JPH0147483B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention uses a specific cation in the molecule as a dispersion stabilizer that has an excellent effect of stabilizing the dispersion of suspended particles and provides a polymer with excellent physical properties during suspension polymerization of ethylenically unsaturated monomers in an aqueous medium. The present invention relates to a suspension polymerization method characterized in that a modified polyvinyl alcohol containing groups is used. In particular, this suspension polymerization method can exhibit the highest industrial value in the polymerization of vinyl chloride. Conventionally, cellulose derivatives, polyvinyl alcohol, gelatin, maleic acid copolymers, etc. have been used as suspension polymerization stabilizers when vinyl chloride monomer is suspended in water. ) has become widely adopted due to its excellent dispersion stabilizing effect. In the suspension polymerization of vinyl chloride, important technical attention has been paid to the processability of the produced polymer in addition to the dispersion stabilizing effect, and in particular, the polymers produced by the current suspension polymerization method have poor plasticizer absorption performance. ,
As a result, molded products often suffer from fish-eye defects, which significantly impairs the appearance of the product. From this point of view, in order to impart better performance to PVA, in addition to adjusting the degree of polymerization and saponification, it is necessary to adjust the saponification degree distribution (Japanese Patent Application Laid-Open No. 54-90385) or the arrangement distribution of acetic acid groups. is being done.
Furthermore, as a method of actively chemically modifying PVA to improve it, PVA with hydrophobic groups introduced (PTK
6546, JP 44-6830, JP 54-44314) or PVA containing crotonic acid, etc.
33580, JP-A-54-46284) or PVA with a lactone ring introduced (JP-A-54-85288) have been proposed, but they have problems in terms of dispersion stability, polymer processability, particle size distribution, workability, etc. All of them have their advantages and disadvantages, and it cannot be said that they are at a fully satisfactory level in terms of performance balance. The present inventors conducted a more extensive study on chemical modification of PVA, and obtained many modified PVA.
As a result of evaluating the performance as a stabilizer for suspension polymerization, we found that
PVA has been found to be extremely effective for such purposes, and on the other hand, PVA is also industrially advantageous.
The present invention was completed by establishing a cation modification method. The technology of cationically modifying water-soluble polymers such as starch or polyacrylamide has been known and is also produced industrially, but PVA modified with cationic groups
The idea of using it as a dispersion stabilizer in suspension polymerization is completely unknown. One of the reasons for this may be that although a small number of methods have been proposed for imparting cationic groups, they all have drawbacks in their modification methods, making it difficult to produce them industrially. The present invention will be explained in more detail below. The cationic group contained in the specific cation-modified PVA as a dispersion stabilizer used in the present invention refers to a chemical structural unit that dissociates in an aqueous solution and becomes positively charged, and specifically refers to a primary amine. , secondary amines, tertiary amines, quaternary ammonium salts, pyridine, pyridinium, imidazole and imidazolinium. The methods for producing cation-modified PVA that have been reported so far include a method in which vinyl pyridine and vinyl acetate are copolymerized and then saponified, N-vinylphthalimide or N-vinyl succinimide and vinyl acetate are copolymerized and then saponified, and then alkali Alternatively, a method of decomposing the imide group with hydrazine, a method of converting PVA into aminoacetal or aminobenzacetal under an acid catalyst, a method of converting PVA to alkoxydimethylamine, glycidyltrimethylammonium hydrochloride or 3-chloro-2-hydroxypropyltrimethyl Known methods include reacting ammonium hydrochloride, and adding Michael acrylamide to PVA and then introducing an amino group by Hofmann decomposition. Cation-modified PVA synthesized by these methods can also be used as a dispersion stabilizer for suspension polymerization of the present invention, but the above-mentioned cation-modified PVA
In addition to various difficulties in the cationization process itself, the PVA manufacturing method is difficult to implement industrially.
These cation-modified PVA alone still have insufficient dispersion stabilization ability. That is, the copolymerization rate of vinylpyridine and vinyl acetate is so slow that it cannot be practically carried out, and the copolymerization rate of N-vinylphthalimide or N-vinylsuccinimide is saponified and then the imide group is added with an alkali or hydrazine. Since the decomposed product is a completely saponified product, its dispersion stabilizing effect is significantly inferior, and it is necessary to use other dispersants in combination. In contrast, the following general formulas (), (),
Modified polyvinyl alcohol containing the copolymerized unit shown by () or () not only exhibits cationic activity, but also allows industrial introduction of cationic groups, and is a method for obtaining a degree of saponification with the best dispersant performance. Both are stable and easily implementable. (Here, R ¹ and R ² are hydrogen atoms or lower alkyl groups, and B is

