Abstract:
A new water-swellable composition of a gelling agent based on hydrolyzed homo- or copolymers of acrylonitrile and of an inert metal oxide was synthesized. In the process, 1 to 22% of the nitrile groups were saponified to amide groups and 99 to 78% to alkali-metal salts. The obtained composition had a spongy structure and was characterized by high values with regard to both swelling capacity and swelling rate. Therefore it is particularly suitable for diaper manufacture and for agricultural use.

Description:
TECHNICAL FIELD 
     The invention relates to a water-swellable composition of a gelling agent based on hydrolyzed homo- or copolymers of acrylonitrile and of an inert metal oxide. It also relates to a process for synthesis thereof as well as use thereof. 
     BACKGROUND 
     The synthesis of such a composition is described in West German Laid-Open Application No. 3,503,458. Therein a water absorbing resin in the presence of a powder of an inert inorganic material is allowed to absorb a cross-linking agent and water. This mixture is then heated while stirring, in order to bring about cross-linking of the resin and removal of water. The resin contains units of a monomer with a carboxyl group in the form of the free acid or of a salt as a structural component thereof. The water-absorbing resin can be preferably, for example, a cross-linked terpolymer of acrylic acid, acrylamide and sulfonated acrylamide as well as the alkali-metal salt thereof. The inorganic material can preferably be finely divided silicon dioxide. The so-synthesized products are supposed to have both good water-absorbing capacity and a high water-absorption rate. This combination of properties is important in particular for use in the hygiene area as well as in the area of agriculture. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to make available compositions which in water, aqueous salt solutions and physiological fluids swell at a very high rate and at the same time to a very large extent. The object of the invention is also to synthesize this composition simply, reliably and inexpensively. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 is a graph depicting swelling rates of compositions according to the invention wherein the absorbed quantity in milliliters of a 1% sodium chloride solution at a pressure of 1.6 mbar is plotted over time as measured in minutes and wherein data points for the compositions of Examples 21, 22 and 48 are illustrated by -, +, and * respectively; 
     FIG. 2 is an IR spectrum of the polymerization product of Example 21(a); 
     FIG. 3 is an IR spectrum of the saponification product of Example 21(b); and 
     FIG. 4 depicts enlarged photographs of compositions according to the invention wherein FIG. 4(A) is a photomicrograph of the composition of Example 22 at a magnification of 100:1; FIG. 4(B) is a photomicrograph of the composition of Example 22 at a magnification of 1000:1; FIG. 4(C) is a photomicrograph of the composition of Example 48 at a magnification of 100:1; and FIG. 4(D) is a photomicrograph of the composition of Example 48 at a magnification of 1000:1. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The achievement of the above and other objects according to the present invention is to be seen in the claims. It is primarily characterized by the choice of a favorable ratio of amide groups to alkali-metal carboxylate groups. It is obtained by partial saponification and neutralization of the nitrile, ester or carboxylic acid groups of homo- or copolymers of acrylonitrile with unsaturated compounds such as acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, maleic acid, maleic anhydride, acrylamide or vinylsulfonic acid. 
     For saponification, alkali-metal hydroxides, especially sodium and potassium hydroxide, are used in a proportion of 0.5 to 1.5, preferably 1.0 to 1.25 mole per mole of component to be saponified. 
     The compositions of the invention are pulverulent and have a porous structure in the manner of a sponge. The pore diameters lie mainly in the range of 0.5 to 10 microns. 
     Essential also is the presence of an inert metal oxide such as Al 2  O 3  and especially SiO 2 . They are preferably added as early as during the polymerization, but can also be added during saponification. Also defined as metal oxide are the corresponding aqueous oxides. The metal oxides are regarded as inert if they either do not react at all during polymerization or if the bonds then formed are cleaved again in the subsequent treatment with lyes. 
     The gelling agent is synthesized by polymerization of acrylonitrile and possibly comonomers in water, and by subsequent partial saponification of the polymer. Coming into consideration as comonomers are other unsaturated compounds, especially acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, maleic acid, maleic anhydride, acrylamide, vinyl acetate, styrene and vinylsulfonic acid. However, even saturated, hydroxy-group-containing polymers, especially polysaccharides, polysaccharide derivatives and polyvinyl alcohol, can be used for formation of graft polymers. Depending on the monomers used, the synthesis is conducted in one or two stages. The two-stage process (Examples 1-36) is used if, during polymerization, a product is formed which swells not at all or only slightly in the aqueous reaction medium. This is the case, for example, if only acrylonitrile or acrylonitrile in combination with vinyl acetate, styrene or acrylic acid or methacrylic acid esters, is polymerized. In this case, the metal oxide (silicic acid, silica gel, Aerosil®, alumina) is added prior to the polymerization. In this case it is particularly important that the metal oxide reacts with the monomers to be polymerized either not at all or to form only a very unstable compound, which is decomposed again at the latest during the saponification. The polymer synthesized in this way is sucked off and then, in a water/alcohol mixture, using the desired alkali-metal hydroxide, is saponified wet or after prior drying. Standard stirring reactors are very suitable for the polymerization and saponification. 
     Vinyl acetate, styrene and the metal oxide can, because of the hydrophobic character thereof, be admixed only in limited proportions. In Examples 2 to 9 and 11 to 14, the relationship between degree of swelling and filler proportion is demonstrated. 
     The water content of the saponification medium must not significantly exceed 30 volume percent, since otherwise a gummy mass and not a granular product is formed during the saponification. 
     The nitrile groups must be saponified to a specified extent only to acyl amide groups and not completely to carboxylate groups, since acyl amide groups influence the swelling behavior of the hydrogel in aqueous salt solutions particularly favorably. This is clearly apparent from Examples 16 to 20 and 28. 
     Gelling agents which were synthesized by this procedure without addition of metal oxide (Comparison Examples 30 and 31) swell very slowly in water and aqueous salt solutions. The swelling rate is greatly improved, however, if the metal oxide is admixed with the saponification charge (Examples 32 to 36). 
     The reaction mixture/conditions during the polymerization are preferably: 
     acrylonitrile content: 50 to 99, preferably 85 to 98 weight percent 
     comonomer content: 0 to 30, preferably 5 to 15 weight percent 
