FR2911501A1 - Emulsion for topical application to keratinous material, for use e.g. in skin- and hair-care products, contains a partly-hydrolysed polystyrene-polyethyl acrylate block copolymer and a silicone-polyol wetting agent - Google Patents

Abstract

An oil-in-water emulsion for topical application to keratinous material, contains (1) a diblock copolymer with a polystyrene block and 40-60 wt.% of a block containing not more than 90 wt.% acrylic acid units and at least 10 wt.% 1-4C alkyl acrylate units, and (2) a water-soluble silicone wetting agent with terminal or pendant polyoxyalkylene groups which can reduce the surface tension of water to below 35 (preferably below 30) mN/m. A composition (I) for topical application to keratinous material, in the form of an oil-in-water emulsion in a cosmetically-acceptable medium, contains (1) at least one diblock copolymer (A)-(B) in which block A comprises at least 90 wt.% styrene units, block B comprises (a) not more than 90 wt.% acrylic acid units (optionally as a salt) and (b) at least 10 wt.% 1-4C alkyl acrylate units, and the proportion of block B in the copolymer is 40-60 wt.%, and (2) at least one wetting agent selected from water-soluble silicones with at least one terminal or pendant monovalent polyoxyalkylene group which can reduce the surface tension of water in an aqueous solution to less than 35 (preferably less than 30) mN/m. An independent claim is also included for a method for the cosmetic treatment of keratinous material by the application of (I).

Description

O / W emulsion with block polymers and a wetting agent

  The present application relates to a composition for topical application to keratinous materials, in emulsion form, containing at least one amphiphilic block polymer, and to the use of said composition in the cosmetic or dermatological fields.

  For various reasons related in particular to a better comfort of use (softness, emollience and others), the current cosmetic or dermatological compositions are most often in the form of an emulsion of the oil-in-water type (O / W ) (ie a support consisting of an aqueous dispersant continuous phase and an oily dispersed discontinuous phase) or an emulsion of the water-in-oil (W / O) type (ie a support consisting of an oily dispersant continuous phase and an aqueous dispersed discontinuous phase). Oil-in-water emulsions are the most requested in the cosmetic field because they provide the skin with the application, a touch softer, less greasy and lighter than water-in-oil emulsion systems .

  In the case of O / W emulsions in which an oily phase is dispersed in an aqueous phase, this dispersion requires the use of an amphiphilic compound in order to stabilize the interface between the droplets of the oily phase and the aqueous phase, and therefore to stabilize the dispersion. Classically, emulsifiers are used which are amphiphilic compounds of low molar mass and which can pose problems of safety, problems of stability, the latter being able to be limited according for example of the nature of the oils and the rate of dispersed phase , problems of cosmetic property (eg soaping problem during application or sticky problem) or even problems of process if it is necessary to heat the phases.

  Moreover, the use of low molecular weight emulsifying compounds does not in itself make it possible to obtain stable emulsions over time, and the introduction of gelling agents is most often necessary to avoid the phenomenon of creaming. that is, decantation of the oily dispersed phase. If the use of amphiphilic polymers or particles is also known, it remains limited to particular textures.

  Furthermore, it is known from EP-A-1,279,398, cosmetic compositions comprising an aqueous phase containing a water-soluble or water-dispersible polymer, of AB diblock structure where A is an ionic water-soluble polymeric block and B a hydrophobic polymeric block, the quantity of polymeric block A being equal to or greater than 60% of the total weight of the diblock polymer. However, these emulsions have the aesthetic disadvantage of spreading inhomogeneously on the skin.

  There is therefore a real need to have O / W emulsions which are stable irrespective of the nature and the quantity of oils, which have good cosmetic properties including for safety, which can have diversified textures and which have a homogeneous spread on the skin.

  Unexpectedly and surprisingly, the Applicant has found that certain diblock copolymers of the polystyrene-alkyl polyacrylate type, partially hydrolysed, combined with one or more wetting agents make it possible to disperse oily phases of varied nature and over a very large concentration range. , the emulsions obtained being stable without it being necessary to add a cosurfactant and / or a gelling agent of the aqueous phase, and giving a homogeneous spreading during application to the skin.

  In addition, the emulsions stabilized by the copolymers used in the present invention have very original textures, with an aqueous touch, slippery and non-sticky at the end of application to the skin.

  The diblock copolymers described in EP-A-1,279,398 are sPolystyrene-sodium polyacrylate copolymers, which means that block A does not contain alkyl acrylate units and that the degree of hydrolysis of block A is equal to 100%, while the copolymer of the present invention comprises a hydrophilic block which is only partially hydrolysed since it contains alkyl acrylate units.

  Thus, the present invention relates to a composition for topical application to keratin materials, in the form of an oil-in-water emulsion comprising, in a physiologically acceptable medium, an oily phase dispersed in an aqueous phase, characterized in that it contains (1) at least one diblock copolymer (block A) - (block B) in which: block A comprises at least 90% by weight of units derived from styrene relative to the total weight of block A; the block B comprises at least (a) units derived from acrylic acid in acid or salified form, in a proportion of at most 90% of the total weight of the block B, and (b) units derived from an acrylate C1-C4 alkyl. in a proportion of at least 10% of the total weight of the block B, the proportion by weight of the block B with respect to the copolymer ranging from 40 to 60%, (2) at least one wetting agent chosen from water-soluble silicones comprising at least minus a monovalent or pendant monovalent polyoxyalkylene group, which, introduced at 0.05% by weight in an aqueous solution, are capable of reducing the surface tension of the water to a value of less than 35 mN / m, and preferably lower at 30 mN / m.

  In the present application, physiologically acceptable medium means a medium that is compatible with all keratin materials such as skin, nails, mucous membranes and hair or any other cutaneous zone of the body (acceptable tolerance, toxicology and touch). The composition of the invention may constitute in particular a cosmetic or dermatological composition.

  The composition of the invention has a pH that can preferably range from 2 to 9, more preferably from 3 to 8 and better still from 5 to 8. The composition can also be an W / O / W emulsion prepared by dispersion of a W / O emulsion in an aqueous phase containing the copolymer of the invention.

  One of the great advantages of the copolymers used according to the invention is that they make it possible to disperse all the types of oily phases, whether based on: triglycerides or alkanes, esters, silicones, perfluorins, or the like , either alone or in a mixture.

  In addition, as indicated above, these copolymers make it possible to obtain stable emulsions, even if they are free of emulsifiers. Stable emulsions are understood to mean emulsions which, after 2 months of storage at all temperatures of between 4 ° C. and 50 ° C., show no macroscopic change in color, odor, viscosity or pH variation.

  According to a preferred embodiment of the invention, the composition of the invention is free of emulsifier. An emulsifier is understood to mean an amphiphilic compound capable of emulsifying an oily phase in an aqueous phase, such an emulsifier being a compound having a molecular weight of less than 500, comprising a polar part and a chain containing from 6 to 30 carbon atoms. The emulsifiers of the O / W emulsions generally have a HLB (Hydrophilic-lipophilic balance) of at least 7, and preferably ranging from 9 to 18.

  By wetting agent is meant any compound which, introduced in aqueous solution at 0.05% (by weight), reduces the surface tension of water to a value of less than 35 mN / m, and preferably lower at 30 mN / m.

  In the present application the term diblock copolymer refers to a block copolymer architecture consisting of two blocks, and having substantially no other block sequence.

  In the present application, the unit derived from a monomer denotes a unit that can be obtained directly from said monomer by polymerization. Thus, for example, a unit derived from an acrylic or methacrylic acid ester does not cover a unit of formula -CH 2 -CH (COOH) -, or -CH 2 -C (CH 3) (COOH) -, obtained for example by polymerizing an acrylic or methacrylic acid ester and then hydrolyzing. Thus, the unit terminology derived from a monomer is only relative to the final constitution of the polymer and is independent of the polymerization process used to synthesize the polymer.

  In the present application, the ratio by weight between the blocks corresponds to the ratio between the masses of the monomers (or mixtures of monomers) used for the preparation of the blocks (taking into account the mass variations related to a subsequent hydrolysis). The proportions by weight of the blocks are the proportions relative to the total diblock copolymer, and correspond to the proportions by weight of the monomers (or mixtures of monomers) used for the preparation of the blocks, with respect to all the monomers used to prepare the diblock copolymer (taking into account mass variations related to subsequent hydrolysis).

  In the present application, the masses and ratios bound to the blocks are indicated in acid equivalents (units derived from acrylic acid in acid form, as opposed to a salified form of sodium acrylate type).

  In the present application, the term "hydrophilic monomer" is understood to mean a monomer which has affinity for water, and which typically is not capable of forming a two-phase macroscopic solution in distilled water at 25 ° C., at a concentration of 1% by weight.

  In the present application, the molar mass MA of a mixture of monomers A1 and A2 of respective molar masses MAI and MA2, present in respective numbers of nAl and nA2, denotes the number-average molar mass MA = MAI nAl / (nAl + nA2) + MA2 nA2 / (nAl + nA2). The molar mass of a mixture of units in a macromolecular chain or part of a macromolecular chain (a block for example) is similarly defined, with the molar masses of each of the units and the number of each of the units.

