Cross-linked polymers with a porous structure

The invention relates to crosslinked synthetic polymers based on acrylic acid and its derivatives having high molecular weight Absorbing capacity and improved absorption rate for water, aqueous solutions and body fluids, A process for their preparation by free-radical polymerization under such conditions as to give polymers Which have a porous structure and a particle density dependent on the degree of swelling so that The polymer particles are floatable in water or aqueous liquids, and the use of these polymers For the absorption and / or retention of water or aqueous solutions and for the delivery of water and / or Of an active ingredient solution to a surrounding medium.

Various synthetic polymers, which have an absorption capacity for water and body fluids, Are described in numerous patents: for example, crosslinked polymers and copolymers based on acrylic or methacrylic acid (US Pat. No. 4,018,951, US Pat. No. 4,066,583, US Pat. No. 4,062,817, US Pat. No. 4,066,583, German Offenlegungsschrift No. 2,613,135, German Offenlegungsschrift No. 2,712,043, German OS) 28 13 634) or acrylamidopropane sulfonic acid copolymers (DE-PS 31 24 008). These absorbents are Virtually insoluble in water and absorb the multiple of their weight in equilibrium with aqueous liquids Water, urine or other aqueous solutions. In addition to high liquid absorption capacity, Further properties of the synthetic absorbers, such as low residual monomer content, low content of Water-soluble fractions and high gel strength of the swollen polymer particles are given in some patents.

US Pat. Nos. 4,529,739 and 4,649,164 disclose polymers having a porous structure based on methacrylic acid Described from ethyl acrylate / methacrylic acid copolymer latices by addition of compounds containing carbon dioxide Such as, for example, sodium bicarbonate. In the Austrian patent AT 391 321 B are crosslinked, porous acrylic polymers prepared by adding a nitrogen-containing propellant to the monomer solution, Described. According to this process, to acrylic acid which is 60-100% with NaOH, KOH or NH₃Is neutralized, an N-containing blowing agent is added before or after the polymerization, said blowing agent being present during drying Decomposed to ammonia and carbon dioxide at 80 to 250 ° C, the amount added being an increase in the degree of neutralization To 102 to 140%. The propellants used are ammonium salts of inorganic or organic Acids and urea, with ammonium carbonate being preferred. Furthermore, also in US Pat 118 719 ammonium and alkali carbonates are described as blowing agents which are added to the monomer solution before the polymerization Are added. Carbon dioxide is produced during the polymerization by carbon dioxide and is then produced in the Hydrogel, the formation of a "microcellular structure", with the improved absorption rate for liquids In the final product.

The use of alkali or ammonium carbonates before or during the polymerization of organic Acids according to US 4 529 739, US 4 649 164 and US 5 118 719 lead to the formation of the carbon dioxide during the Neutralization of the monomer solution. Because of the limited solubility of CO₂ In the monomer solution and in the The polymer gel mass can only contain relatively small amounts of CO₂ Into the polymer during polymerization or Drying. The second variant according to AT 391 321 B, the addition of the blowing agent to the Polymerisate gel before drying, does not bring about the desired effect due to the superficial effect of the Aftertreatment and this method is associated with the disadvantage of the additional amount of water during drying to remove. Excessive use of ammonia also does not lead to highly porous structures in the swollen Gel state, since ammonia is readily soluble in water or aqueous fluids, so that during the And the porous structure of the hydrogel particles largely disappears. Furthermore, the PH value of the end product is increased by the ammonia or carbonate addition rate well above 7, whereby the application Of the products is severely restricted.

In WO 88/09801, starting from a water-soluble polymer based on acrylic acid, the preparation is carried out Of a cross-linked foamed ethyl acrylate / acrylic acid copolymer having a specific gravity of 0.20 g / cm³ Described. The final product was prepared in aqueous solution, with subsequent crosslinking and Foaming with the addition of a crosslinking agent and a propellant, for example sodium bicarbonate, p-toluenesulfonylhydrazine Or azocarbonamide, can be carried out in one process step. A disadvantage of this method is the It is necessary to work in an aqueous solution, the concentration of the copolymer being adjusted Is limited to 18% by weight, for example, because of the high viscosity. Furthermore, it is necessary to make large Propellant amounts, for example 27% by weight, based on the copolymer.

As is known from AT 391 321 B, azo compounds are usually used in very small amounts, for example To 0.056% by weight, based on the monomer, as polymerization initiators Concentrations of such free-radical radicals are reduced to polymers having a lower molar mass And products with insufficient absorptive properties.

