JP2015196700A - Stabilizer for suspension polymerization - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stabilizer for suspension polymerization, which provides excellent polymerization stability during suspension polymerization, can provide a vinyl polymer having high bulk specific gravity, and can decrease a residual amount of PVA in waste water after polymerization.SOLUTION: Provided is a stabilizer for suspension polymerization, comprising a vinyl alcohol-based polymer (A). A ratio of a weight average molecular weight (Mw(A)) to a number average molecular weight (Mn(A)) of the vinyl alcohol-based polymer (A), (Mw(A)/Mn(A)), is 3 or more and 8 or less. A ratio of a weight average molecular weight (Mw(B)) and a number average molecular weight (Mn(B)) of the vinyl alcohol-based polymer (B), (Mw(B)/Mn(B)), is 2 or more and less than 3, the vinyl alcohol-based polymer (B) being obtained by treating the vinyl alcohol-based polymer (A) in a sodium hydroxide solution at 40°C for 1 hour.

Description

  The present invention relates to a stabilizer for suspension polymerization.

  As a method for producing a vinyl polymer such as vinyl chloride used for various applications such as molding materials, adhesives, and paints, a suspension polymerization method in which temperature adjustment and polymer isolation are easy is often used. . In this suspension polymerization method, a stabilizer such as a vinyl alcohol polymer (hereinafter sometimes abbreviated as “PVA”) having a hydrophobic group and a hydrophilic group and having an excellent surface activity is generally used. Added. In addition, the particulate vinyl polymer obtained by this suspension polymerization has a high bulk specific gravity from the viewpoints of space saving during storage, improvement in transport efficiency, and improvement in throughput during extrusion molding. It has been demanded.

  In response to such a request, a technique using a combination of one or more PVA and hydroxypropylmethylcellulose as a stabilizer for suspension polymerization (see Patent Document 1 and Patent Document 2), having an unsaturated double bond Techniques using modified PVA (see Patent Document 3 and Patent Document 4) have been developed.

  However, conventional stabilizers for suspension polymerization have insufficient polymerization stability during suspension polymerization, so that coarse vinyl polymer particles are formed, and the distribution of the particle size distribution of the vinyl polymer particles varies. There is a disadvantage that occurs. Further, the bulk specific gravity of the vinyl polymer is not sufficiently controlled. Furthermore, there is a disadvantage that a lot of PVA remains in the waste water after suspension polymerization of the vinyl polymer, and the cost of waste water treatment increases.

JP 2003-238606 A JP 2005-281680 A JP 2007-63369 A JP 2009-108218 A

  The present invention has been made based on the circumstances as described above, can provide a vinyl polymer having excellent polymerization stability during suspension polymerization, a high bulk specific gravity, and in waste water after polymerization. An object of the present invention is to provide a stabilizer for suspension polymerization that can reduce the residual amount of PVA.

  The invention made to solve the above-mentioned problems is a stabilizer for suspension polymerization containing a vinyl alcohol polymer (A), wherein the vinyl alcohol polymer (A) has a number average molecular weight (Mn (A )) Is a weight average molecular weight (Mw (A)) ratio (Mw (A) / Mn (A)) of 3 to 8, and the vinyl alcohol polymer (A) is 40 in a sodium hydroxide solution. Ratio (Mw (B) / Mn (B)) of weight average molecular weight (Mw (B)) to number average molecular weight (Mn (B)) of vinyl alcohol polymer (B) obtained by treatment at 1 ° C. for 1 hour Is a stabilizer for suspension polymerization having 2 or more and less than 3.

  The suspension polymerization stabilizer contains the above-mentioned ratio (Mw (A) / Mn (A)) of the vinyl alcohol polymer (A) contained therein and the vinyl alcohol polymer (A) under specific conditions. By making the ratio (Mw (B) / Mn (B)) of the vinyl alcohol polymer (B) obtained by alkali treatment within the above range, the polymerization stability during suspension polymerization is excellent, and the bulk specific gravity is high. A high vinyl polymer can be obtained, and the residual amount of vinyl alcohol polymer in the waste water after polymerization can be reduced.

  The vinyl alcohol polymer (A) is obtained by polymerizing a vinyl ester monomer in the presence of the monomer (a), followed by saponification and heat treatment, and the monomer (a ) Is a carboxylic acid having an unsaturated double bond, an alkyl ester of a carboxylic acid having an unsaturated double bond, an acid anhydride of a carboxylic acid having an unsaturated double bond, a carboxylic acid having an unsaturated double bond. It may be at least one selected from the group consisting of a salt and a silyl compound having an unsaturated double bond. The vinyl alcohol polymer (A) is obtained by using a vinyl ester polymer obtained by polymerizing a vinyl ester monomer in the presence of the monomer (a). The vinyl alcohol polymer (A) has a hydrophilic carboxyl group or silyl group derived from the monomer (a). Thereby, the hydrophilic property of the stabilizer for suspension polymerization containing the vinyl alcohol polymer (A) is improved, and a vinyl polymer having excellent bulk stability and high bulk specific gravity can be obtained. In addition, since the carboxyl group or silyl group and the hydroxyl group can be ester-bonded by heat treatment to form a branched structure as a whole, the vinyl polymer obtained by using the suspension polymerization stabilizer can be used. It is considered that the specific gravity is improved and the residual amount of the vinyl alcohol polymer in the waste water after polymerization is reduced.

