JP5501913B2 - Production method of block copolymer - Google Patents

Description

  The present invention relates to a method for producing a block copolymer.

  A block copolymer consisting of a combination of polymer components with different properties has various different physical properties corresponding to the variety of combinations of polymer components, and is used as an impact-resistant resin, polymer emulsifier, dispersant, etc. Recently, it has been attracting attention as a film agent and a medical material, and its research examples are wide-ranging with graft copolymers. With regard to polyvinyl alcohol polymers (hereinafter sometimes abbreviated as PVA polymers), many researches and applications have been conducted on graft polymers based on PVA polymers. There are almost no examples of block copolymers having a coalescence as one component. However, as is well known, PVA-based polymers are few crystalline polymers among water-soluble polymers, and are used as water-soluble polymers with excellent mechanical and interfacial chemical properties. A block copolymer containing a PVA polymer as one component is expected as a material imparting new properties while maintaining the properties of the PVA polymer.

  In response to these requirements, Patent Document 1 (Japanese Patent Laid-Open No. 59-189111) proposes radical polymerization of a monomer capable of radical polymerization in the presence of a polymer having a mercapto group at the terminal. .

JP 59-189111 A

  An object of the present invention is to provide a method for producing a block copolymer containing a PVA polymer as one component.

  As a result of intensive studies on the above problems, the present inventors have a group represented by the following general formula (I) at the end, and in the presence of a PVA polymer having a viscosity average polymerization degree of 10 to 3000, The inventors have found that a block copolymer having a PVA polymer as one component can be produced by radical polymerization of a radical polymerizable monomer, and the present invention has been completed.

（式中、Ｍは、水素原子、アルカリ金属原子、１／２アルカリ土類金属原子またはアンモニウム基を表す。）

(In the formula, M represents a hydrogen atom, an alkali metal atom, a 1/2 alkaline earth metal atom or an ammonium group.)

  In the above case, the monomer is preferably at least one selected from the group consisting of vinyl esters and (meth) acrylic acid esters.

  The present invention is also a block copolymer containing a PVA polymer block obtained by the above production method.

  According to the production method of the present invention, it is possible to obtain a copolymer comprising a polymer block comprising a radical polymerizable monomer and a PVA polymer block. In particular, a block copolymer of polyvinyl ester or poly (meth) acrylic acid ester having low alkali resistance and a PVA polymer can be obtained.

  The PVA polymer used in the production method of the present invention has a group represented by the above general formula (I) at the terminal.

Examples of the alkali metal atom represented by M include a sodium atom and a potassium atom. Examples of the ½ alkaline earth metal atom represented by M include a ½ magnesium atom and a ½ calcium atom. When M is a ½ alkaline earth metal atom, the remaining ½ alkaline earth metal atom (that is, the remaining bond of the divalent alkaline earth metal atom) is oxygen in the general formula (I). atom, an oxygen atom in the following general formula (II), may be combined with _{P (H 2 O} 2) or the like.

（ただし、Ｍは水素原子、アルカリ金属原子、１／２アルカリ土類金属原子、またはアンモニウム基を表す。）

(However, M represents a hydrogen atom, an alkali metal atom, a 1/2 alkaline earth metal atom, or an ammonium group.)

  The PVA polymer used in the production method of the present invention may contain a group represented by the general formula (II) in the main chain.

The viscosity average polymerization degree P (hereinafter simply referred to as the polymerization degree) of the PVA polymer used in the production method of the present invention needs to be 10 to 3000. When the degree of polymerization is more than 3000 or less than 10, the productivity of the PVA polymer is lowered and impractical. The degree of polymerization of the PVA polymer is a value measured according to JIS K6726. That is, after re-saponifying the PVA polymer to a saponification degree of 99.5 mol% or more and purifying it, the intrinsic viscosity [η] measured in water at 30 ° C. can be obtained by the following formula.

P = ([η] × 1000 / 8.29) ^{(1 / 0.62)}

  The saponification degree of the PVA polymer used in the production method of the present invention is not particularly limited as long as it is water-soluble or water-dispersible, but the lower limit of the saponification degree is a viewpoint in the production of a partially saponified PVA polymer. Therefore, it is preferably 5 mol% or more, more preferably 7 mol% or more, and further preferably 10 mol% or more. There is no particular limitation on the upper limit of the saponification degree.

