DE69124976T2 - Stable emulsions from perfluoropolyethers and fatty substances and process for their preparation - Google Patents

Description

Stable emulsion of perfluoropolyethers and fatty substances and process for its preparation

The present invention relates to stable emulsions of perfluoropolyethers with perfluoroalkyl end groups and fatty substances.

It is known that perfluoropolyethers exhibit very high hydrophobicity and lipophobicity, which is why it was only possible to prepare stable aqueous emulsions thereof using special combinations of components of the same emulsions.

US-A-4 803 067 discloses stable emulsions of perfluoropolyethers with perfluoroalkyl end groups in oil/water/ emulsions or water/oil/emulsions obtained by using emulsifiers. These emulsions have been used in particular in lotions and creams for cosmetics and dermatology in view of the excellent properties of the perfluoropolyethers in these applications due to the partial formation of a water-repellent, oxygen-permeable and carbon dioxide-permeable protective film on the skin, which allows normal skin respiration.

EP-A-0 390 206 describes stable emulsions of perfluoropolyethers with perfluoroalkyl end groups in glycerin or other polyhydroxylated compounds, prepared using emulsifiers. In the preparation of the cosmetic or dermatological products, the above-mentioned emulsions are added to basic formulations containing other components.

Until now, it has not been possible to obtain stable emulsions of perfluoropolyethers with fatty substances, although the need for such emulsions of anhydrous or substantially anhydrous nature has been strongly felt in the cosmetic and dermatological fields or in industrial applications, these anhydrous or substantially anhydrous emulsions essentially retaining the hydrophobic nature of the anhydrous products into which they were to be introduced.

It has now been found that it is possible to obtain stable emulsions of perfluoropolyethers with perfluoroalkyl end groups (hereinafter referred to as perfluoropolyethers) and fatty substances, in the presence of a surfactant which is soluble in glycerol or in other polyhydroxylated compounds, if one or more fatty substances in liquid state are added with stirring to an emulsion of perfluoropolyether in glycerol or other polyhydroxylated compounds.

The existence of stable emulsions of perfluoropolyethers and fatty substances in glycerin or other polyhydroxylated compounds is very surprising since it is not possible to emulsify a fatty substance in glycerin or in another polyhydroxylated compound and it is not possible to emulsify a perfluoropolyether in a fatty substance. Surprisingly, it has been found that the presence of perfluoropolyether in an emulsion in glycerin or other polyhydroxylated compounds enables the emulsification of the fatty substances in the perfluoropolyether-glycerin system or in the perfluoropolyether-other polyhydroxylated compounds system.

It is therefore an object of the present invention to provide stable, anhydrous or substantially anhydrous emulsions of perfluoropolyethers and fatty substances.

A further object is to provide a process for producing such emulsions.

The first task is solved by a stable emulsion of a first dispersed phase consisting of perfluoropolyethers with perfluoroalkyl end groups and a second dispersed phase consisting of one or more fatty substances selected from:

a liquid product (oil) which is insoluble in water and in the polyhydroxylated compounds mentioned below and a product which is solid at room temperature (fat) insoluble in water and in the polyhydroxylated compounds is insoluble and has a melting temperature not exceeding 100ºC,

these two phases being dispersed in a continuous phase, characterized in that the continuous phase consists of one or more polyhydroxylated compounds selected from glycerol and polyalcohols other than glycerol and saccharides and containing at least three hydroxyl groups, the emulsion having the following weight composition:

(a) a perfluoropolyether or perfluoropolyethers: 1 - 50% by weight of the emulsion;

(b) polyhydroxylated compound or compounds: 10% or more by weight of the emulsion;

(c) Fatty substance or substances: 10 - 80% by weight of the emulsion and

(d) one or more emulsifiers which are soluble in the polyhydroxylated compound or compounds and are selected from

- sodium lauryl sulfate,

- Sulfosuccinate (sulfosuccinic acid hemiester),

- Cocoamphocarboxyglycinate,

- potassium cetyl phosphate,

- Sodium alkyl polyoxyethylene ether carboxylate,

- Benzalconium chloride,

- Alkylamidopropyl betaine,

- Cocoamidopropyl betaine:

0.1 - 10 wt.% of the emulsion;

and in that the emulsion optionally comprises up to 20% by weight of the total emulsion of water or an alcohol, wherein components (a), (b), (c) and (d) remain in their relative proportions.

