JPH09208802A - Water-in-oil microemulsion of water-soluble vinyl polymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a water-in-oil microemulsion of a water-sol. vinyl polymer excellent in aging stability by incorporating a specific oil-sol. polyoxyalkylene compd. into the same and by controlling the average particle size of the water phase to a specified value or lower. SOLUTION: This microemulsion is prepd. by incorporating an oil-sol. polyoxyalkylene compd. represented by the general formula: R<1> -[(OR<2> )n -(OR<3> )]m (wherein R<1> is a residue formed by removing OH groups from a mono to hexahydroxyl compd. or from a mono - to hexacarboxylic acid; R<2> is a 2-4C alkylene; R<3> is H, a 1-2C alkyl, alkenyl, alkyloyl, or alkenyloyl; (n) is 1-120; and (m) is 1-6) into a water-in-oil microemulsion comprising a water-sol. vinyl polymer, water, a liq. hydrocarbon having an initial b.p. of 150 deg.C or higher, and a surface and has an average particle size of the water phase of 700μm or lower.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a water-in-oil type microemulsion. More specifically, it relates to a water-in-oil type microemulsion of a water-soluble vinyl polymer which is useful as a wastewater treatment agent, a papermaking agent, a thickening agent, a drilling mud additive and the like.

[0002]

2. Description of the Related Art Conventionally, the following water-in-oil emulsions of water-soluble vinyl polymers are known. A water-in-oil emulsion containing a water-soluble vinyl polymer, water, an aliphatic hydrocarbon liquid such as isoparaffin, and an emulsifier, and having a transmittance and a viscosity within specific ranges (Japanese Patent Laid-Open No. 54-1544).
37, JP-A-54-102388, etc.). It contains a water-soluble vinyl polymer, a water-soluble water-in-oil emulsifier, a hydrocarbon liquid such as kerosene and an aqueous phase, and the aqueous phase is 25 to 70% by weight, preferably 34 to 3% by weight of the whole emulsion.
Water-in-oil emulsion accounting for 5% by weight (JP-A-60-
127302). A water-in-oil emulsion of a polyacrylamide polymer using a polyalkenyl succinic anhydride derivative as an emulsifier (JP-A-63-69531). A water-in-oil emulsion of a polyacrylamide polymer obtained by adding amines described in JP-A-54-154437 during polymerization (JP-A-57-6).
5706). A water-in-oil emulsion of a water-soluble copolymer in which a hydrocarbon liquid such as isoparaffin is used and the amount of the emulsifier used is specified (JP-A-61-2706).

[0003]

However, these conventional water-in-oil emulsions of water-soluble vinyl polymers have the following problems.
There are drawbacks in that the viscosity changes over time, and serious phase separation occurs.

[0004]

The present inventors have arrived at the present invention as a result of extensive studies to obtain a water-in-oil emulsion that solves the above problems. That is, the present invention provides a water-in-oil microemulsion of a water-soluble vinyl polymer, which comprises a water-soluble vinyl polymer (a), water (b), a hydrocarbon liquid (c) and a surfactant (d), and A water-in-oil type microemulsion containing the oil-soluble polyoxyalkylene compound (e) represented by the formula (1) and having an average particle diameter of the water phase of 700 mμ or less. R ¹ -[(OR ² ) _n -OR ³ ] _m (1) [In the formula, R ¹ is a residue obtained by removing an OH group from a monovalent to hexavalent hydroxyl group-containing compound, or an OH from a monovalent to hexavalent carboxylic acid. R ² is an alkylene group having 2 to 4 carbon atoms (provided that at least a part of n R ² is an alkylene group having 3 to 4 carbon atoms); R ³ is H and has a carbon number. 1 to 26 alkyl group, alkenyl group, alkyloyl group or alkenyloyl group; n is an integer of 1 to 120; m is an integer of 1 to 6. ]

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the water-soluble vinyl monomer (a ') constituting the water-soluble vinyl polymer (a) is a nonionic, anionic or cationic water-soluble vinyl monomer. One or more monomers selected from the group consisting of Among these, examples of the nonionic vinyl monomer include acrylamide and methacrylamide.

