JPH0588251B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a dispersion stabilizer used in the suspension polymerization of unsaturated monomers such as vinyl compounds, particularly to a dispersion stabilizer for the suspension polymerization of vinyl chloride. [Prior art] When producing vinyl chloride resin industrially, a suspension polymerization method is used in which vinyl chloride monomers are dispersed in an aqueous medium in the presence of a suspension dispersion stabilizer and polymerized using an oil-soluble catalyst. is widely practiced. In general, the factors that control the quality of the resin are polymerization rate, water
Examples include monomer ratio, polymerization temperature, amount of catalyst, and type and amount of dispersion stabilizer, among which the dispersion stabilizer is said to have the greatest influence. The performance required for a dispersion stabilizer for vinyl chloride polymerization is that it exhibits sufficient dispersion power even when used in small amounts.
It works to sharpen the particle size distribution of the vinyl chloride polymer particles obtained, and the particles have a high porosity to increase the absorption rate of plasticizer in the polymer particles and facilitate molding processability. It has the function of converging the porosity of each polymer particle within a substantially constant range in order to remove vinyl chloride monomer remaining in porous particles or improve the physical properties of molded products. can be mentioned. Vinyl chloride resins obtained using dispersion stabilizers that meet these requirements yield good molded products with almost no buildup. [Problems to be Solved by the Invention] However, as conventional dispersion stabilizers, cellulose derivatives such as methyl cellulose and carboxymethyl cellulose, partially saponified polyvinyl alcohol, etc. have been put into practical use either alone or in combination; None of them can satisfy the above requirements. As one such measure, it has been proposed to introduce carbonyl groups into polyvinyl alcohol molecules, but sufficient effects have not yet been obtained. [Means for Solving the Problem] However, as a result of intensive research in order to solve this problem, the present inventors found that the average degree of polymerization is 500 or more, and the weight average degree of polymerization (hereinafter abbreviated as Pw) and number average The ratio (Pw/
Pn) is 3.0 or less and has a carbonyl group in the molecule and a vinylene group adjacent to it.
280mμ by ultraviolet absorption spectrum of 0.1% aqueous solution
and 320mμ absorbance coefficients are 0.30 or higher and
Polyvinyl alcohol (hereinafter referred to as
The present inventors have discovered that a dispersion stabilizer for suspension polymerization of vinyl compounds consisting of PVA (abbreviated as PVA) can achieve the above object, and have completed the present invention. Pw and Pn in the dispersion stabilizer of the present invention are PVA
Gel permeation chromatography (GPC) of polyvinyl acetate obtained by reacetylation of
It is determined from measurements by The measurement is carried out under the following conditions: Equipment: HLC-802R (manufactured by Toyo Soda Kogyo Co., Ltd.) Column: GHM6 (manufactured by Toyo Soda Kogyo Co., Ltd.) x 2 Solvent: Tetrahydrofuran Temperature: 23 ± 1°C. It is an essential condition of the present invention that Pw/Pn is 3.0 or less, preferably 2.0 to 2.8, and it is difficult to obtain the effects of the present invention outside this range. Furthermore, it is necessary that PVA has a carbonyl group and a vinylene group adjacent to it, and the absorbance coefficients of 280 mμ and 320 mμ and the ratio of the absorbance coefficients according to the ultraviolet absorption spectrum of a 0.1% aqueous solution are within the above specified range. . The above-mentioned absorption at 280 mμ is due to carbonyl group-containing

[Formula] This structure is generated by a decarboxylic acid reaction of a vinyl ester residue or a dehydration reaction of a hydroxyl group. As mentioned above, the dispersion stabilizer of the present invention needs to have an absorbance coefficient of 0.3 or more at 280nμ, and more preferably one of 0.3 to 0.55, which improves sharpness of particle size distribution, uniformity of porosity, and absorption of plasticizer. It is advantageously used in terms of its good properties. In addition to absorption at 280 mμ, it must exhibit absorption at 320 mμ. The absorption of 320 mμ is

〔Illustration〕

Hereinafter, the dispersion stabilizer of the present invention will be explained in more detail by giving examples. In addition, "parts" and "%" in the examples are based on weight unless otherwise specified. Example 1 Preparation of dispersion stabilizer 1200 parts of vinyl acetate, 745 parts of methanol, and 28 parts of acetaldehyde were placed in a reactor, the atmosphere was sufficiently replaced with nitrogen, and then the external temperature was raised to 65°C. When the internal temperature reached 60°C, 2. 2'-Azobisisobutyronitrile
10 parts of methanol containing 0.172 parts were added. When the polymerization rate reaches 30%, a polymerization inhibitor is added, and then the reactor is cooled and unreacted vinyl acetate and acetaldehyde are expelled from the system together with methanol under reduced pressure. A methanol solution of was obtained. Pw/Pn at this time was 2.2. Next, take a portion of this methanol solution and adjust the concentration.
Prepare the solution to 50% and place it in a kneader, and set the solution temperature to 35%.
While keeping the temperature at ℃, add 2% sodium hydroxide-methanol solution and knead at about 35℃ to determine the average degree of polymerization.
700 polyvinyl alcohol was obtained. The polyvinyl alcohol was heated to 165°C by a conventional method.
After heat treatment for 2.5 hours, the average degree of polymerization was 700, Pw/Pn=
2.3, degree of saponification 70.0 mol%, absorbance coefficient 0.39 at 280 mμ by ultraviolet absorption spectrum of 0.1% aqueous solution,
A polyvinyl alcohol dispersion stabilizer with an absorbance coefficient of 320 mμ of 0.25 and a ratio of absorbance coefficients of 0.64 was obtained. 100 parts by weight of vinyl chloride monomer in a 100 capacity stainless steel autoclave equipped with a stirrer;
Suspension polymerization was carried out by charging 150 parts of water, 0.1 part of the dispersion stabilizer, and 0.2 part of lauroyl peroxide as a polymerization catalyst, and adjusting the temperature to 60° C. while stirring at a rotation speed of 400 rpm. Table 1 shows the performance of the obtained vinyl chloride resin particles. Examples 2-3, Comparative Examples 1-4 Experiments were conducted according to Example 1, except that the dispersion stabilizers shown in Table 1 were prepared and used according to Example 1. The results are shown in Table 1.

【table】

Claims (1)

[Claims] 1 The average degree of polymerization is 500 or more, the ratio of the weight average degree of polymerization to the number average degree of polymerization is 3.0 or less, and has a carbonyl group in the molecule and a vinylene group adjacent to it, and has ultraviolet absorption of a 0.1% aqueous solution. The absorbance coefficient of 280mμ and 320mμ according to the spectrum is 0.3 respectively.
A dispersion stabilizer for suspension polymerization of a vinyl compound, which is made of polyvinyl alcohol and has a ratio of absorbance coefficient of 320 mμ to 280 mμ of 0.30 or more with the above and 0.15 or more.