WO2008086928A1

WO2008086928A1 - O/w cosmetic emulsion comprising a lipophilic uv screening agent, a polar oil and a polystyrene-block-poly(acrylic acid-stat-c1-c4 alkyl acrylate) diblock copolymer

Info

Publication number: WO2008086928A1
Application number: PCT/EP2007/063995
Authority: WO
Inventors: Didier Candau; Fabien Aubert
Original assignee: L'oreal
Priority date: 2007-01-19
Filing date: 2007-12-14
Publication date: 2008-07-24
Also published as: FR2911504B1; FR2911504A1

Abstract

The present invention relates to an oil-in-water emulsion comprising, in a physiologically acceptable medium: a) at least one continuous aqueous phase; b) at least one fatty phase dispersed in the said aqueous phase comprising at least one polar oil; c) at least one lipophilic organic UV screening agent; d) and optionally at least one insoluble inorganic UV screening agent and/or one insoluble organic UV screening agent; e) at least one (block A)-(block B) diblock copolymer in which: the block A comprises at least units derived from styrene; the block B comprises at least (a) units deriving from acrylic acid in the acid or salified form and (b) at least units deriving from a C1-C4 alkyl acrylate. The present invention also relates to the use of at least one diblock copolymer as defined above in a fluid oil-in-water emulsion comprising a) at least one fatty phase comprising at least one polar oil, b) at least one lipophilic organic UV screening agent and optionally c) at least one insoluble inorganic UV screening agent and/or at least one insoluble organic UV screening agent, for the purpose of improving the cosmetic properties and/or of improving the stability of the said emulsion and/or for the purpose of increasing the sun protection factor (SPF) and/or of improving the persistence towards water of the photoprotective power.

Description

O/W COSMETIC EMULSION COMPRISING A LIPOPHILIC UV SCREENING AGENT, A POLAR OIL AND A POLYSTYRENE-BLOCK- POLY (ACRYLIC ACID-STAT-Ci-C₄ ALKYL ACRYLATE) DIBLOCK

COPOLYMER

The present patent application relates to an oil-in- water cosmetic emulsion comprising, in a physiologically acceptable medium: a) at least one continuous aqueous phase,- b) at least one fatty phase dispersed in the said aqueous phase comprising at least one polar oil; c) at least one lipophilic organic UV screening agent; d) and optionally at least one insoluble inorganic UV screening agent and/or one insoluble organic UV screening agent; e) at least one (block A) - (block B) diblock copolymer in which:

- the block A comprises at least units derived from styrene,- - the block B comprises at least (a) units deriving from acrylic acid in the acid or salified form and (b) at least units deriving from a Ci-C₄ alkyl acrylate.

It is well known that light radiation with wavelengths of between 280 nm and 400 nm makes possible browning of the human epidermis and that rays with wavelengths of between 280 and 320 nm, known under the name of UV-B radiation, cause erythemas and skin burns which may be harmful to the development of natural tanning; this UV-B radiation must therefore be screened out.

It is also known that UV-A rays, with wavelengths of between 320 and 400 nm, which cause browning of the skin, are capable of bringing about a detrimental change in the latter, in particular in the case of sensitive skin or of skin continually exposed to solar radiation. UV-A rays cause in particular a loss in elasticity of the skin and the appearance of wrinkles, resulting in premature ageing. They promote the triggering of the erythemal reaction or accentuate this reaction in some subjects and can even be the cause of phototoxic or photoallergic reactions. It is therefore desirable also to screen out UV-A radiation.

Numerous cosmetic compositions intended for the photoprotection of the skin have been provided to date.

Among these products, fluid oil-in-water emulsions are generally more appreciated by the consumer than thicker emulsions, due in particular to their pleasant feel and their easy-to-apply presentation. These compositions, intended for the photoprotection of the skin, are composed of a continuous aqueous dispersing phase and of a noncontinuous oily dispersed phase which comprise, at various concentrations, one or more conventional lipophilic and/or hydrophilic organic screening agents capable of selectively absorbing UV radiation. Lipophilic organic screening agents have to be dissolved in polar oils. The proportion of polar oil of the noncontinuous internal phase of the emulsion will thus increase as the solubility of the screening compounds decreases and/or as their concentration increases .

Furthermore, the use in these compositions of metal oxide pigments is particularly advantageous as inorganic UV screening agents of this type make it possible to obtain high protection factors in combination with conventional, in particular lipophilic, organic UV screening agents.

The prior art reveals micronized insoluble organic UV screening agents with a mean particle size ranging from 10 nm to 2 μm which exhibit the advantage of being more effective than their soluble homologues comprising the same chromophoric group at an equivalent level . UV screening agents of this type are described in particular in Patent Applications EP 746 305 and EP 8 405 395.

The preparation of stable emulsions comprising polar oils and lipophilic organic UV screening agents presents numerous difficulties, in particular when the development of strong protection is involved and thus the introduction of large amounts of lipophilic organic screening agents and of solubilizing polar oils is involved. This is reflected by instability of the composition, which is thus harmful to the quality of the product and to the effectiveness of the protection. Generally, this instability is overcome by the use of thickeners introduced in the external phase of the composition.

These difficulties in stabilizing emulsions comprising polar oils and lipophilic organic UV screening agents become accentuated as soon as it is a matter of obtaining compositions of very low viscosity because the level of thickening of the formulation is then intentionally limited in order to be able to maintain the viscosity at the desired level, the consequence of which is to further worsen the phenomena of instability.

One means for obtaining emulsions of low viscosity is then to use extremely powerful stirring means, such as high pressure homogenizers . The manufacture of emulsions with such equipment makes it possible effectively to obtain very fluid 0/W dispersions, in particular with polar oils, but this process limits the use of the screening means which are available to the formulator and in particular the introduction in addition of screening agents in the form of insoluble particles during the manufacturing operation.

These insoluble screening agents are incompatible with this equipment, either because of the size of the particles, which can block the orifices of this equipment, or because of the abrasive, indeed even destructive nature of very hard pigments, such as titanium oxide, introduced at high pressure into such equipment. This thus limits the active principles which can be used to develop high protection factors.

Thus, the need still remains to be able to produce antisun compositions in the form of an oil-in-water emulsion of low viscosity comprising lipophilic organic UV screening agents and polar oils for dissolving them which are stable over time and contribute effective antisun protection, while having cosmetic performances of lightness and of ease of application related to the fluidity; this being the case without having to resort to extremely powerful stirring means, such as high pressure homogenizers . Such compositions should be able to additionally comprise insoluble organic or inorganic UV screening agents without exhibiting the disadvantages set out above.

The Applicant Company has discovered, surprisingly and unexpectedly, that this object could be achieved by using at least one linear (block A) - (block B) diblock copolymer in which:

- the block A comprises at least units deriving from styrene,-

- the block B comprises at least (a) units deriving from acrylic acid in the acid or salified form and (b) at least units deriving from a Ci-C₄ alkyl acrylate.

These copolymers thus make it possible to obtain very fluid oil-in-water emulsions comprising both lipophilic organic UV screening agents and polar oils without a high-pressure homogenizer, that is to say with stirring means of conventional rotor- stator type.

It is thus possible to use a wide range of lipophilic organic UV screening agents dissolved by polar oils. It is also possible to introduce, in addition, insoluble screening agents at any point in the manufacture without damaging the stirring equipment and without being obliged to go through a predispersion or a concentrated emulsion.

The compositions thus obtained make it possible not only to obtain antisun compositions having cosmetic performances superior to those generally obtained with a conventional oil-in-water emulsion but also exhibit an improved photoprotective effectiveness (increase in the sun protection factor (SPF) ) and an improved persistence towards water.

Consequently, a subject-matter of the present invention is an oil-in-water cosmetic emulsion comprising, in a physiologically acceptable medium: a) at least one continuous aqueous phase,- b) at least one fatty phase dispersed in the said aqueous phase comprising at least one polar oil; c) at least one lipophilic organic UV screening agent; d) at least one (block A) - (block B) diblock copolymer in which:

- the block A comprises at least units derived from styrene,-

Another subject-matter of the present invention is an emulsion as defined above additionally comprising at least one insoluble organic or inorganic UV screening agent .

Another subject-matter of the present invention is the cosmetic use of at least one linear diblock copolymer as defined above in an oil-in-water emulsion, in particular a fluid oil-in-water emulsion, comprising, in a physiologically acceptable medium: a) at least one fatty phase dispersed in the said aqueous phase comprising at least one polar oil, b) at least one lipophilic organic screening agent and optionally in addition at least one insoluble organic or inorganic UV screening agent, for the purpose of improving the cosmetic properties and/or for improving the stability of the said composition and/or for the purpose of increasing the sun protection factor (SPF) and/or of improving the persistence towards water of the photoprotective power.

Definitions

The term "physiologically acceptable medium" is understood to mean a nontoxic medium capable of being applied to the skin, lips, hair, eyelashes, eyebrows or nails. The composition of the invention can constitute in particular a cosmetic or dermatological composition.

The term "lipophilic UV screening agent" is understood to mean any agent which screens out UV radiation capable of being completely dissolved in the molecular state in a fatty phase of the emulsion or else of being solubilized in the colloidal form (for example in the micelle form) in a fatty phase.

The term "polar oil" is understood to mean any oil having an oil/water interfacial tension, measured at 25⁰C using a Krϋss model K12 tensiometer equipped with a ring of du Nouy type, of less than 45 mN.m^"1. The values are recorded when the standard deviation between the last three measurements becomes less than 0.01. They have been corrected by the Harkins-Jordans factor, which takes into account the characteristics of the liquid studied (density) and of the ring (geometry) .

The term "fluid emulsion" is understood to mean any emulsion not existing in a solid form. Its viscosity can be measured using a Rheomat 180 viscometer at 25⁰C with a measuring body 2, 3 or 4 at a rotational speed of 200 rpm after rotating for 30 seconds and is preferably less than or equal to 20 Pa- s, more preferably less than 5 Pa- s, more preferably still less than or equal to 2 Pa-s and more particularly less than or equal to 0.5 Pa-s.

In the present patent application, the term "diblock copolymer" relates to a block copolymer architecture composed of two blocks which does not substantially exhibit another sequence of blocks.

In the present patent application, the term "unit deriving from a monomer" denotes a unit which can be obtained directly from the said monomer by polymerization. Thus, for example, a unit deriving from an ester of acrylic or methacrylic acid does not cover a unit of formula -CH₂-CH(COOH)- or -CH₂-C(CH₃) (COOH)- obtained, for example, by polymerizing an ester of acrylic or methacrylic acid and by then hydrolysing. Thus, the terminology "unit deriving from a monomer" relates only to the final constitution of the polymer and is independent of the polymerization process used to synthesize the polymer.

In the present patent application, "ratio by weight between the blocks" corresponds to the ratio between the weights of the monomers (or mixtures of monomers) used for the preparation of the blocks (taking into account the variations in weight related to subsequent hydrolysis) . The proportions by weight of the blocks are the proportions with respect 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 the combined monomers used to prepare the diblock copolymer (taking into account the variations of weights related to subsequent hydrolysis) . In the present patent application, the weights and ratios related to the blocks are indicated as "acid equivalents" (units derived from acrylic acid in the acid form, in contrast to a salified form of sodium acrylate type) .

In the present patent application, hydrophilic monomer is understood to mean a monomer which has affinity for water and which typically is not able to form a macroscopic two-phase solution in distilled water at 25⁰C at a concentration of 1% by weight.

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

In the present patent application, the average molecular weight measured for a first block or for 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 molecular weight measured for the same block in a copolymer comprising n blocks is defined as the difference between the average molecular weight measured for the copolymer and the average molecular weight measured for the copolymer comprising (n-1) blocks from which it is prepared.

For the sake of simplicity, it is common to express the average molecular weights of the blocks as "theoretical" or "targeted" average molecular weights, taking into consideration a complete and perfectly controlled polymerization. In this case, one macromolecular chain is formed per transfer functional group of a transfer agent; in order to obtain the molecular weight, it is sufficient to multiply the average molar mass of the units of a block by the number of units per block (amount by number of monomer by amount by number of transfer agent) . The differences caused by small amounts of comonomers, such as methacrylic acid, can be ignored in these calculations. The theoretical or targeted average molecular weights of the block B are expressed taking into consideration complete hydrolysis (the weights are expressed with the fiction of a degree of hydrolysis of 1) . The theoretical average molecular weight Mblock of a block is typically calculated according to the following formula :

M block

precursor

where M₁ is the molar mass of a monomer i, U₁ is the number of moles of the monomer i and n_preCursor is the number of moles of functional groups to which the macromolecular chain of the block will be bonded. The functional groups can originate from a transfer agent

(or a transfer group) or an initiator, a preceding block, and the like. If a preceding block is concerned, the number of moles can be regarded as the number of moles of a compound to which the macromolecular chain of the said preceding block has been bonded, for example a transfer agent (or a transfer group) or an initiator. In practice, the theoretical average molecular weights are calculated from the number of moles of monomers introduced and from the number of moles of precursor introduced.

The "theoretical" or "targeted" average molecular weight of a block copolymer is considered to be the addition of the average molecular weights of each of the blocks, taking into consideration complete hydrolysis (the weights are expressed with the fiction of a degree of hydrolysis of 1) , if such a hydrolysis has been carried out .

In the present patent application, the targeted or theoretical total weight of a block is defined as the weight of the macromolecular chain, taking into consideration a complete and perfectly controlled polymerization. In order to obtain the total weight, 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 weights thus obtained for each type of unit in the block. The differences caused by small amounts of comonomers, such as methacrylic acid, can be ignored in these calculations. The theoretical or targeted total weights of the block B are expressed taking into consideration the effects of a partial hydrolysis (the fiction of a degree of hydrolysis of 1 is not used for this descriptor) , if such a hydrolysis has been carried out .

In the present patent application, the degree of hydrolysis T is defined as the ratio of the number of units deriving from acrylic acid or an acrylic acid salt to the number of units deriving from Ci-C₄ alkyl acrylate present in a copolymer before hydrolysis. The number of units deriving from Ci-C₄ alkyl acrylate is regarded as being equal to the amount by number of alkyl acrylate monomer used for the preparation of the copolymer before hydrolysis. The number of units deriving 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, for example using hydrochloric acid. In the present patent application, transfer agent is understood to mean an agent capable of bringing about a controlled radical polymerization in the presence of unsaturated monomers and optionally of a source of free radicals.

Copolymer

The diblock copolymers in accordance with the invention are advantageously linear. The block B comprises two different units. They will generally be distributed randomly in the block B. The block B is then a random block.

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 in accordance with the invention are more particularly characterized in that they are linear (block A) - (block B) diblock copolymers in which: - the block A comprises at least 90% by weight of units deriving from styrene, with respect to the total weight of the block A; - the block B is a random block comprising, with respect to the total weight of the block B: (i) from 34 to 95% by weight of units deriving from acrylic acid in the acid form or in the salified form; (ii) from 5 to 66% by weight of units deriving from Ci-C₄ alkyl acrylate.

It is mentioned that the block A can comprise up to 10% of units other than the units deriving from styrene, with respect to the total weight of the block A. It is mentioned that the block B can comprise units other than the units deriving from acrylic acid and the units deriving from alkyl acrylate. Such units are taken into account in the composition of the block B (proportion of the different units) , the total of the units being 100%.

It is mentioned that the ratio by weight of the units deriving from acrylic acid to the units deriving from Ci-C₄ alkyl acrylate is preferably between 34/66 and 95/5, preferably between 64/36 and 75/25.

The Ci-C₄ alkyl acrylate is preferably an alkyl acrylate which can be hydrolysed to give acrylic acid. The units deriving from Ci-C₄ alkyl acrylate are preferably derived from an alkyl acrylate which can be hydrolysed to give acrylic acid. Thus, by a preferred process, the units deriving from acrylic acid can be generated from units deriving from alkyl acrylate, during a partial hydrolysis .

Mention is in particular made, as Ci-C₄ alkyl acrylates, of ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate or tert-butyl acrylate. Ethyl acrylate and tert-butyl acrylate are known in particular as being able to be easily hydrolysed.

The Ci-C₄ alkyl acrylate of the copolymer of the invention is advantageously ethyl acrylate (often denoted EA or EtA) .

The block A and/or the block B can comprise up to 10% by weight (in particular from 0.1% to 5% by weight), preferably up to 5% by weight (in particular from 0.1% to 5% by weight), of an additional, ionic or nonionic, hydrophilic comonomer, with respect to the total weight of the block A or of the block B comprising the said hydrophilic comonomer.

Mention may be made, among additional, ionic or nonionic, hydrophilic comonomers, for example, of acrylamide, hydroxyethyl (meth) acrylate or methacrylic acid (MAA) in the acid or salified form. Preference is given more particularly to the use of methacrylic acid in the acid or salified form. The block A can also comprise, as additional hydrophilic monomer, acrylic acid in the acid or salified form.

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

A first family of diblock copolymers in accordance with the invention which is particularly preferred is composed of (block A) - (block B) diblock copolymers of the type (1) in which the proportion by weight of the block B with respect to the copolymer is between 50 and 85%.

