The present invention relates to a branched block copolymer, an onion micelle comprising the branched block copolymer, an inkjet ink comprising the branched block copolymer and an inkjet ink deposit comprising the branched block copolymer. Methods of providing the copolymer, onion micelle, inkjet ink and inkjet ink deposit are also described. The branched block copolymer is useful, in one embodiment, in the provision of a water-based inkjet ink having an improved drying time.

BACKGROUND OF THE INVENTION

Linear amphiphilic block copolymers and branched amphiphilic block copolymers are known in the art.

The self-assembly of linear amphiphilic block copolymers in block-selective solvents has been widely studied and aggregates with many interesting morphologies have been reported, including spherical micelles (e.g. Gao, Z.; Varshney, S. K.; Wong, S.; Eisenberg, A. Macromolecules 1994, 27 (26), 7923-7927), rods (e.g. Won, Y.-Y.; Davis, H. T.; Bates, F. S. Science 1999, 283 (5404 ), 960-963) vesicles (e.g. Discher, B. M.; Won, Y.-Y.; Ege, D. S.; Lee, J. C.-M.; Bates, F. S.; Discher, D. E.; Hammer, D. A. Science 1999, 284 (5417 ), 1 143-1 146) and more complex structures (Pochan, D. J.; Chen, Z.; Cui, H.; Hales, K.; Qi, K.; Wooley, K. L. Science 2004, 306 (5693), 94-97).

It is known that onion-like micelles have been formed during the self-assembly of linear block copolymers; for example the stepwise aggregation of AB and BC diblock copolymers in solution (e.g. Prochazka, K.; Martin, T. J.; Webber, S. E.; Munk, P. Macromolecules 1996, 29 (20), 6526-6530; and Talingting, M. R.; Munk, P.; Webber, S. E.; Tuzar, Z.

Macromolecules 1999, 32, 1593-1601 ). It is also understood that onion-like micelles can be formed from a single block copolymer through applying shear to Pluronic® systems, and later by solvent exchange processes using either double-hydrophobic or amphiphilic block copolymers.

Meanwhile, branched copolymers are subject to different mechanisms of self-assembly. This is because branching within copolymer molecules results in intra-molecular overall globular structures. Assembly of segments from different molecules is thus severely impaired. Therefore branched block copolymers tend to form unimolecular micelles in solution, that then undergo secondary aggregation into multimicellar aggregates. Such assembly processes in water are largely driven by the minimisation of interfacial energies. It is therefore understood in the art that branched polymers, encompassing dendritic, multi- branched and highly branched architectures, exhibit unique properties in terms of solution behaviour and rheology in comparison to linear analogues (see, for example, Magnusson, H.; Malmstrom, E.; Hult, A.; Johansson, M. Polymer 2002, 43 (2), 301 -306; and Zhu, X.; Zhou, Y.; Yan, D. J. Polym. Sci. Part B Polym. Phys. 201 1 , 49 (18), 1277-1286).

One object of the present invention is therefore to provide a branched amphiphilic block copolymer which is able to form self-assemblies useful in a variety of applications.

Such applications include the effective delivery of agents to desired locations, with high loading capacities and preferably other advantages. For example, one such application is inkjet printing.

Inkjet printing is widely used for the coding and marking of products on production lines. Typically, ink is jetted onto a surface such that ink is deposited onto a substrate without physical contact between the printing device and the surface. Two major systems for coding products are continuous and drop-on-demand inkjet printing.

Continuous inkjet printing systems normally employ inks that are based on volatile organic solvents such as methyl ethyl ketone and ethanol. Ink droplets are formed by vibrating a stream of ink ejected from a nozzle under pressure. These droplets are charged and then deflected with an electrostatic charging device to form a pattern on the substrate. If the ink droplets are not printed, the ink is recycled for later use. In contrast, in drop-on-demand printing systems, the inkjet inks are typically based upon water and glycols. These ink droplets are propelled from a nozzle by heat or by a pressure wave. The drop-on-demand printers have a plurality of nozzles, which eject drops when required.

Ideally, an ink has a number of desirable characteristics such as high optical density; short drying time of the ink on the substrate; good adhesion to the substrate; reliable droplet formation that is free of satellite droplets; indelibility or resistance of the ink to solvent or water after drying; good long-term storage stability; compatibility with the printing technology such that there is minimum corrosion of printer parts or nozzle clogging; and being easy to dispose of without creating hazardous waste. Most inks fail to satisfy every one of these characteristics and represent a best fit compromise to a subset of these goals.

Often, the inclusion of an ink component meant to satisfy one of the above characteristics can prevent another characteristic from being met.

Commonly the short drying time is achieved by the use of a volatile organic solvent as the carrier for a mixture of resins, colourants and other additives such as adhesion promoters, whereby the volatile organic compounds evaporates to leave a dried code. However, volatile organic chemicals present hazards in their use as they are typically highly flammable, and are often harmful to the environment. The use of water as a solvent would be a more environmentally friendly alternative were it not for the fact that most water based inks known in the art are not fast drying.

Water based inks having acceptable drying times on specially coated substrates are known. For example EP1284200 relates to an aqueous ink containing a metalized dye for use with a coated porous substrate, whilst US6773101 discloses a pigment-containing aqueous ink for printing onto a porous layer comprising alumina hydrate and a resin binder. In the context of industrial coding and marking, the use of special substrates is undesirable, as products are often printed directly and substrates are chosen not for their suitability for printing but for their ability to preserve or protect the product inside them.

It is one object of the present invention to overcome or address the problems of prior art polymers and/or inks or to at least provide commercially useful alternatives thereto.

Furthermore, one object of the present invention is to provide a water-based inkjet ink having improved or comparable adhesion to a variety of different substrates, including non- porous substrates.

Furthermore, one object of the present invention is to provide a water-based inkjet ink having a fast or comparable drying time on a variety of different substrates, including non- porous substrates.

It is an alternative and/or additional object to provide a method of providing an inkjet ink deposit on a variety of substrates with a faster or comparable drying time than known water based inkjet inks. SUMMARY OF THE INVENTION

In the first aspect of the present invention there is provided a branched block copolymer comprising a hydrophobic block and a hydrophilic block, the hydrophobic block comprising a poly (alkyl methacrylate), wherein the alkyl group comprises from 1 to 20 carbon atoms; and the hydrophilic block comprising poly (acrylic acid).

The present inventors have surprisingly found that this branched amphiphilic block copolymer is useful in inkjet inks, specifically water-based inkjet inks. Advantageously, the inkjet ink thereby provided displays good adhesion to substrates.

Furthermore, surprisingly, the present inventors have found that when the inkjet ink has a short or comparable drying time compared to other water-based inkjet inks and a short or comparable drying time compared to inkjet inks using a volatile organic solvent.

In a further aspect of the present invention there is provided an onion micelle having two or more layers, the two or more layers comprising the branched block copolymer as described herein.

In a further aspect of the present invention there is provided an inkjet ink comprising the branched block copolymer as described herein, a colourant, and water.

In a further aspect of the present invention there is provided an inkjet ink deposit comprising the branched block copolymer as described herein, and a colourant.

In a further aspect of the present invention there is provided a method of making a branched block copolymer comprising a hydrophobic block and a hydrophilic block, the method comprising:

(1 ) providing a hydrophobic monomer;

(2) polymerising the hydrophobic monomer a with a Reversible Addition- Fragmentation chain Transfer (RAFT) agent to provide a hydrophobic branched polymer having chain end groups;

(3) chain-extending the hydrophobic branched polymer having chain end groups with a hydrophilic monomer to provide the branched block copolymer comprising a hydrophobic block and a hydrophilic block; wherein the hydrophobic monomer an alkyl methacrylate, wherein the alkyl group comprises from 1 to 20 carbon atoms; and

wherein the hydrophilic monomer is acrylic acid.

