WO2005116112A1

WO2005116112A1 - Cystine-based polycondensate

Info

Publication number: WO2005116112A1
Application number: PCT/EP2005/003698
Authority: WO
Inventors: Sabine Kainz; Ursula Huchel; Olaf Lammerschop; Andre HÄTZELT; Ina KRÜGERMANN
Original assignee: Henkel Kommanditgesellschaft Auf Aktien
Priority date: 2004-05-18
Filing date: 2005-04-08
Publication date: 2005-12-08
Also published as: EP1749045A1; DE102004024505A1

Abstract

The invention relates to a method for production of a polycondensate, in which cystine or a salt thereof is reacted with an activated dicarboxylic acid of formula (I): X-C(O)-A-C(O)-Y, in a molar ratio of 10:1 to 1:10, whereby in formula (I), A is a bond or a divalent saturated or singly or multiply unsaturated aliphatic or aromatic hydrocarbon group with 1 to 20 carbon atoms, which can be substituted with one or several halo, hydroxy or free or derivatised carboxyl groups and whereby the shortest bonding between the two carbonyl groups adjacent to group A is made up of up to 12 carbon atoms, X is a halogen, a 1-imidazolyl group, an acyloxy group, R-C(O)-O- or scuh a group as is suitable for activcation of a carboxyl group HO-C(O)-A-, Y is the same as X, where X and Y may be the same or different, the salt is preferably an alkali metal, earth alkali metal or ammonium salt, whereby in the cation the last 1 to 4 hydrogen atoms can be substituted by alkyl groups with 1-4C atoms. The invention further relates to the polycondensate itself, the use thereof for the restructuring of keratin fibres and cosmetic agents for hair treatment comprising such a polycondensate.

Description

Cvstin-based polycondensate

The invention relates to a method for producing a polycondensate from cystine or a salt thereof and an activated dicarboxylic acid. The invention further relates to the polycondensate itself, its use for restructuring keratin fibers, and cosmetic agents for hair treatment which contain such a polycondensate.

Keratin fibers, especially hair, are an important part of everyday life as an integral part of the human body and as an essential part of human clothing and home textiles. The treatment with washing, cleaning, styling and coloring products for cleaning and design purposes, as well as their exposure to environmental influences such as ozone, salt and chlorine water, IR, UV and heat radiation (blow-drying) lead to over time cumulative damage to the fibers and thus to a reduction in their quality. For example, both cleaning hair with shampoos and decorating the hairstyle by dyeing or perming are interventions that influence the natural structure and properties of the hair. Consequently, after such a treatment, for example, the wet and dry combability, hold, fullness, shine and tactility of the hair can be unsatisfactory. In the case of colored hair, the hold of the color on the hair can continue to be unsatisfactory, particularly with frequent shampooing, so that there is a gradual bleeding of the color.

Not least because of the heavy stress on the hair, for example through dyeing or perming, as well as through cleaning the hair with shampoos and through environmental pollution, the importance of care products with a sufficiently strong and long-lasting effect increases. Care products of this type influence the natural structure and properties of the hair. After such treatments, for example, the wet and dry combability of the hair, the hold and the fullness of the hair can be improved or the hair can be protected from an increased split rate.

It has therefore long been customary to subject the hair to a special after-treatment. The hair, usually in the form of a rinse, is treated with special active ingredients, for example quaternary ammonium salts or special polymers. Depending on the formulation, this treatment improves the combability, hold and fullness of the hair and reduces the split rate. The active substances available both for separate aftertreatment agents and for combination preparations generally act preferentially on the hair surface. Hair care products are known which give the hair shine, hold, fullness or better wet or dry combability or prevent split ends. However, just as important as the external appearance of the hair is the internal structural cohesion of the hair fibers, which can be greatly influenced in particular in oxidative and reductive processes such as coloring and perms.

Keratinic fibers are particularly exposed to deformation processes such as hair perms. A negative side effect of permanent hair waving is often embrittlement and dulling of the hair. Furthermore, in many cases, other properties such as wet and dry combability, grip, smoothness, softness, gloss and tear resistance are also influenced in an undesirable manner.