Examples of the anionic vinyl monomer include a carboxylic acid (salt) group-containing anionic vinyl monomer and a sulfonic acid (salt) group-containing anionic vinyl monomer. Specific examples of the carboxylic acid (salt) group-containing anionic vinyl monomer include unsaturated monocarboxylic acids such as (meth) acrylic acid, unsaturated dicarboxylic acids such as maleic acid, and salts thereof (alkali metal salts, ammonium salts). Salt, amine salt, etc.) and the like. Examples of the sulfonic acid (salt) group-containing anionic vinyl monomer include vinyl sulfonic acid, styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid and salts thereof (alkali metal salt, ammonium salt, amine salt). Etc.) and the like.

Examples of the cationic water-soluble vinyl monomer include the following [1] to [4]. [1] Cationic (meta) represented by the following general formula (2)
Acrylic vinyl monomer (In the formula, R ¹ is H or CH ₃ ; R ² and R ³ are each independently an alkyl group having 1 to 4 carbon atoms or a hydroxyalkyl group having 2 to 4 carbon atoms; R ⁴ is H and 1 to 4 carbon atoms. Alkyl group, C2-C4 hydroxyalkyl group or benzyl group; A is an oxygen atom or NH; Z is C1-C4
Or an alkylene group having 2 to 4 carbon atoms; X represents an anion. )

Specific examples of the cationic (meth) acrylic vinyl monomer represented by the general formula (2) include quaternary nitrogen-containing (meth) acrylate [2- (meth) acryloyloxyethyltrimethylammonium chloride. Two
-(Meth) acryloyloxyethyldimethylbenzylammonium chloride, (meth) acryloyloxyethyltrimethylammonium methosulfate and other (meth) acryloyloxyalkyltrialkylammonium salts], tertiary nitrogen-containing (meth) acrylates [Sulfate of 2-dimethylaminoethyl (meth) acrylate, salt of dialkylaminoalkyl (meth) acrylate such as hydrochloride of 2-diethylaminoethyl (meth) acrylate], quaternary nitrogen-containing (meth) acrylamide [ A (meth) acryloylaminoalkyltrialkylammonium salt such as 2- (meth) acryloylaminoethyltrimethylammonium sulfate], a salt of a tertiary nitrogen-containing (meth) acrylamide [2-dimethylaminoethyl (meth Hydrochloride acrylamide, 2-dimethylaminoethyl (meth) dialkylaminoalkyl (meth) salts of acrylamide, such as acetates acrylamide], and the like.

[2] Cationic vinylbenzyl monomer Vinylbenzyltrimethylammonium chloride and the like. [3] Cationic Dialkyldiallyl Vinyl Monomer Dialkyldiallylammonium salt such as dimethyldiallylammonium chloride. [4] Other cationic vinyl monomers Vinyl imidazoline, vinyl pyridine, vinyl dimethylaminoacetate hydrochloride and the like.

Among the above-exemplified water-soluble vinyl monomers (a '), preferable ones are acrylamide and acrylic acid, considering that an emulsion having more excellent stability can be obtained and from an industrial viewpoint. And a salt thereof, 2- (meth) acryloyloxyethyltrimethylammonium chloride, and a combination of two or more thereof.

As a monomer constituting the water-soluble vinyl polymer (a), if necessary, together with the water-soluble vinyl monomer (a ') exemplified above, a water-insoluble vinyl monomer copolymerizable therewith [Styrene, vinyl acetate, butyl (meth)
Acrylate, acrylonitrile, etc.] in an amount within the range in which the produced vinyl polymer maintains water solubility (usually 30% by weight or less based on all vinyl monomers, preferably 1
5 wt% or less) may be used.

