Dispersion stabilizer for suspension polymerization, and manufacturing method for vinyl resin

Abstract

A dispersion stabilizer for suspension polymerization of vinyl compounds comprising a vinyl alcohol polymer (A) which has a saponification degree of 30 mol % or more and less than 60 mol % and a viscosity-average polymerization degree (P) of more than 200 and less than 600, and has a terminal alkyl group having 6 to 18 carbon atoms, and in which a content of monomer units having an oxyalkylene group is 0.3 mol % or less and the relationship between the viscosity-average polymerization degree (P) and a modification rate (S) (mol %) of the alkyl group satisfies Formula (1). Thus, there can be provided a dispersion stabilizer for suspension polymerization with which, during suspension polymerization of vinyl compounds including vinyl chloride, even when it is used in a small amount, the absorbency of a plasticizer is high, resulting in easy processing and formation of coarse particles is little and the remaining monomer components can be easily removed.
50≦S×P/1.880<100  (1)

Claims

1. A solution or dispersion, comprising: a dispersion stabilizer; and methanol or a compound (C) of formula (I) ##STR00003## wherein R.sup.1, R.sup.2 and R.sup.5 represent, independently of each other, a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; R.sup.3 represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or a hydroxyalkyl group having 1 to 6 carbon atoms; R.sup.4 represents a hydrogen atom, a hydroxyl group or an alkoxyl group having 1 to 6 carbon atoms; n represents an integer of 1 to 6, wherein a content of methanol or the compound (C) in the solution or dispersion is 1 to 50% by mass, and wherein the dispersion stabilizer comprises: a vinyl alcohol polymer (A) which has a saponification degree of 35 mol % or more and less than 60 mol % and a viscosity-average polymerization degree (P) of more than 200 and 400 or less, and has a terminal alkyl group having 6 to 18 carbon atoms, wherein a content of monomer units having an oxyalkylene group is 0.3 mol % or less and the relationship between the viscosity-average polymerization degree (P) and a modification rate (S)(mol %) of the alkyl group satisfies Formula (1):
50≦S×P/1.880<100  (1); and a vinyl alcohol polymer (B) having a saponification degree of 65 mol % or more and a viscosity-average polymerization degree of 600 or more, wherein a mass ratio between the vinyl alcohol polymer (A) and the vinyl alcohol polymer (B) (A/B) is 10/90 to 55/45.

2. The solution or dispersion of claim 1, wherein a block character of the residual vinyl ester groups in the vinyl alcohol polymer (A) is 0.6 or less.

3. The solution or dispersion of claim 1, wherein the terminal alkyl group has 8 to 15 carbon atoms.

4. The solution or dispersion of claim 1, wherein the terminal alkyl group is a straight-chain alkyl group or a branched alkyl group.

5. A method for manufacturing a vinyl resin, comprising conducting suspension-polymerization of vinyl compounds in the presence of the solution or dispersion of claim 1.

6. The method of claim 5, comprising: charging a pre-prepared solution or dispersion comprising the dispersion stabilizer and methanol or a compound (C) of formula (I) in a reactor; and then initiating suspension polymerization: ##STR00004## wherein R.sup.1, R.sup.2 and R.sup.5 represent, independently of each other, a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; R.sup.3 represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or a hydroxyalkyl group having 1 to 6 carbon atoms; R.sup.4 represents a hydrogen atom, a hydroxyl group or an alkoxyl group having 1 to 6 carbon atoms; and n represents an integer of 1 to 6.

7. The method of claim 5, wherein the suspension polymerization is conducted at a temperature of 60° C. or higher.

Description

EXAMPLES

(1) The present invention will be further detailed with reference to Examples. In Examples and Comparative Examples below, “part (s)” and “%” denote, unless otherwise stated, part(s) by mass and % by mass, respectively.

(2) PVA(A)s produced by the production examples below were evaluated by the following methods.

(3) [Viscosity-Average Polymerization Degree of PVA]

(4) A viscosity-average polymerization degree of PVA was calculated using Nakajima's equation (Akio Nakajima, “Kobunshi-Kagaku” (Polymer Science) 6 (1949)) from a limiting viscosity determined for an acetone solution of the vinyl ester polymer produced by substantially completely saponifying a PVA polymer followed by acetylization.

