Title of the invention: Polymer gel having a sponge-like porous structure Technical field [0001] 　The present invention relates to a novel polymer gel having a porous structure composed of two regions, a concentrated phase and a dilute phase of a prosolvent polymer component, and a method for producing the same. Background technology [0002] 　In recent years, polymer gels having a network structure have characteristics such as excellent water retention ability and biocompatibility, and therefore have medical purposes such as artificial tissues, materials for regenerated scaffolds, sealing, adhesion prevention, drug delivery, and contact lenses. Not only this, it is a material expected to be applied to various applications such as sensors and surface coatings (for example, Non-Patent Document 1). In particular, in applications such as materials for recycled scaffolding, it is desired to develop a polymer material having a porous structure having a size of μm scale. [0003] 　However, conventionally, in order to obtain a μm-scale porous structure, a top-down method such as microfabrication of a gel or polymer structure prepared in advance by lithography or the like is used, or a solvent-insoluble polymer is used. It was necessary to prepare a polymer material using the raw materials. On the other hand, when a pro-solvent polymer raw material is used, the material itself is dissolved in the solvent in the first place, or only a gel having a small porous structure on the nm scale can be prepared. Prior art literature Non-patent literature [0004] Non-Patent Document 1: Sakai et al., Macromolecules, 41, 5379-5384, 2008 Outline of the invention Problems to be solved by the invention [0005] 　Therefore, the present invention provides a gel material composed of a pro-solvent polymer having a porous structure on a μm scale, and further, in order to prepare such a polymer gel material from a pro-solvent polymer raw material. It is an object of the present invention to provide a manufacturing method suitable for the above. Means to solve problems [0006] 　As a result of diligent studies to solve the above problems, the present inventors have conventionally been unable to achieve this by cross-linking the pro-solvent polymer raw materials under the conditions of less than the overlapping concentration and less than the critical gelation concentration. It has been found that a gel having a μm-scale porous structure can be prepared from a pro-solvent polymer in one pot in a solvent by a bottom-up method. In addition, the obtained gel material behaves as if it were phase-separated in a poorly solvent-poor polymer, and has a sponge-like three-dimensional network structure (porous) consisting of a concentrated region in which polymer components are densely present and a dilute region in which polymer components are sparsely present. It was found that it has a peculiar structure of forming (body structure), which is not found in conventional polymer gels. Based on these findings, the present invention has been completed. [0007] 　That is, in one aspect, the present invention is a polymer gel in which <1> pro-solvent polymer units are crosslinked with each other, 　and contains a solvent, and the first region in which the polymer units are densely present. It has a three-dimensional network structure having two regions of a second region in which the polymer unit is sparsely present, and the network size composed of the first region has a size of 1 to 500 μm. , The polymer gel is provided. [0008] 　Further, a preferred embodiment of the polymer gel of the present invention is the polymer gel according to <1> above, which has a lower permeability than the permeability of the polymer unit before <2> gelation; <3> before gelation. The polymer gel according to <1> or <2> above, which has an osmotic pressure in the range of 1/5 to 1/2 with respect to the osmotic pressure of the polymer unit of <4>. The polymer gel according to any one of <1> to <3> above, wherein the osmotic pressure (Π os ) and the elastic pressure (Π ell ) have a relationship of Π el > Π os . <5> The above-mentioned <1> to <4>, wherein the polymer concentration in the first region is 10 to 99% by weight, and the polymer concentration in the second region is 0 to 1% by weight. Polymer gel according to any one of <1> to <5> above, which has a polymer content of <6> 5% by weight or less; <7> The polymer unit is a hydrophilic polymer. The polymer gel according to any one of <1> to <6>; <8> The polymer gel according to <7>, wherein the hydrophilic polymer is a polymer having a polyethylene glycol skeleton or a polyvinyl skeleton. ; <9> The polymer unit has a first polymer unit having one or more nucleophilic functional groups on the side chain or the terminal, and a second polymer having one or more electrophilic functional groups on the side chain or the terminal. composed of the unit, the <1> polymer gel according to any one of to <8>; and the <10> the nucleophilic functional group, a thiol group, an amino group, and -CO 2 PhNO 2 consisting Selected from the group, the electrophilic functional group consists of a maleimidyl group, an N-hydroxy-succinimidyl (NHS) group, a sulfosuccinimidyl group, a phthalimidyl group, an imidazolyl group, an acryloyl group, and a nitrophenyl group. It provides the polymer gel according to <9> above, which is selected . [0009] 　In another aspect, the present invention also relates to the above-mentioned method for producing a polymer gel, which is <11> a method for producing a polymer gel, wherein a) a pro-solvent raw material polymer is less than an overlapping concentration and a critical gelation