JP2008255313A - Novel high strength interpenetrating network gel synthesized from monomer having n-vinylalkylamide structure and novel crosslinking agent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a novel gel which has an interpenetrating network structure using N-vinylalkylamide as a monomer, and a novel crosslinking agent used to form the gel. <P>SOLUTION: The poly(N-vinylalkylamide) gel in an interpenetrating network structure is synthesized by using an N-vinylalkylamide monomer and a crosslinking agent represented by formula (II) as the constituent units. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a novel polymer gel having an interpenetrating network structure (IPN).

  Polymer materials play a major role in medical development. Dermatological drugs are absorbed directly from the skin and transferred to the systemic circulation when compared to oral administration where drug inactivation is a problem due to skin damage and pain during drug administration and treatment through the liver This is a patient-friendly and reliable treatment.

  Poly (N-vinylacetamide (NVA) derivative) is an isomer of a biopolymer polypeptide similar to polyacrylamide, and also because its chemical structure is similar to pyrrolidone used in soft contact lenses and the like. High biocompatibility is expected. In addition, it is considered to have biocompatibility equivalent to or higher than that of polyacrylamide and polyacrylic acid that are generally used as poultices, and poly (NVA derivatives) are amphipathic, so oil gelling agents that take in oil Application examples are reported, and it is expected that poorly water-soluble drugs and lipophilic drugs can be easily taken in compared with existing polymer materials.

  Polyacrylamide is an isomer of biopolymer polypeptide, and exhibits excellent biocompatibility and at the same time a lower critical solution temperature (LCST) around 32 ° C., so that it can be used for drug delivery systems (DDS), cell sheet desorption surfaces, etc. It is applied as a functional material. On the other hand, N-vinylacetamide (NVA), which is another polypeptide isomer, and derivatives thereof have been reported since our laboratory has reported a simple synthetic method that has already been industrialized. The properties of polymers and the like are becoming clear.

On the other hand, it is known that the physical and chemical properties of polymer materials are greatly influenced by the three-dimensional structure. For example, in polyacrylamide, it has been reported that the mechanical strength is remarkably changed by controlling the primary structure of the main chain (Non-Patent Document 4) or introducing an interpenetrating network structure (IPN) (Non-Patent Documents 1 to 3). . On the other hand, little is known about examples in which a three-dimensional structure control of poly (NVA derivative) or an IPN structure is introduced, and it has not yet been applied to biomaterials.
JP Gong et al., Adv. Mater., 15, 1155 (2003). H. Tsukeshiba, et al., J. Phys. Chem. B 109, 16304 (2005). K. Yasuda, et al, Biomaterials, 26, 4468 (2005). Y. Isobe, et al., J. Am. Chem. Soc., 123, 7180 (2001).

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a novel gel having an interpenetrating network structure (IPN) using N-vinylalkylamide as a monomer and a novel crosslinking agent for forming the gel. .

（式中、Ｒ_１は、水素原子、または炭素原子数１〜８のアルキル基を表す）を提供するものである。 That is, the present invention relates to a poly (N-vinylalkylamide) gel having an interpenetrating network structure synthesized with an N-vinylalkylamide monomer represented by the chemical formula (I) as a structural unit:

(Wherein R ₁ represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms).

The present invention provides a novel poly (N-vinylalkylamide) gel having an interpenetrating network structure.
Moreover, this invention provides the novel crosslinking agent useful for manufacturing the said gel.

The unit monomer constituting the gel of the present invention is an N-vinylalkylamide represented by the chemical formula (I) (hereinafter sometimes simply referred to as “N-vinylalkylamide”). In the formula, R ₁ represents a hydrogen atom or an optionally branched alkyl group having 1 to 8 carbon atoms.

By changing R ₁ , the function of poly (N-vinylalkylamide) can be controlled. For example, when R ₁ is a hydrogen atom, the polymer can be made hydrophilic. When R ₁ is a methyl group, the polymer can be made amphiphilic. When R ₁ is an isobutyl group, heat responsiveness can be further imparted. If the carbon number of R ₁ is further extended, the polymer can be made oleophilic.

