Hydrogel, method for producing hydrogel, and method for producing molded body

Abstract

Provided is a hydrogel which has an interpenetrating network structure or a semi-interpenetrating network structure, and which contains a first polymer having a three-dimensional network structure and a second polymer introduced into gaps of the three-dimensional network structure of the first polymer, wherein the first polymer contains, as monomeric unit, a cross-linkable monomer A1 having a bond with a bonding energy of 80 to 250 kJ / mol, the crosslinking degree of the second polymer is smaller than the crosslinking degree of the first polymer, and the content of the second polymer is 2-100 parts by mass relative to 1 part by mass of the first polymer.

Description

[Technical Field]

[0001] The present invention relates to a hydrogel, a method for producing a hydrogel, and a method for producing a molded article. [Background technology]

[0002] Polymer gels are formed when polymers with a three-dimensional network structure formed by crosslinking absorb liquid and swell to form a gel. Among polymer gels, those in which the liquid is water are called hydrogels. Hydrogels are useful materials that have attracted attention due to their excellent properties, such as flexibility and water retention. Therefore, hydrogels are expected to be used in a wide range of fields, including medicine, food, civil engineering, bioengineering, and sports.

[0003] One of the challenges to enable the use of hydrogels in such diverse fields is to improve the strength of the hydrogels. In response to this challenge, the present inventors discovered that hydrogels having an interpenetrating network structure or a semi-interpenetrating network structure formed by synthesizing a second polymer in a first polymer having a three-dimensional network structure exhibit high mechanical strength (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 03 / 093337 Brochure Summary of the Invention [Problem to be solved by the invention]

[0005] Hydrogels with an interpenetrating network structure or semi-interpenetrating network structure have poor moldability, for example, because the first polymer (a polymer with a higher degree of crosslinking) is easily destroyed by mechanical load. Currently, a common method for obtaining a hydrogel of a predetermined shape is to simultaneously synthesize and mold the first polymer by molding, thereby obtaining the first polymer of the predetermined shape, and then synthesize the second polymer within the first polymer. However, molding makes it difficult to obtain molded articles of complex shapes. Furthermore, the need to prepare a mold according to the desired shape and the time required for molding make it difficult to achieve sufficient production efficiency.

[0006] Therefore, the main object of the present invention is to provide a hydrogel as a molding material, a method for producing the same, and a method for producing a molded body using the hydrogel, which enable the easy production of a molded body of a complex shape with excellent production efficiency. [Means for solving the problem]

[0007] The present inventors focused on the phenomenon that when a mechanical load is applied to a hydrogel having an interpenetrating network structure or a semi-interpenetrating network structure, the crosslinked structure of the first polymer (the polymer with a higher degree of crosslinking) is destroyed, resulting in the generation of mechanoradicals. When a hydrogel is impregnated with a monomer having two or more ethylenically unsaturated bonds and then subjected to a mechanical load, the mechanoradicals generated by the mechanical load can cause the monomer to react and form a crosslinked network. Therefore, the present inventors reasoned that if the crosslinked network formed by this method could be strengthened, the hydrogel could be fixed in a deformed state. Based on this idea, the present inventors conducted extensive research and completed the present invention.

[0008] The present invention provides the following [1] to

[11] .

[0009] [1] A hydrogel having an interpenetrating network structure or a semi-interpenetrating network structure, comprising: a first polymer having a three-dimensional network structure; and a second polymer that penetrates into the gaps in the three-dimensional network structure of the first polymer, wherein the first polymer comprises, as a monomer unit, a crosslinkable monomer A1 having a bond with a bond energy of 80 to 250 kJ / mol; the degree of crosslinking of the second polymer is smaller than the degree of crosslinking of the first polymer; and the content of the second polymer is 2 to 100 parts by mass per part by mass of the first polymer.

[0010] [2] The hydrogel according to [1], wherein the crosslinkable monomer A1 contains a compound represented by the following formula (1): [ka] [In formula (1), multiple R's represent monovalent groups having an ethylenically unsaturated bond, X1 represents an m-valent organic linking group, X2 represents an n-valent organic linking group, Y represents -N=N-, -OO-, or -SS-, m and n each represent an integer of 2 or greater, multiple R's may be the same or different, X1 and X2 may be the same or different, and m and n may be the same or different.]

[0011] [3] The hydrogel according to [1] or [2], wherein the degree of crosslinking of the first polymer is 0.1 mol% or more.

[0012] [4] The hydrogel according to any one of [1] to [3], wherein the degree of crosslinking of the second polymer is 20 mol % or less.

[0013] [5] The hydrogel according to any one of [1] to [4], which is impregnated with a monomer C having two or more ethylenically unsaturated bonds.

[0014] [6] The hydrogel according to [5], wherein the amount of the monomer C impregnated is 10 to 1000 parts by mass per 100 parts by mass of the solid content of the hydrogel.

[0015] [7] A method for producing a hydrogel having an interpenetrating network structure or a semi-interpenetrating network structure, comprising: a step a) of reacting a first monomer composition containing a crosslinkable monomer A1 having a bond with a bond energy of 80 to 250 kJ / mol to form a first polymer; and a step b) of impregnating the first polymer with a second monomer composition optionally containing a crosslinkable monomer A2 and then reacting the second monomer composition to form a second polymer, wherein r2 / r1 is smaller than 1, where r1 is the molar ratio of the amount of the crosslinkable monomer A1 to the total amount of monomers in the first monomer composition, and r2 is the molar ratio of the amount of the crosslinkable monomer A2 to the total amount of monomers in the second monomer composition, and r2 is the molar ratio of the amount of the second monomer composition to the total amount of monomers in the second monomer composition.

[0016] [8] The method for producing a hydrogel according to [7], further comprising a step c of impregnating the hydrogel obtained in the step b with a monomer C having two or more ethylenically unsaturated bonds.

[0017] [9] A method for producing a molded body, comprising: an impregnation step of impregnating a hydrogel according to any one of [1] to [4] or a hydrogel obtained by the production method according to [7] with a monomer C having two or more ethylenically unsaturated bonds; a deformation step of deforming the hydrogel into a predetermined shape by applying a mechanical load after the impregnation step or simultaneously with the impregnation step; and a holding step of holding the hydrogel in the deformed state into the predetermined shape for a predetermined period of time after the deformation step.

[0018]

[10] A method for manufacturing a molded body, comprising: a deformation step of deforming the hydrogel described in [5] or [6], or the hydrogel obtained by the manufacturing method described in [8], into a predetermined shape by applying mechanical load; and a holding step of holding the hydrogel in the deformed state into the predetermined shape for a predetermined period of time after the deformation step.