  The suspension polymerization stabilizer may further contain water. By containing water in this way, the vinyl alcohol polymer (A) is dispersed or dissolved in water, and as a result, the stabilizer for suspension polymerization performs polymerization of the vinyl monomer more easily and reliably. be able to.

  As described above, according to the stabilizer for suspension polymerization of the present invention, a vinyl polymer having excellent polymerization stability during suspension polymerization and a high bulk specific gravity can be obtained. Moreover, the residual amount of the vinyl alcohol polymer in the waste water after polymerization can be reduced. Therefore, according to the stabilizer for suspension polymerization, a high-quality vinyl polymer can be obtained at low cost.

<Stabilizer for suspension polymerization>
The suspension polymerization stabilizer is a vinyl alcohol polymer (A) containing a vinyl alcohol unit (—CH ₂ —CHOH—) (hereinafter, the vinyl alcohol polymer may be abbreviated as “PVA”). Containing. Moreover, it is preferable to contain water further and you may contain other components, such as PVA other than PVA (A), in the range which does not prevent the effect of this invention. By using the stabilizer for suspension polymerization, a vinyl polymer can be obtained from the vinyl monomer.

[PVA (A)]
PVA (A) has a ratio of weight average molecular weight (Mw (A)) to number average molecular weight (Mn (A)) (Mw (A) / Mn (A)) of 3 or more and 8 or less. The lower limit of the ratio is preferably 3.2, more preferably 3.4, further preferably 3.6, and the upper limit of the ratio is preferably 6 and more preferably 5.

  PVA (B) is obtained by treating the PVA (A) in a sodium hydroxide solution at 40 ° C. for 1 hour. As this treatment, the method of complete saponification described in the column of average degree of polymerization in JIS-K6726 can be employed, and specifically, it can be obtained as follows. That is, about 10 g of PVA (A) is weighed into a common Erlenmeyer flask, 200 mL of methanol is added, and then 12.5 mol / L sodium hydroxide solution is added when the saponification degree of PVA (A) is 97 mol% or more. If the saponification degree of PVA (A) is less than 97 mol%, add 10 mL, stir and heat in a water bath at 40 ° C. for 1 hour, then add phenolphthalein as an indicator and observe an alkaline reaction. It can be obtained by washing with methanol until it disappears, removing sodium hydroxide, and finally transferring to a watch glass and drying at 105 ° C. for 1 hour until methanol is exhausted.

  The PVA (B) has a ratio of the weight average molecular weight (Mw (B)) to the number average molecular weight (Mn (B)) (Mw (B) / Mn (B)) of 2 or more and less than 3. The lower limit of the ratio is preferably 2.1, more preferably 2.2, and the upper limit of the ratio is preferably 2.9 and more preferably 2.8.

  In the PVA (A) contained in the stabilizer for suspension polymerization of the present invention, (Mw (A) / Mn (A)) and (Mw (B) / Mn (B)) are in the above range, In PVA (A), it is considered that PVA chains are bonded to each other to form a branched structure. And it is thought by this branched structure that the stabilizer for suspension polymerization containing PVA (A) becomes the thing excellent in the polymerization stability at the time of suspension polymerization.

The number average molecular weight (Mn) and the weight average molecular weight (Mw) in the above PVA (A) and PVA (B) are determined by gel permeation chromatography using hexafluoroisopropanol as a mobile phase and a differential refractive index detector. It can obtain | require as a polymethylmethacrylate conversion value by a graphic (GPC) measurement, As a more concrete method, the following can be employ | adopted.
GPC column: 2 “GHH _HR (S)” manufactured by Tosoh Corporation Mobile phase: hexafluoroisopropanol Flow rate: 0.2 mL / min Sample concentration: 0.100 wt / vol%
Sample injection volume: 10 μL
Detector: Differential refractive index detector Standard material: Polymethacrylic acid (for example, “EasiVial PMMA 4 mL tri-pack” manufactured by Agilent Technologies)

  It is preferable to add a salt such as sodium trifluoroacetate to hexafluoroisopropanol used as the mobile phase in order to suppress the adsorption of the sample to the GPC column filler. The concentration of the salt is usually 1 mmol / L to 100 mmol / L, preferably 5 mmol / L to 50 mmol / L.

  The ratio of the weight average molecular weight (Mw) of the PVA (A) to the weight average molecular weight (Mw) of the PVA (B) (Mw (A) / Mw (B)) is not particularly limited. Is preferable, and 1.5 is more preferable. On the other hand, the upper limit of the ratio (Mw (A) / Mw (B)) is preferably 3.0, and more preferably 2.5. When the ratio (Mw (A) / Mw (B)) is not less than the above lower limit, the polymerization stability during suspension polymerization of the suspension polymerization stabilizer is further improved. On the other hand, when the ratio (Mw (A) / Mw (B)) is not more than the above upper limit, the bulk specific gravity of the obtained vinyl polymer is further improved, and the residual amount of PVA in the polymerization wastewater is further reduced.

