Method for producing low-odor hydrogel-forming polymers

• US 20050209411A1
• Filed: 05/12/2003
• Published: 09/22/2005
• Est. Priority Date: 05/13/2002
• Status: Active Grant

• Current Assignee: BASF AG (BASF SE)
• Original Assignee: BASF AG (BASF SE)
• Inventors: Nestler, Gerhard, Muller-Engel, Klaus Joachim, Wickel, Stefan
• Granted Patent: US 7,307,132 B2
• Time in Patent Office: Days
• US Class Current: 525/329.700
• CPC Class Codes: C08F 20/06 Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof

Abstract

This invention relates to a process for preparing a low-odor hydrogel-forming acrylic acid polymer, which comprises the steps of: a) preparing a polymeric hydrogel by free-radically polymerizing a monomer composition comprising at least 50% by weight of acrylic acid in an aqueous polymerization medium and converting said hydrogel into a particulate hydrogel or into hydrogel-forming powder; and optionally b) treating said particulate hydrogel or said hydrogel-forming powder with a crosslinking substance which, actually or latently, contain at least two functional groups capable of reacting with the carboxyl groups on the addition polymer; characterized by the acrylic acid used in step a) containing less than 400 ppm of acetic acid and propionic acid. It further relates to the hydrogel-forming addition polymers obtainable by the process and to their use.

Claims

1. A process for preparing a low-odor hydrogel-forming acrylic acid polymer, which comprises the steps of:

a) preparing a polymeric hydrogel by free-radically polymerizing a monomer composition comprising at least 50% by weight of acrylic acid in an aqueous polymerization medium and converting said hydrogel into a particulate hydrogel or into hydrogel-forming powder; and

optionally

b) treating said particulate hydrogel or said hydrogel-forming powder with a crosslinking substance which, actually or latently, contain at least two functional groups capable of reacting with the carboxyl groups on the addition polymer;

characterized by the acrylic acid used in step a) containing less than 400 ppm (by weight, based on acrylic acid) of volatile saturated carboxylic acids selected from the group consisting of acetic acid and propionic acid.

2. A process as claimed in claim 1, wherein step a) is effected using an acrylic acid obtained by a single or multiple stage crystallization of a crude acrylic acid having an acetic and/or propionic acid content in the range from 0.1 to 5% by weight.

3. A process as claimed in claim 2, wherein step a) is effected using an acrylic acid obtained by single or multiple stage crystallization of said crude acrylic acid at from 0 to 13°

C.

4. A process as claimed in claim 1, wherein the acrylic acid used in step a) is in the form of a partially or completely neutralized aqueous acrylic acid solution.

5. A process as claimed in claim 1, wherein the crosslinker in step b) is selected from compounds capable of forming ester groups with the carboxyl groups on the addition polymer.

6. A process as claimed in claim 1, wherein the monomer mixture to be polymerized in step a) comprises, based on its total weight,

from 50 to 99.99% by weight of acrylic acid as monomer A,

from 0 to 49.99% by weight of one or more monoethylenically unsaturated monomers B which are copolymerizable with acrylic acid, and

from 0.01 to 30% by weight of at least one crosslinking compound C.

8. Hydrogel-forming addition polymer obtainable by a process as claimed in claim 1.

9. A method for preparing a hygiene article comprising utilizing the hydrogel-forming addition polymer as claimed in claim 8.

10. Hygiene articles comprising an absorbent core which includes at least one hydrogel-forming addition polymer as claimed in claim 8.

7. A method for preparing a low-odor hydrogel-forming acrylic acid polymer comprising using an acrylic acid having a propionic acid and acetic acid content of less than 400 ppm as a starting material.