JPS6142721B2 - - Google Patents

Description

Detailed Description of the Invention The present invention involves heat-treating a modified polyvinyl alcohol polymer containing a soluble carboxyl group obtained by reacting a polyvinyl alcohol polymer with a cyclic acid anhydride in an anhydrous state at 80°C to 250°C. The present invention relates to a method for producing an insoluble polymeric material with extremely excellent water absorption, which involves introducing a slight crosslinking bond into the molecule.

In recent years, as the use of hydrophilic polymer materials in the medical industry, food industry, and agricultural separation has progressed, polymer materials that are particularly water-soluble and have hydrophilic or water-absorbing properties are being used for separation and purification such as various membranes and liquid chromatography carriers. It has come to be used as a material, a culture medium for microorganisms and plants, a medical material such as contact lenses and suture coverings, and a variety of other uses that utilize its water absorption and water retention properties. Among these applications, it is desired that polymeric materials used in applications that utilize water absorption in particular have the ability to absorb as much water as possible in a short period of time upon contact with water. So far, polymer materials for such uses include natural and synthetic polymers such as modified polyethylene oxide, cross-linked polyvinylpyrrolidone and sulfonated polystyrene, and saponified starch-acrylonitrile graft copolymers. Several materials using substances have been proposed.

However, except for saponified starch-acrylonitrile copolymers, their water absorption capacity is low and they are not satisfactory as water-absorbing materials. In addition, even in the case of saponified starch-acrylonitrile graft copolymers, which have a water absorption capacity of 30 times or more than their own weight, although various improvements have been made to the manufacturing methods, the process is relatively complicated. However, when used in a hydrated state for a long period of time, there are several practical problems, such as the possibility that the starch component will rot and the gel structure will be destroyed.

On the other hand, the present inventors have previously discovered that a modified polyvinyl alcohol-based polymer whose side chain has been modified with a cyclic acid anhydride can be used as a polymeric material with water absorption ability, and has filed a patent application (patent application) for its production method. Gansho 52
-85353).

As a result of further research into industrially advantageous methods for manufacturing such water-absorbing polymer materials, the present inventors have discovered that soluble polymers obtained by reacting polyvinyl alcohol-based polymers with cyclic acid anhydrides in an anhydrous state The method of heat-treating a modified polyvinyl alcohol-based polymer containing carboxyl groups at 80°C to 250°C to introduce slight cross-linking bonds between molecules is extremely advantageous for producing insoluble polymer materials with excellent water absorption performance. We have discovered that this is the case, and have completed the present invention.

The polyvinyl alcohol polymer used as a raw material in the present invention has a saponification degree of 50 to 100 mol% obtained by saponifying vinyl acetate, other various vinyl ester polymers, and copolymers thereof.
Not only that, but also various unsaturated monomers such as α-olefins, vinyl chloride, 30 mol% or less based on vinyl acetate and other various vinyl esters.
It includes copolymers of acrylonitrile, acrylamide, acrylic esters, and methacrylic esters with a degree of saponification of 50 to 100 mol%.

The polyvinyl alcohol polymer to be subjected to the reaction is preferably in powder form. Further, the degree of polymerization is preferably in the range of 100 to 5,000.

There are the following five methods for obtaining soluble modified polyvinyl alcohol to be subjected to heat treatment in the present invention.

(1) A polyvinyl alcohol polymer is reacted with a cyclic acid anhydride in the presence or absence of an esterification catalyst such as sodium bicarbonate or triethylamine. The esterification catalyst is used in an amount of 5% by weight or less based on the polyvinyl alcohol polymer.

(2) A polyvinyl alcohol polymer is reacted with a cyclic acid anhydride in the presence of monovalent metal hydroxides, alkoxides, salts, etc. The amount of the monovalent metal hydroxide, alkoxide, salt, etc. used is equal to or less than the amount of the cyclic acid anhydride used.

