JPS6051489B2 - Manufacturing method of polyvinyl alcohol hydrogel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the production of a polyvinyl alcohol-based hydrogel.

More specifically, the side chain obtained by reacting one compound selected from the group consisting of radically polymerizable or copolymerizable unsaturated bonds and unsaturated aldehydes with a polyvinyl alcohol polymer has double A modified polyvinyl alcohol-based polymer having a bond is dissolved in water alone or together with a water-soluble unsaturated monomer, a water-soluble radical polymerization catalyst alone or a water-soluble radical polymerization catalyst is added thereto, and the mixture is heated at room temperature. The present invention relates to a method for producing a polyvinyl alcohol hydrogel, which is characterized by polymerization and crosslinking under heating or under heating. Conventionally, known methods for producing hydrogels of polyvinyl alcohol include a method of freezing an aqueous solution of polyvinyl alcohol into a gel, or a method of gelling it by adding borax, etc. However, the former method requires refrigeration equipment. There are some disadvantages, such as the fact that it takes quite a long time for the gelation to occur, and in the latter case, the gelation speed is too fast, so it is difficult to obtain the desired result by pouring it into a mold or coating it on the surface of the base material. The problem was that it was difficult to mold it into the desired shape. The present inventors have conducted various studies on methods for producing polyvinyl alcohol-based hydrogels that do not have these drawbacks, and as a result, they have developed a method for producing polyvinyl alcohol-based hydrogels that is free from these difficulties. A modified polyvinyl alcohol polymer having a double bond in the side chain obtained by the reaction of one compound obtained by the reaction with a polyvinyl alcohol polymer is dissolved in water alone or together with a water-soluble unsaturated monomer. The present invention was completed by discovering a method of polymerizing and crosslinking at room temperature or heating by adding a water-soluble radical polymerization catalyst alone or a water-soluble radical polymerization promoter together with the catalyst.

According to the method of the present invention, the degree of polymerization of the raw material polyvinyl alcohol polymer, the degree of saponification, the type of modifier, the degree of modification, the solution concentration, the type and amount of water-soluble unsaturated monomer added, the type and amount of the polymerization catalyst By appropriately adjusting the gelling temperature and the like, it is possible to easily produce a hydrogel having a desired gelling rate and a desired gel strength.

The polyvinyl alcohol polymer used as a constituent raw material of the modified polyvinyl alcohol polymer used in the present invention has a degree of saponification obtained by saponifying vinyl acetate, other various vinyl ester polymers, and copolymers thereof. 50 mol% or more, various unsaturated monomers of 30 mol% or less based on vinyl acetate and other various vinyl esters, such as α-olefins, vinyl chloride, acrylonitrile, acrylamide, acrylic esters, methacrylic acid Copolymers prepared by copolymerizing esters and having a saponification degree of 50 mol% or more are also included.

The degree of polymerization of these polyvinyl alcohol polymers to be subjected to the reaction is preferably in the range of 100 to 5,000, and the form of the polymer is preferably a powder.
On the other hand, examples of cyclic compounds having radically polymerizable or copolymerizable unsaturated bonds, which are other constituent raw materials of the modified polyvinyl alcohol polymer used in the present invention, include maleic anhydride, itaconic anhydride, Preferred examples include diketene, and unsaturated aldehydes such as acrolein and crotonaldehyde. In some cases, it is also possible to use a suitable mixture of these.

The reaction between the cyclic compound and the polyvinyl alcohol polymer must be carried out in the absence of moisture as much as possible, but compounds with active hydrogen that are reactive with the cyclic compound can also be used as reaction solvents. Unsuitable compounds having no active hydrogen, such as benzene, toluene, hexane, acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, etc., are used. For example, toluene, dioxane, etc. are suitable. There are the following three methods for obtaining a soluble modified polyvinyl alcohol polymer. (1) A polyvinyl alcohol polymer is reacted with an unsaturated cyclic compound in the presence or absence of a catalyst such as sodium bicarbonate or triethylamine.

c(2)
Polyvinyl alcohol polymer with monovalent metal hydroxide,
An unsaturated cyclic compound is reacted in the presence of an alkoxide, salt, etc. However, monovalent metal hydroxides, alkoxides,
The amount of salts etc. added is equal to or less than the amount of the unsaturated cyclic compound. 4(3) Reacting an unsaturated cyclic compound with a polyvinyl alcohol polymer in the presence or absence of a catalyst,
Then, it is treated with a monovalent metal hydroxide, alkoxide salt, ammonium salt, or amine salt. The treatment involves dissolving these compounds in water or other solvents and bringing them into contact with modified polyvinyl alcohol powder to neutralize the carboxyl groups, or by dissolving these compounds or modified polyvinyl alcohol resin in an amount equivalent to or less than the reacted unsaturated cyclic compound. This can be done by simply mixing.