[0019]

[11] The method for producing a molded article according to [9] or

[10] , wherein the deformation step involves deforming the hydrogel by blow molding or press molding. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide a hydrogel as a molding material, a method for producing the same, and a method for producing a molded body using the hydrogel, which enable the easy production of a molded body of a complex shape with excellent production efficiency. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic cross-sectional view illustrating a method for producing a molded body according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing a mold plate used to prepare a molded body of the example and a molded body obtained using the mold plate. [Figure 3] FIG. 3 is a diagram showing a molded body of an example and a molding method thereof. DETAILED DESCRIPTION OF THE INVENTION

[0022] In this specification, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this specification, the upper or lower limit of a numerical range in a certain stage may be replaced with the upper or lower limit of a numerical range in another stage. Furthermore, in the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with a value shown in the examples. Furthermore, the upper and lower limits individually described can be combined in any way. Furthermore, in this specification, "(meth)acryloyl" means at least one of acryloyl and the corresponding methacryloyl.

[0023] Preferred embodiments of the present invention will be described below, but the present invention is not limited to the following embodiments.

[0024] <Hydrogel> In one embodiment, the hydrogel comprises a first polymer having a three-dimensional network structure and a second polymer that penetrates into the gaps in the three-dimensional network structure of the first polymer. This hydrogel is also called a double-network gel because it has an interpenetrating network structure or a semi-interpenetrating network structure.

[0025] Here, "a hydrogel having an interpenetrating network structure" means that a polymer constituting a base three-dimensional network structure is entangled with a polymer having another three-dimensional network structure, resulting in the hydrogel having multiple network structures within the gel. Also, "a hydrogel having a semi-interpenetrating network structure" means that a polymer constituting a base three-dimensional network structure is entangled with a polymer having a non-three-dimensional network structure, resulting in the hydrogel having one or more network structures and one or more non-network structures within the gel.

[0026] The first polymer contains, as monomer units, a crosslinkable monomer A1 (hereinafter simply referred to as "monomer A1") having a bond with a bond energy of 80 to 250 kJ / mol (hereinafter simply referred to as a "low energy bond"), and optionally, a monofunctional polymerizable monomer B1 (hereinafter simply referred to as "monomer B1"). The first polymer may or may not contain monomer B1 as a monomer unit. In this specification, a "monomer unit" is a unit derived from a monomer, and is a structural unit of a polymer formed by a polymerizable functional group in a monomer reacting with another polymerizable functional group and bonding with another monomer. Therefore, when a polymer contains monomer X as a monomer unit, it means that the polymer contains a structural unit (monomer unit) derived from monomer X. A monomer unit may also be referred to as a repeating unit.

[0027] The second polymer contains, as monomer units, a monofunctional polymerizable monomer B2 (hereinafter simply referred to as "monomer B2") and, optionally, a crosslinkable monomer A2 (hereinafter simply referred to as "monomer A2"). The second polymer may or may not contain the monomer A2 as a monomer unit.

[0028] When the second polymer contains monomer A2 as a monomer unit, the second polymer has a three-dimensional network structure. In this case, the hydrogel has an interpenetrating network structure. When the second polymer does not contain monomer A2 as a monomer unit, the second polymer has a non-three-dimensional network structure, such as a linear structure. In this case, the hydrogel has a semi-interpenetrating network structure.

[0029] The degree of crosslinking of the second polymer is lower than that of the first polymer. Here, the degree of crosslinking refers to the proportion (unit: mol%) of monomer units derived from crosslinkable monomers based on the amount of all monomer units in the polymer. If the first polymer does not contain monomer B1 as a monomer unit, the degree of crosslinking of the first polymer is 100 mol%, and if the second polymer does not contain monomer A2 as a monomer unit, the degree of crosslinking of the second polymer is 0 mol%.

[0030] The content of the second polymer is 2 to 100 parts by mass relative to 1 part by mass of the first polymer, i.e., the mass ratio of the content of the second polymer to the content of the first polymer is 2 to 100.

[0031] The hydrogel is, for example, in the form of a sheet.

[0032] A hydrogel having the above-described characteristics exhibits good shape fixability even when the deformed state is maintained for a short period of time in a method in which the hydrogel is impregnated with a monomer C having two or more ethylenically unsaturated bonds (hereinafter simply referred to as "monomer C"), deformed by mechanical load, and then fixed by maintaining the deformed state. Here, shape fixability refers to the ability to fix the deformed state and maintain the deformed shape even after the mechanical load is removed. Therefore, by using the hydrogel as a molding material (e.g., master sheet) in the above-described molding method, it is possible to produce a molded hydrogel body with excellent production efficiency. Furthermore, since the above-described molding method can employ molding methods capable of forming complex shapes, such as blow molding and press molding, even molded bodies with complex shapes can be easily produced.

[0033] The reason for the above-mentioned effect is presumed to be as follows. First, when a mechanical load is applied to the hydrogel, the load is concentrated on the first polymer (particularly the crosslinked portion of the first polymer) because the degree of crosslinking of the second polymer is lower than that of the first polymer. At this time, because the monomer A1 constituting the crosslinked portion of the first polymer has a low-energy bond (i.e., the first polymer has a low-energy bond at the crosslinked portion), structural destruction occurs at the bond, generating a large amount of mechanoradicals. Therefore, by impregnating the hydrogel with the monomer C beforehand or simultaneously with the application of a mechanical load, the monomer C reacts with the mechanoradicals to form a new crosslinked structure. The inventors' investigations revealed that when a common crosslinking agent such as N,N'-methylenebisacrylamide is used instead of the monomer A1, the amount of mechanoradicals generated is small, and even if a new crosslinked structure is formed, sufficient shape fixation cannot be achieved. Furthermore, if a large amount of a general crosslinking agent is used to increase the amount of mechano radicals generated, the flexibility (stretchability) of the hydrogel decreases, making it difficult to deform under mechanical load, and therefore difficult to mold. On the other hand, in this embodiment, the introduction of low-energy bonds significantly increases the amount of mechano radicals generated by mechanical load, allowing the formation of a dense crosslinked structure, and it is presumed that the hydrogel exhibits good shape fixation properties. Note that in this embodiment, even if a large amount of monomer A1 is used, the flexibility (stretchability) of the hydrogel is restored by the cleavage of the low-energy bonds under mechanical load, so it is possible to further improve shape fixation properties by using a large amount of monomer A1.

