CA2319455A1 - Postcrosslinking of hydrogels using boric esters - Google Patents

Abstract

The invention relates to a method for the surface secondary cross-linking of water-absorbent polymers by treatment of the polymers with a solution for surface secondary cross-linking. According to said method the polymers during or after spraying are subjected to secondary cross-linking and dried by raising the temperature to 50-250 ~C and the cross-linking agent contains a boric acid ester with a bivalent or trivalent alcohol dissolved in an inert solvent. The invention also relates to water-absorbent polymers obtainable in accordance with the above method and to their use in hygiene articles, packing materials and non-woven materials.

Description

' CA 02319455 2000-08-02 Postcrosslinking of hydrogels using boric esters Description The present invention relates to a process for the gel or surface postcrosslinking of water-absorbing hydrogels using boric esters of polyhydric alcohols, to the water-absorbing polymers obtainable in this way and to their use in hygiene articles and packaging materials.
Hydrophilic highly swellable hydrogels are, in particular, polymers composed of (co)polymerized hydrophilic monomers, or are graft (co)polymers of one or more hydrophilic monomers on a suitable graft base, crosslinked cellulose ethers or crosslinked starch ethers, crosslinked carboxymethylcellulose, partially crosslinked polyalkylene oxide, or natural products that are swellable in aqueous liquids: guar derivatives, for example.
Hydrogels of this kind are used as products for absorbing aqueous solutions in the production of diapers, tampons, sanitary towels and other hygiene articles, and as water retainers in market gardening.
To improve service properties such as diaper rewet and AUL
(absorbency under load), for example, hydrophilic highly swellable hydrogels are generally subjected to surface or gel postcrosslinking. This postcrosslinking is known to the person skilled in the art and is preferably carried out in the aqueous gel phase or as'surface postcrosslinking of the milled and sieved polymer particles.
Crosslinkers suitable for this purpose are compounds comprising at least two groups which are able to form covalent bonds with the carboxyl groups of the hydrophilic polymer. Examples of suitable crosslinkers are diglycidyl or polyglycidyl compounds, such as diglycidyl phosphonate, alkoxysilyl compounds, polyaziridines, polyamines and polyamidoamines, and these compounds can also be used in mixtures with one another (see for example EP-A-0 083 022, EP-A-0 543 303 and EP-A-0 530 438).
Polyamidoamines which are suitable as crosslinkers are described in particular in EP-A-0 349 935.
A major. disadvantage of these crosslinkers is their high reactivity. Although this is desirable in terms of chemical reaction, it carries with it a relatively high toxicological potential. In production operations, the processing of such crosslinkers necessitates special protective measures in order to meet the requirements of the governing safety provisions and workplace hygiene. Furthermore, the use of polymers modified in this way in hygiene articles appears to be objectionable.

5 Polyfunctional alcohols are also known crosslinkers. For example, EP-A-0 372 981, US-4 666 983 and US-5 385 983 teach the use of hydrophilic polyalcohols and the use of polyhydroxy surfactants.
According to these documents the reaction is carried out at temperatures of 120 - 250°C. The process has the disadvantage that 10 the esterification reaction which leads to crosslinking is relatively slow even at such temperatures.
The object was therefore, using compounds which are relatively slow to react yet are reactive with carboxyl groups, to achieve 15 just as good if not better gel or surface postcrosslinking compared with the prior art. This object was to be achieved with a very short reaction time and a very low reaction temperature.
Ideally, the prevailing reaction conditions should be the same as those obtaining when highly reactive epoxides are used.
It has surprisingly now been found that esters of boric acid with polyhydric alcohols are highly suitable surface postcrosslinking agents. These esters are readily synthesizable by reacting boric acid or boron oxide with alcohol.
The invention provides a process for the surface postcrosslinking of water-absorbing polymers by treating the polymers with a surface postcrosslinking solution, the polymers being postcrosslinked and dried by means of an increase in temperature during or after the treatment, wherein the crosslinker comprises an ester of boric acid with a dihydric or polyhydric alcohol in solution in an inert solvent.
A boric ester is a compound of the formula B(OR)3. Boric esters are formed, for example, in the reaction of boric anhydride B203 with alcohols, accompanied by formation of boric acid, as follows:
B203 + 3 ROH -+ B(OR)3 + H3B03 or in the case of a higher alcohol excess, in accordance with B203 + 6 ROH -+ 2 B ( OR ) 3 + 3 H20 or by the reaction of boric acid with alcohols, which is accompanied by elimination of water during the esterification reaction, in accordance with B(OH)3 + 3 ROH ~ B(OR)3 + 3 H20 Higher esters of boric acid can be obtained, for example, by transesterification reactions:
B(OR1)3 + 3 RZOH --~ B(ORZ)3 + 3 R10H, the lower-boiling alcohol R10H being separated from the mixture by distillation.
The boric esters used in the process of the invention for surface postcrosslinking are esters of difunctional or polyfunctional alcohols. In the reaction of boric acid or boric anhydride or in the transesterification reaction with bifunctional or polyfunctional alcohols, cyclic compounds or polyesters may also be formed. Considering the reaction of ethylene glycol (R1=H in the formulae la-ld) or 1,2-propanediol (R1=CH3 in the formulae la-ld), the following boric esters may be formed:
With a stoichiometric deficit of alcohol, a partially esterified boric acid is formed preferentially first of all, e.g.
O
--B-OH ( la) O