  In the PVA polymer used in the production method of the present invention, the modification amount of the group represented by the general formula (I) is preferably 0.01 to 18 mol%. If it is less than 0.01 mol%, the degree of polymerization may exceed 3000, the productivity of the PVA polymer may be reduced, and the utility may be impaired. When it exceeds 18 mol%, the degree of polymerization may be less than 10, which may reduce the productivity of the PVA polymer and impair practicality.

The modification amount of the group represented by the general formula (I) of the PVA polymer used in the production method of the present invention contains the group represented by the general formula (I) which is a precursor of the PVA polymer. ¹ H-NMR of polyvinyl acetate (hereinafter, polyvinyl acetate may be abbreviated as PVAc). Specifically, the modified PVAc is reprecipitated and purified three times or more with n-hexane / acetone and then dried under reduced pressure at 50 ° C. for 2 days to prepare the modified PVAc for analysis. The PVAc is dissolved in CDCl ₃ and measured at room temperature using 500 MHz ¹ H-NMR (JEOL GX-500). Peak α (4.7 to 5.2 ppm) derived from the main chain methine of vinyl ester and peak β (7.5 to 7.8 ppm) derived from protons attached to phosphorus of the group represented by formula (I) And 6.3 to 6.5 ppm), the amount of modification of the group represented by the general formula (I) is calculated using the following formula.

Modification amount of group represented by general formula (I) (mol%) = {(peak area β) / ((peak area α) + (peak area β))} × 100

The modification amount of the group represented by the general formula (I) of the PVA polymer used in the production method of the present invention can also be determined from ¹ H-NMR of the PVA polymer. Specifically, the PVA polymer is purified by Soxhlet extraction with methanol for 48 hours, dissolved in d ₆ -DMSO, and measured using ¹ H-NMR (JEOL GX-500) of 500 MHz. The peak γ (1.1 to 1.9 ppm) derived from the main chain methylene of the PVA polymer and the peak ε (7.5 to 7 derived from the proton attached to the phosphorus of the group represented by the general formula (I) (7 ppm and 6.3 to 6.6 ppm), the amount of modification of the group represented by the general formula (I) is calculated using the following formula.

Modification amount of group represented by general formula (I) (mol%) = {(peak area ε) / ((peak area γ) / 2 + (peak area ε))} × 100

  In the present invention, the PVA polymer may be used alone, or two or more kinds having different characteristics may be mixed and used.

  The production method of the PVA polymer used in the production method of the present invention is not particularly limited as long as the obtained PVA has a group represented by the general formula (I) at the terminal. For example, a vinyl ester monomer Can be produced by a method comprising a step of radical polymerization in the presence of a compound containing phosphorus and a step of saponifying the obtained polymer.

  Examples of vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, vinyl caproate, vinyl caprylate, vinyl laurate, vinyl palmitate, Examples include vinyl stearate, vinyl oleate, vinyl benzoate, etc. Among them, vinyl acetate is most preferable.

  Compounds containing phosphorus include hypophosphorous acid, sodium hypophosphite, potassium hypophosphite, calcium hypophosphite, magnesium hypophosphite, ammonium hypophosphite and hydrates thereof. Examples of the compound include sodium hypophosphite or a hydrate thereof, which is the most inexpensive industrially.

  There is no restriction | limiting in particular in the usage-amount of the compound containing phosphorus, What is necessary is just to set suitably according to the quantity of group represented by general formula (I) to introduce | transduce into a PVA-type polymer. As for the usage-amount of the compound containing phosphorus, 0.001-30 weight part is preferable with respect to 100 weight part of vinyl ester monomers.

  The polymerization of the vinyl ester monomer can be performed in a solvent such as an alcohol solvent or without a solvent.

  As a polymerization method used for the polymerization of the vinyl ester monomer, any of batch polymerization, semi-batch polymerization, continuous polymerization, and semi-continuous polymerization may be used. As the polymerization method, any known method such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method can be used. Among them, a bulk polymerization method or a solution polymerization method in which polymerization is performed without a solvent or an alcohol solvent is suitably employed, and an emulsion polymerization method is employed for the purpose of producing a copolymer having a high degree of polymerization. As the alcohol solvent, methanol, ethanol, n-propanol or the like can be used, but is not limited thereto. These solvents can be used in combination of two or more.

