JPH08208724A - Dispersant for suspension polymerization and production of polymer using the same - Google Patents

Abstract

PURPOSE: To obtain a dispersant which is used for the suspension polymn. of an ethylenically unsatd. monomer and can give an easily processible high-quality polymer by using a polyvinyl alcohol having a specific structure. CONSTITUTION: This dispersant for the suspension polymn. of an ethylenically unsatd. monomer is a polyvinyl alcohol polymer which has a structure represented by the formula in the molecule, gives a 1wt.% aq. soln, having an absorbance at 280nm of 2.5 or higher, and has an average degree of polymn. of 500 or higher, a degree of saponification of 60-90mol.%. a ratio (Mw/Mn) of wt. average mol.wt. (Mw) to number average mol.wt. (Mn) of 2.5 or lower, a block character to degree of saponification of 0.45 or lower, and a methanol- sol. content of 10wt.% or lower. The dispersant is esp. suitable for polymerizing vinyl chloride or a monomer mixture contg. vinyl chloride.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a dispersant used for suspension polymerization of a monomer having an ethylenically unsaturated double bond and a method for producing a polymer using the dispersant.

[0002]

2. Description of the Related Art A suspension polymerization method is known as a method for polymerizing a monomer having an ethylenically unsaturated double bond. In this suspension polymerization method, the dispersion state of the monomer in the aqueous medium has a great influence on the quality of the polymer obtained. Therefore, in order to obtain a high-quality polymer, that is, a polymer particle having a sharp particle size distribution and a high porosity, selection of a dispersant is one of important requirements.

Most of the partially saponified polyvinyl alcohol conventionally used as a dispersant in suspension polymerization has a particle size distribution, bulk density, porosity,
In order to improve various properties such as plasticizer absorbability and heat stability in a well-balanced manner, those having a broadly adjusted saponification degree distribution and the like can be mentioned. However, in such partially saponified polyvinyl alcohol, the porosity of the obtained polymer is low, so that the plasticizer absorbability is poor and the processability is insufficient.

Therefore, for the purpose of obtaining a polymer of high quality and easy to process, a partially saponified polyvinyl alcohol having a sharp saponification degree distribution or a carbonyl group and a vinylene group adjacent to the carbonyl group are introduced into the molecule. A method of using the above-mentioned polyvinyl alcohol as a dispersant has been proposed (Japanese Patent Publication No. 5-88251 and Japanese Patent Publication No. 58-2).
962, Japanese Patent Publication No. 6-21125), the quality and processability of the obtained polymer are still insufficient.

[0005]

An object of the present invention is to enable a monomer having an ethylenically unsaturated double bond to be uniformly and stably dispersed in an aqueous medium, and to have a sharp particle size distribution. It is an object of the present invention to provide a dispersant capable of obtaining a polymer having high porosity, excellent processability, and less generation of fish eyes, and a method for producing a polymer using the dispersant.

[0006]

The first aspect of the present invention is to provide the following formula (1) in the molecule:

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It has a structure represented by
The absorbance at 280 nm is 2.5 or more, and the average degree of polymerization is
The saponification degree is 500 or more, the degree of saponification is 60 to 90 mol%, and the ratio of the weight average molecular weight Mw to the number average molecular weight Mn (Mw /
Mn) is 2.5 or less, the block character relating to the degree of saponification is 0.45 or less, and the methanol-soluble content is 10
Consisting of polyvinyl alcohol-based polymer in an amount of not more than% by weight,
It is a dispersant for suspension polymerization of a monomer having an ethylenically unsaturated double bond.

A second aspect of the present invention is a method for producing a polymer in which a monomer having an ethylenically unsaturated double bond is subjected to suspension polymerization in an aqueous medium in the presence of a dispersant. The following formula (1) in the molecule:

[Chemical 4]

It has a structure represented by
The absorbance at 280 nm is 2.5 or more, and the average degree of polymerization is
The saponification degree is 500 or more, the degree of saponification is 60 to 90 mol%, and the ratio of the weight average molecular weight Mw to the number average molecular weight Mn (Mw /
Mn) is 2.5 or less, the block character relating to the degree of saponification is 0.45 or less, and the methanol-soluble content is 10
It is a method for producing a polymer using a polyvinyl alcohol polymer in an amount of not more than wt%.