Two types of preferred copolymers are distinguished among these diblock copolymers of type (1) :

- Type (Ia) , those where the proportion by weight of the block B is greater than or equal to 75% and preferably between 75 and 85%;

- Type (Ib) : those where the proportion by weight of the block B, with respect to the copolymer, is less than 75% and preferably between 50 and 75% by weight.

A second family of diblock copolymers in accordance with the invention which is particularly preferred is composed of (block A) - (block B) diblock copolymers of the type (2) in which the proportion by weight of the block B with respect to the copolymer is greater than or equal to 85%.

Two types of copolymers are advantageously distinguished among these diblock copolymers of type (2) : - Type (2a) : where 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%, Type (2b) : where 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%.

Two types of copolymers are advantageously distinguished among these diblock copolymers of type (2a) :

- Type (2al) : where, in the block B:

- the proportion by weight of units deriving from acrylic acid in the free or salified form is between 64% (obtained, for example, by a hydrolysis at a degree of T=O.7) and 75% (obtained, for example, by a hydrolysis at a degree of T=O.8), and - the proportion by weight of units deriving from Ci-C₄ alkyl acrylate is between 25% (obtained, for example, by a hydrolysis at a degree of T=O.8) and 36% (obtained, for example, by a hydrolysis at a degree of T=O .7) ;

- Type (2a2) : where, in the block B:

- the proportion by weight of units deriving from acrylic acid in the free or salified form is between 75% (obtained, for example, by a hydrolysis at a degree of T=O.8) and 95% (obtained, for example, by a hydrolysis at a degree of T=O.96), and

- the proportion by weight of units deriving from Ci-C₄ alkyl acrylate is between 5% (obtained, for example, by a hydrolysis at a degree of T=O.96) and 25% (obtained, for example, by a hydrolysis at a degree of T=O .8) .

According to a specific form of the invention, use will be made, in the emulsions, of a blend of at least one diblock copolymer of the type (1) and of at least one diblock copolymer of the type (2) and more particularly still a blend of at least one diblock copolymer of the type (Ia) (BOL 20) and of at least one diblock copolymer of the type (2b) (BOL 55) as defined above.

The copolymer of the invention can in particular be presented in one of the following ways:

- in the solid or dry form, or

- in the form of a concentrated fluid ingredient comprising a carrier, in a concentration preferably of greater than 8% by weight.

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

Process

The copolymer of the invention can be prepared by any appropriate process comprising a polymerization phase. The copolymer according to the invention can be obtained by any known method, whether by controlled or uncontrolled radical polymerization, by ring opening polymerization (in particular anionic or cationic) , by anionic or cationic polymerization, or by chemical modification of a polymer.

An advantageous process comprises the following stages: stage I) : the following are prepared:

- a (block A) - (block B') diblock copolymer, or

- a triblock copolymer or star copolymer of (core) - [ (block A) - (block B¹I]_x or (core) - [ (block B ' ) - (block A) ] _x architecture where x is a mean number greater than or equal to 2, where

- the block A comprises units deriving from styrene, and

- the block B' comprises units deriving from a Ci-C₄ alkyl acrylate, stage I'): optionally, for a triblock or star copolymer, the (core) - (block B') or (core) - (block A) bonds are cleaved, so as to obtain a (block A) - (block B') diblock copolymer, stage II) : the block B' is hydrolysed to give a block B, in order to obtain the (block A) - (block B) diblock copolymer, the hydrolysis bringing about, if appropriate, for a triblock or star copolymer, cleavage of the (core) - (block B') or (core) - (block A) bonds, so as to obtain a (block A) - (block B) diblock copolymer.

The process can in addition optionally comprise a stage III) , during and/or after stage II) , of deactivation of transfer groups carried by macromolecular chains and/or of purification of the (block A) - (block B) diblock copolymer and/or of destruction of hydrolysis byproducts and/or of deactivation.

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

It is mentioned that the terminologies of the (block A) - (block B') type do not, however, rule out the presence of chemical groups (transfer groups or residues) of use in polymerization, in particular at ends of chains or at the centre of chains. Thus, the diblock copolymer can exhibit in reality 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 formula -S- CS-Z or a residue of such a group) . Stage I) is a polymerization stage. Stage I') is optional and it can optionally be applied if the copolymer prepared in stage I) is a triblock or star copolymer. However, if the copolymer prepared in stage

I) is a triblock or star copolymer, it is possible to cleave the bonds during the hydrolysis stage. If the cleavage can be carried out during the hydrolysis stage, then stage I') will not be of great usefulness and it will preferably be omitted.

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

The (block A) - (block B) diblock copolymers used in the context of the invention can in particular be obtained as follows:

during stage I), a (block A) - (block B') diblock copolymer is prepared by a process comprising the following intermediate stages Ia) and Ib) :

Ia) a first block A is prepared by bringing together: - n_τ moles of a transfer agent comprising a single transfer group,

- n_A moles of styrene or of a mixture of monomers comprising at least 90% by weight of styrene and where n_A/n_T > 5 and preferably < 5000, - and optionally a free radical initiator,

Ib) a second block B' is prepared, in order to obtain a (block A) - (block B') diblock copolymer, by bringing together: - the block A obtained in the preceding stage,

- n_B moles of a Ci-C₄ alkyl acrylate or of a mixture of monomers comprising at least 90% by weight of a Ci-C₄ alkyl acrylate, so that n_B/n_T > 5 and preferably < 5000, - and optionally a free radical initiator,

- during stage II) subsequent to stage I), the block B' is then hydrolysed at a degree T in moles of between 0.4 and 0.96, in order to obtain the said (block A)- (block B) diblock copolymer, and

- 20 000 < n_A/n_T M_A + M_AA n_B/n_T

- [T MAA n_B + (1-T) M_B n_B] / [M_An_A + T MAA n_B + (1-T) M_B n_B] ≥ 50%, where MA is the molar mass of the styrene or of the mixture of monomers comprising styrene employed in stage Ia) and MB is the molar mass of Ci-C₄ alkyl acrylate or of a mixture of monomers comprising Ci-C₄ alkyl acrylate employed in stage Ib) .

The process can in addition optionally comprise a stage III) , during and/or after stage II) , of deactivation of transfer groups carried by macromolecular chains and/or of purification of the (block A) - (block B) diblock copolymer and/or of destruction of hydrolysis by- products and/or of deactivation.

According to an advantageous form, stages Ia) and Ib) of stage 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 equal to 0.75.

Transfer agents of use for the implementation of the process (during stage I) ) are known to a person skilled in the art and include in particular compounds comprising an -S-CS- transfer group for the implementation of polymerization processes known under the terms of RAFT and/or MADIX. Such processes and agents are described in detail below.

During stage I) described above, it is possible to carry out the preparation of a first block from monomers or a mixture of monomers, from initiators and/or from agents which promote the control of the polymerization (transfer agents comprising -S-CS- groups, nitroxides, and the like) and then to carry out the growth of a second block from the first block, in order to obtain a diblock copolymer, with different monomers from those used for the preparation of the preceding block and optionally with addition of initiators and/or of agents which promote the control of the polymerization. These processes for the preparation of block copolymers are known to the person skilled in the art. It is mentioned that the copolymer can exhibit, at the chain end, a transfer group or a residue of a transfer group, for example a group comprising an -S-CS- group (for example resulting from a xanthate or from a dithioester) or a residue of such a group.

During stage II) , the units deriving from the hydrolysable monomers of the block B' are partially hydrolysed to form a block B comprising units deriving from acrylic acid or from a salt (hydrolysed units) and units deriving from the alkyl acrylate monomer

(unhydrolysed units) . These two types of units are distributed randomly in the block B; it can thus be considered that the block B is a block in the form of a random copolymer comprising units deriving from alkyl acrylate and units deriving from acrylic acid or from an acrylic acid salt. Naturally, the block B can comprise other units, in minimal amounts, if a mixture of monomers is used during the implementation of stage Ib) .

The block A comprises units deriving from styrene. The block A can be obtained from a mixture of monomers comprising at least 90% by weight, preferably at least

95%, of styrene ("St") and a hydrophilic comonomer or several hydrophilic comonomers . The block A can thus be a random copolymer comprising at least 90% by weight

(in particular from 90% to 99.9% by weight), preferably at least 95% by weight (in particular from 95% to 99.9% by weight) , of units deriving 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), of other units deriving from hydrophilic comonomer(s) .

The block B' comprises units deriving from a Ci-C₄ alkyl acrylate. The block B' can be obtained from a mixture of monomers 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 a Ci-C₄ alkyl acrylate and one or more hydrophilic comonomer(s) . The block B' can 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 deriving from Ci-C₄ alkyl acrylate and up to 10% by weight (in particular from 0.1% to 10%), preferably up to 5% (in particular from 0.1% to 5%), by weight, of other units deriving from hydrophilic comonomer(s) .

The block B obtained from the block B' after hydrolysis comprises units deriving from hydrolysable Ci-C₄ alkyl acrylate, units deriving from acrylic acid or a salt and optionally units deriving from a hydrophilic comonomer employed during stage Ib) of growth of the block B', for example units deriving from methacrylic acid. The methacrylic acid is generally present in the block B in the form of a salt. This form generally results from the conditions under which hydrolysis is carried out and the reactants used. It is generally an alkali metal salt, such as the sodium or potassium salt. Consequently, the block B generally comprises units deriving from acrylic acid in the form of sodium acrylate or potassium acrylate.

Mention is made, among the hydrophilic comonomer (s) which can be of use in the preparation of the block A and/or the block B', of hydrophilic comonomer(s) capable of stabilizing an emulsion of monomers and/or 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 (MAA) and their salts. It is preferable to use methacrylic acid or its salts. Methacrylic acid is not sensitive to hydrolysis. However, it can be salified during hydrolysis. Use may also be made, for the preparation of the block A, as hydrophilic comonomer, of acrylic acid and its salts.

Mention is in particular made, among hydrolysable Ci-C₄ alkyl acrylates, of ethyl acrylate (EA or EtA) .

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

Thus, during stage Ia) , use may be made of a mixture of monomers comprising at least 90% by weight, preferably at least 95% by weight, of styrene and up to 10% by weight, preferably up to 5% by weight, of methacrylic acid in the acid or salified form.

During stage Ib) , use may be made of a mixture of monomers comprising at least 90% by weight, preferably at least 95% by weight, of Ci-C₄ alkyl acrylate, such as ethyl acrylate, and up to 10% by weight, preferably up to 5% by weight, of methacrylic acid in the acid or salified form.

Some characteristics of the process for the preparation of the copolymers of the invention are given in detail below. Stage I )

Preferably, for the polymerization of stage I) , use is made of "living" or "controlled" radical polymerization methods and particularly preferably controlled or living radical polymerization methods employing a transfer agent comprising a transfer group of formula -S-CS- which are known in particular under the names of RAFT or MADIX.

Reference may in particular be made, as examples of "living" or "controlled" polymerization processes, to: - the processes of applications WO 98/58974, WO 00/75207 and WO 01/42312, which employ a radical polymerization controlled by control agents of xanthate type, the process for radical polymerization controlled by control agents of dithioester or trithiocarbonate type of Application WO 98/01478, the process for radical polymerization controlled by control agents of dithiocarbamate type of Application WO 99/31144, - the process for radical polymerization controlled by control agents of dithiocarbazate type of Application WO 02/26836, the process for radical polymerization controlled by control agents of dithiophosphoro ester type of Application WO 02/10223, the process of application WO 99/03894, which employs a polymerization in the presence of nitroxide precursors, or the processes employing other nitroxides or nitroxide/alkoxyamine complexes, the process of application WO 96/30421, which uses atom transfer radical polymerization (ATRP) , the process for radical polymerization controlled by control agents of iniferter type according to the teaching of Otu et al . , Makromol . Chem. Rapid.

Commun., 3, 127 (1982), the process for radical polymerization controlled by degenerative transfer of iodine according to the teaching of Tatemoto et al . , Jap. 50, 127, 991

(1975), Daikin Kogyo Co. Ltd, Japan, and

Matyjaszewski et al . , Macromolecules, 28, 2093

(1995) , the process for radical polymerization controlled by tetraphenylethane derivatives disclosed by

D. Braun et al . , in Macromol . Symp . Ill, 63 (1996), or even the process for radical polymerization controlled by organocobalt complexes described by Wayland et al. in J. Am. Chem. Soc . , 116, 7973 (1994), the process for radical polymerization controlled by diphenylethylene (WO 00/39169 or WO 00/37507) .

The polymerizations can be carried out in an emulsion in water ("latex" process). These processes can employ emulsifying agents, generally surfactants. Without wishing to be committed to any one theory, it is believed that the emulsion preparation processes lead to the formation of nodules of blocks 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 a person skilled in the art. Use may be made, for example, of sodium persulphate. It is possible typically to employ amounts of initiators of 5 to 50% by number, with respect to the amount of transfer agent.

It is mentioned that it would not be departing from the scope of the invention to employ and adapt preparation processes resulting in triblock or star copolymers which are subsequently modified (during a stage I') or during stage II)) so as to obtain diblock copolymers. In particular, it is possible to envisage employing transfer agents comprising several transfer groups (for example, trithiocarbonates Z-S-CS-S-Z) , resulting in telechelic copolymers of type R- [ (block B') -(block A)]_w, such as triblocks or stars of type (core) -[ (block

A) - (block B')]χ (for example (block A) - (block B') -R-

(block B') -(block A), such as (block A) - (block B')-

(core) - (block B') -(block A) triblock) , and then cleaving the telechelic copolymers in order to obtain (block A) - (block B') diblock copolymers. Cleavage can occur during the hydrolysis, in which case (block A)-

(block B) diblock copolymers are obtained directly. In such cases, a person skilled in the art will adjust the processing conditions in order 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.

It is specified that, during stage I) , a triblock copolymer is not typically prepared by a sequence of 3 polymerization phases where at least one of the blocks could not be separated from the others by cleavage during the hydrolysis. Thus, the copolymer prepared during stage I) is not typically obtained by a polymerization process comprising a stage of polymerization of styrene or of a mixture of monomers based on styrene, then a stage of polymerization of ethyl acrylate or of a mixture of monomers based on ethyl acrylate, and then a stage of polymerization of styrene or of a mixture of monomers based on styrene, the polymerizations being carried out using a monofunctional transfer agent carrying a group of formula -S-CS-.

Stage II)

During stage II) , the respective amounts of the different units in the block B are controlled by the degree of hydrolysis. The composition of the block A may remain unchanged during hydrolysis, if the block A does not comprise hydrolysable units. However, it is not ruled out for the block A to be slightly modified during the hydrolysis stage.

Preferably, the hydrolysis stage II) is carried out by addition of a strong base, such as sodium hydroxide or potassium hydroxide. Typically, a proportion by number of base, with respect to the amount of hydrolysable monomer used during stage Ib) , is added corresponding approximately to the degree of hydrolysis targeted, with optionally an excess of a few %. For example, an amount of sodium hydroxide of 75% by number of the amount of hydrolysable ethyl acrylate employed during stage Ib) is introduced. Homogeneous hydrolysis is preferably carried out, the sodium hydroxide being added gradually to the copolymer.

The hydrolysis stage can in particular result in the deactivation and/or the cleavage of certain transfer groups or other groups attached to the macromolecular chains. Stage II) can thus generate by-products which it is desirable to remove or can generate groups on the macromolecular chains which it is desirable to chemically modify. Such operations can be carried out during a stage III) .

Stage III)

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

During the optional stage III) , the block copolymers obtained or the hydrolysis by-products can be subjected to a reaction for purification from or destruction of certain entities, for example by processes of hydrolysis, oxidation, reduction, pyrolysis, ozonolysis or substitution type. A stage of oxidation with aqueous hydrogen peroxide solution is particularly appropriate for treating sulphur-comprising entities. It is mentioned that some of these reactions or operations can take place in all or part during stage II) . In this case, for these reactions or operations, the two stages are simultaneous.

As indicated above, the average molecular weights of the (block A) - (block B') diblock copolymer before hydrolysis or of each of the blocks typically depend on the relative amounts of the monomers and transfer agent employed during stage I) . Of course, the average molecular weights of the (block A) - (block B) diblock copolymer after hydrolysis or of each of the blocks depend on these same relative amounts and also on the degree of hydrolysis, for example depend on the amount of reactant introduced, generally a base, for this hydrolysis .

For the sake of simplicity, it is common to express the average molecular weights of the blocks as "theoretical" or "targeted" average molecular weights, taking into consideration a complete and perfectly controlled polymerization. In this case, one macromolecular chain is formed per transfer agent; in order to obtain the molecular weight, it is sufficient to multiply the average molar mass of the units of a block by the number of units per block (amount by number of monomer by amount by number of transfer agent) . The differences caused by small amounts of comonomers, such as methacrylic acid, can be ignored in these calculations. The theoretical or targeted average molecular weights of the block B are expressed taking into consideration complete hydrolysis (the weights are expressed with the fiction of a degree of hydrolysis of D . For the process for which stages Ia) and Ib) have been described in detail above, the theoretical total weight of the block A can be expressed by:

M_An_A.

