JPS6031842B2 - Method for producing hydrophilic crosslinked polymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a hydrophilic crosslinked polymer using an alkali-functional polymer as a raw material, and more specifically, the present invention relates to a method for producing a hydrophilic cross-linked polymer using an alkali-functional polymer as a raw material. After introducing a hydrophilic group into the polymer, a purification operation is performed in which the resulting aqueous solution containing the hydrophilic polymer is brought into contact with an acid-type acidic group-containing polymer. By forming a cross-linked structure in a mixed polymer consisting of group-containing polymers, it is possible to effectively eliminate the problem of impurities such as basic substances remaining in hydrophilic cross-linked polymer products, resulting in hydrophilic products with excellent compositional uniformity. The present invention relates to an industrially advantageous method for producing a crosslinked polymer.

In recent years, substantially water-insoluble and water-swellable substances obtained by imparting a crosslinked structure to water-soluble or hydrophilic polymers, i.e., hydrophilic crosslinked polymers, have been developed to have hydrophilic properties, water retention properties, and instantaneous large water absorption properties. It has attracted attention for its characteristic functions such as hygroscopicity and affinity for human tissue, and there is active research into the use of this substance in various applications such as soft contact lenses, soil water retention agents, disposable diapers, and sanitary products. It is becoming more and more.

As one of the useful methods for producing such hydrophilic crosslinked polymers, a base such as an aqueous sodium hydroxide solution has been used to produce polymers obtained by polymerizing acrylonitrile, acrylamide, methyl acrylate, vinyl acetate, etc. A basic aqueous solution is applied to an alkali-functional polymer that can easily introduce hydrophilic groups such as carboxylate groups, hydroxyl groups, and amide groups into the polymer,
A method of forming a cross-sectional structure in the obtained hydrophilic polymer has been proposed. However, in such a method for producing a hydrophilic cross-linked polymer, the basic substance used in the first step of introducing hydrophilic groups into the alkali-functional polymer remains in the hydrophilic cross-linked polymer, resulting in a loss of quality in the final product. There were inherent drawbacks that significantly reduced the quality of the product.

In order to eliminate the residual of such harmful basic substances in hydrophilic cross-linked polymer products, the conventional method is to wash the hydrophilic cross-linked polymer with water to make it basic. A method of drying after removing substances; basic substances remaining in the hydrophilic crosslinked polymer are neutralized with known acidic substances such as mineral acids and organic acids to form salts with low toxicity. After that, if necessary, the polymer is washed with water, and then further subjected to a drying process.A method in which a basic aqueous solution is applied to an alkali-functional polymer to introduce a hydrophilic group into the polymer and dissolve it. By adding an acidic substance to an aqueous solution of a hydrophilic polymer and converting some or all of the acidic groups in the hydrophilic polymer into an acid form, the polymer is precipitated and precipitated as a water-swollen product. A method has been proposed in which the water-swollen product is washed with an acidic aqueous solution and then a crosslinked structure is formed in the polymer.

However, in any of the known methods, many problems have been pointed out when putting them into practical use. That is, in the simple water washing method exemplified first, since the hydrophilic crosslinked polymers used in the above-mentioned application fields are usually highly water-swellable, they absorb a large amount of washing water and swell.
In order to remove the swollen water, it is necessary to carry out evaporative drying treatment, which requires a large amount of fuel consumption, which poses a problem in the economic efficiency of the process, and even if methods such as centrifugal dehydration are used, Due to problems such as extremely poor moatability, it is surprising to find that this method can be used industrially, and after neutralizing the basic substance in the hydrophilic crosslinked polymer with an acidic substance such as a mineral acid. In the method of evaporative dehydration, it is true that impurities in the hydrophilic crosslinked polymer are contained in the form of salts, which are generally less harmful than the basic substances mentioned above, but they are not suitable for the above-mentioned application fields. When using the product, it is difficult to ignore the negative effects it has on the human body, plants, etc., and its practical application has been considered virtually impossible.

