Cross-linked polymers with a porous structure, high absorbency rate for water, aqueous solutions and bodily fluids, process for producing them and their use for absorbing and/or retaining water and/or aqueous liquids

NETWORK SYNTHETIC POLYMERS WITH POROUS STRUCTURE

p0002The invention relates to crosslinked synthetic polymers based on acrylic acid and its derivatives with high Aufiiahmevermögen and improved Aufnahmegeschwindig¬ speed for water, aqueous solutions and body fluids, a process for their preparation by radical polymerization under such conditions that lead to saten Polymeri¬, which has a porous structure and which depends on the degree of swelling Partikel¬ tight have, so that the polymer particles are buoyant in water or aqueous liquids and the use of these polymers for the absorption and / or retention of water or aqueous solutions, and the release of water and / or egg ¬ ner drug solution to a surrounding medium.

p0003Various synthetic polymer products having absorptive capacity for water and body fluids are described in numerous patents: for example, crosslinked polymers and copolymers of acrylic or methacrylic acid-(US 4,018,951, US 4,066,583, US 4,062,817, US 4,066,583, DE-OS 26 13 135, DE-A 27 12 043, DE-OS 28 13 634) or Acrylamidopropansulfonsäurecopolymerisate (DE-PS 31 24 008). These absorbents are virtually insoluble in water and absor¬ beers in equilibrium with aqueous liquids many times their weight in water, urine or other aqueous solutions. other properties of synthetic absorbents such as low residual monomer content, low ratio of water solubles and high gel strength of the swollen polymer particles are addition to a high Flüssigkeitsaufhah- mevermögen indicated in some patents.

p0004In US 4,529,739 and US 4,649,164 are described polymers having a porous structure on the basis of methacrylic acid, which were prepared from ethyl acrylate / methacrylic acid Copolymerisat- latices by adding compounds capable of releasing carbon dioxide such as sodium bicarbonate obtained. In Austrian Patent AT 391 321 B are cross-linked, porous acrylic polymers prepared by addition of a stickstoffhalti¬ gen blowing agent to the monomer described. According to this method is to acrylic acid, to from 60 to 100% with NaOH, KOH or NH₃ is neutralized, optionally before or after the polymerization, an N-containing blowing agent which decomposes during the drying at 80 to 250 ° C into ammonia and carbon dioxide, wherein the amount added an increase in the degree of neutralization to 102-140%, respectively. Suitable blowing agents are ammonium salts of inorganic or organic acids and urea^" mentioned are, where A is moniumcarbonat preferred. Furthermore 5,118,719 ammonium and alkali metal carbonates are described as a blowing agent also in US, the nomerlösung be added prior to the polymerization for acetals. By Carbonatzerfall wäh¬ rend the polymerization produces carbon dioxide and then causes the hydrogel the Bil¬ formation of a "microcellular structure" by which the improved Aufiiahmegeschwindigkeit for liquids can be explained in the final product.

p0005The use of alkali metal or ammonium carbonates before or during the polymerization of Poly organic acids as described in US 4,529,739, US 4,649,164 and US 5,118,719 results in the formation of carbon dioxide during the neutralization of the acetals nomerlösung. Because of the limited solubility of CO₂ in the monomer solution in the polymer gel and only relatively small amounts of CO₂ be incorporated into the polymer during the polymerization or drying. Also, the second Varian¬ TE according to AT 391 321 B, the addition of the blowing agent to the polymer gel before drying, does not bring the desired effect due to the superficial Wir¬ effect the post-treatment and this method is associated with the disadvantage that zu¬ remove additional amount of water during the drying process. Excessive use of ammonia also does not lead to highly porous structures in swollen Gelzu¬ stood since ammonia is readily soluble in water or aqueous liquids, so that it is released during the swelling process and the porous structure of the hydrogel largely disappears. Furthermore, the pH of the final product is increased by the ammonia or Carbonatzusatz more than 7, whereby the application of Pro¬ is severely restricted products.