For the process for which stages Ia) and Ib) have been described in detail above, the theoretical or targeted average molecular weight of the block A can be expressed by:

M_An_A/n_T.

For the process for which stages Ia) and Ib) have been described in detail above, the theoretical total weight of the block B' can be expressed by:

M_Bn_B.

For the process for which stages Ia) and Ib) have been described in detail above, the theoretical or targeted average molecular weight of the block B' can be expressed by:

M_Bn_B/n_T.

For the process for which stages Ia) and Ib) have been described in detail above, the theoretical total weight of the block B can be expressed by:

T M_AA n_B + (1-T) M_B n_B.

For the process for which stages Ia) and Ib) have been described in detail above, the theoretical or targeted average molecular weight of the block B can be expressed by:

M_AA n_B/n_T (as T=I according to the definition of the theoretical or targeted average molecular weight) . For the process for which stages Ia) and Ib) have been described in detail above, the theoretical total weight of the copolymer can be expressed by:

M_An_A + T MAA n_B + (1-T) M_B n_B .

For the process for which stages Ia) and Ib) have been described in detail above, the theoretical average molecular weight of the copolymer can be expressed by: n_A/n_T M_A + M_AA n_B/n_T.

In the above expressions:

- M_A is the molar mass of styrene or of the mixture of monomers comprising styrene employed in stage Ia) ,

- M_AA is the molar mass of acrylic acid, - M_B is the molar mass of Ci-C₄ alkyl acrylate or of a mixture of monomers comprising Ci-C₄ alkyl acrylate employed in stage Ib) .

The following correspondences are given as reference points: n_A/n_T = 5 corresponds to a theoretical average molecular weight of the block A of approximately 500 g/mol,

- n_A/n_T = 5000 corresponds to a theoretical average molecular weight of the block A of approximately

500 000 g/mol, n_B/n_T = 5 corresponds to a theoretical average molecular weight of the block B' of approximately 500 g/mol - n_B/n_T = 5000 corresponds to a theoretical average molecular weight of the block B' of approximately 500 000 g/mol,

- n_A/n_T M_A + M_AA n_B/n_T = 13 000 g/mol (resp. 2000, resp. 8000, resp. 20 000, resp. 50 000) corresponds to a theoretical average molecular weight of the (block A) -

(block B) diblock of approximately 13 000 g/mol (resp.

2000, resp. 8000, resp. 20 000, resp. 50 000), taking into consideration a total hydrolysis, 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 targeted total weights (the fiction of a degree of hydrolysis of 1 is not used for this descriptor) .

Thus :

- M_An_A < T M_AA n_B + (1-T) M_B n_B, indicates that the (block B) /(block A) ratio by weight ≥ 1. This is a characteristic of the copolymer employed according to the invention,

- M_An_A / [M_An_A + T M_AA n_B + (1-T) M_B n_B] indicates the amount by weight of block A in the (block A) - (block B) diblock copolymer, that is to say the proportion of block A,

- [T M_ΛA n_B + (1-T) M_B n_B] / [M_An_A + T M_M n_B + (1-T) M_B n_B] indicates the amount by weight of block B in the (block A) - (block B) diblock copolymer, that is to say the proportion of block B.

Preferably, the linear (block A) - (block B) diblock copolymers of the type (1) in which the proportion by weight of the block B with respect to the copolymer [T M_AA n_B + (1-T) M_B n_B] / [M_An_A + T M_AA n_B + (1-T) M_B n_B] is between 50 and 85% and generally have a theoretical average molecular weight (n_A/n_T M_A + M_AA n_B/n_T ) of less than 13 000 g/mol .

Among these copolymers : those particular of the type (Ia) where the proportion by weight of the block B with respect to the copolymer [T M_AA n_B + (1-T) M_B n_B] / [M_An_A + T M_AA n_B + (1-T) M_B n_B] is greater than or equal to 75% (BOL 20) and preferably between 75 and 85% generally have a theoretical average molecular weight (n_A/n_T M_A + M_AA n_B/n_T) of less than 8000 g/mol and preferably of between 2000 and 8000 g/mol, those particular of the type (Ib) where the proportion by weight of the block B with respect to the copolymer [T M_AA n_B + (1-T) M_B n_B] / [M_An_A + T M_AA n_B + (1-T) M_B n_B] is less than 75% by weight (BOL 21) , preferably between 50% and 75% by weight, generally have a theoretical average molecular weight (n_A/n_T M_A + M_AA n_B/n_T) of greater than or equal to 8000 g/mol and preferably of between 8000 g/mol and 13 000 g/mol.

Preferably, the linear (block A) - (block B) diblock copolymers of the type (2) in which the proportion by weight of the block B with respect to the copolymer

[T M_AA n_B + (1-T) M_B n_B] / [M_An_A + T M_AA n_B + (1-T) M_B n_B] is greater than or equal to 85% (BOL 44 and 55 and 64) and generally have a theoretical average molecular weight

(n_A/n_T M_A + M_AA n_B/n_T) of greater than or equal to 13 000 g/mol.

Among these copolymers of the type (2) : those particular of the type (2a) , where 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) , where 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 weight of greater than or equal to 20 000 g/mol and preferably of greater than or equal to 25 000 g/mol, more preferably of between 20 000 and 50 000 g/mol and more preferably still of between 25 000 and 50 000 g/mol and more particularly between 28 000 and 40 000 g/mol.

According to a specific form of the invention, use will be made, in the emulsions, of a blend of at least one diblock copolymer of the type (1) and of at least one diblock copolymer of the type (2) and more particularly still of a blend of at least one diblock copolymer of the type (Ia) and of at least one diblock copolymer of the type (2b) as defined above.

The diblock copolymer or copolymers in accordance with the invention are preferably present in concentrations of active material ranging from 0.01 to 5% of the total weight of the composition. More preferably, this amount varies from approximately 0.05 to 2% by weight in the composition.

The polar oils used in accordance with the invention preferably have an oil/water interfacial tension, measured at 25⁰C using a Krϋss model K12 tensiometer equipped with a ring of du Nouy type, of less than 35 mN.m^"1.

The polar oils in accordance with the invention can be chosen from oils of vegetable origin, animal origin or mineral origin or synthetic oils. They can be used in the form of a mixture .

Mention may be made, as examples of polar oils, of those shown in the following table and categorized by decreasing order of oil/water interfacial tension:

The polar oil or the polar oils are preferably present in concentrations ranging from 3 to 50% by weight, with respect to the total weight of the composition. More preferably, this amount varies from 5 to 40% by weight, with respect to the total weight of the composition.

Mention may be made, among lipophilic UV screening agents which can be used according to the invention, of those chosen from anthranilates ; cinnamic derivatives; dibenzoylmethane derivatives; salicylic derivatives; camphor derivatives; triazine derivatives, such as those described in Patent Applications US 4 367 390, EP 863 145, EP 517 104, EP 570 838, EP 796 851, EP 775 698, EP 878 469, EP 933 376, EP 507 691, EP 507 692, EP 790 243 and EP 944 624; benzophenone derivatives; β, β-diphenylacrylate derivatives; benzotriazole derivatives; benzalmalonate derivatives, in particular those mentioned in Patent US 5 624 663; benzimidazole derivatives; imidazolines; p-aminobenzoic acid (PABA) derivatives; benzoxazole derivatives, such as described in Patent Applications EP 0 832 642, EP 1 027 883, EP 1 300 137 and DE10162844; screening polymers and screening silicones, such as those described in particular in Application WO-93/04665; dimers derived from α-alkylstyrene, such as those described in Patent Application DE19855649, 4,4-diaryl- butadienes, such as those described in Patent Applications DE19755649, EP 916 335, EP 1 133 980, EP 1 133 981 and EP-A-I 008 586, and their mixtures.

Mention may be made, as examples of lipophilic organic screening agents, of those denoted below under their

INCI names :

para-Aminobenzoic acid derivatives:

Ethyl PABA,

Ethyl Dihydroxypropyl PABA,

Ethylhexyl Dimethyl PABA, sold in particular under the name "Escalol 507" by ISP,

Salicylic derivatives:

Homosalate, sold under the name "Eusolex HMS" by Rona/EM Industries, Ethylhexyl Salicylate, sold under the name "Neo Heliopan OS" by Haarmann and Reimer,

TEA Salicylate, sold under the name "Neo Heliopan TS" by Haarmann and Reimer,

Dibenzoylmethane derivatives:

Butyl Methoxydibenzoylmethane, sold in particular under the trade name "Parsol 1789" by Hoffmann-LaRoche, Isopropyl Dibenzoylmethane,

Cinnamic derivatives:

Ethylhexyl Methoxycinnamate, sold in particular under the trade name "Parsol MCX" by Hoffmann-LaRoche, Isopropyl Methoxycinnamate,

Isoamyl Methoxycinnamate, sold under the trade name "Neo Heliopan E 1000" by Haarmann and Reimer, Cinoxate, Diisopropyl Methylcinnamate,

J3,]3-Diphenylacrylate derivatives : Octocrylene, sold in particular under the trade name

"Uvinul N539" by BASF,

Etocrylene, sold in particular under the trade name

"Uvinul N35" by BASF,

Benzophenone derivatives:

Benzophenone-1 , sold under the trade name "Uvinul 400" by BASF,

Benzophenone-2 , sold under the trade name "Uvinul D50" by BASF,

Benzophenone-3 or Oxybenzone, sold under the trade name

"Uvinul M40" by BASF,

Benzophenone- 6 , sold under the trade name "HeIisorb 11" by Norquay, Benzophenone- 8 , sold under the trade name "Spectra-Sorb

UV-24" by American Cyanamid,

Benzophenone- 9 , sold under the trade name "Uvinul DS-

49" by BASF, n-Hexyl 2- (4-diethylamino-2-hydroxybenzoyl) benzoate, sold under the trade name "Uvinul A+" or as a mixture with octyl methoxycinnamate under the trade name "Uvinul A+B" by BASF,

Phenylbenzimidazole derivatives: Phenylbenzimidazole Sulfonic Acid, sold in particular under the trade name "Eusolex 232" by Merck,

Disodium Phenyl Dibenzimidazole Tetrasulfonate, sold under the trade name "Neo Heliopan AP" by Haarmann and

Reimer,

Benzylidenecamphor derivatives:

3-Benzylidene camphor, manufactured under the name

"Mexoryl SD" by Chimex,

4-Methylbenzylidene camphor, sold under the name "Eusolex 6300" by Merck,

Triazine derivatives:

Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine, sold under the trade name "Tinosorb S" by Ciba Geigy, Ethylhexyl triazone, sold in particular under the trade name "Uvinul T150" by BASF,

Diethylhexyl Butamido Triazone, sold under the trade name "Uvasorb HEB" by Sigma 3V, 2 , 4 , 6-Tris (dineopentyl 4 ' -aminobenzalmalonate) -s- triazine,

2 , 4 , 6-Tris (diisobutyl 4 ' -aminobenzalmalonate) -s- triazine,

Benzotriazole derivatives:

Drometrizole Trisiloxane, sold under the name "Silatrizole" by Rhodia Chimie,

Anthranilic derivatives: Menthyl anthranilate, sold under the trade name "Neo Heliopan MA" by Haarmann and Reimer,

Imidazoline derivatives:

Ethylhexyl Dimethoxybenzylidene Dioxoimidazoline Propionate,

Benzalmalonate derivatives: Dineopentyl 4' -methoxybenzalmalonate,

Polyorganosiloxane comprising benzalmalonate functional groups, such as Polysilicone-15 , sold under the trade name "Parsol SLX" by Hoffmann LaRoche,

4 , 4 -Diarylbutadiene :

1, 1-dicarboxy- (2' ,2' -dimethylpropyl) -4,4- diphenylbutadiene,

Benzoxazole derivatives:

2,4-Bis [5-1 (dimethylpropyl) benzoxazol-2-yl- (4 -phenyl) - imino] -6- (2 -ethylhexyl) imino-1, 3, 5-triazine, sold under the name Uvasorb K2A by Sigma 3V; and their mixtures. The lipophilic organic screening agents which are more particularly preferred are chosen from the following compounds :

Homosalate, Ethylhexyl Salicylate,

Ethylhexyl Methoxycinnamate,

Octocrylene,

Butyl Methoxydibenzoylmethane,

Phenylbenzimidazole Sulfonic Acid, Disodium Phenyl Dibenzimidazole Tetrasulfonate,

Benzophenone-3 , n-Hexyl 2- (4-diethylamino-2-hydroxybenzoyl) benzoate,

4-Methylbenzylidene camphor,

2,4, 6-Tris (dineopentyl 4 ' -aminobenzalmalonate) -s- triazine,

2,4, 6-Tris (diisobutyl 4 ' -aminobenzalmalonate) -s- triazine,

Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine,

Ethylhexyl Triazone, Diethylhexyl Butamido Triazone,

Drometrizole Trisiloxane,

Polysilicone 15,

Dineopentyl 4' -methoxybenzalmalonate,

1, 1-Dicarboxy- (2' ,2' -dimethylpropyl) -4,4- diphenylbutadiene,

2 , 4-Bis [5-1 (dimethylpropyl) benzoxazol-2 -yl- (4-phenyl) - imino] -6- (2 -ethylhexyl) imino-1 , 3 , 5-triazine, and their mixtures,

and more preferably still from: Homosalate,

Ethylhexyl Salicylate, Ethylhexyl Methoxycinnamate, Octocrylene, Butyl Methoxydibenzoylmethane,

Ethylhexyl Triazone,

Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine,

Diethylhexyl Butamido Triazone,

Drometrizole Trisiloxane. The lipophilic screening agents in accordance with the invention are preferably present in the compositions according to the invention at a content ranging from 0.1% to 30% by weight and preferably from 0.5 to 15% by weight, with respect to the total weight of the composition.

The insoluble inorganic UV screening agents used in accordance with the present invention are metal oxide pigments. More preferably, the inorganic UV screening agents of the invention are metal oxide particles having a mean individual particle size of less than or equal to 500 nm, more preferably of between 5 nm and 500 nm, and more preferably still of between 10 nm and

100 nm, and preferably between 15 and 50 nm.

They can in particular be chosen from titanium, zinc, iron, zirconium or cerium oxides or their mixtures.

Such coated or uncoated metal oxide pigments are described in particular in Patent Application EP-A-O 518 773. Mention may be made, as commercial pigments, of the products sold by Kemira, Tayca, Merck and Degussa.

The metal oxide pigments may be coated or uncoated.

The coated pigments are pigments which have been subjected to one or more surface treatments of chemical, electronic, mechanochemical and/or mechanical nature with compounds such as amino acids, beeswax, fatty acids, fatty alcohols, anionic surfactants, lecithins, sodium, potassium, zinc, iron or aluminium salts of fatty acids, metal alkoxides (titanium or aluminium alkoxides) , polyethylene, silicones, proteins (collagen, elastin) , alkanolamines, silicon oxides, metal oxides or sodium hexametaphosphate . The coated pigments are more particularly titanium oxides coated: with silica, such as the product "Sunveil" from Ikeda, - with silica and with iron oxide, such as the product "Sunveil F" from Ikeda,

- with silica and with alumina, such as the products "Microtitanium Dioxide MT 500 SA" and "Microtitanium Dioxide MT 100 SA" from Tayca and "Tioveil" from Tioxide,

- with alumina, such as the products "Tipaque TTO-55 (B)" and "Tipaque TTO-55 (A)" from Ishihara and "UVT 14/4" from Kemira,

- with alumina and with aluminium stearate, such as the products "Microtitanium Dioxide MT 100 T, MT 100 TX, MT

100 Z or MT-Ol" from Tayca, the products "Solaveil CT- 10 W" and "Solaveil CT 100" from Uniqema and the product "Eusolex T-AVO" from Merck,

- with silica, with alumina and with alginic acid, such as the product "MT-100 AQ" from Tayca,

- with alumina and with aluminium laurate, such as the product "Microtitanium Dioxide MT 100 S" from Tayca,

- with iron oxide and with iron stearate, such as the product "Microtitanium Dioxide MT 100 F" from Tayca, - with zinc oxide and with zinc stearate, such as the product "BR 351" from Tayca, with silica and with alumina and treated with a silicone, such as the products "Microtitanium Dioxide MT 600 SAS", "Microtitanium Dioxide MT 500 SAS" or "Microtitanium Dioxide MT 100 SAS" from Tayca,

- with silica, with alumina and with aluminium stearate and treated with a silicone, such as the product "STT- 30-DS" from Titan Kogyo,

- with silica and treated with a silicone, such as the product "UV-Titan X 195" from Kemira,

- with alumina and treated with a silicone, such as the products "Tipaque TTO-55 (S)" from Ishihara or "UV Titan M 262" from Kemira, - with triethanolamine, such as the product "STT-65-S" from Titan Kogyo,

- with stearic acid, such as the product "Tipaque TTO- 55 (C) " from Ishihara, - with sodium hexametaphosphate, such as the product "Microtitanium Dioxide MT 150 W" from Tayca,

TiO₂ treated with octyltrimethylsilane, sold under the trade name "T 805" by Degussa Silices,

- TiO₂ treated with a polydimethylsiloxane, sold under the trade name "70250 Cardre UF TiO2S13" by Cardre,

- anatase/rutile TiO₂ treated with a polydimethyl- hydrosiloxane, sold under the trade name "Microtitanium Dioxide USP Grade Hydrophobic" by Color Techniques.

