JP5867851B2 - Method for producing N-vinyl lactam polymer - Google Patents

Description

  The present invention relates to a method for producing an N-vinyl lactam polymer. More specifically, the present invention relates to a method for producing an N-vinyl lactam polymer that is less colored after heating.

  N-vinyl lactam polymers such as polyvinyl pyrrolidone are used in a wide range of fields as water-soluble and safe functional polymers. For example, it is used for applications such as cosmetics, medical and agrochemical intermediates, food additives, photosensitive electronic materials, tackifiers, and various special industrial applications (for example, production of hollow fiber membranes). In particular, low molecular weight polyvinyl pyrrolidone is useful for the above various applications.

  Low molecular weight polyvinylpyrrolidone is generally produced by polymerizing N-vinyl-2-pyrrolidone in an aqueous medium in the presence of a metal catalyst and using hydrogen peroxide as a polymerization initiator (Patent Document 1). 2, 3). In particular, as a method for producing polyvinyl pyrrolidone having a relatively low molecular weight that is useful for various applications at a low temperature and in a short time, vinyl pyrrolidone in the presence of hydrogen peroxide, a metal catalyst, ammonia and / or an amine compound is used. A method for producing a polyvinyl pyrrolidone by carrying out a polymerization reaction of a monomer component containing benzene has been reported (see Patent Document 3).

  However, the polyvinylpyrrolidone obtained by the above method has a problem that it may be colored when stored for a long time after being dried and powdered, and the product value is remarkably lowered.

Japanese Patent Laid-Open No. 62-62804 JP-A-11-71414 JP 2002-155108 A

  Accordingly, the present invention has been made to provide a production method capable of suppressing the coloring of the N-vinyl lactam polymer.

  The present invention comprises a step of polymerizing a monomer component essentially containing N-vinyl lactam in an aqueous solvent essentially containing alcohol in the presence of an azo polymerization initiator and / or an organic peroxide and a reducing agent. Is a method for producing an N-vinyl lactam polymer.

  In the polymerization step, it is preferable to perform polymerization in the presence of hypophosphorous acid and / or a salt thereof.

  The present invention provides an N-vinyl lactam obtained by the above production method, having a yellowness of 25 or less after heating at 260 ° C. for 60 minutes under nitrogen flow, and a b value of 13 or less in Hunter Lab color space. An N-vinyl lactam polymer having a structural unit derived from hypophosphorous acid and / or a salt thereof at the end of the main chain is also included.

  In the method for producing an N-vinyl lactam polymer of the present invention, polymerization is carried out using a specific polymerization initiator and a reducing agent in an aqueous solvent essentially containing alcohol. An N-vinyl lactam polymer which does not occur can be easily obtained.

  The method for producing the N-vinyl lactam polymer of the present invention is such that polymerization is carried out in an aqueous solvent essentially containing alcohol in the presence of an azo polymerization initiator and / or an organic peroxide and a reducing agent. Has characteristics. Hereinafter, the present invention will be described in detail.

[Method for producing N-vinyl lactam polymer (polymerization step)]
<Monomer component>
The method of the present invention is a method for polymerizing a monomer component essentially containing N-vinyl lactam. N-vinyl lactam is a monomer having a lactam ring. For example, N-vinyl-2-pyrrolidone, N-vinylcaprolactam, N-vinyl-4-butylpyrrolidone, N-vinyl-4-propylpyrrolidone, N -Vinyl-4-ethylpyrrolidone, N-vinyl-4-methylpyrrolidone, N-vinyl-4-methyl-5-ethylpyrrolidone, N-vinyl-4-methyl-5-propylpyrrolidone, N-vinyl-5-methyl -5-ethylpyrrolidone, N-vinyl-5-propylpyrrolidone, N-vinyl-5-butylpyrrolidone, N-vinyl-4-methylcaprolactam, N-vinyl-6-methylcaprolactam, N-vinyl-6-propylcaprolactam , N-vinyl-7-butylcaprolactam and the like.

  Among N-vinyl lactams, N-vinyl-2-pyrrolidone and / or N-vinyl caprolactam is essential since it has good polymerizability and good color stability at high temperatures. It is preferable to use a polymer.

