METHOD FOR THE PRODUCTION OF MICROCAPLES AND MICROPARTICLES

Description

[0001] The present invention relates to a process for preparing microparticles and microcapsules of controlled size, in the absence of photopolymerization.

[0002] In many industries, including the chemical, cosmetic, agrochemical, paint, or fuel and lubricant industries, it is important to encapsulate and isolate an active material from the surrounding environment, in order to protect the active from hydrolysis, thermal degradation, oxidation, or other processes that can reduce the active's performance. In addition, many applications within these industries require the particles or capsules produced to have a narrow size range, typically in the micrometer range (especially between 0.1 µm and 20 µm), for example, to have better control over their overall performance.

[0003] In many products manufactured by the chemical industry, such as cosmetics, paints, coatings, or sealants, polymer microparticles are sometimes added to modify their rheological properties or texture. The rheological performance achieved is extremely dependent on the average size of the microparticles and the size range in which they extend (commonly called the size distribution).

[0004] The problem of isolating an active ingredient from the surrounding environment to improve its performance is a relatively new area for a number of industries. In most non-biological industries, performance losses associated with factors such as hydrolysis, thermal degradation, oxidation, and cross-reactivity are addressed by increasing the concentration of the active ingredient to achieve the desired level of performance, which increases the cost and also generates other problems associated with the product formed from such processes.

[0005] In recent years, a large number of particle or capsule manufacturing processes have been developed and reported in the literature, including spray drying, solvent evaporation, interfacial polymerization, and centrifugal extrusion, among many others. However, for industrial-scale particle and capsule manufacturing processes, emulsion techniques dominate. Such processes employ an emulsion-forming step of a hydrophobic oil or wax phase dispersed in an aqueous medium, or alternatively, an aqueous phase dispersed in a hydrophobic oil or wax medium. The two phases are emulsified using either a homogenizer or a stirred vessel equipped with baffles and stabilized using surfactants, lipids, or polymeric emulsifiers. Alternatively, an interface reaction between the two phases can be used for the formation of a polymer shell.

[0006] However, these systems produce emulsions and capsules that are polydisperse or too large (above 20 µm).

[0007] Additionally, these systems require the use of water to form one of the phases. They also require the use of surfactants or similar emulsifiers to stabilize the emulsion, which have the disadvantage of being able to react with the encapsulant or provide contaminants into the different phases.

[0008] The present invention aims to provide particles and capsules containing an active ingredient by implementing a mass process in order to satisfy the volumes to meet the demands of non-biological industries.

[0009] The present invention also aims to provide an emulsification process making it possible to obtain particles and capsules of controlled size, in particular of a size less than 20 µm, or even 5 µm.

[0010] The present invention also aims to provide a method for encapsulating active ingredients which can be carried out in the absence of water and / or surfactants and emulsifiers.

[0011] The present invention also aims to provide a method for manufacturing microparticles and microcapsules by means of emulsions made up of materials which make the drops which compose them on the one hand monodisperse and on the other hand extremely stable.

[0012] Thus, the present invention relates to a process for preparing solid microparticles and microcapsules comprising the following steps: a) the addition with stirring of a composition C'2 into a composition C3, the compositions C'2 and C3 not being miscible in each other, the composition C'2 being either a crosslinkable single-phase composition C2 or an emulsion (E1) comprising drops of a composition C1, comprising at least one active agent, dispersed in a crosslinkable polymeric composition C2, the compositions C1 and C2 not being miscible in each other, the viscosity of the composition C3 being greater than 10,000 mPa.s at 25°C at a shear rate of 10 s -1< and being less than 10,000 mPa.s.s at 25°C at a shear rate of between 100 s -1< and 100,000 s -1< , whereby an emulsion (E2) comprising drops of composition C'2 dispersed in composition C3 is obtained; b) applying shear to the emulsion (E2), said applied shear rate being between 100 s -1< and 100,000 s -1< , whereby an emulsion (E3) comprising drops of composition C'2 of controlled size dispersed in composition C3 is obtained; and c) polymerizing composition C'2, whereby solid microparticles or microcapsules are obtained dispersed in composition C3, and during step c), the emulsion (E3) is left to stand for a period of up to 100 hours.

[0013] Depending on the nature of the composition C'2, the process of the invention makes it possible to obtain microparticles or microcapsules. When the composition C'2 comprises at least one active ingredient, it will then be referred to as microcapsules.

[0014] Depending on the nature of composition C'2, emulsion (E2) is either a simple emulsion comprising drops of composition C2 dispersed in composition C3, or a double emulsion comprising drops dispersed in composition C3 (corresponding to emulsion (E'2) mentioned later).

[0015] Depending on the nature of composition C'2, emulsion (E3) is either a simple emulsion comprising drops of controlled size of composition C2 dispersed in composition C3, or a double emulsion comprising drops of controlled size dispersed in composition C3 (corresponding to emulsion (E'2) mentioned later).

[0016] According to one embodiment, the method of the invention comprises the following steps: a") the addition with stirring of a crosslinkable composition C2 into a composition C3, compositions C2 and C3 not being miscible in each other, the viscosity of composition C3 being greater than 10,000 mPa.s at 25°C at a shear rate of 10 s -1< and being less than 10,000 mPa.s at 25°C at a shear rate of between 100 s -1< and 100,000 s -1< , whereby an emulsion (E2) comprising drops of composition C2 dispersed in composition C3 is obtained; b) applying shear to the emulsion (E2), said applied shear rate being between 100 s -1< and 100,000 s -1< , whereby an emulsion (E3) comprising drops of composition C2 of controlled size dispersed in composition C3 is obtained; and c) polymerizing the composition C2, whereby solid microparticles dispersed in composition C3 are obtained, and during step c), the emulsion (E3) is left to stand for a period of up to 100 hours.

[0017] According to this embodiment, the method of the invention thus allows the production on an industrial scale of populations of emulsion drops of controlled size and in particular less than 20 µm. The control of the size of the drops obtained by the method of the invention is due in particular to the control of the rheological properties of the continuous phase C3.

[0018] According to this embodiment, the method of the invention allows the production of microparticles of controlled size by implementing a polymerization step of the emulsion drops. This polymerization step in particular allows the drops to be solidified and thus eliminates any coalescence.

[0019] According to another embodiment, the aforementioned composition C'2 is an emulsion (E1) obtained by the addition with stirring of a composition C1, comprising at least one active agent, in a crosslinkable polymeric composition C2, the compositions C1 and C2 not being miscible in each other.

[0020] According to this embodiment, the method of the invention comprises the following steps: a1) the addition with stirring of a composition C1, comprising at least one active agent, into a crosslinkable composition C2, the compositions C1 and C2 not being miscible in each other, whereby an emulsion (E1) is obtained comprising drops of composition C1 dispersed in the composition C2; a2) the addition with stirring of the emulsion (E1) into a composition C3, the compositions C2 and C3 not being miscible in each other, the viscosity of the composition C3 being greater than 10,000 mPa.s at 25°C at a shear rate of 10 s -1< and being less than 10,000 mPa.s.s at 25°C at a shear rate of between 100 s -1< and 100,000 s -1< , whereby a double emulsion (E'2) comprising drops dispersed in composition C3 is obtained; b) applying shear to the emulsion (E'2), said applied shear rate being between 100 s -1< and 100,000 s -1< , whereby a double emulsion (E'3) comprising drops of controlled size dispersed in composition C3 is obtained; and c) polymerizing composition C2, whereby solid microcapsules dispersed in composition C3 are obtained, and during step c), the emulsion (E'3) is left to stand for a period of up to 100 hours.