In a further aspect of the present invention there is provided a method of making a dispersion of onion micelles, comprising:

(a) dissolving the branched block copolymer of any of claims 1 to 9, comprising a hydrophobic block and a hydrophilic block, in a first solvent to provide a first solution;

(b) adding a second solvent to the first solution to provide a second solution;

(c) evaporating the first solvent from the second solution to provide the dispersion of onion micelles;

wherein the hydrophilic block is soluble in both the first solvent and the second solvent and the hydrophobic block is more soluble in the first solvent than in the second solvent; or

wherein the hydrophobic block is soluble in both the first solvent and the second solvent and the hydrophilic block is more soluble in the first solvent than in the second solvent.

In a further aspect of the present invention there is provided a method of making an inkjet ink, comprising

(a) dissolving the branched block copolymer of any of claims 1 to 9, comprising a hydrophobic block and a hydrophilic block, in a first solvent to provide a first solution;

(b) adding a second solvent and a colourant to the first solution to provide a second solution;

(c) evaporating the first solvent from the second solution to provide the inkjet ink; wherein the hydrophilic block is soluble in both the first solvent and the second solvent, the hydrophobic block is more soluble in the first solvent than in the second solvent; and the colourant is more soluble in the first solvent than in the second solvent; and

wherein the second solvent is water.

In a further aspect of the present invention there is provided a method of making an inkjet ink, comprising (a) dissolving the branched block copolymer of any of claims 1 to 9, comprising a hydrophobic block and a hydrophilic block, and a colourant in a first solvent to provide a first solution;

(b) adding a second solvent to the first solution to provide a second solution;

(c) evaporating the first solvent from the second solution to provide the inkjet ink; wherein the hydrophilic block is soluble in both the first solvent and the second solvent, the hydrophobic block is more soluble in the first solvent than in the second solvent; and the colourant is more soluble in the second solvent than in the first solvent; and

wherein the second solvent is water.

In a further aspect of the present invention there is provided a method of making an inkjet ink, comprising adding the branched block copolymer as described herein and a colourant to water.

In a further aspect of the present invention, there is provided a method of providing an inkjet ink deposit, comprising depositing the inkjet ink as described herein onto a substrate; and exposing the deposited inkjet ink to an energy source to form the inkjet ink deposit.

Other preferred embodiments of the products and methods according to the invention appear throughout the specification and in particular in the examples.

DETAILED DESCRIPTION OF THE INVENTION

Unless otherwise defined herein, scientific and technical terms used in connection with the present invention shall have the meanings that are commonly understood by those of ordinary skill in the art. The meaning and scope of the terms should be clear, however, in the event of any latent ambiguity, definitions provided herein take precedent over any dictionary or extrinsic definition.

As used herein, the term 'branched polymer or copolymer' means a polymer or copolymer having at least one branch point intermediate between the boundary units.

As used herein, the term 'onion micelle' means an organised auto-assembly having a layered structure composed of amphiphilic macromolecules. Short drying time is typically achieved for an inkjet ink through the use of a volatile organic solvent as the carrier for a mixture of resins, colourants and other additives such as adhesion promoters, whereby, when the ink is printed, the volatile organic compounds evaporate to leave a dried deposit. However, volatile organic chemicals present hazards in their use as they are typically highly flammable, and are often harmful to the environment. While the use of water as a solvent would be more environmentally friendly, water based inks in the art for use on various substrates, including non-porous substrates, are not fast drying. Further factors are discussed above.

To address these problems, the present inventors have surprisingly found that using a branched block copolymer, comprising a hydrophobic block and a hydrophilic block, in the formulation of a water-based inkjet ink provides an environmentally friendly ink that is fast drying on various substrates, including non-porous substrates.

The present inventors have surprisingly found that this branched amphiphilic block copolymer is useful in inkjet inks, specifically water-based inkjet inks. Advantageously, the inkjet ink thereby provided displays good adhesion and has a short or comparable drying time compared to other water-based inkjet inks and a short or comparable drying time compared to inkjet inks using a volatile organic solvent.

Without wishing to be bound by theory, it is thought that the branched block copolymer of the present invention forms onion micelles. These onion micelles are thought to be formed by the successive alignment of hydrophobic and hydrophilic parts of the branched block copolymer to form a generally spherical structure comprising layers, similar in appearance to an onion. In inkjet ink applications, it is thought that a colourant may be located between the layers in either a hydrophilic or hydrophobic environment, depending on the colourant's structure.

The present invention will now be further described. In the following passages different aspects of the invention are defined in more detail. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

In one embodiment of the present invention, there is provided a branched block copolymer comprising a hydrophobic block and a hydrophilic block, the hydrophobic block comprising a poly (alkyl methacrylate), wherein the alkyl group comprises from 1 to 20 carbon atoms; and the hydrophilic block comprising poly (acrylic acid).

Preferably, the molar ratio of the poly (alkyl methacrylate) to the poly (acrylic acid) in the branched block copolymer is about 0.5:1 to about 2:1 . More preferably, the molar ratio is about 0.6:1 to about 1 .9:1 , or about 0.6:1 to about 1 .8:1 , or about 0.6:1 to about 1 .7:1 . More preferably still, the molar ratio is about 0.7:1 to about 1 .6:1 .

The molar ratio of the poly (alkyl methacrylate) to the poly (acrylic acid) in the branched block copolymer is measured by ¹ H NMR.

Preferably, the alkyl group of the poly (alkyl methacrylate) comprises from 1 to 18 carbon atoms, or from 1 to 15 carbon atoms, or from 1 to 12 carbon atoms, or from 1 to 10 carbon atoms, or from 1 to 8 carbon atoms, or from 1 to 6 carbon atoms, or from 1 to 5 carbon atoms. More preferably, the alkyl group of the poly (alkyl methacrylate) comprises from 1 to 4 carbon atoms.

Alternatively, the alkyl group comprises 2 to 12 carbon atoms, or 2 to 10 carbon atoms, or 2 to 8 carbon atoms, or 1 to 6 carbon atoms, or 2 to 5 carbon atoms, or 3 to 4 carbon atoms.

Alternatively, preferably, the poly (alkyl methacrylate) is selected from poly (methyl methacrylate), poly (butyl methacrylate) and poly (lauryl methacrylate). Most preferably, the poly (alkyl methacrylate) is poly (butyl methacrylate).

Preferably, when the poly (alkyl methacrylate) is poly (methyl methacrylate), the molar ratio of the poly (alkyl methacrylate) to the poly (acrylic acid) in the branched block copolymer is about 0.8:1 to about 1 .5:1 , more preferably about 0.9:1 to about 1 .3:1 , or about 1 :1 to about 1 .2:1 .

Preferably, when the poly (alkyl methacrylate) is poly (butyl methacrylate), the molar ratio of the poly (alkyl methacrylate) to the poly (acrylic acid) in the branched block copolymer is about 0.8:1 to about 1 .8:1 , or about 0.9:1 to about 1 .7:1 , or about 1 :1 to about 1 .7:1 , more preferably about 1 .2:1 to about 1 .7:1 , most preferably about 1 .3:1 to about 1 .6:1 .

