WO2010097561A2

WO2010097561A2 - Novel amphiphilic copolymers containing a dye group, preparation method thereof and use of same as pigments

Info

Publication number: WO2010097561A2
Application number: PCT/FR2010/050347
Authority: WO
Inventors: Laurent Billon; Hélène GARAY; Leila Ghannam
Original assignee: Uppa - Université De Pau Et Des Pays De L'adour
Priority date: 2009-02-27
Filing date: 2010-03-01
Publication date: 2010-09-02
Also published as: FR2942626B1; WO2010097561A3; FR2942626A1

Abstract

The invention relates to novel amphiphilic copolymers containing at least one dye group, the preparation method thereof and dispersed media containing same, as well as pigments containing these copolymers absorbed on the substrate thereof and the use of said pigments.

Description

NOVEL AMPHIPHILIC COPOLYMERS COMPRISING A GROUP

COLOR, PROCESS FOR THEIR PREPARATION

AND THEIR USES AS PIGMENTS

The present invention relates to novel amphiphilic copolymers comprising at least one dye group, to their process of preparation, to the dispersed media containing them, to the pigments comprising said copolymers adsorbed on a substrate, and to the uses of said pigments.

Pigments must meet several requirements: first, the ability to adhere to a substrate, organic or inorganic, but also the ability to be soluble in water.

The incorporation of a dye into an amphiphilic molecule, especially a copolymer, is therefore particularly desirable. In recent years, macromolecular chemistry has seen the emergence of a new concept of polymerization to obtain macromolecular chains with controlled dimensions: Controlled Radical Polymerization or PRC. Unlike the ionic polymerizations previously used, the PRC makes it possible to study a wide range of monomers (vinyl, acrylic, methacrylic ...) under much less drastic experimental conditions while maintaining a high control of the degree of polymerization and a distribution of lengths of narrow strings.

PRC is based on the existence of a balance between an active (radical) species and an inactive dormant species so as to limit and considerably reduce the concentration of radicals. Several types of PRC are described in the literature, among which mention may be made of Atomic Radical Radiation Polymerization (ATRP), Reversible Chain Transfer Addition-Fragmentation (RAFT) or Nitroxyl (NMP). For the latter, the reaction is based on a thermo-reversible equilibrium between an alkoxyamine (dormant Pn-X species) and a stable (Pn-) / nitroxyl radical pair (X-) (active species) ^{1> 2} under pressure (~ 2 bars).

NMP makes it possible to predict and control the macromolecular dimensions, and also allows the reintroduction of the polymerization to from the previously synthesized homopolymer (macro-initiator), to form well-defined diblock copolymers.

The control of dimensions combined with the possibility of creating complex macromolecular architectures are the reasons for its considerable growth in academic as well as industrial research ³ .

This technique has recently been used for the production of monolayers or polymer brushes from inorganic surface (silica ⁴ , colloidal silica ⁵ , mica ⁶ , flat substrate of silicon ⁷ ) or organic (carbon nanotubes ⁸ , cyclodextrin ⁹ ). More recently, macromolecular architectures such copolymers in blocks ¹⁰ or gradient ¹⁰ ^'11 could be obtained through NMP. Gradient copolymers are macromolecular chains composed of two or more types of monomeric units whose molar composition progressively varies throughout the chain.

This new type of macromolecular architecture can be obtained i) by difference of the reactivity ratios n and r ₂ of the two monomers (intrinsic properties) ¹¹³ or ii) by continuous addition of a second monomer during the polymerization ("forced" polymerization : semi "batch" process) ^{11 b} .

The present inventors have therefore developed, quite unexpectedly, novel amphiphilic copolymers comprising at least one dye group, by PRC NMP.

The present invention therefore relates to novel amphiphilic copolymers comprising at least one dye group, comprising: a hydrophobic end linked by covalent bonding to a chain comprising hydrophilic and hydrophobic monomers, said monomers being linked together by covalent bonding, and assembled in a statistical, block or hydrophilic gradient, said copolymers being characterized in that said hydrophilic and / or hydrophobic units comprise at least one dye group.

Preferably, said hydrophobic end comprises an initiator, or a fragment of such an initiator, and at least one hydrophobic polymer.

