JP2009270032A - Hydrogel and method for producing it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogel and a method for producing it having adhesiveness while maintaining high strength. <P>SOLUTION: The hydrogel has an interpenetrating network structure consisting of first network structure (A) formed by polymerizing and crosslinking a first monomer (a), and second network structure (B) formed inside the first network structure (A) by introducing a second monomer (b) in the first network structure (A) and polymerizing and crosslinking the second monomer (b). In the hydrogel, the first monomer (a) includes ≥10 mol% of an anionic unsaturated monomer (a1), the second monomer (b) includes an anionic unsaturated monomer (b1), and a molar ratio (a)/(b) of units derived from the first monomer (a) to units derived from the second monomer (b) in the hydrogel is from 1/5 to 1/100. The degree of cross-linking of the second network structure (B) is lower than that of the first network structure (A). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a hydrogel and a method for producing the same.

  Gel materials have been conventionally used for highly water-absorbent resins, disposable diapers, sanitary products, soft contact lenses, water-containing sheets for indoor greening, and the like as materials capable of holding a solvent several hundred to several thousand times their own weight. It also has sustained drug release and is applied to minimally invasive diagnosis such as drug delivery. It is also used for shock absorbing materials, vibration control / soundproof materials, etc., and its uses are diverse. However, the gel material is generally not strong and the structure is destroyed by a minute stress, so that it is not suitable for an application where strength is required.

In recent years, various novel gel materials have been proposed that have greatly improved strength from conventional gel materials. For example, the following three types of gels are called three major high-strength gels and are attracting attention.
(1) Topological gel in which cross-linking points move along the main chain (for example, Patent Document 1).
(2) A nanocomposite gel using hydrophilic clay as a crosslinking point (for example, Patent Document 2).
(3) A double network gel in which two types of network structures enter each other (for example, Patent Document 3).

However, although the gel of (1) has an extremely high elongation when stretched, its elastic modulus and breaking strength are not sufficient. In addition, the manufacturing process is complicated.
In the gel of (2), it is possible to balance elongation and strength by appropriately selecting a clay as a crosslinking point and adjusting the amount of addition. However, as the added amount of clay increases, there are problems such as loss of transparency, and there is a limit to applications.
The gel (3) has a good balance between elongation and strength, and a highly transparent gel can be obtained. It is also known that the friction coefficient of the gel surface is extremely low. However, due to its unique surface properties, it is unsuitable for applications that adhere to other substrates.
Japanese Patent No. 3475252 Japanese Patent No. 3914489 International Publication No. 2003/093337 Pamphlet

  The present invention provides a hydrogel having tackiness while maintaining high strength and a method for producing the same.

  The hydrogel of the present invention comprises a first network structure (A) formed by polymerizing and crosslinking the first monomer (a), and a second monomer (A) in the first network structure (A). An interpenetrating network structure comprising the second network structure (B) formed in the first network structure (A) by introducing b), polymerizing and crosslinking the second monomer (b) The first monomer (a) contains 10 mol% or more of an anionic unsaturated monomer (a1) out of 100 mol% of the first monomer (a), and the second monomer (a) contains The monomer (b) contains an anionic unsaturated monomer (b1), and the molar ratio of the unit derived from one monomer (a) and the unit derived from the second monomer (b) in the hydrogel ((a ) / (B)) is 1/5 to 1/100, Degree of crosslinking of the network structure (B) may be smaller than the degree of crosslinking the first network structure (A).

  The hydrogel of the present invention comprises a first network structure (A) formed by polymerizing and crosslinking the first monomer (a), and a second network structure in the first network structure (A). It has a semi-interpenetrating network structure composed of the polymer (B ′) formed in the first network structure (A) by introducing the monomer (b) and polymerizing the second monomer (b). In the hydrogel, the first monomer (a) contains 10 mol% or more of the anionic unsaturated monomer (a1) in 100 mol% of the first monomer (a), and the second monomer ( b) contains an anionic unsaturated monomer (b1), the molar ratio of the unit derived from the first monomer (a) and the unit derived from the second monomer (b) in the hydrogel ((a) / (B)) is 1/5 to 1/100 And butterflies.

