EMULSION POLYMERISATION

This invention relates generally to emulsion polymerisation. More specifically, although not exclusively, this invention relates to stabilisers for use in an emulsion polymerisation process, methods of making the same, and particles produced from the same.

Emulsion polymerisation is a well-established polymer preparation technique, in which monomer droplets are dispersed in a continuous aqueous phase and may be kept colloidally stable through the use of a surfactant. At the beginning of the process, the monomer is dispersed in the water phase to form relatively large droplets. Concurrently, the surfactant molecules form micelles in the water phase. Small amounts of monomer are then able to diffuse from the droplets into the micelles. The polymerisation process is initiated with a radical initiator, which causes the monomer within the micelles to polymerise to form polymer chains, which in turn form latex particles. The latex particles continue to grow until all of the monomer in the system has reacted. The result of the emulsion polymerisation process is an aqueous dispersion of latex particles, often called a ‘latex’ or an ‘emulsion’. The latex may be used as an aqueous dispersion in industrial applications, or alternatively the latex particles may be isolated for use in a specific application.

Many different latexes may be manufactured for different purposes. Emulsion polymerisation is used in the manufacture of wide ranges of different products including adhesives, paints and coatings, offset inks, paper & paperboards, textiles, and construction chemicals. Most commonly, the monomers used in the process of emulsion polymerisation are styrene, acrylonitrile, butadiene, vinyl acetate and derivatives, acrylate esters and methacrylate esters. Advantageously, the process is considered to be environmentally friendly because the solvent used is water rather than volatile organic compounds (VOCs).

Traditional surfactants that are used in emulsion polymerisations include sodium lauryl sulphate (SLS),“quats” (quaternary ammonium salts), and betaines. It is also known to use‘Pickering-type emulsifiers, e.g. silica, clays, ceramic particles, to stabilise hydrophobic particles in water by both electrostatic and mechanical mechanisms.

An example of an emulsion polymerisation process stabilised using solid particles is disclosed by the inventor in J. Am. Chem. Soc. 2008, 130, 50, 16850-16851 . This publication describes the use of nanosized silica particles as a replacement for surfactants in an emulsion polymerisation process. The silica particles function as Pickering stabilisers to stabilise the interface between the water and oil phase.

The selection of the surfactant used in an emulsion polymerisation is critical, for example, to enable a suitable rate of polymerisation, and to minimise the formation of coagulum. In addition, for use in paints and coating applications, the surfactants often affect the final finish of coatings applied using a latex dispersion.

For example, is known that waterborne paints and coatings may suffer from the problem of surfactant migration. This produces an undesirable surface effect on the final coating, which may appear as a mottled effect or hazy film on the paint surface.

It is therefore a first non-exclusive object of the invention to provide a surfactant for use in a composition, e.g. a composition for use in an emulsion polymerisation, which does not suffer from the negative effects of surfactant migration in or on finished coatings (e.g. reduced surface gloss, increased accumulation of dirt and dust, sensitivity to moisture).

Accordingly, a first aspect of the invention provides a colloidal stabiliser for use in an emulsion polymerisation process, the colloidal stabiliser comprising a crosslinked hydrophilic polymeric particle.

The colloidal stabiliser may function as, or be, a surfactant for use in an emulsion polymerisation process.

The inventors have surprisingly found that crosslinked hydrophilic polymeric particles may be used as stabilisers in an emulsion polymerisation process. Advantageously, the colloidal stabilisers of the invention are ‘soft’, i.e. are composed of crosslinked polymer chains rather than conventional Pickering emulsifiers that are composed of‘hard’ particles such as silica. More advantageously, the colloidal stabilisers are hydrophilic and so are easily dispersed and suspended in an aqueous composition for use in an emulsion polymerisation process.

Without wishing to be bound by any particular theory, it is thought that the colloidal stabilisers of the invention may bind to, or be associated with, the latex particles produced in an emulsion polymerisation process. For example, the colloidal stabilisers may be covalently bonded to the latex particles produced in an emulsion polymerisation process, e.g. via a carbon-carbon covalent bond, and/or a carbon-oxygen covalent bond. Advantageously, this overcomes problem of surfactant migration, which is a key factor affecting stability of the latex dispersion produced from emulsion polymerisation processes, and also the properties of final coatings when the latex dispersion is used in paint and/or coating applications.

More advantageously, the colloidal stabiliser of the invention is able to stabilise latex formation in an emulsion polymerisation by providing electrosteric stabilisation. This is a combination of electrostatic stabilisation, and steric stabilisation. The hydrophilic nature of the colloidal stabilisers is able to interact with the solvent in the emulsion polymerisation to provide better steric stabilisation. In contrast, Pickering-type stabilisers such as silica provide electrostatic stabilisation only.

In embodiments, the crosslinked hydrophilic polymeric particle, may be a nanoparticle, e.g. a nanogel, that is a nanoparticle comprising, or composed of, a cross-linked hydrophilic polymer network.

The colloidal stabiliser typically is smaller than 100 nm in diameter for example, between 5 to 50 nm in diameter, e.g. 10 to 40 nm, or 20 to 30 nm in diameter. In embodiments, the colloidal stabiliser is between 10 to 25 nm in diameter.

The colloidal stabiliser, e.g. the crosslinked hydrophilic polymeric particle, may comprise functional moieties, for example, on its surface. In embodiments, the colloidal stabiliser, e.g. the crosslinked hydrophilic polymeric particle, may comprise at least one carboxylic acid moiety on its surface. In embodiments, the colloidal stabiliser, e.g. the crosslinked hydrophilic polymeric particle, may comprise at least one ethylene oxide moiety on its surface, e.g. polyethylene oxide) functionality. In embodiments, the colloidal stabiliser, e.g. the crosslinked hydrophilic polymeric particle, may comprise both of at least one carboxylic acid moiety and at least one ethylene oxide moiety on its surface. In embodiments, the colloidal stabiliser may contain a carboxylic acid group, a polyethylene glycol) moiety and/or a polyethylene glycol) methyl ether moiety.

The colloidal stabiliser, e.g. the crosslinked hydrophilic polymeric particle, may comprise at least one reactive moiety, for example, an alkene, e.g. a vinyl alkene. The colloidal stabiliser, e.g. the crosslinked hydrophilic polymeric particle, may comprise more than one type of alkene, e.g. vinyl alkene.

The colloidal stabiliser, e.g. the crosslinked hydrophilic polymeric particle, may comprise a core and a periphery or peripheral surface. Cross linking may provide a core portion and one or more tail portions. In an embodiment the one or more tail portions are outermost with respect to the core portion.

The peripheral surface of the colloidal stabiliser may be homogeneous in nature. That is, the same type of functional groups may be dispersed evenly throughout the peripheral surface. This is in contrast to a Janus particle or a patchy particle, which comprise heterogeneous surfaces with two or more different regions exhibiting different chemistries and/or comprising different functional groups in each region.

The colloidal stabiliser, e.g. the crosslinked hydrophilic polymeric particle, may comprise crosslinking at the core of the particle. In embodiments, the core may comprise or consist of a hydrophobic region, for example, the colloidal stabiliser may comprise a hydrophobic core. In embodiments, the core, e.g. the hydrophobic core, may comprise or consist of a region or block of poly(butyl methacrylate).

The colloidal stabiliser may comprise a hydrophilic surface, e.g. outer surface; and/or periphery. The surface and/or periphery of the colloidal stabiliser may comprise at least one, e.g. plural, polymeric chains. For example, the surface and/or periphery of the colloidal stabiliser may be formed from plural polymer chains, e.g. plural pendant polymer chains. In embodiments, the at least one polymeric chain may comprise a hydrophilic region.

In embodiments, the at least one polymeric chain may comprise one or more hydrophilic and/or polar and/or charged groups or moieties. The one or more hydrophilic and/or polar and/or charged groups or moieties may be selected from one or more of a carboxylic acid moiety, a carboxylate moiety, an ethylene oxide moiety, a polyethylene glycol (PEG) moiety, and/or a polyethylene glycol) methyl ether moiety.

In embodiment, the at least one polymeric chain (e.g. each polymeric chain) may comprise at least one reactive moiety. The reactive moiety may be usable to form a covalent bond with the latex particle during an emulsion polymerisation process. In embodiments, the at least one reactive moiety may be an alkene, e.g. a vinyl alkene.

