PRODUCTION METHOD FOR MODIFIED VINYL ALCOHOL POLYMER PARTICLE AND PARTICLE OBTAINED THEREBY

Abstract

A method of producing modified vinyl alcohol-based polymer particles, includes mixing vinyl alcohol-based polymer particles with a mixed medium containing unsaturated carboxylic acid, an acid catalyst, and water, wherein, by mixing the vinyl alcohol-based polymer particles with the mixed medium, the vinyl alcohol-based polymer particles are reacted with the unsaturated carboxylic acid to obtain modified vinyl alcohol-based polymer particles containing a vinyl ester unit represented by a formula (2) below, having a vinyl alcohol unit content based on the total constitutional units of 60 mol % or more and less than 95 mol %, and having an average particle diameter from 50 to 2000 μm. The production method is capable of controlling the particle shape and does not cause the problem of the residual sulfur content, and is further convenient and economically advantageous.

##STR00001##

Claims

1. A method for producing modified vinyl alcohol-based polymer particles, the method comprising: mixing vinyl alcohol-based polymer particles with a mixed medium comprising an unsaturated carboxylic acid, an acid catalyst, and water, wherein by mixing the vinyl alcohol-based polymer particles with the mixed medium, the vinyl alcohol-based polymer particles are reacted with the unsaturated carboxylic acid to obtain modified vinyl alcohol-based polymer particles comprising a vinyl ester unit, having a vinyl alcohol unit content based on a total constitutional units of 60 mol % or more and less than 95 mol %, and having an average particle diameter from 50 to 2000 μm, wherein the unsaturated carboxylic acid is a compound of formula (1): ##STR00008## wherein X denotes a carbon-carbon bond or a divalent saturated hydrocarbon group having a carbon number from 1 to 10 optionally having a branched structure, Y denotes a hydrogen atom or a saturated hydrocarbon group having a carbon number from 1 to 6 optionally having a branched structure, and Z denotes a hydrogen atom or a methyl group, and the vinyl ester unit is a unit of formula (2): ##STR00009##

2. The method according to claim 1, wherein the modified vinyl alcohol-based polymer particles have a specific surface area from 0.01 to 1.0 m.sup.2/g.

3. The method according to claim 1, wherein the mixed medium has a water content from 1 to 20 mass %.

4. The method according to claim 1, wherein the mixed medium further comprises acetic acid.

5. The method according to claim 1, wherein Y denotes a hydrogen atom.

6. The method according to claim 1, wherein X denotes a carbon-carbon bond.

7. The method according to claim 1, further comprising washing the modified vinyl alcohol-based polymer particles.

8. Modified vinyl alcohol-based polymer particles comprising a vinyl ester unit, wherein a ratio of three or more consecutive vinyl ester units to a total vinyl ester units is 30% or less, a vinyl alcohol unit content based on a total constitutional units is 60 mol % or more and less than 95 mol %, and an average particle diameter is from 50 to 2000 μm, and the vinyl ester unit is a unit of formula (2): ##STR00010## wherein X denotes a carbon-carbon bond or a divalent saturated hydrocarbon group having a carbon number from 1 to 10 optionally having a branched structure, Y denotes a hydrogen atom or a saturated hydrocarbon group having a carbon number from 1 to 6 optionally having a branched structure, and Z denotes a hydrogen atom or a methyl group.

9. The modified vinyl alcohol-based polymer particles

8. ng to claim 8, wherein a sulfur content is from 0.01 to 20000 ppm.

10. The modified vinyl alcohol-based polymer particles according to claim 8, wherein a yellow index (YI) measured in accordance with ASTM D1925 is 50 or less.

11. The modified vinyl alcohol-based polymer particles according to claim 8, wherein a content of the vinyl ester unit based on the total constitutional units is from 0.01 to 10 mol %.

12. The modified vinyl alcohol-based polymer particles according to claim 8, wherein Y denotes a hydrogen atom.

13. The modified vinyl alcohol-based polymer particles according to claim 8, wherein X denotes a carbon-carbon bond.

Description

EXAMPLES

[0065] Although the present invention is described in more detail below with reference to Examples, the present invention is not at all limited by Examples below. It should be noted that “%” and “parts” in Examples and Comparative Examples respectively indicate “mass %” and “parts by mass” unless otherwise specified.