The uncoated titanium oxide pigments are, for example, sold by Tayca under the trade names "Microtitanium Dioxide MT 500 B" or "Microtitanium Dioxide MT600 B", by Degussa under the name "P 25", by Wacker under the name "Oxyde de titane transparent PW" , by Miyoshi Kasei under the name "UFTR", by Tomen under the name "ITS" and by Tioxide under the name "Tioveil AQ" .

The uncoated zinc oxide pigments are, for example:

- those sold under the name "Z-cote" by Sunsmart; - those sold under the name "Nanox" by Elementis; those sold under the name "Nanogard WCD 2025" by Nanophase Technologies .

The coated zinc oxide pigments are, for example: - those sold under the name "Oxide zinc CS-5" by Toshibi (ZnO coated with polymethylhydrosiloxane) ;

- those sold under the name "Nanogard Zinc Oxide FN" by Nanophase Technologies (as a 40% dispersion in Finsolv TN, Ci₂-Ci₅ alkyl benzoate) ; - those sold under the name "Daitopersion Zn-30" and "Daitopersion Zn-50" by Daito (dispersions in oxyethylenated polydimethylsiloxane/ cyclopolymethylsiloxane comprising 30% or 50% of zinc nanooxides coated with silica and polymethylhydrosiloxane) ; those sold under the name "NFD Ultrafine ZnO" by Daikin (ZnO coated with phosphate of perfluoroalkyl and copolymer based on perfluoroalkylethyl as a dispersion in cyclopentasiloxane) ;

- those sold under the name "SPD-Zl" by Shin-Etsu (ZnO coated with silicone-grafted acrylic polymer dispersed in cyclodimethylsiloxane) ; those sold under the name "Escalol ZlOO" by ISP (alumina-treated ZnO dispersed in the ethylhexyl methoxycinnamate/PVP-hexadecene copolymer/methicone mixture) ; - those sold under the name "Fuji ZnO-SMS-IO" by Fuji Pigment (ZnO coated with silica and polymethylsilsesquioxane) ;

- those sold under the name "Nanox Gel TN" by Elementis (ZnO dispersed at 55% in Ci₂-Ci₅ alkyl benzoate with hydroxystearic acid polycondensate) .

The uncoated cerium oxide pigments, for example, can be those sold under the name "Colloidal Cerium Oxide" by Rhone-Poulenc .

The uncoated iron oxide pigments are, for example, sold by Arnaud under the names "Nanogard WCD 2002 (FE 45B)", "Nanogard Iron FE 45 BL AQ", "Nanogard FE 45R AQ" or "Nanogard WCD 2006 (FE 45R)" or by Mitsubishi under the name "TY-220" .

The coated iron oxide pigments are, for example, sold by Arnaud under the names "Nanogard WCD 2008 (FE 45B FN)", "Nanogard WCD 2009 (FE 45B 556)", "Nanogard FE 45 BL 345" or "Nanogard FE 45 BL" or by BASF under the name "Oxyde de fer transparent" .

Mention may also be made of mixtures of metal oxides, in particular of titanium dioxide and of cerium dioxide, including the mixture of equal weights of titanium dioxide coated with silica and of cerium dioxide coated with silica sold by Ikeda under the name "Sunveil A", and also the mixture of titanium dioxide and of zinc dioxide coated with alumina, with silica and with silicone, such as the product "M 261" sold by Kemira, or coated with alumina, with silica and with glycerol, such as the product "M 211" sold by Kemira.

According to the invention, coated or uncoated titanium oxide pigments are particularly preferred.

The insoluble inorganic screening agents in accordance with the invention generally represent from 0.5 to 40%, preferably from 1 to 30%, of the total weight of the emulsion.

Depending on their more or less pronounced lipophilic or, on the contrary, hydrophilic nature, the inorganic screening agents can be present either in the fatty phase of the emulsion or in the aqueous phase or else even again in the two phases simultaneously.

The insoluble organic UV screening agents comprising at least one group which absorbs UV radiation can be chosen in particular from insoluble organic UV screening agents of oxalanilide, triazine, benzotriazole, vinyl amide, cinnamamide, benzazole, benzofuran, arylvinylene ketone, acrylonitrile amide, acrylonitrile sulphonamide, acrylonitrile carbamate or phenylenebis (benzoxazinone) type.

Mention may be made, among insoluble UV screening agents of oxalanilide type, of those corresponding to the formula:

in which Ti, Ti', T₂ and T₂' each independently represent a Ci-C₈ alkyl radical or a Ci-C₈ alkoxy radical . These compounds are described in Patent Application WO 95/22959. Mention may be made, as examples, of the commercial products Tinuvin^® 315 and Tinuvin^® 312, sold by Ciba-Geigy, corresponding respectively to the formulae:

The insoluble screening agents of triazine type correspond to the following general formula:

in which R¹, R² and R³ each independently represent a phenyl, phenoxy or pyrrolo group which are unsubstituted or which each independently carry one, two or three substituents chosen from -OH, Ci-Ci₈ alkyl, Ci-Ci₈ alkoxy, carboxy (Ci-Ci₈ alkyl) , C₅-C₈ cycloalkyl, methylbenzylidenecamphor or - (CH=CR' ) _n (CO) -OR⁴, where R' represents a hydrogen atom, a cyano group or a COOR⁴ group, with R⁴ = Ci-Ci₈ alkyl or cinnamyl, and n has a value 0 or 1. These compounds are described in WO 97/03643, GB 2 286 774, EP 743 309, WO 98/22447, GB 2 319 523 and EP-A-O 790 243.

Mention will more particularly be made of the following compounds :

2 , 4 , 6-tris (diethyl 4 ' -aminobenzalmalonate) -s- triazine,

2 , 4 , 6-tris (diisopropyl 4 ' -aminobenzalmalonate) -s- triazine,

2 , 4 , 6-tris (dimethyl 4 ' -aminobenzalmalonate) -s- triazine,

2 , 4 , 6-tris (ethyl α-cyano-4-aminocinnamate) -s- triazine .

Mention may also be made, among UV screening agents of triazine type which can be used for the present invention, of insoluble s-triazine derivatives carrying benzotriazole and/or benzothiazole groups, such as those described in Application WO 98/25922.

Mention may more particularly be made, among these compounds, of 2 , 4 , 6-tris [ (3 '- (benzotriazol-2-yl) -2 '- hydroxy- 5 ' -methylphenyl) amino] -s-triazine and 2,4,6- tris [ (3' - (benzotriazol-2-yl) -2' -hydroxy- 5' - (tert- octyl) phenyl) amino] -s-triazine.

Mention may also be made, among UV screening agents of triazine type which can be used for the present invention, of the symmetrical triazine screening agents described in Patent US 6 225 467, Patent Application WO 2004/085412 (see compounds 6 and 9) or the document "Symmetrical Triazine Derivatives", IP. Com Journal, IP. Com Inc., West Henrietta, N. Y., USA (20 September 2004), in particular 2 , 4 , 6-tris (biphenyl) -1 , 3 , 5- triazines, especially 2 , 4 , 6-tris (biphenyl -4 -yl) -1 , 3 , 5- triazine and 2 , 4 , 6-tris (terphenyl) -1 , 3 , 5-triazine, which is taken up in Patent Applications WO 06/035000, - A A -

WO 06/034982, WO 06//034991, WO 06/035007, WO 2006/034992 and WO 2006/034985.

Mention may be made, among insoluble organic UV screening agents of benzotriazole type, of those of formula (III) below, for example described in Internal Application WO 95/22959:

in which R⁵ denotes a hydrogen atom or a Ci-Ci₈ alkyl radical and R⁶ and R⁷, which are identical or different, each independently denote a Ci-Ci₈ alkyl radical optionally substituted by a phenyl group.

Mention may be made, as examples of compounds of formula (III), of the commercial products Tinuvin^® 328, 320, 234 and 350 from Ciba-Geigy, respectively corresponding to the following formulae:

Mention may also be made, among insoluble organic UV screening agents of benzotriazole type, of the compounds described in Patents US 5 687 521, US 5 373 037 and US 5 362 881 and, among them, in particular of 2 , 4 ' -dihydroxy-3- (2H-benzotriazol-2-yl) - 5- (1, 1, 3, 3-tetramethylbutyl) -2' - (n-octoxy) -5' - benzoyldiphenylmethane of the formula:

sold under the name Mixxim^® PB30 by Fairmount Chemical.

Other insoluble organic UV screening agents of benzotriazole type are the methylenebis- (hydroxyphenylbenzotriazole) derivatives with the following structure:

in which R⁸ and R⁹, which are identical or different, each represent a Ci-Ci₈ alkyl radical which can be substituted by one or more radicals chosen from Ci-C₄ alkyl, C₅-Ci₂ cycloalkyl or aryl . These compounds are known and are described in Applications US 5 237 071,

US 5 166 355, GB-A-2 303 549, DE 19726184 and EP-A-893119.

In the formula (IV) defined above, the Ci-Ci₈ alkyl groups can be linear or branched and are, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, tert-octyl, n-amyl, n-hexyl, n-heptyl, n-octyl, iso-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, tetradecyl, hexydecyl or octadecyl; the C₅- Ci₂ cycloalkyl groups are, for example, cyclopentyl, cyclohexyl or cyclooctyl; the aryl groups are, for example, phenyl or benzyl.

Preference is more particularly given, among the compounds of formula (IV) , to those with the following structures :

compound (a)

compound (b)

compound (c)

Compound (a), with the nomenclature 2 , 2 ' -methylenebis- [6- (2H-benzotriazol-2-yl) -4- (1, 1, 3 , 3-tetramethylbutyl) - phenol] , is sold in the solid form under the name Mixxim BB/100 by Fairmount Chemical and in a micronized form under the name Tinosorb M by Ciba Specialty Chemicals .

Compound (c) , with the nomenclature 2 , 2 ' -methylenebis- [6- (2H-benzotriazol-2-yl) -4-methylphenol] , is sold in the solid form under the name Mixxim BB/200 by Fairmount Chemical .

Mention may be made, among insoluble organic screening agents of the vinyl amide type, for example of the compounds of formula (V) which are described in Application WO 95/22959:

T₃- (Y)r-C(=0) -C(T₄J=C(T₅) -N(T₆) (T₇) (V)

in which T₃ is a Ci-Ci₈, preferably Ci-C₅, alkyl radical or a phenyl group optionally substituted by one, two or three radicals chosen from OH, Ci-Ci₈ alkyl, Ci-C₈ alkoxy or -C(=O)-OT₈, T₈ represents a Ci-Ci₈ alkyl group,- T₄, T₅, T₆ and T₇ each independently represent a Ci-Ci₈, preferably Ci-C₅, alkyl radical or a hydrogen atom; Y represents an -NH- group or an oxygen atom and r has a value 0 or 1.

Mention will more particularly be made, among these compounds, of:

4 -octylamino-3 -penten-2 -one ; ethyl 3-octylamino-2-butenoate,-

3 -octylamino- 1 -phenyl -2 -buten- 1 -one 3-dodecylamino-l-phenyl-2-buten-l-one .

Mention may be made, among organic screening agents of cinnamamide type, of compounds such as those described in Application WO 95/22959 and corresponding to the following formula:

in which:

Rio represents a hydrogen atom or a Ci-C₄ alkyl group, preferably methyl or ethyl,

R¹¹ represents a hydrogen atom or a Ci-C₄ alkyl group, preferably methyl or ethyl,

R¹² represents a - (CONH) _s-phenyl group where s has the value 0 or 1 and the phenyl group can be substituted by one, two or three groups chosen from OH, Ci-Ci₈ alkyl, Ci-C₈ alkoxy or -C(=O)-OR¹³ where R¹³ is a Ci-Ci₈ alkyl, and more preferably R¹² represents a phenyl, 4- methoxyphenyl or phenylaminocarbonyl group.

Mention may also be made of bis [D,D-disubstituted cinnamamide] dimers, for example described in Patent US 5 888 481, with the structure:

in which:

Ari and Ar₂, which are identical or different, each represent a phenyl radical, an aromatic heterocycle, a group comprising a condensed phenyl ring or a group comprising a condensed aromatic heterocycle and can carry one or more identical or different substituents, B and D, which are other than a hydrogen atom, each independently represent an organic radical,

A and C each independently represent an organic radical, and

E represents a divalent organic radical, with the exclusion of the compounds for which Ari and Ar₂ both represent a phenyl group carrying an -OR substituent where R represents a hydrogen atom or an organic radical, A and C both represent a cyano group, B and D both represent a Ci-C₃₅ alkyl or alkenyl group and E represents a divalent organic radical, and in particular the compound with the structure:

Mention may be made, among insoluble organic screening agents of benzazole type, of those corresponding to one of the following formulae:

in which: each of the Y symbols independently represents an oxygen or sulphur atom or an NRi₅ group, each of the Z symbols independently represents a nitrogen atom or a CH group, each of the Ri₄ symbols independently represents an OH group, a halogen atom, a linear or branched Ci-C₈ alkyl group, optionally comprising a silicon atom, or a linear or branched Ci-C₈ alkoxy group, each of the numbers m independently has the value 0, 1 or 2, n represents an integer of between 1 and 4 inclusive, p is equal to 0 or 1, each of the numbers q is independently equal to 0 or 1, each of the Ri₅ symbols independently represents a hydrogen atom, a benzyl group or a linear or branched

Ci-C₈ alkyl group, optionally comprising a silicon atom,

A represents a radical with a valency n chosen from those of formulae:

in which each of the Ri₆ symbols independently represents a halogen atom, a linear or branched Ci_₄ alkyl or alkoxy group or a hydroxyl group,

Ri₇ represents a hydrogen atom or a linear or branched

Ci-C₄ alkyl group, c = 0-4, d = 0-3, e = O or l and f =

0-2. These compounds are described in particular in Patents DE 676 103 and CH 350763, Patent US 5 501 850, Patent US 5 961 960, Patent Application EP 0 669 323, Patent US 5 518 713, Patent US 2 463 264, the paper in J. Am. Chem. Soc . , 79, 5706-5708, 1957, the paper published in J. Am. Chem. Soc, 82, 609-611, 1960, Patent Application EP 0 921 126 and Patent Application EP 0 712 855.

Mention may be made, as examples of preferred compounds of formula (VIII) of the family of the 2-arylbenz- azoles, of 2- (benzoxazol-2-yl) -4-methylphenol, 2-(1H- benzimidazol-2-yl) -4-methoxyphenol or 2- (benzothiazol- 2 -yl) phenol, it being possible for these compounds to be prepared, for example, according to the processes described in Patent CH 350 763.

Mention will be made, as examples of preferred compounds of formula (VIII) of the family of the benzimidazolylbenzazoles, of 2 , 2 ' -bisbenzimidazole, 5 , 5 ' , 6 , 6 ' -tetramethyl-2 , 2 ' -bisbenzimidazole, 5,5'- dimethyl-2 , 2 ' -bisbenzimidazole, 6-methoxy-2 , 2 ' -bisbenzimidazole, 2- (lH-benzimidazol-2-yl) benzothiazole, 2- (lH-benzimidazol-2-yl) benzoxazole and N, N' -dimethyl - 2 , 2 ' -bisbenzimidazole, it being possible for these compounds to be prepared according to the procedures described in Patents US 5 961 960 and US 2 463 264.

Mention will be made, as examples of preferred compounds of formula (VIII) of the family of the phenylenebenzazoles, of 1 , 4-phenylenebis (2-benzox- azolyl) , 1 , 4-phenylenebis (2-benzimidazolyl) , 1,3- phenylenebis (2-benzoxazolyl) , 1 , 2-phenylenebis (2- benzoxazolyl) , 1 , 2-phenylenebis (benzimidazolyl) , 1,4- phenylenebis (N-2-ethylhexyl-2-benzimidazolyl) and 1,4- phenylenebis (N-trimethylsilylmethyl-2-benzimidazolyl) , it being possible for these compounds to be prepared according to the procedures described in Patent US 2 463 264 and in the publications J. Am. Chem. Soc., 82, 609 (1960) and J. Am. Chem. Soc . , 79, 5706-5708 (1957) .

Mention will be made, as examples of preferred compounds of formula (VIII) of the family of the benzofuranylbenzoxazoles, of 2- (2-benzofuranyl) benzox- azole, 2- (benzofuranyl) -5-methylbenzoxazole and 2- (3- methyl-2-benzofuranyl) benzoxazole, it being possible for these compounds to be prepared according to the procedures described in Patent US 5 518 713.