  As a monomer, you may use together other monomers (henceforth other monomers) other than N-vinyl lactam. Examples of other monomers include acrylic acid, methacrylic acid, alkyl esters of acrylic acid (such as methyl acrylate and ethyl acrylate), alkyl esters of methacrylic acid (such as methyl methacrylate and ethyl methacrylate), and aminoalkyl esters of acrylic acid. (Diethylaminoethyl acrylate, etc.), aminoalkyl ester of methacrylic acid, monoester of acrylic acid and glycol, monoester of methacrylic acid and glycol (hydroxyethyl methacrylate, etc.), alkali metal salt of acrylic acid, alkali metal of methacrylic acid Salts, ammonium salts of acrylic acid, ammonium salts of methacrylic acid, quaternary ammonium derivatives of aminoalkyl esters of acrylic acid, quaternary compounds of aminoalkyl esters of methacrylic acid Monium derivatives, quaternary ammonium compounds of diethylaminoethyl acrylate and methyl sulfate, vinyl methyl ether, vinyl ethyl ether, alkali metal salts of vinyl sulfonic acid, ammonium salts of vinyl sulfonic acid, styrene sulfonic acid, styrene sulfonate, allyl Sulfonic acid, allyl sulfonate, methallyl sulfonic acid, methallyl sulfonate, vinyl acetate, vinyl stearate, N-vinyl imidazole, N-vinyl acetamide, N-vinyl formamide, N-vinyl carbazole, acrylamide, methacrylamide , N-alkylacrylamide, N-methylolacrylamide, N, N-methylenebisacrylamide, glycol diacrylate, glycol dimethacrylate, divinylbenzene, glycol Over Luzia Lil ether.

  For example, when the obtained polymer is used for the production of a hollow fiber membrane, the productivity of the hollow fiber membrane is improved. Therefore, the total of N-vinyl lactam and other monomers (hereinafter, all monomer components) The proportion of N-vinyllactam used in the case of 100% by mass is preferably 50% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and most preferably 100% by mass. Therefore, the proportion of other monomers used in all monomer components is preferably less than 50% by mass, more preferably less than 20% by mass, further preferably less than 10% by mass, and most preferably 0% by mass.

  In addition, when calculating the use ratio of other monomers in all monomer components, when the other monomer has a salt of an acid group, the salt of the acid group as a corresponding acid group ( In the case of having an amino group salt, the amino group salt is calculated as the corresponding amino group (amine conversion). When calculating structures derived from other monomers relative to structural units derived from all monomer components, calculate structural units derived from reducing agents (chain transfer agents) with respect to the total mass of the N-vinyl lactam polymer. Similarly, if applicable, the acid shall be calculated in terms of acid and amine.

<Polymerization initiator>
In the polymerization of the monomer, a polymerization initiator is used. In the present invention, an azo polymerization initiator and / or an organic peroxide is used as the polymerization initiator. An azo polymerization initiator refers to a compound having an azo bond and generating radicals by heat or the like.

  As the azo polymerization initiator that can be used in the present invention, 2,2′-azobis-2-amidinopropane dihydrochloride, 2,2′-bis (2-imidazolin-2-yl) [2,2′- Azobispropane] dihydrochloride, 2,2′-bis (2-imidazolin-2-yl) [2,2′-azobispropane] disulfate, 2,2′-azobis [2- (2-imidazoline) -2-yl) propane] disulfate dihydrate, 2,2′-azobis- (propane-2-carbomidine) dihydrochloride, 2,2′-azobis [N- (2-carboxyethyl)- 2-methylpropionamidine], 2,2′-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} dihydrochloride, 2,2′-azobis [2- ( 2-Imidazolin-2-yl) propane], 2,2′-azo (1-Imino-1-pyrrolidino-2-methylpropane) dihydrochloride, 2,2′-azobis {2-methyl-N- [1,1-bis (hydroxymethyl) -2-hydroxyethyl] propionamide }, 2,2′-azobis [N- (2-hydroxyethyl) -2-methylpropanamide], 4,4′-azobis-4-cyanovaleric acid, azobisisobutyronitrile, 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile) and the like are exemplified. Among these, since a low molecular weight N-vinyl lactam polymer can be efficiently produced, and the color tone at high temperature of the resulting polymer is good, the 10-hour half-temperature is 30 ° C. or higher and 90 ° C. or lower. More preferably, the 10-hour half-life temperature is 40 ° C. or higher and 70 ° C. or lower. Specifically, 2,2'-azobis-2-amidinopropane dihydrochloride is preferable. In addition, an azo polymerization initiator having a carboxyl group (2,2′-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] etc.) may adversely affect the coloration. You should refrain.

  Examples of the organic peroxide that can be used in the present invention include tertiary butyl hydroperoxide, ditertiary butyl peroxide, cumene hydroperoxide, tertiary hexyl hydroperoxide, and p-menthane hydroperoxide; tertiary butyl peroxyacetate , Disuccinoyl peroxide, peracetic acid and the like. Among the above organic peroxides, an alkyl hydroperoxide is preferable because a low molecular weight N-vinyl lactam polymer can be efficiently produced, and the resulting polymer has good color tone at high temperature. Butyl hydroperoxide is particularly preferred. Among these organic peroxides, those having a 10-hour half-temperature of 30 ° C. or more and 180 ° C. or less are preferred, and those having a 10-hour half-life temperature of 40 ° C. or more and 170 ° C. or less are more preferred.

  The polymerization initiator used in the present invention is essentially one or more selected from the above-mentioned azo polymerization initiators and the above organic peroxides, but other polymerization initiators may be used in combination. . Examples of such an initiator include persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate, and hydrogen peroxide.