The known polymers which absorb water or aqueous liquids are also distinguished by this From being introduced into water or aqueous liquids in the non-swollen state and after liquid absorption Are not buoyant on the surface of the liquid unless they are auxiliary such as cork flour as described in EP 0 285 404 B1.

The object, therefore, was to provide, in order to avoid the disadvantages mentioned, absorptive agents with a porous structure, Good absorption properties, such as, in particular, improved pick-up speed, as well as lower average Overall density of the individual particles, so that the polymer particles, in particular in the swollen Condition on the water surface.

Surprisingly, it has now been found that water-swellable, cross-linked, particulate polymers as claimed in claim 1 with Porous structure and high absorption rate for water and aqueous liquids and a density below 1.0 g / cm³ In the swollen state and a density above 1.0 g / cm 3³ In the dry state by radical polymerization In aqueous solution using at least one azo compound simultaneously as a polymerization initiator And propellants can be produced at a higher concentration. Suitable azo compounds which can be used are those , Which have a half-life of 10 hours or more, at a temperature in the range of 30 to 120 ° C., preferably in the temperature range from 60 to 120 ° C. The azo compounds are added to the monomer solution Before polymerization. The following azo compounds are preferably used<sl><li>1. Azonitrile Compounds:<sl><li>2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile),</li><li>2,2'-azobis (2-cyclopropylpropionitrile),</li><li>2,2'-azobis (2,4-dimethylvaleronitrile),</li><li>2,2'-azobis (2-methylpropionitrile),</li><li>2,2'-azobis (2-methylbutyronitrile),</li><li>1,1'-azobis (cyclohexane-1-carbonitrile),</li><li>1 - [(1-cyano-1-methylethyl) azo] formamide (2- (carbamoylazo) isobutyronitrile) and 2-phenylazo-4-methoxy-2,4-dimethylvaleronitrile.</li></sl></li><li>2. Azoamidine Compounds:<sl><li>2,2'-azobis (2-methyl-N-phenylpropionamidine) dihydrochloride,</li><li>2,2'-azobis [N- (4-chlorophenyl) -2-methylpropionamidine] dihydrochloride,</li><li>2,2'-azobis [N- (4-hydroxyphenyl) -2-methylpropionamidine] dihydrochloride,</li><li>2,2'-azobis [N- (4-aminophenyl) -2-methylpropionamidine] tetrahydrochloride,</li><li>2,2'-azobis [2-methyl-N- (phenylmethyl) -propionamidine] dihydrochloride,</li><li>2,2'-azobis [2-methyl-N-2-propenylpropionamidine] dihydrochloride,</li><li>2,2'-azobis (2-methylpropionamidine) dihydrochloride and</li><li>2,2'-azobis [N- (2-hydroxyethyl) -2-methyl-propionamidine] dihydrochloride.</li></sl></li><li>3. Cyclic Azoamidine Compounds:<sl><li>2,2'-azobis [2- (5-methyl-2-imidazolin-2-yl) propane] dihydrochloride,</li><li>2,2'-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride,</li><li>2,2'-azobis [2- (4,5,6,7-tetrahydro-1 H -1,3-diazepin-2-yl) propane] dihydrochloride,</li><li>2,2'-azobis [2- (3,4,5,6-tetrahydropyrimidin-2-yl) propane] dihydrochloride,</li><li>2,2'-azobis [2- (5-hydroxy-3,4,5,6-tetrahydropyrimidin-2-yl) propane] dihydrochloride,</li><li>2,2'-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} dihydrochloride and</li><li>2,2'-azobis [2- (2-imidazolin-2-yl) propane].</li></sl></li><li>4. Azoamide Compounds:<sl><li>2,2'-azobis {2-methyl-N- [1,1-bis (hydroxymethyl) -2-hydroxyethyl] propionamide},</li><li>2,2'-azobis {2-methyl-N- [1,1-bis (hydroxymethyl) ethyl] propionamide},</li><li>2,2'-azobis [2-methyl-N- (2-hydroxyethyl) propionamide] and</li><li>2,2'-azobis (2-methylpropionamide) dihydrate.</li></sl></li><li>5. Alkylazo and other azo compounds:<sl><li>2,2'-azobis (2,4,4-trimethylpentane),</li><li>2,2'-azobis (2-methylpropane),</li><li>Dimethyl 2,2'-azobis (2-methylpropionate), </li><li>4,4'-azobis (4-cyanovaleric acid) and</li><li>2,2'-azobis [hydroxymethyl) propionitrile].</li></sl></li></sl>

The water-swellable, cross-linked, particulate polymers according to the invention preferably comprise in the swollen, State has a mean particle density of 0.900 to 0.999 g / cm 2³ And a grain distribution of the particles in one Range of 0.1 to 5.0 mm, in particular of 0.8 to 3 mm.

