DE1911360A1 - Process for stabilizing self-crosslinking polymers - Google Patents

Description

File: 2074

Applicant: Reichhold-Albert-Chemie Aktiengesellschaft Hamburg 70, Iversstr. 57

Process for stabilizing self-crosslinking polymers

It is known that crosslinkable polymers can be produced by polymerization at certain pH values and at low temperatures to produce by adding acrylic or methacrylic acid amides, in which the amide groups by reactive groups such as methylol, methylol alkyl ether or tert-aminomethylene groups are substituted, polymerized under such conditions that one soluble in organic solvents with polymers Film-forming properties are obtained in which the monomers mentioned are polymerized without splitting off the reactive group have been.

The reactive groups, namely methylol, Methylolälkyläther- or tert-aminomethylene groups on acrylamide or methacrylamido esters of these polymers can under the action of Heat and / or split by acidic catalysts, the polymers being converted into crosslinked, insoluble products will. However, these polymers do not meet all practical requirements in some areas of application, because copolymers with free methylol groups for longer Standing at room temperature slowly cross-link and thus become unusable.

Polymers with methylol ether groups show this phenomenon not, but their crosslinking temperatures are too high for some purposes. In general, the known polymers of this type in the presence of acids and / or Cross-linked acid donors, since under these conditions the cross-linking takes place faster and at lower temperatures, than when applying heat alone. For certain purposes, however, it is desirable to use polymers that Crosslink just as quickly and easily without the addition of acids and / or acid donors as the well-known products in

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- 2 presence of these catalysts.

In the German Auslegeschrift 1 212 729 is already a Process for the production of self-crosslinkable polymers by homopolymerization or copolymerization of olefinically unsaturated ones substituted amides containing methylol groups, if necessary in a mixture with other olefinically unsaturated monomers, in aqueous emulsion at pH values between 3 and 9 and temperatures not exceeding 80 ° C in the presence of catalysts, described, which is characterized in that one as olefinically unsaturated substituted methylol group-bearing Acid amides N-methylolamides ^ .- olefinically unsaturated Carboxylic acids used whose methylol groups are acylated.

The object of the present invention is to improve the thermal stability of self-crosslinkable polymers, the N-hydroxyalkylated Amide of a c ^ ß-unsaturated mono- or dicarboxylic acid contain polymerized in their solutions, preferably in their aqueous dispersions, so as to improve without introducing a protective group and without discoloration of the stabilized solution or dispersion sooner or later occurs and without the reactivity of the reactive groups being reduced as a result.

This task is solved by using the solutions or Subjecting dispersions of the same to the process according to the invention.

The present invention relates to a process for stabilizing self-crosslinkable polymers which are copolymerized by homopolymerization or copolymerization of olefinically unsaturated amides containing methylol groups, cC, ß-unsaturated mono- or dicarboxylic acids, optionally in a mixture with other olefinically unsaturated monomers, by adding a stabilizer, characterized in that an α-aminocarboxylic acid of the general formula is used as the stabilizer

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HO

! H

R-C-C-OH

NH ₂

in which R = -H or -CH ,, - ^C 2 ^Hf 5 '" ^C " 3 ^H 7 ^or - ^ Hq, as a free acid or its soluble salts, individually or in a mixture, during or after the preparation of polymers which N-methylolamides containing an or, ß-unsaturated .mono- or dicarboxylic acid are added.

A particular embodiment of the method is characterized in that o, l. - 1 wt% of the labeled α-aminocarboxylic acid, based on the polymer to be stabilized, inflicts. Preferred Oc-amino carboxylic acid is f

Oc-aminoacetic acid or its alkali, ammonium or amine salts. As monomeric N-hydroxyalkylated acrylamide or methacrylamide Polymers or dispersions of this type which contain polymerized units and are suitable for stabilization are used Question, which contain N-hydroxyalkylated acrylamide compounds of the following general formula in polymerized form;

H 0
'■ U
C = CCN-R ₀

HR ₁ H
where R ₁ = -H or -CH _{1, R g} = -CH ₃ OH.

Polymerized in as monomeric amides ot, ß-unsaturated dicarboxylic acids Polymers containing, which are suitable for stabilization, are also those polymers in question which Contain N-hydroxyalkylated fumaric acid or maleic acid mono- or diamide compounds.