In the present invention, the N-vinylalkylamide monomer may be used as a mixed monomer of two or more types of N-vinylalkylamides having different R ₁ , and as long as the reactivity is similar and a gel can be formed. It is also possible to use a part of the above by replacing with other vinyl monomers such as vinyl acetate, (a general vinyl polymer such as acrylamide, methacrylamide, acrylic acid, methyl methacrylate, etc.).

  In the production of the gel of the present invention, first, an N-vinylalkylamide monomer is polymerized in a suitable solvent with a crosslinking agent and a polymerization initiator to form a gel. The gel synthesized in the first stage is referred to as a host gel in the present invention. The polymer constituting the host gel is referred to as “host polymer”.

で表される架橋剤を使用するようにする。該架橋剤は、Ｎ−ビニルアルキルアミドモノマーと類似の骨格構造を有しているので、ラジカル共重合性が低いＮ−ビニルアルキルアミドモノマーを重合するに際して架橋点を確実に導入することができる。架橋剤は種々のものが知られているが、例えば既知の架橋剤Ｎ，Ｎ−メチレンビスアクリルアミド（ＭＢＡ）を使用すると架橋反応が不十分となったりする。 In the present invention, the following chemical formula (II):

It is made to use the crosslinking agent represented by these. Since the crosslinking agent has a skeleton structure similar to that of the N-vinylalkylamide monomer, a crosslinking point can be surely introduced when polymerizing the N-vinylalkylamide monomer having low radical copolymerizability. Various crosslinking agents are known. For example, when the known crosslinking agent N, N-methylenebisacrylamide (MBA) is used, the crosslinking reaction may be insufficient.

In formula (II), R ₁ is as defined above, and represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. R ₁ may be the same or different.

（式中、ｎ_１、ｎ_２はそれぞれ独立して２または４を表す；ｍは０または１を表す）で表される。 In formula (II), Y represents the following chemical formula (III):

(Wherein n ₁ and n ₂ each independently represent 2 or 4; m represents 0 or 1).

In chemical formula (II), examples of Y include the following.

The crosslinking agent of the present invention is obtained by anionizing a secondary amine of a compound represented by the formula (I) with sodium hydride in a nitrogen atmosphere using anhydrous dimethylformamide as a solvent, and then formula (IV):
XYX (IV)
(Wherein Y is as defined above, X represents a halogen atom)
It can obtain by making it react with the compound represented by these. This reaction is generally known as a nucleophilic substitution reaction and can be prepared by one skilled in the art.

  The polymerization is carried out under various known polymerization initiators and radical generating conditions such as gamma rays. For example, radical generators such as 2,2′-azobis [2- (2-imidazolin-2-yl) propanedihydrochloride] 2,2′-azobis (2-methylpropionamidine) dihydrochloride, 2,2′-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] hydrate, 2,2′-azobis {2 -[1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} dihydrochloride, 2,2′-azobis [2- (2-imidazolin-2-yl) propane], 2,2′- Azobis {2-methyl-N- [1,1-bis (hydroxymethyl) -2-hydroxyethyl] propionamide}, 2,2′-azobis [ -Methyl-N- (2-hydroxyethyl) propionamide] and the like, and redox initiators such as potassium persulfate and ammonium persulfate can be exemplified, but in the present invention, suitable solubility in a solvent. And 2,2′-azobis (2-methylpropionamidine) dihydrochloride is preferably used from the viewpoint that it can be sufficiently permeated in a cool and dark place for a long time.

  Although there is no restriction | limiting in the solvent used when synthesize | combining host gel, What is necessary is just to select from a soluble viewpoint of N-vinyl alkylamide, In the case of N-vinylformamide, alcohol, such as water, methanol, and ethanol, N-vinyl In the case of acetamide, in addition to water and alcohols, as with other N-alkylvinylalkylamides, organic solvents such as benzene and toluene can be used. Replacement is also possible.

  Polymerization is carried out by applying heat and UV light to a solution prepared by dissolving the N-vinylalkylamide monomer, the crosslinking agent, and the polymerization initiator in an appropriate solvent under an inert gas atmosphere. In that case, the shape of the gel can be arbitrarily controlled by performing the solution in a container having a desired shape.