Suitable monomers are, in particular, acrylic acid, methacrylic acid, acrylamidomethyl-propanesulfonic acid, the salts thereof Acids, in particular the alkali metal, alkaline earth metal and ammonium salts, as well as acrylamide and methacrylamide. The above monomers can be mixed alone for the preparation of homopolymers or among themselves For the preparation of copolymers. The abovementioned monomers can also be used for the preparation Of copolymers with further water-soluble monomers, such as water-soluble, polymerizable acids, Preferably maleic, fumaric, itaconic or vinylsulfonic acid or the salts of these acids. Continue Useful monomers are acrylonitrile, methacrylonitrile, vinylpyridine, vinyl acetate, and also hydroxyl-containing esters Polymerizable acids, in particular the hydroxyethyl and hydroxypropyl esters of acrylic and methacrylic acid And amino - containing and ammonium - containing esters and amides of polymerizable acids, such as The dialkylamino esters, in particular the dimethyl and diethylaminoalkyl esters of acrylic and methacrylic acid, And the trimethyl and trimethylammonium alkyl esters as well as the corresponding amides. In small amounts Additionally water-insoluble monomers can be copolymerized with the above monomers, for example Esters of acrylic and / or methacrylic acid with C₁-C₁₀Alcohols, styrene and alkylated styrenes. In general, the Fraction of the water-soluble monomers is from 80 to 100% by weight, based on the entirety of the monomers. The Water-insoluble (hydrophobic) monomers generally make up from 0 to 20% by weight, preferably up to 10% by weight, Of the monomers. The polymerization can also be complete or partial as graft polymerization in the presence Of other polymer substances, such as oligo- and polysaccharides, or polyvinyl alcohol.

The azo compounds mentioned can also be obtained by utilizing the different decomposition properties Can be used in combination. The concentration of the blowing agent additive in the monomer solution is 0.1 To 5.0% by weight, preferably 0.2 to 2.0% by weight.

The water-absorbing polymeric absorbers are usually prepared using at least one Crosslinking monomers. Crosslinking monomers used are compounds which contain at least 2 Or more functional groups, for example double bonds or epoxide groups, and are capable of being formed during Of the polymerization into the growing polymer chains. Thus, in the polymer during the Polymerization or a subsequent reaction of the functional groups at various points in the polymer Crosslinking points which link the individual polymer chains and cause the polymer particles to be dissolved in a liquid However, sources can not dissolve. Through the chemical structure of the crosslinker, the number of Crosslinking sites, but also by their distribution in the polymer chains, the properties of the crosslinked Polymers. Crosslinking monomers which may be mentioned are bi- or multifunctional monomers, for example amides such as The methylenebisacryl- -methacrylamide or ethylenebisacrylamide, furthermore esters of polyols, such as diacrylates or Triacrylates, for example butanediol or ethylene glycol diacrylate, trimethylolpropane triacrylate, glycidyl methacrylate, glycerol triglycidyl ether, Vinylmethacrylate and allyl compounds such as allyl (meth) acrylate, triallyl cyanurate, maleic acid diallyl ester, Polyallyl esters, tetraallyloxiethane, triallylamine, tetraallylethylenediamine, allyl esters of phosphoric acid or phosphorous Acid, furthermore crosslinkable monomers, such as the N-methylol compounds of amides such as the methacrylamide Or acrylamide and the ether derived therefrom. The proportion of the crosslinking comonomers is included 0.01 to 10% by weight, preferably 0.10 to 2.0% by weight, based on the entirety of the monomers. With optimal Cross-linked polymers in which cross-linking sites are uniform are formed by incorporating the crosslinker into the polymer , So that hardly uncrosslinked regions or even non-crosslinked, ie water-soluble, low molecular weight fractions are obtained In the polymer. A suitable concentration and uniform distribution of the crosslinking sites in the Polymer results in a product which has an optimum retention capacity for water and aqueous liquids, As well as an optimal gel strength in the swollen state.