[0021] According to this embodiment, the method of the invention thus allows the production on an industrial scale of populations of double emulsion drops of controlled size and in particular less than 20 µm. The control of the size of the drops obtained by the method of the invention is due in particular to the control of the rheological properties of the continuous phase C3.

[0022] According to this embodiment, the method of the invention allows the production of capsules of controlled size by implementing a polymerization step of the intermediate phase of the double emulsion. This polymerization step allows in particular to solidify the intermediate layer of the capsules and thus eliminates any coalescence.

[0023] Preferably, the microparticles and microcapsules obtained according to the method of the invention have an average diameter (as measured by optical microscopy or by TEM or by light scattering technique) of between 0.1 µm and 20 µm, and preferably between 1 µm and 20 µm. Step a)

[0024] During step a), a composition C'2 is added to a composition C3, this step being carried out with stirring, which means that the composition C3 is stirred, typically mechanically, while the composition C'2 is added, in order to emulsify the mixture of the compositions C'2 and C3.

[0025] The addition of composition C'2 to composition C3 is typically carried out dropwise.

[0026] According to one embodiment, composition C'2 may be an emulsion (E1) as defined above. This emulsion (E1) is prepared according to step a1) as described below.

[0027] During step a1), a composition C1 is added to a crosslinkable composition C2, this step being carried out with stirring, which means that composition C2 is stirred, typically mechanically, while composition C1 is added, in order to emulsify the mixture of compositions C1 and C2.

[0028] The addition of composition C1 to composition C2 is typically carried out dropwise.

[0029] During step a1), composition C1 is at a temperature between 0°C and 100°C, preferably between 10°C and 80°C, and preferentially between 15°C and 60°C. During step a1), composition C2 is at a temperature between 0°C and 100°C, preferably between 10°C and 80°C, and preferentially between 15°C and 60°C.

[0030] Under the addition conditions of step a1), compositions C1 and C2 are not miscible with each other, which means that the quantity (by weight) of composition C1 capable of being solubilized in composition C2 is less than or equal to 5%, preferably less than 1%, and preferentially less than 0.5%, relative to the total weight of composition C2, and that the quantity (by weight) of composition C2 capable of being solubilized in composition C1 is less than or equal to 5%, preferably less than 1%, and preferentially less than 0.5%, relative to the total weight of composition C1.

[0031] Thus, when composition C1 comes into contact with composition C2 under stirring, the latter is dispersed in the form of drops, called simple drops.

[0032] The immiscibility between compositions C1 and C2 also makes it possible to avoid the migration of the active ingredient from composition C1 to composition C2.

[0033] Composition C2 is stirred to form an emulsion comprising drops of composition C1 dispersed in composition C2. This emulsion is also called a “simple emulsion” or C1-in-C2 emulsion.

[0034] To carry out step a1), any type of agitator usually used to form emulsions may be used, such as, for example, a mechanical paddle agitator, a static emulsifier, an ultrasonic homogenizer, a membrane homogenizer, a high-pressure homogenizer, a colloid mill, a high-shear disperser or a high-speed homogenizer. Composition C1

[0035] Composition C1 comprises at least one active ingredient A. This composition C1 serves as a vehicle for active ingredient A in the process of the invention, within the drops formed during the process of the invention and the solid capsules obtained.

[0036] According to a first variant of the process of the invention, composition C1 is single-phase, that is to say that it is pure active ingredient A or a solution comprising active ingredient A in solubilized form.

[0037] According to one embodiment, the active ingredient is solubilized in composition C1.

[0038] According to this variant, composition C1 typically consists of a solution of active ingredient A in an aqueous solution, or an organic solvent, or a mixture of organic solvents, active ingredient A being present in a mass content of from 1% to 99%, relative to the total mass of composition C1. Active ingredient A may be present in a mass content of from 5% to 95%, from 10% to 90%, from 20% to 80%, from 30% to 70%, or from 40% to 60%, relative to the total mass of composition C1.

[0039] According to one embodiment, composition C1 consists of active ingredient A.

[0040] According to another embodiment of the invention, composition C1 is a biphasic composition, which means that the active ingredient is dispersed, either in liquid form or in solid form, in composition C1 and is not completely solubilized in said composition C1.

[0041] According to one embodiment, the active ingredient is dispersed in the form of solid particles in composition C1.

[0042] According to this embodiment, composition C1 may consist of a dispersion of solid particles of the active ingredient in an organic solvent or in a mixture of organic solvents.

[0043] According to this embodiment, composition C1 may consist of a dispersion of solid particles of the active ingredient in an aqueous phase, which comprises water and optionally hydrophilic organic solvents.

[0044] The asset used is for example: a crosslinker, a hardener, an organic or metallic catalyst (such as an organometallic or inorganometallic complex of platinum, palladium, titanium, molybdenum, copper, zinc) used to polymerize polymer, elastomer, rubber, paint, adhesive, sealant, mortar, varnish or coating formulations; a colorant or pigment intended for elastomer, paint, coating, adhesive, sealant, mortar, or paper formulations; a perfume (as defined in the list of molecules established by the International Fragrance Association (IFRA) and available on the website www.ifraorg.org) intended for detergent products such as laundry detergents, household care products, cosmetic and personal care products, textiles, paints, coatings; an aroma, a vitamin, an amino acid, a protein, a lipid, a probiotic, an antioxidant, a pH regulator,a preservative for food compounds and animal feed; a softener, a conditioner for detergent products, laundry detergents, cosmetics and personal care products. In this respect, the active ingredients that can be used are, for example, listed in US patents 6,335,315 and US 5,877,145; an anti-coloration agent (such as an ammonium derivative), an anti-foaming agent (such as an alcohol ethoxylate, an alkylbenzene sulfonate, a polyethylene ethoxylate, an alkylethoxysulfate or alkylsulfate) intended for detergent products and laundry detergents and home care products; a brightening agent, also called a color enhancer (such as a stilbene derivative, a coumarin derivative, a pyrazoline derivative, a benzoxazole derivative or a naphthalimide derivative) for use in detergents, laundry detergents, cosmetics and personal care products; a biologically active compound such as an enzyme, a vitamin,a protein, a plant extract, an emollient agent, a disinfectant agent, an antibacterial agent, an anti-UV agent, a drug intended for cosmetic and personal care products, textiles. These biologically active compounds include: vitamins A, B, C, D and E, para-aminobenzoic acid, alpha hydroxy acids (such as glycolic acid, lactic acid, malic acid, tartaric acid or citric acid), camphor, ceramides, polyphenols (such as flavonoids, phenolic acid, ellagic acid, tocopherol, ubiquinol), hydroquinone, hyaluronic acid, isopropyl isostearate, isopropyl palmitate, oxybenzone, panthenol, proline, retinol, retinyl palmitate, salicylic acid, sorbic acid, sorbitol, triclosan, tyrosine; a disinfectant agent, an antibacterial agent, an anti-UV agent, intended for paints and coatings; a fertilizer, a herbicide, an insecticide, a pesticide,a fungicide, repellent or disinfectant for agrochemicals; a flame retardant (such as a brominated polyol like tetrabromobisphenol A, a halogenated or non-halogenated organophosphorus compound, a chlorinated compound, an aluminum trihydrate, an antimony oxide, a zinc borate, a red phosphorus, a melamine, or a magnesium dihydroxide) for plastics, coatings, paints and textiles; a photonic crystal or photochromophore for paints, coatings and polymeric materials forming curved and flexible screens; a product known to those skilled in the art as phase change materials (PCMs) capable of absorbing or releasing heat when they undergo a phase change,intended for energy storage. Examples of PCMs and their applications are described in "A review on phase change energy storage: materials and applications", Farid et al., Energy Conversion and Management, 2004, 45(9-10), 1597-1615. Examples of PCMs include molten salts of aluminum phosphate, ammonium carbonate, ammonium chloride, cesium carbonate, cesium sulfate, calcium citrate, calcium chloride, calcium hydroxide, calcium oxide, calcium phosphate, calcium saccharate, calcium sulfate, cerium phosphate, iron phosphate, lithium carbonate, lithium sulfate, magnesium chloride, magnesium sulfate, manganese chloride, manganese nitrate, manganese sulfate, potassium acetate, potassium carbonate, potassium chloride, potassium phosphate, rubidium carbonate, rubidium sulfate, disodium tetraborate,sodium acetate, sodium bicarbonate, sodium bisulfate, sodium citrate, sodium chloride, sodium hydroxide, sodium nitrate, sodium percarbonate, sodium persulfate, sodium phosphate, sodium propionate, sodium selenite, sodium silicate, sodium sulfate, sodium tellurate, sodium thiosulfate, strontium hydrophosphate, zinc acetate, zinc chloride, sodium thiosulfate, paraffin hydrocarbon waxes, polyethylene glycols. ,