Preferably, when the poly (alkyl methacrylate) is poly (lauryl methacrylate), the molar ratio of the poly (alkyl methacrylate) to the poly (acrylic acid) in the branched block copolymer is about 0.4:1 to about 1 :1 , more preferably about 0.5:1 to about 0.9:1 , or about 0.6:1 to about 0.8:1 .

Preferably, the degree of branching (DB) in the branched block copolymer is at least about 0.05, or at least about 0.06, or at least about 0.07, or at least about 0.08, or at least about 0.09. More preferably, the degree of branching (DB) in the branched block copolymer is at least about 0.1 , or at least about 0.1 1 .

Alternatively, preferably, the degree of branching (DB) in the branched block copolymer is about 0.05 to 0.5, or about 0.05 to about 0.4, or about 0.1 to about 0.3. Alternatively, preferably, the degree of branching (DB) in the branched block copolymer is about 0.05 to about 0.25, or about 0.05 to about 0.2, or about 0.05 to about 0.15, or about 0.08 to about 0.15.

Preferably, the branched block copolymer is a highly branched copolymer.

Preferably, the branched block copolymer is not a dendritic or multi-branched copolymer.

Preferably, the branched block copolymer has a dispersity (D) of about 1 to about 15, or about 2 to about 12, or about 3 to about 10. More preferably, the branched block copolymer has a dispersity (D) of about 3.5 to about 9.50. Alternatively, preferably, the branched block copolymer has a dispersity (D) of about 4 to about 10, or about 5 to about 10, or about 6 to about 10, or about 7 to about 10, or about 8 to about 10, more preferably about 9 to about 10.

Preferably, the poly (alkyl methacrylate) comprises about 20 to about 100 alkyl

methacrylate monomers. More preferably, the poly (alkyl methacrylate) comprises about 25 to about 80 alkyl methacrylate monomers, or about 25 to about 70 alkyl methacrylate monomers, or about 25 to about 60 alkyl methacrylate monomers, most preferably about 30 to about 50 alkyl methacrylate monomers.

Preferably, the poly (acrylic acid) comprises about 10 to about 200 acrylic acid monomers. More preferably, the poly (acrylic acid) comprises about 20 to about 100 acrylic acid monomers. Most preferably the poly (acrylic acid) comprises about 20 to about 40 acrylic acid monomers. In one embodiment of the present invention, there is provided an onion micelle having two or more layers, the two or more layers comprising the branched block copolymer of any of the preceding claims.

Preferably, the two or more layers of the onion micelle are formed from the branched block copolymer.

Preferably, the onion micelle has three or more layers, or four or more layers, or five or more layers, or six or more layers, or seven or more layers. More preferably, the onion micelle has at least eight layers. More preferably still, the onion micelle has at least nine layers, or at least ten layers.

Alternatively, preferably, the onion micelle has about 2 to about 20 layers, or about 3 to about 19 layers, or about 4 to about 18 layers, or about 5 to about 17 layers, or from about 6 to about 16 layers, or about 7 to about 15 layers. More preferably, the onion micelle has about 8 to about 14 layers. More preferably still, the onion micelle has about 9 to about 13 layers, or about 10 to about 12 layers.

Without wishing to be bound by theory, in some applications, the more layers an onion micelle has, the higher loading capacity it may exhibit (for example, the larger the volume and/or amount of agent(s) it may carry. In an inkjet ink application, the agent may be a dye, for example).

Preferably, the onion micelle has a diameter of from about 50 nm to about 300 nm, as determined by PALS. More preferably, the onion micelle has a diameter of from about 60 nm to about 250 nm, or from about 70 nm to about 225 nm, or from about 80 nm to about 200 nm, as determined by PALS.

In one embodiment of the present invention, there is provided an inkjet ink comprising the branched block copolymer as described herein, a colourant, and water.

Preferably, the branched block copolymer in the inkjet ink is in the form of an onion micelle having two or more layers. More preferably, the branched block copolymer in the inkjet ink is in the form of an onion micelle having three or more layers, or four or more layers, or five or more layers, or six or more layers, or seven or more layers. Most preferably, the branched block copolymer in the inkjet ink is in the form of an onion micelle having eight or more layers, or nine or more layers, or ten or more layers.

Alternatively, preferably, the branched block copolymer in the inkjet ink is in the form of an onion micelle having about 2 to about 20 layers, or about 3 to about 19 layers, or about 4 to about 18 layers, or about 5 to about 17 layers, or from about 6 to about 16 layers, or about 7 to about 15 layers. More preferably, the branched block copolymer in the inkjet ink is in the form of an onion micelle having about 8 to about 14 layers. More preferably still, the branched block copolymer in the inkjet ink is in the form of an onion micelle having about 9 to about 13 layers, or about 10 to about 12 layers.

Preferably, the colourant is at least partially located within the onion micelle. More preferably, the colourant is located entirely within the onion micelle.

Preferably, when the colourant is at least partially located within the onion micelle, the colourant is at least partially located between two or more layers of the onion micelle, i.e. between two or more layers of the block copolymer. More preferably, when the colourant is located entirely within the onion micelle, the colourant is located entirely between two or more layers of the onion micelle, i.e. between two or more layers of the block copolymer, and there is no colourant present outside the onion micelle, e.g. on the outer layer of the micelle, or elsewhere in any solution/dispersion containing the onion micelle.

This may be advantageous as it may assist in using a solvent to carry an agent, e.g. a dye, in which the agent would otherwise be insoluble or less soluble.

Preferably, the inkjet ink further comprises one or more of the group consisting of an adhesion promoter, a humectant and a plasticiser. Alternatively, preferably, the inkjet ink further comprises two or more of the group consisting of an adhesion promoter, a humectant and a plasticiser. Alternatively, preferably, the inkjet ink further comprises other additives such as an adhesion promoter, a humectant and a plasticiser.

Suitable adhesion promoters are known in the art... Any suitable adhesion promoter known in the art can be used. For example, adhesion promoters such as rosins, rosin esters (both modified and unmodified materials), terpenes (modified and unmodified) and terpene phenolic resins may be used. Suitable humectants are known in the art. Humectants are typically hydrophilic solvents having high boiling points, preferably above 100 °C, and more preferably from 150 °C to 250 °C. Any suitable humectant known in the art can be used. Examples of suitable humectants include glycols such as ethylene glycol, propylene glycol, glycerin, diglycerin, and diethylene glycol; glycol ethers such as ethylene glycol dimethyl ether, ethylene glycol diethylether, propyleneglycol methylether, cellosolve, diethylene glycol monoethylether (Carbitol), diethylene glycol dimethylether, and diethylene glycol diethylether; dialkyl sulfoxides such as dimethyl sulfoxide, and other solvents such as sulfolane and N- methylpyrrolidone. The humectant may be present in an amount of from about 0 to about 10 % by weight of the ink, or from about 0.1 to about 8 % by weight of the ink, and preferably from about 1 to about 5% by weight of the ink.

Suitable plasticisers are known in the art. Any suitable plasticiser known in the art can be used. For example, plasticisers may be selected from the adipate, citrate or epoxy based families, and provided at a concentration of about 0.1 to about 2 % by weight of the ink.

Preferably the ionic strength of the inkjet ink is about 1 x 10 ^~5 M to about 10 x 10 ^~5 M, more preferably about 3 x 10 ^~5 M to about 9 x 10 ^~5 M.

In one embodiment of the present invention, there is provided an inkjet ink deposit comprising the branched block copolymer as described herein, and a colourant.

