JP6027419B2 - Alkenyl-modified vinyl alcohol polymer and thickener containing the same - Google Patents

Description

  The present invention relates to a novel alkenyl-modified vinyl alcohol polymer and a thickener containing the same.

  A vinyl alcohol polymer (hereinafter sometimes abbreviated as “PVA”) is a few crystalline water-soluble polymers, and has excellent film-forming properties, interfacial properties, and strength properties. For this reason, PVA is widely used as a raw material for thickeners, paper coating agents, adhesives, fiber processing agents, binders, emulsion stabilizers, films, fibers and the like. In order to improve the specific performance of PVA, various modified PVAs by controlling crystallinity and introducing functional groups have been developed.

  Among such modified PVA, alkyl-modified PVA into which an alkyl group has been introduced is known to exhibit hydrophobic group interaction due to an alkyl group in an aqueous solvent and to exhibit excellent thickening properties (Japanese Patent Application Laid-Open (JP-A)). (See Sho 55-47256). For this reason, alkyl-modified PVA is useful as a thickener for paints and adhesives, and alkyl-modified PVA containing various monomer units has been developed (Japanese Patent Laid-Open No. 2008-291120 and Japanese Patent Laid-Open No. Hei 10-). 338714). However, this alkyl-modified PVA is insufficient in water solubility, and it takes time to prepare the aqueous solution, which makes the manufacturing work complicated.

JP 55-47256 A JP 2008-291120 A JP 10-338714 A

  This invention is made | formed based on the above situations, and it aims at providing the novel modified PVA which is excellent in water solubility, exhibiting sufficient viscosity.

（式（Ｉ）中、Ｒ^１は、炭素数８〜２９の直鎖状又は分岐状のアルケニル基である。Ｒ^２は、水素原子又は炭素数１〜８のアルキル基である。） The present invention made to achieve the above object
It contains a monomer unit represented by the following formula (I) (hereinafter also referred to as “monomer unit (a)”), has a viscosity average polymerization degree of 100 or more and 5,000 or less, and a saponification degree of 20 mol%. An alkenyl-modified vinyl alcohol copolymer having a monomer unit content of 0.05 mol% or more and 5 mol% or less.

(In Formula (I), R ¹ is a linear or branched alkenyl group having 8 to 29 carbon atoms. R ² is a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.)

  The alkenyl-modified PVA is water-soluble when dissolved due to the low crystallinity of the alkenyl group based on the presence of the hydrophobic and double bond alkenyl group of the monomer unit (a) and the hydrophilic amide bond. In spite of its superiority, it can exhibit sufficient thickening in the solution state due to hydrophobic interaction. Moreover, in the said alkenyl modified PVA, this water solubility and thickening can be improved by making a viscosity average polymerization degree, a saponification degree, and the content rate of the said monomer unit (a) into the said range.

The number of carbon atoms of the alkenyl group ^{R 1} in the above formula (I), the preferably 15 to 26. Thus, by using the alkenyl group having the specific carbon number for R ¹ , water solubility and thickening can be further increased.

  The saponification degree of the alkenyl-modified PVA is preferably 60 mol% or more and 99.9 mol% or less. By setting it as such a saponification degree, the interaction of the hydrophobic groups of the said alkenyl modified PVA is expressed more effectively, and the above-mentioned viscosity can be further increased.

（式（ＩＩ）中、Ｒ^１及びＲ^２の定義は上記式（Ｉ）と同様である。） The alkenyl-modified PVA is preferably obtained by saponifying a copolymer of an unsaturated monomer represented by the following formula (II) and a vinyl ester monomer.

(In formula (II), the definitions of R ¹ and R ² are the same as in formula (I) above.)

  Since the alkenyl-modified PVA is obtained by saponifying the copolymer of the specific monomer, adjustment of the saponification degree of the alkenyl-modified PVA becomes easy, and the water-solubility and The thickening can be further increased.

  The thickener of the present invention contains the alkenyl-modified PVA. Since the thickener contains the alkenyl-modified PVA, it can exhibit an excellent thickening function even when used in a small amount.

  As described above, the alkenyl-modified PVA of the present invention is excellent in water solubility and can exhibit sufficient viscosity. Therefore, the alkenyl-modified PVA can be suitably used for, for example, a thickener, a paper coating agent, an adhesive and a film. Further, the thickener of the present invention can exhibit an excellent thickening function even when used in a small amount.