Specific examples of the water-soluble vinyl polymer (a) include the following. Nonionic water-soluble vinyl polymer: poly (meth) acrylamide, etc. Anionic water-soluble vinyl polymer: (meth) acrylamide- (meth) acrylic acid sodium copolymer, (meth) acrylamide- (meth) acryloylamino-2,2-
Sodium dimethyl ethane sulfonate- (meth) acrylic acid sodium copolymer and the like. Cationic water-soluble vinyl polymer: (meth) acrylamide- (meth) acryloyloxyethyltrimethylammonium chloride copolymer, (meth) acrylamide- (meth) acryloyloxyethyldimethylbenzylammonium chloride copolymer, and the like. Amphoteric water-soluble vinyl polymer: (meth) acrylamide-
(Meth) acrylic acid- (meth) acryloyloxyethyltrimethylammonium chloride copolymer, (meth)
Acrylamide-itaconic acid-dimethylaminoethyl (meth) acrylate sulfate copolymer etc.

The molecular weight of the water-soluble vinyl polymer (a) is not particularly limited, but the intrinsic viscosity is usually 3 to 30 dl / g,
It is preferably 5 to 25 dl / g. When the intrinsic viscosity is within the usual range, it is preferable in terms of practical performance and workability. The intrinsic viscosity is a value measured at 30 ° C. in a 1N sodium nitrate aqueous solution.

The water (b) in the water-in-oil type microemulsion of the present invention is preferably distilled water or ion-exchanged water, but tap water or the like may be used depending on the water quality.

The hydrocarbon liquid (c) in the present invention has an initial boiling point of usually 150 ° C or higher, preferably 200 ° C or higher. Those having an initial boiling point in the normal range are preferable from the viewpoint of stability of emulsion over time. The (c) is mainly obtained as a by-product of petroleum refining, and is obtained by extracting a hydrocarbon liquid satisfying this condition or blending a plurality of hydrocarbon liquids in the petroleum refining process.

Examples of the surfactant (d) in the present invention include a nonionic surfactant, an anionic surfactant, a cationic surfactant or an amphoteric surfactant. Examples of nonionic surfactants include higher alcohol ethylene oxide adducts such as lauryl alcohol polyoxyethylene ether; higher fatty acid esters such as sorbitan diester stearate and sorbitan oleic acid monoester; polyoxyethylene nonyl phenyl ethers and the like. Oxyethylene alkyl ether;
Long-chain alkyl alkanolamides such as N, N-dihydroxyethyllaurylamide; fatty acid sorbitan ester ethylene oxide adducts such as oleic acid sorbitan ester ethylene oxide adduct. Of these, fatty acid sorbitan ester ethylene oxide adducts, higher alcohol ethylene oxide adducts, higher fatty acid esters and long-chain alkylalkanolamides are preferable, and fatty acid sorbitan ester ethylene oxide adducts (d1) are particularly preferable. The fatty acid of the fatty acid sorbitan ester ethylene oxide adduct has a carbon number of 8 to 30, and for example, lauric acid,
Examples thereof include oleic acid and stearic acid.

Examples of the anionic surfactant include carboxylate type such as oleic acid soap; sulfate ester type such as higher alcohol sulfate ester salt; sulfonate type such as sulfosuccinic acid diester; higher alcohol phosphoric acid. Examples thereof include phosphate ester salt types such as ester salts.
Of these, the sulfonate type is preferable, and the sulfosuccinic acid diester type (d2) is particularly preferable.
Examples of the cationic surfactants include amine salt types such as aliphatic amine ethylene oxide adducts or aromatic amine ethylene oxide adducts and salts of higher aliphatic amines; quaternary ammonium salt types such as higher alkyl amine ammonium salts. Is mentioned. Of these, amine salt type is preferable, and amine ethylene oxide adduct (d3) is particularly preferable. Examples of the amphoteric surfactant include amino acid type such as higher alkylaminocarboxylic acid salt; betaine type such as higher alkyldimethylbetaine.