concentration. The step of cross-linking under less than conditions to form a gel precursor, wherein the gel precursor has a G' a method for producing a polymer gel, c. ) In the presence of a non-reactive polymer of a predetermined concentration, the step of obtaining the polymer gel by cross-linking the pro-solvent raw materials polymers having a concentration less than the overlapping concentration and more than the critical gelation concentration with each other is included, wherein the non-reactive polymer is obtained. The reactive polymer is a polymer having no functional group capable of cross-linking with the raw material polymer in the molecule, and the polymer gel has a first region in which a polymer unit derived from the raw material polymer is densely present, and the above. The present invention provides the production method, which comprises a structure in which a polymer unit derived from a raw material polymer is composed of two regions of a second region in which sparsely existing ones are present. [0010] 　A preferred embodiment of the production method of the present invention is <13> the production method according to <11> or <12>, wherein the raw material polymer is a hydrophilic polymer; <14> the hydrophilic polymer is a polyethylene glycol skeleton or The production method according to <13> above, which is a polymer having a polyvinyl skeleton; <15> The raw material polymer has a side chain or a side chain or a first polymer having one or more nucleophilic functional groups at the end. The production method according to any one of <11> to <14> above, which comprises a second polymer having one or more electrophilic functional groups at the terminal; <16> The nucleophilic functional group is Selected from the group consisting of a thiol group, an amino group, and -CO 2 PhNO 2 , the electrophobic functional group is a maleimidyl group, an N-hydroxy-succinimidyl (NHS) group, a sulfosuccinimidyl group, a phthalimidyl group, The polymer gel according to <15> above, selected from the group consisting of an imidazolyl group, an acryloyl group, and a nitrophenyl group; <17> the gel precursor has a diameter in the range of 10 to 1000 nm. 11>. <18> The gel precursor is composed of a first gel precursor and a second gel precursor, and the first gel precursor and the second gel precursor are both 1 at the side chain or at the end. The first gel precursor is composed of a first polymer having the above nucleophilic functional groups and a second polymer having one or more electrophilic functional groups at the side chains or terminals, and the first gel precursor is a first polymer. The production according to <11> above, wherein the content of the polymer is higher than the content of the second polymer, and the content of the second gel precursor is higher than the content of the first polymer. Method; <19> The production method according to <11> above, wherein the step b) is carried out in the presence of a non-reactive polymer having no functional group capable of cross-linking with the gel precursor in the molecule. <20> The production method according to <12> or <19> above, wherein the non-reactive polymer is polyethylene glycol or cell roll having no cross-linking reactive group . Effect of the invention [0011] 　The polymer gel of the present invention forms a sponge-like three-dimensional network structure consisting of a concentrated region in which a prosolvent polymer component is densely present and a dilute region in which a prosolvent polymer component is sparsely present, thereby forming a μm-scale porous structure. Therefore, it can be a suitable material for cell infiltration and adhesion. Since such a porous structure can selectively reflect infrared light, it can also be applied to optical material applications such as optical filters. [0012] 　Further, according to the production method of the present invention, a gel having such a μm-scale porous structure, which has not been achieved in the past, is produced from a pro-solvent polymer in a solvent in one pot by a bottom-up method. can do. In addition, by using a method of gelling using a gel precursor formed in a state just before gelation as a seed, it is possible to carry out a gelation reaction on the spot after injecting the gel precursor into a living body or the like. Therefore, it can be used as an injectable gel material in closed or semi-closed cavities in the living body. A brief description of the drawing [0013] FIG. 1 is a graph showing the time scale of the gelation reaction in the polymer gel of the present invention prepared in Example 2. FIG. 2 is a graph showing a change in transmittance in the gelation step of the present invention. FIG. 3 is a graph showing changes in the transmittance of a comparative example gel that does not pass through a gel precursor. FIG. 4 is a graph showing the time variation of the swelling degree of the polymer gel of the present invention. FIG. 5 is a graph showing changes in the osmotic pressure (Π os ) of the polymer gel of the present invention . FIG. 6 is a fluorescence microscope image of the polymer gel (right) and the comparative example gel (left) of the present invention. Mode for carrying out the invention [0014] 　Hereinafter, embodiments of the present invention will be described. The scope of the present invention is not limited to these explanations, and other than the following examples, the scope of the present invention can be appropriately modified and implemented as long as the gist of the present invention is not impaired. [0015] (1) Polymer gel 　The polymer gel of the present invention is a polymer gel in which