  The amount of the polymerization initiator used (the total amount when multiple types are used) is 15 g or less, more preferably 0.1 to 12 g, based on 1 mol of all monomer components, unless otherwise specified. It is preferable.

  Among the above polymerization initiators, when an azo polymerization initiator is used because a low molecular weight N-vinyl lactam polymer can be efficiently produced and the color tone of the resulting polymer at a high temperature is improved. Is preferably 1.9 g or less, more preferably 1.6 g or less, still more preferably 1.2 g or less, and 1.1 g or less per mole of all monomer components. The following is particularly preferable. The lower limit of the amount of the azo polymerization initiator used is preferably 0.1 g or more and more preferably 0.2 g or more with respect to 1 mol of all monomer components. Also when using an organic peroxide, the preferred range of the amount used is the same as that of the azo polymerization initiator.

  The method for adding the polymerization initiator to the reaction system (polymerization kettle) is not particularly limited, but the amount added substantially continuously during the polymerization is 50% by mass or more of the total amount of the polymerization initiator used. Preferably there is. Especially preferably, it is 80 mass% or more, and it is most preferable to add the whole quantity continuously. When the polymerization initiator is continuously added, the dropping rate may be changed.

  In the present invention, “in polymerization” means the time after the start of polymerization and before the end of polymerization. In the present invention, “polymerization start point” refers to a point in time when at least part of the monomer and at least part of the initiator are both added to the polymerization apparatus, and “polymerization end point” refers to the monomer component. The time when the addition of the total amount of to the polymerization apparatus is completed.

  The polymerization initiator may be added as it is without dissolving in the aqueous solvent, but it is preferably dissolved in the aqueous solvent and added to the reaction system (polymerization kettle).

<Reducing agent>
In the present invention, a reducing agent (chain transfer agent) is used to obtain a low molecular weight N-vinyl lactam polymer. Usable reducing agents are mercaptoethanol, thioglycerol, thioglycolic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, thiomalic acid, octyl thioglycolate, octyl 3-mercaptopropionate, 2-mercaptoethanesulfonic acid , N-dodecyl mercaptan, octyl mercaptan, butyl thioglycolate, etc., thiol compounds; carbon tetrachloride, methylene chloride, bromoform, bromotrichloroethane, and other halides; isopropanol, glycerin, and other secondary alcohols; phosphorous acid Phosphites, hypophosphites, hypophosphites, and hydrates thereof; bisulfites (such as sulfite, hydrogen sulfite, dithionite, metabisulfite, and salts thereof) Including compounds that dissolve and generate bisulfite) Lower oxides and salts thereof. These salts are metal salts such as sodium, ammonium salts or organic amine salts. Two or more reducing agents may be used.

  In the present invention, as the reducing agent (chain transfer agent), one containing hypophosphorous acid and / or a salt thereof (hereinafter, hypophosphorous acid (salt)) is preferably used. Thereby, the structure derived from hypophosphorous acid (salt) can be introduce | transduced into the principal chain terminal of an N-vinyl lactam polymer. The reason why the structure derived from hypophosphorous acid (salt) is introduced at the end of the main chain is that the color tone of the N-vinyllactam polymer at a high temperature becomes particularly good. Moreover, a low molecular weight N-vinyl lactam polymer can be produced efficiently.

  When hypophosphorous acid (salt) is used as the reducing agent (chain transfer agent), the hypophosphite part is a hypophosphite part having a pH of 6 or more at 25 ° C. when prepared in a 10% by mass aqueous solution. Japanese salts are preferred. If a hypophosphorous acid partial neutralized salt or hypophosphorous acid having a pH of less than 6 during the preparation is used, the N-vinyllactam monomer may be hydrolyzed.

  In order for hypophosphorous acid (salt) to be present in the reaction system (polymerization kettle), an embodiment in which hypophosphorous acid (salt) is added to the reaction system, hypophosphorous acid, and a compound that forms a salt with this are added. Any of the modes of adding to the reaction system separately may be used.

  The reducing agent (chain transfer agent) may be added to the reaction vessel (polymerization kettle) before the start of polymerization (referred to as initial charge), or all or part of it is added to the reaction vessel (polymerization kettle) during the polymerization. However, an embodiment in which the entire amount is added (initially charged) to the reaction vessel (polymerization kettle) before the start of polymerization is preferred. According to this embodiment, since the reducing agent (chain transfer agent) reacts efficiently, not only a polymer having a low K value can be obtained, but also the remaining amount of the reducing agent (chain transfer agent) can be reduced. In the present invention, “before polymerization” means before the polymerization start point, and “after polymerization” means after the polymerization end point. When the reducing agent (chain transfer agent) is added substantially continuously to the reaction system (polymerization kettle) during the polymerization, for example, the amount added substantially continuously is 50% by mass or more of the total amount used. It can be.

