Method for cross-linking hydrogels with bis- and poly-2-oxazolidinones

A process for the surface post-crosslinking of a water-absorbing polymer in which the polymer is treated with a surface postcrosslinking solution comprising a crosslinker and during or after the treatment are postcrosslinked by means of an increase in temperature and are dried, wherein the crosslinker comprises a bis-2-oxazolidinone or a poly-2-oxazolidinone comprising structural units of the formula

• in which R1 is branched or unbranched C1-C18-alkylene, branched or unbranched C2-C18-alkylene, phenylene, naphthylene, anthracenylene, hydrocarbon-substituted phenylene, naphtlylene or anthracenylene or another substituted or unsubstituted C6-C16-arylene radical, R2 is branched or unbranched C1-C16-alkylene and n is an integer from 1 to 50 or a mixture of bis-2-oxazolidinones and polyoxazolidinones dissolved in an inert solvent,
• wherein the bis-2-oxazolidinone or poly-2-oxazolidinone crosslinker is endgroup-capped by a radical, wherein said radical is selected from the group consisting of hydrogen, branched C1-C18-alkyl, unbranched C1-C18-alkyl, branched C2-C18-alkenyl, unbranched C2-C18-alkenyl, substituted C6-C18 aryl, or unsubstituted C6-C18 aryl.