Perfluoropolyethers with perfluoroalkyl end groups, i.e. without functional groups, are known compounds which, in addition to their preparation process, are described in various publications, including GB-A-1 104 482, US-A-3 242 218, 3 665 041, 3 715 378, 4 523 039, EP-A-148 482, 151 877 and 191 490 and WO/A-87/00538 and WC/A-87/02992. Some perfluoropolyethers are on the market available under the trade names FomblinR, GaldenR, KrytoxR and DemnumR.

Suitable perfluoropolyethers are those characterized by the presence of one or more repeating perfluorooxyalkylene units:

a) (CF₂-CF₂O)

b) (CF₂O)

c) (C₃F₆O) , simplified formula for

d) (CF₂O-CF₂-CF₂O)

e) (CF₂-CF₂-CF₂O)

where the Rf"' groups, identical or different, represent a fluorine atom or a perfluoroalkyl group preferably containing 1 to 3 carbon atoms.

Preferably, the perfluoropolyethers suitable for the present invention exhibit the following individual perfluorooxyalkylene units or the following combinations of perfluorooxyalkylene units:

I) (CF₂-CF₂-O) and (CF₂O) , these units are randomly distributed along the perfluoropolyether chain; or

where the units are statistically distributed along the chain or

where X is F or CF₃ and the units are randomly distributed along the chain; or

V) (CF₂-CF₂-CF₂O) ; or

VI) (CF₂-CF₂O); or

where the Rf"' groups are the same or different and represent a fluorine atom or a perfluoroalkyl group preferably containing 1 to 3 carbon atoms; or

VIII) (CF₂O-CF₂-CF₂O).

Perfluoropolyethers containing perfluorooxyethane rings are also suitable

wherein T, A, B and R are identical or different and are perfluorooxyalkyl, perfluoropolyoxyalkyl or perfluoroalkyl radicals which preferably contain 1 to 6 carbon atoms.

Examples of suitable perfluoropolyethers containing repeating polyfluorooxyalkylene units are those belonging to the following classes:

wherein: Rf and R'f, identical or different, are selected from the group consisting of CF₃, C₂F₅ and C₃F₇; the units C₃F₆O (oxytrifluoromethyltrifluoroethylene),

and CF₂O are randomly distributed along the chain;

a is an integer;

b and c represent integers or zero;

and if the sum (b+c) is not zero, the ratio a/(b+c) is in the range 5 to 40;

B) CF₃O-(C₂F₄O)d(CF₂O)e-CF₃

where the units C₂F₄O and CF₂O are statistically distributed along the chain; d and e are integers; the ratio d/e varies from 0.3 to 5;

C) CF₃O-(C₃F₆O)f(C₂F₄O)g-(CFXO)h-CF₃

wherein the units C₃F₆O, C₂F₄O and CFXO are statistically distributed along the chain;

X represents F or CF₃;

f, g and h represent integers;

the ratio f/(g+h) is in the range 1 to 50;

and the ratio g/h is in the range 1 to 10;

D) Rg³O-(CF₂CF₂CF₂O)jRg�sup4;g

where Rg³ and Rg⁴, the same or different, are -CF₃ or C₂F₅ and j is an integer.

The perfluoropolyethers suitable for use in the present invention generally have a number average molecular weight in the range 500 to 20,000 and more usually 1,000 to 10,000.

The polyhydroxylated compounds useful in the present invention are described in more detail in the applicant's cited EP-A-390 206.

If the polyhydroxylated compound is a solid, it is dissolved in water or in a hydrophilic solvent. It is advisable to use a minimum amount of water or hydrophilic solvent necessary to dissolve the compound.

