JPS591721B2 - Dispersion stabilizer for suspension polymerization of vinyl compounds - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dispersion stabilizer for suspension polymerization of vinyl compounds.

Conventionally, vinyl monomers or copolymerizable vinyl monomer mixtures have been used in aqueous media to produce water-soluble materials such as starch gelatin, alkyl cellulose, polyvinyl alcohol, polyacrylates, copolymers of vinyl acetate and maleic acid, etc. A known method includes suspension polymerization in the presence of an oil-soluble polymerization initiator and one or more suspension stabilizers selected from polymeric substances or inorganic substances such as talc, calcium carbonate, barium sulfate, and bentonite. It is being

Generally, dispersion stabilizers are used to obtain polymers with uniform particle sizes from various vinyl monomers, but especially when the vinyl monomer is vinyl chloride, it depends on the type of dispersion stabilizer used. The physical properties and processability of the polyvinyl chloride beads produced during processing, such as the particle size and porosity, the speed of plasticizer absorption, and the ease with which fish eyes are formed during processing, usually change significantly. For these reasons, many proposals have been made regarding improved dispersion stabilizers for suspension polymerization and suspension polymerization methods using the same. However, in many industrial cases, partially saponified polyvinyl acetate is produced by partially saponifying a methanol solution of polyvinyl acetate using an alkali or acid catalyst, and the degree of polymerization and saponification are limited to a specific range. A similar one is used. (
Hereinafter, according to common practice, the above-mentioned partially saponified polyvinyl acetate will be simply referred to as partially saponified polyvinyl alcohol. ) Recently, in the era of resource and energy crisis, production efficiency has been improved.
Cost reduction and safe operation through labor saving have become strong demands of the times.

Regarding suspension polymerization, in general, if conditions such as good suspension stability during polymerization, particle size consistent with the target particle size, and no wall scale formation can be achieved using as small a amount of dispersion stabilizer as possible, such conditions can be achieved. It is safe to assume that the request can be achieved. Furthermore, regarding the production of polyvinyl chloride resin, the particle size of the resin obtained must be in a range suitable for molding, have a sharp particle size distribution, have appropriate porosity, and have good plasticizer absorption. and that no fin air is generated during formation.

Dispersion stabilizers that have been improved to meet such demands are also limited to polyvinyl alcohol-based ones, such as those disclosed in Japanese Patent Application Laid-Open No. 48
-75486, Japanese Patent Publication No. 49-532700, or in the old days, Special Publication No. 27-3794, or recently, Special Publication No. 48-
42224, Japanese Patent Publication No. 49-23831, etc., but none of these can actually fully satisfy the above-mentioned required performance. Therefore, the present inventors have diligently pursued in detail the possibility of a suspension polymerization dispersion stabilizer with even higher performance. As a result, we have found that an aliphatic aldehyde having 8 or more carbon atoms is added to vinyl acetate and subjected to bulk polymerization, or A method of polymerizing in a solution system to which methanol is added in some cases, and then saponifying the obtained polyvinyl acetate in a single or mixed solvent with a weight ratio of methyl acetate/methanol of 0 to 1.5. The average degree of polymerization obtained by
000 and saponification degree of 70 to 95 moles? It has been discovered that a specific terminal-modified partially saponified polyvinyl alcohol satisfies the above requirements, and the present invention has been achieved.

When vinyl monomers are subjected to suspension polymerization using terminally modified partially saponified polyvinyl alcohol produced by this method as a dispersion stabilizer, adhesion of suspended beads to each other during polymerization is extremely small, and the amount of wall scale formed is also extremely small. Polymer beads with a narrow particle size distribution can also be obtained.

In particular, in the case of suspension polymerization of vinyl chloride, in addition to the above-mentioned advantages, many other effects have been known for a long time, including good molding processability, moderately high porosity, good plasticizer absorption, and little build-up during molding. This can be achieved more efficiently than partially saponified polyvinyl alcohol or terminally modified polyvinyl alcohol. In the production of the suspension polymerization dispersion stabilizer in the present invention, it is essential to add an aliphatic aldehyde having 8 or more carbon atoms during the polymerization of vinyl acetate.