[expression] or

[Formula] R ³ , R ⁴ , R ⁵ are hydrogen atoms or lower alkyl groups (may contain substituents), X is an anion, A is B
It means a group that connects the nitrogen atom in the amide group with the nitrogen atom in the amide group. ) (Here, R ⁶ , R ⁷ , R ⁸ are hydrogen atoms, lower alkyl groups or phenyl groups, R ⁹ is lower alkyl groups,
Each X represents an anion. ) (Here, B is

[expression] or

[Formula] R ³ , R ⁴ , R ⁵ are hydrogen atoms or lower alkyl groups (which may contain substituents),
represents an anion, and D represents an aliphatic group connecting the nitrogen atom and oxygen atom in B, respectively. ) Modified PVA containing copolymerized units represented by the above general formulas () to () can be produced by combining vinyl esters, especially vinyl acetate, and the following formulas (a) to (d). (Here, the meanings of R ¹ , R ² , R ⁶ to ^{R 9} , X, A, B, and D are the same as above.) in the presence of a radical polymerization initiator. After that, the alcohol solution of the copolymer is treated with an alkali or acid catalyst to partially or highly saponify the vinyl ester units in the copolymer depending on the purpose, resulting in vinyl alcohol units. It can be produced effectively and easily by In the monomer represented by general formula (a), R ¹ is a hydrogen atom or a lower alkyl group, but a hydrogen atom or a methyl group is usually preferred, and furthermore, the polymerization rate in the copolymerization reaction with vinyl acetate is high. and is preferably a hydrogen atom. R ² is also a hydrogen atom or a lower alkyl group, but usually a hydrogen atom or a methyl group is preferred. B is an amino group -N<R ³ R ⁴ or a quaternary ammonium salt

