Hydrophilic hydrogels with a high swelling capacity and method for producing and using them

A hydrophilic, highly swellable hydrogel based on (co)polymerized monomers or based on graft (co)polymers and prepared by

• a) free-radically (co)polymerizing one or more hydrophilic monomers
• where
• R1 is hydrogen, methyl or ethyl,
• R2 is —COOR4, hydroxysulfonyl, phosphonyl, a (C1-C4)-alkanol-esterified phosphonyl group or a group of the general formula (II)
• R3 is hydrogen, methyl, ethyl or carboxyl,
• R4 is hydrogen, amino-(C1-C4)-alkyl or hydroxy-(C1-C4)-alkyl, and
• R5 is hydroxysulfonyl, phosphonyl or carboxyl;
• or
• graft (co)polymerizing one or more hydrophilic monomers of the formula (I) onto a grafting base, the average degree of neutralization of the acid-functional monomers being from 0 to 40 mol %;
• b) comminuting the acidic hydrogel;
• c) neutralizing the acidic hydrogel to an ultimate degree of neutralization of 50-85 mol % by adding a neutralizing agent;
• and
• d) drying, grinding and sieving the hydrogel particles characterized by
• a centrifuge retention of at least 29 g/g for a 0.9% aqueous NaCl solution, and
• a vertical absorption (1 g) swell height of at least 3.5 cm coupled with an extractables content (16 h value) of less than 5%;
• or
• a centrifuge retention of at least 23 g/g for a 0.9% aqueous NaCl solution, and
• a vertical absorption (3 g) swell height of at least 5 cm
• an extractables content (16 h value) of less than 4%.