Crosslinked polymer, molded body of crosslinked polymer and container package for food

Abstract

To provide a low-water-absorbing crosslinked polymer containing a structural unit derived from (vinylbenzyl)trimethylammonium chloride, which can be used as a molded body such as a sheet.SOLUTION: There is provided a crosslinked polymer containing a structural unit derived from (vinylbenzyl)trimethylammonium chloride and a structural unit derived from a hydrophobic monomer, which is crosslinked by a compound having two or more radical-polymerizable functional groups, wherein the content of the structural unit derived from (vinylbenzyl)trimethylammonium chloride in all structural units of the crosslinked polymer is 1 mol% or more and less than 15 mol%, the content of the structural unit derived from a hydrophobic monomer in all structural units of the crosslinked polymer is 55 to 89 mol%, the content of the structural unit derived from the compound having two or more radical-polymerizable functional groups in all structural units of the crosslinked polymer is 10 to 30 mol% and the hydrophobic monomer is at least one selected from the group consisting of an aromatic vinyl monomer and an olefin monomer.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a crosslinked polymer, a molded article of the crosslinked polymer, and a food container / packaging. [Background technology]

[0002] (Vinylbenzyl)trialkylammonium chloride is a useful antibacterial compound. From the viewpoint of preventing leaching, copolymerization of (vinylbenzyl)trialkylammonium chloride with other monomers and use in the form of a polymer has been investigated.

[0003] Patent Document 1 (JP 2003-55108 A) describes an antibacterial polymeric substance obtained by copolymerizing a (vinylbenzyl)trialkylammonium chloride having a specific structure with a hydrophilic monomer, and an antibacterial polymer gel obtained by incorporating water into the antibacterial polymeric substance.

[0004] Patent Document 2 (WO 2023 / 027090) describes polymer particles containing structural units derived from a cationic polymerization initiator, a main monomer containing a carbon-carbon double bond, and a cationic comonomer containing a carbon-carbon double bond such as (vinylbenzyl)trimethylammonium chloride. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-55108 [Patent Document 2] International Publication No. 2023 / 027090 Summary of the Invention [Problem to be solved by the invention]

[0006] The present inventors focused on the antibacterial properties of (vinylbenzyl)trimethylammonium chloride and investigated the development of a sheet-like material that can be used for food container packaging and the like. When the sheet-like material is used for food container packaging for meat and the like, the sheet-like material is used in contact with water. Therefore, it is desirable for the sheet-like material to have low water absorption in order to maintain its shape.

[0007] An object of the present invention is to provide a low water-absorbent crosslinked polymer containing structural units derived from (vinylbenzyl)trimethylammonium chloride, which can be used as a molded article such as a sheet. [Means for solving the problem]

[0008] The present inventors have discovered that a sheet-like molded article with low water absorbency can be produced by copolymerizing hydrophilic (vinylbenzyl)trimethylammonium chloride with a hydrophobic monomer in a specific blending ratio, and have thus completed the present invention.

[0009] The present disclosure encompasses the following aspects. [Aspect 1] a structural unit derived from (vinylbenzyl)trimethylammonium chloride; a structural unit derived from a hydrophobic monomer; Contains A crosslinked polymer crosslinked by a compound having two or more radically polymerizable functional groups, the content of the structural units derived from (vinylbenzyl)trimethylammonium chloride in all structural units of the crosslinked polymer is 1 mol % or more and less than 15 mol %; the content of the structural units derived from the hydrophobic monomer in all structural units of the crosslinked polymer is 55 to 89 mol %; the content of the structural units derived from the compound having two or more radically polymerizable functional groups is 10 to 30 mol % of all structural units of the crosslinked polymer, A crosslinked polymer, wherein the hydrophobic monomer is at least one selected from the group consisting of an aromatic vinyl monomer and an olefin monomer. [Aspect 2] a structural unit derived from (vinylbenzyl)trimethylammonium chloride; a structural unit derived from an aromatic vinyl monomer; A crosslinked polymer comprising: The crosslinked polymer is The structural unit derived from the (vinylbenzyl)trimethylammonium chloride is contained in an amount of 1.0 to 24.0% by mass, The aromatic vinyl monomer-derived structural unit is contained in an amount of 35.0 to 78.0% by mass, A crosslinked polymer having a swelling index in water of 1.00 to 1.35. [Aspect 3] The crosslinked polymer according to aspect 1 or 2, which has a tensile strength of 2 to 7 MPa. [Aspect 4] A molded article of the crosslinked polymer according to any one of the above aspects 1 to 3. [Aspect 5] An antibacterial sheet comprising the molded article according to aspect 4. [Aspect 6] A food container / packaging comprising the molded article according to aspect 4. [Aspect 7] A cooking utensil comprising the molded article according to aspect 4. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a low water-absorbent crosslinked polymer containing structural units derived from (vinylbenzyl)trimethylammonium chloride, which can be used as a molded article such as a sheet. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a graph showing the relationship between the VBTMA content and the decomposition temperature for the copolymers of Reference Examples 1 to 7. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described, but it should be understood that the present invention is not limited to these embodiments and that various applications are possible within the spirit and scope of the present invention.