[Formula] where R ³ , R ⁴ and R ⁵ represent a hydrogen atom or a lower alkyl group even if it contains a substituent, and X represents an anion. R ³ , R ⁴ , and R ⁵ are all preferably methyl groups for normal purposes, but substituents such as lower alkyl groups such as ethyl groups and propyl groups, methylol groups, or aminoalkyl groups for the purpose of improving the density of cationic groups. A lower alkyl group containing may also be used. X is a halogen atom such as chlorine, silium, iodine, CH ₃ OSO ₃ or
CH ₃ C ₆ H ₄ SO ₃ is preferred, and chlorine atoms are particularly preferred from the economic, safety, and physical properties of modified PVA. When B is in the form of a quaternary ammonium salt, the effects of the present invention can be exhibited even with primary to tertiary amines, which are preferable for ease of handling in the production of modified PVA. Any group containing a stable bond can be used as A, but a linear or branched aliphatic group is usually used. Among the monomers represented by the above general formula (A), the following are specific examples of monomers in the form of tertiary amines. N-(2-dimethylaminoethyl)acrylamide, N-(2-dimethylaminoethyl)methacrylamide, N-(3-dimethylaminopropyl)acrylamide, N-(3-diethylaminopropyl)acrylamide, N-(3-dimethyl aminopropyl) methacrylamide, N-(3-
diethylaminopropyl) methacrylamide, N
-(1,1-dimethyl-3-dimethylaminopropyl)acrylamide, N-(1,1-dimethyl-3-dimethylaminopropyl)methacrylamide, N-(1,1-diethyl-3-dimethylaminobutyl)acrylamide , N-(1-methyl-
1,3-diphenyl-3-diethylaminopropyl)methacrylamide, N-(3-dimethylaminohexyl)acrylamide, N-(3-methylethylaminopropyl)methacrylamide, N-
Methyl-N-(3-dimethylaminopropyl)acrylamide. Among the monomers represented by the above general formula (a), those in the form of quaternary ammonium can be easily obtained by quaternizing the above-mentioned tertiary amine type monomer with the following quaternizing agent. be able to. Dialkyl sulfate, e.g. dimethyl sulfate, diethyl sulfate, dipropyl sulfate, alkyl or aryl sulfonic acid C ₁ ~
C ₄ -esters, e.g. methyl-, ethyl-, propyl- or butyl esters, such as methanesulfonic acid, benzenesulfonic acid or toluenesulfonic acid, benzyl halides, e.g. benzyl chloride or benzyl bromide, alkyl halides, e.g. methyl chloride. , methyl bromide, methyl iodide, ethyl chloride, ethyl bromide or ethyl iodide. The following four types of monomers among the various examples mentioned above as monomers represented by the above general formula (A). N-(1,1-dimethyl-3-dimethylaminopropyl)acrylamide trimethyl-(3-acrylamide-3,3-
dimethylpropyl) ammonium chloride N-(3-dimethylaminopropyl)methacrylamide Trimethyl-(3-methacrylamidopropyl)ammonium chloride is superior in producing the modified PVA according to the present invention from the viewpoint of polymerization rate, stability of the amide group, and economical efficiency during monomer production. Furthermore, examples of the monomer shown in (b) above include the following. 1-vinylimidazole, 1-vinyl-2-methylimidazole, 1-
Vinyl-2-ethylimidazole, 1-vinyl-
2-phenylimidazole, 1-vinyl-2,
4,5-trimethylimidazole. Further, the monomer represented by the above general formula (c) can be easily obtained by quaternizing the monomer represented by the above general formula (b) with the above-mentioned quaternizing agent. Examples of the monomer represented by the above general formula (2) include dimethylaminoethyl vinyl ether, dimethylaminopropyl vinyl ether, quaternized products thereof, and vinyloxyethylamine. The amount of cationic groups, degree of saponification, or degree of polymerization in the cationically modified PVA used in the present invention is appropriately selected depending on the purpose and is not particularly limited. It is important to combine them. It has become clear that even a small amount of the cationic group is effective, and it is usually preferable to select the cationic group from the range of 0.001 to 10 mol%. Regarding the degree of saponification, in general, complete saponification has a low suspension stability ability, so partial saponification is preferable. In many cases, the cloud point of the aqueous solution is 10~
It is preferable to adjust the saponification degree so that it is in the range of 90°C, and is usually selected from the range of 20 to 86 mol%. Further, a saponification method may be adopted in which the acetate groups in the modified PVA are arranged in a block shape along the molecular chain, or the saponification degree distribution is within a narrow range. The degree of polymerization is usually selected from the range of 200 to 3000. In the present invention, when cation-modified PVA is used for suspension polymerization of vinyl chloride, the polymerization is carried out stably, has a large tolerance to fluctuations in polymerization temperature and dispersant concentration, and has low foaming during polymerization. Furthermore, the resulting polymer has a narrow particle size distribution, has high plasticizer absorption, and has excellent processability with extremely low occurrence of fish eyes. The reason why such excellent effects are obtained is not fully elucidated, but the following mechanism is presumed. (1) Above the cloud point of an aqueous solution of cation-modified PVA,
Normal suspension polymerization is carried out, but cationic modification
The suspension state of PVA aqueous solution is conventionally known.
Compared to PVA, it is less sensitive to small changes in temperature, stirring force, or concentration and maintains good dispersion stability. (2) Fine droplets are stably dispersed in the early stage of polymerization, and as the polymerization progresses, their coalescence progresses smoothly, resulting in the formation of particles with excellent porosity without the generation of fine powder or coarse particles. be done. This ideal polymerization process is presumed to occur through electrostatic interactions between the cationic groups in the modified PVA and the vinyl chloride monomer and polymer. In carrying out the present invention, any commonly used suspension polymerization method can be applied. As the polymerization initiator, azobisisobutyronitrile, dialkyl peroxy carbonate, lauroyl peroxide, sulfonyl peroxide, etc. can be used. In addition to cation-modified PVA, conventionally known dispersion stabilizers such as PVA, modified PVA, and cellulose derivatives, and small amounts of chain transfer agents or surfactants can also be used depending on the purpose. Although the above description has focused on suspension polymerization of vinyl chloride, it is also useful as a method for carrying out the sole or copolymerization of ethylenically unsaturated monomers such as styrene, methacrylate, and vinyl acetate. Next, the present invention will be explained in more detail with reference to Examples. Example 1 and Comparative Examples 1 to 3 Trimethyl-(3-acrylamide-3,3-
A copolymer of dimethylpropyl) ammonium chloride and vinyl acetate is saponified to form trimethyl-
Contains 2 mol% (3-acrylamido-3,3-dimethylpropyl)ammonium chloride units, and the degree of saponification of vinyl acetate units is 71 mol% and 4%.
We synthesized a cationic group-modified PVA whose aqueous solution had a viscosity of 48 cP (centipoise) at 20°C (as measured by a Bruckfield viscometer, hereinafter the same) and a cloud point of 52°C. Next, the above cationic group modification was synthesized with 200Kg of deionized water in a stainless steel autoclave.
After charging 53 g of PVA, 25 g of dicetyl peroxycarbonate, and 20 ml of 1% sulfuric acid, and evacuating the autoclave, 67 kg of vinyl chloride monomer was introduced.
Polymerization was carried out at 56° C. for 8 hours while stirring. After releasing the unreacted vinyl chloride monomer to the outside of the system, the polyvinyl chloride slurry was dehydrated using a centrifuge and dried. Table 1 shows the results of evaluating the physical properties of the obtained polyvinyl chloride. For comparison, in place of the cationic group-modified PVA in Example 1, PVA (Comparative Example 1 ), PVA with a saponification degree of 76 mol%, a viscosity of a 4% aqueous solution at 20°C of 28 cP, and a cloud point of the same aqueous solution of 53°C (Comparative Example 2), or 0.1 mol% monomethyl maleate copolymerized and modified, The viscosity at 20°C of a 4% aqueous solution with a degree of 73 mol% is 23 cP, and the cloud point of the same aqueous solution is 28°C.
Table 1 shows the results of suspension polymerization of polyvinyl chloride carried out in the same manner as in Example 1 except that PVA (Comparative Example 3) was used. Vinyl chloride polymerized in the presence of the cationic group-modified PVA of the present invention had a good plasticizer absorption rate and no stickiness was observed, showing excellent physical properties. Furthermore, the vinyl chloride particles have high porosity despite their high bulk density, and the excellent plasticizer absorption is thought to be related to this fact.
Further, the content of coarse particles and fine particles is small, and the particle size is uniform within a narrow range, which is a favorable result. On the other hand, compared to the present invention, the comparative examples have lower porosity and plasticizer absorption, more fissures, and a wider particle size distribution.