Advantageously, the at least one reactive moiety, e.g. at least one alkene, is usable to form a covalent bond with a latex particle such that it remains bound to the latex particle after the emulsion polymerisation process has finished. This is particularly advantageous when using the resulting latex for coating and/or paint applications because the colloidal stabiliser is not able to migrate to the surface of the coating, and thereby mitigates and/or prevents haze in in the finished coating.

In embodiments, the colloidal stabiliser comprises a hydrophobic core, e.g. a crosslinked hydrophobic core, and a hydrophilic periphery, e.g. a hydrophilic periphery comprising at least one polymeric chain, the at least one polymeric chain comprising a hydrophilic and/or polar and/or charged group or moiety. In embodiments, the hydrophilic periphery does not comprise crosslinking of the at least one polymeric chain(s).

The colloidal stabiliser, e.g. the crosslinked hydrophilic polymeric particle, may comprise crosslinked polymer micelles. For example, the colloidal stabiliser may be fabricated from a block copolymer. The block copolymer may form or may be able to form a micelle (or at least form a micelle-type structure) in water, for example to form an oil-in-water emulsion. The at least one block of the block copolymer may undergo a crosslinking step to form the colloidal stabiliser. In embodiments, the at least one block of the block copolymer to undergo a crosslinking step to form the colloidal stabiliser, may comprise or consist of a hydrophobic region or block. In embodiments, the at least one block of the block copolymer may undergo a crosslinking step to form the core of the colloidal stabiliser. For example, the at least one block of the block copolymer may undergo a crosslinking step to form a hydrophobic core of the colloidal stabiliser.

In embodiments, the block copolymer may comprise one or more blocks that do not undergo crosslinking. In embodiments, the block copolymer may comprise one or more blocks that are hydrophilic. In embodiments, the block copolymer may comprise one or more blocks, e.g. hydrophilic blocks, which form the outer surface or the periphery of the colloidal stabiliser. For example, the outer surface or periphery of the colloidal stabiliser may comprise or be formed from plural pendant polymeric chains, e.g. plural polymeric chain comprising a hydrophilic and/or polar and/or charged group or moiety.

The crosslinked polymer micelles may comprise a number of or consist of a number of copolymer chains comprising methacrylate, methacrylic acid, polyethylene glycol) methacrylate, polyethylene glycol) methyl ether methacrylate, butyl methacrylate and/or a polyethylene glycol) methyl ether monomer, for example, a (polyeiethyl methacrylate-methacrylic acid)-block-poly(butyl methacrylate) copolymer, i.e. a (P(MMA)(MAA)-PBMA copolymer. The crosslinker used to crosslink the colloidal stabiliser, e.g. the crosslinked hydrophilic polymeric particle, may be a plurifunctional crosslinker, e.g. a trifunctional methacrylate crosslinker and/or an ethoxylated acrylate. Suitable trifunctional methacrylate crosslinkers include trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, and/or trimethylolpropane ethoxylated triacrylate (avg. Mw = 428 g/mol). In embodiments, the crosslinker may be difunctional, e.g. the crosslinker may comprise divinyl benzene.

In embodiments, the colloidal stabiliser may be formed from one or more block copolymer(s), each block copolymer comprising one or more hydrophobic block(s) and one or more hydrophilic block(s), wherein the one or more hydrophobic block(s) forms a crosslinked core of the colloidal stabiliser, and the one or more hydrophilic block(s) forms plural pendant polymeric chains, e.g. non-crosslinked plural pendant polymeric chains, comprising hydrophilic or polar or charged moieties.

In embodiments, a block copolymer used to produce the colloidal stabiliser may comprise one or more (poly(methyl methacrylate-methacrylic acid) block(s). The one or more poly(butyl methacrylate) block(s) may form plural pendant polymeric chains, e.g. non-crosslinked plural pendant polymeric chains, comprising hydrophilic or polar or charged moieties.

In embodiments, a block copolymer used to produce the colloidal stabiliser may comprise one or more poly(butyl methacrylate) block(s). The one or more poly(butyl methacrylate) block(s) may form a crosslinked core of the colloidal stabiliser. In embodiments, a block copolymer used to produce the colloidal stabiliser may comprise or consist of a (poly(methyl methacrylate-methacrylic acid)-block-poly(butyl methacrylate) copolymer.

Advantageously, the (poly(methyl methacrylate-methacrylic acid) block is a hydrophilic block, which forms the peripheral surface of the colloidal stabiliser. The (poly(methyl methacrylate-methacrylic acid) block comprises one or more hydrophilic groups, e.g. carboxylic acid and/or carboxylate groups, and/or polyethylene glycol moieties. Advantageously, these hydrophilic groups enable the colloidal stabiliser to exhibit hydrophilicity in an emulsion polymerisation to stabilise the formation of the latex particles. The (poly(methyl methacrylate-methacrylic acid) block also comprises a reactive moiety in the form of one or more alkene moieties, e.g. a terminal alkene moiety. Advantageously, the reactive moiety is usable to form a covalent bond with the latex formed during the emulsion polymerisation to prevent surface migration of the colloidal stabiliser when the latex is used, for example, to form a coating.

The hydrodynamic diameter (d _hi ) of the colloidal stabiliser, e.g. the crosslinked hydrophilic polymeric particle, may be between 10 to 120 nm, for example, between 10 to 70 nm, or 20 to 60 nm, or 20 to 50 nm or 25 to 60 nm, e.g. the hydrodynamic diameter (d _hi ) may be between 30 nm to 57 nm.

The polydispersity index (PDI) of the colloidal stabiliser as measured by dynamic light scattering, e.g. the crosslinked hydrophilic polymeric particle, may be between 0.005 and 0.50, e.g. between 0.04 to 0.14.

The colloidal stabiliser of the invention may be provided as a powder, e.g. a freeze dried or desiccated powder. For example, the colloidal stabiliser of the invention may be freeze dried after synthesis to remove the water phase. The colloidal stabiliser of the invention may comprise a powder wherein the water content of the colloidal stabiliser is less than 20 wt.%, e.g. less than 10 wt.%, or less than 5 wt.%, or less than 1 wt.%, of the total weight of the colloidal stabiliser.

Advantageously, the colloidal stabiliser of the invention is stable in the absence of a water phase, e.g. as a powder in a freeze dried or desiccated, state. This enables the colloidal stabiliser to be transported and stored for long periods of time. Moreover, this is environmentally advantageous because less fuel and space is required to transport the colloidal stabiliser in the absence of water.

More advantageously, the colloidal stabiliser of the invention is able to self-disperse and/or self- exfoliate when added to an aqueous phase and/or oil-in-water system for use in an emulsion polymerisation process. This is in contrast to the use of Pickering-type stabilisers, e.g. clays and silica particles, which do not exhibit this type of behaviour. A further aspect of the invention provides a method of forming a colloidal stabiliser for use in an emulsion polymerisation process, the method comprising forming or providing a block copolymer comprising at least one hydrophilic block, and crosslinking the block copolymer to produce the colloidal stabiliser.

The method of forming a colloidal stabiliser may further comprise forming a block copolymer comprising at least one hydrophilic block and at least one hydrophobic block, e.g. the block copolymer may be (poly(methyl methacrylate-methacrylic acid)-block-poly(butyl methacrylate) copolymer.

The method may further comprise forming a block copolymer by providing a macromonomer latex comprising poly(methyl methacrylate-methacrylic acid). The method may further comprise forming a block copolymer by crosslinking a macromonomer latex comprising poly(methyl methacrylate- methacrylic acid) with butyl methacrylate to produce a (poly(methyl methacrylate-methacrylic acid)- block-poly(butyl methacrylate) copolymer.

The method of forming a colloidal stabiliser may further comprise dispersing the block copolymer in an aqueous phase, e.g. to form micelles. The method may further comprise basifying the aqueous phase comprising the block copolymer, e.g. using a base such as sodium hydroxide.

The method may further comprise adding a crosslinker to the aqueous phase, e.g. a trifunctional methacrylate crosslinker and/or an ethoxylated acrylate crosslinker.

The method may further comprise adding an initiator to the aqueous phase. In embodiments, the initiator is a metal persulfate, for example, a Group 1 persulfate, e.g. potassium persulfate or sodium persulfate.

The method may further comprise crosslinking the block copolymer, for example, crosslinking one or more hydrophobic region(s) of the block copolymer, e.g. to form a hydrophobic core.

The method may further comprise removing the water from the aqueous phase to form a powder of the colloidal stabiliser, e.g. using a freeze-drying or another desiccation process.

