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

• US 6,503,979 B1
• Filed: 08/28/2000
• Issued: 01/07/2003
• Est. Priority Date: 02/26/1998
• Status: Expired due to Fees

• Current Assignee: Basf Aktiegeneschaft
• Original Assignee: BASF AG (BASF SE)
• Inventors: Daniel, Thomas, Engelhardt, Fritz, Riegel, Ulrich, Weismantel, Matthias, Frenz, Volker, Funk, Rudiger
• Primary Examiner(s): WILSON, DONALD R
• Application Number:
  US09/622,853
• Time in Patent Office: 862 Days
• Field of Search: 525/327.6,329.9,375,107 524/556,916
• US Class Current: 524/556
• CPC Class Codes: A61L 15/60 Liquid-swellable gel-forming materials, e.g. super-absorbents
• CPC Class Codes: C08F 8/30 Introducing nitrogen atoms or nitrogen-containing groups
• CPC Class Codes: C08G 73/06 Polycondensates having nitrogen-containing heterocyclic rings in the main chain of the macromolecule
• CPC Class Codes: C08J 2300/14 Water soluble or water swellable polymers, e.g. aqueous gels
• CPC Class Codes: C08J 3/245 Differential crosslinking of one polymer with one crosslinking type, e.g. surface crosslinking
• CPC Class Codes: Y10S 524/916 Hydrogel compositions

Abstract

The invention contains a process for the surface postcrosslinking of water-absorbing polymers in which the polymers are treated with a surface postcrosslinking solution and during or after the treatment are postcrosslinked by means of an increase in temperature and are dried, wherein the crossiinker 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-alkenylene, C₅-C₁₈-cycloalkylene, phenylene, naphthylene, anthracenylene, hydrocarbon-substituted phenylene, naphthylene or anthracenylene or another substituted or unsubstituted C₆-C₁₈-arylene radical, R² is branched or unbranched C₁-C₁₈-alkylene and n is an integer from 1 to 50 or a mixture of bis-2-oxazolidinones and poly-2-oxazolidinones dissolved in an inert solvent.

Claims

1. 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.

2. The process as claimed in claim 1, wherein the water-absorbing polymer is a polymeric acrylic acid or a polyacrylate.

3. The process as claimed in claim 1, further comprising a catalyst for crosslinking, wherein the catalyst used for crosslinking is selected from the group consisting of an inorganic acid, an inorganic anhydride, a polymeric inorganic acid, an inorganic acid salt, an organic acid, an organic acid anhydride, and an organic acid salt.

4. The process as claimed in claim 3, wherein the catalyst is boric acid, sulfuric acid, phosphoric acid, or a polymer, anhydride or salt thereof, or hydriodic acid or salt thereof.

5. The process as claimed in claim 1, wherein the inert solvent is water, a mixture of water with an organic solvent of unlimited miscibility with water, or a mixture of water with a simple or polyfunctional alcohol.

6. The process as claimed in claim 5, wherein the simple or polyfunctional alcohol in said mixture of water with said simple or polyfunctional alcohol is 10-90% by weight.

7. The process as claimed in claim 5, wherein the simple or polyfunctional alcohol is methanol, ethanol, isopropanol, ethylene glycol, 1,2-propanediol or 1,3-propanediol.

8. The process as claimed in claim 1, wherein the surface postcrosslinking solution is employed in a proportion of 1-20% by weight, based on the mass of the polymer.

9. A liquid-absorbing polymer prepared by the process as claimed in claim 1.

10. The process as claimed in claim 1, wherein the water-absorbing polymer is a polymeric acrylic acid or a polyacrylate obtained by means of free-radical addition polymerization using a polyfunctional ethylenically unsaturated free-radical crosslinker which may in addition carry one or more free hydroxyl groups.

11. The process as claim in claim 1, wherein the surface postcrosslinking solution is employed in a proportion of 2.5-15% by weight, based on the mass of the polymer.

12. The process as claimed in claim 5, wherein the simple or polyfunctional alcohol in said mixture of water with said simple or polyfunctional alcohol is 30-70% by weight.

13. The process as claimed in claim 5, wherein the simple or polyfunctional alcohol in said mixture of water with said simple or polyfunctional alcohol is 40-60% by weight.

14. A hygiene article, packaging material or nonwoven comprising a water-absorbing hydrogel, wherein said water-absorbing hydrogel comprises a polymer produced by the process as claimed in claim 1.

15. The process as claimed in claim 3, wherein the catalyst is tartaric acid, acetic acid, toluenesulfonic acid, or an anhydride or salt thereof.