JP2018203869A - Crosslinking agent - Google Patents

Abstract

To provide a novel crosslinking agent including a vinyl alcohol-based polymer that has both high crosslinking reactivity and safety and to provide a method for producing the crosslinking agent.SOLUTION: The crosslinking agent includes a vinyl alcohol-based polymer having aldehyde groups or acetalized products thereof at both terminals of a molecular chain, having a content of the aldehyde groups or the acetalized products thereof based on the total structural units of the vinyl alcohol-based polymer of 0.4 to 2.0 mol%, having a molecular weight distribution (Mw/Mn) of 1.01 to 1.90, having a number-average molecular weight of 500 to 20,000 and being negative in test results for mutagenicity by AMES test. The method for producing the crosslinking agent comprises performing controlled radical polymerization in the presence of a radical polymerization initiator and a polyfunctional iodine compound to thereby produce a vinyl ester-based polymer having a plurality of C-I bonds introduced thereinto, bringing the polymer into contact with water to convert the C-I bond into aldehyde and further saponifying the vinyl ester-based polymer to produce the vinyl alcohol-based polymer.SELECTED DRAWING: None

Description

  The present invention relates to a novel crosslinking agent having both high reactivity and safety and a method for producing the same.

  Hydrophilic polymers typified by vinyl alcohol polymers have excellent strength and barrier properties due to hydrogen bonding, so they are used for paper processing, fiber processing, stabilizers for barrier materials and emulsions, etc. Has been. On the other hand, since hydrophilic polymers have high hydrophilicity, a water resistance treatment after molding may be required depending on applications. In particular, when a high level of water resistance such as hot water resistance is required, a method of chemically introducing a crosslinked structure is necessary. There are various methods for making a hydrophilic polymer such as a vinyl alcohol polymer water resistant by chemical crosslinking. The most widely used technique is a technique of chemical crosslinking by a reaction between a polyfunctional aldehyde compound and a hydroxyl group of a hydrophilic polymer. In this method, for example, water-soluble dialdehydes such as glyoxal and glutaraldehyde have been conventionally used suitably, but these compounds are mutagenic substances and are a safety problem caused by residues and decomposition products. Have

  On the other hand, polyfunctional aldehyde compounds that are not mutagenic substances are also known. For example, nonangial is known to show negative mutagenicity in the AMES test. However, a polyfunctional aldehyde compound having a long-chain alkyl group such as nonanediol is hydrophobic and insoluble in water, and when the hydrophilic polymer is subjected to a crosslinking treatment, the compatibility with the hydrophilic polymer is poor, and There was a problem that water could not be used as a solvent.

  Patent Documents 1 and 2 describe vinyl alcohol polymers having an aldehyde group at one or both ends of a molecular chain. Non-Patent Document 1 describes polyvinyl acetate in which an aldehyde group is introduced into one end of a molecular chain, and exemplifies a method for efficiently introducing an aldehyde group into a terminating end of a vinyl ester polymer.

Japanese Patent Laid-Open No. 7-301913 JP 2001-288219 A

Macromolecules 2003, 36, 9346-9354

However, in Patent Documents 1 and 2, although the basic skeleton is a vinyl alcohol polymer, water solubility is excellent. However, since the vinyl alcohol polymer is obtained by oxidative decomposition of a molecular chain, the structure control is difficult, and the crosslinking agent It was difficult to control the reactivity and safety as. In Non-Patent Document 1, since an aldehyde group is introduced only at one end, it does not have a function as a crosslinking agent. Therefore, there is a demand for a crosslinking agent containing a vinyl alcohol polymer that has an excellent crosslinking effect and has safety.
An object of this invention is to provide the novel crosslinking agent which has high crosslinking reactivity and safety | security, and its manufacturing method.

  As a result of intensive studies, the present inventors have found that the above-described problems can be solved by a specific vinyl alcohol polymer having an aldehyde group or an acetalized compound, and further studies have been made based on this finding. The present invention has been completed.

According to the present invention, the present invention relates to the following [1] to [10].
[1] A cross-linking agent comprising a vinyl alcohol polymer having an aldehyde group or an acetalized product thereof and having negative mutagenicity by an AMES test.
[2] The crosslinking agent according to [1], wherein the vinyl alcohol polymer has a molecular weight distribution (Mw / Mn) of 1.01-1.90.
[3] The crosslinking agent according to [1] or [2], wherein the vinyl alcohol polymer has a number average molecular weight of 500 to 20,000.
[4] The crosslinking agent according to any one of [1] to [3], wherein the content of the aldehyde group or an acetalized product thereof is 0.4 to 2.0 mol% with respect to all the structural units of the vinyl alcohol polymer. .
[5] The crosslinking agent according to any one of [1] to [4], wherein the vinyl alcohol polymer has an aldehyde group or an acetalized product thereof at both ends of the molecular chain.
[6] The crosslinking agent according to any one of [1] to [5], wherein the saponification degree of the vinyl alcohol polymer is 50 mol% or more.
[7] The crosslinking agent according to any one of [1] to [6], which dissolves 30 parts by mass or more with respect to 100 parts by mass of water at 25 ° C.
[8] The method for producing a crosslinking agent according to any one of [1] to [7], comprising a step of radical polymerization of a vinyl ester monomer in the presence of a polyfunctional iodine compound.
[9] The method for producing a crosslinking agent according to [8], comprising the following steps 1 to 3.
Step 1: Polymerize a vinyl ester monomer by controlled radical polymerization in the presence of a radical polymerization initiator and a polyfunctional iodine compound to obtain a vinyl ester polymer (1) into which a plurality of carbon-iodine bonds are introduced. Step Step 2: The vinyl ester polymer (1) obtained in Step 1 is brought into contact with water, and the carbon-iodine bond in the vinyl ester polymer (1) is converted to an aldehyde group to give a vinyl ester. Step of obtaining a polymer (2) Step 3: Saponifying the vinyl ester polymer (2) obtained in Step 2 to obtain the vinyl alcohol polymer [10] The polyfunctional iodine compound is 2 , 4-Diiodo-1,5-pentanedioic acid dimethyl, 2,5-diiodo-1,6-hexanedioic acid diethyl ester, methyl 2,2-diiodoacetate and 2,2-diiodoacetonitrile At least one selected from the group consisting method of crosslinking agent of the [8] or [9].

  ADVANTAGE OF THE INVENTION According to this invention, the novel crosslinking agent which has high crosslinking reactivity and safety | security, and its manufacturing method can be provided. Therefore, taking advantage of such features, the crosslinking agent of the present invention is suitably used as a highly safe crosslinking agent in various applications.

2 is a ¹ H-NMR spectrum of the crosslinking agent 1 obtained in Example 1. 6 is a ¹³ C-NMR spectrum of the crosslinking agent 5 obtained in Example 5. 2 is a two-dimensional ¹ H / ¹³ C-NMR spectrum of the crosslinking agent 5 obtained in Example 5. FIG.

  Hereinafter, an example of an embodiment to which the present invention is applied will be described. The numerical value specified in this specification is a value obtained by the method disclosed in the embodiment or the example. It should be noted that other embodiments are also included in the scope of the present invention as long as they meet the spirit of the present invention.

[Crosslinking agent]
The cross-linking agent of the present invention includes a vinyl alcohol polymer (hereinafter also simply referred to as “PVA”) having an aldehyde group or an acetalized product thereof and having negative mutagenicity by the AMES test. In the present invention, an aldehyde group or an acetalized product thereof is also simply referred to as a “reactive group”.
The cross-linking agent of the present invention has an effect of having both high cross-linking reactivity and safety while having a reactive group that is generally highly toxic from the viewpoint of mutagenicity. Therefore, it can be used for a wide range of applications as a highly safe crosslinking agent for hydrophilic polymers.