p0006In WO 88/09801, starting from a water-soluble polymer based on acrylic acid, the preparation of a crosslinked foamed ethyl acrylate / acrylic acid co-polymer having a specific gravity of 0.20 g / cm³ described. The final product was prepared in aqueous solution, with subsequent crosslinking and foaming Auf¬ the addition of a crosslinking agent and a blowing agent, such as sodium bicarbonate, p-Toluc sulfonylhydrazin or azocarbonamide be carried out in one process step. A disadvantage of this method is the need to have to work in an aqueous solution, wherein the handling of the copolymer, the concentration by weight because of high viscosity, for example, at 18.% Is limited. Furthermore%, it is necessary, large amounts of blowing agent, for example, 27 wt. Bezo¬ gene on the copolymer, to be used. How 391321 B is known from AT, typically% are azo compounds in very ge ringer volume, for example, about 0.056 wt. Based on the monomer as Polymeri¬ zation initiators used, where to by using higher concentrations of such radical formers, the excess of free radicals polymers with lower Mol¬ mass and products with inadequate absorber properties.

p0007The known water or aqueous fluid absorbent polymers further distinguished by the fact that they th when placed in water or aqueous Flüssigkei¬ in unswollen condition and after liquid absorption is not on the surface are Flüssigkeits¬ schwimmfahig unless it aids such as cork flour, as in EP 0285404 Bl, included.

p0008It was therefore the object, while avoiding the disadvantages mentioned Absorpti¬ onsmittel with porous structure, good absorption properties, especially ver¬ Patched-up speed and to obtain a low average total density of the individual particles, so that the polymer particles especially in aufge¬ swollen state on the water surface are buoyant.

p0009It has now been surprisingly found that water-swellable, crosslinked, particulate polymers having a porous shaped structure and a high absorption rate for water and aqueous liquids and a density below 1.0 g / cm³ in the swollen Zu¬ stood by radical polymerization in aqueous solution using minde¬ least one azo compound simultaneously as polymerization initiator and blowing agent in hö¬ heren concentration can be obtained. Suitable azo compounds there may be used, 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 of 60 to 120 ° C. The azo compounds are added to the monomer solution before Polymeri¬ organization. The following azo compounds are preferably used

p00101. Azonitril- compounds:

p00112.2^lAzobis (4-methoxy-2,4-dimethylvaleronitrile),

p00122,2'-azobis (2-cyclopropylpropionitrile),

p00132,2'-azobis (2,4-dimethylvaleronitrile),

p00142,2'-azobis (2-methylpropionitrile),

p00152,2'-azobis (2-methylbutyronitrile),

p00161, 1 '- azobis (cyclohexane-carbonitrile 1) 1 - [(1-cyano-1-methylethyl) azo] formamide (2- (carbamoylazo) isobutyronitrile), and 2-phenylazo-4-methoxy-2,4-dimethylvaleronitrile.

p00172. Azoamidin- compounds:

p00182, 2'-azobis (2-methyl-N-phenylpropionamidin) dihydrochloride, 2,2^.Azobis [N- (4-chlorophenyl) -2-methylpropionamidine] dihydrochloride, 2,2'-azobis [N- (4-hydroxyphenyl) -2-methylpropionamidine] dihydrochloride, 2,2'-azobis [N- (4- aminophenyl) -2-methylpropionamidine] tetrahydrochloride, 2,2'-azobis [2-methyl-N- (phenylmethyl) -propionamidin] dihydrochloride, 2,2'-azobis [2-methyl-N-2-propenylpropionamidin] dihydrochloride, 2 , 2'-azobis (2-methylpropionamidine) dihydrochloride and 2,2'-AzobispST- (2-hydroxyethyl) -2-methyl-propionamidine] dihydrochloride.

p00193. cyclic Azoamidin- compounds:

p00202,2'-azobis [2- (5-methyl-2-imidazolin-2-yl) propane] dihydrochloride, 2,2'-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, 2, 2'-azobis [2- (4,5,6,7-tetrahydro-lH-l, 3-diazepin-2-yl) propane] dihydrochloride, 2,2'-azobis [2- (3, 4, 5, 6-tetrahydropyrimidine-2-yl) propane] dihydrochloride, 2,2'-azobis [2- (5-hydroxy-3,4,5,6-tetrahydropyrimidin-2-yl) propane] dihydrochloride, 2,2'-azobis {2- [l- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} dihydrochloride and 2,2'-azobis [2- (2-imidazolin-2-yl) propane].

p00214. azoamide compounds:

p00222,2'-azobis {2-methyl-N- [l, l-bis (hydroxymethyl) -2-hydroxyethyl] propionamide}, 2,2'-azobis {2-methyl-N- [1, 1 -bis ( hydroxymethyl) ethyl] propionamide}, 2,2'-azobis [2-methyl-N- (2-hydroxyethyl) propionamide] and 2,2'-azobis (2-methylpropionamide) dihydrate.