     metal oxide: 1 to 50, preferably 2 to 10 weight percent reaction medium: water 
     reaction temperature: 30° to 80° C., preferably 40° to 60° C. 
     initiator: standard, e.g., persulfates, peroxides, ammonium cerium nitrate 
     The reaction mixture/conditions during the saponification are preferably: 
     alkali-metal hydroxide: sodium hydroxide, potassium hydroxide 
     alkali proportion: 0.5 to 1.5, preferably 1 to 1.25 mole per mole of component to be saponified 
     reaction medium: water/alcohol with 1 to 4 C atoms (alcohol: preferaby methanol or ethanol) 
     water content: 5 to 40 volume percent, preferably 10 to 30 volume percent 
     reaction temperature: reflux temperature 
     N content after saponification: 0.1 to 16%, preferably 0.5 to 7%, corresponding respectively to an acyl amide-group content of 0.3 to 50% or 1.5 to 22% 
     The one-stage process (Examples 37 to 59) is used if, during the polymerization, a product is formed which swells very strongly in the aqueous reaction medium. This is the case, for example, if acrylonitrile is polymerized in combination with acrylic acid, maleic acid, vinylsulfonic acid and other anionic unsaturated compounds or acrylamide. Formed during the polymerization are gels, which without prior isolation are saponified or neutralized by addition of the desired alkali-metal hydroxide and alcohol (Examples 37 to 47). 
     Various polysaccharides such as cellulose, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), methyl cellulose (MC), ethyl cellulose (EC), starch, starch ethers, e.g., carboxymethyl starch (CMS), sodium alginate, guar gum or even other hydroxy-group-containing polymers such as polyvinyl alcohol can be admixed with the unsaturated compounds, these reacting with the saturated compounds to form graft polymers (Examples 48 to 59). Particularly suitable for the one-stage process are mixers, especially Drais Co. mixers, since after the polymerization a gel-like product is obtained. 
     The acrylonitrile content in these hydrogels must not be less than 10%, since otherwise only soluble products are formed. 
     The polymers synthesized using the reaction mixtures/conditions described above swell only very slowly in water and aqueous salt solutions, unless a metal oxide is added during the saponification. 
     The reaction mixture/conditions during the polymerization are preferably: 
     acrylonitrile content: 10 to 95, preferably 15 to 80 weight percent 
     unsaturated acid component content: 5 to 90, preferably 10 to 85 weight percent 
     unsaturated, neutral component content: 1 to 50, preferably 2 to 25 weight percent 
     saturated, hydroxy-group-containing component content: 1 to 50, preferably 2 to 25 weight percent 
     reaction medium: water 
     reaction temperature: 30° to 80° C., preferably 40° to 60° C. 
     initiator: standard 
     reaction apparatus: kneader 
     The reaction mixture/conditions during the saponification or neutralization are preferably: 
     admixture of the metal oxide 
     alkali: sodium hydroxide, potassium hydroxide 
     alkali proportion: 0.5 to 1.5, preferably 1 to 1.25 mole per mole of component to be saponified 
     reaction medium: water/alcohol with 1 to 4 C atoms (alcohol: preferably methanol or ethanol) 
     water content: 10 to 70 volume percent, preferably 30 to 50% 
     reaction temperature: reflux temperature 
     The swelling properties of the synthesized compositions are determined by 
     (i) the porous-plate test (Johnson and Johnson Co.) 
     (ii) the demand test (B. M. Lichstein, INDA 2nd Annual Symposium, Nonwoven Product Development, Mar. 5 and 6, 1974, Washington, D.C.) and 
     (iii) the so-called glass-frit test in which the test substance is mixed in a glass beaker with an excess of the desired liquid, e.g., demineralized water, or with a physiological fluid, and allowed to swell for 1/2 hour. Thereafter the contents of the glass beaker are decanted onto a G1 glass frit; as soon as excess liquid no longer flows off (usually after 2 to 4 hours), the absorbed quantity of liquid is determined by weighing. 
     The measured results show that the products of the invention swell both very strongly and very rapidly with water. Therefore they are particularly well-suited for applications in which a small quantity of gelling agent (possibly in a thin layer) is supposed to absorb suddenly a large quantity of water. This is the case in the hygiene area, especially for diapers. However, the product of the invention is also of great importance for special areas of agriculture, e.g., for flat-roof sowing. The potassium and nitrogen content is then also of importance. 
     Compared with the process described in West German Laid-Open Application No. 3,503,458, the process of the invention has the advantage that the therein essential cross-linking reactions of the gelling agent in the swollen state and in the presence of the metal oxide are not necessary. 
     EXAMPLE 1 
     (a) Polymerization 
     In a 2-liter three-necked flask, equipped with stirrer, reflux condenser, 2 dropping funnels and thermometer, 5 g of silica gel (fine-pored) were suspended with vigorous stirring in 1 liter of water. The apparatus was then purged for 1/2 hr with nitrogen. Thereafter, 100 g of freshly distilled acrylonitrile and 70 ml of ammonium cerium nitrate solution (13.7 g of ammonium cerium nitrate and 25 g of 65% nitric acid in 250 ml of water) were rapidly added to the reaction mixture in succession from the dropping funnels. The reaction mixture heated up within 1/2 hr to 40° to 45° C., and the initial yellow coloration vanished rapidly. The mixture was further stirred at this temperature for 3 hr, until a slurry which was no longer stirrable was formed. After cooling, normally over night, the reaction product was sucked off, washed with water and dried at 70° C. in the vacuum drying oven. 
     Yield: 100 g (95.2% of theoretical) 
     (b) Saponification 
     In a 2-liter three-necked flask with stirrer and reflux condenser, 30 g of polymer and 30 g of potassium hydroxide were added to a mixture of 150 ml of water and 640 ml of ethanol (19:81). The mixture was then boiled under reflux. In the process, a dark-brown coloration rapidly developed, and disappeared again with continuing reaction. After 24 hr the reaction mixture was neutralized with acetic acid, the slightly yellow product was sucked off, first washed twice with ethanol/water (90:10), then three times with pure ethanol, and dried in the vacuum drying oven at 70° C. 
     Yield: 38 g (95.5% of theoretical) 
     SiO 2  content: 2.4% 
     N content: 0.5% 
     Acyl amide group content: 1.57% 
     The composition synthesized by the procedure described above swelled particularly rapidly in water and aqueous salt solutions and exhibited the following swelling values: 
     Porous-plate test: 
     Absorption after 30 min: 42 ml of a 1% NaCl solution per g of composition 
     Demand test: 
     Absorption after 30 min: 45 ml of artificial urine per g of composition 
     Glass-frit test: 
     47 ml of artificial urine per g of composition 
     580 ml of demineralized water per g of composition 
     EXAMPLES 2 TO 9 
     On the basis of the mode of operation of Example 1 and the reaction conditions of Table 1, starting from acrylonitrile and various quantities as well as types of silicic acid, the compositions listed in Table 1 were synthesized by saponification of the polymer with potassium hydroxide. 
     
