 C5 or Cg High-density polyethylene (HDPE) C21-C34 - Low-density polyethylene (LDPE) C18-C34 - Polycarbonate (PC) C8-C23 C4 or Cs Polyethylene terephthalate (PET) C7-C21 c8 Polylactic acid (PLA) C7-C13 C5, Cg or Cg Polypropylene (PP) C22-C34 - Polyurethane (PU) C7-C18 C5 or C8 Styrene-butadiene rubber (SBR) C12-C34 - 10 According to the above, when the alkyl group is a branched alkyl group, it may be in many different arrangements depending on the number of carbons present in the branched alkyl group. Preferably, when the alkyl group is a C4 branched alkyl group, it is preferably tert-butyl. Preferably, when the alkyl group is a C5 branched alkyl group, it is preferably 1,1-dimethylpropyl. Preferably, when the alkyl group is a Cg branched alkyl group, it is preferably 1,3,3-trimethylpropyl. Preferably, when the alkyl group is 15 a Cg branched alkyl group, it is preferably 2-ethyl-hexyl. In exemplary embodiments, the FWA or optical brightener compounds may be selected from, but not limited to, the following, which fall within the definition of the compounds above: Properties of Fluorescent Whitening Agents According to the invention the polymeric composition incorporates at least one compound of structure (I) as a fluorescent whitening agent or optical brightener. The excitation and de-excitation properties of the FWAs or optical brighteners in accordance with the invention may be mechanistically understood with reference to prior art studies such as Sci. Adv., 2015, 5, 34795, which attributes the fluorescence in the 420 - 470 nm range of similar compounds to n*- n transitions in the same carbon-oxygen double bond, as is found in scaffolds based on pyridone. The carboxyl groups, particularly the carboxylic acid groups, present in the structures of the present invention are believed to contribute to the required number of n-electrons associated with fluorescence in the desired range. The FWAs and optical brighteners in the polymer compositions in accordance with the invention have smaller fluorescent cores and are thus more biodegradable as they are more prone to biological attacks, whilst still providing enough stability to oxidation and hydrolysis to be of use in the intended applications. In embodiments of the invention, the molecular weight of the FWAand optical brightener compounds may be below about 1000 Da, below about 750 Da, below about 500 Da, below about 400 Da, or below about 300 Da. In embodiments of the invention, the molecular weight of the FWA and optical brightener compounds may be from about 200 Da to about 1000 Da, from about 250 Da to about 750 Da, from about 250 Da, to about 500 Da, from about 250 Da to about 400 Da, or from about 250 Da to about 300 Da. In preferred embodiments, the molecular weight of the FWA and optical brightener compounds is below about 500 Da. In embodiments of the invention, the quantum yield of the FWA and optical brightener compounds may be at least about 30%, at least about 40%, at least about 50%, at least about 60%, or at least about 70%. In embodiments of the invention, the quantum yield of the FWA and optical brightener compounds may be from about 30% to about 100%, from about 30% to about 80%, from about 40% to about 80%, from about 50% to about 80%, from about 60% to about 80%, or from about 70% to about 80%. In preferred embodiments, the quantum yield of the FWA and optical brightener compounds is at least about 60%. As used herein, the term "quantum yield" will be understood to mean the ratio of the number of photons emitted as fluorescence to the number of photons absorbed. Therefore, the quantum yield is a dimensionless quantity representing the efficiency of a light-induced process, such as fluorescence. Advantageously, the FWAs or optical brighteners of the present invention exhibit much higher relative quantum yields than current industry standards. For example, only DSPB gives a comparable value of greater than 70%. As a result, the FWAs or optical brighteners contained within the polymer compositions of the invention are advantageous over current industry standards as they provide comparable or enhanced fluorescence whilst using a smaller compound, with a lower molecular weight. Additionally, further functionalisation of the structures of the invention to modulate application performance may be readily achieved, with little effect on the fluorescent behaviour of the FWA or optical brightener. Additionally, the FWA or optical brightener compounds contained within the polymer compositions according to the present invention, have excellent chemical stability at relatively high pHs and high thermal stability. Particularly, the compounds may be stable at temperatures up to about 300 °C, up to about 250 °C, up to about 200 °C, or up to about 150 °C; and / or the compounds may be stable at temperatures from about 100 °C to about 300 °C, from about 150 °C to about 300 °C, from about 200 °C to about 300 °C, or from about 250°C to about 300 °C. These temperatures are suitable for plastic processing, such as extrusion and moulding. Synthesis of Fluorescent Whitening Agents According to the invention there is provided a method of synthesising the FWA or optical brightener compound of structure (I). Advantageously, the FWA and optical brightener compounds of structure (I) in the polymer compositions in accordance with the invention may be synthesised from readily available and biorenewable starting materials, such as for example, citric acid. Additionally, the method of synthesis may be