p00235. Alkylazo- and other azo compounds:

p00242,2'-azobis (2,4,4-trimethylpentane), 2,2'-azobis (2-methylpropane), dimethyl 2,2'-azobis (2-methylpropionate), 4,4'-azobis (4- cyanovaleric acid) and 2,2'-azobis [hydroxymethyl) propionitrile]. As monomers, especially acrylic acid, methacrylic acid, acrylamidomethyl-pro- pansulfonsäure, the salts of these acids, in particular the alkali metal, alkaline earth metal and ammonium salts as well as ammonium are acrylamide and methacrylamide used. can mers The above monoethylenically alone for preparing homopolymers or among themselves ge mixes are used for preparing copolymers. can mers The monoethylenically called also for preparing copolymers with other water-soluble monomers such as water-soluble polymerizable acids, preferably maleic, fumaric, itaconic or vinylsulfonic or the salts of these acids. Next useful monomers are acrylonitrile, methacrylonitrile, vinyl pyridine, vinyl acetate, hydroxyl-containing ester further polymerisationsfahiger acids, particularly the hydroxyethyl and hydroxypropyl esters of acrylic and methacrylic acid and amino-nogruppenhaltige and ammonio-containing esters and amides of polymerizable acids, such as dialkylamino esters, particularly the dimethyl - and the Diethylaminoal- alkyl esters of acrylic and methacrylic acid, as well as the trimethyl- and trimethylammonium niumalkylester and the corresponding amides. In small amounts in addition water-insoluble monomers can with the above monomers copolymerized are the, for example, esters of acrylic and methacrylic acid or with C_j-C ^ Alcohols, styrene and alkylated styrenes. In general, the proportion of the water-soluble acetals monomers compared at 80 to 100.% By weight, based on the total of the monomers. Making the was¬ insoluble (hydrophobic) monomers generally 0 to 20 wt.% of the monomers. The polymerization can also be completely or partially as Pfropfpo¬ polymerization in the presence of other polymeric substances, such as oligo- and polysaccharides, or polyvinyl alcohol can be performed.

p0025The azo compounds mentioned can utilizing the different characteristics Zerset¬ tion also be used in combination. The concentration of the blowing agent additive in the monomer solution is 0.1 to 5.0 wt.%, Preferably 0.2 to 2.0 wt.%.

p0026The water-absorbing polymeric absorbents are mostly under Verwen¬ training received at least one crosslinking monomer. Crosslinking monomers compounds are used which contain at least 2 or more functional groups such as double bonds or epoxy groups and are capable of being incorporated during the polymerization into the growing polymer chains. This creates the Poly polymerisate during polymerization or a subsequent reaction of the functional groups at various locations in the polymer cross-linking points that link the individual polymer chains and cause the polymer particles in a liquid but can not dissolve therein swell up. the properties of the crosslinked polymers are mer chains by the chemical structure of Vernet¬ dec, the number of crosslinking sites, but also by their distribution in the Poly determined. As vernet¬ collapsing monomer include bi- or multifunctional monomers, eg amides such as metal thylenbisacryl- or methacrylamide or ethylene, further esters of polyols len as diacrylates or triacrylates, eg butanediol or ethylene glycol, trimethylolpropane triacrylate, glycidyl, glycerol triglycidyl ether, further methacrylate vinyl and allyl compounds such as allyl (meth) acrylate, triallyl cyanurate, maleic rediallylester, polyallyl, Tetraallyloxiethan, triallylamine, tetraallylethylenediamine, allyl esters of phosphoric acid or phosphorous acid, and also cross-linkable acetals-monomers, such as N-methylol compounds of amides such as methacrylamide or acrylamide and the ethers derived therefrom. The proportion of the cross-linking comonomers is from 0.01 to 10 wt.%, Preferably 0.10 to 2.0 wt.%, Based on the total monomers. For optimum incorporation of crosslinker into the polymer formed crosslinked polymers in which crosslinking sites are uniformly distributed, so that non-crosslinked regions or even non-crosslinked, ie, water-soluble, nieder¬ molecular weight fractions in the polymer are present. A suitable concentration and uniform distribution of the crosslinking sites within the polymer results in a product having an optimum retention capacity for water and aqueous liquids and optimum gel strength in the swollen state.