                                           TABLE 1__________________________________________________________________________(a)  Polymerization conditions                      (b)                        Saponification conditions  Reaction medium: 1000 ml of water                        Reaction medium: water/ethanol  Initiator: 70 ml of ammonium cerium nitrate solution                        (19:81 volume percent,  Reaction temperature: 40 to 45° C.                        10 parts per one part polymer)  Reaction time: 6 hr        Reaction temperature: reflux                        Reaction time: 24 hr                        Saponification with: potassium hydroxide                        (1 mole KOH/1 mole acrylonitrile)                             Swelling capacity          Yield after                    after    Glass-frit testStarting products          polymer-  saponifi-                             ml artificial                                      ml demineralizedExampleg acrylo-     g silicic          ization                % of                    cation                         % of                             urine per g                                      H.sub.2 O per gNo.  nitrile     acid g     theory                    g    theory                             composition                                      composition__________________________________________________________________________2    100  5 silicic          102   97.1                    201  97.4                             55       475     acid3    100  10 silicic          103   93.6                    195  96.1                             49       465     acid4    100  50 silicic          140   93.3                    225  95.0                             25       120     acid5    100  5 silica          103   98.1                    200  96.9                             54       500     gel     (coarse-     pored)6    100  10 silica          105   95.1                    198  97.5                             45       440     gel     (coarse-     pored)7    100  5 Aero-          101   96.2                    200  97.9                             43       430     sil.sup.(1)8    100  50 Aero-          145   96.7                    235  95.1                             30       100     sil.sup.(1)9    100  100 Aero-          190   95.0                    270  94.1                             24        45     sil.sup.(1)__________________________________________________________________________ .sup.(1) Sold under this trademark is a silicic acid prepared by hydrolysis of silicon tetrachloride in an oxyhydrogen flame and having a SiO.sub.2 content of more than 99.8%. 
    