  The abundance of hypophosphorous acid (salt) in the reaction system is preferably 5.0 g or less, more preferably 4.5 g or less, with respect to 1 mol of all monomer components. More preferably, it is as follows. The lower limit of the amount of hypophosphorous acid (salt) is preferably 0.5 g or more, more preferably 1.0 g or more, per 1 mol of all monomer components. If there is too much hypophosphorous acid (salt), hypophosphorous acid (salt) that does not contribute to chain transfer (hypophosphorous acid (salt) that is not incorporated into the polymer terminal) increases, for example, hollow fiber When used in the production of membranes, the performance tends to decrease. Moreover, when there are too few amounts, the quantity of the structure derived from hypophosphorous acid (salt) will become less than a suitable range, and there exists a possibility that the effect which suppresses coloring and hygroscopicity may not fully express. Hypophosphorous acid (salt) includes hydrates. Ammonium hypophosphite also has a function as a chain transfer agent and may be used in the polymerization. However, it is desirable not to use a large amount of ammonium salt because it causes odor.

  The addition amount (total amount) of the reducing agent (chain transfer agent) is 0.5 to 20 g with respect to 1 mol of all monomer components, including hypophosphorous acid (salt), unless otherwise specified. More preferably, it is 1.0-15g. If it is less than 0.5 g, the molecular weight may not be controlled or the effect of suppressing coloring may not be exhibited. Conversely, if it exceeds 20 g, the chain transfer agent remains and the purity of the polymer composition is low. May decrease.

<Reducing compound>
Heavy metal ions (or heavy metal salts) may be used as the reducing compound that acts as a decomposition catalyst for the polymerization initiator. In the present invention, the heavy metal means a metal having a specific gravity of 4 g / cm ³ or more. Among the heavy metals, iron and / or copper are preferable. As the reducing compound, the molle salt (Fe (NH ₄ ) ₂ (SO ₄ ) ₂ .6H ₂ O), ferrous sulfate · 7 hydrate, ferrous chloride Heavy metal salts such as iron, ferric chloride, copper (I) sulfate and / or its hydrate, copper (II) sulfate and / or its hydrate, copper (II) chloride and / or its hydrate, etc. Is preferably used.

  When using the said heavy metal ion, it is preferable that the usage-amount is 0.1-10 ppm with respect to the total mass of the polymerization reaction liquid at the time of polymerization reaction completion. If the content of heavy metal ions is less than 0.1 ppm, the effect of heavy metal ions may not be sufficiently exhibited. On the other hand, if the content of heavy metal ions exceeds 10 ppm, the color tone of the resulting polymer may be deteriorated.

<Other additives>
In the polymerization reaction, ammonia and / or an amine compound may be used for the purpose of accelerating the polymerization reaction or preventing hydrolysis of N-vinyl lactam. Ammonia and amine compounds function as promoters in the polymerization reaction. That is, when ammonia and / or an amine compound is included in the reaction system, the progress of the polymerization reaction is further promoted as compared with the case where ammonia and / or amine compound are not included. It can also function as a basic pH regulator. In addition, since ammonia causes odor and also affects coloring, it is preferable to use it in a reduced amount. When ammonia is used, it may be used as it is as a gaseous simple substance at room temperature or as an aqueous solution (ammonia water). Ammonia and / or amine compound can be added by any appropriate method. For example, ammonia and / or an amine compound may be charged into the reaction vessel from the beginning of polymerization, or may be added sequentially into the reaction vessel during polymerization. Good.

  Any appropriate amine compound can be adopted as the amine compound. Specific examples include primary amines, secondary amines, and tertiary amines. 1 type may be sufficient as the said amine, and 2 or more types may be sufficient as it.

  Examples of the primary amine include monoethanolamine, allylamine, isopropylamine, diaminopropylamine, ethylamine, 2-ethylhexylamine, 3- (2-ethylhexyloxy) propylamine, 3-ethoxypropylamine, 3- ( Diethylamino) propylamine, 3- (dibutylamino) propylamine, tetramethylethylenediamine, t-butylamine, sec-butylamine, propylamine, 3- (methylamino) propylamine, 3- (dimethylamino) propylamine, 3-methoxy And propylamine. Only 1 type may be used for the said primary amine and it may use 2 or more types together.

  Examples of the secondary amine include dimethylamine, diethylamine, dipropylamine, diisopropylamine, N-methylethylamine, N-methylpropylamine, N-methylisopropylamine, N-methylbutylamine, N-methylisobutylamine, Aliphatic compounds such as N-methylcyclohexylamine, N-ethylpropylamine, N-ethylisopropylamine, N-ethylbutylamine, N-ethylisobutylamine, N-ethylcyclohexylamine, N-methylvinylamine, N-methylallylamine, etc. Secondary amine: N-methylethylenediamine, N-ethylethylenediamine, N, N′-dimethylethylenediamine, N, N′-diethylethylenediamine, N-methyltrimethylenediamine, N-ethyltrimethylenedia , N, N′-dimethyltrimethylenediamine, N, N′-diethyltrimethylenediamine, diethylenetriamine, dipropylenetriamine and other aliphatic diamines and triamines; N-methylbenzylamine, N-ethylbenzylamine, N-methyl Aromatic amines such as phenethylamine and N-ethylphenethylamine; Monomers such as N-methylethanolamine, N-ethylethanolamine, N-propylethanolamine, N-isopropylethanolamine, N-butylethanolamine and N-isobutylethanolamine Alkanolamines; dialkanolamines such as diethanolamine, dipropanolamine, diisopropanolamine, dibutanolamine; pyrrolidine, piperidine, piperazine, N-methylpiperazine, - ethylpiperazine, morpholine, cyclic amines, such as thiomorpholine; and the like. The secondary amine may be used alone or in combination of two or more. Of these secondary amines, dialkanolamines and dialkylamines are preferred, dialkanolamines are more preferred, and diethanolamine is particularly preferred.