Nourishing additives and film formers are often added to the permanent waving agent without, however, significantly improving the hair structure. For this purpose, high-molecular polymers are used, for example, which attach to the top layer of skin and hair and there produce an external, subjectively perceptibly improved grip on the hair. The structural damage to the interior of the hair, which is caused by the reduction process in the case of perms, cannot be reduced, however, because the substances cannot penetrate the hair due to their size.

EP 723 772 describes that alkalizing agents such as basic amino acids together with cationic polymers in the waving agent cause the hair to swell more. On the one hand it leads to stronger shaping and longer durability of the perm, but on the other hand it also leads to hair damage.

The published patent application GB 216 041 9 describes a method in which hair is first treated with a reducing agent which is then rinsed out. Then an aqueous protein hydrolyzate, preferably with a molecular weight greater than 50,000 daltons, is applied to the areas to be treated, after which the Neutralization takes place. Subjectively, the area treated in this way felt better, but there was no reduction in hair damage inside.

The object of the present invention was to provide an improved active substance for the restructuring of keratin fibers, which has advantages over the prior art. In particular, the active ingredient should be technically easily and inexpensively accessible and have an improved fiber-reinforcing effect. It should, for example, be advantageously applicable in the context of conventional permanent wave treatments and should be able to reduce the damage to the hair fibers associated therewith.

This object is achieved by providing a polycondensate which can be obtained by a process in which free or in the form of one of its salts cystine is reacted with an activated dicarboxylic acid.

The invention thus firstly relates to a process for the preparation of a polycondensate, in which cystine or a salt thereof with an activated dicarboxylic acid of the formula (I)

X-C (O) -A-C (O) -Y (I)

is reacted in a molar ratio of 10: 1 to 1:10, wherein in formula (I) A denotes a bond or a divalent saturated or mono- or polyunsaturated aliphatic or aromatic hydrocarbon radical having 1 to 20 carbon atoms, which means with one or can be substituted by several halogen, hydroxyl or free or de-dated carboxy groups and the shortest connection between the two carbonyl groups adjacent to group A consists of up to 12 carbon atoms,

X represents a halogen atom, a 1-imidazolyl group, an acyloxy group R-C (O) -O- or another group which is suitable for activating a carboxyl group HO-C (O) -A-, and

Y has the same meanings as X, where X and Y can be the same or different.

Because of its amphoteric character, cystine can form salts with both acids and bases. In the process according to the invention, salts are suitable which are formed from cystine by the action of bases, for example alkali or alkaline earth metal hydroxides or ammonia and amines. Accordingly, alkali metal, alkaline earth metal and ammonium salts of cystine are particularly suitable according to the invention, it being possible for 1 to 4 hydrogen atoms in the cation of the latter to be substituted by alkyl radicals having 1 to 4 carbon atoms. According to the invention, the lithium, sodium, potassium, cesium, calcium and triethylammonium salts of cystine are preferred.

In formula (I), X and Y are preferably selected from chlorine, bromine and the acetoxy group. In a particular embodiment of the invention, X and Y together represent an oxygen bridge linking the carbon atoms of the carbonyl carbon atoms. In this case, the activated dicarboxylic acid of the formula (I) is an acid anhydride.

It is further preferred if A in formula (I) is a divalent saturated aliphatic hydrocarbon radical having 2 to 6 carbon atoms and in particular the ethane-1,2-diyl radical.

In the event that A is a hydrocarbon radical which is substituted by one or more derivatized carboxy groups, derivatization is preferably understood to be an esterification with an alcohol having 1 to 4 carbon atoms.

In the process according to the invention, the reaction of the cystine or one of its salts with an activated dicarboxylic acid of the formula (I) is preferably carried out in a molar ratio of 2: 1 to 1: 2, in particular 1: 1 to 1: 1, 2.

For the purposes of the invention, it is further preferred if the reaction is carried out as interfacial condensation in a reaction mixture which comprises two liquid phases which are essentially immiscible with one another.

In this embodiment, it is particularly preferred if, in addition to an aqueous phase, there is an essentially immiscible organic phase which comprises at least one solvent which is selected from methylene chloride, chloroform, ethyl acetate, toluene, alkanes with 5 to 8 carbon atoms, in particular n-octane, and ethers with 5 to 16 carbon atoms, especially methyl tert-butyl ether. Depending on the solvent used, the organic phase can be lighter or heavier than the aqueous phase.