[0034] First, the first polymer and the second polymer that constitute the hydrogel will be described in detail below.

[0035] (First polymer) The first polymer contains a monomer A1 as a monomer unit. The monomer A1 itself is a compound (crosslinkable monomer) having two or more polymerizable functional groups, and constitutes an intersection (crosslinked portion) of a three-dimensional network structure in the polymer. The monomer A1 (monomer unit derived from the monomer A1) in the polymer may not have any unreacted polymerizable functional groups. The number of polymerizable functional groups is, for example, 2 to 8. Examples of the polymerizable functional group include groups having an ethylenically unsaturated bond, such as a vinyl group, an allyl group, a styryl group, an alkenyl group, an alkenylene group, a (meth)acryloyl group, and a maleimide group. The molecular weight of the monomer A1 is, for example, 70 to 15,000, and may be 100 to 3,000 or 50 to 1,000.

[0036] Monomer A1 has at least one low-energy bond (a bond having a bond energy of 80 to 250 kJ / mol). The number of low-energy bonds is, for example, 1 to 10, and may be 1 to 2 or 2 to 10. If the bond energy is less than 80 kJ / mol, the bond will be too easily cleaved, which may impair the stability of the hydrogel. If the bond energy is more than 250 kJ / mol, the bond will be difficult to cleave, making it difficult to achieve sufficient shape fixation. From this perspective, the bond energy of the low-energy bond may be 100 kJ / mol or more, or 150 kJ / mol or less. That is, the bond energy of the low-energy bond may be 80 to 150 kJ / mol, 100 to 150 kJ / mol, or 100 to 250 kJ / mol.

[0037] Monomer A1 may be a compound represented by the following formula (1), from the viewpoint of easily obtaining superior shape fixation properties. [ka]

[0038] In formula (1), multiple Rs represent monovalent groups having an ethylenically unsaturated bond, X1 represents an m-valent organic linking group, X2 represents an n-valent organic linking group, Y represents -N=N-, -OO-, or -SS-, and m and n each represent an integer of 2 or more. Multiple Rs may be the same or different. X1 and X2 may be the same or different. m and n may be the same or different. Each of m and n may be 2 to 18, or 2 to 4.

[0039] The organic linking group represented by X1 or X2 is not particularly limited as long as it has a carbon atom as a terminal atom (atom bonding to R or Y), and may have a heteroatom such as O, N, or S. The organic linking group represented by X1 or X2 may have a heteroatom-containing functional group such as a carbonyl group.

[0040] The compound represented by the above formula (1) may be a compound represented by the following formula (1A), from the viewpoint of making it easier to obtain even better shape fixation properties. [ka]

[0041] The compound represented by formula (1A) has two bonds (-CN=) with a bond energy of about 105 kJ / mol. When monomer A1 contains the compound represented by formula (1A), monomer B1 contains at least one compound selected from the group consisting of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), acrylic acid (AA), methacrylic acid, and salts thereof, thereby achieving excellent shape fixation while simultaneously achieving excellent stretchability and strength of the hydrogel.

[0042] Monomer A1 may be one type of compound or may contain multiple types of compounds.

[0043] The first polymer optionally contains a monomer B1 as a monomer unit. The monomer B1 itself is a compound having one polymerizable functional group (a monofunctional polymerizable monomer). Examples of the polymerizable functional group include the same as the polymerizable functional group of the monomer A1. The molecular weight of the monomer B1 is, for example, 40 to 5,000, and may be 60 to 1,000 or 70 to 300.

[0044] Monomer B1 may be a positively or negatively charged compound. Specifically, it may be, for example, a compound having an acidic group such as a carboxyl group, a phosphate group, or a sulfonic acid group, or a compound having a basic group such as an amino group. When monomer B1 contains a positively or negatively charged compound, monomer B2 in the second polymer may contain an electrically neutral compound. In this case, during the hydrogel production process, the second polymer is formed in greater amounts in the gaps between the three-dimensional network structure of the first polymer, which tends to result in a hydrogel with higher strength. To facilitate such an effect, monomer B1 may contain 5 mol % or more, 10 mol % or more, or 30 mol % or more (e.g., 5 to 100 mol %, 10 to 100 mol %, or 30 to 100 mol %) of a positively or negatively charged compound based on the total amount of monomer B1. From a similar viewpoint, monomer B2 may contain 30 mol % or more, 75 mol % or more, or 95 mol % or more (for example, 30 to 100 mol %, 75 to 100 mol %, or 95 to 100 mol %) of an electrically neutral compound based on the total amount of monomer B2. Note that monomer B1 may be an electrically neutral compound.

[0045] Specific examples of compounds contained in Monomer B1 include acrylamide; acrylamide derivatives such as N,N-dimethylacrylamide, N-isopropylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-methylolacrylamide, and acryloylmorpholine; methacrylamide derivatives such as methacrylamide, dimethylmethacrylamide, N-isopropylmethacrylamide, N-methylolmethacrylamide, and methacryloylmorpholine; acrylic acid; acrylic acid derivatives such as hydroxyethyl acrylate, hydroxypropyl acrylate, dimethylaminoethyl acrylate, and dimethylaminopropyl acrylate; methacrylic acid; methyl methacrylate, 2-hydroxy methacrylate Examples of suitable methacrylic acid derivatives include methacrylic acid derivatives such as ethyl methacrylate, hydroxypropyl methacrylate, dimethylaminoethyl methacrylate, and dimethylaminopropyl methacrylate; acrylonitrile; 2-vinylpyridine; 4-vinylpyridine; N-vinylpyrrolidone; styrene; styrenesulfonic acid; vinyl acetate; fluorine-containing unsaturated compounds such as 2,2,2-trifluoroethylmethyl acrylate, 2,2,3,3,3-pentafluoropropyl methacrylate, 3-(perfluorobutyl)-2-hydroxypropyl methacrylate, 1H,1H,9H-hexadecafluorononymethacrylate, 2,2,2-trifluoroethyl acrylate, 2,3,4,5,6-pentafluorostyrene, and vinylidene fluoride. Among the above compounds, salts of compounds having an acidic or basic group can also be used. Among these, when the monomer B1 contains at least one compound selected from the group consisting of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), acrylic acid (AA), methacrylic acid, and salts thereof, the hydrogel tends to have higher strength.

[0046] Monomer B1 may be one type of compound or may contain multiple types of compounds.