0 0

Ί! I

HO-C-C = CH-C-N-R ₀ ;

H H

R ₀ -N- C -C = CCN- R ₀ ² I Il 1 I Ά ι ² HOHHOH ..

where Rp = CHpOH.

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Preferred monomers which are polymerized into the polymers present, and the stabilization of which is particularly pronounced, are N-methylolacrylamide and / or N-methylol methacrylamide.

The process which uses polymers which are in the aqueous phase is preferred.

The stabilizer is added to the solution or dispersion to be treated in solid or dissolved form. Adding in solid Form is preferred, the addition of the free aminocarboxylic acids is part of the preferred embodiment. However, the use of amine salts can be very useful, as these are more soluble in many organic media.

In the preferred embodiment of the invention such Homopolymers or copolymers of N-methylol groups Acid amides of olefinically α, β-unsaturated mono- or dicarboxylic acids stabilized, which were prepared by copolymerization in aqueous emulsion.

The copolymers contain

I. o, 25-50 wt.% Of N-Methylolamids a c \> ß-unsaturated mono- or dicarboxylic acid and

II · 99 * 75- 50 wt.% Of at least one other olefinically unsaturated, polymerizable compound.

In the process of the invention, the monomers can be polymerized individually or as a mixture with one another in an aqueous emulsion. However, the monomers are preferably used for the ^c Hersteilung of copolymers with other olefinically unsaturated monomers, said first-mentioned monomers in amounts of about 0.25 to reach 5Oi preferably 0.5 to 30 wt.% Is applied.

Suitable olefinically unsaturated monomers used as copolymerization components can be used are, for example,

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a) Qi, ß-olefinically unsaturated monocarboxylic acids and their derivatives, such as acrylic and methacrylic acid amides, acrylic and methacrylonitrile, esters of acrylic and methacrylic acid, especially those with saturated monohydric aliphatic alcohols with 1 to 20 carbon atoms, such as esters of the acids mentioned Methyl, ethyl, propyl, isopropyl,

. Isobutyl, hexyl, octyl, stearyl alcohol, cyclohexanol, methyl cyclohexanol, also with benzyl alcohol, phenol, cresol, furfuryl alcohol; cXjß-olefinically unsaturated dicarboxylic acids and their derivatives, such as fumaric acid and maleic acid, mono- or diamides, fumaric acid and maleic acid mono- or dinitrile, mono- or diesters of fumaric acid or maleic acid, especially those with saturated monohydric aliphatic or cycloaliphatic alcohols 1 to 20 carbon atoms, such as ä esters of said acids with methyl, ethyl, propyl, isopropyl, isobutyl, hexyl, octyl, stearyl alcohol, cyclohexanol, methylcyclohexanol, further comprising benzyl alcohol, phenol, cresol, furfuryl alcohol;

b) aromatic monoviny compounds, such as styrene, 6> c-methylstyrene, Vinyl toluene, p-chlorostyrene or other ring-substituted ones Vinylbenzenes;

c) esters of vinyl alcohol with carboxylic acids or with hydrohalic acids, Vinyl ethers, vinyl ketones such as vinyl chloride, vinylidene chloride, vinyl isobutyl ether;

d) conjugated diolefins with 4 to β carbon atoms, such as butadiene, isoprene, 2,3-dimethylbutadiene, chloroprene.

There are also other mono-olefinically unsaturated ones Monomers can be used as copolymerization components, such as maleic acid, fumaric acid or crotonic acid esters, styrene sulfonic acid, unsaturated aliphatic or cycloaliphatic hydrocarbons. Furthermore, they can also have a crosslinking effect Monomers with several non-conjugated olefinically unsaturated groups in amounts of about 0.01 to 5> preferably 0.01 to 3 wt. ^, based on the weight of the total monomers, used such as glycol diacrylate, glycol dimethacrylate, acrylic acid and / or methacrylic acid allyl ester, divinylbenzene, triacrylol

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perhydro-s-triazine, triallyl cyanurate or substitution products of the compounds mentioned.

It is possible to produce copolymers from two as well as from a larger number of monomers belonging to different classes of compounds; Choosing this Monomers takes place depending on the desired properties of the copolymers.