or else the corresponding anhydride of these compounds:

O
/ B-O-~ ( lb ) O

Complete esterification leads preferentially to the following products:

O
~ H
r--B CH2- C~~~ ( lc ) °O

along with a smaller amount of cyclic compounds and polyesters having the following repeating unit O H
B~ ~CHZ-C~ (ld) ' °J
Using difunctional or polyfunctional alcohols other than ethylene glycol or 1,2-propanediol, the analogous boric esters are formed.
The radical R1 is hydrogen or an alkyl group having preferably 1 to 12, especially 1 to 6, carbon atoms.
The postcrosslinking temperature is preferably 50-250~C, in particular between 50-200~C, specifically between 100-180~C.
In order to accelerate the reaction of the surface postcrosslinking solution, an acidic catalyst can be added.
Catalysts which can be used in the process of the invention are all inorganic acids, their corresponding anhydrides, and organic acids and their corresponding anhydrides. Examples are boric acid, sulfuric acid, hydroiodic acid, phosphoric acid, tartaric acid, acetic acid, and toluenesulfonic acid. Also suitable in particular are their polymeric forms, anhydrides, and the acid salts of the polybasic acids. Examples of these are boron oxide, sulfur trioxide, diphosphorus pentoxide, and ammonium dihydrogen phosphate.
The process of the invention is preferably carried out by spraying a solution of the surface postcrosslinker onto the dry base polymer powder. Following spray application, the polymer powder is dried thermally, it being possible for the crosslinking reaction to take place either before or during drying. Preference is given to the spray application of a solution of the crosslinker in reaction mixers and spray mixers or in mixing and drying systems such as, for example, Lodige mixers, ~BEPEX
mixers, ~NAUTA mixers, ~SHUGGI mixers or ~PROCESSALL. It is, moreover, also possible to use fluidized-bed dryers. Drying can take place in the mixer itself, by heating the outer casing, or by blowing hot air in. Likewise suitable is a downstream dryer, such as a shelf dryer, a rotary dryer or a heatable screw, for example. Alternatively, azeotropic distillation, for example, can 5 be utilized as a drying technique. The residence time at the preferred temperature in the reaction mixer or dryer is from 5 to 90 minutes, preferably less than 30 minutes and, with very particular preference, less than 10 minutes.
As the inert solvent, preference is given to the use of water and of mixtures of water with monohydric or polyhydric alcohols. It is, however, also possible to use any organic solvent of unlimited miscibility with water, such as certain esters and ketones, for example, which are not themselves reactive under the process conditions. where an alcohol/water mixture is used, the alcohol content of this solution is, for example, 10-90% by weight, preferably 30-70% by weight, in particular 40-60% by weight. Any alcohol of unlimited miscibility with water can be used, as can mixtures of two or more alcohols (e.g., methanol +