  In the present invention, “the acetalized product” means a product in which an aldehyde group has an acetal structure. The structure of the acetalized product of the aldehyde group contained in the PVA according to the present invention is not particularly limited, and examples thereof include acyclic acetals such as dimethyl acetal and diethyl acetal; cyclic acetals acetalized with ethylene glycol, pinacol, and the like . In particular, when the cross-linked product is a hydrophilic polymer having a hydroxyl group, acyclic acetals such as dimethyl acetal and diethyl acetal are preferable, and dimethyl acetal is more preferable from the viewpoint of crosslinking reactivity with the hydroxyl group of the hydrophilic polymer.

The PVA contains an aldehyde group or an acetalized product thereof as a reactive group, but is preferably an aldehyde group from the viewpoint of crosslinking reactivity.
The content of the reactive group with respect to all the structural units of the PVA can be appropriately set according to the required crosslinking reactivity within a range in which the mutagenicity by the AMES test is negative, but is 0.1 to 2.0 mol%. Preferably there is. If it is 0.1 mol% or more, the crosslinking reactivity is improved, and if it is 2.0 mol% or less, mutagenicity can be lowered and safety can be improved. From this viewpoint, more preferably 0.4 to 2.0 mol%, still more preferably 0.5 to 2.0 mol%, still more preferably 0.6 to 2.0 mol%, and particularly preferably 0.7 to 2. mol%. 0 mol%, most preferably 1.0 to 1.5 mol%.
The content of the aldehyde group is measured from ¹ H-NMR according to the method described in Examples. When the PVA contained in the crosslinking agent of the present invention is produced using a control agent having no hydrogen atom, which will be described later, it is measured from ¹³ C-NMR according to the method described in the examples. Further, the content of the acetalized product of the aldehyde group can be measured by the same method as the content of the aldehyde group after the acetalized product is converted into an aldehyde group.
For example, in the production of PVA contained in the crosslinking agent of the present invention, when vinyl acetate is used as the vinyl ester monomer and dimethyl 2,4-diiodo-1,5-pentanedioate is used as the control agent, Based on the structure shown in Formula (1), it calculates as follows.

(In Formula (1), a ¹ and a ² are the number of repeating units of vinyl alcohol units and may be the same or different from each other. B ¹ and b ² are the number of repeating units of vinyl acetate units and are the same as each other. (In formula (1), the arrangement of each unit is not particularly limited, and may be block-like or random.)

In the ¹ H-NMR spectrum of the PVA having the above structure, the integrated value of the peak of δ 2.7 to 3.0 ppm (the proton of the lactone ring (—CHC (O) O—)) is A, and δ 3.3 to 3.9 ppm. The integrated value of the peak (methine proton of vinyl alcohol unit (—CH ₂ CH (OH) —)) is B, and the peak of δ 1.9 to 2.0 ppm (methyl proton of acetyl group of vinyl acetate unit (CH ₃ C (O )-)) Is calculated according to the following formula, where 1/3 is the integrated value of C and D is the integrated value of the peak of δ 9.4 to 9.7 ppm (the proton of the terminal aldehyde group (-CHO)).
Aldehyde group content [mol%] = D / (A + B + C + D) × 100

The position at which the reactive group is introduced into PVA in the crosslinking agent of the present invention is not particularly limited as long as the desired crosslinking reactivity is obtained, but it is preferably introduced at the molecular chain end of PVA. By introducing a reactive group at the end of a molecular chain with high molecular mobility, it is possible to efficiently perform a cross-linking reaction and obtain high cross-linking reactivity, resulting in reduced mutagenicity and safety. Can be improved. From this viewpoint, the PVA preferably has reactive groups at both ends of the molecular chain.
The PVA may be linear or branched. Although a star polymer can be designed by the production method described later, it is preferably a linear polymer from the viewpoint of ease of production, and more preferably reactive groups are introduced at both ends of the linear polymer. .

  The number average molecular weight (Mn) of the PVA is not particularly limited, but is preferably 500 to 30,000. When the number average molecular weight is 500 or more, the mutagenicity can be lowered and the safety can be improved while maintaining the crosslinking reactivity. When the number average molecular weight is 30,000 or less, the crosslinking efficiency is improved. From this viewpoint, it is more preferably 1,000 or more, further preferably 3,000 or more, particularly preferably 5,000, more preferably 20,000 or less, still more preferably 15,000 or less, and particularly preferably 12,000. 000 or less.

The molecular weight distribution (Mw / Mn) of the PVA is not particularly limited, but is preferably 1.01 to 1.90 from the viewpoint of controlling the molecular weight distribution narrowly and obtaining uniform crosslinking reactivity. From this viewpoint, more preferably 1.05 to 1.85, still more preferably 1.10 to 1.85, still more preferably 1.20 to 1.80, particularly preferably 1.30 to 1.80, Preferably it is 1.40 to 1.75, and most preferably 1.50 to 1.70.
The weight average molecular weight (Mw) and the number average molecular weight (Mn) in the present invention are measured with a hexafluoroisopropanol (HFIP) column using polymethyl methacrylate as a standard substance by gel permeation chromatography (GPC) method. It is the value. The specific measurement method is as described in the examples.

The degree of saponification of the PVA according to the present invention is not particularly limited, but when the cross-linked product is a hydrophilic polymer, it is preferably 50 mol% or more, more preferably from the viewpoint of improving compatibility with the hydrophilic polymer. It is 60 mol% or more, more preferably 70 mol% or more, particularly preferably 80 mol% or more, and most preferably 90 mol% or more. The upper limit of the saponification degree of PVA contained in the crosslinking agent of this invention is not specifically limited, What is necessary is just 100 mol% or less. The degree of saponification is measured from ¹ H-NMR in accordance with the method described in the Examples. For example, in the same manner as the above-described method for calculating the content of aldehyde groups, from the integrated values A to D in the ¹ H-NMR spectrum, It is calculated according to the following formula.
Degree of saponification [mol%] = (A + B + D) / (A + B + C + D) × 100

  The PVA contains vinyl alcohol units. Furthermore, you may contain a vinyl ester unit. The PVA is produced by saponifying a vinyl ester polymer obtained by polymerizing a vinyl ester monomer. The arrangement of each unit in the PVA is not particularly limited, and the PVA may be a block polymer or a random polymer.

Examples of the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, n-vinyl butyrate, i-vinyl butyrate, vinyl pivalate, vinyl caprylate, vinyl caprate, vinyl laurate, and myristic acid. Aliphatic vinyl esters such as vinyl, vinyl stearate, vinyl versatate and vinyl valelate; aromatic vinyl esters such as vinyl benzoate; halogen-containing vinyl esters such as vinyl chloroacetate, vinyl trichloroacetate and vinyl trifluoroacetate; Is mentioned. The vinyl ester monomers can be used alone or in combination of two or more. Of these, aliphatic vinyl esters are preferable, and vinyl acetate is more preferable from the economical viewpoint.
The content of vinyl ester units in the vinyl ester polymer is preferably more than 90 mol%, more preferably more than 95 mol%, still more preferably 100 mol%.