Hereinafter, the present invention will be described in detail. Polyvinyl alcohol-based polymer The dispersant of the present invention is a polyvinyl alcohol-based polymer (hereinafter referred to as PVA-based polymer) having a structure represented by the above formula (1). This structure is produced by subjecting partially saponified PVA produced by saponification described below to further deacetic acid reaction or dehydration reaction.
It is generated at one end of VA polymer (published by The Polymer Society of Japan, "Polymer Chemistry" Vol. 16, No. 174, 1959, P571-P57).
8; published by the Society of Polymer Science, "Water-soluble polymer / water-dispersible resin comprehensive technical data collection", January 23, 1981, P211 to P213).

The PVA polymer is a 1% by weight aqueous solution.
Absorbance at 280 nm is 2.5 or more, preferably
It is in the range of 2.8 to 4.0. PV whose absorbance is too small
When the A-based polymer is used as the dispersant, the particle size distribution of the obtained polymer becomes broad and the coarse particles increase. Further, the absorbency of the plasticizer of the obtained polymer is lowered and the generation of fish eyes is increased. The absorption at 280 nm is calculated by the above formula.
This is due to the structure of (1).

The average degree of polymerization of the PVA polymer is 500 or more, preferably 500 to 3500, and more preferably
It is in the range of 500 to 2500. If the average degree of polymerization is too small,
The stability of the dispersed state of the monomer and the thermal stability become low. Further, if the average degree of polymerization is too large, the solubility in water decreases,
Alternatively, it is often difficult to handle because the viscosity of the aqueous solution becomes high.

The PVA polymer has a saponification degree of 60 to 90.
It is in the range of mol%, preferably in the range of 65 to 85 mol%. If the degree of saponification is too low, the solubility in water will be reduced, while if it is too high, the surface-active ability will be reduced and the dispersibility will be reduced.

The PVA polymer has a number average molecular weight Mn of
Ratio (Mw / Mn) of the weight average molecular weight Mw to 2.5 is 2.5.
It is below, preferably below 2.2. If this ratio is too large, the molecular weight distribution of the PVA-based polymer becomes too broad and the dispersion characteristics vary. As a result, the bulk density of the obtained polymer is lowered and the generation of fish eyes is also increased. The weight average molecular weight Mw of the PVA-based polymer
And the number average molecular weight Mn are values measured by gel permeation chromatography (GPC) of polyvinyl acetate obtained by reacetylating the PVA polymer.

The above-mentioned PVA-based polymer has a block character η with respect to the degree of saponification of 0.45 or less, preferably
It is less than 0.40. The PVA-based polymer having a block character in such a range has a high block property described later. A PVA-based polymer having a high block property has a large dispersive power for a monomer having an ethylenically unsaturated double bond and can stably disperse and disperse the monomer in an aqueous medium. The resulting polymer particles have a sharp particle size distribution. Further, when a PVA-based polymer having an excessively large block character is used, the particle size distribution of the obtained polymer particles becomes broad, the plasticizer absorbability is lowered, and the generation of fish eyes is increased.

The block character η is the following formula (2) having an acetoxy group in the PVA polymer:

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It is an index showing the chain distribution state of the structural unit (vinyl acetate unit) represented by. The block character η is determined by measuring the ¹³ C-NMR spectrum of the PVA solution and analyzing the three peaks appearing in the methylene region in the spectrum. The above three peaks are, from the left side, three types of two-unit chain structures (dyad) corresponding to (OH, OH), (OH, OAc), and (OAc, OAc), that is, the following formula:

[0018]

[Chemical 6]

(In the formula, Ac represents an acetyl group), which corresponds to a two-unit chain structure, and the absorption intensities of these peaks are proportional to the proportion of each two-unit chain structure. The block character η is expressed by the following formula (3): η = (OH, OAc) / [2 (OH) (OAc)] (3) [where (OH, OAc) is 2 units obtained from the above measurement. Represents the ratio (molar fraction) of chain structure (OH, OAc), (OH)
Represents the degree of saponification (molar fraction), and (OAc) represents the proportion (molar fraction) of acetoxy groups. ], 0 to 2
Can take values up to. The distribution state of the chain (OAc, OAc) of the structural unit having an acetoxy group is a completely blocked state when η = 0, and when 0 <η <1, the blockiness becomes closer to 0. It is high, and the closer to 1, the stronger the randomness is. Further, when η = 1, it is completely random, and when 1 <η ≦ 2, it is shown that acetoxy groups and hydroxyl groups are relatively alternately present.

