Block copolymer, method for producing the same, absorbent and absorbent article using the same

Abstract

A block copolymer (A) comprising a vinyl alcohol polymer block (b) and an ionic polymer block (c) containing monomer units having an ionic group in which a salt is formed and a vinyl alcohol monomer, wherein the ionic group is a carboxyl group, a sulfonic acid group or an ammonium group, and the number-average molecular weight (Mn b ) of the polymer block (b) is 15,000 to 220,000, the content of the vinyl alcohol monomer unit in the ionic polymer block (c) relative to all monomer units is 5 to 95 mol%, the number-average molecular weight (Mn A ) of the block copolymer (A) is 20,000 to 440,000, and the ratio (Mn b ) of the number-average molecular weight (Mn A ) to the number-average molecular weight (Mn b / Mn A ) is 0.1 to 0.9. Such a block copolymer has both high absorbency for water, brine, etc., gel shape retention and water solubility.

Description

Technical Field

[0001] The present invention relates to a block copolymer having excellent absorbency for water, brine, etc. and a method for producing the same. Further, the present invention relates to an absorbent and an absorbent article using the block copolymer. Background Art

[0002] Heretofore, superabsorbent resins have been widely used in sanitary materials such as physiological products and disposable diapers, and soil water retention agents. As such superabsorbent resins, for example, crosslinked polyacrylates, self-crosslinking polyacrylates, starch-acrylate graft copolymer crosslinked products, hydrolyzates of acrylamide copolymer crosslinked products, neutralized products of crosslinked isobutene-maleic anhydride copolymers, crosslinked products of carboxyalkylcellulose salts, etc. are known.

[0003] However, these polymers are crosslinked and insoluble in water, so they cannot flow into the sewer and a large amount of waste is generated, which is a problem. In addition, the biodegradability of these polymers is also insufficient, so they may cause soil pollution, marine pollution, etc., and there are also problems in terms of the environment.

[0004] Patent Document 1 describes a superabsorbent resin using a crosslinked polymer of an ethylenically unsaturated monomer having acrylic acid and / or acrylate as a main constituent unit. However, such a crosslinked polymer is not only insoluble in water but also insufficient in biodegradability. Patent Document 2 describes an absorbent formed by further crosslinking a biodegradable water-absorbent resin formed by crosslinking a carboxyalkylcellulose salt or the like with an amino acid or the like using a surface crosslinking agent. However, this absorbent is not only insoluble in water but also sometimes insufficient in biodegradability.

[0005] On the other hand, polyvinyl alcohol is a crystalline water-soluble polymer material and is widely used as an emulsifier, a suspending agent, a surfactant, a fiber processing agent, various adhesives, a paper processing agent, an adhesive, a film, etc. due to its excellent water solubility and film-forming properties (strength, oil resistance, film-forming property, oxygen barrier property, etc.).

[0006] Non-Patent Document 1 and Non-Patent Document 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, these block copolymers sometimes have insufficient water absorbency and sometimes have difficulty in maintaining their shape after absorbing water. In addition, there is no description of the water absorbency of the block copolymer in these documents.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Patent Laid-Open No. 7-033818

[0010] Patent Document 2: Japanese Unexamined Patent Application Publication No. 8-196901

[0011] Non-Patent Document

[0012] Non-Patent Document 1: Highly Stretchable Free-Standing Poly(acrylic acid)-block-poly(vinyl alcohol)Films Obtained from Cobalt-Mediated RadicalPolymerization,Macromolecules,2017,vol.50,p6054-6063

[0013] 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,vol41,p2353-2360 Summary of the Invention

[0014] Problems to be Solved by the Invention

[0015] The present invention has been completed in order to solve the above problems, and an object thereof is to provide a block copolymer having both high absorbency for water, brine, etc., gel shape retention, and water solubility.

[0016] Means for Solving the Problems

[0017] The above problems are solved by providing the following block copolymer (A), which comprises a vinyl alcohol polymer block (b) and an ionic polymer block (c) containing monomer units having an ionic group forming a salt and vinyl alcohol monomer units, wherein the ionic group is a carboxyl group, a sulfonic acid group, or an ammonium group, the number average molecular weight (Mn b ) of the polymer block (b) is 15,000 to 220,000, the content of the vinyl alcohol monomer units in the ionic polymer block (c) relative to all the monomer units is 5 to 95 mol%, the number average molecular weight (Mn A ) of the block copolymer (A) is 20,000 to 440,000, and the number average molecular weight (Mn b)Relative to the number-average molecular weight (Mn A ) ratio (Mn b / Mn A ) is 0.1 to 0.9.

[0018] At this time, the above ionic group is preferably a carboxyl group. The counter ion of the above ionic group is preferably an ion of an element in Group 1, 2, 12, 13 or 17 of the periodic table. The content (J A ) of the above monomer unit having an ionic group forming a salt in the block copolymer (A) relative to all monomer units is preferably 2 to 90 mol%. The content (K c ) of the above monomer unit having an ionic group forming a salt in the polymer block (c) relative to all monomer units is preferably 5 to 95 mol%.

[0019] The saponification degree of the block copolymer (A) is preferably 80 to 99.99 mol%. The molecular weight distribution (Mw A / Mn A ) of the block copolymer (A) is preferably 1.05 to 1.95. The block copolymer (A) is preferably biodegradable.

[0020] The amount of deionized water absorbed per 0.1 g of the block copolymer (A) at 20°C is preferably 20 g or more. The amount of 0.9 mass% sodium chloride aqueous solution absorbed per 1 g of the block copolymer (A) at 20°C is preferably 20 g or more.

[0021] The amount of soluble components when dissolved in water at 95°C is preferably 95 mass% or more, and the amount of soluble components when dissolved in water at 20°C is more preferably 95 mass% or more.

[0022] The absorbent material containing the block copolymer (A) is a preferred embodiment of the present invention. The absorbent is preferably in the form of particles. The absorbent article having the above absorbent material is a more preferred embodiment. The above absorbent article is preferably for sanitary use, daily necessities use, construction / civil engineering use, industrial use, agricultural use, medical use or food use.

[0023] The above problems can also be solved by providing a method for producing a block copolymer (A), the method for producing the block copolymer (A) having a polymerization step and a saponification step as essential steps. In the polymerization step, vinyl ester monomers are polymerized and vinyl ester monomers are copolymerized with ionic monomers having an ionic group or a derivative thereof by controlled radical polymerization in the presence of a radical polymerization initiator and a controller, to obtain a vinyl ester block copolymer containing a vinyl ester polymer block (b1) and an ionic polymer block (c1) containing vinyl ester monomer units and ionic monomer units; in the saponification step, vinyl ester monomer units in the vinyl ester block copolymer obtained in the above polymerization step are saponified to form vinyl alcohol monomer units, and the method for producing the block copolymer (A) has a salt formation step of forming a salt of the above ionic monomer units as an optional step.

[0024] Advantages of the Invention

[0025] The block copolymer (A) of the present invention has both high absorbency for water, brine, etc., gel shape retention, and water solubility. Therefore, the block copolymer (A) is suitable for use as an absorbent for water, brine, etc., and an absorbent article. According to the production method of the present invention, the block copolymer (A) can be produced. Detailed Embodiments

[0026] The block copolymer (A) of the present invention contains a vinyl alcohol polymer block (b) and an ionic polymer block (c) containing monomer units of an ionic group forming a salt and vinyl alcohol monomer units, wherein the above ionic group is a carboxyl group, a sulfonic acid group, or an ammonium group, the number average molecular weight (Mn b ) of the polymer block (b) is 15,000 to 220,000, the content of vinyl alcohol monomer units in the ionic polymer block (c) relative to all monomer units is 5 to 95 mol%, the number average molecular weight (Mn A ) of the block copolymer (A) is 20,000 to 440,000, and the ratio (Mn b ) of the number average molecular weight (Mn A ) to the number average molecular weight (Mn b / Mn A ) is 0.1 to 0.9.

[0027] The block copolymer (A) of the present invention has both high absorbency for water, brine, etc., gel shape retention, and water solubility. It is considered that the high absorbency is due to the ionic polymer block (c), and the gel shape retention and water solubility are due to the vinyl alcohol polymer block (b).

[0028] A preferred method for producing the block copolymer (A) of the present invention has a polymerization step and a saponification step as essential steps. In the polymerization step, polymerization of a vinyl ester monomer and polymerization of a vinyl ester monomer and an ionic monomer having an ionic group or a derivative thereof are carried out by controlled radical polymerization in the presence of a radical polymerization initiator and a controller, to obtain a vinyl ester block copolymer containing a vinyl ester polymer block (b1) and an ionic polymer block (c1) containing vinyl ester monomer units and ionic monomer units; in the saponification step, the vinyl ester monomer units in the vinyl ester block copolymer obtained in the above polymerization step are saponified to form vinyl alcohol monomer units. Hereinafter, the production method thereof will be described in detail.

[0029] First, the polymerization step will be described. In the polymerization step, polymerization of a vinyl ester monomer and polymerization of a vinyl ester monomer and an ionic monomer are carried out by controlled radical polymerization in the presence of a radical initiator and a controller. The vinyl ester polymer block (b1) is synthesized by polymerizing a vinyl ester, and the ionic polymer block (c1) is synthesized by polymerizing a vinyl ester monomer and an ionic monomer. In the synthesis step of the ionic polymer block (c1), a copolymer containing ionic monomer units and vinyl ester monomer units, that is, the ionic polymer block (c1), is synthesized by copolymerizing an ionic monomer and a vinyl ester monomer, whereby the gel shape retention of the obtained block copolymer (A) is improved.

[0030] Examples of the vinyl ester monomer used in the production method of the present invention include vinyl formate, vinyl acetate, vinyl trifluoroacetate, vinyl propionate, vinyl valerate, vinyl butyrate, isobutyl vinyl acetate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl neodecanoate, etc. From the viewpoint of economy, vinyl acetate is preferably used.

[0031] The ionic monomer used in the production method of the present invention is a monomer having an ionic group or a derivative thereof. The above ionic group is a carboxyl group, a sulfonic acid group or an ammonium group. These groups can be used alone or in combination of two or more. As the above ionic group, a carboxyl group is preferred. The monomer having the ionic group may form a salt or may not form a salt.

