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US-12616957-B2 - Block copolymer, method for producing same, and absorber and absorbent article using same

US12616957B2US 12616957 B2US12616957 B2US 12616957B2US-12616957-B2

Abstract

A block copolymer (A) including a vinyl alcohol-based polymer block (b) and an ionic polymer block (c) containing a monomer unit with an ionic group forming a salt and a vinyl alcohol-based monomer unit. The ionic group is a carboxylic acid group, a sulfonic acid group, or an ammonium group. The vinyl alcohol-based polymer block (b) has a number-average molecular weight (Mn b ) from 15,000 to 220,000. The ionic polymer block (c) has a content of the vinyl alcohol-based monomer unit from 5 to 95 mol % based on the total monomer units. The block copolymer (A) has a number-average molecular weight (Mn A ) from 20,000 to 440,000. A ratio (Mn b /Mn A ) of the number-average molecular weight (Mn b ) to the number-average molecular weight (Mn A ) is from 0.1 to 0.9.

Inventors

  • Takumi TAKAYAMA
  • Kazuhiko Maekawa
  • Kazutoshi MISHIMA

Assignees

  • KURARAY CO., LTD.

Dates

Publication Date
20260505
Application Date
20210607
Priority Date
20200608

Claims (20)

  1. 1 . A block copolymer (A), comprising: a vinyl alcohol-based polymer block (b); and an ionic polymer block (c) comprising (c-i) a first monomer unit comprising an ionic group forming a salt and (c-ii) a vinyl alcohol-based monomer unit, wherein the ionic group is a carboxylic acid group, a sulfonic acid group, or an ammonium group, wherein the vinyl alcohol-based polymer block (b) has a number-average molecular weight (Mn b ) in a range of from 15,000 to 220,000, wherein the ionic polymer block (c) comprises the vinyl alcohol-based monomer unit (c-ii) in a range of from 5 to 95 mol. %, based on total monomer units, wherein the block copolymer (A) has a number-average molecular weight (Mn A ) in a range of from 20,000 to 440,000, and wherein an Mn b /Mn A ratio of the number-average molecular weight (Mn b ) to the number-average molecular weight (Mn A ) is in a range of from 0.1 to 0.9.
  2. 2 . The block copolymer (A) of claim 1 , wherein the ionic group is the carboxylic acid group.
  3. 3 . The block copolymer (A) of claim 1 , wherein a counterion of the ionic group is an ion of an element in Group 1, 2, 12, 13, or 17 of the periodic table.
  4. 4 . The block copolymer (A) of claim 1 , wherein the block copolymer (A) has a content (J A ) of the first monomer unit (c-i) in a range of from 2 to 90 mol. %, based on the total monomer units.
  5. 5 . The block copolymer (A) of claim 1 , wherein the ionic polymer block (c) has a content (K c ) of the first monomer unit (c-i) in a range of from 5 to 95 mol. %, based on the total monomer units.
  6. 6 . The block copolymer (A) of claim 1 , wherein the block copolymer (A) has a degree of saponification in a range of from 80 to 99.99 mol. %.
  7. 7 . The block copolymer (A) of claim 1 , wherein the block copolymer (A) has a molecular weight distribution (Mw A /Mn A ) in a range of from 1.05 to 1.95.
  8. 8 . The block copolymer (A) of claim 1 , wherein the block copolymer (A) is biodegradable.
  9. 9 . The block copolymer (A) of claim 1 , which absorbs 20 g or more of deionized water per 0.1 g of the block copolymer (A) at 20° C.
  10. 10 . The block copolymer (A) of claim 1 , which absorbs 20 g or more of a 0.9 mass % aqueous sodium chloride solution per 1 g of the block copolymer (A) at 20° C.
  11. 11 . The block copolymer (A) of claim 1 , wherein, when the block copolymer (A) is dissolved in water at 95° C., a soluble amount is 95 mass % or more.
  12. 12 . The block copolymer (A) of claim 11 , wherein, when the block copolymer (A) is dissolved in water at 20° C., a soluble amount is 95 mass % or more.
  13. 13 . An absorber, comprising: the block copolymer (A) of claim 1 .
  14. 14 . The absorber of claim 13 , in the form of particles.
  15. 15 . An absorbent article, comprising: the absorber of claim 13 .
  16. 16 . The absorbent article of claim 15 , which is a sanitary, commodity, construction, civil engineering, industrial, agricultural, medical, or food application article.
  17. 17 . A method for producing the block copolymer (A) of claim 1 , comprising: polymerizing a vinyl ester monomer and copolymerization of a vinyl ester monomer and an ionic monomer with an ionic group or a derivative thereof by controlled radical polymerization in the presence of a radical polymerization initiator and a control agent to obtain a vinyl ester-based block copolymer comprising a vinyl ester polymer block (b1) and an ionic polymer block (c1) comprising a vinyl ester monomer unit and an ionic monomer unit; and saponifying vinyl ester monomer units in the vinyl ester-based block copolymer obtained in the polymerizing to form vinyl alcohol monomer units.
  18. 18 . The method of claim 17 , wherein the control agent is an organic cobalt complex.
  19. 19 . The method of claim 17 , further comprising: forming a salt of the ionic monomer unit.