(5) [Saponification Degree of PVA]

(6) A saponification degree of PVA can be determined by measuring a ratio of hydroxyl groups to residual acetic acid groups by means of .sup.1H-NMR or as described in JIS K6726. In this example, a saponification degree was determined as described in JIS K6726. However, in PVA produced by saponifying a vinyl ester polymer synthesized by co-polymerization using an unsaturated monomer having an oxyalkylene group, repeating units in PVA contain, in addition to repeating units of a vinyl ester monomer and repeating units of vinyl alcohol, repeating units of an unsaturated monomer having an oxyalkylene group. Therefore, in the equation calculating a saponification degree described in JIS K6726, a saponification degree was calculated with correction using an average molecular weight adding the unsaturated monomer units co-polymerized. A saponification degree determined by the above method is substantially equal to that determined by .sup.1H-NMR.

(7) [Block Character of PVA]

(8) A block character of the residual vinyl ester groups in PVA was determined as follows; the PVA was subjected to .sup.13C-NMR spectrometry in a mixed solvent of deuterated water and deuterated methanol at a measurement temperature of 70° C. with a cumulative number of 18,000 to give integrated values of a methylene carbon peak sandwiched between a residual ester group and a hydroxyl group, a methylene carbon peak sandwiched between residual ester groups and a methylene carbon peak sandwiched between hydroxyl groups, from which a block character was determined. Measuring methods and calculation methods are described in “Poval” (Kobunshi Kanko Kai, published 1984, pp. 246 to 249) and Macromolecules, 10, 532 (1977).

Production Example 1 (Production of PVA(A1))

(9) In a polymerization can were charged 1174 parts of vinyl acetate (hereinafter, abbreviated as “VAc”), 626 parts of methanol and 0.43 parts of n-dodecanethiol (hereinafter, abbreviated as “DDM”). After nitrogen substitution, the mixture was heated to its boiling point and then 0.03% of azobisisobutyronitrile based on VAc and 10 parts of methanol were added. Immediately, addition of a solution of DDM in methanol (concentration: 5 wt %) at room temperature to the polymerization can was started, and polymerization was conducted while addition of the DDM/methanol solution was continued to keep a DDM concentration in the polymerization can constant based on VAc. Once a polymerization rate became 40%, polymerization was stopped. While adding methanol, remaining VAc together with methanol was expelled from the system under a reduced pressure, to give a solution of vinyl acetate polymer (hereinafter, abbreviated as “PVAc”) (concentration: 63%). Next, the vinyl acetate polymer at a concentration of 30% in a methanol solvent was saponified for one hour at a temperature of 40° C. with a water content 1% of the saponification solution using sodium hydroxide as a saponification catalyst at a molar ratio of 0.002 based on PVAc, neutralized with water and then dried to give PVA(A1) with a viscosity-average polymerization degree of 270, a saponification degree of 48 mol %, a block character of 0.447 and “S×P/1.880” in Formula (1) of 75.

Production Examples 2 to 9, 11, 15 to 19, 21 (Production of PVAs (A2 to 9, 11, 15 to 19, 21))

(10) PVAs (A2 to 9, 11, 15 to 19, 21) in Table 2 were produced as described in Production Example 1, changing the polymerization conditions such as the charge amounts of vinyl acetate and methanol, the type, the amount and the addition concentration of a chain transfer agent having an alkyl group used in polymerization and the amount of an initiator, and the saponification conditions such as a saponification catalyst, its amount, its concentration, its water content and a temperature. The production conditions are shown in Table 1, and the types of chain transfer agents used and the saponification conditions are shown in Tables 3 and 5.

Production Example 10 (Production of PVA(A10))

(11) PVA(A1) produced was heated at 130° C. under nitrogen atmosphere for 6 hours to give PVA(A10). The physical properties of PVA(A10) produced are shown in Table 2.