In one embodiment of the present invention, there is provided a method (I) of making a branched block copolymer comprising a hydrophobic block and a hydrophilic block, the method comprising:

(1 ) providing a hydrophobic monomer;

(2) polymerising the hydrophobic monomer a with a Reversible Addition- Fragmentation chain Transfer (RAFT) agent to provide a hydrophobic branched polymer having chain end groups;

(3) chain-extending the hydrophobic branched polymer having chain end groups with a hydrophilic monomer to provide the branched block copolymer comprising a hydrophobic block and a hydrophilic block;

wherein the hydrophobic monomer an alkyl methacrylate, wherein the alkyl group comprises from 1 to 20 carbon atoms; and

wherein the hydrophilic monomer is acrylic acid. Reversible Addition-Fragmentation chain Transfer (RAFT) polymerisation is known in the art. In particular, chain (growth) polymerisation is propagated by radicals that are deactivated reversibly, bringing them into active/dormant equilibria of which there might be more than one.

Preferably, the RAFT agent comprises 4-vinylbenzyl-1 -pyrrole carbodithioate and the chain end groups are pyrrole dithioester chain end groups.

Preferably, step (2) is carried out at a temperature of about 50 °C to about 70 °C. More preferably, step (2) is carried out at a temperature of about 55 °C to about 65 °C, or from about 58 °C to about 62 °C.

Preferably, step (3) is carried out at a temperature of about 50 °C to about 70 °C. More preferably, step (3) is carried out at a temperature of about 55 °C to about 65 °C, or from about 58 °C to about 62 °C.

A reaction scheme exemplifying method (I) is shown in Figure 1 .

In one embodiment of the present invention, there is provided a method (II) of making a dispersion of onion micelles, comprising:

(a) dissolving the branched block copolymer as described herein, comprising a hydrophobic block and a hydrophilic block, in a first solvent to provide a first solution;

(b) adding a second solvent to the first solution to provide a second solution;

(c) evaporating the first solvent from the second solution to provide the dispersion of onion micelles;

wherein the hydrophilic block is soluble in both the first solvent and the second solvent and the hydrophobic block is more soluble in the first solvent than in the second solvent; or

wherein the hydrophobic block is soluble in both the first solvent and the second solvent and the hydrophilic block is more soluble in the first solvent than in the second solvent.

Preferably, in method (II), the hydrophilic block is soluble in both the first solvent and the second solvent and the hydrophobic block is more soluble in the first solvent than in the second solvent. Preferably, in method (II), the second solvent is water. More preferably, in method (II), the second solvent is deionised water.

Preferably the dispersion is a unimodal or a bimodal dispersion of onion micelles. In a unimodal dispersion, the micelles are one population of particles having the same or a similar diameter. In a bimodal dispersion, the dispersion comprises two populations of particles, the two particles exhibiting a different average particle size.

In one preferable embodiment, the dispersion is a bimodal dispersion of onion micelles comprising a first population of micelles having a diameter of about 60 nm to about 100 nm, as determined by PALS, and a second population of micelles having a diameter of about 180 to 230 nm, as determined by PALS. More preferably, the dispersion is a bimodal dispersion of onion micelles comprising a first population of micelles having a diameter of about 70 nm to about 90 nm, as determined by PALS, and a second population of micelles having a diameter of about 190 to 220 nm, as determined by PALS.

Preferably the ionic strength of the dispersion is about 1 x 10 ^~5 M to about 10 x 10 ^~5 M, more preferably about 3 x 10 ^"5 M to about 9 x 10 ^"5 M.

In one embodiment of the present invention, there is provided a method (III) of making an inkjet ink, comprising

(a) dissolving the branched block copolymer as described herein, comprising a hydrophobic block and a hydrophilic block, in a first solvent to provide a first solution;

(b) adding a second solvent and a colourant to the first solution to provide a second solution;

(c) evaporating the first solvent from the second solution to provide the inkjet ink; wherein the hydrophilic block is soluble in both the first solvent and the second solvent, the hydrophobic block is more soluble in the first solvent than in the second solvent; and the colourant is more soluble in the first solvent than in the second solvent; and

wherein the second solvent is water.

In one embodiment of the present invention, there is provided a method (IV) of making an inkjet ink, comprising (a) dissolving the branched block copolymer as described herein, comprising a hydrophobic block and a hydrophilic block, and a colourant in a first solvent to provide a first solution;

(b) adding a second solvent to the first solution to provide a second solution;

(c) evaporating the first solvent from the second solution to provide the inkjet ink; wherein the hydrophilic block is soluble in both the first solvent and the second solvent, the hydrophobic block is more soluble in the first solvent than in the second solvent; and the colourant is more soluble in the second solvent than in the first solvent; and

wherein the second solvent is water.

The colourant may comprise a dye or pigment, for example a fine pigment dispersion.

In one embodiment, the colourant comprises a dye. Any dye which is soluble in the carrier solvent and which is compatible with the other raw materials may be used. Mixtures of dyes may be used to achieve the desired colour. Preferably, the colourant comprises one or more dyes selected from the group consisting of rhodamine B, Solvent Black 3, Solvent Black 27, Solvent Black 28, Solvent Black 29, Solvent Black 35, Solvent red 8, Solvent red 18, Solvent red 1 18, Solvent red 122, Solvent red 125, Solvent red 132, Solvent blue 5, Solvent blue 44, Solvent blue 45, Solvent blue 67, Solvent blue 70, Acid yellow 42, Solvent yellow 29, Solvent yellow 79, Solvent yellow 82, Solvent yellow 83:1 .

In an alternative embodiment, the colourant comprises a pigment. Preferably, the colourant comprises one or more pigments selected from the group consisting of titanium dioxide, carbon black, CI Pigment Red 176, CI Pigment Red 254, CI Pigment Red 255, CI Pigment Red 272, CI Pigment Red 254, CI Pigment Orange 64, CI Pigment Orange 73, CI Pigment Yellow 83, CI Pigment Yellow 138, CI Pigment Yellow 139, CI Pigment Yellow 151 , CI Pigment Yellow 154, CI Pigment Blue 15:2, CI Pigment Blue 15:3, CI Pigment Blue 15:4, CI Pigment Green 3, CI Pigment Violet 23 and CI Pigment Violet 37. When the colourant comprises a pigment, the pigment concentration is preferably about 2 - 25 wt % by weight of the ink, and the pigment preferably has an average particle size of less than 1 μηι.

In an alternative embodiment, the colourant comprises one or more of the above dyes and one or more of the above pigments. In each of methods (II), (III) and (IV), preferably the pH of the second solution is about 3 to about 8. More preferably, the pH of the second solution is about 4 to about 7. More preferably still, the pH of the second solution is about 4.5 to about 6.5, or about 5 to about 6, or about 5.5 to about 6.

In each of methods (II), (III) and (IV), preferably the ionic strength of the first solution is about 1 x 10 ^"5 M to about 10 x 10 ^"5 M, more preferably about 3 x 10 ^"5 M to about 9 x 10 ^"5 M.

In each of methods (II), (III) and (IV), preferably the ionic strength of the second solution is about 1 x 10 ^"5 M to about 10 x 10 ^"5 M, more preferably about 3 x 10 ^"5 M to about 9 x 10 ^"5 M.

In each of methods (II), (III) and (IV), preferably the ionic strength of the inkjet ink is about 1 x 10 ^"5 M to about 10 x 10 ^"5 M, more preferably about 3 x 10 ^"5 M to about 9 x 10 ^"5 M.

Preferably, the ionic strengths of the first solution, the second solution and the inkjet ink are maintained as constant (i.e. the same).

