Method of preparing water-absorbing resin

• US 5,652,309 A
• Filed: 06/28/1996
• Issued: 07/29/1997
• Est. Priority Date: 06/28/1995
• Status: Expired due to Term

• Current Assignee: Mitsubishi Chemical Corporation (Mitsubishi Chemical Group Corp.)
• Original Assignee: Mitsubishi Chemical Corporation (Mitsubishi Chemical Group Corp.)
• Inventors: Iida, Seiichiro, Itoh, Kiichi
• Primary Examiner(s): ZEMEL, IRINA SOPJIA
• Application Number:
  US08/671,621
• Time in Patent Office: 396 Days
• Field of Search: 525/243, 525/252, 525/267, 526/317.1
• US Class Current: 525/243
• CPC Class Codes: C08F 291/00 Macromolecular compounds obtained by polymerising monomers on to macromolecular compounds according to more than one of the groups C08F251/00 - C08F289/00

Abstract

A method of preparing a water-soluble resin, which comprises the steps of: subjecting an aqueous solution of a first water-soluble ethylenically unsaturated monomer to a first-stage water-in-oil type of reverse-phase suspension polymerization using a water-soluble radical polymerization initiator in a hydrophobic organic solvent in the presence of an emulsifier and optionally a crosslinking agent, thereby forming a slurry containing hydrous polymer gel particles; adding to said slurry a nonionic or anionic surface active agent having an HLB of at least 7 and higher than that of said emulsifier and an aqueous solution of a second water-soluble ethylenically unsaturated monomer so as to absorb the aqueous solution of the second monomer in said hydrous polymer gel particles; and carrying out a second-stage polymerization of said second monomer.

Claims

1. A method of preparing a water-soluble resin, which comprises the steps of:

subjecting an aqueous solution of a first water-soluble ethylenically unsaturated monomer to a first-stage water-in-oil type of reverse-phase suspension polymerization using a water-soluble radical polymerization initiator in a hydrophobic organic solvent in the presence of an emulsifier and optionally a crosslinking agent, thereby forming a slurry containing hydrous polymer gel particles;

adding to said slurry a nonionic or anionic surface active agent having an HLB of at least 7 and higher than that of said emulsifier and an aqueous solution of a second water-soluble ethylenically unsaturated monomer so as to absorb the aqueous solution of the second monomer in said hydrous polymer gel particles; and

carrying out a second-stage polymerization of said second monomer.

2. The method according to claim 1, wherein the addition of the second monomer solution and the second-stage polymerization are repeated at least one time.

3. The method according to claim 1 or 2, wherein the temperature of the aqueous solution of the second monomer which has just been absorbed in the polymer gel particles is lower than the decomposition temperature of the water-soluble radical polymerization initiator.

4. The method according to claim 1 or 2, wherein the surface active agent is added to said slurry in such a manner that it is previously dissolved in or intimately mixed with the aqueous solution of the second monomer.

5. The method according to claim 1 or 2, wherein the amount of the second monomer used is 5 to 300% by weight of the first monomer.

6. The method according to claim 1 or 2, wherein the water-soluble ethylenically unsaturated monomer is at least one monomer selected from the group consisting of acrylic acid or a salt thereof, methacrylic acid or a salt thereof, acrylamide, and methacrylamide.

7. The method according to claim 1 or 2, wherein the surface active agent has an HLB of 9 to 17.

8. The method according to claim 2, wherein the second-stage polymerization reaction is repeated two to four times.