Production Examples 12 to 14 (Production of PVAs (A12 to 14))

(12) PVAs (A12 to 14) shown in Table 2 were produced as described in Production Example 1, except that the polymerization conditions such as the charge amounts of vinyl acetate and methanol, the amount and the addition concentration of a chain transfer agent having an alkyl group used in polymerization and the amount of an initiator, and the saponification conditions such as a saponification catalyst were changed, and an unsaturated monomer to be co-polymerized before initiating polymerization in an amount shown in Table 1 was charged in a polymerization can. Contents of monomer units having an oxyalkylene group in these PVAs were 0.3 mol % for PVA(A12), 1.2 mol % for PVA(A13), and 2.4 mol % for PVA(A14). The production conditions are shown in Table 1 and unsaturated monomers to be co-polymerized are shown in Table 4.

Production Example 20 (Production of PVA(A20))

(13) n-Docosanethiol used as a chain transfer agent was insoluble in methanol. Therefore, it could not be added to a polymerization can as a methanol solution at room temperature, so that PVA was not produced.

Production Example 22 (Production of PVA(A22))

(14) PVA(A22) shown in Table 2 was produced as described in Production Example 1, except that a chain transfer agent having an alkyl group was not used and the polymerization conditions such as the charge amounts of vinyl acetate and methanol and the amount of an initiator were changed. The production conditions were shown in Table 1.

(15) TABLE-US-00001 TABLE 1 Charge Saponification Unsaturated conditions Chain transfer agent monomer to be co- Catalyst having an alkyl group polymerization Initi- based on Saponi- Post- Vinyl Initial Initial ator Polymer- PVAc fication treat- acetate Methanol charge Addition charge (wt %/ ization (molar condi- ment PVA(A) (part(s)) (part(s)) Type (part(s)) (part(s)) Type (part(s)) VAc) rate (%) ratio) tions Heating Production PVA(A1) 1174 626 A 0.43 6.24 — — 0.03 40 0.002 A x Example 1 Production PVA(A2) 1174 626 A 0.43 6.24 — — 0.03 40 0.0026 A x Example 2 Production PVA(A3) 1174 626 A 0.43 6.24 — — 0.03 40 0.0016 A x Example 3 Production PVA(A4) 1170 630 B 0.31 4.50 — — 0.023 40 0.002 A x Example 4 Production PVA(A5) 1172 628 C 0.61 8.82 — — 0.023 40 0.0024 A x Example 5 Production PVA(A6) 1548 252 A 0.25 1.96 — — 0.005 21 0.0017 A x Example 6 Production PVA(A7) 1494 306 A 0.64 3.71 — — 0.004 15 0.002 A x Example 7 Production PVA(A8) 900 900 A 0.28 4.60 — — 0.1 50 0.0019 A x Example 8 Production PVA(A9) 1174 626 A 0.43 6.24 — — 0.03 40 0.002 A x Example 9 Production PVA(A10) 1174 626 A 0.43 6.24 — — 0.03 40 0.0019 A ∘ Example 10 Production PVA(A11) 1174 626 A 0.43 6.24 — — 0.03 40 0.016 B x Example 11 Production PVA(A12) 960 240 A 0.37 9.57 A  50 0.25 80 0.0045 A x Example 12 Production PVA(A13) 960 240 A 0.33 8.18 A 203 0.25 80 0.005 A x Example 13 Production PVA(A14) 924 276 A 0.31 7.56 B 350 0.25 80 0.0044 A x Example 14 Production PVA(A15) 1174 626 A 0.43 6.24 — — 0.03 40 0.0013 A x Example 15 Production PVA(A16) 1174 626 A 0.43 6.24 — — 0.03 40 0.0034 A x Example 16 Production PVA(A17) 707 1093 A 0.65 11.76  — — 0.095 50 0.0021 A x Example 17 Production PVA(A18) 1566 234 A 0.16 1.18 — — 0.004 20 0.002 A x Example 18 Production PVA(A19) 1170 630 D 0.16 2.35 — — 0.023 40 0.002 A x Example 19 Production PVA(A20) — — E — — — — — — — A x Example 20 Production PVA(A21) 720 1080 A 0.21 3.19 — — 0.1 60 0.0021 A x Example 21 Production PVA(A22) 396 1404 — — — — — 0.4 55 0.002 A x Example 22