The PVA may contain a structural unit derived from a monomer other than the vinyl alcohol unit and the vinyl ester monomer as long as the effect of the present invention is obtained. Other monomers include, for example, α-olefins such as ethylene, propylene, n-butene, isobutylene, 1-hexene; acrylic acid, methyl acrylate, ethyl acrylate, N-propyl acrylate, i-acrylate Unsaturated monomers having an acrylate group such as propyl, N-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacrylic acid, Methyl methacrylate, ethyl methacrylate, N-propyl methacrylate, i-propyl methacrylate, N-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, methacrylic acid Methacrylic acid esters such as octadecyl Unsaturated monomers having N; alkyl N-alkyl (C 1-18) acrylamide such as N-methyl acrylamide, N-ethyl acrylamide, N, N-dimethyl acrylamide, diacetone acrylamide, 2-acrylamidopropane sulfonic acid Acrylamides such as acrylamide-2-methylpropane sulfonic acid or the salt thereof, acrylamidopropyldimethylamine or the acid salt thereof or the quaternary salt thereof; N- such as methacrylamide, N-methyl methacrylamide, N-ethyl methacrylamide, etc. Alkyl (C 1-18) acrylamide, N, N-dimethylmethacrylamide, 2-methacrylamidepropanesulfonic acid or its salt, methacrylamideamidopropylamine or its acid salt or its quaternary salt Tacrylamides; alkyl (C 1-18) vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether , Hydroxyalkyl vinyl ethers, vinyl ethers such as alkoxyalkyl vinyl ethers such as 2,3-diacetoxy-1-vinyloxypropane; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl chloride, vinyl fluoride, vinyl bromide, etc. Vinyl halides; vinylidene halides such as vinylidene chloride and vinylidene fluoride; allyl acetate, 2,3-diacetoxy-1-allyloxy Allyl compounds such as lopan, allyl alcohol, dimethylallyl alcohol, and allyl chloride; unsaturated dicarboxylic acids such as maleic acid, itaconic acid, fumaric acid, crotonic acid, and their salts, or mono- or dialkyl (carbon number 1 to 18) esters thereof N-vinyl amides such as N-vinyl pyrrolidone, N-vinyl formamide, N-vinyl acetamide; vinyl silyl compounds such as vinyl trimethoxysilane; isopropenyl acetate.
The above-mentioned other monomers can be used alone or in combination of two or more.
The content of structural units derived from other monomers is preferably less than 10 mol%, more preferably less than 5 mol%, based on the total structural units constituting the PVA as the amount contained in the PVA. .

  In the present invention, the term “vinyl alcohol polymer” means that the sum of vinyl alcohol units and vinyl ester units is more than 50 mol% (preferably more than 70 mol%, more preferably more than 90 mol%) with respect to all structural units constituting the polymer. , More preferably more than 95 mol%).

The cross-linking agent of the present invention preferably has water solubility that dissolves 30 parts by mass or more with respect to 100 parts by mass of water at 25 ° C. By dissolving in water at a high concentration, it is possible to design a process with a low environmental load in various applications, and to exhibit high crosslinking reactivity as a crosslinking agent for a hydrophilic polymer. Specifically, the water solubility is determined by the following method.
At room temperature (25 ° C.), 30 parts by mass of the crosslinking agent of the present invention is added to 100 parts by mass of ion-exchanged water. The resulting mixture is heated to 100 ° C. at 10 ° C./min while stirring (150 rpm), and then stirring is continued at the temperature. At this time, whether the crosslinking agent dissolves within 120 minutes after the temperature is raised to 100 ° C. is used as a water-soluble index. From the viewpoint of improving the cross-linking reactivity, it is preferable that the cross-linking agent dissolves without remaining within 60 minutes after the temperature is raised to 100 ° C.
And after dissolving 30 mass parts of crosslinking agents with respect to 100 mass parts of 100 degreeC water, when the obtained crosslinking agent aqueous solution is naturally cooled to room temperature (25 degreeC), the crosslinking agent in the said aqueous solution precipitates. It is preferable that the dissolved state can be maintained without being carried out, and it is more preferable to maintain the dissolved state without precipitation of the cross-linking agent even after one day has passed after the aqueous crosslinking agent solution has been cooled to 25 ° C. The presence or absence of the cross-linking agent remains or is visually observed.

The cross-linking agent of the present invention contains the PVA. The content of the PVA in the crosslinking agent is preferably 95% by mass or more, more preferably 99% by mass or more, and further preferably 100% by mass.
The cross-linking agent of the present invention may contain components other than the PVA as long as the effects of the present invention are not impaired. Examples of other components include light stabilizers and antioxidants. The content of other components in the crosslinking agent is preferably 5% by mass or less, more preferably 1% by mass or less.

[Method for producing crosslinking agent]
The method for producing the crosslinking agent of the present invention is not particularly limited. For example, (i) a method including a step of radical polymerization of a vinyl ester monomer in the presence of a control agent, and (ii) an acetalized aldehyde group. Saponification after copolymerization of the monomer with vinyl ester monomer, hydrolysis of acetal if necessary and introduction of aldehyde group, (iii) 1,2-glycol bond of vinyl alcohol polymer Examples include a method of cleaving with chemical, thermal, or mechanical energy. Especially, the manufacturing method of said (i) is preferable. Thereby, the said reactive group can be reliably introduce | transduced by the molecular chain end of PVA. The production method of (i) above using a polyfunctional iodine compound as the control agent is more preferred.

The crosslinking agent of the present invention is preferably produced by a method having the following steps 1 to 3 from the viewpoint of improving the crosslinking reactivity and safety.
Step 1: A step of polymerizing a vinyl ester monomer by controlled radical polymerization in the presence of a radical polymerization initiator and a polyfunctional iodine compound to obtain a vinyl ester polymer (1) into which a plurality of carbon-iodine has been introduced. Step 2: The vinyl ester polymer (1) obtained in Step 1 is brought into contact with water, and the carbon-iodine bond in the vinyl ester polymer (1) is converted into an aldehyde group to produce a vinyl ester type. Step of obtaining the polymer (2) Step 3: Step of saponifying the vinyl ester polymer (2) obtained in Step 2 to obtain the vinyl alcohol polymer Hereinafter, Step 1 to Step 3 will be described in detail. .

(Process 1)
In Step 1, a vinyl ester monomer is polymerized by controlled radical polymerization in the presence of a radical polymerization initiator (hereinafter also simply referred to as “initiator”) and a polyfunctional iodine compound, and a plurality of carbon-iodine is introduced. This is a step of obtaining a vinyl ester polymer (1) (hereinafter also simply referred to as “vinyl ester polymer (1)”).
Controlled radical polymerization is a polymerization reaction in which an equilibrium state exists between a growth radical terminal (active species) and a covalently bonded species (dormant species) in which the active species is bound to a control agent, and the polymerization reaction proceeds. That is. In the above production method, a polyfunctional iodine compound is used as a control agent.

Examples of the polymerization method of the vinyl ester monomer include known methods such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. Among these, from the viewpoint of obtaining a polymer having a narrow molecular weight distribution, a bulk polymerization method in which polymerization is performed without a solvent or a solution polymerization method in which polymerization is performed in various organic solvents is preferable. From the viewpoint of not using a solvent or dispersion medium that may cause a side reaction such as chain transfer, the bulk polymerization method is preferable, and from the viewpoint of adjusting the viscosity of the reaction solution or controlling the polymerization rate, solution polymerization is preferable.
Examples of the organic solvent used as a solvent at the time of solution polymerization include esters such as methyl acetate and ethyl acetate; aromatic hydrocarbons such as toluene; lower alcohols such as methanol and ethanol. Among these, from the viewpoint of preventing chain transfer, esters and aromatic hydrocarbons are preferable, esters are more preferable, and ethyl acetate is more preferable. The addition amount of the organic solvent may be determined in consideration of the viscosity of the reaction solution in accordance with the number average molecular weight of the target PVA. For example, the mass ratio of the organic solvent to the vinyl ester monomer (organic solvent / vinyl ester monomer) is preferably 0.01 to 10. The mass ratio (organic solvent / vinyl ester monomer) is preferably 0.1 or more, and preferably 5 or less.

(Radical polymerization initiator)
As the radical polymerization initiator (initiator), conventionally known azo initiators, peroxide initiators, redox initiators and the like are appropriately selected.
As the azo initiator, 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (4-methoxy-2,4- Dimethylvaleronitrile) (trade name “V-70” manufactured by Wako Pure Chemical Industries, Ltd.).
Peroxide initiators include perisopropyl compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, diethoxyethyl peroxydicarbonate; t-butyl peroxyneodecanate, α-kumi Perester compounds such as ruperoxyneodecanate and t-butylperoxyneodecanate; acetylcyclohexylsulfonyl peroxide; diisobutyryl peroxide; peroxidation such as 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate Things. These may be further combined with potassium persulfate, ammonium persulfate, hydrogen peroxide, or the like to form a peroxide-based initiator.
Examples of the redox initiator include a combination of the above-described peroxide and a reducing agent such as sodium hydrogen sulfite, sodium hydrogen carbonate, tartaric acid, L-ascorbic acid, Rongalite and the like.
Among these initiators, azo initiators are preferable, and 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile) is more preferable from the viewpoint of polymerization at a relatively low temperature and suppressing side reactions. preferable. The addition amount of the initiator differs depending on the polymerization catalyst and cannot be determined unconditionally, and is arbitrarily selected according to the polymerization rate. For example, when 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile) is used as the radical polymerization disclosure agent, the added amount of the initiator is relative to the vinyl ester monomer. Preferably it is 0.01-2 mol%, More preferably, it is 0.1-1.7 mol%, More preferably, it is 0.3-1.5 mol%, Most preferably, it is 0.5-1.5 mol%.

