AT395592B - METHOD FOR PRODUCING WATER-SOLUBLE SULFONED POLYMERS - Google Patents

Description

AT 395 592 B

The synthesis of water-soluble sulfonated polymers has generally been limited to the use of certain vinyl monomers containing the sulfonate functional group. Examples of such monomers are sodium vinyl sulfone, sulfonated styrene and 2-acrylamido-2-methylpropanesulfonic acid (AMPS). In addition, the synthesis of sulfonated vinyl polymers containing the sulfonate group has been limited in that only certain such sulfonated monomers are commercially produced and commercially available.

Therefore, the use of these sulfonated water-soluble polymers is limited only to the structures mentioned above. It would therefore be an advance if other water-soluble polymeric chemical structures could be attached to a polymer backbone that contain the sulfonate group in either acidic or salt form, and so on may contain other functional groups that could improve the applicability of these water-soluble sulfonated polymers for certain uses, such as water treatment dispersants, inhibitors of lime scale in natural and industrial waters, flocculants and coagulants, and the like.

The object of the invention is therefore a process for the production of water-soluble polymers which contain a sulfonate group and which can also contain other functional groups which are advantageous when the polymer is applied to aqueous solutions or in aqueous environments, the process according to the invention being generally applicable to the synthesis of various Types of water-soluble polymers that contain the sulfonate group and optionally other functional groups that may be useful when these polymers are used in aqueous systems. Other functional groups come e.g. B. hydroxy, chlorine, bromine, iodine and / or mixtures thereof in question. Such polymers were previously unknown.

According to the present invention, water-soluble polymers which contain pendant functional amide groups, such as polymers which are mainly derived from acrylamide-containing vinyl polymers / copolymers or from alkyl-substituted acrylamide-containing vinyl polymers or copolymers, the polymers / copolymers being water-soluble and containing pendant functional amide groups, which are derived from acrylamide, methylacrylamide, ethylacrylamide and the like.

The invention thus relates to a process for the preparation of water-soluble, sulfonated polymers having statistically recurring subunits of the general formula

-H I * C I -H

Rn 1 ΓΗ ΚΙ I pH R-t | I 1 p "1 I 1 1 np I uv IJ a 1 lh b 1 LH t NH,, (V) M 'NR I (R' + - < OH) m (S0'3 > t +) n where R each is independently hydrogen or lower alkyl having 1 to 4 carbon atoms; M independently of one another a hydrogen, alkali metal, alkaline earth metal ·, tert. Amine and / or ammonium ion, R 'is a multicovalent hydrocarbon bridging group with 1 to 16 carbon atoms, selected from one or more linear or branched alkylene, cyclic, aromatic and olefinic groups, a, b and d integers in the following relationship are: a / b = zero to 100 b / d = 0.01 to 100 a / d = zero to 100, and the sum a + b + d is sufficient to give a molecular weight of at least 1000, and that Ratio d: (a + b) 20: Ibis is 1: 100, m is zero to 16 and η is 1 to 8, provided that when m is zero, R 'is a bridging group selected from one or more linear alkylene -, cyclic, olefinic and aromatic groups, with the further proviso that the sum of m + η = 1 to 20, which is characterized by -2-

AT 395 592 B that A. a polymer with a molecular weight of at least 500 and with pendant functional amide groups of the general formula

wherein R, M, a and b have the above meaning, with a chemical reactant of the general formula

R

I HN-f-R'-ie-SO, M) I 3 n <0H> n, where R, R ', M, m and n have the above meaning, in a solvent at a temperature of at least 100 ° C implemented, the molar ratio of the chemical reactant to pendant amide groups in the polymer is about 5: 1 to about 1: 100 and the reaction on the amide nitrogen group is allowed to proceed so long that an at least 25% conversion of the chemical reactant into the pendant groups of the sulfonicrtcn Polymer takes place, water, dimethylformamide and / or dimethyl sulfoxide being used as the solvent.

Starting compounds are preferably used, in which R is in each case independently of one another hydrogen, methyl or ethyl, M is in each case independently of one another in each case hydrogen, sodium, potassium, tert-amine and / or ammonium, R 'has at least 2 C atoms and one or more linear, cyclic , aromatic groups, m is zero to 4 and η is 1 to 4, a water-soluble sulfonated polymer having a molecular weight of about 2,000 to 20,000,000 being obtained.

