WO2010054441A1

WO2010054441A1 - Nanopigments

Info

Publication number: WO2010054441A1
Application number: PCT/AU2009/001486
Authority: WO
Inventors: Sati Nath Bhattacharya; Ivan Ivanov; Sumanta Raha; Nurul Quazi
Original assignee: Nva Ip Holdings Pty Ltd
Priority date: 2008-11-14
Filing date: 2009-11-13
Publication date: 2010-05-20

Abstract

The present invention relates to a dye monomer of general formula (I): A - X - R - O - C(O) - O - CH₂- C(H) = CH_2,wherein A is a dye molecule and both X and R are optional linkers. The present invention also relates to particles comprising a copolymer of said dye monomer and an ethylenically unsaturated monomer, to a method of producing said particles, to the use of said particles as nanopigments and to polymer dispersions comprising said particles as nanopigments.

Description

NANOPIGMENTS

Field of the Invention

The present invention relates to nanopigments. In particular, the present invention relates to a dye monomer comprising a dye molecule functionalised with an allyl carbonate group, to particles comprising a copolymer of said dye monomer and an ethylenically unsaturated monomer, to a method of producing said particles, to the use of said particles as nanopigments and to polymer dispersions comprising said particles as nanopigments.

Background of the Invention

A colorant is a substance that interacts with light by absorbing some wavelengths and reflecting others, thereby imparting colour to materials (e.g., paints, printing inks, plastics, textiles, glass, ceramics, jewellery, cosmetics). Two important classes of colorants are dyes (which are typically soluble in the application medium, resulting in a transparent solution) and pigments (which are typically insoluble in the application medium, resulting in an opaque suspension).

Colorants are susceptible to fading when exposed to electromagnetic radiation (e.g., sunlight) over extended periods of time due to photodegradation (i.e., oxidation or reduction of the colorant). In addition, colorants have a tendency to bleed (i.e., migrate) within the application medium and into other applied materials. The extent to which a colorant undergoes fading and/or bleeding depends upon the environmental conditions to which the colorant is subjected and the substrate on which the colorant resides.

A number of attempts have been made to improve the light-fastness (i.e., ability to resist fading) and colour-fastness (i.e., ability to resist bleeding) of colorants. However, there is still a need for colorants that exhibit reduced levels of fading and substantially no bleeding. The present invention goes at least some way to addressing this need. The superior properties of the nanopigments described herein may be attributed to the unique functionality of the compounds used to prepare the nanopigments and to the novel synthetic route adopted.

Summary of the Invention

A first aspect of the present invention relates to a dye monomer of general formula (I),

A-X-R-O-C(O)-O-CH₂-C(H) = CH₂ (I)

wherein A is a dye molecule and both X and R are optional linkers.

In one embodiment, there is provided a fluorescent dye monomer of formula (II).

(H)

In another embodiment, there is provided a non-fluorescent dye monomer of formula (III).

In a further embodiment, there is provided a non-fluorescent dye monomer of formula (IV).

(IV)

A second aspect of the present invention relates to a method of producing particles, wherein the particles comprise a copolymer of a dye monomer according to any one of formulae (I), (II), (III) or (IV) and an ethylenically unsaturated monomer, wherein the copolymer is produced via precipitation polymerisation.

Brief Description of the Drawings

The present invention will be described with reference to the accompanying non-limiting drawings.

Figure 1. A particle size distribution (derived from dynamic light scattering) of a nanopigment prepared from the fluorescent dye monomer of formula (II). The main peak (which represents about 82 wt% of the sample) corresponds to an average particle radius of about 28 nm, that is, an average particle diameter of about 56 nm.

Figure 2. A schematic illustration of a general method for preparing nanopigments from dye monomers of formula (I). The method comprises the following steps: (1) a precursor is chemically modified to yield a dye molecule; (2) the dye molecule is reacted with allyl chloroformate in tetrahydrofuran in the presence of pyridine to yield a dye monomer of formula (I); and (3) the dye monomer is copolymerised with an ethylenically unsaturated monomer via precipitation polymerisation to yield a nanopigment. - A -

Figure 3. The results of a bleeding test (ASTM D279, Test Method A) conducted on a nanopigment/polymer composite (comprising a nanopigment based upon Solvent Yellow 98 (Registry Number: 12671-74-8) dispersed within a polypropylene matrix) and the corresponding dye/polymer composite (comprising Solvent Yellow 98 (Registry Number: 12671-74-8) dispersed within a polypropylene matrix). The nanopigment/polymer composite exhibits substantially no bleeding over a 24-hour period relative to the corresponding dye/polymer composite.