  As PVA (A), what is obtained by saponifying a vinyl ester polymer can be used. Although PVA (A) may consist only of a vinyl alcohol unit, it is preferable that the unit derived from a monomer (a) is further included.

  The vinyl ester monomer used for the production of the vinyl ester polymer is not particularly limited. For example, vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, versatic acid Examples thereof include vinyl, vinyl caproate, vinyl caprylate, vinyl laurate, vinyl palmitate, vinyl stearate, vinyl oleate, and vinyl benzoate. Among these, vinyl acetate is preferable from the economical viewpoint.

  The monomer (a) includes a carboxylic acid having an unsaturated double bond, an alkyl ester of the carboxylic acid, an acid anhydride of the carboxylic acid, a salt of the carboxylic acid, and a silyl compound having an unsaturated double bond. At least one monomer selected from the group consisting of:

  Examples of the carboxylic acid having an unsaturated double bond, an alkyl ester of the carboxylic acid, an acid anhydride of the carboxylic acid, and a salt of the carboxylic acid include maleic acid, maleic acid monomethyl ester, maleic acid dimethyl ester, Maleic acid monoethyl ester, maleic acid diethyl ester, maleic anhydride, citraconic acid, citraconic acid monomethyl ester, citraconic acid dimethyl ester, citraconic acid diethyl ester, citraconic anhydride, fumaric acid, fumaric acid monomethyl ester, fumaric acid dimethyl ester, Fumaric acid monoethyl ester, fumaric acid diethyl ester, itaconic acid, itaconic acid monomethyl ester, itaconic acid dimethyl ester, itaconic acid monoethyl ester, itaconic acid diethyl ester, itaconic anhydride Acrylate, methyl acrylate, ethyl acrylate, methacrylic acid, methyl methacrylate, and ethyl methacrylate.

  Examples of the silyl compound having an unsaturated double bond include compounds having an unsaturated double bond and a trialkoxysilyl group such as trialkoxysilane such as vinyltrimethoxysilane and vinyltriethoxysilane. .

  Among these monomers (a), maleic acid monomethyl ester, citraconic acid monomethyl ester, itaconic acid monomethyl ester, methyl acrylate, methyl methacrylate, vinyltrimethoxysilane are preferred, maleic acid monomethyl ester, methyl acrylate, More preferred are methyl methacrylate and vinyltrimethoxysilane.

  As a minimum of the content rate of the unit derived from the monomer (a) in PVA (A), 0.02 mol% is preferable based on the number-of-moles of all the monomer units which comprise PVA (A), 0 0.05 mol% is more preferable, and 0.1 mol% is more preferable. On the other hand, the upper limit of the content of units derived from the monomer (a) in PVA (A) is preferably 5 mol% based on the number of moles of all monomer units constituting PVA (A), 2 mol% is more preferable and 1 mol% is further more preferable. By making this content rate more than the said minimum, the polymerization stability at the time of suspension polymerization of the said stabilizer for suspension polymerization improves more. On the other hand, when the content is less than or equal to the above upper limit, the bulk specific gravity of the obtained vinyl polymer is further improved, and the residual amount of PVA in the polymerization waste water is further reduced.

Content of units derived from monomer (a) can be determined from the ^{1 H-NMR} of the vinyl ester polymer which is a precursor of PVA (A). For example, when monomethyl maleate is used as the monomer (a), the content is determined by the following procedure. That is, after reprecipitation and purification of the 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. This sample is dissolved in CDCl ₃ and measured at room temperature using ¹ H-NMR of 500 MHz (“GX-500” manufactured by JEOL Ltd.). In the vinyl ester polymer, a peak derived from the methine structure of a vinyl ester unit (4.7 to 5.2 ppm) and a peak derived from a methyl group of a methyl ester portion of a unit derived from the monomer (a) From β (3.6 to 3.8 ppm), the content S of the unit derived from the monomer (a) can be calculated using the following formula.
S (mol%) = {(number of protons of β / 3) / (number of protons of α + (number of protons of β / 3))} × 100

  Moreover, PVA (A) may contain the unit derived from other monomers other than the unit derived from a vinyl alcohol unit and a monomer (a) in the range which does not impair the meaning of this invention. Examples of the unit derived from the other monomer include α-olefins such as ethylene, propylene, n-butene, and isobutylene; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, and n-butyl vinyl ether. Vinyl ethers such as i-butyl vinyl ether, t-butyl vinyl ether and 2,3-diacetoxy-1-vinyloxypropane; vinyl cyanides 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 and allyl chloride; vinylsilyl compounds such as vinyltrimethoxysilane; It includes units derived from such a propenyl. The content rate of the unit derived from the said other monomer in PVA (A) can be 15 mol% or less based on the number-of-moles of all the monomer units which comprise PVA (A), for example. .

  There is no particular limitation on the order of arrangement of the vinyl alcohol unit, the unit derived from the monomer (a) and the unit derived from the other monomer in PVA (A), which may be random, block, or alternating. Good.

The primary structure of PVA (A) can be quantified by ¹ H-NMR. CDCl ₃ may be used as a solvent for ¹ H-NMR measurement.