  The hydrogel production method of the present invention comprises (x) a step of polymerizing and crosslinking the first monomer (a) to form the first network structure (A), and (y) the first network structure. The second network structure (B) is introduced into the first network structure (A) by introducing the second monomer (b) into (A) and polymerizing and crosslinking the second monomer (b). In the method for producing a hydrogel having an interpenetrating network structure, wherein the first monomer (a) is anionic unsaturated in 100 mol% of the first monomer (a) The monomer (a1) is contained in an amount of 10 mol% or more, the second monomer (b) contains an anionic unsaturated monomer (b1), a unit derived from the first monomer (a) in the hydrogel and the second The molar ratio of units derived from the monomer (b) ((a) / b)) is 1 / 5-1 / 100, degree of crosslinking of the second network structure (B) may be smaller than the degree of crosslinking the first network structure (A).

  The hydrogel production method of the present invention comprises (x) a step of forming the first network structure (A) by polymerizing and crosslinking the first monomer (a), and (y ′) the first The second monomer (b) is introduced into the network structure (A) of the polymer, and the second monomer (b) is polymerized to form the polymer (B ′) in the first network structure (A). A hydrogel having a semi-interpenetrating network structure, wherein the first monomer (a) is an anionic unsaturated monomer out of 100 mol% of the first monomer (a). (A1) 10 mol% or more, the second monomer (b) contains an anionic unsaturated monomer (b1), a unit derived from the first monomer (a) in the hydrogel and a second Molar ratio with unit derived from monomer (b) ((a) (B)), characterized in that a 1 / 5-1 / 100.

The hydrogel of the present invention has tackiness while maintaining high strength.
According to the method for producing a hydrogel of the present invention, a hydrogel having tackiness can be produced while maintaining high strength.

<Hydrogel>
The hydrogel means a gel in which water is incorporated as a solvent in a network structure composed of a polymer.
The amount of the solvent contained in the hydrogel of the present invention is not particularly limited. Further, it may contain a solvent that dissolves in water or a solvent that is miscible with water to the extent that the physical properties of the hydrogel are not affected.

Examples of the hydrogel of the present invention include the following two types of hydrogels.
(I) A hydrogel having an interpenetrating network structure comprising a first network structure (A) and a second network structure (B) formed in the first network structure (A).
(Ii) A hydrogel having a semi-interpenetrating network structure comprising the first network structure (A) and the polymer (B ′) formed in the first network structure (A).

The network structure means a network-like structure stretched three-dimensionally by cross-linking polymers formed by polymerizing unsaturated monomers. Unlike the linear polymer, the structure can hold various solvents in the network.
An unsaturated monomer means a monomer having one or more carbon-carbon unsaturated double bonds in one molecule.

The interpenetrating network structure means a structure in which two network structures of the first network structure (A) and the second network structure (B) are overlapped and intertwined with each other.
The semi-interpenetrating network structure is a structure in which the first network structure (A) and the linear polymer (B ′) having no crosslinking point do not exist separately but are intertwined with each other. means.

(First network structure (A))
The first network structure (A) is a network structure formed by polymerizing and crosslinking the first monomer (a).
The first monomer (a) is a mixture containing an anionic unsaturated monomer (a1) and, if necessary, another unsaturated monomer (a2).

  The anionic unsaturated monomer (a1) means a monomer that is negatively charged in water. When the first network structure (A) is immersed in the aqueous solution of the second monomer (b), the acidic group of the unit derived from the anionic unsaturated monomer (a1) constituting the first network structure (A) By dissociating, the anions repel each other to develop swelling behavior, and the second monomer (b) can be introduced into the first network structure (A).