The colloidal stabiliser may be dehydrated nor otherwise dried. Advantageously, we have found that the colloidal stabiliser may be dehydrated, e.g. presented in a powdered or dried form, rehydrated or otherwise suspended in a fluid and still retain its activity. This is beneficial because it allows for the colloidal stabiliser to be stored and/or shipped in its dried/dehydrated form.

The colloidal stabiliser of the invention is for use in an emulsion polymerisation process. A further aspect of the invention provides use of a crosslinked hydrophilic polymer particle(s) as a colloidal stabiliser, e.g. a surfactant or a surfactant replacement, in an emulsion polymerisation process.

A yet further aspect of the invention provides a composition for use in an emulsion polymerisation process, the composition comprising the colloidal stabilisers of the invention, and further comprising an emulsion comprising water and at least one monomer.

Preferably the emulsion polymerisation uses water as the continuous phase.

The monomer of the composition may comprise any monomer(s) suitable for use in an emulsion polymerisation process. For example, the monomer may comprise an alkene, e.g. a vinyl alkene. The monomer may comprise one or more of styrene, methyl methacrylate and/or butyl acrylate. A single type of monomer may be used, or a mixture of more than one type of monomer may be used, in the composition of the invention. The monomer may be cationic or anionic.

The composition may have a weight ratio of the crosslinked hydrophilic polymeric particle to the monomer is between 0.05 or 0.10 to 400, for example, between 0.05 or 0.10 to 375, 350, 325, 300, 275, 250, 225, 200, 175, 150, 125, 100, 90, 80, 70, 60, or 50. In embodiments the weight ratio may be between 0.05 and 35, or 0.05 to 30 or 0.05 to 25, or 0.05 to 15, or 0.05 to 10. In embodiments, the composition may have a weight ratio (of the crosslinked hydrophilic polymeric particle to the monomer of between 0.10 to 5.0, for example, between 0.10 to 4.0. Preferably, the composition has a weight ratio of the crosslinked hydrophilic polymeric particle to the monomer of between 0.05 to 3.0.

A yet further aspect of the invention provides a method of performing an emulsion polymerisation process using a crosslinked hydrophilic polymeric particle or the composition of the invention, the method comprising contacting the composition with an initiator, e.g. a radical initiator.

Initiators known to the skilled person for use in emulsion polymerisations are suitable for use in the method of the invention. In embodiments, the initiator is a metal persulfate, for example, a Group 1 persulfate, e.g. potassium persulfate or sodium persulfate. The initiator may be an azo initiators, e.g. 4,4’-azobis(4-cyanovaleric acid). The initiator may be a redox system, for example an oxidant (e.g. a persulfate or a hydroperoxide), or for example a reducing agent (e.g. a bisulfite, metabisulfite, or a formaldehyde sulfoxylate).

The method may further comprise adjusting the pH to a value between 4 to 10, for example, between The method may further comprise heating the composition to a temperature above 50 °C, for example, above 60 °C, e.g. 75 °C.

In embodiments where the initiator is a redox system, the method may comprise heating the composition to a temperature above 25 °C.

Lower temperatures may be usable if a redox initiator is used, for example, metal ion redox systems, e.g. cerium(IV), manganese(lll), manganese(VIII), vanadium(V), and/or chromium(IV) systems.

In embodiments, the method may not require heating the composition to a temperature above ambient temperature, i.e. the method may be conducted at 5 °C and/or at room temperature.

The method may further comprise contacting the composition with an inorganic salt, for example, a Group 1 (monovalent) or Group 2 (divalent) salt (or indeed a tri or higher functional salt), which is soluble in water, e.g. NaCI. The method may further comprise contacting the composition with a buffer, for example, NaHC03.

The method of performing an emulsion polymerisation process results in an aqueous dispersion of latex particles, e.g. Janus particles and/or patchy particles. The method of the invention may include a method of forming Janus particles and/or patchy particles.

Advantageously, the method according to the invention is scalable, and provides easy access to latex particles, e.g. Janus particles and/or patchy particles and/or armoured, using industrially- scalable emulsion polymerisation processes. Janus particles and/or patchy particles and/or armoured particles are an interesting class of particle, with a wide range of potential uses in applications including coating compositions.

More advantageously, the method of performing an emulsion polymerisation may be carried out as a continuous, batch, or semi-batch process.

A yet further aspect of the invention provides an aqueous suspension of latex particles, e.g. Janus particles and/or patchy particles produced from the method of the invention.

A further aspect of the invention comprises a patchy or Janus particle comprising a latex particle to which one or more cross-linked, hydrophilic polymeric particles is covalently bound.

The suspension of latex particles may comprise one or more patchy particles. By patchy particles, we mean particles, e.g. colloidal particles, with functional sites with a distinct physiochemical characteristic on their surface. The simplest sub-class of patchy particles are Janus particles, which consists of particles having one‘patch’ or protrusion on their surface.

The patches of the patchy and/or Janus particles of the suspension of latex particles are provided by the colloidal stabiliser of the invention. For example, the colloidal stabiliser may be associated with the latex particle. The colloidal stabiliser may be bonded, e.g. via an electrostatic and/or intermolecular interaction, with the latex particle. Additionally or alternatively, the colloidal stabiliser may be reactive, and/or be ionically and/or covalently bonded to the particles. For example, the colloidal stabiliser may be covalently bonded by a pendant alkene group, e.g. a vinyl group, to the particle. This enables the colloidal stabiliser to be‘locked into place’ on to the latex particle during and after emulsion polymerisation.

The hydrodynamic diameter (d _hi ) of the latex particles of the aqueous suspension of latex particles may be between 50 and 45000 nm, for example, between 60 and 1000 nm, say from 50 to 600 nm, or between 80 and 300 nm.

The polydispersity index (PDI) of the latex particles of the aqueous suspension of latex particles may be between 0.001 to 1 .00, preferably between 0.001 to 0.50.

The aqueous suspension of latex particles may be used in a wide range of applications, for example, as a paint, or as a coating, or as an adhesive.

Additionally or alternatively, the latex particles may be isolated from the aqueous suspension of latex particles for use in other industrial applications.

The patches may be distinct functional patches, e.g. pH responsive patches. The patches may be on the surface of the latex particle only, i.e. not located in the core of the latex particle.

Advantageously, the morphology of the particles, e.g. the number of patches on a patchy particle and/or the spatial control of the patches on the particle, may be controlled or controllable during the emulsion polymerisation by controlling the reaction conditions, e.g. salt concentration, for example, NaCI concentration; and/or the pH of the emulsion polymerisation reaction mixture; and/or the temperature at which the emulsion polymerisation is conducted. This enables the density of the patches on the latex particles (i.e. the surface coverage) to be controlled and/or tuned. Moreover, this enables the final latex particles to exhibit pH responsive behaviour.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. For the avoidance of doubt, the terms“may”,“and/or”,“e.g.”,“for example” and any similar term as used herein should be interpreted as non-limiting such that any feature so-described need not be present. Indeed, any combination of optional features is expressly envisaged without departing from the scope of the invention, whether or not these are expressly claimed. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1 is a schematic synthesis of a nanogel, according to an embodiment of the invention; Figure 2 is a schematic synthesis of a macromonomer latex via cobalt catalysed polymerisation of a methacrylate monomer of the prior art;

Figure 3 is a schematic illustration of the use of the nanogel N of Figure 1 as a stabiliser in emulsion polymerisation according to embodiments of the invention;

Figure 4 is a ¹ H NMR spectrum of an intermediate during the synthesis of nanogel N2;

Figure 5A is a cryogenic transmission electron microscopy (cryo-TEM) image of a 1 .0 wt% aqueous suspension of the copolymer micelles of Procedure 3 prior to crosslinking;

Figure 5B is cryo-TEM images of the nanogel N1 and nanogel N2 after crosslinking with trimethylolpropane trimethacrylate in Procedures 3 and 6 respectively;

Figure 6 is a graph showing the hydrodynamic diameter (d _hi ) of nanogel N1 and nanogel N2 before and after crosslinking;

Figure 7 is ¹ H-NMR spectra of the vinyl region of nanogel N1 and nanogel N2;

Figure 8 is a graph showing the size distribution by dynamic light scattering of nanogel N1 before freeze drying, and after freeze drying;