     EXAMPLE 10 
     (a) Polymerization 
     In a 4-liter three-necked flask, equipped with stirrer, reflux condenser, 2 dropping funnels and thermometer, 5 g of silicic acid were suspended, with vigorous stirring, in 2 liters of water. After the apparatus had been purged for 1/2 hr with nitrogen, 200 g of freshly distilled acrylonitrile and 6 g of ammonium peroxydisulfate, dissolved in 50 ml of water, were rapidly added to the reaction mixture in succession from the dropping funnels, the reaction solution was heated within 1/2 hr to 40° to 45° C. and further stirred for 6 hr at this temperature. After cooling, the reaction product was sucked off, washed once with water and dried at 70° C. in the vacuum drying oven. 
     Yield: 198 g (96.6% of theoretical) 
     (b) Saponification 
     500 ml of water and 1500 ml of methanol were placed in a 4-liter three-necked flask with stirrer and reflux condenser, and 150 g of polymer and 150 g of sodium hydroxide were added. The reaction mixture was heated for 20 hr under reflux, sucked off, washed to neutrality with methanol and dried in the vacuum drying oven at 70° C. 
     Yield: 240 g (91.3% of theoretical) 
     SiO 2  content: 1.5% 
     N content: 2.5% 
     Acyl amide group content: : 7.86% 
     The composition synthesized in this way swelled spontaneously in water and aqueous salt solutions and exhibited the following swelling values: 
     Porous-plate test: 
     Absorption after 30 min: 48 ml of 1% NaCl solution per g of composition 
     EXAMPLES 11 TO 14 
     On the basis of the mode of operation of Example 10 and the reaction conditions of Table 2, the compositions listed in Table 2 were synthesized on the basis of acrylonitrile and silicic acid. 
     
                                           TABLE 2__________________________________________________________________________(a) Polymerization conditions                       (b)                         Saponification conditions    Reaction medium: 1000 ml of water                         Reaction medium: water/ethanol    Initiator: 3 g of ammonium peroxydisulfate                         (22:78 volume percent, 10 parts per    Reaction temperature: 40 to 45° C.                         1 part polymer)    Reaction time: 6 hr       Reaction temperature: reflux                         Reaction time: 24 hr                         Saponification with: NaOH or KOH                         (1.2 mole per mole acrylonitrile)                                PropertyPolymerization                       Porous-plate testStarting products        Saponification                                ml 1% NaCl solution perExampleg acrylo-     g silicic            Yield                % of    Yield                            % of                                g compositionNo.  nitrile     acid   g   theory                    Agent                        g   theory                                Absorption after 30__________________________________________________________________________                                min1    100  2.5    101 98.5                    KOH 198 95.7                                392    100  5.0    102 97.1                    NaOH                        172 96.1                                463    100  2.5 Silica gel            100 97.6                    NaOH                        169 96.3                                464    100  5.0 Silica gel            101 96.2                    NaOH                        170 94.9                                43__________________________________________________________________________ 
    
     EXAMPLE 15 
     (a) Polymerization 
     In a 2-liter three-necked flask, equipped with stirrer, reflux condenser, 2 dropping funnels and thermometer, 2.5 g of alumina were suspended, with stirring. After purging of the apparatus with nitrogen, 100 g of freshly distilled acrylonitrile and 3 g of ammonium peroxydisulfate, dissolved in 25 ml of water, were rapidly added to the reaction mixture in succession from the dropping funnels, the reaction solution was heated within 1/2 hr to 40° to 45° C. and maintained for 6 hr at this temperature. On the next day, the reaction product was sucked off, washed with water and dried at 70° C. in the vacuum drying oven. 
     Yield: 96 g (93.7%). 
     (b) Saponification 
     250 ml of water and 750 ml of methanol were placed in a 2-liter three-necked flask with stirrer and reflux condenser, and 90 g of polymer and 90 g of sodium hydroxide were added. The reaction mixture was heated for 20 hr under reflux, sucked off, washed to neutrality with methanol and dried in the vacuum drying oven at 70° C. 
     Yield: 130 g (95.1% of theoretical) 
     Al 2  O 3  content: 1.45% 
     N content: 5.2% 
     Acyl amide group content: : 16.34% 
     Porous-plate test: 
     Absorption after 30 min: 43 ml of 1% NaCl solution per g of composition 
     EXAMPLES 16 TO 20 
     On the basis of the mode of operation of Example 1, 206 g (98.1% of theoretical) of cross-linked polymer was synthesized from 200 g of acrylonitrile and 10 g of silica gel (finepored). Starting from this polymer, compositions with different acyl amide content were then synthesized according to the reaction conditions listed in Table 3 and the swelling capacity thereof determined. 
     