  In the present application, the measured average molecular weight of a first block or of a copolymer denotes the number-average molecular weight in polystyrene equivalents of a block or of a copolymer, measured by steric exclusion chromatography (SEC). in THF with calibration using polystyrene standards. The average measured molecular weight of a single block in an n-block copolymer is defined as the difference between the measured average molecular weight of the copolymer and the measured average molecular weight of the (n-1) block copolymer from which it is prepared. .

  For the sake of simplicity, it is common to express the average molecular masses of the blocks in "theoretical" or "target" average molecular weights, considering a complete and perfectly controlled polymerization. In this case, a macromolecular chain is formed by the transfer function of a transfer agent; to obtain the molecular mass it suffices to multiply the average molar mass of the units of a block by the number of units per block (quantity in number of monomers per quantity in number of transfer agent). In these calculations, the differences induced by small amounts of co-momoners such as methacrylic acid can be neglected. The theoretical or target average molecular masses of the B block are expressed by considering a total hydrolysis (the masses are expressed with the fiction of a hydrolysis rate of 1). The theoretical average molecular weight Mbloc of a block is typically calculated according to the following formula: Mbloc = 1. * n precursor where Mi is the molar mass of a monomer i, n; is the number of moles of the monomer i, nprecursor is the number of moles of functions to which the macromolecular chain of the block will be bound. The functions can come from a transfer agent (or a transfer group) or an initiator, a previous block etc. If it is a preceding block, the number of moles can be considered as the number of moles of a compound to which the macromolecular chain of said previous block has been linked, for example a transfer agent (or a group of transfer) or an initiator. In practice, the theoretical average molecular weights are calculated from the number of moles of monomers introduced and the number of moles of introduced precursor.

  The "theoretical" or "target" average molecular weight of a block copolymer is considered as the addition of the average molecular weights of each of the blocks, considering a total hydrolysis (we express the masses with the fiction of a rate hydrolysis of 1), if such hydrolysis has been carried out.

  In the present application, the target or theoretical total mass of a block is defined as the mass of the macromolecular chain by considering a complete and perfectly controlled polymerization. To obtain the total mass it is sufficient to multiply the molar mass of a unit of a block by the number per block of this unit and to add the masses thus obtained for each type of unit in the block. In these calculations, the differences induced by small amounts of co-momoners such as methacrylic acid can be neglected. The theoretical or target total masses of the B block are expressed considering the effect of a partial hydrolysis (for this descriptor the fiction of a degree of hydrolysis of 1) is not used, if such hydrolysis has been performed.

  In the present application, the degree of hydrolysis T is defined as the ratio between the number of units derived from acrylic acid or a salt of acrylic acid, and the number of units derived from the alkyl acrylate in Cl. -C4, present in a copolymer before hydrolysis. The number of units derived from the C 1 -C 4 alkyl acrylate is considered to be equal to the amount by number of alkyl acrylate monomer used for the preparation of the copolymer before hydrolysis. The number of units derived from acrylic acid or from an acrylic acid salt can be determined by any known method, in particular by acidobasic potentiometric titration of the number of COONa groups using a strong acid, for example In the present application, the term "transfer agent" is understood to mean an agent capable of inducing a controlled radical polymerization in the presence of unsaturated monomers and possibly of a source of free radicals.

  Block Copolymers The diblock copolymers according to the invention are advantageously linear. Block B comprises two different units. They will generally be randomly distributed in block B. Block B is then a statistical block.

  The proportion by weight of block B with respect to the copolymer ranges from 40 to 60%.

  The average molecular weight of the diblock copolymers according to the invention is greater than or equal to 20,000 g / mol. It may in particular be greater than or equal to 25,000 g / mol or even 28,000 g / mol. It may be less than 50,000 g: mole or even 40,000 g / mole. It is preferably between 20,000 and 50,000 g / mol and more preferably between 25,000 and 50,000 g / mol.

  The diblock copolymers in accordance with the invention are more particularly characterized by the fact that they are diblock linear copolymers (block A) - (block B) in which: block A comprises at least 90% by weight of units derived from styrene based on the total weight of block A; Block B is a statistical block comprising, based on the total weight of block B: (i) from 34 to 90% by weight of units derived from acrylic acid in acid form or in salified form; (ii) from 10 to 66% by weight of units derived from C1-C4 alkyl acrylate.

  Block A may comprise up to less than 10% of units other than units derived from styrene based on the total weight of block A. Block B may comprise units other than units derived from acrylic acid and units of the alkyl acrylate. Such units are taken into account in the composition of block B (proportion of different units), the total units being 100%.

  The ratio by weight between the units derived from acrylic acid and the units derived from the C 1 -C 4 alkyl acrylate is preferably between 34/66 and 90/10, preferably between 64/36 and 75/25. .

  The C1-C4 alkyl acrylate is preferably an alkyl acrylate hydrolyzable to acrylic acid. The units derived from the C1-C4 alkyl acrylate are preferably derived from an alkyl acrylate hydrolyzable to acrylic acid. Thus, by a preferred method, units derived from acrylic acid may be generated from units derived from alkyl acrylate, upon partial hydrolysis.

  C1-C4 alkyl acrylates include, in particular, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, acrylate, and the like. tert. In particular, ethyl acrylate and t-butyl acrylate are known to be easily hydrolysed.

  The C 1 -C 4 alkyl acrylate of the copolymer of the invention is advantageously ethyl acrylate (often denoted EA or AE or AEt).

  Block A and / or block B may comprise up to 10% by weight (in particular from 0.1% to 10% by weight), preferably comprising up to 5% by weight (in particular from 0.1% to 5% by weight, for example about 2% or 0.1% to 1.8%), of an additional hydrophilic comonomer, ionic or nonionic relative to the total weight of block A or block B containing said hydrophilic co-monomer.

  By hydrophilic comonomer is meant a monomer which has affinity for water, and which typically is not capable of forming a two-phase macroscopic solution in distilled water at 25 ° C. at a concentration of 1%. in weight.

  Among the additional hydrophilic comonomers, ionic or nonionic, there may be mentioned for example acrylamide, hydroxyethyl (meth) acrylate, methacrylic acid (AMA) in acid or salified form. It is more particularly preferred to use methacrylic acid in acid or salified form. Block A can also comprise, as additional hydrophilic monomer, acrylic acid in acidic or salified form.

  Preferably, the copolymer does not comprise a boronic function, in acid or salified form.

  The diblock copolymers according to the invention are diblock copolymers (block A) - (block B) in which the proportion by weight of block B relative to the copolymer is between 45 and 60%.

  Among these diblock copolymers, use is preferably made of those in which the proportion by weight of the block B with respect to the copolymer is preferably between 50 and 60% by weight.

  The copolymer of the invention may in particular be presented in one of the following ways: in solid or dry form, or in the form of a fluid concentrated ingredient comprising a vector, in a concentration preferably of greater than 8% by weight.

  If it is in the form of a fluid concentrated ingredient comprising a vector, in a concentration preferably of greater than 8% by weight, the vector may in particular comprise water and / or an alcohol solvent, the alcohol being preferably chosen from ethanol or isopropanol. In particular, the alcohol can contribute to fluidizing the copolymer and to making its industrial use easier. The vector may be water or a mixture of more than 50% by weight of water and less than 50% by weight of alcohol. The copolymer concentration may be at least 25% by weight, and preferably at most 75% by weight.

  Process The copolymer of the invention may be prepared by any suitable method, comprising a polymerization phase. The copolymer according to the invention can be obtained by any known method, whether by radical polymerization, controlled or not, by ring-opening polymerization (in particular anionic or cationic), by anionic or cationic polymerization, or by chemical modification of the polymer. a polymer.

  An advantageous process comprises the following steps: step I): a diblock copolymer (block A) - (block B ') is prepared, or - a triblock copolymer or architecture star (core) - [(block A) - (block B ')] x where (core) - [(block B') - (block A)] x or x is an average number greater than or equal to 2, where - block A comprises units derived from styrene, and the block B 'comprises the units derived from a C 1 -C 4 alkyl acrylate, step I') optionally, for a triblock or star copolymer, the bonds (core) - (block B ') or (core) are broken ) - (block A), so as to obtain a diblock copolymer (block A) - (block B '), step II) the block B' is hydrolyzed into a block B to obtain the diblock copolymer (block A) - (block B), the hydrolysis inducing, if appropriate for a triblock or star copolymer, a break in the (core) - (block B ') or (core) - (block A) bonds, so as to obtain a diblock copolymer (block A ) - (block B).

  The method may further optionally comprise a step III) during and / or after step II), deactivation of transfer groups carried by macromolecular chains and / or purification of the diblock copolymer (block A) - (Block B) and / or destruction of byproducts of hydrolysis and / or deactivation.

  The polymerization process as described above, applied to the preparation of copolymers resembling those of the invention, is described in particular in document WO-A-01/16187.

  The terminologies of the type (block A) - (block B ') however do not exclude the presence of useful chemical groups (transfer groups or residues) for the polymerization, in particular at chain ends or at the center of the chains. Thus the diblock copolymer may actually have a formula of the type R- (block A) - (block B ') - X where X is a transfer group (for example X is a transfer group of the formula ûS-CS-Z or a residue of such a group).

  Step I) is a polymerization step. Step l ') is optional and may optionally be applied if the copolymer prepared in step I) is a triblock or star copolymer. However, if the copolymer prepared in step I) is a triblock or star copolymer, it is possible to break the bonds during a hydrolysis step. If the break can be performed during the hydrolysis step, then step I ') will not be very useful, and will preferably be omitted.