The surfactant (d) may be added during the polymerization of (a) or after the polymerization. In the present invention, when the water-soluble vinyl polymer (a) is a nonionic or anionic water-soluble polymer, the surfactant (d) is preferably a combination of (d1) and (d2). When (d1) and (d2) are used in combination, the weight ratio of (d1) and (d2) is usually 99/1 to 1/99, preferably 70/30.
-30/70, more preferably 60 / 40-40 / 6
0. When the water-soluble vinyl polymer (a) is a nonionic or cationic water-soluble polymer, the surfactant (d) is preferably a combination of (d1) and (d3). When (d1) and (d3) are used in combination, the weight ratio is usually 99/1 to 1/99, preferably 90/10 to 5
It is 0/50, more preferably 85/15 to 60/40.

The oil-soluble polyoxyalkylene compound (e) in the present invention is a compound represented by the above general formula (1). In the general formula (1), R ¹ is a residue obtained by removing an OH group from a ^1- to 6-valent hydroxyl group-containing compound, or 1 to 6
It is a residue obtained by removing an OH group from a carboxylic acid. Examples of the 1- to 6-valent hydroxyl group-containing compound include a monovalent hydroxyl group-containing compound such as butanol; a divalent hydroxyl group-containing compound such as ethylene glycol; a trivalent hydroxyl group-containing compound such as glycerin; Examples thereof include pentavalent hydroxyl group-containing compounds such as fructose; and hexavalent hydroxyl group-containing compounds such as sorbitol.

Examples of the mono- and hexavalent carboxylic acids include monovalent carboxylic acids such as octyl acid; divalent carboxylic acids such as succinic acid; trivalent or more valent acids such as trimellitic acid, pyromellitic acid and other polycarboxylic acids. Examples thereof include carboxylic acids.

R ² is an alkylene group having 2 to 4 carbon atoms (provided that at least a part thereof is an alkylene group having 3 to 4 carbon atoms). The weight ratio of the alkylene group having 3 to 4 carbon atoms and the alkylene group having 2 carbon atoms is usually 100/0 to 70/30.
Range, preferably 100/0 to 80/20, and more preferably 100/0 to 90/10. Carbon number 2
When the weight ratio of the alkylene group is more than 30, the hydrophilicity becomes strong and the oil-soluble characteristic disappears. R ³ is H or an alkyl group, an alkenyl group, an alkyloyl group or an alkenyloyl group, which usually has 1 to 26, preferably 2 to 20 carbon atoms. n represents an integer of usually 1 to 120, preferably 2 to 90, more preferably 5 to 50. m usually represents an integer of 1 to 4, preferably 1 to 3.

The weight average molecular weight of (e) is usually 90 to 7,000, preferably 200 to 5,000, and more preferably 300 to 3,000 from the viewpoint of emulsion stability.
It is.

Of the water-soluble vinyl polymer (a), water (b), hydrocarbon liquid (c), surfactant (d) and oil-soluble polyoxyalkylene compound (e) in the microemulsion of the present invention, The weight ratio is the following formulas 1-3.
The range satisfying the above is preferable. Formula 1: 0.40 ≦ (a) / [(a) + (b)] (weight ratio) ≦ 0.65 Formula 2: 0.30 ≦ (c) / [(a) + (b)] (weight Ratio) ≦ 0.50 Formula 3: 0.15 ≦ [(d) + (e)] / (c) (weight ratio) ≦ 0.40 Formula 1 to further improve the stability of the emulsion
The more preferable range of 3 is as follows. More preferable range in formula 1: 0.40 ≦ (a) / [(a) + (b)] ≦ 0.63 Further preferable range in formula 2: 0.30 ≦ (c) / [(a) + (b )] ≦ 0.49 More preferable range in formula 3: 0.16 ≦ [(d) + (e)] / (c) ≦ 0.38

Among the microemulsions of the invention are:
If necessary, known pH buffers, polymer deterioration inhibitors, deodorants, preservatives, rust preventives, decolorizers and the like may be contained. These amounts are usually 5 based on the weight of the emulsion.
% By weight or less. When the water-in-oil type microemulsion of the present invention is diluted and used, a surfactant having a high HLB may be added to the microemulsion so that the phase of the microemulsion is quickly changed when the microemulsion is added to water. However, even in this case,
It is preferred that the total amount of surfactant in the microemulsion falls within the normal range of Formula 3. From the viewpoint of maintaining stability, the more preferable range of the total amount of the surfactants in this case is the same as the more preferable range in the above formula 3.