The chemical reactant is primarily an amino-substituted compound that also contains a functional sulfonate group and in which the functional amino group contains at least one active hydrogen atom on the amino nitrogen, although sulfonate compounds can react with both primary and secondary amino groups under transamidation reaction conditions to form modified sulfonate-containing polymers , it is preferred that when a secondary amine is used to carry out this modification of polymers having pendant amide groups, the alkyl group substituted on the amino nitrogen atom contains no more than 4 carbon atoms, i. H. the alkyl substituent is said to be limited to methyl, ethyl, propyl and butyl and their isomers.

However, it is particularly preferred that the amino substituent on the sulfonate-containing chemical reactant be a functional primary amino group. If a primary amino group is used for the transamidation reaction, the reaction proceeds easily and at least 25, preferably 60 mole percent of the reactant used is incorporated into the water-soluble polymer containing pendant amide groups, whereby a sulfonate-containing functional group causes an originally existing pendant Amide group replaced.

In addition to the amine substituent in the reactant described above, it contains at least one functional sulfonate group, either in acidic form or in salt form, the salt form being a salt of an alkali metal, alkaline earth metal, tertiary amine and ammonium ions and mixtures thereof. The salt form may be before the transamidation reaction or may be formed by changing the pH with bases containing alkali metals, alkaline earth metals, tertiary amines or ammonia, either before or during the transamidation reaction or after it has ended. -3-

AT 395 592 B

In addition to the functional sulfonate group and the functional amino group, the chemical reactant can also contain other functional groups from the group chlorine, bromine, hydroxyl and the mixtures from the group chlorine, bromine, hydroxyl and mixtures thereof. Preferably, the reactant contains a primary amino group responsible for the transamidation reaction, at least one sulfonate group which enables the formation of an anionic sulfonate-containing water-soluble polymer, and a hydroxyl group or a chlorine atom, the presence of which can increase the activity of the water-soluble sulfonate group-containing polymers obtainable according to the invention.

Most preferably the chemical reactant contains a primary amine, zero or more hydroxyl groups and one or more sulfonate groups either in the free acid form, in salt form or in the form of mixtures of the free acid and salts.

Various preferred chemical reactants are given by the following formulas:

H2N-CH2S03M (Ra) h2n-CH2CH-S03M OH m H2N-CH2CH2-S03M m H2N-CH2-CH-CH2S03M 1 (ΠΦ OH

The pendant polymers containing acrylamide groups are water-soluble polymers whose general structure enables the presence of pendant amide groups, of the general formula

Polymer wherein the pendant amide group can be a primary, secondary or tertiary amide, or a mixture thereof. Preferably, in order to achieve acceptable conversions from these pendant amide groups to the sulfonate-containing groups described above, the pendant amide group is a primary amide group.

The most water-soluble polymers with pendant amide groups, which can be easily modified under the conditions of the transamidation reaction according to the invention, are those of the general formula -CH, R-I I -c- 4M +

Yes • CH,

Rt I U 0 = -4-, (iv)

AT395592B wherein R independently of one another is hydrogen or low. Alkyl with 1 to 4 carbon atoms; M independently represents a hydrogen, alkali metal, alkaline earth metal and / or ammonium ion; and a and b are integers in the following relationship: a / b between zero and 100, and a + b sufficient to produce a polymer with a molecular weight of at least 1000. The sum a + b is preferably large enough to give a molar mass between 1000 and 20,000,000.

It will be appreciated that the polymers described above can be homopolymers of acrylamide or its alkyl homologues, i.e. H. Methacrylamide and the like; they can also copolymers of acrylamide with acrylic acid or their homologs, such as methacrylic acid and the like, terpolymers and especially with other vinyl monomers, the acrylamide and acrylic acid and their homologs, such as methacrylic acid, methacrylamide and the like. Ä. included.

The chemical reaction which is preferred for the production of the sulfonated polymers according to the invention is a reaction which can generally be referred to as a transamidation reaction. In this reaction, the nitrogen portion of a pendant amide group contained on the main polymer chain as described above is substituted with an amino compound which may also contain other functional groups such as the sulfonate functional group. This transamidation reaction has proven to be a general reaction which can be used to replace the amido nitrogen group of a water-soluble polymer having a pendant amido group with a group containing an amino and a sulfonate group, thereby obtaining unique sulfonated polymers.