  As the initiator used for the polymerization, conventionally known azo initiators, peroxide initiators, redox initiators and the like are appropriately selected according to the polymerization method. As the azo initiator, 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (4-methoxy-2,4- Dimethyl valeronitrile) and the like, and peroxide initiators include perisopropyl compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate and diethoxyethyl peroxydicarbonate; t-butyl Perester compounds such as peroxyneodecanate, α-cumylperoxyneodecanate, and t-butylperoxydecanate; acetylcyclohexylsulfonyl peroxide; 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate, etc. Is mentioned. Furthermore, the initiator can be combined with potassium persulfate, ammonium persulfate, hydrogen peroxide, or the like to form an initiator. Moreover, as a redox-type initiator, what combined said peroxide and reducing agents, such as sodium hydrogen sulfite, sodium hydrogencarbonate, tartaric acid, L-ascorbic acid, Rongalite, is mentioned.

  In addition, when the polymerization of the vinyl ester monomer is performed at a high temperature, coloring of PVA due to the decomposition of the vinyl ester monomer may be seen. It is safe to add an antioxidant such as tartaric acid to the polymerization system in an amount of 1 to 100 ppm (relative to the vinyl ester monomer).

  0-200 degreeC is preferable and the temperature employ | adopted when superposing | polymerizing a vinyl ester-type monomer has more preferable 30-140 degreeC. When the polymerization temperature is lower than 0 ° C., a sufficient polymerization rate cannot be obtained, which is not preferable. Moreover, when the temperature which performs superposition | polymerization is higher than 200 degreeC, since it becomes difficult to obtain the target PVA, it is unpreferable. As a method for controlling the temperature employed in the polymerization to 0 to 200 ° C., for example, a method of balancing the heat generated by the polymerization and the heat radiation from the surface of the reactor by controlling the polymerization rate. Alternatively, a method of controlling by an external jacket using an appropriate heating medium can be mentioned, but the latter method is preferable from the viewpoint of safety.

  When the vinyl ester monomer is polymerized, other monomers may be copolymerized as long as the gist of the present invention is not impaired. Examples of monomers that can be used include α-olefins such as ethylene, propylene, n-butene, and isobutylene; acrylic acid and its salts; methyl acrylate, ethyl acrylate, n-propyl acrylate, and i-propyl acrylate. Acrylic acid esters such as n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate and octadecyl acrylate; methacrylic acid and salts thereof; methyl methacrylate, methacryl Methacrylic acid such as ethyl acetate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate Esters; N-methyl acrylamide, N-ethyl acrylamide, N, N-dimethyl acrylamide, diacetone acrylamide, acrylamide propane sulfonic acid and its salt, acrylamide propyl dimethylamine and its salt or its quaternary salt, N-methylol acrylamide and its Acrylamide derivatives such as derivatives; methacrylamide; N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid and its salts, methacrylamidepropyldimethylamine and its salts or quaternary salts thereof, N-methylolmethacrylamide and Methacrylamide derivatives such as derivatives thereof; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether , Vinyl ethers such as n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether and stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; Vinylidene halides such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; unsaturated dicarboxylic acids such as maleic acid, itaconic acid and fumaric acid, and salts or esters thereof; vinyltrimethoxysilane, etc. Vinylsilyl compounds; polyoxyethylene (meth) acrylate, polyoxypropylene (meth) acrylate, polyoxyethylene (meth) acrylic amide, polyoxypropylene (meth) acrylic amide, polyoxy Oxyalkylene groups such as ethylene (1- (meth) acrylamide-1,1-dimethylpropyl) ester, polyoxyethylene (meth) allyl ether, polyoxypropylene (meth) allyl ether, polyoxyethylene vinyl ether, polyoxypropylene vinyl ether Containing monomer; isopropenyl acetate and the like.