  Examples of the tertiary amine include trialkanolamines such as trimethylamine, triethylamine, tripropylamine, triisopropylamine, triethanolamine, tripropanolamine, triisopropanolamine, and tributanolamine. The tertiary amine may be used alone or in combination of two or more. Of these tertiary amines, trialkanolamine is preferable, and triethanolamine is particularly preferable.

  When the ammonia and the amine compound are used, the total amount used is preferably 0.02 parts by mass or more and more preferably 0.05-1 part by mass with respect to 100 parts by mass of N-vinyl lactam. If it is the said range, it exists in the tendency for reaction rate to improve and the effect which suppresses the hydrolysis and coloring of N-vinyl lactam accompanying the fall of pH during reaction is acquired.

In addition, when a copper salt is used as the heavy metal salt and the ammonia is further used, a copper ammine complex salt can be formed. Examples of copper ammine complex salts include diammine copper salts ([Cu (NH ₃ ) ₂ ] ₂ SO ₄ .H ₂ O, [Cu (NH ₃ ) ₂ ] Cl, etc.), tetraammine copper salts ([Cu (NH _{3 4} ] SO ₄ .H ₂ O, [Cu (NH ₃ ) ₄ ] Cl _2, etc.).

<Polymerization solvent>
The method for producing an N-vinyl lactam polymer of the present invention is a method in which a monomer component essentially containing N-vinyl lactam is polymerized in an aqueous solvent essentially containing alcohol. Examples of the alcohol that can be used include methyl alcohol, ethyl alcohol, isopropyl alcohol, n-propyl alcohol, n-butyl alcohol, sec-butyl alcohol, and t-butyl alcohol. Two or more kinds of alcohols may be used. The reason why the aqueous solvent containing alcohol is used is because the effect of suppressing coloring (particularly high-temperature heating coloring) of the resulting polymer has been found, although the reason is not clear.

  In the present invention, the aqueous solvent represents a mixed solvent containing water and alcohol. In addition to water and alcohol, glycerin; polyethylene glycol; amides such as dimethylformaldehyde; ethers such as diethyl ether and dioxane may be mixed, but water and alcohol are preferable. In the aqueous solvent, the amount of alcohol is preferably 20 to 95% by mass, and more preferably 40 to 90% by mass. When the amount of alcohol is less than 20% by mass, the effect of suppressing coloring may not be sufficiently exhibited. On the other hand, if it exceeds 95% by mass, the reactivity of the reducing agent may decrease. In this case, the balance is water.

  The polymerization step is preferably performed so that the solid content concentration after polymerization is completed (the concentration of nonvolatile content in the solution) is 10 to 80% by mass with respect to 100% by mass of the polymerization solution, 20-70 mass% is more preferable, and 30-60 mass% is further more preferable.

<Other polymerization conditions>
The temperature during the polymerization is preferably 70 ° C. or higher, more preferably 75 to 110 ° C., and further preferably 80 to 105 ° C. If the temperature at the time of polymerization is in the above range, the residual monomer component is reduced and the dispersibility of the polymer tends to be improved. The temperature at the time of polymerization need not always be kept constant during the progress of the polymerization reaction. For example, the polymerization is started from room temperature, and the temperature is increased to a set temperature at an appropriate temperature increase time or temperature increase rate. Thereafter, the set temperature may be maintained, or the polymerization temperature may be varied (increased or decreased) over time during the course of the polymerization reaction, depending on the dropping method of the monomer component, initiator, and the like. Also good.

  The pH during the polymerization is preferably 6 or more, more preferably 7 or more, and preferably 11 or less from the viewpoint of suppressing the generation of impurities or by-products.

  The pressure in the reaction system may be any of normal pressure (atmospheric pressure), reduced pressure, and increased pressure, but from the viewpoint of the molecular weight of the polymer obtained, the reaction system is sealed under normal pressure. However, it is preferably performed under pressure. Moreover, it is preferable to carry out under normal pressure (atmospheric pressure) in terms of equipment such as a pressurizing device, a decompressing device, a pressure-resistant reaction vessel, and piping. The atmosphere in the reaction system may be an air atmosphere, but is preferably an inert atmosphere. For example, the inside of the system is preferably replaced with an inert gas such as nitrogen before the start of polymerization.