Calculation of Vinyl Alcohol Unit Content

[0066] Using a nuclear magnetic resonance apparatus “LAMBDA 500” manufactured by JEOL Ltd., .sup.1H-NMR of modified vinyl alcohol-based polymer particles was measured at room temperature with a DMSO-d6 solvent, and the vinyl alcohol unit content of the polymer particles was calculated from an integral of a peak (from 3.4 to 4.0 ppm) derived from methine protons bonded to the hydroxyl groups and an integral of a peak (from 4.7 to 5.3 ppm) derived from methine protons of the vinyl ester groups.

Calculation of Degree of Modification

[0067] Using a nuclear magnetic resonance apparatus “LAMBDA 500” manufactured by JEOL Ltd., .sup.1H-NMR of modified vinyl alcohol-based polymer particles was measured at room temperature with a DMSO-d6 solvent, and a degree of modification of the polymer particles [content (mol %) of the vinyl ester unit represented by the formula (2) based on the total constitutional units] was calculated from an integral of a peak (from 5.0 to 7.5 ppm) derived from olefin protons. For example, in Example 1, the degree of modification was calculated from an integral of the peak derived from olefin protons appearing at 5.6 ppm and 6.0 ppm.

Calculation of Ratio of Three or more Consecutive Vinyl Ester Groups

[0068] Using a nuclear magnetic resonance apparatus “LAMBDA 500” manufactured by JEOL Ltd., .sup.1H-NMR of modified vinyl alcohol-based polymer particles was measured at 80° C. with a DMSO-d6 solvent. A ratio of the three or more consecutive vinyl ester groups based on the total vinyl ester units was calculated in accordance with a formula below from an integral of (a) from 4.7 to 4.9 ppm (central methine proton in hydroxyl group-vinyl ester group-hydroxyl group), (b) from 4.9 to 5.05 ppm (central methine proton in hydroxyl group-vinyl ester group-vinyl ester group), and (c) from 5.05 to 5.2 ppm (central methine proton in three consecutive vinyl ester groups).

Ratio of Three or more Consecutive Vinyl Ester Groups (%)=(c)/{(a)+(b)+(c)}×100

Measurement of Average Particle Diameter

[0069] Modified vinyl alcohol-based polymer particles were dispersed in methanol and a volume-average particle diameter (μm) was measured using a laser diffractometer “LA-950V2” manufactured by Horiba, Ltd.

Measurement of Specific Surface Area

[0070] Using a specific surface area measurement apparatus “MONOSORB” manufactured by Yuasa Ionics Co., Ltd., a specific surface area (m.sup.2/g) of modified vinyl alcohol-based polymer particles was determined by the BET single point method employing nitrogen adsorption.

Measurement of Hue (Yellow Index: YI)

[0071] The YI (ASTM D1925) of the modified vinyl alcohol-based polymer particles obtained in any of Examples and Comparative Examples was measured using a spectral colorimeter “CM-8500d” manufactured by Konica Minolta, Inc. (using D65 light source, CM-A120 white calibration plate, CM-A126 petri dish set, regular reflection measurement SCE, measurement diameter cp 30 mm). To a petri dish, 5 g of the sample was added and the petri dish was shaken by lightly tapping on a side not to press the powder to uniformly spread the powder. In this state, measurement was performed 10 times in total (remeasured after shaking the petri dish once in each time) to define an average value of them as the YI of the polymer particles.

Evaluation of Photosensitivity

[0072] To an aqueous solution dissolving the modified vinyl alcohol-based polymer particles obtained in any of Examples and Comparative Examples (concentration of 5 mass %), 1 part by mass of 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone as a photoinitiator was added based on 100 parts by mass of the particles and then dissolved to prepare a coating liquid. The coating liquid was cast into a 15 cm×15 cm mold formed by folding the edges of a polyethylene terephthalate film, and the solvent was sufficiently evaporated at room temperature under atmospheric pressure to obtain a film with a thickness of approximately 100 μm. The film was irradiated with ultraviolet rays at an intensity of 10 J/cm.sup.2 to prepare an evaluation film and then measure a mass (W2). The evaluation film thus obtained was immersed in a boiling water for 1 hour and then taken out of the water. After vacuum drying at 40 ° C. for 12 hours, a mass (W1) was measured. From the mass (W1) thus obtained and the mass (W2) of the film before immersion, an elution rate under the boiling conditions was calculated in accordance with a formula below, and the elution rate was used as an index of photosensitivity (a lower elution rate indicates higher photosensitivity). It should be noted that, in the case where an evaluation film was dissolved during immersion in water, it was evaluated as “unmeasurable” and indicated with “-” in Table 1.