(16) TABLE-US-00002 TABLE 2 Physical properties of PVA(A) Viscosity-average Saponification polymerization degree Block Value of PVA(A) degree (mol %) character Formula (1) Production PVA(A1) 270 48 0.447 75 Example 1 Production PVA(A2) 270 57 0.445 75 Example 2 Production PVA(A3) 270 39 0.434 75 Example 3 Production PVA(A4) 260 46 0.448 72 Example 4 Production PVA(A5) 260 53 0.438 72 Example 5 Production PVA(A6) 520 42 0.447 70 Example 6 Production PVA(A7) 260 50 0.449 89 Example 7 Production PVA(A8) 250 47 0.459 57 Example 8 Production PVA(A9) 270 50 0.379 75 Example 9 Production PVA(A10) 270 45 0.522 75 Example 10 Production PVA(A11) 270 43 0.725 75 Example 11 Production PVA(A12) 250 52 0.457 69 Example 12 Production PVA(A13) 260 54 0.479 68 Example 13 Production PVA(A14) 260 52 0.480 67 Example 14 Production PVA(A15) 270 25 0.477 75 Example 15 Production PVA(A16) 270 66 0.460 75 Example 16 Production PVA(A17) 100 53 0.450 77 Example 17 Production PVA(A18) 800 49 0.427 66 Example 18 Production PVA(A19) 250 52 0.438 75 Example 19 Production PVA(A20) — — — — Example 20 Production PVA(A21) 270 53 0.441 41 Example 21 Production PVA(A22) 250 50 0.471 — Example 22

(17) TABLE-US-00003 TABLE 3 Type Chain transfer agent Carbon number A n-Dodecanethiol 12 B n-Octanethiol 8 C n-Octadecanethiol 18 D n-Propanethiol 3 E n-Docosanethiol 22

(18) TABLE-US-00004 TABLE 4 Type Unsaturated monomer A Polyoxypropylene allyl ether (n = 25) B Polyoxyethylene allyl ether (n = 30)

(19) TABLE-US-00005 TABLE 5 PVAc Saponification Saponification concentration system system Concentation Temperature Water content Type Catalyst used (% ) (° C.) (%) A Sodium hydroxide 30 40 1 B p-Toluenesulfonic 30 65 0.5 acid

Example 1

(20) In a 5 liter autoclave were charged PVA(B1) with a polymerization degree of 2400 and a saponification degree of 80 mol % in an amount of 1000 ppm based on vinyl chloride monomers as 100 parts of an deionized-water solution, and PVA(A1) in an amount of 400 ppm based on vinyl chloride monomers as 100 parts of a solution (methanol:deionized water=3:22), and further deionized water in such an amount that the total amount of deionized water charged was to be 1640 parts. Next, 1.07 parts of a 70% solution of di(2-ethylhexyl) peroxydicarbonate in toluene was charged in the autoclave. Nitrogen was introduced to such an autoclave pressure of 0.2 MPa and then nitrogen introduced was purged, and the operation was repeated five times in total, to completely substitute the atmosphere with nitrogen for removing oxygen. Then, 940 parts of vinyl chloride was charged in the autoclave, and the content in the autoclave was heated to 65° C. with stirring, to initiate polymerization of vinyl chloride monomers. A pressure in the autoclave at the initiation of polymerization was 1.05 MPa. At the time that a pressure in the autoclave became 0.70 MPa about three hours after the initiation of polymerization, the polymerization was stopped. Unreacted vinyl chloride monomers were removed, and the polymerization product was collected and dried at 65° C. for 16 hours to give vinyl chloride polymer particles.

(21) [Evaluation of Vinyl Chloride Polymer Particles]

(22) The vinyl chloride polymer particles produced in Example 1 was evaluated for (1) an average particles size, (2) a particle size distribution, (3) a plasticizer absorbency and (4) monomer removal as described below. The evaluation results are shown in Table 6.

(23) (1) Average Particle Size

(24) A particle size distribution was measured by dry-sieve analysis using a metal mesh on the Tyler mesh scale, to determine an average particle size of vinyl chloride polymer particles.

(25) (2) Particle Size Distribution

(26) A content of JIS standard sieve 42 mesh-on was given in % by mass.

(27) A: less than 0.5%

(28) B: 0.5% or more and less than 1%

(29) C: 1% or more

(30) A content of JIS standard sieve 60 mesh-on was given in % by mass.

(31) A: less than 5%

(32) B: 5% or more and less than 10%

(33) C: 10% or more

(34) It is indicated that the smaller both contents of 42 mesh-on and of 60 mesh-on are, the less coarse particles are and the sharper a particle size distribution is, and thus the more stable polymerization is.