Figure 4. A schematic illustration of the synthesis of a nanopigment from the fluorescent dye monomer of formula (II).

Figure 5. A schematic illustration of the synthesis of a nanopigment from the non- fluorescent dye monomer of formula (III).

Figure 6. A schematic illustration of the synthesis of a nanopigment from the non- fluorescent dye monomer of formula (IV).

Detailed Description of the Invention

Throughout this specification, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

The term "dye monomer" is used herein to refer to a compound comprising a dye molecule (i.e., a moiety capable of interacting with light by absorbing some wavelengths and - 3 -

reflecting others, thereby imparting colour to a material) and a polymerisable functionality (i.e., a moiety capable of undergoing polymerisation). The dye molecule and the polymerisable functionality are optionally separated by one or more linkers, wherein a linker can comprise a single atom or a group of atoms.

A - X - R - O - C(O) - O - CH₂ - C(H) = CH₂ (I)

wherein the dye molecule A is optionally separated from the polymerisable functionality (allyl carbonate group) by linkers X and/or R.

In its broadest sense, the optional linker R (if present) can comprise any divalent atom or molecule that can covalently bind to the neighbouring entities (oxygen and either dye molecule A or optional linker X) and that will not substantially adversely affect the polymerisation of the monomer or the colorant properties of the dye. For example, the optional linker R can comprise one or more of C_3-I0 alkylene, C_3-I₀ alkoxylene, C_6-I0 arylene, (C_6-I0) aryl-(C_!-6) alkylene, (Ci_-6) alkyl-(C₆-io) arylene, C_]-6 alkoxyl, C_6-I0 aryloxy and halogen, wherein the alkylene and/or arylene radicals are optionally substituted by hydroxyl. In one embodiment of the present invention, the optional linker R is C_3-6 alkylene.

In its broadest sense, the optional linker X (if present) can comprise any divalent atom or molecule that can covalently bind to the neighbouring entities (dye molecule A and either optional linker R or oxygen) and that will not substantially adversely affect the polymerisation of the monomer or the colorant properties of the dye. For example, the optional linker X can comprise one or more of oxygen, sulphur, secondary amine, tertiary amine, secondary phosphine, tertiary phosphine, secondary carbon, tertiary carbon, quaternary carbon, secondary silicon, tertiary silicon and quaternary silicon. In one embodiment of the present invention, the optional linker X is oxygen, secondary amine and/or tertiary amine. In its broadest sense, the dye molecule A can comprise any fluorescent or non-fluorescent moiety that is soluble in organic solvents and that can be suitably functionalised with an allyl carbonate group.

For fluorescent dye monomers, the dye molecule A can comprise one or more of Fluorescent Brightener 184 (Registry Number: 7128-64-5), Fluorescent Brightener 393 (Registry Number: 1533-45-5), Solvent Green 5 (Registry Number: 79869-59-3), Solvent Orange 7 (Registry Number: 23679-56-3), Solvent Orange 63 (Registry Number: 79869- 59-3), Solvent Red 196 (Registry Number: 52372-36-8), Solvent Yellow 43 (Registry Number: 19125-99-6), Solvent Yellow 98 (Registry Number: 12671-74-8), Vat Red 1 (Registry Number: 2379-74-0) and Vat Violet 3 (Registry Number: 2379-75-1). In one embodiment of the present invention, the dye molecule A is Solvent Yellow 98 (Registry Number: 12671-74-8).

For non-fluorescent dye monomers, the dye molecule A can comprise one or more of Disperse Red 60 (Registry Number: 17418-58-5), Solvent Blue 4 (Registry Number: 6786- 83-0), Solvent Blue 35 (Registry Number: 17354-14-2), Solvent Blue 36 (Registry Number: 14233-37-5), Solvent Red 1 (Registry Number: 1229-55-6), Solvent Red 24 (Registry Number: 85-83-6), Solvent Red 49 (Registry Number: 509-34-2), Solvent Yellow 14 (Registry Number: 842-07-9), Solvent Yellow 18 (Registry Number: 6407-78- 9) and Solvent Yellow 56 (Registry Number: 2481-94-9). In one embodiment of the present invention, the dye molecule A is Solvent Yellow 14 (Registry Number: 842-07-9).