The hydrophilic units comprise at least one dye group. Preferably, the dye group is specifically grafted onto the hydrophilic units. According to a particular aspect, the hydrophilic and hydrophobic monomers are bonded to each other by covalent bonding, and assembled in blocks or in hydrophilic gradient, preferably in bulk.

Said initiator may be chosen from the initiators usually used for the NMP PRC polymerization. Thus, there may be mentioned in particular azo type initiators, such as those of the class VAZO sold by Dupont de Nemours, such as VAZO 56 or alkoxyamine type initiators carrying a cationic group.

The fragment of the initiator comprises any radical fragment created by radical cleavage of said initiator. Said cleavage can be achieved by any method known per se to cause a radical break, such as thermal, chemical or photochemical. Thus, for example, the initiator VAZO 56 leads to the reactive radical moiety bearing a cationic group, according to the following reaction:

VAZO 56

Hydrophobic monomers that may be mentioned include vinyls such as acrylates and methacrylates, especially those having a low glass transition temperature (TG), that is to say those for which the glass transition temperature is lower or near. the ambient temperature. Indeed, to improve the adhesive capacity of the copolymer to the substrate, it is preferable that the hydrophobic end is in elastic viscous form, and not in solid form. Thus, mention may especially be made of the following alkyl (metha) crylates: butyl, ethyl, methyl.

As hydrophobic monomers, mention may also be made of styrenic derivatives or acrylonitrile. Cationic or ionizable monomers respectively, such as phosphonate groups or cyclo amino acids, Aminoalkyls and sulfones can be used. Cationic or ionizable groups must be able to have a positively charged ionic group.

As hydrophilic monomer, there may be mentioned in particular acrylic acid, methacrylic acid, acrylamides, methacrylamides, polyalkylene glycol acrylates and polyalkylene glycol methacrylates in which the polyalkylene glycol chain comprises up to 100 alkylene glycol units and the alkylene group is C2 or C3 (ethylene or propylene glycol).

By "statistical assembly" is meant the random succession of hydrophilic and hydrophobic monomers.

The term "block assembly" means the succession of hydrophilic and hydrophobic blocks, said blocks possibly distinct from each other, comprising at least two monomers.

The term "hydrophilic gradient" is understood to mean the succession of monomers or blocks of hydrophobic and hydrophilic monomers, such that the density of hydrophilic monomers per unit length of chain increases as one moves away from the hydrophobic end. .

By "dye group" is meant any group having a visible absorption spectrum. Said dye group can in particular be chosen from pH-sensitive, photosensitive or thermochromic dye groups, preferably pH-sensitive dyes. As a pH-sensitive dye, there may be mentioned in particular azobenzene derivatives or anthraquinone derivatives, such as alizarin and its derivatives. For pH-sensitive dyes, the derivatives of these compounds are particularly preferred such that they comprise at least one function that can be ionized as a function of the pH, thus capable of relocating the filler and modifying the absorption spectrum of the dye. Thus, for example, one of the OH groups of alizarin, in anionic form at basic pH results in a delocalisation of the charge on the aromatic rings and thus modifies the absorption spectrum of alizarin. Generally, the dye suitable for the invention comprises a polymerizable function capable of copolymerizing with one or more hydrophobic and / or hydrophilic monomer unit (s). Thus, it may be necessary to functionalize a starting dye, known and / or commercially available, so as to introduce such a polymerizable function. By way of illustration, in the case of a polymerization with a unit of acrylic acid type, the functionalization reaction is of the type:

X

Colorαnt-y ⁺ O = C ** Colorαnt ^{^ Z ^} C ^{^ Œ ~ CH2}

CH = CH ₂ O

(I) (H)

For this, the starting dye advantageously has a reactive function Y of hydroxy (OH) or amine type (NH ₂ , NHR where R is an alkyl or aromatic group), so as to react as above. Thus, the dye (II) suitable for the invention will be said to be "functionalized".

The starting dye (I) will be said to be functionalizable.

The copolymers according to the invention therefore have the following properties: i) to change color under the effect of an external stimuli (pH, temperature or wavelength); ii) solubilize both in organic medium and in aqueous medium; iii) adsorb to an inorganic or organic particle.