(35) (3) Plasticizer Absorbency

(36) A 5 mL syringe filled with 0.02 g of absorbent cotton was weighed (A g). To the syringe was added 0.5 g of vinyl chloride polymer particles, and the syringe was weighed (B g). To the syringe was added 1 g of dioctyl phthalate (DOP). After standing for 15 min, it was centrifuged at 3000 rpm for 40 min, and then was weighed (C g). Then, a plasticizer absorbency (%) was determined from the calculating formula below.
Plasticizer absorbency (%)=100×[{(C−A)/(B−A)}−1]
(4) Monomer Removability (Rate of Remaining Monomers)

(37) A polymerization product in suspension polymerization of vinyl chloride was collected, dried at 75° C. for 1 hour and 3 hours, at which the amount of remaining monomers was measured by head-space gas chromatography, to determine a rate of the remaining monomers from the formula: (the amount of remaining monomers at 3 h/the amount of remaining monomers at 1 h)×100. A smaller value means that a more proportion of remaining monomers in vinyl chloride polymer particles was removed by drying for 2 hours from 1 hour to 3 hour time points. Therefore, this value can be an indicator of ease of removing remaining monomers, that is, monomer removability.

Examples 2 to 12

(38) Suspension polymerization of vinyl chloride was conducted to produce vinyl chloride polymer particles as described in Example 1, except that each of PVAs (A2 to 12) was used. The evaluation results of the vinyl chloride polymer particles are shown in Table 6.

Example 13

(39) Suspension polymerization of vinyl chloride was conducted to produce vinyl chloride polymer particles as described in Example 1, except that PVA(A1) was charged in a polymerization tank not as a solution but as a solid. The evaluation results of the vinyl chloride polymer particles are shown in Table 6.

Example 14

(40) Suspension polymerization of vinyl chloride was conducted to produce vinyl chloride polymer particles as described in Example 1, except that PVA(B2) with a polymerization degree of 2000 and a saponification degree of 80 mol % was charged in amount of 800 ppm based on vinyl chloride monomers, PVA(A1) was charged in an amount of 200 ppm based on vinyl chloride monomers, a polymerization temperature was 57° C., and the amount of water charged was 1390 parts in total. The evaluation results of the vinyl chloride polymer particles are shown in Table 7.

Examples 15 to 22

(41) Suspension polymerization of vinyl chloride was conducted to produce vinyl chloride polymer particles as described in Example 1, except that PVA(A1) was dissolved in a mixed solvent of compound (C) shown in Table 9 and water to prepare a 30 wt % aqueous solution, which was then charged in a 5 liter autoclave in such an amount that a concentration of PVA(A1) in the aqueous solution was to be 400 ppm based on vinyl chloride monomers as a solid ratio. The evaluation results of the vinyl chloride polymer particles are shown in Table 8.

Comparative Example 1

(42) Suspension polymerization of vinyl chloride was conducted as described in Example 1, except that PVA(A1) was not used. The evaluation results of the vinyl chloride polymer particles are shown in Table 6. Here, the vinyl chloride polymer particles obtained were unsatisfactory in a plasticizer absorbency and monomer removability.

Comparative Example 2

(43) Suspension polymerization of vinyl chloride was conducted as described in Example 1, substituting PVA(A13) having polyoxypropylene units for PVA(A1). The evaluation results of the vinyl chloride polymer particles are shown in Table 6. Here, the vinyl chloride polymer particles obtained were excellent in a plasticizer absorbency and monomer removability, but vinyl chloride particles were very coarse, leading to unstable polymerization.

Comparative Example 3

(44) Suspension polymerization of vinyl chloride was conducted as described in Example 1, substituting PVA(A14) having polyoxypropylene units for PVA(A1). The evaluation results of the vinyl chloride polymer particles are shown in Table 6. Here, the vinyl chloride polymer particles obtained were unsatisfactory in a plasticizer absorbency and monomer removability.

Comparative Example 4

(45) Suspension polymerization of vinyl chloride was conducted as described in Example 1, substituting PVA(A15) with a saponification degree of 25 mol % for PVA(A1). The evaluation results of the vinyl chloride polymer particles are shown in Table 6. Here, the vinyl chloride polymer particles obtained were unsatisfactory in a plasticizer absorbency and monomer removability.