  The degree of saponification of PVA (A) (the molar fraction of hydroxyl groups relative to the total of hydroxyl groups and ester bonds in PVA (A)) is measured according to JIS-K6726. As a minimum of saponification degree, 20 mol% is preferable, 60 mol% is more preferable, 70 mol% is further more preferable, 80 mol% is especially preferable, and 87 mol% is the most preferable. When the degree of saponification of PVA (A) is not less than the above lower limit, the polymerization stability at the time of suspension polymerization of the stabilizer for suspension polymerization and the bulk specific gravity of the resulting vinyl polymer are further improved. The residual amount of PVA is further reduced.

  As an upper limit of the viscosity average polymerization degree of PVA (A), 5,000 is preferable and 4,000 is more preferable. On the other hand, as a minimum of the viscosity average degree of polymerization of PVA (A), 100 is preferred, 500 is more preferred, and 1,000 is still more preferred. When the viscosity average polymerization degree of PVA (A) is not less than the above lower limit, the polymerization stability during suspension polymerization of the suspension polymerization stabilizer is further improved. On the other hand, when the viscosity average polymerization degree of PVA (A) is not more than the above upper limit, the productivity of PVA (A) is improved. Therefore, PVA (A) can be manufactured at a lower cost.

The viscosity average degree of polymerization (P) of PVA (A) is measured according to JIS-K6726. That is, after PVA (A) is completely saponified and purified, PVA (A) containing units derived from monomer (a) is about 30 ° C. in a sodium chloride aqueous solution (0.5 mol / L). Intrinsic viscosity [η] (unit: deciliter / g) was measured, and for PVA (A) not containing the unit derived from monomer (a), the intrinsic viscosity [η] (unit: deciliter) in an aqueous solution at 30 ° C. / G) is measured. From this intrinsic viscosity [η], the viscosity average degree of polymerization (P) of PVA (A) is obtained by the following formula.
P = ([η] × 10 ³ /8.29) ^{(1 / 0.62)}

  Moreover, since PVA (B) is obtained by treating PVA (A) in a sodium hydroxide solution at 40 ° C. for 1 hour, the viscosity average polymerization degree of PVA (B) is the viscosity of PVA (A). The average polymerization degree is substantially the same value.

  The suspension polymerization stabilizer preferably contains water in addition to PVA (A). Examples of other components that may be contained in the suspension polymerization stabilizer include additives such as PVA other than PVA (A), water-soluble cellulose ethers, water-soluble polymers, oil-soluble emulsifiers, and water-soluble emulsifiers. , Solvent and the like.

  The said stabilizer for suspension polymerization can be made into the dispersion liquid or solution of said PVA (A) by containing water. As a result, the suspension polymerization stabilizer can carry out suspension polymerization of vinyl monomers more easily and reliably. The upper limit of the content of PVA (A) when the suspension polymerization stabilizer is a dispersion or solution of PVA (A) is preferably 20% by mass, and more preferably 15% by mass. On the other hand, as a minimum of content of the said PVA (A), 0.1 mass% is preferable and 0.5 mass% is more preferable. If the content of PVA (A) exceeds the above upper limit, the dispersion or dissolution of PVA (A) may be insufficient. On the other hand, when the amount is less than the above lower limit, the suspension polymerization reaction may not sufficiently occur.

  PVA other than the above PVA (A) is a PVA having a saponification degree of 70 mol% or more and less than 98.5 mol% and a viscosity average polymerization degree of 500 to 3500, a saponification degree of 20 mol% or more and less than 60 mol%, and a viscosity average polymerization degree. PVA etc. which are 200-600 are mentioned.

  Examples of the water-soluble cellulose ether include methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methylcellulose and the like. Examples of the water-soluble polymer include gelatin.

  Examples of the oil-soluble emulsifier include sorbitan monolaurate, sorbitan trioleate, glycerin tristearate, ethylene oxide propylene oxide block copolymer, and the like. Examples of the water-soluble emulsifier include polyoxyethylene sorbitan monolaurate, polyoxyethylene glycerol oleate, and sodium laurate.

  Although there is no restriction | limiting in particular about the addition amount of these additives, 0.01 mass part or more and 1.0 mass part or less are preferable with respect to 100 mass parts of vinylic compounds.

  Examples of the solvent include lower 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 solvents may be used alone or in combination of two or more.

<Method for producing stabilizer for suspension polymerization>
The method for producing the suspension polymerization stabilizer is not particularly limited. For example, a step of polymerizing a monomer containing a vinyl ester monomer (hereinafter also referred to as “polymerization step”), A step of saponifying the obtained vinyl ester polymer (hereinafter also referred to as “saponification step”). In addition, it is preferable to further include a step of heating the vinyl ester polymer or the saponified PVA (hereinafter also referred to as “heating step”).

[Polymerization process]
In this step, a monomer containing a vinyl ester monomer is polymerized to synthesize a vinyl ester polymer. As described above, the monomer containing the vinyl ester monomer includes only the vinyl ester monomer, and as described above, the vinyl ester monomer, the monomer (a) and / or Or it may contain either the said other monomer.