The polymerization can be started with a redox catalyst system as an initiator or by photopolymerization will. The redox catalyst system usually consists of two components, an inorganic or organic Peroxide-containing compound and a reducing component such as, for example, sulfite, hydrosulfite, thiosulfate, Sulfinic acid, ascorbic acid and its salts, copper, iron (II) or manganese salts. As inorganic peroxide compounds The alkali metal or ammonium peroxides, such as potassium peroxydisulfate, hydrogen peroxide or peroximono- Or diphosphoric acid and its salts or organic peroxides, such as, for example, benzoyl peroxide, butyl hydroperoxide be used. In addition to the first initiator system normally consisting of two components, One or more azo compounds can be used as initiators and blowing agents. For photopolymerization, Which can be initiated by UV-containing light, are so-called photoinitiators, for example benzoin or benzoin derivatives, Such as benzoin ethers, benzil, benzil ketal and other derivatives, acryldiazonium salts, or acetophenone derivatives. Here, too, the propellants used can serve as initiators, whereupon the dosage of the UV light quantity Is decisive for the polymerization. The amounts of the peroxide - containing component and the reducing component Component are in the range from 0.0005 to 0.5% by weight, preferably from 0.001 to 0.1% by weight, On the monomer solution. The amount of photoinitiators which are not azo compounds are in the range of 0.001 to 0.1 % By weight, preferably from 0.002 to 0.05% by weight, On the monomer solution.

The polymerization can be carried out in solution or in suspension, but preferably by the known methods In aqueous solution batchwise in a polymerization vessel or continuously on an endless belt, For example, according to DE-PS 35 44 770. With a practically adiabatic course of the polymerization Is formed at an appropriate initial concentration of from 15 to 50% by weight of the monomers, based on the monomer solution, An aqueous polymer gel. By choosing the initial monomer concentration and a low starting temperature In the temperature range from 0 to 50 ° C., preferably from 10 to 25 ° C., the polymerization can be carried out in this way That the maximum temperature in the resulting aqueous polymer gel in the range of 100-130 ° C. is preferred Of 110-120 ° C. The polymerization can be carried out at a normal or elevated pressure, but preferably at a normal pressure Pressure. In the final phase of the polymerization, the resulting polymer gel has such a consistency with sufficient strength, In order to obtain the partial decomposition of the initiator and propellant in this production phase Nitrogen fines distributed as separate gas bubbles at elevated temperatures of, for example, 100 ° to 120 ° C., relative Small volume and optionally under elevated pressure.

The polymer gel produced is comminuted after completion of the polymerization and heated at temperatures of from 100 to 100.degree 240 ° C, preferably at 120 to 180 ° C. During the drying process, In excess and not decomposed during the polymerization, of the azo compound. The liberation Nitrogen is also enclosed in the form of very small microbubbles in the dry polymer and remains there. In this case, a polymer with a very porous structure is formed, the average total density of which after grinding Is below the density of the polymer itself. In the application of the inventive Polymers together with water or aqueous liquids increase during the swelling process The finely divided gas volumes, wherein, in the equilibrium state, a swollen hydrogel having a reduced gel strength Is generated. At the same time, the average overall density of the swollen particles continuously decreases as a function of the temperature From the degree of swelling to a value less than 1.0 g / cm³ Is reached. The polymer particles, which are present in the solid, Dry state were initially heavier than water, rising and swelling in a swollen state On the Wasserbzw. Liquid surface.

The polymers according to the invention are used in products for the absorption and / or retention of water And / or aqueous liquids, in particular of body fluids, such as urine or blood, preferably in absorbent Disposable products for hygienic purposes, such as babymindles, incontinence articles, sanitary napkins and tampons As well as for medical purposes.

In addition to being used as a liquid absorbing component with an increased absorption rate in Hygiene products, the novel polymers can also advantageously be used for the following purposes.<sl><li>1) The polymers can be used for a controlled and controlled delivery of polymers which are subsequently incorporated into the polymer, for example By absorption, or already by other substances contained in the polymer To other bodies, for example for the dosing of medicaments, nutrients, insecticides and herbicides in aqueous Medium, preferably in larger water tanks, water basins or on large water surfaces, such as in inland waters Or in the sea, for example also for the release of nutrients in water plants, Or on culture media for the cultivation of plants. Both in fresh water and in Salt water, can be used specifically for insect control, eg against mosquito larvae, Or for the herbicide distribution, preferably on larger water surfaces, the distribution Of the active substances contained in the polymer advantageously takes place, in particular, on the surface of the water.</li><li>2) To a limited extent, these polymers can also be used to absorb and / or Retention of substances dissolved or dispersed in water, even of only partially water - soluble substances Or even water-insoluble substances, which are floating on the water surface will.</li><li>3) The polymers can be used for the production of such absorption materials, in which a Separation of the polymers according to the invention from other non-floating materials (such as, for example, cellulose, Plastics, earth, clay, etc.) due to the difference in the specific weight of the polymers in the swollen For example during recycling.</li></sl>

When the polymers according to the invention are used in absorber materials, the absorber materials Mechanically comminuted and placed in water or aqueous liquids, and the polymer particles in the swollen State.