  Hereinafter, embodiments of the alkenyl-modified PVA of the present invention will be described in detail.

<Alkenyl modified PVA>
The alkenyl-modified PVA contains a monomer unit (a) represented by the following formula (I). The alkenyl-modified PVA is based on the low crystallinity of the alkenyl group based on the presence of the hydrophobic and double-bonded alkenyl group (R ¹ ) of the monomer unit (a) and the hydrophilic amide bond. Despite being excellent in water solubility at the time of dissolution, sufficient thickening can be exhibited in a solution state by hydrophobic interaction. The alkenyl-modified PVA is a copolymer having the monomer unit (a) and a vinyl alcohol monomer unit (—CH ₂ —CHOH—), and further has other monomer units. Also good.

In formula (I), R ¹ is a linear or branched alkenyl group having 8 to 29 carbon atoms. R ² is a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. The R ¹ and R ² may have a substituent such as a halogen atom as long as the effect of the present invention is not impaired, but preferably does not have these substituents. .

The linear or branched alkenyl group represented by R ¹ has 8 to 29 carbon atoms, preferably 10 to 28, more preferably 12 to 27, and even more preferably 15 to 26. 17 to 24 is particularly preferable. Examples of R ¹ include an erucyl group (—C ₂₂ H ₄₃ ), an oleyl group (—C ₁₈ H ₃₅ ), a myristol group (—C ₁₄ H ₂₇ ), and the like. When the number of carbon atoms is less than 8, the interaction between alkenyl groups in the alkenyl-modified PVA does not appear, so that the viscosity increase is not sufficiently exhibited. On the contrary, when this carbon number exceeds 29, the water solubility etc. of the said alkenyl modified PVA fall. The terminal of the alkenyl group is preferably a methyl group. That is, the position of the double bond in the alkenyl group is to reduce the crystallinity of the entire alkenyl group and improve the mobility, and to prevent side reactions during the copolymerization reaction and the decrease in viscosity stability of the aqueous solution. It is preferable that it exists other than the terminal. The number of double bonds in the alkenyl group is preferably 1 from the viewpoint of availability of the monomer and the stability of the aqueous solution or the coated product.

R ² is a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and a hydrogen atom or a methyl group is preferable from the viewpoint of ease of synthesis.

  The content rate of the said monomer unit (a) in the said alkenyl modified PVA is 0.05 mol% or more and 5 mol% or less. This content is preferably 0.1 mol% or more, and more preferably 0.2 mol% or more. Further, the content is preferably 2 mol% or less, and more preferably 1 mol% or less. In addition, the content rate of this monomer unit (a) is a content rate of the monomer unit (a) represented by the said Formula (I) which occupies for all the structural units which comprise alkenyl modified PVA.

  When the content of the monomer unit (a) exceeds 5 mol%, the proportion of hydrophobic groups contained in one molecule of alkenyl-modified PVA increases, and the water solubility of the alkenyl-modified PVA decreases. On the other hand, when the content of the monomer unit (a) is less than 0.05 mol%, the water solubility of the alkenyl-modified PVA is excellent, but the number of alkenyl chains contained in the alkenyl-modified PVA is small. Further, physical properties based on alkenyl modification such as thickening are not sufficiently exhibited.

The content of the monomer unit (a) can be determined from proton NMR of an alkenyl-modified vinyl ester polymer that is a precursor of the alkenyl-modified PVA. Specifically, after reprecipitation and purification of the alkenyl-modified vinyl ester polymer with n-hexane / acetone 3 times or more sufficiently, drying is performed under reduced pressure at 50 ° C. for 2 days to prepare a sample for analysis. To do. This sample is dissolved in CDCl ₃ and measured at room temperature using 500 MHz proton NMR (JEOL GX-500).

In this case, for example, when the alkenyl-modified monomer unit other than the monomer unit (a) is not included, the alkenyl group of R ¹ has —CH═CH—, and R ² is a hydrogen atom, It can be calculated by the following method. That is, the peak α (4.2 to 4.8 ppm) derived from the main chain methine of the alkenyl-modified vinyl ester polymer and the peak β (5.0 to 5.4 ppm) derived from the alkenyl group —CH═CH—. From the above, the content S of the monomer unit (a) is calculated using the following formula.
S (mol%)
= {(Number of protons of β / 2) / (number of protons of α + (number of protons of β / 2))} × 100

  The viscosity average polymerization degree of the alkenyl-modified PVA is 100 or more and 5,000 or less. The viscosity average degree of polymerization may be simply referred to as the degree of polymerization. If the degree of polymerization exceeds 5,000, the productivity of the alkenyl-modified PVA is lowered, which is not practical. On the other hand, when the degree of polymerization is less than 100, each characteristic of the alkenyl-modified PVA such as thickening may not be sufficiently exhibited. The lower limit of the degree of polymerization is preferably 500 and more preferably 1,000 from the viewpoint of increasing the viscosity of the alkenyl-modified PVA.