The average particle size of the water phase of the water-in-oil type microemulsion of the present invention is 700 mμ or less, preferably 500 mμ or less. Average particle size of water phase is 700m
If it exceeds μ, stability with time deteriorates and separation occurs. The average particle diameter is a value measured by an electrophoretic light scattering photometer "ELS-800" manufactured by Otsuka Electronics Co., Ltd.

Illustrating the production method of the water-in-oil type microemulsion of the present invention, a monomer (a ') which is a constitutional unit of the water-soluble vinyl polymer (a), water (b), a hydrocarbon liquid (c). ) It is obtained by making a surfactant (d) and an oil-soluble polyoxyalkylene compound (e) into a W / O type emulsion and emulsion-polymerizing. The method of this emulsion polymerization is a known method, for example, JP-A-54-154437,
It can be carried out by the method described in JP-A-54-102388. A chain transfer agent such as mercaptan, a pH buffering agent, and a chelating agent may be added to the polymerization system, if necessary. After emulsion polymerization, low volatile components such as water are distilled off under reduced pressure to dissolve the water-soluble vinyl polymer (a), water (b), hydrocarbon liquid (c) surfactant (d) and oil-soluble polymer. You may adjust the ratio of the polyoxyalkylene compound (e) so that it may become the range of said Formula 1-3.

The water-in-oil type microemulsion of the present invention is used as a wastewater treatment agent, a thickener, an antistatic agent, a fiber treatment agent, a papermaking agent such as a drainage improving agent, a crude oil recovery agent, etc. When used, the emulsion of the present invention is optionally added with water or another solvent at a suitable concentration, for example, 100 to
It is diluted 5,000 times before use.

[0028]

EXAMPLES The present invention will be further described with reference to the following examples, but the present invention is not limited to these examples. The tests described in the examples were carried out by the following method. Test method (1) Stability test 5 ° C. × 1 week and 40 ° C. × 1 week are repeated for 3 months to examine the separation rate and viscosity change of the emulsion. (2) Intrinsic viscosity of polymer Measured at 30 ° C. in 1N sodium nitrate aqueous solution. (3) Average particle size of water phase Electrophoretic light scattering photometer "ELS-8" manufactured by Otsuka Electronics Co., Ltd.
00 "at 25 ° C.

Example 1 In a 1 L 4-neck separable flask equipped with a stirrer, a reflux tube, a nitrogen introducing tube and a thermometer, (c) component: oil 250 g (d) component: pentaoxyethylene oleyl alcohol ether 5 g (〃 ) Component: sorbitan oleate 15 g (d1) Component: sorbican triester of oleic acid ethylene oxide 20 mol adduct 15 g (e) Component: Polyoxypropylene butyl ether (molecular weight 1200) 25 g was charged and mixed with stirring. The oil used was a mixture of 97% normal paraffin and 3% total of naphthene and aromatic (initial boiling point 203 ° C.). Next, a mixed solution of component (a ′): sodium acrylate 40% aqueous solution 300 g and acrylamide 240 g (b) component: water 150 g was adjusted to pH 7 with caustic soda and added to the above mixture to emulsify. This was adjusted to 50 ° C. with stirring, and nitrogen gas was blown into the liquid for 30 minutes. Then, while flowing nitrogen into the gas phase, 2,2'-azobis (2,4,2
1 g of a toluene solution containing 6% by weight of (dimethylvaleronitrile) was added, and the mixture was polymerized at 45 to 55 ° C. for 8 hours. The obtained emulsion was a translucent stable emulsion. The intrinsic viscosity of this polymer was 21.9 dl / g.
The stability test results of this emulsion are shown in Table 1.