[0032] Examples of the monomer having an ionic group or its derivative used as the above ionic monomer include: monomers having a carboxyl group such as (meth)acrylic acid, maleic acid, itaconic acid, fumaric acid, etc. or their derivatives; monomers having a sulfonic acid group such as vinylsulfonic acid, allylsulfonic acid, styrenesulfonic acid, 2-(meth)acrylamide-2-methylpropanesulfonic acid, 2-(meth)acryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid, etc. or their derivatives; monomers having an ammonium group such as ethenyloxyethyltrimethylammonium chloride, ethenyloxybutyltrimethylammonium chloride, N-acrylamidomethyltrimethylammonium chloride, 3-(methacrylamide)propyltrimethylammonium chloride, N-acrylamidoethyltrimethylammonium chloride, allyltrimethylammonium chloride, methallyltrimethylammonium chloride, etc. or their derivatives. Among them, monomers having a carboxyl group or their derivatives are preferred, and monomers having a carboxyl group or their esters are more preferred.

[0033] As the monomer having a carboxyl group or its ester, (meth)acrylate is preferred. Examples of the above (meth)acrylate include: methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, octadecyl (meth)acrylate, etc. Methyl (meth)acrylate is more preferred. The above (meth)acrylate can be methyl acrylate or acrylate, but acrylate is more preferred.

[0034] As the monomer having a sulfonic acid group, (meth)acrylamide monomers are preferred, 2-(meth)acrylamide-2-methylpropanesulfonic acid is preferred, and 2-acrylamide-2-methylpropanesulfonic acid is more preferred.

[0035] As the monomer having an ammonium group, (meth)acrylamide monomers are preferred, and 3-(methacrylamide)propyltrimethylammonium chloride is preferred.

[0036] In addition, the block copolymer (A) of the present invention may contain monomer units derived from an ethylenically unsaturated monomer (e) capable of copolymerizing with the vinyl ester monomer and the above ionic monomer within a range not impairing the effects of the present invention. Examples of the ethylenically unsaturated monomer (e) include: olefins such as ethylene, propylene, 1-butene, and isobutene; acrylamides such as acrylamide, N-alkyl (having 1 to 18 carbon atoms) acrylamide, and N,N-dimethylacrylamide; methacrylamides such as methacrylamide, N-alkyl (having 1 to 18 carbon atoms) methacrylamide, and N,N-dimethylmethacrylamide; N-vinylamides such as N-vinylpyrrolidone, N-vinylformamide, and N-vinylacetamide; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl ethers such as alkyl (having 1 to 18 carbon atoms) vinyl ether, hydroxyalkyl vinyl ether, and alkoxyalkyl vinyl ether; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, and vinyl bromide; vinyl silanes such as trimethoxyvinylsilane; allyl compounds such as allyl acetate, allyl chloride, allyl alcohol, and dimethylallyl alcohol. When using the ethylenically unsaturated monomer (e), copolymerization can be carried out during the polymerization of the vinyl ester polymer block (b1), during the polymerization of the ionic polymer block (c1), or separately from the polymerization of the vinyl ester polymer block (b1) and the ionic polymer block (c1).

[0037] With respect to all the monomer units in each block, the content of the ethylenically unsaturated monomer (e) in the vinyl alcohol polymer block (b) and the ionic polymer block (c) constituting the block copolymer (A) is preferably 10 mol% or less, more preferably 3 mol% or less, still more preferably 1 mol% or less, and particularly preferably substantially free of it. In addition, with respect to all the monomer units of the block copolymer (A), the content of the ethylenically unsaturated monomer (e) is preferably 10 mol% or less, more preferably 3 mol% or less, still more preferably 1 mol% or less, and particularly preferably substantially free of it.

[0038] The controlled radical polymerization employed in the production method of the present invention refers to a polymerization reaction that proceeds under an equilibrium state between a growing radical end (active species) and a covalent bond species (dormant species) bonded to a controlling agent. Examples of the controlling agent used in the production method of the present invention include organic cobalt complexes, organic iodine compounds, thiocarbonyl compounds, organic tellurium compounds, organic compounds having a redox center, organic compounds having a stable radical, etc., among which organic cobalt complexes are preferred.

[0039] As the above-mentioned organic cobalt complex, complexes containing divalent cobalt atoms and organic ligands can be cited, for example. As preferred organic cobalt complexes, cobalt(II) acetylacetonate [Co(acac)2], cobalt(II) porphyrin complexes, etc. can be cited, for example. Among them, from the viewpoint of manufacturing cost, cobalt(II) acetylacetonate is preferred.

[0040] As the polymerization method, known methods such as bulk polymerization method, solution polymerization method, suspension polymerization method, emulsion polymerization method, etc. can be cited. Among them, the bulk polymerization method of carrying out polymerization without a solvent or the solution polymerization method of carrying out polymerization in various organic solvents is usually adopted. In order to obtain a polymer with a narrow molecular weight distribution, the bulk polymerization method that does not use solvents and dispersion media that may cause side reactions such as chain transfer is preferred.

[0041] On the other hand, from the aspects of viscosity adjustment of the reaction solution, control of polymerization rate, etc., solution polymerization is sometimes also preferred. As the organic solvents used as solvents in solution polymerization, the following can be cited: esters such as methyl acetate and ethyl acetate; aromatic hydrocarbons such as benzene and toluene; lower alcohols such as methanol and ethanol; etc. Among them, in order to prevent chain transfer, esters and aromatic hydrocarbons are preferably used. When using a solvent, the amount of the solvent used can be determined according to the number average molecular weight of the target block copolymer (A) and considering the viscosity of the reaction solution. For example, the mass ratio (solvent / monomer) can be selected from the range of 0.01 to 10. The mass ratio (solvent / monomer) is preferably 0.1 or more and preferably 5 or less.

[0042] As the radical initiator used in the polymerization step, known azo initiators, peroxide initiators, redox initiators, etc. in the past are appropriately selected. As azo initiators, 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), etc. can be cited. As peroxide initiators, diperoxydicarbonate compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, diethoxyethyl peroxydicarbonate, etc.; peracid ester compounds such as tert-butyl peroxypivalate, α-cumyl peroxypivalate, tert-butyl peroxypivalate, etc.; acetylcyclohexylsulfonyl peroxide, diisobutyryl peroxide; 2,4,4-trimethylpentyl-2-peroxybenzoate, etc. can be cited. In addition, potassium persulfate, ammonium persulfate, hydrogen peroxide, etc. can be combined with the above-mentioned initiators as initiators. In addition, as redox initiators, combinations of the above-mentioned peroxides and reducing agents such as sodium bisulfite, sodium bicarbonate, tartaric acid, L-ascorbic acid, sodium formaldehyde bisulfite (Rongalite), etc. can be cited. The amount of the initiator used varies depending on the polymerization catalyst and cannot be generalized, and is arbitrarily selected according to the polymerization rate.

[0043] In the controlled radical polymerization used in the present invention, first, radicals generated by the decomposition of a radical initiator bond to a small number of monomers, and the radicals at the growth ends of the resulting short-chain polymers covalently bond to a controller to form dormant species. During a certain period after the start of the reaction, only short-chain polymers are generated and converted into dormant species, and essentially no high degree of polymerization occurs. This period is called the induction period. After the controller is consumed, the reaction enters the growth period of high degree of polymerization, and the molecular weights of almost all molecular chains in the reaction system increase proportionally to the polymerization time. Thus, a vinyl ester block copolymer with a narrow molecular weight distribution can be obtained. Regarding the time required for the polymerization process of the monomer, the induction period and the growth period are added together, and it is usually 3 to 50 hours.

[0044] As described above, in the controlled radical polymerization of the present invention, in theory, one polymer chain is formed from one molecule of the added controller. Therefore, the amount of the controller added to the reaction solution is determined in consideration of the target number average molecular weight and the polymerization rate. Generally, it is preferable to use 0.001 to 1 mole of the controller relative to 100 moles of the monomer.

[0045] If the number of moles of the generated radicals is not more than the number of moles of the controller, the polymerization reaction proceeds only by the mechanism of thermally dissociating the controller from the dormant species. Therefore, depending on the reaction temperature, the polymerization rate becomes extremely small. Thus, if it is considered that the radical initiator generates 2 radicals, the amount of the radical initiator used needs to be more than 1 / 2 times the number of moles of the controller. Generally, the amount of active radicals supplied by the initiator depends on the initiator efficiency, so there is actually an initiator that is inactivated and not used for the formation of dormant species. Therefore, the number of moles of the radical initiator used is preferably more than 1 times the number of moles of the controller, and more preferably more than 1.5 times. On the other hand, when the number of moles of the generated radicals is excessive compared to the number of moles of the controller, the proportion of uncontrolled radical polymerization increases, and thus the molecular weight distribution becomes wider. The number of moles of the radical initiator used is preferably 10 times or less the number of moles of the controller, and more preferably 6 times or less.

[0046] As long as it is a method for generating dormant seeds and controlling the high polymerization degree of polymers, the mixing method of the radical initiator, the controller, and the monomer is not particularly limited. For example, the following methods can be cited: a method of mixing the radical initiator and the controller first and then mixing the resulting mixture with the monomer; a method of mixing the radical initiator, the controller, and the monomer all at once; a method of mixing the controller and the monomer first and then mixing the resulting mixture with the radical initiator, etc. In addition, the radical initiator, the controller, and the monomer can also be mixed separately. For example, the following methods can be cited: by mixing the radical initiator and the controller with a part of the monomer to generate dormant seeds in which the controller is covalently bonded to the short-chain polymer terminal, and then mixing the dormant seeds with the remaining part of the monomer to achieve high polymerization degree. It should be noted that the dormant seeds can be separated as a macroinitiator and then mixed with the remaining part of the monomer for high polymerization degree.

[0047] In the above polymerization step, either the synthesis of the vinyl ester polymer block (b1) or the synthesis of the ionic polymer block (c1) can be carried out first. In the case of first carrying out the synthesis of the vinyl ester polymer block (b1), the vinyl ester monomer, the ethylenically unsaturated monomer (e) as required, the radical initiator, and the controller are mixed by the above method to initiate the polymerization of the vinyl ester monomer. When synthesizing the vinyl ester polymer block (b1), it is preferable not to use ionic monomers.

[0048] Then, after the number-average polymerization degree of the vinyl ester polymer block (b1) reaches the target value, the synthesis of the ionic polymer block (c1) is carried out by polymerizing the vinyl ester monomer and the ionic monomer. At this time, after removing the remaining vinyl ester monomer, the ionic monomer can be added to the reaction solution to initiate the polymerization of the ionic monomer, but from the viewpoint of further improving the gel shape retention, it is preferable to add the ionic monomer to the reaction solution without removing the vinyl ester monomer to initiate the copolymerization of the remaining vinyl ester monomer and the ionic monomer. The method of adding the ionic monomer is not particularly limited, and methods such as adding all at once and feeding over time can be cited, but from the viewpoint of further improving the gel shape retention by uniformly introducing ionic monomer units, the latter is preferable. In addition, if necessary, an additional vinyl ester monomer and the ethylenically unsaturated monomer (e) can be added together with the ionic monomer. The number-average polymerization degree of the polymer can be confirmed by the GPC (gel permeation chromatography) method. Specifically, the method described in the following examples can be adopted.