                       TABLE 3______________________________________Swelling capacity as a function of acyl amide groupcontent of the compositionCharge:       40 g of polymer         40 g of potassium hydroxide         800 ml of water/ethanol (19:81)         Reaction temperature: reflux                    Glass-frit test            Acyl    with demineralized                                artificial  Saponifica-            amide   water per g urine per g  tion time content composition compositionExample  hr        %       ml          ml______________________________________16     1         60       85         2017     2         28      265         3618     4         16      380         5519     40         2      545         5020     60         1      600         45______________________________________ 
    
     The results showed clearly that the product which was extensively saponified had the maximum water absorption. The urine absorption also increased at first and then decreased again at complete saponification. 
     EXAMPLE 21 
     (a) Polymerization 
     In a 20-liter round-bottomed flask, equipped with stirrer, reflux condenser, 2 dropping funnels and thermometer, 32.5 g of precipitated silicic acid were suspended, with vigorous stirring, in 13 liters of water. The apparatus was purged for 1 hr with nitrogen. Thereafter, 1300 g of acrylonitrile and 910 ml of ammonium cerium nitrate solution (see Example 1) were rapidly added in succession from the dropping funnels, the reaction mixture was heated to 50° C. and stirred at this temperature for 6 hr. After cooling, the reaction product was sucked off, washed with water and dried at 70° C. in the vacuum drying oven. 
     Yield: 1315 g (98.7% of theoretical; IR spectrum No. 1 (FIG. 2)). 
     (b) Saponification 
     In a 20-liter round-bottomed flask with stirrer and reflux condenser, 1300 g of polymer and 1300 g of sodium hydroxide were added to a mixture of 3.25 liters of water and 9.75 liters of methanol (25:75), and the mixture was boiled for 20 hr under reflux. After cooling, the reaction product was sucked off, washed four times with methanol/water (90:10), then once with absolute methanol, and dried in the vacuum drying oven at 70° C. 
     Yield: 2160 g (99.1% of theoretical, IR spectrum No. 2 (FIG. 3)) 
     N content: 4.8% 
     Acyl amide group content: : 15.1% 
     The composition synthesized in this way swelled very rapidly in water and aqueous salt solutions (FIG. 1). 
     Swelling capacity 
     Porous-plate test: 
     Absorption after 30 min: 52 ml of 1% NaCl solution per g of composition 
     Demand test: 
     Absorption after 30 min: 56 ml of 1% NaCl solution per g of composition 
     Glass-frit test: 
     61 ml of 1% NaCl solution per g of composition 
     440 ml of demineralized water per g of composition 
     EXAMPLE 22 
     (a) Polymerization 
     In a 20-liter round-bottomed flask, equipped with stirrer, reflux condenser, 2 dropping funnels and thermometer, 32.5 g of precipitated silicic acid were suspended, with vigorous stirring, in 13 liters of water containing 100 ml of concentrated nitric acid. The apparatus was purged for 1 hr with nitrogen. Thereafter, 1300 g of acrylonitrile and 39 g of ammonium peroxydisulfate, dissolved in 125 ml of water, were rapidly added in succession from the dropping funnels. The reaction mixture was heated up to 50° C. and stirred at this temperature for 6 hr. After cooling, the reaction product was sucked off, washed with water and dried at 70° C. in the vacuum drying oven. 
     Yield: 1310 g (98.3% of theoretical) 
     (b) Saponification 
     In a 20-liter round-bottomed flask with stirrer and reflux condenser, 1300 g of polymer and 1300 g of sodium hydroxide were added to a mixture of 3.64 liters of water and 9.36 liters of methanol (28:72), and the mixture was boiled for 20 hr under reflux. After cooling, the reaction product was sucked off, washed four times with methanol/water (90:10), then once with absolute methanol, and dried in the vacuum drying oven at 70° C. 
     Yield: 2140 g (97.9% of theoretical) 
     N content: 4.6% 
     Acyl amide group content: 14.46% 
     Structure: 
     The composition has a spongy structure. 
     The surface is rugged in the manner of a walnut (see FIG. 4). 
     Swelling capacity 
     Porous-plate test: 
     Absorption after 30 min: 54 ml of 1% NaCl solution per g of composition 
     Demand test: 
     Absorption after 30 min: 56 ml of 1% NaCl solution per g of composition 
     Glass-frit test: 
     61 ml of 1% NaCl solution per g of composition 
     485 ml of demineralized water per g of composition 
     The composition synthesized in this way swelled very rapidly in water and aqueous salt solutions (FIG. 1). 
     EXAMPLES 23 TO 25 
     On the basis of the mode of operation of Example 22 and the reaction conditions of Table 4, the compositions listed in Table 4 were synthesized on the basis of acrylonitrile and silicic acid with various initiators. 
     