  Assuming that the concentration [M] of the N-vinylalkylamide monomer [M], the concentration [I] of the initiator, and the concentration [C] of the crosslinking agent, [M] is 1.0 to 4.0 mol / L, and [M] 100. On the other hand, the concentration [C] of the crosslinking agent may be 5 to 1, and the concentration [I] of the initiator may be prepared at a ratio of about 10 to 1.

The degree of swelling of the resulting gel can be controlled by changing the type of N-vinylalkylamide monomer, the type of crosslinking agent, the ratio of each component used, and the solvent. For example, N- (in the formula (I) _{R 1} is a methyl group) vinyl alkyl amide monomer as N- vinylamide monomers Using a concentration (1~4mol / L), the type of the crosslinking agent [M], each component Ratio of the cross-linking agent [C] 1 to 3 and the initiator concentration 1 to 5 with respect to [M] 100, the degree of swelling varies from 10 to 26. A host gel can be prepared.

  After polymerization, unreacted monomers and residues of crosslinking agent are removed from the system. The removal can be performed by, for example, immersing the obtained gel in the solvent used for the reaction and driving out those compounds from the gel into the solvent. It is more effective to perform this operation multiple times. The completion of such washing may be based on the case where the gel is in an equilibrium swelling state where the weight of the gel does not change.

  The poly (N-vinylalkylamide) gel having an interpenetrating network structure is obtained by using the above-obtained host gel or dry poly (N-vinylalkylamide) gel with the N-vinylalkylamide monomer, the crosslinking agent, and the polymerization initiator. Immerse in a solution dissolved in a suitable solvent, diffuse each component into the host gel until the same concentration as the solution, polymerize and crosslink the N-vinylalkylamide monomer in the host gel in the same way as the host gel was synthesized. Can be obtained. The polymer synthesized in the second stage is referred to as “guest polymer”.

  The N-vinylalkylamide monomer, the crosslinking agent, the polymerization initiator, and the use ratio thereof used in forming the guest polymer may be the same as or different from those in forming the host gel.

The interpenetrating network structure (IPN structure) is defined as a structure in which different types of cross-linking networks are entangled with each other without having a chemical bond. For example, by forming an intertwined IPN structure using poly-2-hydroxy-3-methacryloyloxypropyltrimethylammonium chloride as a crosslinked hydrophilic polymer and melamine resin as a crosslinked hydrophobic polymer, a film insoluble in any solvent is formed. . (Y. Sakai, et al., Proc. 3 rd Inter. Meet. Chemical Sencers, 273 (1990)) Also, where by use of ethylene glycol dimethacrylate in place of the melamine resin, can enhance the water resistance It is possible (Y. Sakai et al., J. Electrochem. Soc., 140, 432 (1993)). In the present invention, a solution having an N-vinylalkylamide monomer concentration [M] is used, and a gel obtained by one-step synthesis and a solution having an N-vinylalkylamide monomer concentration [M] / 2 are used. Thus, it can be confirmed by comparing the strength per unit area and the breaking strength (penetration depth at break, pressure) with the gel obtained by the two-step synthesis. If the strength per unit area of the latter gel is higher than that of the former gel, it can be said that an interpenetrating network structure is formed and exists.

  Gels having an IPN structure using an amphiphilic N-vinylalkylamide as a monomer have not been known so far, and are expected to be used as a strong carrier for carrying various drugs. I think there is sex.

As described above, both the host polymer and the guest polymer have been described with respect to the polymer gel having an IPN structure composed of crosslinked poly (N-vinylalkylamide). In the present invention, either the host polymer or the guest polymer is replaced with another polymer other than the N-vinylalkylamide polymer, for example, a polymer comprising a salt or ester compound of acrylic acid or methacrylic acid, a vinyl acetate polymer, or an acrylamide polymer. It can also be composed of a methacrylamide polymer.
For example, a gel having an IPN structure using an acrylamide polymer as a host polymer and a guest polymer and a preparation method thereof are already known (for example, Non-Patent Document 1, JT Zhang et al., J. Polym. Sci. Part A: Polym Chem., 42, 1249 (2004)) When preparing a polymer gel with an IPN structure by composing either a host polymer or a guest polymer with an acrylamide polymer, preparation of (crosslinked) polyacrylamide which is already known Apply the method. As the crosslinking agent, the crosslinking agent of the present invention represented by the formula II can be used, or the crosslinking agent used in the preparation of (crosslinked) polyacrylamide can be used.