[0013] In this specification, when "~" is used to describe a numerical range, the numerical values ​​at both ends are the upper and lower limits, respectively, and are included in the numerical range. When multiple upper or lower limits are listed, numerical ranges can be created using all combinations of the upper and lower limits. Similarly, when multiple numerical ranges are listed, separate numerical ranges can be created by individually selecting and combining upper and lower limits from those numerical ranges.

[0014] As used herein, "antibacterial" refers to the property of inhibiting the development, growth, and / or proliferation of microorganisms. Here, "microorganisms" refers to organisms that are classified as "microorganisms" in biological taxonomy, and is a concept that includes, for example, gram-positive bacteria such as Staphylococcus aureus, gram-negative bacteria such as Escherichia coli, fungi, yeasts, viruses, etc.

[0015] [Crosslinked polymer] The present disclosure relates to crosslinked polymers containing structural units derived from (vinylbenzyl)trimethylammonium chloride.

[0016] In one embodiment, the crosslinked polymer contains structural units derived from (vinylbenzyl)trimethylammonium chloride and structural units derived from a hydrophobic monomer, and is crosslinked with a compound having two or more radically polymerizable functional groups, wherein the content of structural units derived from (vinylbenzyl)trimethylammonium chloride among all structural units of the crosslinked polymer is 1 mol % or more but less than 15 mol %, the content of structural units derived from hydrophobic monomer among all structural units of the crosslinked polymer is 55 to 89 mol %, the content of structural units derived from compounds having two or more radically polymerizable functional groups among all structural units of the crosslinked polymer is 10 to 30 mol %, and the hydrophobic monomer is at least one selected from the group consisting of aromatic vinyl monomers and olefin monomers.

[0017] Of all structural units in the crosslinked polymer, the content of structural units derived from (vinylbenzyl)trimethylammonium chloride is 1 mol% or more and less than 15 mol%, preferably 3 to 10 mol%, and more preferably 5 to 8 mol%. By making the content of structural units derived from (vinylbenzyl)trimethylammonium chloride 1 mol% or more, antibacterial properties can be improved. By making the content of structural units derived from (vinylbenzyl)trimethylammonium chloride less than 15 mol%, a material with low water absorbency can be obtained. By making the content of structural units derived from (vinylbenzyl)trimethylammonium chloride less than 15 mol%, the heat resistance of the material can be improved.

[0018] Of all structural units in the crosslinked polymer, the content of structural units derived from hydrophobic monomers is 55 to 89 mol%, preferably 60 to 87 mol%, and more preferably 62 to 85 mol%. By making the content of structural units derived from hydrophobic monomers 55 mol% or more, a material with low water absorption can be obtained. By making the content of structural units derived from hydrophobic monomers 89 mol% or less, the antibacterial function of the structural units derived from (vinylbenzyl)trimethylammonium chloride can be exerted.

[0019] Of all structural units in the crosslinked polymer, the content of structural units derived from compounds having two or more radically polymerizable functional groups is 10 to 30 mol %, preferably 10 to 25 mol %, and more preferably 10 to 20 mol %. By making the content of structural units derived from compounds having two or more radically polymerizable functional groups 10 mol % or more, the mechanical strength of the material can be increased. By making the content of structural units derived from compounds having two or more radically polymerizable functional groups 30 mol % or less, the degree of swelling in water can be reduced while ensuring hardness suitable for sheet use.