[0049] In the case where the synthesis of the vinyl ester polymer block (b1) is carried out first, when obtaining a binary vinyl ester block copolymer having one vinyl ester polymer block (b1) and a polymer block (c1) containing a vinyl ester monomer unit and an ionic monomer unit, it is preferable to stop the reaction before the ionic monomer disappears. On the other hand, when obtaining a multi-vinyl ester block copolymer of three or more components, it is preferable to continue the polymerization even after the ionic monomer disappears to synthesize the vinyl ester polymer block (b1). According to this method, a ternary vinyl ester block copolymer called block (b1)-block (c1)-block (b1) can be obtained. In the present invention, the portion obtained by polymerizing vinyl ester in a state where the molar ratio of the ionic monomer unit to vinyl ester (ionic monomer / vinyl ester) in the reaction solution is 0.00001 or less is taken as the vinyl ester polymer block (b1). The moment when the molar ratio (ionic monomer / vinyl ester) reaches 0.00001 is determined by the method described in the examples. When the number average degree of polymerization of the vinyl ester block copolymer reaches the target value, the reaction can be stopped. In addition, when obtaining a multi-vinyl ester block copolymer of four or more components, an ionic monomer can be added again to the reaction solution of the ternary vinyl ester block copolymer and the polymerization can be continued.

[0050] In the above polymerization step, in the case where the synthesis of the ionic polymer block (c1) is carried out first, polymerization is initiated by mixing an ionic monomer, a radical initiator, and an organic cobalt complex by the above method. At this time, from the viewpoint of further improving the gel shape retention, it is preferable to further add a vinyl ester monomer. In addition, an ethylenically unsaturated monomer (e) can be further added as needed. In this way, a polymer block (c1) containing a vinyl ester monomer unit and an ionic monomer unit is synthesized, and then each block is formed in sequence.

[0051] The polymerization temperature when synthesizing the vinyl ester polymer block (b1) and the ionic polymer block (c1) is preferably, for example, 0°C to 80°C. When the polymerization temperature is less than 0°C, the polymerization rate tends to become insufficient and the productivity decreases. From this point of view, the polymerization temperature is more preferably 10°C or higher, and further preferably 20°C or higher. On the other hand, when the polymerization temperature is greater than 80°C, the molecular weight distribution of the obtained block copolymer (A) tends to broaden. From this point of view, the polymerization temperature is more preferably 65°C or lower, and further preferably 50°C or lower.

[0052] In the above polymerization step, a termination step of terminating the polymerization reaction by adding a polymerization terminator when the number-average degree of polymerization and the polymerization rate of the vinyl ester block copolymer reach the target values is preferably carried out. Examples of the polymerization terminator include: 1,1-diphenylethylene; styrene compounds such as styrene, α-methylstyrene, and 4-tert-butylstyrene; hydroxyaromatic compounds such as p-methoxyphenol, hydroquinone, cresol, 4-tert-butylcatechol, and p-nitrophenol; quinone compounds such as benzoquinone and naphthoquinone; conjugated carboxylic acids such as muconic acid and sorbic acid; thioethers such as phenothiazine, distearyl thiodipropionate, and dilauryl thiodipropionate; aromatic amines such as p-phenylenediamine and N-nitrodiphenylamine; nitroxides such as 2,2,6,6-tetramethylpiperidin-1-oxy and 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxy; transition metal salts such as copper acetate, copper dithiocarbamate, and manganese acetate. Among them, 1,1-diphenylethylene, sorbic acid, and benzoquinone are preferred, and 1,1-diphenylethylene is more preferred.

[0053] The molar number of the added polymerization terminator is preferably 1 to 100 moles relative to 1 mole of the added controller. When the molar number of the above polymerization terminator is too small, the radicals at the polymer terminals cannot be sufficiently trapped, and the hue of the obtained block copolymer (A) may deteriorate. On the other hand, when the molar number of the above polymerization terminator is too large, the production cost may increase.

[0054] The temperature of the reaction solution in the termination step may be any temperature at which the polymerization terminator can react with the radicals at the terminals of the vinyl ester block copolymer, and is preferably 0 to 80°C. The time required for the termination step is usually 10 minutes to 5 hours.

[0055] When a cobalt complex is used as the above controller, an extraction step is preferably carried out before the saponification step. In the extraction step, the obtained vinyl ester block copolymer solution is brought into contact with an aqueous solution containing a water-soluble ligand, and the cobalt complex is extracted and removed from the vinyl ester block copolymer solution. In this way, by carrying out the saponification step after previously removing the cobalt complex contained in the vinyl ester block copolymer solution, a block copolymer (A) with good hue can be obtained. Specifically, the following operations can be carried out: The above aqueous solution and the above vinyl ester block copolymer solution that are mutually insoluble are vigorously stirred to increase the area of the interface between the two, and then left standing to separate into an oil layer and a water layer, and then the water layer is removed. This operation can be repeated multiple times.

[0056] The water-soluble ligand used in the extraction step is preferably an acid having a pKa of 0 to 12 at 25°C. When a strong acid with a pKa less than 0 is used, it is difficult to efficiently extract the cobalt complex, and the pKa is preferably 2 or more. In addition, when a weak acid with a pKa greater than 12 is used, it is also difficult to efficiently extract the cobalt complex, and the pKa is preferably 7 or less. When the above acid is a polybasic acid, the first dissociation constant (pKa1) needs to be within the above range. For the water-soluble ligand, an acid having a pKa of 0 to 12 is preferably a carboxylic acid or phosphoric acid (pKa1 is 2.1), more preferably a carboxylic acid. Among them, acetic acid (pKa is 4.76) is particularly preferred.

[0057] The pH of the aqueous solution containing the water-soluble ligand is preferably 0 to 5. The pH is more preferably 1 or more, further preferably 1.5 or more. The pH is more preferably 4 or less, further preferably 3 or less.

[0058] In the saponification step, by saponifying the vinyl ester monomer units contained in the vinyl ester polymer block (b1) and the ionic polymer block (c1) in the vinyl ester block copolymer obtained in the above polymerization step, vinyl alcohol monomer units are formed. Through the saponification step, the vinyl ester polymer block (b1) is converted into a vinyl alcohol polymer block (b).

[0059] In the saponification step, the vinyl ester block copolymer produced by the above method is saponified in a state dissolved in an alcohol, whereby the vinyl ester monomer units in the vinyl ester block copolymer are converted into vinyl alcohol monomer units. In addition, when saponifying a vinyl ester block copolymer obtained using an acrylate as an ionic monomer, sometimes the acrylate monomer units in the copolymer are converted into acrylic acid monomer units, and the converted acrylic acid monomer units form salts. In addition, the acrylate monomer units or acrylic acid monomer units can form a lactone ring with adjacent vinyl alcohol monomer units.

[0060] Examples of the alcohol used in the saponification reaction include lower alcohols such as methanol and ethanol, and methanol is particularly preferably used. In addition, the above alcohol can be a hydrous alcohol or a dehydrated alcohol. The alcohol used in the saponification reaction can contain esters such as acetone, methyl acetate, and ethyl acetate, and solvents such as toluene. Examples of the catalyst used in the saponification reaction include hydroxides of alkali metals such as potassium hydroxide and sodium hydroxide; base catalysts such as sodium methoxide; and acid catalysts such as inorganic acids. Regarding the temperature of the saponification reaction, a range of 20 to 70°C is appropriate, for example. When a gel-like product precipitates as the saponification reaction proceeds, the product is crushed, washed, and then dried at that time.

[0061] The production method of the present invention has a salt formation step of forming a salt of the ionic monomer unit in the block copolymer after the saponification step as an optional step. The method for forming a salt of the ionic monomer unit is not particularly limited, and a known method can be appropriately adopted according to the type of the ionic monomer unit. Through the saponification step and the salt formation step, the ionic polymer block (c1) is converted into an ionic polymer block (c) containing a monomer unit having an ionic group forming a salt and a vinyl alcohol monomer unit. It should be noted that when the ionic polymer block (c1) after the saponification step contains a monomer unit having an ionic group forming a salt, since the block (c1) is equivalent to the block (c), the block copolymer (A) of the present invention can be obtained without passing through the salt formation step.

[0062] When an acrylate is used as the above ionic monomer, it is preferable to perform the above salt formation step on the block copolymer after the saponification step. Thereby, the acrylate unit, the acrylic acid unit, and the lactone ring are converted into an acrylic acid monomer unit forming a salt. As a specific method, a method of mixing the block copolymer after the saponification step with an aqueous solution of a metal hydroxide and an alcohol can be cited. As the above metal hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, etc. can be cited. As the above alcohol, methanol, ethanol, etc. can be cited. The salt formation step is appropriately carried out, for example, in the range of 20 to 100 °C.

[0063] The monomer unit having an ionic group in the ionic polymer block (c) is formed from the above ionic monomer. The above ionic group is a carboxyl group, a sulfonic acid group, or an ammonium group, and among them, a carboxyl group is preferable. The monomer unit having an ionic group is as described above, and among them, a monomer unit having a carboxyl group is preferable, and an acrylic acid monomer unit is more preferable.

[0064] The monomer unit having an ionic group in the ionic polymer block (c) forms a salt. The counter ion of this monomer unit is not particularly limited, and ions of Group 1, 2, 12, 13, or 17 elements of the periodic table are preferable, and among them, cations such as sodium ions, potassium ions, magnesium ions, calcium ions, zinc ions, and aluminum ions, and anions such as chloride ions are preferable. As the above cations, sodium ions and calcium ions are more preferable, and sodium ions are further preferable.

[0065] The block copolymer (A) of the present invention obtained in such a manner comprises a vinyl alcohol polymer block (b) and an ionic polymer block (c) containing monomer units having an ionic group forming a salt and vinyl alcohol monomer units. The block copolymer (A) may be a binary block copolymer composed of one block (b) and one block (c), a ternary block copolymer composed of one block (b) and two blocks (c), or a ternary block copolymer composed of two blocks (b) and one block (c), or a multi-block copolymer composed of a total of four or more blocks (b) and blocks (c). Among them, the block copolymer (A) is preferably a binary block copolymer or a ternary block copolymer. The bonding form of the block (b) and the block (c) is preferably linear. The block copolymer (A) may contain blocks other than the block (b) and the block (c), but its content is preferably 10 mol% or less, more preferably 1 mol% or less.