The dye may be introduced indifferently into one or the other segment of the random, block or hydrophilic gradient copolymers.

According to another object, the present invention also relates to the process for preparing said copolymers according to the invention, by controlled radical polymerization, via nitroxyl derivative (NMP). Generally, said method comprises: i) the step of preparing the macroinitiator by polymerization of one or more hydrophobic monomers in the presence of an initiator or a radical moiety thereof, and a nitroxyl derivative, said initiator and nitroxyl derivative being single and same molecule; ii) stopping this step; iii) the (co) polymerization step between said macro-initiator and one or more hydrophilic and optionally hydrophobic monomers.

The initiator and the radical moiety thereof are as defined above.

As a nitroxyl derivative, mention may be made especially of those marketed by Arkema, such as SG1:

and its derivatives capable of forming the radical species SG1, such as the alkoxyamine derivatives, "Blockbuilder" MAMA: HO-C (= O) -C (CH ₃ ) ₂ -ON (tBu) -CH (tBu) - P (= O) (OEt) ₂ ; or MONANS CH ₃ OC (= O) -C (CH ₃ ) 2-ON (tBu) -CH (tBu) -P (= O) (OEt) 2. When the initiator and the nitroxyl derivative are one and the same molecule, this molecule may for example be derivatives of the "Blockbuilder" MAMA. The first step i) may advantageously be carried out: by using a large excess of hydrophobic monomer relative to the initiator or fragment thereof; thus, the ratio of the concentration of hydrophobic monomer to the concentration of initiator or fragment thereof can generally be between 50 to 2000, for example [butyl acrylate] / [VAZO 56] ≈50 to 1500, and / or using a nitroxyl derivative excess relative to the initiator or fragment thereof; thus, in the case of the initiator VAZO 56 corresponding to 2 molecules of reactive radical fragment, the ratio [SG1] / [VAZO 56] is advantageously greater than 2, for example between 2 and 3, preferably equal to 2.1; and / or operating at a temperature of between 50 ° and 150 ° C; more specifically, in the case of the hydrophobic methacrylate monomer, it is preferred to operate at a temperature of between 70 ° and 90 ° C .; in the case of the hydrophobic acrylate monomer, it is preferred to operate at a temperature of between 100 ° and 120 ° C .; and / or by adjusting the duration of the polymerization so as to obtain a macroinitiator having a desired average molar mass (in number).

It is thus possible to obtain adjustable and controllable molecular weight macroamorers up to 150,000 g. mol ^"1. Generally, increasing the temperature and reaction time allows to increase the average molecular weight.

The duration of the reaction can be controlled by the temperature of the reaction mixture. Indeed, the preparation reaction of the macroinitiator takes place at high temperature as indicated above.

Stopping this reaction can therefore be achieved by simply lowering the temperature below the threshold temperature necessary for the progress of the polymerization reaction, for example return to ambient temperature.

An isolation step of the macroinitiator obtained after steps i) and ii) can be performed before implementing step iii).

The (co) polymerization step between said macro-initiator thus formed in step i) and one or more hydrophilic and optionally hydrophobic monomers may advantageously be carried out:

using a large excess of the hydrophilic and optionally hydrophobic monomer concentration relative to the macroinitiator concentration; thus, the ratio of the concentration of acrylic acid monomer [AA] to the butyl polyacrylate [PBA] macroinitiator concentration can be between 50 and 1500; using a dye defect with respect to the hydrophilic and optionally hydrophobic monomer; and the [Colorant] / [AA] ratio may advantageously be between 0.1 and 1%; and or

in the presence of nitroxyl derivative, especially if it is desired to control the growth of the hydrophilic block; advantageously, a defect of nitroxyl derivative with respect to the macroinitiator is used; thus, the ratio [SG1] / [PBA] may advantageously be between 0.07 and 0.095, preferably around 0.09; and or

by operating at a temperature of between 100 and 120 ° C .; and / or - adjusting the duration of the (co) polymerization so as to obtain an amphiphilic copolymer having a desired average molar mass (in number).