Substances which can be incorporated into the polymer according to the invention are, for example, Nutrients for plants, herbicides, fungicides, various insecticides, disinfectants, medicines, antibacterial Agents, fragrances for perfuming, as well as other substances mentioned, for example, in DE 40 29 591 A1. The Integration of the active compounds into the polymer can be effected directly by addition of these substances to the monomer solution, If the polymerization course is not thereby disturbed. If these substances influence the polymerization, Their incorporation during or after completed polymerization can be prevented by their incorporation into the already obtained polymer Polymer gel as described, for example, in DE 40 29 591 A1, DE 40 29 592 A1 or DE 40 29 593 A1. In addition Can also be fabrics whose density is lower than 1.0 g / cm³ Such as, for example, ground foams on plastic or Natural base, or cork flour, can be incorporated in this way. For a controlled release of the polymers present in the polymer It is advantageous if the incorporated substances are water-soluble. On the other hand, especially If a slow delivery of the active substances to other bodies is to be effected, can also be water-insoluble Or only partially water-soluble substances can be used. Good dispersibility of the active ingredients in water Can also be sufficient for their use according to the invention.

The invention is illustrated by the following examples.

example 1

In a polymerization vessel, 0.9 g of methylenebisacrylamide and 192 g of acrylamide were first dissolved in 500 g of water And mixed with 84 g of acrylic acid. Thereafter, the monomer solution was neutralized with 102 g of potassium hydroxide solution (45%), Cooled to 10 ° C. and blown out with nitrogen. After the addition of the catalyst solutions (1.6 g of sodium peroxydisulfate, 0.2 g of hydrogen peroxide (35%) and 0.01 g of ascorbic acid) and 10 g of 2,2'-azobis (2-methylpropionamidine) Dihydrochloride as propellant, the polymerization was started. Good mixing of the catalyst solutions With the monomer solution is a prerequisite for a homogeneous polymerization in the entire polymer block. The maximum temperature Of 100 ° C (in a well isolated polymerization vessel) was achieved within 10 minutes. After the polymerization had ended, the polymer gel was comminuted, dried at 120 ° C. and the desired product was added Grain fraction. A crosslinked potassium acrylate / acrylamide copolymer with a porous structure was formed, which Through the enclosed nitrogen bubbles.

The sieved grain fraction 1000 to 2000 μm was used for further investigations:<tables><table><tgroup cols="2"><tbody><row><entry align="left">The average particle density (dried)</entry><entry align="left">1.30 g / cm³</entry></row><row><entry align="left">The average particle density (swollen)</entry><entry align="left">0.96 g / cm³</entry></row><row><entry align="left">Floating capacity in tap water</entry><entry align="left">100% particles after 1 h</entry></row><row><entry align="left" /><entry align="left">100% particles after 120 h</entry></row><row><entry align="left">Floatability in 0.9% NaCl solution</entry><entry align="left">100% particles after 1 h</entry></row><row><entry align="left" /><entry align="left">100% particles after 120 h</entry></row><row><entry align="left">Floating in sea water</entry><entry align="left">100% particles after 1 h</entry></row><row><entry align="left" /><entry align="left">100% particles after 24 h</entry></row><row><entry align="left" /><entry align="left">32% particles after 120 h</entry></row></tbody></tgroup></table></tables>

The absorbing capacity was 140 ml / g of tap water, 110 ml / g of 0.9% NaCl solution and 75 ml / g Sea water. The mean particle density was determined pyknometrically. The particle density of the swollen particles resulting from the degree of swelling Was determined after 1 hour of swelling time.

Example 2

Under the same conditions as in Example 1, the polymerization with 20 g of blowing agent was 2,2'-azobis (2-methylpropionamidine) dihydrochloride Carried out. After completion of the polymerization, the polymer gel was comminuted, 120 ° C. and milled to the desired grain fraction. A crosslinked potassium acrylate / acrylamide copolymer was formed With porous structure and enclosed nitrogen bubbles.