p0027The polymerization can be initiated with a redox catalyst system as initiator or photopolymerization. The redox catalyst system consisting customarily of two components, an inorganic or organic peroxide-containing compound and a reducing component such as sulfite, hydrosulfite, Thiosul- sulfate, sulfinic acid, ascorbic acid and its salts, copper, iron (H) - or manganese salts , As inorganic peroxide, the alkali metal or Ammoniumperoxide,^•such as potassium peroxydisulfate, hydrogen peroxide or Peroximono- or -diphosphor- acid and its salts, or organic peroxides such as benzoyl peroxide, butyl hydroperoxide are used. In addition to the first initiator system usually consists of two components beste¬ Henden one or more azo compounds can be used as the initiator and propellant. For photopolymerization which can be initiated by UV-containing light, so-called. Photoinitiators such as benzoin or benzoin are zoinderivate as benzoin, benzil, benzil, and other derivatives, Acryldiazo- niumsalze, or used acetophenone. Here, too, can be used as initiators, the blowing agent used, in which case the dosage of the amount of UV light for polymerization is decisive. The amounts of peroxide-containing component and the re- facturing component lie in the range of 0.0005 to 0.5 wt.%, preferably from 0.001 to 0.1 wt.% based. to the monomer solution. The amount of the photoinitiators that are not azo compounds are in the range of 0.001 to 0.1 wt.%, Preferably from 0.002 to 0.05 wt.% Rel. to the monomer solution.

p0028The polymerization can according to known methods in solution or in Sus¬ pension, are continuously on an endless belt, for example in accordance with DE-PS 35 44 770. However, preferably in aqueous solution batchwise tion vessel in a Polymerisa¬ or. Given a virtually adiabatic course of polymerization% of the monomers, based on the monomer, an aqueous polymer gel is formed at a corresponding initial concentration by weight of 15 to 50.. By selecting the initial monomer and a low starting temperature in the temperature range of 0 to 50 ° C, preferably from 10 to 25 ° C, the polymerization may be carried out so that the maximum temperature in the aqueous polymer gel is in the range 100-130 ° C, preferably 110-120 ° C, is. The polymerization may be at a normal or elevated pressure, but preferably carried out at atmospheric pressure.

p0029In the final stage of the polymerization, the resulting polymer has such Konsi¬ tence with sufficient strength to the resultant in this production phase during the partial decomposition of the initiator and propellant nitrogen dispersed as separa¬ te gas bubbles at elevated temperatures such as 100 to 120 ° C, relatively small volume and possibly keep trapped under increased pressure.

p0030The polymer gel obtained is comminuted after completion of the polymerization and dried at temperatures of 100 to 240 ° C, preferably at 120 to 180 ° C. During drying decomposes at these temperatures the present in excess and not decomposed during polymerization proportion of the azo compound. The released nitrogen is also included in the form of very small microbubbles in the dry polymer and remains there. Here, a polymer having a very porous structure whose average overall density, the resulting after grinding Polymerparti¬ kel, is below the density of the polymer itself forms. In applying the inventive polymers vergrö¬ together with water or aqueous liquids express its during the swelling process the finely distributed gas volumes, wherein the weight Gleich¬ state a swollen hydrogel with a reduced gel strength arises. At the same time the average total density of the swollen particles reduced kontinu¬ nuously depending on the degree of swelling, to a value of less than 1.0 g / cm³ is achieved. The polymer particles which initially heavier in solid, dry state Water were to rise to it and swim in the swollen state on the Was¬ ser- or liquid surface.

p0031Besides the use as liquid-absorbing component with increased Absorp¬ tion rate in hygiene products can also make sate advantageously used for the following purposes Polymeri¬ the invention:

p00321) The polymers can be a controlled and targeted delivery of in the Poly polymerisate subsequently incorporated, for example by absorption, or already contained in the polymer other substances to other bodies, eg for dosing of drugs, nutrients, insecticides and herbicides in aqueous medium , be¬ preferably in larger water containers, tanks or large bodies of water, such as used in inland waters or in the sea, for example, for the delivery of nutrients to water plants, or culture media for the cultivation of plants. The floatable both in freshwater and in seawater polymers can selectively control insects, treatment as against mosquito larvae, or herbicide Vertei¬, are preferably used on larger bodies of water, the distribution of the active substances contained in Polymeriat surface advantageously primarily on the hydrogen peroxide solution takes place.

p00332) In a limited extent, these polymers can punch because of their large surface and for receiving and / or retention of dissolved or dispersed in water Sub¬, also only partially water-soluble or even water Substan¬ zen, the swimming located on the water surface, used will.