(Polyfunctional iodine compound)
The polyfunctional iodine compound used as a control agent has at least two carbon-iodine bonds in one molecule. In the controlled radical polymerization of the present invention, theoretically, one molecular chain is generated from one carbon-iodine bond of the polyfunctional iodine compound to be added. Therefore, the degree of branching of the resulting vinyl alcohol polymer can be adjusted by the number of carbon-iodine bonds in one molecule of the polyfunctional iodine compound. From the viewpoint of ease of production, the polyfunctional iodine compound is preferably a bifunctional iodine compound having two carbon-iodine bonds in one molecule.

  Examples of the bifunctional iodine compound include aliphatic hydrocarbons such as diiodomethane, 1,2-diiodoethane, 1,4-diiodobutane, 1,6-diiodohexane, 1,8-diiodooctane, and 1,10-diiododecane. Type: Perfluoroalkyl type such as 1,2-diiodoperfluoroethane, 1,4-diiodoperfluorobutane, 1,6-diiodoperfluorohexane; 2,4-diiodo-1,5-pentane Dimethyl acid, Diethyl 2,4-diiodo-1,5-pentanedioate, Dimethyl 2,5-diiodo-1,6-hexanedioate, Diethyl 2,5-diiodo-1,6-hexanedioate, 2, Carbohydrates such as dimethyl 6-diiodo-1,7-heptanedioate, diethyl 2,6-diiodo-1,7-heptanedioate, methyl 2,2-diiodoacetate Acid ester type; Nitrile type such as 2,2-diiodoacetonitrile; 1,2-bis (1-iodoethoxy) ethane, 1-iodo-1- [2- {2- (1-iodoethoxy) ethoxy} ethoxy ] Ethane, 1,4-bis {(1-iodoethoxy) methyl} cyclohexane, 1,4-bis {2- (1-iodoethoxy) ethoxy} benzene, 4,4 ′-(propane-2,2-diyl) ) Ether type such as bis [{2- (1-iodoethoxy) ethoxy} benzene]; and aromatic hydrocarbon type such as 1,4-bis (1′-iodoethyl) benzene. Among these, from the viewpoint of production cost and polymerization control, at least one selected from the group consisting of a carboxylic acid ester type and a nitrile type is preferable, dimethyl 2,4-diiodo-1,5-pentanedicarboxylate, 2,5 -One or more selected from the group consisting of diethyl diiodo-1,6-hexanedioate, methyl 2,2-diiodoacetate and 2,2-diiodoacetonitrile is more preferred, and 2,4-diiodo-1,5 -More preferred is dimethyl pentanedioate. The addition amount of the polyfunctional iodine compound added to the reaction solution is the target vinyl ester polymer (1) and the number average molecular weight and polymerization rate of PVA obtained through the vinyl ester polymer (1). Decided in consideration. For example, with respect to 100 parts by mass of the vinyl ester monomer, it is preferably 0.05 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, further preferably 0.3 to 3 parts by mass, and particularly preferably 0. .5 to 1.5 parts by mass.

  The polymerization temperature in step 1 is preferably 0 ° C to 80 ° C. When the polymerization temperature is 0 ° C. or higher, the polymerization rate becomes sufficient and the productivity is improved. From this viewpoint, the polymerization temperature is preferably 5 ° C or higher, more preferably 10 ° C or higher. On the other hand, when the polymerization temperature is 80 ° C. or lower, a vinyl ester polymer having a narrow molecular weight distribution can be obtained. From this viewpoint, the polymerization temperature is preferably 70 ° C or lower, more preferably 50 ° C or lower, and further preferably 40 ° C or lower.

When the target polymerization rate is reached in step 1, the polymerization reaction is stopped by simultaneously quenching the reaction system, adding a polymerization terminator, or both. The number of moles of the added polymerization terminator is preferably 1 to 100 times the number of moles of the added polyfunctional iodine compound. When the number of moles of the polymerization terminator is 1 or more times the number of moles of the polyfunctional iodine compound, the polymerization can be stopped quickly. On the other hand, when the number of moles of the polymerization terminator is 100 times or less of the number of moles of the polyfunctional iodine compound, the production cost can be reduced.
When the inside of the reaction system is rapidly cooled, there is a method of flowing cooling water through the jacket of the reactor, but a method of adding a liquid medium cooled in advance to the reactor is preferable. In the case of the latter method, when water is used as the liquid medium, a reaction in which the carbon-iodine bond is converted to an aldehyde occurs simultaneously with the termination of the polymerization. Therefore, even if the polymerization termination operation and Step 2 described later are performed at the same time. Good.

In the present invention, the terminal introduction rate of iodine in the vinyl ester polymer (1) is a carbon-iodine bond introduction rate with respect to all molecular chain terminals. The upper limit of the terminal introduction rate is theoretically 100%. However, the production method by controlled radical polymerization of the present invention is a side reaction such as chain transfer or termination reaction compared with a general radical polymerization method which is not controlled at all. However, some of these side reactions occur during the polymerization. Therefore, from the viewpoint of improving the crosslinking reactivity, the terminal introduction rate is preferably 60% or more, more preferably 65% or more, still more preferably 70% or more, and may be 100%. The upper limit of the terminal introduction rate is not particularly limited, but is preferably 90% or less, more preferably 85% or less, and still more preferably 80% or less from the viewpoints of production ease and availability.
The terminal introduction rate of iodine in the vinyl ester polymer (1) is measured from ¹ H-NMR according to the method described in Examples. When the PVA contained in the crosslinking agent of the present invention is produced using the above-mentioned control agent having no hydrogen atom, the measurement is performed from ¹³ C-NMR according to the method described in the examples. For example, when vinyl acetate is used as the vinyl ester monomer of PVA and 2,4-diiodo-1,5-pentanedioic acid dimethyl is used as the control agent, based on the structure represented by the following formula (2) Calculate as follows.

(In formula (2), c ¹ and c ² are the number of repeating units of vinyl acetate units, and may be the same or different from each other.)

In the ¹ H-NMR spectrum of the vinyl ester polymer (1) having the above structure, the integrated value of the peak at δ 3.7 ppm (methyl proton of the methyl ester group at the center of the molecular chain (CH ₃ OC (O) —)) is 6, the integrated value α of the peak of δ 6.7 to 6.8 ppm (methine proton adjacent to the terminal iodine (—CH (OAc) I)) is calculated. When a carbon-iodine bond is introduced at the end of all molecular chains (that is, when the terminal introduction rate is 100%), the peak area of the methyl ester at the center of the molecular chain and the peak area of the methine proton adjacent to the terminal iodine are the above structures. Therefore, the terminal introduction rate of carbon-iodine bond is calculated according to the following formula.
Terminal introduction rate [%] = α / 2 × 100