Mention may be made, as preferred compounds of formula (IX), for example of 2 , 6-diphenyl-l , 7-dihydrobenzo [1 , 2- d;4, 5-d^τ ] diimidazole, corresponding to the formula

or 2, 6-distyryl-l, 7-dihydrobenzo [1, 2-d;4, 5-d^τ ] diimidazole or 2 , 6-di (p-tert-butylstyryl) -1 , 7-dihydrobenzo [1, 2-d;4, 5-d' ] diimidazole, which compounds can be prepared according to the processes described in Application EP 0 669 323.

Mention may be made, as preferred compound of formula (X), of 5 , 5 ' -bis (2-phenylbenzimidazole) of formula:

the preparation of which is described in J. Chim.

Phys. , 64, 1602 (1967) .

Preference is very particularly given, among these insoluble organic compounds which screen out UV radiation, to 2- (lH-benzimidazol-2-yl) benzoxazole, 6- methoxy-2 , 2 ' -bisbenzimidazole, 2- (lH-benzimidazol-2- yl) benzothiazole, 1 , 4-phenylenebis (2-benzoxazolyl) ,

1 , 4-phenylenebis (2-benzimidazolyl) , 1 , 3-phenylenebis (2- benzoxazolyl) , 1 , 2-phenylenebis (2-benzoxazolyl) , 1,2- phenylenebis (2-benzimidazolyl) and 1 , 4-phenylenebis (N- trimethylsilylmethyl-2-benzimidazolyl) .

Another family of insoluble screening agents is that of the arylvinylene ketones chosen from those corresponding to either of the following formulae (XI) and (XII) :

in which: n = 1 or 2,

A, in the formula (XI) when n = 1 or in the formula

(XII) , is an aryl radical chosen from the following formulae (a) to (d) or, in the formula (XI) when n = 2, is a radical chosen from the following formulae (e) to

(h) :

(a) (b) (C) (d)

(e) (f) (g) (h)

in which: each of the R₄ symbols independently represents an OH group, a halogen atom, a linear or branched Ci-C₆ alkyl group optionally comprising a silicon atom, a linear or branched Ci-C₆ alkoxy group optionally comprising a silicon atom, a linear or branched Ci-C₅ alkoxycarbonyl group, or a linear or branched Ci-C₆ alkylsulphonamide group optionally comprising a silicon atom or an amino acid functional group, p represents an integer between 0 and 4 inclusive, q represents 0 or 1 ,

Ri represents hydrogen or an OH group,

R₂ represents hydrogen, a linear or branched Ci-C₆ alkyl group optionally comprising a silicon atom, a cyano group, a Ci-C₆ alkylsulphonyl group or a phenylsulphonyl group,

R₃ represents a linear or branched Ci-C₆ alkyl group optionally comprising a silicon atom or a phenyl group which can form a bicycle and which is optionally substituted by one or two R₄ radicals, or R₂ and R₃ together form a monocyclic, bicyclic or tricyclic C₂-Ci₀ hydrocarbon residue, optionally interrupted by one or more nitrogen, sulphur and oxygen atoms and which can comprise another carbonyl, and optionally substituted by a linear or branched Ci-C₈ alkylsulphonamide group, and optionally comprising a silicon atom or an amino acid functional group,- provided that, when n = 1, R₂ and R₃ do not form a camphor nucleus.

Mention may be made, as examples of compounds of formula (XI) in which n=l, which are insoluble and which screen out UV radiation, of the following families : styryl ketone (Kao, JP 04 134 042) such as l-(3,4- dimethoxyphenyl) -4 , 4-dimethylpent-l-en-3-one :

benzylidenecineole (E. Mariani et al, 16th IFSCC Congress, New York (1990)), such as 1 , 3 , 3-trimethyl-5-

(4-methoxybenzylidene) -2-oxabicyclo [2.2.2] octan-6-one :

benzylidenechromanone (Kao, JP 04 134 043), such as 3 - (4 -methoxybenzylidene) -2,3,4a, 8a-tetrahydrochromen-4 one :

benzylidenethiochromanone (Kao, JP 04 134 043) , such as 3 - (4 -methoxybenzylidene) -2,3,4a, 8a-tetrahydrochromene- 4-thione :

benzylidenequinuclidinone (Merck, EP 0 576 974), such as 4-methoxybenzylidene-l-azabicyclo [2.2.2] octan-3-one :

benzylidenecycloalkanone (Henkel, FR 2 395 023), such as 2- (4 -methoxybenzylidene) cyclopentanone and 2- (4- methoxybenzylidene) cyclohexanone :

benzylidenehydantoin (Ajinomoto, JP 01 158 090), such as 5- (3 , 4-dimethoxybenzylidene) imidazolidine-2 , 4-dione :

benzylideneindanone (Kao, JP 04 134 043) , such as 2- (4-methoxybenzylidene) indan-1-one :

benzylidenetetralone (Kao, JP 04 134 043) , such as 2- (4-methoxybenzylidene) -3 , 4-dihydro-2H-naphthalen-l- one:

benzylidenefuranone (L'Oreal, EP 0 390 683), such as 4- (4-methoxybenzylidene) -2,2,5, 5-tetramethyldihydro- furan-3-one :

benzylidenebenzofuranone (Kao, JP 04 134 041) , such as 2 -benzylidenebenzofuran-3 -one :

benzylideneindanedione, such as 2- (3 , 5-di (tert-butyi; 4-hydroxybenzylidene) indane-1 , 3-dione :

benzylidenebenzothiofuranone (Kao, JP 04,134,043), such as 2 -benzylidenebenzo [b] thiophen-3 -one :

benzylidenebarbituric, such as 5- (4-methoxybenzyl - idene) -1 , 3-dimethylpyrimidine-2 , 4 , 6-trione :

benzylidenepyrazolone, such as 4- (4-methoxybenzyl- idene) -5 -methyl -2 -phenyl -2 , 4-dihydropyrazol-3-one :

benzylideneimidazolone, such as 5- (4-methoxybenzyl - idene) -2 -phenyl -3 , 5-dihydroimidazol-4-one :

chalcone, such as 1- (2-hydroxy-4-methoxyphenyl) -3- phenylpropenone :

benzylidenone (screening tautomeric form of dibenzoylmethanes; L'Oreal FR 2 506 156), such as 3- hydroxy-1- (2-hydroxy-4-methoxyphenyl) -3- phenylpropenone :

Mention may be made, as examples of compounds of formula (XI) in which n=2 which are insoluble and which screen out UV radiation, of the following families:

phenylenebis (methylidenenorcamphor) (Merck,

EP 0 693 471), such as 1 , 4 -phenylenebis { 3 -methylidene- bicyclo [2.2.1] heptan-2-one} :

phenylenebis (methylidenecamphor) (L'Oreal,

FR 2 528 420), such as 1 , 4 -phenylenebis { 3 -methylidene- 1,7, 7-trimethylbicyclo [2.2.1] heptan-2-one} :

or 1, 3 -phenylenebis { 3 -methylidene-1, 7, 7-trimethylbicyclo [2.2.1] heptan-2-one} :

phenylenebis (methylidenecamphorsulphonamide (L'Oreal, FR 2 529 887), such as 1 , 4 -phenylenebis {3 , 3 ' - methylidenecamphor-10, 10' -ethylsulphonamide or -(2- ethylhexyl) sulphonamide} :

Et

or

phenylenebis (methylidenecineole) (E. Mariani et al, 16th IFSCC Congress, New York (1990)), such as 1,4- phenylenebis{ 5-methylidene-3 , 3 -dimethyl -2- oxabicyclo [2.2.2] octan-6-one} :

phenylenebis (methylideneketotricyclodecane) (Merck, EP 0 694 521), such as 1 , 4 -phenylenebis (octahydro-4 , 7- methano-6-inden-5-one) :

phenylenebis (alkylene ketone) (Kao, JP 04 134 041] such as 1, 4 -phenylenebis (4, 4-dimethylpent-l-en-3-one) :

phenylenebis (methylidenefuranone) (L'Oreal,

FR 2 638 354), such as 1 , 4 -phenylenebis (4 -methylidene- 2,2,5, 5-tetramethyldihydrofuran-3-one) :

phenylenebis (methylidenequinuclidinone) (Merck,

EP 0 714 880), such as 1 , 4 -phenylenebis { 2 -methylidene- 1-azabicyclo [2.2.2] octan-3-one} :

Mention may be made, as compounds of formula (XII) , of the following families: : bis (benzylidene) cycloalkanone, such as 2,5- di (benzylidene) cyclopentanone :

γ-pyrone (Kao, JP 04 290 882), such as 2 , 6-bis (3 , 4- dimethoxyphenyl) pyran-4-one :

Another family of insoluble screening agents which can be used in the present invention are the acrylonitrile amide, sulphonamide and carbamate derivatives corresponding to the following formula:

in which: X₂ represents a divalent radical of formula - (C=O) -R'₃- (C=O)-, -SO₂-R"₃-SO₂- or - (C=O) -0-R"₃-0- (C=O) -, Y represents a -(C=O)-R₄ or -SO₂R₅ radical, R₂ represents a linear or branched Ci-C₈ alkyl group, n has the value 0, 1 or 2 ,

R' 3 represents a single bond or R"₃,

R"₃ represents a linear or branched divalent Ci-C₃₀ alkylene or C₃-C₃₀ alkenylene radical which can carry one or more hydroxyl substituents and which can comprise, in the carbon chain, one or more heteroatoms chosen from oxygen, nitrogen and silicon atoms, R₄ represents an -OR₆ or -NHR₆ radical,

R₅ represents a linear or branched Ci-C₃₀ alkyl radical or a phenyl ring which can be substituted by Ci-C₄ alkyl or alkoxy radicals,

R₆ represents a linear or branched Ci-C₃₀ alkyl or C₃-C₃₀ alkenyl radical which can carry one or more hydroxyl substituents and which can comprise, in the carbon chain, one or more heteroatoms chosen from oxygen, nitrogen and silicon atoms.

Although, in the above formula (XIII) , only the isomers in which the cyano substituent is in the cis position with respect to the para-aminophenyl substituent are represented, this formula should be understood as also encompassing the corresponding trans isomers for each of the two double bonds and, independently, the cyano and para-aminophenyl substituents can be in the cis or trans configuration with respect to one another.

Another family of insoluble organic screening agents which can be used according to the present invention is formed by phenylenebis (benzoxazinone) derivatives of formula :

in which R represents a divalent aromatic residue chosen from the following formulae (e) to (h) :

^(e) (f) (g) (h)

in which: each of the R₄ symbols independently represents an OH group, a halogen atom, a linear or branched Ci-C₆ alkyl group optionally comprising a silicon atom, a linear or branched Ci-C₆ alkoxy group optionally comprising a silicon atom, a linear or branched Ci-C₅ alkoxycarbonyl group, or a linear or branched Ci-C₆ alkylsulphonamide group optionally comprising a silicon atom or an amino acid functional group, p represents an integer of between 0 and 4 inclusive, q represents 0 or 1.

Mention may be made, as examples of compounds of formula (XIV) which are insoluble and which screen out UV radiation, of the following derivatives: 2 , 2 ' -p-phenylenebis (3 , l-benzoxazin-4-one) , commercial product Cyasorb^® UV-3638 from Cytec, 2 , 2 ' - (4 , 4 ' -biphenylene) bis (3 , l-benzoxazin-4-one) , 2 , 2 ' - (2 , 6-naphthylene) bis (3 , l-benzoxazin-4-one) .

Another specific family of insoluble organic screening agents are the polyvalent metal salts (for example Ca²⁺, Zn²⁺, Mg²⁺, Ba²⁺, Al³⁺ or Zr⁴⁺) of sulphonated or carboxylated organic screening agents, such as the polyvalent metal salts of sulphonated derivatives of benzylidenecamphor, such as those described in Application FR-A 2 639 347, the polyvalent metal salts of sulphonated derivatives of benzimidazole, such as those described in Application EP-A-893 119, and the polyvalent metal salts of cinnamic acid derivatives, such as those described in Application JP-87 166 517. Mention may also be made of metal or ammonium or substituted ammonium complexes of UV-A and/or UV-B organic screening agents, such as those described in Patent Applications WO93/10753, WO93/11095 and WO95/05150.

The choice will more particularly be made, as insoluble organic screening agent, of methylenebis (hydroxyphenyl- benzotriazole) derivatives with the following structure:

in which R₈ and R₉, which are identical or different, each represent a Ci-Ci₈ alkyl radical which can be substituted by one or more radicals chosen from Ci-C₄ alkyl, C₅-Ci₂ cycloalkyl or aryl and more particularly the compound (a) with the name 2 , 2 ' -methylenebis [6- (2H- benzotriazol-2-yl) -4- (1,1,3, 3-tetramethylbutyl) phenol] or Methylene Bis-Benzotriazolyl Tetramethylbutylphenol , which is sold in the solid form under the name Mixxim BB/100 by Fairmount Chemical and in a micronized form under the name Tinosorb M by Ciba Specialty Chemicals.

The insoluble organic screening agents according to the invention are generally provided in the form of particles with a mean size ranging from 10 nm to 5 μm. More preferably, their mean size varies from 10 nm to 2 μm and in particular between 20 nm and 1.5 μm and ideally between 30 nm and 1.0 μm. Generally, the mean size of the particles will correspond to the mean diameter of the distribution by number .

The mean size of the particles can be determined by any conventional method, such as optical methods (quasielastic scattering or laser scattering) , centrifuging methods or microscope visualization and image analysis methods.

The insoluble organic screening agents according to the invention can be brought to the desired particulate form by any ad hoc means, such as in particular dry milling or milling in a solvent medium, sieving, atomization, micronization or spraying.

The insoluble organic screening agents according to the invention in a micronized form can in particular be obtained by a process for milling an insoluble organic UV screening agent in the form of large-size particles in the presence of an appropriate surfactant which makes it possible to improve the dispersion of the particles thus obtained in cosmetic formulations.

An example of a process for the micronization of insoluble organic screening agents is described in Applications GB-A-2 303 549 and EP-A-893 119, which form an integral part of the description. The milling device used according to these documents can be an air jet mill, bead mill, vibration mill or hammer mill and preferably a mill with a high stirring speed or an impact mill and more particularly a rotary bead mill, a vibrating mill, a tube/rod mill or a mill.

According to this specific process, use is made, as surfactants for the milling of the said screening agents, of alkyl polyglucosides with the structure C_nH_2n+IO (C₆H_I0O₅) _xH in which n is an integer from 8 to 16 and x is the mean degree of polymerization of the (C₆H_I0O₅) unit and varies from 1.4 to 1.6. They can be chosen from Ci-Ci₂ esters of a compound with the structure C_nH_2n+IO (C₆H_I0O₅) _XH and more specifically an ester obtained by reaction of a Ci-Ci₂ carboxylic acid, such as formic, acetic, propionic, butyric, sulphosuccinic, citric or tartaric acid, with one or more free OH functional groups on the (C₆Hi₀O₅) glucoside unit. The said surfactants are generally used at a concentration ranging from 1 to 50% by weight and more preferably from 5 to 40% by weight, with respect to the insoluble screening agent in its micronized form.

Use may also be made, in order to improve the dispersibility of the insoluble organic screening agents in the cosmetic vehicle, of amphiphilic copolymers comprising at least one hydrophilic sequence and at least one hydrophobic sequence, such as those described in Patent Application EP 1 353 642.

The insoluble UV screening agent or agents of the invention are preferably present at a total concentration of between 0.1 and 25% by weight approximately and preferably between 0.2 and 20% by weight approximately, with respect to the total weight of the composition.

The compositions in accordance with the invention can additionally comprise other additional water-soluble organic photoprotective agents active in the UV-A and/or UV-B regions.

The term "hydrophilic photoprotective agent" is understood to mean any agent which screens out UV radiation and which is capable of being completely dissolved in the molecular state in the aqueous phase of the emulsion or else of being solubilized in the colloidal form (for example, in the micelle form) in the aqueous phase of the emulsion. Mention may be made, among hydrophilic organic UV screening agents which can be used according to the invention, of those denoted below under their INCI names :

(1) p-aminobenzoic acid (PABA) derivatives, such as:

- PABA,

- Glyceryl PABA, - PEG-25 PABA, sold under the name "Uvinul P25" by BASF,

(2) benzophenone derivatives comprising at least one sulphonic radical, such as - Benzophenone-4 , sold under the trade name "Uvinul MS40" by BASF,

- Benzophenone- 5 ,

- Benzophenone- 12 ,

(3) benzylidenecamphor derivatives comprising at least one sulphonic radical, such as, for example:

- Benzylidene Camphor Sulfonic Acid, manufactured under the name "Mexoryl SL" by Chimex,

- Camphor Benzalkonium Methosulfate, manufactured under the name "Mexoryl SO" by Chimex,

- Terephthalylidene Dicamphor Sulfonic Acid, manufactured under the name "Mexoryl SX" by Chimex,

(4) benzimidazole derivatives comprising at least one sulphonic radical, such as, for example:

- Phenylbenzimidazole Sulfonic Acid, sold in particular under the trade name "Eusolex 232" by Merck, bis-benzazolyl derivatives, such as described in

Patents EP 669 323 and US 2 463 264 and more particularly the compound Disodium Phenyl

Dibenzimidazole Tetrasulfonate, sold under the trade name "Neo Heliopan AP" by Haarmann and Reimer, (5) hydrophilic cinnamate derivatives, such as, for example, DEA Methoxycinnamate,

(6) their mixtures.