p00343) The polymers can be used for the production of such absorbent materials in which a separation of the polymers of the invention by other non-buoyant materials (such as cellulose, plastics, earth, clay, etc.) due to the difference in specific weight of the polymers in the swollen state, for example, recycling, is to take place.

p0035As substances which can be incorporated in the polymer according to the invention, are suitable as nutrients for plants, herbicides, fungicides, various In¬ sektizidmittel, disinfectants, drugs, antibacterials, fragrances for perfuming, and others, for example in DE 4029 591 AI genannnte substances. The incorporation of active ingredients into the polymer can be effected by addition of these substances directly to the monomer when the polymerization process and do not disrupt becomes. If these substances affect the polymerization, their integration can take place during or after polymerization through their incorporation into the already erhal¬ tene polymer, as for example in DE 40 29 591 Al, DE 40 29 592 AI or DE 40 29 593 AI describes , In addition, even materials having a density lower than 1.0 g / cm³ is such as ground foam to plastic, and nature-based or ground cork, be incorporated in this manner. For a controlled release of the active substances contained in the polymer, it is advantageous if the incorporated Substan¬ are zen water. On the other hand, especially when a slow release of Wirk¬ to materials to other body take place, water-insoluble or only partially water-soluble substances can be used. A good dispersibility of Wirk¬ substances in water may also be sufficient for their use according to the invention.

p0036The invention is illustrated by the following examples.

p0037example 1

p0038In a polymerization 0.9 g methylene bisacrylamide were first in 500 g of water and dissolved 192 g of acrylamide and mixed with 84 g of acrylic acid. Thereafter, the monomer solution was neutralized with 102 g potassium hydroxide (45%), cooled to 10 ° C. ge and purged with nitrogen. After the addition of the catalyst solutions (1.6 g sodium peroxidisulfate, 0.2 g hydrogen peroxide (35% strength) and 0.01 g ascorbic acid) and 10 g of 2,2^.Azobis (2-methylpropionamidine) dihydrochloride as a foaming agent, polymerization was started. A good mixing of the catalyst solutions with the monomer solution is one precondition for homogeneous polymerization throughout the polymer block. The maximum temperature of 100 ° C (in a well-insulated Polymeri¬ sationsgefäß) was achieved within 10 minutes. the polymer gel was After completed Polyme¬ zation crumbled, dried at 120 ° C and ground to the desired grain fraction ge. There was a crosslinked Kaliumacry- lat / acrylamide copolymer with a porous structure, which has been achieved by the entrapped nitrogen bubbles.

p0039The screened grain fraction from 1000 to 2000 .mu.m was used for further study: the mean particle density (dried): 1.30 g / cm³ the mean particle density (swollen): 0.96 g / cm³

p0040Floatability in tap water: 100% of particles after 1 h

p0041100% particles after 120 h floatability in 0.9% NaCl solution: 100% of particles after 1 h 100% particles after 120 h floatability in sea water: 100% of particles after 1 h

p0042100% particle after 24 h 32% of particles after 120 h The absorptive capacity was 140 ml / g of tap water, 110 ml / g to 0.9% NaCl solution and 75 ml / g of seawater.

p0043The average particle density was determined pycnometrically. The particle density of the ge-swollen particles, which is the degree of swelling depends, was determined after 1 hour Quell¬ time.

p0044example 2

p0045Under the same conditions as in Example 1, the polymerization with 20 g blowing agent 2,2'-azobis (2-methylpropionamidine) dihydrochloride was conducted. After completed polymerization, the polymer gel was crumbled, dried at 120 ° C and ground to the desired grain fraction. There was a cross-linked potassium acrylate / acrylamide copolymer having a porous structure and entrapped Stick¬ material bubbles.

p0046The screened grain fraction from 1000 to 2000 .mu.m was used for further study: the mean particle density (dried): 1.25 g / cm³ the average particle density (swollen): 0.95 g / cm³

p0047Floatability in tap water: 100% of particles after 1 h

p0048100% particles after 120 h floatability in 0.9% NaCl solution: 100% of particles after 1 h

p0049100% particles after 120 h floatability in sea water: 100% of particles after 1 h

p0050100% of particles after 24 h

p005150% of particles after 120 h

p0052The absorption capacity was 135 ml / g of tap water, 110 ml / g to 0.9% NaCl solution and 85 ml / g of seawater.