[0047] The first polymer may include, as a monomer unit, a crosslinkable monomer that does not have a low energy bond.

[0048] The degree of crosslinking of the first polymer may be 0.1 mol% or more, 1 mol% or more, or 2 mol% or more, from the viewpoint of further improving the shape fixation property of the hydrogel. The degree of crosslinking of the first polymer may be 100 mol%. The degree of crosslinking of the first polymer may be 50 mol% or less, 20 mol% or less, or 10 mol% or less, from the viewpoint of increasing the flexibility (stretchability) of the hydrogel and making it easier to deform due to mechanical load. From these viewpoints, the degree of crosslinking of the first polymer may be 0.1 to 100 mol%, 0.1 to 50 mol%, 1 to 20 mol%, or 2 to 10 mol%.

[0049] The content of the first polymer is, for example, 0.05 to 30% by mass, and may be 0.1 to 5% by mass, or 0.5 to 2% by mass, based on the total mass of the hydrogel.

[0050] (Second Polymer) The second polymer contains a monomer B2 as a monomer unit. The monomer B2 itself is a compound having one polymerizable functional group (a monofunctional polymerizable monomer). Examples of the polymerizable functional group include the same polymerizable functional groups as those of the monomer A1. The molecular weight of the monomer B2 is, for example, 40 to 5,000, or may be 60 to 1,000 or 70 to 300.

[0051] Specific examples of the compound contained in the monomer B2 are omitted because they are the same as those of the monomer B1. The monomer B2 may be the same as the monomer B1, but when the monomers B1 and B2 are different, the hydrogel tends to have higher strength.

[0052] Monomer B2 may include at least one compound selected from the group consisting of styrene, acrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, vinylpyridine, styrene, methyl methacrylate, fluorine-containing unsaturated compounds (such as trifluoroethyl acrylate), hydroxyethyl acrylate, and vinyl acetate, in which case the hydrogel tends to have higher strength.

[0053] Monomer B2 may be one type of compound or may contain multiple types of compounds.

[0054] In the hydrogel, the amount of monomer B2 contained as a monomer unit in the second polymer may be 2 to 100 molar parts, 3 to 50 molar parts, or 3 to 30 molar parts per 1 molar part of the total amount of monomers contained as monomer units in the first polymer, from the viewpoint of improving the mechanical strength of the hydrogel.

[0055] The second polymer optionally contains a monomer A2 as a monomer unit. The monomer A2 itself is a compound having two or more polymerizable functional groups (a crosslinkable monomer). The number of polymerizable functional groups is, for example, 2 to 6. Examples of the polymerizable functional groups include the same polymerizable functional groups as those of the monomer A1. The molecular weight of the monomer A2 is, for example, 70 to 15,000, and may be 100 to 3,000 or 150 to 1,000.

[0056] As the monomer A2, a compound used as a crosslinking agent in the technical field can be used depending on the type of the monomer B2. Specific examples include N,N'-methylenebisacrylamide, ethylene glycol dimethacrylate, N,N'-diacryloyl-4,7,10-trioxa-1,13-tridecanediamine, N,N',N''-triacryloyldiethylenetriamine, N,N',N'',N'''-tetraacryloyltriethylenetetramine, and N,N'-{[(2-acrylamido-2-[(3-acrylamidopropoxy)methyl]propane-1,3-diyl)bis(oxy)]bis(propane-1,3-diyl)}diacrylamide. The monomer A2 may be any of the compounds exemplified as the monomer A1.

[0057] The degree of crosslinking of the second polymer may be 0.0001 mol% or more, 0.01 mol% or more, or 0.05 mol% or more, from the viewpoint of easily obtaining the effects of crosslinking. The degree of crosslinking of the second polymer may be 20 mol% or less, 5 mol% or less, or 1 mol% or less, from the viewpoint of imparting high extensibility to the second polymer. The degree of crosslinking of the second polymer may be 0 mol%. From these viewpoints, the degree of crosslinking of the second polymer may be 0 to 20 mol%, 0.0001 to 20 mol%, 0.01 to 5 mol%, or 0.05 to 1 mol%.

[0058] As described above, the degree of crosslinking of the second polymer is smaller than that of the first polymer. That is, the ratio of the degree of crosslinking of the second polymer to the degree of crosslinking of the first polymer (degree of crosslinking of the second polymer / degree of crosslinking of the first polymer) is smaller than 1. The ratio of the degree of crosslinking of the second polymer to the degree of crosslinking of the first polymer may be 0.1 or less or 0.02 or less, from the viewpoint of obtaining a tougher hydrogel by making the breaking strain of the first network (network derived from the first polymer) sufficiently smaller than the breaking strain of the second network (network derived from the second polymer).

[0059] The content of the second polymer is 2 to 100 parts by mass relative to 1 part by mass of the first polymer. When the content of the second polymer is 2 parts by mass or more, the mechanical strength of the hydrogel tends to be superior. When the content of the second polymer is 100 parts by mass or less, the stretchability of the hydrogel tends to be superior. From these viewpoints, the content of the second polymer may be 3 parts by mass or more, 50 parts by mass or less, or 30 parts by mass or less relative to 1 part by mass of the first polymer. From the above viewpoints, the content of the second polymer may be 2 to 50 parts by mass or 3 to 30 parts by mass relative to 1 part by mass of the first polymer.

[0060] The hydrogel containing the first polymer and the second polymer described above contains water. The water content is, for example, 10 to 99.9% by mass, or may be 50 to 99% by mass, or 70 to 90% by mass, based on the total mass of the hydrogel.

[0061] The hydrogel generates mechanoradicals when deformed by a mechanical load. The amount of radicals generated can be adjusted by the magnitude of the applied load, the type of monomer A1, the amount of monomer units derived from monomer A1 in the first polymer, and other factors. Specifically, for example, the amount of radicals generated inside the hydrogel as measured by the Fenton reaction (a method in which 500 μmol / L of (NH4)2Fe(SO4)2, 500 μmol / L of xylenol orange, and 20 mmol / L of sulfuric acid are introduced into the hydrogel, and the amount of radicals generated is estimated from the degree of color change associated with deformation) may be 50 μmol / L or more or 100 μmol / L or more (e.g., 50 to 1000 μmol / L or 100 to 1000 μmol / L). When the amount of radicals generated is equal to or greater than the above-mentioned lower limit, better shape fixation tends to be achieved.