water-based or use green chemistry methods. As used herein, the term "bio-renewable" refers to materials and resources derived from natural sources, such as plants or animals, i.e. recently living organisms (biomass), that can be replenished at a rate that makes them available for future use. Examples of bio-renewable materials include, but are not limited to, algae, sugars, starches, corns, natural fibres, sugarcanes, beets, citrus fruits, woody plants, cellulosics, lignocelluosics, hemicelluloses, potatoes, plant oils, other polysaccharides such as pectin, chitin, levan, and pullulan, and a combination thereof. As used herein, the term "green chemistry" means the design of products and associated processes that reduce or eliminate the use of hazardous substances throughout the entire life cycle of a chemical product. The approach aims to prevent pollution at its source by developing chemicals and processes that are inherently safer for human health and the environment, promoting efficiency in resource and energy use. For example, one green chemistry approach would be to use bio-renewable materials as described above. A general synthesis of the compounds of structure (I) from citric acid is shown below in Scheme 1, where X, Q, and A are as defined above. Scheme 1 As shown above, the compounds may be synthesised by heating citric acid with a second amine building block in the presence of water, with water itself as the major by-product. Advantageously, water-based synthesis is safer, cleaner, more environmentally friendly, and highly scalable industrially. The skilled person would be able to readily adapt the above to access a range of chemical structures in accordance with structure (I). Further functionalisation of the core units to modify and / or improve substantivity of the resultant FWA or optical brightener compound in the desired polymer composition or for a specific application may be readily achieved by a second, facile reaction with either an alcohol or amine. Suitable groups will be known to the skilled person. Generally, such groups would not significantly detrimentally affect the function of the substituted group or of a larger moiety to which the substituted group is attached. In some cases, the skilled person would expect the substituent to improve the function of the substituted group. In particularly advantageous embodiments, the other reagents, such as the alcohol and amine can also be bio-derived or bio-renewable. For example, they may be derived from fatty alcohols. Advantageously, the synthesis of the FWA and optical brightener compounds is highly tuneable and enables easily achieved alteration of the side groups, increasing the adaptability of compounds to different polymer matrices by matching the side groups accordingly. Tailoring the structure of the FWA and optical brightener compound properties for specific polymer compatibility and / or processing conditions means that both the dispersibility and processability of the resultant polymeric composition can be tuned for a desired application. Additionally, the tunability of the side groups enables the tailoring of the compounds to have a good miscibility in a broad range of different matrices. Another advantage associated with the molecules of the invention is that they are intrinsically stable at high temperature, which makes the compounds suitable for plastic processing, where the compounds are co-extruded with the plastic matrix. Additionally, the FWAs and optical brighteners are preferably UV stable. Hansen Solubility Parameters and Biodegradation The FWA or optical brightener compounds used in the composition may be designed according to assessment of their Hansen solubility parameters. Hansen solubility parameters may be used to screen different side groups for compatibility with different plastics and / or polymers. In preferred embodiments, the fluorescent whitening agent and optical brightener may be selected according to its Hansen solubility in the polymer. Hansen solubility parameters are a means of predicting whether one material will dissolve in another and form a solution. The parameters are based on the principle that like dissolves like where one molecule is defined as being 'like' another if it bonds to itself in a similar way. In the method, each molecule is given three Hansen parameters, each generally measured in MPa05: 6d (the energy from dispersion forces between molecules), 6P (the energy from dipolar intermolecular forces between molecules), and 6h (the energy from hydrogen bonds between molecules). These three parameters can be treated as co-ordinates for a point in three dimensions also known as the Hansen space. The nearer two molecules are in this three-dimensional space, the more likely they are to dissolve into each other. From these parameters, a combined relative energy difference (RED) of the compound and the system may be determined. If the RED is less than 1, the molecules are alike and will dissolve; if RED is equal to 1, the molecules will partially dissolve; and if RED is greater than 1 the molecules are not alike and will not dissolve. In preferred embodiments, the FWA or optical brightener will have a Hansen solubility RED of less than about 1.0, less than about 0.8, less than about 0.6, less than about 0.4, less than about 0.2, or less than about 0.1, relative to the polymer of the polymer composition. The FWA or optical brightener compounds contained within the polymer compositions are inherently biodegradable, as they have