prosolvent polymer units are crosslinked with each other to form a gel, and contains a solvent. i) The polymer unit is It has a three-dimensional network structure having two regions, a first region in which the polymer unit is densely present and a second region in which the polymer unit is sparsely present. Ii) The network size composed of the first region is 1 to 1. It is characterized by having a size of 500 μm. [0016] 　That is, although the polymer gel of the present invention is formed from a pro-solvent polymer unit, it behaves as if the poor solvent polymer is phase-separated in the solvent, and the polymer is contained in the gel. It has a structure in which two regions having different polymer concentrations, a concentrated phase (first region) in which components are densely present and a dilute phase (second region) in which components are sparsely present, are formed. The polymer gel of the present invention forms a sponge-like three-dimensional network structure / porous structure by this phase separation (hereinafter, such a structure may be referred to as a “sponge-like porous structure”. It is also characterized in that its mesh size is on the order of μm, which is much larger than the order of nm obtained by conventional gels. Here, the first region is called a "rich phase" in the relative sense that the concentration (density) of the polymer unit existing in the region is higher than the density in the second region. Preferably, the first region has a concentration (density) of about 100 times that of the second region. [0017] 　In the present specification, the "gel" is generally a dispersion system of a polymer having a high viscosity and losing its fluidity, and the relationship between the storage elastic modulus G'and the loss elastic modulus G "is G'≥ G". Refers to the state of having. [0018] 　As described above, the polymer gel of the present invention is characterized by having a porous body structure on the order of μm. Specifically, the mesh size composed of the first region can be as large as 1 to 500 μm, preferably 10 to 100 μm. The mesh size means the length of the long side in the mesh unit (that is, the hole) in which the outer circumference is formed by the first region which is the dense phase. Alternatively, when the mesh unit is substantially circular, it may be the length of its diameter. Inside such a network unit, there is a second region and / or a solvent which is a dilute phase. [0019] 　Typically, the first region, which is the rich phase, has a polymer concentration of 10 to 99% by weight based on the entire gel containing the solvent, and the second region, which is the dilute phase, is 0 to 1% by weight. Has a high molecular concentration. Preferably, the first region has a polymer concentration of 40-80% by weight and the second region has a polymer concentration of 0.01-0.1% by weight. [0020] 　The polymer content of the entire polymer gel of the present invention is 5% by weight or less, preferably 4% by weight or less, and more preferably 1.5 to 3.0% by weight. [0021] 　As the solvent contained in the polymer gel of the present invention, water or an organic solvent can be used. As the organic solvent, alcohols such as ethanol and polar solvents such as DMSO can be used. Preferably, the solvent is water. When water is used as the solvent, the polymer gel containing such a solvent is a hydrogel. [0022] 　Hereinafter, the polymer unit constituting the polymer gel of the present invention and the characteristic physical properties exhibited by the polymer gel of the present invention will be described. [0023] 1-a. Polymer Unit 　The polymer unit　 used to form the polymeric gel of the present invention is a polysolvent, ie, soluble in the solvent contained in the gel. For example, when the gel is a hydrogel containing water as a solvent, the polymer unit is preferably a hydrophilic polymer. If the polymer unit can form a gel by a gelation reaction (crosslinking reaction, etc.) in a solution, a polymer unit known in the art is used according to the final gel application, shape, etc. Can be done. More specifically, in the final gel, polymer units capable of forming a network structure, particularly a three-dimensional network structure, by cross-linking the polymer units with each other are preferable. [0024] 　The hydrophilic polymer used as the polymer unit is preferably a polymer having a polyethylene glycol skeleton or a polyvinyl skeleton. Typical examples of the polymer having a polyethylene glycol skeleton include a polymer species having a plurality of branches of a polyethylene glycol skeleton, and a polymer species having four branches of a polyethylene glycol skeleton is particularly preferable. Such a gel composed of a tetrabranched polyethylene glycol skeleton is generally known as a Tele-PEG gel, and has an electrophilic functional group such as an active ester structure and a nucleophilic functional group such as an amino group at the terminals, respectively. A network structure network is constructed by an AB type cross-end coupling reaction between two types of tetrabranched polymers having In addition, Tetra-PEG gel can be easily prepared on the spot by a simple two-component mixing of each polymer solution, and the gelation time can be controlled by adjusting the pH and ionic strength at the time of gel preparation. Is. And since this gel contains PEG as a main component, it is also excellent in biocompatibility. [0025] 　Polymers other than the polyethylene glycol skeleton can be used as long as they can be crosslinked with each other and gelled. For example, a polymer having a polyvinyl skeleton such as methyl