  As a polymerization method of the monomer containing 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 employed. Among these, a bulk polymerization method or a solution polymerization method in which polymerization proceeds in a solvent-free or solvent such as alcohol is usually employed. In order to obtain a vinyl ester polymer having a high degree of polymerization, one of the options is to employ an emulsion polymerization method. The solvent for the solution polymerization method is not particularly limited, and examples thereof include alcohol. The alcohol used as the solvent for the solution polymerization method is, for example, a lower alcohol such as methanol, ethanol, or n-propanol. A solvent may be used individually by 1 type, or may use 2 or more types together. The amount of solvent used in the polymerization system may be selected in consideration of the chain transfer of the solvent according to the degree of polymerization of the target PVA (A). For example, when the solvent is methanol, it is included in the solvent and the polymerization system. What is necessary is just to select from the range of 0.01-10, preferably the range of 0.05-3 by mass ratio {= (solvent) / (total monomer)} with respect to all the monomers.

The polymerization initiator used for such polymerization may be appropriately selected from known polymerization initiators such as azo initiators, peroxide initiators, redox initiators and the like according to the polymerization method. Examples of the azo initiator include 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (4-methoxy-2, 4-dimethylvaleronitrile) and the like. Examples of the peroxide initiator include percarbonate compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate; t-butyl peroxyneodecanate, α -Perester compounds such as cumylperoxyneodecanate and t-butylperoxydecanate; acetyl peroxide; acetylcyclohexylsulfonyl peroxide; 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate . The initiator may be combined with potassium persulfate, ammonium persulfate, hydrogen peroxide, or the like. Examples of the redox initiator include a combination of the above peroxide initiator and a reducing agent such as sodium hydrogen sulfite, sodium hydrogen carbonate, tartaric acid, L-ascorbic acid, or longalite.
The amount of the polymerization initiator used varies depending on the polymerization catalyst and the like and cannot be determined unconditionally, but may be appropriately selected according to the polymerization rate. For example, when 2,2′-azobisisobutyronitrile or acetyl peroxide is used as the polymerization initiator, 0.01 to 0.2 mol% is preferable with respect to the vinyl ester monomer, and 0.02 to 0 More preferred is 15 mol%.

  As a minimum of temperature in a polymerization process, 0 ° C is preferred and 30 ° C is more preferred. As an upper limit of polymerization temperature, 200 degreeC is preferable and 140 degreeC is more preferable. When the polymerization temperature is equal to or higher than the above lower limit, the polymerization rate is improved. On the other hand, when the polymerization temperature is not more than the above upper limit, for example, even when the monomer (a) is used, the content of units derived from the monomer (a) in the PVA (A) is kept at an appropriate ratio. It becomes easy. As a method of controlling the polymerization temperature within the above range, for example, by controlling the polymerization rate, a method of balancing the heat generated by polymerization and the heat radiation from the surface of the reactor, or using an appropriate heat medium is used. A method of controlling with an external jacket is preferable, but the latter method is preferable from the viewpoint of safety.

  The polymerization may be carried out in the presence of a chain transfer agent as long as the gist of the present invention is not impaired. Examples of chain transfer agents include aldehydes such as acetaldehyde and propionaldehyde; ketones such as acetone and methyl ethyl ketone; mercaptans such as 2-hydroxyethanethiol; halogenated hydrocarbons such as trichloroethylene and perchloroethylene; sodium phosphinate Examples thereof include phosphinic acid salts such as monohydrate. Of these, aldehydes and ketones are preferred. The amount of chain transfer agent added to the polymerization system can be determined according to the chain transfer coefficient of the chain transfer agent to be added, the degree of polymerization of the target PVA (A), etc., and is generally a vinyl ester monomer. 0.1-10 mass parts is preferable with respect to 100 mass parts.

  In addition, when the said polymerization is performed under high temperature, coloring etc. of PVA (A) resulting from decomposition | disassembly of a vinyl ester-type monomer may be seen. In this case, an antioxidant such as tartaric acid may be added to the polymerization system for the purpose of preventing coloring from about 1 to 100 ppm with respect to the vinyl ester monomer.

[Saponification process]
In this step, the vinyl ester polymer is saponified. By saponifying this polymer, the vinyl ester unit in the polymer is converted into a vinyl alcohol unit.

  Although it does not restrict | limit especially as reaction used for the saponification of a vinyl ester polymer, The well-known alcohol decomposition reaction or hydrolysis reaction performed in the state which the said polymer melt | dissolved in the solvent is employable.

  Examples of the solvent used for saponification include lower 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 solvents may be used alone or in combination of two or more. Among these, methanol and a mixed solution of methanol and methyl acetate are preferable.

  Examples of the catalyst used for saponification include alkali catalysts such as alkali metal hydroxides (potassium hydroxide, sodium hydroxide, etc.), sodium alkoxides (sodium methoxide, etc.); acids such as p-toluenesulfonic acid and mineral acids. A catalyst etc. are mentioned. Among these, it is preferable to use sodium hydroxide because it is simple.