The sieved grain fraction 1000 to 2000 μm was used for further investigations:<tables><table><tgroup cols="2"><tbody><row><entry align="left">The average particle density (dried)</entry><entry align="left">1.25 g / cm³</entry></row><row><entry align="left">The average particle density (swollen)</entry><entry align="left">0.95 g / cm³</entry></row><row><entry align="left">Floating capacity in tap water</entry><entry align="left">100% particles after 1 h 100% particles after 120 h</entry></row><row><entry align="left">Floatability in 0.9% NaCl solution</entry><entry align="left">100% particles after 1 h 100% particles after 120 h</entry></row><row><entry align="left">Floating in sea water</entry><entry align="left">100% particles after 1 h 100% particles after 24 h 50% particles after 120 h</entry></row></tbody></tgroup></table></tables>

The absorbing capacity was 135 ml / g of tap water, 110 ml / g of 0.9% NaCl solution and 85 ml / g Sea water.

Examples 3 and 4

Under the same conditions as in Examples 1 and 2, the polymerization a) with 2.9 g and b) with 10.0 G propellant 4,4'-azobis (4-cyanovaleric acid). After completion of the polymerization, the polymer gel Crushed, dried at 120 ° C. and ground to the desired grain fraction. A networked one emerged Potassium acrylate / acrylamide copolymer having a porous structure and enclosed nitrogen bubbles.

The sieved grain fraction 1000 to 2000 μm was used for further investigations:<tables><table><tgroup cols="2"><tbody><row><entry align="left">A) the average particle density (dried)</entry><entry align="left">1.40 g / cm³</entry></row><row><entry align="left">The average particle density (swollen)</entry><entry align="left">0.995 g / cm³</entry></row><row><entry align="left">B) the average particle density (dried)</entry><entry align="left">1.29 g / cm³</entry></row><row><entry align="left">The average particle density (swollen)</entry><entry align="left">0.99 g / cm³</entry></row><row><entry align="left">Floating capacity in tap water</entry><entry align="left">A) 35% particles after 1 h B) 85% particles after 1 h</entry></row></tbody></tgroup></table></tables>

Examples 5 and 6

Under the same conditions as in Examples 3 and 4, the polymerization was carried out with the difference that a Terpolymerate of acrylamide, acrylic acid and acrylamido (2-methylpropane) sulfonic acid (AMPS) in the ratio 70/28/02 Mol%. As propellant, 5.0 g of 4,4'-azobis (4-cyanovaleric acid) was added to the monomer solution. After the polymerization had ended, the polymer gel was comminuted, dried at 120 ° C. and the desired product was added Grain fraction. A cross-linked potassium acrylate / acrylamide (AMPS terpolymer with porous Structure and enclosed nitrogen bubbles. The approach was used to determine the reproducibility Twice.

The sieved grain fraction 1000 to 2000 μm was used for further investigations:<tables><table><tgroup cols="2"><tbody><row><entry align="left">A) the average particle density (dried)</entry><entry align="left">1.31 g / cm³</entry></row><row><entry align="left">The average particle density (swollen)</entry><entry align="left">0.985 g / cm³</entry></row><row><entry align="left">B) the average particle density (dried)</entry><entry align="left">1.33 g / cm³</entry></row><row><entry align="left">The average particle density (swollen)</entry><entry align="left">0.98 g / cm³</entry></row><row><entry align="left">Floating capacity in tap water</entry><entry align="left">A) 80% particles after 1 h B) 82% particles after 1 h</entry></row></tbody></tgroup></table></tables>

Examples 7 and 8

Under the same conditions as in Example 1, the polymerization a) was carried out with 2.9 g and b) with 10.0 g of propellant 2,2'-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride. After completion of the polymerization, Polymer gel, dried at 120 ° C. and ground to the desired grain fraction. A networked one emerged Copolymer having a porous structure and enclosed nitrogen bubbles.