So that when using an aqueous phase the cystine can dissolve sufficiently and at the same time a sufficient amount of free amino groups are available for reaction with the activated dicarboxylic acid of formula (I), it is expedient if the aqueous phase is alkaline.

In one embodiment of the invention, the aqueous phase is kept in a pH range between 8 and 14, in particular between 10 and 13, during the entire reaction by continuously adding a base. Suitable bases are, for example, aqueous solutions of alkali or alkaline earth metal hydroxides or ammonia, preferably sodium hydroxide solution or potassium hydroxide solution.

The process according to the invention is carried out particularly advantageously such that the reaction takes place with the introduction of shear energy, in particular with intensive stirring.

In a further preferred embodiment of the invention, the reaction is carried out at a temperature of from 0 to 50 ° C., but in particular from 2 to 20 ° C. Of course, the reaction temperature should be chosen so that the solvent used is in the liquid state.

When using methylene chloride as solvent, it has proven particularly useful to carry out the process in such a way that cystine or a salt thereof is initially introduced in dissolved form, and then an activated dicarboxylic acid of the formula (I), dissolved in methylene chloride, is metered in.

When using methyl tert-butyl ether as solvent, it has proven particularly useful to carry out the process in such a way that an activated dicarboxylic acid of the formula (I), dissolved in methyl tert-butyl ether, is initially introduced, and then cystine or a salt thereof is added in dissolved form. The cystine or a salt thereof is presented, for example, in the form of a 1 to 30% by weight solution, but in particular a 15 to 25% by weight solution, based on the total weight of the solution.

When the process according to the invention is carried out, solids can separate out during the reaction and form, for example, at the interface between the aqueous and organic phases.

The reaction mixture is worked up in the event that the process according to the invention has been carried out in a two-phase system with an aqueous and organic phase, preferably in such a way that any solid which may have formed is first separated off in a suitable manner, e.g. by filtration or centrifugation. The organic phase is then separated off. To improve the yield, the organic phase can be washed with water, which is preferably made alkaline. The aqueous phase from the reaction is then optionally combined with the wash water and, if appropriate, with the previously separated solid and then largely or completely freed from the water. This is done in a manner known per se, for example by evaporation under reduced pressure or by freeze-drying (lyophilization).

The remaining residue is the polycondensate according to the invention.

In a further embodiment of the invention, the reaction of cystine or its salt with an activated dicarboxylic acid of the formula (I) takes place in the melt. For this purpose, for example, the reactants are initially introduced in solid form and the mixture is then heated, with stirring, to a temperature at which the reactants are in liquid form. The temperature naturally depends on the type of reactants chosen. However, heating to 150 to 200 ° C is usually sufficient. It is of course also possible to initially only provide one reaction partner, convert it into the molten state and meter in the second reaction component in the solid or likewise molten state. The reaction mixture is kept in the molten state with stirring for some time, usually 1 to 5 hours, and then cooled and worked up. Another object of the invention is a polycondensate which can be obtained by a process as described above.

It has now been found that the polycondensate according to the invention is outstandingly suitable for restructuring keratin fibers.

In principle, all animal hair such as e.g. Wool, horsehair, angora hair, furs, feathers and silk and products or textiles made from them can be used. However, the method according to the invention is preferably suitable for shaping human hair and wigs made therefrom. Because of the gentle process conditions, it is particularly suitable for deforming the hair on the living body, e.g. in connection with the production of permed hair or the straightening of curly hair.

Surprisingly, it has now been found that the inner and outer structure of keratinic fibers can be changed in an advantageous manner by using the polycondensate according to the invention, i.e. in other words, a restructuring of keratin fibers is made possible. Restructuring in the sense of the present invention means in particular a fiber reinforcement, an increase in tear strength and / or a reduction in the damage to keratin fibers caused by the most varied of influences. Here, for example, the restoration of natural strength plays an important role. Restructured fibers can be characterized, for example, by an increased tensile strength, an increased strength, an increased elasticity and / or an increased volume, which can be shown in greater abundance, for example, in a hairstyle. Furthermore, they can have an improved gloss, an improved grip and / or easier combability.