p0053Examples 3 and 4

p0054Under the same conditions as in Examples 1 and 2 the polymerization a) with 2.9 g and b) with 10.0 g blowing agent 4,4'-azobis (4-cyanovaleric acid) durchge leads. After completed polymerization, the polymer was crushed in dried 120 ° C and ground to the desired grain fraction. There was a veraetztes potassium / acrylamide copolymer having a porous structure and closed einge¬ Stickstofϊbläschen.

p0055The screened grain fraction from 1000 to 2000 .mu.m was used for further study: a) the mean particle density (dried): 1, 40 g / cm³ the mean particle density (swollen): 0.995 g / cm³ b) the average particle density (dry): 1, 29 g cm³ the average particle density (swollen): 0.99 g / cm³

p0056Floatability in tap water: a) 35% of particles after 1 h b) 85% of particles after 1 h

p0057Examples 5 and 6

p0058Under the same conditions as in Example 3 and 4 was the polymerization with the difference that a Terpolymeriat of acrylamide, acrylic acid and acrylamidomethylpropanesulfonic do (2-methylpropane) sulfonic acid (AMPS) in the ratio 70/28/02 mol% was prepared. As a blowing agent to the monomer solution was 5.0 g of 4,4'-azobis (4-cyanovale- riansäure) was added. After completed polymerization, the polymer gel was kleinert comminuted, dried at 120 ° C and ground to the desired grain fraction. There was a veraetztes potassium / acrylamide (AMPS terpolymer having a porous structure and entrapped nitrogen bubbles. To determine the availability of reproducibly approach was repeated twice.

p0059The screened grain fraction from 1000 to 2000 .mu.m was used for further study: a) the mean particle density (dried): 1.31 g / cm³ the mean particle density (swollen): 0.985 g / cm³ b) the mean particle density (dried): 1.33 g / cm³ the average particle density (swollen): 0.98 g / cm³

p0060Floatability in tap water: a) 80% of particles after 1 h b) 82% of particles after 1 h

p0061Examples 7 and 8

p0062Under the same conditions as in Example 1, the polymerization a) with 2.9 g and b) with 10.0 g blowing agent 2,2'-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride performed. After completed polymerization, the polymer gel was crumbled, dried at 120 ° C and ground to the desired grain fraction. There was a veraetztes copolymer having a porous structure and entrapped Stickstoffbläs¬ chen.

p0063The screened grain fraction from 1000 to 2000 .mu.m was used for further study: a) the mean particle density (dried): 1.49 g / cm³ the mean particle density (swollen): 0.995 g / cm³ b) the average particle density (dry): 1.45 g / cm³ the average particle density (swollen): 0.99 g / cm³

p0064Floatability in tap water: a) 45% of particles after 1 h b) 58% of particles after 1 h

p0065Examples 9 to 13

p0066Under the same conditions as in Example 1, the polymerization was carried out with 2.9 g each of the following blowing agents: a) 2,2'-azobis [2- (4,5,6,7-tetrahydro-lH-l, 3-diazepin-2 -yl) propane] dihydrochloride, b) 2,2'-azobis [2- (5-hydroxy-3,4,5,6-tetrahydropyrimidin-2-yl) propane] dihydrochloride, c) 2,2'-azobis { 2- [l- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} dihydrochloride and d) 2,2'-azobis [2-methyl-N- (2-hydroxyethyl) propionamide].

p0067After completed polymerization, the polymer gel was comminuted, dried ge at 120 ° C and ground to the desired grain fraction. The result is a crosslinked copolymer having a porous structure and entrapped nitrogen bubbles.

p0068The screened grain fraction from 1000 to 2000 .mu.m was used for further study: the mean particle density (dried): a) 1.49 g / cm³ b) 1.54 g / cm³ c) 1.51 g / cm³ d) 1.54 g / cm³ the average particle density (swollen): a) 0.99 g / cm³ b) 0.99 g / cm³ c) 0.995 g / cm³ d) 0.995 g / cm³ Floatability in tap water: a) 62% of particles after 1 h b) 58% of particles after 1 h c) 45% of particles after 1 h b) 32% of particles after 1 h