                                           TABLE 4__________________________________________________________________________(a)     Polymerization conditions                            (b)                              Saponification conditions   Starting products: 1300 g acrylonitrile                              Reaction medium: water/methanol   32.5 g silicic acid, precipitated                              (28:72 volume percent, 10 parts per 1                              part                              polymer)   Reaction medium: 13 liters of water                              Reaction temperature: reflux   Reaction temperature: 50° C.                              Reaction time: 20 hr   Reaction time: 6 hr        Saponification with: NaOH (1 mole per                              1 mole   Initiator addition time: 4 hr                              acrylonitrile)                          Saponification product                                             Porous-plate test             dissolved             N   --CONH.sub.2                                             ml 1% NaCl solution per                                             gInitiator    in ml                  Yield   Yield    content                                       content                                             compositionExampletype     g   water                  g   %   g   %    %   %     Absorption after 30__________________________________________________________________________                                             min22   Ammonium  1  100  1250                      93.8                          2000                              95.5 4.9 15.4  53peroxydisulfate24   Potassium per-          10 100  1320                      99.1                          2180                              98.7 5.1 16.0  52oxydisulfate +         +Sodium hydrogen         192 100sulfite25   Potassium per-         17.5             100  1315                      98.7                          2150                              98.1 5.5 17.3  47oxydisulfate +         +Sodium form-          0.9             100aldehydesulfoxylate__________________________________________________________________________ 
    
     EXAMPLE 26 
     (comparison) 
     (a) Polymerization 
     100 g of acrylonitrile and 2.5 g of silicic acid were polymerized by the mode of operation of Example 10. In the process, 100 g (97.6% of theoretical) of polymer were obtained and were saponified to polyacrylamide by the following procedure. 
     (b) Saponification 
     10 g of polymer was suspended in 400 ml of 85% sulfuric acid and stirred for 5 hr at 15° to 20° C. The reaction product was sucked off, washed to neutrality with methanol and dried at 70° C. in the vacuum drying oven. 
     Yield: 12.0 g (91.9% of theoretical) 
     Porous-plate test: 
     Absorption after 30 min: 25 ml of 1% NaCl solution per g of composition. 
     EXAMPLES 27 TO 29 
     On the basis of the mode of operation of Example 10 and the reaction conditions of Table 5, the compositions with gelling agents from copolymers, listed in Table 1, were synthesized from acrylonitrile and silicic acid and acrylic acid ethyl ester or vinyl acetate or styrene. 
     
                                           TABLE 5__________________________________________________________________________(a)  Polymerization conditions                    (b)                      Saponification conditions  Reaction medium: 1000 ml of water                      Reaction medium: water/methanol  Initiator: 3 g of (NH.sub.4).sub.2 S.sub.2 O.sub.8 in 100 ml of                      (25:75 volume percent, 10 parts per 1 part                      polymer)  Addition time: 6 hr      Reaction temperature: reflux  Reaction temperature: 50 to 55° C.                      Reaction time: 20 hr                      Saponification with: NaOH (1.25 mole per mole                      monomer)                                     Porous-plate testStarting products            g silicic     Saponification                                     ml 1% NaCl per gg acrylo-   acid, Yield                      % of                          product                                 % of                                     compositionExamplenitrile     g comonomer            precipitated                  g   theory                          g      theory                                     Absorption after 30__________________________________________________________________________                                     min27   85   15 Acrylic acid            2.5   95  92.7                          145    93.5                                     45     ethyl ester28   85   15 Vinyl acetate            2.5   90  87.8                          125    90.8                                     3929   90   10 Styrene            2.5   94  91.7                          140    91.0                                     35__________________________________________________________________________ 
    