This block character η is, for example,
Even with partially saponified PVA having the same degree of saponification, the closer it is to 0, that is, the higher the block property, the higher the surfactant activity and the greater the dispersive power. As described above, the surface-active ability of partially saponified PVA depends not only on the content of acetoxy groups in partially saponified PVA but also on the distribution state thereof. Therefore, if the surface-active ability is different, the dispersive power in suspension polymerization and the physical properties of the obtained polymer are also different.

The PVA polymer has a methanol-soluble content of 10% by weight or less, preferably 5% by weight or less. When a PVA-based polymer having too much methanol-soluble content is used as the dispersant, the uniform dispersion of the monomer is hindered and the amount of scale attached to the wall of the polymerization vessel increases. The vinyl-based polymer obtained using such a PVA-based polymer has a broad particle size distribution, a low bulk specific gravity, and an increased number of fish eyes.

The above methanol-soluble matter is obtained by the following equation. Methanol-soluble content (% by weight) = 100 · B / A [wherein A is the weight (g) of the dried PVA-based polymer, and B is the dry PVA-based polymer of A (g) Soxhlet extraction is performed for 24 hours, and the solid content in the extract is the weight (g).] The solid content in the extract is, for example, acetic acid produced as a by-product during the production of the PVA-based polymer. Acetic acid salts such as sodium, low saponification degree PVA, low polymerization degree PVA and the like are included.

Production of PVA Polymer The above PVA polymer can be obtained by saponifying a polyvinyl ester polymer by a conventionally known production method. The polyvinyl ester polymer is obtained by polymerizing a vinyl ester monomer in the presence of a radical polymerization initiator and a chain transfer agent.

As the vinyl ester monomer, in addition to vinyl acetate, for example, vinyl trifluoroacetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl 2-ethylhexanoate, vinyl caprylate,
Vinyl caprate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl methacrylate, vinyl crotonate, vinyl sorbate, vinyl benzoate, vinyl cinnamate, vinyl tert-butyl benzoate and vinyl versatate monomers. Etc. The polyvinyl ester polymer may be a homopolymer of these monomers or a copolymer composed of two or more of these monomers. Further, a copolymer of these monomers and another monomer may be used as long as the physical properties are not impaired. Examples of such other monomers include unsaturated polycarboxylic acids or salts thereof, partial alkyl esters thereof, complete alkyl esters thereof, anhydrides thereof, amide compounds thereof, imide compounds thereof or nitrile compounds thereof; Saturated sulfonic acid or its salt; vinyl ether; ethylene; vinyl chloride;
Examples thereof include α-olefins having 3 to 30 carbon atoms.

Examples of the radical polymerization initiator include α, α′-azobisisobutyronitrile and α, α ′.
-Azobis- (4-methoxy-2,4-dimethylvaleronitrile), α, α'-azobis- (2,4-dimethylvaleronitrile) and other azo compounds; benzoyl peroxide, diisopropyl peroxydicarbonate and other perazo compounds Known radical polymerization initiators such as oxides may be mentioned, and among them, azo compounds are preferable because they are easy to handle.

The chain transfer agent introduces a carbonyl group into the polyvinyl ester polymer. This carbonyl group is 280% of a 1% by weight aqueous solution of a PVA polymer obtained by saponifying the polyvinyl ester polymer.
It controls the absorbance at nm. That is, the more carbonyl groups contained in the polyvinyl ester polymer, the higher the absorbance of the PVA polymer.