smaller fluorescent cores, and are derived from naturally available sources, such as citric acid, and are thus more biodegradable as they are more prone to biological attacks, whilst still providing enough stability to oxidation and hydrolysis to be of use in the intended applications. Estimation of biodegradation based on chemical structures is complex due to variations in the physicochemical properties of organic compounds. Predictive methods for estimating biodegradation previously relied on metabolic pathways and on microbial diversity. More recently, predictive methods use group contribution, QSAR, or machine learning methods. As detailed in Ecotoxicol. Environ. Saf. 1989, 18, 252-267, from a survey conducted with 22 biodegradation experts, a hierarchy was constructed to represent the approximate order in which various groups were viewed as contributing to aerobic biodegradability: ester = amide = anhydride >hydroxyl >carboxylic acid = epoxide = site of unsaturation >benzene ring = methyl = methylene group. The general inference was that compounds already partially oxidised were generally considered to be more prone to biological attack than those which were not partially oxidised, all other things being equal, and that hydrolysable chemicals are considered to be more easily degraded still. The time taken for ultimate degradation was generally deduced from consideration of molecular weight, branching, halogenation, functional groups, solubility, and other factors. Advantageously, the FWAs and optical brighteners contained within the polymer compositions in accordance with the invention are biodegradable. Preferably they contain at least one functional group which is not oxidised, or which is only partially oxidised, and thereby is oxidisable or further oxidisable. Preferably they contain at least one hydrolysable group. Therefore, the FWA or optical brightener may comprise at least one labile group. Inherently biodegradable fluorescent whitening agents may be defined as >20% but <60% biodegradability in water as measured by standard OECD 301A-F testing. A readily biodegradable fluorescent whitening agent or optical brightener may be characterised by the ability of the material to biodegrade quickly and completely in water (either >70% dissolved organic carbon removal, >60% theoretical carbon dioxide or >60% theoretical oxygen demand, depending on standard OECD 301A-F test methods) in a 10-day window within 28 days. Uses of Polymeric Composition and Plastic Products According to the invention there is provided the use of the polymeric composition, and a plastic product comprising the polymeric product. In some embodiments, the polymeric composition may be used as a masterbatch for plastic production. In some embodiments, the polymeric composition may be used within plastic products, such as, but not limited to, plastic films or packaging. In embodiments of the invention, the product may be a masterbatch for use in plastic production, or the final plastic product itself. The use and / or plastic product may be selected from any suitable plastic product known in the art, such as, but not limited to, inks, films, packaging, household plastics, textiles, furniture, consumer goods, automotive materials, or industrial plastics. In specific examples, the use and / or plastic product may be selected from moulded thermoplastics, plastic films and sheets, fibres (such as PET fibres for textiles and carpets), synthetic leather, plastic bottles, plastic products for home use (water cups, buckets, etc.), adhesives and coatings for plastics, raffia, non-wovens, and / or injection-moulded items. Advantageously in these applications, the FWA or optical brightener has the advantage of enhancing whites and bright colours in consumer products, compensating yellowing due to polymer impurities or aging, improving light reflectivity and surface gloss for premium visual standards, increasing perceived thickness and uniformity of recycled or coloured plastics, and / or reducing the amount of toner or pigment needed. The invention will now be more particularly described with reference to the figures and drawings in which: Figure 1 shows lOOppm of Compound A dispersed in different plastics (top row) compared to unfunctionalised samples (bottom row). Lto R: PLA, PE, PE. EXAMPLES EXAMPLE 1: Relative quantum yield of the FWA cores The relative quantum yield of the FWA cores in solution was calculated against quinine sulphate in 0.5M sulfuric acid (¢=0.55), and is shown in Table 2, with a comparison to the industry standard, DSPB. The cores themselves are the fluorescent components of the compounds according to the invention, and the different functionalities that can be added do not significantly affect their fluorescing properties. Therefore, the cores fluorescence is indicative of the fluorescence of the compounds compatibilised for use in polymer compositions via the addition of side functionalities. Table 2: Fluorescence properties of the FWA core (I) compared to DSPB Structure Excitation lex(nm) Emission lem(nm) Relative quantum yield (¢) _____ .. ,O.. ..••■'v. :'-'- Benchmark (DSPB) CAS 27344-41-8 350 429 0.78 HO^O O^N^s OH 350 418 0.72 HO^O o^nAs 344 418 0.61 EXAMPLE 2: Modulation of FWAs Through Changes in Side Chains Emission of blue light via fluorescence for optical brighteners based on Core 1 is the results of the n*-n transitions of the carbon-oxygen double bond, found in the pyridone scaffolds based on pyridone. 