FR2911502A1 - COSMETIC COMPOSITION COMPRISING A DIBLOC COPOLYMER - Google Patents

Abstract

The present invention relates to a composition comprising in a physiologically acceptable medium: e) at least one diblock copolymer (block A) - (block B) in which block A comprises at least units derived from styrene; minus (a) units derived from acrylic acid in free or salified form and (b) at least units derived from a C 1 -C 4 alkyl acrylate. The diblock copolymer has hydrating properties of keratin materials. Application to the care and makeup of keratin materials.

Description

The present application relates to a cosmetic composition comprising a

  block copolymer based on styrene and such a copolymer as moisturizing agents for keratin materials and more particularly on the skin.

  The Stratum Corneum is the thin stratum corneum that forms the interface between the body and the drying environment. It is formed of the upper epithelial tissue: the epidermis, and connective tissue located below: the dermis.

  The Stratum Corneum, about 10 to 15 μm thick, consists of vertically stacked corneocytes surrounded by a matrix of lipids organized in lamellar liquid crystal phase. Thus, it is a two-compartment system that can be compared to a brick wall, consisting of anucleate cells (bricks) and intercellular lamellar liquid crystal phase (cement).

  One of the functions of the Stratum Corneum is to regulate the flow of water into and out of the skin and thus to delay the excessive loss of water from the deeper layers of the epidermis. The Stratum Corneum also protects against mechanical aggression and the passage of chemicals and foreign microorganisms. It is also the first defense against UV radiation. In general, a moisturizing agent is defined as a substance that decreases the feeling of dry skin by affecting the water content of the skin by addition or retention.

  Generally, corneometry is the method used to measure the hydration provided by humectants such as glycerol, urea and its derivatives. But this method can not be used to highlight the moisturizing properties of polymers, so it was necessary to develop a suitable method to highlight the moisturizing properties of polymers.

  Different methods based on spectroscopic techniques (infrared, Raman, NMR, etc.) have been developed in recent years with the aim of improving the knowledge of the skin, in particular in the medical field. These techniques have the advantage of not requiring any special preparation of the sample and are non-invasive and non-destructive. These methods are described in particular in: 1. K. Wichrowski, G. Sore, and A. Khaiat, "Use of infrared spectroscopy for in vivo measurement of stratum corneum moisturization after application of cosmetic preparations," Int. J. Cos. Sci. 17, 1-11 (1995). 2. Querleux B, Richard S, Bittoun J, Jolivet O, Idy-peretti I, Bazin R, Lévêque JL: In vivo hydration profile in skin layers by high-resolution magnetic resonance imaging. Skin Pharmacol 1994; 7: 210-216. 3. B. Schrader, B. Dippel, S. Fendel, S. Keller, T. Lochte, M. Riedl, R. Schulte, and E. Tatsch, "NIR FT Raman Spectroscopy, New Tool in Medical Diagnosis," Mol. Struct. 408/409, 23-31 (1997).

  In the context of the present application, the method adopted for measuring the amount of water supplied by polymer solutions at 1% by weight is laser confocal microscopy associated with Raman spectroscopy.

  Raman spectroscopy provides information on the molecular composition and structure of the test sample. Associated with confocal microscopy, it offers the advantage of providing information on the Stratum Corneum from the surface of the skin to a depth of a few tens of microns. In addition, the method used in the present application has the advantage of being non-invasive and non-destructive.55 This method has established that the polymers used in accordance with the present application are such that a solution of 1 % by weight of these polymers provides a water content at least equal to that provided by a 7% by weight solution of glycerol.

  To implement this method, Isolated Stratum Corneum, compacted Stratum Corneum dander pellets, artificial skin (Episkin, Matek, Skinethic ...) from cosmetic surgery skin can be used as an evaluation support. . These examples are not limiting, all the media modeling the skin can be used.

  In the context of the present application, compacted dander pellets having a weight of 80 to 100 mg, a thickness of more than 100 μm and a surface area of approximately 1 cm 2 are used as a Stratum Corneum model; 5 measurements are made on each plantar pellet and 5 pellets are used for each polymer solution, 25 measurements for each polymer solution.

  The amount of polymer solution applied to each pellet is about 50 μl. A Raman laser confocal microscope of LabRam type (Jobin Yvon - Horiba) equipped with a He: Ne laser (At = 633 nm power approximately 8.4mW) and a CCD detector is used to carry out the measurements. The laser beam is focused in the skin with an X50 objective and the Raman spectra are recorded using a point-to-point mode, from the sample surface, to the depth. The acquisition parameters of the spectra are: hole and slit: 200pm, acquisition time: 30s on a frequency of 2800 to 4000 cm-1. The microscope in question was the subject of a technical modification essential to the measurement of water, with the incorporation of an enclosure allowing to control during the acquisitions the temperature and the humidity: the parameters are of 25 C and 50% Relative Humidity Quantification of water is determined by the ratio of the water OH bands / CH3 protein bands, in Raman spectrography, as described in: 1 Chrit L, Hadjur C, Morel S, Sockalingum GD , Lebourdon G, Leroy F, Manfait M: In vivo chemical investigation of Human skin using a confocal Raman Optic microprobe. J. Biomed Opt 2005. 2 Caspers PJ, Lucassen GW, EA Carter, Bruining HA, GJ Puppels: In vivo confocal Raman microspectroscopy of the skin: noninvasive determination of molecular concentration profiles. Journal of Investigative Dermatology 2001; 116 (3): 434-442.

  The water / protein ratios in the Stratum Corneum were determined in Raman spectrography, by calculating the ratio between the intensity of the OH bands of the water (area under the curve) integrated between 3350cm_, and 3550 cm-1 and the intensity. protein CH3 bands (area under the curve) integrated between 2910cm_ and 2965 cm-1. Quantification of water is calculated from the following equations: W / P = (mW / mp) R Water content (%): rom (mW + mp) -100% (W / P) / (W / () P + R))

  mW and mp being the water and protein masses respectively in the volume of the test sample; Where W is the intensity of the Raman signal of the integrated water (OH bands of the water (area under the curve) integrated); Where P is the intensity of the Raman signal of integrated proteins (integrated CH3 bands of protein (area under the curve)); R is a proportionality constant expressing the ratio between the Raman signals of water and proteins in a 50% solution. The water content is expressed in gram of water per 100 g of wet tissue. These features are integrated into Jobin-Yvon Horiba's LabSpec software.