Examples of the chain transfer agent include aldehydes such as acetaldehyde, propionaldehyde, n-butyraldehyde and benzaldehyde; acetone,
Examples thereof include ketones such as methyl ethyl ketone, hexanone and cyclohexanone.

Examples of the method for polymerizing the PVA polymer include bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization and the like. Industrially, solution polymerization using methanol as a solvent is preferable. The polymerization system may be, for example, batch system, semi-continuous system or continuous system.

As a method for obtaining a PVA-based polymer having an Mw / Mn of 2.5 or less as described above, for example, a method of stopping and terminating the polymerization at a stage where the polymerization conversion rate is in the low range of 30 to 70%, , A method of continuously or intermittently supplying the monomer to the polymerization system.

The average degree of polymerization of the PVA-based polymer can be increased to 500 or more by adjusting the monomer / solvent ratio and the polymerization conversion rate during the polymerization of the above-mentioned monomers by a known method. be able to. The polymerization temperature cannot be unconditionally determined depending on the type of radical polymerization initiator used and the amount thereof used, but the polymerization is usually carried out at 10 to 90 ° C. After the polymerization, unreacted monomers are removed by a conventional method to obtain a polyvinyl ester polymer.

The PVA polymer can be obtained by saponifying the thus obtained polyvinyl ester polymer by a conventional method. Examples of the saponification method include a method of saponifying a polyvinyl ester polymer in an organic solvent in the presence of a saponification catalyst. Examples of the organic solvent include alcohols such as methanol and ethanol; esters such as methyl acetate and ethyl acetate;
Examples thereof include ketones such as acetone and methyl ethyl ketone; aromatic hydrocarbons such as benzene and toluene, and these can be used alone or in combination of two or more kinds. Of these, methanol is industrially preferable. These organic solvents are not limited to anhydrides, and may contain a small amount of water.

To reduce the block character to 0.45 or less, saponification may be carried out in the presence of a low dielectric constant solvent such as benzene, toluene and methyl acetate. Examples of the saponification catalyst include alkaline catalysts such as sodium hydroxide, potassium hydroxide, and metallic sodium; acid catalysts such as sulfuric acid. Among them, industrially, alkaline catalysts are preferable. The amount of the saponification catalyst used is usually 1 to 20 mmol per 1 mol of the vinyl ester unit (for example, the vinyl acetate unit of the above formula (2)). If the amount used is too large, the obtained PVA-based polymer will be colored, and it will be difficult to remove the saponification catalyst remaining after the saponification and the by-produced acetate salts such as sodium acetate. On the other hand, when the amount used is too small, the reaction time becomes long and the efficiency is lowered. The saponification temperature is usually from room temperature to 70 ° C.

The methanol-soluble content of the PVA polymer was adjusted to 10
Examples of the method for reducing the content by weight or less include known methods such as the type and concentration of the solvent of the polyvinyl ester polymer, the type and amount of the saponification catalyst, the method of mixing with the polymer solution, the reaction temperature, the reaction time, and the like. Acetate salt and PV with low saponification degree
A method of reducing A; a method of pulverizing the obtained PVA-based polymer, then washing this with a solvent such as methanol, and further performing solid-liquid separation. These methods are
A single method or a combination of two or more methods may be used.

The structure represented by the above formula (1) is formed by subjecting partially saponified PVA produced by saponification to a deacetic acid reaction or a dehydration reaction in a saponification step, a drying step or the like. Production of Vinyl Polymer The method for producing a polymer of the present invention is carried out by a conventionally known suspension polymerization except that the above PVA polymer is used as a dispersant.

Examples of the monomer having an ethylenically unsaturated double bond which is polymerized by applying the production method of the present invention include vinyl halides such as vinyl chloride; for example, vinyl acetate, vinyl propionate, benzoic acid. Examples thereof include vinyl esters such as acid vinyl; acrylic acid, methacrylic acid, and their esters; maleic acid and anhydrides; for example, olefins such as ethylene and propylene; vinylidene halides; vinyl ethers; styrene and the like. These are used alone or in combination of two or more. Further, the production method of the present invention is particularly suitable for polymerization of vinyl chloride alone or a monomer mixture containing vinyl chloride.