This viscosity average degree of polymerization (P) is measured according to JIS-K6726. That is, after re-saponifying and purifying the alkenyl-modified PVA, it is obtained from the intrinsic viscosity [η] (unit: deciliter / g) measured in water at 30 ° C. by the following formula.
P = ([η] × 10 ³ /8.29) ^{(1 / 0.62)}

  The saponification degree of the alkenyl-modified PVA needs to be 20 mol% or more and 99.99 mol% or less, and preferably 60 mol% or more and 99.9 mol% or less from the viewpoint of increasing the viscosity of the alkenyl-modified PVA. 70 mol% or more and 99.9 mol% or less are more preferable, 80 mol% or more and 99.9 mol% or less are more preferable, and 96 mol% or more and 99.9 mol% or less are especially preferable.

  When this saponification degree is less than 20 mol%, the water solubility etc. of the said alkenyl modified PVA fall. In addition, as the association performance (crosslinking performance) expressed by the hydrophobic group interaction decreases, the viscosity increase also decreases. On the contrary, if the degree of saponification exceeds 99.99 mol%, production of alkenyl-modified PVA becomes difficult, which is not practical. The saponification degree of the alkenyl-modified PVA is a value that can be measured according to JIS-K6726.

  As described above, the alkenyl-modified PVA is excellent in water solubility due to the presence of the hydrophobic and double-bonded alkenyl group of the monomer unit (a) and the hydrophilic amide bond. Can increase viscosity. Moreover, in the said alkenyl modified PVA, water solubility and thickening can be improved by making a viscosity average polymerization degree, a saponification degree, and the content rate of the said monomer unit (a) into the said range. Therefore, the alkenyl-modified PVA can be suitably used for, for example, a thickener, a paper coating agent, an adhesive, and a film.

<Method for producing alkenyl-modified PVA>
Although the method for producing the alkenyl-modified PVA is not particularly limited, the alkenyl-modified vinyl ester system obtained by copolymerizing an unsaturated monomer represented by the following formula (II) with a vinyl ester monomer is obtained. A method of saponifying the polymer is preferred. Here, the above copolymerization is preferably performed in an alcohol solvent or without a solvent.

In the formula (II), the definitions of R ¹ and R ² are the same as those in the above formula (I).

  Specific examples of the unsaturated monomer represented by the formula (II) include N-octenylacrylamide, N-decenylacrylamide, N-dodecenylacrylamide, N-tetradecenylacrylamide, N -Octadecenyl acrylamide, N-docosenyl acrylamide, N-hexacocenyl acrylamide, N-octenyl methacrylamide, N-decenyl methacrylamide, N-dodecenyl methacrylamide, N-tetradece Nyl methacrylamide, N-octadecenyl methacrylamide, N-docosenyl methacrylamide, N-hexacocenyl methacrylamide and the like. Among these, N-octadecenyl acrylamide, N-tetradecenyl methacrylamide, N-octadecenyl methacrylamide and N-docosenyl methacrylamide are preferable, and N-octadecenyl acrylamide, N- Octadecenyl methacrylamide and N-docosenyl methacrylamide are more preferred, and N-octadecenyl acrylamide and N-octadecenyl methacrylamide are more preferred.

  Examples of the vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, vinyl caproate, vinyl caprylate, vinyl laurate, and vinyl palmitate. , Vinyl stearate, vinyl oleate, vinyl benzoate and the like, among which vinyl acetate is preferred.

When the unsaturated monomer represented by the above formula (II) and the vinyl ester monomer are copolymerized, other monomers may be copolymerized within a range not impairing the gist of the present invention. Examples of monomers that can be used include:
Α-olefins such as ethylene, propylene, n-butene, isobutylene;
Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, 2,3-diacetoxy-1-vinyloxypropane;
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, 2,3-diacetoxy-1-allyloxypropane, allyl chloride;
Vinylsilyl compounds such as vinyltrimethoxysilane;
And isopropenyl acetate.