The polycondensate according to the invention is suitable for strengthening, protecting and repairing keratin fibers and very particularly for improving the hair structure and / or strengthening human hair. In particular, fiber properties such as strength, elasticity or volume are positively influenced in the sense of an increase in these properties. The polycondensate is also suitable for styling purposes, such as shaping and maintaining shape, and for increasing the color fastness, in particular the wash fastness of colored keratin fibers, in particular colored human hair. Under washing fastness, the preservation of color is one to understand dyed keratin fiber with regard to color shade and / or color intensity if the dyed fiber is exposed to the influence of aqueous agents, in particular surfactant-containing agents such as shampoos. The polycondensate according to the invention is also suitable for protecting fibers from the damaging influence of light.

The invention thus also relates to the use of a polycondensate according to the invention for restructuring keratin fibers.

In the context of this use according to the invention, a polycondensate according to the invention is brought into contact with a keratinic fiber. This is preferably done in the form of a preparation which can be obtained by adding the polycondensate according to the invention to a conventional hair treatment composition.

The invention therefore furthermore relates to a cosmetic agent for hair treatment, comprising a polycondensate according to the invention in a physiologically compatible carrier.

The polycondensate according to the invention is a mixture of substances which, in addition to polymeric constituents, can also contain cystine and / or the dicarboxylic acid used, preferably succinic acid and salts. The content of cystine and / or dicarboxylic acid can be influenced via the quantitative ratio of the starting materials used in the production of the polycondensate and via the manner in which the reaction product is worked up.

If the polycondensate according to the invention is used for restructuring keratin fibers, it can a) preferably 30 to 60% by weight, but in particular 35 to 50% by weight of polymeric constituents, b) preferably 0.5 to 7% by weight, but especially 2 to 4 wt .-% cystine and c) preferably contain 2 to 20 wt .-%, but especially 3 to 10 wt .-% succinic acid, each based on the total weight of the polycondensate. The amounts given for the polymeric constituents relate to values which were determined by means of GPC based on a polyethylene glycol standard. Furthermore, that can Polycondensate salts contain, for example, chlorides in an amount of 10 to 20 wt .-% Cl, based on the total weight of the polycondensate.

A product is known from US Pat. No. 5,646,239 which is formed by reacting a cystine ester with a dicarboxylic acid halide and subsequent saponification of the ester groups. The inventors of the present invention have found that this product known from the US document differs from the polycondensate which can be obtained from cystine and the otherwise identical dicarboxylic acid halide by the process of the present invention. This could be shown, for example, by the fact that both substances show different effects when examining their cosmetic effects on hair. For example, a clearly superior restructuring and hair-strengthening effect was observed for the polycondensate obtainable according to the present invention when used on damaged hair.

The following examples are intended to explain the invention in more detail.

Examples

Unless stated otherwise, all percentages are to be understood as% by weight and all amounts are as parts by weight.

Synthesis Examples 1 to 4: Production of polycondensates from cystine and succinic acid dichloride by interfacial condensation

Synthesis example 1

0.5 mol succinic acid dichloride was dissolved in 1 I dichloromethane. 0.5 mol of cystine was dissolved in 1 I 2N NaOH and cooled with ice water. The two solutions were combined and dispersed with vigorous stirring. After a short time, a solid started to precipitate at the interface. After about 1 hour the succinic acid dichloride had reacted and the reaction was complete. The solid was then filtered off and washed with ice-cold water and with dichloromethane. Yield: 86 g of a yellowish solid.

Synthesis example 2

Succinic dichloride (0.07 mol) was dissolved in 50 ml dichloromethane. Cystine (0.05 mol) was dissolved in 100 ml of 1N NaOH, placed in the reaction vessel and cooled with ice water. The two solutions were combined and dispersed with vigorous stirring. After a short time, a solid started to precipitate at the interface. As soon as the acid chloride had reacted, the reaction was stopped. The precipitated solid was filtered off, washed with ice-cold water and with dichloromethane and dried in vacuo. Yield 8.2 g of a slightly yellowish powder. The product obtained contained cystine.