[0045] According to one embodiment, composition C'2 may be a composition C2 as defined above.

[0046] According to this embodiment, step a) corresponds to step a") described above.

[0047] During step a"), a crosslinkable composition C2 is added to a composition C3, this step being carried out with stirring, which means that composition C3 is stirred, typically mechanically, while composition C2 is added, in order to emulsify the mixture of compositions C2 and C3.

[0048] The addition of composition C2 to composition C3 is typically carried out dropwise.

[0049] During step a"), composition C2 is at a temperature between 0°C and 100°C, preferably between 10°C and 80°C, and preferentially between 15°C and 60°C. During step a"), composition C3 is at a temperature between 0°C and 100°C, preferably between 10°C and 80°C, and preferentially between 15°C and 60°C.

[0050] Under the addition conditions of step a"), compositions C2 and C3 are not miscible with each other, which means that the quantity (by weight) of composition C2 capable of being solubilized in composition C3 is less than or equal to 5%, preferably less than 1%, and preferentially less than 0.5%, relative to the total weight of composition C3, and that the quantity (by weight) of composition C3 capable of being solubilized in composition C2 is less than or equal to 5%, preferably less than 1%, and preferentially less than 0.5%, relative to the total weight of composition C2.

[0051] Thus, when composition C2 comes into contact with composition C3 under stirring, the latter is dispersed in the form of drops, called single drops.

[0052] The immiscibility between compositions C2 and C3 also makes it possible to avoid the migration of the active ingredient from composition C2 to composition C3.

[0053] Composition C3 is stirred to form an emulsion comprising drops of composition C2 dispersed in composition C3. This emulsion is also called a “simple emulsion” or C2-in-C3 emulsion.

[0054] To carry out step a"), any type of agitator usually used to form emulsions may be used, such as an ultrasonic homogenizer, a membrane homogenizer, a high-pressure homogenizer, a colloid mill, a high-shear disperser or a high-speed homogenizer. Composition C2

[0055] Composition C2 is a crosslinkable composition, meaning that it is a composition capable of polymerizing (crosslinking) to give a solid material, to form the polymerized shell of the solid microcapsules of the invention.

[0056] According to the invention, composition C2 is not a photocrosslinkable composition.

[0057] According to one embodiment, composition C2 is a liquid whose viscosity at 25°C is between 500 mPa.s and 100,000 mPa.s at a shear rate of 10 s -1< .

[0058] Viscosity is measured using a Haake Rheostress ™< 600 rheometer equipped with a 60 mm diameter cone with a 2 degree angle, and a temperature control cell set at 25°C.

[0059] Preferably, the viscosity of composition C2 at 25°C is between 1,000 mPa.s and 50,000 mPa.s at a shear rate of 10 s -1< , preferably between 2,000 mPa.s and 25,000 mPa.s, and for example between 3,000 mPa.s and 15,000 mPa.s.

[0060] Preferably, the viscosity of composition C2 is greater than the viscosity of composition C1.

[0061] According to this embodiment, regardless of the viscosity of the active ingredient or its chemical properties, the destabilization kinetics of the emulsion drops (E1) is significantly slow, which allows the shell of the microcapsules to be polymerized during step d) before the emulsion destabilizes. The polymerization, once completed, then provides thermodynamic stabilization.

[0062] Thus, the relatively high viscosity of composition C2 ensures the stability of the emulsion (E1) obtained at the end of step a).

[0063] Preferably, the interfacial tension between compositions C1 and C2 is low. Typically, these interfacial tensions vary between 0 mN / m and 50 mN / m, preferably between 0 mN / m and 20 mN / m.

[0064] The low interfacial tension between compositions C1 and C2 also advantageously ensures the stability of the emulsion (E1) obtained at the end of step a1).

[0065] According to one embodiment, the ratio between the volume of composition C1 and the volume of composition C2 varies between 1:10 and 10:1. Preferably, this ratio is between 1:3 and 5:1, preferably between 1:3 and 3:1.

[0066] This ratio can be adapted to control the thickness of the polymerized microcapsule shell.

[0067] According to one embodiment, composition C2 comprises at least one monomer or polymer, at least one crosslinking agent, and optionally at least one catalyst.

[0068] According to an advantageous embodiment, composition C2 does not comprise a photoinitiator.

[0069] According to one embodiment, composition C2 comprises from 50% to 99% by weight of monomer or polymer, or a mixture of monomers or polymers, relative to the total weight of composition C2.

[0070] According to one embodiment, composition C2 comprises from 1% to 20% by weight of crosslinking agent or a mixture of crosslinking agents, relative to the total weight of composition C2.

[0071] According to one embodiment, composition C2 comprises from 0.001% to 5% by weight of catalyst or a mixture of catalysts, relative to the total weight of composition C2.

[0072] According to one embodiment, composition C2 comprises from 0.001% to 70% by weight of crosslinking agent relative to the total weight of composition C2.

[0073] According to the invention, the term "monomer" or "polymer" designates any basic unit suitable for the formation of a solid material by polymerization, either alone or in combination with other monomers or oligomers.

[0074] These monomers may be chosen from monomers comprising at least one reactive function chosen from the group consisting of acrylate, methacrylate, vinyl ether, N-vinyl ether, mercaptoester, thiolene, siloxane, epoxy, oxetane, urethane, isocyanate and peroxide functions.

[0075] In particular, the monomers may be chosen from monomers carrying at least one of the aforementioned reactive functions and also carrying at least one function chosen from the group consisting of primary, secondary and tertiary alkylamine functions, quaternary amine functions, sulfate, sulfonate, phosphate, phosphonate, carboxylate, hydroxyl, halogen functions, and mixtures thereof.

[0076] The polymers used in composition C2 may be chosen from polyethers, polyesters, polyurethanes, polyureas, polyethylene glycols, polypropylene glycols, polyamides, polyacetals, polyimides, polyolefins, polysulfides and polydimethylsiloxanes, said polymers also carrying at least one reactive function chosen from the group consisting of acrylate, methacrylate, vinyl ether, N-vinyl ether, mercaptoester, thiolene, siloxane, epoxy, oxetane, urethane, isocyanate and peroxide functions.