methacrylate can also be used. [0026] 　In order to form a sponge-like porous structure in the final gel, the polymer unit has one or more nucleophilic functional groups on the side chains or ends, but not necessarily limited to these. A means for reacting and cross-linking two kinds of polymer types, a first polymer unit and a second polymer unit having one or more nucleophilic functional groups at the side chain or the terminal, is preferable. Here, the total of the nucleophilic functional group and the electrophilic functional group is preferably 5 or more. It is more preferred that these functional groups are present at the ends. Further, the content of the first polymer unit can be higher than the content of the second polymer unit, or the content of the second polymer unit is higher than the content of the first polymer unit. Can also be. As will be described later, in a preferred embodiment, two or more types of gel precursors having different compositions can be formed once, and then the gel precursors can be further crosslinked to obtain a polymer gel. [0027] 　Examples of the nucleophilic functional group present in the polymer unit include a thiol group (-SH), an amino group, or -CO 2 PhNO 2 (Ph indicates an o-, m-, or p-phenylene group). A nucleophilic functional group known to those skilled in the art can be appropriately used. Preferably, the nucleophilic functional group is a -SH group. The nucleophilic functional groups may be the same or different, but they are preferably the same. When the functional groups are the same, the reactivity with the electrophilic functional group that forms a cross-linking bond becomes uniform, and it becomes easy to obtain a gel having a uniform three-dimensional structure. [0028] 　As the electrophilic functional group present in the polymer unit, an active ester group can be used. Examples of such an active ester group include a maleimidyl group, an N-hydroxy-succinimidyl (NHS) group, a sulfosuccinimidyl group, a phthalimidyl group, an imidazole group, an acryloyl group, a nitrophenyl group and the like. If so, other known active ester groups can be appropriately used. Preferably, the electrophilic functional group is a maleimidyl group. The electrophilic functional groups may be the same or different, but they are preferably the same. When the functional groups are the same, the reactivity with the nucleophilic functional group that forms a cross-linking bond becomes uniform, and it becomes easy to obtain a gel having a uniform three-dimensional structure. [0029] 　A preferred non-limiting example of a polymer unit having a nucleophilic functional group at the end is represented by the following formula (I), for example, having a branch of four polyethylene glycol skeletons and having a thiol group at the end. Examples include compounds. [Chemical 1] [0030] 　n 11 to n 14 may be the same or different from each other. The closer the values ​​of n 11 to n 14, the more uniform the three-dimensional structure can be obtained, and the higher the strength becomes. Therefore, in order to obtain a high-strength gel, it is preferable that they are the same. If the values ​​of n 11 to n 14 are too high, the strength of the gel will be weakened, and if the values ​​of n 11 to n 14 are too low, the gel will not be easily formed due to steric hindrance of the compound. Therefore, n 11 to n 14 include integer values ​​of 25 to 250, preferably 35 to 180, more preferably 50 to 115, and particularly preferably 50 to 60. The molecular weight thereof includes 5 × 10 3 to 5 × 10 4 Da, preferably 7.5 × 10 3 to 3 × 10 4 Da, and more preferably 1 × 10 4 to 2 × 10 4 Da. [0031] 　In the above formula (I), R 11 to R 14 are linker sites that connect the functional group and the core portion. R 11 to R 14 may be the same or different from each other, but are preferably the same in order to produce a high-strength gel having a uniform three-dimensional structure. R 11 ~ R 14 is, C 1 -C 7 alkylene group, C 2 -C 7 alkenylene group, -NH-R 15 -, - CO-R 15 -, - R 16 -O-R 17 -, - R 16 -R -NH 17 -, - R 16 -CO 2 -R 17 -, - R 16-CO 2 -NH-R 17 -, - R 16 -CO-R 17 -, R 16 -NH-CO-R 17 - or -R 16 -CO-NH-R 17 - shows the. Here, R 15 is C 1 -C 7 represents an alkylene group. R 16 is C 1 -C 3 shows an alkylene group. R 17 is C 1 -C 5 represents an alkylene group. [0032] 　Here, "C 1 -C 7 and the alkylene group" carbon atoms, which may have a branch means 1 to 7 alkylene group, a linear C 1 -C 7 or one alkylene group or 2 One or more C having a branched 2 -C 7 alkylene group (number of carbon atoms including branching 2 to 7) means. C 1 -C 7 Examples of alkylene groups include methylene, ethylene, propylene, butylene group. C 1 -C 7 Examples of alkylene groups, -CH 2 -, - (CH 2 ) 2 -, - (CH 2 ) 3 -, - CH (CH 3 ) -, - (CH 2 ) 3 -, - ( CH (CH 3))) 2 -,-(CH 2 ) 2- CH (CH 3 )-,-(CH 2 ) 3- CH (CH 3 )-,-(CH 2 ) 2- CH (C 2 H 5 )-,- (CH 2 ) 6 -,-(CH 2 ) 2- C (C 2 H 5 ) 2- , and-(CH 2 ) 3 C (CH 3 ) 2 CH 2-And so on. [0033] 　"C 2 -C 7 and the alkenylene group" is a one or two or more Jo or branched having 2 to 7 carbon atoms alkenylene group having a double bond in the chain, for example, the Examples thereof include a divalent group having a double bond formed by removing 2 to 5 hydrogen atoms of adjacent carbon atoms from an alkylene group. [0034] 　On the other hand, as a non-limiting specific example preferable as a polymer unit having an electrophilic functional group at the terminal, for example, it is represented by the following formula (II) having a branch of four polyethylene glycol skeletons and a maleimidyl group at the end. Examples of the compound to be used. [Chemical 