In each of methods (II), (III) and (IV), preferably the polymer concentration in the first solution is about 0.1 to about 1 .0 w/v %. More preferably, the polymer concentration in the first solution is about 0.2 to about 0.9 w/v %, or about 0.3 to about 0.8 w/v %, or about 0.4 to about 0.7 w/v %. More preferably still, the polymer concentration in the first solution is about 0.4 to about 0.6 w/v %, or about 0.45 to about 0.55 w/v %.

In each of methods (II), (III) and (IV), preferably the polymer concentration in the second solution is about 0.1 to about 1 .0 w/v %. More preferably, the polymer concentration in the second solution is about 0.2 to about 0.9 w/v %, or about 0.3 to about 0.8 w/v %, or about 0.4 to about 0.7 w/v %. More preferably still, the polymer concentration in the second solution is about 0.4 to about 0.6 w/v %, or about 0.45 to about 0.55 w/v %.

In each of methods (II), (III) and (IV), preferably, the first solvent is an organic solvent. More preferably, the first solvent is an organic solvent which is miscible with water.

Organic solvents which are miscible with water are known in the art. More preferably still, the first solvent is selected from the group consisting of tetrahydrofuran (THF), ethanol and dioxane. Most preferably, the first solvent is tetrahydrofuran (THF).

In each of methods (III) and (IV), the second solvent is preferably deionised water. In each of methods (II), (III) and (IV), preferably, the second solvent is added dropwise.

In each of methods (II), (III) and (IV), preferably, the first solvent is evaporated at a temperature of about 15 °C to about 25 °C. More preferably, the first solvent is evaporated at a temperature of about 17 °C to about 23 °C, or about 18 °C to about 22 °C.

In one embodiment of the present invention, there is provided a method (V) of making an inkjet ink, comprising adding the branched block copolymer as described herein and a colourant to water, preferably deionised water.

Preferably, each of methods (III), (IV) and (V) further comprises adding to the inkjet ink one or more of the group consisting of an adhesion promoter, a humectant and a plasticiser. Alternatively, preferably, each of methods (III), (IV) and (V) further comprises adding to the inkjet ink two or more of the group consisting of an adhesion promoter, a humectant and a plasticiser. Alternatively, preferably, each of methods (III), (IV) and (V) further comprises adding to the inkjet ink an adhesion promoter, a humectant and a plasticiser. Suitable adhesion promoters, humectants and plasticisers are listed above.

In one embodiment of the present invention, there is provided a method (VI) of providing an inkjet ink deposit, comprising depositing the inkjet ink as described herein onto a substrate; and exposing the deposited inkjet ink to an energy source to form the inkjet ink deposit.

Preferably, the energy source is a light source or a heat source. Most preferably, the energy source is a light source.

Preferably, the substrate is a non-porous substrate.

Preferably, the substrate comprises a polymer, preferably a non-porous polymer. More preferably, the substrate comprises polypropylene and/or high density polyethylene.

Without wishing to be bound by theory, it is thought that when the inkjet ink is exposed to an energy source, the colourant and/or the onion micelle is heated, which causes the onion micelle to unravel. As a result, the hydrophilic and hydrophobic parts become less soluble in the water and bond to the substrate, allowing the water to essentially run free and evaporate, leaving behind the colourant and the branched block copolymer as a fixed inkjet ink deposit.

When introducing elements of the present disclosure or the preferred embodiments(s) thereof, the articles "a", "an", "the" and "said" are intended to mean that there are one or more of the elements. The terms "comprising", "including" and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements.

The foregoing detailed description has been provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art, and remain within the scope of the appended claims and their equivalents.

These and other aspects of the invention will now be described with reference to the accompanying Figures, in which:

Figure 1 : shows the synthesis of branched PnMA-b-PAA Block Copolymers with Pyrrole Chain Ends in a Two-Step RAFT-SCVP Polymerisation

Figure 2: is a comparison of molecular weight distributions obtained from GPC: A) branched PMMA (dashed line) and branched PMMA-b-PAA (solid line), B) branched PBMA (dashed line) and branched PBMA-b-PAA (solid line) and C) branched PLMA (dashed line) and branched PLMA-b-PAA (solid line).

Figure 3: shows TEM micrographs of dispersions of branched block PnMA-b-PAA copolymers in water, stained with uranyl formate: A branched PMMA-b-PAA, B branched PBMA-b-PAA and C branched PLMA-b-PAA.

Figure 4: shows SEM images of the spheres formed by branched PBMA-b-PAA. A TEM grid with adsorbed branched PBMA-b-PAA, stained with uranyl formate, was sputter- coated with Au and imaged by SEM.

Figure 5: shows TEM images of onion micelles formed from branched PBMA-b-PAA dispersed in water A) immediately following preparation and B) after 5 weeks storage at ambient conditions. Figure 6: provides representative TEM images of copolymers A: branched PMMA-b-PAA, B: branched PBMA-b-PAA and C: branched PLMA-b-PAA self-assembled in water and D: branched PMMA-b-PAA, E: branched PBMA-b-PAA and F: branched PLMA-b-PAA following annealing at 45 °C for 12 hours. Samples were stained with uranyl formate prior to imaging. Inset text displays the results of particle sizing measurements.

Figure 7: provides representative TEM images of branched PBMA-b-PAA copolymers with varying ratios of BMA to AA self-assembled in water: A) 0.5:1 .0, B) 0.75:1 .0, C) 1 .0:1 .0, D) 1 .5:1 .0, E) 2.0:1 .0. Samples were stained with uranyl formate prior to imaging.

The following non-limiting examples further illustrate the present invention.

EXAMPLES

Experimental

Materials

Sodium hydride (60% in mineral oil dispersion, Aldrich), carbon disulfide (99+%, Aldrich), 4- vinylbenzyl chloride (90%, Aldrich), 4,4'-azobis (4-cyanovaleric acid) (ACVA,≥98%, Aldrich), methanol (Fisher), diethyl ether (Fisher), hexane (Fisher), 1 ,4-dioxane (Aldrich, sure-seal, anhydrous 99.8%) and petroleum ether 40-60 (Fisher) were used as purchased. Pyrrole (99%, Aldrich) was distilled over calcium hydride (95%, Aldrich) under reduced pressure to give a colourless liquid. Acrylic acid (99%, Aldrich) was distilled under reduced pressure to remove inhibitors. Dimethyl formamide (DMF) was obtained from the Grubb's dry solvent system. MEHQ inhibitors were removed from methyl methacrylate (99%, Aldrich), butyl methacrylate (99%, Aldrich) and lauryl methacrylate (96%, Lancaster) by running through a column packed with inhibitor removing beads (Aldrich). Deionized water was used in all experiments.

Synthesis of 4-Vinylbenzyl-1 -pyrrolecarbodithioate

Pyrrole (5.0 g, 74.5 mmol) and DMF (10 ml) were added dropwise over 30 minutes to a rapidly stirring suspension of sodium hydride (2.98 g, 124.2 mmol) in DMF (80 ml) to produce a yellow foam. The solution was stirred at room temperature for 30 minutes then cooled to 0°C using an ice bath. Carbon disulfide (5.68 g, 4.50 ml, 74.6 mmol) and DMF (10 ml) were added dropwise over 10 minutes to create a dark red solution. This was stirred at room temperature for 30 minutes and then cooled to 0 ^* Ό. 4-vinylbenzyl chloride (1 1 .37 g, 10.50 ml, 74.5 mmol) and DMF (10 ml) were then added dropwise over 20 minutes. The brown solution was stirred overnight at room temperature. The solution product was placed in a separating funnel with diethyl ether (80 ml) and distilled water (80 ml). The organic layer was recovered and the aqueous layer was extracted with diethyl ether (3 x 160 ml). The organic extracts were combined and dried over magnesium sulfate, before gravity filtration. The solvent was then removed by rotary evaporation to give a brown oil. The oil was purified by flash chromatography using 100% hexane as the eluent, then the solvent was removed by rotary evaporation to give a bright yellow oil (5.93 g).