Furthermore, even if some or all of the acidic groups in a hydrophilic polymer are made into an acid form, the polymer can be precipitated and separated as a water-swollen product, and then crosslinked. The yield of the polymer obtained cannot normally exceed 90% by weight based on the total amount of polymer present in the aqueous solution, and therefore a large amount of hydrophilic polymer is washed away during the process. It has been pointed out that there are serious obstacles to industrialization, such as a significant decrease in production efficiency and the release of such polymers into process wastewater, causing environmental problems. As described above, in the method for producing a hydrophilic crosslinked polymer in which an alkali-functional polymer is used as a raw material, the polymer is made hydrophilic by acting on the polymer with a basic aqueous solution, and then crosslinked. Although the use of an aqueous solution has the advantage of being able to very advantageously introduce hydrophilic groups into the raw material polymer, it has the disadvantage that impurities such as base substances remain in the resulting hydrophilic crosslinked polymer. Establishing a method to effectively prevent the residue of impurities caused by products such as At present, no concrete and industrial means have been found for this, and there have been great expectations for the progress of its development and the establishment of corresponding technology.

In this), the present inventors completely solved the above-mentioned unresolved problems, and in a method for producing a hydrophilic crosslinked polymer using an alkali-functional polymer as a raw material, impurities such as basic substances were eliminated. As a result of continuing intensive research to establish a purification method that effectively prevents residue from remaining in product polymers, we introduced hydrophilic groups into an alkali-functional polymer by applying a basic aqueous solution to the polymer. After that, an acid type acidic group-containing polymer is brought into contact with the obtained hydrophilic polymer-containing aqueous solution,
A method of removing the basic substance remaining in the aqueous solution containing the hydrophilic polymer by causing an ion exchange reaction with the acid type acidic group-containing polymer, that is, prior to the crosslinking treatment step, The present invention was achieved by discovering the fact that the above-mentioned limitations can be effectively overcome by introducing a purification process using a polymer having the following composition.

The main object of the present invention is to obtain a hydrophilic crosslinked polymer by using an alkali-functional polymer as a raw material, treating the polymer with a basic aqueous solution to make it hydrophilic, and then subjecting the polymer to a crosslinking treatment. The object of the present invention is to propose an industrially advantageous manufacturing method for hydrophilic crosslinked polymers that effectively prevents the residue of impurities such as base substances in the polymer product.

Another object of the present invention is to introduce a purification process using a polymer having a specific composition, thereby achieving efficiency of the subsequent drying process and high yield of the product, and achieving compositional uniformity. The purpose of this study is to propose a new method for producing hydrophilic crosslinked polymers with excellent properties. Other objects of the present invention will become apparent from the following description. The above-mentioned object of the present invention is to introduce a hydrophilic group into an alkali-functional polymer by reacting a basic aqueous solution to the polymer, and then to form an acid form into the resulting aqueous solution containing the hydrophilic polymer. A group-containing polymer is brought into contact with the aqueous solution containing the hydrophilic polymer, and the basic substance remaining in the aqueous solution containing the hydrophilic polymer is removed by causing an ion exchange reaction with the acid type acidic group-containing polymer. This is achieved by forming a crosslinked structure in a mixed polymer consisting of an acidic polymer and an acidic group-containing polymer.

The present invention will be explained in more detail below.

The alkali-functional polymer used in the present invention is a general term for polymers that can form hydrophilic groups such as carboxylate groups, hydroxyl groups, and amide groups in the molecule when exposed to a basic aqueous solution; To give a concrete example,
One or more vinyl monomers containing nitrile groups, amide groups, ester groups, etc., such as acrylonitrile, methacrylonitrile, acrylamide, methyl acrylate, methyl methacrylate, and vinyl acetate. or a mixture thereof, or a monomer mixture consisting of these monomers or a mixture thereof and another ethylene monomer as required, and preferably, A polymer copolymerized with at least one monomer capable of forming an acidic group such as a carboxylate group when treated with a basic aqueous solution can be used, and among them, acrylonitrile, methacrylonitrile, acrylamide, etc. By treating with a basic aqueous solution, a polymer containing substituents such as amide groups that can become crosslinking functional groups is formed in addition to acidic groups, and subsequent crosslinking is facilitated. The method of the present invention can be carried out particularly preferably by using as a raw material a polymer that can be processed advantageously.

Incidentally, there are no particular restrictions on the copolymerization composition, molecular weight, etc. of such polymers, and the polymerization method, etc., can be selected from a wide range of known methods.