[0020] The hydrophobic monomer is at least one selected from the group consisting of an aromatic vinyl monomer and an olefin monomer, and is preferably an aromatic vinyl monomer. The hydrophobic monomer may be used alone or in combination of two or more kinds.

[0021] In this specification, the aromatic vinyl monomer refers to a monomer having a structure in which one hydrogen atom of an aromatic ring is substituted with a vinyl group. Specific examples thereof include styrene, α-methylstyrene, 2-methylstyrene, 4-methylstyrene, methoxystyrene, 4-t-butylstyrene, 4-t-butoxystyrene, 4-chlorostyrene, and 3-chlorostyrene.

[0022] In this specification, an olefin monomer is a hydrocarbon having one double bond formed between carbon atoms excluding carbon atoms forming an aromatic ring, and specific examples thereof include ethylene and propylene.

[0023] The hydrophobic monomer is preferably at least one selected from styrene, α-methylstyrene, 2-methylstyrene, 4-methylstyrene, 4-t-butylstyrene, 4-t-butoxystyrene, 4-chlorostyrene, and 3-chlorostyrene, more preferably at least one selected from styrene, 4-methylstyrene, and 4-t-butylstyrene, and even more preferably styrene.

[0024] Examples of compounds having two or more radically polymerizable functional groups include diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, ethylene glycol diacrylate, methylene bisacrylamide, and divinylbenzene. Compounds having two or more radically polymerizable functional groups may be used alone or in combination of two or more.

[0025] The crosslinked polymer may contain structural units derived from other monomers other than (vinylbenzyl)trimethylammonium chloride and hydrophobic monomers. The content of the structural units derived from other monomers in the crosslinked polymer may be 0 to 20 mol %, or 10 to 20 mol %. Examples of other monomers include acrylic acid, ethyl acrylate, 2-ethylhexyl acrylate, butyl acrylate, methacrylic acid, isobutyl methacrylate, glycidyl methacrylate, butyl methacrylate, and methyl methacrylate.

[0026] In this embodiment, the swelling degree of the crosslinked polymer in water is preferably 1.35 or less, more preferably 1.25 or less, and even more preferably 1.15 or less. The lower limit of the swelling degree of the crosslinked polymer in water is not particularly limited, but may be 1.00 or 1.01. If the swelling degree of the crosslinked polymer in water is 1.35 or less, deformation of the material when it comes into contact with water can be suppressed.

[0027] In this specification, the swelling degree of a crosslinked polymer in water is a value determined by the following method. The crosslinked polymer is dried in an oven at 40°C for 48 hours and then dried under reduced pressure for one day. The mass of the crosslinked polymer after drying is measured and determined as the mass (mg) of the crosslinked polymer after drying. 20 mL of water vapor, a sufficient amount of water for swelling, is added to 30 mg of the crosslinked polymer after drying, and the mixture is allowed to stand at 25°C for 24 hours. The crosslinked polymer is removed from the distilled water, the surface of which is lightly wiped with a paper cloth, and the mass of the crosslinked polymer is then measured and determined as the mass (mg) of the crosslinked polymer after immersion in water. The obtained value is used to calculate the swelling degree of the crosslinked polymer in water using the following formula. Swelling degree of crosslinked polymer in water = mass of crosslinked polymer after immersion in water (mg) / mass of crosslinked polymer after drying (mg)

[0028] The crosslinked polymer of one embodiment contains structural units derived from (vinylbenzyl)trimethylammonium chloride and structural units derived from an aromatic vinyl monomer, and the crosslinked polymer contains 1.0 to 24.0 mass% of structural units derived from (vinylbenzyl)trimethylammonium chloride and 35.0 to 78.0 mass% of structural units derived from an aromatic vinyl monomer, and has a swelling index in water of 1.00 to 1.35.

[0029] The crosslinked polymer contains 1.0 to 24.0 mass% of structural units derived from (vinylbenzyl)trimethylammonium chloride, preferably 4.0 to 17.0 mass%, and more preferably 7.0 to 14.0 mass%. By making the content of structural units derived from (vinylbenzyl)trimethylammonium chloride 1.0 mass% or more, antibacterial properties can be enhanced. By making the content of structural units derived from (vinylbenzyl)trimethylammonium chloride 24.0 mass% or less, a material with low water absorption can be obtained.