[0077] Examples of such monomers or oligomers include, but are not limited to, the following polymers: poly(2-(1-naphthyloxy)-ethyl acrylate), poly(2-(2-naphthyloxy)-ethyl acrylate), poly(2-(2-naphthyloxy)-ethyl methacrylate), polysorbitol dimethacrylate, polyacrylamide, poly((2-(1-naphthyloxy) ethanol), poly(2-(2-naphthyloxy) ethanol), poly(1-chloro-2,3-epoxypropane), poly(n-butyl isocyanate), poly(N-vinyl carbazole), poly(N-vinyl pyrrolidone), poly(p-benzamide), poly(p-chlorostyrene), poly(p-methyl styrene), poly(p-phenylene oxide), poly(p-phenylene sulfide), poly(N-(methacryloxyethyl)succinimide), polybenzimidazole, polybutadiene, polybutylene terephthalate, polychloral, polychloro trifluoroethylene, polyether imide, polyether ketone, polyether sulfone, polyhydridosilsesquioxane, poly(m-phenylene isophthalamide), poly(methyl 2-acrylamido-2-methoxyacetate), poly(2-acrylamido-2-methylpropanesulfonic acid), poly-mono-butyl maleate, polybutylmethacrylate,poly(N-tert-butylmethacrylamide), poly(Nn-butylmethacrylamide), polycyclohexylmethacrylamide, poly(m-xylenebisacrylamide 2,3-dimethyl-1,3-butadiene,N,N-dimethylmethacrylamide), poly(n-butyl methacrylate), poly(cyclohexyl methacrylate), polyisobutyl methacrylate, poly(4-cyclohexylstyrene), polycyclol acrylate, polycyclol methacrylate, polydiethyl ethoxymethylenemalonate, poly(2,2,2-trifluoroethyl methacrylate), poly(1,1,1-trimethylolpropane trimethacrylate), polymethacrylate, poly(N,N-dimethylaniline, dihydrazide), poly(isophthalic dihydrazine), polyisophthalic acid, polydimethyl benzilketal, epichlorohydrin, poly(ethyl-3,3-diethoxyacrylate), poly(ethyl-3,3-dimethylacrylate), poly(ethyl vinyl ketone), poly(vinyl ethyl ketone), poly(penten-3-one), polyformaldehyde poly(diallyl acetal), polyfumaronitrile, polyglyceryl propoxy triacrylate, polyglyceryl trimethacrylate, polyglycidoxypropyltrimethoxysilane, polyglycidyl acrylate, poly(n-heptyl acrylate),poly(n-heptyl acrylic acid ester), poly(n-heptyl methacrylate), poly(3-hydroxypropionitrile), poly(2-hydroxypropyl acrylate), poly(2-hydroxypropyl methacrylate), poly(N-(methacryloxyethyl)phthalimide), poly(1,9-nonanediol diacrylate), poly(1,9-nonanediol dimethacrylate), poly(N-(n-propyl) acrylamide), poly(orthophthalic acid), poly(isophthalic acid), poly(1,4-benzenedicarboxylic acid), poly(1,3-benzenedicarboxylic acid), poly(phthalic acid), poly(mono-2-acryloxyethyl ester), polyterephthalic acid, polyphthalic anhydride, polyethylene glycol diacrylate, polyethylene glycol methacrylate, polyethylene glycol dimethacrylate, poly(isopropyl acrylate), polysorbitol pentaacrylate, polyvinyl bromoacetate, polychloroprene, poly(di-n-hexyl silylene), poly(di-n-propyl siloxane), polydimethyl silylene, polydiphenyl siloxane, polyvinyl propionate, polyvinyl triacetoxysilane, polyvinyl tris-tert-butoxysilane, polyvinyl butyral, polyvinyl alcohol, polyvinyl acetate,polyethylene co-vinyl acetate, poly(bisphenol-A polysulfone), poly(1,3-dioxepane), poly(1,3-dioxolane), poly(1,4-phenylene vinylene), poly(2,6-dimethyl-1A-phenylene oxide), poly(4-hydroxybenzoic acid), poly(4-methyl pentene-1), poly(4-vinyl pyridine), polymethylacrylonitrile, polymethylphenylsiloxane, polymethylsilmethylene, polymethylsilsesquioxane, poly(phenylsilsesquioxane), poly(pyromellitimide-1,4-diphenyl ether), polytetrahydrofuran, polythiophene, poly(trimethylene oxide), polyacrylonitrile, polyether sulfone, polyethylene-co-vinyl acetate, poly(perfluoroethylene propylene), poly(perfluoroalkoxyl alkane), or poly(styrene-acrylonitrile).,

[0078] By "crosslinking agent" is meant a compound carrying at least two reactive functions capable of crosslinking a monomer or a polymer, or a mixture of monomers or polymers, during its polymerization.

[0079] The crosslinking agent may be chosen from molecules carrying at least two functions chosen from the group consisting of acrylate, methacrylate, vinyl ether, N-vinyl ether, mercaptoester, thiolene, siloxane, epoxy, oxetane, urethane, isocyanate and peroxide functions.

[0080] As crosslinking agents, we can notably cite: diacrylates, such as 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, polyethylene glycol dimethacrylate, 1,9-nonanediol dimethacrylate, 1,4-butanediol dimethacrylate, 2,2-bis(4-methacryloxyphenyl)propane, 1,3-butanediol dimethacrylate, 1,10-decanediol dimethacrylate, bis(2-methacryloxyethyl) N,N'-1,9-nonylene biscarbamate, 1,4-butanediol diacrylate, ethylene glycol diacrylate, 1,5-pentanediol dimethacrylate, 1,4-Phenylene diacrylate, allyl methacrylate, N,N'-methylenebisacrylamide, 2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane, tetraethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, , triethylene glycol dimethacrylate, polyethylene glycol diglycidyl ether, N,N-diallylacrylamide, 2,2-bis[4-(2-acryloxyethoxy)phenyl]propane, glycidyl methacrylate;multifunctional acrylates such as dipentaerythritol pentaacrylate, 1,1,1-trimethylolpropane triacrylate, 1,1,1-trimethylolpropane trimethacrylate, ethylenediamine tetramethacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate; acrylates also having another reactive function, such as propargyl methacrylate, 2-Cyanoethyl acrylate, tricyclodecane dimethanol diacrylate, hydroxypropyl methacrylate, N-acryloxysuccinimide, N-(2-Hydroxypropyl)methacrylamide, N-(3-aminopropyl)methacrylamide hydrochloride, N-(t-BOC-aminopropyl)methacrylamide, 2-aminoethyl methacrylate hydrochloride, monoacryloxyethyl phosphate, o-nitrobenzyl methacrylate, acrylic anhydride, 2-(tert-butylamino)ethyl methacrylate, N,N-diallylacrylamide, glycidyl methacrylate, 2-hydroxyethyl acrylate, 4-(2-acryloxyaehoxy)-2-hydroxybenzophenone, N-(Phthalimidomethyl)acrylamide, cinnamyl methacrylate.;

[0081] The catalyst may be chosen from organic, metallic, organometallic or inorganometallic catalysts.

[0082] As catalysts, we can notably cite organometallic or inorganometallic complexes of platinum, palladium, titanium, molybdenum, copper, zinc.

[0083] According to one embodiment, composition C2 may further comprise an additional monomer or polymer capable of improving the properties of the shell of the microcapsules and / or of giving new properties to the shell of the microcapsules.

[0084] Among these additional monomers or polymers, we can cite monomers or polymers carrying a group sensitive to pH, temperature, UV or IR.

[0085] These additional monomers or polymers can induce the rupture of solid microcapsules and subsequently the release of their contents, after stimulation via pH, temperature, UV or IR.

