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

• US 6,559,239 B1
• Filed: 05/29/2001
• Issued: 05/06/2003
• Est. Priority Date: 11/26/1998
• Status: Expired due to Fees

• Current Assignee: BASF AG (BASF SE)
• Original Assignee: BASF AG (BASF SE)
• Inventors: Daniel, Thomas, Riegel, Ulrich, Weismantel, Matthias, Frenz, Volker, Engelhardt, Fritz
• Primary Examiner(s): WILSON, DONALD R
• Application Number:
  US09/831,920
• Time in Patent Office: 707 Days
• Field of Search: 525/329.7, 525/329.9, 525/375, 524/556, 524/560, 524/561
• US Class Current: 525/329.7
• CPC Class Codes: C08F 220/06 Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
• CPC Class Codes: C08F 8/30 Introducing nitrogen atoms or nitrogen-containing groups
• CPC Class Codes: C08J 2300/14 Water soluble or water swellable polymers, e.g. aqueous gels
• CPC Class Codes: C08J 2333/02 Homopolymers or copolymers of acids; Metal or ammonium salts thereof
• CPC Class Codes: C08J 3/245 Differential crosslinking of one polymer with one crosslinking type, e.g. surface crosslinking

Abstract

Liquid-absorbent polymers are prepared by a process for the gel and/or surface postcrosslinking of water-absorbent polymers by the polymer being treated with a surface postcrosslinking solution and being postcrosslinked and dried during and after the treatment by raising the temperature, wherein the surface postcrosslinking solution comprises as crosslinker a compound of the formula I

where

R¹, R², R³ and R⁴ are 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

dissolved in an inert solvent,

and are used in hygiene articles, packaging materials and nonwovens.

Claims

1. 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.

2. The process of claim 1, wherein R⁵ is —

(CH₂)_n—

COOM or —

(CH₂)_n—

SO₃M;

wherein

n=1-10 and

M=Na⁺, K⁺, NH₄⁺ or (HO—

CH₂—

CH₂)₃NH⁺.

3. The process of claim 1, wherein said water-absorbent polymer comprises structural units derived from acrylic acid or esters thereof or obtained by graft copolymerization of acrylic acid esters onto a water-soluble polymer matrix.

4. The process of claim 1, wherein surface postcrosslinking is effected using a catalyst comprising an acid or anhydride thereof.

5. The process of claim 4, wherein surface postcrosslinking is effected using a catalyst selected from the group consisting of boric acid, sulfuric acid, hydroiodic acid, phosphoric acid, tartaric acid, acetic acid, toluenesulfonic acid, an acidic salt of boric acid, an acidic salt of sulfuric acid, an acidic salt of hydroiodic acid, an acidic salt of phosphoric acid, an acidic salt of tartaric acid, an acidic salt of acetic acid and an acidic salt of toluenesulfonic acid.

6. The process of claim 1, wherein said inert solvent is water or a mixture of water and from 10 to 90% by weight of a mono- or polyhydric alcohol.

7. The process of claim 1, wherein said crosslinker is used in an amount of from 0.01 to 5% by weight, based on a weight of the polymer.

8. The process of claim 1, wherein in said crosslinker R¹, R², R³ and R⁴ are each hydrogen and R⁵ is methyl.

9. A water-absorbent polymer prepared by the process of claim 1.

10. The process of claim 1, wherein said crosslinker of formula I is N-acetyl-2-oxazolidinone.

11. The process of claim 1, wherein said postcrosslinking temperature occurs at a temperature of from 50 to 250°

C.

12. The process of claim 1, wherein surface postcrosslinking is effected using a catalyst selected from the group consisting of boron oxide, sulfur trioxide, diphosphorus pentoxide, and ammonium dihydrogenphosphate.

13. The process of claim 1, wherein said inert solvent is an aqueous solution of a member selected from the group consisting of methanol, ethanol, isopropanol, ethylene glycol, 1,2-propanediol and 1,3 propanediol.

14. The process of claim 1, wherein an amount of said surface postcrosslinking solution is 1-20% by weight based a weight of said water-absorbent polymer.