Examples of the anionic unsaturated monomer (a1) include unsaturated monomers having a sulfonic acid group (2-acrylamido-2-methylpropanesulfonic acid, p-styrenesulfonic acid, vinylsulfonic acid, etc.), unsaturated having a carboxylic acid group Examples thereof include monomers (acrylic acid, methacrylic acid, maleic acid, succinic acid, itaconic acid, etc.), unsaturated monomers having a phosphoric acid group (methacryloxyethyl trimeric acid, etc.), salts thereof and the like.
As the anionic unsaturated monomer (a1), an unsaturated monomer having a sulfonic acid group is preferable from the viewpoint of introducing the second monomer.

  Examples of the other unsaturated monomer (a2) include a cationic unsaturated monomer and a nonionic unsaturated monomer. Among them, a nonionic unsaturated monomer is used as the other unsaturated monomer (a2), and this and an anionic unsaturated monomer (a1) are copolymerized, whereby unprecedented strength can be expressed.

  The nonionic unsaturated monomer means a monomer that is not charged either positively or negatively in water and is extremely weak even when charged. The nonionic unsaturated monomer is preferably water-soluble.

Nonionic unsaturated monomers include known water-soluble monomers such as acrylamide derivatives (acrylamide, dimethylacrylamide, N-isopropylacrylamide, N-methylolacrylamide, acryloylmorpholine, etc.), methacrylamide derivatives (methacrylamide, dimethyl). Methacrylamide, N-isopropylmethacrylamide, N-methylolmethacrylamide, methacryloylmorpholine, etc., acrylate (hydroxyethyl acrylate, hydroxypropyl acrylate, dimethylaminoethyl acrylate, dimethylaminopropyl acrylate, etc.), methacrylate (hydroxyethyl methacrylate, hydroxypropyl) Methacrylate, dimethylaminoethyl methacrylate, dimethyl Mino propyl methacrylate), acrylonitrile, 2-vinylpyridine, 4-vinylpyridine, N- vinylpyrrolidone, vinyl acetate and the like. A nonionic unsaturated monomer (a1) may be used individually by 1 type, and may use 2 or more types together.
As the nonionic unsaturated monomer, an acrylamide derivative and a methacrylamide derivative are preferable from the viewpoint of mechanical strength.

Nonionic unsaturated monomers having poor water solubility as other unsaturated monomers (a2) are alkyl (meth) acrylates (methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl acrylate). , (Meth) acrylate (2-hydroxyethyl (meth) acrylate, glycidyl (meth) acrylate, etc.) having a reactive functional group, such as lauryl (meth) acrylate and stearyl (meth) acrylate.
Examples of the cationic unsaturated monomer include quaternary ammonium salts (methacrylamidopropyltrimethylammonium chloride and the like) having a carbon-carbon unsaturated double bond.
As the other unsaturated monomer (a2), one type may be used alone, or two or more types may be used in combination.

  The proportion of the anionic unsaturated monomer (a1) is 10 mol% or more, more preferably 30 mol% or more, out of 100 mol% of the first monomer (a). When the proportion of the anionic unsaturated monomer (a1) is less than 10 mol%, the first network structure (A) is insufficiently swelled, and the second monomer is contained in the first network structure (A). Since it becomes difficult to introduce (b), the mechanical properties and tackiness of the hydrogel may be impaired.

  The ratio of another unsaturated monomer (a2) is a range which does not impair the characteristic of hydrogel, and 0-90 mol% is preferable among 100 mol% of 1st monomer (a). When the proportion of the other unsaturated monomer (a2) exceeds 90 mol%, the first network structure (A) is insufficiently swelled, and the second monomer (A) is contained in the first network structure (A). Since it becomes difficult to introduce b), the mechanical properties and tackiness of the hydrogel may be impaired.