The most preferred, among these hydrophilic screening agents, are chosen from:

Terephthalylidene Dicamphor Sulfonic Acid, Benzophenone-4 , Phenylbenzimidazole Sulfonic Acid,

Disodium Phenyl Dibenzimidazole Tetrasulfonate and their mixtures.

The additional hydrophilic photoprotective agents are generally present in the compositions according to the invention in proportions ranging from 0.01 to 20% by weight, with respect to the total weight of the composition, and preferably ranging from 0.1 to 10% by weight, with respect to the total weight of the composition.

The emulsions according to the invention can also comprise agents for the artificial tanning and/or artificial browning of the skin (self-tanning agents) .

The self-tanning agents are generally chosen from mono- or polycarbonyl compounds, such as, for example, isatin, alloxan, ninhydrin, glyceraldehyde, mesotartaric aldehyde, glutaraldehyde, erythrulose, pyrazoline-4, 5-dione derivatives, such as described in Patent Application FR 2 466 492 and WO 97/35842, dihydroxyacetone (DHA) or 4 , 4-dihydroxypyrazolin-5-one derivatives, such as described in Patent Application EP 903 342. Use will preferably be made of DHA.

The DHA can be used in the free and/or encapsulated form, for example encapsulated in lipid vesicles, such as liposomes, described in particular in Application WO 97/25970. The mono- or polycarbonyl self-tanning agents are generally present in the compositions according to the invention in proportions ranging from 0.1 to 10% by weight, with respect to the total weight of the composition, and preferably from 0.2 to 8% by weight, with respect to the total weight of the composition.

The compositions of the invention can comprise all the additives commonly used in cosmetics and will find applications in the care field, makeup field and field of antisun products.

The aqueous compositions in accordance with the present invention can additionally comprise conventional cosmetic adjuvants chosen in particular from fatty substances other than the polar oils defined above, organic solvents, ionic or nonionic and hydrophilic or lipophilic thickeners, softening agents, humectants, opacifiers, stabilizing agents, emollients, silicones, antifoaming agents, fragrances, preservatives, anionic, cationic, nonionic, zwitterionic or amphoteric surfactants, active principles, fillers, polymers, propellants, basifying or acidifying agents or any other ingredient commonly used in the cosmetics and/or dermatological field.

The fatty substances can be composed of an oil or a wax or their mixtures. The term "oil" is understood to mean a compound which is liquid at ambient temperature. The term "wax" is understood to mean a compound which is solid or substantially solid at ambient temperature and which has a melting point generally of greater than 35⁰C.

Mention may be made, among organic solvents, of lower alcohols and polyols. The latter can be chosen from glycols and glycol ethers, such as ethylene glycol, propylene glycol, butylene glycol, dipropylene glycol or diethylene glycol .

Mention may be made, as hydrophilic thickeners, of carboxyvinyl polymers, such as the Carbopols (carbomers) and the Pemulens (acrylate/Ci_O-C₃o-alkyl acrylate copolymer); polyacrylamides, such as, for example, the crosslinked copolymers sold under the names Sepigel 305 (CTFA name: polyacrylamide/C13-14 isoparaffin/Laureth 7) or Simulgel 600 (CTFA name: acrylamide/sodium acryloyldimethyltaurate copolymer/ isohexadecane/polysorbate 80) by Seppic,- optionally crosslinked and/or neutralized polymers and copolymers of 2-acrylamido-2-methylpropanesulphonic acid, such as the poly (2-acrylamido-2-methylpropanesulphonic acid) sold by Hoechst under the trade name "Hostacerin AMPS"

(CTFA name: ammonium polyacryldimethyltauramide) ; cellulose derivatives, such as hydroxyethylcellulose,- polysaccharides and in particular gums, such as xanthan gum; and their mixtures.

Mention may be made, as lipophilic thickeners, of synthetic polymers, such as the poly (Ci₀-C₃₀ alkyl acrylate) sold under the name "Doresco IPA 13-1" by Landec, or of modified clays, such as hectorite and its derivatives, for example the products sold under the Bentone names .

Of course, a person skilled in the art will take care to choose the additional optional compound or compounds mentioned above and/or their amounts so that the advantageous properties intrinsically attached to the compositions in accordance with the invention are not, or not substantially, detrimentally affected by the envisaged addition or additions.

The compositions according to the invention can be prepared according to techniques well known to a person skilled in the art of an oil-in-water emulsion. The proportion of the oily phase of the emulsion can range from 1 to 80% by weight, preferably from 2 to 50% by weight and better still from 2 to 40% by weight, with respect to the total weight of the composition. The fatty substances of the oily phase, in particular the oils, and the emulsifiers and coemulsifiers optionally present, used in the composition in the emulsion form, are chosen from those conventionally used in the cosmetics or dermatological field. The emulsifier and the coemulsifier, when they are present, are generally present in a proportion ranging from 0.1 to 30% by weight, preferably from 0.3 to 20% by weight and better still from 0.5 to 15% by weight, with respect to the total weight of the composition.

The emulsions in accordance with the invention generally comprise at least one emulsifier chosen from amphoteric, anionic, cationic or nonionic emulsifiers, used alone or as a mixture. The emulsifiers are appropriately chosen in order to form an oil-in-water emulsion.

Mention may be made, as emulsifiers, of nonionic emulsifiers, such as oxyalkylenated (more particularly polyoxyethylenated) esters of fatty acids and of glycerol; oxyalkylenated esters of fatty acids and of sorbitan; oxyalkylenated (oxyethylenated and/or oxypropylenated) fatty acid esters, such as the PEG-100 stearate/glyceryl stearate mixture sold, for example, by ICI under the name Arlacel 165; oxyalkylenated

(oxyethylenated and/or oxypropylenated) fatty alcohol ethers; sugar esters, such as sucrose stearate; ethers of fatty alcohol and of sugar, in particular alkyl polyglucosides (APG) , such as decyl glucoside and lauryl glucoside, for example sold by Henkel under the respective names Plantaren 2000 and Plantaren 1200, cetearyl glucoside, optionally as a mixture with cetearyl alcohol, for example sold under the name Montanov 68 by Seppic, under the name Tegocare CG90 by Goldschmidt and under the name Emulgade KE3302 by Henkel, and arachidyl glucoside, for example in the form of the mixture of arachidyl and behenyl alcohols and of arachidyl glucoside sold under the name Montanov 202 by Seppic . According to a specific embodiment of the invention, the mixture of the alkyl polyglucoside as defined above with the corresponding fatty alcohol can be in the form of a self-emulsifying composition, for example as described in the document WO-A-92/06778.

The aqueous phase of the latter can comprise a nonionic vesicular dispersion prepared according to known methods (Bangham, Standish and Watkins, J. MoI. Biol., 13, 238 (1965), FR 2 315 991 and FR 2 416 008).

According to a specific form of the invention, fluid emulsions will be used.

The term "fluid emulsion" is understood to mean an emulsion not existing in a solid form. Its viscosity can be measured using a Rheomat 180 viscometer at 25⁰C at a rotational speed of 200 rpm after rotating for

30 seconds, with a 2, 3 or 4 measurement body, and is preferably less than or equal to 20 Pa- s, more preferably less than 5 Pa- s, more preferably still less than or equal to 2 Pa • s and more particularly less than or equal to 0.5 Pa • s .

The compositions according to the invention have applications in a large number of treatments, in particular cosmetic treatments, of the skin, lips and hair, including the scalp, in particular for protecting and/or caring for the skin, lips and/or hair and/or for making up the skin and/or lips.

Another subject-matter of the present invention is composed of the use of the compositions according to the invention as defined above in the manufacture of products for the cosmetic treatment of the skin, lips, nails, hair, eyelashes, eyebrows and/or scalp, in particular care products, sun protection products and makeup products.

The cosmetic compositions according to the invention can, for example, be used as care product and/or sun protection product for the face and/or body with a liquid to semi-liquid consistency, such as milks or relatively fluid creams. They can optionally be packaged in an aerosol and be provided in the foam or spray form.

The cosmetic compositions according to the invention can, for example, be used as makeup product.

The compositions according to the invention in the form of vaporizable fluid lotions in accordance with the invention are applied to the skin or hair in the form of fine particles by means of pressurizing devices. The devices in accordance with the invention are well known to a person skilled in the art and comprise non-aerosol pumps or "atomizers", aerosol containers comprising a propellant and aerosol pumps using compressed air as propellant. The latter are disclosed in Patents US 4 077 441 and US 4 850 517 (forming an integral part of the content of the description) .

The compositions packaged as an aerosol in accordance with the invention generally comprise conventional propellants, such as, for example, hydrofluorinated compounds, dichlorodifluoromethane, difluoroethane, dimethyl ether, isobutane, n-butane, propane or trichlorofluoromethane . They are preferably present in amounts ranging from 15 to 50% by weight, with respect to the total weight of the composition.

Concrete but in no way limiting examples illustrating the invention will now be given. Synthesis Examples

Example 1 :

Preparation of a polystyrene-block-poly (ethyl acrylate- stat-acrylic acid sodium salt) diblock copolymer of type (2b) by synthesis of a polystyrene-block- poly (ethyl acrylate) diblock copolymer with targeted Mn values 2000-block-42 000 (g/mol) and then 75% hydrolysis of the ethyl acrylate ester groups

Stage Ia: Preparation of a first polystyrene block with a theoretical molecular weight of approximately 2000 g/mol

3000 g of water, 17.6 g of sodium dodecyl sulphate and 0.290 g of sodium carbonate Na₂CO₃ are introduced into the reactor at ambient temperature. The mixture obtained is stirred under nitrogen for 30 minutes. The temperature is subsequently raised to 75⁰C and then a mixture 1 is added, which mixture 1 comprises:

- 10.00 g of styrene (St),

- 0.200 g of methacrylic acid (MAA) and

- 10.42 g of xanthate (CH₃) (CO₂CH₃)CH-S(C=S)OCH₂CH₃.

The mixture is brought to 85⁰C and then a solution of 1.19 g of sodium persulphate Na₂S₂O₈ dissolved in 20.0 g of water is introduced.

After 5 minutes, the addition is begun of a mixture 2 comprising :

- 90.0 g of styrene (St) and

- 1.80 g of methacrylic acid (MAA) .

The addition is continued for 60 minutes. After complete addition of the various ingredients, the copolymer emulsion obtained is maintained at 85⁰C for one hour . A sample (5 g) is then withdrawn and analysed by steric exclusion chromatography (SEC) in THF. Its measured number-average molecular weight Mn is equal to 2000 g/mol in polystyrene equivalents (calibration by linear polystyrene standards) . Its polydispersity index Mw/Mn is equal to 2.0.

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

Stage Ib: Growth of a second block of poly (ethyl acrylate) with a theoretical molecular weight of approximately 42 000 g/mol in order to obtain a polystyrene-block-poly (ethyl acrylate) diblock copolymer

The starting material is the emulsified copolymer obtained above in stage Ia after having withdrawn therefrom 5 g for analysis and without halting the heating. 1.19 g of sodium persulphate Na₂S₂O₈ diluted in 50.0 g of water are introduced continuously over three hours .

Simultaneously, a mixture 3 is added at 85⁰C over three hours, which mixture 3 comprises:

- 200.0 g of water,

- 2.20 g of sodium carbonate Na₂CO₃ and

- 4.40 g of sodium dodecyl sulphate.

Simultaneously, a mixture 4 is added, which mixture 4 comprises :

- 2100 g of ethyl acrylate (EA) and

- 42.0 g of methacrylic acid (MAA) .

After complete addition of the various ingredients, the copolymer emulsion obtained is maintained at 85⁰C for one hour. 4.40 g of tert-butylbenzyl peroxide are then introduced all at once and the addition is begun of a mixture 5 comprising:

- 2.20 g of erythorbic acid,

- 50.0 g of water.

The addition is continued for 60 minutes. After complete addition of the various ingredients, the emulsion is cooled to -25⁰C over one hour. A sample (5 g) is then withdrawn and analysed by steric exclusion chromatography (SEC) in THF. Its measured number-average molecular weight Mn is equal to 41 000 g/mol in polystyrene equivalents (calibration by linear polystyrene standards) . Its polydispersity index Mw/Mn is equal to 6.

An 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) with a solids content of approximately 41%.

Stage II: Partial hydrolysis (to targeted 75%) of the poly (ethyl acrylate) block of the copolymer obtained above in stage Ib in order to obtain the polystyrene- block-poly (ethyl acrylate-stat-acrylic acid sodium salt) diblock of the type (2b)

750 g of water, 250 g of 2-propanol and 1347 g of emulsified copolymer (making 550 g of copolymer on a dry basis) obtained above in stage Ib are introduced into the reactor at ambient temperature. The mixture obtained is stirred for 15 minutes. The temperature is subsequently raised to 75⁰C and then 678 g of sodium hydroxide (23.2% by weight solution in water) are added continuously over one hour. After 30 minutes from the beginning of the addition of sodium hydroxide, the continuous addition over one hour is begun of 12 g of aqueous hydrogen peroxide solution (30% solution) . After complete addition of the various ingredients, the copolymer solution obtained is maintained at 75⁰C for four hours and then cooled to 25⁰C over one hour.

The product recovered at the end of the reaction is a translucent gel in water with a solids content of approximately 20%.

The copolymer thus obtained exhibits the following characteristics : - Theoretical average molecular weight of the block A: 2000 g/mol

- Theoretical average molecular weight of the block B: 30 000 g/mol

- Proportion by weight of the block B: 96% - Proportion by weight of the block A: 4%

Amount by weight of units deriving from ethyl acrylate in the block B: 31%

Example 2 :

Preparation of a polystyrene-block-poly (ethyl acrylate- stat-acrylic acid sodium salt) diblock copolymer of type (Ib) by synthesis of a polystyrene-block- poly (ethyl acrylate) diblock copolymer with targeted Mn values 5000-block-7000 (g/mol) and then 75% hydrolysis of the ethyl acrylate ester groups

Stage Ia: Preparation of a first polystyrene block with a theoretical molecular weight of approximately 5000 g/mol

1000 g of water, 6.50 g of sodium dodecyl sulphate and 0.30 g of sodium carbonate Na₂CO₃ are introduced into the reactor at ambient temperature. The mixture obtained is stirred under nitrogen for 30 minutes. The temperature is subsequently raised to 75⁰C and then a mixture 1 is added, which mixture 1 comprises:

- 83.7 g of styrene (St),

- 1.67 g of methacrylic acid (MAA) and - 17.4 g of xanthate (CH₃) (CO₂CH₃)CH-S(C=S)OCH₂CH₃.

The mixture is brought to 85⁰C and then a solution of 2.00 g of sodium persulphate Na₂S₂O₈ dissolved in 20.0 g of water is introduced.

After 5 minutes, the addition is begun of a mixture 2 comprising:

- 334.7 g of styrene (St) and - 6.69 g of methacrylic acid (MAA) .

The addition is continued for 60 minutes. After complete addition of the various ingredients, the copolymer emulsion obtained is maintained at 85⁰C for one hour.

A sample (5 g) is then withdrawn and analysed by steric exclusion chromatography (SEC) in THF. Its measured number-average molecular weight Mn is equal to 5800 g/mol in polystyrene equivalents (calibration by linear polystyrene standards) . Its polydispersity index Mw/Mn is equal to 1.9.

Stage Ib: Growth of a second block of poly (ethyl acrylate) with a theoretical molecular weight of approximately 7000 g/mol in order to obtain a polystyrene-block-poly (ethyl acrylate) diblock copolymer

The starting material is the emulsified copolymer obtained above in stage Ia after having withdrawn therefrom 5 g for analysis and without halting the heating.

2.00 g of sodium persulphate Na₂S₂O₈ diluted in 50.0 g of water are introduced continuously over three hours. Simultaneously, a mixture 3 is added at 85⁰C over three hours, which mixture 3 comprises:

- 200.0 g of water,

- 1.00 g of sodium carbonate Na₂CO₃ and - 2.00 g of sodium dodecyl sulphate.

Simultaneously, a mixture 4 is added, which mixture 4 comprises :

- 581.6 g of ethyl acrylate (EA) and

- 11.63 g of methacrylic acid (MAA) .

After complete addition of the various ingredients, the copolymer emulsion obtained is maintained at 85⁰C for one hour .

2.00 g of tert-butylbenzyl peroxide are then introduced all at once and the addition is begun of a mixture 5 comprising :

- 1.00 g of erythorbic acid,

- 50.0 g of water.

The addition is continued for 60 minutes. After complete addition of the various ingredients, the emulsion is cooled to -25⁰C over one hour.