In addition, the alkali-functional polymer is not limited to synthetic polymers such as the above-mentioned polymers, but can also be made of natural polymers as starting materials, such as a polymer obtained by craft polymerizing acrylonitrile with starch. Polymers that can be used can also be suitably used. As the basic aqueous solution to act on the above-mentioned alkali-functional polymer in the practice of the present invention, aqueous solutions of known inorganic or organic basic substances can be used, especially sodium hydroxide,
Aqueous solutions of alkali metal hydroxides such as potassium hydroxide can be suitably used.

Further, water is suitable as a solvent for the aqueous solution, and if necessary, a mixed solvent of water and a water-miscible organic solvent such as methanol, ethanol, or propanol can be used.
It is also possible to coexist organic or inorganic substances other than the above basic substances. In this case, it is impossible to unambiguously define the processing conditions such as the concentration of the basic substance in the basic aqueous solution used and the ratio of the basic aqueous solution to the alkali-functional polymer. Depending on the water absorption performance of the hydrophilic crosslinked polymer required in the field of application of the final product, physical properties such as strength in the water absorption state of the polymer, or hydrophilic reactivity with a basic aqueous solution of the raw material polymer, etc. can be selected as appropriate.

However, as a practical condition, the basic substance concentration is 0.5 to 35% by weight, and the weight ratio of the basic aqueous solution to the alkali-functional polymer is 99.5/0.6.
It is preferable to use a range of ˜65/35, respectively. In other words, if a basic aqueous solution with a low concentration outside the above range is used, the hydrophilization reaction rate of the alkali-functional polymer will decrease, and a long treatment process will be required to introduce the desired amount of hydrophilic groups. However, if the upper limit of the above recommended concentration is exceeded, efficiency can be achieved by shortening the hydrophilization reaction time, but
On the other hand, this is not preferable because the amount of the basic substance remaining in the reaction system increases and a large amount of the acid type acidic group-containing polymer is required for the removal treatment. On the other hand, when the ratio of the basic aqueous solution to the alkali-functional polymer is higher than the above range, the amount of solvent in the obtained aqueous solution containing the hydrophilic polymer becomes extremely large, and therefore the crosslinking process If the ratio is low, the viscosity of the aqueous solution containing the hydrophilic polymer increases, making it difficult to transport such a solution during the process. This is not desirable because it causes inconvenience. In addition, such hydrophilization reaction is allowed to proceed under arbitrary temperature conditions, in an air atmosphere or an inert gas atmosphere such as a nitrogen atmosphere as necessary, under normal pressure or under increased pressure or reduced pressure as necessary. be able to. In this way, the alkali-functional polymer treated with a basic aqueous solution undergoes a hydrophilic reaction such as a hydrolysis reaction on specific functional groups in the polymer to form a hydrophilic polymer, and generally the base The basic substance in the aqueous solution is consumed and dissolved in the aqueous solution.

Regarding the state of the polymer in the obtained aqueous solution containing a hydrophilic polymer, it is preferable that the polymer is in a substantially uniformly dissolved state;
There is no particular problem even if cloudiness, opacity, etc. are observed, and even if the solution remains only partially dissolved, or if a swelling gel-like substance is formed as it becomes hydrophilic,
In a state where it comes into contact with the acidic group-containing polymer described below and exhibits appropriate fluidity to the extent necessary to enable mixing of the acidic group-containing polymer and the hydrophilic polymer and removal of the basic substance. In other words, it does not pose a particular obstacle to the implementation of the present invention. In order to remove the basic substances remaining in the obtained hydrophilic polymer-containing aqueous solution by causing an ion exchange reaction, the acid type acidic group-containing polymers that can be used in the present invention include carboxyl groups, sulfonic acid groups, etc. It is a polymer containing an acidic group such as a group, a phosphoric acid group, and a part or all of the acidic group is an acid type, and more specifically, acrylic acid, methacrylic acid, methacrylic acid, One or more monomers selected from the group consisting of acidic group-containing monomers such as meta-allylsulfonic acid and P-styrenesulfonic acid, and their salts, or a mixture thereof, or if necessary, A polymer obtained by polymerizing a monomer mixture consisting of a monomer such as or a mixture thereof and another ethylene monomer, or if necessary, in order to convert an acidic group into an acid form, Examples include polymers obtained by subjecting the polymer to acid treatment, and the polymerization method, acid treatment method, etc. of the polymer can be arbitrarily selected from known methods.