Moreover, when using a water-soluble nonionic unsaturated monomer as another unsaturated monomer (a2), the water-soluble nonionic unsaturated monomer is 70-90 mol% out of 100 mol% of the first monomer (a). By including, unprecedented strength can be expressed.
In the case of a combination capable of forming a complex by interaction between the nonionic monomer unit constituting the first network and the anionic unsaturated monomer (b1) constituting the second network, the second monomer is polymerized. Since the reaction does not progress uniformly and the strength may be uneven when the mixture is used, other combinations are desirable. A combination of acrylamide as the other unsaturated monomer (a2) and acrylic acid as the anionic unsaturated monomer (b1) may not provide a uniform gel.

(Second network structure (B))
The second network structure (B) is obtained by introducing the second monomer (b) into the first network structure (A), polymerizing and crosslinking the second monomer (b). It is a network structure formed in the network structure (A).
The second monomer (b) is a monomer or a mixture containing an anionic unsaturated monomer (b1) and, if necessary, another unsaturated monomer (b2).

Examples of the anionic unsaturated monomer (b1) include unsaturated monomers having a sulfonic acid group (2-acrylamido-2-methylpropanesulfonic acid, p-styrenesulfonic acid, vinylsulfonic acid, etc.), unsaturated having a carboxylic acid group Examples thereof include monomers (acrylic acid, methacrylic acid, maleic acid, succinic acid, itaconic acid, etc.), unsaturated monomers having a phosphoric acid group (methacryloxyethyl trimeric acid, etc.), salts thereof and the like.
As the anionic unsaturated monomer (b1), an unsaturated monomer having a carboxylic acid group is preferable from the viewpoint of introduction into the first network structure.
An anionic unsaturated monomer (b1) may be used individually by 1 type, and may use 2 or more types together.

  The proportion of the anionic unsaturated monomer (b1) is preferably 5 mol% or more, more preferably 30 mol% or more, further preferably 70 mol% or more, out of 100 mol% of the second monomer (b). Preferably it is 100 mol%.

(Polymer (B '))
The polymer (B ′) is prepared by introducing the second monomer (b) into the first network structure (A) and polymerizing the second monomer (b). It is a linear polymer having no crosslinking points formed therein.

The second monomer (b) is a monomer or a mixture containing an anionic unsaturated monomer (b1) and, if necessary, another unsaturated monomer (b2).
The kind and ratio of the anionic unsaturated monomer (b1) are the same as those of the anionic unsaturated monomer (b1) in the second network structure (B).

(Hydrogel)
The molar ratio ((a) / (b)) between the unit derived from the first monomer (a) and the unit derived from the second monomer (b) in the hydrogel of the present invention is good elongation during tension. From the point of expressing strength, it is 1/5 to 1/100, preferably 1/7 to 1/80, and more preferably 1/10 to 1/50. If the unit derived from the second monomer (b) is less than the molar ratio (1/5), sufficient elongation may not be exhibited during tension. When the unit derived from the second monomer (b) is larger than the molar ratio (1/100), sufficient strength may not be exhibited at the time of tension.

In the hydrogel of the present invention, it is necessary to make the degree of crosslinking of the second network structure (B) smaller than the degree of crosslinking of the first network structure (A). If the degree of cross-linking of the second network structure (B) is greater than or equal to the degree of cross-linking of the first network structure (A), the mechanical properties of the hydrogel, particularly elongation, may be impaired.
The degree of crosslinking means the amount of polyfunctional monomer added to 100 mol% of monomer when crosslinking is performed by the method (α) described later. When the crosslinking is performed by other methods, the ratio of the monomer units contributing to the crosslinking among the monomer units constituting the polymer can be represented by a value obtained by dividing the ratio by the number of polymer chains linked to the crosslinking points. The number of polymer chains to which the crosslinking points are linked is 2 when, for example, two monomers are reacted to form a crosslinking point. In the case of ionic bonding with trivalent charged boric acid, it is 3.

  If necessary, the hydrogel of the present invention may contain additives such as known colorants, plasticizers, stabilizers, reinforcing agents, inorganic fillers, impact modifiers, flame retardants and the like.