Of particular interest are copolymers which contain one or more "reinforcing" monomers (ie monomers whose copolymerization increases the hardness of the copolymers) and at least one "elasticizing" monomer in copolymerized form. Conjugated diolefins, esters of acrylic acid with more than 2 carbon atoms in the ester group and esters of methacrylic acid with more than 4 carbon atoms in the ester group can be used as "elasticizing" monomers. The proportion of "elasticizing" monomers in the total amount of monomers is preferably 40 to 90 wt. Suitable "reinforcing" monomers are, for example, styrene, substituted styrenes, acrylonitrile, methacrylonitrile, vinyl chloride, vinylidene chloride, esters of acrylic or methacrylic acid with lower alcohols. These monomers are suitably used in an amount of 1 to 40 wt.% On total used.

The monomers containing carboxyl groups, such as acrylic and methacrylic acid, are generally polymerized into the copolymers in relatively small amounts, unless copolymers with strongly hydrophilic properties are to be produced. For the preparation of copolymers, which are obtained by polymerization of the monomers in aqueous emulsion, said olefinically unsaturated acids are preferably calculated in amounts of 0.1 to 10 wt.% "Are by weight of the total monomers used. The amides of the acids mentioned are also preferred in the amounts mentioned

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- 7 deployed.

Aqueous copolymer dispersions are obtained when the abovementioned monomers copolymerize in an aqueous dispersion using emulsifiers in a manner known per se at pH values between J> and 9. Both cationic, anionic and nonionic emulsifiers and combinations of these emulsifiers can be used here.

Examples of suitable anionic emulsifiers are higher fatty acids, resin acids, acidic fatty alcoholsulfuric acid esters, higher alkylsulfonates and alkylarylsulfonates, sulfonated castor oil, higher oxyalkylsulfonates, sulfosuccinic acid esters, Λ salts of fatty acid condensation products with oxyalkylcarboxylic acids, aminoalkylcarboxylic acids of wateroxylated carboxylic acids, aminoalkylcarboxylic acids.

Examples of cationic emulsifiers are: salts of alkylamines, aryl, alkylaryl or resin amines and inorganic acids and salts of quaternary ammonium compounds.

The known reaction products of ethylene oxide with long-chain emulsifiers are nonionic in character Fatty alcohols such as cetyl, lauric, oleyl, octadecyl alcohol

or phenols, such as octylphenol or dodecylphenol, are suitable, in particular reaction products of more than 10 mol, preferably 15 to 50 mol, of ethylene oxide with 1 mol of fatty alcohol or phenol being used.

The total amount of the abovementioned emulsifiers can be between 0.5 and 20 %, calculated on the total amount of monomers. It is preferably between 2 and 10 %.

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According to a particular embodiment of the invention, exclusively nonionic emulsifiers or mixtures of these emulsifiers with up to 0.5 % of cationic and / or anionic emulsifiers, based on the polymer, are used. In this way, latices of particularly high stability are obtained. _{If —COOH, —CONH 2} , —SO ₇ H or other hydrophilic groups are present in the polymer at the same time, the latexes show a high degree of re-emulsifiability. Re-emulsifiability is understood here to mean that the film obtained from the copolymer latex by drying at room temperature and at a pH of about 7 can still be redispersed smoothly with water for a certain time.

Although the polymerization is preferably at temperatures of about 10 to 50 ⁰ C., but temperatures up to about 80 C are anwandbar.

The pH to be maintained in the preparation of the copolymers can vary between 3 and 9, expediently between pH ^ and 9, whereby in the case of the production of reemulsifiable latexes the maintenance of a pH value between 4 and proven. After the polymerization has ended, the latexes are generally adjusted to pH values of about 6.5 to 9, as a result of which the stability of the products is increased. Compounds that regulate molecular weight, such as long chain alkyl mercaptans, Diisopropyl xanthate, etc., can be used in the polymerization.

Inorganic per compounds are used as polymerization catalysts, such as potassium or ammonium persulfate, hydrogen peroxide, percarbonates, organic feroxide compounds such as Acyl peroxides, for example benzoyl peroxide, alkyl hydroperoxides such as tert-butyl hydroperoxide, cumene hydroperoxide, p-menthane hydroperoxide, Dialkyl peroxides such as di-tert-butyl peroxide are suitable. The inorganic or organic per compounds in combination with reducing agents applied in a known manner. Suitable reducing agents are, for example, sodium pyrosulfite or bisulfite,

009840/2032 bao above, nal

Sodium formaldehyde sulfoxylate, triethanolamine.