Both the fluorescent and non-fluorescent dye molecules listed above are commercially available from a range of colorant suppliers, such as BASF, Clariant, Merck and Ciba Specialty Chemicals.

The dye monomers of formulae (II), (III) and (IV) below are specific examples of the dye monomer of general formula (I).

The fluorescent dye monomer of formula (II)

(II)

is based upon a fluorescent dye molecule A (benzothioxanthene dicarboxylic anhydride), which is separated from the polymerisable functionality (allyl carbonate group) by a linker R (C₆ alkylene).

The non-fluorescent dye monomer of formula (III)

is based upon a non-fluorescent dye molecule A ((E)-I -((3- hydroxyphenyl)diazenyl)naphthalen-2-ol), which is not separated from the polymerisable functionality (allyl carbonate group) by a linker.

The non-fluorescent dye monomer of formula (IV)

(IV)

is based upon a non-fluorescent dye molecule A ((E)-N-(6-hydroxyhexyl)-4'-((2- hydroxynaphthalen-l-yl)diazenyl)biphenyl-3-carboxamide), which is not separated from the polymerisable functionality (allyl carbonate group) by a linker.

The present invention also relates to particles comprising a copolymer of a dye monomer according to any one of formulae (I), (II), (III) or (IV) and an ethylenically unsaturated monomer.

In its broadest sense, the ethylenically unsaturated monomer can comprise any compound containing two sites of ethylenic unsaturation. For example, the ethylenically unsaturated monomer can comprise one or more of ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate and neopentyl glycol dimethacrylate. In one embodiment of the present invention, the ethylenically unsaturated monomer is ethylene glycol dimethacrylate.

The dye monomer content of the particles of the present invention can vary from about 0.01 wt% to about 30 wt% (based on the total weight of copolymer). In one embodiment of the present invention, the dye monomer content of the particles varies from about 1 wt% to about 5 wt% (based on the total weight of copolymer).

Dynamic light scattering measurements indicate that the particles of the present invention possess a size distribution that is narrow (i.e., within the nanometre range) and controllable (i.e., influenced by experimental parameters, particularly the amount of solvent used in the precipitation polymerisation). For example, the average particle diameter can range from about 10 nm to about 500 nm, preferably from about 15 nm to about 200 nm, more preferably from about 20 nm to about 100 nm and most preferably from about 30 nm to about 80 nm. In one embodiment of the present invention, the average particle diameter is about 56 nm (Figure 1).

A second aspect of the present invention relates to a method of producing the particles described above. A general method for preparing nanopigments from dye monomers of formula (I) is depicted schematically in Figure 2. First, a precursor is chemically modified to yield a dye molecule. Next, the dye molecule is reacted with allyl chloroformate in tetrahydrofuran in the presence of pyridine to yield a dye monomer of formula (I). Then, the dye monomer is copolymerised with an ethylenically unsaturated monomer via precipitation polymerisation to yield a nanopigment.

The present invention also relates to applications of the particles described above. For example, the particles can be used as nanopigments in paints, printing inks, plastics, textiles, glass, ceramics, jewellery and cosmetics. In one embodiment of the present invention, the particles are dispersed as nanopigments within a polymer matrix comprising one or more polyolefin (e.g., polyethylene, polypropylene, polybutylene, ethylene propylene diene, ethylene vinyl acetate), styrenic polymer (e.g., polystyrene, high-impact polystyrene, styrene butadiene styrene, styrene ethylene butadiene styrene, styrene acrylonitrile, acrylonitrile butadiene styrene), acrylic polymer (e.g., polymethacrylate, polymethylmethacrylate, polyethylmethacrylate), polyester, polyurethane, poly(vinyl chloride), biodegradable polymer (e.g., polylactic acid) and epoxy. The resulting nanopigment/polymer composites exhibit reduced levels of fading and substantially no bleeding relative to the corresponding dye/polymer composites (Figure 3).