  The polymerization time (between the polymerization start point and the polymerization end point) is preferably 30 minutes or longer and 5 hours or shorter. As the polymerization time becomes longer, the color of the polymerization solution tends to increase. After the completion of the polymerization, for the purpose of reducing the monomer remaining in the polymerization solution, an aging step (referred to as a step of maintaining under warming / warming conditions after polymerization) may be provided. The aging time is usually 1 minute or more and 4 hours or less. It is preferable to add a polymerization initiator (booster) during the aging time because the monomer remaining in the polymerization solution can be reduced.

  In the late stage of polymerization, it is preferable to delay the dropping end time of the initiator from the end time of addition of the monomer because the monomer remaining in the polymerization solution can be reduced. More preferably, it is delayed for 1 to 120 minutes, more preferably delayed for 5 to 60 minutes.

<Addition of organic acid>
In the present invention, it is preferable to add an organic acid or an aqueous solution thereof to the reaction solution after completion of the polymerization reaction. At this time, it is preferable to carry out the reaction while maintaining the reaction temperature during the polymerization reaction. Thereby, since the remaining N-vinyl lactam is hydrolyzed by the acid, the amount of unreacted monomer (that is, the remaining amount of monomer in the reaction solution) can be reduced. For example, if the monomer is N-vinyl-2-pyrrolidone, it is hydrolyzed to 2-pyrrolidone with an acid.

  A preferable organic acid that can be used to reduce the amount of residual monomer is a carboxylic acid having a boiling point (for example, 100 ° C. or higher) higher than the reaction liquid temperature at the time of addition of the organic acid. , Formic acid, acetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, aspartic acid, citric acid, glutamic acid, fumaric acid, malic acid, maleic acid, phthalic acid, trimellitic acid, pyromellitic acid and the like. These organic acids may be used alone or in combination of two or more.

  The amount of organic acid used may be appropriately adjusted according to the amount of N-vinyl lactam used during the polymerization reaction, and is not particularly limited. For example, the pH of the reaction solution after polymerization is preferably 5 or less. More preferably, it may be 3 or more and 4 or less. Specifically, the use amount of the organic acid is preferably 100 ppm or more and 30,000 ppm or less, more preferably 500 ppm or more and 20,000 ppm or less with respect to the use amount of N-vinyl lactam.

<Drying process>
In order to obtain an N-vinyl lactam polymer from the N-vinyl lactam polymer solution obtained in the polymerization step, a drying step is performed. The drying process is a process for pulverization and the like, and includes a pulverization process. Drying and pulverization may be performed by a known general method. For example, powder can be obtained by spray drying, freeze drying, fluidized bed drying, drum drying, belt-type drying, or the like. When heating and drying at normal pressure, the drying temperature is preferably about 100 to 200 ° C., and the drying time is preferably about 0.2 to 180 minutes. When drying under reduced pressure, the drying temperature may be appropriately selected according to the degree of reduced pressure.

<Other processes>
In order to obtain a powder (product) of the N-vinyl lactam polymer, a purification step, a desalting step, a concentration step, a dilution step, and the like may be included before the drying step. By treating the reaction solution (polymer solution) with a cation exchange resin, the color tone of the resulting N-vinyl lactam polymer solution can be improved. The step of treating with a cation exchange resin can be performed during the polymerization (in parallel with the polymerization step) or after the polymerization. The treatment with the cation exchange resin during the polymerization reaction may be carried out by any appropriate method. Preferably, it is carried out by adding a cation exchange resin into a reaction vessel in which the polymerization reaction of the monomer component is carried out. Specifically, for example, a method in which a cation exchange resin is added to a reaction vessel in which a polymerization reaction is performed and suspended finely, and then filtered is used. Arbitrary appropriate time can be employ | adopted for the time of the process by a cation exchange resin. It is preferably 1 minute to 24 hours, more preferably 3 minutes to 12 hours, and even more preferably 5 minutes to 2 hours. If the treatment time is too short, the color tone improving effect may not be sufficiently exhibited. If the treatment time is too long, the productivity may deteriorate.

<N-vinyl lactam polymer of the present invention>
The N-vinyl lactam polymer of the present invention contains a structural unit derived from N-vinyl lactam as an essential component. The structural unit derived from N-vinyl lactam is a structural unit formed by radical polymerization of N-vinyl lactam, and a structure in which a polymerizable carbon-carbon double bond of N-vinyl lactam is a carbon-carbon single bond. It is.

  In 100% by mass of structural units derived from all monomer components contained in the N-vinyl lactam polymer of the present invention (total amount of structural units derived from N-vinyl lactam and other monomers) The proportion (% by mass) of the structural unit derived from N-vinyllactam is 50% by mass or more because the productivity of the hollow fiber membrane is improved when the obtained polymer is used, for example, in the production of the hollow fiber membrane. It is preferably 80% by mass or more, more preferably 90% by mass or more, and most preferably 100% by mass. Therefore, the proportion (% by mass) of structural units derived from other monomers is preferably less than 50% by mass, more preferably less than 20% by mass, and further preferably less than 10% by mass. Preferably, it is 0% by mass.