Synthesis example 3

Succinic dichloride (0.05 mol) was dissolved in 50 ml dichloromethane. Cystine (0.05 mol) was dissolved in 100 ml of 2N NaOH, placed in the reaction vessel and cooled with ice water. The two solutions were added together and dispersed with vigorous stirring. The formation of a solid was observed at the interface. After the reaction was complete, the solid was isolated and the organic phase was separated from the aqueous phase. Then the aqueous phase with the solid united and freeze-dried. Yield: 15.3 g of beige-yellow powder. The product obtained contained cystine and succinic acid.

Synthesis example 4

A solution of 0.5 mol of succinic acid dichloride in 500 ml of methylene chloride, which was pre-cooled to 0 ° C, was added with vigorous stirring to a temperature of 20 ° C did not exceed. After 1 h, the solid formed during the reaction was removed by filtration, phase separation was carried out and the organic phase was discarded. The aqueous phase was then combined with the previously filtered solid and lyophilized, giving 147 g of a beige-yellow lyophilizate, which is the polycondensate according to the invention.

Synthesis Example 5: Preparation of a polycondensate from cystine and succinic anhydride by interfacial condensation:

0.05 mol L-cystine was dissolved in 100 ml 2N NaOH and cooled with ice water. A solution of 0.05 mol of succinic anhydride in 500 ml of chloroform was added with vigorous stirring, the temperature being kept constantly below 10 ° C. After the addition had ended, the mixture was stirred at below 10 ° C. for 2 hours and then the reaction mixture was warmed to room temperature. The organic and aqueous phases were separated and the aqueous phase was neutralized with concentrated hydrochloric acid, a solid precipitating out. The precipitate was filtered off and then freeze-dried. The remaining filtrate was also freeze-dried, whereby further solid was obtained.

Synthesis example 6: Production of a polycondensate from cystine and succinic anhydride by reaction in the melt:

0.05 mol of L-cystine and 0.05 mol of succinic anhydride were charged to a reaction vessel and heated under anhydrous conditions in a nitrogen atmosphere with vigorous stirring at 185 ^C C (oil bath temperature). The reaction mixture was stirred at the temperature reached for about 3.5 hours and then cooled to room temperature. A solid reaction mixture was obtained, which was dissolved in 75 ml of 2N NaOH, mixed with 5 g of activated carbon and heated under reflux for about 1 hour. The mixture was then filtered, the filtrate neutralized with concentrated hydrochloric acid until a light brown solid began to precipitate, and finally the filtrate was freeze-dried. Comparative Synthesis Example 7: Preparation of a polymer by polycondensation of cystine dimethyl ester hydrochloride and succinic acid dichloride and subsequent ester hydrolysis:

The synthesis was carried out in accordance with US Pat. No. 5,646,239, a polymeric ester initially being obtained (corresponding to US Pat. No. 5,646,239, Example 2), which was then saponified (corresponding to US Pat. No. 5,646,239, Example 3).

Application examples: tear-elongation tests on hair

To clarify the effects according to the invention, those according to the

Substances obtained in the course of a cold wave process were investigated

(Hair type: Natural dark brown code # 6634 from Alkinco). The remained

Exposure times in the permanent wave process unchanged. The treatment temperature was

32 ° C.

1. Measuring equipment

To demonstrate the effects according to the invention, tension values, gradients, elastic modulus, elongation at break and tensile strength at break of the wet hair were determined with the aid of a tension-stretching device from Dia-Stron (MTT 670). The hair cross-sectional area of the wet individual hair was determined by means of contactless projection measurement using laser technology known in the prior art. A universal dimension meter of the type UMD5000A from Zimmer was used for this.

2. Statistical evaluation

The t-test, a statistical evaluation with which the series of measurements are compared on both sides, in pairs, gives percentage probabilities with which the series of measurements are differentiated (distinction 90-95%: series of measurements tend to be different,> 95%: series of measurements significantly differentiated ).