<Method for producing hydrogel>
As a manufacturing method of the hydrogel of this invention, the following two types of manufacturing methods are mentioned.
(I) (x) a step of polymerizing and crosslinking the first monomer (a) to form a first network structure (A), and (y) a second in the first network structure (A). And the second monomer (b) is polymerized and crosslinked to form a second network structure (B) in the first network structure (A). Production method.
(II) (x) a step of polymerizing and crosslinking the first monomer (a) to form a first network structure (A), and (y ′) a second network in the first network structure (A). A step of introducing a second monomer (b) and polymerizing the second monomer (b) to form a polymer (B ′) in the first network structure (A).

(Process (x))
First, the first monomer (a), the polymerization initiator, and the like are dissolved in water to prepare a first aqueous monomer solution.
Then, the first monomer (a) is polymerized by pouring the first aqueous solution into a container or a frame and applying heat or light to the aqueous solution.
The crosslinking of the polymer may be performed simultaneously with the polymerization of the first monomer (a) or after the polymer is obtained.
As described above, an arbitrarily shaped gel having the first network structure (A) is obtained.

Examples of the polymerization method include a radical polymerization method using a thermal polymerization initiator and a photopolymerization method using a photopolymerization initiator.
Examples of the thermal polymerization initiator include general water-soluble polymerization initiators such as potassium persulfate and ammonium persulfate.
Examples of the photopolymerization initiator include general photopolymerization initiators such as benzophenone-based initiators.

  Examples of the crosslinking method include a crosslinking method using a chemical bond, a crosslinking method using an ionic bond, and a physical crosslinking method. Specific examples include the following crosslinking method, and the method (α) is preferable because it does not require special equipment, does not complicate the manufacturing process, is simple in operation, and easily controls the network structure.

(Α) A method in which a polyfunctional monomer having two or more carbon-carbon unsaturated double bonds in one molecule is used together with the first monomer (a) to crosslink simultaneously with polymerization.
(Β) A method in which radicals are generated in the polymer by irradiation to crosslink.
(Γ) A method in which functional groups of side chains of units derived from unsaturated monomers constituting a polymer are directly reacted with each other.
(Δ) A method of cross-linking functional groups of side chains of units derived from unsaturated monomers constituting the polymer with a crosslinking agent.
(Ε) A method in which polyvalent metal ions (copper ions, zinc ions, calcium ions, etc.) are used for crosslinking by ionic bonds or coordinate bonds.

  Examples of the polyfunctional monomer include N, N-methylenebisacrylamide, monoethylene glycol dimethacrylate, diethylene glycol dimethacrylate, monopropylene glycol dimethacrylate, and the like.

  The addition amount of the polyfunctional monomer is preferably 0.5 to 10 mol%, more preferably 1 to 8 mol%, still more preferably 1 to 6 mol% with respect to 100 mol% of the first monomer (a). 1 to 4 mol% is particularly preferable. When the addition amount of the polyfunctional monomer is less than 0.5 mol%, it is difficult to maintain the shape of the gel having the first network structure (A), and handling when the second monomer (b) is introduced. May be difficult. When the addition amount of the polyfunctional monomer exceeds 10 mol%, the first network structure (A) may not swell sufficiently, and it may be difficult to sufficiently absorb the second monomer (b).

(Process (y))
By introducing the second monomer (b), a polymerization initiator, etc. into the first network structure (A), the second monomer (b) is added to the solvent contained in the first network structure (A). The polymerization initiator is uniformly diffused.
Next, the second monomer (b) is polymerized by applying heat or light to the first network structure (A) in which the second monomer (b) is introduced.
The crosslinking of the polymer may be performed simultaneously with the polymerization of the second monomer (b) or may be performed after obtaining the polymer.
By forming the second network structure (B) in the first network structure (A) as described above, a hydrogel having an arbitrary shape having an interpenetrating network structure can be obtained.

  As an introduction method, the gel having the first network structure (A) is immersed in the second aqueous solution in which the second monomer (b), the polymerization initiator and the like are dissolved, and the first network structure (A). The method of incorporating the second monomer (b) into the first network structure (A) in the process of water absorption and swelling is simple.