  According to an advantageous embodiment, stage I) is carried out by emulsion polymerization in water.

  The diblock copolymers (block A) - (block B) used in the context of the invention may in particular be obtained as follows: in step I), a diblock copolymer (block A) - (block B ') is prepared ) by a process comprising the following intermediate steps la) and lb): a) preparing a first block A, by bringing into contact: - nT moles of a transfer agent comprising a single transfer group - nA moles of styrene or a monomer mixture comprising at least 90% by weight of styrene and where nA / nT> 5 and preferably <5000; - and possibly an initiator of free radicals

  1b) a second block B 'is prepared to obtain a diblock copolymer (block A) - (block B'), by placing in contact with: - the block A obtained in the preceding step, - nB moles of a C1-C4 alkyl or a monomer mixture comprising at least 90% by weight of a C1-C4 alkyl acrylate such that nB / nT> 5 and preferably <5000; and optionally a free radical initiator, during step II) subsequent to stage I), the block B 'is then hydrolyzed at a molar ratio T of between 0.4 and 0.96 for obtain said diblock copolymer (block A) - (block B) and - 20000 nA / nT MA + MAA nB / nT - [T MAA nB + (1-T) MB nB] / [MAnA + T MAA nB + (1- T) MB nB]? 50% where MA is the molar mass of styrene or monomer mixture comprising styrene used in step 1a), and MB is the molar mass of C1-C4 alkyl acrylate or monomer mixture comprising the C1-C4 alkyl acrylate employed in step 1b).

  The method may further optionally include a step III) during and / or after step II), deactivating transfer groups carried by macromolecular chains and / or purifying the diblock copolymer (block A) - ( Block B) and / or destruction of hydrolysis and / or deactivation byproducts.

  According to an advantageous embodiment, steps la) and lb) of step I) are carried out by emulsion polymerization in water.

  The degree of hydrolysis T can advantageously be between 0.7 and 0.8; preferably T is 0.75. Transfer agents useful for the implementation of the process (in step I) are known to those skilled in the art and include especially compounds comprising a transfer group -S-CS-, for the implementation of polymerization processes known as RAFT and / or MADIX. Such methods and agents are detailed below.

  During step I) described above, the preparation of a first block can be carried out starting from monomers or from a mixture of monomers, initiators and / or agents promoting the control of the polymerization ( transfer agents with groups -S-CS-, nitroxides etc ...), then the growth of a second block on the first block to obtain a diblock copolymer with monomers different from those used for the preparation of the previous block, and optionally with addition of initiators and / or agents promoting the control of the polymerization. These methods of preparing block copolymers are known to those skilled in the art. It is mentioned that the copolymer may have, at the end of the chain, a transfer group or a residue of a transfer group, for example a group comprising a ûS-CS- group (for example derived from a xanthate, a dithioester, a dithiocarbamate or a trithiocarbonate) or a residue of such a group.

  In step II), the units derived from the hydrolyzable monomers of block B 'are hydrolyzed partially to form a block B comprising units derived from acrylic acid or a salt (hydrolysed units), and units derived from the monomer alkyl acrylate (unhydrolyzed units). These two types of units are statistically distributed in block B; it can therefore be considered that block B is a block in the form of a random copolymer comprising units derived from alkyl acrylate and units derived from acrylic acid or from an acrylic acid salt. Naturally, the block B may comprise other units, in minimal amounts, if a monomer mixture is used during the implementation of step 1b).

  Block A includes units derived from styrene. Block A can be obtained from a monomer mixture comprising at least 90% by weight, preferably at least 95%, styrene ("St") and a comonomer or several hydrophilic comonomers (s). Block A may thus be a random copolymer comprising at least 90% (in particular from 90% to 99.9% by weight), preferably at least 95% by weight (especially from 95% to 99.9% by weight). units derived from styrene, and up to 10% by weight (in particular from 0.1% to 10% by weight), preferably up to 5% by weight (in particular from 0.1% to 5% by weight) other units derived from hydrophilic co-monomer (s).

  Block B 'comprises units derived from a C 1 -C 4 alkyl acrylate hydrolyzable. Block B 'can be obtained from a monomer mixture comprising at least 90% (in particular from 90% to 99.9%); preferably at least 95% (especially 95% to 99.9%) by weight of a C 1 -C 4 alkyl acrylate and one or more hydrophilic comonomer (s). Block B 'may thus be a random copolymer comprising at least 90% (in particular from 90% to 99.9%), preferably at least 95% (in particular from 95% to 99.9%), by weight of units derived from C1-C4 alkyl and up to 10% (in particular from 0.1 to 10%), preferably up to 5% (especially from 0.1 to 5%), for example about 2% or from 0.1 to 1.8% by weight of other units, derived from hydrophilic co-monomer (s).

  Block B obtained from block B 'after hydrolysis, comprises units derived from hydrolyzable C1-C4 alkyl acrylate, units derived from acrylic acid in acid or salified form, and optionally units derived from a hydrophilic comonomer used during stage lb) of growth of block B ', for example units derived from methacrylic acid. Acrylic acid is generally present in block B as a salt. This form generally results from the conditions for carrying out the hydrolysis and the reagents used. It is usually an alkali metal salt such as sodium or potassium. Therefore, block B generally comprises units derived from acrylic acid in the form of sodium or potassium acrylate.

  Among the hydrophilic comonomers which may be useful for the preparation of block A and / or of block B ', mention may be made of hydrophilic comonomers capable of stabilizing a monomer emulsion and / or of stabilizing the polymer. obtained by emulsion polymerization. Mention may in particular be made of ionic or nonionic hydrophilic comonomers such as acrylamide, hydroxyethyl (meth) acrylate, methacrylic acid (AMA) and their salts. It is preferred to use methacrylic acid or its salts. Methacrylic acid is not sensitive to hydrolysis. It can, however, be salified during hydrolysis. For the preparation of the block A, acrylic acid in acidic or salified form can also be used as hydrophilic comonomer.

  Among the hydrolyzable C1-C4 alkyl acrylates, mention is made in particular of ethyl acrylate (EA or AE or AEt).

  According to one particular embodiment, the block A and / or the block B 'or B comprises from 0.1 to 10%, preferably from 0.1 to 5%, by weight of hydrophilic comonomer, in particular the acid methacrylic acid or salified form relative to the total weight of block A, block B 'or block B containing said hydrophilic comonomer.

  Thus, during step la), or may use a monomer mixture comprising at least 90%, preferably at least 95%, by weight of styrene, and up to 10%, preferably up to 5%, by weight of methacrylic acid in acid or salified form.

  In step 1b), or may use a monomer mixture comprising at least 90%, preferably at least 95%, by weight of C 1 -C 4 alkyl acrylate such as ethyl acrylate, and up to 10%, preferably up to 5%, by weight of methacrylic acid in acid or salt form.

  Some characteristics of the process for preparing the copolymers of the invention are described below.

  Step I) Preferably, for the polymerization step I), so-called living or controlled radical polymerization methods are used, and particularly preferably controlled or living radical polymerization methods using a transfer agent. comprising a transfer group of the formula ûS-CS-, especially known under the names of RAFT or MADIX. By way of examples of so-called living or controlled polymerization processes, it is particularly possible to refer to: the processes of the applications WO 98/58974, WO 00/75207 and WO 01/42312 which implement a controlled radical polymerization by means of xanthate type control agents, to the radical polymerization process controlled by dithioester or trithiocarbonate type control agents of the application WO 98/01478, to the radical polymerization process controlled by dithiocarbamate type control agents of the application WO 99/31144, the radical polymerization process controlled by dithiocarbazate type control agents of the application WO 02/26836, - to the radical polymerization process controlled by dithiophosphoroesters type control agents of the application WO 02/10223 to the process of the application WO 99/03894 which implements a polymerization in the presence of nitroxide precursors, or processes employing other nitroxides or nitroxide / alkoxyamine complexes - the process of WO 96/30421 which uses atom transfer radical polymerization (ATRP), - the controlled radical polymerization process with agents Iniferters type control according to the teachings of Otu et al., Makromol. Chem. Rapid. Commun., 3, 127 (1982), - to the controlled radical polymerization process by degenerative transfer of iodine according to the teaching of Tatemoto et al., Jap. 50, 127, 991 (1975), Daikin Kogyo Co. Itd Japan and Matyjaszewski et al., Macromolecules, 28, 2093 (1995), - the radical polymerization process controlled by tetraphenylethane derivatives, disclosed by D. Braun et al. In Macromol. Symp. 111, 63 (1996), or else to the process of radical polymerization controlled by organocobalt complexes described by Wayland et al. In J.Am.Chem.Soc. 116,7973 (1994) - the controlled radical polymerization process with diphenylethylene (WO 00/39169 or WO 00/37507).

  The polymerizations can be carried out in emulsion in water (so-called "latex" process). These processes can use emulsifying agents, most often surfactants. Without wishing to be bound to any theory, it is believed that the emulsion preparation processes lead to the formation of A block nodules, which can influence the physicochemical properties of the copolymer.

  The polymerizations may be carried out in the presence of free radical initiators, known to those skilled in the art. For example, sodium persulfate may be used. Initiator quantities of from 5 to 50% by number relative to the amount of transfer agent can typically be used.