The reaction conditions require that polymers having pendant amide groups be dissolved or easily dispersed in a solvent which is a common solvent for the chemical reactant of the class described above. That is, both the polymer to be modified and the chemical reactant should be soluble or dispersible in the same solvent system. Common solvents that have proven suitable for this reaction are e.g. As water, dimethylformamide, dimethyl sulfoxide, their mixtures and mixtures of these solvents either alone or together with other miscible solvents, such as ethanol, tert-butanol and the like.

A preferred common solvent for both the amide pendant polymer and the chemical reactant is water, especially if the amide pendant polymer is water soluble from the start, as is the case with most acrylamide-containing vinyl polymers. Another preferred common solvent for the reaction according to the invention is a water-in-oil emulsion, in which the disperse aqueous phase contains both the polymers with pendant amide groups and the chemical reactants described above.

After the pendant amide group polymers are dissolved in the common solvent, preferably water, the chemical reactant can be added to obtain a solution or dispersion of the amide-containing polymer and the chemical reactants. Whether the polymer or reactant is added to the common solvent first has no consequence. This mixture is then placed in or contained in a reaction vessel which can withstand a chemical reaction carried out under pressure, e.g. B. a tube of the type a Paa flask. The vessel is closed and then heated to a temperature of at least 100 ° C, preferably at least 110 ° C and in particular at least 120 ° C. If the temperature is raised above 100 ° C, the contents of the reaction vessel can expand and the pressure inside the vessel can exceed 1 bar and, depending on the solvent, the sulfonates or the reactants used, can reach up to about 5 to 15 bar and possibly more . The pressure inside the reaction vessel is an uncontrolled variable that is determined only by the extent to which the vessel is enclosed that the temperature reaches at least 100 ° C or above, and the vessel may contain solvents or reactants that more or are less volatile and have such a vapor pressure that pressure vessels at temperatures above 100 ° C are required.

Once the contents of the reaction vessel have reached at least 100 ° C, and preferably 110 ° C, the reaction is allowed to proceed for at least 3 minutes at this temperature and preferably as long as is necessary to achieve an at least 25% conversion of the added portion chemical reactants. The chemical reactant is of course converted into a pendant amide group containing sulfonate, which is the product of the transamidation reaction according to the invention. If the polymer is a homopolymer of acrylamide, methacrylamide, or a copolymer of vinylamide-containing monomers so that there are no other functional pendant groups besides the functional amide groups, the reaction conditions are such that at least some degree of amide hydrolysis can occur in such reactions which use water or a water-based solvent. In such cases, a functional carboxylate group is also obtained from the starting polymer in addition to the sulfonate-modified amide group and any unreacted starting amide groups. -5-

AT 395 592 B

Polymer recovery can be carried out in various ways known to those skilled in the art. For example, the polymers can be precipitated by adding precipitating solvents or non-solvents to the reaction mixture. For example, methanol or acetone can be added to the reaction mixture either as such or after being concentrated by distillation or vacuum distillation to precipitate the polymers. The polymers can also be separated from the reaction mixture by distilling off the solvent and the unreacted chemical reactant in vacuo. The polymers can also be obtained by chromatographic gel permeation methods. Mainly, however, the polymers are simply recovered and used as a solution in the solvent used to carry out the transamidation reaction

The present invention preferably relates to a process for the preparation of water-soluble, sulfonated polymers of the general formula

Rn R-i

R-T • CH, l

H -CH, T NH, -CH, o = c NH 1 (R'-J- (OH) (ε ° -3 #) η m in which R independently of one another is hydrogen or lower alkyl having 1 to 4 carbon atoms ; M independently represents a hydrogen, alkali metal, tertiary amine or ammonium ion; R 'is multicovalent branched alkylene, linear alkylene or a cyclic hydrocarbon bridging group with 1 to 8 C atoms; m is zero to 6, η 1 to 4 and a, b and d are integers in the following relationship: a / b = zero to 100 a / d = zero to 100 b / d = 0.01 to 100, where the ratio d: (a + b) is between about 5: 1 and 1:25, the occurrence of the subunits a, b and d is arbitrary, and the sum of a-ι- b + d gives a molar mass of at least 2000 which is characterized in that A. a polymer with pendant functional amide groups of the general formula Ri r-

R ~ i

I c- a 0

where R, M, a and b have the meaning given above and the sum of a + b gives a molecular weight of at least 500, with -6-