Elution Rate (mass %)=100×([W2]−[W1])/[W2]

Evaluation of Lipophilicity

[0073] In 4.5 parts by mass of 4-acryloylmorpholine as an organic compound, 0.5 parts by mass of the modified vinyl alcohol-based polymer particles obtained in any of Examples and Comparative Examples were immersed at room temperature for 2 days. The particles were, 2 days later, filtered with a PET mesh with an opening diameter of 56 pm and the liquid on the surface was sufficiently absorbed by a paper wipe. From a mass (W3) of the swollen particles after immersion and a mass (W4) of the particles before immersion, a degree of swelling in ACMO was calculated in accordance with a formula below to define the affinity for organic substances, that is, an index of lipophilicity (a higher degree of swelling indicates higher lipophilicity).

[0074] Degree of Swelling=W3/W4

[0075] A: Degree of Swelling of 1.6 or more

[0076] B: Degree of Swelling of 1.3 or more and less than 1.6

[0077] C: Degree of Swelling of less than 1.3

Evaluation of Liquid Flow

[0078] The modified vinyl alcohol-based polymer particles obtained in any of Examples and Comparative Examples were irradiated with electron beams at 150 kGy to impart water resistance by crosslinking. A chromatographic column (having a glass filter, with an inner diameter of 50 mm and an opening diameter from 40 to 50 μm, and a stopcock) was filled with 100 parts by mass of the modified vinyl alcohol-based polymer particles thus crosslinked. The column was then filled with 130 parts by mass of a mixture of methanol/water=9/1 (mass ratio), and then the stopcock was opened to start filtration. The filtrate was recovered and the point when 90% (i.e., 117 parts by mass) of the added mixture was collected as the filtrate was defined as “completion of filtration” and the liquid flow was evaluated by the time taken from start of filtration to completion of filtration.

[0079] A: Filtration Completed in less than 150 seconds

[0080] B: Filtration Completed in 150 seconds or more and less than 300 seconds

[0081] C: Filtration Completed taking 300 seconds or more

Evaluation of Sulfur Content

[0082] The modified vinyl alcohol-based polymer particles obtained in any of Examples and Comparative Examples were dried at 80° C. for 12 hours and then a sulfur content of the modified vinyl alcohol-based polymer particles was measured using an organic element analyzer 240011 manufactured by PerkinElmer, Inc.

Example 1

[0083] Into a reactor provided with a stirrer, a reflux condenser, and an inlet port, 538.7 parts by mass of methacrylic acid, 28.4 parts by mass of ion exchange water, 1.3 parts by mass of p-methoxyphenol, and 9.1 parts by mass of paratoluenesulfonic acid monohydrate were sequentially charged, and while stirring at room temperature,100 parts by mass of a commercially available polyvinyl alcohol resin (viscosity-average degree of polymerization of 500, degree of saponification of 82 mol %, and average particle diameter of 710 pm) was added and heated, while stirring, to 75° C. and reacted in the state of a slurry for 3 hours. Then, the mixture was cooled to room temperature and the contents were filtrated to recover modified polyvinyl alcohol particles. The particles were washed with a large amount of methanol and then dried at 40° C. and 1.3 Pa for 12 hours to obtain target particles. The structural analysis results and the physical property evaluation results of the modified vinyl alcohol-based polymer particles thus obtained are shown in Table 1.

Example 2

[0084] Into a reactor provided with a stirrer, a reflux condenser, and an inlet port, 527.3 parts by mass of methacrylic acid, 39.7 parts by mass of ion exchange water, 1.3 parts by mass of p-methoxyphenol, and 7.5 parts by mass of 47% sulfuric acid were sequentially charged, and while stirring at room temperature, 100 parts by mass of a commercially available polyvinyl alcohol resin (viscosity-average degree of polymerization of 1700, degree of saponification of 88 mol %, and average particle diameter of 750 μm) was added and heated, while stirring, to 70° C. and reacted in the state of a slurry for 2 hours. Then, posttreatment was performed in the same manner as in Example 1 to obtain target particles. The structural analysis results and the physical property evaluation results of the modified vinyl alcohol-based polymer particles thus obtained are shown in Table 1.