[0066] The saponification degree of the block copolymer (A) of the present invention is preferably 80 to 99.99 mol%. In the present invention, the saponification degree means the proportion (mol%) of the number of moles of vinyl alcohol monomer units in the total number of moles of vinyl ester monomer units and vinyl alcohol monomer units in the block copolymer (A). When the saponification degree is less than 80 mol%, the crystallinity of the block copolymer is too low, the gel shape retention is reduced, and the desired absorption performance may not be obtained. The saponification degree is preferably 85 mol% or more, more preferably 90 mol% or more, and further preferably 95 mol% or more. On the other hand, when the saponification degree is greater than 99.99 mol%, the production of the block copolymer (A) tends to become difficult. The saponification degree is preferably 99.95 mol% or less. The saponification degree can be determined by 1 1H-NMR measurement of the vinyl alcohol-based block copolymer (A). Specifically, the method described in the examples can be used.

[0067] The content (Z A ) of the units derived from ionic monomers having an ionic group or its derivative in the block copolymer (A) of the present invention relative to all monomer units is preferably 2 to 90 mol%. When an acrylate is used as the ionic monomer, the units derived from the above ionic monomer contain acrylate monomer units forming a salt, acrylate monomer units not forming a salt, acrylate monomer units, and lactone rings, and the content (Z A ) is the total amount of these units.

[0068] By the content (Z A ) being 2 mol% or more, the absorbency of the block copolymer (A) is further improved. The content (Z A)More preferably, it is 3 mol% or more, still more preferably 4 mol% or more, and particularly preferably 5 mol% or more. On the other hand, when the content (Z A ) is 90 mol% or less, the gel shape retention of the block copolymer (A) is further improved. The content (Z A ) is more preferably 60 mol% or less, still more preferably 40 mol% or less, and particularly preferably 20 mol% or less.

[0069] The content (J A ) of the monomer unit having an ionic group formed into a salt in the block copolymer (A) of the present invention relative to all monomer units is preferably 2 to 90 mol%. By making the content (J A ) 2 mol% or more, the absorbency of the block copolymer (A) is further improved. The content (J A ) is more preferably 3 mol% or more, still more preferably 4 mol% or more, and particularly preferably 5 mol% or more. On the other hand, when the content (J A ) is 90 mol% or less, the gel shape retention of the block copolymer (A) is further improved. The content (J A ) is more preferably 60 mol% or less, still more preferably 40 mol% or less, and particularly preferably 20 mol% or less.

[0070] The content of the vinyl alcohol monomer unit in the vinyl alcohol polymer block (b) relative to all monomer units is preferably 80 mol% or more, more preferably 90 mol% or more, still more preferably 95 mol% or more, and particularly preferably 99 mol% or more. In the present invention, the vinyl alcohol monomer unit refers to a vinyl ester monomer unit and a vinyl alcohol monomer unit, and the content of the vinyl alcohol monomer unit refers to the total content of the vinyl ester monomer unit and the vinyl alcohol monomer unit.

[0071] The content of the vinyl alcohol monomer unit in the above-mentioned vinyl alcohol polymer block (b) relative to all monomer units is preferably 80 mol% or more, more preferably 90 mol% or more, still more preferably 95 mol% or more, and particularly preferably 99 mol% or more.

[0072] The content of the unit derived from the above ionic monomer in the vinyl alcohol polymer block (b) relative to all monomer units is usually less than 0.1 mol%.

[0073] The content (R c ) of the unit derived from the above ionic monomer in the ionic polymer block (c) relative to all monomer units is preferably 5 to 95 mol%. By making the content (R c ) 5 mol% or more, the absorbency of the block copolymer (A) is further improved. The content (R c)More preferably, it is 6 mol% or more, still more preferably 8 mol% or more, and particularly preferably 10 mol% or more. On the other hand, from the viewpoint of further improving the gel shape retention of the block copolymer (A), the content (R c ) is more preferably 80 mol% or less, still more preferably 40 mol% or less, and particularly preferably 25 mol% or less.

[0074] The content (K c ) of the monomer unit having an ionic group that forms a salt in the ionic polymer block (c) relative to all monomer units is preferably 5 to 95 mol%. By making the content (K c ) 5 mol% or more, the absorbency of the block copolymer (A) is further improved. The content (K c ) is more preferably 6 mol% or more, still more preferably 8 mol% or more, and particularly preferably 10 mol% or more. On the other hand, from the viewpoint of further improving the gel shape retention of the block copolymer (A), the content (K c ) is more preferably 80 mol% or less, still more preferably 40 mol% or less, and particularly preferably 25 mol% or less.

[0075] The ionic polymer block (c) contains a vinyl alcohol monomer unit. Thereby, the gel shape retention and absorbency of the block copolymer (A) are improved. The content (total content of vinyl alcohol unit and vinyl acetate unit) of the vinyl alcohol monomer unit in the ionic polymer block (c) relative to all monomer units is 5 to 95 mol%. When the content is less than 5 mol%, the improvement effects of the gel shape retention and absorbency of the block copolymer (A) cannot be obtained. The above content is preferably 20 mol% or more, more preferably 60 mol% or more, and still more preferably 75 mol% or more. On the other hand, when the content of the above vinyl alcohol monomer unit is more than 95 mol%, the absorbency of the block copolymer (A) decreases. The above content is preferably 94 mol% or less, more preferably 92 mol% or less, and still more preferably 90 mol% or less.

[0076] The number average molecular weight (Mn A ) of the block copolymer (A) of the present invention is 20,000 to 440,000. By using controlled polymerization, a block copolymer (A) with a narrow molecular weight distribution and a high number average molecular weight (Mn A ) can be obtained. By making Mn A 20,000 or more, the absorbency of the block copolymer (A) is improved. Mn A is preferably 30,000 or more, more preferably 40,000 or more, still more preferably 50,000 or more, and particularly preferably 60,000 or more. On the other hand, by making Mn Ais 440,000 or less, and the gel shape retention is improved. Mn A is preferably 300,000 or less, more preferably 250,000 or less, and still more preferably 200,000 or less. The number average molecular weight (Mn A ) and the molecular weight distribution (Mw A / Mn A ) are values obtained by measuring the block copolymer (A) using polymethyl methacrylate as a standard substance by the GPC method and using a tetrahydrofuran (THF) column. The measurement method is as described in the examples.

[0077] The number average molecular weight (Mn b ) of the vinyl alcohol polymer block (b) is 15,000 to 220,000. When there are a plurality of vinyl alcohol polymer blocks (b) in the block copolymer (A), the sum of the number average molecular weights of the respective vinyl alcohol polymer blocks (b) is taken as the number average molecular weight (Mn b ). By making Mn b 15,000 or more, while maintaining the absorbency, the gel shape retention is improved. Mn b is preferably 20,000 or more, more preferably 30,000 or more, still more preferably 35,000 or more, and particularly preferably 40,000 or more. On the other hand, when Mn b exceeds 220,000, the absorbency decreases. Mn b is preferably 180,000 or less, more preferably 150,000 or less, and still more preferably 120,000 or less. Regarding Mn b , after performing GPC measurement of the polymer sampled from the reaction solution during polymerization and, if necessary, 1 1H-NMR measurement, it is calculated from the number average molecular weight of the obtained polymer and the content of each monomer unit. Specifically, the method described in the examples below is used.

[0078] The ratio (Mn b ) of the number average molecular weight (Mn A ) of the vinyl alcohol polymer block (b) to the number average molecular weight (Mn b ) of the block copolymer (A) (Mn A / Mn b / Mn A ) is 0.1 to 0.9. By making the ratio (Mn b / Mn A ) 0.1 or more, the gel shape retention and water solubility of the block copolymer (A) are improved. The ratio (Mn b / Mn A) is 0.9 or less, and the absorbability of the block copolymer (A) is improved. The ratio (Mn b / Mn A ) is preferably 0.8 or less, more preferably 0.7 or less.

[0079] The molecular weight distribution (Mw A / Mn A ) of the block copolymer (A) of the present invention is preferably 1.05 to 1.95. By carrying out polymerization by controlled radical polymerization, a block copolymer (A) with a narrow molecular weight distribution can be obtained. The molecular weight distribution (Mw A / Mn A ) is preferably 1.80 or less, more preferably 1.65 or less, and further preferably 1.55 or less. When the molecular weight distribution (Mw A / Mn A ) is within the above range, the block (b) and the block (c) form a dense phase separation structure, and the absorbability and shape retention are improved.

[0080] In the above polymerization step, polymerization of a monomer containing a vinyl ester monomer and polymerization of a monomer containing an ionic monomer and a vinyl ester monomer are carried out, and a vinyl ester-based block copolymer containing a vinyl ester polymer block (b1) and an ionic polymer block (c1) can be obtained. By subjecting the vinyl ester-based block copolymer to the above saponification step and an optional salt formation step, in a preferred mode, a block copolymer (A) containing a polyvinyl alcohol-based polymer block (b) and an ionic polymer block (c) containing a monomer unit having an ionic group forming a salt and a polyvinyl alcohol-based monomer unit is obtained.

[0081] In the case where (meth)acrylic acid or (meth)acrylate is used as the ionic monomer, in the polymer obtained by heating the block copolymer (A) in an acidic aqueous solution and then drying, the molar ratio (V A ) [lactone ring / total of acrylic acid monomer unit and lactone ring] of the lactone ring is preferably 0.75 or more.

[0082] By heating the block copolymer (A) in an acidic aqueous solution, the acrylic acid monomer unit adjacent to the polyvinyl alcohol monomer unit and capable of forming a lactone ring with the polyvinyl alcohol monomer unit is converted into a lactone ring. On the other hand, in the case where acrylic acid monomer units are continuous, even if the above treatment is carried out, a lactone ring is not formed and remains as an acrylic acid monomer unit. Therefore, when the proportion of the part where polyvinyl alcohol monomer units and acrylic acid monomer units are alternately arranged is large, that is, when the proportion of the part where acrylate monomer units and acrylic acid monomer units are continuous is small, the molar ratio (V A ) [lactone ring / total of acrylic acid monomer unit and lactone ring] becomes high. That is, the molar ratio (VA ) [Total of lactone ring / acrylic monomer unit and lactone ring] serves as an index of the randomness of the ionic polymer block (c) containing a vinyl alcohol monomer unit and a salt-formed acrylic monomer unit. By making the molar ratio (V A ) [Total of lactone ring / acrylic monomer unit and lactone ring] 0.75 or more, the gel shape retention of the block copolymer (A) is further improved. The molar ratio (V A ) [Total of lactone ring / acrylic monomer unit and lactone ring] is more preferably 0.80 or more, further preferably 0.85 or more, and particularly preferably 0.90 or more. The conditions for heat treatment and drying of the block copolymer (A) are those described in the examples.