  In the polymerization of the vinyl ester monomer, for the purpose of adjusting the degree of polymerization of the resulting PVA polymer, the polymerization is carried out in the presence of a chain transfer agent as long as the gist of the present invention is not impaired. There is no problem. Chain transfer agents include aldehydes such as acetaldehyde and propionaldehyde; ketones such as acetone and methyl ethyl ketone; mercaptans such as 2-hydroxyethanethiol, n-dodecanethiol and 3-mercaptopropionic acid; tetrachloromethane, bromotrichloro Halogens such as methane, trichlorethylene, and perchlorethylene are listed.

  As the PVA polymer used in the production method of the present invention, a PVA polymer having a high 1,2-glycol bond content obtained by polymerizing a vinyl ester monomer under a higher temperature condition than usual. It can also be used. In this case, the content of 1,2-glycol bonds is preferably 1.9 mol% or more, more preferably 2.0 mol% or more, and even more preferably 2.1 mol% or more.

  For the saponification reaction of vinyl ester polymers, alcoholysis or hydrolysis using a conventional basic catalyst such as sodium hydroxide, potassium hydroxide or sodium methoxide or an acidic catalyst such as p-toluenesulfonic acid. Reaction can be applied. Examples of the solvent that can be used in this reaction include alcohols such as methanol and ethanol; esters such as methyl acetate and ethyl acetate; ketones such as acetone and methyl ethyl ketone; aromatic hydrocarbons such as benzene and toluene; These can be used alone or in combination of two or more. Among them, it is convenient and preferable to perform the saponification reaction using methanol or a methanol / methyl acetate mixed solution as a solvent and sodium hydroxide as a catalyst.

  In the production method of the block copolymer of the present invention, radical polymerization of a monomer capable of radical polymerization is carried out in the presence of a PVA polymer having a terminal represented by the general formula (I) at the terminal. As the polymerization method, generally known methods such as bulk polymerization, solution polymerization, pearl polymerization, emulsion polymerization and the like can be adopted, but in a solvent that can dissolve the PVA polymer, for example, in a medium mainly composed of water or dimethyl sulfoxide. It is preferred to carry out the polymerization. As the polymerization process, any of a batch method, a semi-batch method, and a continuous method can be employed.

  In the above radical polymerization, among usual radical polymerization initiators such as 2,2′-azobisisobutyronitrile, benzoyl peroxide, lauroyl peroxide, diisopropyl peroxydicarbonate, potassium persulfate, ammonium persulfate and the like. The one suitable for the polymerization system can be used. In the case of polymerization in aqueous system, redox initiation by the group represented by the above general formula (I) at the terminal of the PVA polymer and an oxidizing agent such as potassium bromate, potassium persulfate, ammonium persulfate, hydrogen peroxide, etc. Among them, potassium bromate alone does not generate radicals under normal polymerization conditions, and is decomposed only by a redox reaction with the group represented by the above general formula (I) at the end of the PVA polymer. Is a particularly preferred initiator because it generates radicals.

  In carrying out the above radical polymerization, it is important and desirable that the polymerization system is acidic. This is because the group represented by the general formula (I) is ionically added to and disappears from the double bond of the monomer under basic conditions. For example, when polymerization is carried out in an aqueous system, it is desirable to carry out all polymerization operations at pH 4 or lower.

  Examples of the radical (co) polymerizable monomer include olefins such as ethylene, propylene, and isobutylene; halogenated olefins such as vinyl chloride, vinyl fluoride, vinylidene chloride, and vinylidene fluoride; vinyl formate, vinyl acetate, and propion. Vinyl esters such as vinyl acid and vinyl versatate; (meth) acrylic acid and salts thereof; methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, 2-hydroxyethyl acrylate, etc. Acrylic acid ester; Methacrylic acid ester such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, 2-hydroxyethyl methacrylate; dimethylaminoethyl acrylate, methacrylate Dimethylaminoethyl acid and quaternized compounds thereof; acrylamide derivatives such as acrylamide, methacrylamide, N-methylolacrylamide, N, N-dimethylacrylamide, acrylamide-2-methylpropanesulfonic acid and sodium, potassium salts thereof; styrene, α -Styrenic monomers such as methylstyrene; N-vinylpyrrolidone and the like may be mentioned, and only one of these may be used, or two or more may be mixed and used. Among these, vinyl ester, acrylic acid ester, and methacrylic acid ester are preferable for the reason described later.