AT 395 592 B B. a reactant of the general formula h2n- -t-R'-h (° H &gt; mm * S03M) n where R ', M, m and n have the meaning given above, in an aqueous solvent under the following reaction conditions implements: a) at a reaction temperature of at least 100 ° C, b) during a reaction time of at least 1/4 h, c) with a molar ratio of the chemical reactant to the polymer between about 2: 1 and about 1:50, and d) a pressure from atmospheric pressure to 35 times atmospheric pressure (1 to 35 bar). Starting compounds are preferably used in which R is independently hydrogen or methyl, M is independently hydrogen, sodium, potassium and / or ammonium, R 'is a linear alkylene bridging group with 2 to 4 carbon atoms and a, b and d integers with the following relationship are: a / b = zero to 50 a / d = zero to 50 b / d = 0.01 to 10, and d: (a + b) is between about 4: 1 and 1:20 , and the sum of a + b + d is such that the sulfonated polymer has a molecular weight of 2,000 to 20,000,000, where A. is a polymer of the general formula Ri R-1

O C-

CH ^ -C

M wherein R, M, a, b have the above meaning and the sum of a + b is such that the molecular weight of the polymer is at least 2000, with B. a chemical reactant of the general formula h9 ne Ri -) - eso, M ) ^ | j n m (OH), where R | and M has the above meaning, m is zero to 3 and η is 1 to 3, and the sum of m + η is 1 to 4, at a temperature of at least 100 ° C for at least 1 1/2 hours in an aqueous solvent -7-

AT 395 592 B, wherein the ratio of reactant to polymer is between about 1: 1 to about 1:10, and the reaction pressure is at least 1.25 bar.

A water-in-oil emulsion is expediently used as the solvent. In particular, the process according to the invention is suitable for producing sulfonated polymers of the general formula R-t R-i r R-i r CH,

M -CH, o-TNH, -CH, 0 = C 'NH (R, _) - (OH) (S0 ~ 3M +) n m where R is independently hydrogen, methyl or ethyl groups; M independently represents a hydrogen, sodium, potassium, tertiary amine and / or ammonium ion; R 'is a linear alkylene bridging group with 1 to 4 carbon atoms; m is zero to 3, η is 1 to 3 and the sum of n + m is 1 to 4, and a, b and d are integers in the following relationship: a / d = zero to 50, a / b = zero to 50, b / d = 0.1 to 20, d: (a + b) = 5: lbisl: 10, and the sum of a + b + is sufficient to give a molar mass of at least 2000, which is thereby characterized in that A. a chemical reactant of the general formula OH) m h2n-eR '• SO &quot; M +) ό n. Where R ', M, m and n are as defined above, with B. a water-soluble vinyl polymer with pendant amide groups of the general formula R-i R-i 2

CH

0

• C

b nh2 -8-

AT 395 592 B wherein R, M, a and b have the meaning given above, in an aqueous solvent for at least 1/2 h at a temperature of at least 110 ° C. in a pressure-controlling reactor, the molar ratio of reactant increasing the pendant amide groups of the polymer is between about 1: 1 to about 1: 5.

The invention is illustrated by the following examples.

Example?;,

In each of the synthetic procedures below, a low molecular weight copolymer of acrylic acid and acrylamide was reacted with 1 - amino-2-hydroxy-propane-sulfonic acid in a homogeneous aqueous solution. The reactions were carried out at temperatures of at least 100 ° C. and on polymer scaffolds of acrylic acid and acrylamide with different molecular weights

The composition of the polymers varied from homopolyacrylamide to copolymers, each with 50 mol% of acrylamide and acrylic acid. The polymers and reactants were placed as aqueous solutions in a paired flask equipped with devices for measuring temperature and pressure and also having means for stirring the contents. The temperatures were raised to at least 100 ° C. in each case. The reaction times ranged from about 20 minutes to more than 4 hours in order to achieve the synthesis of the polymers, as indicated in Table I.