The amount of catalyst to be considered is within the limits usually applicable in the case of polymerization of this type, ie between 0.01 and 5 %, calculated on the total monomers used.

The effect of the stabilizer used is surprising because according to the invention treated solutions or dispersions containing for stabilizing polymers, remain stable at about 3O ⁰ C over 100 days, while non-stabilized otherwise identical polymers containing - solutions or dispersions after 32 days crosslink spontaneously, which is clearly shown by an increase in viscosity. ™

example 1

In a reaction vessel with a stirrer, thermometer, two addition vessels, protective gas inlet capillary and one Reflux condenser is provided, 2 parts of sodium dodecyl sulfate and 2 parts of a reaction product of p-alkylphenol and 13-15 mol of ethylene oxide dissolved, the p-alkyl radical containing 6-15 carbon atoms.

For this purpose, 100 ml of an emulsion optionally prepared deionized of 500 parts water, 274 parts of butyl acrylate, 12 parts of acrylamide, 172 parts of styrene, 13 parts of sodium dodecyl sulfate and 13 parts of a reaction product of ä p-alkyl phenol (as already described) and 13-15 moles of ethylene oxide.

In addition, 2.5 ml of a solution of 15 parts of N-methylolacrylamide added in 25 parts of deionized water. After the temperature has been raised to 40 ° C, they are successively 2 parts of a solution of 2 parts of potassium peroxydisulfate in 30 parts of water and 2 parts of sodium propysulfate in 30 parts of water were added.

As soon as the polymerization has started, the main amounts of pre-emulsion, N-methylolacrylamide solution and potassium persulfate or Na bisulfite solution was added dropwise within 2 hours.

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- ίο -

A copolymer dispersion is obtained with a solids viscosity of about 41 #. A portion of this dispersion is stabilized by the process according to the invention by adding 150 mg of aminoacetic acid per 100 g of solid polymer. One sample each of the stabilized and the unstabilized dispersion were stored at elevated temperatures. Bio unstabilized sample crosslinked at 40 ^° C. after 14 days, while the stabilized sample showed an unchanged viscosity after 120 days.

Example 2

The procedure is as in Example 1. Only N-methylol methacrylamide is used instead of N-methylolacrylamide. the Storage stability of the unstabilized dispersion is 20 days compared to 120 days of the stabilized dispersion, in each case at

Example 3

In a reaction vessel equipped with a stirrer, two monomer feed vessels, thermometer and protective gas inlet capillary, 10 g of a reaction product of p-alkylphenyl (with 6-15 C atoms in the alkyl radical) and 20-30 mol of ethylene oxide are added to 500 grams of deionized water E sodium dodecyl sulfate and 10 g sodium dioctyl sulfosuccinate dissolved. The air is then displaced from the apparatus with nitrogen and then: 10/5 of the monomer mixture A ₃ which was prepared from 400 grams of ethyl acrylate and 77 g of acrylonitrile, and 10% of the monomer solution B, a solution of 23 C N-methylolacrylamide in 100 g deionized water added. After the temperature has been increased to 40 ° C., 15% of a solution of 0.5 g of potassium peroxydisulfate in 30 g of deionized water and 15% of a solution of 0.2 g of sodium pyrosulfite in 30 g of deionized water are added. After the start of polymerization, the remaining amounts of solutions A and B, such as the potassium peroxydisulfate solution and the sodium bisulfate solution, are added within three hours.

A dispersion is obtained which has a solids content of et ^T .ra 4-2.2. The D ^ 'pr """" ¹ * "" ^T "i-" · - roteilen and a part ..- 1.

BAO ORIGINAL

00984072832

given as 150 mg of aminoacetic acid per 100 g of polymer stabilized. This part has a significantly improved thermal stability compared to that not according to the invention treated dispersion.

Example 4

The procedure is as indicated in Example 3, but the monomer solution B is prepared from 100 g of deionized water in which 23 g of N-methylolacrylamide and 0.75 mg of aminoacetic acid are dissolved. The dispersion obtained with a solids content of about 42% shows a significantly improved thermal stability compared to that obtained according to Example 3 without the addition of aminoacetic acid.