Generally, increasing the temperature and the duration of the reaction makes it possible to increase the average molar mass of the copolymer obtained.

The present invention also relates to amphiphilic copolymers obtainable by the process according to the invention.

The diblock copolymers (FIG. 1 a) can be obtained by carrying out step iii) in the presence of a hydrophilic monomer.

Hydrophilic gradient copolymers (FIG. 1b) can be obtained by implementing step iii) by gradual addition of hydrophilic monomer in the reaction medium containing a hydrophobic monomer.

The random copolymers can be obtained by implementing step iii) in the simultaneous presence of hydrophilic and hydrophobic monomer.

According to another object, the present invention also relates to dispersed media comprising at least one copolymer according to the invention. Thus, mention may in particular be made of aqueous media in which at least one copolymer according to the invention is dispersed. Generally, in such a medium, the copolymers according to the invention self-assemble by their hydrophobic end so as to form micelles. An exemplary micelle representative of the present invention is shown schematically in Figure 2. Generally, said media may have a copolymer concentration of between 1 and 50% by weight, advantageously between 3% and 10%.

The present invention also relates to the process for preparing these media. Thus, these can be prepared by simply suspending said copolymers in the medium in question.

According to another object, the present invention also relates to pigments comprising an organic or inorganic substrate on which said copolymers according to the invention are adsorbed.

As an inorganic substrate, there may be mentioned silica, colloidal silica, mica, flat silicon substrates); as organic support, there may be mentioned carbon nanotubes or cyclodextrins, for example. Mica is particularly preferred. Said pigments are generally in the form of powder.

The present invention also relates to the process for preparing these pigments.

Thus, said process comprises: the step of preparing a dispersed medium according to the invention,

optionally adjusting the desired color of said medium,

suspending the dispersed medium in said substrate, optionally with stirring, and

filtration and drying of the particles in suspension.

Adjustment of the desired color may be necessary when the copolymer does not exhibit the desired color spontaneously in solution.

Thus, the adjustment can be made by changing the color-controlling parameter (s), such as pH, temperature, or wavelength.

In the case of a pH-sensitive dye, the pH variation is managed by adding concentrated acid solution (HCl, H ₂ SO ₄ , ...) to lower the pH or base values (NaOH, KOH ...) to raise these values. The polymers according to the present invention thus make it possible, from a known dye, to obtain a variety of color passing from yellow to blue by a simple modification of the electronic environment (eg: pH in an aqueous medium) of the dye incorporated in such a way. covalent to a macromolecular chain adsorbed on the surface of an inorganic or organic particle.

This approach of random amphiphilic copolymers, with blocks or with hydrophilic gradient, makes it possible to widen the spectrum of colors and especially a greater flexibility and adaptability of the method to be used, because in aqueous medium. This way makes it possible to overcome the usual toxicology and environmental problems with the usual polymers.

The synthesis of amphiphilic diblock copolymers including one of the (hydrophobic) blocks makes it possible to "anchor" the macromolecular chains on the surface of the particles while the hydrophilic segment containing the dye is particularly advantageous in that it makes it possible to modulate the color at will and in an aqueous medium. The colored polymers according to the invention can easily be adsorbed on the particles by dispersion in the solution of said (co) polymers.

FIGURES

Figure 1a schematically shows the synthesis of a diblock copolymer, and Figure 1b schematically shows a random copolymer, where the white spheres represent the hydrophobic units and the gray spheres the hydrophilic units.

Figure 2 shows an example of self-assembled amphiphilic block copolymers, soluble in aqueous medium.

Figures 3a and 3b respectively represent the spectrum of the UV-visible characterization of alizarin a) before and b) after modification, according to example 1.

Figure 4 shows the color variation of the dye chemically bonded to the macromolecular chain by pH adjustment (eg amphiphilic block copolymers). FIG. 5 represents the chromatograms of CES of the macro-initiator PBA and the PBA-b-PAA copolymer obtained by chain extension of the PBA according to Example 2.

FIG. 6 represents an example of adsorption of amphiphilic block copolymers with different pH:

(a) self-assembled copolymers in aqueous medium in the presence of micrometric particles of mica;

(b) micrometric particles recovered after adsorption of copolymers (= pigments).