  It is not beyond the scope of the invention to implement and adapt preparation processes leading to triblock copolymers or stars, subsequently modified (during a step I ') or during step II. ) so as to obtain diblock copolymers. In particular it is conceivable to use transfer agents comprising several transfer groups (for example trithiocarbonates ZS-CSS-Z) leading to telechelic copolymers of type R - [(block B ') - (block A)] w as triblocks or stars of type (core) - [(block A) - (block B ')] x (for example (block A) - (block B') - 35 R- (block B ') - (block A ) as triblock (block A) - (block B ') - (core) - (block B') - (block A)), then break (cut, "cleave") the telechelic copolymers, to obtain diblock copolymers (block A) - (block B '). The section can intervene during the hydrolysis, in which case diblock copolymers (block A) - (block B) are obtained directly. In such cases, those skilled in the art will adapt the operating conditions to target average molecular weights equivalent to those indicated, for example by multiplying the quantities of monomers introduced by the number of transfer groups included in the agent of the invention. transfer. It is specified that during stage I) a triblock copolymer is typically not prepared by a succession of 3 polymerization phases in which at least one of the blocks could not be separated from the others by a break during hydrolysis. Thus, the copolymer prepared in step I), is not typically obtained by a polymerization process comprising a step of polymerization of styrene or a styrene-based monomer mixture, and then a polymerization step of ethyl acrylate or a mixture of monomers based on ethyl acrylate, then a step of polymerization of styrene or a mixture of styrene-based monomers, the polymerizations being carried out using a monofunctional transfer agent carrying a group of formula ûS-CS-.

  Step II) In step II) the respective amounts of the different units in the B block are controlled by the rate of hydrolysis. The composition of the block A may remain unchanged during the hydrolysis, if the block A does not comprise hydrolysable units. However, it is not excluded that the block A is slightly modified during the hydrolysis step.

  Preferably, the hydrolysis step II) is carried out by adding a strong base such as sodium hydroxide or potassium hydroxide. Typically, a proportion by number of base is added relative to the amount of hydrolysable monomer used in step 1b), corresponding approximately to the desired hydrolysis rate, with possibly an excess of a few%. For example, a quantity of sodium hydroxide 75% by number of the amount of hydrolyzable ethyl acrylate implemented in step lb) is introduced. It is preferably carried out by homogeneous hydrolysis by gradually adding the sodium hydroxide to the copolymer.

  The hydrolysis step may notably result in the deactivation and / or the sectioning of certain transfer groups or other groups attached to the macromolecular chains. Step II) can thus generate by-products that it is desirable to eliminate, or generate groups on the macromolecular chains that are desirable to chemically modify. Such operations can be implemented during a step III).

  Step III) Step III) is a step of deactivation of transfer groups carried by macromolecular chains, and / or purification of the diblock copolymer (block A) - (block B) and / or destruction of by-products of hydrolysis and / or deactivation.

  In the optional step III), the block copolymers obtained or the hydrolysis byproducts may undergo a purification or destruction reaction of certain species, for example by hydrolysis, oxidation, reduction, pyrolysis, ozonolysis or substitution. An oxidation step with hydrogen peroxide is particularly suitable for treating sulfur species. It is mentioned that some of these reactions or operations may take place in whole or in part during step II). In this case, for these reactions or operations, the two steps simultaneously.

  As indicated above, the average molecular weights of the diblock copolymer (block A) - (block B ') before hydrolysis or of each of the blocks, are typically a function of the relative amounts of the monomers and of the transfer agent used during the treatment. step I). Of course, the average molecular weights of the diblock copolymer (block A) - (block B) after hydrolysis or of each of the blocks are a function of these same relative amounts and also of the degree of hydrolysis, for example a function of the amount of reagent introduced. , usually a base, for this hydrolysis.

  For the sake of simplicity, it is common to express the average molecular masses of the blocks in "theoretical" or "target" average molecular weights, considering a complete and perfectly controlled polymerization. In this case a macromolecular chain is formed by transfer agent; to obtain the molecular mass, it suffices to multiply the average molar mass of the units of a block by the number of units per block (quantity in number of monomers per quantity in number of transfer agent). In these calculations, the differences induced by small quantities of comononers such as methacrylic acid can be neglected. The theoretical or target average molecular masses of the B block are expressed by considering a total hydrolysis (the masses are expressed with the fiction of a hydrolysis rate of 1).

  For the process of which steps 1a) and 1b) have been detailed above, the theoretical total mass of block A can be expressed as: MAnA.

  For the process of which steps la) and lb) have been detailed above, the theoretical or target average molecular weight of block A can be expressed as: MAnA / nT.

  For the process whose steps la) and lb) have been detailed above, the theoretical total mass of the block B 'can be expressed as: MBnB.

  For the process whose steps la) and lb) have been detailed above, the theoretical or target average molecular weight of the block B 'can be expressed as: MBnB / nT

  For the process whose steps la) and lb) have been detailed above, the theoretical total mass of the block B can be expressed by: TMAAnB + (1-T) MBnB

  For the process of which steps la) and lb) have been detailed above, the theoretical or target average molecular weight of block B can be expressed as: MAA nB / nT. (because T = 1 according to the definition of the theoretical or target average molecular weight)

  For the process whose steps la) and lb) have been detailed above, the total theoretical mass of the copolymer can be expressed by: MAnA + T MAA nB + (1-T) MB nB For the process whose steps la) and 1b) have been detailed above, the theoretical average molecular weight of the copolymer can be expressed as: nA / nT MA + MAA nB / nT

  In the above expressions: - MA is the molar mass of styrene or monomer mixture comprising styrene used in step 1a), - MAA is the molar mass of acrylic acid, - MB is the molar mass of the C1-C4 alkyl acrylate or monomer mixture comprising C1-C4 alkyl acrylate employed in step 1b).

  By way of reference, the following correspondences are given: 25 - nA / nT = 5 corresponds to a theoretical average molecular weight of block A of approximately 500 g / mol - nA / nT = 5000 corresponds to a theoretical average molecular weight of block A of about 500000 g / mol, nB / nT = 5 corresponds to a theoretical average molecular weight of the block B 'of about 500 g / mol - nB / nT = 5000 corresponds to a theoretical average molecular weight of the block B' d about 500000 g / mol. - nA / nT MA + MAA nB / nT = 13000 g / mol (respectively 2000, respectively 8000, respectively 20000 or 50000) corresponds to a theoretical average molecular weight of the diblock (block A) - (block B) about 13000 g / mol (respectively 2000, respectively 8000, 20000 or 50000 respectively), considering a total hydrolysis and for the case where the alkyl acrylate is ethyl acrylate.

  The ratios by weight between the blocks are defined as the ratios between the theoretical or target total masses (for this descriptor the fiction of a degree of hydrolysis of 1) is not used. Thus :: - MAnA <T MAA nB + (1-T) MB nB, indicates that the ratio by weight (block B) / (block A)? 1. This is a characteristic of the copolymer used according to the invention, - MAnA / [MAnA + T MAA nB + (1-T) MB nB] indicates the quantity by weight of block A in the diblock copolymer (block A) - (block B), that is to say the proportion of block A. - [T MAA nB + (1-T) MB nB] / [MAnA + T MAA nB + (1-T) MB nB] indicates the amount by weight of block B in the diblock copolymer (block A) - (block B), that is to say the proportion of block B.

  Preferably, the diblock (block A) - (block B) linear copolymers used according to the invention have a proportion by weight of block B with respect to the copolymer [T MAA nB + (1-T) MB nB] / [MAnA + T MAA nB + (1-T) MB nB], between 50 and 85%. and they generally have a theoretical average molecular weight (nA / nT MA + MAA nB / nT) of less than 13000 g / mol.

  Among these copolymers, use is made in particular of: - those of the type (b) in which the proportion by weight of the block B with respect to the copolymer [T MAA nB + (1-T) MB nB] / [MAnA + T MAA nB + ( 1-T) MB nB] is less than 75% by weight, preferably between 50% and 75%. They generally have a theoretical average molecular weight (nA / nT MA + MAA nB / nT) greater than or equal to 8000 g / mol and preferably between 8000 g / mol and 13000 g / mol. This is the case of the polymer of the synthetic example.

  The preferred block copolymer (block A) - (block B) is a linear diblock polymer of the synthesis example described below.

  The diblock copolymer or copolymers according to the invention are preferably present in a concentration (of active material) ranging from 0.1 to 10% of the total weight of the composition. More preferably, this amount varies from about 0.2 to 5% by weight and better still from 0.3 to 3% by weight relative to the total weight of the composition.

  Wetting agents of the water-soluble silicone type The wetting agents in accordance with the invention are chosen from water-soluble silicones comprising at least one terminal monovalent polyoxyalkylene group or which, introduced at 0.05% by weight in an aqueous solution, are capable of reducing the surface tension of the water at a value of less than 35 mN / m, and preferably less than 30 mN / m.