[0086] These additional monomers or polymers may be chosen from monomers or polymers carrying at least one reactive function chosen from the group consisting of acrylate, methacrylate, vinyl ether, N-vinyl ether, mercaptoester, thiolene, siloxane, epoxy, oxetane, urethane, isocyanate and peroxide functions, and also carrying one of the following groups: a hydrophobic group such as a fluorinated group, for example, trifluoroethyl methacrylate, trifluoroethyl acrylate, tetrafluoropropyl methacrylate, pentafluoropropyl acrylate, hexafluorobutyl acrylate, or fluorophenyl isocyanate; a pH-sensitive group such as primary, secondary, or tertiary amines, carboxylic acids, phosphate, sulfate, nitrate, or carbonate groups; a UV-sensitive or UV-cleavable group (or photochromic group) such as azobenzene, spiropyran, 2-diazo-1,2-naphthoquinone, o-nitrobenzyl, thiol, or 6-nitro-veratroyloxycarbonyl groups, for example, poly(ethylene oxide)-block-poly(2-nitrobenzylmethacrylate), and other block copolymers, as described in particular in Liu et al., Polymer Chemistry 2013, 4, 3431-3443; an IR-sensitive or IR-cleavable group such as o-nitrobenzyl or 2-diazo-1,2-naphthoquinone, e.g., the polymers described in Liu et al., Polymer Chemistry 2013, 4, 3431-3443; and a temperature-sensitive group such as poly(N-isopropylacrylamide). . Step a2)

[0087] During step a2), the emulsion (E1) obtained in step a') is added to a composition C3, this step being carried out with stirring, which means that the composition C3 is stirred, typically mechanically, while the emulsion (E1) is added, in order to emulsify the mixture of compositions C1, C2 and C3.

[0088] The addition of the emulsion (E1) into the composition C3 is typically carried out dropwise.

[0089] During step a2), the emulsion (E1) is at a temperature between 15°C and 30°C. During step a2), the composition C3 is at a temperature between 15°C and 30°C.

[0090] Under the addition conditions of step a2), compositions C2 and C3 are not miscible with each other, which means that the quantity (by weight) of composition C2 capable of being solubilized in composition C3 is less than or equal to 5%, preferably less than 1%, and preferentially less than 0.5%, relative to the total weight of composition C3, and that the quantity (by weight) of composition C3 capable of being solubilized in composition C2 is less than or equal to 5%, preferably less than 1%, and preferentially less than 0.5%, relative to the total weight of composition C2.

[0091] Thus, when the emulsion (E1) comes into contact with the composition C3 under stirring, the latter is dispersed in the form of drops, called double drops, the dispersion of these drops of emulsion (E1) in the continuous phase C3 being called emulsion (E2').

[0092] Typically, a double drop formed during step a2) corresponds to a single drop of composition C1 as described above, surrounded by an envelope of composition C2 which totally encapsulates said single drop.

[0093] The double drop formed during step a2) may also comprise at least two single drops of composition C1, said single drops being surrounded by an envelope of composition C2 which totally encapsulates said single drops.

[0094] Thus, said double drops comprise a core consisting of one or more single drops of composition C1, and a layer of composition C2 surrounding said core.

[0095] The resulting emulsion (E'2) is usually a polydisperse double emulsion (C1-in-C2-in-C3 emulsion or C1 / C2 / C3 emulsion), meaning that the double drops do not have a clear size distribution in the emulsion (E2').

[0096] The immiscibility between compositions C2 and C3 makes it possible to avoid mixing between the layer of composition C2 and composition C3 and thus ensures the stability of the emulsion (E'2).

[0097] The immiscibility between compositions C2 and C3 also makes it possible to prevent the active ingredient of composition C1 from migrating from the core of the drops to composition C3.

[0098] To carry out step a2), any type of agitator usually used to form emulsions may be used, such as an ultrasonic homogenizer, a membrane homogenizer, a high-pressure homogenizer, a colloid mill, a high-shear disperser or a high-speed homogenizer. Composition C3

[0099] According to the invention, the viscosity of composition C3 at 25°C is greater than 10,000 mPa.s at a shear rate of 10 s -1< and less than 10,000 mPa.s at the shear rate at which c' is carried out), i.e. at a shear rate of between 100 s -1< and 100,000 s -1<.

[0100] Composition C3 can also be referred to as a gelled composition.

[0101] Preferably, the viscosity of composition C3 at 25°C is between 15,000 mPa.s and 100,000 mPa.s at a shear rate of 10 s -1< and less than 5,000 mPa.s at the shear rate at which c' is carried out), i.e. at a shear rate of between 100 s -1< and 100,000 s -1<.

[0102] Preferably, the interfacial tension between compositions C2 and C3 is low. The low interfacial tension between compositions C2 and C3 also advantageously ensures the stability of the emulsion (E2) or (E'2).

[0103] According to one embodiment, the ratio between the volume of emulsion (E1) and the volume of composition C3 varies between 1:10 and 10:1. Preferably, this ratio is between 1:9 and 3:1, preferably between 1:9 and 1:1.

[0104] This ratio can be adapted to control the total amount of active material encapsulated among the resulting population of polymerized microcapsules.

[0105] According to one embodiment, composition C3 comprises at least one branched polymer, preferably with a molecular weight greater than 5,000 g.mol -1<, preferably between 10,000 g.mol -1< and 500,000 g.mol -1<, for example between 50,000 g.mol -1< and 300,000 g.mol -1<.

[0106] Branched polymer means a polymer having at least one branch point between its two terminal groups, a branch point (also called a branch point) being a point on a chain to which a side chain, also called a branch or pendant chain, is attached.

[0107] Among the branched polymers, we can for example cite grafted polymers, comb polymers or even star polymers or dendrimers.

[0108] According to one embodiment, composition C3 comprises at least one polymer with a molecular weight greater than 5,000 g.mol -1< .

[0109] As polymers that can be used in composition C3, the following compounds can be mentioned, used alone or mixed together: cellulose derivatives, such as cellulose ethers: methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, methylhydroxyethyl cellulose, ethylhydroxyethyl cellulose, carboxymethyl cellulose, hydroxypropyl cellulose or methylhydroxypropyl cellulose; polyacrylates (also called carbomers), such as polyacrylic acid (PAA), polymethacrylic acid (PMAA), poly(hydroxyethyl methacrylate) (pHEMA), poly(N-2-hydroxypropyl methacrylate) (pHPMA); polyacrylamides such as poly(N-isopropylacrylamide) (PNIPAM); polyvinylpyrrolidone (PVP) and its derivatives; polyvinyl alcohol (PVA) and its derivatives; polyethylene glycol, polypropylene glycol and their derivatives, such as polyethylene glycol acrylate / methacrylate, polyethylene glycol diacrylate / dimethacrylate, polypropylene carbonate;polysaccharides such as carrageenans, locust bean gums or tara gums, dextran, xanthan gums, chitosan, agarose, hyaluronic acids, gellan gum, guar gum, gum arabic, tragacanth gum, diutan gum, oat gum, karaya gum, ghatti gum, curdlan gum, pectin, konjac gum; protein derivatives such as gelatin, collagen, fibrin, polylysine, albumin, casein; silicone derivatives such as polydimethylsiloxane (also called dimethicone), alkyl silicones, aryl silicones, alkyl aryl silicones, polyethylene glycol dimethicones, polypropylene glycol dimethicone;waxes, such as diester waxes (alkanediol diesters, hydroxyl acid diesters), triester waxes (triacylglycerols, 1,2-alkanediol, ω-hydroxy acid and fatty acid triesters, hydroxymalonic acid, fatty acid and alcohol esters, hydroxyl acid, fatty acid and fatty alcohol triesters, fatty acid, hydroxyl acid and diol triesters) and polyester waxes (fatty acid polyesters). Fatty acid esters which can be used as waxes in the context of the invention are, for example, cetyl palmitate, cetyl octanoate, cetyl laurate, cetyl lactate, cetyl isononanoate, cetyl stearate, stearyl stearate, myristyl stearate, cetyl myristate, isocetyl stearate, glyceryl trimyristate, glyceryl tripalmitate, glyceryl monostearate or glyceryl cetyl palmitate;fatty acids usable as waxes such as cerotic acid, palmitic acid, stearic acid, dihydroxystearic acid, behenic acid, lignoceric acid, arachidic acid, myristic acid, lauric acid, tridecyclic acid, pentadecyclic acid, margaric acid, nonadecyclic acid, heneicosylic acid, tricosylic acid, pentacosylic acid, heptacosylic acid, montanic acid or nonacosylic acid; fatty acid salts, in particular aluminum salts of fatty acids such as aluminum stearate, hydroxyl aluminum bis(2-ethylhexanoate); isomerized jojoba oil; hydrogenated sunflower oil; hydrogenated coconut oil; hydrogenated lanolin oil; castor oil and its derivatives, in particular modified hydrogenated castor oil or compounds obtained by esterification of castor oil with fatty alcohols; polyurethanes and their derivatives; styrenic polymers such as styrene butadiene;and polyolefins such as polyisobutene. ;