Higher aldehydes used in this case include n-octyl aldehyde, 2-ethyl-hexyl aldehyde.
n-capraldehyde, n-decylaldehyde, n
-Undecylaldehyde, laurylaldehyde, n-tridecylaldehyde, cetylaldehyde, palmitylaldehyde. Examples include stearyl aldehyde, 3-methyl/nitrile aldehyde, 3-methyldodecyl aldehyde, and the like. The appropriate amount of these higher aldehydes to be used is usually about 0.5 to 7 percent by weight based on vinyl acetate. On the other hand, methanol is used in the polymerization of vinyl acetate if necessary, and the amount thereof can be up to 30% by weight based on the total amount of vinyl acetate and higher aldehyde. As for the timing of this addition, it may be added before the start of the polymerization reaction, or it may be added at an appropriate time after the start of the polymerization reaction. After the polymerization reaction is completed, the polyvinyl acetate from which vinyl acetate has been removed from the reaction solution is saponified in methanol alone or a methyl acetate-methanol mixed solvent in which the weight ratio of methyl acetate to methanol is 0 to 1.5.
Generally, unpolymerized vinyl acetate is removed by blowing methanol vapor into the reaction solution after the polymerization reaction, and in this case polyvinyl acetate is obtained as a methanol solution containing a small amount of unreacted higher aldehyde. Therefore, methyl acetate alone or a methanol-monomethyl acetate solution is added to this polyvinyl acetate solution, if necessary. The weight ratio of methyl acetate to methanol at the start of the saponification reaction varies depending on the type of monomers to be suspended, but when the weight ratio is 1.5 or more, it is industrially difficult to produce the desired dispersion stabilizer. It is difficult and therefore inappropriate. During such a saponification reaction, methyl acetate is produced as a by-product as the reaction progresses, so its concentration increases somewhat, but this does not pose any problem in carrying out this process.

As a catalyst for the saponification reaction, an alkali, particularly a methanol solution of sodium hydroxide, is preferably used. Saponification degree is 70 to 95 moles? Carry out the saponification reaction so that the In the present invention, the temperature during saponification is 5 to 60°C.
The temperature is preferably 20 to 45°C.

The present invention will be further explained below with reference to Examples, but the present invention is not limited thereto.

Example 1 258 parts of vinyl acetate (parts by weight, the same applies hereinafter) and 35 parts of stearyl aldehyde were mixed, α,d-azobisisobutyronitrile was added as a polymerization initiator, and the mixture was heated at 53 to 61°C. Polymerize for 6 hours by keeping at a temperature of
Polymerization was stopped when the polymerization rate was 77% to obtain polyvinyl acetate.

Methanol vapor was blown to drive out unpolymerized vinyl acetate to obtain a methanol solution of polyvinyl acetate containing a trace amount of stearyl aldehyde. After adding 26 parts of methyl acetate to 172 parts of this methanol solution (polymer concentration 5070) of polyvinyl acetate, the temperature was kept at 30°C and a methanol solution of 0.5N sodium hydroxide was added. The saponification reaction was carried out by adding 0.006 equivalents and the degree of saponification was 71.7 mol? , degree of polymerization 7
30 bourivinyl alcohol was obtained. Next, in a 51 stainless steel autoclave equipped with a stirrer, water in an amount twice as much as the vinyl chloride monomer, 0.27% of the above stabilizer, and 0.2% of lauroyl peroxide as a polymerization initiator were added.
At a ratio of 70 rpm, the rotation speed is 350 r. p. m. Suspension polymerization was carried out while stirring and adjusting the temperature within the range of 50 to 60°C. The performance of the obtained polyvinyl chloride powder is shown in the table. In addition, in the table, porosity (Cc/9) indicates the pore volume measured by a mercury intrusion porosimeter,
In addition, dry blend time G) is vinyl chloride resin 100
9 and dioctyl phthalate 509 were thoroughly mixed in a beaker at room temperature for 3 minutes. The above mixture was placed in a small lipon blender kept at 90°C and stirred, and a portion of the mixture was taken out every 10 seconds, sandwiched between pieces of finished paper, and the time until dioctyl phthalate stopped leaching into the finished paper was measured. be.

