Method for the secondary cross-linking of hydrogels with N-acyl-2-oxazolidinones

A process for the gel and/or surface postcrosslinking of a water-absorbent polymer, comprising:

• treating said water-absorbent polymer with a surface postcrosslinking solution, to obtain a treated water-absorbent polymer;
• postcrosslinking said treated water-absorbent polymer to obtain a postcrosslinked water-absorbent polymer;
• and
• drying said polymer during and after said treating and said crosslinking by raising a temperature;
• wherein the surface postcrosslinking solution comprises, dissolved in an inert solvent, as crosslinker a compound of formula I
• wherein
• R1, R2, R3 and R4 are each independently hydrogen, C1-C12-alkyl, C1-C12-alkenyl, C6-C12-aryl or C1-C12-alkoxy,
• R5 is C1-C16-alkyl, C1-C4-hydroxyalkyl, C6-C12-aryl, C1-C16-alkenyl or a group of the formula —(CH2)n—COOH or —(CH2)n—SO3H in the form of the acid or a respective metal salt, ammonium salt or triethanolammonium salt thereof or —(CH2—CH2—O—)m—R6,
• R6 is hydrogen or C1-C16-alkyl,
• n is from 1 to 10,
• m is from 1 to 20.