The suspension polymerization is carried out by adding a dispersant composed of the above PVA polymer and a monomer to an aqueous medium to suspend and disperse the monomer, and then 30 to 70 in the presence of an oil-soluble catalyst. It is carried out in the temperature range of ° C. The dispersant is added to the aqueous medium in powder form or in solution. As the solvent to be added in the form of a solution, water, for example, alcohol solvents such as methanol, ethanol and propanol; for example, ketone solvents such as acetone and methyl ethyl ketone;
Ester solvents such as methyl acetate and ethyl acetate are exemplified, and a mixed solvent of water and the alcohol solvent, the ketone solvent or the ester solvent may be used. Further, the whole amount of the dispersant may be charged all at once before the start of the polymerization, or may be divided and charged during the polymerization. The amount of the dispersant added during the polymerization is 0.02 to 100 parts by weight of the monomer.
A range of 0.5 part by weight is preferable, and a range of 0.
It is in the range of 04 to 0.2 parts by weight. If the amount of the dispersant is too large, a skin layer is formed on the surface of the obtained polymer particles, so that the porosity of the polymer particles becomes poor. As a result, the plasticizer absorbability of the polymer decreases, and fish eyes increase in the molded product. On the other hand, if the amount used is too small, the particles of the obtained polymer become coarse, the particle size distribution becomes broad, and the bulk specific gravity decreases, which is not preferable.

Examples of the oil-soluble catalyst include benzoyl peroxide, lauroyl peroxide, diisopropyl peroxydicarbonate, α, α'-azobisisobutyronitrile, α, α'-azobis (2,4).
-Dimethylvaleronitrile), acetylcyclohexylsulfonyl peroxide, etc., and these can be used alone or in combination of two or more kinds. The amount of oil-soluble catalyst added during the polymerization is 1
The range of 0.03 to 0.2 parts by weight per 00 parts by weight is preferable.

Further, during the polymerization, a known dispersant other than the dispersant of the present invention can be used in combination within a range not impairing the effects of the present invention. Examples of such a dispersant include an average degree of saponification of 10 to 100 mol% and an average degree of polymerization of 100 to 30.
Partially saponified polyvinyl alcohol of 00 or a derivative thereof; for example, cellulose derivatives such as methyl cellulose, ethyl cellulose, hydroxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxybutyl methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, aminomethyl hydroxypropyl cellulose, aminoethyl hydroxypropyl cellulose; starch. Tragant; Pectin; Glue; Alginic acid and its salts; Gelatin; Polyvinylpyrrolidone; Polyacrylic acid and its salts; Polyacrylamide; Polymethacrylamide; Vinyl acetate and maleic acid;
Copolymers of unsaturated acids such as maleic anhydride, acrylic acid, methacrylic acid, itaconic acid, fumaric acid, crotonic acid; copolymers of vinyl ether and the above unsaturated acids; salts and esters of the above copolymers, etc. Is mentioned. The amount of the dispersant used is 0.0 per 100 parts by weight of the total amount of the dispersant.
The range of 2 to 0.5 parts by weight is preferable, and the proportion of these known dispersants is preferably 50% by weight or less in the total amount of the dispersants.

In addition, various surfactants, inorganic dispersants and the like can be appropriately used together as an auxiliary agent during the polymerization.

[0040]

Example Preparation of PVA Polymer [Partially Saponified PVA (No. 1)] 800 parts by weight of vinyl acetate, 165 parts by weight of methanol and 25 parts by weight of acetaldehyde were charged into a reactor equipped with a reflux condenser, and the reactor After replacing the inside of the reaction vessel with nitrogen while stirring the contents inside, the jacket temperature arranged around the reactor was raised to 64 ° C.,
When the temperature of the contents of the reactor reached 60 ° C, 10 parts by weight of a methanol solution containing 0.52 parts by weight of α, α'-azobisisobutyronitrile was charged into the reactor.

When the polymerization conversion rate reached 50%, the reactor was cooled to stop the polymerization. Then, an operation of removing unreacted vinyl acetate and acetaldehyde together with methanol outside the reactor under reduced pressure was performed while adding methanol to obtain a methanol solution of polyvinyl acetate.