Examples 2 and 3 The proportions of the water-soluble vinyl polymer (a), water (b), hydrocarbon liquid (c) surfactant (d) and oil-soluble polyoxyalkylene compound (e) are shown below. The emulsions of Examples 2 and 3 were obtained in the same manner as in Example 1 except that the emulsion was changed as shown in 1. Table 1 shows the stability test results and the like of each emulsion.

[0031]

[Table 1]

Example 4 In a 1 L 4-neck separable flask equipped with a stirrer, a reflux tube, a nitrogen introduction tube and a thermometer, (c) component: oil 250 g (d) component: pentaoxyethylene oleyl alcohol ether 5 g (〃 ) Component: sorbitan oleate 15 g (d1) component: oleic acid sorbitan triester ethylene oxide 20 mol adduct 10 g (d2) component: dioctyl sulfosuccinate soda 10 g (e) component: polyoxypropylene butyl ether (molecular weight 1200) 20 g is charged and stirred Mixed. The oil used was a mixture of 97% normal paraffin and 3% total of naphthene and aromatic (initial boiling point 203 ° C.). Next, a mixed solution of component (a ′): sodium acrylate 40% aqueous solution 300 g and acrylamide 240 g (b) component: water 150 g was adjusted to pH 7 with caustic soda and added to the above mixture to emulsify. This was adjusted to 50 ° C. with stirring, and nitrogen gas was blown into the liquid for 30 minutes. Then, while flowing nitrogen into the gas phase, 2,2'-azobis (2,4,-
1 g of a toluene solution containing 6% by weight of dimethylvaleronitrile) was added, and the mixture was polymerized at 45 to 55 ° C. for 8 hours. The obtained emulsion was a translucent stable emulsion. The intrinsic viscosity of this polymer was 20.6 dl / g. The stability test results of this emulsion are shown in Table 2.

Examples 5, 6 Water-soluble vinyl polymer (a), water (b), hydrocarbon liquid (c) surfactant (d) and oil-soluble polyoxyalkylene compound (e) Proportion of each component and ( d1) and (d
Example 4 except that the weight ratio of 2) was changed as shown in Table 2.
The emulsions of Examples 5 and 6 were obtained in the same manner as in. Table 2 shows the stability test results and the like of each emulsion.

[0034]

[Table 2]

Example 7 In a 1 L 4-neck separable flask equipped with a stirrer, a reflux tube, a nitrogen introducing tube and a thermometer, (c) component: oil 250 g (d) component: pentaoxyethylene oleyl alcohol ether 5 g (〃 ) Component: sorbitan oleate 15 g (d1) component: oleic acid sorbitan triester ethylene oxide 17 g 20 mol adduct (d3) component: oleylamine ethylene oxide 15 mol adduct 6 g (e) Component: polyoxypropylene butyl ether (molecular weight 1200) 17 g And mixed with stirring. The oil used was a mixture of 90% normal paraffin and 10% total of naphthene and aromatic (initial boiling point 155 ° C.). Then, a mixed solution of component (a ′): 2-acryloyloxyethyltrimethylammonium chloride 80% aqueous solution 150 g and acrylamide 240 g (b) component: water 300 g is adjusted to pH 4 with dilute sulfuric acid and added to the mixture to emulsify. Let This was adjusted to 50 ° C. with stirring, and nitrogen gas was blown into the liquid for 30 minutes. Then, while flowing nitrogen into the gas phase, 1% of a toluene solution containing 6% by weight of 2,2′-azobis (2,4, -dimethylvaleronitrile) was used.
g, and the resulting emulsion polymerized at 45 to 55 ° C. for 8 hours was a translucent stable emulsion. The intrinsic viscosity of this polymer was 14.8 dl / g. Table 3 shows the stability test results and the like of this emulsion.