     EXAMPLE 30 
     (comparison example) 
     (a) Polymerization 
     3 liters of water were placed in a 4-liter three-necked flask, equipped with stirrer, reflux condenser, 2 dropping funnels and thermometer. The apparatus was purged for 1/2 hr with nitrogen, and thereafter 300 g of freshly distilled acrylonitrile and 180 ml of ammonium cerium nitrate (see Example 1) were added in succession from the dropping funnels, the reaction mixture was heated to 50° C., and maintained for 6 hr at this temperature. After cooling, the reaction product was sucked off, washed with water and dried at 70° C. in the vacuum drying oven. 
     Yield: 295.5 g (98.5% of theoretical) 
     (b) Saponification with sodium hydroxide 
     150 ml of water and 850 ml of ethanol were placed in a 2-liter three-necked flask with stirrer and reflux condenser, and 100 g of polymer and 100 g of sodium hydroxide were added. The reaction mixture was heated for 20 hr under reflux, the product was sucked off, washed first with 10% aqueous methanol, then to neutrality with absolute methanol and dried at 70° C. in the vacuum drying oven. 
     Yield: 170 g (98.1% of theoretical) 
     N content: 2.5% 
     Acyl amide group content: 7.85% 
     Swelling capacity 
     Porous-plate test: 
     Absorption after 30 min: 8 ml of 1% NaCl solution per g of gelling agent 
     Demand test: 
     Absorption after 30 min: 10 ml of 1% NaCl solution per g of gelling agent 
     (c) Saponification with potassium hydroxide 
     The saponification with potassium hydroxide was conducted by the mode of operation described in Example 30(b). In the process, 191.5 g (95.3% of theoretical) of the potassium salt with an N content of 2.4% (corresponding to an acyl amide group content of 7.54%) was obtained from 100 g of polymer and 100 g of potassium hydroxide. 
     Swelling capacity 
     Porous-plate test: 
     Absorption after 30 min: 10 ml of 1% NaCl solution per g of gelling agent 
     Demand test: 
     Absorption after 30 min: 13 ml of 1% NaCl solution per g of gelling agent 
     EXAMPLE 31 (comparison example) 
     (a) Polymerization 
     2 liters of water were placed in a 4-liter three-necked flask, equipped with stirrer, reflux condenser, 2 dropping funnels and thermometer. The apparatus was purged for 1/2 hr with nitrogen. Thereafter 200 g of freshly distilled acrylonitrile and 6 g of ammonium peroxydisulfate, dissolved in 50 ml of water, were rapidly added in succession from the dropping funnels. The reaction mixture was heated to 50° C. and was maintained for 6 hr at this temperature. After cooling, the reaction product was sucked off, washed with water and dried at 70° C. in the vacuum drying oven. 
     Yield: 197.6 g (98.8% of theoretical) 
     (b) Saponification 
     250 ml of water and 750 ml of methanol were placed in a 2-liter three-necked flask with stirrer and reflux condenser, and 100 g of polymer and 100 g of sodium hydroxide were added. The reaction mixture was heated for 20 hr under reflux, the product was sucked off, washed with 10% aqueous methanol and to neutrality with absolute methanol and dried at 70° C. in the vacuum drying oven. 
     Yield: 163.5 g (96.6% of theoretical) 
     N content: 5.0% 
     Carboxylic acid amide group content: 15.71% 
     Swelling capacity 
     Porous-plate test: 
     Absorption after 30 min: 6 ml of 1% NaCl solution per g of gelling agent 
     Demand test: 
     Absorption after 30 min: 8 ml of 1% NaCl solution per g of gelling agent 
     EXAMPLES 32 TO 36 
     The pronounced water-blocking effect of the gelling agent without any addition of metal oxides can also be avoided if the metal oxide is added to the saponification charge. The so-synthesized compositions have a much higher swelling rate and swelling capacity than the corresponding gelling agents alone. By this procedure, compositions with satisfactory swelling properties can be obtained from the polymers of Example 31 by addition of metal oxides (see Table 6). 
     
                       TABLE 6______________________________________                           Porous-plate test                           Absorption after                           30 min: ml 1%  Filler          Quantity NaCl solution perExample  type            %        g composition______________________________________32     Silicic acid, precipitated                  1        2433     Silicic acid, precipitated                  2.5      3934     Silicic acid, precipitated                  5        4735     Silicic acid, precipitated                  10       4036     Product from Example 22                  30       52______________________________________ 
    
     EXAMPLE 37 
     3 liters of water were placed in a 10-liter Drais Co. mixer, equipped with reflux condenser and 2 dropping funnels. The apparatus was purged for 1 hr with nitrogen. Thereafter a mixture of 80 g of acrylonitrile and 320 g of acrylic acid and 12 g of ammonium peroxydisulfate, dissolved in 100 ml of water, were rapidly added in succession from the dropping funnels, the mixture was heated to 55° C. and polymerized at this temperature for 4 hr. Thereafter 260 g of sodium hydroxide, 4 liters of methanol and 27 g of silicic acid were added and the reaction mixture was boiled for 6 hr under reflux. After cooling, the reaction product was sucked off, washed with to neutrality with methanol and dried in the vacuum drying oven at 70° C. 
     Yield: 572 g (97.4% of theoretical) 
     Swelling capacity 
     Porous-plate test: 
     Absorption after 30 min: 45 ml of 1% NaCl solution per g of composition 
     EXAMPLES 38 TO 47 
     On the basis of the mode of operation of Example 37 and the reaction condition of Table 7, the composition of Table 7 are synthesized. 
     