  Although it does not specifically limit as temperature which performs saponification, 20 to 60 degreeC is preferable. When a gel-like product precipitates as saponification progresses, it is preferable to pulverize the product and further promote saponification. Then, saponification is complete | finished by neutralizing the obtained solution, and it can wash | clean and dry and can obtain PVA. As a saponification method, not only the method mentioned above but a well-known method is employable.

[Heating process]
In this step, the vinyl ester polymer or the saponified PVA is heated. Specifically, the vinyl ester polymer is heated by heating simultaneously with the saponification step, or the PVA obtained after the saponification step is heated. PVA (A) in which a branched structure is formed by this heating can be easily obtained, and the polymerization stability during suspension polymerization of the stabilizer for suspension polymerization and the bulk specific gravity of the resulting vinyl polymer are further improved. In addition, the residual amount of PVA in the polymerization wastewater is further reduced. The heat treatment is preferably performed in an air or nitrogen atmosphere. Moreover, it is preferable that a heating process is performed with respect to PVA after saponification.

  As a minimum of heating temperature in a heating process, 70 ° C is preferred and 90 ° C is more preferred. As an upper limit of the said heating temperature, 150 degreeC is preferable and 130 degreeC is more preferable. The lower limit of the heating time in the heating step is preferably 30 minutes, more preferably 1 hour, and even more preferably 2 hours. The upper limit of the heating time is preferably 10 hours, more preferably 7 hours, and even more preferably 5 hours. By setting the heating temperature and the heating time within the above ranges, PVA (A) satisfying the provisions of the present invention can be easily obtained, and the polymerization stability during suspension polymerization of the stabilizer for suspension polymerization can be obtained. The bulk specific gravity of the vinyl polymer obtained is further improved, and the residual amount of PVA in the polymerization waste water is further reduced.

  The stabilizer for suspension polymerization can be produced by appropriately mixing the PVA (A) obtained by the above production method and optional components.

<Vinyl polymer>
The vinyl polymer can be obtained by suspension polymerization of a vinyl monomer. Further, monomers other than vinyl monomers may be further copolymerized. In this suspension polymerization, the stabilizer for suspension polymerization can be suitably used. Although the usage-amount of the said stabilizer for suspension polymerization is not specifically limited, 0.008 mass part or more and 0.025 mass part or less are preferable with respect to 100 mass parts of vinylic monomers.

  Examples of the vinyl monomer include vinyl halides such as vinyl chloride; vinyl esters such as vinyl acetate and vinyl propionate; acrylic acid, methacrylic acid, acrylic acid ester, methacrylic acid ester, acrylate, and methacrylate. Maleic acid, fumaric acid, maleic acid ester, fumaric acid ester, maleate, fumarate; styrene, acrylonitrile, vinylidene chloride, vinyl ether and the like.

  Examples of monomers other than vinyl monomers include vinyl esters such as vinyl acetate and vinyl propionate; (meth) acrylic esters such as methyl (meth) acrylate and ethyl (meth) acrylate; ethylene and propylene Α-olefins such as; unsaturated dicarboxylic acids such as maleic anhydride and itaconic acid; acrylonitrile, styrene, vinylidene chloride, vinyl ether and the like.

  Among these, it is preferable to use vinyl chloride, and it is more preferable to polymerize vinyl chloride alone.

  As the polymerization initiator used for the suspension polymerization, those conventionally used for polymerization of vinyl chloride monomers and the like can be used. Examples of the polymerization initiator include oil-soluble or water-soluble polymerization initiators. A polymerization initiator may be used independently and may use 2 or more types together.

  Examples of the oil-soluble polymerization initiator include percarbonate compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate; t-butyl peroxyneodecanate, t -Perester compounds such as butyl peroxypivalate, t-hexyl peroxypivalate, α-cumyl peroxyneodecanate; acetylcyclohexylsulfonyl peroxide, 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate Peroxides such as 3,5,5-trimethylhexanoyl peroxide and lauroyl peroxide; azo compounds such as azobis-2,4-dimethylvaleronitrile and azobis (4-2,4-dimethylvaleronitrile) It is below.

  Examples of the water-soluble polymerization initiator include potassium persulfate, ammonium persulfate, hydrogen peroxide, cumene hydroperoxide, and the like.

  The temperature during the suspension polymerization may be a low temperature of about 20 ° C. or a high temperature exceeding 90 ° C. In order to increase the heat removal efficiency of the polymerization reaction system, it is also one of preferred embodiments to use a polymerization vessel with a reflux condenser.

  In addition, during suspension polymerization, in addition to the stabilizer for suspension polymerization, other additives usually used in suspension polymerization may be added. Examples of the additive include the same additives as those exemplified as other additives that may be contained in the above-mentioned stabilizer for suspension polymerization. Although there is no restriction | limiting in particular about the addition amount of these additives, 0.01 mass part or more and 1.0 mass part or less are preferable with respect to 100 mass parts of vinylic compounds.

  Hereinafter, the present invention will be described in detail by way of examples and comparative examples. In the following examples and comparative examples, “parts” and “%” are based on mass unless otherwise specified.

  About the physical property value of PVA of the following Example and comparative example, it measured in accordance with the following method.