10 The carboxyl groups of Core 1 are believed to have a minimal contribution to this system; it is therefore possible to modify the structure of Core 1 with minimal impact on the fluorescent behaviour. This is demonstrated by Table 3 below: Table 3: Comparison of varying core side chains, highlighting the minimal changes in fluorescence 15 emission wavelength within the desired blue range of 420 - 470nm Structure Emission lem at lex350nm (nm) HO^O jfjl O^NAS 0^ / ' OH 418 433 0 1 r p s- / 431 0 8—* 423 0 ,° 423 0 CC^AG ixx^ 422 o 434 HO^-O JxL 0^s 418 0 J s- / 431 O tA" o=\ o 431 0 p^^xXx° 433 0 h A\ s- / 422 0 Ax H A\ s- / 421 0 \„zX / 0___-x^JA^x^O A s— / 433 EXAMPLE 3: Modifications to Core 1 Physical Properties Through Side Chain Variation Processing different plastics during compounding can require a range of different temperatures. It is 5 therefore advantageous to be able to modify the physical behaviour of FWAs to match the required processing conditions, including but not limited to; physical form, melting point, and decomposition temperature. Thermal behaviour of various FWA structures has been assessed by Differential Scanning Calorimetry (DSC), and the results are shown in Table 4 below. 10 Table 4: Comparison of Physical Thermal Properties of Different FWA Candidates by DSC Structure Physical Form Melting Point (°C) Approx. Initial Decomposition 20-400°C (°C) HO^O O^N^s O^Z OH Yellow powder 246.3 265 o Beige powder 76.0 230 0 Yellow-green waxy powder 34.4 260 0 Yellow waxy solid 86.1 - Beige solid 194.3 280°C 0 Off-white solid 184.7 220 0 Lo s- / Yellow oil <20 330 w Yellow powder 270.5 300 o o=( o b Brown oil <20 210 J Beige solid 45.7 340 o vs S— / Yellow waxy solid 87.1 340 0 s- / White solid <20 230 0 s- / White solid 108.1 - 0 V) S-V Yellow oil <20 - 0 'O^ / ^Xs^O^J ^OH yellow solid 88.3 320 The results in Tables 3 and 4 highlight that FWAs based on Core 1 can be heavily modified to fit the desired plastic compounding application, while advantageously having little effect on the desired wavelength of emitted fluorescence. 5 EXAMPLE 4: Biodegradability Assessment Biowin™ software was used to provide predictions of biodegradability. This method of prediction of biodegradability is available as part of the Estimation Program Interface (EPI) Suite™ of software 10 provided by the United States Environmental Protection Agency (EPA). Environ. Sci. Technol., 1994, 28, 459-465, shows an example of the group contribution method for predicting probability and the rate of aerobic biodegradation. This is the type of method used by Biowin™. Biowin 3 and Biowin 5 models are of particular relevance to the present invention. The predicted biodegradability of some of the FWA cores according to the present invention were assessed using these models. The cores were assessed due to their molecular complexity, as indicative of the biodegradability of the compounds according to the invention. The side groups incorporated for 5 polymer compatibility are linked to the cores by chemical bonds, such as esters, recognised as biodegradable, as explained above. If the Biowin 3 (ultimate survey model) result is >= 2.75 (i.e. "weeks" or faster) and the Biowin 5 (MITI linear model) probability is >= 0.5, then the prediction is YES (readily biodegradable). If this condition 10 is not satisfied, the prediction is NO (not readily biodegradable). The results are provided below in Tables. Table 5: Biodegradability Assessment of FWA Cores Structure Biowin 3 Biowin 5 Interpretation of Biowin 3 &5 prediction. O~N Benchmark (OBI) CAS 1533-45-5 2.2833 -0.3770 Very poor HO^O O^N^s OH 3.3411 0.528 Readily biodegradable according to Biowin criteria (Biowin 3 >2.75 AND Biowin 5 >0.5). co 3.0738 0.4851 Expected to be biodegradable: Biowin 3 above threshold, Biowin 5 close to it. HO^O O^nH 3.1359 0.5691 Readily biodegradable according to Biowin criteria. Modification of FWA cores as described in the current invention can affect the predicted biodegradability of FWA candidates. Table 6 highlights some of the structural changes to Core 1 and the corresponding change to biodegradability predictions as a representative example. 5 Table 6: Biodegradability Assessment for FWA Candidates Structure Biowin 3 Biowin 5 Interpretation of Biowin 3 &5 prediction. Benchmark (OBI) CAS 1533-45-5 2.2833 -0.3770 Very poor HO^O O^N^s OH 3.3411 0.528 Readily biodegradable according to Biowin criteria (Biowin 3 >2.75 AND Biowin 5 >0.5). O^N^s 0:= / 2.1581 0.6724 Expected to be ultimately biodegradable: Biowin 3 below threshold, Biowin 5 above it. O^N^s 2.9310 0.8935 Readily biodegradable according to Biowin criteria. / °---^o^xzOY° jA O^N^s 0-^ __ 2.4062 0.6475 Expected to be ultimately biodegradable: Biowin 3 below threshold, Biowin 5 above it. xl 2.6063 0.5448 Expected to be biodegradable according to Biowin criteria: Biowin 3 score is within 2.25-2.75 range (weeks to months), Biowin 5 score is above threshold. O^NH2 JUL O^N^s 0= / nh2 2.5078 0.2767 Expected to be biodegradable according to Biowin criteria: Biowin 3 score is within 2.25-2.75 range (weeks to months), Biowin 5 score is close to threshold and significantly higher than any of the benchmarks. Although functionalisation of FWA cores typically reduces the rate of biodegradation, as per Biowin 3 predictions, the core proposed FWA candidates retain good predicted ultimate biodegradability through careful selection of side chains. EXAMPLE 5: Hansen Solubility Assessment Hansen solubility parameters were used to screen and identify favourable side groups for a range of plastics. The tables shown below (Tables 7-15) show the relative energy difference (RED) for the top 5 compounds assessed in each plastic. These are grouped by core structure, with the most compatible FWA or optical brightener compound, the one with the lowest RED score, first. 