Figure 9 is an SEM image of the polystyrene latex particles of Comparative Example 1 ; Figure 10 is data for the hydrodynamic diameter (d _hi ) and polydispersity index (PDI) of latex particles obtained via emulsion polymerisation of styrene at pH 8.8 using nanogels N1 , N2; Figure 1 1 is an SEM image of the emulsion polymerisation of styrene according to Example 27 of the invention;

Figure 12 is an SEM image of the emulsion polymerisation of styrene according to Example 2 of the invention;

Figure 13 is an SEM image of an emulsion polymerisation of styrene conducted at pH 8.8 using un-crosslinked nanogel N2 polymer micelles; Figure 14 is a graph showing the size variation of latex particles obtained from an emulsion polymerisation using nanogel N1 , and the z-potential variation of latex particles obtained from an emulsion polymerisation using nanogel N1 , both as a function of pH;

Figure 15 is a graph showing the size variation of latex particles obtained from an emulsion polymerisation using nanogel N2, and the z-potential variation of latex particles obtained from an emulsion polymerisation using nanogel N2, both as a function of pH;

Figure 16 is graphs showing the effect of initial nanogel dispersion pH on the latex particle size and distribution in the emulsion polymerisation of styrene in the presence of nanogel N1 and nanogel N2;

Figure 17 is an SEM images of emulsion polymerisations using nanogel N1 at different pH values;

Figure 18 is an SEM image showing the formation of bigger patchy particle in an emulsion polymerisation of styrene using nanogel N1 as stabilisers;

Figure 19 is an estimate of the variation in the number of patches found on the polystyrene surface when the polymerisation was started at different pH, using nanogel N1 as stabilisers; Figure 20 is a graph showing the variation of the [H ⁺ ] in a blank version of Example 14 and Example 26;

Figure 21 is an SEM image of the emulsion polymerisation of styrene according to Example 26 of the invention; and

Figure 22 is graphs showing the effect of the concentration of NaCI on latex particle size and distribution in an emulsion polymerisation of styrene in the presence of nanogel N1 and nanogel N2;

Figure 23 is an SEM image of an emulsion polymerisation of styrene using nanogel N1 ; and Figure 24 is an SEM image of an emulsion polymerisation of styrene using nanogel N2.

Referring first to Figure 1 , there is shown a schematic synthesis 1 A of a nanogel N, according to a first embodiment of the invention. In the schematic synthesis 1 A, there is shown a macromonomer latex 1 1 , a chain-extended polymer latex 12, and the nanogel N. The schematic synthesis 1 A comprises a chain-extension reaction (i) and a cross-linking reaction (ii). In this embodiment, the chain-extension reaction (i) comprises reaction of the macromonomer latex 1 1 with butyl methacrylate (BMA). The cross-linking reaction (ii) comprises treatment with base (NaOH) followed by a reversible addition-fragmentation chain transfer (RAFT) reaction.

The macromonomer latex 1 1 represents particles that consist predominantly of w-end unsaturated poly(methyl methacrylate-methacrylic acid) P(MMA-MAA) macromonomers.

In the schematic synthesis 1 A, the macromonomer latex 1 1 underwent the chain-extension reaction (i) with butyl methacrylate (BMA) in the presence of potassium persulfate (KPS) to produce chain- extended polymer latex 12. The conditions for the chain-extension reaction (i) were adapted from that originally reported by Moad et al, Macromol. Symp. 1996, 1 1 1 , 13-23.

In the cross-linking reaction (ii), the chain-extended polymer latex 12 was treated with base (NaOH). This caused the chain-extended polymer latex 12 to disassemble to form an aqueous dispersion of copolymer micelles (not shown). The resulting copolymer micelles (not shown) underwent cross- linking with a trifunctional (meth)acrylate monomer crosslinker (e.g. trimethylolpropane tri methacrylate) to produce the nanogel N.

The nanogel N was synthesised by core-crosslinking of w-end unsaturated poly(methyl methacrylate-methacrylic acid)-block-poly(butyl methacrylate) P(MMA-MAA)-PBMA copolymer micelles by reversible addition-fragmentation chain transfer (RAFT) to produce core-crosslinked poly(methyl methacrylate-methacrylic acid)-block-poly(butyl methacrylate) P(MMA-MAA)-PBMA copolymer nanogels (nanogel N).

Advantageously, the nanogels of Figure 1 contain two types of carbon-carbon double bond, which are both reactive towards further polymerisation; (i) the w-end macromonomer vinyl groups; and (ii) the pendant vinyl groups from the trifunctional (meth)acrylate crosslinker (e.g. trimethylolpropane tri methacrylate).

In Figure 1 , there is also shown a graph 1 B showing hydrodynamic diameter (d _hi ) data for size distribution via dynamic light scattering (DLS) of the macromonomer latex 1 1 . The graph 1 B shows a plot 13 for the hydrodynamic diameter (d _hi ) of the macromonomer latex 1 1 before the addition of base (NaOH) and a plot 14 for the hydrodynamic diameter (d _hi ) of the macromonomer latex 1 1 after the addition of base (NaOH).

In Figure 1 , there is also shown a graph 1 C showing hydrodynamic diameter (d _hi ) data for size distribution via dynamic light scattering (DLS) of the chain-extended polymer latex 12. The graph 1 C shows a plot 15 for the hydrodynamic diameter (d _hi ) of the chain-extended polymer latex 12 before the addition of base (NaOH) and a plot 16 for the hydrodynamic diameter (d _hi ) of the chain-extended polymer latex 12 after the addition of base (NaOH).

Referring also to Figure 2, there is shown a schematic synthesis 1 D of the macromonomer latex 1 1 via cobalt-mediated catalytic chain transfer polymerisation (CCTP) using bis[(difluoroboryl) dimethylglyoximato]cobalt(ll) (CoBF) as a catalyst and a methacrylate monomer 10.

Although CoBF is specified in this embodiment, any suitable cobalt catalyst, e.g. low-spin Co(ll) complexes, may be used forthe CCTP reaction. The best-known catalysts forthis reaction are shown as general cobaloxime structures 6 to 9 in the publication by Gridnev et. al. Chem. Rev. , 2001 , 101 (12), pp 361 1-3660.

Referring now to Figure 3, there is shown a schematic illustration 3 of the use of the nanogel N as a stabiliser in emulsion polymerisation processes according to embodiments of the invention. There is shown the nanogel N synthesised in Figure 1 , and two different routes, A and B, to produce particles 30A and 30B, e.g. Janus and/or patchy particles. In this embodiment, the reaction conditions of route A to produce particles 30A are adjusted to pH 5.5 prior to polymerisation, and the reaction conditions of route B to produce particles 30B are adjusted to pH 5.0 prior to polymerisation. In this way, the density of the patches of nanogel N on the particles 30A, 30B may be tuned by adjusting the pH of the reaction prior to polymerisation. In other embodiments, the pH may be adjusted to pH 4.5.

To further exemplify the invention, reference is made to the following non-limiting Examples.

Synthesis of Nanogel N1 , N2

Two nanogels were synthesised; Nanogel N1 and Nanogel N2. Nanogel N2 is larger in size and molecular weight, than nanogel N1 .

Materials: Methyl methacrylate (99%), butyl methacrylate (99%) and styrene (> 99%) were purchased from Sigma Aldrich and filtered through activated basic aluminium oxide prior to use to remove the inhibitors. Potassium persulfate (KPS) (99%), 4-4’-azobis(4-cyanovaleric acid) (ACVA) (98%), methacrylic acid (99%), trimethylolpropane tri methacrylate (technical grade), trimethylolpropane triacrylate (technical grade), trimethylolpropane ethoxylated triacrylate avg. M _w 428 g/mol (technical grade), sodium dodecyl sulphate (> 98.5%), sodium hydrogen carbonate (NaHCC>3) (³ 99.7 %), sodium hydroxide (NaOH) (> 97%), sodium dodecyl sulfate (SDS) (> 99.0 %) and d6-DMSO (99.9 atom % D) were purchased from Sigma Aldrich and used as received. Bis[(difluoroboryl) dimethylglyoximatojcobalt(ll) (CoBF) and bis[(difluoroboryl) diethylglyoximatojcobalt(ll) (Et-CoBF) were synthetized according to the literature (Bakac A, et. al. Inorg Chem 1986, 25 (23), 4108-41 14; Bakac, A. et. al. J. Am. Chem. Soc. 1984, 106 (18), 5197- 5202).