(Synthesis of crosslinking agent)
A cross-linking agent having an NVA skeleton was synthesized as shown in the following reaction formula using Cl—Y—Cl (Y is shown in Table 1). The solvent dimethylformamide used at this time was 60 mL, 2.4 g of sodium hydride equivalent to 1.02 equivalent in oil, which is a commercial product, was used, reacted with 5 g of NVA, reacted with Cl—Y—Cl, and nucleophilic. A crosslinking agent was synthesized by a substitution reaction.

ａ）収量（ｇ）は、シリカゲルクロマトグラフィーにより単離された重量である。
ｂ）収率（％）は、リンカーの使用量（２３ｍｍｏｌ）に基づいて計算した値である。

a) Yield (g) is the weight isolated by silica gel chromatography.
b) Yield (%) is a value calculated based on the amount of linker used (23 mmol).

  Proton NMR (400 MHz) spectra obtained by measuring the obtained crosslinking agents (entry Nos. 1 to 3) in deuterated acetonitrile at room temperature are shown in FIGS.

(Synthesis of host gel 1: Influence of swelling degree by crosslinking agent)

  NVA (0.34 g, 4 mmol), crosslinker 2 (12 mg, 0.04 mmol), and initiator 2,2′-azobis (2-methylpropionamidine) dihydrochloride (11 mg, 0.04 mmol) were degassed. It melt | dissolved in 2 mL of ultrapure water (NVA density | concentration is 2 mol / L), and after introducing into two glass plates (gap 1 mm thickness) under nitrogen atmosphere, the polymerization reaction was started by heating to 37 degreeC. The solution gelled in about 30 minutes. The gel obtained after the reaction for 4 hours was cooled to deactivate radicals to stop the reaction, and 2.12 g of a transparent gel was obtained.

  The obtained gel was washed by immersing it in ultrapure water for 5 days while changing the washing water every day to obtain 6.03 g of gel (host gel 2) in an equilibrium swelling state.

  From the weight (0.023 g) obtained by freeze-drying a part (0.347 g) of the obtained gel, the degree of swelling at 25 ° C. was 14, and the yield was 99% or more. The results are shown in Table 2 below.

  Transparent gels (host gels 1 and 3) were prepared in the same manner as described above using the crosslinking agents 1 and 3 instead of the crosslinking agent 2. In the case of using the crosslinking agents 1 and 3, the polymerization proceeded quantitatively in the same manner as in the case of the crosslinking agent 2. The results are shown in Table 2 below.

  The degree of swelling of the gel obtained using the cross-linking agent 1 showed a larger value than the others. This is probably because the cross-linking reaction was insufficient compared to the cross-linking agents 2 and 3 because the size of the cross-linking agent was small.

(Synthesis of host gel 2: Consideration of polymerization conditions)
Using the crosslinking agent 2, the concentration of the NVA monomer [M] and the concentration ratio of the NVA monomer [M], the initiator [I], and the crosslinking agent [C] ([M]: [I]: [C]) A gel was synthesized in the same manner as in the above host gel synthesis 1 except that the conditions shown in Table 3 below were used. The results are shown in Table 3.

上記表３に示したようにＮＶＡの濃度は１ｍｏｌ／Ｌから４ｍｏｌ／Ｌまで広範囲で定量的にゲルの調製ができる

As shown in Table 3, the gel concentration can be quantitatively prepared over a wide range of NVA concentrations from 1 mol / L to 4 mol / L.

(Preparation of gel having interpenetrating network structure)

  Host gels 1, 2, 3, 4, 5, 6, and 9 prepared with a thickness of 1 mm were used in the amounts shown in Table 4, respectively, and NVA (2.38 g, 28 mmol) and crosslinking agent 2 (83 mg, 0.28 mmol) And the same initiator (77 mg, 0.28 mmol) used in Synthesis 1 of the host gel and mixed with ultrapure water to make a total of 8 mL, and left to stand at 10 ° C. for 24 hours. By this operation, each component is diffused into the gel at the same concentration, and the NVA concentration becomes 2 mol / L.