The polymerization method is the same as the polymerization method in step (x).
In addition, when the 1st network structure (A) is opaque and does not permeate | transmit light enough, the radical polymerization method by a thermal-polymerization initiator is preferable. In addition, when an unsaturated monomer whose behavior changes with temperature is used, a photopolymerization method using a photopolymerization initiator may be preferable.
The polymerization method of the first monomer (a) and the polymerization method of the second monomer (b) may be different.

The crosslinking method is the same as the polymerization method in the step (x), and the method (α) is preferable.
The addition amount of the polyfunctional monomer needs to be smaller than the addition amount of the polyfunctional monomer in the step (x).

(Process (y ′))
By introducing the second monomer (b), a polymerization initiator, etc. into the first network structure (A), the second monomer (b) is added to the solvent contained in the first network structure (A). The polymerization initiator is uniformly diffused.
Next, the second monomer (b) is polymerized by applying heat or light to the first network structure (A) into which the second monomer (b) has been introduced to obtain a polymer (B ′).
By forming the polymer (B ′) in the first network structure (A) as described above, a hydrogel having an arbitrary shape having a semi-interpenetrating network structure can be obtained.
The introduction method and the polymerization method are the same as the introduction method and the polymerization method in step (y).

  In the hydrogel production method of the present invention described above, since a specific monomer is used at a specific ratio, a hydrogel having tackiness can be manufactured while maintaining high strength. The hydrogel can be used for applications that require higher strength than conventional ones. In addition, when the elongation is within a certain range, there is no structural breakage due to tension and there is no hysteresis, so that it can be used for applications where stress is repeatedly applied.

  Depending on the use of the hydrogel of the present invention, it may not be necessary to crosslink the polymer comprising the second monomer (b). The interpenetrating network structure and the semi-interpenetrating network structure can be freely selected according to the physical properties required for the hydrogel.

  Hereinafter, the present invention will be described in more detail with reference to examples. In the following description, “part” means “part by mass” and “%” means “mol%” unless otherwise specified.

Example 1
Step (x):
A first monomer (a) comprising 100% of 2-acrylamido-2-methylpropanesulfonic acid, 4% N, N-methylenebisacrylamide with respect to 100% of the first monomer (a), 0.1% of photopolymerization initiator (Ciba Geigy, DAROCURE 1173, 2-hydroxy-2-methyl-1-phenylpropan-1-one) with respect to 100% of one monomer (a), 100 parts of the monomer (a) were dissolved in 300 parts of distilled water to prepare a first monomer aqueous solution.

After removing dissolved oxygen from the first monomer aqueous solution by nitrogen bubbling, the first monomer aqueous solution is poured between glass plates sealed around with silicone rubber, and the chemical solution (manufactured by Toshiba Corporation, Using a fluorescent lamp for insect trap FL20S / BL-A), ultraviolet rays are irradiated for 90 minutes at an irradiation energy of 120 mJ / cm ^{2 for} 1 minute to complete the polymerization, and a gel having the first network structure (A) is obtained. It was.

Step (y):
A second monomer (b) comprising 100% of acrylic acid, 0.1% N, N-methylenebisacrylamide with respect to 100% of the second monomer (b), and a second monomer (b) 0.001% of the photopolymerization initiator (same as above) was dissolved in 100 parts of the second monomer (b) in 300 parts of distilled water to prepare a second aqueous monomer solution. .

After removing dissolved oxygen from the second monomer aqueous solution by nitrogen bubbling, the gel having the first network structure (A) is immersed in the second monomer aqueous solution and left in this state overnight. The monomer aqueous solution was sufficiently absorbed in the first network structure (A).
A gel having a first network structure (A) sufficiently swollen with the second monomer aqueous solution is sandwiched between glass plates, and a chemical lamp (same as above) is used to irradiate the gel with an energy of 120 mJ / cm for 1 minute. Ultraviolet rays were irradiated at ^{2 for} 90 minutes to complete the polymerization, and a hydrogel having an interpenetrating network structure in which the second network structure (B) was formed in the first network structure (A) was obtained.