Similarly, the polymers shown in Table II can be obtained from the specified starting materials. (Table I follows.) -9-

AT 395 592 B bO S 3 Ό

£ S * «n in Sä Sä © Sä $ + o O vo Os Os r- o O r- o CO 3 E 100 1 200 750 200 800 200 §» -3 o CO vo 00 m 00 00 s T * r- CS cs cs cs cs

o CO © o m o o ci fH m rH d SO o o »n o o g in § rH CO o o o CO 00 in in CS CS

Table I

w ä § g u U &lt; J U U o υ ü 1 § · o O 0 O o O O O o O o O o O 8 S in * n in m m m m in 05 £ rH 1 — H H ^ H ^ H rH tH

«Sä CO i« 'S bO (m «! E sn 5ΕΓ κ o - * r u6 o cs s o &quot; 2- ub ώ ° sT u &amp; o ö 3 · 2 &quot; ä U - peT u &amp; s © © m rH CO in r-%%% s &lt; s o &quot; o &quot; cf CO CO X b &amp; Γ uo ü υ b ώ b ώ b ώ b ώ 0 &amp; u &amp;

° 5f U U sif u &amp; &lt; J - sf u &amp; 2ns sf υ ώ α - &amp; for u &amp;

ffi O «4 / -IHi« ’m, &lt; S £ 3 "'S &gt; · m O" j ίδί &lt; ä

% S o Ό

O IO i 42 m! in cs &lt; ä m t &gt; * n cs 42 »η r- in cs 1 AA = acrylic acid monomer unit 2 AcAm = acrylamide monomer unit m m o cs m cs o co m co 10 AT 395 592 B table Π

4AA3-tAcAmiT-4CH_-CH'J, a d i »α 0 = C OH OH OH NH precipitated polymer product

• {CH2 - t € H2 ~ CH + b — tCH 2 - oi o = c oi NH 4- M + I NH „CH4a L · * Na + ho3sch2 INI -CH-CH-CH-CH, -fAA] a4AcAmtg-4GH2- CHt ^ - i = o

Ai

CI NH H03S-CH2 ~ CH-CH-CH2

-f-AA-h; —EAcAmi ^ —ECH2 ~ CHt ^ * 0 = C

YH

OH so3h

—FrAA] 1 ™ 1 [AcAm-l · ^ —tCH2 ~ ^ H ^ - 0 = C 1 QH N-CH.

.CH-CH / Z ΟΗ n I 1 -ch-c ho3s

-11- AT 395 592 B table Π (continued ·)

-12-

Claims (6)