2] [0035] 　In the above formula (II), n 21 to n 24 may be the same or different from each other. The closer the values ​​of n 21 to n 24 are, the more uniform the three-dimensional structure can be obtained and the higher the strength of the gel, which is preferable, and it is preferable that the gels are the same. If the values ​​of n 21 to n 24 are too high, the strength of the gel will be weakened, and if the values ​​of n 21 to n 24 are too low, the gel will not be easily formed due to steric hindrance of the compound. Therefore, n 21 to n 24 may be an integer value of 5 to 300, preferably 20 to 250, more preferably 30 to 180, further preferably 45 to 115, and even more preferably 45 to 55. Examples of the molecular weight of the second tetrabranched compound of the present invention include 5 × 10 3 to 5 × 10 4 Da, preferably 7.5 × 10 3 to 3 × 10 4 Da, and 1 × 10 4 to 2 ×. 10 4Da is more preferred. [0036] 　In the above formula (II), R 21 to R 24 are linker sites that connect the functional group and the core portion. R 21 to R 24 may be the same or different from each other, but are preferably the same in order to produce a high-strength gel having a uniform three-dimensional structure. Wherein (II), R 21 ~ R 24 are the same or respectively, C 1 -C 7 alkylene group, C 2 -C 7 alkenylene group, -NH-R 25 -, - CO-R 25 -, - R 26 -O-R 27 -, - R 26 -NH-R 27 -, - R 26 -CO 2 -R 27 -, - R 26 -CO 2 -NH-R 17 -, - R 26 -CO-R 27 -, - R 26 -NH-CO-R 27 -, or -R 26 -CO-NH-R 27 - shows the. Here, R 25 is C 1 -C 7 represents an alkylene group. R 26 is C 1 -C 3 shows an alkylene group. R 27 is C 1 -C 5 represents an alkylene group. [0037] 　In the present specification, the alkylene group and the alkenylene group may have one or more arbitrary substituents. Examples of the substituent include an alkoxy group, a halogen atom (which may be a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom), an amino group, a mono or di-substituted amino group, a substituted silyl group, and an acyl group. Groups, aryl groups and the like can be mentioned, but are not limited thereto. If the alkyl group has two or more substituents, they may be the same or different. The same applies to the alkyl moiety of other substituents containing the alkyl moiety (eg, alkyloxy group, aralkyl group, etc.). [0038] 　Further, in the present specification, when it is defined that a certain functional group "may have a substituent", the type of the substituent, the position of the substituent, and the number of the substituents are not particularly limited. If they have two or more substituents, they may be the same or different. Examples of the substituent include, but are not limited to, an alkyl group, an alkoxy group, a hydroxyl group, a carboxyl group, a halogen atom, a sulfo group, an amino group, an alkoxycarbonyl group, an oxo group and the like. Substituents may be further present in these substituents. [0039] 1-b. Physical Properties 　of Polymer Gel As described above, the polymer gel of the present invention has a μm-order sponge-like porous structure formed in the gel by a thick phase (first region) and a dilute phase (second region). It has and has characteristic properties in terms of various physical properties depending on such a structure. [0040] 　The polymer gel of the present invention has a lower transmittance than the transmittance of the polymer unit before gelation. This is because the polymer gel of the present invention has two regions in the gel, a concentrated phase (first region) and a dilute phase (second region), which have different polymer concentrations, as if a poor solvent polymer is the solvent. Because it behaves as if it is phase-separated inside, it is not completely transparent but becomes cloudy. Preferably, the polymeric gel of the present invention has a permeability in the range of 90-96%. In terms of such transmittance, it exhibits properties completely different from those of ordinary polymer gels, which are almost transparent. [0041] 　The polymer gel of the present invention has an osmotic pressure in the range of 1/5 to 1/2 with respect to the osmotic pressure of the polymer unit before gelation. It also has a lower osmotic pressure than a single phase polymer gel formed from the same polymer unit. [0042] 　Further, in the polymer gel of the present invention, the osmotic pressure (Π os ) and the elastic pressure (Π el ) after a lapse of a certain period of time from gelation have a relationship of Π el > Π os . The relationship that Π el is larger than Π os indicates that the gel is in a contracting state. In contrast, ordinary polymer gels generally have a relationship of Π el <Π os and tend to swell. [0043] 　Although not necessarily bound by theory, the polymer gel of the present invention has a structure like a two-phase separation of a concentrated phase and a dilute phase, so that the osmotic pressure (Π os ) of the dilute phase is increased. It is understood that the gel is lower than that of a normal single-phase polymer gel, while the gel tends to shrink due to an increase in elastic pressure. In these respects, it can be said that the polymer gel of the present invention has characteristic properties that are significantly different from those of conventional polymer gels. [0044] 　Further, as described above, since the polymer densities of the polymer units are different between the concentrated phase and the dilute phase, the polymer gel of the present invention can have different water contents in these two regions. Specifically, in the polymer gel of the present invention, the water content of the first region (concentrated phase) is in the