  The wetting agents in accordance with the invention are more preferably chosen from water-soluble silicones comprising at least one polyoxyalkylene group of general formula (a) below: (R 2) 3 SiO [(R 2) 2 SiO] p (R 2 PESiO) q Si (R 2) 3 ( at)

  in which - the radicals R2, identical or different, denote a monovalent hydrocarbon radical chosen from alkyl, aryl and aralkyl radicals having at most 10 carbon atoms; some of the R2 radicals may also contain in addition an ethylcyclohexylenemonoxide group of formula 2H4 and are in a small proportion in the polysiloxane chain; p varies from 0 to 150, preferably from 0 to 100 and more preferably from 0 to 30; q ranges from 1 to 12, preferably from 1 to 10 and more preferably from 1 to 8. - the polyether PE group has the following formula (b) - CXH2x (OC2H4) v (OC3H6) ZOR3 (b) in which x varies from 1 to 8 and preferably ranges from 2 to 4 and more preferably is equal to 3; y is greater than 0 z is greater than or equal to 0; the values of y and z are such that the total molecular weight of the polyoxyalkylene portion of the polyether E group ranges from 200 to 10,000 and more preferably from 350 to 4,000; R3 denotes hydrogen, a C1-C8 alkyl group or a C2-C8 acyl group.

  It should be noted that when z is different from 0, the polyoxyethylene and polyoxypropylene units may be randomly distributed along the polyether PE chain or distributed in blocks or at the same time randomly distributed in blocks.

  Preferably, the radicals R2 are chosen from C1-C6 lower alkyls such as methyl, ethyl, butyl or hexyl; phenyl and benzyl. And more particularly, the radicals R2 are chosen from C1-C4 lower alkyls and even more particularly designate the methyl group.

  Preferably, the radicals R3 are chosen from C1-C4 lower alkyls and even more particularly designate the methyl group.

  The number of oxyethylene units of group E must be sufficient to produce a turbidity point in water between 25 and 90 C and more preferably between 40 and 70 C.

  The water-soluble silicones of formula (a) can be obtained according to the process described in US-A-4,847,398.

  Among the water-soluble silicones of formula (a), use will preferably be made of the following formula (a '): Me3SiO (Me2SiO) p (MePESiO) gSIMe3 (a')

  where Me denotes the methyl group; PE means:

  - (CH 2) 3 (OC 2 H 4) v (OC 3 H 6) ZOR 3 (b ') where x, z and z have the same values indicated above and R 3 denotes hydrogen or a C 1 -C 4 alkyl group. and more particularly the methyl group. As another family of water-soluble silicones that can be used according to the invention, mention may be made of the branched silicones of formula (c) below: Me 3 SiO (Me 2 SO) q 3 [(SIOMe 2) p, gOPE] q (c)

  where p, q have the same values given above in formula (a); Me means methyl, PE denotes the group of formula (d) below: - (OC2H4) y (OC3H6) ZR3 (d) where y and z have the same values indicated above in formula (b) and R3 denotes a group C1-C4 alkyl. and more particularly the methyl group.

  The water-soluble silicones according to the invention are known and in particular described in US Pat. No. 5,338,352 and their method of preparation is described in particular in US Pat. No. 4,847,398.

  Such silicones are for example sold by the company OSI under the trade names Silwet L-720, Silwet L-7002, Silwet L-7600, Silwet L-7604, Silwet L-7605, Silwet L-7607, Silwet 1614, Silwet L -7657, Silwet L-7200, Silwet L7230, Silsoft 305, Silsoft 820, Silsoft 880 or by Goldschmidt under the trade names Tego wet 260, Tegowet 500, Tegowet 505 and Tegowet 510.

  The following table gathers surface tension values at 25 C of aqueous solutions comprising 0.05% (by weight) of different wetting agents. Wetting agent Surface tension at 0.05% in water (mN / m), 25 C Tegowet 500 33 Tegowet 510 29 Silwet L-77 20.5 Silsoft 880 26 Silsoft 305 21 According to the invention, the wetting agent (s) are present at a concentration ranging from 0.01% to 10% by weight, preferably from 0.05% to 5% by weight and more particularly from 0.1% to 3% by weight relative to the total weight of the composition.

  Oily phase The amount of oily phase in the emulsion according to the invention may range, for example, from 2% to 70% by weight, preferably from 2% to 50% by weight and better still from 2% to 40% by weight relative to the total weight. of the composition. The weight ratio of the amount of oily phase to the amount of block copolymer can range, for example, from 2 to 80 and preferably from 5 to 50. This ratio shows that a small amount of copolymer is sufficient to obtain a stable dispersion. .

  The oily phase of the composition of the invention contains at least one oil. The term "oil" means a fatty substance that is liquid at room temperature (25 ° C.). As oils which can be used in the composition of the invention, mention may be made for example of: hydrocarbon-based oils of animal origin, such as perhydrosqualene (or squalane); hydrocarbon oils of plant origin, such as liquid triglycerides of fatty acids containing from 4 to 10 carbon atoms, for example triglycerides of heptanoic or octanoic acids, or else, for example, sunflower, corn or soya bean oils. , squash, grape seed, sesame, hazelnut, apricot, macadamia, arara, coriander, castor oil, avocado, triglycerides of caprylic / capric acids such as those sold by the company Stearineries Dubois or those sold under the names Miglyol 810, 812 and 818 by Dynamit Nobel, jojoba oil, shea butter oil and liquid shea butter fractions; esters and synthetic ethers, in particular of fatty acids or of fatty alcohols, such as the oils of formulas R'COOR2 and R'OR2 in which R 'represents the residue of a fatty acid comprising from 8 to 29 atoms of carbon, and R2 represents a hydrocarbon chain, branched or unbranched, containing from 3 to 30 carbon atoms, such as, for example, purcellin oil, isononyl isononanoate, isopropyl myristate, palmitate, 2-ethylhexyl (or octyl palmitate), octyl-2-dodecyl stearate, octyl-2-dodecyl erucate, isostearyl isostearate; hydroxylated esters such as isostearyl lactate, octyl hydroxystearate, octyldodecyl hydroxystearate, diisostearyl malate, triisocetyl citrate, heptanoates, octanoates, decanoates of fatty alcohols; polyol esters, such as propylene glycol dioctanoate, neopentyl glycol diheptanoate and diethylene glycol diisononanoate; pentaerythritol esters such as pentaerythritol tetraisostearate; lipophilic derivatives of amino acids, such as isopropyl lauroyl sarcosinate (INCI name: Isopropyl Lauroyl sarcosinate) sold under the name Eldew SL 205 by the company Ajinomoto; linear or branched hydrocarbons of mineral or synthetic origin, such as mineral oils (mixture of hydrocarbon oils derived from petroleum, INCI name: Ore), paraffin oils, volatile or not, and derivatives thereof, petroleum jelly, polydecenes, isohexadecane, isododecane, hydrogenated isoparaffin such as hydrogenated polyisobutene such as Parléam oil marketed by NOF Corporation (INCI name; Hydrogenated Polyisobutene); fatty alcohols having from 8 to 26 carbon atoms, such as cetyl alcohol, stearyl alcohol and mixtures thereof (cetearyl alcohol), octyl dodecanol, 2-butyloctanol, 2-hexyldecanol and 2-undecylpentadecanol; or oleic alcohol; partially fluorinated hydrocarbon oils and / or silicone oils such as those described in document JP-A-2-295912; silicone oils such as volatile or non-volatile polymethylsiloxanes (PDMSs) with a linear or cyclic silicone chain, which are liquid or pasty at room temperature, in particular volatile silicone oils that are either linear or cyclic, such as cyclopolydimethylsiloxanes (cyclomethicones) such as cyclopentasiloxane and cyclohexadimethylsiloxane; polydimethylsiloxanes comprising alkyl, alkoxy or phenyl groups, during or at the end of the silicone chain, groups having from 2 to 24 carbon atoms; phenyl silicones such as phenyltrimethicones, phenyldimethicones, phenyltrimethylsiloxydiphenylsiloxanes, diphenyl-dimethicones, diphenylmethyldiphenyltrisiloxanes, 2-phenylethyltrimethylsiloxysilicates, and polymethylphenylsiloxanes; - their mixtures.

  According to a particular embodiment of the invention, the oily phase contains at least one oil chosen from fatty acid esters and silicone oils. The other fatty substances that may be present in the oily phase are, for example, fatty acids containing from 8 to 30 carbon atoms, such as stearic acid, lauric acid and palmitic acid; gums such as silicone gums (dimethiconol); silicone resins such as trifluoromethyl-C1-4-alkyldimethicone and trifluoropropyldimethicone, and silicone elastomers such as the products sold under the names "KSG" by the company Shin-Etsu, under the name "Trefil" by the company Dow Corning or under the names "Gransil" by the company Grant Industries; pasta such as Petrolatum; waxes such as microcrystalline waxes, paraffin waxes, lignite waxes, ceresin, ozokerite, montan wax, beeswax, lanolin and its derivatives, Candelilla wax, Ouricurry waxes , Carnauba, Japan, cocoa butter, palm oil in the form of paste at 20 C, cork fiber or sugarcane waxes, 25 C hydrogenated oils, fatty esters and concrete glycerides at 25 ° C., polyethylene waxes, waxes obtained by Fischer-Tropsch synthesis, silicone waxes; and mixtures of these fats.

  Aqueous phase The emulsion comprises an aqueous phase whose quantity may range, for example, from 30 to 98% by weight, preferably from 40 to 98% by weight, better still from 50 to 98% by weight and even more preferably from 55 to 98% by weight. weight relative to the total weight of the emulsion.