[0083] The crystal melting temperature (Q A ) [°C] of the polymer obtained by further saponifying the block copolymer (A) to a saponification degree of 99 mol% or more is preferably 210°C or more. In this way, by making the block copolymer (A) have a relatively high crystal melting temperature (Q A ), the gel shape retention is further improved. Q A is more preferably 215°C or more, further preferably 220°C or more. Q A can be measured by the method described in the examples.

[0084] The amount of deionized water absorbed per 0.1 g of the block copolymer (A) at 20°C is preferably 20 g or more. Although there is no particular upper limit, it is usually less than 100 g. The amount of 0.9 mass% sodium chloride aqueous solution absorbed per 1 g of the block copolymer (A) at 20°C is preferably 20 g or more. Although there is no particular upper limit, it is usually less than 100 g. The amounts of deionized water and sodium chloride aqueous solution absorbed are measured by the method described in the examples. In this way, the block copolymer (A) with high absorbency for deionized water and brine is suitable for various uses.

[0085] The amount of soluble components when 1 g of the block copolymer (A) is dissolved in 1000 ml of water at 95°C is preferably 95 mass% or more, and more preferably the amount of soluble components when dissolved in 1000 ml of water at 20°C is 95 mass% or more. In this way, the block copolymer (A) with high solubility in water is excellent in environmental aspects. In addition, since the block copolymer (A) can absorb water, brine, etc. and then be discharged into the sewer, waste can be reduced. Furthermore, it is considered that new uses can be developed using the properties of such a block copolymer (A). The amount of soluble components is calculated by the method described in the examples.

[0086] The block copolymer (A) is preferably high in biodegradation rate. Because of the high biodegradation rate, it is excellent in terms of the environment. In addition, by both the amount of soluble components when dissolved in water and the biodegradation rate being high as described above, the waste of the block copolymer (A) can be further reduced. The biodegradation rate is preferably 20% or more, more preferably 40% or more. The biodegradation rate can be determined by the method described in the examples.

[0087] The absorbency and water solubility of the block copolymer (A) of the present invention can be appropriately changed according to the design of the block copolymer (A). For example, when the amount of deionized water absorbed per 0.1 g is set as X DIW [g], and the amount of soluble components when 1 g of the block copolymer (A) is dissolved in 1000 ml of water at 95°C is set as Y 95 [mass%], and the amount of soluble components when 1 g of the block copolymer (A) is dissolved in 1000 ml of water at 20°C is set as Y 20 [mass%], copolymers can be produced such that X DIW is 20 or more, Y 95 is 95 or more, Y 20 is 95 or more; X DIW is 20 or more, Y 95 is 95 or more, Y 20 is 0 or more and 95 or less; X DIW is 40 or more, Y 95 is 95 or more, Y 20 is 95 or more; X DIW is 40 or more, Y 95 is 95 or more, Y 20 is 0 or more and 95 or less; etc. block copolymers (A). In addition, the amount of soluble components in water within a temperature range other than 95°C and 20°C can be adjusted according to the use.

[0088] An absorbent material containing the block copolymer (A) is a preferred embodiment of the present invention. The form of the absorbent material is not particularly limited, and examples thereof include particles, sheets, tapes, gels, pastes, films, fibers, etc., and particles are preferred. The content of the block copolymer (A) in the above absorbent material is not particularly limited, and is preferably 1 mass% or more, more preferably 5 mass% or more, and further preferably 10 mass% or more.

[0089] As a component other than the block copolymer (A) in the above absorbent material, a material that prevents the block copolymer (A) from falling off and does not hinder liquid permeation can be appropriately used. For example, it can include: papers such as cotton paper, pulp, various non-woven fabrics (spunbond non-woven fabric, meltblown non-woven fabric, heat-bonded non-woven fabric, needle-punched non-woven fabric, hydroentangled non-woven fabric, air-laid non-woven fabric, etc.). These can be subjected to water-solubilization treatment, hydrolysis treatment, hydrophilization treatment, and pore-opening treatment as needed. As the constituent components of these, polymers such as polyvinyl alcohol, polyacrylic acid, polyacrylamide, polyurethane, polylactic acid, starch, cellulose, polyalkylene oxide, polyethylene, polypropylene, polyethylene terephthalate can be used alone or in combination.

[0090] An absorbent article having the above absorbent material is a more preferred embodiment. The absorbent article is suitable for uses such as sanitary uses, daily necessities uses, construction / civil engineering uses, industrial uses, agricultural uses, medical uses, or food uses. Specifically, the absorbent article is suitable as a sanitary absorbent article such as a disposable diaper, urine pad, sanitary napkin, breast pad, incontinence pad, sweatband, water-soluble sanitary material, etc.; daily necessities uses such as gel air freshener, disposable heating pad material, cat litter, pet pad, deodorant, portable toilet, etc.; construction / civil engineering absorbent articles such as droplet absorbent, sealing construction material, concrete curing material, leak-proof mud material, water-proofing material, sealing material, desert greening material, etc.; other industrial absorbent articles such as anti-condensation agent sheet for containers, fire extinguisher, water-stopping material for communication cables, alkaline battery material, water-swellable coating, water stain coating, artificial snow compounding agent, water remover in oil, etc.; agricultural absorbent articles such as soil water retainer, seedling raising pad, seed coating, fertilizer slow-release agent, disintegration aid for pesticides / fertilizers, etc.; medical absorbent articles such as moisturizer, wound protection dressing, waste blood solidifying agent, medical padding, poultice, body fluid absorbent, etc.; food absorbent articles such as cold storage agent, freshness retainer, etc. An absorbent article having an absorbent material composed of water-soluble and hydrolyzable components can, for example, easily discard the absorbent article itself or the absorbent material part desorbed from the absorbent article into water after absorbing body fluid. Therefore, the absorbent article can be suitably used as a sanitary material that flows into water without pre-treatment such as pulverization. By using a block copolymer with excellent biodegradability, it can be decomposed by activated sludge and discarded into the sewer. In addition, for an absorbent material that holds components such as detergents, pesticides, and fertilizers in liquid absorption, release control triggered by the amount of water can be performed.

[0091] [Examples]

[0092] Hereinafter, the present invention will be described more specifically using examples.

[0093] [Materials Used in Examples]

[0094] · Cobalt(II) acetylacetonate (Co(acac)2)

[0095] · Cobalt(II) tetrakis(trimethylphenyl)porphyrin (Co(TMP))

[0096] · [2,2’-Azobis(4-methoxy-2,4-dimethylvaleronitrile)] (V-70)

[0097] · 2,2'-Azobisisobutyronitrile (AIBN)

[0098] · Vinyl acetate (VAc)

[0099] · Methyl acrylate (MA)

[0100] · 2-Acrylamido-2-methylpropanesulfonic acid (AMPS)

[0101] · 3-(Methacrylamido)propyltrimethylammonium chloride (MAPTAC)

[0102] · 1,1-Diphenylethylene (1,1-DPEt)

[0103] [Number-average molecular weight (Mn A ), number-average molecular weight (Mn b ) and molecular weight distribution (Mw A / Mn A )]

[0104] The number-average molecular weight (Mn) and molecular weight distribution (Mw / Mn) of the polymer were measured using a gel permeation chromatography apparatus manufactured by Shimadzu Corporation. The measurement conditions are as follows.

[0105] Column: Two THF columns "KF-806M" manufactured by Showa Denko K.K. in series

[0106] Standard sample: Polymethyl methacrylate

[0107] Solvent and mobile phase: Tetrahydrofuran (THF)

[0108] Flow rate: 1.0 mL / min

[0109] Temperature: 40 °C

[0110] Sample solution concentration: 0.2 mass% (filtered using a filter with an opening diameter of 0.45 μm)

[0111] Injection volume: 100 μL

[0112] Detector: RI

[0113] [Content (U) of ionic monomer units in the vinyl ester block copolymer]

[0114] The content (U) (mol%) of acrylate monomer units (ionic monomer units) in the vinyl ester block copolymer is determined by the following method. The 1 1H-NMR measurement of the vinyl ester block copolymer is carried out. Let the integral value (4.8 ppm) of the peak of the methylene proton (-CH2CH(OCOCH3)-) from the vinyl acetate monomer unit be T, and the integral value (3.6 ppm) of the peak of the side-chain proton (-CH2CH(COOCH3)-) from the methyl acrylate monomer unit be S. The content (U) (mol%) of acrylate monomer units in the vinyl ester block copolymer is calculated according to the following formula.

[0115] (U) (mol%) = (S / 3) / (S / 3 + T) × 100

[0116] When using MAPTAC as the ionic monomer, let the integral value of the peak of the N-methyl proton (-N(CH3)3) (the peak detected in the range of 3.1 - 3.3 ppm) be S'. The content (U) (mol%) of MAPTAC monomer units in the vinyl ester block copolymer is calculated according to the following formula.

[0117] (U) (mol%) = (S' / 9) / (S' / 9 + T) × 100

[0118] When using AMPS instead of the acrylate monomer, let the integral value of the peak of the side-chain methylene proton (-CH2SO3H) (the peak detected in the range of 2.9 - 3.2 ppm) be S". The content (U) (mol%) of AMPS monomer units in the vinyl ester block copolymer is calculated according to the following formula.

[0119] (U) (mol%) = (S" / 2) / (S" / 2 + T) × 100

[0120] [The number-average degree of polymerization DP of block copolymer (A) A and the number-average degree of polymerization DP of polymer block (b) b

[0121] The number-average degree of polymerization DP of polymer block (b) in copolymer (A) is determined in the following manner b .

[0122] Polymer block (b) is formed by saponifying the vinyl ester polymer block (b1) in the vinyl ester block copolymer. Since the number-average degree of polymerization DP of the polymer b substantially does not change before and after saponification, the number-average degree of polymerization determined from the GPC measurement result of the polymer before saponification is taken as the number-average degree of polymerization DP of polymer block (b) b ​Similarly, the number-average degree of polymerization obtained from the GPC measurement results of the polymer after polymerization termination and before saponification is defined as the number-average degree of polymerization DP of the copolymer (A). A .