Next, a part of a methanol solution of polyvinyl acetate was taken and methanol and benzene were added thereto to prepare a 40 wt% solution of polyvinyl acetate (benzene concentration: 15 wt%). Next, while maintaining the temperature of this solution at 40 ° C., a methanol solution of sodium hydroxide was added to this solution and 7 mmol of sodium hydroxide was added to 1 mol of vinyl acetate unit of polyvinyl acetate, and the mixture was mixed in a gel form. The PVA-based polymer of was obtained and pulverized. The pulverized PVA-based polymer had a PVA-based polymer concentration of 15% by weight.
After that, methanol was added so that the solid-liquid separation was repeated twice, followed by drying to obtain a PVA polymer.

The degree of saponification (mol%), the average degree of polymerization, and the ratio of the weight average molecular weight Mw to the number average molecular weight Mn (Mw / Mn) of the obtained PVA-based polymer (Mw / Mn), 280% of a 1% by weight aqueous solution
The absorbance at nm, the block character and the methanol-soluble matter were measured by the methods described below. The results are shown in Table 1
It is shown as a VA polymer (No. 1).

Measurement of saponification degree It was measured according to JIS K 6726. Measurement of Ratio (Mw / Mn) The weight average molecular weight Mw and number average molecular weight Mn of the polyvinyl alcohol-based polymer are determined by gel permeation chromatography (GP) after completely saponifying the PVA-based polymer.
C) was used for measurement under the following conditions, and Mw / Mn was calculated from the obtained measured value. Conditions: Column: Shodex KB-800P (1 bottle) KB-800P (2 bottles) Eluent: 0.1 M NaNO ₃ aqueous solution Column temperature: 35 ° C. Flow rate: 0.7 ml / min Injection volume: 200 μl Sample concentration: 0 0.05 wt%

Measurement of Absorbance The absorbance at 280 nm of a 1% by weight aqueous solution sample in a 10 mm square quartz cell was measured by an ultraviolet-visible spectrophotometer (U manufactured by Shimadzu Corporation).
V160A). Measurement of Block Character It was determined from the peak absorption intensity of the methylene region of ¹³ C-NMR measured by FT-NMR (GSX-270, manufactured by JEOL Ltd.) using the above formula (3).

Measurement of Methanol-Soluble Content About 6 g of the dried PVA polymer was precisely weighed, then subjected to Soxhlet extraction with methanol for 24 hours, and the obtained extract was evaporated to dryness to obtain a solid content. And PVA used for extraction
The methanol-soluble content was defined as the weight percentage of the solid content relative to the polymer.

[PVA-based polymer (No. 2 to 7)] In addition, in the method for producing the PVA-based polymer (No. 1), Table 1 shows the blending amount of methanol, the blending amount of acetaldehyde and the polymerization conversion rate. Other than the above, the above N
o. Polyvinyl acetate was obtained in the same manner as in the production method of 1.
Then, except that the benzene concentration was changed to the concentration shown in Table 1, the above No. In the same manner as in the manufacturing method of 1,
A 40 wt% solution was prepared. Then, the 40 wt% solution of polyvinyl acetate was saponified to obtain a gel-like PVA-based polymer, and the number of washings of this gel was changed to the number of times shown in Table 1 above. A dry PVA-based polymer was obtained in the same manner as in the production method of 1. Degree of saponification (mol%) of the obtained PVA-based polymer,
The average degree of polymerization, the ratio of the weight average molecular weight Mw to the number average molecular weight Mn (Mw / Mn), the absorbance at 280 nm of a 1 wt% aqueous solution, the block character, and the methanol-soluble content were measured in the same manner as above. The results are shown in Table 1.