  According to the block copolymer production method of the present invention, the degree of polymerization of the PVA polymer having a group represented by the above general formula (I) at the terminal, the degree of saponification, and the PVA polymer contains a copolymer component. A block copolymer having a very wide range of properties can be provided by appropriately selecting the composition and further selecting and combining the types and amounts of monomers capable of radical polymerization. For example, if a monomer that gives a water-soluble polymer such as acrylic acid, acrylamide, dimethylaminoethyl methacrylate, sodium p-styrenesulfonate, or the like is used as a radical-polymerizable monomer, the resulting block copolymer is also obtained. Further, it is water-soluble, and if it is polymerized in an aqueous system, it can be used as an aqueous solution of a block copolymer as it is after polymerization. In addition, when using a monomer that gives a water-insoluble polymer such as acrylic acid ester and methacrylic acid ester, depending on conditions, it becomes an emulsion when polymerized in an aqueous system, and can be used as it is after polymerization. .

  A further feature of the method for producing a block copolymer of the present invention is that a block copolymer of polyvinyl ester or poly (meth) acrylic acid ester having a low alkali resistance and a PVA polymer can be obtained. A block copolymer containing a PVA polymer as a component can also be obtained by saponifying a block copolymer containing a polyvinyl ester polymer as a component, but the other polymer block has low alkali resistance. In the saponification step, these polymers are also hydrolyzed, and the target block copolymer cannot be obtained.

  The block copolymer obtained by the production method of the present invention contains a PVA polymer block and a polymer block composed of other radically polymerizable monomers. When the other polymer block is composed of a plurality of monomer units, the inside of the block is preferably random copolymerization. The composition, molecular weight, molecular weight distribution, etc. of the copolymer are not particularly limited, but the weight ratio of the PVA polymer to other polymer blocks is preferably 1 / 0.1 to 1/20, Preferably it is 1 / 0.5 to 1/1.

  The above-mentioned block copolymer has a wide range of properties as described above, and further has properties different from the polymer blend, such as a polymer of one component of the block copolymer and a polymer of the other component. Therefore, it can be applied to various uses. For example, internal paper sizing agent, paper surface sizing agent, paper coating agent, textile product sizing agent, warp glue, fiber processing agent, paint, glass fiber coating agent, metal surface coating agent, antifogging agent, etc. Coating materials, adhesives such as wood, paper, aluminum foil, plastics, nonwoven fabric binders, fibrous binders, binders for building materials such as plasterboard and fiberboard, thickeners for various emulsion adhesives, urea resin adhesives Additives for adhesives, inorganic binders or additives for cement, mortar or ceramic, various adhesives such as hot melt adhesives, pressure sensitive adhesives, ethylene, styrene, vinyl acetate, (meth) acrylic esters, Dispersion for emulsion polymerization of ethylenically unsaturated monomers such as vinyl chloride, vinylidene chloride, acrylonitrile, and butadiene monomers Pigment dispersion stabilizers such as paints and adhesives, dispersion stabilizers for suspension polymerization of various ethylenically unsaturated monomers such as vinyl chloride, vinylidene chloride, styrene, (meth) acrylic acid ester, vinyl acetate, fibers, Films, sheets, pipes, tubes, water-soluble fibers, molded products such as temporary coatings, hydrophilicity imparting agents for hydrophobic resins, composite fibers, films and other synthetic resin blending agents such as molded products, soil properties It can be applied to a wide range of applications such as improvers, soil stabilizers, and photosensitive resin applications.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples. In the following examples and comparative examples, parts and% indicate parts by weight and% by weight, respectively, unless otherwise specified.