RAFT Polymerization of Methacrylates using 4-Vinylbenzyl-1 -pyrrolecarbodithioate to form Branched PnMA Macro-Chain Transfer Agent

The procedure for the synthesis of branched PMMA was as follows: MMA (1 g, 9.99 mmol), 4-vinylbenzyl-1 -pyrrole carbodithioate (0.0852g, 0.329 mmol), ACVA (0.0184 g, 6.6 μηιοΙ, CTA/ACVA molar ratio = 5.0) and dioxane (10 g, 10% w/w) were mixed together until the solid initiator had dissolved. The resulting solution was transferred into a glass ampoule and freeze-pump-thawed on a high vacuum line (10-4 mbar, three cycles) then flame- sealed and heated in a water bath set 60 °C by a thermostat for up to 36 h to undergo polymerization. Products were precipitated into rapidly stirring methanol. The methanol was removed by decanting and the polymer was dried in vacuo at room temperature for 24 h. The precipitation procedure was repeated once more to remove any traces of residual monomer, giving polymer products as yellow polymeric solids.

Synthesis of Branched PnMA-b-PAA Block Copolymers via RAFT Polymerization of PnMA Macro-Chain Transfer Agent and Acrylic Acid

The procedure for the synthesis of branched PMMA-b-PAA was as follows: branched PMMA macro-CTA (0.4 g) was dissolved in dioxane then AA (0.4 g, 5.55 mmol) and ACVA (0.0022 g, 8 μηιοΙ, CTA/ACVA molar ratio = 5.0) and dioxane (7.2 g, 10% w/w) were mixed together until the solid initiator had dissolved. The resulting solution was transferred into a glass ampoule and freeze-pump-thawed on a high vacuum line (10-4 mbar, three cycles) then flame-sealed and heated in a water bath set 60 °C by a thermostat for up to 36 h to undergo polymerisation. Products were then precipitated into rapidly stirring ice cold petroleum ether 40-60 °C. The petroleum ether was removed by decanting and the polymer was dried in vacuo at room temperature for 24 h. The procedure was repeated once more to remove any traces of residual monomer, giving polymer products as pale yellow powdery solids. Preparation of Copolymer Dispersions in Water

Dispersions were prepared using a solvent switch method. Copolymer was dissolved in THF at a concentration of 5 mg ml-1 (0.5% w/v) and stirred overnight. A Razel R-99 syringe pump was used to add an equal volume of ultrapure H20 at a constant rate of 0.1 ml min- 1 . The dispersion was then stirred uncovered for 3 h to allow the THF to evaporate. Study by 1 H NMR showed that no residual THF was present after this time.

Annealing of Copolymer Dispersions

Copolymer dispersions prepared as above were sealed in sample tubes to prevent evaporation and placed into an oil bath set to 45 °C whilst stirring for 12 h.

Characterisation (Test methods)

1 H NMR Spectroscopy

All NMR spectra were recorded at ambient temperature on a Bruker AV-400 at 400 MHz

(64 scans averaged per spectrum). Samples of mass 20-40 mg were dissolved in CDCI ₃

(4-vinylbenzyl-1 -pyrrole carbodithioate, branched PnMA) or 1 :1 CDCI ₃ :d-DMSO (branched

PnMA-b-AA), filtered and placed in 7 mm NMR tubes.

Mass Spectroscopy Electron Ionization (El)

MS was carried out using a VG Autospec Mass Spectrometer.

Gel Permeation Chromatography

Average molecular weights and molecular weight distributions were measured relative to polystyrene standards by gel permeation chromatography (GPC) with PL gel mixed-B (10 μηι particle size, 100-10 ⁶ A pore size, effective MW range 10 ³ -10 ⁶ , 3x 30 cm + guard columns) (Polymer Laboratories, UK) on a refractive index detector. The mobile phase was THF (GPC grade) set at a flow rate of 1 ml min ^"1 . Sample concentration used was 2 mg ml ^"1 , filtered before injection. Samples were injected using a Gilson 234 auto injector. Samples containing PAA were methylated before analysis using trimethylsilyldiazomethane to prevent column interaction, following standard procedure.

Particle Size and Zeta Potential Measurements

Particle (e.g. onion micelle) diameters were calculated using Phase Analysis Light

Scattering (PALS). Such particle size (diameter) analysis was carried out on a Brookhaven Instruments Corporation ZetaPALS Zeta Potential Analyzer with the 90Plus/BI-MAS Multi Angle Particle Sizing Option. 15 μΙ of copolymer dispersion was added to 3 ml of 10 mmol KCI solution, sonicated for 20 seconds, and filtered through a 1 μηι filter. Measurements were made at 25 °C. 10 analysis runs were made in triplicate for each sample. For zeta potential measurement, 15 μΙ of copolymer dispersion was added to 1.5 ml of 1 mmol KCI solution. Measurements were made at 25 °C in triplicate for each sample in 5 cycles of 2 minute runs.

Small Angle Neutron Scattering

SANS measurements were performed at the Rutherford Appleton Laboratory (ISIS

Spallation Neutron Source, Didcot, UK) using the fixed-geometry, time-of-flight LOQ spectrometer. The LOQ instrument uses incident neutron wavelengths from 2.2 to 10.0 A, which covers a scattering wavevector, Q, range of 0.009 to 1 .3 A ^"1 at a sample-detector distance of 4.1 m. Polymer samples were prepared as 0.5% solutions, 5 mg of polymer in 1 ml D ₂ 0. All samples were transferred to 2 mm path-length quartz Hellma cells. The temperature was controlled by using circulating fluid baths to maintain constant temperature at 25 °C. Scattering intensities were reduced and normalized using the standard procedures on MantidPlot software to obtain the differential scattering cross section, d∑/dQ, in absolute units (cm ¹ ), which is referred to here as l(Q).

Transmission Electron Microscopy

TEM imaging was carried out using a Philips CM 100 instrument operating at 100 kV. Polymer samples dispersed in ultrapure H ₂ 0 as described above were prepared for TEM by adsorbing a 5 μΙ drop of sample onto a glow-discharged carbon-coated grid for 1 min. The grid was blotted, washed in a drop of distilled water and blotted again. The grid was then washed in a drop of uranyl formate, blotted and then negatively stained by holding the grid in a drop of uranyl formate for 20 s before blotting. Particle diameters were obtained using Image J analysis software to measure enough particles to represent a statistically significant sample; where possible at least 100 particles were required.

Scanning Electron Microscopy

For the SEM imaging, a TEM grid as described with sample adsorbed was applied to an aluminium stub of 1 .27 cm diameter using a carbonised sticky tab as an adhesive. Stubs were sputter-coated with gold using an Edwards S150b coater and viewed using a Philips XL-20 SEM operating at 20 kV.