  To evaluate the moisturizing performance, the measurements are made at T = 0, before the treatment and at T + 1 hour after the treatment, the surface at 20pm of depth.

  The problem posed by the present application was to propose families of compounds that can be used as moisturizing agents for keratin materials and more particularly for the skin.

  The inventors of the present application have shown that this problem can be solved by means of particular diblock copolymers based on styrene.

  The Applicant has surprisingly and unexpectedly discovered that this objective could be achieved by using at least one diblock copolymer (block A) - (block B) in which - block A comprises at least units derived from styrene; - Block B comprises at least (a) units derived from acrylic acid in free or salified form and (b) at least units derived from a C 1 -C 4 alkyl acrylate.

  More specifically, the subject of the present invention is a cosmetic composition comprising, in a physiologically acceptable medium: a diblock copolymer (block A) - (block B) in which - block A comprises at least units derived from styrene; - Block B comprises at least (a) units derived from acrylic acid in free or salified form and (b) at least units derived from a C 1 -C 4 alkyl acrylate.

  The subject of the invention is also a non-therapeutic cosmetic process for the care or makeup treatment of keratinous substances, in particular the skin, comprising the application to the keratin materials, in particular to the skin, of a cosmetic composition as defined above . The cosmetic process is in particular a cosmetic process for moisturizing the skin.

  The subject of the present invention is also the use of a diblock copolymer as defined above as a moisturizing agent for keratinous substances, in particular the skin.

  Physiologically acceptable medium means a non-toxic medium that can be applied to the skin, lips, hair, eyelashes, eyebrows and nails. The composition of the invention may constitute in particular a cosmetic or dermatological composition.

  The diblock copolymers according to the invention are advantageously linear.

  More preferably the proportion by weight of the block B with respect to the copolymer is greater than or equal to 50%.

  The diblock copolymers according to the invention are more particularly characterized in that they are diblock 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, relative to the total weight of block B, (i) from 34 to 95% by weight of units derived from acrylic acid in acid form or in salified form; (ii) from 5 to 66% by weight of units derived from C1-C4 alkyl acrylate.

  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 the formula CH 2 -CH (COOH) - or CH 2 -C (CH 3) (COOH) -, obtained for example by polymerizing an ester of acrylic or methacrylic acid 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.

  The ratio by weight between the blocks corresponds to the ratio between the masses of the monomers (or monomer mixtures) 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).

  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 salt form of sodium acrylate type.) Preferably, the C 1 -C 4 alkyl acrylate monomer is ethyl acrylate.

  According to a preferred form of the invention, the block A and / or the block B comprises up to 10% by weight (in particular from 0.1% to 10% by weight) and preferably up to 5% by weight. (in particular from 0.1% to 5% by weight) of an additional hydrophilic comonomer, ionic or nonionic, relative to the weight of the block A or block B containing said hydrophilic monomer. By hydrophilic monomer is meant a monomer which has affinity for water, and which is typically not capable of forming a two-phase macroscopic solution in distilled water at 25 ° C. at a concentration of 1% by weight. weight. Among the additional hydrophilic comonomers, ionic or nonionic, mention may be made, for example, of acrylamide, hydroxyethyl (meth) acrylate, methacrylic acid (AMA) and their salts. It is more particularly preferred to use methacrylic acid or one of its salts. Block A may also comprise as additional hydrophilic monomer acrylic acid and its salts.

  A first family of diblock copolymers according to the invention which is particularly preferred consists of diblock copolymers (block A) - (block B) of the type (1) in which the proportion by weight of block B with respect to the copolymer is between 50 and 85%, and preferably between 50% and 75%. A second family of diblock copolymers according to the invention which is particularly preferred is constituted by diblock copolymers (block A) - (block B) of the type (2) in which the proportion by weight of block B with respect to the copolymer is greater than or equal to equal to 85%. Among these diblock copolymers of type (2), two types of copolymers are advantageously distinguished:

  Type (2a): where the proportion by weight of block B with respect to the copolymer is greater than or equal to 87%, especially greater than or equal to 87% and less than 94%.

  - Type (2b): where the proportion by weight of the block B relative to the copolymer is greater than or equal to 94%, in particular ranging from 94% to 97%.

  Among these diblock copolymers of type (2a), two types of copolymers are advantageously distinguished:

  - Type (2a1): where in block B: the proportion by weight of units derived from acrylic acid in free or salified form is between 64% (obtained for example by a hydrolysis at a rate of T = 0.7) and 75% (obtained for example by a hydrolysis at a rate of T = 0.8), and the proportion by weight of units derived from the C 1 -C 4 alkyl acrylate is between 25% (obtained for example by a hydrolysis at a T = 0.8) and 36% (obtained for example by a hydrolysis at a rate of T = 0.7).

  - Type (2a2): where in block B: the proportion by weight of units derived from acrylic acid in free or salified form is between 75% (obtained for example by a hydrolysis at a rate of T = 0.8) and 95% (obtained for example by a hydrolysis at a rate of T = 0.96), and the proportion by weight of units derived from the C 1 -C 4 alkyl acrylate is between 5% (obtained for example by a hydrolysis at a rate of T = 0.96) and 25% (obtained for example by a hydrolysis at a rate of T = 0.8). The diblock copolymers (Block A) - (Block B) used in the context of the invention may be obtained by a process comprising the following steps:

  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 styrene and where nA / nT> 5 and preferably <5000; - and possibly an initiator of free radicals

  lb) a second block B 'is prepared to obtain a diblock copolymer (block A) - (block B'), by bringing into contact: - the block A obtained in the preceding step, - nB moles of an acrylate 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, II) hydrolysis of the B 'block is then carried out at a molar ratio T between 0.4 and 0.96 to obtain said diblock copolymer (block A) - (block B). III) optionally, 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 hydrolysis products and / or deactivation and preferably: - T is between 0.4 and 0.96, preferably between 0.7 to 0.8, preferably about 0.75, or about 0, 90 - nA / nT> 5, and preferably nA / nT <5000, - nB / nT> 5, and preferably nB / nT <5000.