Suitable hydrophilic solvents are, for example, glycerine, glycerin, lower alcohols, ethereal solvents and diglyme, also when mixed with water.

However, water should usually be used as a solvent.

Concentrated aqueous solutions (syrups) of polyalcohols and saccharides, which are commercially available, are suitable.

Usually the concentration of the solutions is in the range of 50% to 80% by weight.

Most preferred polyhydroxylated compounds are glycerin, diglycerin, triglycerin and tetraglycerin.

The oils and fats according to the present invention can be of vegetable, animal, hydrocarbon or synthetic nature. They are in particular fatty alcohols, -acids, -esters and -amides, silicone oils and hydrocarbon oils and fats.

The emulsifier should be soluble in the polyhydroxylated compound and is in particular of the ionic type. The emulsifier is selected from the following compounds:

- sodium lauryl sulfate,

- Sulfosuccinate (sulfosuccinic acid hemiester)

- Cocoamphocarboxyglycinate,

- potassium cetyl phosphate,

- Sodium alkyl polyoxyethylene ether carboxylate,

- Benzalconium chloride,

- Alkylamidopropyl betaine,

- Cocoamidopropyl betaine.

The emulsions according to the invention preferably have the following composition:

- a perfluoropolyether or perfluoropolyethers: 5 to 25% by weight;

- one or more polyhydroxylated compounds: 10 to 59% by weight;

- Fatty substances or substances: 35 to 80% by weight;

- Emulsifier or emulsifiers: 0.3 to 3 wt.%.

The most preferred emulsions contain 10 to 40 wt.% polyhydroxylated compound.

Usually, the emulsions contain only one perfluoropolyether and only one polyhydroxylated compound.

Depending on the nature and proportion of components, the emulsions according to the invention exhibit a very wide range of viscosities, which makes them suitable for a wide range of applications. The least viscous emulsions have, for example, a viscosity of 2000 cPs (centipoises) at 25°C, while the most viscous emulsions have, for example, a viscosity of 1,000,000 cPs or more.

The viscosity increases with the concentration of fatty substances and perfluoropolyethers and when use is made of more viscous polyhydroxylated compounds.

At the same concentration, the nature of the fatty substances also influences the viscosity.

The viscosity of the emulsions can, if desired, be reduced by adding water or alcohols. Suitable alcohols are, for example, alkyl alcohols with 1 to 4 carbon atoms and ethylene glycols with 2 to 4 carbon atoms.

The addition of water or alcohol generally reduces the stability of the emulsions, making it inadvisable to add more than about 20% of them, calculated on the total weight of the emulsion.

The minimum amount of water or alcohol to be added is, for example, 1%. When water or alcohol is added, the percentage of the other components is naturally reduced, although their reciprocal proportions remain unchanged.

The water- or alcohol-containing emulsions are suitable for those applications where a low or relatively low viscosity without high hydrophobicity is desired.

According to the present invention, stable emulsions are considered to be those which show no cause for phase separation phenomena after centrifugation at 4000 rpm for a period of 30 minutes and subsequent treatment in an oven at 50°C for one week.

The emulsions according to the invention can be prepared as follows: to an emulsion of one or more fluoropolyethers in one or more polyhydroxylated compounds containing one or more emulsifiers soluble in the polyhydroxylated compounds (such an emulsion is referred to briefly as "pre-emulsion"), one or more fatty substances in the liquid state are added with stirring.

The pre-emulsion is at a temperature that is not critical; in most cases this is room temperature.

If the fatty substance is a solid at room temperature, it is added to the pre-emulsion in the molten state or dissolved, for example, in a liquid fatty substance consistent with the present invention, for example, added to a hydrocarbon oil, if necessary with heating to promote dissolution.

If the fatty substance is added at a temperature above room temperature, it is advisable to preheat the pre-emulsion to a temperature close to or equal to the temperature of the fatty substance.

The preparation of the pre-emulsions is described in detail in EP-A-390 206, which has already been cited above.