Example 5

In a reaction vessel equipped with a stirrer, thermometer, protective gas inlet capillary and two monomer feed vessels, 5 g of sodium dioctyl sulfosuccinate, 3.5 g of sodium tetrapropylene benzene sulfonate and 20 g of a reaction product of p-alkylphenol (with 6-15 carbon atoms in the alkyl chain) with I5 - 20 mol of ethylene oxide dissolved in 300 g of deionized water. The pH is adjusted to about 5 and then the air in the reaction space is displaced with nitrogen. There are 10 % of the monomer mixture A, which was prepared from 300 g of vinyl acetate, 175 g of butyl acrylate and 10 g of a reaction product of p-alkylphenol and 15-20 mol of ethylene oxide (see above) and 10 % of a solution B of 20 g of N- Methylolacrylamide in 150 g of deionized water was added. After brief stirring, 40 % of a solution of 2.5 g of ammonium peroxydisulfate in 130 g of deionized water and 40 % of a solution of 3 S Na pyrosulfite in 130 g of deionized water are added. As soon as the polymerization has started, the remaining solutions A and B, such as those of potassium peroxydisulfate and sodium bisulfite, are added over a period of 2 hours.
The pH of the dispersion having a solids content of about 42 $> is adjusted to 5-6 with KH OH.

0 0 98 A 0/2032 BADORtGINAL

The dispersion is divided and one part in the manner indicated with 150 mg of aminoacetic acid per 100 g of polymer stabilized.

Example 6

The procedure given in Example 5 is followed. However, the monomer solution B is prepared as follows:

Dissolve 20 g of N-methylolacrylamide and 0.75%. Aminoacetic acid in 150 g deionized water. A dispersion is obtained which contains about 42 % solids and has a significantly improved thermal stability compared to that according to Example 5 without the addition of aminoacetic acid.

Example 7

In a reaction vessel, as indicated in Example 3, 3 g of sodium dodecyl sulfate are dissolved in 600 g of deionized water and the pH of the solution is adjusted to 4. The air is displaced from the reaction vessel by flushing with nitrogen, after which 10 % of the monomer mixture A, prepared from 540 g of ethyl acrylate, 110 g of acrylonitrile, 12 g of a reaction product of p-alkylphenol (6-15 C atoms in the alkyl chain) with 10 Moles of ethylene oxide and 12 g of a p-alkylphenol with 30 moles of ethylene oxide, the alkylphenol having 6-15 C atoms in the alkyl group, and 10% of a monomer solution B, consisting of 50 g of di-N-methylol fumaramide and 100 g of deionized V / must be admitted. Then 2.0 g of ammonium peroxydisulfate dissolved in 20 ml of deionized water and 2.0 g of sodium pyrosulfite in 25.0 g of deionized water are added to the reaction mixture. As soon as the polymerization begins, the remaining amounts of the monomer mixtures A and B, as well as the solutions of 2.5 g of ammonium peroxydisulfate in 50 g of deionized water and 2.5 g of sodium pyrosulfite in 50 g of deionized water, are dissolved in the course of two Dripped in for hours. The reaction temperature must be kept at 45 ° C. during this time. A dispersion is obtained with about 39 % solids content,

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The dispersion is divided and a part according to the invention Process by adding 150 mg of aminoacetic acid each 100 g polymer stabilized.

Example 8 -

The procedure given in Example 7 is followed. The monomer solution B, however, consists of 50 g of di-N-Me thylolfumararnid, o.75 g of aminoacetic acid and 100 g of water / water. A dispersion, the pesticide content of which is 39 %, is obtained with improved thermal stability.

The polymers and copolymers stabilized according to the invention have free methylolamide groups which, up to elevated temperatures between 20 and 150 ° C. and / or the action of acidic catalysts, are condensed with elimination of water, with the formation of insoluble crosslinking products. Because of these properties, they turn into insoluble products even under mild conditions. The polymers and copolymers stabilized according to the invention can therefore be used for the production of structures of any shape, such as coatings, impregnations and bonds. It is surprising that the stabilization carried out according to the invention does not adversely affect the catalytically triggered crosslinking when these polymers and / or copolymers are used. λ

Example 9

In a reaction vessel as specified in Example 1, a solution of I ₃ H parts of a 35 ^ strength aqueous solution of a potassium polymethacrylate, which has a viscosity of 1500 to 25ΟΟ cP, is dissolved in 250 parts of deionized water. This water phase is adjusted to a pH of 4.5 to 4.0 with formic acid after the addition of 0.5 part of an aqueous iron trichloride solution and 0.25 part of an aqueous cobalt chloride solution. The reaction vessel is then freed from oxygen in the air by purging with nitrogen. In this, then ^{heated to 30 0} C:} solution, 10 % of a mixture