[0030] The crosslinked polymer contains 35.0 to 78.0 mass% of structural units derived from aromatic vinyl monomers, preferably 40.0 to 75.0 mass%, and more preferably 41.0 to 72.0 mass%. By making the content of structural units derived from aromatic vinyl monomers 35.0 mass% or more, a material with low water absorption can be obtained. By making the content of structural units derived from aromatic vinyl monomers 78.0 mass% or less, antibacterial properties can be exerted by the structural units derived from (vinylbenzyl)trimethylammonium chloride.

[0031] The total content of structural units derived from (vinylbenzyl)trimethylammonium chloride and structural units derived from aromatic vinyl monomers in the crosslinked polymer is preferably 36.0 to 82.0 mass%, more preferably 44.0 to 79.0 mass%, and even more preferably 48.0 to 79.0 mass%.

[0032] The crosslinked polymer may contain structural units derived from other monomers other than (vinylbenzyl)trimethylammonium chloride and aromatic vinyl monomers. The content of the structural units derived from other monomers in the crosslinked polymer may be 0 to 33.0% by mass, or 0 to 17.0% by mass. As described below, when the crosslinked structure is formed using functional groups possessed by the other monomers, the content of the structural units derived from other monomers in the crosslinked polymer is preferably 4.0 to 33.0% by mass, more preferably 4.0 to 17.0% by mass.

[0033] In this embodiment, the crosslinked structure in the crosslinked polymer is not particularly limited. Examples of methods for forming the crosslinked structure include a method in which a functional group is introduced into a polymer side chain using a monomer having a functional group such as a carboxy group or a glycidyl group as another monomer, and a crosslinked structure is formed using a crosslinking agent that is reactive with the introduced functional group. Examples of preferred crosslinking agents for polymers having a carboxy group include isocyanate crosslinking agents and epoxy crosslinking agents. Examples of preferred crosslinking agents for polymers having a glycidyl group include amine crosslinking agents.

[0034] Examples of methods for forming a crosslinked structure include copolymerizing (vinylbenzyl)trimethylammonium chloride, an aromatic vinyl monomer, and optionally other monomers with a compound having two or more radically polymerizable functional groups.

[0035] The content of the structural unit derived from the compound having two or more radically polymerizable functional groups in the crosslinked polymer may be 18.0 to 49.7% by mass, or 19.0 to 48.0% by mass.

[0036] In this embodiment, examples of the aromatic vinyl monomer include styrene, α-methylstyrene, 2-methylstyrene, 4-methylstyrene, methoxystyrene, 4-t-butylstyrene, 4-t-butoxystyrene, 4-chlorostyrene, and 3-chlorostyrene. The aromatic vinyl monomer is preferably at least one selected from styrene, α-methylstyrene, 2-methylstyrene, 4-methylstyrene, 4-t-butylstyrene, 4-t-butoxystyrene, 4-chlorostyrene, and 3-chlorostyrene, more preferably at least one selected from styrene, 4-methylstyrene, and 4-t-butylstyrene, and even more preferably styrene. The aromatic vinyl monomer may be used alone or in combination of two or more.

[0037] In this embodiment, examples of the other monomer include olefin monomers such as ethylene and propylene, acrylic acid, ethyl acrylate, 2-ethylhexyl acrylate, butyl acrylate, methacrylic acid, isobutyl methacrylate, glycidyl methacrylate, butyl methacrylate, and methyl methacrylate. The other monomer is preferably at least one selected from acrylic acid, ethyl acrylate, 2-ethylhexyl acrylate, butyl acrylate, methacrylic acid, isobutyl methacrylate, glycidyl methacrylate, butyl methacrylate, and methyl methacrylate.

[0038] In this embodiment, the compound having two or more radically polymerizable functional groups is the same as that described above.

[0039] In this embodiment, the swelling index of the crosslinked polymer in water is 1.00 to 1.35, preferably 1.01 to 1.25, and more preferably 1.03 to 1.15. If the swelling index of the crosslinked polymer in water is 1.35 or less, deformation of the material when it comes into contact with water can be suppressed.

[0040] [Mechanical properties of cross-linked polymers] The tensile strength of the crosslinked polymer is preferably 2 to 7 MPa, more preferably 3 to 5 MPa. In this specification, the tensile strength of the crosslinked polymer is a value measured by the following method.