[Table] Examples 2 to 7 In place of the cationic group-modified PVA in Example 1,
Polyvinyl chloride was polymerized and physical properties were evaluated in the same manner as in Example 1, except that the cationic group-modified PVA shown in Table 2 was used. The results are shown in Table 3.
All examples show high porosity and good plasticizer absorption.

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Claims (1)

[Scope of Claims] 1. In the presence of modified polyvinyl alcohol containing a cationic group selected from primary amine, secondary amine, tertiary amine, quaternary ammonium salt, pyridine, pyridinium, imidazole and imidazolinium in the molecule. A method for suspension polymerization of ethylenically unsaturated monomers. 2. The method according to claim 1, wherein the cationic group is a copolymerized unit represented by the following general formula (). (Here, R ¹ and R ² are hydrogen atoms or lower alkyl groups, B is [Formula] or [Formula] R ³ , R ⁴ , and R ⁵ are hydrogen atoms or lower alkyl groups (which may contain substituents), X is an anion, A is B
It means a group that connects the nitrogen atom in the amide group with the nitrogen atom in the amide group. ) 3 The cationic group has the following general formula () or ()
Claim 1, which is a copolymerized unit represented by
The method described in section. (Here, R ⁶ , R ⁷ , R ⁸ are hydrogen atoms, lower alkyl groups or phenyl groups, R ⁹ is lower alkyl groups,
Each X represents an anion. ) 4 The method according to claim 1, wherein the cationic group is a copolymerized unit represented by the following general formula (). (Here, B is [Formula] or [Formula] R ³ , R ⁴ , R ⁵ is a hydrogen atom or a lower alkyl group (which may contain a substituent),
represents an anion, and D represents an aliphatic group connecting the nitrogen atom and oxygen atom in B, respectively. )