(Example 2)
A hydrogel having an interpenetrating network structure was obtained in the same manner as in Example 1 except that the second monomer (b) was changed to a mixture composed of 70% acrylic acid and 30% acrylamide.

(Example 3)
A hydrogel having an interpenetrating network structure was obtained in the same manner as in Example 1 except that the second monomer (b) was changed to a mixture composed of 30% acrylic acid and 70% acrylamide.

Example 4
A hydrogel having a semi-interpenetrating network structure in the same manner as in Example 1 except that the amount of N, N-methylenebisacrylamide used in the preparation of the second aqueous solution was changed from 0.1% to 0%. Got.

(Example 5)
The first monomer (a) was changed to a mixture consisting of 30% 2-acrylamido-2-methylpropanesulfonic acid and 70% N-methylolacrylamide, and the N, N- used in the preparation of the first aqueous solution. A hydrogel having an interpenetrating network structure was prepared in the same manner as in Example 1 except that the amount of methylenebisacrylamide added was changed from 4% to 2% and the amount of distilled water used was changed from 300 parts to 400 parts. Obtained.

(Example 6)
A hydrogel having an interpenetrating network structure was obtained in the same manner as in Example 5 except that the second monomer (b) was changed to a mixture composed of 70% acrylic acid and 30% acrylamide.

(Example 7)
A hydrogel having an interpenetrating network structure was obtained in the same manner as in Example 5 except that the second monomer (b) was changed to a mixture composed of 30% acrylic acid and 70% acrylamide.

(Example 8)
It has an interpenetrating network structure in the same manner as in Example 5 except that the first monomer (a) was changed to a mixture consisting of 10% 2-acrylamido-2-methylpropanesulfonic acid and 90% acrylamide. A hydrogel was obtained.

(Comparative Example 1)
A hydrogel having an interpenetrating network structure was obtained in the same manner as in Example 1 except that the second monomer (b) was changed to 100% of acrylamide.

(Comparative Example 2)
A hydrogel having an interpenetrating network structure was obtained in the same manner as in Example 5 except that the second monomer (b) was changed to 100% of acrylamide.

  In Examples 1 to 8 and Comparative Examples 1 and 2, the blending of raw materials used in step (x) and the blending of raw materials used in step (y) are shown in Table 1. The raw materials other than water are “mol%”, and water is “parts by mass”.

Abbreviations in the table are as follows.
AMPS: 2-acrylamido-2-methylpropanesulfonic acid,
AAc: acrylic acid,
AAm: acrylamide,
NMAAm: N-methylolacrylamide,
MBAA: N, N-methylenebisacrylamide,
DAR 1173: DAROCURE 1173,

(Evaluation)
The hydrogels produced in Examples 1 to 8 and Comparative Examples 1 and 2 were evaluated as follows (1) to (4). The results are shown in Table 2.

(1) Tensile strength:
The obtained hydrogel was punched into a No. 3 dumbbell test piece and subjected to a tensile test. The tensile test measured the tensile breaking strength of the test piece based on JIS-K6251. The distance between chucks was 50 mm, and the tensile speed was 50 mm / min.

(2) Swelling degree:
The degree of swelling was calculated from the mass ratio of the obtained hydrogel before and after drying. The calculation formula is as follows.
(Swelling degree) = (mass before drying) / (mass after drying) × 100 (%).

(3) Tackiness:
About the obtained hydrogel, the sheet | seat with a smooth surface was prepared and it was made to contact | adhere on a board | substrate. Any material may be used as the substrate, and there is no problem if the gel does not fall even if the substrate is turned upside down.
A 2 cm square aluminum plate (weight 1 g) was prepared and placed gently on the gel so as not to apply pressure. Thereafter, the substrate was turned upside down with the gel, and whether or not the aluminum plate had fallen before 5 minutes passed was evaluated by the number of times it did not fall when repeated 5 times.