  The N-vinyl lactam polymer of the present invention is characterized by little coloration even when subjected to a heating acceleration test such as heat treatment at a high temperature. Specifically, for example, the yellowness when heated at 260 ° C. for 60 minutes under nitrogen flow is preferably 25 or less, and more preferably 20 or less. Further, the b value in the Hunter Lab color space is preferably 13 or less, more preferably 10 or less. Within this range, there is little coloring even during long-term storage, and the product value is not reduced.

The N-vinyl lactam polymer of the present invention has a structural unit derived from hypophosphorous acid (salt) (a structural unit containing phosphorus) when a reducing agent containing hypophosphorous acid (salt) is used. doing. The proportion (mass%) of the structural unit derived from hypophosphorous acid (salt) in the total mass of 100 mass% of the N-vinyl lactam polymer is preferably 0.01 mass% or more and 5 mass% or less. . Here, the structural unit derived from hypophosphite is represented by -PH (= O) (OM) (M is a metal element or an organic amine residue). When the structural unit is in the above range, the color tone of the N-vinyl lactam polymer at a high temperature becomes particularly good. The proportion of the structural units can be determined using ³¹ P-NMR as will be described in the examples described later.

  Also when using other phosphorous acid (salt) etc., it is preferable that the sum total of the structural unit (it is also mentioned the atomic group containing phosphorus) derived from a phosphorus chain transfer agent is the said range.

  10-50 are preferable, as for K value by the Fikenture method of the N-vinyl lactam polymer of this invention, 20-40 are more preferable, and 25-35 are more preferable. This is because the production method of the present invention has a large effect of suppressing coloring of the low molecular weight N-vinyl lactam polymer. If K value is the said range, the capability to disperse | distribute a dispersion | distribution object and the capability to disperse | distribute a polymer itself to a medium are high. The K value according to the fixture method can be determined by the following measurement method. When the K value is less than 20, the viscosity of a 5% by mass (g / 100 ml) solution is measured, and when the K value is 20 or more, the viscosity of a 1% by mass (g / 100 ml) solution is measured. Sample concentration is converted to dry matter. When the K value is 20 or more, 1.0 g of the sample is accurately measured, put into a 100 ml volumetric flask, add distilled water at room temperature, dissolve completely with shaking, add distilled water to make exactly 100 ml. To do. This sample solution is allowed to stand for 30 minutes in a thermostatic chamber (25 ± 0.2 ° C.), and then measured using an Ubbelohde viscometer. Measure the time for the solution to flow between the two markings. Measure several times and take the average value. In order to measure relative viscosity, distilled water is measured similarly. The two obtained flow times are corrected based on the Hagenbach-Couette correction.

上記式中、Ｚは濃度Ｃの溶液の相対粘度（ηｒｅｌ）、Ｃは濃度（質量％：ｇ／１００ｍｌ）である。相対粘度ηｒｅｌは次式により得られる。
ηｒｅｌ＝（溶液の流動時間）÷（水の流動時間）

In the above formula, Z is a relative viscosity (ηrel) of a solution having a concentration C, and C is a concentration (mass%: g / 100 ml). The relative viscosity ηrel is obtained by the following equation.
ηrel = (solution flow time) ÷ (water flow time)

  The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples. Unless otherwise specified, “part” means “part by mass” and “%” means “% by mass”.

  Further, the K value of the polymer, the amount of structural units derived from the hypophosphorous acid (salt) at the end of the main chain, the yellowness, and the Hunter color space b value were measured according to the following methods.

<Measurement of K value of polymer>
It measured by the measuring method of said K value.

<Analysis of structural units derived from hypophosphorous acid (salt) at the end of the polymer main chain>
The structural unit derived from the hypophosphorous acid (salt) at the end of the polymer main chain was measured by quantifying the hypophosphorous acid structure at the end of the main chain using ³¹ P-NMR. That is, from the integrated intensity ratio of ³¹ P-NMR, the ratio of the hypophosphite group at the end of the main chain of the polymer to all phosphorus compounds was calculated. Furthermore, the ratio (mass%) of the structural unit containing phosphorus at the end of the main chain in the total mass of 100 mass% of the N-vinyl lactam was calculated from the amounts used of the monomer and the phosphorus compound.
³¹ P-NMR measurement conditions:
The polymer to be measured was dried under reduced pressure at room temperature, and the obtained solid content was dissolved in heavy water (Aldrich) so as to be 10%, and Varian's UnityPlus-400 (400 MHz, pulse sequence: s2pu1, measurement interval: 100.00 seconds, pulse: 45.0 degrees, capture time: 0.800 seconds, number of integrations: 128).