In addition, the purpose of the present invention is to adjust the degree of polymerization of the copolymer obtained in the copolymerization of the unsaturated monomer represented by the above formula (II) and the vinyl ester monomer. Copolymerization may be carried out in the presence of a chain transfer agent within a range that does not impair. As this chain transfer agent,
Aldehydes such as acetaldehyde and propionaldehyde;
Ketones such as acetone and methyl ethyl ketone;
Mercaptans such as 2-hydroxyethanethiol;
Halogenated hydrocarbons such as trichlorethylene and perchlorethylene;
Examples thereof include phosphinic acid salts such as sodium phosphinate monohydrate, among which aldehydes and ketones are preferably used.

  The addition amount of the chain transfer agent can be determined according to the chain transfer constant of the chain transfer agent to be added and the degree of polymerization of the target alkenyl-modified vinyl ester polymer. 0.1-10 mass% is preferable with respect to it.

  The temperature employed when copolymerizing the unsaturated monomer represented by the above formula (II) and the vinyl ester monomer is preferably 0 ° C to 200 ° C, more preferably 30 ° C to 140 ° C. . When the copolymerization temperature is lower than 0 ° C., it is difficult to obtain a sufficient polymerization rate. Moreover, when the temperature which superposes | polymerizes is higher than 200 degreeC, it is difficult to obtain the alkenyl modified PVA which satisfies the content rate of the monomer unit (a) prescribed | regulated by this invention. As a method of controlling the temperature employed in carrying out the copolymerization to 0 ° C. to 200 ° C., for example, by controlling the polymerization rate, the balance between the heat generated by the polymerization and the heat radiation from the surface of the reactor can be achieved. Or the method of controlling by an external jacket using an appropriate heat medium, and the latter method is preferred from the viewpoint of safety.

  The polymerization method employed for copolymerizing the unsaturated monomer represented by the above formula (II) and the vinyl ester monomer is batch polymerization, semi-batch polymerization, continuous polymerization, semi-continuous polymerization. Either of these 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 employed. Among these, a bulk polymerization method or a solution polymerization method in which polymerization is performed in a solvent-free or alcohol-based solvent is preferably employed, and an emulsion polymerization method is employed for the purpose of producing a copolymer having a high degree of polymerization. .

  Examples of the alcohol solvent include methanol, ethanol, n-propanol, and the like, but are not limited thereto. Moreover, these solvents can be used by mixing two or more kinds.

  As the initiator used for copolymerization, 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 copolymerization of the unsaturated monomer represented by the above formula (II) and the vinyl ester monomer is performed at a high temperature, the alkenyl modified PVA caused by the decomposition of the vinyl ester monomer Coloring may be seen. In this case, an antioxidant such as tartaric acid may be added to the polymerization system in an amount of about 1 to 100 ppm based on the vinyl ester monomer for the purpose of preventing coloring.

  The saponification reaction of the alkenyl-modified vinyl ester polymer obtained by the above copolymerization is publicly known using a basic catalyst such as sodium hydroxide, potassium hydroxide or sodium methoxide or an acidic catalyst such as p-toluenesulfonic acid. An alcoholysis reaction or a hydrolysis 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 these, it is simple 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.

<Thickener>
The thickener of the present invention contains the alkenyl-modified PVA. Thereby, the said thickener can exhibit the outstanding thickening.

  The thickener may be a powdery thickener made of the alkenyl-modified PVA, or may be a liquid thickener containing water or a water-containing solvent. This liquid thickener is suitable for use in water-dispersible emulsion-containing materials such as paints and adhesives.

  The solvent other than water contained in the water-containing solvent is not particularly limited. For example, alcohol solvents such as methanol and ethanol; ester solvents such as methyl acetate and ethyl acetate; diethyl ether, 1,4-dioxane and methyl Ether solvents such as cellosolve, cellosolve, butyl cellosolve, MTBE (methyl-t-butyl ether) and butyl carbitol; ketone solvents such as acetone and diethyl ketone; glycol solvents such as ethylene glycol, propylene glycol, diethylene glycol and triethylene glycol Glycol ether solvents such as diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, propylene glycol monomethyl ether, 3-methoxy-3-methyl-1-butanol; Glycol monomethyl ether acetate, PMA (propylene glycol monomethyl ether acetate), diethylene glycol monobutyl ether acetate, can be mentioned glycol esters solvents such as diethylene glycol monoethyl ether acetate.