Such emulsions are preferably prepared by adding the perfluoropolyether or perfluoropolyethers with stirring to a solution of one or more emulsifiers in one or more polyhydroxylated compounds.

At the end of the addition, it is advisable to stir at a lower speed, for example 30 to 120 minutes, to achieve the best homogenization.

It is believed that the external phase of the emulsions of the invention consists of the polyhydroxylated compound or compounds, while the perfluoropolyether or perfluoropolyethers and the fatty substance or substances constitute the internal dispersed phases. In fact, these emulsions are dilutable with glycerin and with water (without repeated mechanical stirring), but are not dilutable with perfluoropolyethers and fatty substances (unless mechanical stirring is used). The fact that the viscosity increases as the content of perfluoropolyethers or fatty substances increases also shows that these two types of components constitute the internal phase.

The emulsions according to the invention have a wide range of applications in cosmetics and dermatology and in the industrial sector.

The introduction of liposoluble substances into the oily phase (such as vitamins or sunscreens) or of glycerol-soluble substances allows cosmetic and dermatological preparations to be functionalized.

Among the cosmetic applications, the following should be mentioned, for example: protective creams, sunscreens, lip ointments and water-free cosmetics such as lipsticks and pencils.

Among the dermatological applications, for example, skin protection preparations and preparations for the slow release of medicinal substances should be mentioned.

Among the industrial applications, lubrication applications and water-repellent treatments of textiles and leather should be mentioned.

The anhydrous nature of the emulsions, or in any case the presence of small amounts of water therein, makes the cosmetic and dermatological products prepared with the emulsions more biologically stable. In fact, the products usually do not require the use of preservatives. The anhydrous nature of the emulsions also ensures a higher resistance of the products to the skin. A further advantage in the same field of application consists in the fact that the emulsions according to the invention require the presence of smaller amounts of surfactant than those contained in emulsions of perfluoropolyethers in water/oil or oil/water emulsions as described in the above-mentioned US-A-4 803 067.

The following examples are provided for illustrative purposes only and should not be construed as limiting the scope of the present invention.

Examples 1 to 33 illustrate various emulsions according to the present invention and conditions for their preparation. All compositions are given in weight percent.

The stability test is the one described above.

The perfluoropolyethers used have the structure and properties shown below: - FomblinR HC/25

n/m = 20 to 40

MW (number average molecular weight) = 3200.

- GaldenRD03

the same formula as the above product

n/m = 20 to 40

Average = 870

- FomblinR HC/R

the same formula as the above product

n/m = 20 to 40

Average = 6600

- DemnumR S-65

F(CF₂-CF₂-CF₂O)nCF₂CF�3;

Average = 4500

- FomblinR Z25

CF₃-(OCF₂CF₂)p(OCF₂)q-OCF₃

p/q = 0.6 to 0.7

Average = 9400

Unless otherwise indicated, the emulsions illustrated in the examples below were prepared as follows.

Vaseline oil was added to a pre-emulsion of FomblinR HC/25, glycerin and TexaponR N/40 (sodium lauryl sulfate (28% solution) manufactured by Henkel) at room temperature while stirring at 5000 to 6000 rpm using a Silverson L/2R turbo emulsifier.

The viscosity of the emulsions of the following examples was determined using a Brookfield digital viscometer, Model RTV-II, with 8 speeds, according to the manufacturer's instructions.

example 1

FomblinR HC/25 29%

Glycerine 59%

TexaponR N/40 2%

Vaseline oil 10%

Viscosity: 2000 cPs (5 rpm, impeller 29) at 25ºC.

Stable emulsion.

Example 2

FomblinR HC/25 20%

Glycerine 39%

TexaponR N/40 2%

Vaseline oil 39%

Viscosity: 50000 cPs (5 rpm, impeller 29) at 25ºC.

Stable emulsion.

Example 3

FomblinR HC/25 15%

Glycerine 29%

TexaponR N/40 2%

Vaseline oil 54%

Viscosity: 950000 cPs (1 rpm, impeller 29) at 25ºC.

Stable emulsion.