FIG. 7 represents the curves obtained in TGA making it possible to demonstrate the hybrid character of the pigments synthesized (a) crude mica, (b) copolymer adsorbed at pH = 3 and (c) copolymer adsorbed at pH = 8.

Figure 8 shows the UV-Visible Spectrum obtained in diffuse reflection of the powders of colored pigments at different pH.

The following examples are given by way of non-limiting illustration of the present invention.

EXAMPLES

Example 1 Functionalization of a dye so as to bind it chemically to a macromolecular chain

This type of chemical modification was carried out on a pH-sensitive dye capable of modifying its color by varying pH: alizarin. It is a natural red dye, extracted from the roots of a plant, the madder (Latin name: Rubia). Alizarin was functionalized by introducing a polymerizable vinyl function according to the scheme: CH ₂

65% Alizarin modified ortho modified in meta For that :

1 - 157 ml of CH ₂ Cl ₂ (dichloromethane) are added to 9.83 g (40.95 mmol) of alizarin and then 4.15 g (52.3.10 ^-3 mol) of N (C ₂ H ₅ ) ₃ (triethylamine) are added to this mixture using a syringe, the flask is then placed in an ice bath and the mixture is stirred.

2- After degassing the two-stop vial under nitrogen for 5 to 10 minutes, 5 ml of acryloyl chloride (C ₃ H ₃ OCI) (61.55 mmol) are added to the mixture. The mixture is stirred for one hour at 0 ° C. and then for 24 hours at room temperature. 3- After filtration, the liquid is recovered and brought into the presence of 100 ml of water to remove the salt present.

After drying for 2 days at room temperature, the new product obtained was characterized by IRFT, ¹ H NMR and ¹³ C. The UV-visible spectra of alizarin a) before modification and b) after modification are shown in FIG. . The 1 H NMR spectrum of the modified alizarin is shown in FIG. 3b.

Example 2 Synthesis of Macromolecular Chains with Stimulable Staining

An amphiphilic diblock copolymer having a hydrophobic butyl polyacrylate block (surface affinity, for example with a mica particle) and a hydrophilic polyacrylic acid block (affinity with the aqueous medium whose pH can be easily modulated) was synthesized in using the controlled radical polymerization technique. This synthesis is done in two stages with, initially, the synthesis of the butyl polyacrylate block (reaction a)) which will serve, in a second step, macroinitiator of the polymerization of acrylic acid (reaction b)) . a) Synthesis of the macroinitiator

y AZO 56

Mαcromαrceur PBA

fcj Polymerization of Acrylic Acid

Block Amphiphilic Copolymer PBA-i> - (PAA-stat-dye) where X ^* represents:

and the reaction b) is carried out with the functionalized alizarin according to Example 1, and wherein: m, n are defined with respect to the molar ratios [M] / [Vazo] and [M] / [MacroPBA] and are between 25 and 1500. x, y are determined by NMR Nuclear Magnetic Resonance and Chronic Exclusion Chromatography CES and equal to / from 25 to 1500. a) Synthesis of the macroinitiator

The polymerization of the ABu butyl acrylate monomer is solvent-free, ie by mass. The amounts of ABu monomer are defined from the molar ratio [M] / [Vazo] between 25 and 1500.

By way of example, for a [M] / [Vazo] ratio = 500, 10 g of ABu (0.0781 mole) are mixed with 0.040 g of VAZO (1.5 × 10 ^-4 mole) in order to control the polymerization. SG1 is added to the solution This excess is calculated in relation to the amount of VAZO used ([SG1] / [Vazo]) and is between 2.05 and 2.3 Generally, an excess of 2.1 is used. which corresponds to 0.285 g of SG1 (6.3 × 10 ^-4 mol). The temperature used is between 100 ° and 120 ° C with polymerization times between 30 min and 10 hours. Typically, a temperature of 120 ° C is applied for 4 hours. At the end of the polymerization, the temperature is lowered to ambient temperature and the polymer is recovered by precipitation in a 10/90 water / ethanol mixture. After drying under dynamic vacuum for 12 hours, the polymer is analyzed by NMR (monomer residue) and CES (molecular weight, polymolecularity index). The molar masses obtained are between 3200 and 192 000 g. mol- ¹ and the polymolecularity indices of between 1.1 and 1.4 In the example described, the molar mass Mn is 64,000 g / mol with a polymolecularity index IP of 1.3. This first block of PBA type is characterized by the particularity of having a very high surface affinity with the mica particles. This affinity is enhanced by a cationic NH ₃ ^{+ end} , which can be exchanged with the surface cations of the mica particles. It should be noted that the same syntheses can be carried out by an alkoxyamine initiator MAMA (BlocBuilder) or MONANS. In this case, the macromolecular chains are not terminated by NH ₃ ⁺ ends, but the adhesion is maintained by the "hydrophobic sticker" PBA.