Equipment: ¹ H-NMR spectra were recorded on freeze-dried polymers on either a Bruker HD-300 or a Bruker HD-400 spectrometer using d6-DMSO as solvent. Average particle sizes and distributions were measured by dynamic light scattering (DLS) on a Malvern Zetasizer Nano ZS or a Malvern Zetasizer Ultra operating at 25°C. Zeta Potential measurement were carried out on the Malvern Zetasizer Ultra at 0.5 wt% in water using disposable folded cuvettes (Malvern). Molecular weights were measured by gel permeation chromatography (GPC) on an Agilent 390-MDS equipped with a Polar Gel Guard and two Polar Gel mixed-D columns operating at 60°C. DMF with 5mM NH4BF4 was used as eluent for the GPC analysis and the system was calibrated using narrow molecular weight poly(methyl methacrylate) standards. The GPC samples were prepared at about 1 -2 mg/ml and they were filtrated through a 0.2 pm hydrophilic PTFE filter before injection. Dialysis was performed using semipermeable cellulose tubing (3.5 kDa molecular weight cutoff). Scanning electron microscopy (SEM) images were collected on a ZEISS Gemini SEM. Cryogenic Transmission electron microscopy (cryo-TEM) analyses were performed on a Jeol 2200FS TEM. Static light scattering (SLS) measurements were collected at 25°C on an ALV-CGS3 operating with a vertically polarized laser with l = 632 nm. The measurements were collected over a wide range of concentrations (0.6-10.0 mg/ml) and scattering wave vectors. The incremental refractive index (dn/dc) was measured using a Shodex Rl detector operating at l = 632 nm.

Synthesis of Polymeric Nanogel (N1 )

Nanogel N1 was synthesised in the following three procedures.

Procedure 1 (Synthesis of a macromonomer latex)

Procedure 1 describes the synthesis of a macromonomer latex (e.g. macromonomer latex 1 1) via catalytic chain-transfer polymerisation (CCTP) in a semi-batch emulsion polymerisation process. This procedure is a modified version of that reported Moad et. al. Macromol. Symp. 1996, 111, 13- 23; Haddleton, D. M. Nat. Chem. 2016, 9 (2), 171-178.

The following procedure was performed in a 250 ml glass reactor equipped with a PTFE coated anchor overhead stirrer and a PTFE coated temperature probe. All reagents added to the reactor were purged with nitrogen for 30 minutes prior to addition. Bis[(difluoroboryl) dimethylglyoximato]cobalt(ll) (CoBF) (8.2 mg) and a mixture of methacrylic acid (MAA) and methyl methacrylate (MMA) (MAA:MMA 30:70 v/v mixture, 25 ml_) were purged with nitrogen in separated sealed vials equipped with magnetic bars for 1 h. After this time, 22.0 ml of the monomer mixture was added to the vial containing CoBF using a degassed syringe. This mixture was stirred vigorously until complete dissolution of the catalyst; mild ultrasound treatment was used to favour dissolution in this step. Meanwhile, sodium dodecyl sulfate (SDS) (0.3 g), FhO (130.0 g), 4-4’-azobis(4- cyanovaleric acid) (ACVA) (0.5 g) were added to a 250 ml reactor and purged with nitrogen for 1 h under vigorous stirring at 300 rpm. Note that ACVA it is not soluble at this stage. After this, the reaction mixture was heated up to 72°C, which rendered ACVA soluble. The reaction was started with the addition of 20% by volume of the monomer mixture (the rest was fed at 0.666 ml/min over 24 min, total volume added to the reactor = 20.0 ml) and it was carried out for 1 h at 72°C. Next, the system was heated to 82°C and the reaction was left to reach full conversion for one extra hour to produce the macromonomer latex. Procedure 2 (Synthesis of a chain-extended polymer latex)

The macromonomer latex produced in Procedure 1 was chain-extended with butyl methacrylate (BMA) via reversible addition-fragmentation chain transfer (RAFT)) to produce a chain-extended polymer latex (e.g. chain-extended polymer latex 12) in the following procedure.

120.0 g of macromonomer latex of Procedure 1 was diluted with 38.0 g of water. The reaction was conducted at 85°C while BMA (14.1 ml) and aqueous KPS solution (12.6 ml, 5.6 mg/ml) were fed over 2 h. After feeding, the reaction was allowed to proceed for extra 30 min to produce the chain- extended macromonomer latex. A theoretical BMA degree of polymerisation (DP) of 10 was targeted.

Procedure 3 (Synthesis of Nanoqel N1)

The chain-extended polymer latex of Procedure 2 was solubilised and underwent polymer micelle crosslinking in the following procedure. 133.1 g of chain-extended polymer latex of Procedure 2 was diluted with 40.0 ml water and 37.3 g of NaOH (1 .0 M, aq.) was injected into the system. NaOH was added to a 1 :1 molar ratio with respect to MAA. The system was left to equilibrate at 85°C for 30 min and during this time it turned from milky white to translucent blue. After this time, trimethylolpropane trimethacrylate was added to the system (5.9 ml) and aqueous potassium persulfate (KPS) solution (12.6 ml, 5.6 mg/ml) was fed in the system over 5 h. The system was then allowed to fully react overnight to produce the Nanogel N1. During this stage limited precipitation occurred, which was filtrated over standard Biichner funnel apparatus (filter paper: Whatman 542, particle retention 2.7 pm). The final solid content was 1 1 .7 wt%.

Synthesis of Polymeric Nanogel (N2)

Nanogel N2 was synthesised in the following three procedures.

Procedure 4 (Synthesis of a macromonomer latex)

Procedure 1 describes the synthesis of a macromonomer latex (e.g. macromonomer latex 1 1) via catalytic chain-transfer polymerisation (CCTP) in a semi-batch emulsion polymerisation process. This procedure is a modified version of that reported Moad et. al. Macromol. Symp. 1996, 111, 13- 23; Haddleton, D. M. Nat. Chem. 2016, 9 (2), 171-178.

The following procedure was performed in a 250 ml glass reactor equipped with a PTFE coated anchor overhead stirrer and a PTFE coated temperature probe. All reagents added to the reactor were purged with nitrogen for 30 minutes prior to addition. Bis[(difluoroboryl) dimethylglyoximato]cobalt(ll) (CoBF) (5.5 mg) and a mixture of methacrylic acid (MAA) and methyl methacrylate (MMA) (MAA:MMA 30:70 v/v mixture, 25 ml_) were purged with nitrogen in separated sealed vials equipped with magnetic bars for 1 h. After this time, 22.0 ml of the monomer mixture was added to the vial containing CoBF using a degassed syringe. This mixture was stirred vigorously until complete dissolution of the catalyst; mild ultrasound treatment was used to favour dissolution in this step. Meanwhile, sodium dodecyl sulfate (SDS) (0.3 g), H2O (130.0 g), 4-4’-azobis(4- cyanovaleric acid) (ACVA) (0.5 g) were added to a 250 ml reactor and purged with nitrogen for 1 hour under vigorous stirring at 300 rpm. Note that ACVA it is not soluble at this stage. After this, the reaction mixture was heated up to 72°C, which rendered ACVA soluble. The reaction was started with the addition of 20% by volume of the monomer mixture (the rest was fed at 0.666 ml/min over 24 min, total volume added to the reactor = 20.0 ml); this stage of the reaction was carried out for a total period of 1 hour at 72°C. Next, the system was heated to 82°C (Procedure 4* of Table 1 below). After the 2 hour reaction time, more water (60.0 g) was added to the system. The macromonomer was chain-extended by feeding monomer (MAA:MMA 30:70 v:v, 16.0 g, 15.4 ml) and aqueous potassium persulfate (KPS) solution (16.0 ml, 5.6 mg/ml) over 3h at 85°C (Procedure 4** of Table 1 below). The reaction mixture was left for extra 30 min after this time to reach full conversion to produce the macromonomer latex.

Procedure 5 (Synthesis of a chain-extended polymer latex)

The macromonomer latex produced in Procedure 4 was chain-extended with butyl methacrylate (BMA) via reversible addition-fragmentation chain transfer (RAFT)) to produce a chain-extended polymer latex (e.g. chain-extended polymer latex 12) in the following procedure.

120.0 g of latex were diluted with 23.0 g of water. The reaction was conducted at 85°C while BMA (5.6 ml) and aqueous KPS solution (5.0 ml, 5.6 mg/ml) were fed over 2 h. After feeding, the reaction was allowed to proceed for an extra 30 minutes to produce the chain-extended macromonomer latex. A theoretical BMA degree of polymerisation (DP) of 10 was targeted.