  When the said thickener is a liquid form, it is preferable that the compounding quantity of the said alkenyl modified PVA is 1-50 mass parts with respect to 100 mass parts of solvent, and 3-30 mass parts is more preferable. Such a liquid thickener is produced by adding the alkenyl-modified PVA to water or a water-containing solvent and mixing them by heating.

  In the liquid thickener, various plasticizers, surfactants, antifoaming agents, ultraviolet absorbers and the like may be blended as long as the effects of the present invention are not impaired.

  Similarly, the thickener may be made of various other water-soluble polymers such as various known PVA, starch, carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, and hydroxypropylmethylcellulose as long as the effects of the present invention are not impaired. You may mix | blend. The blending amount of these other water-soluble polymers is preferably 50 parts by mass or less with respect to 100 parts by mass of the alkenyl-modified PVA.

  The thickener exhibits a high viscosity in a small amount and also exhibits a stable viscosity. Therefore, the said thickener can be conveniently used as a thickener used for water-system solutions and water-system emulsion solutions, such as a paint, cement, concrete, a binder, an adhesive agent, and cosmetics.

  Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. In the following examples and comparative examples, “part” and “%” mean mass basis unless otherwise specified.

  The obtained PVA (alkenyl-modified PVA, alkyl-modified PVA and unmodified PVA) was evaluated according to the following method.

[Modification rate]
The content of the monomer unit (a) represented by the formula (I) in PVA (hereinafter also referred to as “alkenyl modification rate”) was determined according to the method using proton NMR described above.

[Degree of polymerization]
The degree of polymerization of PVA was determined by the method described in JIS-K6726.

[Saponification degree]
The degree of saponification of PVA was determined by the method described in JIS-K6726.

<Manufacture of PVA>
Example 1 (Production of PVA1)
Into a 3 L reactor equipped with a stirrer, reflux condenser, nitrogen inlet, comonomer addition port and initiator addition port, 750 g of vinyl acetate, 250 g of methanol and N-octadecenyl methacrylamide (N-oleyl methacrylamide) ) 1.1 g was charged and the system was purged with nitrogen for 30 minutes while bubbling nitrogen. Further, a comonomer solution in which N-octadecenyl methacrylamide was dissolved in methanol to a concentration of 5% was prepared as a delay solution, and this comonomer solution was purged with nitrogen by bubbling nitrogen gas. The temperature of the reactor was increased, and when the internal temperature reached 60 ° C., 0.25 g of 2,2′-azobisisobutyronitrile (AIBN) was added to initiate polymerization. The delay solution was added dropwise to the reactor so that the monomer composition in the polymerization solution was constant, and polymerization was performed at 60 ° C. for 3 hours, followed by cooling to stop the polymerization. The total amount of comonomer added until the polymerization was stopped was 4.8 g. The solid content concentration when the polymerization was stopped was 29.9%. Subsequently, unreacted vinyl acetate monomer was removed while occasionally adding methanol under reduced pressure at 30 ° C. to obtain a methanol solution (concentration 35%) of an alkenyl-modified vinyl acetate polymer (alkenyl-modified PVAc). Furthermore, 777.9 g of methanol solution of alkenyl-modified PVAc prepared by adding methanol to this (200.0 g of alkenyl-modified PVAc in the solution) was added 27.9 g of alkaline solution (10% methanol solution of sodium hydroxide). Saponification was performed by adding. Here, the concentration of alkenyl-modified PVAc in the saponification solution was 25%, and the molar ratio of sodium hydroxide to vinyl acetate units in the alkenyl-modified PVAc was 0.03. A gel was formed about 1 minute after the addition of the alkaline solution. The gel-like material was pulverized with a pulverizer and allowed to stand at 40 ° C. for 1 hour to allow saponification to proceed. Then, 500 g of methyl acetate was added to neutralize the remaining alkali. After confirming the completion of neutralization using a phenolphthalein indicator, the mixture was filtered to obtain a white solid. To this white solid, 2,000 g of methanol was added, and the mixture was left to wash at room temperature for 3 hours. This washing operation was repeated three times, and then the white solid obtained by centrifugal drainage was left in a dryer at 65 ° C. for 2 days to obtain alkenyl-modified PVA (PVA1).