(Process 2)
In step 2, the vinyl ester polymer (1) obtained in step 1 is brought into contact with water, and the carbon-iodine bond in the vinyl ester polymer (1) is converted to an aldehyde group to produce a vinyl ester. This is a step of obtaining a polymer (2).
The amount of water added in step 2 may be equal to or greater than the equivalent mole of the polyfunctional iodine compound. In order to convert the carbon-iodine bond to an aldehyde group in a short time, the vinyl ester polymer ( 1) 50 mass parts or more are preferable with respect to 100 mass parts, 100 mass parts or more are more preferable, 200 mass parts or more are further more preferable, 300 mass parts is especially preferable.
In Step 2, since the carbon-iodine bond is converted into an aldehyde relatively easily by contact with water, the vinyl ester polymer (2) can be obtained without excessive heating. The temperature of the reaction solution in step 2 is preferably 5 ° C to 50 ° C, more preferably 10 ° C to 40 ° C.
When polymerization is performed using a solvent-free or water-insoluble solvent in Step 1, water is added as it is to convert the carbon-iodine bond to an aldehyde group, and then the organic layer in which the vinyl ester polymer (2) is present. It is also possible to obtain a vinyl ester polymer (2) by removing the aqueous layer after removing the vinyl ester monomer and the solvent remaining in the organic layer. Step 3 may be performed after the vinyl ester polymer (2) is isolated by extraction or the like.
In Step 2, from the viewpoint of sufficiently converting the carbon-iodine bond to an aldehyde group, the vinyl ester polymer (1) is isolated after Step 1 and the vinyl ester polymer (1) is a solvent miscible with water. It is preferable to carry out by adding water after melt | dissolving in this. As the solvent, dimethylformamide, dimethylacetamide, dimethylsulfoxide, acetone, 1,4-dioxane, tetrahydrofuran and the like are preferable.

(Process 3)
Step 3 is a step of saponifying the vinyl ester polymer (2) obtained in Step 2 to obtain the PVA. By saponifying the vinyl ester polymer (2) obtained in step 2, the vinyl ester units in the polymer are converted into vinyl alcohol units, and the vinyl alcohol polymer according to the present invention is obtained.

  The saponification is preferably performed in a state where the vinyl ester polymer (2) is dissolved in an alcohol or a hydrous alcohol. When the vinyl ester polymer (2) obtained in Step 2 is isolated, it is preferably dissolved again in alcohol or hydrous alcohol. In addition, when polymerization is performed using a solvent-free or water-insoluble solvent in Step 1, a water layer and a vinyl ester polymer (2) are present after the carbon-iodine bond is converted to an aldehyde group in Step 2. After separating into two layers with the organic layer and removing the aqueous layer, the vinyl ester monomer and solvent remaining in the organic layer are distilled off while feeding the alcohol or hydrous alcohol to give a vinyl ester heavy polymer. An alcohol or hydrous alcohol solution of the combined (2) can also be prepared.

Examples of the alcohol used for the saponification reaction include lower alcohols such as methanol and ethanol, and methanol is preferred. The alcohol used in the saponification reaction may contain other solvents such as acetone, esters such as methyl acetate and ethyl acetate, and toluene, but the content of other solvents contained in the alcohol is preferably Is 10% by mass or less, more preferably 5% by mass or less.
The addition amount of the alcohol is preferably 50 to 300 parts by mass, more preferably 100 to 200 parts by mass with respect to 100 parts by mass of the vinyl ester polymer (2).
Examples of the catalyst used for the saponification reaction include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkali catalysts such as sodium methylate, and acid catalysts such as mineral acid. Among these, sodium hydroxide is preferable from the viewpoint of easy handling. The amount of sodium hydroxide added is preferably 0.3 to 5 parts by mass, more preferably 0.5 to 3 parts by mass with respect to 100 parts by mass of the vinyl ester polymer (2).

The temperature of the saponification reaction is preferably 20 to 60 ° C, for example. A saponification reaction can be rapidly advanced as it is 20 degreeC or more. When it is 60 ° C. or lower, polyene formation due to dehydration of the hydroxyl group adjacent to the terminal aldehyde group can be prevented, and deterioration of hue can be suppressed.
In addition, when saponifying with an alcoholate such as sodium methylate, a part or all of the terminal aldehyde group may be acetalized, but as described above, it can be used as a crosslinking agent as it is. When converting to an aldehyde group again, the obtained PVA may be brought into contact with an excessive amount of water. As for the temperature at the time of making it contact with water, 20-90 degreeC is preferable.
When a gel-like product is precipitated as the saponification reaction proceeds, the product is separated at that time, and the product is pulverized, washed, and dried to obtain the cross-linking agent of the present invention. .

  The PVA contained in the crosslinking agent of the present invention obtained by the above production method is based on a group derived from a polyfunctional iodine compound, and includes a plurality of vinyl alcohol units and vinyl ester units, and, if necessary, other structural units. It has a polyvinyl alcohol chain and has the reactive group in the polyvinyl alcohol chain. The PVA has two polyvinyl alcohol chains through a group derived from a bifunctional iodine compound from the viewpoint of improving the cross-linking reactivity and the ease of production, and the end of each polyvinyl alcohol chain. A linear polymer having a reactive group is more preferred.

  The cross-linking agent of the present invention can be used for various applications by utilizing its high cross-linking reactivity and safety. For example, it is used for paper coating agents, paper internal additives, pigment binders, adhesives, nonwoven fabric binders, paints, fiber processing agents, fiber glues, films, sheets, bottles, fibers, thickeners, flocculants, etc. It can be used as a crosslinking agent for hydrophilic polymers. Thereby, hydrophilic polymer can be highly water-resistant.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited at all by these Examples. In the examples and comparative examples, “%” and “parts” represent “% by mass” and “parts by mass”, respectively, unless otherwise specified.

[Measurement of number average molecular weight (Mn) and molecular weight distribution (Mw / Mn) of vinyl alcohol polymer]
Size exclusion high performance liquid chromatography device “HLC-8320GP” manufactured by Tosoh Corporation
C ”was used to measure the number average molecular weight (Mn) and the molecular weight distribution (Mw / Mn). The measurement conditions are as follows.
Column: Two HFIP-based columns “GMHHR-H (S)” manufactured by Tosoh Corporation Standard connection: Polymethyl methacrylate Solvent and mobile phase: Sodium trifluoroacetate-HFIP solution (concentration 20 × 10 ⁻³ mol / L)
Flow rate: 0.2mL / min
Temperature: 40 ° C
Sample solution concentration: 0.1% (filtered with a 0.45 μm aperture diameter filter)
Injection volume: 10 μL
Detector: RI

[Measurement of ¹ H-NMR measurement for calculating terminal introduction rate of carbon-iodine bond of vinyl ester polymer (1)]
Using a nuclear magnetic resonance apparatus “LAMBDA 500” manufactured by JEOL Ltd., ¹ H-NMR measurement of the vinyl ester polymer (1) into which a carbon-iodine bond was introduced was performed. The measurement conditions are as follows.
(Measurement condition)
Observation frequency: 500 MHz
Solvent: CDCl ₃
Polymer concentration: 2%
Measurement temperature: 25 ° C
Integration count: 32 times Pulse delay time: 7 seconds Sample rotation speed: 20 Hz
Pulse width (45 ° pulse): 7.5 μsec

[Measurement of ¹ H-NMR measurement for calculating content of aldehyde group (reactive group) of vinyl alcohol polymer]
Calculation was performed by ¹ H-NMR measurement of a vinyl alcohol polymer using a nuclear magnetic resonance apparatus “LAMBDA 500” manufactured by JEOL Ltd. The measurement conditions are as follows.
(Measurement condition)
Observation frequency: 500 MHz
Solvent: DMSO-d ₆
Polymer concentration: 2%
Measurement temperature: 25 ° C
Integration count: 32 times Pulse delay time: 7 seconds Sample rotation speed: 20 Hz
Pulse width (45 ° pulse): 7.5 μsec

[Saponification degree]
The degree of saponification of the vinyl alcohol polymer was determined by performing ¹ H-NMR measurement in the same manner as the ¹ H-NMR measurement method for calculating the content of the aldehyde group (reactive group). From D, the degree of saponification was calculated according to the following formula.
Degree of saponification [mol%] = (A + B + D) / (A + B + C + D) × 100