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

  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. The number of units derived from acrylic acid or from an acrylic acid salt can be determined by any known method, in particular by acid-base potentiometric titration of the number of COONa groups using a strong acid, by example using hydrochloric acid.

  In the present application, the molar mass MA of a mixture of monomers AI 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 nA1 / (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. .

  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. Such agents 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.

  The polymerization process as described above is described in particular in WO 01/16187.55. In step I) described above, the preparation of a first block can be carried out using monomers or a mixture of monomers, initiators and / or agents promoting the control of the polymerization (transfer agents with groups -S-CS-, nitroxydes 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 preceding 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 or a dithioester). 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. 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% (especially from 0.1% to 10%), preferably up to 5% (in particular from 0.1% to 5%), by weight of other units, derived from hydrophilic co-monomer (s).

  Block B obtained from block B 'after hydrolysis, comprises units derived from the hydrolyzable C1-C4 alkyl acrylate, units derived from acrylic acid or a salt, and optionally units derived from a comonomer hydrophilic used during step lb) of growth of the block B ', for example units derived from acrylic 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, it is also possible to use acrylic acid and its salts 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 a salt thereof, based on the total weight of block A or block B or 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 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 or a salt thereof.

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

Step I)

  The copolymers 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 a polymer.

  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 group of transfer of formula S-CS-, especially known under the names of RAFT or MADIX. By way of examples of so-called living or controlled polymerization processes, it is possible to refer in particular 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 control agents of the type 45 xanthates, - the radical polymerization process controlled by dithioesters or trithiocarbonates type control agents of the application WO 98/01478, - the radical polymerization process controlled by dithiocarbamate type control agents of the WO 99/31144, 50 the controlled radical polymerization process with dithiocarbazate type control agents of the application WO 02/26836, - the radical polymerization process controlled by dithiophosphoroesters type control agents of the application WO 02 / 10223, 15 to the process of the application WO 99/03894 which implements a polymerization in the presence of nitroxide precursors , or methods employing other nitroxides or nitroxide / alkoxyamine complexes - the process of WO 96/30421 which uses atom transfer radical polymerization (ATRP), - the radical polymerization process controlled by Iniferters-type control agents 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 radiolucent polymerization process controlled by tetraphenylethane derivatives, disclosed by D. Braun et al. In Macromol. Symp. 111, 63 (1996), or alternatively, to the process of radical polymerization controlled by organocobalt complexes described by Wayland et al. In J.Am.Chem.Soc. 116,7973 (1994) - to the radical polymerization process controlled by 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 block nodules A, which can influence the physicochemical properties of the copolymer. The polymerizations can 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. 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 block A may remain unchanged during hydrolysis if 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 base proportion is added based on the amount of hydrolyzable 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. The operation 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 byproducts which 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 deactivating transfer groups carried by macromolecular chains, and / or purification of the diblock copolymer (Block A) - (Block B) and / or destruction of by-products 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 are simultaneous.

  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 stage a). 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 amounts of comonomer 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 mass Mb, 00 of a block is typically calculated according to the following formula: Mbioc = 1M. * Nprecursor where M; 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 will be bound the macromolecular chain of the block. 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 (the masses are expressed with the fiction of a hydrolysis rate of 1), if such hydrolysis has been carried out.

  The total target or theoretical mass of a block is defined as the mass of the macromolecular chain, 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.

  Thus: - the total theoretical or target mass of block A is MAnA; the theoretical or target average molecular weight of block A is: MAnA / nT. the total theoretical or target mass of the block B 'is MBnB; the theoretical or target average molecular weight of the block B 'is: MBnB / nT. the total theoretical or target mass of the block B is T MAA nB + (1-T) MB nB; the theoretical or target average molecular weight of the B block is: MAA nB / nT (because T = 1 for the theoretical or target average molecular weight) - the theoretical or target total mass of the block copolymer is MAnA + T MAA nB + (1 -T) MB nB; the theoretical or target average molecular weight of the block copolymer (block A) - (block B) is nA / nT MA + MAA nB / nT. where: - MA is the molar mass of styrene or monomer mixture comprising styrene used in step la), - MAA is the molar mass of acrylic acid, - MB is the molar mass of acrylate C1-C4 alkyl or monomer mixture comprising the C1-C4 alkyl acrylate employed in step 1b).

  By way of reference, the following correspondences are given: nA / nT = 5 corresponds to a theoretical average molecular mass of block A of about 500 g / mol - nA / nT = 5000 corresponds to a theoretical average molecular mass of block A of approximately 500000 g / mol, nB / nT = 5 corresponds to a theoretical average molecular weight of the block B 'of approximately 500 g / mol - nB / nT = 5000 corresponds to a theoretical average molecular weight of the block B' of 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 C 1 -C 4 alkyl acrylate is the acrylate 'ethyl.

  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 weight ratio (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 amount 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, the proportion of block B.

  It is mentioned that it is not beyond the scope of the invention implementing and adapting other preparation processes leading to substantially identical diblock copolymers. In particular it is conceivable to use transfer agents comprising several transfer groups (for example trithiocarbonates ZS-CS-SZ) leading to telechelic copolymers of type R - [(block B ') - (block A)]. (for example (block A) - (block B ') - R- (block B') - (block A), then to section ("cleave") the telechelic copolymers, to obtain diblock copolymers (block A) - ( Block B '). The section may 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 conditions of use. to target average molecular weights equivalent to those indicated, for example by multiplying the amounts of monomers introduced by the number of transfer groups included in the transfer agent.

  Preferably, the diblock linear copolymers (block A) - (block B) of the type (1) 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 between 50 and 85%, preferably between 50% and 75%, and generally have a theoretical average molecular weight (nA / nT MA + MAA nB / nT) less than or equal to 13000 g / mol, and in particular between 8000 and 13000 g / mol.

  Preferably, the diblock linear copolymers (block A) - (block B) of the type (2) 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] which is greater than or equal to 85% (BOL 44 and 55 and 64) and generally have a theoretical average molecular weight (nA / nT MA + MAA nB / nT) greater than or equal to 13000 g / mol.