Examples 2 to 13 and Comparative Examples 1 to 3 and 6 (Production of PVA 2 to 13 and PVAi to iii and vi)
Charge amount of vinyl acetate and methanol, polymerization conditions such as type and amount of unsaturated monomer having alkenyl group used during polymerization, concentration of alkenyl-modified PVAc during saponification, molar ratio of sodium hydroxide to vinyl acetate unit Various alkenyl-modified PVA (PVA2 to 13 and PVAi to iii) and alkyl-modified PVA (PVAvi) were produced in the same manner as in Example 1 except that the saponification conditions were changed as shown in Table 1.

Comparative Example 4 (Production of PVAvi)
A 3 L reactor equipped with a stirrer, a reflux condenser, a nitrogen inlet and an initiator addition port was charged with 750 g of vinyl acetate, 250 g of methanol and 57.3 g of oleyl vinyl ether, and the inside of the system was maintained for 30 minutes while bubbling nitrogen. Replaced with nitrogen. The temperature of the reactor was increased, and when the internal temperature reached 60 ° C., 1.0 g of 2,2′-azobisisobutyronitrile (AIBN) was added to initiate polymerization. After polymerization at 60 ° C. for 2 hours, the polymerization was stopped by cooling. The solid content concentration when the polymerization was stopped was 30.4%. Subsequently, unreacted vinyl acetate monomer was removed while occasionally adding methanol under reduced pressure at 30 ° C. to obtain a methanol solution (concentration 35%) of an alkenyl-modified vinyl acetate copolymer (alkenyl-modified PVAc). Furthermore, 7.0 g of an alkali solution (10% methanol solution of sodium hydroxide) was added to 792.9 g of methanol solution of alkenyl-modified PVAc prepared by adding methanol thereto (200.0 g of alkenyl-modified PVAc in the solution). Saponification was performed by adding. Here, the concentration of the alkenyl-modified PVAc in the saponification solution was 25%, and the molar ratio of sodium hydroxide to the vinyl acetate unit in the alkenyl-modified PVAc was 0.0075. A gel-like material was formed about 12 minutes after the addition of the alkaline solution. The gel-like material was pulverized with a pulverizer and allowed to stand at 40 ° C. for 1 hour to allow saponification to proceed. Then, 500 g of methyl acetate was added to neutralize the remaining alkali. After confirming the completion of neutralization using a phenolphthalein indicator, the mixture was filtered to obtain a white solid. To this white solid, 2,000 g of methanol was added, and the mixture was left to wash at room temperature for 3 hours. This washing operation was repeated three times, and then the white solid obtained by centrifugal deliquoring was left in a dryer at 65 ° C. for 2 days to obtain modified PVA (PVAvi).

Comparative Example 5 (Production of PVAv)
900 g of vinyl acetate and 100 g of methanol were charged into a 3 L reactor equipped with a stirrer, reflux condenser, nitrogen inlet tube and initiator addition port, and the system was purged with nitrogen for 30 minutes while bubbling nitrogen. The temperature of the reactor was increased, and when the internal temperature reached 60 ° C., 0.25 g of 2,2′-azobisisobutyronitrile (AIBN) was added to start polymerization, and polymerization was performed at 60 ° C. for 3 hours. Then, the polymerization was stopped by cooling. The solid content concentration when the polymerization was stopped was 31.0%. Subsequently, unreacted vinyl acetate monomer was removed while sometimes adding methanol under reduced pressure at 30 ° C. to obtain a methanol solution (concentration 30%) of polyvinyl acetate (PVAc). Furthermore, 27.9 g of an alkaline solution (sodium hydroxide in 10% methanol) was added to 971.1 g of PVAc methanol solution prepared by adding methanol to this solution (200.0 g of PVAc in the solution) to saponify. Went. Here, the concentration of PVAc in the saponification solution was 20%, and the molar ratio of sodium hydroxide to vinyl acetate units in PVAc was 0.03. A gel was formed about 1 minute after the addition of the alkaline solution. The gel-like material was pulverized with a pulverizer and allowed to stand at 40 ° C. for 1 hour to allow saponification to proceed. Then, 500 g of methyl acetate was added to neutralize the remaining alkali. After confirming the completion of neutralization using a phenolphthalein indicator, the mixture was filtered to obtain a white solid. To this white solid, 2,000 g of methanol was added, and the mixture was left to wash at room temperature for 3 hours. This washing operation was repeated three times, and then the white solid obtained by centrifugal drainage was left in a dryer at 65 ° C. for 2 days to obtain unmodified PVA (PVAv).