  The aqueous phase of the composition of the invention contains at least water. According to a preferred embodiment of the invention, the amount of water is at least 20% and preferably at least 30% of the total weight of the composition.

  In a conventional manner, the aqueous phase may contain, in addition to water, one or more water-soluble solvents chosen from polyols (or polyhydric alcohols), water-soluble lower alcohols (s) and mixtures thereof. By "lower alcohol" is meant an alcohol having 1 to 8 and preferably 1 to 6 carbon atoms. Lower alcohols include, for example, ethanol, isopropanol, butanol and mixtures thereof.

  Examples of polyols that may be mentioned include glycerine; glycols such as propylene glycol, butylene glycol; sorbitol; sugars such as glucose, fructose, maltose, lactose, sucrose; and their mixtures.

  The amount of water-soluble solvents (lower alcohols and polyols) can range, for example, from 0.5 to 30% by weight, preferably from 0.5 to 20% by weight, and better still from 1 to 15% by weight relative to the weight. total of the composition.

  Adjuvants In a known manner, the composition of the invention may also contain adjuvants usual in the cosmetic and / or dermatological fields, such as active ingredients, preservatives, antioxidants, complexing agents, pH adjusters (acidic or basic) perfumes, fillers, bactericides, odor absorbers, dyestuffs (pigments and dyes), hydrophilic polymers, and even lipid vesicles. The amounts of these various adjuvants are those conventionally used in the field under consideration, and for example from 0.01 to 20% of the total weight of the composition. These adjuvants, depending on their nature, can be introduced into the fatty phase, into the aqueous phase and / or into the lipid vesicles.

  Of course, one skilled in the art will take care to choose the optional compounds to be added to the composition according to the invention in such a way that the advantageous properties intrinsically attached to the composition according to the invention are not, or substantially not, altered by the proposed addition.

  As hydrophilic polymers, mention may be made of modified or unmodified carboxyvinyl polymers, such as the products sold under the names Carbopol (INCI name: carbomer) and Pemulen (INCI name: Acrylates / C10-30 alkyl acrylate crosspolymer) by the company Noveon; polymers derived from 2-acrylamido-2-methylpropanesulphonic acid, such as poly (2-acrylamido-2-methylpropanesulphonic acid) marketed by Hoechst under the name Hostacerin AMPS (INCI name: ammonium polyacryldimethyltauramide), crosslinked anionic copolymers of acrylamide and of AMPS, in the form of an W / O emulsion, such as those marketed under the name SEPIGEL 305 (CTFA name: Polyacrylamide / C13-14 Isoparaffin / Laureth-7) and the name SIMULGEL 600 (CTFA name: Acrylamide / Sodium acryloyldimethyltaurate copolymer / Isohexadecane / Polysorbate 80) by the company SEPPIC, AMPS copolymers sold under the name Aristoflex by the company Clariant; synthetic neutral polymers such as poly N-vinylpyrrolidone; polysaccharides such as guar gum, xanthan gum. and cellulosic derivatives; water-soluble or water-dispersible silicone derivatives such as acrylic silicones, polyether silicones and cationic silicones.

  The compositions of the invention may contain all the active ingredients normally used in cosmetics in the field of skincare, make-up and personal hygiene.

  As active ingredients, vitamins (A or retinol, C or ascorbic acid, E or tocopherol, K, PP or B3 or niacinamide) can be used, in particular, or in mixtures, as well as their derivatives and in particular their esters; solar filters; keratolytic and / or desquamating agents such as R-hydroxy acids such as salicylic acid and its derivatives, α-hydroxy acids such as glycolic acid, lactic acid and citric acid, ascorbic acid and its derivatives; anti-inflammatory agents; soothing agents; depigmenting agents; vegetable proteins; polysaccharides of plant origin in form or not of microgels; starches; wax dispersions; mixed silicates and colloidal particles of inorganic fillers; mattifying agents; anti-hair loss and / or regrowth agents or anti-wrinkle agents and mixtures thereof.

  The compositions according to the invention may be free of a lipophilic organic UV filter and / or an inorganic UV filter.

  The average size of the oil droplets of the emulsions obtained according to the invention can range from 10 nm to 10 μm (0.1 to 10 μm). The viscosity of the emulsions obtained can range from very fluid (spray = sprayable product) to very viscous (cream), and this viscosity is adjusted according to the content of block copolymer introduced, the amount of emulsified oily phase and the process of emulsification used (micron and submicron emulsions).

  The compositions of the invention may be prepared by any known emulsification process. Emulsification processes that can be used can for example be done with blades, with propellers, with a rotor-stator or under high pressure (HHP = homogenization under high pressure).

  To obtain stable emulsions with a low level of polymer, that is to say with a ratio of amount of oily phase / amount of block copolymer greater than 25, it is possible to make the dispersion in concentrated phase and then to dilute the dispersion with the rest of the aqueous phase.

  It is also possible, by HHP (between 50 and 800 bar), to obtain stable dispersions with droplet sizes of up to 100 nm.

  In order to form the emulsion and to obtain a fine, low polydispersed and stable dispersion, it is necessary to neutralize the block copolymer at a pH ranging from 6.5 to 7.5. However, it is possible after emulsification to modify the pH to have a pH ranging from 5 to 8, without the dispersion being affected.

  It is also known that polyacrylic acid (PAA) is sensitive to ionic species such as salts and some sunscreens. It will then be necessary to add them after the emulsification step.

  Although the compositions according to the invention are preferably free from emulsifiers, it is possible, in order to facilitate the emulsification of the oily phase when the block copolymer is in a small amount, for example in an amount of less than 2%, adding at least one co-emulsifier provided that the content of co-emulsifier (s) is less than 50% by weight relative to the weight of diblock copolymer used according to the invention. Without being limiting, the HLB of the emulsifier is greater than 5, and by way of indication, the emulsifiers may belong to the following families: Alkyl polyglucosides (APG), oxyethylenated C8-C18 fatty acid esters, ethers of oxyethylenated C8C18 fatty alcohol, C8-C18 fatty acid esters and glycerol, C8-C18 fatty alcohol ethers and glycerol, optionally C8-C18 fatty acid esters and optionally oxyethylenated sorbitan, ethers of C8-C18 fatty alcohol and optionally oxyethylenated sorbitan, dimethicone copolyols, gemini surfactants, mono- or disodium acylglutamates. When a co-emulsifier is added, it is preferably selected from branched chain fatty acid esters of polyol, in particular glycerol and sorbitan, such as glyceryl isostearate.

  The compositions of the invention can be used in any cosmetic or dermatological application, for example in cosmetics for the care of the skin, the hair, the scalp, the eyelashes, the eyebrows, the nails or the mucous membranes (lips), for example. for example as protection, treatment or care products for the face, for the hands or for the body, as products for the cleaning of the skin (of the face or the body), as products for the make-up (example of the foundations ), as hair products.

  Another subject of the invention is a process for the cosmetic treatment of a keratin material such as the skin, the scalp, the hair, the eyelashes, the eyebrows, the nails or the mucous membranes, characterized in that it is applied on the keratinous material a composition as defined above, according to the usual technique of this composition.

  The following examples illustrate the invention without being limiting in nature.

  1. Synthesis Example Preparation of a diblock copolymer Polystyrene-block-polv (acrvlate of ethyl-stat-sodium salt of acrylic acid) by synthesis of a diblock copolymer Polystyrene-block-poly (ethyl acrylate) Mn target 5000-block-7000 (g / mole) and then hydrolyzed to 75% of the ester group of ethyl acrylate.

  Step la): Preparation of a first block of polystyrene with a theoretical molecular weight of approximately 5000 g / mol 1000 g of water, 6.50 g of sodium dodecyl sulphate and sodium dodecyl sulphate are introduced into the reactor at ambient temperature. 30 g of sodium carbonate Na2CO3. The resulting mixture is stirred for 30 minutes under nitrogen. The temperature is then raised to 75 ° C., then a mixture 1 comprising: 83.7 g of styrene (St), 1.67 g of methacrylic acid (AMA), and 17.4 g of xanthate ( CH3) (CO2CH3) CH-S (C = S) OCH2CH3.

  The mixture is heated to 85 ° C. and then a solution of 2.00 g of sodium persulfate Na 2 S 2 O 8 solubilized in 20.0 g of water is introduced.

  After 5 minutes, the addition of a mixture 2 comprising: 334.7 g of styrene (St) and 6.69 g of methacrylic acid (AMA) is started.

  The addition is continued for 60 minutes. After complete addition of the various ingredients, the copolymer emulsion obtained is maintained at 85 ° C. for one hour. A sample (5 g) is then taken and analyzed by steric exclusion chromatography (SEC) in THF. Its measured average molecular weight Mn is equal to 5800 g / mol in polystyrene equivalents (calibration by linear polystyrene standards). Its polymolecularity index Mw / Mn is equal to 1.9.

  An analysis of the sample by gas chromatography reveals that the conversion of the monomers is greater than 99%.

  Step lb: Growth of a second block of poly (ethyl acrylate) with a theoretical molecular weight of approximately 7000 g / mol to obtain a diblock copolymer polystyrene-block-poly (ethyl acrylate), starting from the copolymer emulsion obtained previously in step la after having taken 5 g for analysis and without stopping the heating.