range of 10 to 99%, and the water content of the second region (lean phase) is 99 to 100%. Is the range of. [0045] 　The polymer gel of the present invention can be processed into various shapes such as a thin film depending on its use. For such processing, any method known in the art can be used. For example, in the case of a thin film, the thin film can be obtained by, for example, applying it on a flat substrate such as glass in a state where the gel has fluidity before it is completely solidified. [0046] (2) Method for Producing Polymer Gel 　Next, the method for producing the polymer gel (gelling step) of the present invention will be described. The polymer gel of the present invention can be produced by the steps shown in the following first and second aspects, and in any of the embodiments, the pro-solvent raw material polymer is crosslinked under the condition of overlapping concentration or less. It is characterized by. In the production method of the present invention, it has been newly found that a polymer gel having a porous structure on the order of μm, which was difficult in the past, can be produced from a prosolvent polymer by performing a gelation step under such conditions. Is. [0047] 2-a. First Aspect of Production Method The production method of the 　present invention is characterized in that, in the first aspect, the following steps are included: a) Conditions under which the prousophilic raw material polymer is less than the overlap concentration and less than the critical gelation concentration. B) A step of cross-linking the gel precursors with a cross-linking agent to obtain a polymer gel, which is the final target product. [0048] 　In step a), the raw material polymer (polymer unit) that finally constitutes the polymer gel is reacted in a state just before gelation, and has a structure that does not yet form a gel, that is, a sol state. This is a step of forming a gel precursor (polymer cluster) of the above. Then, in step b), if desired, an appropriate cross-linking agent is added, these gel precursors are further reacted with each other, and the gel precursors are three-dimensionally cross-linked with each other to obtain a polymer gel as a final product. Here, the gel precursor is not necessarily limited to a single species having the same composition as described later, and a plurality of gel precursors having different compositions can also be used. As described above, the first aspect of the production method of the present invention is based on the concept of using a gel precursor as a so-called final gel intermediate. [0049] 　In step a), conditions are used in which the initial concentration of the raw material polymer is less than the overlapping concentration and less than the critical gelation concentration. By using the initial concentration of such a raw material polymer, a gel precursor having a sol state that does not lead to gelation, preferably a structure on the verge of gelation, can be formed. [0050] 　The initial concentration of the starting polymer in step a), the overlap concentration C * is less than, preferably 1 / 3C * is less than. Here, the "overlapping concentration" (also referred to as "overlapping concentration") is the concentration at which the polymers in the solvent start to come into spatial contact with each other. Generally, the overlapping concentration C * is expressed by the following formula. expressed. [Number 1] (wherein, M w is an weight average molecular weight of the polymer; alpha had a specific gravity of the solvent; N A is Avogadro constant; R g is the radius of gyration of the polymer.). [0051] For the calculation method of the 　overlap concentration C * , for example, Polymer Physics (written by M. Rubinstein, R. Colby) can be referred to. Specifically, for example, it can be obtained by using the Flory Fox formula from the viscosity measurement of a dilute solution. [0052] 　Further, in step a), the initial concentration of the raw material polymer is set to be less than the critical gelation concentration. Here, "critical gelation concentration" means the minimum concentration of the raw material polymer required to achieve the gelation in a system for constructing a gel having a three-dimensional structure by cross-linking the raw material polymer, and the minimum gelation. Also called concentration. In the present invention, the term critical gelation concentration refers to, for example, in a system in which two or more kinds of raw material polymers are used, in addition to the case where the total concentration does not reach the concentration leading to gelation, one kind of raw material polymer. The case where only the concentration of the polymer is low, that is, the case where the ratio of each raw material polymer is non-equivalent does not cause gelation is also included. [0053] 　In general, the critical gelation concentration (minimum gelation concentration) depends on the type of raw material polymer used, but such concentration is known in the art or can be easily grasped experimentally by those skilled in the art. Can be done. Typically, it is 0.5 to 5% by weight, and the lower limit is a concentration of about 1/5 of the overlapping concentration. [0054] 　As a method for adjusting the initial concentration of the raw material polymer to a condition lower than the critical gelation concentration, for example, when two types of polymer units having a nucleophilic functional group or an electrophilic functional group are used as described above, they are used. Conditions that do not cause gelation by using low concentration conditions that contain equivalent amounts but are