The present invention will now be described further, and by way of example only, with reference to the following non-limiting examples. Examples

Example 1

Figure 2 illustrates a general method for preparing nanopigments from dye monomers of formula (I). The method involves:

(1) chemical modification of a precursor to yield a dye molecule;

(2) reaction of the dye molecule with allyl chloroformate in tetrahydrofuran in the presence of pyridine to yield a dye monomer of formula (I); and

(3) copolymerisation of the dye monomer with an ethylenically unsaturated monomer via precipitation polymerisation to yield a nanopigment.

The nature of the chemical modification step depends upon the type of dye molecule involved. Consider, for example, dye molecules (A) to (F) below:

Anthraquinone dye molecule (A) is prepared by reacting bromoanthraquinone with 6- amino-1-hexanol in dimethylformamide.

Anthraquinone dye molecule (B) is prepared by reacting l-amino-2-bromo-4- hydroxyanthraquinone with an appropriate phenol in the presence of potassium carbonate and 2, 3,4, 5-tetrahydrothiophene- 1,1 -dioxide at 120 ⁰C.

Azo dye molecule (C) is prepared by reacting 2-naphthol with an appropriate aniline via a diazotisation reaction.

Diazotisation Reaction

Azo dye molecule (D) is prepared by reacting N,N-dimethylbiphenyl-4-amine with an appropriate aniline via a diazotisation reaction.

(E)

Fluorescent dye molecule (E) is prepared by reacting m-hydroxy-N,N-diethylaniline with 4-bromophthalic anhydride in dichlorobenzene at 175 ⁰C to yield a dye derivative, and then coupling the dye derivative with an appropriate boronic acid via a Suzuki reaction.

(F)

Fluorescent dye molecule (F) is prepared by reacting 5-bromo-2-methyl-l,3-benzoxazole with iodomethane in acetone to yield an iodo salt, reacting the iodo salt with an appropriate aldehyde in ethanol to yield a dye derivative, and then coupling the dye derivative with an appropriate boronic acid via a Suzuki reaction.

Following the chemical modification step, dye molecules (A) to (F) above are each reacted with allyl chloroformate in tetrahydrofuran in the presence of pyridine to yield a dye monomer of formula (I), which is then copolymerised with an ethylenically unsaturated monomer via precipitation polymerisation to yield a nanopigment. Example 2

Figure 4 illustrates the synthesis of a nanopigment from the fluorescent dye monomer of formula (II). The synthesis involved:

(i) Synthesis of dye molecule

A mixture of anhydride (5 g) and 6-amino-l-hexanol (5 g) in dimethylformamide (50 mL) was heated under reflux for 16 hours, after which the reaction mixture was cooled to 0 ⁰C. The precipitated solid was then filtered, washed with cold dimethylformamide, recrystallised from dimethylformamide, washed with ethanol, washed with ether and dried to give the dye molecule (ca. 6 g) in quantitative yield (ca. 90 %). The ¹H-NMR (DMSO- d6) spectrum of the product comprised: 1.29 - 1.52, m, 8H, CH₂; 3.36, m, 2H, OCH₂; 3.83, t, 2H, NCH₂; 4.31, t, IH, OH; 7.29, m, 4H, ArH; 7.96, m, 4H, ArH.

(ii) Synthesis of dye monomer

Allyl chloroformate (3.6 g) and pyridine (2.3 g) were added to a solution of the dye molecule (4 g) in tetrahydrofuran (100 mL). After stirring at 0 ⁰C for 15 min, the reaction mixture was left at room temperature for 16 hr. The solid precipitate was poured into 10 % hydrochloric acid (200 mL) and the solution was stirred. The solid precipitate was then filtered, washed with water and dried to give the dye monomer (ca. 4.8 g) in quantitative yield (ca. 100 %). The ¹H-NMR (DMSO-d6) spectrum of the product comprised: 1.32 - 1.57, m, 8H, CH₂; 3.87, t, 2H, NCH₂; 4.05, t, 2H, OCH₂; 4.53, d, 2H, OCH₂CH; 5.25, m, 2H, CHCH₂; 5.88, m, IH₅ CH; 7.35, m, 4H, ArH; 8.08, m, 4H, ArH.