[Evaluation of water solubility]
After adding 30 parts of the crosslinking agent obtained in the following Examples or Comparative Examples to 100 parts of ion-exchanged water at room temperature (25 ° C.), the resulting mixture was stirred at 150 rpm for 10 ° C./min. The temperature was raised to 100 ° C. and stirring was continued at 100 ° C. And when a crosslinking agent melt | dissolved, heating was stopped and the obtained crosslinking agent aqueous solution was naturally cooled to room temperature (25 degreeC). The dissolution state of the cross-linking agent in this series of operations (remaining cross-linking agent and presence or absence of precipitation) was evaluated visually based on the following criteria. If it is A or more according to the following evaluation criteria, it has sufficient water solubility as a crosslinking agent for the hydrophilic polymer.
A +: After the temperature of the mixture was raised to 100 ° C., the cross-linking agent was dissolved without remaining within 60 minutes, and the obtained cross-linking agent aqueous solution was cooled and dissolved without precipitation even after 1 day. Maintained.
A: After the temperature of the mixture was raised to 100 ° C., the cross-linking agent was dissolved within 120 minutes without remaining, and the obtained aqueous solution of the cross-linking agent was cooled and dissolved without precipitation even after 1 day. Maintained.
B: Even if 120 minutes passed after raising the temperature of the mixture to 100 ° C., the crosslinking agent remained in the mixture and did not dissolve.

[Evaluation of crosslinking reactivity]
70 parts of a commercially available polyvinyl alcohol resin (Kuraray Co., Ltd., grade “PVA 28-98”) as a hydrophilic polymer and 30 parts of a crosslinking agent obtained in the following Examples or Comparative Examples were dissolved in water, and polyvinyl After preparing an aqueous solution in which the concentration of the alcohol resin was 10%, hydrochloric acid was further added to obtain a coating solution adjusted to pH 2.
Next, the coating solution was cast on a 5 cm × 8 cm mold formed by bending the end of a polyethylene terephthalate film, dried in a hot air dryer at 80 ° C. for 30 minutes, and an evaluation film having a thickness of about 40 μm was formed. Produced.
The obtained film for evaluation was immersed in boiling water for 1 hour and boiled, then taken out from the water and vacuum-dried at 80 ° C. for 3 hours, and the mass (W1) was measured. From the obtained mass (W1) and the mass before immersion (W2), the elution rate under boiling conditions was calculated according to the following formula, and the elution rate was used as an index of crosslinking reactivity. If the elution rate is 50% or less, it indicates that the crosslinking reaction is sufficient. From this viewpoint, it is preferably 40% or less, more preferably 30% or less, and still more preferably 20% or less. In addition, when the film for evaluation melt | dissolved during immersion in water, it evaluated as "impossible to measure."
Elution rate (%) = [([W2] − [W1]) / [W2]] × 100

[Safety evaluation (AMES test)]
The crosslinking agents obtained in the following Examples or Comparative Examples were used as OECD Test Guideline No. In accordance with 471, an AMES test (mutagenicity test) by a preincubation method was performed using Salmonella TA98 and TA100 strains. Water and dimethyl sulfoxide were used as solvents, and test substances were evaluated in a volume range of 20 to 5000 μg / plate, both with and without metabolic activity by rat liver homogenate (S9mix). The negative control was dimethyl sulfoxide, and when the number of colonies forming more than twice that of the negative control was determined to be positive, a cross-linking agent that was positive in any one of the above concentration ranges was determined as “ “Positive”, a cross-linking agent for which no positive determination was observed in all concentration ranges was defined as “negative”.
In addition, the validity of the test was confirmed by simultaneously evaluating benzopyrene, which is a positive standard substance, and forming more than twice as many colonies as compared with the negative control.

[Synthesis Example 1]
In a reactor equipped with a stirrer and a reflux tube, 2.8 parts of copper (I) chloride, 13.9 parts of N, N, N ′, N ″, N ″ -pentamethyldiethylenetriamine, 857 parts of methyl dichloroacetate, acrylic 138 parts of methyl acid and 8.7 parts of toluene were added and stirred at 80 ° C. for 82 hours. Then, it moved to the dry ice / methanol bath (-78 degreeC), and quenched and stopped reaction. Residual methyl acrylate and toluene were distilled off under reduced pressure, and then the copper catalyst was removed by a silica column using hexane / diethyl ether as a developing solvent. The resulting residue was purified by distillation to synthesize dimethyl 2,4-dichloro-1,5-pentanedioate.
Next, a reactor equipped with a stirrer and a reflux tube was charged with 89.9 parts of sodium iodide, 29.6 parts of dimethyl 2,4-dichloro-1,5-pentanedioate obtained above, and 315 parts of acetone. And stirred at 50 ° C. for 10 hours. Acetone was distilled off under reduced pressure, methylene chloride and an aqueous sodium thiosulfate solution (concentration 20%) were added, and the methylene chloride layer was extracted. The methylene chloride layer was distilled off under reduced pressure, and the resulting residue was recrystallized and purified with hexane / diethyl ether to synthesize dimethyl 2,4-diiodo-1,5-pentanedioate.

[Example 1]
(Process 1)
In a reactor equipped with a stirrer, reflux condenser, and initiator addition port, 0.9 part of dimethyl 2,4-diiodo-1,5-pentanedioate obtained in Synthesis Example 1 as a control agent, initiator 2.8 parts of 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile) (manufactured by Wako Pure Chemical Industries, Ltd., trade name “V-70”) was added, and the inside of the reactor was evacuated. After that, inert gas substitution into which nitrogen was introduced was performed three times.
Thereafter, 79.1 parts of vinyl acetate purified by simple distillation and 9.5 parts of ethyl acetate as an organic solvent were added, and then the reactor was immersed in a water bath and stirred at an internal temperature of 20 ° C. Sampling was performed as appropriate, and the progress of polymerization was confirmed from the solid content concentration. When the conversion rate of vinyl acetate reached 25%, the water bath was replaced with a dry ice / acetone bath (-78 ° C) and quenched to stop the reaction. did. Residual vinyl acetate and ethyl acetate were distilled off under reduced pressure, and ethyl acetate was added and dissolved again. The solution was added dropwise to hexane to precipitate and collect polyvinyl acetate. Thereafter, it was dried in a vacuum dryer at 40 ° C. for 24 hours to obtain polyvinyl acetate (1-1) having iodine introduced into both ends. The structure of polyvinyl acetate (1-1) was confirmed by the following formula (2) by ¹ H-NMR spectrum.

(In formula (2), c ¹ and c ² are the same as above.)

(Calculation of terminal introduction rate)
From the NMR spectrum of polyvinyl acetate (1-1), the integral value of the peak at δ 3.7 ppm (methyl proton of the methyl ester group at the center of the molecular chain (CH ₃ OC (O) —)) is 6, and δ6.7 to 6.8ppm peak was calculated integral value alpha ¹ for (adjacent to the terminal iodine methine proton (-OCHI)).
As described above, the terminal introduction rate of the carbon-iodine bond of polyvinyl acetate (1-1) calculated according to the following formula was 75%.
Terminal introduction rate ^{[%] = α 1/2} × 100

(Process 2)
Next, 20 parts of polyvinyl acetate (1-1) obtained in Step 1 and 120 parts of tetrahydrofuran were dissolved in the same reactor as above, and then 60 parts of water was added and stirred at room temperature for 1 hour. . Tetrahydrofuran was distilled off under reduced pressure, ethyl acetate and water were added, and the ethyl acetate layer was extracted. The ethyl acetate layer was distilled off under reduced pressure to obtain polyvinyl acetate (2-1) having aldehyde groups introduced at both ends. When polyvinyl acetate (2-1) was analyzed by ¹ H-NMR, it was confirmed that the peak of the methine proton adjacent to the terminal iodine confirmed in Step 1 completely disappeared and an aldehyde group was introduced at the terminal. confirmed.