not sufficient to lead to gelation as a whole, or by making the concentration of one polymer unit low, that is, non-equivalent. Can be used. [0055] 　Step a) can typically be performed by mixing or stimulating a solution containing the two raw material polymers. It can also be carried out by radical polymerization of a monomer using a radical initiator. The concentration, addition rate, mixing rate, and mixing ratio of each solution are not particularly limited and can be appropriately adjusted by those skilled in the art. Further, it will be clear that even when three or more kinds of raw material polymers are used, a solution containing the corresponding raw material polymer can be prepared in the same manner and they can be appropriately mixed. As the solvent of the solution containing the raw material polymer, water, alcohols such as ethanol, DMSO and the like can be used. When the solution is an aqueous solution, an appropriate pH buffer solution such as a phosphate buffer solution can be used. [0056] 　As a means of mixing, for example, a two-component mixing syringe as disclosed in WO2007 / 083522 can be used. The temperature of the two liquids at the time of mixing is not particularly limited, and may be any temperature as long as the precursor units are dissolved and each liquid has fluidity. For example, the temperature of the solution at the time of mixing may be in the range of 1 ° C. to 100 ° C. The temperatures of the two liquids may be different, but it is preferable that the two liquids have the same temperature because the two liquids are easily mixed. [0057] 　The gel precursor obtained in step a) has a structure in which precursor units are bonded or crosslinked with each other, but is formed under conditions that do not yet lead to gelation. Therefore, the gel precursor has a G' G ”relationship at the end point of the reaction, and that a polymer gel was formed by cross-linking the gel precursor. (Fig. 1). Example 3 [0077] Permeability of Polymer Gel 　FIG. 2 shows a change in the transmittance in the gelation step of Example 2. The transmittance was calculated from the time change of the absorbance at 25 ° C. and a wavelength of 400 nm after mixing the two liquids of the gel precursor and injecting them into the cell. In the figure, changes in G'and G'are also shown, and the point where G'= G'is is the gel point. [0078] 　Further, as a comparative example, the change in transmittance of a single-phase polymer gel obtained by mixing two liquids of a 60 g / L SHPEG solution and a MPEG solution, respectively, without passing through a gel precursor, and G'and G. "Changes are shown in FIG. [0079] 　From the comparison between FIGS. 2 and 3, in the normal gel without the gel precursor (FIG. 3), almost no change in the transmittance was observed before and after gelation (T = around 98%), whereas in the examples. It was found that in the polymer gel No. 2 (FIG. 2), the transmittance T decreased significantly from about 99% to about 94% with gelation, and the gel became cloudy. This is because, in the polymer gel of the present invention, two regions, a concentrated phase in which polymer units are densely present and a dilute phase in which polymer units are sparsely present, are generated due to gelation, and phase separation occurs. Example 4 [0080] Swelling test 　of polymer gel A swelling test was conducted on three types of the polymer gel (a, b) of the present invention and the gel (c) of the comparative example. Gels a and b were synthesized according to Example 2. a) Oligo-Tetra-PEG gel (10 g / L): 　According to Example 2, two gel precursors were prepared at 20 g / L, r = 0.78; 20 g / L, r = 0.22. Each gel precursor solution is diluted to 10 g / L, and the two solutions are mixed to form a gel. b) Oligo-Tetra-PEG gel (20 g / L): 　Two gel precursors were prepared at 20 g / L, r = 0.78, 20 g / L, r = 0.22 according to Example 2. Each gel precursor solution is mixed as it is and gelled. c) Tetra-PEG gel (comparative example): 　Gelation was performed by mixing two solutions of 60 g / L SHPEG solution and MALPEG solution. [0081] 　A cylindrical sample (height 7 mm, diameter 15 mm) was prepared, and after the gelation reaction was sufficiently completed (1 day), it was immersed in pure water and the time change of the swelling degree was measured at 25 ° C. The obtained results are shown in FIG. [0082] 　In normal gel c that did not pass through the gel precursor, swelling of the gel was observed over time. On the other hand, the polymer gel of the present invention showed a characteristic property of shrinking with long relaxation. Example 5 [0083] Osmotic pressure test 　of polymer gel The osmotic pressure (Π os ) and elastic pressure (Π el ) of the polymer gel of the present invention prepared according to Example 2 were measured. As a comparative example, the same measurement was carried out for a normal gel that did not pass through the raw material polymer before gelation and the gel precursor. 　-Polymer gel of the present invention: According to Example 2, a gel prepared under a plurality of conditions where the concentration of the gel precursor solution was 10, 12.5, 15, 17.5, and 20 g / L was used. -Ingredient polymer: 　10, 20, 30, 40, 50, 60 g / L each MALEP solution was used. 　