p0069example 14

p0070A polymerization initially 256 g of acrylic acid -were presented, diluted with 335 g water and neutralized with 209 g of sodium bicarbonate. Thereafter, 1.8 g triallylamine the monomer was dissolved in the monomer solution, cooled to 10 ° C and purged with nitrogen. After addition of the Katalysatorlösun¬ gene (0.9 g sodium peroxidisulfate, 0.2 g hydrogen peroxide (35% strength) and 0.01 g ascorbic acid) and 8.8 g of 4,4'-azobis (4-cyanovaleric acid) as a blowing agent was the polymerization started. The maximum temperature of 103 ° C was reached within 7 minutes. After completed polymerization, the polymer gel was zerklei¬ nert, dried at 150 ° C and ground to the desired grain fraction. It was a ent veraetztes acrylic acid homopolymer, partially as sodium salt, with porö¬ ser structure that has been achieved by the entrapped nitrogen bubbles.

p0071The screened grain fraction 850-2000 .mu.m was used for further study: the mean particle density (dried): 1, 70 g / cm³ the average particle density (swollen): 0.99 g / cm³

p0072Floatability in tap water: 86% of particles after 1 h

p007380% of particles after 24 h floatability in 0.9% NaCl solution: 65% of particles after 1 h floatability in sea water: 60% of particles after 1 h

p0074example 15

p0075Under otherwise the same conditions as in Example 14, the polymerization also with 8.8 g blowing agent 4,4'-azobis (4-cyanovaleric acid) was carried out, but in contrast to Example 14, the acrylic acid monomer solution was charged with 310 g Kali¬ caustic (45% ) neutralized. After completed polymerization, the Polymer¬ was crushed gel, dried at 150 ° C and ground to the desired grain fraction. There was a cross-linked acrylic acid homopolymer, partially as potassium salt, having a porous structure and entrapped nitrogen bubbles. The screened grain fraction 850-2000 .mu.m was used for further study: the mean particle density (dried): 1.63 g / cm³ the average particle density (swollen): 0.97 g / cm³

p0076Floatability in tap water: 100% of particles after 1 h

p007796% of particles after 24 h

p0078Floatability in 0.9% NaCl solution: 95% of particles after 1 h floatability in sea water: 80% of particles after 1 h

p0079Examples 16 to 21

p0080In a polymerization vessel 256 g acrylic acid were presented, diluted with 335 g and 200 g sodium hydroxide solution (50% strength). The mixture was then dissolved in the acetals nomerlösung 0.77 g of triallylamine, the monomer solution cooled to 10 ° C, purged with nitrogen and run with the same catalyst system as in Example 14, the polymerization. As an additive the following listed in Table 1 amounts of 2,2'-azobis (2-methylpropionamidine) dihydrochloride were used (ABAH), and 4,4'-azobis (4-cyanovaleric acid) (ABCVS). The maximum temperatures of 100 to 102 ° C were reached within 7 to 12 minutes. After completed polymerization, the polymer gels were crumbled, dried at 150 ° C and ground to the desired grain fraction. The produced cross-linked acrylic acid homo- polymers, partially as sodium salts, have a porous structure that has been achieved by the entrapped nitrogen bubbles. a polymer% ABAH yet to compare with only 0.08 wt. prepared which could not have porous structure due to the small amount of used and during the polymerization completely decomposed ABAH.

p0081The screened grain fractions 150 to 850 microns were then used to determine the recording speed and the Aufiiahmevermögens after Teebeuteltestme¬ method:

p0082The liquid absorption of 0.2 g test substance was determined gravimetrically in a tea bag after 15, 60 and 600 seconds. The retention value was also determined after spinning in a centrifuge, for example, in a commercial Wäscheschleu¬ at 1400 rpm gravimetrically and converted to 1 g product. As test fluid, the aqueous 0.9% NaCl solution was used. Table 1: Dependence of the absorption rate and the Absorptions¬ assets of the ABAH- or ABCVS additive amount used.

p0083Additional supplementary amount Tea Bags Tea Bags Tea Bag 15 sec 60 sec retention

p0084(Wt.%) (G / g) (g / g) (g / g)

p0085Example 16 ABAH 0.28 10.5 21.1 34.3

p0086Example 17 ABAH 0.58 12.4 25.8 38.8

p0087Example 18 ABAH 1.08 18.2 34.4 40.2

p0088Example 19 0.2 10.2 16.7 32.9 ABCVS

p0089Example 20 0.5 9.7 17.6 36.7 ABCVS

p0090Example 21 1.0 10.1 27.7 41.0 ABCVS

p0091Comparison ABAH 0.08 8.1 13.1 33.6