3. Investigation of the restructuring effect

3.1 hair treatment

40 individual hairs were divided into two parts. One part was damaged by two cold waves, the other part was treated with two cold waves, in the preparation of which the reducing agent contained about 2 minutes before application to the hair Synthesis example 1 was added. All 80 individual hairs were subjected to a hair cross-sectional area determination in the wet state before the tear curves were determined.

3.2 Treatment steps

The following treatment steps were used in the following experiments. a) 30 min application of a cold wave (7% TGA = thioglycolic acid, 0.3% Turpinal SL = 1-hydroxyethane-1, 1-diphosphonic acid, 3.5% (NH ₄ ) ₂ CO ₃ , pH 8.4) ,

The hair was then rinsed with water for 5 minutes. b) 10 min application of fixation (2% H ₂ O ₂ , 1% Turpinal SL, pH 4.0). The hair was then rinsed with water for 5 minutes. c) At least 24h storage of the hair at RT (approx. 20 ° C) d) Measurement of the hair cross-sections of the wet individual hair. e) Determination of the tear values of the wet individual hair. f) 30 minutes application of a cold wave (12% ammonium thioglycolate, 5% NH ₄ HCO ₃ , 0.5% NH ₃ , 1% Cremophor RH 40, 1% Lamepon S, 0.5% perfume).

The hair is then rinsed with water for 5 minutes. g) 10 minutes application of a fixation diluted 1: 1 with water before use (5% H ₂ O ₂ , 0.2% NH ₃ , 1, 7% Turpinal SL, 6% Texapon NSO UP (sodium lauryl ether sulfate), water fully desalinated to 100 %).

The hair is then rinsed with water for 5 minutes.

3.3 Results damage potential of a cold wave (comparison): Reference example: untreated, i.e. healthy and undamaged hair. Comparative example: double permanent wave, i.e. damaged hair as described under 3.2: steps a), b), c); Repetition of steps a), b), c); then d) and e).

The influence of the perm on hair was examined by means of tensile strain measurement when wet.

untreated

Double corrugated

t-test. two-sided, in pairs

untreated

Double corrugated

t-test. two-sided, in pairs

The damage to the hair by the permanent wave method is clearly evident in the increase in the hair cross-sectional area, the reduction in the modulus of elasticity, the gradient, the tension values and the work values. An increase in the elongation at break can also be observed.

Under the influence of substances having a restructuring effect, the parameter changes which characterize hair damage should be reduced, ie a change should take place in the direction of the parameter values typical of untreated and undamaged hair. This could be confirmed in the following tests, in which the polycondensate according to the invention was used. 3.4 Results in a commercially available cold wave with 1% product from synthesis example 1: Reference example: permed twice with a commercially available perm: as described under 3.2 steps f), g) c); Repetition of steps f), g), c); then d) and e). Example according to the invention: double permanent hair with 1% product from synthesis example 1 in the cold wave, as described under 3.2: steps f) with 1% product from synthesis example 1, g), c); Repetition of steps f) with 1% product from synthesis example 1, g), c); then d) and e).

The influence of the composition according to the invention on hair was investigated by means of tensile strain measurement in the wet state.

Reference damaged twice by KW

Comparative example, double corrugated with addition of 1% product from example 1

t-test in pairs, two-sided

Reference damaged twice by KW

Comparative example double-corrugated with addition of 1% product from synthesis example 1

Result: By adding the product from synthesis example 1, a significant improvement in the hair structure compared to the reference was found. A significant increase in the modulus of elasticity, the gradient, the stress values and the work values could be observed.

3.5 Results in a commercial cold wave with 1% product from comparative synthesis example 7:

Reference example: permed twice with a standard perm: as described under 3.2 steps f), g) c); Repetition of steps f), g), c); then d) and e). Comparative example: double-permed hair with 1% product from synthesis example 7 in the cold wave, as described under 3.2: steps f) with 1% product from synthesis example 7, g), c); Repetition of steps f) with 1% product from synthesis example 7, g), c); then d) and e).

reference

Perm - »- 1% product from synthesis example 5

Result: The perm with 1% product from synthesis example 7 shows a positive effect, since the tension and work values, as well as the gradient and the modulus of elasticity increase significantly.