Procedure 6 (Synthesis of Nanoqel N2)

The chain-extended polymer latex of Procedure 5 was solubilised and underwent polymer micelle crosslinking in the following procedure.

133.1 g of BMA chain-extended latex were diluted with 22.0 ml water and 51 .3 ml_ of NaOH (1 .0 M, aq.) were injected into the system. NaOH was added to a 1 :1 molar ratio with respect to MAA. The system was left to equilibrate at 85°C for 30 min and during this time it turned from milky white to translucent blue. Afterthis time, trimethylolpropane trimethacrylate was added to the system (5.6 ml) and aqueous KPS solution (6.0 ml, 5.6 mg/ml) was fed in the system over 5 h. The system was then allowed to fully react overnight to produce the Nanogel N2. During this stage limited precipitation occurred, which was filtrated over standard Biichner funnel apparatus (filter paper: Whatman 542, particle retention 2.7 pm). Final solid content: 1 1 .4 wt%.

It should be noted that Procedures 1 and/or 4 may be carried out using other suitable cobaloximes. For example, bis[(difluoroboryl) diethylglyoximato]cobalt(ll) (Et-CoBF) may also be used in place of CoBF to produce comparable results in terms of polymer molecular weight distributions and dispersities. Advantageously, if bis[(difluoroboryl) diethylglyoximato]cobalt(ll) (Et-CoBF) is employed in either of Procedures 1 or 4 then the concentration of the catalyst used may be lower, e.g. four times lower than the concentration required if CoBF is employed. Without wishing to be bound by theory, it is thought that this is because Et-CoBF has a much higher MMA/water partitioning coefficient than that of CoBF.

It should be noted that Procedure 3 and/or 6 may instead be carried out using trimethylolpropane triacrylate or trimethylolpropane ethoxylated triacrylate (avg. Mw = 428 g/mol) in place of trimethylolpropane trimethacrylate to obtain nanogels with similar results to those described.

Analysis of Nanogel N1 and Nanogel N2

Referring now to Table 1 , there is shown the number (M _n ) average molecular weight, weight (M _w ) average molecular weight, polymer dispersity (PD) as measured by gel permeation chromatography (GPC), and the degree of polymerisation, for the products of Procedures 1 and 2 (macromonomer latexes), and Procedures 4 and 5 (chain-extended macromonomer latexes) during the synthesis of nanogel N1 and nanogel N2. Average molecular weights were rounded up to the closest hundred.

Referring also to Figure 4, there is shown the ¹ H-NMR spectrum 4 after completion of Procedure 4* (before addition of KPS) during the synthesis of nanogel N2. There is shown the labels a and b in the ¹ H-NMR spectrum, which are the integrals used to calculate the degree of polymerisation (DP) = m + 1 of the polymers. The DP was determined on the first block (Procedure 4*) via ¹ H-NMR using the following equation:

The average degree of polymerisation (DP) of the corona hydrophilic block of Procedures 1 and 4 was 17 and 53 respectively, whereas the average degree of polymerisation (DP) of the butyl methacrylate (BMA) core hydrophobic block was 10 in both Procedure 2 and Procedure 5.

Table 1 Analysis of polymer products from Procedures 1 , 2, 4 and 5

‘Procedure 4 before addition of KPS,“Procedure 4 after addition of KPS.

aDegree of polymerisation. Referring now to Table 2A, there is shown data from analysis of the P(MMA-MAA)-PBMA unimers of nanogel N1 , N2 during Procedures 2 and Procedure 5 respectively but prior to crosslinking in Procedures 3 and 6 respectively. Referring also to Table 2B, there is shown the data from analysis of the nanogels N1 , N2 after Procedures 3 and 6 respectively. There is shown the number (Mn) average molecular weight, the weight (Mw) average molecular weights, the polymer dispersity (PD), the radius of radius of gyration (R _g ), the form factor p, the hydrodynamic diameter (d _hi ), and the polydispersity index (PDI), for the unimers of nanogels N1 , N2. Gel permeation chromatography (GPC) was performed on the P(MMA-MAA)-PBMA unimers prior to self-assembly. Static light scattering (SLS) was performed on the crosslinked micelles to obtain the radius of gyration (R _g ) and the form factor p = R _g /R _h , where R _h is the radius of hydration.

Table 2A Analysis of the P(MMA-MAA)-PBMA unimers of Nanogel N1 and N2 synthesised in Procedures 2 and 5 respectively

aEluent for GPC: DMF + 5 mM NH ₄ BF ₄ , calibration: PMMA narrow standards.

Table 2B Analysis of the Nanogel N1 and N2 synthesised after Procedures 3 and 6 respectively

Referring now to Figure 5A, there is shown a cryogenic transmission electron microscopy (cryo- TEM) image 5 of a 1.0 wt% aqueous suspension of the copolymer micelles of Procedure 3 prior to crosslinking. The scale bar is 50 nm. The copolymer micelles were produced in Procedure 3 by addition of base (NaOH) to the chain-extended polymer latex of Procedure 2, which caused the chain-extended polymer latex to disassemble to form an aqueous dispersion of copolymer micelles (shown in image 5). Subsequently in Procedure 3, the copolymer micelles were cross-linked with trimethylolpropane trimethacrylate to form nanogel N1.

Referring also to Figure 5B, there is shown cryo-TEM images 5a, 5b of the nanogel N1 (4a) and nanogel N2 (4b) after crosslinking with trimethylolpropane tri methacrylate in Procedures 3 and 6 respectively. The scale bar is 50 nm. Referring now to Figure 6, there is shown a graph 6 showing the hydrodynamic diameter (d _hi ) of nanogel N1 and nanogel N2 before and after crosslinking. The data was obtained using dynamic light scattering (DLS) analysis of the micelles suspended in methanol. There is shown the hydrodynamic diameter (d _hi ) of nanogel N1 before crosslinking 61 a, the hydrodynamic diameter (d _hi ) of nanogel N1 after crosslinking 61 b, the hydrodynamic diameter (d _hi ) of nanogel N2 before crosslinking 62a, and the hydrodynamic diameter (d _hi ) of nanogel N2 after crosslinking 62b. The graph 6 shows that the cross-linking step of Procedures 3 and 6 was successful.

In addition, the graph 6 shows complete solvation of the unimers of the nanogel N1 , N2 if the crosslinking step is not carried out. For both the nanogels, N1 and N2, it is shown that the hydrodynamic diameter distribution (d _H /nm) changes when the non-crosslinked polymer micelles are added to methanol and analysed. It is shown that the hydrodynamic diameter (d _hi ) of the nanogels before crosslinking 62a is very low and comparable to that of the unimers before forming the micelles, in comparison with the hydrodynamic diameter (d _hi ) of the nanogels after crosslinking 62b.

Referring now to Figure 7, there is shown ¹ H-NMR spectra of the vinyl region of nanogel N1 7a and nanogel N2 7b. The ¹ H-NMR spectra 7a and 7b show that the residual vinyl groups are still present after crosslinking during Procedures 3 and 6 respectively. Additionally, the ¹ H-NMR spectra 7a and 7b also confirm the presence of two different types of carbon-carbon double bond, which are reactive towards further polymerisation; (i) the w-end macromonomer vinyl groups; and (ii) the pendant vinyl groups from the trifunctional crosslinker.

Referring now to Figure 8, there is shown a graph 8 showing the size distribution by dynamic light scattering of nanogel N1 before freeze drying 8a, and after freeze drying 8b. There is also shown a photograph 80 of the freeze-dried powder of nanogel N1 . Advantageously, the freeze-dried powder of the nanogels of the invention can be used instead of the colloidal suspension in applications, e.g. emulsion polymerisation of styrene, by being easily re-dispersed in water. More advantageously, the nanogels, e.g. nanogel N1 , can be stored as a dried powder, for example, a dried powder obtained by freeze-drying.

Examples 1 to 33: Use of Nanogel N1 or N2 as Stabilisers in Emulsion Polymerisation

The nanogel N1 and N2 synthesised in Procedures 1 to 6 were used as stabilisers in emulsion polymerisations of styrene in Examples 1 to 14 (Nanogel N1) and Examples 15 to 33 (Nanogel N2) according to Examples of latex particles of the invention. The reactions of the Examples 1 to 33 were carried out in either a 250 ml reactor apparatus, or a sealed 250 ml round bottom flask equipped with an oval stirrer bar. No difference was found when repeating the same reactions with the two set ups. The reactions were carried out in deionized water at 75°C, pH 8.8, using potassium persulfate (KPS) as initiator. The amount of nanogel stabiliser (N1 or N2) was varied in each of the following Examples.