-Comparative Example Gel: A gel obtained by mixing two solutions of 10, 20, 30, 40, 50, and 60 g / L SHPEG solution and MALEP solution, respectively, was used. [0084] 　A sample was prepared in the dialysis membrane, dialyzed against a PVP solution (29 k, 5-120 g / L), and the concentration of PVP that did not swell from the initial state was determined. In that respect, the swelling pressure of the gel (Π os -Π el ) and the osmotic pressure of PVP (Π PVP ) are balanced. Separately, the elastic pressure (Π el = G') was measured with a rheometer, and Π os was calculated using the following formula . [Number 2] [0085] A plot of 　the osmotic pressure (Π os ) obtained at each gelation concentration (C) is shown in FIG. As a result, it was found that the polymer gel of the present invention had a low osmotic pressure with respect to both the raw material polymer and the comparative example gel having the same concentration at the overlapping concentration (C * ) or less. Example 6 [0086] Fluorescence microscope image of polymer gel 　Two structures of the gel of the present invention and the gel of Comparative Example were observed using a two-photon laser microscope (Zeiss). a) Oligo-Tetra-PEG gel (10 g / L): 　According to Example 2, two gel precursors were prepared at 20 g / L, r = 0.78; 20 g / L, r = 0.22. Each gel precursor solution is diluted to 10 g / L, and the two solutions are mixed to form a gel. b) Tetra-PEG gel (comparative example): 　Gelation was performed by mixing two solutions of 60 g / L SHPEG solution and MALPEG solution. [0087] 　After preparing the gel samples a and b above, the gel samples were allowed to stand in water for 7 days. Primary staining: Immersed in anti-PEG solution (0.04 g / L), allowed to stand for 1 hour, and washed for 15 minutes three times. Secondary staining: Immersed in antibody-AlexaFloar488 (0.04 g / L), allowed to stand for 1 hour, and washed 3 times for 15 minutes. [0088] 　The obtained fluorescence microscope image is shown in FIG. The Terra-PEG gel of the comparative example (right figure) has a network structure on the order of nm, whereas the polymer gel of the present invention (figure on the left) has a structure on the order of μm much larger than the structure predicted from the molecular structure. It was found to have a network structure (porous structure). The μm-order network structure has an outer circumference formed by a dense phase in which a polymer is densely present, and the inside thereof is a dilute phase or a solvent. Example 7 [0089] Cell Adhesion of Polymer Gel The cell adhesion to the polymer gel of 　the present invention prepared in Example 2 was also evaluated. As a result, it was confirmed that the polymer gel of the present invention can adhere ATDC5 (somatic cell-type universal cell) more efficiently than a normal Tetra-PEG gel (comparative example) that does not pass through a gel precursor. [0090] 　The above results can be obtained by cross-linking the polymer raw materials under the conditions of less than the overlapping concentration and less than the critical gelation concentration, and the obtained gel behaves as if it were phase-separated in a poor solvent polymer, which cannot be achieved in the past. This is to demonstrate that a gel having a μm-scale porous structure can be prepared in a solvent in one pot. The scope of the claims [Claim 1] 　A polymer gel in which pro-solvent polymer units are crosslinked with each other 　, and there are two regions, a first region 　containing a solvent and in which the polymer units are densely present, and a second region in which the polymer units are sparsely present. The 　polymer gel having a three-dimensional network structure having one region, and having a network size of 1 to 500 μm composed of the first region. [Claim 2] 　The polymer gel according to claim 1, which has a transmittance lower than the transmittance of the polymer unit before gelation. [Claim 3] 　The polymer gel according to claim 1 or 2, which has an osmotic pressure in the range of 1/5 to 1/2 with respect to the osmotic pressure of the polymer unit before gelation. [Claim 4] 　Osmotic pressure after a predetermined time has elapsed since gelation ([pi os ) and elastic pressure ([pi el ) is, [pi el > [pi os have the relationship of a polymer gel according to any one of claims 1-3. [Claim 5] 　The polymer gel according to any one of claims 1 to 4, wherein the polymer concentration in the first region is 10 to 99% by weight, and the polymer concentration in the second region is 0 to 1% by weight. [Claim 6] 　The polymer gel according to any one of claims 1 to 5, which has a polymer content of 5% by weight or less. [Claim 7] 　The polymer gel according to any one of claims 1 to 6, wherein the solvent is water and the polymer unit is a hydrophilic polymer. [Claim 8] 　The polymer gel according to claim 7, wherein the hydrophilic polymer is a polymer having a polyethylene glycol skeleton or a polyvinyl skeleton. [Claim 9] 　The polymer unit comprises a first polymer unit having one or more nucleophilic functional groups in the side chain or terminal and a second polymer unit having one or more electrophilic functional groups in the side chain or terminal. , The polymer gel according to any one of claims 1 to 8. [Claim 10] 　The nucleophilic functional group is selected from the group consisting of a thiol group, an amino group, and -CO 2 PhNO 2 , and the electrophilic functional group is a maleimidyl group, an N-hydroxy-succinimidyl (NHS) group, a sulfosque. The high molecular weight gel according to claim 9, which is selected from the group consisting of a synimidyl group, a phthalimidyl group, an imidazolyl group, an acryloyl group, and a nitrophenyl group. [Claim 11] 　A method for producing a polymer gel, a) a step of cross-linking a pro-solvent raw material polymer under conditions of less than an overlapping concentration and less than a critical gelation concentration to form a gel precursor, wherein the gel precursor is formed. Has a relationship of G'