[0123] Herein, the vinyl ester polymer block (b1) refers to a block (b1) obtained by polymerizing a vinyl ester in the absence of an acrylate-based ionic monomer; and a copolymer block (c1) containing a vinyl ester monomer unit and an ionic monomer unit obtained by polymerizing a vinyl ester in the presence of an ionic monomer in the initial stage or during polymerization, and then polymerizing a vinyl ester monomer in a state where the molar ratio of the ionic monomer to the vinyl ester (ionic monomer / vinyl ester) in the reaction solution is 0.00001 or less after the ionic monomer is consumed prior to the vinyl ester.

[0124] The boundary between the "vinyl ester polymer block (b1)" and the "copolymer block (c1) containing a vinyl ester monomer unit and an ionic monomer unit" is determined as follows. Sampling is appropriately performed during polymerization, and the number-average degree of polymerization (DP) and the content of ionic monomer units (U) (mol%) of the polymer at each sampling time are measured by GPC and 1 1H-NMR. The time when the molar ratio (ionic monomer / vinyl ester) reaches 0.00001 is obtained by simulation using the Mayo-Lewis equation, which is a copolymerization theoretical formula, and the reactivity ratio values (r VAc = 0.01, r MA = 30). At this time, the content of ionic monomer units contained in the vinyl ester polymer block (b1) formed in a state where the molar ratio (ionic monomer / vinyl ester) is 0.0001 or less is less than 0.1 mol%.

[0125] The number-average degree of polymerization (DP) of the sampled polymer is calculated using the number-average molecular weight Mn of the polymer obtained by GPC and 1 1H-NMR, the content of acrylic monomer units (U) (mol%), and the molecular weights of the acrylate monomer unit and the vinyl ester monomer unit (MA: 86, VAc: 86) according to the following formula.

[0126] (DP) = Mn / {(U / 100)×86 + [(100 - U) / 100]×86}

[0127] The number-average degree of polymerization DP of the copolymer (A) A is calculated using the values obtained by GPC and 1 1H-NMR of the vinyl ester block copolymer after polymerization termination. In the case of obtaining a vinyl ester polymer block in the initial stage of polymerization, the polymer sampled immediately before adding the ionic monomer is measured, and the number-average degree of polymerization DP of the polymer block (b) is obtained bWhen obtaining a vinyl ester polymer block after copolymerizing an acrylate and a vinyl ester, the number-average degree of polymerization DP of the polymer block (b) is determined by finding the difference in the number-average degree of polymerization of the polymer sampled at the moment of the boundary of the block and the vinyl ester block copolymer after polymerization cessation. b 。

[0128] [Content (Z A )(mol%) of units derived from ionic monomers in block copolymer (A)]

[0129] When using an acrylate as the ionic monomer, the obtained copolymer (A) is stirred in an aqueous hydrochloric acid solution at pH 2 at 100 °C for 1 hour, and then dried and cured at 120 °C, thereby converting all the acrylic monomer units (acrylic acid units, acrylate units, acrylate salt units) in the copolymer into acrylic acid monomer units or lactone ring structures (the lactone ring is formed by reacting an acrylic acid monomer unit or an acrylate monomer unit with an adjacent vinyl alcohol monomer unit). The copolymer is washed with methanol to remove salts, and then dried under reduced pressure at 90 °C for 2 days. Thus, a polymer dried after heat treatment in an acidic aqueous solution is obtained. Using the nuclear magnetic resonance apparatus "LAMBDA 500" manufactured by JEOL Ltd., the 1 1H-NMR measurement of this copolymer (the polymer dried after heat treatment in an acidic aqueous solution) is carried out at 40 °C and 95 °C. As the solvent, DMSO-d6 is used. The content (Z A )(mol%) of acrylic monomer units relative to all monomer units of copolymer (A) is calculated in the following manner.

[0130] The content (Z A )(mol%) of acrylic monomer units relative to all monomer units of copolymer (A) is calculated according to the following formula.

[0131] (Z A )(mol%) = (X + Y) / (W + 2X + Y + (P / 3)) × 100

[0132] The meanings of the symbols in the formula are as follows.

[0133] Y: Integration value of the peak of side-chain protons (-CH2CH(COOH)-) from acrylic acid (broad peak detected in the range of 11.0 - 13.0 ppm)

[0134] X: Methylene proton (-CH2C HIntegrated value of the peak of (R1)CH2CH(R2)- (wherein R1 and R2 form a bond with each other, and -R1-R2- represents a -CO-O- structure) (doublet at 2.6 ppm to 3.0 ppm)

[0135] W: Integrated value of the peak of the methylene proton (-CH2CH(OH)-) derived from vinyl alcohol (peak at 3.6 ppm to 4.0 ppm)

[0136] P: Integrated value of the peak of the side-chain proton (-CH2CH(OCOCH3)-) derived from vinyl acetate (1.9 ppm to 2.0 ppm)

[0137] When using MAPTAC in place of the acrylate monomer, the integrated value of the peak of the N-methyl proton (-N(C H 3)3) (peak detected in the range of 3.1 to 3.3 ppm) is designated as F2, and the content (Z A )(mol%) of the MAPTAC monomer unit in the copolymer (A) is calculated according to the following formula using the above P and W. When using AMPS in place of the acrylate monomer, the integrated value of the peak of the side-chain methylene proton (-C H 2SO3H) (peak detected in the range of 2.9 to 3.2 ppm) is designated as F3, and the content (Z A )(mol%) of the AMPS monomer unit in the copolymer (A) is calculated according to the following formula using the above P and W.

[0138] (Z A )(mol%) = (F2 / 9) / ((F2 / 9) + W + (P / 3)) × 100

[0139] (Z A )(mol%) = (F3 / 2) / ((F3 / 2) + W + (P / 3)) × 100

[0140] [Molar ratio of lactone ring (V A ) [lactone ring / total of lactone ring and acrylate monomer unit]]

[0141] Using the above X and Y, the molar ratio (V A ) [lactone ring / total of lactone ring and acrylate monomer unit] of the lactone ring in the polymer (the polymer dried after heat treatment in an acidic aqueous solution) relative to the total of the acrylate monomer unit and the lactone ring is calculated according to the following formula.

[0142] (V A ) = X / (X + Y)

[0143] [Content of the unit derived from the ionic monomer in the polymer block (c) (Rc )]

[0144] Using the number-average degree of polymerization DP of the copolymer (A) A and the number-average degree of polymerization DP of the polymer block (b) b , the content (R c )(mol%) of the acrylic acid monomer units in the polymer block (c) containing vinyl alcohol monomer units and acrylic acid monomer units in the copolymer (A) is calculated according to the following formula.

[0145] (R c )(mol%) = (Z A ) × DP A / (DP A - DP b )

[0146] [Content (H c ) of the units derived from vinyl alcohol monomers in the polymer block (c)]

[0147] The content (H c )(mol%) of the vinyl alcohol monomer units in the polymer block (c) containing vinyl alcohol monomer units and acrylic acid monomer units in the copolymer (A) is calculated according to the following formula.

[0148] (H c )(mol%) = 100 - (R c )

[0149] [Saponification degree]

[0150] Using the above P and W, the saponification degree (mol%) of the copolymer (A) is calculated according to the following formula.

[0151] Saponification degree (mol%) = 1 - (P / 3) / (W + (P / 3)) × 100

[0152] [Content (J A ) of the monomer units having ionic groups that have formed salts in the block copolymer (A)]

[0153] The content (J A ) of the monomer units having ionic groups that have formed salts relative to all the monomer units in the copolymer (A) is, for example, determined using the integral value F1 of the peak of the methylene protons (-CH2C 1 (COOM)-) of acrylate detected in the 1H-NMR measurement of the copolymer (A), W, X, Y, P, and the peak detected in the range of 2.4 to 2.7 ppm. Here, M represents the counter cation of acrylate. H (COOM)-) and is calculated according to the following formula.

[0154] (J A )(mol%) = F1 / (F1 + W + 2X + Y + (P / 3)) × 100

[0155] In the case of using AMPS or AMPS in place of the acrylate monomer, the above W, P, F2, and F3 are used and calculated by the following formula.

[0156] (J A )(mol%) = (F2 / 9) / ((F2 / 9) + W + (P / 3)) × 100

[0157] (J A )(mol%) = (F3 / 2) / ((F3 / 2) + W + (P / 3)) × 100

[0158] [Content (K c ) of the salt-formed monomer unit having an ionic group in the ionic polymer block (c)

[0159] Content (K c ) of the salt-formed ionic monomer unit in the polymer block (c) is calculated according to the following formula.

[0160] (K c )(mol%) = (J A ) × DP A / (DP A - DP b )

[0161] [Crystal melting temperature (Q A )]

[0162] To 100 parts by mass of the copolymer (A), 1860 parts by mass of methanol and 50 parts by mass of sodium hydroxide are added, and the mixture is heated at 40 °C for 2 hours to completely saponify the remaining vinyl ester groups (saponification degree ≥ 99.9 mol%). In the case of insufficient saponification, additional sodium hydroxide is added and the reaction is continued until the remaining vinyl ester groups are completely saponified. Then, a phenolphthalein solution is added and washed with methanol until no alkaline reaction is observed in the washing liquid (methanol), and sodium hydroxide and sodium acetate are removed. The washed polymer is dried and cured at 120 °C until methanol disappears, obtaining a polymer for measuring the crystal melting temperature.

[0163] The crystal melting temperature (Q A of the above polymer in a nitrogen atmosphere is measured using a differential scanning calorimeter device "DSC25" manufactured by TA Instruments Co., Ltd.)。3 mg of the above polymer dried under reduced pressure at 90 °C for 2 days was sealed in an aluminum container, placed in a differential scanning calorimeter device, heated from 40 °C to 250 °C at a rate of 10 °C per minute, then held for 1 minute, cooled to -80 °C at a rate of 10 °C per minute, and then held for 1 minute. Then, the temperature at the maximum point of the endothermic peak observed between 150 °C and 250 °C when heating to 250 °C at a rate of 10 °C per minute was taken as (Q A )(°C).

[0164] [Evaluation of Deionized Water (DIW) Absorbency of Block Copolymer (A)]

[0165] 0.1 g of copolymer (A) was placed in a 100 mL beaker, and 10, 20, 30, 40, 50, or 60 g of deionized water was slowly added to the beaker under a 20 °C atmosphere and allowed to stand for 10 minutes. Thereafter, the contents of the beaker were immediately transferred to a sieve with a mesh size of 74 μm. If no water droplets dripped from the sieve within 1 minute, it was judged that the entire amount was absorbed, and thus the maximum amount of deionized water that could be completely absorbed [deionized water (g) / copolymer (A) (g)] was determined. This value was evaluated as "absorbency".