15 Table 7: Hansen Assessment for Acrylonitrile Butadiene Styrene (ABS) Core RED Structure 1 o HOV^OO S-Z'OH 0.09 1 0 -¾, 0.11 o r r o s— / 0.13 s- / 0.14 0 0.17 0 s— / 2 o VS s—f 0.12 0 8—' 0.13 0 8- / 0.14 0 r^Xz'XzZ-XzZX^zx~JkY£^^ 8— / 0.16 0 8— / 0.17 0 -^X^zx^xx^z-X^zx. 8- / Commercial Benchmarks 0.27 Wv , °i / r 0.35 €>^ / =\ X' - / V 0.47 J O-vy=w=v V Tv / =\ 0.89 Table 8: Hansen Assessment for High Density Polyethylene (HDPE) Core RED Structure 1 o -Wo n s- / °H 1.1 0000^°^^ 1.1 0 s- / Oz'Xz-XzzX / Xz'X. 1.11 0 1.11 0 1.11 0 Table 9: Hansen Assessment for Low Density Polyethylene (LDPE) Core RED Structure z o \=o I z-X \ '° o^° I 0.52 0 .--------- s-' 0.57 0 0.65 o 0.73 o 0.75 0 I o 4’ ~ 0.74 0.76 0.83 o \^-\ / XzxJ S- / 0.87 o XxX / xJ 8- / 0.91 o CxC^-C^ Commercial Benchmark 0.91 'Awn °-QH- Table 10: Hansen Assessment for Polycarbonate (PC) Core RED Structure 1 o -M°o S-ZOH 0.26 0 ^r°\G 0.29 S- / 0.29 0 l^-N^ ff 0.35 o 0.35 o 2 o VS s— / 0.22 0 0.22 1 ° AV / Y? 0.26 o 0.28 0 0.29 0 Commercial Benchmark 0.49 O-^y=\ / =\ 0.56 / d^7=U=V <r 0.6 Table 11: Hansen Assessment for Polyethylene terephthalate (PET) Core RED Structure I o X’ . I 0.15 0 0.17 sY yx / x / x^ 0.18 0 3- / 0.24 o 0.24 o r r o 2 o s— / 0.14 0 0.17 0.19 o 0.19 0.21 o Commercial Benchmark 0.29 / O^ / =\ V' -TA / A A 0.36 0.37 / O^y=w=v^ yv / ^X 1.01 Table 12: Hansen Assessment for Polylactic acid (PLA) Core RED Structure 1 o HO^X^0 Q s- / oH 0.27 o T j o S— / O'"'' A / \Z 0.29 1 0 ',<ACG , s— / ’'V 0.3 S- / 'qA / X / A / A 0.32 0 IT'Oy.^ 0.36 0 l^,Nft 3- / ~ 2 o s— / 0.26 O 0.27 0 V) s-7 0.28 0 0.28 o s— / 0.29 1 1 ° a? S— / Commercial Benchmark 0.33 °"O+ 0.34 O^ / =\ X' -TA / A r 0.49 O^y=w=v^ yv / ^X 0.82 Table 13: Hansen Assessment for Polypropylene (PP) Core RED Structure 1 o HO^^0 Q S-_ / oH 0.3 0 / X / X / X / xJ 8- / ( / vAAAA 0.31 0 zX / X / X / X / ^oA^xzO I T jT p 0.31 0 1 1 J p 0.31 0 0.33 0 2 o Ho^^y0 S— / 0.44 0.45 0.46 0.47 COOCX^^ 0.49 cooc^^^ Commercial Benchmark 0.88 O-^y=W=\ / / % / / ^ A 0.97 0.98 4s. z^O £ 1.01 o^ / =\ Table 14: Hansen Assessment for Polyurethane (PU) Core RED Structure I o y° o^° I 0.39 S- / 0.4 o T J .O S— / 0.4 1 0 s— / o-\X 0.41 0 0.42 0 l^,Nft 3- / ZS 'X / X ■ .F‘ o X 0.42 O 0.43 o ¢000^^^° 0.43 o 0.43 0.43 0 Commercial Benchmark 0.26 yaw'll °"O+ Table 15: Hansen Assessment for Styrene-butadiene rubber (SBR) Core RED Structure 1 o o S-Z^OH 0.08 0 0.09 0 0.09 0 0.11 0 0.11 0 ---0 2 o HO^^^-0 s— / 0.09 o 0.09 0 0.12 o 0.13 0 0.16 Commercial Benchmark 0.24 z^O Is 0.4 47 O^y=\ NZ 0.45 O-^y=W=\ / / % / / ^ A 0.89 EXAMPLE 6: Synthesis of Fluorescent Whitening Agents General Synthesis of Fluorescent Whitening Agent Core 1 In a typical procedure, a mixture of citric acid (1 e.q.) and desired amine (1 e.q.) were dissolved in water (1 vol.). Following removal of water under reduced pressure, the resulting white residue was heated to 130°C with an anchor stirrer to ensure efficient mixing. The reaction mixture was heated to 100°C to allow all water to distil. The molten mixture was then stirred for 2.5h and the water of reaction allowed to distil. The resulting resinous material was cooled <100°C before adding fresh water (1 vol.) to slurry the product. The mixture was then cooled to ambient temperature with vigorous stirring to disperse the product before filtration. The isolated solids were washed with fresh water (0.5 vol.) before drying in a vacuum oven to give the desired Core 1. General Esterification of Fluorescent Whitening Agent Core 1 with Alcohols In a typical procedure, a mixture of FWA Core 1 (1 e.q.), desired alcohol (2 e.q. per acid group) and p-toluene sulphonic acid (0.1 e.q.) were heated to 130°C under a blanket of nitrogen. Once at temperature, the water of reaction was allowed to distil over a period of 5h, after which point no further distillation was typically observed. Analysis by HPLC was used to confirm no unreacted FWA core 1 remained. The reaction mixture was then cooled to room temperature and washed with water (2 x 250ml) to remove the p-toluene sulphonic acid. Any excess alcohol was then removed under reduced pressure, or azeotropically with water where possible, to give the desired product without further purification. General Esterification of Fluorescent Whitening Agent Core 1 with Polyethyleneglycols In a typical procedure, a mixture of FWA Core 1 (1 e.q.), desired PEG side chain (2 e.q. per acid group) and sulphuric acid (0.01 e.q.) were heated to 130°C under a blanket of nitrogen. Once at temperature, the water of reaction was allowed to distil over a period of 5h, after which point no further distillation was typically observed. Crude mixtures were then diluted with saturated NaHCOs and extracted with EtOAc (3 x 20 vol.). The solvent was then removed under reduced pressure to give the desired product. Purification was achieved by column chromatography where necessary. General Amidation of Fluorescent Whitening Agent Core In a typical procedure, a mixture of FWA Core 1 (1 e.q.) and desired amine side chain (2 e.q. per acid group) were heated to 130°C under a blanket of nitrogen. Once at temperature, the water of reaction was allowed to distil until such a time no further distillation was observed. Completion of reaction was