  2.00 g of sodium persulfate Na 2 S 2 O 8 diluted in 50.0 g of water are introduced continuously for three hours. Simultaneously for three hours, a mixture 3 comprising: 200.0 g of water, -1.00 g of sodium carbonate Na 2 CO 3 and 2.00 g of sodium dodecyl sulphate are added at 85 ° C. Simultaneously a mixture 4 comprising: 581.6 g of ethyl acrylate (EA) and 11.63 g of methacrylic acid (AMA). After complete addition of the various ingredients, the copolymer emulsion obtained is maintained at 85 C for one hour.

  Then 2.0 g of tert-butylbenzyl peroxide are introduced in one go and the addition of a mixture comprising: 1.00 g of erythorbic acid - 50.0 g of water is started.

  The addition is continued for 60 minutes. After complete addition of the various ingredients, the emulsion is cooled to -25 C for one hour.

  A sample (5 g) is then taken and analyzed by steric exclusion chromatography (SEC) in THF. Its measured average molecular weight Mn is equal to 12700 g / mol in polystyrene equivalents (calibration by linear polystyrene standards). Its polymolecularity index Mw / Mn is equal to 1.9.

  Analysis of the sample by gas chromatography reveals that the conversion of the monomers is greater than 99.8%.

  The product obtained is a dispersion in water of the copolymer (latex), dry extract of about 44%.

  Step II: Partial Hydrolysis (75% Targeted) of the Poly (ethyl acrylate) Block of the Copolymer Obtained Previously in Step 2 to Obtain the Polystyrene-Block-Poly Diblock (Ethyl Acrylate -Sodium Sodium Salt) acrylic acid) of type (1b).

  638 g of water, 212 g of 2-propanol and 1485 g of emulsion copolymer (ie 650 g of dry copolymer) obtained previously in step 1b are introduced into the reactor at ambient temperature. The resulting mixture is stirred for 15 minutes. The temperature is then raised to 75 ° C., and then 488 g of sodium hydroxide (solution in water at 23.2% by weight) are added continuously over an hour.

  After 30 minutes of the beginning of the addition of sodium hydroxide, the addition is continued continuously over one hour of 37 g of hydrogen peroxide (30% solution).

  After complete addition of the various ingredients, the copolymer solution obtained is maintained at 75 ° C. for four hours and then cooled to -25 ° C. for one hour.

  The product recovered at the end of the reaction is a translucent gel in the water of dry extract of about 18%.

  The copolymer thus obtained exhibits the following characteristics: theoretical average molecular mass of block A: 5000 g / mol; theoretical average molecular weight of block B: 5000 g / mol; proportion by weight of block B: 57%; proportion by weight of Block A: 43% - Quantity by weight of units derived from ethyl acrylate in Block B: 31%

  He. Examples of Composition Emulsion Preparation Method: The amphiphilic copolymer of the invention, supplied in aqueous-alcoholic solution, was diluted with water for 30 minutes while stirring at 25 ° C .; the resulting solution was macroscopically homogeneous. The emulsion was prepared by introducing at ambient temperature the oily phase B into the aqueous phase A with vigorous stirring using a Moritz type homogenizer under a stirring speed of 2000 RPM for 15 minutes. Then phase C was introduced with gentle stirring in the emulsion.

  The droplet size of the emulsions was measured using a Hydro 2000 S / G laser granulometer (Malvern) considering the average surface diameter D (3.2). The polymer used in Examples 1 to 3 of the invention is a diblock copolymer Polystyrene (PS) / polyacrylic acid (PAA) (PS / PAA copolymer) whose PS block has a molar mass of 5000 g / mol, and the hydrophilic block has a molar mass of 5000 g / mol, the degree of hydrolysis being of 75 mol%, ie a proportion of ethyl acrylate of 25%. This polymer, supplied by Rhodia, is obtained by hydrolysis in a basic medium of a diblock polymer Polystyrene / ethyl polyacrylate. The mass proportion of the hydrophilic block in the polymer is equal to 50%.

  Examples 1 to 3: Fluid Milks for the Body Example 1 Example 2 Example 3 Phase A Distilled water 65.218% 65.218% 65.218% Glycerin 3% 3% 3% Preservative 0.1% 0.1% 0.1% Citric acid 0.062% 0.062% 0.062% PS / PAA (5,000 / 5,000) hydrolyzed to 5.62% 5.62% 5.62% 75% (25% ethyl acrylate), to 16.5% active phase B Parleam oil 13% 13% 13% Cyclohexadimethylsiloxane 7% 7% 7% Glyceryl isostearate 0.5% 0.5% 0.5% Phase C Distilled water 5% 5% 5% Dimethicone copolyol (Silwet L-77 the 0.5% 0 0 company Crompton Osi Specialties) Dimethicone copolyol (Silsoft 305 from the 0 0.5% 0 company Crompton Osi Specialties) PEG 12 Dimethicone (Silsoft 880 from GE 0 0 0.5% Bayer Silicones) Average size of drops 5 pm 4 pm 5 pm Viscosity 0.043 Pa.s 0.046 Pa.s <0.035 Pa.s Rhéomat 180, 25 C, 200 RPM, Mobile 2 Homogenous Homogeneous Homogeneous Stability after 24 hours Yes Yes Yes Examples 1 to 3 are oil-in-water emulsions stabilized by a copolymer PS / Ethyl polyacrylate reblocks partially hydrolysed and comprising a water-soluble silicone-type wetting agent. They are stable for at least 24 hours and are in the form of fluid milks.

  Spreading properties When applied to the skin, the emulsions of Examples 1 to 3 form a continuous film on the skin with the naked eye during application.

  An in vitro evaluation was performed, using as a model of Bioskin skin, polyurethane elastomer whose surface characteristics are close to those of the skin. The critical surface tension of the skin was determined in vivo on the forearm. The measurements were made in a glove box at 30 C and 75% humidity, according to the Zisman method with as known surface tension liquids: water (y = 72 mN / m) and diiodomethane (y = 50.8). mN / m). The critical surface tension of the skin on the forearm is 40 mN / m and that of Bioskin is 41 + 1-2 mN / m. 0.2 grams of emulsion was fingered on a Bioskin plate and left partially dried for 5 minutes. The homogeneity of the spreading was evaluated with the naked eye. Examples 1 to 3 lead to more homogeneous films on bioskin than the equivalent emulsion without a wetting agent of water-soluble silicone type (Comparative Example 1); this is in keeping with their behavior on the skin.

  COMPARATIVE EXAMPLES 1 TO 3: Fluid Milks for the Body Example Example Comparative Example 1 Comparative 2 Comparative 3 Phase A Distilled Water 70.618% 65.118% 65.118% Glycerin 3% 3% 3% Preservative 0.1% 0.1% 0.1 % Citric acid 0.062% 0.062% 0.062% PS / PAA (5,000 / 5,000) hydrolyzed to 5.62% 5.62% 5.62% 75% (25% ethyl acrylate) to 16.5 % active ingredient Phase B Parleam oil 13% 13% 13% Cyclohexadimethylsiloxane 7% 7% 7% Glyceryl isostearate 0.5% 0.5% 0, 5% Preservative 0.1% 0.1% 0.1% Phase C Distilled water 0 5% 4.25% Disodium stearoyl glutamate 0 0.5% 0 (Amisoft HS 21P from Ajinomoto) Sucrose Laurate (Sisterna L70C from 0 0 1.25% Dai Ichi company) Average size of drops 3 pm 4 pm 3 pm Viscosity 0.040 Pa.s <0.035 Pa.s 0.048 Pa.s5 Rheomat 180, 25 C, 200 RPM, Cell 2 Inhibitory Inhomogen Inhomogen Inhomogen Stability after 24 hours Yes No Yes The block polymer of these comparative examples is identical to that of Examples 1 to 3.

  The emulsion of Comparative Example 1 is stabilized by a diblock copolymer used according to the invention but it does not comprise a wetting agent.

  Comparative Examples 2 to 3 are oil-in-water emulsions stabilized with a diblock polymer used according to the invention and comprising an amphiphilic compound of alkyl sugar or alkyl glutamate type. The emulsion of Comparative Example 2 is not stable because a creaming phenomenon is observed after 10 minutes.

  The following table gathers the surface tension values at 25 C of aqueous solutions comprising 0.05% (by weight) of these two amphiphilic compounds. Wetting agent Surface tension at 0.05% in water (mN / m), 25 C Amisoft HS 21 P 27 Sisterna L70C 29 Plating properties When applying to the skin, the emulsions of Comparative Examples 1 and 3 form a discontinuous film on the skin with the naked eye during application.

  An in vitro evaluation was carried out according to the same protocol as that described in Examples 1 to 3. As for the skin, the spread of the emulsions of Comparative Examples 1 and 3 on bioskin is heterogeneous: Comparative Example 1: the whole area where the emulsion is spread, less than 50% are covered by the emulsion during the observation, 25 - Comparative Example 3: areas not covered by the emulsion are visible during the observation ; the homogeneity of the film is poorer than that of Examples 1 to 3 15. These data show that hydrocarbon amphiphilic compounds making it possible to lower the surface tension of water below 35 mN / m do not lead, after introduction into a emulsion stabilized by the block copolymers of the invention, to improve the homogeneity of the film on the skin. Note that the emulsions of Examples 1 to 3 and Comparative Examples 1 and 3 have viscosities of the same order of magnitude; the differences in spreading properties observed are therefore not related to a greater or lesser fluidity of certain emulsions. In addition, ionic amphiphilic compounds of alkyl glutamate type do not lead to stable emulsions.