[0166] [Evaluation of Saline Absorbency and Retention of Block Copolymer (A)]

[0167] 1 g of copolymer (A) was placed in a 100 mL beaker, and 10, 20, 30, 40, 50, or 60 g of 0.9 mass% sodium chloride aqueous solution was slowly added to the beaker under a 20 °C atmosphere and allowed to stand for 10 minutes. Then, the contents of the beaker were immediately transferred to a sieve with a mesh size of 74 μm. If no water droplets dripped from the sieve within 1 minute, it was judged that the entire amount was absorbed, and thus the maximum amount of the aqueous solution that could be completely absorbed [aqueous solution (g) / copolymer (A) (g)] was determined. This value was evaluated as "absorbency". In addition, after the above 10-minute standing, the maximum amount of the aqueous solution [aqueous solution (g) / copolymer (A) (g)] when the beaker was tilted and stood still without the contents leaking out of the beaker was evaluated as "retention".

[0168] [Evaluation of Amount of Soluble Components of Block Copolymer (A) in Deionized Water (DIW)]

[0169] 1 g of copolymer (A) was added to 1000 mL of deionized water, stirred for 60 minutes under a 20 °C or 95 °C atmosphere, and then filtered through a 200-mesh metal sieve. The mass of the residue on the sieve after heating and drying at 120 °C for 4 hours was taken as D (g). The amount of soluble components E (dissolution rate in water), which is an index of water solubility, was calculated by the following formula.

[0170] E (mass %) = (1 - D) × 100

[0171] [Evaluation of biodegradation rate of block copolymer (A)]

[0172] According to JIS K 6951, 20 mg of copolymer (A) was added to 200 ml of a standard test culture solution obtained by dissolving 8.5 g of anhydrous potassium dihydrogen phosphate, 21.75 g of anhydrous dipotassium hydrogen phosphate, 33.4 g of disodium hydrogen phosphate, and 0.5 g of ammonium chloride in 1000 ml of distilled water. Then, standard activated sludge was added to make it reach 20 ppm. While stirring this culture solution, it was cultured at 22 °C for 28 days. The amount of carbon dioxide generated during the above period was measured regularly, and the total amount F (mg) of carbon dioxide generated was obtained. In addition, the total amount G (mg) of carbon dioxide generated from the culture solution without adding copolymer (A) was obtained in the same way. Furthermore, based on the calculated value H (mg) of the amount of carbon dioxide generated when copolymer (A) was completely decomposed, the biodegradation rate (%) was obtained according to the following formula.

[0173] Biodegradation rate (%) = {(F - G) / H} × 100

[0174] [Example 1]

[0175] <Polymerization process>

[0176] [Synthesis of block b]

[0177] 0.19 parts by mass of Co(acac)2 and 0.67 parts by mass of V-70 as an initiator were added to a reactor equipped with a stirrer, a reflux condenser, and an initiator addition port. The inside of the reactor was evacuated three times and then purged with nitrogen for an inert gas replacement. Then, 500 parts by mass of VAc that had been purified by simple distillation was added. Then, the reactor was immersed in a water bath and heated and stirred to make the internal temperature reach 30 °C.

[0178] [Synthesis of block c]

[0179] While stirring, appropriate sampling was carried out, and the progress of polymerization was confirmed by its solid component concentration. When the conversion rate of VAc reached 19% by mass, 7.8 parts by mass of MA (equivalent to a one-time addition of the additional monomer in Table 1) was added. The number average molecular weight (Mn) of the polymer at a conversion rate of 19% by mass was 129,000. Appropriate sampling was continued, and the progress of polymerization was confirmed by its solid component concentration. When the total conversion rate of VAc and MA reached 26% by mass, 1 1H-NMR was used to confirm that MA was completely consumed [molar ratio (acrylate / vinyl ester) less than 0.00001], and 0.66 parts by mass of 1,1-DPEt as a polymerization inhibitor was added. The number average molecular weight (Mn) at this time was 182,600.

[0180] The induction period of polymerization for obtaining block b was 6 hours, and the growth period from the start of high polymerization degree to the addition of the polymerization inhibitor was 4 hours.

[0181] [Purification of block copolymer]

[0182] After adding the polymerization inhibitor, the internal temperature was raised to 60 °C, and it was heated and stirred for 1 hour. 500 parts by mass of an aqueous acetic acid solution with a concentration of 25% by mass (pH 2.0) was added thereto, and it was stirred for 5 minutes, then allowed to stand for 30 minutes, separated into two layers, and the aqueous layer was removed. Connected to a vacuum line, the unreacted monomers were removed by vacuum distillation at 30 °C, methanol was added to dissolve the vinyl ester block copolymer, and this solution was dropped into deionized water to precipitate the vinyl ester block copolymer. The vinyl ester block copolymer was recovered by a filtration operation and dried in a vacuum dryer at 40 °C for 24 hours to obtain the vinyl ester block copolymer. The details of the above polymerization process are shown in Table 1.

[0183] <Soap saponification process>

[0184] Next, 100 parts by mass of the obtained vinyl ester block copolymer and 1833.6 parts by mass of dehydrated methanol were added to the same reactor as above and dissolved, and then heated in a water bath and heated and stirred until the internal temperature reached 40 °C. 66.4 parts by mass of a methanol solution of sodium hydroxide (concentration 14% by mass, 9.3 parts by mass in terms of sodium hydroxide) was added thereto. A saponification reaction was carried out at 65 °C for 1 hour using the vinyl ester block copolymer solution with a concentration of 5% by mass prepared in this way.

[0185] <Salt formation process>

[0186] 46.5 parts by mass of sodium hydroxide, 2000 parts by mass of dehydrated methanol, and 210 parts by mass of ion-exchanged water were added to the saponified product obtained by liquid separation, and it was further heated at 65 °C for 1 hour. After liquid separation, a phenolphthalein solution was added to the washing liquid (methanol), and it was washed with methanol until no alkaline reaction was observed to remove sodium hydroxide and sodium acetate. The solid obtained by centrifugal dehydration was dried in a vacuum dryer at 40 °C for 24 hours to obtain the target copolymer (A) (a diblock copolymer of block b - block c).

[0187] <Physical properties of block copolymer (A)>

[0188] Various physical properties of the obtained copolymer (A) were measured to evaluate the performance. The number average molecular weight (Mn A ) of copolymer (A) was 99,800, and the number average molecular weight (Mn b ) of the polymer block (b) in copolymer (A) was 66,100. The ratio (Mn b / MnA ) was 0.66, and the molecular weight distribution (Mw A / Mn A ) was 1.30, and the saponification degree was 99.9 mol%. The above results are summarized in Table 2.

[0189] [Example 2]

[0190] Except for changing [the synthesis of block c] in <Polymerization step> in Example 1 as shown in Table 1, the same operations as in Example 1 were carried out, and copolymer (A) (a diblock copolymer of block b-block c) was obtained. The evaluation results of the obtained copolymer (A) are shown in Table 2.

[0191] [Example 3]

[0192] <Polymerization step>

[0193] [Synthesis of block b]

[0194] In a reactor equipped with a stirrer, a reflux condenser, an initiator addition port, and a feed pump, 0.19 parts by mass of Co(acac)2 and 0.67 parts by mass of V-70 as an initiator were added. After evacuating the inside of the reactor to vacuum 3 times and introducing nitrogen for inert gas replacement. Then, 500 parts by mass of VAc purified by simple distillation was added, and then the reactor was immersed in a water bath, heated and stirred to make the internal temperature reach 30 °C.

[0195] [Synthesis of block c]

[0196] While stirring, appropriate sampling was carried out, and the progress of polymerization was confirmed by its solid component concentration. When the conversion rate of VAc reached 13% by mass, 1.3 parts by mass of MA (equivalent to a one-time addition of the additional monomer in Table 1) was added. The number average molecular weight (Mn) of the polymer at a conversion rate of 13% by mass was 86000. Immediately thereafter, a mixture of 25 parts by mass of VAc and 6.2 parts by mass of MA was polymerized while being fed over time. The progress of polymerization was confirmed by this solid component concentration, and GPC measurement and 1 1H-NMR measurement of the sampled polymer were carried out. When the total conversion rate of VAc and MA reached 18% by mass, the feeding was completed (equivalent to the feeding in Table 1).

[0197] Then, at the moment when the total conversion rate of VAc and MA was 22%, it was confirmed by 1 1H-NMR that MA was completely consumed [molar ratio (acrylate / vinyl ester) less than 0.00001]. The number average molecular weight (Mn) at this time was 161700. When the total conversion rate of VAc and MA reached 22% by mass, 0.66 parts by mass of 1,1-DPEt as a polymerization inhibitor was added.

[0198] The induction period of the polymerization for obtaining block b was 6 hours, and the growth period from the start of high polymerization degree to the addition of the polymerization inhibitor was 3 hours.

[0199] [Purification of the block copolymer]

[0200] Then, purification was carried out in the same manner as in Example 1 to obtain a vinyl ester block copolymer. The details of the above polymerization process are shown in Table 1.

[0201] <Saponification process and salt formation process>

[0202] After that, the saponification process and the salt formation process were carried out in the same manner as in Example 1 to obtain the target copolymer (A) (a diblock copolymer of block b - block c). The measurement and evaluation results of the obtained copolymer (A) are summarized in Table 2.

[0203] [Example 4]

[0204] Except for changing [Synthesis of block c] in the <Polymerization process> of Example 3 as shown in Table 1, the same operations as in Example 3 were carried out to obtain copolymer (A) (a diblock copolymer of block b - block c). The evaluation results of the obtained copolymer (A) are shown in Table 2.

[0205] [Example 5]

[0206] Except for changing [Synthesis of block c] in the <Polymerization process> of Example 3 as shown in Table 1, the same operations as in Example 3 were carried out to obtain the target copolymer (A) (a diblock copolymer of block b - block c). The evaluation results of the obtained copolymer (A) are shown in Table 2.

[0207] [Example 6]

[0208] In [Synthesis of block b] and [Synthesis of block c] in the <Polymerization process> of Example 3, changes were made as described in Table 1. Other than that, the target copolymer was obtained in the same manner as in Example 3. The evaluation results of the obtained copolymer are shown in Table 2.

[0209] It should be noted that in Example 6, in the step corresponding to [Synthesis of block c], polymerization was continued even after the comonomer MA was completely consumed, and then a polymerization terminator was added. Therefore, the finally obtained copolymer became a triblock of block b - block c - block b.