b) Polymerization of Acrylic Acid

From this macro initiator of PBA (5 g or 7.8 × 10 ^-5 mol), the polymerization of acrylic acid AA in solution in dioxane (maximum concentration of AA equal to 3 mol.l ^-1 ) is reinitiated between 100.degree. ° and 120 ° C., in the presence of 0.024 g (8.2 × 10 ^-5 mol) of SG1, 0.0156 g (2.2 × 10 ^-4 mol) of acrylic acid, 0.001 g (4.4 × 10 ^-6 mol) of functionalized dye according to US Pat. Example 1. After 4 hours of polymerization at 120 ° C., the polymer solution is cooled to room temperature and precipitated in ethanol.The polymer is recovered after drying under dynamic vacuum at room temperature.

Thus, amphiphilic diblock copolymers P BA-> - (P AA-stat-Colorant) are prepared.

Thus, the dye was introduced into the hydrophilic segment of PAA, thus leaving a great possibility and flexibility to modulate the pH of the aqueous solution. Colored micelles can thus be obtained over a wide pH range, as shown in FIG. 4. These copolymers have been characterized in order to determine their macromolecular structures and their dimensions by various techniques: ¹ H, ¹³ C, and ¹⁵ P NMR. , CES (chromatogram shown in Figure 5), IRTF and UV-visible spectroscopies, DSC, TGA, light scattering ... EXAMPLE 3 Adsorption of pH-sensitive (pH) sensitive amphiphilic (co) polymers and their counterparts to inorganic or organic particles

Solutions are prepared of the polymers obtained in Example 2 in water at concentrations between 100 and 10 ^"3 g. ^{L" 1.}

The pH of these solutions is varied by adding concentrated solution (mol / l) of acid (HCl, H ₂ SO ₄ , ...) to lower the pH or base (NaOH, KOH. ..) to raise these values between pH 2 and 14.

The following balances take place:

This coloration is possible by virtue of the fact that the dye incorporated in the macromolecular chain can be stimulated by the residual hydroxyl function OH.

The micelles obtained were characterized by DDL, UV-visible spectroscopy and fluorescence so as to demonstrate the amphiphilic nature of these diblock copolymers PBA-> - (PAA-steM3olorant).

In DDL, the hydrodynamic radii of the micelles formed could be determined by hydrophobic interactions of the "sticker" PBA varying between 15 and

40 nm at a pH = 7. This micellization of the amphiphilic copolymers can also be determined by fluorescence using a pyrene probe sensitive to its environment. Subsequently, the polymer is adsorbed on mica particles of nano or micron size to create pigments using the same solution. An example of adsorption of amphiphilic diblock copolymers PBA- b- (P AA-stat-dye) is shown in FIG. 6. This adsorption is carried out by dispersion with magnetic stirring of the micron-sized virgin mica particles in an aqueous solution of amphiphilic block copolymers of 3% concentration whose pH has been adjusted to obtain the desired color. After a variable agitation time of between 1 and 8 hours, the mica particles are recovered by simple filtration and drying. The particles thus filtered retain the color of their original solution.

The inorganic / organic pigments obtained based on PBA-β- (PAA-sfc / -Colorant) copolymers adsorbed on mica particles have been characterized in particular by TGA (FIG.7) so as to highlight the hybrid side of these materials (particles / polymers) as well as by a UV-Visible solid-state spectroscopy technique to highlight the different adsorption spectra as a function of pH (Fig. 8).