glycerol + water). Particular preference is given to the use of the following alcohols in aqueous solution: methanol, ethanol, isopropanol, ethylene glycol and, with particular preference, 1,2-propanediol and also 1,3-propanediol. The surface postcrosslinking solution is used in a ratio of 1-20% by weight, based on the polymer mass. Particular preference is given to a solution quantity of 2.5-15% by weight with respect to polymer.
The crosslinker itself is used in an amount of 0.01-1.0% by weight, based on the polymer used.
The water-absorbing polymer is preferably a polymeric acrylic acid or a polyacrylate. This water-absorbing polymer can be prepared in accordance with a method known from the literature.
Preference is given to polymers containing crosslinking comonomers (0.001-10 mol%); very particular preference is given, however, to polymers obtained by free-radical addition polymerization using a polyfunctional ethylenically unsaturated free-radical crosslinker which additionally carries at least one free hydroxyl group (such as, for example, pentaerythritol triallyl ether or trimethylolpropane diallyl ether).
The hydrophilic highly swellable hydrogels to be employed in the process of the invention are in particular, polymers composed of (co)polymerized hydrophilic monomers, or are graft (co)polymers of one or more hydrophilic monomers on a suitable graft base, crosslinked cellulose ethers or crosslinked starch ethers, or natural products which are swellable in aqueous liquids: guar derivatives, for example. These hydrogels are known to the person skilled in the art and are described, for example, in US-A-4 286 082, DE-C-27 06 135, US-A-4 340 706, DE-C-37 13 601, DE-C-28 40 010, DE-A-43 44 548, DE-A-40 20 780, DE-A-40 15 085, DE-A-39 17 846, DE-A-38 07 289, DE-A-35 33 337, DE-A-35 03 458, DE-A-42 44 548, DE-A-42 19 607, DE-A-40 21 847, DE-A-38 31 261, DE-A-35 11 086, DE-A-31 18 172, DE-A-30 28 043, DE-A-44 18 881, EP-A-0 801 483, EP-A-0 455 985, EP-A-0 467 073, EP-A-0 312 952, EP-A-0 205 874, EP-A-0 499 774, DE-A-26 12 846, DE-A-40 20 780 EP-A-0 205 674, US-5 145 906, EP-A-0 530 438, EP-A-0 670 073, US-A-4 057 521, US-A-4 062 817, US-A-4 525 527, US-A-4 295 987, US-A-5 011 892, US-A-4 076 663 or US-A-4 931 497. The content of the abovementioned patent documents is expressly incorporated into the present disclosure by reference.
Examples of hydrophilic monomers suitable for preparing these hydrophilic highly swellable hydrogels are polymerizable acids, such as acrylic acid, methacrylic acid, vinylsulfonic acid, vinylphosphonic acid, malefic acid including its anhydride, fumaric acid, itaconic acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-acrylamido-2-methylpropanephosphonic acid, alkali metal salts and ammonium salts of monomers containing acid groups, and also their amides, hydroxyalkyl esters and amino alkyl- or ammonium-containing esters and amides. Also suitable, furthermore, are water-soluble N-vinyl amides such as N-vinylformamide or else diallyldimethylammonium chloride.
Preferred hydrophilic monomers are compounds of the formula \ /
C=C (2) / \