[Degree of polymerization]
In each Example or Comparative Example, the viscosity average degree of polymerization of PVA (A) was determined by the method described in JIS-K6726.

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

[Modification rate]
The modification rate of each PVA (the content of units derived from the monomer (a) in the PVA (A)) is determined by using the vinyl ester polymer that is the precursor of the PVA (A), and the above ¹ H- It calculated | required by the method using NMR.

[Preparation of PVA (B)]
About 10 g of PVA (A) was weighed into a common Erlenmeyer flask, 200 mL of methanol was added, 10 mL of 12.5 mol / L sodium hydroxide solution was added, and the mixture was stirred and heated in a 40 ° C. water bath for 1 hour. Next, phenolphthalein was added as an indicator, and sodium hydroxide was removed by washing with methanol until no alkaline reaction was observed. Finally, it was transferred to a watch glass and dried at 105 ° C. for 1 hour until methanol disappeared to prepare PVA (B).

[Number average molecular weight (Mn) and weight average molecular weight (M in PVA (A) and PVA (B)
w)]
It calculated | required as a polymethylmethacrylate conversion value by the gel permeation chromatography (GPC) measurement using the differential refractive index detector, using hexafluoro isopropanol for a mobile phase. Specifically, the following conditions were adopted.
GPC column: Tosoh "GMHHR (S)" 2 mobile phase: hexafluoroisopropanol (20mmo sodium trifluoroacetate)
(contained at a concentration of 1 / L)
Flow rate: 0.2 mL / min Sample concentration: 0.100 wt / vol%
Sample injection volume: 10 μL
Detector: Differential refractive index detector Standard material: Polymethacrylic acid (for example, “EasiVial PMMA 4 mL tri-pack” manufactured by Agilent Technologies)

[Synthesis Example 1] (Production of PVA-1)
A reactor equipped with a stirrer, reflux condenser, nitrogen inlet, comonomer dropping port and polymerization initiator addition port was charged with 740 parts of vinyl acetate and 260 parts of methanol, and nitrogen was bubbled through the system for 30 minutes. Replaced. Further, monomethyl maleate was selected as monomer (a), and a methanol solution of monomethyl maleate (concentration 20%) was replaced with nitrogen by bubbling nitrogen gas. The temperature of the reactor was increased, and when the internal temperature reached 60 ° C., 0.25 part of 2,2′-azobisisobutyronitrile (AIBN) was added to initiate polymerization. The methanol solution of monomethyl maleate was dropped into the reactor to polymerize at 60 ° C. for 3 hours while keeping the monomer composition ratio in the polymerization solution constant, and then cooled to stop the polymerization. The total amount of monomer (a) added until the termination of polymerization was 0.9 part, and the solid content concentration at the termination of polymerization was 33.3%. Subsequently, unreacted monomers were removed while sometimes adding methanol under reduced pressure at 30 ° C. to obtain a methanol solution (concentration 35%) of a vinyl ester polymer. Next, 790.8 parts of a methanol solution of a vinyl ester polymer prepared by adding methanol to this methanol solution (200.0 parts of the polymer in the solution) was added to a 10% methanol solution of sodium hydroxide 9. Two parts were added and saponification was carried out at 40 ° C. (25% of the polymer concentration in the saponification solution, 0.01 molar ratio of sodium hydroxide to vinyl acetate units in the polymer). After adding a sodium hydroxide methanol solution, a gel was formed in about 15 minutes. This was pulverized with a pulverizer and further allowed to stand at 40 ° C. for 1 hour to proceed with saponification, and then 500 parts 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 parts of methanol was added, and the mixture was left to wash at room temperature for 3 hours. After repeating this washing | cleaning operation 3 times, the white solid obtained by carrying out centrifugation liquid removal was heat-processed at 120 degreeC with the dryer for 4.5 hours, and PVA (A) (PVA-1) was obtained. Table 2 shows the physical properties of PVA-1.

[Synthesis Examples 2 to 17] (Production of PVA-2 to PVA-17)
Polymerization conditions such as the amount of vinyl acetate and methanol charged, the type and amount of monomer (a) used during polymerization, the concentration of vinyl ester polymer during saponification, the molar ratio of sodium hydroxide to vinyl acetate units, etc. Various PVA (A) were produced by the same method as in Synthesis Example 1 except that the saponification conditions; and the heat treatment conditions were changed as shown in Table 1. Table 2 shows the physical properties of each PVA (A) and PVA (B) obtained therefrom. In Synthesis Example 13, after producing two types of PVA (A), PVA-13a and PVA-13b, two types of PVA are used so that 45 parts of PVA-13a and 55 parts of PVA-13b are included. (A) was mixed.

[Example 1]
(Preparation of stabilizer for suspension polymerization)
0.164 parts by mass of PVA-1 and 0.564 parts by mass of PVA-L-10 (Kuraray Co., Ltd., saponification degree: 72.5 mol%, viscosity of 4% aqueous solution is 6 mPa · s) to 60 parts by mass of deionized water It was dissolved to prepare a stabilizer for suspension polymerization.