  Thus, only the emulsions of the invention, comprising a partially hydrolysed PS / polyacrylate type copolymer and a water-soluble silicone wetting agent, are stable and lead to an improvement in the spread of emulsions on the skin.

Claims (14)

  1. Composition for topical application to keratin materials, in the form of an oil-in-water emulsion comprising, in a physiologically acceptable medium, an oily phase dispersed in an aqueous phase, characterized in that it contains: (1) minus a diblock copolymer (block A) - (block B) in which: block A comprises at least 90% by weight of units derived from styrene; the block B comprises at least (a) units derived from acrylic acid in acid or salified form, in a proportion of at most 90% of the total weight of the block B, and (b) units derived from an acrylate C1-C4 alkyl. in a proportion of at least 10% of the total weight of the block B, the proportion by weight of the block B with respect to the copolymer ranging from 40 to 60%; (2) at least one wetting agent chosen from water-soluble silicones comprising at least one terminal or pendant monovalent polyoxyalkylene group and which, introduced at 0.05% by weight in an aqueous solution, are capable of reducing the surface tension of the water at a value less than 35 mN / m, and preferably less than 30 mNIm.   2. Composition according to claim 1, characterized in that said diblock copolymer is linear, and the block B is a statistical block.   3. Composition according to claim 1 or 2, characterized in that the C 1 -C 4 alkyl acrylate is ethyl acrylate.   4. Composition according to any one of the preceding claims, characterized in that block A and / or block B comprises up to 10% by weight and preferably up to 5% by weight of a hydrophilic comonomer. ionic or nonionic relative to the total weight of block A or block B containing said hydrophilic comonomer   5. Composition according to the preceding claim, characterized in that the hydrophilic comonomer is methacrylic acid in acid or salified form.   6. Composition according to any one of the preceding claims, characterized in that the diblock copolymer (block A) - (block B) is obtainable by a polymerization process comprising at least the following steps: step I) : a diblock copolymer (block A) - (block B '), or - a triblock copolymer or architecture star (core) - [(block A) - (block B')) x where (core) are prepared: - [(block B ') - (block A)] x where x is an average number greater than or equal to 2, where - block A comprises units derived from styrene, and - block B' comprises units deriving from a C1-C4 alkyl acrylate, step l ') optionally, for a triblock or star copolymer, the bonds (core) - (block B') or (core) - (block A) are broken, so as to obtain a diblock copolymer (block A) - (block B '), stage II) the block B' is hydrolyzed into a block B to obtain the diblock copolymer (block A) - (block B), the hydrolysis inducing, if appropriate, to a triblock or star copolymer, a break in the bonds (core) - (block B ') or (core) - (block A), so as to obtain a diblock copolymer (block A) - (block B).   7. Composition according to the preceding claim, characterized in that, in step I), a diblock copolymer (block A) - (block B ') is prepared by a process comprising the following intermediate steps la) and lb): 1a), a first block A is prepared by bringing into contact: - nT moles of a transfer agent comprising a single transfer group - nA moles of styrene or a monomer mixture comprising at least 90% by weight of styrene and where nA / nT> 5 and preferably <5000; and optionally a free radical initiator lb), a second block B 'is prepared to obtain a diblock copolymer (block A) - (block B'), by placing in contact with: the block A obtained in the preceding step, nB moles of a hydrolyzable C1-C4 alkyl acrylate or a mixture of monomers comprising at least 90% by weight of a C1-C4 alkyl acrylate such that nB / nT> 5 and preferably <5000; and optionally a free radical initiator, during stage II), the block B 'is subsequently hydrolysed at a molar ratio T of between 0.4 and 0.96 to obtain said diblock copolymer (block A) - (block B).   8. Composition according to Claim 6 or 7, characterized in that an additional step III) is carried out, during and / or after step II) of deactivation of transfer groups carried by macromolecular chains and / or purification of the copolymer. diblock (block A) - (block B) and / or destruction of byproducts of hydrolysis and / or deactivation.   9. Composition according to any one of claims 6 to 8, characterized in that step I) is carried out by emulsion polymerization in water.   10. Composition according to any one of claims 6 to 9, characterized in that the degree of hydrolysis T is between 0.7 and 0.8; preferably T is 0.75.   11. Composition according to any one of claims 6 to 10, characterized in that the block A and / or the block B 'or the block B comprises from 0.1 to 10% by weight and preferably from 0.1. at 5% by weight of an ionic or nonionic hydrophilic comonomer relative to the total weight of block A, block B or block B 'containing said hydrophilic comonomer.   12. Composition according to the preceding claim, characterized in that the hydrophilic comonomer is methacrylic acid in acid or salified form.   13. Composition according to one of claims 6 to 12, characterized in that the C 1 -C 4 alkyl acrylate is ethyl acrylate.   14. Composition according to any one of the preceding claims, characterized in that the diblock copolymer (block A) - (block B) is such that: the proportion by weight of block B relative to the copolymer ranges from 40 to 60% (or less than 60%, - its theoretical average molecular weight is between 8000 and 13000 g / mol 17. Composition according to any one of the preceding claims, characterized in that the proportion of block B ranges from 45 to 60%. by weight relative to the total weight of the diblock copolymer 18. Composition according to any one of the preceding claims, characterized in that the diblock copolymer or copolymers are present in concentrations ranging from 0.1 to 10% by weight and preferably 0.2 to 5% by weight relative to the total weight of the composition 19. Composition according to any one of the preceding claims, characterized in that the wetting agent is chosen from water-soluble silicones containing at least a polyoxyalkylene group of the following general formula (a): (R 2) 3 SiO [(R 2) 2 SiO] p (R 2 PESiO) q Si (R 2) 3 (a) t 0 in which - the radicals R 2, which are identical or different, denote a monovalent hydrocarbon radical chosen from alkyl, aryl and aralkyl radicals having at most 10 carbon atoms; some of the R2 radicals may also contain in addition an ethylcyclohexylenemonoxide group of formula C2H4 O and are in a small proportion in the polysiloxane chain; p varies from 0 to 150, preferably from 0 to 100 and more preferably from 0 to 30; q varies from 1 to 12, preferably from 1 to 10 and more preferably from 1 to 8. - the polyether PE group has the following formula (b) -CXH2X (OC2H4) v (OC3H6) ZOR3 (b) in which: x varies from 1 to 8 and preferably ranges from 2 to 4 and more preferably is equal to 3; y is greater than 0 z is greater than or equal to 0; the values of y and z are such that the total molecular weight of the polyoxyalkylene portion of the polyether PE group ranges from 200 to 10,000 and more preferably from 350 to 4,000; R3 denotes hydrogen, a C1-C8 alkyl group or a C2-C8 acyl group. 18. Composition according to the preceding claim, characterized in that the radicals R2 are chosen from C1-C6 lower alkyls; phenyl and benzyl. 19. Composition according to the preceding claim, characterized in that the R2 radicals are chosen from C1-C4 lower alkyl and even more particularly designate the methyl group. 20. Composition according to any one of claims 17 to 19, characterized in that the radicals R3 are chosen from C1-C4 lower alkyl and even more particularly indicate the methyl group. Composition according to any one of claims 17. at 20, characterized in that the water-soluble silicones of formula (a) are chosen from those of formula (a ') below: MeSiO (MeSiO) p (MePESiO) qSlMe3 (a') where Me denotes the methyl group; PE denotes the group of formula (b '): - (CH 2) 3 O (OC 2 H 4) y (OC 3 H 6) ZOR 3 (b') where x, z and z have the same values indicated in claim 30 and R 3 denotes hydrogen or a group C1-C4 alkyl. and more particularly methyl 22. Composition according to any one of the preceding claims, characterized in that the wetting agent is chosen from branched silicones of formula (c) below: (MeSiO) g_2 [SiOMe2) piq OPE] q (c where - p varies from 0 to 150, preferably from 0 to 100 and more preferably from 0 to 30; q varies from 1 to 12, preferably from 1 to 10 and more preferably from 1 to 8. - Me means the methyl group; - PE denotes the group of formula (d) below: - (OC2H4) y (OC3H6) = R3 (d) where - y is greater than 0 - z is greater than or equal to 0; the values of y and z are such that the total molecular weight of the polyoxyalkylene portion of the polyether PE group ranges from 200 to 10,000 and more preferably from 350 to 4,000; - R3 denotes a C1-C4 alkyl group. 23. Composition according to any one of the preceding claims, characterized in that the wetting agent (s) are present in a concentration ranging from 0.01 to 10% by weight, preferably from 0.05 to 5% by weight relative to to the total weight of the composition. 24. Composition according to any one of the preceding claims, characterized in that the amount of oily phase is from 2 to 70% by weight relative to the total weight of the composition. Composition according to any one of the preceding claims, characterized in that it constitutes a product for protection, treatment or care for the face, a product for the hands or for the body, a product for cleaning the skin, a product for make-up and a hair product. 26. Process for the cosmetic treatment of a keratinous material, characterized in that a composition according to any one of Claims 1 to 24 is applied to the keratinous material.