Example 3

[0085] Into a reactor provided with a stirrer, a reflux condenser, and an inlet port, 476.3 parts by mass of methacrylic acid, 62.4 parts by mass of acetic acid, 28.4 parts by mass of ion exchange water, 1.3 parts by mass of p-methoxyphenol, and 9.1 parts by mass of paratoluenesulfonic acid monohydrate were sequentially charged, and while stirring at room temperature,100 parts by mass of a commercially available polyvinyl alcohol resin (viscosity-average degree of polymerization of 500, degree of saponification of 82 mol %, and average particle diameter of 710 μm) was added and heated, while stirring, to 65° C. and reacted in the state of a slurry for 5 hours. Then, posttreatment was performed in the same manner as in Example 1 to obtain target particles. The structural analysis results and the physical property evaluation results of the modified vinyl alcohol-based polymer particles thus obtained are shown in Table 1.

Example 4

[0086] Into a reactor provided with a stirrer, a reflux condenser, and an inlet port, 464.9 parts by mass of methacrylic acid, 85.1 parts by mass of acetic acid, 17.0 parts by mass of ion exchange water, 1.3 parts by mass of p-methoxyphenol, and 3.9 parts by mass of paratoluenesulfonic acid monohydrate were sequentially charged, and while stirring at room temperature, 100 parts by mass of a commercially available polyvinyl alcohol resin (viscosity-average degree of polymerization of 500, degree of saponification of 74 mol %, and average particle diameter of 696 μm) was added and heated, while stirring, to 60° C. and reacted in the state of a slurry for 8 hours. Then, posttreatment was performed in the same manner as in Example 1 to obtain target particles. The structural analysis results and the physical property evaluation results of the modified vinyl alcohol-based polymer particles thus obtained are shown in Table 1.

Example 5

[0087] Into a reactor provided with a stirrer, a reflux condenser, and an inlet port, 476.3 parts by mass of 4-pentenoic acid, 62.4 parts by mass of acetic acid, 28.4 parts by mass of ion exchange water, 1.3 parts by mass of p-methoxyphenol, and 9.1 parts by mass of paratoluenesulfonic acid monohydrate were sequentially charged, and while stirring at room temperature, 100 parts by mass of a commercially available polyvinyl alcohol resin (viscosity-average degree of polymerization of 500, degree of saponification of 82 mol %, and average particle diameter of 710 μm) was added and heated, while stirring, to 65° C. and reacted in the state of a slurry for 2 hours. Then, posttreatment was performed in the same manner as in Example 1 to obtain target particles. The structural analysis results and the physical property evaluation results of the modified vinyl alcohol-based polymer particles thus obtained are shown in Table 1.

[0088] It should be noted that, as a result of .sup.1H-NMR measurement of the modified vinyl alcohol-based polymer particles thus obtained, the olefin proton peak derived from the unsaturated hydrocarbon group and the methine proton peak of the vinyl ester group were overlapped, and thus it was not possible to calculate the ratio of the three or more consecutive vinyl ester groups. Then, the modified vinyl alcohol-based polymer particles were dissolved (modified vinyl alcohol-based polymer particle content of 5 wt %) in water, and then 1 mol of propanethiol was added per mol of the olefin, and 1 mol of 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone was further added as a photoinitiator per mol of propanethiol. The solution thus prepared was irradiated with ultraviolet rays at an intensity of 3000 mJ/cm.sup.2. The solution thus obtained was added to a large amount of methanol to precipitate polymer particles, and then the particles were analyzed by .sup.1H-NMR and this time it was possible to calculate the ratio of the three or more consecutive vinyl ester groups because the olefin proton peak was disappeared due to the addition of thiol.

Example 6

[0089] Into a reactor provided with a stirrer, a reflux condenser, and an inlet port, 499.0 parts by mass of acrylic acid, 39.7 parts by mass of acetic acid, 28.4 parts by mass of ion exchange water, 1.3 parts by mass of p-methoxyphenol, and 3.4 parts by mass of paratoluenesulfonic acid monohydrate were sequentially charged, and while stirring at room temperature,100 parts by mass of a commercially available polyvinyl alcohol resin (viscosity-average degree of polymerization of 500, degree of saponification of 88 mol %, and average particle diameter of 680 μm) was added and heated, while stirring, to 60° C. and reacted in the state of a slurry for 7 hours. Then, posttreatment was performed in the same manner as in Example 1 to obtain target particles. The structural analysis results and the physical property evaluation results of the modified vinyl alcohol-based polymer particles thus obtained are shown in Table 1.