(Production of vinyl chloride polymer)
A 5 L autoclave was charged with the above suspension polymerization stabilizer, 0.65 part of 70% toluene solution of cumylperoxyneodecanoate and 1.05 part of 70% toluene solution of t-butylperoxyneodecanoate, and the autoclave. After deaeration until the internal pressure reached 0.0067 MPa to remove oxygen, 940 parts of vinyl chloride monomer was added. The content of PVA-1 with respect to the vinyl chloride monomer was 200 ppm, and the content of PVA-L-10 with respect to the vinyl chloride monomer was 600 ppm. Next, the temperature of the autoclave was raised to 57 ° C., and polymerization of the vinyl chloride monomer was started with stirring. The pressure in the autoclave at the start of polymerization was 0.80 MPa. After 3.5 hours from the start of polymerization, when the pressure in the autoclave reached 0.70 MPa, the polymerization was stopped, the unreacted vinyl chloride monomer was removed, and the polymerization reaction product was taken out. This polymerization reaction product was dried at 65 ° C. for 16 hours to obtain a vinyl chloride polymer.

[Examples 2 to 10 and Comparative Examples 1 to 9]
A vinyl chloride polymer was produced in the same manner as in Example 1 except that the type and amount of PVA (A) used were changed as shown in Table 3. In Comparative Examples 2 and 4, PVA-10 and PVA-12 were not completely dissolved in deionized water, and a vinyl chloride polymer could not be obtained.

<Evaluation>
About the polyvinyl chloride polymer of an Example and a comparative example, the grade of particle size distribution, bulk specific gravity, and the amount of residual PVA in superposition | polymerization waste water was evaluated in accordance with the following method. The evaluation results are shown in Table 3.

[Particle size distribution]
The particle size distribution was evaluated on the basis of the following criteria by applying a vinyl chloride polymer to a sieve having a nominal opening width of 250 μm of JIS-Z8801-1, and determining the ratio of what remained on the sieve. In addition, the smaller the amount of the residue on the sieve, the smaller the coarse particles and the sharper the particle size distribution, which indicates that the polymerization stability during suspension polymerization is excellent.
A: Less than 5% by mass B: 5% by mass or more and less than 10% by mass C: 10% by mass or more

[Bulk specific gravity]
The bulk specific gravity was measured according to JIS-K6720-2, and judged according to the following criteria.
A: 0.54 g / mL or more B: 0.48 g / mL or more and less than 0.54 g / mL C: Less than 0.48 g / mL

[Remaining PVA in polymerization waste water]
Residual PVA in the polymerization waste water was judged by the following criteria based on the degree of foaming by observing the polymerization waste water after taking out the polymerization reaction product with the naked eye. In addition, it shows that there are few residual PVA in polymerization waste water, so that the degree of foaming is small.
A: Not foamed.
B: Slightly foamed.
C: Foamed.

  As shown in Table 3, according to the stabilizers for suspension polymerization of Examples 1 to 10, vinyl chloride polymers having excellent polymerization stability during suspension polymerization and high bulk specific gravity were obtained. Furthermore, the amount of residual PVA in the polymerization waste water was also reduced. In particular, with the suspension polymerization stabilizers of Examples 9 and 10, a high effect could be obtained with a small amount of use, and the production cost of the vinyl chloride polymer could be further reduced.

  On the other hand, with the stabilizer for suspension polymerization of Comparative Examples 1 to 9, all of the polymerization stability, bulk specific gravity and residual PVA at the time of suspension polymerization could not be sufficiently satisfied. In particular, PVA in Comparative Examples 2 and 4 could not be used as a stabilizer for suspension polymerization.

According to the stabilizer for suspension polymerization of the present invention, a vinyl polymer having excellent polymerization stability during suspension polymerization and a high bulk specific gravity can be obtained. Moreover, the residual amount of the vinyl alcohol polymer in the waste water after polymerization can be reduced. Therefore, according to the stabilizer for suspension polymerization, a high-quality vinyl polymer can be obtained at low cost.

Claims (3)

A stabilizer for suspension polymerization containing a vinyl alcohol polymer (A),
The ratio (Mw (A) / Mn (A)) of the weight average molecular weight (Mw (A)) to the number average molecular weight (Mn (A)) of the vinyl alcohol polymer (A) is 3 or more and 8 or less,
Weight average molecular weight (Mw) relative to the number average molecular weight (Mn (B)) of the vinyl alcohol polymer (B) obtained by treating the vinyl alcohol polymer (A) in a sodium hydroxide solution at 40 ° C. for 1 hour. (B)) is a suspension polymerization stabilizer having a ratio (Mw (B) / Mn (B)) of 2 or more and less than 3. The vinyl alcohol polymer (A) is obtained by polymerizing a vinyl ester monomer in the presence of the monomer (a), followed by saponification and heat treatment,
The monomer (a) is a carboxylic acid having an unsaturated double bond, an alkyl ester of a carboxylic acid having an unsaturated double bond, an acid anhydride of a carboxylic acid having an unsaturated double bond, or an unsaturated double bond. The stabilizer for suspension polymerization according to claim 1, which is at least one selected from the group consisting of a carboxylic acid salt having a bond and a silyl compound having an unsaturated double bond. The stabilizer for suspension polymerization according to claim 1 or 2, further comprising water.