Degree of Branching (DB)

Degree of branching of the branched polymer or copolymers is determined by 1 H NMR Dispersity (D)

The dispersity of the branched polymer or copolymer is determined by GPC (THF, PMMA standards). Results and Discussion

Synthesis of Branched PnMA-b-PAA Copolymers

Branched polymers of three different alkyl methacrylates (methyl, butyl and lauryl) were synthesized by RAFT solution polymerisation in dioxane at 60 °C using the RAFT CTA 4- vinylbenzyl-1 -pyrrole carbodithioate, a dithioate ester that also possesses alkene functionality. The dual action of the CTA enabled branching to occur during the polymerisation, due to the occurrence of both copolymerisation with the styryl double bond and reversible addition-fragmentation chain transfer with the dithioate group.

Polymerisations were stopped at intermediate conversion to preserve RAFT chain end functionality. These branched homopolymer macro-CTAs were each then chain-extended with acrylic acid (AA) to form branched poly (alkyl methacrylate)-block-poly (acrylic acid) (PnMA-b-PAA) copolymers, again using RAFT solution polymerization in dioxane. Each AA polymerisation proceeded to high conversion (>90% as determined by ¹ H NMR spectroscopy, see Table 1 ). The molar ratio of the poly (alkyl methacrylate) to the poly (acrylic acid), the degree of branching (DB), Number Average Molecular Weight (M _n ), Weight Average Molecular Weight (M _w ) and dispersity (D) of the polymers are provided in Table 1 .

Table 1 . Results of RAFT Polymerisation of Alkyl Methacrylates to Form Branched PnMA (Poly (alkyl methacrylate)) Macro-CTAs and Branched PnMA-b-PAA (Poly (alkyl methacrylate-block-acrylic acid)) Block Copolymers.

determined by 1H NMR ^b determined by GPC (THF, PMMA standards)

The structures in Figure 1 demonstrate that the pyrrole groups are situated at the chain ends of the polymer whereas the styryl groups create a branching point within the polymer structure. Analysis of these polymers by ¹ H NMR showed the presence of the pyrrole groups at the ends of the polymer branches at δ = 6.34 and 7.72 ppm. Broad peaks due to the styryl units were also observed between 7.30 and 7.45 ppm. Average values of degrees of branching (DB) were calculated by first comparing the methacrylate protons at around 0.90 ppm to the aromatic protons from the styryl and pyrrole groups in the region 6.34 - 7.72 ppm to give the average number of monomers per branch (MB). DB is then calculated as the reciprocal of the MB value.

Table 1 displays the results of the syntheses of both the homopolymer macro-CTAs (Examples 1 -3), and also the copolymers (Examples 4-6). ¹ H NMR analysis showed the appearance of peaks in the ¹ H NMR spectra of the copolymers at δ = 1.63 and 2.22 ppm due to PAA. The ratio of methacrylate to acrylic acid within the copolymers could also be calculated from the ¹ H NMR spectra. Equal mass fractions of PnMA and PAA were targeted for each copolymer, in addition to equal molecular weights for all three

copolymers, with the intention that any observed differences in self-assembly could be attributed to the change in hydrophobicity. The amount of PAA in all three copolymers was less than the feed ratio. However, all three copolymerisations of AA went to high conversion. This indicates that PAA homopolymer was formed during the reaction, which is not unusual for either RAFT or RAFT-SCVP polymerisations. DB was calculated for all of the macro-CTAs and the block copolymers, except for branched PLMA-b-PAA where the pyrrole and styryl groups could not be clearly seen in the ¹ H NMR spectrum. DB values for the PnMA cores were close to the 0.25 targeted, then values decreased following PAA addition as the branch lengths increased.

THF GPC analysis of the copolymers following methylation with trimethylsilyldiazomethane demonstrated an increase in molar mass in each case compared to that of the macro-CTA. A large increase in dispersity was also observed for all three copolymers compared to their macro-CTA, which is indicative of a large degree of branching within the copolymer structure. This is shown in Figure 2, which is a comparison of molecular weight

distributions obtained from GPC: A) branched PMMA (dashed line) and branched PMMA-b- PAA (solid line), B) branched PBMA (dashed line) and branched PBMA-b-PAA (solid line) and C) branched PLMA (dashed line) and branched PLMA-b-PAA (solid line).

Self-assembly of branched PnMA-b-PAA Copolymers in Water

These branched copolymers (Examples 4-6) were dispersed into water via the dropwise addition of deionised water at a controlled rate of 0.1 ml min ^"1 using a syringe pump into a stirring solution of the amphiphilic copolymer in THF, which is a good solvent for both the hydrophilic block and the hydrophobic block. This was followed by evaporation of the THF to form an aqueous dispersion of self-assembled copolymer particles. The self-assemblies were carried out at the pH of the deionized water (pH 5) without any addition of acid, base or salts to buffer pH to simplify the system, and all dispersions were prepared at the same concentration (0.5 w/v%).

The three branched PnMA-b-PAA copolymers (Examples 4-6) self-assembled into onion micelles (Examples 7-9) of varying sizes, as shown by the TEM images in Figure 3, which are TEM micrographs of dispersions of branched block PnMA-b-PAA copolymers in water, stained with uranyl formate: A. Onion micelles of branched PMMA-b-PAA (Example 7), B. Onion micelles of branched PBMA-b-PAA (Example 8) and C. Onion micelles of branched PLMA-b-PAA (Example 9).

A combination of TEM, particle sizing and zeta potential measurements (made by PALS), and SANS was used to characterise the dispersions of each copolymer. The results are summarised in Table 2 below. Diameters measured from TEM images are typically smaller than those determined by PALS and SANS as dispersions are dried onto grids to allow TEM imaging, whereas PALS and SANS measure particles in their hydrated state. This is true for the branched PLMA-b-PAA sample (Example 9). However in the case of branched PMMA-b-PAA (Example 7) and branched PBMA-b-PAA (Example 8) there is no clear trend in size measured by the different techniques. A greater dispersity in particle size was observed for the branched PBMA-b-PAA (Example 8) dispersion, shown to be a biomodal dispersion, with populations of larger (191 ± 1 nm) and smaller (82± 1 nm) onion micelle structures visible in the TEM image in Figure 3. The branched PLMA-b-PAA dispersion (Example 9) was notably uniform. All three dispersions were shown to be stable by the zeta potential results, which indicate negative charge on the particle surfaces due to ionisation of the carboxylic acid groups of the PAA segments. At the native pH of the deionised water (~pH 5) the PAA is partially ionized.

Table 2. Summary of Results for the Characterization of Dispersions of Branched Block PnMA-b-PAA Copolymers in Water Using Particle Sizing and Zeta Potential Measurements, TEM and SANS

These results demonstrate that changing the alkyl group on the methacrylate monomer has an effect on the mean diameter of the structures formed by the self-assembled branched copolymer. The architecture, degree of branching and molecular weights were kept as constant as possible and could not account for the differences in self-assembled structures observed.

Scanning electron microscopy (SEM) was used to investigate whether the PBMA-b-PAA onion micelles (Example 8) had flat disc-like structures or three-dimensional spherical structures. SEM was used to study the surface of the sample whereas TEM can enable visualisation of the internal structure. A TEM grid to which a stained branched PBMA-b- PAA dispersion (Example 8) was adsorbed was sputter-coated with Au and used for SEM imaging to allow direct comparison between the TEM and SEM images. The SEM images in Figure 4 show that the onion micelles of Example 8 were in fact spherical, and the lamellar structure observed by TEM was a series of internal concentric shells (i.e. layers).

SANS was used to study dispersions of the copolymers in D ₂ 0. Diverse scattering profiles were obtained for the three samples. A clear Bragg peak was observed for the branched PBMA-b-PAA sample (Example 8) which is characteristic of a multilayered structure.