(3) A polyvinyl alcohol polymer is reacted with a cyclic acid anhydride in the presence of a tertiary amine. The tertiary amine is used in an amount equal to or less than the cyclic acid anhydride.

(4) A polyvinyl alcohol polymer is reacted with a cyclic acid anhydride in the presence of a monovalent metal hydroxide, alkoxide, salt, etc. and a tertiary amine or tertiary amine salt. The amount of the mixture of these two used is equal to or less than the amount of the cyclic acid anhydride.

(5) React a cyclic acid anhydride with a polyvinyl alcohol polymer in the presence or absence of an esterification catalyst, and then react with a monovalent metal hydroxide, alkoxide, salt, ammonia, ammonium salt, amine salt, or amine. Treat with any of the salts. The treatment is carried out by dissolving these in a solvent and bringing them into contact with modified polyvinyl alcohol so that the carboxyl groups in the side chains are neutralized to a desired ratio.

Each of the above reactions is carried out in the absence of water as much as possible, but compounds with active hydrogen that are reactive with cyclic acid anhydrides are unsuitable as reaction solvents. Compounds without active hydrogen, such as benzene, toluene, hexane, acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, etc., are used. Particularly suitable are toluene, dioxane, etc. When maleic anhydride is used in the reaction, since this compound has a low melting point, it can also function as a solvent. The amount of solvent used is preferably 2 to 5 times the amount of the polyvinyl alcohol polymer powder. The reaction is carried out by dissolving a predetermined amount of cyclic acid anhydride in a predetermined amount of solvent, adding a predetermined amount of a polyvinyl alcohol polymer, a monovalent metal compound, a tertiary amine, etc., stirring and dispersing the mixture, and stirring and dispersing the mixture at a predetermined temperature for a predetermined time. Carry out the reaction.

Since the reaction proceeds in a heterogeneous system, it is carried out with sufficient stirring so that the polyvinyl alcohol polymer powder and the monovalent metal compound powder can come into sufficient contact and the esterification reaction can occur uniformly.

The reaction temperature is 30-150℃, preferably 50-100℃.The reaction time is 30 minutes-10 hours, preferably 1-5 hours.
The time is appropriate. The degree of esterification can be from 1 to 100 mol%, but for the purpose of the present invention it is from 5 to 100 mol%.
50 mol% is preferred.

Cyclic acid anhydrides used in the reaction include maleic anhydride, phthalic anhydride, trimellitic anhydride,
Examples include succinic anhydride, glutaric anhydride, adipic anhydride, itaconic anhydride, and the like. Depending on the case, it is also possible to use a mixture of these. It is necessary to use the cyclic acid anhydride in an amount corresponding to the desired degree of esterification or more.

The reaction mixture is filtered, centrifuged, etc.
Separate the solids. The liquid is collected and reused. The solid portion is washed with methanol (boiling point 64.7°C), acetone (boiling point 56.3°C), etc., and dried to obtain a powdery soluble modified polyvinyl alcohol polymer.

Since such modified polyvinyl alcohol is soluble, it is necessary to further heat-treat it in order to make it insoluble and impart water absorption ability. The heat treatment conditions vary depending on the degree of polymerization and modification of the modified polyvinyl alcohol, so it is difficult to define them unconditionally, but the heat treatment temperature is usually 80°C to 250°C, preferably 100°C to 200°C, and the heat treatment time is 1 second. -2 hours, preferably 1 minute - 1 hour. By subjecting the modified polyvinyl alcohol to such a heat treatment operation, about one intermolecular crosslinking bond is introduced per polymer, and the entire powder particle is made to be slightly reticulated. The crosslinking bond is a diester crosslinking that occurs between a carboxyl group and a hydroxyl group. In addition, when method (1) mentioned above is adopted as a method for producing modified PVA, that is, a method in which a cyclic acid anhydride is reacted with a PVA-based polymer in the presence or absence of an ester catalyst, the polymer after heat treatment is It is also possible to treat with a monovalent metal hydroxide, ammonia, etc., or to mix an appropriate amount of a monovalent metal carbonate, bicarbonate, etc.