Alternatively, in order to obtain an acid-type acidic group-containing polymer, instead of the method of polymerizing the acidic group-containing monomer as described above, the molecule is treated with an acid, a base, an oxidizing agent, a reducing agent, etc. A method can be adopted in which a polymer capable of introducing an acidic group into a polymer is used as a precursor substance.

Among these polymers, nitrile groups, amide groups,
Polymers containing ester groups and the like and capable of forming acidic groups such as carboxylate groups when treated with a basic aqueous solution can be suitably used in the practice of the present invention, such as acrylonitrile, methacrylonitrile, etc. 1 selected from the group of vinyl monomers containing nitrile groups, amide groups, ester groups, etc., such as , methyl acrylate, methyl methacrylate, acrylamide, vinyl acetate, etc.
Seed seed is a polymer obtained by polymerizing two or more monomers or a mixture thereof, or a monomer mixture consisting of these monomers or a mixture thereof and another ethylene monomer as necessary. A basic aqueous solution is applied to the polymer to introduce acidic groups into the polymer, and an acidic substance is added to the resulting aqueous solution of the acidic group-containing polymer. By converting all of the polymer into acid form, it is possible to precipitate the polymer, or to use a polymer obtained by evaporating the aqueous solution to dryness.

Here, the method for producing such a precursor polymer can be selected from a wide range of known methods, and the basic aqueous solution used can be selected from a wide range of known aqueous solutions of inorganic and organic bases. In particular, aqueous solutions of alkali metal hydroxides such as sodium hydroxide and potassium hydroxide can be suitably used. Further, as the acidic substance added to the above acidic group-containing polymer aqueous solution, known key acids or organic acids can be used.
In particular, sulfuric acid, hydrochloric acid, etc. can be suitably used. It is impossible to uniquely limit the conditions under which such an acidic substance is added to an aqueous solution of an acidic group-containing polymer and the polymer is converted into an acid form and precipitated from the solution. Conditions such as the amount of acidic substance added can be appropriately selected depending on the type or content of acidic groups in the combination. As the acidic group-containing polymer according to the present invention, a polymer having the same or similar composition as the above-mentioned alkali-functional polymer, which is a raw material for the hydrophilic crosslinked polymer, is used as a precursor material, and the acidic group-containing polymer is used as a precursor material. The object of the present invention can be achieved particularly effectively by using a polymer having a similar composition to the above-mentioned hydrophilic polymer which can be formed by the action of an aqueous solution. Such a polymer can be obtained by introducing a simple process in which a part of the aqueous solution containing the hydrophilic polymer is subjected to an acid treatment process, an acidic substance such as a key acid is added as described above, and the hydrophilic polymer is precipitated and separated. It can be easily formed. Therefore, the process sequence of the present invention in which the above-mentioned acid type acidic group-containing polymer is brought into contact with the above-mentioned hydrophilic polymer-containing aqueous solution and subjected to crosslinking treatment is such that the basic substance is removed and the hydrophilic polymer and acidic groups are removed. This has an important meaning in order to satisfy the gist of the present invention, which is to effectively perform both mixing with the containing polymer.

On the other hand, when adopting a step sequence in which a hydrophilic polymer is formed with a crosslinked structure prior to a purification step in which it is brought into contact with an acid type acidic group-containing polymer, the aqueous solution is absorbed by the hydrophilic crosslinked polymer. The aqueous solution becomes solid and granular, and the aqueous solution loses its fluidity, making it virtually impossible to achieve the object of the present invention. Regarding the amount of such an acid-type acidic group-containing polymer added to an aqueous solution containing a hydrophilic polymer, it is necessary to select an amount necessary and sufficient to neutralize the basic substance present in the aqueous solution. More specifically, it is preferable to select the amount added to maintain the pH of the aqueous solution at 6 to 8.