(iii) Synthesis of nanopigment

A solution of the dye monomer (0.15 g) in dichloromethane (5 mL) was added to a solution of ethylene glycol dimethacrylate (5 g) in ethanol (500 mL), after which nitrogen was bubbled through the reaction mixture for 15 min. Benzoyl peroxide (0.25 g) was then added and the reaction mixture was heated at 85 ⁰C under nitrogen for 16 hr without stirring. The solid precipitate was filtered, washed with dichloromethane thoroughly to remove the excess dye monomer and oven-dried to give the nanopigment (ca. 5 g) in quantitative yield. Example 3

Figure 5 illustrates the synthesis of a nanopigment from the non-fluorescent dye monomer of formula (III). The synthesis involved:

(i) Synthesis of dye molecule

A solution of sodium nitrite (3.3 g) in water (25 mL) was added to a suspension of 3- aminophenol (5 g) in 5 M hydrochloric acid (30 mL) at 0 ⁰C. After 2 min, a solution of saturated naphthol (7 g) in 2 M sodium hydroxide (2.13 mL) was added drop- wise to the reaction mixture whilst stirring continuously at 0 ⁰C. The reaction mixture was then stirred continuously at room temperature for 18 hr, after which the precipitated solid was filtered, washed with water (0.5 L) and dried to give the dye molecule (ca. 9.5 g) in quantitative yield (ca. 75 %). The ¹H-NMR (DMSO-d6) spectrum of the product comprised: 6.75, d, IH, ArH; 6.87, d, IH, ArH; 7.22 - 7.30, m, 2H, ArH.; 7.45, t, IH, ArH; 7.58, t, IH, ArH; 7.75, d, IH, ArH; 7.91, d, IH, ArH; 8.45, d, IH, ArH; 9.85, s, IH, ArH.

(ii) Synthesis of dye monomer

Allyl chloroformate (4.5 g) was added to a solution of the dye molecule (5 g) and pyridine (5 mL) in dichloromethane (50 mL). After stirring at 0 ⁰C for 15 min, the reaction mixture was left at room temperature for 3 hr. The reaction mixture was then poured into 10 % hydrochloric acid (200 mL) and the solution was stirred. The dye monomer was extracted with dichloromethane (100 mL x 3), washed with 10 % sodium hydroxide (50 mL x 2), washed with water and dried over sodium sulphate under vacuum to remove the dichloromethane. The ¹H-NMR (DMSO-d6) spectrum of the product comprised: 4.73, d, 2H, OCH₂CH; 5.35, m, 2H, CHCH₂; 6.01, m, IH, CH; 6.85, d, IH, ArH; 7.20, d, IH, ArH; 7.43, t, IH, ArH; 7.51 - 7.59, m, 2H, ArH; 7.73, t, IH, ArH; 7.79, s, IH, ArH; 7.91, d, IH, ArH; 8.50, d, IH₅ ArH.

(iii) Synthesis of nanopigment

A solution of the dye monomer (0.15 g) in dichloromethane (5 mL) was added to a solution of ethylene glycol dimethacrylate (5 g) in ethanol (500 mL), after which nitrogen was bubbled through the reaction mixture for 15 min. Benzoyl peroxide (0.25 g) was then added and the reaction mixture was heated at 85 ⁰C under nitrogen for 16 hr without stirring. The solid precipitate was filtered, washed with dichloromethane thoroughly to remove the excess dye monomer and oven-dried to give the nanopigment (ca. 5 g) in quantitative yield.

Example 4

Figure 6 illustrates the synthesis of a nanopigment from the non-fluorescent dye monomer of formula (IV). The synthesis involved:

(i) Synthesis of precursor

A mixture of N-(6-hydroxyhexyl)-3-(4,4,5,5-tetramethyl-l,3,2-dioxaborolan-2- yl)benzamide (5 g), 4-iodoaniline (3 g) and potassium fluoride (3 g) in 95 % methanol (150 mL) was heated at 80 ⁰C for 5 hr in the presence of palladium acetate (150 mg). The reaction mixture was then dried to remove all the methanol and water, extracted with heptane and cooled to 0 ⁰C, after which the precipitated solid was filtered and dried to give the dye molecule precursor (2.5 g). The ¹H-NMR (CDCl₃) spectrum of the product comprises: 1.41, m, 4H; 1.55 - 1.66, m, 4H; 3.45, q, 2H; 3.62, t, 2H; 3.73, bs, 2H, NH₂; 6.29, bt, IH, NH; 6.74, dd, 2H, ArH; 7.42, m, 3H, ArH; 7.63, m, 2H, ArH; 7.92, s, IH, ArH.