Bragg's equation Q = 2π / d was used to predict the layer spacing. Using the Q value of the Bragg peak, an average spacing of 12 nm is predicted for the onion micelles of branched PBMA-b-PAA (Example 8). The scattering of all three copolymers fitted to a lamellar paracrystal model, suggesting an onion micelle structure composed of layers with the hydrophobic PnMA on the inside to avoid the D ₂ 0 and PAA segments on the outer surfaces. This model was used to calculate the scattering from a stack of ordered lamellae, which is considered as a paracrystal to account for the repeat spacing.

Table 3 summarises the values of the fitting parameters obtained from the model. The model fit gives a layer spacing of 11 .4 nm for the branched PBMA-b-PAA onion micelles (Example 8), which is consistent with the spacing obtained from the Bragg peak, and demonstrates some associated dispersity which can be observed in the TEM images. The model suggests an average of ten layers for this sample which also agrees with the TEM results. The scattering length density (SLD) of the layers is approximately 2.07 x 10 ^"6 A ^"2 . This shows that there is water within the layered structure as the calculated SLD for the copolymer alone is 1 .4 x 10 ^"6 A ^"2 .

Onion micelle structures were also indicated for branched PMMA-b-PAA (Example 7) and branched PLMA-b-PAA (Example 9), but with fewer layers. The results suggest a mixture of bi- and tri-layered micelles, with much thicker layers than calculated for branched PBMA- b-PAA. Increased values of SLD again indicate the presence of D ₂ 0 within the micelle structure.

Table 3. Summary of Values Obtained for Fitting Parameters from Model Fit to Branched PnMA-b-PAA SANS Data

Stability of the onion micelles

The stability of the onion micelles under ambient conditions was also investigated. A sample of branched PBMA-b-PAA dispersed in water (Example 8) was prepared and analysed by TEM and PALS to confirm that onion micelles were formed. This sample was then kept at room temperature for a period of 5 weeks and subsequently re-analysed. Figure 5 shows TEM images of the sample before and after storage. It is clear that the onion micelle structure remains intact during this period. A bimodal distribution was again observed, with an increase in diameter of both the smaller and larger particles,

accompanied by an increase in dispersity, as shown in Table 4 below.

Table 4. Results of PALS Analysis of the Onion Micelles formed from branched PBMA-b- PAA Dispersed in Water (Example 8) Immediately Following Preparation (t = 0) and After Storage for 5 Weeks in Ambient Conditions (t = 5 weeks)

Table 4 suggests some growth or swelling of the onion micelles had occurred during the storage period; but significantly the onion micelle structure was maintained. The onion micelles were thus found to be stable when stored at room temperature over a period of five weeks.

Temperature Dependency

Annealing was carried out on the dispersions to investigate whether the self-assembled structures responded to temperature. Sample tubes containing copolymer dispersion in water were sealed and immersed in an oil bath heated to 45 °C for 12 hours. Samples were removed and imaged by TEM before and after the annealing period, as shown in Figure 6. Particle sizing measurements were also performed.

The branched PMMA-b-PAA micelles (Example 7) and branched PLMA-b-PAA micelles (Example 9) underwent a small increase in size, and their shapes appeared to become slightly more irregular. The branched PBMA-b-PAA micelles (Example 8) also underwent a small increase in particle size. However, more significantly for the branched PBMA-b-PAA copolymer, the layered onion micelle structure was no longer present, with more of a vesicle-like structure observed. These results can be rationalised by considering the glass transition temperature (T _g ) of the three alkyl methacrylate polymers. PMMA has a high T _g of 105°C, similar to that of PAA (106°C), and PLMA has a low T _g of -65°C. PBMA, on the other hand, has a known T _g of 25°C i.e. at or close to ambient temperature at which the onion micelles are assembled. When the temperature of the dispersion is increased to 45°C, this has little effect on the self-assembled branched PMMA-b-PAA (Example 7) and branched PLMA-b-PAA (Example 9) micelle structures since they remain well above or well below their respective T _g . However, the PBMA segment of branched PBMA-b-PAA within the onion micelles (Example 8) is heated to above its T _g during the annealing process and hence the layers are able to coalesce to form an amorphous 'vesicular' structure.

Molar ratio of hydrophilic to hydrophobic segments

The molar ratio of hydrophilic to hydrophobic segments in the branched block copolymers was studied. Branched PBMA-b-PAA copolymers with varying molar ratios of BMA to AA monomer were synthesized according to the method described above. Five different polymers were prepared, with BMA:AA molar ratios of 0.84:1 .0 (Example 10), 1 .51 :1 .0 (Example 1 1 ), 1 .69:1 .0 (Example 12), 1 .72:1 .0 (Example 13) and 1 .80:1 .0 (Example 14). Dispersions in water were prepared as described above. These were imaged by TEM and are shown in Figure 7 (A) (Example 10) 0.84:1 .0, B) (Example 1 1 ) 1 .51 :1 .0, C) (Example 12) 1 .69:1 .0, D) (Example 13) 1 .72:1 .0, E) (Example 14) 1 .80:1 .0). Samples were stained with uranyl formate prior to imaging.

The images in Figure 7 show that the ratio of hydrophobic to hydrophilic segments within these copolymers has an effect on self-assembly behaviour. Larger spheres are seen when less AA is present relative to the amount of BMA, whereas smaller spheres are formed where copolymers contain more AA relative to BMA. It is thought that a longer hydrophilic 'stabilizer' block disfavours micelle fusion, whilst a shorter stabilizer block leads to more favourable micelle fusion. In the case of linear block copolymers, this leads to the formation of fibres or 'worms' when the stabilizer block is shorter. In contrast, in the case of the branched copolymers of the present invention, when there is less hydrophilic polymer the small unimolecular micelles fuse to form more energetically favourable large multi- micellar aggregates, whereas when more hydrophilic polymer is present it can adequately stabilize the smaller micelles. Figure 7 shows that the optimum ratio for formation of onion micelles for branched PBMA-b-PAA copolymers is between 0.84:1 .0 and 1 .69:1 .0

PBMA:PAA.

Effect of Printing

Example 15

The dispersion of Example 8 was printed onto a substrate using an inkjet ink printer. The printed deposit on the substrate was analysed and the onion micelle structure was found to be maintained. As mentioned above with regard to temperature dependency, subjecting the onion micelles to a heat source causes the onion micelle structure to unravel.

Inkiet Ink Example

Example 16

An inkjet ink was formulated using the method described below:

A branched P(BMA-b-AA) copolymer (poly (butyl methacrylate)-block-poly (acrylic acid)) was made as per Example 5 above. 10 mg of the branched P(BMA-b-AA) copolymer was dissolved in 2 ml of THF (tetrahydrofuran) to provide a first solution. Meanwhile, a 0.2 mg ml ^"1 solution of Rhodamine B in deionized water was prepared.

Rhodamine B

2 ml of the aqueous Rhodamine B solution was then added at a rate of 0.1 ml min ^"1 to the first solution to provide a second solution. The THF was then evaporated off at a temperature of 25 °C to provide an inkjet ink.

The inkjet ink thereby formed was found to contain onion micelle structures with

Rhodamine B encapsulated between their layers.

Subjecting the inkjet ink to a temperature of 40 °C caused the Rhodamine B to be released from the micelles due to the unravelling of the onion micelle structures. This was monitored using UV-visible spectroscopy.

Example 16 proves the concept that a dye may be encapsulated within the onion micelles and then released in a controlled manner upon subjection to a trigger (e.g. heat).