Production Example 1
(Production of PVA-1)
A reactor was charged with 600 g of methanol and 11.4 g of sodium phosphinate monohydrate to prepare a methanol solution of sodium phosphinate monohydrate. Next, 1200 g of vinyl acetate was charged into the reactor, and the inside of the reactor was purged with nitrogen by bubbling nitrogen gas. The temperature of the reactor was increased, and when the internal temperature reached 60 ° C., 0.5 g of 2,2′-azobisisobutyronitrile was added to the reactor to initiate polymerization. The polymerization temperature was maintained at 60 ° C. during the polymerization. After 4 hours, when the polymerization rate reached 50%, the polymerization was stopped by cooling. Next, unreacted vinyl acetate was removed under reduced pressure to obtain a methanol solution of polyvinyl acetate (PVAc). The PVAc solution adjusted to 40% was saponified by adding a NaOH methanol solution (10% concentration) so that the alkali molar ratio (number of moles of NaOH / number of moles of vinyl acetate units in PVAc) was 0.03. After adding the alkaline solution, a gel was formed in about 5 minutes. This was pulverized with a pulverizer and allowed to stand at 40 ° C. for 1 hour to proceed with saponification. The alkali was neutralized. After confirming the completion of neutralization using a phenolphthalein indicator, a white solid was obtained by filtration, 4000 g of methanol was added thereto, and the mixture was left to wash at room temperature for 3 hours. After the above washing operation was repeated three times, the white solid obtained by centrifugal drainage was left in a dryer at 65 ° C. for 2 days to obtain PVA-1. This polymer had a viscosity-average polymerization degree of 210 and a saponification degree of 98.5 mol%.

The modification amount of the group represented by the general formula (I) of the obtained PVA-1 was determined by ¹ H-NMR as follows. The obtained PVA-1 was purified by Soxhlet extraction with methanol for 48 hours, then dissolved in d ₆ -DMSO, and analyzed using ¹ H-NMR (JEOL GX-500) of 500 MHz. Peaks (7.5 to 7.7 ppm and 6.5) derived from protons attached to phosphorus of the group represented by the formula (I) and the area α of the peak derived from chain methylene (1.1 to 1.9 ppm). The amount of modification of the group represented by the general formula (I) was calculated from the area β of 3 to 6.6 ppm) using the following formula. In PVA-1, the modification amount of the group represented by the general formula (I) was 0.46 mol%. The results are shown in Table 1.

Modification amount of group represented by general formula (I) (mol%) = {(peak area β) / ((peak area α) / 2 + (peak area β))} × 100

Production Examples 2 to 4
(Production of PVA-2 to PVA-4)
PVA-2 to PVA-4 were obtained in the same manner as in Production Example 1 except that the amounts of methanol and sodium phosphinate monohydrate charged and the molar ratio of sodium hydroxide to vinyl acetate units during saponification were changed. . The results are shown in Table 1.

Example 1
110 parts of distilled water was added to 10 parts of PVA-1 obtained in Production Example 1, and PVA was dissolved at 95 ° C. Subsequently, it cooled to 30 degreeC under nitrogen stream, and 10 parts of acrylic acid substituted by nitrogen beforehand was added. Next, a total amount of an aqueous solution obtained by dissolving 0.32 part of potassium bromate in 10 parts of distilled water substituted with nitrogen was added, and polymerization was started at 30 ° C. The acrylic acid charged in 2 hours was completely consumed, and a polymerization solution having a solid concentration of 15% was obtained. ¹ H-NMR analysis confirmed that the obtained polymer was a block copolymer of PVA-polyacrylic acid. The polymerization conditions and results are shown in Table 2.

Example 2
108 parts of distilled water was added to 10 parts of PVA-3 obtained in Production Example 3, and PVA was dissolved at 95 ° C. Subsequently, it cooled to room temperature under nitrogen stream, and 10 parts of acrylic acid substituted by nitrogen beforehand was added. Next, the temperature was raised to 60 ° C., and an aqueous solution prepared by dissolving 12 parts of distilled water in which 0.15 part of potassium bromate was replaced with nitrogen was added to initiate polymerization. The potassium bromate aqueous solution was added uniformly at a rate of 2 ml / 5 minutes for 30 minutes. The acrylic acid charged in 1 hour was completely consumed, and a polymerization solution having a solid content concentration of 14.5% was obtained. ¹ H-NMR analysis confirmed that the obtained polymer was a block copolymer of PVA-polyacrylic acid. The polymerization conditions and results are shown in Table 2.