[0041] (Sample production method) After synthesis of the crosslinked polymer, the crosslinked polymer is purified as follows without being dried. (1) The crosslinked polymer was immersed in a large amount of ethanol for 5 days, with the ethanol being changed once a day. (2) The cross-linked polymer was removed and immersed in a large amount of distilled water for 5 days, with the water being changed once a day. A test piece measuring 55 mm in length, 8 mm in width, and 4.5 mm in depth is taken from the purified crosslinked polymer.

[0042] (Measurement conditions) Temperature: 25℃ Humidity: 70% Load cell: USM-500N Pulling speed: 10 mm / min Distance between gauge lines: 35mm

[0043] [Method of manufacturing cross-linked polymer] The crosslinked polymer can be produced, for example, by copolymerizing a monomer component with a compound having two or more radically polymerizable functional groups. The polymerization method is not particularly limited, but a radical polymerization reaction using a radical polymerization initiator is preferred.

[0044] The radical polymerization initiator is not particularly limited, but examples thereof include hydrogen peroxide, ammonium persulfate, potassium persulfate, t-butyl hydroperoxide, azobisisobutyronitrile, and 4,4'-azobis(4-cyanovaleric acid).

[0045] Examples of the solvent used in the polymerization reaction include dimethyl sulfoxide, N,N-dimethylformamide, benzene, ethanol, methanol, water, and mixed solvents thereof.

[0046] The reaction temperature and reaction time may be appropriately selected depending on the raw materials and the types of radical polymerization initiator used, etc. Usually, the reaction temperature is 25 to 70° C., and the reaction time is 1 to 24 hours.

[0047] [Applications of cross-linked polymers] The crosslinked polymer can be used in the form of a molded article such as a sheet. The shape of the molded article of the crosslinked polymer is not particularly limited, and examples thereof include sheets. The molded article of the crosslinked polymer can be used as an antibacterial sheet, and specific examples thereof include protective films for handrails, handles, elevator buttons, etc., and mats. The molded article of the crosslinked polymer can also be used as food containers and packaging or cooking utensils. Since the crosslinked polymer has low water absorption, it is less likely to deform even when in contact with water. Therefore, the crosslinked polymer is preferably used in applications where it is used in contact with water and antibacterial properties are required. Examples of such applications include food containers and packaging and cooking utensils.

[0048] Specific examples of food containers and packaging include food storage containers and containers and packaging for meat or fresh fish.

[0049] Examples of cooking utensils include cutting boards and bowls.

[0050] [Method for manufacturing crosslinked polymer molded body] A crosslinked polymer molded article can be produced, for example, by copolymerizing a monomer component and a compound having two or more radically polymerizable functional groups in a vessel. The polymerization conditions are the same as those in the above-mentioned method for producing a crosslinked polymer. A sheet-like molded article can be obtained by carrying out the reaction in a vessel with a flat bottom. [Example]

[0051] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0052] [Raw materials] (Vinylbenzyl)trimethylammonium chloride (VBTMA), Sigma-Aldrich Styrene, Tokyo Chemical Industry Co., Ltd. Diethylene glycol dimethacrylate, Sigma-Aldrich Azobisisobutyronitrile, Tokyo Chemical Industry Co., Ltd. 4,4'-Azobis(4-cyanovaleric acid), Sigma-Aldrich

[0053] [Example 1] A monomer solution was prepared by adding 0.10587 g (0.5 mmol) of (vinylbenzyl)trimethylammonium chloride, 0.88528 g (8.5 mmol) of styrene, and 0.24227 g (1 mmol) of diethylene glycol dimethacrylate to 4.5 mL of dimethyl sulfoxide in a 20 mL vial. 14.01 mg (0.05 mmol) of 4,4'-azobis(4-cyanovaleric acid) was added to 1.0 mL of dimethyl sulfoxide in a 2.2 mL vial and dissolved. The resulting solution was added to the monomer solution. The wall of the 2.2 mL vial was washed with 0.5 mL of dimethyl sulfoxide, and this solution was added to the monomer solution. The total amount of dimethyl sulfoxide used was 6.0 mL. The mixture was heated to 60 °C in an oil bath and reacted for 20 hours to obtain a reaction solution containing a crosslinked polymer. The reaction was carried out under a nitrogen atmosphere. The solid was removed from the resulting reaction solution and immersed in 300 mL of ethanol for one week to remove unreacted monomers and other components. The ethanol was replaced once a day. The solid was then immersed in 300 mL of distilled water for one week. The distilled water was replaced once a day. These procedures yielded a crosslinked polymer sheet approximately 2 cm in diameter.