[0062] As described above, the hydrogel is used by impregnating it with monomer C during molding, but the hydrogel may also be pre-impregnated with monomer C. Hereinafter, for convenience, a hydrogel impregnated with monomer C will be referred to as a "monomer C-impregnated hydrogel," and a hydrogel not impregnated with monomer C (the hydrogel of the above embodiment) will be referred to as a "monomer C-non-impregnated hydrogel."

[0063] The monomer C-impregnated hydrogel comprises a monomer C-non-impregnated hydrogel (the hydrogel of the above embodiment) and monomer C impregnated in the hydrogel.

[0064] Monomer C is a monomer having two or more ethylenically unsaturated bonds, and has a group having an ethylenically unsaturated bond, such as a vinyl group, an allyl group, a styryl group, an alkenyl group, an alkenylene group, a (meth)acryloyl group, or a maleimide group. The number of ethylenically unsaturated bonds is, for example, 2 to 6. Monomer C may be a compound exemplified as the above-mentioned Monomer A1 or Monomer A2. From the viewpoint of obtaining higher shape fixation property, Monomer C may be a compound having no low-energy bond.

[0065] The amount of impregnated monomer C may be 10 parts by mass or more, 30 parts by mass or more, or 70 parts by mass or more per 100 parts by mass of the solid content of the hydrogel (hydrogel not impregnated with monomer C), from the viewpoint of obtaining higher shape fixation properties. The amount of impregnated monomer C may be 1,000 parts by mass or less, 800 parts by mass or less, or 500 parts by mass or less per 100 parts by mass of the solid content of the hydrogel, from the viewpoint of easily obtaining a molded product with excellent flexibility. From these viewpoints, the amount of impregnated monomer C may be 10 to 1,000 parts by mass, 30 to 800 parts by mass, or 70 to 500 parts by mass per 100 parts by mass of the solid content of the hydrogel. In this specification, the solid content of the hydrogel refers to the total amount of components other than water in the hydrogel, such as the total amount of the first polymer and the second polymer.

[0066] The hydrogel impregnated with monomer C may be impregnated with a monomer having one ethylenically unsaturated bond (hereinafter referred to as "monomer D"). Examples of monomer D include the monofunctional polymerizable monomers exemplified as monomer B1 and monomer B2.

[0067] The total impregnation amount of monomer C and monomer D (the sum of the impregnation amount of monomer C and the impregnation amount of monomer D) may be 20 parts by mass or more, 50 parts by mass or more, or 100 parts by mass or more, relative to 100 parts by mass of the solid content of the hydrogel (hydrogel not impregnated with monomer C), from the viewpoint of obtaining higher shape fixation properties. The total impregnation amount of monomer C and monomer D may be 1000 parts by mass or less, 800 parts by mass or less, 500 parts by mass or less, or 300 parts by mass or less, relative to 100 parts by mass of the solid content of the hydrogel, from the viewpoint of easily obtaining a molded product having excellent flexibility. From these viewpoints, the total impregnation amount of monomer C and monomer D may be 20 to 1000 parts by mass, 50 to 800 parts by mass, 100 to 500 parts by mass, or 100 to 300 parts by mass, relative to 100 parts by mass of the solid content of the hydrogel.

[0068] The hydrogels (monomer C-unimpregnated hydrogels and monomer C-impregnated hydrogels) may contain, as necessary, known additives such as colorants, plasticizers, stabilizers, reinforcing agents, inorganic fillers, impact modifiers, flame retardants, etc. For example, if these additives are high molecular weight additives, they may be added to the solution during polymerization, and if they are low molecular weight additives, they may be incorporated into the finally obtained hydrogel by free diffusion.

[0069] As described above, the hydrogel is suitable for use as a molding material, but the use of the hydrogel is not limited to this purpose.

[0070] <Hydrogel manufacturing method> One embodiment of a method for producing a hydrogel having an interpenetrating network structure or a semi-interpenetrating network structure includes step a) of reacting a first monomer composition to form the first polymer, and step b) of impregnating the first polymer with a second monomer composition and then reacting the second monomer composition to form the second polymer. Here, the "monomer composition" refers to a composition containing a compound (monomer) having a polymerizable functional group. The first monomer composition contains the monomer A1 and, optionally, further contains a monomer B1. The second monomer composition contains the monomer B2 and, optionally, further contains a monomer A2.

[0071] In the above method, when the molar ratio of the amount of monomer A1 to the total amount of monomers in the first monomer composition (e.g., the total amount of monomer A1 and monomer B1) is r1, and the molar ratio of the amount of monomer A2 to the total amount of monomers in the second monomer composition (the total amount of monomer A2 and monomer B2) is r2, r2 / r1 is less than 1, and the amount of impregnated second monomer composition is 2 to 100 parts by mass per part by mass of the first polymer. By adjusting the molar ratio r2 / r1 and the amount of impregnated second monomer composition as described above, the monomer C-non-impregnated hydrogel of the above embodiment can be obtained. Note that when the molar ratio r1 is x, a polymer having a crosslinking degree of 100x [mol %] is likely to be obtained as the first polymer, and when the molar ratio r2 is y, a polymer having a crosslinking degree of 100y [mol %] is likely to be obtained as the second polymer.

[0072] In step a, for example, a first monomer composition is reacted (polymerized) in the presence of a polymerization initiator (polymerization initiator for the first monomer composition) to form a first polymer. The polymerization initiator can be selected depending on the type of monomer, the type of polymerizable functional group, and the type of crosslinkable functional group. The polymerization initiator may be a photopolymerization initiator or a thermal polymerization initiator. Examples of photopolymerization initiators include α-ketoglutaric acid and benzophenone. Examples of thermal polymerization initiators include water-soluble thermal catalysts such as potassium persulfate, redox initiators such as potassium persulfate-sodium thiosulfate, azobisisobutyronitrile, and benzoyl peroxide. The light irradiation conditions when a photopolymerization initiator is used as the polymerization initiator, and the heating conditions when a thermal polymerization initiator is used as the polymerization initiator, may be appropriately adjusted depending on the type of polymerization initiator, the physical properties of the desired first polymer, and the like.

[0073] The reaction (polymerization) is carried out in a solvent such as water. In step a, the first polymer is produced in the solvent, thereby obtaining a polymer gel containing the first polymer and the solvent impregnated in the first polymer. When carrying out the reaction (polymerization), oxygen in the solvent may be removed using an inert gas such as nitrogen.