<Yellowness, Hunter color space b value>
The color tone under high temperature conditions was evaluated by the following procedure.
(1) The polymers (powder) obtained in Examples and Comparative Examples were heated at 260 ° C. for 60 minutes under nitrogen flow, and then allowed to cool in air.
(2) Subsequently, L, a, and b were measured using a color difference meter under the following conditions for a sample that had been air-cooled in a desiccator and returned to room temperature.
Apparatus: Nippon Denshoku Industries Co., Ltd. “Color difference meter SE-2000”
Measuring method: The sample after heating is put in a quartz cell and measured in the “reflection mode” under light shielding. The yellowness (YI) was calculated from the obtained L, a, and b.

Example 1
Polymerization of N-vinylpyrrolidone (NVP) was performed. First, in a SUS reaction vessel equipped with a Max blend (registered trademark of Sumitomo Heavy Industries, Ltd.) type stirring blade and a glass lid, 237.80 parts of ion-exchanged water, 237.80 parts of isopropanol (IPA), Sodium hypophosphite (SHP) 3.90 parts and diethanolamine (DEA) 0.50 parts were charged, and the temperature was raised to 83-86 ° C.

  Add 500.00 parts of NVP to a dropping funnel, add 1.00 parts of 2,2′-azobis-2-amidinopropane dihydrochloride (manufactured by Wako Pure Chemical Industries, Ltd .; V-50) to ion-exchanged water 19 in another dropping funnel. The initiator solution dissolved in 0.000 part was added and dripping was started at the same time. NVP was added dropwise over 180 minutes, and the initiator solution was added dropwise over 210 minutes. The reaction temperature was maintained at 83-86 ° C. After 210 minutes and 240 minutes from the start of the polymerization, 5 parts of a 10% aqueous V-50 solution was added all at once. Stirring was continued while maintaining 83 to 86 ° C., and after 270 minutes had elapsed from the start of polymerization, polymerization and aging were completed.

  The aqueous solution after polymerization was dried at 130 ° C. for 20 seconds with a multi-roll field drum dryer (manufactured by Katsuragi Kogyo Co., Ltd.), and then pulverized with a hammer mill. The pulverized powder had an opening of 250 μm for JIS testing. The sieve was classified using a sieve having an opening of 150 μm to prepare a powder (polymer of the present invention) having a particle size of 150 to 250 μm. Table 3 shows the characteristic values of the obtained polymer. Moreover, the ratio of the structural unit containing phosphorus at the end of the main chain measured by the above method was 0.42% by mass.

Example 2 and Comparative Examples 1-3
NVP was polymerized in the same manner as in Example 1 except that each component shown in Table 1 was used and polymerization was performed under the conditions shown in Table 2. Table 3 shows the characteristic values of the obtained polymer. “V-59” is 2,2′-azobis (2-methylbutyronitrile) manufactured by Wako Pure Chemical Industries. Further, 1.0 / 6 in B-2 of Comparative Example 3 means that 1.0 part is equally divided into 6 times.

  The N-vinyl lactam polymer obtained by the method of the present invention is less colored and useful for a wide range of applications. Examples of applications include various inorganic and organic dispersants, flocculants, thickeners, adhesives, adhesives, surface coating agents, crosslinkable compositions, and more specifically, mud dispersants, Cement material dispersant, cement material thickener, detergent builder, detergent color transfer inhibitor, heavy metal scavenger, metal surface treatment agent, dyeing assistant, dye fixing agent, foam stabilizer, emulsion stabilizer, ink dye Dispersants, water-based ink stabilizers, paint pigment dispersants, paint thickeners, pressure sensitive adhesives, paper adhesives, stick glues, medical adhesives, adhesives for patches, adhesives for cosmetic packs, resins Filler dispersant, coating agent for recording paper, surface treatment agent for inkjet paper, dispersant for photosensitive resin, antistatic agent, moisturizer, binder for fertilizer, polymer cross-linking agent, resin compatibilizer, photographic additive, Cosmetic preparation additives, hairdressing aids , Hair spray additive, sunscreen compositions additives, or used in a variety of industrial applications (e.g., production of the hollow fiber membrane).

Claims (3)

N comprising a step of polymerizing a monomer component essentially comprising N-vinyl lactam in an aqueous solvent essentially comprising alcohol in the presence of an azo polymerization initiator and / or organic peroxide and a reducing agent. -A method for producing a vinyl lactam polymer,
The alcohol is one or more of methyl alcohol, ethyl alcohol, isopropyl alcohol, n-propyl alcohol, n-butyl alcohol, sec-butyl alcohol and t-butyl alcohol,
The monomer component contains 90% by mass or more of N-vinyl lactam in 100% by mass of all monomer components,
The method for producing an N-vinyl lactam polymer, wherein the reducing agent contains hypophosphorous acid and / or a salt thereof.   The production method according to claim 1, wherein the amount of the hypophosphorous acid and / or salt thereof used is 0.3 g or more and 5.0 g or less with respect to 1 mol of all monomer components.   The production method according to claim 1 or 2, wherein the N-vinyl lactam polymer has a K value of 10 to 50.