Example 15

An aqueous dispersion of nanogel N2 (3.90 g) was diluted with H2O (148.5 g). The pH of the suspension was adjusted to 8.8 using aq. HC1 1 .0 M. The reaction mixture was charged into a 250 ml reactor and was purged with nitrogen for 30 minutes. Next, styrene (16.6 ml), which had been previously purged with nitrogen for 30 min, was injected into the reactor using a degassed syringe. The system was heated up to 75°C. The reaction was started upon injection of an aqueous KPS solution (1 .0 ml, 1 1 .3 mg/ml) and was run overnight to afford the latex of Example 15.

Examples 1 to 14, and Examples 15 to 33

Referring now to Table 3 and Table 4, there is shown reaction conditions used for the emulsion polymerisations of styrene (Sty) of Examples 1 to 14 (Table 3) using Nanogel N1 as a stabiliser, and Examples 15 to 33 (Table 4) using Nanogel N2 as a stabiliser. The Examples were conducted using a comparable procedure to that described for Example 15 with the appropriate reaction conditions and reagent quantities to afford latex particles according to Examples of the invention.

It is noted that when NaCI was included in the reaction, an aqueous solution of NaCI was adopted instead of deionised water in the initial dilution of the nanogel dispersion.

Table 3 Reaction conditions and analysis of resulting latex particles of Examples 1 to 14

Key: Solid content (SC), Initial (pHO) and final (pHf) pH, hydrodynamic diameter (dH) and polydispersity index (PDI) from DLS measurements. KPS/Sty: 0.07 wt%. ^b ln the polymerisations including NaCI, a NaCI aqueous solution of a given concentration was used instead of deionized water in order to obtain the desired [NaCI]; °Calculated using the equation (N 1 *11 7)/Sty where 11.7 is the %solid content of Nanogel N1 suspension

Table 4 Reaction conditions and analysis of resulting latex particles of Examples 15 to 33

Key: KPS/Sty: 0.15 wt%. ^a An aqueous solution of 1 .82x10 ^-3 M sodium hydrogen carbonate (NaHC0 ₃ ) was adopted instead of deionized water; ^b Calculated using the equation (N2 ^* 1 1 4)/Sty, where 1 1.4 is the %solid content of Nanogel N2 suspension.

Comparative Example 1 : Emulsion polymerisation in the absence of nanogels

An emulsion polymerisation was carried out in the absence of the nanogels (N) of the invention (e.g. nanogel N1 or nanogel N2). Referring to Table 5, there is shown reaction conditions used for the soap-free emulsion polymerisation of styrene of Comparative Example 1 , which was conducted using a comparable procedure to that described for Example 15 with the appropriate conditions and quantities of reactants, in the absence of nanogels as stabilisers. Table 5 Reaction conditions and analysis of the resulting latex particles of Comparative Example 1

Key: KPS/Sty: 0.15 wt%. ^a An aqueous solution of 1.82x10 ^-3 M sodium hydrogen carbonate (NaHC0 ₃ ) was adopted instead of deionized water; Calculated using the equation (Nanogel N/Styrene) * 100

Referring now to Figure 9, there is shown an SEM image 9 of the polystyrene latex particles of Comparative Example 1. The scale bar is 200 nm. This image 9 shows that in the absence of nanogels, a polystyrene latex of narrow spherical particle size distribution is obtained ( d _H = 292 nm). The resulting latex particles of CE1 were diluted in deionised water before the SEM image 9 was taken. The pH was adjusted to 8.1 and a 1 :1 NaHCC>3:KPS was used to bufferthe drop in pH resulted by the KPS decomposition.

Referring now to Figure 10, there is shown data for the hydrodynamic diameter (d _H ) (represented with solid circles) and polydispersity index (PDI) (represented with crosses) of latex particles obtained via emulsion polymerisation of styrene at pH 8.8 using nanogels N1 , N2. There is shown graph 10A showing the data for latex particles obtained via emulsion polymerisation using the nanogel N1 , and graph 10B showing the data for latex particles obtained via emulsion polymerisation using the nanogel N2. Data points labelled with a‘b’ refer to emulsion polymerisation reactions run in the presence of a buffering agent, sodium hydrogen carbonate (NaHCC>3), to counteract the pH drop from the KPS decomposition.

The data shown in graph 10B shows that the use of the nanogel N2 in particular had a pronounced effect on the average particle diameter, and its distribution. Upon addition of small amounts of the nanogels of the invention, a marked reduction in particle diameter was observed, with a broadening of the particle size distribution upon further increased amounts of nanogels.

Without wishing to be bound by theory, it is thought that the addition of the nanogels had a major effect on the latex particle formation step in the emulsion polymerisation. It is thought that in a soap- free emulsion polymerisation (i.e. also in the absence of nanogels), nucleation of latex particles takes place in the water phase following the so-called homogenous nucleation mechanism (HUFT-theory); the monomer dissolved in the continuous phase polymerises until it reaches a degree of polymerisation, j _C nt , at which the waterborne oligomer collapses forming a primary particle. In the present case, growing oligomers in the water phase can be captured by the nanogels instead before j _c ri _t is reached, hereby influencing the latex particle nucleation process. This phenomenon resembles the influence on the nucleation of latex particles and their stabilization by inorganic nanoparticles of various morphologies (e.g. spheres, disks, sheets) and organic Janus particles in the so-called ab initio Pickering emulsion polymerisation process. In Pickering emulsion polymerisations using inorganic nanoparticles the morphology of the resulting latex generally is that of a polymer particle with an outer armour of relatively close packed nanoparticles.

Instead, electron microscopy analysis of the polymer latexes made in presence of relatively small amounts of nanogels (< 3.0 wt.% with respect to monomer) revealed polystyrene particles with no more than one nanogel lobe on the surface. Referring also to Figure 1 1 , there is shown an SEM image 1 1 of the emulsion polymerisation of styrene conducted at pH 8.8 and at 2.9 wt% of nanogel N2 with respect to the monomer (Example 27, Table 4). The scale bar is 200 nm. It is shown that no more than one nanogel can be seen on the surface on the polystyrene latex particles. It is noted that some particles may comprise more than one nanogel lobe on the surface on the side of the particle that is not visible in the SEM image 1 1 .

Advantageously, the nanogels and the method of emulsion polymerisation of the invention provides versatile access to polymer Janus particles, characterized by a single nanogel protrusion.

Referring now to Figure 12, there is shown an SEM image 12 of the emulsion polymerisation of styrene conducted at pH 8.8 and at 15.2 wt% of nanogel N1 with respect to monomer (Example 2, Table 3). The scale bar is 100 nm. It is shown that more patches can be seen on top of the polystyrene sphere.

Therefore, Figure 12 shows that emulsion polymerisations carried out at higher concentrations of nanogels of the invention produced latex particles with multiple lobes of attached nanogels.

Moreover, it has been shown to be important that the nanogels are crosslinked rather than using non-crosslinked polymer micelles instead. Referring now to Figure 13, there is shown an SEM image 13 of an emulsion polymerisation of styrene conducted at pH 8.8 using un-crosslinked nanogel N2 polymer micelles (2.9 wt% with respect to monomer) (Procedure 6) showing mostly spherical particles. The scale bar is 100 nm. This shows mostly spherical latex particles without distinct patches were observed when non-crosslinked polymer micelles were used.

Advantageously, the reaction conditions of the emulsion polymerisation can be varied in a simple way to obtain particles with a range of different morphologies. Specifically, for example, the pH of the emulsion polymerisation may be altered to obtain particles with different morphologies. The inventors have surprisingly found that patchy particles, as well as the patch density (i.e. the number of patches per particle), can be selectively targeted by changing the reaction conditions of the emulsion polymerisation.

Referring now to Figure 14, there is shown a graph 14 showing the size variation 14A of latex particles obtained from an emulsion polymerisation using nanogel N1 , and the z-potential variation 14B of latex particles obtained from an emulsion polymerisation using nanogel N1 , both as a function of pH. There is further shown the different particle morphologies 14C, 14D, 14E that are obtained as the reaction conditions are varied. It is shown that as the double layer is compressed, different particle morphologies 14C, 14D, 14E can be obtained in the styrene emulsion polymerisation.