Example 2 1290 parts of vinyl acetate and 25 parts of lauryl aldehyde were mixed and agglomeration polymerization was carried out using α,α5-azobisisobutyronitrile as a polymerization catalyst, followed by a saponification reaction in the same manner as in Example 1. The degree of silicification was 72.6 mol 7.
0. A terminally modified partially saponified polyvinyl alcohol having a degree of polymerization of 730 was obtained.

Suspension polymerization of vinyl chloride was carried out in the same manner as in Example 1 except that the above-mentioned polyvinyl alcohol was used as a dispersion stabilizer.The performance of the resulting polyvinyl chloride powder is shown in the table.

Example 3 1290 parts of vinyl acetate and 21 parts of 2-ethyl-hexylaldehyde were mixed and bulk polymerization was carried out using α,α5-azobisisobutyronitrile as a polymerization catalyst, and then quenched in the same manner as in Example 1. The saponification degree is 7.
3.5 mol of polyvinyl alcohol with a degree of polymerization of 706 and 740 was obtained.

Suspension polymerization of vinyl chloride was carried out in the same manner as in Example 1 except that the above polyvinyl alcohol was used as a dispersion stabilizer. The performance of the obtained polyvinyl chloride powder is shown in the table.

Example 4 1290 parts of vinyl acetate, 120 parts of methanol, and 21 parts of lauryl aldehyde were mixed and a polymerization reaction was carried out using α,α5-azobisisobutyronitrile as a polymerization catalyst, followed by saponification in the same manner as in Example 1. The reaction was carried out and the degree of silicification was 72.0 mol 70. A terminally modified partially saponified polyvinyl alcohol having a polymerization degree of 340 was obtained.

Suspension polymerization of vinyl chloride was carried out in the same manner as in Example 1 except that the above polyvinyl alcohol was used as a dispersion stabilizer.

The performance of the obtained polyvinyl chloride powder is shown in the table.

Control Example 1 2,580 parts of vinyl acetate, 500 parts of methanol, and 22 parts of acetaldehyde were mixed, and α and α were added as polymerization initiators.
Add 0.5 part of 7-azobisisobutyronitrile to perform a polymerization reaction, and perform a saponification reaction in the same manner as in Example 1 to obtain polyvinyl alcohol with a saponification degree of 72.0 mol and a polymerization degree of 71.0. I got it.

The performance of polyvinyl chloride powder obtained by carrying out suspension polymerization of vinyl chloride in the same manner as in Example 1 using the above-mentioned dispersion stabilizer is shown in the table.

Control Example 2 Polymerization and saponification reactions were carried out in the same manner as in Example 1, except that 1290 parts of vinyl acetate and 750 parts of methanol were used, and the use of acetaldehyde was omitted. Suspension polymerization of vinyl chloride was carried out in the same manner as in Example 1 using ordinary partially saponified polyvinyl alcohol having a degree of polymerization of 720 as a dispersion stabilizer, and the performance of the obtained polyvinyl chloride powder is also shown in the table.

Control Example 3 A saponification degree of 72.9 mol? , polyvinyl alcohol with a degree of polymerization of 730 was obtained.

Suspension polymerization of vinyl chloride was carried out in the same manner as in Example 1 using this polyvinyl alcohol. The performance of the obtained polyvinyl chloride powder is shown in the table. Control Example 4 The same method as in Example 1 except that n-valeraldehyde was used instead of stearylaldehyde in Example 1,
Polyvinyl alcohol with a degree of saponification of 72.5 mol% and a degree of polymerization of 720 was obtained.

Claims (1)

[Claims] 1 Bulk polymerization of vinyl acetate in the coexistence of a higher aliphatic monoaldehyde having 8 or more carbon atoms, or further polymerization in the coexistence of methanol, and the resulting polyvinyl acetate having a weight ratio of methyl acetate to methanol of 0 to 1. Average degree of polymerization obtained by alkali saponification in a mixed solvent of methyl acetate and methanol represented by .5 300 to 1500, degree of saponification 70
A dispersion stabilizer for suspension polymerization of vinyl compounds consisting of ~95 mol% polyvinyl alcohol.