Examples 8 and 9 Ratios of water-soluble vinyl polymer (a), water (b), hydrocarbon liquid (c) surfactant (d) and oil-soluble polyoxyalkylene compound (e), and ( d1) and (d
Example 7 except that the weight ratio of 3) was changed as shown in Table 3.
The emulsions of Examples 8 and 9 were obtained in the same manner as in. Table 3 shows the stability test results and the like of each emulsion.

[0037]

[Table 3]

Examples 10 to 12 Emulsions of Examples 10 to 12 were obtained in the same manner as in Example 1 except that the kind of the polyoxyalkylene compound (e) was changed. Table 4 shows the type of polyoxyalkylene compound (e) used in each example, the stability test results of the obtained polymers, and the like.

[0039]

[Table 4]

(Note) (1) Polyoxypropylene butyl ether, molecular weight 190 (2) Polyoxypropylene glycerin ether, molecular weight 6000 (3) Polyoxyethylene propylene glycol butyrate ester, molecular weight 1200, ethylene / propylene weight ratio = 10/90

[0041]

The water-in-oil type microemulsion of the present invention is superior in stability over time, has good freeze stability, is excellent in fluidity and is easy to handle as compared with the conventional ones. Because of the above effects, the emulsion of the present invention is useful as a wastewater treatment agent, a thickening agent, an antistatic agent, a fiber treatment agent, a papermaking agent such as a drainage improving agent, a crude oil recovery agent and the like.

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Claims (7)

[Claims] 1. A water-soluble vinyl polymer (a), water (b),
A water-in-oil water-in-oil microemulsion of a water-soluble vinyl polymer comprising a hydrocarbon liquid (c) and a surfactant (d), containing an oil-soluble polyoxyalkylene compound (e) represented by the following general formula (1). And a water-in-oil microemulsion characterized by having an average particle diameter of the water phase of 700 mμ or less. R ¹ -[(OR ² ) _n -OR ³ ] _m (1) [In the formula, R ¹ is a residue obtained by removing an OH group from a monovalent to hexavalent hydroxyl group-containing compound, or an OH from a monovalent to hexavalent carboxylic acid. R ² is an alkylene group having 2 to 4 carbon atoms (provided that at least a part of n R ² is an alkylene group having 3 to 4 carbon atoms); R ³ is H and has a carbon number. 1 to 26 alkyl group, alkenyl group, alkyloyl group or alkenyloyl group; n is an integer of 1 to 120; m is an integer of 1 to 6. ] 2. (a) is an acrylamide homopolymer or a polymer containing acrylamide and another water-soluble vinyl monomer as a constitutional unit, and has an intrinsic viscosity measured at 30 ° C. in a 1N sodium nitrate aqueous solution. Is 3 to 30 dl / g, The microemulsion according to claim 1. 3. The microemulsion according to claim 1, wherein (d) contains a fatty acid sorbitan ester ethylene oxide adduct (d1) as an essential component. 4. (a) is a nonionic or anionic water-soluble polymer, and (d) contains a fatty acid sorbitan ester ethylene oxide adduct (d1) and a sulfosuccinic acid diester type anionic surfactant (d2) as essential components. The microemulsion according to claim 1 or 2, which is contained as. 5. (a) is a nonionic or cationic water-soluble polymer, and (d) contains a fatty acid sorbitan ester ethylene oxide adduct (d1) and an amine ethylene oxide adduct (d3) as essential components. The microemulsion according to 1 or 2. 6. The micro according to claim 1, wherein the weight relationships among the components (a), (b), (c), (d) and (e) satisfy the following formulas 1 to 3. Emulsion. Formula 1: 0.40 ≦ (a) / [(a) + (b)] (weight ratio) ≦ 0.65 Formula 2: 0.30 ≦ (c) / [(a) + (b)] (weight Ratio) ≦ 0.50 Formula 3: 0.15 ≦ [(d) + (e)] / (c) (weight ratio) ≦ 0.40 7. The microemulsion according to claim 1, wherein the initial boiling point of (c) is 150 ° C. or higher.