The above reaction involves dissolving a predetermined amount of an unsaturated cyclic compound in a predetermined amount of a solvent, adding a predetermined amount of a polyvinylalcofur polymer, a catalyst, additives, etc., stirring and dispersing the mixture, and heating at a predetermined temperature for a predetermined period of time. Heat and stir.

Since all reactions proceed in a heterogeneous system, it is preferable to carry out the reaction with sufficient stirring so that the polyvinyl alcohol polymer powder is uniformly modified. Also, the reaction temperature is 30
-150'C, preferably 50-100C, and reaction time is 3 to 1 hour, preferably 1 to 5 hours. Modification with an unsaturated cyclic compound can be carried out at will within the range of degree of modification from 1 to 100 mol%, but the amount of unsaturated cyclic compound used must be at least the amount necessary to achieve the desired degree of modification. . The degree of modification of the modified polyvinyl alcohol used for the purpose of the present invention is particularly preferably from 5 to 50 mol%. In addition, the amount of solvent used during the modification reaction is preferably 2 to 5 times the amount of polyvinyl alcohol polymer powder. The solvent used in the reaction is reused. The separated solids are washed with methanol, acetone, etc., and dried. On the other hand, the reaction between the aforementioned unsaturated aldehyde and polyvinyl alcohol polymer is (1)
After dissolving the polyvinyl alcohol polymer in water, the above-mentioned aldehydes, a catalyst, etc. are added and reacted in a homogeneous system.

(2) The reaction can be carried out by dispersing polyvinyl alcohol polymer powder in a solvent such as alcohol, adding the aldehydes, a catalyst, etc., and reacting in a heterogeneous system. Reaction temperature is 30~100C1 reaction time is 30 minutes~
For 10 hours, hydrochloric acid, sulfuric acid, etc. are used as a catalyst, and the degree of modification is preferably 5 to 50 mol%.

In the case of the above-mentioned homogeneous reaction (1), the reaction mixture is filtered, washed and dried after adding a precipitant to precipitate the polymer.

(2) In the case of a heterogeneous system, the solid content is separated by methods such as filtration or centrifugation, and the liquid is collected and reused, while the solid content is washed with methanol, acetone, etc. and dried. .
In the present invention, the modified polyvinyl alcohol polymer having a double bond in the side chain obtained as described above is usually used in 1
It is used by dissolving it in water or other solvents to a concentration of ~5% by weight.

Examples of water-soluble unsaturated monomers used in combination with these modified polyvinyl alcohol polymers include acrylamide, acrylic acid, acrylates, vinylpyrrolidone, hydroxyethyl acrylate, and vinylpyridine salts. It is also possible to use a mixture.
These water-soluble unsaturated monomers can be used in place of 1 to 50% by weight of the modified polyvinyl alcohol polymer. Examples of the water-soluble radical polymerization catalyst used in the present invention include hydrogen peroxide, potassium persulfate, and ammonium persulfate. The amount of these catalysts used is about 0.001 to 10% by weight based on the aqueous solution of the modified polyvinyl alcohol polymer alone or a mixture of the polymer and a water-soluble unsaturated monomer. Further, water-soluble radical polymerization promoters used together with the catalyst include Rongarite, ferrous salts, acidic sodium sulfite, sodium thiosulfate, etc., and the amount used is 0.001 to 10% by weight based on the aqueous solution. It is about %. When these polymerization catalysts and polymerization promoters are used, they can be added simultaneously to the aqueous solution containing the modified polyvinyl alcohol polymer or the polymer and the water-soluble unsaturated monomer; A preferred method is to separately prepare a solution A, in which a catalyst is added to the aqueous solution, and a solution B, in which a promoter is added to the aqueous solution, and then mix the solutions A and B at the time of use to effect polymerization and crosslinking. In some cases, it is also possible to carry out heating polymerization and gelation using only a polymerization catalyst without using the promoter. The polymerization gelation temperature ranges from 0 to 100'C, but preferably from room temperature to 8
The temperature is in the range of 0°C, and the gelation time is about 2 to 4 hours. In the present invention, it is also possible to polymerize and gel after adding various additives to the aqueous polymer solution depending on the use and purpose.

Such additives include inorganic fine particles to make the gel opaque, dyes and pigments to color the gel, fragrances to impart fragrance, water-soluble polymers to adjust the viscosity of the aqueous solution, and additives that modify the aqueous solution. A far-modifying additive for imparting
These include a mold release agent to facilitate mold release, a foaming agent to obtain a foamed gel, and an antifoaming agent to suppress foaming. Furthermore, glass fibers, organic fibers, etc. can also be added for the purpose of reinforcing the gel. Further, the hydrous gel obtained by polymerization gelation can be further frozen to improve the gel strength. In this way, according to the present invention, hydrogels with various properties ranging from highly flexible to hard ones can be obtained, and are expected to be used as ice pillows, deodorants, etc. Applications are expected to be developed in various applications where polymer gels are used, or in various fields that take advantage of the characteristics of gel manufacturing. Hereinafter, the present invention will be specifically explained with reference to Examples. Example 1 Partially saponified polyvinyl alcohol (polymerization degree 1700, saponification degree 88 mol%, hereinafter polyvinyl alcohol is abbreviated as PVA) powder 5 was placed in a 500cc separable flask.
0f, 40 da of maleic anhydride, 17.2 y of sodium bicarbonate, and 200 cc of dioxane as a solvent were added, and the mixture was reacted at 70°C for 1 hour.