  Among these copolymers of the type (2), those particular of the type (2a), in which the proportion by weight of the block B with respect to the copolymer is greater than or equal to 87%, in particular greater than or equal to 87% and less than 94% generally have a theoretical average molecular weight of between 13,000 and 20,000 g / mol. those particular of the type (2b) in which the proportion by weight of the block B with respect to the copolymer is greater than or equal to 94%, in particular ranging from 94% to 97%, generally have a theoretical average molecular mass greater than or equal to 20,000; g / mol and preferably between 20000 and 50000 g / mol.

  The diblock copolymer or copolymers according to the invention may be present in the composition according to the invention in a content ranging from 0.01 to 10% by weight, relative to the total weight of the composition, preferably ranging from 0.05 to at 10% by weight, and preferably ranging from 0.1 to 5% by weight.

  The cosmetic composition according to the invention contains physiologically acceptable medium, that is to say compatible with cutaneous tissues such as the skin and the scalp. This physiologically acceptable medium may more particularly consist of water and optionally of a physiologically acceptable organic solvent chosen, for example, from lower alcohols containing from 1 to 8 carbon atoms and in particular from 1 to 6 carbon atoms, such as ethanol, isopropanol, propanol, butanol; polyethylene glycols having from 6 to 80 ethylene oxide units and polyols such as propylene glycol, isoprene glycol, butylene glycol, glycerine and sorbitol.

  The compositions that can be used can be in any of the galenical forms conventionally used for topical application and especially in the form of aqueous, hydroalcoholic solutions, oil-in-water (O / W) or water-in-oil (W / O) emulsions. multiple (triple: E / H / E or H / E / H), aqueous gels, or dispersions of a fatty phase in an aqueous phase using spherules, these spherules may be polymeric nanoparticles such as nanospheres and nanocapsules or lipid vesicles of ionic and / or nonionic type (liposomes, niosomes, oleosomes). These compositions are prepared according to the usual methods.

  In addition, the compositions that can be used according to the invention can be more or less fluid and have the appearance of a white or colored cream, an ointment, a milk, a lotion, a serum, a paste or foam. They may optionally be applied to the skin in the form of an aerosol. They may also be in solid form, for example in the form of a stick.

  When the composition that can be used according to the invention comprises an oily phase, the latter preferably contains at least one oil. It may also contain other fatty substances. As oils that 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; hydrocarbon-based oils of vegetable origin, such as liquid triglycerides of fatty acids containing from 4 to 10 carbon atoms, for instance triglycerides of heptanoic or octanoic acids or, for example, sunflower, corn or soybean oils, squash, grape seed, sesame, hazelnut, apricot, macadamia, arara, castor oil, avocado, triglycerides of caprylic / capric acids such as those sold by Stearineries Dubois or those sold under the names Miglyol 810, 812 and 818 by Dynamit Nobel, jojoba oil, shea butter oil; esters and synthetic ethers, in particular of fatty acids, such as the oils of formulas R 1 COOR 2 and R 1 OR 2 in which R 1 represents the residue of a fatty acid comprising from 8 to 29 carbon atoms, and R 2 represents a hydrocarbon-based chain , branched or unbranched, containing from 3 to 30 carbon atoms, for example purcellin oil, isononyl isononanoate, isopropyl myristate, 2-ethylhexyl palmitate, stearate of octyl-2-dodecyl, 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; and pentaerythritol esters such as pentaerythrityl tetraisostearate; linear or branched hydrocarbons of mineral or synthetic origin, such as paraffin oils, volatile or not, and their derivatives, petroleum jelly, polydecenes, hydrogenated polyisobutene such as parleam oil; fatty alcohols having from 8 to 26 carbon atoms, such as cetyl alcohol, stearyl alcohol and their mixture (cetylstearyl alcohol), octyldodecanol, 2-butyloctanol, 2-hexyldecanol, 2-undecylpentadecanol, oleic alcohol or linoleic 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 (PDMS) with a linear or cyclic silicone chain, which are liquid or pasty at room temperature, in particular cyclopolydimethylsiloxanes (cyclomethicones) such as cyclohexasiloxane; 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.

  By hydrocarbon oil is meant in the list of oils mentioned above, any oil predominantly comprising carbon and hydrogen atoms, and optionally ester, ether, fluoro, carboxylic acid and / or alcohol groups.

  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, palmitic acid and oleic acid; waxes such as lanolin, beeswax, carnauba or candelilla wax, paraffin waxes, lignite waxes or microcrystalline waxes, ceresin or ozokerite, synthetic waxes such as polyethylene waxes, waxes Fischer-Tropsch; 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 names Trefil, BY29 or EPSX by the company Dow Corning or under the names Gransil by the company Grant Industries. These fatty substances may be chosen in a varied manner by those skilled in the art in order to prepare a composition having the desired properties, for example of consistency or texture.

  The emulsions generally contain at least one emulsifier chosen from amphoteric, anionic, cationic or nonionic emulsifiers, used alone or as a mixture, and optionally a co-emulsifier. The emulsifiers are suitably selected according to the emulsion to be obtained (W / O or O / W). The emulsifier and the coemulsifier are generally present in the composition, in a proportion ranging from 0.3 to 30% by weight, and preferably from 0.5 to 20% by weight relative to the total weight of the composition.

  For W / O emulsions, examples of emulsifiers that may be mentioned include dimethicone copolyols such as the mixture of cyclomethicone and dimethicone copolyol, sold under the name DC 5225 C by Dow Corning, and alkyl dimethicone copolyols such as Laurylmethicone copolyol sold under the name Dow Corning 5200 Formulation Aid by the company Dow Corning and cetyl dimethicone copolyol sold under the name Abil EM 90 by the company Goldschmidt. It is also possible to use, as surfactant of W / O emulsions, a crosslinked solid elastomeric organopolysiloxane comprising at least one oxyalkylene group, such as those obtained according to the procedure of Examples 3, 4 and 8 of US Pat. No. 5,412,004 and examples US-A-5,811,487, especially the product of Example 3 (synthetic example) of US-A-5,412,004. and such as that sold under the reference KSG 21 by Shin Etsu. For O / W emulsions, mention may be made, for example, as emulsifiers, of nonionic emulsifiers such as oxyalkylenated (more particularly polyoxyethylenated) fatty acid esters of glycerol; oxyalkylenated fatty acid and sorbitan esters; oxyalkylenated fatty acid esters (oxyethylenated and / or oxypropylenated); oxyalkylenated fatty alcohol ethers (oxyethylenated and / or oxypropylenated); sugar esters such as sucrose stearate; and mixtures thereof such as the mixture of glyceryl stearate and PEG-40 stearate.