Example 3
To 10 parts of PVA-2 obtained in Production Example 2, 108 parts of distilled water was added, and PVA was dissolved at 95 ° C. Next, the mixture was cooled to room temperature and adjusted to pH = 5 by adding N / 2-H ₂ SO _4, and then 10 parts of acrylamide was added and dissolved. Next, nitrogen substitution was performed, the temperature was raised to 60 ° C., and an aqueous solution in which 0.22 g of potassium bromate was dissolved in distilled water substituted with nitrogen was added to initiate polymerization. The potassium bromate aqueous solution was added uniformly at a rate of 2 ml / 5 minutes for 30 minutes. The acrylamide charged in 90 minutes was completely consumed, and a polymerization solution having a solid content of 14.2% was obtained. It was confirmed by ¹ H-NMR analysis that the obtained polymer was a PVA-polyacrylamide block copolymer. The polymerization conditions and results are shown in Table 2.

Examples 4-7
Polymerization was carried out in the same manner as in Example 3 except that the polymerization conditions were changed as shown in Table 2. The polymerization conditions and results are shown in Table 2.

Example 8
110 parts of distilled water was added to 10 parts of PVA-3 obtained in Production Example 3, and PVA was dissolved at 95 ° C. Then cooled to room temperature, was adjusted to pH = 3 by addition of _{N / 2-H 2 SO 4} , acrylamide 10 parts was added and dissolved. Next, nitrogen substitution was performed, the temperature was raised to 60 ° C., and an aqueous solution in which 0.2 g of potassium persulfate was dissolved in distilled water substituted with nitrogen was added to initiate polymerization. The acrylamide charged in 2 hours was almost consumed, and a polymerization solution having a polymerization rate of 99.5% and a solid content concentration of 14.3% was obtained. It was confirmed by ¹ H-NMR analysis that the obtained polymer was a PVA-polyacrylamide block copolymer. The polymerization conditions and results are shown in Table 2.

Example 9
Polymerization was carried out in the same manner as in Example 8 except that methyl acrylate was used instead of acrylamide. The methyl acrylate charged in 2 hours was almost consumed, and a polymerized emulsion having a polymerization rate of 99.5% and a solid content concentration of 14.3% was obtained. It was confirmed by ¹ H-NMR analysis that the obtained polymer was a block copolymer of PVA-polymethyl acrylate. The polymerization conditions and results are shown in Table 2.

Example 10
After adding 43 parts of distilled water to 10 parts of 30% aqueous solution of PVA-1 obtained in Production Example 1 and adjusting to pH = 3 with N / 2-H ₂ SO ₄ , 40 parts of methanol, 17 parts of methyl methacrylate. And nitrogen substitution was performed. Next, the temperature was raised to 65 ° C., and an aqueous solution in which 0.03 part of 2,2′-azobisisobutyronitrile was dissolved in 10 parts of methanol substituted with nitrogen was added to initiate polymerization. The polymerization rate after 6 hours from the start was 95%, and some precipitation occurred. ¹ H-NMR analysis confirmed that the obtained polymer was a PVA-polymethyl methacrylate block copolymer. The polymerization conditions and results are shown in Table 2.

Example 11
Polymerization was performed in the same manner as in Example 2 except that PVA-4 was used instead of PVA-3. The acrylic acid charged in 1 hour was completely consumed, and a polymerization solution having a solid content concentration of 14.5% was obtained. ¹ H-NMR analysis confirmed that the obtained polymer was a block copolymer of PVA-polyacrylic acid. The polymerization conditions and results are shown in Table 2.

Claims (3)

In the presence of a polyvinyl alcohol polymer having a group represented by the following general formula (I) at the end and a viscosity average polymerization degree of 10 to 3000, a radical polymerizable monomer is radicalized under acidic conditions. A process for producing a block copolymer, characterized by polymerization.

(In the formula, M represents a hydrogen atom, an alkali metal atom, a 1/2 alkaline earth metal atom or an ammonium group.)   The method for producing a block copolymer according to claim 1, wherein the monomer is at least one selected from the group consisting of vinyl esters and (meth) acrylic acid esters.   A block copolymer containing a polyvinyl alcohol polymer block obtained by the production method according to claim 1.