The sieved grain fraction 1000 to 2000 μm was used for further investigations:<tables><table><tgroup cols="2"><tbody><row><entry align="left">A) the average particle density (dried)</entry><entry align="left">1.49 g / cm³</entry></row><row><entry align="left">The average particle density (swollen)</entry><entry align="left">0.995 g / cm³</entry></row><row><entry align="left">B) the average particle density (dried)</entry><entry align="left">1.45 g / cm³</entry></row><row><entry align="left">The average particle density (swollen)</entry><entry align="left">0.99 g / cm³</entry></row><row><entry align="left">Floating capacity in tap water</entry><entry align="left">A) 45% particles after 1 h B) 58% particles after 1 h</entry></row></tbody></tgroup></table></tables>

Examples 9 to 13

Under the same conditions as in Example 1, the polymerization was carried out with 2.9 g of the following propellants carried out:<sl><li>A) 2,2'-azobis [2- (4,5,6,7-tetrahydro-1 H -1,3-diazepin-2-yl) propane] dihydrochloride,</li><li>B) 2,2'-azobis [2- (5-hydroxy-3,4,5,6-tetrahydropyrimidin-2-yl) propane] dihydrochloride,</li><li>C) 2,2'-azobis {2- [1- (2-hydroxyethyi) -2-imidazolin-2-yl] propane} dihydrochloride and</li><li>D) 2,2'-azobis [2-methyl-N- (2-hydroxyethyl) propionamide].</li></sl>

After the polymerization had ended, the polymer gel was comminuted, dried at 120 ° C. and the desired product was added Grain fraction. A crosslinked copolymer with a porous structure and entrapped was formed Nitrogen bubbles.

The sieved grain fraction 1000 to 2000 μm was used for further investigations:<tables><table><tgroup cols="2"><tbody><row><entry align="left">The average particle density (dried)</entry><entry align="left">A) 1.49 g / cm³ B) 1.54 g / cm 3³ C) 1.51 g / cm 3³ D) 1.54 g / cm 3³</entry></row><row><entry align="left">The average particle density (swollen)</entry><entry align="left">A) 0.99 g / cm³ B) 0.99 g / cm 2³ C) 0.995 g / cm³ D) 0.995 g / cm³</entry></row><row><entry align="left">Floating capacity in tap water</entry><entry align="left">A) 62% particles after 1 h B) 58% particles after 1 h C) 45% particles after 1 h B) 32% particles after 1 h</entry></row></tbody></tgroup></table></tables>

Example 14

In a polymerization vessel, 256 g of acrylic acid were initially introduced, diluted with 335 g of water and washed with water 209 g of sodium hydrogencarbonate. Thereafter, 1.8 g of triallylamine, the monomer solution, was dissolved in the monomer solution Cooled to 10 ° C. and blown out with nitrogen. After the addition of the catalyst solutions (0.9 g of sodium peroxidisulfate, 0.2 g of hydrogen peroxide (35%) and 0.01 g of ascorbic acid) and 8.8 g of 4,4'-azobis (4-cyanovaleric acid) As a propellant, the polymerization was started. The maximum temperature of 103 ° C was determined within 7 minutes. After the completed polymerization, the polymer gel was comminuted, dried at 150 ° C., and dried To the desired grain fraction. A crosslinked acrylic acid homopolymer was formed, partly as a sodium salt, With a porous structure achieved by the enclosed nitrogen bubbles.

The sieved grain fraction 850 to 2000 μm was used for further investigations:<tables><table><tgroup cols="2"><tbody><row><entry align="left">The average particle density (dried)</entry><entry align="left">1.70 g / cm³</entry></row><row><entry align="left">The average particle density (swollen)</entry><entry align="left">0.99 g / cm³</entry></row><row><entry align="left">Floating capacity in tap water</entry><entry align="left">86% particles after 1 h</entry></row><row><entry align="left" /><entry align="left">80% particles after 24 h</entry></row><row><entry align="left">Floatability in 0.9% NaCl solution</entry><entry align="left">65% particles after 1 h</entry></row><row><entry align="left">Floating in sea water</entry><entry align="left">60% particles after 1 h</entry></row></tbody></tgroup></table></tables>

Example 15

Under otherwise identical conditions as in Example 14, the polymerization was also carried out with 8.8 g of propellant 4,4'-azobis (4-cyanovaleric acid) , But in contrast to Example 14, the acrylic acid monomer solution Neutralized with 310 g of potassium hydroxide solution (45% strength). After the completed polymerization, the polymer gel was crushed, Dried at 150 ° C. and ground to the desired grain fraction. A crosslinked acrylic acid homopolymer was formed, Partly as potassium salt, with porous structure and enclosed nitrogen bubbles.