[0110] According to one embodiment, composition C3 comprises solid particles such as clays, silicas and silicates.

[0111] As solid particles that can be used in composition C3, mention may be made of clays and silicates belonging in particular to the category of phyllosilicates (also called layered silicas). As examples of silicates that can be used in the context of the invention, mention may be made of Bentonite, Hectorite, Attapulgite, Sepiolite, Montmorillonite, Saponite, Sauconite, Nontronite, Kaolinite, Talc, Sepiolite, Chalk. Synthetic pyrogenic silicas can also be used. The clays, silicates and silicas mentioned above can advantageously be modified by organic molecules such as polyethers, ethoxylated amides, quaternary ammonium salts, long-chain diamines, long-chain esters, polyethylene glycols, polypropylene glycols.

[0112] These particles can be used alone or mixed together.

[0113] According to one embodiment, composition C3 comprises at least one polymer with a molecular weight greater than 5,000 g.mol -1< and solid particles. Any mixture of the compounds mentioned above can be used. Step b)

[0114] In step b), the emulsion (E2) or the emulsion (E'2), consisting of polydisperse drops dispersed in a continuous phase, is subjected to shearing, for example in a mixer, at a shear rate of between 100 s -1< and 100,000 s -1< .

[0115] According to one embodiment, the shear rate applied in step b) is between 100 s -1< and 50,000 s -1< .

[0116] Preferably, the shear rate applied in step b) is between 1,000 s -1< and 20,000 s -1< .

[0117] During step b), emulsion (E2) or (E'2) is introduced into a mixer and is then subjected to shearing which results in the formation of a third emulsion, emulsion (E3) or (E'3), respectively.

[0118] Since the viscosity of composition C3 is less than 10,000 mPa.s at the shear rate at which step b) is carried out, the emulsion (E2) or (E'2) can easily be mixed with any type of stirrer. Thus, to carry out step b), any type of stirrer usually used to form emulsions can be used, such as, for example, a mechanical paddle stirrer, a static emulsifier, an ultrasonic homogenizer, a membrane homogenizer, a high-pressure homogenizer, a colloid mill, a high-shear disperser or a high-speed homogenizer.

[0119] Emulsion (E3) or (E'3) is chemically identical to emulsion (E2) (or (E'2) respectively) but it is made up of monodisperse drops, not polydisperse like (E2) or (E'2).

[0120] Typically, the emulsion (E'3) consists of a dispersion of double drops comprising a core consisting of one or more single drops of composition C1, and a layer of composition C2 surrounding said core, said double drops being dispersed in composition C3.

[0121] The difference between emulsion (E2) (or (E'2)) and emulsion (E3) (or (E'3)) is the variation in drop size: the drops of emulsion (E2) (or (E'2)) are polydisperse in size while the drops of emulsion (E3) (or (E'3)) are monodisperse thanks to the fragmentation mechanism taking place during step c).

[0122] The emulsion drops (E2) (or (E'2)) can only be efficiently fragmented into fine, monodisperse emulsion drops (E3) (or (E'3)) if a high shear stress is applied to them.

[0123] The shear stress σ applied to a drop of emulsion (E2) (or (E'2)) is defined as the tangential force per unit area of ​​drop resulting from the macroscopic shear applied to the emulsion during its stirring during step c).

[0124] The shear stress σ (expressed in Pa), the viscosity of composition C3 η (expressed in Pa.s) and the shear rate γ (expressed in s -1< ) ​​applied to the emulsion (E2) (or (E'2)) during its stirring during step c) are linked by the following equation: σ = ηγ

[0125] Thus, the combination of the viscosity of composition C3 and the shear applied by the mixer makes it possible to apply a high shear stress to the emulsion drops (E2) (or (E'2)) and thus to fragment them into monodisperse drops. Step c)

[0126] Step c) consists of subjecting the emulsion (E3) (or (E'3)) to polymerization, which will allow the polymerization of the composition C2.

[0127] According to one embodiment of the invention, during step c), the simple drops of emulsion (E3) consisting of crosslinkable composition C2 are crosslinked and thus converted into viscoelastic polymeric microparticles.

[0128] According to another embodiment, during step c), the envelope of the double emulsion drops (E'3), consisting of crosslinkable composition C2, is crosslinked and thus converted into a viscoelastic polymeric envelope, encapsulating and protecting the active ingredient from its release in the absence of mechanical stress.

[0129] During step c), the emulsion (E3) (or (E'3)) is left to stand for a period of up to 100 hours. During this time, many emulsion destabilization phenomena well known to those skilled in the art can make the emulsion (E3) (or (E'3)) polydisperse again, such as coalescence, ripening, sedimentation or creaming. An important feature of the present invention is to suppress these phenomena throughout the duration of step c). Indeed, since the viscosity of the composition C3 is greater than 10,000 mPa.s at a shear rate of 10 s -1 < , the mobility of the drops of emulsion (E3) or (E'3) is very greatly reduced and the kinetics of destabilization of the emulsion is very slow compared to the duration of step c).

[0130] Thus, the very high viscosity of composition C3 at a shear rate of 10 s -1< ensures the stability of the emulsion (E3) or (E'3) until step c) is completed.

[0131] According to the invention, the term "polymerization" encompasses any polymerization that does not need to be initiated by exposure to a light source. In particular, the polymerization according to the invention is not photoinitiated.

[0132] The polymerization according to the invention can, for example, be initiated by exposure to heat (thermal initiation), or by simply bringing the reactants into contact with each other, or by simply bringing the reactants into contact with a catalyst.

[0133] According to one embodiment, the method of the invention does not comprise a step of exposure to a UV light source.

[0134] According to one embodiment, polymerization step c) is not a photopolymerization step.

[0135] According to one embodiment, step c) of polymerization of composition C2 is carried out for a period of between 8 hours and 100 hours.

[0136] According to one embodiment, step c) of polymerization of composition C2 is carried out at a temperature between 20°C and 80°C.

[0137] Preferably, step c) of polymerization of composition C2 is carried out for a period of between 8 hours and 100 hours, at a temperature of between 20°C and 80°C.

[0138] The composition obtained at the end of step c), comprising solid microparticles or microcapsules dispersed in composition C3, is ready to use and can be used without being washed or without additional treatment.

[0139] The thickness of the shell of the microcapsules thus obtained is typically between 10 nm and 2.5 µm, preferably between 100 nm and 1000 nm.