[0054] [Examples 2 to 4] The same procedure as in Example 1 was carried out, except that the amounts of (vinylbenzyl)trimethylammonium chloride, styrene, and diethylene glycol dimethacrylate were changed as shown in Table 1. By these procedures, a crosslinked polymer sheet having a diameter of approximately 2 cm was obtained.

[0055] [Comparative Examples 1 to 2] The same procedure as in Example 1 was carried out, except that the blending amounts of (vinylbenzyl)trimethylammonium chloride, styrene, and diethylene glycol dimethacrylate were as shown in Table 1. In Comparative Example 1, a crosslinked polymer sheet was obtained that expanded to a diameter of about 5 cm. In Comparative Example 2, the crosslinked polymer absorbed a large amount of water and expanded significantly. The crosslinked polymer of Comparative Example 2 was prone to crumbling and was unable to maintain its shape.

[0056] [Table 1]

[0057] [Example 5] A monomer solution was prepared by adding 0.42 g (2 mmol) of (vinylbenzyl)trimethylammonium chloride, 3.54 g (34 mmol) of styrene, and 0.97 g (4 mmol) of diethylene glycol dimethacrylate to 25 mL of dimethyl sulfoxide in a 300 mL Erlenmeyer flask. 0.056 g (0.2 mmol) of 4,4'-azobis(4-cyanovaleric acid) was dissolved in 4 mL of dimethyl sulfoxide in a 20 mL vial. The resulting solution was then poured into the monomer solution. The wall of the 20 mL vial was rinsed with 1 mL of dimethyl sulfoxide, and this solution was then poured into the monomer solution. The total amount of dimethyl sulfoxide used was 30 mL. The mixture was heated to 60 °C in an oil bath and reacted for 20 hours to obtain a reaction solution containing a crosslinked polymer. The reaction was carried out under a nitrogen atmosphere. The solid was removed from the resulting reaction solution and immersed in 1000 mL of ethanol for 5 days to remove unreacted monomers and other components. The ethanol was replaced once a day. The solid was then immersed in 1000 mL of distilled water for 5 days. The distilled water was replaced once a day. These procedures yielded a crosslinked polymer sheet approximately 6 cm in diameter.

[0058] [Example 6] The same procedure as in Example 5 was carried out, except that the amounts of (vinylbenzyl)trimethylammonium chloride, styrene, and diethylene glycol dimethacrylate were changed as shown in Table 2. By these procedures, a crosslinked polymer sheet having a diameter of approximately 6 cm was obtained.

[0059] [Table 2]

[0060] [Reference example 1] A monomer solution was prepared by adding 1.0415 g (10 mmol) of styrene to 4 mL of a mixed solvent of N,N-dimethylformamide and distilled water (volume ratio 4:1) in a 50 mL polymerization tube. 0.00821 g (0.05 mmol) of azobisisobutyronitrile was dissolved in 0.5 mL of a mixed solvent of N,N-dimethylformamide and distilled water (volume ratio 4:1) in a 2.2 mL vial. The resulting solution was added to the monomer solution. The wall of the 2.2 mL vial was washed with 0.5 mL of a mixed solvent of N,N-dimethylformamide and distilled water (volume ratio 4:1), and this solution was added to the monomer solution. The total amount of mixed solvent used was 5 mL. The mixture was heated to 70 °C in an oil bath and reacted for 20 hours with stirring to obtain a reaction solution containing styrene homopolymer. The reaction was carried out under a nitrogen atmosphere. The mixture was then purified by dialysis using acetone. Further, the mixture was dried under reduced pressure to recover a styrene homopolymer.