AT 395 592 B PATENT CLAIMS 1. Process for the preparation of water-soluble, sulfonated polymers with statistically recurring subunits of the general formula , (V) NR 1 (R '* 3- (OH) imn (SO &quot; 3M +) where R is each independently hydrogen or lower alkyl having 1 to 4 carbon atoms; M is independently a hydrogen, alkali metal, Alkaline earth metal, tertiary amine and / or ammonium ion, R 'is a multicovalent hydrocarbon bridging group having 1 to 16 carbon atoms, selected from one or more linear or branched alkylene, cyclic, aromatic and olefinic groups, a, b and d are integers in the following relationship: a / b = zero to 100 b / d = 0.01 to 100 a / d = zero to 100, and the sum a + b + d is sufficient to have a molecular weight of at least 1000 and the ratio d: (a +, b) is 20: 1 to 1: 100, m is zero to 16 and η is 1 to 8, provided that when m is zero, R 'selects a bridging group from one or more linear alkylene, cyclic, olefinic and aromatic groups, with the further proviso that the sum of m + η = 1 to 20, characterized in that A. a polymer with a »molecular weight of at least 500 and with pendant functional amide groups of the general formula where R, M, a and b have the above meaning, with -13 AT 395 592 B B. a chemical reactant of the general formula RI HK-f-R '-) - tSO, M) j 3 n * (OH) m wherein R, R ', M, m and n have the meaning given above, in a solvent at a temperature of at least 100 ° C., the molar ratio of the chemical reactant to pendant amide groups in the polymer being about 5: 1 to about 1: 100 is and the reaction on the amide nitrogen group is allowed to continue until at least 25% conversion of the chemical reactant into the pendant groups of the sulfonated polymer takes place, water, dimethylformamide and / or dimethyl sulfoxide being used as the solvent or water or in as the solvent a continuous oil phase emulsified water is used so that the water-soluble sulfonated polymer is obtained either as a water-in-oil emulsion or as an aqueous solution. 2. The method according to claim 1, characterized in that starting compounds are used in which R is in each case independently of one another hydrogen, methyl or ethyl, M is independently of one another in each case hydrogen is sodium, potassium, tert.amine and / or ammonium, R 'is at least 2 C- Has atoms and one or more linear, cyclic, aromatic groups, m is zero to 4 and η is 1 to 4, a water-soluble sulfonated polymer having a molecular weight of about 2000 to 20,000,000 being obtained. 3. The method according to claim 1 for the preparation of water-soluble, sulfonated polymers of the general formula R-i R-1 r G CH ^ -CH, R-T I • c a 0 O TNH, 0 = C NH (R '-) - (OH) (SO-3M +) n m in which R independently of one another is hydrogen or lower alkyl having 1 to 4 carbon atoms; M is independently a hydrogen, alkali metal, tert. Represents amine or ammonium ion; R 'is multicovalent branched alkylene, linear alkylene or a cyclic hydrocarbon bridging group with 1 to 8 C atoms; m is zero to 6, η is 1 to 4 and a, b and d are integers in the following relationship: a / b = zero to 100 a / d = zero to 100 b / d = 0.01 to 100, where the ratio d: (a + b) is between about 5: 1 and 1:25, the occurrence of the subunits a, b and d is arbitrary, and the sum of a + b + d gives a molar mass of at least 2000, characterized in that man -14- AT395592B A. a polymer with pendant functional amide groups of the general formula wherein R, M, a and b have the meaning given above and the sum of a + b gives a molecular weight of at least 500, with B. a reactant of the general formula h2n-fS03M) n -i-R'-t (° H &gt; mm wherein R ', M, m and n have the meaning given above, in an aqueous solvent under the following reaction conditions: a) at a reaction temperature of at least 100 ° C., b) during a reaction time of at least 1/4 h, c) with a Molar ratio of chemical reactant to polymer between about 2: 1 and about 1:50, and d) at a pressure from atmospheric to 35 times atmospheric (1 to 35 bar). 4. The method according to claim 3, characterized in that one uses starting compounds in which R independently of one another is hydrogen or methyl, M independently of one another is hydrogen, sodium, potassium and / or ammonium, R 'is a linear alkylene bridge group with 2 to 4 C. -Atoms is and a, b and d are integers with the following relationship: a / b = zero to 50 a / d = zero to 50 b / d = 0.01 to 10, and d: (a + b) between is about 4: 1 and 1:20, and the sum of a + b + d is such that the sulfonated polymer has a molecular weight of 2,000 to 20,000,000, characterized in that A. a polymer of the general formula -15- AT395592B wherein R, M, a, b have the above meaning and the sum of a + b is such that the molecular weight of the polymer is at least 2000, with B. a chemical reactant of the general formula h2n-e-Ri- } —Eso3M) n <OH> m wherein Rj and M have the above meanings, m is zero to 3 and η is 1 to 3, and the sum of m + η 1 to 4, at a temperature of at least 100 ° C during at least 1/2 in an aqueous solvent, the ratio of reactant to polymer being between about 1: 1 to about 1:10, and the reaction pressure being at least 1.25 bar. 5. The method according to claim 3 or 4, characterized in that a water-in-oil emulsion is used as the solvent. 6. The method according to claim 1 for the preparation of a sulfonated polymer of the general formula R — I R ~ l r R-7 CH, -QL -CH, a Γ 0— I 0 —c | 0 H + NH2 NH 1 (R '- &gt; m (SO-3M +) n where R is independently hydrogen, methyl or ethyl groups; M is independently hydrogen, sodium, potassium, tertiary amine and / or Represents ammonium ion; R 'is a linear alkylene bridging group with 1 to 4 carbon atoms; m is zero to 3, η is 1 to 3 and the sum of n + m is 1 to 4, and a, b and d are integers in the following relationship are: a / d = zero to 50, a / b = zero to 50, b / d = 0.1 to 20, d: (a + b) = 5: 1 to 1:10, and the sum of a + b + d is sufficient to give a molecular weight of at least 2000, characterized in that A. a chemical reactant of the general formula -16- AT 395 592 B wherein R ', M, m and n are as defined above, with B. a water-soluble vinyl polymer with pendant amide groups of the general formula wherein R, M, a and b have the above meaning, in an aqueous solvent for at least 1/2 h tm at a temperature of at least 110 ° C in a pressure-controlling reactor, wherein the Molvcrhülum of reactant to the pendant amide groups of Polymer is between about 1: 1 to about 1: 5. -17-