(Process 3)
Next, 15.0 parts of polyvinyl acetate (2-1) obtained in Step 2 and 21.7 parts of methanol were added to the same reactor as described above, and the mixture was stirred and dissolved at 40 ° C. To this, 0.8 parts of methanol solution of sodium hydroxide (concentration 18%) was added while maintaining the internal temperature at 40 ° C., and saponification reaction was performed at 40 ° C. for 1 hour.
Thereafter, 10.0 parts of methyl acetate and 5.0 parts of water were added to neutralize the remaining alkali, and the powdered precipitate produced by saponification was filtered off and washed with methanol. Thereafter, the powdery precipitate was again filtered and dried in a vacuum dryer at 40 ° C. for 24 hours to obtain PVA in which the aldehyde group was dimethylacetalized. After dissolving the PVA in water and stirring at 80 ° C. for 1 hour, it was cast into a 5 cm × 8 cm mold formed by bending the end of a polyethylene terephthalate film, and dried in a hot air dryer at 80 ° C. for 30 minutes. The obtained film was pulverized to obtain the desired crosslinking agent 1. ^{By 1} H-NMR, it was confirmed that the structure of the crosslinking agent 1 was the following formula (1). Table 1 shows the structural analysis results and the evaluation results. A ¹ H-NMR spectrum of the crosslinking agent 1 is shown in FIG.

(In the formula (1), a ¹ , a ² , b ¹ and b ² are the same as described above. In the formula (1), the arrangement of each unit is not particularly limited. May be.)

[Aldehyde group content]
From the ¹ H-NMR spectrum of the crosslinking agent 1, the integrated value of the peak at δ2.7 to 3.0 ppm (-CHC (O) O— of the lactone ring) is A ¹ , and the peak at δ3.3 to 3.9 ppm (vinyl) The integral value of the methine proton (—CH ₂ CH (OH) —) of the alcohol unit is B ¹ , the peak of δ1.9 to 2.0 ppm (the methyl proton of the acetyl group of the vinyl acetate unit (CH ₃ C (O) — 1/3 of the integral value of the)) ^{C 1,} the integral value of the peak of Deruta9.4～9.7Ppm (protons of the terminal aldehyde groups (-CHO)) was ^{D 1.} The aldehyde group content of the crosslinking agent 1 was calculated according to the following formula.
Aldehyde group content [mol%] = D ¹ / (A ¹ + B ¹ + C ¹ + D ¹ ) × 100

[Example 2]
In Step 1 of Example 1, 0.4 parts of dimethyl 2,4-diiodo-1,5-pentanedioate as a control agent and 2,2′-azobis (4-methoxy-2,4-dimethyl as an initiator) Valeronitrile) (V-70) 1.2 parts and 11.6 parts of ethyl acetate as an organic solvent were added, and the polymerization reaction was stopped at a conversion rate of 30%. Thus, polyvinyl acetate (1-2) was obtained. The terminal introduction rate of polyvinyl acetate (1-2) was 74%.
Next, the reaction similar to the process 2 of Example 1 was performed using polyvinyl acetate (1-2), and the polyvinyl acetate (2-2) was obtained. When polyvinyl acetate (2-2) was analyzed by ¹ H-NMR, it was confirmed that the peak of the methine proton adjacent to the terminal iodine disappeared completely and an aldehyde group was introduced at the terminal.
Next, polyvinyl acetate (2-2) was saponified in the same manner as in Step 3 of Example 1 to obtain the intended crosslinking agent 2. Table 1 shows the structural analysis results and the evaluation results.

[Example 3]
In Step 1 of Example 1, 0.2 part of dimethyl 2,4-diiodo-1,5-pentanedioate as a control agent and 2,2′-azobis (4-methoxy-2,4-dimethyl as an initiator Valeronitrile) (V-70) 0.6 parts and 12.7 parts of ethyl acetate as an organic solvent were added, and the polymerization reaction was stopped at a conversion rate of 25%. Thus, polyvinyl acetate (1-3) was obtained. The terminal introduction rate of polyvinyl acetate (1-3) was 74%.
Next, the reaction similar to the process 2 of Example 1 was performed using the polyvinyl acetate (1-3), and the polyvinyl acetate (2-3) was obtained. When polyvinyl acetate (2-3) was analyzed by ¹ H-NMR, it was confirmed that the peak of the methine proton adjacent to the terminal iodine disappeared completely and an aldehyde group was introduced at the terminal.
Next, polyvinyl acetate (2-3) was saponified in the same manner as in Step 3 of Example 1 to obtain the intended crosslinking agent 3. Table 1 shows the structural analysis results and the evaluation results.

[Example 4]
In Step 1 of Example 1, 0.1 part of dimethyl 2,4-diiodo-1,5-pentanedioate was used as a control agent, and 2,2′-azobis (4-methoxy-2,4-dimethyl was used as an initiator. Valeronitrile) (V-70) 0.3 parts and 13.2 parts of ethyl acetate as an organic solvent were added, and the polymerization reaction was stopped at a conversion rate of 20%. Thus, polyvinyl acetate (1-4) was obtained. The terminal introduction rate of polyvinyl acetate (1-4) was 72%.
Next, the reaction similar to the process 2 of Example 1 was performed using polyvinyl acetate (1-4), and the polyvinyl acetate (2-4) was obtained. When polyvinyl acetate (2-4) was analyzed by ¹ H-NMR, it was confirmed that the peak of the methine proton adjacent to the terminal iodine disappeared completely and an aldehyde was introduced at the terminal.
Next, the polyvinyl acetate (2-4) was saponified in the same manner as in Step 3 of Example 1 to obtain the desired crosslinking agent 4. Table 1 shows the structural analysis results and the evaluation results.

[Example 5]
Steps 1 and 2 were performed in the same manner as in Example 1. In step 3, PVA having an aldehyde group converted to dimethylacetal is dissolved in water, stirred at 80 ° C. for 1 hour, and then cast on a 5 cm × 8 cm form made by bending the end of a polyethylene terephthalate film. It was carried out in the same manner as in Example 1 except that the drying operation was performed at 80 ° C. for 30 minutes in the dryer and the operation for crushing the obtained film was not performed. That is, in Step 3 of Example 1, after the saponification reaction, the generated powdery precipitate was filtered, washed with methanol, and then dried in a vacuum dryer at 40 ° C. for 24 hours to obtain the desired crosslinking agent 5 Got.
When ¹ H-NMR measurement of the crosslinking agent 5 was performed (solvent: DMSO-d ₆ ), the peak of the aldehyde group could not be confirmed. The results of ¹³ C-NMR measurement and two-dimensional ¹ H / ¹³ C-NMR measurement are shown in FIGS. ^{The 13} C-NMR peak at δ 52 ppm is the peak of the methoxy group of the dimethyl acetal compound (—CH (OCH ₃ ) ₂ ), and the peak of δ 102 to 103 ppm is the peak of the methine group of the dimethyl acetal compound (—CH (OCH ₃ )). ₂ ). Table 1 shows the structural analysis results and the evaluation results. In addition, after converting this acetalization body into an aldehyde group, content of the acetalization body of an aldehyde group was measured by the method similar to content of the said aldehyde group.

[Comparative Example 1]
A commercially available polyvinyl alcohol resin (manufactured by Kuraray Co., Ltd., grade “PVA 3-98”) was used as the crosslinking agent C1. Table 1 shows the structural analysis results and the evaluation results.

[Comparative Example 2]
To a reactor equipped with a stirrer and a reflux condenser, 10 parts of a commercially available polyvinyl alcohol resin (manufactured by Kuraray Co., Ltd., grade “PVA 60-98”) and 90 parts of dimethyl sulfoxide are added and stirred at 80 ° C. Dissolved. Thereafter, it was cooled with ice and cooled to an internal temperature of 5 ° C. To this, 1.05 part of a sodium periodate-dimethyl sulfoxide solution having a concentration of 5% was dropped. After the entire amount was dropped, the internal temperature was raised to 50 ° C. and stirred for 5 hours while maintaining the temperature at 50 ° C. Thereafter, the reaction solution cooled to room temperature was dropped into methanol, and the resulting powdery precipitate was filtered off and dried at 40 ° C. for 24 hours in a vacuum dryer to obtain the desired crosslinking agent C2. Table 1 shows the structural analysis results and the evaluation results.