A sample (5 g) is then withdrawn and analysed by steric exclusion chromatography (SEC) in THF. Its measured number-average molecular weight Mn is equal to 12 700 g/mol in polystyrene equivalents (calibration by linear polystyrene standards) . Its polydispersity 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 99.8%.

The product obtained is a dispersion in water of the copolymer (latex) with a solids content of approximately 44%. Stage II: Partial hydrolysis (to targeted 75%) of the poly (ethyl acrylate) block of the copolymer obtained above in stage Ib in order to obtain the polystyrene- block-poly (ethyl acrylate-stat-acrylic acid sodium salt) diblock of type (Ib)

638 g of water, 212 g of 2-propanol and 1485 g of emulsified copolymer (making 650 g of copolymer on a dry basis) obtained above in stage Ib are introduced into the reactor at ambient temperature. The mixture obtained is stirred for 15 minutes. The temperature is subsequently raised to 75⁰C and then 488 g of sodium hydroxide (23.2% by weight solution in water) are added continuously over one hour.

After 30 minutes from the beginning of the addition of sodium hydroxide, the continuous addition over one hour is begun of 37 g of aqueous hydrogen peroxide solution (30% solution) .

After complete addition of the various ingredients, the copolymer solution obtained is maintained at 75⁰C for four hours and then cooled to -25⁰C over one hour.

The product recovered at the end of the reaction is a translucent gel in water with a solids content of approximately 18%.

The copolymer thus obtained exhibits the following characteristics:

- Theoretical average molecular weight of the block A: 5000 g/mol

- Theoretical average molecular weight of the block B: 5000 g/mol - Proportion by weight of the block B: 57%

- Proportion by weight of the block A: 43%

- Amount by weight of units deriving from ethyl acrylate in the block B: 31% Example 3 :

Preparation of a polystyrene-block-poly (ethyl acrylate- stat-acrylic acid sodium salt) diblock copolymer of type (2a) by synthesis of a polystyrene-block- poly (ethyl acrylate) diblock copolymer with targeted Mn values 2000 -block-20 000 (g/mol) and then 75% hydrolysis of the ethyl acrylate ester groups

2150 g of water, 6.00 g of sodium dodecyl sulphate and 0.650 g of sodium carbonate Na₂CO₃ are introduced into the reactor at ambient temperature. The mixture obtained is stirred under nitrogen for 30 minutes. The temperature is subsequently raised to 75⁰C and then a mixture 1 is added, which mixture 1 comprises: - 18.2 g of styrene (St),

- 0.360 g of methacrylic acid (MAA) and

- 18.9 g of xanthate (CH₃) (CO₂CH₃)CH-S(C=S)OCH₂CH₃.

The mixture is brought to 85⁰C and then a solution of 2.16 g of sodium persulphate Na₂S₂O₈ dissolved in 20.0 g of water is introduced.

After 5 minutes, the addition is begun of a mixture 2 comprising : - 163.6 g of styrene (St) and

- 3.30 g of methacrylic acid (MAA) .

The addition is continued for 60 minutes. After complete addition of the various ingredients, the copolymer emulsion obtained is maintained at 85⁰C for one hour .

A sample (~5 g) is then withdrawn and analysed by steric exclusion chromatography (SEC) in THF. Its measured number-average molecular weight Mn is equal to 2000 g/mol in polystyrene equivalents (calibration by linear polystyrene standards) . Its polydispersity index Mw/Mn is equal to 2.1.

Stage Ib: Growth of a second block of poly (ethyl acrylate) with a theoretical molecular weight of approximately 20 000 g/mol in order to obtain a polystyrene-block-poly (ethyl acrylate) diblock copolymer

The starting material is the emulsified copolymer obtained above in stage Ia after having withdrawn therefrom 5 g for analysis and without halting the heating .

2.16 g of sodium persulphate Na₂S₂O₈ diluted in 50.0 g of water are introduced continuously over three hours. Simultaneously, a mixture 3 is added at 85⁰C over three hours, which mixture 3 comprises: - 200.0 g of water,

- 4.00 g of sodium carbonate Na₂CO₃ and

- 8.00 g of sodium dodecyl sulphate.

Simultaneously, a mixture 4 is added, which mixture 4 comprises : - 1818 g of ethyl acrylate (EA) and

- 33.4 g of methacrylic acid (MAA) .

After complete addition of the various ingredients, the copolymer emulsion obtained is maintained at 85⁰C for one hour.

4.00 g of tert-butylbenzyl peroxide are then introduced all at once and the addition is begun of a mixture 5 comprising : - 2.00 g of erythorbic acid,

- 50.0 g of water.

A sample (5 g) is then withdrawn and analysed by steric exclusion chromatography (SEC) in THF. Its measured number-average molecular weight Mn is equal to 17 500 g/mol in polystyrene equivalents (calibration by linear polystyrene standards) . Its polydispersity index Mw/Mn is equal to 2.9.

The product obtained is a dispersion in water of the copolymer (latex) with a solids content of approximately 44%.

Stage II: Partial hydrolysis (to targeted 75%) of the poly (ethyl acrylate) block of the copolymer obtained above in stage Ib in order to obtain the polystyrene- block-poly (ethyl acrylate-stat-acrylic acid sodium salt) diblock of type (2al)

900 g of water, 300 g of 2-propanol and 1563 g of emulsified copolymer (making 700 g of copolymer on a dry basis) obtained above in stage Ib are introduced into the reactor at ambient temperature. The mixture obtained is stirred for 15 minutes. The temperature is subsequently raised to 75⁰C and then 822 g of sodium hydroxide (23.2% by weight solution in water) are added continuously over one hour.

After 30 minutes from the beginning of the addition of sodium hydroxide, the continuous addition over one hour is begun of 25 g of aqueous hydrogen peroxide solution (30% solution) .

The product recovered at the end of the reaction is a translucent gel in water with a solids content of approximately 17%.

The copolymer thus obtained exhibits the following characteristics :

- Theoretical average molecular weight of the block A: 2000 g/mol

- Theoretical average molecular weight of the block B: 14 000 g/mol

- Proportion by weight of the block B: 90%

- Proportion by weight of the block A: 10% - Amount by weight of units deriving from ethyl acrylate in the block B: 31%.

Example 4 :

Preparation of a polystyrene-block-poly (ethyl acrylate- stat-acrylic acid sodium salt) diblock copolymer of type (2a) by synthesis of a polystyrene-block- poly (ethyl acrylate) diblock copolymer with targeted Mn values 2000 -block-20 000 (g/mol) and then 90% hydrolysis of the ethyl acrylate ester groups

2150 g of water, 6.00 g of sodium dodecyl sulphate and 0.650 g of sodium carbonate Na₂CO₃ are introduced into the reactor at ambient temperature. The mixture obtained is stirred under nitrogen for 30 minutes. The temperature is subsequently raised to 75⁰C and then a mixture 1 is added, which mixture 1 comprises:

- 18.2 g of styrene (St),

- 0.360 g of methacrylic acid (MAA) and - 18.9 g of xanthate (CH₃) (CO₂CH₃)CH-S(C=S)OCH₂CH₃.

After 5 minutes, the addition is begun of a mixture 2 comprising:

- 163.6 g of styrene (St) and

- 3.30 g of methacrylic acid (MAA) .

A sample (5 g) is then withdrawn and analysed by steric exclusion chromatography (SEC) in THF. Its measured number-average molecular weight Mn is equal to 2000 g/mol in polystyrene equivalents (calibration by linear polystyrene standards) . Its polydispersity index Mw/Mn is equal to 2.1.

2.16 g of sodium persulphate Na₂S₂O₈ diluted in 50.0 g of water are introduced continuously over three hours. Simultaneously, a mixture 3 is added at 85⁰C over three hours, which mixture 3 comprises:

- 200.0 g of water,

- 4.00 g of sodium carbonate Na₂CO₃ and - 8.00 g of sodium dodecyl sulphate.

Simultaneously, a mixture 4 is added, which mixture 4 comprises :

- 1818 g of ethyl acrylate (EA) and

- 33.4 g of methacrylic acid (MAA) .

After complete addition of the various ingredients, the copolymer emulsion obtained is maintained at 85⁰C for one hour. 4.00 g of tert-butylbenzyl peroxide are then introduced all at once and the addition is begun of a mixture 5 comprising:

- 2.00 g of erythorbic acid,

- 50.0 g of water.

The addition is continued for 60 minutes. After complete addition of the various ingredients, the emulsion is cooled to 25⁰C over one hour.

An 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) with a solids content of approximately 44%.

Stage II: Partial hydrolysis (to targeted 90%) of the poly (ethyl acrylate) block of the copolymer obtained above in stage Ib in order to obtain the polystyrene- block-poly (ethyl acrylate-stat-acrylic acid sodium salt) diblock of type (2a)

1209 g of water, 206 g of 2-propanol and 1670 g of emulsified copolymer (making 700 g of copolymer on a dry basis) obtained above in stage Ib are introduced into the reactor at ambient temperature. The mixture obtained is stirred for 15 minutes. The temperature is subsequently raised to 7O⁰C and then 1038 g of sodium hydroxide (23.2% by weight solution in water) are added continuously over one hour.

After 30 minutes from the beginning of the addition of sodium hydroxide, the continuous addition over one hour is begun (stage c) of 27 g of aqueous hydrogen peroxide solution (30% solution) .

After complete addition of the various ingredients, the copolymer solution obtained is maintained at 7O⁰C for four hours. The reaction mixture is then cooled to -25⁰C over one hour.

The copolymer thus obtained exhibits the following characteristics:

- Theoretical average molecular weight of the block A: 2000 g/mol

- Theoretical average molecular weight of the block B: 14 000 g/mol - Proportion by weight of the block B: 89%

- Proportion by weight of the block A: 11%

- Amount by weight of units deriving from ethyl acrylate in the block B: 13%

Example 5 :

Preparation of a polystyrene-block-poly (ethyl acrylate- stat-acrylic acid sodium salt) diblock copolymer of type (Ia) by synthesis of a polystyrene-block- poly (ethyl acrylate) diblock copolymer with targeted Mn values lOOO-block-5600 (g/mol) and then 75% hydrolysis of the ethyl acrylate ester groups

Stage Ia: Preparation of a first polystyrene block with a theoretical molecular weight of approximately 1000 g/mol

2400 g of water, 13.0 g of sodium dodecyl sulphate and 0.60 g of sodium carbonate Na₂CO₃ are introduced into the reactor at ambient temperature. The mixture obtained is stirred under nitrogen for 30 minutes. The temperature is subsequently raised to 75⁰C and then a mixture 1 is added, which mixture 1 comprises: - 61.0 g of styrene (St),

- 1.22 g of methacrylic acid (MAA) and

- 63.5 g of xanthate (CH₃) (CO₂CH₃)CH-S(C=S)OCH₂CH₃.

The mixture is brought to 85⁰C and then a solution of 7.26 g of sodium persulphate Na₂S₂O₈ dissolved in 20.0 g of water is introduced.

After 5 minutes, the addition is begun of a mixture 2 comprising: - 243.9 g of styrene (St) and

- 4.88 g of methacrylic acid (MAA) .

A sample (5 g) is then withdrawn and analysed by steric exclusion chromatography (SEC) in THF. Its measured number-average molecular weight Mn is equal to 960 g/mol in polystyrene equivalents (calibration by linear polystyrene standards) . Its polydispersity index Mw/Mn is equal to 2.1.

Stage Ib: Growth of a second block of poly (ethyl acrylate) with a theoretical molecular weight of approximately 5600 g/mol in order to obtain a polystyrene-block-poly (ethyl acrylate) diblock copolymer of type (Ia)

7.26 g of sodium persulphate Na₂S₂O₈ diluted in 50.0 g of water are introduced continuously over three hours. Simultaneously, a mixture 3 is added at 85⁰C over three hours, which mixture 3 comprises: - 200.0 g of water,

- 2.00 g of sodium carbonate Na₂CO₃ and

- 4.00 g of sodium dodecyl sulphate.

Simultaneously, a mixture 4 is added, which mixture 4 comprises:

- 1695 g of ethyl acrylate (EA) and

- 33.90 g of methacrylic acid (MAA). After complete addition of the various ingredients, the copolymer emulsion obtained is maintained at 85⁰C for one hour .

4.00 g of tert-butylbenzyl peroxide are then introduced all at once and the addition is begun of a mixture 5 comprising :

- 2.00 g of erythorbic acid,

- 50.0 g of water.

A sample (5 g) is then withdrawn and analysed by steric exclusion chromatography (SEC) in THF. Its measured number-average molecular weight Mn is equal to 5900 g/mol in polystyrene equivalents (calibration by linear polystyrene standards) . Its polydispersity index Mw/Mn is equal to 2.3.

The product obtained is a dispersion in water of the copolymer (latex) with a solids content of approximately 40%.

Stage II: Partial hydrolysis (to targeted 75%) of the poly (ethyl acrylate) block of the copolymer obtained above in stage Ib in order to obtain the polystyrene- block-poly (ethyl acrylate-stat-acrylic acid sodium salt) diblock of type (Ia)

1200 g of water and 3070 g of emulsified copolymer (1200 g of copolymer on a dry basis) obtained above in stage Ib are introduced into the reactor at ambient temperature. The mixture obtained is stirred for 15 minutes. The temperature is subsequently raised to 75⁰C and then 1314 g of sodium hydroxide (23.2% by weight solution in water) are added continuously over one hour.

After 30 minutes from the beginning of the addition of sodium hydroxide, the continuous addition over one hour is begun of 124 g of aqueous hydrogen peroxide solution (30% solution) .

After complete addition of the various ingredients, the copolymer solution obtained is maintained at 75⁰C for four hours. The reaction mixture is then cooled to 25⁰C over one hour .

The copolymer thus obtained exhibits the following characteristics :

- Theoretical average molecular weight of the block A: 1000 g/mol

- Theoretical average molecular weight of the block B: 4000 g/mol

- Proportion by weight of the block B: 84%

- Proportion by weight of the block A: 16%

Amount by weight of units deriving from ethyl acrylate in the block B: 31%

Composition Examples

The fluid oil-in-water emulsions b and c according to the invention are compared with respect to a composition a obtained from an emulsifying polymer Diglycol/Cyclohexanedimethanol/Isophthalates/Sulfoisoph thalates Copolymer and by high pressure homogenization.

PROCEDURE : For the formulations b and c according to the invention :

The aqueous phase (A) comprising all of its ingredients is heated to 85⁰C on a water bath. The fatty phase (Bl) comprising all of its ingredients is heated to 85⁰C on a water bath. Cooling is carried out to 5O⁰C and B2 is added to Bl. Cooling is continued to 25⁰C. Phase A is poured into phase B with stirring of rotor- stator type and the mixture is homogenized at 25⁰C for 10 minutes. Phase C is added and the mixture is homogenized.

For the formulation a outside the invention:

The aqueous phase (A) comprising all of its ingredients is heated to 85⁰C on a water bath. The fatty phase (Bl) comprising all of its ingredients is heated to 85⁰C on a water bath. Cooling is carried out to 5O⁰C and B2 is added to Bl. Cooling is continued to 25⁰C.

The preparation obtained is sent to a high pressure homogenizer (HPH) adjusted to 500 bar. Three successive passes are carried out, care being taken to cool the mixture between each pass. Phase D is added and the mixture is homogenized. The titanium dioxide of phase E is predispersed in the water of phase E. Phase E is added to the emulsion with stirring. Phase F is introduced so as to adjust the pH to the desired value.

Test of effectiveness in vitro:

The mean SPF of each formulation is measured according to the method of evaluation of the protection factor used is the in vitro method described by B. L. Diffey et al . in J. Soc. Cosmet . Chem. , 40, 127-133 (1989), which consists in determining the monochromatic protection factors every 5 nm in a wavelength range from 290 to 400 nm and in calculating, from these, the sun protection factor according to a given mathematical equation. Each composition tested is applied to ground quartz sheets at a dose of 0.75 mg/cm² with 4 sheets per test and 4 measurements per sheet. The spectrophotometric device used is an Optometries SPF 2900.

Results

The emulsions b and c according to the invention comprising the combination of the two diblock copolymers, obtained without a high pressure homogenizer (HPH) , are fine and homogeneous and exhibit a substantially higher SPF than that of the reference formulation a obtained with an HPH.

Example d: Photoprotective milk:

Phase A:

Distilled water 48.25% Glycerol 3%

Preservative 0.2%

Citric acid 0.27%

Copolymer of type (Ib) 75% hydrolysed

(25% of ethyl acrylate) with an MA content of 16.5% 18.18%

Phase B:

Parleam oil 12%

Cyclohexadimethylsiloxane 8%

Preservative 0.1%

Octocrylene 7%

Butyl Methoxydibenzoylmethane 3% Phase B is added with vigorous stirring to phase A comprising 60% of the water. The remaining water is added at the end of emulsification, by simple dilution.