(2) When selecting an amount to be added that is outside the preferred pH range,
This is not preferred because basic substances in the hydrophilic crosslinked polymer product may not be removed sufficiently or the hydrophilic crosslinked polymer may become acidic when swollen with water. Furthermore, as a treatment method for bringing the acidic group-containing polymer into contact with the hydrophilic polymer-containing aqueous solution, known methods can be used, such as using a slurry device such as a kneader, a deep cutting device such as a mixer, or a screw-type foundation layer. It can be processed by There are no particular restrictions on the method of forming a crosslinked structure in the mixed polymer thus obtained, including formaldehyde aqueous solution treatment, heat treatment, in the aqueous solvent or in a dry state after evaporating the aqueous solvent. Any method can be selected from known crosslinking treatment methods such as radiation irradiation and the like.

By carrying out the method of the present invention described above, an alkali-functional polymer is used as a raw material, the polymer is made hydrophilic by acting on the polymer with a basic aqueous solution, and then a hydrophilic cross-linked polymer is obtained by performing a cross-linking treatment. The problem of impurities such as basic substances remaining in hydrophilic cross-linked polymer products, which had traditionally been the biggest problem that had been desired to be solved during manufacturing, has been effectively solved, and the product has excellent compositional uniformity. The formation of hydrophilic crosslinked polymers has been achieved with industrial advantage.

Furthermore, by implementing the method of the present invention, the amount of washing water required for purification of hydrophilic crosslinked polymers, the amount of heat of evaporation required for dehydration, and the process loss of hydrophilic polymers are all significantly reduced, and productivity is significantly improved. This also deserves special mention as an effect unique to the present invention.

EXAMPLES The present invention will be described below in more detail with reference to Examples, but the gist of the present invention is not limited in any way by the description of these Examples.

It should be noted that all percentages and parts shown in the examples are expressed on a weight basis unless otherwise specified. Example 1 90% acrylonitrile and 10% acrylic acid,
Acrylonitrile copolymer containing methyl (30q
Intrinsic viscosity of C in dimethylformamide solution; 1
．． 5) Suspend 17 parts in 83 parts of a 9.2% sodium hydroxide aqueous solution and light at 90o0 for 45 minutes to obtain an aqueous polymer solution containing sodium acrylate and acrylamide (polymer concentration: 26.5%). , residual sodium hydroxide concentration: about 1.2%), and the aqueous polymer solution was prepared as an aqueous solution containing a hydrophilic polymer.

On the other hand, the same acrylonitrile copolymer as above was treated with an aqueous sodium hydroxide solution according to the same recipe as above, and acidic groups having substantially the same composition as the above hydrophilic polymer containing sodium acrylate and acrylamide were obtained. An aqueous solution of the containing polymer is prepared, and then diluted by adding 10 parts of a sulfuric acid aqueous solution to 10 parts of the aqueous solution at room temperature and adjusting the pH to 2.5 to precipitate the polymer to form a solid. The acid type acidic group-containing polymer was separated as a 35% water-swollen product.

By performing such a separation operation, 95% or more of the total amount of Mitsuishi produced by treating the acidic group-containing polymer aqueous solution containing sodium hydroxide with a sulfuric acid aqueous solution is removed from the acidic group-containing polymer. Obtained. The thus prepared acid type acidic group-containing polymer in a water-containing state is added to the aqueous solution containing the hydrophilic polymer, and subjected to oak floating in a kneader at room temperature to remove the sodium hydroxide remaining in the aqueous solution. is removed through an ion exchange reaction with the acid-type acidic group-containing polymer, and the acidic group-containing polymer is dissolved to reach a pH of 7.
．． A mixed polymer aqueous solution of 0 was prepared.

The obtained aqueous solution is an aqueous solution of a polymer with excellent compositional uniformity, which is obtained by mixing and dissolving a hydrophilic polymer and an acidic group-containing polymer having substantially the same composition, so it is extremely stable over time. Therefore, it was possible to use it even after long-term storage without causing state changes such as phase separation. Next, 6.7 parts of a 3.0% formaldehyde aqueous solution was added to 100 parts of the polymer in the above mixed polymer aqueous solution, and the mixture was stirred at 9,000 °C for 15 minutes.