[0074] In step b, for example, a solution containing a second monomer composition and a polymerization initiator (polymerization initiator for the second monomer composition) is prepared in advance, and the first polymer is impregnated with this solution to impregnate the first polymer with the second monomer composition. Specifically, for example, a gel containing the first polymer is immersed in the solution and then left for a sufficient time (e.g., one day or more) to allow the second monomer composition and polymerization initiator to diffuse uniformly throughout the gel. Next, the gel is removed from the solution, and the second monomer composition is reacted (polymerized) in the same manner as in step a to form a second polymer (the second polymer that has penetrated into the gaps in the three-dimensional network structure of the first polymer). To prevent the reaction from proceeding during diffusion, the temperature of the solution when the gel is immersed may be below room temperature (around 4°C). The reaction (polymerization) may be carried out in an oxygen-free environment.

[0075] The solution may be one from which oxygen has been removed using an inert gas such as nitrogen. The solvent used for the solution is, for example, water. From the viewpoint of facilitating uniform diffusion of the second monomer composition in the gel, the solvent used for the reaction in step a and the solvent used for the reaction in step b may be the same. When a solvent other than water is used as the solvent, the solvent may be replaced with water by solvent exchange after step b.

[0076] In step b, the content ratio of the first polymer to the second polymer in the hydrogel can be adjusted by adjusting the amount of the second monomer composition impregnated relative to 1 part by mass of the first polymer. The amount of the second monomer composition impregnated relative to 1 part by mass of the first polymer may be 2 to 100 parts by mass, 3 to 50 parts by mass, or 3 to 30 parts by mass. The amount of the second monomer composition impregnated can be adjusted by the concentration of the second monomer composition in the solution.

[0077] According to the above method, a monomer C-non-impregnated hydrogel (for example, the monomer C-non-impregnated hydrogel of the above embodiment) can be obtained, but the method for producing the hydrogel is not limited to the above. For example, a first polymer that has been produced in advance may be used. In other words, the method for producing the hydrogel does not need to include step a.

[0078] In another embodiment, the method for producing a hydrogel further includes, in addition to the steps a and b, a step c of impregnating the hydrogel obtained in step b (hydrogel not impregnated with monomer C) with the monomer C. In step c, in addition to the monomer C, the hydrogel may be impregnated with the monomer D.

[0079] Step c can be carried out in the same manner as step b. Specifically, for example, a solution containing monomer C (and optionally monomer D) is prepared in advance, and the monomer C-non-impregnated hydrogel is immersed in this solution, thereby impregnating the monomer C-non-impregnated hydrogel with monomer C (and optionally monomer D). The concentrations of monomer C and monomer D in the solution and the amount of the solution used may be adjusted so as to obtain the impregnation amounts of monomer C and monomer D in the above-mentioned embodiment.

[0080] The solution may be one from which oxygen has been removed using an inert gas such as nitrogen. The solvent used for the solution is, for example, water. When a solvent other than water is used as the solvent, the solvent may be replaced with water by solvent exchange after step c.

[0081] According to the above method, a monomer C-impregnated hydrogel (for example, the monomer C-impregnated hydrogel of the above embodiment) can be obtained. Note that the method for producing a hydrogel is not limited to the above, and for example, a pre-produced monomer C-unimpregnated hydrogel may be used. In other words, the method for producing a monomer C-impregnated hydrogel does not have to include the above steps a and b.

[0082] <Method for manufacturing a molded hydrogel body> In the method for producing a molded body of the first embodiment, the monomer C-free hydrogel of the above embodiment or the monomer C-free hydrogel obtained by the method of the above embodiment is used as the molded body (molding material). The method for producing a molded body of the first embodiment includes an impregnation step of impregnating a hydrogel (monomer C-free hydrogel) with monomer C, a deformation step of deforming the hydrogel into a predetermined shape by applying a mechanical load after or simultaneously with the impregnation step, and a holding step of holding the hydrogel in the deformed state into the predetermined shape for a predetermined period of time after the deformation step. Note that, as described below, when the deformation step is performed simultaneously with the impregnation step, the hydrogel may be deformed while being impregnated with monomer C, for example.

[0083] In the impregnation step, the hydrogel may be impregnated with monomer D in addition to monomer C. The impregnation step may be carried out, for example, by applying a solution containing monomer C (and optionally monomer D) prepared in advance to the hydrogel. The impregnation step may be carried out before the deformation step, or may be carried out simultaneously with the deformation step. When the impregnation step is carried out before the deformation step, it may be carried out in the same manner as in step c described above. When the impregnation step is carried out simultaneously with the deformation step, for example, the deformation step and the impregnation step may be carried out by using a solution containing monomer C (and optionally monomer D) as the liquid used for blow molding. The concentrations of monomer C and monomer D in the solution and the amounts of these solutions used may be adjusted so that the impregnation amounts of monomer C and monomer D fall within the above-mentioned ranges.

[0084] The deformation method in the deformation step is not particularly limited as long as it can deform the hydrogel by mechanical load, and examples thereof include a method of deforming the hydrogel by pressure generated by blowing a gas (e.g., compressed air) or liquid into the hydrogel (blow molding, pressure molding), a method of deforming the hydrogel by pressing with a mold (press molding), a method of compressing the hydrogel and extruding it from a mold to form a cross section of the required shape (extrusion molding), a method of creating a vacuum between the hydrogel and the mold to tightly adhere them together and obtain the desired shape (vacuum forming), a method of laminating the hydrogel to a three-dimensional substrate (three-dimensional laminate molding), etc. Among these, blow molding or press molding can easily deform the hydrogel into a complex shape.

[0085] In the deformation step, the hydrogel may be stretched twice or more (for example, 2 to 20 times) in order to increase the amount of radicals generated and improve shape fixation.

[0086] The holding time in the holding step varies depending on the amount of deformation, the shape after deformation, etc., but may be 1 minute or more, or 5 minutes or more. There is no particular upper limit to the holding time, but the holding time may be 24 hours or less.

[0087] The method for producing a molded body of the second embodiment uses the monomer C-impregnated hydrogel of the above embodiment as the molded body (molding material). The method for producing a molded body of the second embodiment includes a process of deforming the hydrogel (monomer C-impregnated hydrogel) into a predetermined shape by applying a mechanical load, and a holding process of holding the hydrogel in the deformed state for a predetermined time after the deformation process. The production method of the second embodiment is the same as that of the first embodiment, except that the impregnation process is not performed. Note that the impregnation process may also be performed in the production method of the second embodiment. For example, the impregnation process may be performed simultaneously with the deformation process by using a solution containing monomer C (and optionally monomer D) as the liquid used for blow molding.