Referring also to Figure 15, there is shown a graph 15 showing the size variation 15A of latex particles obtained from an emulsion polymerisation using nanogel N2, and the z-potential variation 15B of latex particles obtained from an emulsion polymerisation using nanogel N2, both as a function of pH in 0.5 wt% in water.

Without wishing to be bound by any theory, at pH 8.8, the nanogels of the emulsion polymerisation are colloidally stable due to the presence of deprotonated carboxylic acid groups in their corona. Upon decreasing the pH of the nanogel dispersion in water, a decrease in the average nanogel hydrodynamic diameter is observed as a result of compression of the double layer down to ca. pH 5.5, below which an increase in size and dispersity was observed. In this lower pH range, the loss of surface charge due to the protonation of the carboxylic acid groups induces particle clustering.

Therefore, it has been found that the ability to control the charge density of the nanogels and the corresponding colloidal stability leads to unprecedented control of patch density in the emulsion polymerisation during synthesis of polymer colloid latexes.

Referring now to Figure 16, there is shown graphs 16A, 16B, showing the effect of initial nanogel dispersion pH on the latex particle size and distribution in the emulsion polymerisation of styrene in the presence of nanogel N1 (graph 16A) and nanogel N2 (graph 16B). There is shown data for the hydrodynamic diameter (d _hi ) (represented with solid circles) and polydispersity index (PDI) (represented with crosses) of latex particles obtained in the emulsion polymerisations of styrene.

In the case of nanogel N2, the polymerisations at pH 4.5 and 5.0 coagulated overnight.

Therefore, it has been shown that emulsion polymerisations conducted using either nanogel N1 or nanogel N2 at different pH result in stable latexes for both nanogel N1 and nanogel N2 down to about pH 5 to 5.5. However, at more acidic conditions, i.e. below pH 5, either coagulation (nanogel N2) or latexes with broad particle size distributions (nanogel N1) are obtained.

Referring now to Figure 17, there is shown a series of false coloured SEM images 17 of emulsion polymerisations using nanogel N1 at 2.8 wt% with respect to monomer, wherein the pH was adjusted to 8.8 (image 17A), 5.5 (image 17B), 5.0 (image 17C) and 4.5 (image 17D) prior to polymerisation. The scale bar is 100 nm in each case. As shown in image 17B, an emulsion polymerisation conducted at pH 5.5 using nanogel N1 results in the formation of monodisperse patchy particles, where instead of just one, a few nanogel lobes can be seen on the polystyrene surface.

As is shown in image 17C and 17D, when the pH is further decreased to 5.0 and 4.5, an increase in patch density on the surface was achieved. In addition, overall larger particles were obtained.

In the emulsion polymerisation of image 17D, which was conducted at pH 4.5, some coagulum was formed. Without wishing to be bound by any theory, we believe that this is logical as this reaction operates well below the pKa of the carboxylic acid groups, placing the nanogels at the edge of their colloidal stability. Under these conditions the nanogels can operate as conventional Pickering stabilizers, in other words, they can adhere to the interface of monomer droplets.

Referring also to Figure 18, there is shown an SEM image 18 showing the formation of bigger patchy particle in an emulsion polymerisation of styrene using nanogel N1 as stabilisers at 2.8 wt% with respect to monomer. The pH of the nanogel dispersion was adjusted to pH 4.5 priorto polymerisation (Example 13, Table 3). The SEM image 18 shows that small amounts of polymerised monomer droplets with a patchy layer of nanogel particles were observed. Without wishing to be bound by any theory, it is thought that, under these conditions, the nanogels are operating as conventional Pickering stabilisers by adhering to the interface of monomer droplets.

Referring now to Figure 19, there is shown a rough estimate of the variation in the number of patches found on the polystyrene surface when the polymerisation was started at different pH, using nanogel N1 as stabilisers at 2.8 wt% with respect to monomer. The patches were manually counted from SEM images and multiplied by two to account for the hidden surface of the bottom half of the particles. In the case of the reaction run at pH 8.8 (labelled as 19a) the average was assumed to be one.

Therefore, by regulating the pH in emulsion polymerisations using nanogel N1 , the number of patches on the polystyrene latex surface could be varied from 1 to roughly 20 per latex particle.

However, as shown in Figure 15 for nanogel N2, the patch density control at pH < 5.5 is not observed. Without wishing to be bound by any theory, it is thought that this is as a result of the reduced stability at low pH values.

It has also been found by the inventors that the latex particles synthesised during the emulsion polymerisation may be prevented from coagulating in pH ranges below 5.5 by decreasing the pH in- situ during particle formation. This can be conveniently achieved by increasing the radical flux, or in other words, by adding more initiator to the system while operating at the same temperature. In fact, the decomposition of persulfates in water is known to release hydrogen sulphate ions and to be acid catalysed. In absence of NaHCC>3 as buffer and at very low nanogel concentrations, for example 0.1 1 wt% with respect to monomer in Example 14 (Table 3) and Example 26 (Table 4), the composition of KPS resulted in pH drop in-situ to ca. 3.4 during the reaction.

Referring now to Figure 20, there is shown a graph 20 showing the variation of the [H ⁺ ] in a blank version of Example 14 (Table 3) and Example 26 (Table 4), which was conducted without styrene and nanogels, at 0.15 mg/ml of KPS and 75°C. The graph 20 shows a qualitative trace interpolation of the data. The point at which the pH would be 5.0 is labelled as 20a.

Significantly, the graph 20 shows that under these reaction conditions, the pH takes about 14 min to drop to ca. 5.0. Therefore, and without wishing to be bound by any theory, the particles may start to grow as small soft peanut-shaped particles that then self-assemble in a supra-colloidal patchy particle when colloidal stability is lost.

Therefore, monodispersed patchy particles of bigger sizes may also be targeted at much lower nanogel concentrations than when the pH is lowered before starting the polymerisation.

Referring also to Figure 21 , there is shown an SEM image 21 of the emulsion polymerisation of styrene conducted using nanogel N2/Sty 0.1 1 wt% and 0.15 mg/ml of KPS (Example 26, Table 3). The scale bar is 200 nm. The nanogel concentration of Example 26 is much lower than other Examples of the invention.

Referring now to Figure 22, there is shown graphs 22A, 22B showing the effect of the concentration of NaCI on latex particle size and distribution in an emulsion polymerisation of styrene in the presence of nanogel N1 (graph 22A) and nanogel N2 (graph 22B). There is shown data for the hydrodynamic diameter (d _hi ) (represented with solid circles) and polydispersity index (PDI) (represented with crosses) of latex particles obtained via emulsion polymerisation of styrene.

In the case of nanogel N2, the emulsion polymerisations at 5.0x10 ^-2 M and 1 .0x10 ^_1 M NaCI coagulated overnight.

Therefore, it has been shown by the inventors that the electrical double layer may be compressed by the introduction of salts. Advantageously, as shown in Figure 22, the latexes formed in the presence of larger salt concentrations were stable up to 1 .0x10 ^-2 M [NaCI] with only partial microcoagulation being observed.

Referring now to Figure 23, there is shown an SEM image of the emulsion polymerisation of styrene operating at 2.8 wt% N1/styrene and 1 .0x10 ^-2 M NaCI. The scale bar is 100 nm. Referring also to Figure 24, there is shown an SEM image of the emulsion polymerisation of styrene operating at 2.9 wt% N2/styrene and 1 .0x10 ^-2 M NaCI. The scale bar is 300 nm. At higher concentrations of NaCI, complete coagulation of the system was observed for both nanogel N1 and nanogel N2. The increase of the ionic strength of the system led to fully armoured polystyrene latex particles, in which a packed shell of nanogel is present at the polystyrene-water interface. These latex particles are generally bigger and more polydispersed than the reaction where no NaCI is added although, for [NaCI] < 1 .0x10 ^-2 M, these do not precipitate over the course of weeks after their synthesis.

It will be appreciated by those skilled in the art that several variations to the aforementioned embodiments are envisaged without departing from the scope of the invention. For example, the invention was mainly investigated in the case of styrene, although it is not only restricted to this monomer. Reactions carried out using other free-radical monomer, such as methyl methacrylate and butyl acrylate, lead to similar results both in terms of stabilization provided by the nanogel and morphology obtained. This shows the universality of this approach which can be extended to all the monomers that are commonly used in emulsion polymerisation processes. It will also be appreciated by those skilled in the art that any number of combinations of the aforementioned features and/or those shown in the appended drawings provide clear advantages over the prior art and are therefore within the scope of the invention described herein.