[0061] [Reference example 2] A monomer solution was prepared by adding 0.21173 g (1 mmol) of (vinylbenzyl)trimethylammonium chloride and 1.97885 g (19 mmol) of styrene to 10 mL of dimethyl sulfoxide in a 50 mL polymerization tube. 0.01642 g (0.1 mmol) of azobisisobutyronitrile was dissolved in 4 mL of dimethyl sulfoxide in a 20 mL vial. The resulting solution was added to the monomer solution. The wall of the 20 mL vial was washed with 1 mL of dimethyl sulfoxide, and this solution was added to the monomer solution. The total amount of dimethyl sulfoxide used was 15 mL. The mixture was heated to 70 °C in an oil bath and reacted for 20 hours with stirring to obtain a reaction solution containing a VBTMA / styrene copolymer. The reaction was carried out under a nitrogen atmosphere. The product was then purified by dialysis using water / ethanol and ethanol. The VBTMA / styrene copolymer was then recovered by drying under reduced pressure.

[0062] [Reference examples 3~6] A copolymer of VBTMA and styrene was obtained by the same operation as in Reference Example 2, except that the amounts of (vinylbenzyl)trimethylammonium chloride and styrene were changed as shown in Table 3. However, in Reference Example 4, a total of 25 mL of dimethyl sulfoxide was used as the polymerization solvent, and in Reference Example 5, a total of 20 mL of dimethyl sulfoxide was used.

[0063] [Reference example 7] A monomer solution was prepared by adding 2.1173 g (10 mmol) of (vinylbenzyl)trimethylammonium chloride to 5 mL of a mixed solvent of N,N-dimethylformamide and distilled water (volume ratio 2:1) in a 50 mL polymerization tube. 0.00821 g (0.05 mmol) of azobisisobutyronitrile was dissolved in 0.5 mL of a mixed solvent of N,N-dimethylformamide and distilled water (volume ratio 2:1) in a 2.2 mL vial. The resulting solution was added to the monomer solution. The wall of the 2.2 mL vial was washed with 0.5 mL of a mixed solvent of N,N-dimethylformamide and distilled water (volume ratio 2:1), and this solution was then added to the monomer solution. The total amount of the mixed solvent used was 6 mL. The mixture was heated to 70 °C in an oil bath and reacted for 20 hours with stirring to obtain a reaction solution containing VBTMA homopolymer. The reaction was carried out under a nitrogen atmosphere. The product was then purified by dialysis using acetone, followed by dialysis using water / ethanol and water, and then freeze-dried to recover the VBTMA homopolymer.

[0064] [Table 3]

[0065] [evaluation] (1) Water absorption The water absorbency of the crosslinked polymer was evaluated by its degree of swelling in water. The lower the degree of swelling in water, the lower the water absorbency. The evaluation of water absorbency was carried out using the crosslinked polymers of Examples 1 to 4 and Comparative Examples 1 and 2. Specifically, the crosslinked polymer was dried in an oven at 40°C for 48 hours and then further dried under reduced pressure for one day. The mass of the crosslinked polymer after drying was measured and determined as the mass (mg) of the crosslinked polymer after drying. 20 mL of water vapor, a sufficient amount of water for swelling, was added to 30 mg of the crosslinked polymer after drying, and the mixture was allowed to stand at 25°C for 24 hours. The crosslinked polymer was removed from the distilled water, and the surface moisture was lightly wiped off with a paper cloth. The mass of the crosslinked polymer was then measured and determined as the mass (mg) of the crosslinked polymer after immersion in water. The obtained value was used to calculate the swelling degree of the crosslinked polymer in water according to the following formula: Swelling degree of crosslinked polymer in water = mass of crosslinked polymer after immersion in water (mg) / mass of crosslinked polymer after drying (mg) The results are shown in Table 1.

[0066] (2) Antibacterial properties Antibacterial properties were evaluated based on JIS Z 2801:2010, "Antibacterial Products - Antibacterial Test Methods, Antibacterial Effect." The antibacterial properties were evaluated using the crosslinked polymers of Examples 5 and 6. Specifically, polyethylene film cut into 4 cm x 4 cm pieces was wiped with alcohol cotton and placed under a UV lamp. The crosslinked polymer sheet was gently wiped dry with a paper rag. Chicken thighs that had been frozen for two days after production were thawed under running water and the drips were collected. The crosslinked polymer sheet was placed in a petri dish (φ100 x 20 mm), and 0.4 mL of the bacterial solution was dropped into the center. A polyethylene film was then placed over the sheet to completely cover the drips. The petri dish lid was closed and the sample was left to stand at 25°C for 24 hours. After standing, the polyethylene film and crosslinked polymer sheet were placed in a stomacher bag, and 10 mL of SCDLP medium was added. The contents of the stomacher bag were kneaded for 60 seconds to wash out microorganisms. The obtained bacterial solution was immediately subjected to the pour plate culture method, and the viable cell counts (CFU / cm) of various microorganisms were measured. 2 As a control, a polyethylene film cut to a size of 5 cm x 5 cm was used instead of the crosslinked polymer sheet, and the same evaluation was carried out. The results are shown in Table 4.