  In a known manner, the cosmetic or dermatological composition that may be used according to the invention may also contain adjuvants that are usual in the cosmetic or dermatological field, such as gelling agents, film-forming polymers, preservatives, solvents, perfumes, fillers, and filters. UV, bactericides, odor absorbers, dyestuffs, plant extracts and salts. 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 and / or into the aqueous phase.

  The cosmetic composition according to the invention may comprise an additional cosmetic or dermatological active agent.

  As such an additional cosmetic asset, there may be mentioned the active agents acting on the barrier function of the skin, the active agents promoting the hydration of the skin and the desquamating agents.

  By desquamating agent is meant any compound capable of acting: either directly on desquamation by promoting exfoliation, such as 13-hydroxy acids, in particular salicylic acid and its derivatives (including n-octanoyl 5 -salicylic); α-hydroxy acids, such as glycolic, citric, lactic, tartaric, malic or mandelic acids; urea; gentisic acid; oligofucoses; cinnamic acid; Saphora japonica extract; resveratrol; or on the enzymes involved in the desquamation or degradation of corneodesmosomes, such as glycosidases, Stratum Corneum chymotryptic enzyme (SCCE) or even other proteases (trypsin, chymotrypsin-like). Mention may be made of the chelating agents for mineral salts: EDTA; N-acyl-N, N ', N', ethylene diaminetriacetic acid; aminosulfonic compounds and in particular N- (2-hydroxyethyl) piperazine-N'-2-ethanesulfonic acid (HEPES); 2-oxothiazolidine-4-carboxylic acid derivatives (procysteine); glycine-type alpha amino acid derivatives (as described in EP-0 852 949, as well as the sodium methyl glycine diacetate marketed by BASF under the trade name TRILON M); honey ; sugar derivatives such as O-octanoyl-6-D-maltose and N-acetyl glucosamine.

  Among the active agents acting on the barrier function of the skin, or promoting the hydration of the skin, mention may be made of: - either the compounds acting on the barrier function, with a view to maintaining the hydration of the stratum corneum, or the occlusive compounds , in particular ceramides, sphingoid-based compounds, lecithins, glycosphingolipids, phospholipids, cholesterol and its derivatives, phytosterols (stigmasterol, R-sitosterol, campesterol), essential fatty acids, 1-2 diacylglycerol, 4-chromanone, pentacyclic triterpenes such as ursolic acid, petrolatum and lanolin; or compounds directly increasing the water content of Stratum Corneum, such as thralose and its derivatives, hyaluronic acid and its derivatives, glycerol, pentanediol, sodium pidolate, serine, xylitol, lactate sodium, glycerol polyacrylate, ectoin and its derivatives, chitosan, oligo- and polysaccharides, cyclic carbonates, N-lauroyl pyrrolidone carboxylic acid, and Na-benzoyl-L-arginine; or compounds that activate the sebaceous glands, such as steroid derivatives (including DHEA) and vitamin D and its derivatives.

  The compositions can show their effectiveness as a non-therapeutic skin care treatment, that is, as a preventive measure. They can also be used as a non-therapeutic treatment of the skin after a manifestation of disorders of the hydration of the skin.

  The composition may be presented as a care product and / or makeup.

  The makeup composition may be chosen from foundations, blushes, eyeshadows, concealer, body make-up, lip makeup products. The diblock copolymer block copolymers (block A) - (block B) as defined above or a mixture thereof can also be used for the preparation of a dermatological composition for hydration of the skin and more particularly in the treatment of dry skin or the treatment of dry skin.

  The following examples are illustrative of the present invention. Synthesis Examples Example 1: Preparation of a diblock copolymer Polystyrene-block-Poly (acrylic acid ethyl acrylate) of type (2b) by synthesis of a diblock copolymer Polystyrene-block-poly (acrylate of ethyl) of Mn 2000-block-42000 (g / mole) and then 75% hydrolysis of ethyl acrylate ester groups.

  Step la: Preparation of a first block of polystyrene with a theoretical molecular mass of about 2000 g / mol 3000 g of water, 17.6 g of sodium dodecyl sulphate and 0.290 g are introduced into the reactor at ambient temperature. 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: 10.00 g of styrene (St), 0.2 g of methacrylic acid (AMA), and 10.42 g of xanthate ( CH3) (CO2CH3) CH-S (C = S) OCH2CH3.

  The mixture is heated to 85 ° C., then a solution of 1.19 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: 90.0 g of styrene (St) and 1.80 g of methacrylic acid (AMA) is begun. 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 size exclusion chromatography (SEC) in THF. Its measured average molecular weight Mn is equal to 2000 g / mol in polystyrene equivalents (calibration by linear polystyrene standards). Its polymolecularity index Mw / Mn is equal to 2.0.

  An analysis of the sample by gas chromatography reveals that the conversion of the 45 monomers is greater than 99%.

  Step lb: Growth of a second block of poly (ethyl acrylate) with a theoretical molecular weight of approximately 42000 g / mol to obtain a diblock copolymer polystyrene-blockpoly (ethyl acrylate). Starting from the emulsion copolymer obtained previously in step after taking 5 g for analysis and without stopping the heating. 1.19 g of sodium persulfate Na2S208 diluted in 50.0 g of water are introduced continuously for three hours.