(ii) Synthesis of dye molecule

A solution of sodium nitrite (1.0 g) in water (5 mL) was added to a suspension of the dye molecule precursor (2.5 g) in 5 M hydrochloric acid (10 mL) at 0 ⁰C. After 2 min, a solution of saturated naphthol (2.5 g) in 2 M sodium hydroxide (2.0 mL) was added drop- wise to the reaction mixture whilst stirring continuously at 0 ⁰C. The reaction mixture was then stirred continuously at room temperature for 4 hr, extracted with ethyl acetate and passed through a silica gel plug to give the dye molecule.

(iii) Synthesis of dye monomer

AUyI chloroformate (0.5 g) was added to a solution of the dye molecule (0.6 g) and pyridine (0.5 g) in dichloromethane (10 mL). After stirring at 0 ⁰C for 15 min, the reaction mixture was left at room temperature for 18 hr. The reaction mixture was then poured into 10 % hydrochloric acid (20 mL) and the solution was stirred. The dye monomer was extracted with dichloromethane (100 mL x 3), washed with 10 % sodium hydroxide (50 mL x 2), washed with water and dried over sodium sulphate under vacuum to remove the dichloromethane. The dye monomer was then re-dissolved in diethyl ether and passed through a silica gel plug, the first fraction collected giving 500 mg of the purified dye monomer. The ¹H-NMR (CDCl₃) spectrum of the product comprises: 1.44, m, 4H; 1.71, m, 4H; 3.50, m, 2H; 4.16, m, 2H; 4.61, m, 2H; 5.25, d, IH; 5.35, d, IH; 5.93, m, IH; 6.24, IH, NH; 6.87, d, IH, ArH; 7.43, t, IH, ArH; 7.50 - 7.61, m, 3H, ArH; 7.72, m, 5H; 7.81, d, 2H; 8.03, m, IH, ArH; 8.58, d, IH, ArH.

(iv) Synthesis of nanopigment

A solution of the dye monomer (50 mg) in dichloromethane (1 mL) was added to a solution of ethylene glycol dimethacrylate (1 g) in ethanol (100 mL), after which nitrogen was bubbled through the reaction mixture for 15 min. Benzoyl peroxide (50 mg) was then added and the reaction mixture was heated at 85 ⁰C under nitrogen for 16 hr without stirring. The solid precipitate was filtered, washed with dichloromethane thoroughly to remove the excess^'dye monomer and oven-dried to give the nanopigment (ca. 1 g) in quantitative yield.

Many modifications will be apparent to those skilled in the art without departing from the scope of the present invention.

Claims

THE CLAIMS:

1. A dye monomer of general formula (I),

A - X - R - O - C(O) - O - CH₂ - C(H) = CH₂ (I)

wherein A is a dye molecule and both X and R are optional linkers.

2. The dye monomer according to claim 1, wherein the optional linker R comprises one or more of C_3-I₀ alkylene, C₃.10 alkoxylene, C₆-io arylene, (C_6-io) aryl-(Ci.6) alkylene, (Ci_-6) alkyl-(C_6-io) arylene, Ci_-6 alkoxyl, C_6-I0 aryloxy and halogen, wherein the alkylene and/or arylene radicals are optionally substituted by hydroxyl.

3. The dye monomer according to claim 2, wherein the optional linker R is C_3-6 alkylene.

4. The dye monomer according to any one of claims 1 to 3, wherein the optional linker X comprises one or more of oxygen, sulphur, secondary amine, tertiary amine, secondary phosphine, tertiary phosphine, secondary carbon, tertiary carbon, quaternary carbon, secondary silicon, tertiary silicon and quaternary silicon.