[0067] The obtained viable cell count was used to calculate the antibacterial activity value R according to the following formula. R=(u t -u0)-(A t -u0)=u t -A t R: Antibacterial activity value u t : Logarithm of viable cell count 24 hours after inoculation of the control bacterial solution u0: logarithm of the number of viable bacteria immediately after inoculation of the control bacterial solution A t : Logarithmic value of viable bacteria count 24 hours after inoculation of bacterial solution on cross-linked polymer sheet The results are shown in Table 4. If the antibacterial activity value R is greater than 2.0, it can be said that there is an antibacterial effect.

[0068] [Table 4]

[0069] (3) Tensile strength The tensile strength was evaluated using the crosslinked polymer of Example 6. Specifically, a test piece 55 mm long and 8 mm wide was cut from the crosslinked polymer sheet using a cutter. The test piece had a thickness of 4.5 mm. A tensile test was performed on this test piece using a benchtop tension / compression testing machine (MCT-2150, A&D Co., Ltd.) under the following conditions. The maximum point stress was 3.93 MPa. (Measurement conditions) Temperature: 25℃ Humidity: 70% Load cell: USM-500N Pulling speed: 10 mm / min Distance between gauge lines: 35mm

[0070] (5) Thermal stability Thermal stability was evaluated based on the decomposition temperature of the copolymer. The higher the decomposition temperature, the higher the thermal stability. Thermal stability was evaluated using the copolymers of Reference Examples 1 to 7. Specifically, measurements were carried out using a differential thermal analyzer (TG-DTA2020S / MS, Bruker) at a heating rate of 10°C / min in a nitrogen gas atmosphere. The decomposition temperature (°C) was determined as the temperature at which the mass of the copolymer decreased by 10%, based on the mass of the copolymer at 150°C. The results are shown in Table 3 and Figure 1.

[0071] FIG. 1 suggests that the thermal stability of the (vinylbenzyl)trimethylammonium chloride copolymer is improved by adjusting the content of (vinylbenzyl)trimethylammonium chloride to less than 15 mol %.

Claims

1. a structural unit derived from (vinylbenzyl)trimethylammonium chloride; a structural unit derived from a hydrophobic monomer; Contains A crosslinked polymer crosslinked by a compound having two or more radically polymerizable functional groups, the content of the structural units derived from (vinylbenzyl)trimethylammonium chloride in all structural units of the crosslinked polymer is 1 mol % or more and less than 15 mol %; the content of the structural units derived from the hydrophobic monomer in all structural units of the crosslinked polymer is 55 to 89 mol %; the content of the structural units derived from the compound having two or more radically polymerizable functional groups is 10 to 30 mol % of all structural units of the crosslinked polymer, A crosslinked polymer, wherein the hydrophobic monomer is at least one selected from the group consisting of an aromatic vinyl monomer and an olefin monomer.

2. a structural unit derived from (vinylbenzyl)trimethylammonium chloride; a structural unit derived from an aromatic vinyl monomer; A crosslinked polymer comprising: The crosslinked polymer is The structural unit derived from the (vinylbenzyl)trimethylammonium chloride is contained in an amount of 1.0 to 24.0% by mass, The aromatic vinyl monomer-derived structural unit is contained in an amount of 35.0 to 78.0% by mass, A crosslinked polymer having a swelling index in water of 1.00 to 1.

35.

3. The crosslinked polymer according to claim 1 or 2, having a tensile strength of 2 to 7 MPa.

4. A molded article of the crosslinked polymer according to claim 1 or 2.

5. An antibacterial sheet comprising the molded article according to claim 4.

6. A food container / packaging comprising the molded article according to claim 4.

7. A cooking utensil comprising the molded article according to claim 4.

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