An example in which the monomer immersion condition is set to 4 ° C. for one week will be described. 0.185 g of the host gel 7 was taken out, immersed in a monomer solution at 4 ° C. for one week, sandwiched again between two glass plates (gap 1 mm thick) in a nitrogen atmosphere, and heated at 37 ° C. for 6 hours. As a result, an NVA gel having an IPN structure is obtained (IPN gel 8). The degree of swelling of the IPN gel obtained here was 10, and the yield was 89%.
The degree of swelling of the IPN gel is calculated as a degree of swelling of 10 from the formula (Ws−Wd) / Wd because the weight in the parallel swelling state is Ws = 0.4712 g and the weight in the dry state is Wd = 0.0432 g. The The yield of the first-stage quantitatively reacted host gel 7 was 1 g / mL because the gel 2 mL corresponding to the initially prepared 2 mol / L concentration changed to 6.03 g in the parallel swelling state. Assuming that the NVA concentration of the host gel in the monomer immersion state is corrected to 0.66 mol / L (see the host gel 2 under the same conditions). That is, the NVA concentration in the second stage IPN gel preparation state can be regarded as 2.66 mol / L as a whole, and the dry weight of the same volume of the host gel 7 (0.66 mol / L) is 0.012 g. When the IPN gel reacted quantitatively, it should be 0.012 g × (2.66 mol / L ÷ 0.66 mol / L) = 0.0484 g, and the dry weight of the IPN gel actually obtained was 0.8. Since it was 0432 g, the yield was calculated as 0.0432 g ÷ 0.0484 g × 100 = 89 (%).

  As shown in Table 3, the gel concentration can be quantitatively prepared over a wide range of NVA concentrations from 1 mol / L to 4 mol / L, but Table 4 shows that the host gel is kept in the monomer solution at 10 ° C. for 24 hours as a preliminary experiment. This is the result of synthesizing the IPN gel after the immersion, and confirming that the IPN structure can be introduced into each of the IPN gels even in a short immersion (IPN). Gels 1-7).

Measurement of breaking point The obtained host gels 2, 4 and IPN gel 8 were cut into 5 mm x 5 mm, the breaking points of the gel were measured three times with a compression tester (manufactured by Shimadzu Corporation, EZ test), and the average values were compared. . The results are shown in Table 5. In Table 5, the breaking strength (mm) represents the compressed distance when the gel broke, and the breaking strength (Pa) represents the stress at that time, and was determined from the maximum value.

The gel having the IPN structure (IPN gel 8) is 16.5 × 10 ⁵ Pa, the gel before introducing the IPN structure (5.1 × 10 ⁵ Pa), and the host gel 4 prepared by doubling the NVA concentration The value was larger than the value (12.6 × 10 ⁵ Pa).

(Biocompatibility)
An adhesion test of mouse L929 fibroblasts was performed using IPN gel 2 shown in Table 4, and its biocompatibility was evaluated.

  When observed one week later, cell adhesion to poly (N-vinylacetamide) (NVA) gel showed a tendency to gradually expand and proliferate, although the initial number of adhesions was small, and the harmfulness to cells was strong. I thought it was not.

(Preparation of interpenetrating network structure by combination of NVA and other monomers)
(NVA and N-isopropylacrylamide NVA (0.51 g, 6 mmol), crosslinker 1 (18 mg, 0.06 mmol), and initiator 2,2′-azobis (2-methylpropionamidine) dihydrochloride (17 mg, 0 (.06 mmol) was dissolved in 3 mL of degassed ultrapure water (NVA concentration was 2 mol / L) The resulting solution was introduced into two glass plates (gap 2 mm thick) under a nitrogen atmosphere, and then 37 ° C. When the polymerization reaction was started by heating, gelation occurred in about 30 minutes, and after 4 hours of reaction, the reaction was stopped by cooling to deactivate radicals to obtain 3.13 g of gel. The gel was washed by immersing in ultrapure water for 24 hours to obtain 8.00 g of gel in an equilibrium swelling state.

Next, a parallel swollen NVA gel having a thickness of 3.00 mm was cut into a disk shape having a diameter of 9 mm, and this was cut into a host gel (disk volume = π × 4.5 mm × 4.5 mm × 3.0 mm = 191 mm3 = 1.91 × 10 ^-4 L).
From the weight (0.011 g) obtained by freeze-drying this 9 mm diameter disk (0.173 g), the degree of swelling at 25 ° C. was calculated to be 14.7 and the yield was 99.8%, respectively. .