in which R1 hydrogen, methyl or ethyl, R2 is -COOR4, a sulfonyl group, a phosphonyl group, a (C1-C4)-alkanol-esterified phosphonyl group, or a group of the formula O
C ~C\ ,R5 (3), ~ 'N ~ CH2 H

in which R3 is hydrogen, methyl, ethyl or a carboxyl group, R4 is hydrogen, alkali metal ion or ammonium ion, amino-(C1-C4)-alkyl or hydroxy-(C1-C4)-alkyl, and RS is a sulfonyl group, a phosphonyl group, a carboxyl group or the alkali metal or ammonium salts of these groups.
Examples of (C1-C4)-alkanols are methanol, ethanol, n-propanol, isopropanol and n-butanol. Particularly preferred hydrophilic monomers are acrylic and methacrylic acid and the sodium, potassium and ammonium salts of these acids. If desired, these acids may also be in partly neutralized form.
Suitable graft bases for hydrophilic hydrogels obtainable by graft copolymerization of olefinically unsaturated acids may be natural or synthetic in origin. Examples are starch, cellulose and cellulose derivatives, and also other polysaccharides and oligosaccharides, polyalkylene oxides, especially polyethylene oxides and polypropylene oxides, and hydrophilic polyesters.
Suitable polyalkylene oxides have, for example, the formula X
R6 - 0- (CHy- CH- O)n- R~ (4) in which R6 and R~ independently of one another are hydrogen, alkyl, alkenyl or acyl, X is hydrogen or methyl, and n is an integer from 1 to 10,000.
R6 and R~ are preferably hydrogen, (C1-C4)-alkyl, (CZ-C6)-alkenyl or phenyl. Particularly preferred hydrogels are polyacrylates, polymethacrylates, and the graft copolymers described in US-A-4 931 497, US-A-5 011 892 and US-A-5 041 496.
The hydrophilic highly soluble hydrogels are preferably in crosslinked form; that is, they include compounds having at least two double bonds which have been copolymerized into the polymer network. Particularly suitable crosslinkers are methylenebisacrylamide and methylene-bismethacrylamide, esters of unsaturated mono- or polycarboxylic acids with polyols, such as diacrylate or triacrylate, examples being the diacrylates and dimethacrylates of butanediol and of ethylene glycol, and trimethylolpropane triacrylate, and also allyl compounds such as allyl (meth)acrylate, triallyl cyanurate, diallyl maleate, polyallyl esters, tetraallyoxyethane, triallylamine, tetraallylethylenediamine, allyl esters of phosphoric acid, and vinylphosphonic acid derivatives as described, for example, in EP-A-0 343 427. In the process of the invention, however, particular preference is given to hydrogels prepared using polyallyl ethers as crosslinkers and by acidic homopolymerization of acrylic acid. Suitable crosslinkers are pentaerythritol tri-and tetraallyl ether, polyethylene glycol diallyl ether, monoethylene glycol diallyl ether, glycerol di- and triallyl ether, polyallyl ethers based on sorbitol, and alkoxylated variants thereof.
The hydrophilic highly swellable hydrogels can be prepared by conventional polymerization processes. Preference is given to addition polymerization in aqueous solution by the process known as gel polymerization. In this process from 15 to 50% by weight strength aqueous solutions of one or more hydrophilic monomers, and, if desired, of a suitable graft base, are polymerized in the presence of a free-radical initiator, preferably without mechanical mixing, utilizing the Trommsdorff-Norrish effect (Makromol. Chem. 1 (1947) 169).
The polymerization reaction can be conducted in the temperature range between 05C and 1505C, preferably between 105C and 1005C, either at atmospheric pressure or under an increased or reduced pressure. The polymerization may also be performed in an inert gas atmosphere, preferably under nitrogen.

The polymerization can be initiated using high-energy electromagnetic radiation or by the customary chemical polymerization initiators. Examples of these are organic peroxides, such as benzoyl peroxide, tert-butyl hydroperoxide, methyl ethyl ketone peroxide and cumene hydroperoxide, azo compounds, such as azodiisobutyronitrile, and inorganic peroxo compounds, such as (NH4)2S208, K2S20s or Hz02. They can if desired be used in combination with reducing agents such as sodium hydrogen sulfite or iron(II) sulfate, or redox systems. Redox systems include a reducing component, which is generally an aliphatic or aromatic sulfinic acid, such as benzenesulfinic acid or toluenesulfinic acid or derivatives of these acids, such as Mannich adducts of sulfinic acid, aldehydes and amino compounds, as described in DE-C-13 O1 566.

The qualities of the polymers can be improved further by continuing to heat the polymer gels for a number of hours within the temperature range from 50 to 130°C, preferably from 70 to 100°C.
The resultant gels are neutralized to the extent of 0-100 mol%
based on monomer employed, preferably 25-100 mol% and with particular preference 50-85 mol%, it being possible to use the customary neutralizing agents, preferably alkali metal hydroxides or alkali metal oxides, and with particular preference sodium hydroxide, sodium carbonate or sodium hydrogen carbonate.
Neutralization is usually effected by mixing in the neutralizing agent as an aqueous solution or else, preferably, as a solid. For this purpose the gel is mechanically comminuted, by means of a mincer for example, and the neutralizing agent is sprayed on, scattered over or poured on, and then carefully mixed in. To effect homogenization the resultant gel mass may be passed through the mincer again a number of times.
The neutralized gel mass is then dried with a belt dryer or roll dryer until the residual moisture content is less than 10% by weight, preferably below 5% by weight. The dried hydrogel is then ground and sieved, the usual grinding apparatus being roll mills, pin mills or vibrator mills. The preferred particle size of the sieved hydrogel lies in the range 45-1000 mm, with particular preference 45-850 mm and with very particular preference 200-850 mm.
The invention further provides a water-absorbing polymer obtainable by the process described above.