[0140] According to one embodiment, the solid microparticles or microcapsules obtained at the end of step c) are free of water and / or surfactant.

[0141] The method of the invention has the advantage of not requiring water in any of the steps described. The method of the invention thus makes it possible to encapsulate water-sensitive compounds.

[0142] The process of the invention has the advantage of not requiring a surfactant in any of the steps described. The process of the invention thus makes it possible to reduce the presence of additives which could modify the properties of the final product obtained after release of the active ingredient. EXAMPLES Example 1 : Preparation of solid microparticles

[0143] This example demonstrates: (i) the use of a gelled C3 composition allowing the production of drops smaller than 20 µm and then preventing the destabilization of the emulsion for 48 hours; (ii) the production of crosslinked microparticles after 48 hours. Composition of C'2 and C3:

[0144] Composition C'2 is a polymerizable PDMS preparation prepared with the Sylgard 184 two-component kit manufactured by Dow Corning. Component 1 of the kit comprises the following products (data provided by Dow Corning): ∘ between 55.0% and 75.0% of dimethyl, methylhydrogen siloxane, ∘ between 15.0% and 35.0% of dimethyl siloxane, dimethylvinyl-terminated, ∘ between 10.0% and 30.0% of dimethylvinylated and trimethylated silica, ∘ between 1.0% and 5.0% of tetramethyl tetravinyl cyclotetrasiloxane, ∘ less than 0.10% of ethylbenzene.

[0145] Kit component #2 includes the following products (data provided by Dow Corning): ∘ less than 200 ppm of a platinum complex, ∘ between 55.0 and 75.0% dimethyl siloxane, dimethylvinyl-terminated, ∘ between 30.0 and 50.0% dimethylvinylated and trimethylated silica, ∘ less than 1.0% tetra(trimethylsiloxy) silane, ∘ 0.5% xylene, ∘ 0.2% ethylbenzene.

[0146] This kit can be considered as the mixture of several polymers, several crosslinkers and a catalyst within the meaning of the invention.

[0147] Composition C'2 includes 15% of component No. 1 and 85% of component No. 2. Composition C3 is a 4% by mass solution of Tego 340FD carbomer (Evonik, Essen, Germany) in distilled water. The solution is stirred at 2000 rpm for 20 minutes using a propeller stirrer. The pH is then adjusted to 6 using a 2M sodium hydroxide solution. The viscosity of composition C3 at 10 s -1< is 52,000 mPa.s. Manufacturing of microparticles:

[0148] Step a"): Composition C'2 is added dropwise to composition C3 while stirring at 500 rpm until a ratio of C'2:C3 = 10:90 by weight is obtained. The agitator used for this step is a mechanical agitator (Heidolph RZR 2021) equipped with a 3 cm diameter deflocculator type propeller.

[0149] Step b): The emulsion (E2) obtained in the previous step is introduced into a Couette type mixer manufactured by the company TSR33. This mixer is composed of 2 concentric cylinders, one mobile and the other fixed, separated by a 100 µm air gap. The rotation of the mobile cylinder makes it possible to apply a uniform shear to all the emulsion contained in the air gap. The emulsion (E2) is subjected to a shear of 1,000 s -1< . At this shear rate, the viscosity of C3 is only 2,500 mPa.s, which allows the emulsion (E2) to easily pass inside the mixer.

[0150] Step c): The emulsion E3) thus obtained is left to stand for 48 hours to allow the particles to polymerize.

[0151] The particles are imaged by interference contrast optical microscopy before and after step c). Image analysis using Image J software provides the size distribution. Figures 1 and 2 represent the size distributions of the capsules obtained at different stages of the process of the invention.

[0152] Before step c), the emulsion drops (E3) have an average size of 8 µm and the width of the size distribution has a full width at half maximum (considered as a simple way to assess monodispersity) of 5 µm ( Figure 1 ). After step c), the polymerized particles have an average size of 8 µm and the width of the size distribution has a width at half-maximum of 5 µm ( Figure 2 ).

[0153] The size distribution is therefore the same before and after 48 hours of polymerization: the emulsion (E3) has not undergone any destabilization thanks to the high viscosity of composition C3. Example 2 : Preparation of solid microcapsules

[0154] This example demonstrates: (i) the use of a gelled C3 composition in order to let the double drops obtained at the end of the shearing step rest for 48 hours without any destabilization; (ii) the obtaining of crosslinked capsules after 48 hours. Composition of C1, C2 and C3:

[0155] Composition C1 is a mixture of paraffin oils (Sigma, St. Louis, MS) with Aerosil 816 (Essen, Germany) (active) at 4% by mass. Composition C2 is a polymerizable PDMS preparation prepared with the Dow Corning Sylgard 184 two-component kit. Composition C2 comprises 30% of component #1 and 70% of component #2. Composition C3 is a solution of Tego 340FD carbomer (Evonik, Essen, Germany) at 4% by mass in distilled water. The solution is stirred at 2,000 rpm for 20 minutes using a propeller stirrer. The pH is then adjusted to 6 using 2M sodium hydroxide solution. The viscosity of composition C3 at 10 s -1< is 52,000 mPa.s. Manufacturing of microcapsules:

[0156] A mechanical stirrer (Heidolph RZR 2021) equipped with a 3 cm diameter deflocculator type stirring propeller is used to carry out all emulsification steps.

[0157] Step a1): Composition C1 is added dropwise to Composition C2 while stirring at 200 rpm until a ratio of C1:C2 = 20:80 by weight is obtained. Stirring is then maintained at 200 rpm for 30 minutes.

[0158] Step a2): the emulsion (E1) thus obtained is added dropwise to the composition C3 with stirring at 500 rpm until a ratio E1:C3 = 10:90 by weight is obtained.

[0159] Step b): The emulsion (E2) thus obtained is stirred at 500 rpm for 20 minutes. Under these conditions, the shear applied to the emulsion (E2), although very little controlled, can be estimated at less than 500 s -1< (for the details of the calculation, refer to: Metzner AB, Otto RE. Agitation of non-Newtonian fluids. AIChE J (1957) 3: 3-10; Wu, J et al., Estimation of agitator flow shear rate. AIChE J (2006) 52: 2323-2332).

[0160] Step c): the emulsion (E3) thus obtained is left to stand for 48 hours without stirring to allow the capsules to polymerize.

[0161] THE Figures 3 to 5 represent interference contrast optical microscopy images taken at different stages of manufacturing.

[0162] There Figure 3 represents double drops of emulsion (E3) after step b).

[0163] There Figure 4 represents polymerized capsules after step c).

[0164] There Figure 5 represents polymerized capsules imaged after undergoing mechanical shear between a microscope slide and coverslip, rubbed against each other. The capsules are intact after this step, showing that they are indeed polymerized.

[0165] An image analysis performed with Image J software allows obtaining the size distribution of the capsules at the different stages of manufacturing. After step b), the double drops have an average size of 6.0 µm and the width of the size distribution has a full width at half maximum (considered as a simple way to evaluate monodispersity) of 5.5 µm. After step c), the polymerized capsules have an average size of 5.8 µm and the width of the size distribution has a full width at half maximum of 5.0 µm. The size distribution is therefore the same before and after the 48 hours of polymerization: the emulsion (E3) has not undergone any destabilization thanks to the high viscosity of the composition C3. Example 3 : Preparation of solid microparticles according to the invention

[0166] This example demonstrates: (i) the use of a gelled C3 composition within the meaning of the invention making it possible to manufacture drops of a size less than 20 µm and then to prevent the destabilization of the emulsion for 48 hours; (ii) the obtaining of crosslinked microparticles after 48 hours. Composition of C'2 and C3:

[0167] • Composition C'2 is a polymerizable PDMS preparation prepared with the Sylgard 184 two-component kit from Dow Corning. Composition C'2 comprises 15% of component No. 1 and 85% of component No. 2. • Composition C3 is a 10% by mass alginate solution. The viscosity of composition C3 is 16,980 mPa.s at 10 s -1< and 6,670 mPa.s at 100 s -1< . This composition C3 is therefore gelled within the meaning of the invention. Manufacturing of microparticles:

[0168] Step a"): Composition C'2 is added dropwise to composition C3 while stirring at 500 rpm until a ratio of C'2:C3 = 10:90 by weight is obtained. The agitator used for this step is a mechanical agitator (Heidolph RZR 2021) equipped with a 3 cm diameter deflocculator type propeller.