  Simultaneously for three hours, a mixture comprising: 50 - 200.0 g of water, 2.20 g of sodium carbonate Na2CO3, and 4.40 g of sodium dodecyl sulphate are added simultaneously at 85 ° C. a mixture 4 is added comprising: 2100 g of ethyl acrylate (EA) and 42.0 g of methacrylic acid (AMA)

  After complete addition of the various ingredients, the copolymer emulsion obtained is maintained at 85 ° C. for one hour. 4.40 g of tert-butylbenzyl peroxide are then introduced all at once and the addition of a mixture comprising: 2.20 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 41000 g / mol in polystyrene equivalents (calibration by linear polystyrene standards). Its polymolecularity index Mw / Mn is equal to 6.

  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 41%. Step II: Partial Hydrolysis (75% Targeted) of the Poly (ethyl acrylate) Block of the Copolymer Obtained Previously in Step Ib to Obtain the Polystyrene-Block-Polyl Diblock (Ethyl Acrylate -Sodium Sodium Salt) acrylic acid) of the type (2b)

  750 g of water, 250 g of 2-propanol and 1347 g of emulsion copolymer (ie 550 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., then 678 g of sodium hydroxide (solution in water at 23.2% by weight) are added continuously over one hour. After 30 minutes from the beginning of the addition of sodium hydroxide, the addition is continued continuously over one hour of 12 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 at 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 20%.

  The copolymer thus obtained has the following characteristics: theoretical average molecular mass of the block A: 2000 g / mol; theoretical average molecular weight of the block B: 30000 g / mol; proportion by weight of the block B: 96%; proportion by weight of block A: 4% - Quantity by weight of units derived from ethyl acrylate in block B: 31%

Example 2

  Preparation of a diblock copolymer Polystyrene-block-poly (ethyl acrylate-acrylic acid sodium stats) by synthesis of a diblock copolymer Polystyrene-block-poly (ethyl acrylate) of the target Mn 5000-block 7000 (g / mole) and then hydrolyzed to 75% of the ester groups of ethyl acrylate.

  Step la: Preparation of a first block of polystyrene with a theoretical molecular mass of about 5000 g / mol 1000 g of water, 6.50 g of sodium dodecyl sulphate and 0 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 about 7000 q / 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 Acridate -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 room 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 continuous addition over one hour of 37 g of hydrogen peroxide (30% solution) is begun.

  After complete addition of the various ingredients, the resulting copolymer solution 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 has 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% 40 - Quantity by weight of units derived from ethyl acrylate in block B: 31%

Example 3

  Preparation of a diblock copolymer Polystyrene-block-poly (ethyl acrylate-acrylic acid sodium stats) by synthesis of a diblock copolymer Polystyreneblock-poly (ethyl acrylate) of the target Mn 2000-block-20000 (g / mole) and then hydrolyzed to 75% of the ester groups of ethyl acrylate. Step la: Preparation of a first block of polystyrene with a theoretical molecular weight of about 2000 q / mol 2150 g of water, 6.00 g of sodium dodecyl sulphate and 0.650 g are introduced into the reactor at ambient temperature. g of Na2CO3 sodium carbonate. The resulting mixture is stirred for 30 minutes under nitrogen. The temperature is then raised to 75 ° C., then a mixture 1 comprising: 18.2 g of styrene (St), 0.360 g of methacrylic acid (AMA), and 18.9 g of xanthate (CH 3). (CO2CH3) CH-S (C = S) OCH2CH3.

  The mixture is heated to 85 ° C. and then a solution of 2.16 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: 163.6 g of styrene (St) and 3.30 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 (û5 g) is then taken and analyzed by steric exclusion chromatography (SEC) in THF. Its measured average molecular weight Mn is equal to 2000 g / mol in polystyrene equivalents (calibration by linear polystyrene standards). Its polymolecularity index Mw / Mn is equal to 2.1.

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

  Step lla: growth of a second block of poly (ethyl acrylate) with a theoretical molecular weight of about 20,000 g / mol to obtain a diblock copolymer polystyrene-block-polv (ethyl acrylonate), starting from the copolymer emulsion obtained previously in step la after having taken 5 g for analysis and without stopping the heating.

  2.16 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, -4.00 g of sodium carbonate Na 2 CO 3 and 8.00 g of sodium dodecyl sulphate are added at 85 ° C. Simultaneously a mixture 4 comprising: 1818 g of ethyl acrylate (EA) and 33.4 g of methacrylic acid (AMA). After complete addition of the various ingredients, the copolymer emulsion obtained is maintained at 85 ° C. for 4 hours. one o'clock. Then 4.0 g of tert-butylbenzyl peroxide are introduced in one go and the addition of a mixture comprising: 2.00 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 17500 g / mol in polystyrene equivalents (calibration by linear polystyrene standards). Its polymolecularity index Mw / Mn is equal to 2.9.50. 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% aimed) of the poly (ethyl acrylate) block of the copolymer obtained above in step 2 to obtain the polystyrene-block-poly diblock (ethyl acrylate - sodium salt) of acrylic acid) of type (2a1).

  900 g of water, 300 g of 2-propanol and 1563 g of emulsion copolymer (ie 700 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 822 g of sodium hydroxide solution (in water at 23.2% by weight) are added continuously over one hour.

  After 30 minutes of the beginning of the addition of sodium hydroxide, the addition is continued continuously over one hour of 25 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 water of dry extract of about 17%.

  The copolymer thus obtained has the following characteristics: theoretical average molecular mass of the block A: 2000 g / mol; theoretical average molecular weight of the block B: 14000 g / mol; proportion by weight of the block B: 90%; proportion by weight of block A: 10% - Quantity by weight of units derived from ethyl acrylate in block B: 31%

Example 4

  Preparation of a diblock copolymer Polystyrene-block-poly (ethyl acrylate-acrylic acid sodium stats) by synthesis of a diblock copolymer Polystyrene-40 block-poly (ethyl acrylate) of the target Mn 2000-block -20000 (g / mole) and then hydrolyzed to 90% of the ester group of ethyl acrylate. Step la: Preparation of a first block of polystyrene with a theoretical molecular weight of about 2000 g / mol 45 2150 g of water, 6.00 g of sodium dodecyl sulphate and 0.650 g are introduced into the reactor at ambient temperature. g of Na2CO3 sodium carbonate. The resulting mixture is stirred for 30 minutes under nitrogen. The temperature is then raised to 75 ° C., then a mixture 1 comprising: 50 - 18.2 g of styrene (St), 0.360 g of methacrylic acid (AMA), and 18.9 g of xanthate (CH 3) is added. ) (CO2CH3) CH-S (C = S) OCH2CH3. The mixture is heated to 85 ° C. and then a solution of 2.16 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: 163.6 g of styrene (St) and 3.30 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 2000 g / mol in polystyrene equivalents (calibration by linear polystyrene standards). Its polymolecularity index Mw / Mn is equal to 2.1.