The invention additionally provides for the use of the products produced by the process of the invention in hygiene articles, packaging materials, and nonwovens.
5 In order to ascertain the quality of surface postcrosslinking the dried hydrogel is then tested using the test methods known from the prior art and described below:
Methods:
1) Centrifuge retention capacity (CRC):
This method measures the free swellability of the hydrogel in a teabag. Approximately 0.200 g of dry hydrogel are sealed into a teabag (format: 60 mm x 60 mm, Dexter 1234T paper) and soaked for 30 minutes in 0.9% strength by weight sodium chloride solution.
The teabag is then spun for 3 minutes in a customary commercial spindryer (Bauknecht WS 130, 1400 rpm, basket diameter 230 mm).
The amount of liquid absorbed is determined by weighing the centrifuged teabag. The absorption capacity of the teabag itself is taken into account by determination of a blank value (teabag without hydrogel), which is deducted from the weighing result (teabag with swollen hydrogel).
Retention CRC [g/g] _ (weighing result teabag - blank value -initial weight of hydrogel) + initial weight of hydrogel 2) Absorbency under load (2068.5 Pa (0.3 psi) / 3447.5 Pa (0.5 psi) / 4826.5 Pa (0.7 psi)) For the absorbency under load, 0.900 g of dry hydrogel is distributed uniformly on the screen base of a measuring cell. The measuring cell consists of a Plexiglas cylinder (height = 50 mm, diameter = 60 mm) whose base is formed by sticking on a screen of steel mesh (mesh size 36 microns, or 400 mesh). A cover plate is placed over the uniformly distributed hydrogel and loaded with an appropriate weight. The cell is then placed on a filter paper (S&S 589 black band, diameter = 90 mm) lying on a porous glass filter plate, this filter plate itself lying in a Petri dish (height = 30 mm, diameter = 200 mm) which contains 0.9$ strength by weight sodium chloride solution so that the liquid level at the beginning of the experiment is level with the top edge of the glass frit. The hydrogel is then left to absorb the salt solution for 60'minutes. Subsequently, the complete cell with the swollen gel is removed from the filter plate and the apparatus is reweighed following removal of the weight.
AMENDED SKEET

The absorbency under load (AUL) is calculated as follows:
AUL [g/gl = ( ~ - Wa ) / Ws where Wb is the mass of the apparatus + gel after swelling, Wa is the mass of the apparatus + initial weight of gel before swelling, and Ws is the initial weight of dry hydrogel.
The apparatus consists of measuring cylinder and cover plate.
Examples Preparation of boric esters Boric ester 1 A three-necked flask with stirrer, internal thermometer and reflux condenser is charged with 9 mol of ethylene glycol, and 1 mol of boric anhydride is added slowly to this initial charge.
The solution is stirred at 80~C for 2 hours. Subsequently, unreacted ethylene glycol and water are separated off by distillation under reduced pressure. On cooling, a white waxlike substance is formed.
Boric ester 2 A three-necked flask with stirrer, internal thermometer and reflux condenser is charged with 4 mol of propanediol (1,2), and 1 mol of boric acid is added to this initial charge. The mixture is heated to boiling and the water is distilled off under atmospheric pressure. Subsequently, the excess 1,2-propanediol is distilled off under reduced pressure. Again, a white waxlike substance is obtained which solidifies on cooling.
These boric esters are used in accordance with the invention for crosslinking superabsorbent polymers. The examples below illustrate the crosslinking action of the boric esters.
Example 1 In a 40 1 plastic bucket, 6.9 kg of pure acrylic acid are diluted with 23 kg of water. 45 g of pentaerythritol triallyl ether are added with stirring to this solution, and the sealed bucket is rendered inert by passing nitrogen through it. The polymerization is then initiated by adding about 400 mg of hydrogen peroxide and 200 mg of ascorbic acid. After the end of the reaction the gel is mechanically comminuted and sodium hydroxide solution is added in an amount sufficient to achieve a degree of neutralization of 75 mol%, based on the acrylic acid employed. The neutralized gel is then dried on a roll dryer, ground with a pin mill and, finally, isolated by sieving. This is the base polymer used in the subsequent examples.
This base polymer (1 kg) is spray-coated with the surface postcrosslinking solution in a Lodige plowshare mixer in a two-stage process.
Stage 1: First of all, a solution of the boric ester 1 (0.5% by weight based on base polymer) in ethylene glycol as solvent (5%
by weight based on base polymer) is applied by spraying.
Stage 2: Subsequently, the temperature of the heating jacket is increased linearly from 50~C to 200~C. As soon as the product temperature has reached 80-90~C, an additional 5% by weight of water (based on base polymer) is sprayed on. The process is over after about 30 minutes, and the hydrogel is sieved again in order to remove lumps and can then be used, for example, as a water-absorbing polymer in diapers. The values measured for CRC
and AUL are indicated in the table.
Example 2 A base polymer prepared in accordance with Example 1 is sprayed with crosslinker solution in a blaring laboratory mixer. The composition of the solution is such that the following dosage, based on base polymer employed, is achieved: 0.5% by weight boric ester 1, 4.5% by weight propylene glycol, and 4.5% by weight water. The moist polymer is then dried at 175~C for 60 minutes.
The table indicates the values measured for CRC and AUL.
Example 3 A base polymer prepared in accordance with Example 1 is sprayed with crosslinker solution in a blaring laboratory mixer. The composition of the solution is such that the following dosage, based on base polymer employed, is achieved: 0.5% by weight boric ester 2, 4.5% by weight propylene glycol, and 4.5% by weight water.. The moist polymer is then dried at 175~C for 60 minutes.
The table indicates the typical properties of the polymer.