Comparative Example 5

(46) Suspension polymerization of vinyl chloride was conducted as described in Example 1, substituting PVA(A16) with a saponification degree of 66 mol % for PVA(A1). The evaluation results of the vinyl chloride polymer particles are shown in Table 6. Here, the vinyl chloride polymer particles obtained were unsatisfactory in a plasticizer absorbency and monomer removability.

Comparative Example 6

(47) Suspension polymerization of vinyl chloride was conducted as described in Example 1, substituting PVA(A17) with a viscosity-average polymerization degree of 100 for PVA(A1). The evaluation results of the vinyl chloride polymer particles are shown in Table 6. Here, the vinyl chloride polymer particles obtained were excellent in a plasticizer absorbency and monomer removability, but vinyl chloride particles were very coarse, leading to unstable polymerization.

Comparative Example 7

(48) Suspension polymerization of vinyl chloride was conducted as described in Example 1, substituting PVA(A18) with a viscosity-average polymerization degree of 800 for PVA(A1). The evaluation results of the vinyl chloride polymer particles are shown in Table 6. Here, the vinyl chloride polymer particles obtained were unsatisfactory in a plasticizer absorbency and monomer removability.

Comparative Example 8

(49) Suspension polymerization of vinyl chloride was conducted as described in Example 1, substituting PVA(A19) produced using n-propanethiol as a chain transfer agent, for PVA(A1). The evaluation results of the vinyl chloride polymer particles are shown in Table 6. Here, the vinyl chloride polymer particles obtained were unsatisfactory in a plasticizer absorbency and monomer removability.

Comparative Example 9

(50) Suspension polymerization of vinyl chloride was conducted as described in Example 1, substituting PVA(A21) in which a value of Formula (1) was 41, for PVA(A1). The evaluation results of the vinyl chloride polymer particles are shown in Table 6. Here, the vinyl chloride polymer particles obtained were unsatisfactory in a plasticizer absorbency and monomer removability.

Comparative Example 10

(51) Suspension polymerization of vinyl chloride was conducted as described in Example 1, substituting unmodified PVA(A22) synthesized without using a chain transfer agent, for PVA(A1). The evaluation results of the vinyl chloride polymer particles are shown in Table 6. Here, the vinyl chloride polymer particles obtained were unsatisfactory in a plasticizer absorbency and monomer removability. Furthermore, because a chain transfer agent was not used in synthesis of PVA(A22) as shown in Table 1, a proportion of vinyl acetate to methanol was very low in comparison with PVA(A1)). Therefore, PVA(A22) is not suitable for large scale synthesis and results in very low production efficiency.

Comparative Example 11

(52) Suspension polymerization of vinyl chloride was conducted as described in Example 14, substituting unmodified PVA(A22) synthesized without using a chain transfer agent, for PVA(A1). The evaluation results of the vinyl chloride polymer particles are shown in Table 7. Here, the vinyl chloride polymer particles obtained were unsatisfactory in a plasticizer absorbency and monomer removability. When Example 1 and 14 and Comparative Examples 10 and 11 were compared each other, PVA(A) of the present invention demonstrated prominent difference in monomer removability at a higher polymerization temperature compared to unmodified PVA(A22) synthesized without using a chain transfer agent.