confirmed by HPLC, before cooling the reaction to room temperature. Crude mixtures were then diluted with IM NaOH and extracted with DCM (3 x 20 vol.). The solvent was then removed under reduced pressure to give the desired product. Purification was achieved either by column chromatography or recrystallisation from MTBE / Ethanol (1:1) where appropriate. General Amidation of Fluorescent Whitening Agent Core with a Peptide Coupling Catalyst In a representative example, FWA Core 1 (1 e.q.) was dissolved in DCM (10 vol.) with triethylamine (2 e.q. per acid group) and the desired amine (1.05 e.q. per acid group). Propanephosphonic acid anhydride (T3P, 50% in THF 1.5 e.q. per acid group) was then added to the mixture before stirring at ambient temperature for 16h. Where the desired amide precipitated from the reaction mixture, solids were isolated by filtration and dried in a vacuum oven to give the isolated product without further purification. Where the amide product did not precipitate, the reaction mixture was washed with IM NaOH (10 vol.) before concentrating the organic phase under reduced pressure. Purification of the crude products was then achieved by column chromatography, or crystallisation from MTBE / EtOH, where appropriate. EXAMPLE 7: Identification, Synthesis and Assessment of Lead Compound A for use in Plastics The molecule with the best Hansen solubility parameter across three plastics; PP, PE and PLA was identified as: Compound A A comparison of the RED compatibility values for Compound A and OBI is provided in Table 14 below, for each of the polymers. Table 16: Hansen Parameters for Compound A Vs OBI in Different Plastics Compound Polymer PP HDPE / LDPE PLA Compound A 0.56 1.8 / 1.08 0.3 OBI 0.97 3.86 / 1.58 0.82 As shown in Table 16, the predicted Hansen parameters for Compound A show an improved affinity for PP, HDPE, LDPE, and PLA when compared to OBI, as evidenced by the lower RED values. Synthesis of Fluorescent Whitening Agent Core 1 In a representative reaction, a mixture of citric acid (384.2g, 2mol) and cysteine (242.2g, 2mol) were dissolved in water (600ml). Following removal of water under reduced pressure, the resulting white residue was heated to 130°C with an anchor stirrer to ensure efficient mixing. The reaction mixture was heated to 100°C to allow all water to distil. The molten mixture was then stirred for 2.5h and the water of reaction allowed to distil. The resulting resinous material was cooled <100°C before adding fresh water (620ml) to slurry the product. The mixture was then cooled to ambient temperature with vigorous stirring to disperse the product before filtration. The isolated solids were washed with fresh water (300ml) before drying in a vacuum oven to give the final product as a yellow powder in 85% yield (412.5g, 1.7mol). Analytical Data: HPLC purity: 99.8%; LCMS (+ve ion): m / z 242.2; 2H NMR (DMSO-d6, 400 = MHz, d): 6.59 (s, 1H), 6.52 (s, 1H), 5.46 (d, 1H), 3.92 (t, 1H), 3.60 ppm (d, lH);nC^H} NMR (DMSO-d6, 75MHz, d): 169.2, 165.6, 160.7, 150.2, 142.7, 114.8, 97.9, 62.6 ppm. Esterification of Fluorescent Whitening Agent Core 1 to give Compound A A mixture of FWA core 1 (412.5g, 1.7mol), n-octanol (664.2g, 5.1mol) and p-toluene sulphonic acid (26.4g, 0.14mol) were heated to 130°C under a blanket of nitrogen to give a brown solution. Once at temperature, the water of reaction was allowed to distil over a period of 5h, after which point no further distillation was observed. Analysis by HPLC confirmed that no FWA core 1 remained, and that the undesired monoester products were below 1%. The reaction mixture was then cooled to room temperature and washed with water (2 x 250ml) to remove the p-toluene sulphonic acid. The excess n-octanol was then removed under reduced pressure azeotropically with water, to give Compound A as a viscous yellow-green oil that set to a wax on standing in 75% yield (600g, 1.3mol). HPLC analysis confirmed a purity of >99%. Assessment of Compound A in Plastics Compound A was prepared in three different polymer compositions with the plastics of interest; polyethylene (Exxon™ LD150BW), polypropylene (Borealis™ HC101BF), and PLA printing filament pellets (Luminy™ LX175). Corresponding polymer compositions were prepared for commercial optical brightener OBI (4,4'-Bis(2-benzoxazolyl)stilbene, Aldrich™). A masterbatch with a 10% by weight loading of each additive (OBI and Compound A) was first prepared using a Brabender™ Plastograph™ EC for each polymer. The conditions used for each polymer are shown in Table 17. Table 17: Masterbatch Preparation Conditions Parameter Material PE PP PLA Chamber Temperature (°C) 190 230 230 Rotor RPM 60 60 60 Equilibrium mixing time (min) 5 5 5 The remainder of the compounding work to create the 100 ppm and 400 ppm polymer composition blends was conducted using a PRISM™ TSE 16TC twin screw extruder, with a 4 mm die and take-off rollers. A multi-stage process was used to dilute the masterbatch to the appropriate levels: Stage 1: Creation of a 1% blend by extruding 20 g of the masterbatch with 180 g virgin polymer. Stage 2a: Creation of a 0.1% blend by extruding 20 g of stage 1 material with 180 g virgin polymer. Stage 2b: Creation of a 0.4% blend by extruding 80 g of stage 1 material with 120 g virgin polymer. Stage 3a: Creation of a 0.01% (lOOppm) blend by extruding 200 g of stage 2a material with 1800 g virgin polymer. Stage 3b: Creation of a 0.04% (400ppm) blend by extruding 200 g of stage 2b material with 1800 g virgin polymer. The extrusion conditions