However, a comparison of the results obtained using the polysulfide according to the invention (product from synthesis example 1) with those using the comparison material (product from synthesis example 7) shows that the polycondensate according to the invention improves the hair structure more effectively: cf. the following table.

Parameter improvement ¹ 'by treatment with a polycondensate comparison material according to the invention

Young's modulus 18.4% 9.7%

Gradient 16.2% 8.9%

Platform tension 13.4% 5.1%

Elongation at break 9% 0%

¹⁾ Extent of improvement = change of the respective parameter compared to the blank value (= hair damaged by cold wave, ie analog treatment, but without the inventive polycondensate or comparative material).

Claims

claims

1. A process for the preparation of a polycondensate, in which cystine or a salt thereof with an activated dicarboxylic acid of the formula (I)

XC (O) -AC (O) -Y (I) is reacted in a molar ratio of 10: 1 to 1:10, wherein in formula (I) A a bond or a divalent saturated or mono- or polyunsaturated aliphatic or aromatic hydrocarbon radical having 1 to 20 carbon atoms, which can be substituted by one or more halogen, hydroxyl or free or derivatized carboxy groups and the shortest connection between the two carbonyl groups adjacent to group A consists of up to 12 carbon atoms, X for is a halogen atom, a 1-imidazolyl group, an acyloxy group RC (O) -O- or another group which is suitable for activating a carboxyl group HO-C (O) -A-, Y has the same meanings as X, where X and Y may be the same or different, and the salt is preferably an alkali metal, alkaline earth metal or ammonium salt, the cation of the latter having 1 to 4 hydrogen atoms through alkyl radicals with 1 to 4 carbon ffatoms can be substituted.

2. The method according to claim 1, characterized in that in formula (I) X and Y are selected from chlorine, bromine and the acetoxy group.

3. The method according to claim 1, characterized in that in formula (I) X and Y together represent an oxygen bridge linking the carbonyl carbon atoms.

4. The method according to any one of claims 1 to 3, characterized in that in formula (I) A means a divalent saturated aliphatic hydrocarbon radical having 2 to 6 carbon atoms.

5. The method according to claim 4, characterized in that in formula (I) A means the ethane-1,2-diyl radical.

6. The method according to any one of claims 1 to 5, characterized in that the reaction takes place in a molar ratio of 2: 1 to 1: 2.

7. The method according to claim 6, characterized in that the reaction takes place in a molar ratio of 1: 1 to 1: 1, 2.

8. The method according to any one of claims 1 to 7, characterized in that the reaction is carried out as an interface condensation in a reaction mixture which comprises two essentially immiscible liquid phases.

9. The method according to claim 8, characterized in that in addition to an aqueous phase, there is an essentially immiscible organic phase which comprises at least one solvent which is selected from methylene chloride, chloroform, ethyl acetate, toluene, alkanes with 5 to 8 carbon atoms , especially n-octane, and ethers with 5 to 16 carbon atoms, especially methyl tert-butyl ether.

10. The method according to claim 9, characterized in that the aqueous phase is alkaline.

11. The method according to any one of claims 8 to 10, characterized in that the reaction takes place with the introduction of shear energy, in particular with intensive stirring.

12. The method according to any one of claims 1 to 11, characterized in that the reaction takes place at a temperature of 0 to 50 ° C, but in particular from 2 to 20 ° C.

13. The method according to any one of claims 1 to 12, characterized in that cystine or a salt thereof is presented in dissolved form, and then an activated dicarboxylic acid of formula (I) is metered in.

14. The method according to any one of claims 1 to 12, characterized in that an activated dicarboxylic acid of the formula (I) is initially introduced, and then cystine or a salt thereof is metered in in dissolved form.

15. The method according to claim 13 or 14, characterized in that cystine or a salt thereof in the form of a 1 to 20 wt .-%, but in particular a 5 to 15 wt .-% solution, based on the total weight of the solution, is presented.

16. The method according to any one of claims 1 to 7, characterized in that the reaction is carried out in the melt.

17. polycondensate obtainable by a process according to any one of claims 1 to 16.

18. Use of a polycondensate according to claim 17 for restructuring keratin fibers.

19. A cosmetic treatment for hair treatment comprising a polycondensate according to claim 17 in a physiologically acceptable carrier.