  The degree of polymerization, modification rate, and saponification degree of each PVA obtained were evaluated by the above methods. The evaluation results are shown in Table 1.

<Evaluation>
About the obtained alkenyl modified PVA etc., water solubility was evaluated according to the following method. In addition, alkenyl-modified PVA was used as a thickener to evaluate thickening. The evaluation results are shown in Table 1.

[Water soluble]
A 300 mL separable flask equipped with a stirrer was charged with 1.5 g of PVA together with 98.5 g of water, heated to 90 ° C. while stirring, and the state of dissolution of PVA was visually observed. The time from the start of temperature increase until complete dissolution was measured and judged according to the following criteria. In addition, when the following evaluation is A or B, it can be said that it is excellent in practicality.
A: Less than 1 hour B: 1 hour or more and less than 3 hours C: 3 hours or more D: Undissolved and remained undissolved.

[Thickening (viscosity of PVA aqueous solution)]
A PVA aqueous solution with a concentration of 1.5% is prepared in the same manner as in the above [Water-soluble] evaluation, and the viscosity (mPa · s) at a rotor temperature of 6 rpm and a temperature of 20 ° C. is measured using a B-type viscometer. did.

[Thickening (thickening test of ethylene-vinyl acetate copolymer emulsion)]
To 100 parts of an ethylene-vinyl acetate copolymer emulsion (Kuraray OM-4200NT, total solid content 55.0%), 5.5 parts of a 10% concentration PVA solution (solvent: water / butyl carbitol = 80/20) Was added to prepare a liquid mixture of PVA and emulsion, and the viscosity at 20 ° C. was measured at a rotor rotation speed of 6 rpm using a BM type viscometer, and judged according to the following criteria.
A: 20,000 mPa · s or more B: 5,000 mPa · s or more and less than 20,000 mPa · s C: 1,000 mPa · s or more and less than 5,000 mPa · s D: 500 mPa · s or more and less than 1,000 mPa · s E: <500 mPa · s

  In Table 1, (* 1) indicates that PVA was not completely dissolved and was not preferable as a thickener.

  As shown in Table 1, the alkenyl-modified PVA of the present invention is excellent in water solubility and can exhibit sufficient thickening. In Examples 5, 8 and 9, the thickening is reduced, which is caused by the low degree of polymerization of the alkenyl-modified PVA, the low degree of saponification, and the low modification rate. it is conceivable that.

  On the other hand, when PVA does not satisfy the prescribed requirements, that is, when the degree of saponification is low (Comparative Example 1), when the modification rate is high (Comparative Example 2), or when the carbon number of the alkenyl group exceeds 29 (Comparative Example 3). ) Has low water solubility, and when it does not contain the monomer unit represented by the formula (I) (Comparative Example 4), unmodified PVA (Comparative Example 5) or alkyl-modified PVA having an alkyl group ( In the case of Comparative Example 6), it was shown that both water solubility and thickening could not be achieved.

As described above, the alkenyl-modified PVA of the present invention is excellent in water solubility while exhibiting sufficient thickening. Therefore, the alkenyl-modified PVA can be suitably used for thickeners, paper coating agents, adhesives, films and the like. Further, the thickener of the present invention can exhibit an excellent thickening function even when used in a small amount.

Claims (4)

It contains a monomer unit represented by the following formula (I), has a viscosity average degree of polymerization of 100 to 5,000, a saponification degree of 60 mol% to 99.9 mol%, An alkenyl-modified vinyl alcohol polymer having a rate of 0.05 mol% or more and 5 mol% or less.

(In Formula (I), R ¹ is a linear or branched alkenyl group having 8 to 29 carbon atoms. R ² is a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.) The alkenyl-modified vinyl alcohol polymer according to claim ¹ , wherein the carbon number of the alkenyl group of R ¹ in the formula (I) is 15 or more and 26 or less. The alkenyl-modified vinyl according to claim 1 or 2 , which is obtained by saponifying a copolymer of an unsaturated monomer represented by the following formula (II) and a vinyl ester monomer. Alcohol polymer.

(In formula (II), the definitions of R ¹ and R ² are the same as in formula (I) above.) A thickener comprising the alkenyl-modified vinyl alcohol polymer according to any one of claims 1 to 3 .