used are shown in Table 18 below, for each polymer. Table 18: Plastic Extrusion Conditions Parameter Material PE PP PLA Pre-Melt Zone (°C) 140 160 160 Melt Zone 1 (°C) 160 170 170 Melt Zone 2 (°C) 170 185 180 Melt Zone 3 (°C) 180 195 180 Die-Head (°C) 190 210 188 Drive RPM 40-45 50-55 50-60 Feed RPM 16 18 11-14 Die pressure (bar) 25 18 7-8 The resultant polymer compositions were assessed for their improved whitening appearance due to the incorporation of the FWA or optical brightener. The compounded plastic matrices comprising Compound A were assessed by colour measurement, in comparison with industry standard versions comprising OBI. Colour measurement is made with a Lovibond™ LC100 spectrocolorimeter. The surface colour of the powder is quantified using a series of values L*, a* , and b* from the colour model CIELAB defined by the International Commission on Illumination's (Commission Internationale de I'Eclairage). "L" is a measure of the amount of white or black in a sample; higher "L" values indicate a lighter coloured sample. A measure of the amount of red or green in a sample is determined by "a*" values. A measure of the amount of blue or yellow in a sample is determined by "b*" values; lower (more negative) b* values indicate more blue on a sample. Colour can also be measured using a different model CIE L*C*H* where C* represents chroma, h* the hue angle. The results of the colour measurement are found in Table 19. Table 19: CieLAB measurements for Compounded Plastics PE PP PLA Blank Comp. A OBI Blank Comp. A OBI Blank Comp. A OBI L* 43.7 43.3 44.6 34.1 36.1 36.8 28.6 29.7 30.4 a* -0.3 0.1 4.3 -0.6 1.5 5.0 -1.4 0.5 1.3 b* -6.0 -7.0 -17.5 -4.2 -4.8 -15.4 0.4 -0.8 -11.4 C* 6.1 7.0 18.0 4.3 5.1 16.2 1.5 0.9 11.5 h* 267.2 271.1 283.6 262.4 287.3 287.8 166.0 304.9 276.5 The results in Table 19 demonstrate a whitening effect on all plastics when compounded with Compound A, comparable to that provided by OBI. Figure 1 shows lOOppm of Compound A dispersed in different plastics (top row) compared to unfunctionalised samples (bottom row). L to R: PLA, PE, PE. As can be seen there is a distinct whitening effect caused by Compound A. EXAMPLE 8: Mechanical Testing of Compounded Polymer Polyethylene (PE) and polylactic acid (PLA) test specimens for tensile, flexural, and impact testing were prepared from nominally 4 mm thick compression moulded plaques in general accordance with ISO-293 (2023), using Compound A. Specimens for polypropylene (PP) testing were prepared by injection moulding ISO-527-2 (2012) Type IB tensile dumbbells and subsequently machined. The compression moulding process used required a melt temperature of 180°C for PE, 200°C for PLA, followed by pre-heating for 10 minutes at melt temperature at low (contact) pressure, followed by moulding for 5 minutes at high (5.0 MPa) pressure, and subsequent cooling at 180°C (PE) or 200°C (PLA) to ambient temperature at a rate of 15°C / min. Tensile testing was carried out in accordance with ISO-527-2 (2012), flexural testing was carried out in accordance with ISO-178 (2019), and Charpy impact testing was carried out in accordance with ISO-179-1 (2023) for the samples. There were no notable differences during the extrusion process between the two additives. Neither impacted the ability of the extrudate to form a consistent filament, nor did they impact structural integrity. The addition of Compound A as an additive did not significantly affect the strength, tensile and flexural properties of the resultant plastics and any little effects observed were comparable to the corresponding effects of the commercial compound, OBI. These results are shown in Tables 20-22 below for PE samples (Table 20), PP samples (Table 21) and PLA samples (Table 22). Table 20: Comparison of mechanical properties of PE samples Property Blank PE lOOppm OBI lOOppm Comp. A Tensile modulus (MPa) 213 ±7 228 ± 36 242 ± 50 Yield strength (MPa) 10.1 ±0.1 10.0 ±0.1 10.1 ±0.2 Strength @ break (MPa) 13.7 ±0.5 13.0 ±0.4 13.8 ±0.4 Elongation @ break (%) 380 ± 12 373 ± 10 388 ± 15 Impact strength (kJ / m2) 73.9 ±1.7 373 ± 10 388 ± 15 Flexural modulus (MPa) 235 ± 16 266 ± 22 240 ± 14 Stress @ max load (MPa) 7.10 ±0.27 8.26 ± 0.47 7.19 ±0.48 Strain @ max load (%) 5.03 ± 0.04 7.85 ±0.36 5.26 ±0.27 Table 21: Comparison of mechanical properties of PP samples Property Blank PP lOOppm OBI lOOppm Comp. A Tensile modulus (MPa) 1119 ±54 1187 ±107 1231±123 Yield strength (MPa) 31.0 ±0.1 31.9 ±0.2 30.9 ±0.3 Strength @ break (MPa) 18.7 ±0.3 18.3 ± 03 18.8 ±0.4 Elongation @ break (%) 48 ± 14 33 ±4 89 ±5 Impact strength (kJ / m2) 2.30 ±0.34 2.62 ±0.20 1.99 ±0.57 Flexural modulus (MPa) 1105 ± T1 1195 ±34 991 ±25 Stress @ max load (MPa) 31.3 ±0.6 33.9 ± 1.0 29.7 ±0.4 Strain @ max load (%) 5.02 ±0.0 5.05 ±0.1 5.11 ±0.1 Table 22: Comparison of mechanical properties of PLA samples Property Blank PLA lOOppm OBI lOOppm Comp. A Tensile modulus (MPa) 3336 ±70 3098 ±127 3242 ±213 Yield strength (MPa) No yield point observer Strength @ break (MPa) 68.2 ±1.6 63.8 ±1.9 53.2 ±7.9 Elongation @ break (%) 3±0 3±0 3±0 Impact strength (kJ / m2) 1.65 ±0.50 1.94 ±0.39 1.88 ±0.39 Flexural modulus (MPa) 3274±112 3077 ±152 3320 ±53 Stress @ max load (MPa) 99.9 ±2.5 99.1 ±1.1 100.9 ± 1.1 Strain @ max load (%) 4.54 ± 0.06 4.03 ±0.1 4.29 ±0.1 The resultant polymer compositions were assessed for the distribution of Compound A in plastic matrices (PLA, PE, PE) by visual examination under UV exposure, showing a homogeneous distribution, as demonstrated in Figure 1.