Example 4 A base polymer prepared in accordance with Example 1 is sprayed with crosslinker solution in a Telschig laboratory mixer. The composition of the solution is such that the following dosage, based on base polymer employed, is achieved: 0.5% by weight boric ester 2, 7% by weight methanol, and 3% by weight water. The moist polymer is then dried at 150~C for 60 minutes. The table indicates the typical properties of this water-absorbing polymer.
Table Polymer from CRC AUL 2068.5 AUL 3447.5 AUL 4826.5 [g/g] Pa (0.3 psi) Pa (0.5 psi) Pa (0.7 psi) [g/gl [g/gl [g/gl Example 1 35 35 26 18 Example 2 37 34 20 14 Example 3 33 32 28 23 Example 4 29 30 27 25 Comparison 42 10 9 9 base polymer AMENDED SHEET

Claims (10)

We claim:

1. A process for the surface postcrosslinking of water-absorbing polymers by treating the polymers with a surface postcrosslinking solution, the polymers being postcrosslinked and dried during or after the treatment by means of an increase in temperature, wherein the crosslinker contains an ester of boric acid having a dihydric or polyhydric alcohol dissolved in an inert solvent.

2. The process as claimed in claim 1, wherein the water-absorbing polymer is a polymeric acrylic acid or a polyacrylate, especially a polymeric acrylic acid or polyacrylate obtained by free-radical addition polymerization in the presence of a polyfunctional ethylenically unsaturated free-radical crosslinker which may additionally carry one or more free hydroxyl groups

3. The process as claimed in claim 1 or 2, wherein the catalyst used for crosslinking comprises an inorganic acid, its anhydride, an organic acid or its anhydride.

4. The process as claimed in claim 3, wherein the acid is boric, sulfuric, hydroiodic, phosphoric, tartaric, acetic or toluenesulfonic acid or the polymeric forms, anhydrides or acid salts thereof.

5. The process as claimed in one or more of claims 1 to 4, wherein the inert solvent is water, a mixture of water with organic solvents of unlimited solubility in water, or a mixture of water with monohydric or polyhydric alcohols.

6. The process as claimed in claim 5, wherein if an alcohol/water mixture is used the alcohol content of this solution is 10-90% by weight, preferably 30-70% by weight.

7. The process as claimed in claim 5 or 6, wherein the alcohol is methanol, ethanol, isopropanol, ethylene glycol, 1,2-propanediol or 1,3-propanediol.

8. The process as claimed in one or more of claims 1 to 4, wherein the surface postcrosslinking solution is employed in a proportion of 1-20% by weight, in particular 2.5-15% by weight, based on the mass of the polymer.

9. A water-absorbing polymer prepared by the process as claimed in one or more of claims 1 to 8.

10. The use of a polymer prepared by the process as claimed in one or more of claims 1 to 8 in a hygiene article, packaging material or nonwoven.