[0169] Step b): The emulsion (E2) obtained in the previous step is stirred at 500 rpm for 10 minutes.

[0170] Step c): The emulsion E3) thus obtained is left to stand for 48 hours to allow the particles to polymerize.

[0171] The particles are imaged by interference contrast optical microscopy before and after step c). Image analysis using Image J software provides the size distribution.

[0172] Before step c), the emulsion drops (E3) have an average size of 6.5 µm and the width of the size distribution has a half-width of 3 µm. After step c), the polymerized particles have an average size of 7 µm and the width of the size distribution has a half-width of 3 µm.

[0173] The size distribution is therefore the same before and after 48 hours of polymerization: the emulsion (E3) has not undergone any destabilization thanks to the high viscosity of composition C3. Example 4 (comparative) : Preparation of solid microparticles

[0174] This example demonstrates the use of a non-gelled C3 composition within the meaning of the invention which does not prevent destabilization of the emulsion for 48 hours. Composition of C'2 and C3:

[0175] Composition C'2 is a polymerizable PDMS preparation prepared with the Dow Corning Sylgard 184 two-component kit. Composition C'2 comprises 15% of component No. 1 and 85% of component No. 2. Composition C3 is a 5% by mass alginate solution. The viscosity of composition C3 is 1340 mPa.s at 10 s -1< and 890 mPa.s at 100 s -1< . This composition C3 is therefore not gelled within the meaning of the invention. Manufacturing of microparticles:

[0176] Step a"): Composition C'2 is added dropwise to composition C3 while stirring at 500 rpm until a ratio of C'2:C3 = 10:90 by weight is obtained. The agitator used for this step is a mechanical agitator (Heidolph RZR 2021) equipped with a 3 cm diameter deflocculator type propeller.

[0177] Step b): The emulsion (E2) obtained in the previous step is stirred at 500 rpm for 10 minutes.

[0178] Step c): The emulsion E3) thus obtained is left to stand for 48 hours to allow the particles to polymerize.

[0179] The particles are imaged by interference contrast optical microscopy before and after step c). Image analysis using Image J software provides the size distribution. Before step c), the emulsion drops (E3) have an average size of 15 µm and the size distribution width has a half-height width of 11 µm. After step c), the polymerized particles have an average size of 31 µm and the size distribution width has a half-height width of 12 µm.

[0180] The emulsion (E3) has therefore undergone significant destabilization due to the unsatisfactory properties of C3.

Claims

1. Method for preparing solid microcapsules comprising the steps of: a) the addition, with stirring, of a composition C'2 in a composition C3, the compositions C'2 and C3 not being miscible with each other, the composition C'2 being either a cross-linkable monophasic composition or an emulsion (E1) comprising drops of a composition C1, comprising at least one active ingredient, dispersed in a crosslinkable polymeric composition C2, the compositions C1 and C2 not being miscible in each other, the viscosity of composition C3 being greater than 10,000 mPa.s at 25°C at a shear rate of 10 s-1 and being less than 10,000 mPa.s at 25°C at a shear rate of between 100 s-1 and 100,000 s-1, wherein an emulsion (E2) comprising drops of composition C'2 dispersed in composition C3, is obtained; b) applying a shear to the emulsion (E2), the applied shear rate being between 100 s-1 and 100,000 s-1, wherein an emulsion (E3) is obtained comprising controlled-size drops of composition C'2 dispersed in the composition C3; and c) the polymerization of the composition C'2, wherein solid microcapsules dispersed in the composition C3 are obtained, and wherein during step c), the emulsion (E3) is allowed to stand for a period of up to 100 hours.

2. Method according to claim 1, in which the composition C'2 is an emulsion (E1) obtained by the addition, with stirring, of a composition C1 comprising at least one active ingredient, in a polymeric composition C2, the compositions C1 and C2 being immiscible in one another.

3. Method according to claim 2, comprising the steps of: a1) the addition, with stirring, of a composition C1, comprising at least one active ingredient, in a polymeric composition C2, the compositions C1 and C2 not being miscible with each other, wherein an emulsion (E1) comprising drops of composition C1 dispersed in composition C2 is obtained; a2) the addition, with stirring, of the emulsion (E1) in a composition C3, the compositions C2 and C3 not being miscible with each other, the viscosity of composition C3 being greater than 10,000 mPa.s at 25°C at a shear rate of 10 s-1 and being less than 10,000 mPa.s at 25°C at a shear rate of between 100 s-1 and 100,000 s-1, wherein a double emulsion (E'2) is obtained comprising drops dispersed in the composition C3; b) applying shear to the emulsion (E'2), the applied shear rate being between 100 s-1 and 100,000 s-1, wherein a double emulsion (E'3) is obtained comprising controlled-size drops dispersed in the composition C3; and c) the polymerization of the composition C2, wherein solid microcapsules dispersed in the composition C3 are obtained, and wherein during step c), the emulsion (E'3) is allowed to stand for a period of up to 100 hours.

4. Method according to any one of claims 1 to 3, wherein the composition C2 is a liquid the viscosity of which at 25°C is between 500 mPa.s and 100 000 mPa.s.

5. Method according to any one of claims 1 to 4, wherein the composition C2 comprises at least one monomer or polymer, at least one crosslinking agent, and optionally at least one catalyst.

6. Method according to any one of claims 1 to 5, wherein the composition C2 does not include a photoinitator.

7. Method according to claim 5 or 6, wherein the composition C2 comprises from 0.001% to 70% by weight of crosslinking agent relative to the total weight of the composition.

8. Method according to any one of claims 1 to 7, wherein the active ingredient is solubilized in the composition C1 or is dispersed in the form of solid particles in the composition C1.

9. Method according to any one of claims 1 to 8, wherein the composition C3 comprises at least one branched polymer, preferably with a molecular weight greater than 5,000 g.mol-1, and / or at least one polymer of molecular weight greater than 5,000 g.mol-1, and / or solid particles such as silicates.

10. Method according to any one of claims 1 to 9, wherein the viscosity of the composition C3 at 25°C is between 15,000 mPa.s and 100,000 mPa.s at a shear rate of 10 s-1 and less than 5,000 mPa.s at a shear rate of between 100 s-1 and 100,000 s-1.

11. Method according to any one of claims 1 to 10, wherein the shear rate applied in step b) is between 10 s-1 and 1,000 s-1.

12. Method according to any one of claims 1 to 11, not including a step of exposure to a UV light source.

13. Method according to any one of claims 1 to 12, wherein the polymerization step of the composition C2 is carried out for a period between 8 hours and 100 hours.

14. Method according to any one of claims 1 to 13, wherein the step of polymerizing the composition C2 is carried out at a temperature between 20°C and 80°C.

15. Method according to any one of claims 1 to 14, wherein the polymerization step of the composition C2 is carried out for a period of between 8 hours and 100 hours, at a temperature between 20°C and 80°C.