Example 7

[0090] Into a reactor provided with a stirrer, a reflux condenser, and an inlet port, 476.3 parts by mass of methacrylic acid, 51.0 parts by mass of acetic acid, 39.7 parts by mass of ion exchange water, 1.3 parts by mass of p-methoxyphenol, and 4.2 parts by mass of paratoluenesulfonic acid monohydrate were sequentially charged, and while stirring at room temperature,100 parts by mass of a commercially available polyvinyl alcohol resin (viscosity-average degree of polymerization of 1700, degree of saponification of 99.5 mol %, and average particle diameter of 128 μm) was added and heated, while stirring, to 80° C. and reacted in the state of a slurry for 5 hours. Then, posttreatment was performed in the same manner as in Example 1 to obtain target particles. The structural analysis results and the physical property evaluation results of the modified vinyl alcohol-based polymer particles thus obtained are shown in Table 1.

Example 8

[0091] Into a reactor provided with a stirrer, a reflux condenser, and an inlet port, 100 parts by mass of a commercially available polyvinyl alcohol resin (viscosity-average degree of polymerization of 500, degree of saponification of 82 mol %, and average particle diameter of 710 μm) was charged, and while stirring at room temperature, a mixture of 56.0 parts by mass of methacrylic acid, 7.3 parts by mass of acetic acid, 3.3 parts by mass of ion exchange water, 0.3 parts by mass of p-methoxyphenol, and 9.1 parts by mass of paratoluenesulfonic acid monohydrate, mixed in advance, was added in small portions. The mixture was sufficiently stirred and uniformly blended into the entire polyvinyl alcohol resin and then heated, while stirring, to 65° C. and reacted in the state of powder for 5 hours. Then, the powder was washed with a large amount of methanol and then dried at 40° C. and 1.3 Pa for 12 hours to obtain target particles. The structural analysis results and the physical property evaluation results of the modified vinyl alcohol-based polymer particles thus obtained are shown in Table 1.

Example 9

[0092] Into a reactor provided with a stirrer, a reflux condenser, and an inlet port, 564.2 parts by mass of methacrylic acid, 2.8 parts by mass of ion exchange water, 1.3 parts by mass of p-methoxyphenol, and 2.6 parts by mass of paratoluenesulfonic acid monohydrate were sequentially charged, and while stirring at room temperature,100 parts by mass of a commercially available polyvinyl alcohol resin (viscosity-average degree of polymerization of 500, degree of saponification of 74 mol %, and average particle diameter of 696 μm) was added and heated, while stirring, to 75° C. and reacted in the state of a slurry for 4 hours. Then, posttreatment was performed in the same manner as in Example 1 to obtain target particles. The structural analysis results and the physical property evaluation results of the modified vinyl alcohol-based polymer particles thus obtained are shown in Table 1.

Comparative Example 1

[0093] A commercially available polyvinyl alcohol resin (viscosity-average degree of polymerization of 500, degree of saponification of 82 mol %, and average particle diameter of 710 μm) was evaluated. The structural analysis results and the physical property evaluation results are shown in Table 1.

Comparative Example 2

[0094] Into a reactor provided with a stirrer, a reflux condenser, and an inlet port, 400.0 parts by mass of dimethyl sulfoxide, and 100 parts by mass of a commercially available polyvinyl alcohol resin (viscosity-average degree of polymerization of 500, degree of saponification of 88 mol %, and average particle diameter of 680 μm) vacuum dried at 80° C. for 24 hours in advance were added and heated, while stirring, to 100° C. to obtain a homogeneous solution. To the solution, 66.7 parts by mass of methyl methacrylate and 1,1 parts by mass of phenothiazine were added and stirred until homogeneity. To the solution thus obtained, 1.9 parts by mass of sodium acetate was added as a transesterification catalyst and reacted for 5 hours and then left for cooling at room temperature. DMSO was added to the reaction solution for dilution, and then dropped into methanol to isolate the polymer and dried at 40° C. and 1.3 Pa for 12 hours. The structural analysis results and the physical property evaluation results of the modified vinyl alcohol-based polymer particles thus obtained are shown in Table 1.