  20. 20 . The block copolymer (A) of claim 1 , wherein the ionic group is the carboxylic acid group, and wherein the block copolymer (A) has a content (J A ) of the first monomer unit (c-i) in a range of from 2 to 90 mol. %, based on the total monomer units.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a National Stage entry under 35 U.S.C. § 371 of PCT/JP2021/021513, filed on Jun. 7, 2021, and claims priority to Japanese Patent Application No. 2020-099593, filed on Jun. 8, 2020. The entire contents of both are incorporated herein by reference. TECHNICAL FIELD The present invention relates to a block copolymer with excellent absorbency of water, salt water, and the like and to a method for producing the same. The present invention also relates to an absorber and an absorbent article using the block copolymer. BACKGROUND ART Conventionally, superabsorbent resins have been widely used for sanitary materials, such as feminine hygiene items and disposable diapers, soil water retention agents, and the like. Known examples of such a superabsorbent resin include polyacrylate crosslinked products, selfcrosslinking polyacrylates, starch-acrylate graft copolymer crosslinked products, hydrolysis products of acrylamide copolymer crosslinked products, neutralized products of crosslinked isobutylene-maleic anhydride copolymers, crosslinked products of carboxyalkyl cellulose salts, and the like. However, these polymers are crosslinked and insoluble in water and thus are not allowed to be thrown into the sewage, causing a problem of generating a large amount of waste. In addition, these polymers are not sufficiently biodegradable and have a risk of causing soil pollution, marine pollution, and the like, resulting in environmental problems. Patent Document 1 describes a superabsorbent resin using a crosslinked polymer of an ethylenic unsaturated monomer containing acrylic acid and/or acrylate as a main component. However, such a crosslinked polymer is insoluble in water and insufficiently biodegradable. Patent Document 2 describes an absorber produced by crosslinking a carboxyalkyl cellulose salt or the like with amino acid or the like and further crosslinking the biodegradable water absorbent resin thus obtained with a surface crosslinker. However, the absorber is insoluble in water and sometimes still insufficient in biodegradability. Meanwhile, polyvinyl alcohols are crystalline water-soluble polymer materials and widely applied to emulsifiers, suspensions, surfactants, fiber treatment agents, various binders, paper processing agents, adhesives, films, and the like using the excellent water solubility and film properties (strength, grease resistance, film formability, oxygen gas barrier properties, etc.). Non-Patent Documents 1 and 2 describe a block copolymer containing a polyacrylic acid block and a polyvinyl alcohol block and a block copolymer containing a potassium polyacrylate block and a polyvinyl alcohol block. However, some of these block copolymers are insufficient in water absorbency or have difficulty in shape retention after water absorption. In addition, these documents have no description at all of the water absorbency of the block copolymers. PRIOR ART DOCUMENTS Patent Documents Patent Document 1: JP 07-033818 APatent Document 2: JP 08-196901 A Non-Patent Documents Non-Patent Document 1: Highly Stretchable Free-Standing Poly(acrylic acid)-block-poly(vinyl alcohol) Films Obtained from Cobalt-Mediated Radical Polymerization, Macromolecules, 2017, vol. 50, p 6054-6063 Non-Patent Document 2: Synthesis of Novel Well-Defined Poly(vinyl acetate)-b-poly(acrylonitrile) and Derivatized Water-Soluble Poly(vinyl alcohol)-b-poly(acrylic acid) Block Copolymers by Cobalt-Mediated Radical Polymerization, Macromolecules, 2008, vol. 41, p 2353-2360 SUMMARY OF THE INVENTION Problems to be Solved by the Invention The present invention has been made to solve the above problems and it is an object thereof to provide a block copolymer having high absorbency of water, salt water, and the like while also having gel shape retentivity and water solubility. Means for Solving the Problems The above problems are solved by providing a block copolymer (A) comprising: a vinyl alcohol-based polymer block (b); and an ionic polymer block (c) containing a monomer unit with an ionic group forming a salt and a vinyl alcohol-based monomer unit, wherein the ionic group is a carboxylic acid group, a sulfonic acid group, or an ammonium group, the polymer block (b) has a number-average molecular weight (Mnb) from 15,000 to 220,000, the ionic polymer block (c) has a content of the vinyl alcohol-based monomer unit from 5 to 95 mol % based on the total monomer units, the block copolymer (A) has a number-average molecular weight (MnA) from 20,000 to 440,000, and a ratio (Mnb/MnA) of the number-average molecular weight (Mnb) to the number-average molecular weight (MnA) is from 0.1 to 0.9. In this situation, it is preferable that the ionic group is a carboxylic acid group. It is also preferable that a counterion of the ionic group is an ion of an element in Group 1, 2, 12, 13, or 17 of the periodic table. It is also preferable that the block copolymer (A) has a content (JA) of the monomer unit