[0210] [Example 7]

[0211] In the <Saponification Step> of Example 1, as shown in Table 1, 46.5 parts by mass of calcium hydroxide was used instead of 46.5 parts by mass of sodium hydroxide, and the operation was the same as in Example 1 except for this, to obtain the target copolymer (A) (a diblock copolymer of block b-block c). The evaluation results of the obtained copolymer are shown in Table 2.

[0212] Specifically, the change was made as follows. Instead of "adding 46.5 parts by mass of sodium hydroxide, 2000 parts by mass of dehydrated methanol, and 210 parts by mass of ion-exchanged water to the obtained saponified product", "adding 46.5 parts by mass of calcium hydroxide, 2000 parts by mass of dehydrated methanol, and 210 parts by mass of ion-exchanged water to the obtained saponified product".

[0213] It should be noted that the part of "adding a methanol solution of 66.4 parts by mass of sodium hydroxide (concentration 14% by mass, 9.3 parts by mass as sodium hydroxide)" was carried out in the same manner as in Example 1.

[0214] [Comparative Example 1]

[0215] <Polymerization Step>

[0216] [Synthesis of Random Copolymer]

[0217] 640 parts by mass of VAc, 1.1 parts by mass of MA (equivalent to the initial monomer in Table 1), and 250 parts by mass of methanol were added to a reactor equipped with a stirrer, a reflux condenser, an argon inlet tube, an initiator addition port, and a feed pump. While nitrogen was bubbled, the inside of the reactor was purged with an inert gas for 30 minutes. The water bath was heated, and the temperature of the reactor was started to rise. When the internal temperature reached 60 °C, 0.15 parts by mass of AIBN as an initiator was added to initiate polymerization.

[0218] While feeding a 40% by mass methanol solution of MA over time, polymerization was carried out, and appropriate sampling was performed. According to the solid content concentration, the progress of polymerization was confirmed. When the total conversion rate of VAc and MA reached 35% by mass, 0.15 parts by mass of p-benzoquinone was added to stop the polymerization. The total feed amount of MA fed over time at this time was equivalent to 11.4 parts by mass (equivalent to the feed of the additional monomer in Table 1).

[0219] The induction period of polymerization for obtaining block c was 0 hour, and the growth period from the start of high polymerization to the addition of the polymerization inhibitor was 3 hours.

[0220] After that, purification, saponification, and salt formation were carried out in the same manner as in Example 1 to obtain the target random copolymer. The evaluation results of the obtained copolymer are shown in Table 2.

[0221] [Comparative Example 2]

[0222] The <Saponification Step> in Example 3 was changed as follows. 46.5 parts by mass of acetic acid and 2000 parts by mass of methanol were added to 100 parts by mass of the vinyl ester block copolymer obtained in the <Polymerization Step> of Example 3, and the mixture was heated at 65°C for 1 hour. After draining the liquid, it was washed with methanol and centrifugally dehydrated, and the obtained solid was dried using a vacuum dryer at 40°C for 24 hours to obtain the target block copolymer. The <Salt Formation Step> was not performed. The results of the measurement and evaluation of the obtained block copolymer are summarized in Table 2.

[0223] [Comparative Example 3]

[0224] Except for changing [Synthesis of Block b] and [Synthesis of Block c] in the <Polymerization Step> of Example 1 as shown in Table 1, the operation was the same as in Example 1 to obtain copolymer (A) (a diblock copolymer of block b - block c). The evaluation results of the obtained copolymer (A) are shown in Table 2.

[0225] [Comparative Example 4]

[0226] The evaluation results using the chemically crosslinked polyacrylic acid-based superabsorbent resin [manufactured by Sumitomo Seika Chemicals Co., Ltd., trade name: Aquakeep SA60S] are summarized in Table 2.

[0227] [Comparative Example 5]

[0228] <Polymerization Step>

[0229] [Synthesis of Block c]

[0230] 1.56 parts by mass of Co(TMP) and 0.91 parts by mass of AIBN as an initiator were added to a reactor equipped with a stirrer, a reflux condenser, and an addition port for the initiator. The inside of the reactor was evacuated 3 times and then purged with nitrogen for an inert gas replacement. Then, 160.0 parts by mass of MA that had been purified by simple distillation and 480 parts by mass of toluene (equivalent to the initial monomers in Table 1) were added. Then, the reactor was immersed in a water bath and heated with stirring so that the internal temperature was 60°C. Appropriate sampling was performed, and the progress of the polymerization was confirmed by the solid content concentration. When the conversion rate of MA reached 18%, it was cooled to 30°C and the polymerization was stopped. The number average molecular weight (Mn) of the polymer at a conversion rate of 18% was 15,500. It was connected to a vacuum line, and the remaining MA and toluene were removed by vacuum distillation at 30°C.

[0231] [Synthesis of Block b]

[0232] 640 parts by mass of VAc was added (equivalent to a one-time addition of the additional monomer in Table 1), and then heating and stirring were carried out to make the internal temperature 60 °C. Appropriate sampling was carried out, and the progress of polymerization was confirmed from the solid content concentration. When the conversion rate of VAc reached 22% by mass, 1.68 parts by mass of 1,1-DPEt as a polymerization inhibitor was added. The number average molecular weight (Mn) at this time was 91,200.

[0233] The induction period until block b polymerization was 5 hours, and the growth period until the addition of the polymerization inhibitor was 4 hours.

[0234] Thereafter, purification, saponification, and salt formation were carried out in the same manner as in Example 1 to obtain the target copolymer (A) (a diblock copolymer of block c - block b). The evaluation results of the obtained copolymer are shown in Table 2.

[0235]

[0236]

[0237] The block copolymers (A) of Examples 1 to 7 were excellent in the absorbency and brine retention (gel shape retention) of DIW and brine, and also excellent in the water dissolution rate (water solubility). Regarding the biodegradation rate, only Example 6 was measured, but it was considered that Examples 1 to 8 all showed an equally good biodegradation rate.

[0238] The copolymer of Comparative Example 1 was a random copolymer not having block (b) and block (c). The copolymer of Comparative Example 2 was a copolymer having block (b) but not having an ionic polymer block (c) containing a monomer unit having an ionic group forming a salt. The copolymer of Comparative Example 3 was Mn A less than 20,000 and Mn b less than 15,000 copolymer. The copolymer of Comparative Example 5 was a copolymer not containing a vinyl alcohol monomer unit in the ionic polymer block (c). For the copolymers of Comparative Examples 1 to 3 and 5, the absorbency of DIW and brine and the brine retention were insufficient. In addition, in the copolymer of Comparative Example 2, the water dissolution rate was also poor. The polyacrylic acid-based superabsorbent resin of Comparative Example 4 did not have block (b), and although its water absorption performance was excellent, etc., it was poor in the water dissolution rate (water solubility) and the biodegradation rate was also poor.

Claims

1. A block copolymer (A) comprising a vinyl alcohol polymer block (b) and an ionic polymer block (c) containing monomer units having an ionic group in which a salt is formed and vinyl alcohol monomer units, wherein, the ionic group is a carboxyl group, a sulfonic acid group or an ammonium group, The number-average molecular weight (Mn b ) of the vinyl alcohol polymer block (b) is 15,000 to 220,000, in the vinyl alcohol polymer block (b), the content of vinyl alcohol monomer units relative to all monomer units is 90 mol% or more, in the ionic polymer block (c), the content of vinyl alcohol monomer units relative to all monomer units is 5 to 95 mol%, The number-average molecular weight (Mn A ) of the block copolymer (A) is from 20,000 to 440,000, and Number average molecular weight (Mn b ) relative to the number average molecular weight (Mn A ) ratio (Mn b / Mn A ) is 0.1 to 0.

9.

2. The block copolymer (A) according to claim 1, wherein, the ionic group is a carboxyl group.

3. The block copolymer (A) according to claim 1 or 2, wherein, The counter ion of the ionic group is an ion of an element of Group 1, 2, 12, 13 or 17 of the periodic table.

4. The block copolymer (A) according to claim 1 or 2, wherein, In the block copolymer (A), the content (J A ) of the monomer unit having an ionic group forming a salt is 2 to 90 mol% based on all monomer units.

5. The block copolymer (A) according to claim 1 or 2, wherein, In the ionic polymer block (c), the content (K c ) of the monomer units having ionic groups that form salts is 5 to 95 mol% with respect to all the monomer units.

6. The block copolymer (A) according to claim 1 or 2, wherein, The saponification degree of the block copolymer (A) is 80 to 99.99 mol%.

7. The block copolymer (A) according to claim 1 or 2, wherein, The molecular weight distribution (Mw A / Mn A ) of the block copolymer (A) is from 1.05 to 1.

95.

8. The block copolymer (A) according to claim 1 or 2, which is biodegradable.

9. The block copolymer (A) according to claim 1 or 2, wherein, The water absorption amount of deionized water per 0.1 g of the block copolymer (A) at 20 °C is 20 g or more.

10. The block copolymer (A) according to claim 1 or 2, wherein, The water absorption amount of a 0.9 mass% sodium chloride aqueous solution per 1 g of the block copolymer (A) at 20 °C is 20 g or more.

11. The block copolymer (A) according to claim 1 or 2, the amount of soluble components when dissolved in water at 95 °C is 95 mass% or more.

12. The block copolymer (A) according to claim 11, the amount of soluble components when dissolved in water at 20 °C is 95 mass% or more.

13. An absorbent material comprising the block copolymer (A) according to any one of claims 1 to 12.

14. The absorbent material according to claim 13, which is in the form of particles.

15. An absorbent article having the absorbent material according to claim 13 or 14.

16. The absorbent article according to claim 15, which is for sanitary use, daily necessities use, construction / civil engineering use, industrial use, agricultural use, medical use or food use.

17. A method for producing the block copolymer (A) according to any one of claims 1 to 12, which has a polymerization step and a saponification step as essential steps, in the polymerization step, polymerization of a vinyl ester monomer and copolymerization of a vinyl ester monomer and an ionic monomer having an ionic group or a derivative thereof are carried out by controlled radical polymerization in the presence of a radical polymerization initiator and a controller to obtain a vinyl ester block copolymer comprising a vinyl ester polymer block (b1) and an ionic polymer block (c1) containing vinyl ester monomer units and ionic monomer units; in the saponification step, vinyl ester monomer units in the vinyl ester block copolymer obtained in the polymerization step are saponified to form vinyl alcohol monomer units, the method for producing the block copolymer (A) has a salt formation step for forming a salt of the ionic monomer units as an optional step.

18. The method for producing the block copolymer (A) according to claim 17, wherein, The controller is an organic cobalt complex.

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