  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 about 20,000 g / mol to obtain a diblock copolymer polystyrene-block-poly (ethyl acrylate), starting from the copolymer emulsion obtained previously in step 1 after having taken 5 g for analysis and without stopping heating.

  2.16 g of sodium persulphate Na2S208 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, -4.00 g of sodium carbonate Na 2 CO 3 and 8.00 g of sodium dodecyl sulphate are added at 85 ° C.

  Simultaneously, a mixture 4 comprising: 1818 g of ethyl acrylate (EA) and 33.4 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 4.0 g of tert-butylbenzyl peroxide are introduced in one go and the addition of a mixture comprising: 2.00 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 17500 g / mol in polystyrene equivalents (calibration by linear polystyrene standards). Its polymolecularity index Mw / Mn is equal to 2.9.

  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 (at 90% aimed for) of the poly (ethyl acrylate) block of the copolymer obtained previously in step 2 to obtain the polystyrene-block-poly diblock (ethyl acrylate -stat- sodium salt of acrylic acid) of type (2a2).

  1209 g of water, 206 g of 2-propanol and 1670 g of emulsion copolymer (ie 700 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 70 ° C., then 1038 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, (c) the continuous addition over one hour of 27 g of hydrogen peroxide (30% solution) is begun.

  After complete addition of the various ingredients, the copolymer solution obtained is maintained at 70 ° C. for four hours. Then reaction mixture is cooled to -25 C for one hour.

  The product recovered at the end of the reaction is a translucent gel in dry extract water of about 17%.

  The copolymer thus obtained has the following characteristics: theoretical average molecular mass of the block A: 2000 g / mol; theoretical average molecular weight of the block B: 14000 g / mol; proportion by weight of the block B: 89%; proportion by weight of block A: 11% - Quantity by weight of units derived from ethyl acrylate in block B: 13%

Example 5

  The moisturizing performance of the following solutions was tested. Solution A 93% Distilled water Glycerol 7% Solution B 99% Distilled water Diblock polymer of Example 1 1% MA Solution C 99% Distilled water Diblock polymer of Example 1 1% MA Solution D 99% Distilled water Polymer diblock Example 3 1% MA Solution E 99% Distilled water Diblock polymer of Example 4 1% MA 55 Solution Moisture performance MCL Raman A 1 B 117 C 1.34 D 1.92 E 2.39 Significantly, diblock copolymers in solution in water at 1%, have a moisturizing performance, measured in confocal laser Raman microscopy, higher than that of glycerol at 7% in water.

  EXAMPLE 6 The following moisturizing cosmetic composition was carried out: Phase A1: sucrose distearate (marketed by the company 2.0% "STEARINERIE DUBOIS") Sorbitan stearate oxyethylenated with 4 moles of ethylene oxide 1.4 ( sold under the name "TWEEN 61" by the company ICI) Stearic acid 0.75% Stearyl heptanoate (marketed by the company 5.50 DRAGOCO under the name PCL solid) Vaseline codex 2, 1% oil Avocado 4.50 Jojoba Oil 4.10% Volatile Silicone Oil 3.70% Vitamin E Acetate 0.50 Phase A2: Silicone Gum (marketed by the company DOW 4.00 CORNING under the name "Q2- 1403 Fluid ") Perfume 0.3 0/0 Propylparaben 0.1% Phase B: Methyl paraben 0.30% Triethanolamine 0.40% Demineralized water qs 100.00% Phase C: Blend of carboxyvinyl polymers (marketed under 0.30% by the name of "CARBOPOL 980" by the company GOODRICH) Diblock copolymer of Example 1 2% Demineralized water 9.70% The two phases Al and B are brought to 65 C before being associated (B in A1) under very vigorous agitation (rotor-stator). After checking a perfect dispersion, it is possible, optionally, to homogenize the dispersion between 20.106 Pascal and 60.106 Pascal, to obtain a dispersion whose oil globule size is less than 500 nm. Phase A2 is dispersed at room temperature in the first dispersion, with vigorous stirring. Phase C, previously prepared, is then dispersed in order to gel the suspension.

  A moisturizing emulsion adapted for dry skin is obtained. The diblock copolymer contributes to this moisturizing activity. 35

Claims (31)

