Polyvinyl alcohol-based crosslinked copolymer
A polyvinyl alcohol-based crosslinked copolymer may include an unsaturated monocarboxylic acid-based structural unit, wherein an amount of carboxylate-forming structural units in the crosslinked copolymer is 1% by mole or more and 35% by mole or less with respect to all structural units constituting the crosslinked copolymer, and a solubility of the crosslinked copolymer in water is 90% or less.
1. A polyvinyl alcohol-based crosslinked copolymer, comprising:
an unsaturated monocarboxylic acid-based structural unit,
vinyl alcohol units, and
acetal crosslinking structures formed with a polyfunctional aldehyde having 2-20 carbon atoms,
wherein
an amount of carboxylate-forming structural units in the crosslinked copolymer is in a range of from 1.5 to 15 mol. %, based on total structural units in the crosslinked copolymer,
an amount of vinyl alcohol units in the polyvinyl alcohol-based crosslinked copolymer is in a range of from 20 to 98.5 mol. %, based on the total structural units in the crosslinked copolymer,
an amount of acetalized vinyl alcohol units of the crosslinked copolymer is from 0.01% to 50% by mole of the total of vinyl alcohol units,
and
a solubility of the crosslinked copolymer in water is 5% or more and 90% or less.
2. The copolymer of claim 1 , comprising a potassium ion as a counter cation of the carboxylate.
3. The copolymer of claim 1 , wherein an amount of water that can be absorbed by a plant per 1 g of the polyvinyl alcohol-based crosslinked copolymer is in a range of from 10 to 100 g.
4. The copolymer of claim 1 , wherein the polyfunctional aldehyde is at least one selected from the group consisting of glyoxal, malonaldehyde, succinaldehyde, glutaraldehyde, adipaldehyde, malealdehyde, fumaraldehyde, tartaraldehyde, citraldehyde, terephthalaldehyde, isophthalaldehyde, phthalaldehyde, 1,9-nonanedial, and ethylenediamine tetraacetaldehyde.
5. The copolymer of claim 1 , wherein the unsaturated monocarboxylic acid-based structural unit is derived from acrylic acid or a derivative thereof, or methacrylic acid or a derivative thereof.
6. A method of producing a polyvinyl alcohol-based crosslinked copolymer, the method comprising:
reacting a polyvinyl alcohol-based copolymer containing an unsaturated monocarboxylic acid-based structural unit with a polyfunctional aldehyde having 2-20 carbon atoms,
wherein an amount of carboxylate-forming structural units in the crosslinked copolymer is in a range of from 1.5 to 15 mol. %, based on total structural units in the crosslinked copolymer,
an amount of vinyl alcohol units in the polyvinyl alcohol-based crosslinked copolymer is in a range of from 20 to 98.5 mol. %, based on the total structural units in the crosslinked copolymer,
an amount of acetalized vinyl alcohol units of the crosslinked copolymer is from 0.01% to 50% by mole of the total of vinyl alcohol units,
and a solubility of the crosslinked copolymer in water is 5% or more and 90% or less.
7. The method of claim 6 , further comprising, in the presence of a solvent capable of swelling the polyvinyl alcohol-based copolymer:
reacting particles of the polyvinyl alcohol-based copolymer swollen with the solvent with the crosslinking agent.
8. A water-retaining material, comprising:
the copolymer of claim 1 .
9. An agricultural water retaining material, comprising the water-retaining material of claim 8 .