(4) Molar ratio of the unit derived from the first monomer (a) to the unit derived from the second monomer (b) (first: second):
The obtained hydrogel was dried, and the ratio between the amount of units derived from the first monomer (a) and the amount of units derived from the second monomer (b) was calculated by elemental analysis.

As is clear from the results in Table 2, the hydrogels obtained in Examples 1 to 8 had high strength and adhesive strength.
On the other hand, the hydrogel obtained in Comparative Examples 1 and 2 did not have adhesive strength because the second monomer (b) did not contain the anionic unsaturated monomer (b1).

  Since the hydrogel of the present invention is excellent in mechanical strength and has tackiness, it can be used for various sealing materials that do not require an adhesive, a gel pad of a low-frequency treatment device, a biological electrode, and the like. It is extremely useful industrially.

Claims (4)

A first network (A) formed by polymerizing and crosslinking the first monomer (a), and introducing the second monomer (b) into the first network (A), In the hydrogel having an interpenetrating network structure composed of the second network structure (B) formed in the first network structure (A) by polymerizing and crosslinking the second monomer (b),
Said 1st monomer (a) contains 10 mol% or more of anionic unsaturated monomers (a1) among 100 mol% of this 1st monomer (a),
Said second monomer (b) comprises an anionic unsaturated monomer (b1);
The molar ratio ((a) / (b)) between the unit derived from the first monomer (a) and the unit derived from the second monomer (b) in the hydrogel is 1/5 to 1/100. And
The hydrogel characterized in that the degree of crosslinking of the second network structure (B) is smaller than the degree of crosslinking of the first network structure (A). A first network (A) formed by polymerizing and crosslinking the first monomer (a), and introducing the second monomer (b) into the first network (A), In a hydrogel having a semi-interpenetrating network structure composed of a polymer (B ′) formed in the first network structure (A) by polymerizing the second monomer (b),
Said 1st monomer (a) contains 10 mol% or more of anionic unsaturated monomers (a1) among 100 mol% of this 1st monomer (a),
Said second monomer (b) comprises an anionic unsaturated monomer (b1);
The molar ratio ((a) / (b)) between the unit derived from the first monomer (a) and the unit derived from the second monomer (b) in the hydrogel is 1/5 to 1/100. Hydrogel characterized by being. (X) forming a first network structure (A) by polymerizing and crosslinking the first monomer (a);
(Y) The second monomer (b) is introduced into the first network structure (A), and the second monomer (b) is polymerized and crosslinked to form the first network structure (A). In the method for producing a hydrogel having an interpenetrating network structure, comprising: forming a second network structure (B)
Said 1st monomer (a) contains 10 mol% or more of anionic unsaturated monomers (a1) among 100 mol% of this 1st monomer (a),
Said second monomer (b) comprises an anionic unsaturated monomer (b1);
The molar ratio ((a) / (b)) between the unit derived from the first monomer (a) and the unit derived from the second monomer (b) in the hydrogel is 1/5 to 1/100. And
The method for producing a hydrogel, wherein the degree of crosslinking of the second network structure (B) is smaller than the degree of crosslinking of the first network structure (A). (X) forming a first network structure (A) by polymerizing and crosslinking the first monomer (a);
(Y ′) The second monomer (b) is introduced into the first network structure (A), and the second monomer (b) is polymerized to form the first network structure (A). In the method for producing a hydrogel having a semi-interpenetrating network structure, comprising a step of forming a polymer (B ′),
Said 1st monomer (a) contains 10 mol% or more of anionic unsaturated monomers (a1) among 100 mol% of this 1st monomer (a),
Said second monomer (b) comprises an anionic unsaturated monomer (b1);
The molar ratio ((a) / (b)) between the unit derived from the first monomer (a) and the unit derived from the second monomer (b) in the hydrogel is 1/5 to 1/100. The manufacturing method of the hydrogel characterized by these.