Example 4

FomblinR HC/25 10%

Glycerine 59%

TexaponR N/40 2%

Vaseline oil 29%

Viscosity: 3100 cPs (5 rpm, impeller 29) at 25ºC.

Stable emulsion.

Example 5

FomblinR HC/25 20%

Glycerine 39%

TexaponR N/40 2%

Silicone oil (350 cPs) 39%

Stable emulsion.

Example 6

FomblinR HC/25 20%

Glycerine 39%

TexaponR N/40 2%

Mixture of 50 % silicone oil and

50 % Vaseline oil 39 %

Stable emulsion.

Example 7

FomblinR HC/25 20%

Glycerine 39%

TexaponR N/40 2%

AbilR K4 (volatile silicone) 39%

Stable emulsion.

Example 8

FomblinR HC/25 20%

Glycerine 39%

TexaponR N/40 2%

Wheat germ oil 39%

Stable emulsion.

Example 9

FomblinR HC/25 20%

Glycerine 39%

TexaponR N/40 2%

Jojoba oil 39%

Stable emulsion.

Example 10

FomblinR HC/25 20%

Glycerine 39%

TexaponR N/40 2%

EutanolR G (2-octyldodecanol), manufactured by Henkel 39%

Stable emulsion.

Example 11

FomblinR HC/25 20%

Glycerine 39%

TexaponR N/40 2%

Mirytol (triglyceride of capric and caproic acids), manufactured by Henkel 39%

Stable emulsion.

Example 12

FomblinR HC/25 20%

Glycerine 39%

TexaponR N/40 2%

Octyl stearate (CetiolR 868, manufactured by Henkel) 39%

Stable emulsion.

Example 13

FomblinR HC/25 20%

Glycerine 39%

TexaponR N/40 2%

Olive oil 39%

Stable emulsion.

Example 14

FomblinR HC/25 20%

Glycerine 39%

TexaponR N/40 2%

Paraffin C10/C13 39%

Stable emulsion.

Example 15

FomblinR HC/25 20%

Glycerine 39%

TexaponR N/40 2%

viscous Vaseline 39%

The viscous Vaseline was introduced in a molten state at a temperature of about 55ºC into the pre-emulsion preheated to 45ºC.

Stable emulsion.

Example 16

FomblinR HC/25 20%

Glycerine 39%

TexaponR N/40 2%

viscous Vaseline 13%

Paraffin C10/C13 26%

The viscous Vaseline and the paraffin were premixed before introduction into the pre-emulsion.

Stable emulsion.

Example 17

FomblinR HC/25 20%

Glycerine 39%

TexaponR N/40 2%

Castor oil 39%

Stable emulsion.

Example 18

FomblinR HC/25 20%

Glycerine 39%

TexaponR N/40 2%

Linseed oil 39%

Stable emulsion.

Example 19

FomblinR HC/25 14%

Glycerine 27%

TexaponR N/40 2%

Vaseline oil 52%

Water 5%

Water was added last.

Stable emulsion.

Viscosity: 37500 cPs at 25ºC (5 rpm, paddle stirrer 21).

Example 20

FomblinR HC/25 13%

Glycerine 27%

TexaponR N/40 2%

Vaseline oil 43%

Water 10%

Stable emulsion.

Viscosity: 7000 cPs at 25ºC (15 rpm, paddle stirrer 21).

Example 21

FomblinR HC/25 12%

Glycerine 23%

TexaponR N/40 2%

Vaseline oil 43%

Water 20%

Stable emulsion.

Example 22

GaldenR D03 20%

Glycerine 39%

TexaponR N/40 2%

Vaseline oil 39%

Stable emulsion.

Example 23

FomblinR HC/R 20%

Glycerine 39%

TexaponR N/40 2%

Vaseline oil 39%

Stable emulsion.

Example 24

DemnumR S/65 20 %

Glycerine 39%

TexaponR N/40 2%

Vaseline oil 39%

Stable emulsion.

Example 25

FomblinR Z 25 20 %

Glycerine 39%

TexaponR N/40 2%

Vaseline oil 39%

Stable emulsion.