REFERENCES

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Claims

Amphiphilic copolymers comprising at least one dye group, comprising a hydrophobic end linked by covalent bonding to a chain comprising hydrophilic and hydrophobic monomers, said monomers being linked together by covalent bonding, and assembled in a statistical manner, in blocks or in hydrophilic gradient, said copolymers being characterized in that said hydrophilic units comprise at least one dye group.

Amphiphilic copolymers according to claim 1, such that said hydrophobic end comprises an initiator, or a fragment of such an initiator, and at least one hydrophobic polymer.

3. Amphiphilic copolymers according to claim 2, wherein said initiator is chosen from NMP PRC polymerization initiators.

Amphiphilic copolymers according to claim 2 or 3, wherein said initiator is an azo initiator.

5. Amphiphilic copolymers according to any one of claims 2, 3 or 4 such that said hydrophobic monomer is selected from acrylates and methacrylates low glass transition temperature (TG) or vinyl monomers.

Amphiphilic copolymers according to any one of the preceding claims, wherein said hydrophilic monomers are selected from acrylic acid, methacrylic acid, acrylamides, methacrylamides, polyalkylene glycol acrylates and polyalkylene glycol methacrylates in which the polyalkylene glycol chain comprises up to 100 units of alkylene glycol and wherein the alkylene group is C2 or C3 (ethylene or propylene glycol).

7. Amphiphilic copolymers according to any one of the preceding claims, wherein said coloring group is chosen from pH-sensitive, photosensitive or thermochromic dye groups.

Amphiphilic copolymers according to any one of the preceding claims, such that said dye is a pH-sensitive dye.

9. Process for preparing an amphiphilic copolymer according to any one of the preceding claims by controlled radical polymerization, via nitroxyl derivative (NMP).

The method of claim 9 comprising: i) the step of preparing a macroinitiator by polymerizing one or more hydrophobic monomers in the presence of an initiator or a radical moiety thereof, and a nitroxyl derivative, said initiator and nitroxyl derivative being able to be one and the same molecule; ii) stopping this step; iii) the (co) polymerization step between said macro-initiator and one or more hydrophilic and optionally hydrophobic monomers.

The method of claim 9 or 10 wherein the initiator or radical moiety thereof is as defined in any one of claims 2 to 4.

12. The method of claim 9, 10 or 1 1, such that the nitroxyl derivative is selected from alkoxyamine derivatives.

13. Process according to any one of claims 9 to 12, wherein said nitroxyl derivative is SG1 of formula:

or its derivatives capable of forming the radical species SG1.

14. Process according to any one of claims 9 to 13, such that step i) is carried out with a ratio of the concentration of hydrophobic monomer to the concentration of initiator or fragment thereof between 50 to 2000.

15. A process according to any one of claims 9 to 14 such that step i) is carried out with an excess of nitroxyl derivative relative to the initiator or fragment thereof.

16. A method according to any one of claims 9 to 15 further comprising a step of isolating the macroinitiator obtained after steps i) and ii) before implementing step iii).

17. Method according to any one of claims 9 to 16 such that step iii) is carried out with an excess of hydrophilic monomer and optionally hydrophobic relative to the macroinitiator.

18. A method according to any one of claims 9 to 17 such that the dye is in default with respect to the hydrophilic monomer and optionally hydrophobic.

19. Amphiphilic copolymer obtainable according to any one of claims 10 to 18.

20. Dispersed medium comprising at least one copolymer according to any one of claims 1 to 8.

21. A process for preparing a dispersed medium according to claim 20 by suspending said copolymers in the medium in question.

22. Pigment comprising an organic or inorganic substrate on which a copolymer according to any one of claims 1 to 8 is adsorbed.

23. Pigment according to claim 22, wherein said substrate is selected from silica, colloidal silica, mica, silicon flat substrates, carbon nanotubes, cyclodextrins.

The process for preparing a pigment of claim 22 comprising:

the step of preparing a dispersed medium according to claim 21,

suspending the dispersed medium in said substrate, and filtering and drying the particles in suspension.

The method of claim 24 further comprising the step of adjusting the desired color of said medium prior to suspending said substrate.