Comparative Example 3

[0095] Into a reactor provided with a stirrer, a reflux condenser, and an inlet port, 400.0 parts by mass of dimethyl sulfoxide, and 100 parts by mass of a commercially available polyvinyl alcohol resin (viscosity-average degree of polymerization of 500, degree of saponification of 82 mol %, and average particle diameter of 710 μm) vacuum dried at 80° C. for 24 hours in advance were added and heated, while stirring, to 100° C. to obtain a homogeneous solution. To the solution, 64.4 parts by mass of 3,3-methyl dimethylpentenoate was added and stirred until homogeneity. To the solution thus obtained, 0.4 parts by mass of tetramethylammonium methyl carbonate was added as a transesterification catalyst and reacted for 5 hours and then left for cooling at room temperature. DMSO was added to the reaction solution for dilution, and then dropped into methanol to isolate the polymer and dried at 40° C. and 1.3 Pa for 12 hours. The structural analysis results and the physical property evaluation results of the modified vinyl alcohol-based polymer particles thus obtained are shown in Table 1.

Comparative Example 4

[0096] Into a reactor provided with a stirrer, a reflux condenser, and an inlet port, 288.0 parts by mass of ion exchange water was charged, and 100 parts by mass of a commercially available polyvinyl alcohol resin (viscosity-average degree of polymerization of 500, degree of saponification of 98 mol %, and average particle diameter of 723 μm) was added while stirring, heated to 95° C., and heated and stirred for 3 hours to obtain a homogeneous solution. The solution was cooled to room temperature, and 329.2 parts by mass of methacrylic acid, 228.8 parts by mass ofacetic acid, 2 parts by mass of p-methoxyphenol, and 27.0 parts by mass of a 36% aqueous hydrochloric acid solution were sequentially charged while stirring, heated to 80° C. while stirring, and reacted in the state of a homogeneous solution for 2 hours, and then cooled to room temperature. The solution thus obtained was diluted and added in small portions to a large amount of strongly stirred methanol to precipitate microparticles of the modified vinyl alcohol-based polymer. The precipitate was recovered and further washed with a large amount of methanol, and then dried at 40° C. and 1.3 Pa for 12 hours to obtain target microparticles. The structural analysis results and the physical property evaluation results of the modified vinyl alcohol-based polymer particles thus obtained are shown in Table 1.

TABLE-US-00001 TABLE 1 Vinyl Alcohol-Based Polymer Particle (Base Polymer) Average Degree of Degree of Particle Medium Water Catalyst Reaction Polymerization Saponification Diameter (Substrate) Content .sup.1) Type Amount .sup.2) Temperature Unit — mol % μm — mass % — mol ° C. h Example 1 500 82 710 Methacrylic 5 p-TsOH•H.sub.2O 0.03 75 3 Acid Example 2 1700 88 750 Methacrylic 7 47% H.sub.2SO.sub.4 0.02 70 2 Acid Example 3 500 82 710 Methacrylic 5 p-TsOH•H.sub.2O 0.03 65 5 Acid/ Acetic Acid Example 4 500 74 696 Methacrylic 3 p-TsOH•H.sub.2O 0.015 60 8 Acid/ Acetic Acid Example 5 500 82 710 4-Pentenoic 5 p-TsOH•H.sub.2O 0.03 65 2 Acid/ Acetic Acid Example 6 500 88 680 Acrylic Acid/ 5 p-TsOH•H.sub.2O 0.01 60 7 Acetic Acid Example 7 1700 99.5 128 Methacrylic 7 p-TsOH•H.sub.2O 0.01 80 5 Acid/ Acetic Acid Example 8 500 82 710 Methacrylic 5 p-TsOH•H.sub.2O 0.03 65 5 Acid/ Acetic Acid Example 9 500 74 696 Methacrylic 0.5 p-TsOH•H.sub.2O 0.01 75 4 Acid Comparative 500 82 710 — — — — — — Example 1 Comparative 500 88 680 Methyl 0.2 AcONa 0.01 100 5 Example 2 Methacrylate/ DMSO Comparative 500 82 710 Mpm/Dmso 0.2 [Me.sub.4N][MeOCOO] 0.001 100 5 Example 3 Comparative 500 98 723 Methacrylic 35 36% HCl aq. 0.1 80 2 Example 4 Acid/ Acetic Acid Structure of Modified Vinyl Alcohol-Based Polymer Particle Reaction Time Ratio of Vinyl Three or More Physical Properties of Modified Vinyl Alcohol Consecutive Average Specific Alcohol-Based Polymer Degree of Unit Vinyl Ester Particle Surface Photosensitivity Liquid Sulfur Modification Content Groups Diameter Area (Elution Rate) Lipophilicity Flow Yi Content Unit mol % mol % % μm m.sup.2/g mass % — — — ppm Example 1 3.9 94.0 10.5 671 0.29 8.7 B A 12.0 1200 Example 2 0.8 93.0 14.8 722 0.3 5.2 B A 18.5 510 Example 3 1.4 81.6 13.5 685 0.29 13.5 A A 11.5 980 Example 4 0.9 73.1 24.0 655 0.32 17.4 A B 25.0 2400 Example 5 2.8 79.2 16.7 680 0.31 35.8 A A 11.5 1030 Example 6 1.0 88.0 15.1 710 0.31 4.8 A A 12.0 450 Example 7 1.2 91.0 8.5 125 1.4 5.0 A B 12.5 430 Example 8 1.5 81.5 13.3 692 0.29 12.7 A A 11.3 780 Example 9 0.9 76.0 16.3 665 0.31 15.5 A B 68.0 2300 Comparative 0.0 82.0 51.2 710 0.32 — C A 9.0 20 Example 1 Comparative 2.8 79.2 39.1 35 0.38 8.5 C C 26.3 28500 Example 2 Comparative 2.5 85.0 13.3 43 0.44 40.2 A C 58.0 43000 Example 3 Comparative 2.2 81.0 9.8 23 0.44 13.3 A C 11.2 18 Example 4 .sup.1) Water Content in Mixed Medium .sup.2) Amount of Catalyst added per mol of Hydroxyl Group in Vinyl Alcohol-Based Polymer