Thereafter, the aqueous solution is heated at 200°C for a minute to dehydrate it, and the mixed polymer is dried and at the same time forms a crosslinked structure in the polymer, so that the sodium hydroxide content is 100 or less and the saccharide content is A hydrophilic crosslinked polymer with excellent compositional uniformity was produced, with impurity content significantly reduced to 0.5% or less. In addition, more than 99% of all the polymers used through the above process were recovered as the final product of hydrophilic cross-linked polymers, so the production efficiency of hydrophilic cross-linked polymers was significantly improved by adopting the method of the present invention. It has been confirmed that you can get it. On the other hand, as a comparative example, an aqueous sulfuric acid solution was added to the aqueous solution containing the hydrophilic polymer described above to neutralize the sodium hydroxide contained in the aqueous solution. 6.7 parts of a 3.0% formaldehyde aqueous solution was added to the ball, heated at 90°C for 15 minutes, and then heated at 20,000°C for 60 minutes to cause dehydration and drying as well as a crosslinking reaction, resulting in hydrophilic crosslinking. However, the obtained hydrophilic cross-linked polymer contained 8.5% ramie and had low purity, and during its purification, the hydrophilic cross-linked polymer absorbed an extremely large amount of water and swelled. In order to reduce the amount of water, it is necessary to wash the water with an amount of water equal to or greater than 50% of the absolute dry weight of the polymer, and in addition,
During drying, it is necessary to evaporate more than 100 times as much swelling water, and judging from the economics of the process, it has been confirmed that the industrial implementation of such a method is completely disadvantageous.

In contrast, according to the method of the present invention, the impurity content can be reduced to a practically satisfactory level without the need for water washing, and the amount of evaporated water in the drying process is about three times the absolute dry weight of the hydrophilic crosslinked polymer. From the fact that the burden of the drying process can be greatly reduced because it can be reduced to a maximum of Example 2 One part of wheat flour starch was suspended in nine parts of water, heated at 85 qo for 1 hour to form a paste, and then cooled.

Next, a 1N nitric acid aqueous solution containing 0.1 mole/cerium ammonium nitrate was added to 10 anchor portions of the pasty material.3.
After adding 14 parts of acrylonitrile, the mixture was stirred at room temperature for 2 seconds to generate radicals for initiating graft polymerization in the starch molecules, and then 14 parts of acrylonitrile was added and stirred for 2 minutes in a nitrogen stream.
The temperature was maintained in the range of 0 to 33°C, and the graft polymerization reaction was allowed to proceed for 3 hours to form a starch-acrylonitrile graft polymer. The obtained polymerization reaction mixture was purified by passing through and washing with water to remove unreacted acrylonitrile, cerium salt and nitric acid, and then the purified graft polymer 1 base was dissolved in a 4.5% aqueous sodium hydroxide solution 9. to cause a hydrolysis reaction in the nitrile groups in the graft polymer by suspending it in 900°C for 45 minutes,
The obtained graft polymer hydrolyzate aqueous solution was prepared as a hydrophilic polymer-containing aqueous solution.

On the other hand, the same starch-acrylonitrile graft polymer as above was treated with an aqueous sodium hydroxide solution according to the same recipe as above, and the obtained aqueous solution of the graft polymer hydrolyzate having substantially the same composition as above was added to the acid group. An aqueous solution containing a polymer is diluted by adding 100 parts of an aqueous sulfuric acid solution to two of the aqueous solutions at room temperature, and the polymer is precipitated by adjusting the pH to 2.5. was prepared as an acid type acidic group-containing polymer. The thus obtained acid-type acidic group-containing polymer in a water-containing state is added to the hydrophilic polymer-containing solution and kneaded in a kneader at room temperature so that it remains in the aqueous solution. Sodium hydroxide I
An aqueous mixed polymer solution having a pH of 7.0 was prepared by dissolving the acidic group-containing polymer while removing Jum based on an ion exchange reaction with the acidic group-containing polymer.

The obtained aqueous solution is an aqueous solution of a polymer with excellent compositional uniformity, which is obtained by mixing and dissolving a hydrophilic polymer and an acidic group-containing polymer having substantially the same composition, so it is extremely economical. It is stable and does not cause state changes such as phase separation.
It was possible to use it even after long-term storage. Next, 6.7 parts of a 3.0% formaldehyde aqueous solution was added to 100 parts of the polymer in the above mixed polymer aqueous solution, and the mixture was heated at 9,000 ℃ for 15 minutes, and then the aqueous solution was heated at 20,000 ℃. The mixed polymer is heated for 6 minutes to dehydrate it, and at the same time as the mixed polymer is dried, a crosslinked structure is formed in the polymer to reduce the impurity content to a sodium hydroxide content of 100% or less, a ramie content of 1% or less. Reduce large-scale
A hydrophilic crosslinked polymer with excellent compositional uniformity was prepared.