The sieved grain fraction 850 to 2000 μm was used for further investigations:<tables><table><tgroup cols="2"><tbody><row><entry align="left">The average particle density (dried)</entry><entry align="left">1.63 g / cm³</entry></row><row><entry align="left">The average particle density (swollen)</entry><entry align="left">0.97 g / cm³</entry></row><row><entry align="left">Floating capacity in tap water</entry><entry align="left">100% particles after 1 h</entry></row><row><entry align="left" /><entry align="left">96% particles after 24 h</entry></row><row><entry align="left">Floatability in 0.9% NaCl solution</entry><entry align="left">95% particles after 1 h</entry></row><row><entry align="left">Floating in sea water</entry><entry align="left">80% particles after 1 h</entry></row></tbody></tgroup></table></tables>

Examples 16 to 21

256 g of acrylic acid were placed in a polymerization vessel, diluted with 335 g of water and treated with 200 g Sodium hydroxide solution (50% strength). Thereafter, 0.77 g of triallylamine, the monomer solution, was dissolved in the monomer solution Cooled to 10 ° C., blown out with nitrogen, and the polymerization was carried out with the same catalyst system as in Example 14 Started. As an additive, the following amounts of 2,2'-azobis (2-methylpropionamidine) Dihydrochloride (ABAH) and 4,4'-azobis (4-cyanovaleric acid) (ABCVS). The maximum temperatures of 100 to 102 ° C were obtained within 7 to 12 minutes. After the completed polymerization, the polymer gels were added Crushed, dried at 150 ° C. and ground to the desired grain fraction. The crosslinked Acrylic acid homopolymers, some as sodium salts, have a porous structure surrounded by the encapsulated Nitrogen bubbles. For comparison, a polymer having only 0.08% by weight of ABAH was prepared, Due to the small amount of ABAH used and completely decomposed during polymerization Could not have a porous structure.

The sieved grain fractions 150 to 850 μm were then used to determine the rate of adsorption and Of the absorbing capacity according to the tea bag test method:    The fluid intake of 0.2 g of test substance was gravimetric in a teabag after 15, 60 and 600 seconds Is determined. The retention value was determined after spinning in a centrifuge, for example in a commercially available Laundry centrifuge at 1400 rpm, also determined gravimetrically and converted to 1 g of product. As The aqueous 0.9% NaCl solution was used.<tables><table><tgroup cols="6"><tbody><row><entry namest="1" nameend="6">Dependence of the absorption rate and the absorption capacity of the ABAH or ABCVS additive used.</entry></row><row><entry align="center" /><entry align="left"><b>addition</b></entry><entry align="left"><b>additional quantity</b></entry><entry align="left"><b>Tea bag 15 sec</b></entry><entry align="left"><b>Tea bag 60 sec</b></entry><entry align="left"><b>tea bag retention</b></entry></row><row><entry align="center" /><entry align="center" /><entry align="left"><b>(Wt.%)</b></entry><entry align="left"><b>(G / g)</b></entry><entry align="left"><b>(G / g)</b></entry><entry align="left"><b>(G / g)</b></entry></row><row><entry align="left"><b>Example 16</b></entry><entry align="left"><b>ABAH</b></entry><entry align="center">0.28</entry><entry align="center">10.5</entry><entry align="center">21.1</entry><entry align="center">34.3</entry></row><row><entry align="left"><b>Example 17</b></entry><entry align="left"><b>ABAH</b></entry><entry align="center">0.58</entry><entry align="center">12.4</entry><entry align="center">25.8</entry><entry align="center">38.8 </entry></row><row><entry align="left"><b>Example 18</b></entry><entry align="left"><b>ABAH</b></entry><entry align="center">1.08</entry><entry align="center">18.2</entry><entry align="center">34.4</entry><entry align="center">40.2</entry></row><row><entry align="left"><b>Example 19</b></entry><entry align="left"><b>ABCVS</b></entry><entry align="center">0.2</entry><entry align="center">10.2</entry><entry align="center">16.7</entry><entry align="center">32.9</entry></row><row><entry align="left"><b>Example 20</b></entry><entry align="left"><b>ABCVS</b></entry><entry align="center">0.5</entry><entry align="center">9.7</entry><entry align="center">17.6</entry><entry align="center">36.7</entry></row><row><entry align="left"><b>Example 21</b></entry><entry align="left"><b>ABCVS</b></entry><entry align="center">1.0</entry><entry align="center">10.1</entry><entry align="center">27.7</entry><entry align="center">41.0</entry></row><row><entry align="left"><b>comparison</b></entry><entry align="left"><b>ABAH</b></entry><entry align="center">0.08</entry><entry align="center">8.1</entry><entry align="center">13.1</entry><entry align="center">33.6</entry></row></tbody></tgroup></table></tables>