[0097] As clearly seen from Examples 1 through 9, the production method of the present invention allows modification without changing the particle shape, and thus allows convenient isolation of the modified vinyl alcohol-based polymer particles without operation of precipitating the reaction product in a poor solvent. The modified vinyl alcohol-based polymer particles of the present invention had excellent high-energy beam reactivity, and had excellent liquid flow, lipophilicity, and hue when used as a column filler after crosslinking. Since the production method of the present invention did not use DMSO, it was also possible to suppress contamination of the sulfur content.

[0098] When vinyl alcohol-based polymer particles were reacted by dissolving in a solvent as in Comparative Examples 2 through 4, modified vinyl alcohol-based polymer particles as a reaction product had to be precipitated in a poor solvent for isolation, and thus the operation was complicated and the particle shape was not readily controlled. The unmodified vinyl alcohol-based polymer particles in Comparative Example 1 did not exhibit photosensitivity. The vinyl alcohol-based polymer particles having the ratio of the three or more consecutive vinyl ester groups of more than 30% in Comparative Examples 1 and 2 had low lipophilicity. As in Comparative Examples 2 through 4, the modified vinyl alcohol-based polymer particles obtained by reacting while the vinyl alcohol-based polymer particles were dissolved had an average particle diameter of less than 50 μm and had poor liquid flow. As in Comparative Examples 2 and 3, use of DMSO caused an extremely large content of sulfur in the modified vinyl alcohol-based polymer particles.

Example 10

[0099] The modified vinyl alcohol-based polymer particles obtained in Example 1 was subjected to evaluation as a column filler. The particles were irradiated with electron beams at 150 kGy for impartation of water resistance by crosslinking. A chromatographic column (having a glass filter with an inner diameter of 50 mm and an opening diameter from 40 to 50 μm and a stopcock) was filled with 100 parts by mass of the modified vinyl alcohol-based polymer particles thus crosslinked and 1000 parts by mass of a methanol/water=9/1 (mass ratio) solution was flown as an eluate to wet the polymer particles. By the polymer particles in an upper area of the column, a methanol/water=9/1 (mass ratio) solution containing 10 mass % of ACMO was adsorbed, and then 100 parts by mass of a methanol/water=9/1 (mass ratio) solution was flown as an eluate. The liquid was recovered from a column outlet for analysis.

[0100] During the above test, good liquid flow was maintained. The recovered liquid was analyzed by .sup.1H-NMR and no ACMO was contained in the recovered liquid, and thus it was confirmed that ACMO was retained in the modified vinyl alcohol-based polymer particles. The recovered liquid was subjected to elementary analysis and found that the sulfur content in the recovered liquid was 10 ppm.