Claims

1. A polymeric composition incorporating a compound of structure (I) as a fluorescent whitening agent or optical brightener, having the structure:Owherein:A is O, or -NH;X is S, 0, -NH, or-NR3;Qis H or-C(O)AR2;R1 is H, alkyl, alkenyl, polyalkylene glycol, or alkoxy-polyalkyene glycol;R2 is H, alkyl, alkenyl, polyalkylene glycol, or alkoxy-polyalkylene glycol;R3 is alkyl, alkenyl, polyalkylene glycol or alkoxy-polyalkylene glycol; and wherein R1, R2 and / or R3 are different from or the same as each other, and wherein, when R1 and / or R2 is a linear alkyl, it is a C7-C34 alkyl, and when R1 and / or R2 is a branched alkyl, it is a C1-C34 alkyl.

2. The polymeric composition according to Claim 1, wherein:when R1, R2 and / or R3 represents a linear or branched alkyl, R1, R2 and / or R3 are selected from heptyl, octyl, 2-ethylhexyl, 1,1-dimethylpropyl, 1,3,3-trimethylpropyl, 2,5-dimethylhexyl, isopropyl, 3-methylpentan-2-yl, 3-methylpentan-3-yl or tert-butyl; and / orwhen R1, R2 and / or R3 is alkenyl, it is a linear or branched alkenyl, and optionally is a C1-C30 alkenyl; and / orwhen R1, R2 and / or R3 is polyalkylene glycol it is PEG, and / or it has from 2 to 1000 repeat units; and / orwhen R1, R2 and / or R3 is alkoxy-polyalkylene glycol it is MeO-PEG, and / or it has from 2 to 1000 repeat units.

3. The polymeric composition according to either Claim 1 or 2, wherein the polymer composition comprises a multiplicity of different fluorescent whitening agent or optical brightener compounds according to structure (I).

4. The polymeric composition according to any one of Claims 1 to 3, wherein the polymer is selected from TPU, PLA, PHA, HD and LD PE, PP, PA, ABS, natural rubber, SBR, BR, isoprene rubber, butyl rubber, EPDM, NBR, chloroprene, PEF, PC, PET, PBT, and / or PPS.

5. The polymeric composition according to any one of Claims 1 to 4, wherein the polymer composition comprises further additives and components to alter and / or control the properties of the composition.

6. The polymeric composition according to Claim 5, wherein the additives are selected from at least one of, pigments or dyes, flow agents, mould release agents, plasticisers, antioxidants, and / or UV stabilisers.

7. The polymeric composition according to either Claim 5 or 6, further comprising at least one of, antioxidants, antiozonants, anti-scratch, anti-static, foaming agents, flame retardants, lubricants, waxes, compatibilisers, nucleating agents, plasticisers, processing aids, release agents, peptisers, thickeners, or pigments.

8. The polymeric composition according to any one of Claims 1 to 7, wherein the polymer is in an amount from about 80% to about 99% w / w, from about 85% to about 99% w / w, from about 90% to about 98% w / w, from about 95% to about 98% w / w of the composition.

9. The polymeric composition according to any one of Claims 1 to 8, wherein the fluorescent whitening agent and optical brightener is biodegradable.

10. The polymeric composition according to any one of Claims 1 to 9, wherein the fluorescent whitening agent and optical brightener is selected according to its Hansen solubility in the polymer.

11. A method of synthesising the compound of structure (I) provided within the polymer composition according to any one of Claims 1 to 10.

12. The method according to Claim 11, wherein the compound is synthesised from bio-renewable starting materials, optionally wherein the starting material is citric acid.

13. The method according to either Claim 11 or 12, wherein the method of synthesis is waterbased or uses green chemistry.

14. Use of the polymeric composition according to any one of Claims 1 to 10.

15. A plastic product comprising a polymeric composition comprising a fluorescent whitening agent or optical brightener according to any one of Claims 1 to 10.T +44(0)30 0300 2000Search report under Section 17 of the Patents Act 1977Application No.: GB2514527.7Claims searched: 1-15Date search completed: 27 February 2026International classificationSubclass and subgroup Valid from C08K5 / 00 01 / 01 / 2006 C08K5 / 46 01 / 01 / 2006 C09K11 / 06 01 / 01 / 2006Field of searchWorldwide search of patent documents classified in the following areas of the IPC:Databases used in the preparation of this search report: CAS ONLINEDocuments considered to be relevantPatent literatureCategory Relevant to claims Document of relevance X 1-2, 4-15 CN 107987248 A (SHENZHEN INST OF ADV TECH CAS) - See especially examples X 1-2 and 11 15 WO 2016 / 164437 A1 (PENN STATE RES FOUND) - See Example 5 and Fig. 1A X 1-2, 4-7, 10-15 CN 109438479 A (SHENZHEN KANGXUN NEW MATERIAL TECH CO LTD) - See Figs 1&2, Examples 1 and 4 X 1-2, 4-7, 9 15 CN 113248787 A (UNIV SHENZHEN) - See Fig 1 and 2 and Examples 1,2 and 6Non-patent literatureT +44(0)30 0300 2000Category Relevant to claims Document of relevance X 1-2, 4-7, 9, 11-15 ACS Sustainable Chem. Eng., 5, 04 / 12 / 2017, Chen et al, Citric Acid / Cysteine-Modified Cellulose-Based Materials: Green Preparation and Their Applications in Anticounterfeiting, Chemical Sensing, and UV Shielding, 11387-11394, See whole document X 1-2, 4-9, 11-15 Journal of Materials Science, 54, 21 / 09 / 2018, Chen et al, Citrate-based fluorophores in polymeric matrix by easy and green in situ synthesis for full-band UV shielding and emissive transparent display, 1236-1247, See especially materials and methods sectionCategoriesLetter or symbol Description X Document indicating lack of novelty or inventive step. Y Document indicating lack of inventive step, if combined with another document of the same category. & Member of the same patent family. A Document indicating technological background. P Document published on or after the priority date but before the filing date of the present application. E Earlier application published on or after the filing date of the present application.

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