[Comparative Example 3]
(Process 1 ')
0.5 parts of AIBN [2,2′-azobis (isobutyronitrile)] as an initiator is added to a reactor equipped with a stirrer, a reflux condenser, and an addition port for the initiator, and the inside of the reactor is evacuated. After that, inert gas substitution into which nitrogen was introduced was performed three times.
Thereafter, 1.1 parts of ethyl iodoacetate and 86.0 parts of simple distilled and purified vinyl acetate were added, and then the reactor was immersed in a water bath and stirred at an internal temperature of 72 ° C. Sampling was performed as appropriate, and the progress of polymerization was confirmed from the solid content concentration. When the conversion rate of vinyl acetate reached 35%, the water bath was replaced with an ice bath and quenched to stop the reaction. Residual vinyl acetate and ethyl acetate were distilled off under reduced pressure, and ethyl acetate was added and dissolved again. The solution was added dropwise to hexane to precipitate and collect polyvinyl acetate. Then, it dried for 24 hours with a 40 degreeC vacuum dryer, and obtained the polyvinyl acetate (1'-3) by which the iodine was introduce | transduced into the one terminal.

(Process 2 ')
Next, 20 parts of the polyvinyl acetate (1′-3) obtained in step 1 ′ and 120 parts of tetrahydrofuran are dissolved in the same reactor as described above, and then 60 parts of water is added for 1 hour at room temperature. Stir. Tetrahydrofuran was distilled off under reduced pressure, ethyl acetate and water were added, and the ethyl acetate layer was extracted. The ethyl acetate layer was distilled off under reduced pressure to obtain polyvinyl acetate (2′-3) having an aldehyde group introduced at one end.

(Process 3 ')
Next, 15.0 parts of polyvinyl acetate (2′-3) obtained in step 2 ′ and 21.7 parts of methanol were added to the same reactor as above, and the mixture was stirred and dissolved at 40 ° C. To this, 0.8 parts of methanol solution of sodium hydroxide (concentration 18%) was added while maintaining the internal temperature at 40 ° C., and saponification reaction was performed at 40 ° C. for 1 hour.
Thereafter, 10.0 parts of methyl acetate and 5.0 parts of water were added to neutralize the remaining alkali, and the powdered precipitate produced by saponification was filtered off and washed with methanol. Thereafter, the powdery precipitate was again filtered and dried in a vacuum dryer at 40 ° C. for 24 hours to obtain PVA in which the aldehyde group was dimethylacetalized. After dissolving the PVA in water and stirring at 80 ° C. for 1 hour, it was cast into a 5 cm × 8 cm mold formed by bending the end of a polyethylene terephthalate film, and dried in a hot air dryer at 80 ° C. for 30 minutes. The obtained film was pulverized to obtain the desired crosslinking agent C3. Table 1 shows the structural analysis results and the evaluation results.
^{From the 1} H-NMR spectrum, the integrated value of the peak of δ 3.3 to 3.9 ppm (methine proton of vinyl alcohol unit (—CH ₂ CH (OH) —)) is B ′, and the peak of δ 1.9 to 2.0 ppm. 1 ′ of the integrated value of (methyl acetate of acetyl group of vinyl acetate unit (CH ₃ C (O) —)) is C ′, peak of δ 9.4 to 9.7 ppm (proton of terminal aldehyde group (—CHO)) ) Was D ′. The aldehyde group content was calculated according to the following formula.
Aldehyde group content [mol%] = D ′ / (B ′ + C ′ + D ′) × 100

[Reference Examples 1-2]
Commercially available glutaraldehyde was used as the crosslinking agent R1, and commercially available nonane dial was used as the crosslinking agent R2. Table 1 shows the structural analysis results and the evaluation results.

The reactive group in Table 1 represents an aldehyde group of PVA or an acetalized product thereof.
* 1: Since the nonane dial used in Reference Example 2 was not dissolved in water and its water solubility was B, the crosslinking reactivity was not evaluated.

  From Table 1, as shown in Examples 1 to 5, when the crosslinking agent of the present invention is used as a crosslinking agent for a polyvinyl alcohol resin, the elution rate into water is low and it has high crosslinking reactivity. From this, the crosslinking agent of the present invention can make the hydrophilic polymer highly water resistant by being combined with the hydrophilic polymer. In addition, the PVA according to the present invention has a reactive group that is generally highly toxic from the viewpoint of mutagenicity, but is negative in the AMES test, and has both high crosslinking reactivity and safety.

  The general-purpose polyvinyl alcohol resin used in Comparative Example 1 did not function as a crosslinking agent. The vinyl alcohol polymer having an aldehyde group at the terminal obtained by oxidatively decomposing the general-purpose polyvinyl alcohol resin used in Comparative Example 2 has no control of the reactive group amount and molecular weight, and AMES mutagenicity. The test is positive and safety cannot be guaranteed. The vinyl alcohol polymer introduced with an aldehyde group at one end using the known controlled radical polymerization technique used in Comparative Example 3 did not function as a crosslinking agent. The glutaraldehyde used in Reference Example 1 has high cross-linking reactivity, but was positive in the AMES test and strong toxicity was observed. Nonanediol used in Reference Example 2 was negative in the AMES test and high in safety, but was not water-soluble and therefore did not function as a crosslinking agent for hydrophilic polymers.

  The cross-linking agent of the present invention has high cross-linking reactivity and safety while having a highly toxic aldehyde group or acetalized compound thereof in general from the viewpoint of mutagenicity. It can be used for a wide range of applications as a crosslinking agent for polymers.

Claims (10)

  A crosslinking agent comprising a vinyl alcohol polymer having an aldehyde group or an acetalized product thereof and having a negative mutagenicity by an AMES test.   The cross-linking agent according to claim 1, wherein the vinyl alcohol polymer has a molecular weight distribution (Mw / Mn) of 1.01-1.90.   The crosslinking agent according to claim 1 or 2, wherein the vinyl alcohol polymer has a number average molecular weight of 500 to 20,000.   The crosslinking agent of any one of Claims 1-3 whose content of the aldehyde group with respect to all the structural units of the said vinyl alcohol-type polymer or its acetalization body is 0.4-2.0 mol%.   The crosslinking agent according to any one of claims 1 to 4, wherein the vinyl alcohol polymer has an aldehyde group or an acetalized product thereof at both ends of a molecular chain.   The crosslinking agent according to any one of claims 1 to 5, wherein the saponification degree of the vinyl alcohol polymer is 50 mol% or more.   The crosslinking agent of any one of Claims 1-6 which melt | dissolves 30 mass parts or more with respect to 100 mass parts of 25 degreeC water.   The manufacturing method of the crosslinking agent of any one of Claims 1-7 including the process of radical-polymerizing a vinyl-ester type monomer in presence of a polyfunctional iodine compound. The manufacturing method of the crosslinking agent of Claim 8 which has the following processes 1-3.
Step 1: Polymerize a vinyl ester monomer by controlled radical polymerization in the presence of a radical polymerization initiator and a polyfunctional iodine compound to obtain a vinyl ester polymer (1) into which a plurality of carbon-iodine bonds are introduced. Step Step 2: The vinyl ester polymer (1) obtained in Step 1 is brought into contact with water, and the carbon-iodine bond in the vinyl ester polymer (1) is converted to an aldehyde group to give a vinyl ester. Step of obtaining a polymer (2) Step 3: Saponifying the vinyl ester polymer (2) obtained in Step 2 to obtain the vinyl alcohol polymer   The polyfunctional iodine compound is dimethyl 2,4-diiodo-1,5-pentanedioate, diethyl 2,5-diiodo-1,6-hexanedioate, methyl 2,2-diiodoacetate and 2,2-diiodine. The manufacturing method of the crosslinking agent of Claim 8 or 9 which is 1 or more types selected from the group which consists of iodoacetonitrile.