5. The dye monomer according to claim 4, wherein the optional linker X is oxygen, secondary amine and/or tertiary amine.

6. The dye monomer according to any one of claims 1 to 5, wherein the dye molecule A comprises one or more of Fluorescent Brightener 184 (Registry Number: 7128- 64-5), Fluorescent Brightener 393 (Registry Number: 1533-45-5), Solvent Green 5 (Registry Number: 79869-59-3), Solvent Orange 7 (Registry Number: 23679-56-3), Solvent Orange 63 (Registry Number: 79869-59-3), Solvent Red 196 (Registry Number: 52372-36-8), Solvent Yellow 43 (Registry Number: 19125-99-6), Solvent Yellow 98 (Registry Number: 12671-74-8), Vat Red 1 (Registry Number: 2379-74- 0) and Vat Violet 3 (Registry Number: 2379-75-1).

7. The dye monomer according to claim 6, wherein the dye molecule A is Solvent Yellow 98 (Registry Number: 12671-74-8).

8. The dye monomer according to any one of claims 1 to 5, wherein the dye molecule A comprises one or more of Disperse Red 60 (Registry Number: 17418-58-5), Solvent Blue 4 (Registry Number: 6786-83-0), Solvent Blue 35 (Registry Number: 17354-14-2), Solvent Blue 36 (Registry Number: 14233-37-5), Solvent Red 1 (Registry Number: 1229-55-6), Solvent Red 24 (Registry Number: 85-83-6), Solvent Red 49 (Registry Number: 509-34-2), Solvent Yellow 14 (Registry Number: 842-07-9), Solvent Yellow 18 (Registry Number: 6407-78-9) and Solvent Yellow 56 (Registry Number: 2481-94-9).

9. The dye monomer according to claim 8, wherein the dye molecule A is Solvent Yellow 14 (Registry Number: 842-07-9).

10. A dye monomer of formula (II).

1 1. A dye monomer of formula (III).

12. A dye monomer of formula (IV).

(IV)

13. A dye monomer according to any one of claims 1, 10, 1 1 or 12 substantially as hereinbefore described with reference to the accompanying drawings and/or examples.

14. Particles comprising a copolymer of a dye monomer according to any one of claims 1 to 13 and an ethylenically unsaturated monomer.

15. The particles according to claim 14, wherein the ethylenically unsaturated monomer comprises one or more of ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate and neopentyl glycol dimethacrylate.

16. The particles according to claim 15, wherein the ethylenically unsaturated monomer is ethylene glycol dimethacrylate.

17. The particles according to any one of claims 14 to 16, wherein the particles comprise from about 0.01 wt% to about 30 wt% of dye monomer (based on the total weight of copolymer).

18. The particles according to claim 17, wherein the particles comprise from about 1 wt% to about 5 wt% of dye monomer (based on the total weight of copolymer).

19. The particles according to any one of claims 14 to 18, wherein the average particle diameter ranges from about 30 ran to about 80 nm.

20. The particles according to claim 19, wherein the average particle diameter is about 56 nm.

21. A method of producing particles, wherein the particles comprise a copolymer of a dye monomer according to any one of formulae (I), (II), (III) or (IV)

A - X - R - O - C(O) - O - CH₂ - C(H) = CH₂ (I)

(H)

(IV)

and an ethylenically unsaturated monomer, wherein the copolymer is produced via precipitation polymerisation.

22. A method according to claim 21 substantially as hereinbefore described with reference to the accompanying drawings and/or examples.

23. Particles when produced by the method according to claim 21 or 22.

24. Use of particles according to any one of claims 14 to 20 or 23 as nanopigments in paints, printing inks, plastics, textiles, glass, ceramics, jewellery and/or cosmetics.

25. Products comprising particles according to any one of claims 14 to 20 or 23 dispersed as nanopigments within a polymer matrix comprising one or more of polyolefin (polyethylene, polypropylene, polybutylene, ethylene propylene diene, ethylene vinyl acetate), styrenic polymer (polystyrene, high-impact polystyrene, styrene butadiene styrene, styrene ethylene butadiene styrene, styrene acrylonitrile, acrylonitrile butadiene styrene), acrylic polymer (polymethacrylate, polymethylmethacrylate, polyethylmethacrylate), polyester, polyurethane, polyvinyl chloride), biodegradable polymer (polylactic acid) and epoxy.