(53) TABLE-US-00006 TABLE 6 Evaluation results of polyvinyl chloride particles Proportion Particle size of the Average distribution Plasticizer remaining particle 42 60 Absorbency monomer PVA (A) size (μm) Mesh-on Mesh-on (%) amount (%) Example 1 PVA(A1) 126.7 A A 17.7 3.5 Example 2 PVA(A2) 135.2 A A 17.0 8.1 Example 3 PVA(A3) 119.9 A A 17.1 8.2 Example 4 PVA(A4) 125.6 A A 17.7 3.4 Example 5 PVA(A5) 129.2 A A 17.9 3.3 Example 6 PVA(A6) 115.7 A A 16.9 7.2 Example 7 PVA(A7) 122.4 A A 18.3 2.6 Example 8 PVA(A8) 129.8 A A 17.9 7.5 Example 9 PVA(A9) 126.1 A A 18.0 3.4 Example 10 PVA(A10) 124.6 A A 17.8 4.7 Example 11 PVA(A11) 133.3 A A 17.2 8.9 Example 12 PVA(A12) 182.2 B B 17.9 4.6 Example 13 PVA(A1) 130.1 A A 17.6 3.7 Comparative — 131.1 B A 6.1 34.9 Example 1 Comparative PVA(A13) 297.6 C C 18.8 3.1 Example 2 Comparative PVA(A14) 150.3 A A 14.2 18.2 Example 3 Comparative PVA(A15) 145.2 B A 16.4 15.2 Example 4 Comparative PVA(A16) 138.5 A A 16.4 14.1 Example 5 Comparative PVA(A17) 191.2 C C 17.7 4.0 Example 6 Comparative PVA(A18) 128.4 B A 14.3 17.9 Example 7 Comparative PVA(A19) 122.2 A A 15.9 12.5 Example 8 Comparative PVA(A21) 130.6 A A 16.2 11.8 Example 9 Comparative PVA(A22) 119.4 A A 14.9 12.8 Example 10

(54) TABLE-US-00007 TABLE 7 Evaluation results of polyvinyl chloride particles Proportion Particle size of the Polymerization Average distribution Plasticizer remaining temperature particle 42 60 Absorbency monomer PVA(A) PVA(B) (° C.) size (μm) Mesh-on Mesh-on (%) amount (%) Example 1 PVA(A1) PVA(B1) 65 126.7 A A 17.7 3.5 Example 14 PVA(A1) PVA(B2) 57 156.6 A A 20.9 2.3 Comparative PVA(A22) PVA(B1) 65 119.4 A A 14.9 12.8 Example 10 Comparative PVA(A22) PVA(B2) 57 175.8 A A 18.7 7.0 Example 11

(55) TABLE-US-00008 TABLE 8 Evaluation results of polyvinyl chloride particles Proportion Particle size of the Average distribution Plasticizer remaining Compound PVA(A):Compound particle 42 60 Absorbency monomer PVA(A) (C) (C):Water size (μm) Mesh-on Mesh-on (%) amount (%) Example 15 PVA(A1) A 30:10:60 120.7 A A 17.6 3.7 Example 16 PVA(A1) A 30:3:67 126.2 A A 17.5 3.7 Example 17 PVA(A1) B 30:10:60 126.1 A A 17.5 3.6 Example 18 PVA(A1) C 30:10:60 119.3 A A 17.4 3.7 Example 19 PVA(A1) D 30:10:60 122.8 A A 17.5 3.7 Example 20 PVA(A1) E 30:10:60 129.9 A A 17.3 4.0 Example 21 PVA(A1) F 30:10:60 128.2 A A 17.4 3.9 Example 22 PVA(A1) G 30:10:60 122.4 A A 17.5 3.9

(56) TABLE-US-00009 TABLE 9 Type Compound (C) A 3-Methoxy-3-methyl-1-butanol B Ethanol C Ethylene glycol monobutyl ether D 3-Methyl-1,5-pentanediol E Ethylene glycol F Propylene glycol G Triethylene glycol

(57) As demonstrated in Examples above, when suspension polymerization of a vinyl compound was conducted using a dispersion stabilizer of the present invention for suspension polymerization of vinyl compounds comprising a vinyl alcohol polymer (A) which had a saponification degree of 30 mol % or more and less than 60 mol % and a viscosity-average polymerization degree (P) of more than 200 and less than 600, and had a terminal alkyl group having 6 to 18 carbon atoms, and in which a content of monomer units having an oxyalkylene group was 0.3 mol % or less and the relationship between the viscosity-average polymerization degree (P) and a modification rate (S) (mol %) of the alkyl group satisfied Formula (1), the polymerization was highly stable, so that formation of coarse particles was reduced and particles with a uniform particle size were produced. It allows for providing polymer particles having excellent plasticizer absorbency, particularly polymer particles which are highly effective in terms of monomer removability and in which remaining monomers can be very efficiently removed. Furthermore, in producing a vinyl resin, it allows for synthesis in a larger scale than synthesis without a chain transfer agent, with a high production efficiency. A dispersion stabilizer for suspension polymerization of the present invention is, therefore, industrially remarkably useful.