The procedure for introducing the IPN structure into an NVA gel having a diameter of 9 mm and a thickness of 3 mm is shown below.
N-isopropylacrylamide (NIPAM) 1.8 g, 16 mmol), crosslinker methylenebisacrylamide (MBAAm) (25 mg, 0.16 mmol), and the same initiator (44 mg, 0.16 mmol) and mixed with ultrapure water. The whole was adjusted to 16 mL and allowed to stand for 24 hours under cooling at 4 ° C. By this operation, each component is diffused into the gel at the same concentration, and the concentration of NIPAM becomes 1 mol / L.

The gel was taken out and sandwiched again between two glass plates (gap 2 mm thick) under a nitrogen atmosphere, and UV irradiation was performed at room temperature for 6 hours to obtain a gel having an IPN structure composed of NVA and NIPAM. This was washed by immersing it in ultrapure water for 5 days to obtain 0.289 g in a state of parallel swelling of one disk. Since the disk is 0.027 g in the dry state, the swelling degree is 9.7, and since the dry state of the charged NVA gel is 0.011 g as described above, the reacted NIPAM polymer is 0.016 g. NIPAM present in the disk volume in the charged state before the reaction was (1 mol / L × 113.08 g / mol × 1.91 × 10 −4 L = 0.0215 g), so the yield was 74%. And calculated respectively.
Further, the breaking point was measured in the same manner as the above breaking point except that a disc-shaped gel having a thickness of 3 mm and a diameter of 9 mm was used. The results are shown in Table 6 below.

(NVA and acrylamide)
From NVA and AAm in the same manner as when N-isopropylacrylamide was used, except that 2.0 mol / L of acrylamide (AAm) was used as a guest polymer constituent monomer and the polymerization was performed by thermal polymerization at 37 degrees instead of UV irradiation. A gel having an IPN structure was obtained. The yield was 99% or more and the degree of swelling was 7.3.
Further, the breaking point was measured in the same manner as the above breaking point except that a disc-shaped gel having a thickness of 3 mm and a diameter of 9 mm was used. The results are shown in Table 6 below.

  The poly (N-vinylalkylamide monomer) gel of the present invention is expected to be applied as a strong carrier for supporting various drugs and can be industrially developed as a new biomaterial.

¹ H-NMR (400 MHz) spectrum of the crosslinking agent (entry No. 1). ¹ H-NMR (400 MHz) spectrum of the crosslinking agent (entry No. 2). ¹ H-NMR (400 MHz) spectrum of the crosslinking agent (entry No. 3).

Claims (5)

A poly (N-vinylalkylamide) gel having an interpenetrating network structure synthesized as a structural unit of a gel network for synthesizing the N-vinylalkylamide monomer represented by the chemical formula (I) in the first stage and the second stage:

(Wherein R ₁ represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms). The poly network (N-) having an interpenetrating network structure synthesized from an N-vinylalkylamide monomer represented by the chemical formula (I), a crosslinking agent and a polymerization initiator is used as the structural unit of the gel network synthesized in the first stage and the second stage. Vinyl alkylamide monomer) gel:

(Wherein R ₁ represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms). The poly (N-vinyl alkylamide monomer) gel according to claim 2, wherein the crosslinking agent is represented by the following chemical formula (II):

(In the formula, R ₁ represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms; Y represents the following chemical formula (III):

(Wherein, n ₁ and n ₂ each independently represents 2 or 4; m represents 0 or 1)). Compound represented by the following chemical formula (II):

(In the formula, R ₁ represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms; Y represents the following chemical formula (III):

(Wherein n ₁ and n ₂ each independently represents 2 or 4; m represents 0 or 1; X represents a halogen atom). The N-vinylalkylamide monomer represented by the chemical formula (I) is a structural unit of a gel network synthesized in the first stage or the second stage, and salts and ester compounds of acrylic acid and methacrylic acid, acrylamide monomer, methacrylamide monomer or A polymer gel with an interpenetrating network constructed as a building block of a gel network that synthesizes vinyl acetate in the second or first stage:

(Wherein R ₁ represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms).

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