                                           TABLE 7__________________________________________________________________________(a)      Polymerization conditions    Reaction medium: 3 liters of water    Initiator: 12 g of ammonium peroxydisulfate, dissolved in    100 ml of water    Reaction temperature: 55° C.    Reaction time: 4 hr(b)      Neutralization/saponification    Reaction medium: water/methanol = 44/56    Alkali: sodium hydroxide    Reaction temperature: reflux    Reaction time: 20 hr    Silica: 20 g                            Porous-plate test:                            Absorption afterMonomer composition          Yield                            30 min., ml 1% NaClEx- Monomer   Monomer        % of                            solution per gample    1      Parts         2        Parts                     g  theory                            composition__________________________________________________________________________38  Acrylonitrile      160         Acrylic acid                  240                     570                        92.7                            4639  Acrylonitrile      240         Acrylic acid                  160                     610                        94.5                            4740  Acrylonitrile      320         Acrylic acid                  80 665                        97.1                            4941  Acrylonitrile      320         Methacrylic acid                  80 650                        95.4                            4342  Acrylonitrile      240         Methacrylic acid                  160                     580                        90.3                            4043  Acrylonitrile      360         Maleic anhydride                  40 610                        84.9                            4244  Acrylonitrile      320         Maleic anhydride                  80 590                        82.6                            4145  Acrylonitrile      320         Acrylamide                  80 620                        93.8                            4046  Acrylonitrile      360         Vinylsulfonic acid                  40 630                        90.0                            3847  Acrylonitrile      360         Carboxymethyl                  40 660                        95.6                            45         Cellulose__________________________________________________________________________ 
    
     EXAMPLE 48 
     In a 10-liter Drais Co. mixer, equipped with reflux condenser and 2 dropping funnels, 10 g of cross-linked carboxymethyl cellulose with a degree of substitution of 0.75 was suspended in 4 liters of water. The apparatus was purged for 1 hr with nitrogen. Thereafter a mixture of 60 g of acrylonitrile and 330 g of acrylic acid and 260 ml of ammonium cerium nitrate solution (see Example 1) were rapidly added in succession from the dropping funnels, the mixture was heated to 55° C. and was stirred for 4 hr at this temperature. Thereafter, 310 g of potassium hydroxide, 5 liters of methanol and 20 g of silicic acid were added and the reaction mixture boiled for 6 hr under reflux. After cooling, the reaction product was sucked off, washed to neutrality with methanol and dried in the vacuum drying oven at 70° C. 
     The composition had a spongy structure (see FIG. 4). 
     Yield: 630 g (95.6% of theoretical) 
     N content: 1.5% 
     Acyl amide group content: 4.71% 
     Swelling capacity 
     Porous-plate test: 
     Absorption after 30 min: 55 ml of 1% NaCl solution per g of composition 
     Swelling rate: see FIG. 1 
     EXAMPLES 49 AND 50 
     On the basis of the mode of operation of Example 48 and the reaction conditions of Table 8, the compositions of Table 8 were synthesized. 
     
                                           TABLE 8__________________________________________________________________________(a) Polymerization conditions  (b)                             Neutralization/saponification    Reaction medium: 4 liters of water                             Reaction medium: water/methanol =                             44/56    Initiator: 12 g of ammonium peroxydisulfate, dissolved                             Alkali: sodium hydroxide    100 ml of water               Reaction temperature: reflux    Reaction temperature: 55° C.                             Reaction time: 10 hours    Reaction time: 4 hr           Silica: 20 g                                        Porous-plate test       Monomer composition              Absorption after 30 minMonomer   Monomer   HO--group content                                 Yield                                    % of                                        ml 1% NaCl solution per gExample1      Parts          2      Parts                    of polymer                              Parts                                 g  theory                                        of composition__________________________________________________________________________48   Acrylonitrile        60          Acrylic acid                 340                    CMC       20 520                                    92.1                                        4849   Acrylonitrile       120          Acrylic acid                 240                    CMC       40 530                                    90.5                                        4550   Acrylonitrile       120          Acrylic acid                 240                    Cellulose 40 535                                    91.4                                        3951   Acrylonitrile       120          Acrylic acid                 240                    HEC       40 525                                    89.7                                        4252   Acrylonitrile       120          Acrylic acid                 240                    HPC       40 520                                    88.8                                        3853   Acrylonitrile       120          Acrylic acid                 240                    MC        40 540                                    92.3                                        4054   Acrylonitrile       120          Acrylic acid                 240                    EC        40 530                                    90.5                                        3955   Acrylonitrile       120          Acrylic acid                 240                    Starch    40 540                                    92.3                                        4156   Acrylonitrile       120          Acrylic acid                 240                    CMS       40 535                                    91.4                                        4457   Acrylonitrile       120          Acrylic acid                 240                    Alginate  40 530                                    90.5                                        4558   Acrylonitrile       120          Acrylic acid                 240                    Guar gum  40 505                                    86.1                                        4259   Acrylonitrile       120          Acrylic acid                 240                    PVA       40 510                                    87.0                                        40__________________________________________________________________________