[0088] The hydrogel molded articles produced by the above method can be used in a variety of applications, including various shock-absorbing and vibration-damping materials, biomaterials such as artificial joints, industrial materials such as various electronic components, expansion and contraction parts or drive parts of office automation equipment, various interlayer films, ship bottom paints, and antifouling agents for piping, substitutes for biological tissues such as joints, cartilage, and blood vessels, and cell culture sheets. [Example]

[0089] The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

[0090] Example 1 (Synthesis of monomer-impregnated double network gel) In a 100 mL round-bottom flask with the inside purged with argon, 1 equivalent of 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] (Fujifilm Wako Pure Chemical Industries, Ltd., product name: VA-086) was added and suspended in dichloromethane (5 mL per 1 mmol of VA-086). The flask was then immersed in a mixture of liquid nitrogen and acetone to cool, and 16 equivalents of triethylamine were added. A solution of 6 equivalents of acryloyl chloride in dichloromethane (concentration: 1 mmol / mL) was then slowly added dropwise, and the mixture was stirred for 5 hours while cooling. The flask was then gradually returned to room temperature, and an excess amount of sodium bicarbonate was added to quench the reaction, synthesizing the compound (AAC) represented by the following formula (1A). [ka]

[0091] Next, 0.1 mol of the monofunctional polymerizable monomer 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 10 mmol of the crosslinkable monomer (AAC) represented by the above formula (1A), and 1 mmol of the polymerization initiator 2,2'-azobis(2,4-dimethyl)valeronitrile were mixed, and N,N-dimethylformamide was added to the resulting mixture until the total volume reached 100 mL to prepare a precursor solution for forming the first polymer (first precursor solution). The first precursor solution was then deoxygenated using argon gas, and the first precursor solution was poured between two glass plates separated by a silicone rubber sheet and held at 44 °C for 10 hours to synthesize a gel containing the first polymer with a three-dimensional network structure (first network gel). After synthesis, the first network gel was immersed in an excess of pure water to replace the solvent inside the gel with pure water.

[0092] 2 moles of acrylamide (AA), a monofunctional polymerizable monomer, 0.4 mmol of N,N'-methylenebisacrylamide (MBAA), a crosslinkable monomer, and 2 mmol of 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, a polymerization initiator, were mixed. Pure water was then added to the resulting mixture until the total volume reached 1 L, preparing a precursor aqueous solution for forming the second polymer (second precursor aqueous solution). The first network gel obtained above was then impregnated with the second precursor aqueous solution. The amount of the second precursor aqueous solution impregnated into the first polymer was adjusted so that the total amount of AA and MBAA impregnated into the first polymer was 8 parts by mass per 1 part by mass of the first polymer. The gel was then sandwiched between two glass plates and incubated at 44°C for 10 hours, synthesizing the second polymer within the first network gel. This resulted in a hydrogel containing the first polymer and the second polymer penetrating into the gaps in the three-dimensional network structure of the first polymer (double-network gel with an interpenetrating network structure). The content of the second polymer in the double-network gel was 8 parts by mass per 1 part by mass of the first polymer.

[0093] A precursor aqueous solution for hydrogel formation (third precursor aqueous solution) was prepared by mixing 100 mmol of the monofunctional polymerizable monomer 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and 10 mmol of the crosslinkable monomer N,N'-methylenebisacrylamide (MBAA). Pure water was then added to the resulting mixture until the total volume reached 100 mL. The resulting double-network gel was then immersed in the third precursor aqueous solution in an oxygen-free environment. The impregnation amounts of the third precursor aqueous solution were adjusted so that the amount of AMPS and MBAA impregnated into the double-network gel was 400 parts by mass per 100 parts by mass of the double-network gel solids, and the amount of MBAA impregnated into the double-network gel was 30 parts by mass per 100 parts by mass of the double-network gel solids. This resulted in a monomer-impregnated double-network gel (monomer-impregnated hydrogel).

[0094] (shape fixation evaluation) The shape fixation of the monomer-impregnated double-network gels obtained above was evaluated by deforming them in an oxygen-free environment and holding them for a certain period of time. Specifically, the monomer-impregnated double-network gels were cut into 2 mm wide x 12 mm long x 2 mm thick pieces. They were stretched uniaxially to a nominal strain of 2, 3, or 4 using a benchtop tension-compression tester (MCT-2150, manufactured by A&D Co., Ltd.) and held for a specified period of time. The specified period was 7, 10, or 15 minutes for a nominal strain of 2, and 10 minutes for nominal strains of 3 and 4. The length after release from the hold was measured, and the length retention ratio Rf (length after release / length at stretch × 100, unit: %) was calculated. The results are shown in Table 1.

[0095] [Table 1]

[0096] (Preparation of hydrogel molded bodies [1]) As shown in FIG. 1, the monomer-impregnated double-network gel (3 in FIG. 1) obtained above was placed between a pair of plates 1 and 2. One plate was a blow molding mold plate 1 with an opening 6. The other plate was a support plate 2. A needle 4 and a gap 5 for supplying liquid were provided between the support plate 2 and the monomer-impregnated double-network gel 3. 30 mL of the precursor aqueous solution for forming the hydrogel (third precursor aqueous solution) was supplied from the needle 4 to deform the monomer-impregnated double-network gel 3 to fit the shape of the opening 6 in the mold plate 1, and the deformed state was maintained for 15 minutes. The supplied solution was then removed to release the gel, yielding molded bodies 10a to 10f shown in the photographs (a2) to (f2) in FIG. 2. Plates 1a to 1f shown in the schematic diagrams (a1) to (f1) in FIG. 2 were used as the mold plate 1 for molding (a2) to (f2) in FIG.

[0097] (Preparation of hydrogel molded bodies [2]) The monomer-impregnated double-network gel obtained above was cut into a size of 5 mm wide x 50 mm long x 2 mm thick and stretched to a nominal strain of 4 in an oxygen-free environment. Next, as shown in Figure 3(a1) to (c1), the stretched monomer-impregnated double-network gels 11a to 11c were immediately wrapped around molds (12a and 12b) to form arbitrary shapes, and immersed in the above-mentioned hydrogel-forming precursor aqueous solution (third precursor aqueous solution) and held in the deformed state for 15 minutes. The gels were then released and removed from the aqueous solution to obtain molded bodies 20a to 20c, as shown in the photographs in Figure 3(a2) to (c2).