[0048]

[Table 1]

Examples 1 to 3 and Comparative Examples 1 to 4 In an autoclave having an internal volume of 2 m ³ , 150 parts by weight of pure water and the PVA-based polymer shown in Table 2 (Nos. 1 to 7) prepared as described above. ) 0.1 part by weight was charged. Next, the internal pressure of the autoclave was 60 mmHg (7.
It was exhausted until it became 99 kPa). Then, 100 parts by weight of vinyl chloride monomer was charged, and 0.05 part by weight of t-butylperoxyneodecanoate was further charged as a polymerization initiator, and then the temperature was started and polymerization was carried out at 57 ° C. It was Internal pressure of autoclave is 6.5kg / cm ² · G
When it reaches (0.64 MPa · G), the reaction is stopped,
Unreacted monomer was recovered, dehydrated and dried to obtain a polymer.

The bulk density, particle size distribution, plasticizer absorption amount, plasticizer absorption time and fish eye of the obtained polymer were measured by the following methods. Table 2 shows the results. Bulk specific gravity: measured according to JIS K-6721. Particle size distribution: # 60, # 8 according to JIS Z-8801
Sieve was performed using each of No. 3, # 100, # 149 and # 200 sieves, and the passing amount (% by weight) was measured.

Plasticizer absorption: inner diameter 25 mm, depth 85 m
Glass fiber is packed in the bottom of a container made of aluminum alloy of m, and 10 g of the polymer is collected and charged. Dioctyl phthalate (hereinafter referred to as DOP) 15cc is added to this,
The polymer was allowed to stand for 30 minutes to allow the DOP to sufficiently permeate the polymer. After that, the excess DOP was centrifuged under an acceleration of 1500 G,
The amount of DOP absorbed in 10 g of polymer was measured and converted per 100 g of polymer.

Plasticizer absorption time: 400 g of the polymer was placed in a Brabender Plastograph (planetary mixer) and preheated (4 minutes) to 80 with stirring at 60 rpm.
° C. Add 20 DOP to this preheated plastograph
0 g was added, and the time from the time of the addition to the time when the torque started to decrease was defined as the plasticizer absorption time. Fish eye: 100 parts by weight of polymer, 1 part by weight of tribasic lead sulfate, 1.5 parts by weight of lead stearate, 0.2 part by weight of titanium oxide, 0.1 part by weight of carbon black and DO.
The mixture prepared in a proportion of 50 parts by weight of P was kneaded with a roll at 145 ° C. for 5 minutes, and then each had a thickness of 0.2 mm.
The sheet was molded, and the number of fish eyes contained in 100 cm ^{2 of} the sheet was counted.

[0053]

[Table 2]

[0054]

The dispersant of the present invention can uniformly and stably disperse a monomer in an aqueous medium. The method for producing a polymer using the dispersant can obtain a polymer having a sharp particle size distribution of polymer particles, high porosity, and excellent processability. Further, the obtained polymer has very little formation of fish eyes in the molded product of the polymer even when it is mixed with various plasticizers or subjected to the molding process under a shallow kneading process condition. It has the advantage of

Claims (2)

[Claims] 1. The following formula (1) in the molecule: Having a structure represented by the following formula: the absorbance of a 1% by weight aqueous solution at 280 nm is 2.5 or more, the average degree of polymerization is 500 or more, the degree of saponification is 60 to 90 mol%, and the number average molecular weight Mn is
Ratio (Mw / Mn) of the weight average molecular weight Mw to 2.5 is 2.5.
Below is the block character for saponification
A dispersant for suspension polymerization of a monomer having an ethylenically unsaturated double bond, which is 0.45 or less and comprises a polyvinyl alcohol-based polymer having a methanol-soluble content of 10% by weight or less. 2. A method for producing a polymer, which comprises subjecting a monomer having an ethylenically unsaturated double bond to suspension polymerization in an aqueous medium in the presence of a dispersant, wherein the dispersant has the following formula in the molecule: (1): [Chemical formula 2] Having a structure represented by the following formula: the absorbance of a 1% by weight aqueous solution at 280 nm is 2.5 or more, the average degree of polymerization is 500 or more, the degree of saponification is 60 to 90 mol%, and the number average molecular weight Mn is
Ratio (Mw / Mn) of the weight average molecular weight Mw to 2.5 is 2.5.
Below is the block character for saponification
A method for producing a polymer using a polyvinyl alcohol-based polymer having a content of 0.45 or less and a methanol-soluble content of 10% by weight or less.