Example 26

FomblinR HC/25 20%

Glycerine 39%

Cocoamidopropyl betaine 2%

Vaseline oil 39%

Stable emulsion.

Example 27

FomblinR HC/25 20%

Glycerine 39%

Benzalconium chloride (solution at 50% in water) 2%

Vaseline oil 39%

Stable emulsion.

Example 28

FomblinR HC/25 20%

Diglycerine 39%

TexaponR N/40 2%

Vaseline oil 39%

Highly viscous, stable emulsion.

Viscosity: 1,000,000 cPs (5 rpm, paddle 29) at 25ºC

Example 29

FomblinR HC/25 20%

Sorbitol (70% in water) 39%

TexaponR N/40 2%

Vaseline oil 39%

Stable emulsion.

Example 30

FomblinR HC/25 8%

Glycerine 27%

Diglycerine 8%

Vaseline oil 55%

TexaponR N/40 2%

Stable emulsion.

Viscosity: 180000 cPs (1 rpm, impeller 4) at 20ºC.

Example 31

FomblinR HC/25 5%

Glycerine 30%

AmphisolR K (*) 2 %

CetiolR 868 (**) 53 %

AbilR K4 (***) 10 %

(*) Potassium cetyl phosphate, manufactured by Givaudan

(**) Octyl stearate, manufactured by Henkel

(***) volatile silicone, manufactured by Tego Cosmetics

Viscosity: 340000 cPs at 20ºC.

Stable emulsion

Example 32

FomblinR HC/25 10%

Glycerine 20%

AmphisolR K 3%

CetiolR 868 63 %

AbilR K4 4%

This preparation was carried out under hot conditions by preheating the pre-emulsion to about 50ºC, since the viscosity increase that occurs at high oil concentrations makes it difficult to maintain under cold conditions.

Viscosity: 500000 cPs at 2000.

Stable emulsion.

Example 33

Examples 33 to 36 illustrate, for comparative purposes, compositions which are not according to the invention.

Glycerine 50%

Vaseline oil 49%

TexaponR N/40 1%

The emulsion was completely unstable, with rapid separation at rest.

Example 34

FomblinR HC/25 20%

Vaseline oil 79%

TexaponR N/40 1%

The emulsion was completely unstable, with rapid separation from Fomblin HC/25 at rest.

Example 35

FomblinR HC/25 50 %

Vaseline oil 49%

TexaponR N/40 1%

Stability: as in example 35.

Example 36

FomblinR HC/25 30%

Vaseline oil 67%

ArlacelR 989 (*) 3 %

(*) ethoxylated fatty acid manufactured by I.C.I.

Stability: as in example 34.

Example 37

This example explains a protective cream and its production:

A) Glycerine 20%

FomblinR HC/R 10%

Potassium cetyl phosphate (AmphisolR K, manufactured by Givaudan) 2%

B) Mineral oil 48 %

Dimethicone 20%

To pre-emulsion A, preheated to about 55ºC, phase B was gradually added with stirring. Stirring was then carried out less intensively until room temperature was reached.

The cream viscosity was 290,000 cPs (1 rpm, blade 6) at 20ºC.

Example 38

This example illustrates a vitamin moisturizer prepared according to the conditions of Example 37 :

A) Glycerine 30%

FomblinR HC/25 10%

Potassium cetyl phosphate 2%

B) Octyldodecanol (EutanolR G, manufactured by Henkel) 50.5%

Cyclomethicone (AbilR K4, manufactured by Tego Cosmetics) 5%

Tocopherol acetate 2%

Retinyl palmitate 0.5%

The cream viscosity was 180,000 cPs (1 rpm, blade 6) at 20ºC.

Example 39

Another vitamin moisturizer, similar to the previous one, was prepared except that 1% glycolic chamomile extract was added.

The presence of this small amount of glycol was sufficient to increase the viscosity from 180,000 cPs to 50,000 cPs.