[0098] <Comparative Example 1> (Synthesis of double network gel) A precursor solution for the first polymer (first precursor solution) was prepared by mixing 0.1 mol of the monofunctional polymerizable monomer 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 6 mmol of the crosslinkable monomer N,N'-methylenebisacrylamide, and 1 mmol of the polymerization initiator 2,2'-azobis(2,4-dimethyl)valeronitrile. N,N-dimethylformamide was added to the resulting mixture until the total volume reached 100 mL. The first precursor solution was then deoxygenated using argon gas. The first precursor solution was then poured between two glass plates separated by a silicone rubber sheet and held at 44 °C for 10 hours to synthesize a gel containing the first polymer with a three-dimensional network structure (first network gel). After synthesis, the first network gel was immersed in an excess of pure water to replace the solvent inside the gel.

[0099] 2 moles of acrylamide (AA), a monofunctional polymerizable monomer, 0.4 mmol of N,N'-methylenebisacrylamide (MBAA), a crosslinkable monomer, and 2 mmol of 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, a polymerization initiator, were mixed. Pure water was then added to the resulting mixture until the total volume reached 1 L, preparing a precursor aqueous solution for forming the second polymer (second precursor aqueous solution). The first network gel obtained above was then impregnated with the second precursor aqueous solution. The amount of the second precursor aqueous solution impregnated into the first polymer was adjusted so that the total amount of AA and MBAA impregnated into the first polymer was 8 parts by mass per 1 part by mass of the first polymer. The gel was then sandwiched between two glass plates and incubated at 44°C for 10 hours, synthesizing the second polymer within the first network gel. This resulted in a hydrogel containing the first polymer and the second polymer penetrating into the gaps in the three-dimensional network structure of the first polymer (double-network gel with an interpenetrating network structure). The content of the second polymer in the double-network gel was 8 parts by mass per 1 part by mass of the first polymer.

[0100] A precursor aqueous solution for hydrogel formation (third precursor aqueous solution) was prepared by mixing 100 mmol of the monofunctional polymerizable monomer 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and 10 mmol of the crosslinkable monomer N,N'-methylenebisacrylamide (MBAA). Pure water was then added to the resulting mixture until the total volume reached 100 mL. The resulting double-network gel was then immersed in the third precursor aqueous solution in an oxygen-free environment. The impregnation amounts of the third precursor aqueous solution were adjusted so that the amount of AMPS and MBAA impregnated into the double-network gel was 400 parts by mass per 100 parts by mass of the double-network gel solids, and the amount of MBAA impregnated into the double-network gel was 30 parts by mass per 100 parts by mass of the double-network gel solids. This resulted in a monomer-impregnated hydrogel.

[0101] (shape fixation evaluation) The shape fixation ability of the monomer-impregnated double network gel obtained above was evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0102] [Table 2]

[0103] <Comparative Example 2> (Synthesis of double network gel) In the same manner as in Example 1, a double-network gel (monomer-non-impregnated double-network gel) was obtained.

[0104] (shape fixation evaluation) The shape fixation ability of the monomer-non-impregnated double network gel obtained above was evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0105] [Table 3] [Explanation of symbols]

[0106] 1...mold plate, 2...support plate, 3...hydrogel, 4...needle, 5...gap, 6...opening.

Claims

1. A hydrogel having an interpenetrating network structure or a semi-interpenetrating network structure, A first polymer having a three-dimensional network structure, and a second polymer penetrating into gaps in the three-dimensional network structure of the first polymer, the first polymer comprises, as a monomer unit, a crosslinkable monomer A1 having a bond with a bond energy of 80 to 250 kJ / mol; the second polymer has a lower degree of crosslinking than the first polymer; A hydrogel, wherein the content of the second polymer is 2 to 100 parts by mass per part by mass of the first polymer.

2. The hydrogel according to claim 1 , wherein the crosslinkable monomer A1 comprises a compound represented by the following formula (1): 【Chemistry 1】 [In formula (1), a plurality of R's represent monovalent groups having an ethylenically unsaturated bond; X １ represents an organic linking group having a valence of m; X ２ represents an n-valent organic linking group, Y represents -N=N-, -O-O-, or -S-S-, m and n each represent an integer of 2 or more, a plurality of R may be the same or different, X １ and X ２ may be the same or different, and m and n may be the same or different.

3. The hydrogel of claim 1 , wherein the degree of crosslinking of the first polymer is 0.1 mol % or more.

4. The hydrogel of claim 1 , wherein the degree of crosslinking of the second polymer is 20 mol % or less.

5. The hydrogel according to claim 1 , which is impregnated with a monomer C having two or more ethylenically unsaturated bonds.

6. The hydrogel according to claim 5, wherein the impregnation amount of the monomer C is 10 to 1000 parts by mass per 100 parts by mass of a solid content of the hydrogel.

7. A method for producing a hydrogel having an interpenetrating network structure or a semi-interpenetrating network structure, comprising the steps of: a step a of reacting a first monomer composition comprising a crosslinkable monomer A1 having a bond with a bond energy of 80 to 250 kJ / mol to form a first polymer; and b) a step of impregnating the first polymer with a second monomer composition, optionally comprising a crosslinking monomer A2, and then reacting the composition to form a second polymer, a molar ratio of the amount of the crosslinkable monomer A1 to the total amount of monomers in the first monomer composition is r1, and a molar ratio of the amount of the crosslinkable monomer A2 to the total amount of monomers in the second monomer composition is r2, r2 / r1 is smaller than 1, The method for producing a hydrogel, wherein the impregnation amount of the second monomer composition is 2 to 100 parts by mass per 1 part by mass of the first polymer.

8. The method for producing a hydrogel according to claim 7, further comprising a step c) of impregnating the hydrogel obtained in the step b with a monomer C having two or more ethylenically unsaturated bonds.

9. An impregnation step of impregnating the hydrogel according to claim 1 with a monomer C having two or more ethylenically unsaturated bonds; a deformation step of deforming the hydrogel into a predetermined shape by applying a mechanical load after the impregnation step or simultaneously with the impregnation step; A method for manufacturing a molded body, comprising: after the deformation step, a holding step of holding the hydrogel in the deformed state into the predetermined shape for a predetermined period of time.

10. A deformation step of deforming the hydrogel according to claim 5 into a predetermined shape by applying a mechanical load; A method for manufacturing a molded body, comprising: after the deformation step, a holding step of holding the hydrogel in the deformed state into the predetermined shape for a predetermined period of time.

11. The method for producing a molded article according to claim 9 or 10, wherein in the deformation step, the hydrogel is deformed by blow molding or press molding.

Images