A highly fluid and sprayable dispersion is obtained which is stable for at least 2 months and which has a droplet size equal to 3 μm. Its viscosity, measured with a Rheomat 180 at 25⁰C at a rotational speed of the 2 spindle of 200 rpm, is less than 0.018 Pa • s .

Claims

1. Oil-in-water cosmetic emulsion comprising, in a physiologically acceptable medium: a) at least one continuous aqueous phase,- b) at least one fatty phase dispersed in the said aqueous phase comprising at least one polar oil; c) at least one lipophilic organic UV screening agent; d) at least one (block A) - (block B) diblock copolymer in which:

- the block A comprises at least units derived from styrene;

2. Emulsion according to Claim 1, where the said diblock copolymer is linear.

3. Emulsion according to Claim 1 or 2 , where the 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. Emulsion according to any one of Claims 1 to 3 , where the copolymer is characterized in that:

- the block A comprises at least 90% by weight of units deriving from styrene, with respect to the total weight of the block A; - the block B is a random block comprising, with respect to the total weight of the block B: (i) from 34 to 95% by weight of units deriving from acrylic acid in the acid form or in the salified form; (ii) from 5 to 66% by weight of units deriving from Ci-C₄ alkyl acrylate;

- the proportion by weight of the block B with respect to the copolymer being greater than or equal to 50%.

5. Emulsion according to any one of Claims 1 to 4 , where the Ci-C₄ alkyl acrylate is ethyl acrylate.

6. Emulsion 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, 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 a hydrophilic ionic or nonionic comonomer, with respect to the total weight of the block A or of the block B comprising the said hydrophilic comonomer.

7. Emulsion according to Claim 6, where the hydrophilic comonomer is methacrylic acid in the acid or salified form.

8. Emulsion according to any one of Claims 1 to 7 , where the (block A) - (block B) diblock copolymer 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%.

9. Emulsion according to Claim 8, where the copolymer is of the type (Ia) in which the proportion by weight of the block B with respect to the copolymer is greater than or equal to 75% by weight and preferably between 75 and 85% by weight.

10. Emulsion according to Claim 8, where the copolymer is of the type (Ib) in which the proportion by weight of the block B is less than 75% and preferably between 50% and 75%.

11. Composition according to Claim 10, where the copolymer 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 87% and less than 94%.

12. Emulsion according to Claim 11, where 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%, in particular ranging from 94% to 97%.

13. Emulsion according to any one of Claims 8 to 13, comprising a blend of at least one diblock copolymer of the type (1) and of at least one diblock copolymer of the type (2) .

14. Emulsion according to Claim 14, comprising a blend of at least one diblock copolymer of the type (Ia) and of at least one diblock copolymer of the type (2b) (BOL 55) .

15. Emulsion according to any one of Claims 1 to 14, where the (block A) - (block B) diblock copolymer is capable of being obtained by a polymerization process comprising at least the following stages: stage I) : the following are prepared:

- a (block A) - (block B') diblock copolymer, or a triblock copolymer or star copolymer of (core) - [ (block A) - (block B¹J]_x or (core) - [ (block B ' ) - (block A) ] _x architecture where x is a mean number greater than or equal to 2, where

- the block A comprises units deriving from styrene, and - the block B' comprises units deriving from a Ci-C₄ alkyl acrylate, stage I'): optionally, for a triblock or star copolymer, the (core) - (block B') or (core) - (block A) bonds are cleaved, so as to obtain a (block A) - (block B') diblock copolymer, stage II) : the block B' is hydrolysed to give a block B, in order to obtain the (block A) - (block B) diblock copolymer, the hydrolysis bringing about, if appropriate, for a triblock or star copolymer, cleavage of the (core) - (block B') or (core) - (block A) bonds, so as to obtain a (block A) - (block B) diblock copolymer.

16. Emulsion according to any one of Claims 1 to 15, where the (block A) - (block B) diblock copolymer is capable of being obtained by a polymerization process comprising at least the following stages:

I) a (block A) - (block B') diblock copolymer is prepared by a process comprising the following intermediate stages Ia) and Ib) :

Ia) a first block A is prepared by bringing together :

- n_τ moles of a transfer agent comprising a single transfer group,

- n_A moles of styrene or of a mixture of monomers comprising at least 90% by weight of styrene and where n_A/n_T > 5 and preferably < 5000,

- and optionally a free radical initiator,

Ib) a second block B' is prepared, in order to obtain a (block A) - (block B') diblock copolymer, by bringing together:

- the block A obtained in the preceding stage, - n_B moles of a hydrolysable Ci-C₄ alkyl acrylate or of a mixture of monomers comprising at least 90% by weight of a Ci-C₄ alkyl acrylate, so that n_B/n_T > 5 and preferably < 5000,

- and optionally a free radical initiator,

II) the block B' is then hydrolysed at a degree T in moles of between 0.4 and 0.96, in order to obtain the said (block A) - (block B) diblock copolymer.

17. Emulsion according to Claim 15 or 16, characterized in that an additional stage III) of deactivation of transfer groups carried by macromolecular chains and/or of purification of the

(block A) - (block B) diblock copolymer and/or of destruction of hydrolysis by-products and/or of deactivation is carried out, during and/or after stage ID .

18. Emulsion according to any one of Claims 15 to 17, characterized in that stage I) is carried out by emulsion polymerization in water.

19. Emulsion according to any one of Claims 15 to 18, characterized in that the degree of hydrolysis T is between 0.7 and 0.8; preferably, T is equal to 0.75.

20. Emulsion according to any one of Claims 15 to 19, 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 to 5% by weight of a hydrophilic ionic or nonionic comonomer, with respect to the total weight of the block A, of the block B or of the block B' comprising the said hydrophilic comonomer.

21. Emulsion according to Claim 20, where the hydrophilic comonomer is methacrylic acid in the acid or salified form.

22. Emulsion according to one of Claims 15 to 21, characterized in that the Ci-C₄ alkyl acrylate is ethyl acrylate .

23. Emulsion according to one of Claims 15 to 22, characterized in that the (block A) - (block B) diblock copolymer 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 13 000 g/mol.

24. Composition according to Claim 23, characterized in that the (block A) - (block B) diblock copolymer is of the type (Ia) in which: - the proportion by weight of the block B with respect to the copolymer is greater than or equal to 75% by weight and preferably between 75 and 85% by weight and

- its theoretical average molecular weight is less than 8000 g/mol and preferably between 2000 and 8000 g/mol .

25. Composition according to Claim 24, characterized in that the (block A) - (block B) diblock copolymer is of the type (Ib) in which: - the proportion by weight of the block B with respect to the copolymer is less than 75% by weight and preferably between 50 and 75% by weight and

- its theoretical average molecular weight is greater than or equal to 8000 g/mol and preferably between 8000 and 13 000 g/mol.

26. Composition according to one of Claims 15 to 22, characterized in that the (block A) - (block B) diblock copolymer is of the type (2) in which: - the proportion by weight of the block B with respect to the copolymer is greater than or equal to 85% and

- its theoretical average molecular weight is greater than or equal to 13 000 g/mol.

27. Composition according to Claim 26, characterized in that the (block A) - (block B) diblock copolymer 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 87% and less than 94%,

- its theoretical average molecular weight is between 13 000 g/mol and 20 000 g/mol.

28. Composition according to Claim 26, characterized in that the (block A) - (block B) diblock 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%, in particular ranging from 94 to 97%, and - its theoretical average molecular weight is greater than or equal to 20 000 g/mol and preferably between 20 000 and 50 000 g/mol and more preferably between 25 000 and 50 000 g/mol and more preferably still between 28 000 and 40 000 g/mol.

29. Emulsion according to any one of Claims 23 to 28, comprising a blend of at least one diblock copolymer of the type (1) and of at least one diblock copolymer of the type (2) .

30. Emulsion according to Claim 29, comprising a blend of at least one diblock copolymer of the type (Ia) and of at least one diblock copolymer of the type (2b) .

31. Emulsion according to any one of Claims 1 to 30, where the diblock copolymer or copolymers are present in concentrations as active material ranging from 0.01 to 5% by weight and preferably from 0.05 to 2% by weight, with respect to the weight of the composition.

32. Emulsion according to any one of Claims 1 to 31, where the lipophilic organic UV screening agents are chosen from cinnamic derivatives; anthranilates ; salicylic derivatives; dibenzoylmethane derivatives; camphor derivatives; benzophenone derivatives; β,β- diphenylacrylate derivatives; triazine derivatives; benzotriazole derivatives; benzalmalonate derivatives; benzimidazole derivatives; imidazolines; bis-benzazolyl derivatives; p-aminobenzoic acid (PABA) derivatives; benzoxazole derivatives; screening polymers and screening silicones, such as those described; dimers derived from α-alkylstyrene,- and their mixtures.

33. Emulsion according to Claim 32, where the lipophilic organic UV screening agents are chosen from: Ethylhexyl Methoxycinnamate, Ethylhexyl Salicylate, Homosalate, Octocrylene,

Butyl Methoxydibenzoylmethane,

Phenylbenzimidazole Sulfonic Acid,

Disodium Phenyl Dibenzimidazole Tetrasulfonate, Benzophenone-3 , n-Hexyl 2- (4-diethylamino-2-hydroxybenzoyl) benzoate,

4-Methylbenzylidene camphor,

Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine,

Ethylhexyl Triazone, Diethylhexyl Butamido Triazone,

2 , 4 , 6-Tris (dineopentyl 4 ' -aminobenzalmalonate) -s- triazine,

2 , 4 , 6-Tris (diisobutyl 4 ' -aminobenzalmalonate) -s- triazine, Drometrizole Trisiloxane,

Polysilicone- 15 ,

1 , 1-Dicarboxy (2 , 2 ' -dimethylpropyl) -4 , 4-diphenylbuta- diene,

2,4-Bis [5-1 (dimethylpropyl) benzoxazol-2-yl (4 -phenyl) - imino] -6- (2 -ethylhexyl) imino-1, 3, 5 -triazine, and their mixtures.

34. Emulsion according to any one of Claims 1 to 33, where the lipophilic organic photoprotective agents are present in proportions ranging from 0.01 to 20% by weight, with respect to the total weight of the composition, and preferably ranging from 0.1 to 10% by weight, with respect to the total weight of the composition.

35. Emulsion according to any one of Claims 1 to 34, characterized in that it additionally comprises at least one insoluble inorganic UV screening agent and/or one insoluble organic UV screening agent.

36. Emulsion according to Claim 35, where the inorganic UV screening agents are metal oxide pigments.

37. Emulsion according to Claim 36, where the metal oxide pigments are chosen from titanium, zinc, iron, zirconium or cerium oxides or their mixtures.

38. Emulsion according to Claim 36 or 37, where the metal oxide pigments are coated or uncoated.

39. Emulsion according to any one of Claims 38 to 40, where the metal oxide pigments are metal oxide particles having a mean individual particle size of less than or equal to 500 nm.

40. Emulsion according to Claim 39, where the mean individual particle size is between 5 nm and 500 nm.

41. Emulsion according to Claim 40, where the mean individual particle size is between 10 nm and 100 nm.

42. Emulsion according to Claim 41, where the mean individual particle size is between 15 nm and 50 nm.

43. Emulsion according to any one of Claims 36 to 42, where the metal oxide pigments are chosen from coated or uncoated titanium oxide pigments.

44. Emulsion according to any one of Claims 1 to 43, where the inorganic UV screening agents represent from 0.5 to 40%, preferably from 1 to 30%, of the total weight of the composition.

45. Emulsion according to Claim 35, where the insoluble organic UV screening agent or agents are chosen from the polyvalent metal salts of sulphonated or carboxylated organic screening agents.

46. Emulsion according to Claim 45, where the insoluble UV screening agents are chosen from the polyvalent metal salts of sulphonated derivatives of benzylidenecamphor; the polyvalent metal salts of sulphonated derivatives of benzimidazole,- and the polyvalent metal salts of cinnamic acid derivatives.

47. Emulsion according to Claim 35, where the insoluble organic UV screening agent or agents are chosen from those of the oxalanilide, triazine, benzotriazole, vinyl amide, cinnamamide, benzazole, benzofuran, arylvinylene ketone, acrylonitrile amide, acrylonitrile sulphonamide, acrylonitrile carbamate or phenylenebis (benzoxazinone) type.

48. Emulsion according to Claim 47, where the insoluble organic UV screening agent or agents are chosen from 2 , 4 , 6-tris (biphenyl-4-yl) -1 , 3 , 5-triazine and 2 , 4 , 6-tris (terphenyl) -1 , 3 , 5-triazine .

49. Emulsion according to Claim 47, where the insoluble organic UV screening agent or agents are chosen from methylenebis (hydroxyphenylbenzotriazole) derivatives with the following structure:

in which R₈ and R₉, which are identical or different, each represent a Ci-Ci₈ alkyl radical which can be substituted by one or more radicals chosen from Ci-C₄ alkyl, C₅-Ci₂ cycloalkyl or aryl .

50. Emulsion according to Claim 49, where the insoluble organic UV screening agent is 2,2'- methylenebis [6- (2H-benzotriazol-2-yl) -4- (1,1,3, 3-tetra- methylbutyl) phenol] .

51. Emulsion according to any one of Claims 35 and 45 to 50, where the insoluble organic UV screening agent or agents are in the form of particles with a mean size ranging from 10 nm to 5 μm.

52. Emulsion according to Claim 51, where the mean size varies from 10 nm to 2 μm, in particular from 20 nm to 1.5 μm and more particularly from 30 nm to 1.0 μm .

53. Emulsion according to any one of Claims 35 and 45 to 52, where the insoluble organic UV screening agent or agents are capable of being obtained by a process for milling an insoluble organic UV screening agent in the form of large-size particles in the presence of a surfactant .

54. Emulsion according to Claim 53, where the surfactant is chosen from alkyl polyglucosides with the structure C_nH_2n+IO (C₆H_I0O₅) _XH in which n is an integer from 8 to 16 and x is the mean degree of polymerization of the (C₆HI₀O₅) unit and varies from 1.4 to 1.6.

55. Emulsion according to Claim 53 or 54, where the surfactant is used at a concentration ranging from 1 to

50% by weight and more preferably from 5 to 40% by weight, with respect to the insoluble screening agent.

56. Emulsion according to any one of Claims 35 and 45 to 55, where the insoluble organic UV screening agent or agents are present at a total concentration of between 0.1 and 25% by weight approximately and preferably between 0.2 and 20% by weight approximately, with respect to the total weight of the composition.

57. Emulsion according to any one of Claims 1 to 56, additionally comprising at least one additional hydrophilic organic photoprotective agent active in the UV-A and/or UV-B regions.

58. Emulsion according to Claim 57, where the hydrophilic photoprotective agent or agents are chosen from: Terephthalylidene Dicamphor Sulfonic Acid, Benzophenone-4 ,

Phenylbenzimidazole Sulfonic Acid,

Disodium Phenyl Dibenzimidazole Tetrasulfonate and their mixtures.

59. Emulsion according to Claim 57 or 58, where the hydrophilic photoprotective agent or agents are present in the compositions according to the invention in proportions ranging from 0.01 to 20% by weight, with respect to the total weight of the composition, and preferably ranging from 0.1 to 10% by weight, with respect to the total weight of the composition.

60. Emulsion according to any one of the preceding claims, where the polar oil or oils have an oil/water interfacial tension, measured at 25⁰C, of less than 35 mN.m^"1.

61. Emulsion according to any one of the preceding claims, where the polar oil or oils are preferably present in concentrations ranging from 3 to 50% by weight and preferably ranging from 5 to 40% by weight, with respect to the total weight of the composition.

62. Emulsion according to any one of the preceding claims, additionally comprising at least one self- tanning agent .

63. Emulsion according to any one of the preceding claims, additionally comprising at least one cosmetic adjuvant chosen from fatty substances other than the polar oils defined in the preceding claims, organic solvents, ionic or nonionic and hydrophilic or lipophilic thickeners, softening agents, humectants, opacifiers, stabilizing agents, emollients, silicones, antifoaming agents, fragrances, preservatives, anionic, cationic, nonionic, zwitterionic or amphoteric surfactants, active principles, fillers, polymers, propellants, basifying or acidifying agents or any other ingredient commonly used in the cosmetics and/or dermatological field.

64. Emulsion according to any one of the preceding claims, characterized in that it is fluid.

65. Use of an emulsion as defined in any one of the preceding claims in the manufacture of products for the cosmetic treatment of the skin, lips, nails, hair, eyelashes, eyebrows and/or scalp, in particular care products, sun protection products and makeup products.

66. Cosmetic use of at least one diblock copolymer as defined according to any one of the preceding claims in an oil-in-water emulsion, in particular a fluid oil-in- water emulsion, comprising, in a physiologically acceptable medium, a) at least one fatty phase comprising at least one polar oil, b) at least one lipophilic organic UV screening agent and c) optionally at least one insoluble inorganic UV screening agent and/or one insoluble organic UV screening agent, for the purpose of improving the cosmetic properties and/or of improving the stability of the said emulsion and/or for the purpose of increasing the sun protection factor (SPF) and/or of improving the persistence towards water of the photoprotective power.