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BAD ORfGINAL

from 250 parts of vinyl acetate, 225 parts of butyl acrylate, 15 parts of a condensation product of p-nonylphenol with 30 moles of ethylene oxide and 15 parts of a condensation product of p-nonylphenol with 10 moles of ethylene oxide, and 10 % of 175 parts of an aqueous solution containing 25 parts Contains N-hydroxymethylacrylamide and 2 parts of Ma-Diiso-tridecylsulfosuccinate, emulsified. Then, in succession, 10 % of a solution of 3 parts of ammonium peroxydisulfate in 97 parts of water and 10 % of a 1.5% aqueous Rongalit solution, which makes up 100 parts, are added. Within 2 to 3 minutes, the temperature begins to rise due to the onset of polymerization. Care must be taken by cooling that the temperature does not exceed 50 ° C. As soon as this initial reaction begins to subside, the remaining solutions are fed into the reaction vessel in parallel within 3 hours. The reaction mixture is then kept at the reaction temperature of 50 ° C. for a further 30 minutes, then cooled and adjusted to a pH of approx. 6 with dilute ammonia solution. The dispersion obtained is divided and a part stabilized in accordance with example 1, which can be stored at 5O ⁰ C for k weeks, without changing the structure of the sample.

Example 10

One works as indicated in Example 9. However, it becomes the Polymerization of already stabilized N-hydroxymethylene acrylamide related. With this method, the same stabilizing effect against thermal influences is achieved.

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Claims (6)

Claims Process for stabilizing self-crosslinkable polymers produced by homopolymerization or copolymerization of olefinically unsaturated methylol group-bearing amides of ά, β-unsaturated mono- or dicarboxylic acids, possibly in a mixture copolymerized with other olefinically unsaturated monomers are present, by adding a stabilizer, characterized in that the stabilizer is an α-aminocarboxylic acid the general formula H Q »Ü R-C-C-OH ■ κ * in the H = -H-. CH ,, -C ₀ H ₅ , - ^c ^ ^h t ^odci * " ⁰ A means, individually or in a mixture during the polymerization or after the polymerization as free acid or its soluble - salts are added. 2. The method according to claim 1, characterized in that 0.1 to 1 wt. % 6 * .- aminocarboxylic acid, based on the polymer to be stabilized, is added. 3. The method according to claim 1 or 2, characterized in that the solutions or dispersions air-crosslinking component polymerized N-hydroxyalkylated acrylamides and / or N-hydroxyalkylated methacrylamides of the general formula i HIGH (J = CCN- R ₀ HR ₁ where R, hydrogen or CH ^ radical and R _{2 is} the CH ₂ OH-ReSt, are. 4. The method according to claim 1 or 2, characterized in that the solutions or dispersions as a crosslinking component Polymerized N-hydroxylated mono- and / or diamides of (X-ß-unsaturated dicarboxylic acids of the general Formulas 009840/2032 _BAD Q. HHOH
HO'-WC = O- ¹ C -If- R ₂ or HIGH HIGH i Ij t I · ^! I R ₂ -NCC = CCN- R ₂ , where R ₂ = CH ₂ - OH, contain. 5. Method according to one or more of Claims 1 to 4, characterized in that Ct-aminoacetic acid is preferably used as the stabilizer. 6. The method according to one or more of claims 1 to 5, characterized in that the .vernetzbaren to be stabilized Copolymers o, 25 to 50 wt.% of a N-n Methylolamids a, ß-unge-saturated monocarboxylic acid and / or a mono- or di-N-methylolamids a qc, ß-u.ngesättigten dicarboxylic acid and 99.75 to 50 wt. % contain at least one other olefinically unsaturated, polymerizable compound in copolymerized form. 7 · Method according to one or more of claims 1 to 6 _S wherein methylol mono-N-that the ".ur preparation of the polymers solutions employed the monomeric N-hydroxymethylated amides of c *, ß-unsaturated monocarboxylic acids and / or of the monomeric and / or the di-N-methylol compound. ~ A, ß-unsaturated dicarboxylic acids already contain the O-aminocarboxylic acid and / or its salts as a stabilizer .. 0 09840/2032