The reaction mixture was filtered, washed repeatedly with acetone, and then dried to obtain modified PVA in powder form. The weight of the modified PVA was 77y, and the modification rate (weight increase rate) determined from the weight increase was 54%. The obtained modified PVA was dissolved in water together with vinylpyrrolidone in the proportion shown in Table 1 below, and 0.8% hydrogen peroxide solution was added thereto to form three types of solutions A (1, 2).
, 3) was prepared.

In addition, three types of B solutions (1, 2, 3) were prepared by adding a 7.8% Rongarite aqueous solution. Next, equal amounts of these liquids A and B were mixed and polymerized to form a gel at room temperature for 5 minutes. In both cases, transparent and hard hydrogels with excellent moldability were obtained. Example 2 The same formulation as in Example 1 was used except that acrylamide or acrylic acid was used in place of vinylpyrrolidone as the water-soluble unsaturated monomer in the proportions shown in Table 2 below. A liquid.

*(4,5) and B solution (4,5) were prepared.Next, equal amounts of A solution and B solution were mixed and polymerization gelation was performed at room temperature for 2@@, and NO. No. 4 is a highly flexible hydrogel, and No. 4 is a highly flexible hydrogel. In case No. 5, a water-containing gel body with excellent elasticity was obtained. Example 3 Partially saponified PV with polymerization degree of 1700 and saponification degree of 88 mol%
Using A5Oy, 20y of diketene, 5y1 of sodium bicarbonate, and 200cc of dioxane as a solvent, the mixture was reacted at 60°C for 4 hours.

Reaction mixture? After repeated washing with filtration and acetone, the powder was dried to obtain modified PVA in powder form. Denatured P as a result of weighing
The weight of VA was 60y. The modification rate (weight increase rate) determined from the weight increase was 20%. This modified PVA powder was dissolved in water to prepare 100 y of a 10% aqueous solution, which was further dissolved with 1 q of potassium persulfate and heated at 60°C for 5 y.
When heated for a period of time to polymerize and gel, a hydrogel with extremely high elasticity was obtained. Example 4 Completely saponified PVA powder 50y,3 with a degree of polymerization of 1700 and a degree of saponification of 99 mol% or more was placed in a 500cc separable flask.
0% water-containing methanol 200cc, crotonaldehyde 1
0y or 20q and 1y of sulfuric acid were added, and an acetalization reaction was carried out at 60°C for 1 hour.

The reaction mixture was filtered, washed repeatedly with acetone, and then dried to obtain powdery modified PVA. The modification rate (weight increase rate) was determined from the weight increase. The above results are summarized in Table 3.

Table 3 then the above No. ．． The modified PVA powder obtained in step 6 was dissolved in water together with vinylpyrrolidone, acrylamide, or acrylic acid in the proportions shown in Table 4 below, and 0.8% hydrogen peroxide was added thereto to form three types of solutions A (6 -1,6-2,6-
3) was prepared.

In addition, three types of B solutions (6-1, 6-2, 6-3) were prepared by adding a 7.8% Rongarit aqueous solution. Next, when liquid A and liquid B were mixed in equal amounts to polymerize and gel, NO.
．． ．． Regarding No. 6-1, a hydrogel was formed at m minutes after the start of the reaction, and NO. ．． 6-2 and NO. Regarding 6-3, a highly elastic hydrogel was obtained in all cases 1 hour after the start of the reaction. Table 4 Example 5 NO. obtained in Example 4. ．． The modified PVM powder No. 7 was dissolved in water to prepare 100 dah of a 10% aqueous solution.

Claims (1)

[Claims] 1 A cyclic compound having a radically polymerizable or copolymerizable unsaturated bond, having a double bond in the side chain obtained by the reaction of one compound selected from the group consisting of unsaturated aldehydes and a polyvinyl alcohol polymer. A modified polyvinyl alcohol-based polymer having a modified polyvinyl alcohol-based polymer is dissolved in water alone or together with a water-soluble unsaturated monomer, and a water-soluble radical polymerization catalyst alone or a water-soluble radical polymerization promoter is added thereto. 1. A method for producing a polyvinyl alcohol-based hydrogel, which comprises adding and polymerizing and crosslinking at room temperature or under heating.