  A cosmetic composition comprising in a physiologically acceptable medium: a diblock copolymer (block A) - (block B) in which - block A comprises at least units derived from styrene; - Block B comprises at least (a) units derived from acrylic acid in free or salified form and (b) at least units derived from a C 1 -C 4 alkyl acrylate.   2. Composition according to claim 1, wherein said diblock copolymer is linear.   3. Composition according to claim 1 or 2, wherein said diblock copolymer is the proportion by weight of the block B with respect to the copolymer being greater than or equal to 50%.   4. Composition according to any one of claims 1 to 3, wherein the copolymer is characterized in that: - block A comprises at least 90% by weight of units derived from styrene; relative to the total weight of block A; block B is a statistical block comprising, relative to the total weight of block B, (i) from 34 to 95% by weight of units derived from acrylic acid in acid form or in salified form, (ii) from 5 to 66% by weight of units derived from C1-C4 alkyl acrylate. the proportion by weight of block B with respect to the copolymer being greater than or equal to 50%.   5. Composition according to any one of claims 1 to 4, wherein the C1-C4 alkyl acrylate is ethyl acrylate.   6. Composition according to any one of claims 1 to 5, characterized in that the block A and / or the block B comprises up to 10% by weight and preferably up to 5% by weight of a co additional hydrophilic monomer, ionic or nonionic.   The composition of claim 6, wherein the hydrophilic comonomer is methacrylic acid or a salt thereof.   8. Composition according to any one of claims 1 to 7, wherein the diblock copolymer (block A) - (block B) is of type (1) in which the proportion by weight of block B with respect to the copolymer is between 50 and 85%. 40   9. The composition of claim 8, wherein the copolymer is of the type (1b) in which the proportion by weight of the block B is between 50% to 75%.   10. A composition according to any one of claims 1 to 7, wherein the diblock copolymer (block A) - (block B) is of type (2) in which the proportion by weight of block B with respect to the copolymer is greater than or equal to equal to 85%.   11. The composition of claim 10, wherein the copolymer is of the type (2a) in which the proportion by weight of the block B relative to the copolymer is greater than or equal to 87% and less than 94%.   12. The composition of claim 10, wherein the copolymer is of the type (2b) in which the proportion by weight of the block B with respect to the copolymer is greater than or equal to 94%.   13. The composition of claim 10, wherein the copolymer is of the type (2b) in which the proportion by weight of the B block with respect to the copolymer ranges from 94% to 97%. 50 5   14. A composition according to any one of claims 1 to 13, wherein the diblock copolymer (block A) - (block B) is obtainable by a polymerization process comprising at least the following steps: I) preparing a diblock copolymer (block A) - (block B ') by a process comprising the following intermediate steps la) and lb): a) preparing a first block A, by bringing into contact: 10 - nT moles of a transfer comprising a single transfer group - nA moles of styrene or a mixture of monomers comprising at least 90% by weight of styrene and where nA / nT> 5 and preferably <5000; - and optionally a free radical initiator 15 lb) a second block B 'is prepared to obtain a diblock copolymer (block A) - (block B'), by bringing into contact: - the block A obtained in the previous 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 so that nB / nT> And preferably <5000; - and optionally a free radical initiator, II) hydrolysis of the B 'block is then carried out at a molar ratio T between 0.4 and 0.96 to obtain said diblock copolymer (block A) - (block B). 25   15. Composition according to the preceding claim, characterized in that an additional step III) is carried out, during and / or after the step II) of deactivation of transfer groups borne by macromolecular chains and / or purification of the diblock copolymer ( block A) - (block B) and / or destruction of hydrolysis and / or deactivation byproducts.   16. Composition according to claim 14 or 15, characterized in that step I) is carried out by emulsion polymerization in water. 35   17. Composition according to any one of claims 14 to 16, characterized in that step I) is carried out by controlled radical polymerization with a transfer agent comprising a transfer group of formula ûS-CS-.   18. Composition according to one of claims 14 to 17, characterized in that in stage la) is carried out a mixture of monomers comprising at least 90% by weight of styrene and up to less than 10% by weight of methacrylic acid, preferably at least 95% by weight of the C1-C4 alkyl acrylate and up to less than 5% by weight of a hydrophilic ionic or non-ionic co-monomer. 45   19. Composition according to one of claims 14 to 18, characterized in that in step lb) is used a monomer mixture comprising at least 90% by weight of the alkyl acrylate C1-C4 and up to less than 10% by weight of methacrylic acid, preferably at least 95% by weight of the C1-C4 alkyl acrylate and up to less than 5% by weight of a comonomer ionic or nonionic hydrophilic. 50   20. The composition of claim 18 or 19, wherein the hydrophilic comonomer is methacrylic acid or a salt thereof.   21. Composition according to one of claims 14 to 20, characterized in that the C 1 -C 4 alkyl acrylate is ethyl acrylate.   22. Composition according to one of claims 14 to 21, characterized in that the diblock copolymer (block A) - (block B) is of the type (1) in which the proportion by weight of the block B with respect to the copolymer is between 50 and 85% and its theoretical average molecular weight is less than or equal to 13000 g / mol.   23. Composition according to the preceding claim, characterized in that the diblock copolymer (block A) - (block B) is of the type (1) in which - the proportion by weight of the block B with respect to the copolymer is between 50 and 75 % by weight and - its theoretical average molecular weight is between 8000 and 13000 g / mol. 15   24. Composition according to one of claims 14 to 21, characterized in that the diblock copolymer (block A) - (block B) is of type (2) in which: the proportion by weight of block B relative to the copolymer is greater than or equal to 85% and its theoretical average molecular weight is greater than or equal to 13000 g / mol.   25. Composition according to the preceding claim, characterized in that the diblock copolymer (block A) - (block B) is of the type (2a) in which: the proportion by weight of the block B with respect to the copolymer is greater than or equal to 25% and - its theoretical average molecular weight is between 13000 g / mol and 20000 g / mol.   26. Composition according to claim 24, characterized in that the diblock copolymer (block A) - (block B) is of the type (2b) in which: the proportion by weight of the block B with respect to the copolymer is greater than or equal to at 94% and - its theoretical average molecular weight is greater than or equal to 20000 g / mol and preferably between 20000 and 50000 g / mol. 35   27. Composition according to any one of claims 1 to 26, wherein the diblock copolymer or copolymers are present in a content ranging from 0.01 to 10% by weight, relative to the total weight of the composition, preferably from 0 to , 5 to 10% by weight, and preferably ranging from 0.1 to 5% by weight. 40   28. Composition according to any one of the preceding claims, further comprising at least one cosmetic adjuvant chosen from fatty substances, organic solvents, ionic or nonionic thickeners, hydrophilic or lipophilic, softeners, humectants, opacifiers, stabilizers, emollients, silicones, anti-foam agents, perfumes, preservatives, anionic, cationic, nonionic, zwitterionic or amphoteric surfactants, actives, fillers, polymers, propellants, agents alkalinizing or acidifying agents.   29. Non-therapeutic cosmetic process for the care or makeup treatment of keratinous substances, in particular the skin, comprising the application to the keratin materials, especially to the skin, of a cosmetic composition according to any one of the preceding claims.   30. Method according to the preceding claim, characterized in that it is a cosmetic process for moisturizing the skin.   31. Cosmetic use of a diblock copolymer (block A) - (block B) in which - block A comprises at least units derived from styrene; - Block B comprises at least (a) units derived from acrylic acid in free or salified form and (b) at least units derived from a C 1 -C 4 alkyl acrylate; as defined in any one of claims 1 to 26, as a moisturizing agent for keratin materials, preferably skin. 10