The insoluble modified polyvinyl alcohol-based polymer obtained in this way has an extremely high water absorption capacity, and can absorb 50 to 500 times its own weight in water in an extremely short period of 1 to 10 minutes, depending on the manufacturing method. do.

Therefore, it exhibits outstanding properties in the various fields mentioned above and has an extremely wide range of uses.

The present invention will be specifically explained below using Examples.

Example 1 In a 500 c.c. separable flask, 50 g of polyvinyl alcohol (hereinafter abbreviated as PVA, degree of polymerization 1700, degree of saponification 88 mol%) powder, 40 g of phthalic anhydride, 2 g of triethylamine, 100 c.c. of dioxane, 100 c. of toluene c. and reacted at 80°C for 4 hours. The reaction mixture was repeatedly washed with filtrate and acetone, and then dried to obtain a modified PVA powder. Weighed and found the denaturation rate (weight increase rate) from the weight increase: 70
It was %. This powder has a water to methanol ratio of
It was soluble in a 50:50 mixed solvent.

Next, this powder was heat-treated at 170°C for 10 minutes, then immersed for 30 minutes in a methanol solution containing an equivalent amount of ammonia or sodium hydroxide to the phthalic anhydride involved in the reaction with PVA, and washed with methanol and acetone. , dried. All of the modified PVA powders obtained in this way absorbed 150 times their own weight of water in 1 minute, showing good water absorption ability.

Example 2 In the preparation of the modified PVA powder of Example 1, 2 g of triethylamine was replaced with 18.8 g of sodium bicarbonate.
A modified PVA powder was obtained by carrying out the reaction in the same manner as in Example 1 except for using g. The modification rate was determined from the weight increase and was 100%. This powder was soluble in water.

This powder was then heat treated at 170°C for 12 minutes.
The obtained powder absorbed 200 times its own weight in water in 1 minute, demonstrating excellent water absorption performance.

Example 3 In the production of the modified PVA powder of Example 1, 50 g of fully saponified PVA powder with a polymerization degree of 1700 and a saponification degree of 99 mol% was used as the raw material PVA, and 18.8 g of baking soda and 2 g of triethylamine were used as the esterification catalyst.
The reaction was carried out in the same manner as in Example 1 except that dimethylformamide 200c.c. was used as the solvent.
Obtained PVA powder. The modification rate was determined from the weight increase and was 80%. This powder was soluble in water.

This powder was then heat treated at 170°C for 10 minutes.
The obtained powder absorbed 150 times its own weight in water in 1 minute, showing excellent water absorption performance.

Example 4 50 g of PVA with a degree of polymerization of 1700 and a degree of saponification of 88 mol%,
Using 30 g of phthalic anhydride, 2 g of triethylamine, and 100 c.c. of dioxane and 100 c.c. of triene as solvents.
The reaction was carried out at 80°C for 4 hours. The reaction mixture was washed repeatedly with filtrate and acetone, and then dried to form modified PVA.
A powder was obtained. The modification rate determined from the weight increase was 60% by weight. This powder was immersed for 30 minutes at room temperature in a methanol solution containing an amount of ammonia or sodium hydroxide equivalent to the amount of phthalic anhydride involved in the reaction with PVA to convert the side chain carboxyl groups in the modified PVA into ammonium and sodium salts. After washing with methanol and acetone, it was dried. All of the obtained powders were soluble in water.

When these powders were then heat-treated at 170°C for 30 minutes, they all absorbed 200 times their own weight in water in one minute, demonstrating excellent water absorption performance.

Claims (1)

[Claims] 1. An insoluble polymeric material with water absorption ability made by heat-treating modified polyvinyl alcohol containing a soluble carboxyl group obtained by reacting a polyvinyl alcohol polymer with a cyclic acid anhydride in an anhydrous state at 80°C to 250°C. manufacturing method.