Example 40

This example concerns a sunscreen prepared according to Example 38, with the difference that phase B was preheated:

A) Glycerine 30%

FomblinR HC/R 10%

Potassium cetyl phosphate 2%

B) Octyl stearate 46%

Ethylhexyl p-methoxycinnamate (Parisol MCX, manufactured by Givaudan) 5%

Cyclomethicone 5%

"Shea Butter" 2%

The cream viscosity was 480000 cPs (1 rpm, Paddle stirrer 6) at 20ºC.

Claims (11)

1. Stable emulsion of a first dispersed phase, consisting of perfluoropolyethers with perfluoroalkyl end groups and a second dispersed phase consisting of one or more fatty substances selected from: a liquid product (oil) which is insoluble in water and in the polyhydroxylated compounds mentioned below and a product which is solid at room temperature (fat), insoluble in water and in the polyhydroxylated compounds and has a melting point of not more than 100ºC, these two phases being dispersed in a continuous phase, characterized in that the continuous phase consists of one or more polyhydroxylated compounds selected from glycerol and polyalcohols other than glycerol and saccharides and containing at least three hydroxyl groups, the emulsion having the following weight composition: (a) the perfluoropolyether or perfluoropolyethers: 1 - 50% by weight of the emulsion; (b) polyhydroxylated compound or compounds: 10% or more by weight of the emulsion; (c) Fatty substance or substances: 10 - 80% by weight of the emulsion and (d) one or more emulsifiers which are soluble in the polyhydroxylated compound or compounds and are selected from - sodium lauryl sulfate, - Sulfosuccinate (sulfosuccinic acid hemiester) - Cocoamphocarboxyglycinate, - potassium cetyl phosphate, - Sodium alkyl polyoxyethylene ether carboxylate, - Benzalconium chloride, - Alkylamidopropyl betaine, - Cocoamidopropyl betaine: 0.1 - 10 wt.% of the emulsion; and in that the emulsion optionally comprises up to 20% by weight of the total emulsion of water or an alcohol, wherein components (a), (b), (c) and (d) remain in their relative proportions. 2. A stable emulsion according to claim 1, wherein, when the polyhydroxylated compounds are solid, the polyhydroxylated compounds are dissolved in water or in a hydrophilic solvent selected from glycols, glycerin, lower alcohols, ethereal solvents, diglymene and mixtures thereof with water, such that the concentration of the polyhydroxylated compound is 50 to 80% by weight of the solution. 3. Stable emulsions according to claim 1 or 2, characterized in that the perfluoropolyether or perfluoropolyethers have a number-average molecular weight in the range from 500 to 20,000. 4. Stable emulsions according to claim 1, 2 or 3, characterized in that the polyhydroxylated compounds are selected from glycerin, diglycerin, triglycerin and tetraglycerin. 5. Stable emulsions according to one or more of the preceding claims, characterized in that the fatty substances are selected from the group consisting of fatty alcohols, acids, esters and amides, silicone oils and hydrocarbon oils and fats. 6. Stable emulsions according to one or more of the preceding claims, characterized in that the emulsifiers are of the ionic type. 7. Stable emulsions according to one or more of the preceding claims, consisting of: - one or more perfluoropolyethers with perfluoroalkyl end groups: 5 to 25% by weight, - one or more polyhydroxylated compounds: 10 - 59 %, - one or more fatty substances: 35 - 80 %, - one or more emulsifiers: 0.3-3%. 8. Stable emulsions according to claim 7, which contain 10 to 40 wt.% of one or more polyhydroxylated compounds. 9. Process for the preparation of the stable emulsions according to claims 1 to 8, characterized in that one or more fatty substances in the liquid state are added with stirring to the pre-emulsion of one or more perfluoropolyethers in one or more polyhydroxylated compounds containing one or more emulsifiers soluble in these compounds. 10. Process according to claim 9, characterized in that, if the fatty substance is solid at room temperature, it is added to the pre-emulsion in the molten state or dissolved in a liquid fatty substance. 11. Use of the stable emulsions according to claims 1 to 8 for the preparation of cosmetic and dermatological products.