Example 3 Acrylamide-based polymer containing 90% acrylamide and 10% sodium acrylate (40q○,
Intrinsic viscosity in 1N aqueous sodium chloride solution: 0
．． 84) was treated with an aqueous sodium hydroxide solution according to the same recipe as in Example 1 to prepare an aqueous solution containing a hydrophilic polymer.

On the other hand, in order to produce an acid-type acidic group-containing polymer, an acrylamide polymer having the same composition as above was used and treated according to the same recipe as above, and the resulting polymer aqueous solution was prepared using the same recipe as in Example 1. The acid type acidic group-containing polymer was precipitated and separated according to the method.

The acid type acidic group-containing polymer thus separated is added to an aqueous solution containing a hydrophilic polymer obtained by reacting the acrylamide-based polymer with an aqueous sodium hydroxide solution,
By treating according to the kneading method of Example 1, residual basic substances in the aqueous solution were removed, and at the same time, a mixed polymer aqueous solution with a pH of 7.0 consisting of a hydrophilic polymer and an acidic group-containing polymer was prepared. The obtained aqueous solution is a polymer aqueous solution with excellent compositional uniformity, which is obtained by mixing and dissolving a hydrophilic polymer and an acidic group-containing polymer having substantially the same composition, and is therefore extremely stable over time. Therefore, it was possible to use it even after long-term storage without causing state changes such as phase separation. To 10 parts of the polymer in this mixed polymer aqueous solution, 6.7 parts of a 3.0% formaldehyde aqueous solution was added, heated at 90°C for 15 minutes, and then heated at 20,000°C for 60 minutes. At the same time as dehydration, a crosslinked structure is formed in the mixed polymer, and the impurity content is greatly reduced to a sodium hydroxide content of less than 10% and a ramie content of less than 0.5%, resulting in compositional uniformity. It was formed into a hydrophilic cross-linked polymer. As an alkali-functional polymer, instead of the acrylamide-based polymer described above, 90
% acrylonitrile and 10% vinyl acetate (intrinsic viscosity in 30 q○ dimethylformamide solution: 1.7) containing 88% acrylonitrile, 10% acrylamide and 2% methalylsulfone. Copolymer containing sodium acid (30q
Intrinsic viscosity of o in dimethylformamide solution: 1
．． The two types of copolymers in 4) were used and treated according to the same recipe as in the case of the acrylamide copolymer described above to obtain two types of hydrophilic crosslinked polymers with excellent purity and homogeneous composition. It was formed by merging. Example 4 In the aqueous solution containing the hydrophilic polymer used in Example 1,
A copolymer containing 50% acrylic acid and 50% acrylamide (40 qo, intrinsic viscosity in a 1N aqueous sodium chloride solution: 1.1) was added, and the following was carried out in the aqueous solution according to the same recipe as in Example 1. At the same time, a mixed polymer aqueous solution having a pH of 7.0 consisting of a hydrophilic polymer and an acidic group-containing polymer was prepared.

Claims (1)

[Scope of Claims] 1. After introducing a hydrophilic group into the polymer by introducing a basic aqueous solution onto the alkali-functional polymer, an acid type acidic group-containing polymer is added to the resulting aqueous solution containing the hydrophilic polymer. The basic substance remaining in the hydrophilic polymer-containing aqueous solution is removed by causing an ion exchange reaction with the acid type acidic group-containing polymer, and then the obtained hydrophilic polymer and A method for producing a hydrophilic crosslinked polymer, which comprises forming a crosslinked structure in a mixed polymer comprising an acidic group-containing polymer. 2. As an acid-type acidic group-containing polymer, a polymer obtained by reacting with an acidic substance in the aqueous solution containing the hydrophilic polymer to convert some or all of the acidic groups in the hydrophilic polymer into an acid form. A method according to claim 1 using coalescence.