Modified polyvinyl alcohol-based polymer and its application
11492436 · 2022-11-08
Assignee
Inventors
- Jyun-Ru Sun (Taipei, TW)
- Huan-Ming Chang (Taipei, TW)
- Cheng-Fan Wang (Taipei, TW)
- Chia-Hao Hsu (Taipei, TW)
Cpc classification
C08F2/20
CHEMISTRY; METALLURGY
C08F8/30
CHEMISTRY; METALLURGY
C08F2/20
CHEMISTRY; METALLURGY
C08F8/30
CHEMISTRY; METALLURGY
International classification
Abstract
The present disclosure provides a modified polyvinyl alcohol-based polymer, which comprises a modifying monomer unit represented by Formula ##STR00001## wherein, X is a moiety comprising an alkenyl group, and the modified polyvinyl alcohol-based polymer has a saponification degree of 67 mol % to 78 mol % and a modification rate of 0.02 mol % to 1.5 mol %. The modified polyvinyl alcohol-based polymer is suitable to be used as a dispersant for suspension polymerization, to make the obtained polyvinyl chloride-based resin have reduced particle diameter and few coarse particles.
Claims
1. A modified polyvinyl alcohol-based polymer, wherein the modified polyvinyl alcohol-based polymer comprises a modifying monomer unit represented by Formula (I): ##STR00083## in Formula (I), X is a moiety comprising an alkenyl group; wherein, the modified polyvinyl alcohol-based polymer has a saponification degree of 67 percent by mole to 78 percent by mole and a modification rate of 0.02 percent by mole to 1.5 percent by mole.
2. The modified polyvinyl alcohol-based polymer as claimed in claim 1, wherein the modifying monomer unit has a structure represented by Formula (I-I): ##STR00084## in Formula (I-I), Y is —C(═O)—, —P(═O)(R.sup.41)—, —P(═S)(R.sup.42)—, —O—, —S—, or a phenylene group; in Formula (I-I), R.sup.1 is a C1 to C10 alkylene group; R.sup.21 and R.sup.22 each independently represent a C1 to C10 alkylene group; R.sup.31, R.sup.32 and R.sup.33 each independently represent a C2 to C6 alkenyl group substituted by none of halo group and aldehyde group, a C2 to C6 alkenyl group substituted by a halo group, or a C2 to C6 alkenyl group substituted by an aldehyde group; R.sup.41 and R.sup.42 each independently represent a C1 to C6 alkyl group; in Formula (I-I), o, p, n1, n2, m1, m2 and m3 each independently represent 0 or 1; the sum of m1, m2 and m3 is 1 to 3; n1 is not larger than m1; n2 is not larger than m2; p is not larger than m3.
3. The modified polyvinyl alcohol-based polymer as claimed in claim 1, wherein the modifying monomer unit has a structure represented by Formula (I-II): ##STR00085## in Formula (I-II), R.sup.1 is a C1 to C6 alkylene group; R.sup.21 and R.sup.22 each independently represent a C1 to C6 alkylene group; R.sup.31 and R.sup.32 each independently represent a C2 to C6 mono-olefin group substituted by none of halo group and aldehyde group; in Formula (I-II), o and m1 are 1; n1, n2 and m2 each independently represent 0 or 1; and n2 is not larger than m2.
4. The modified polyvinyl alcohol-based polymer as claimed in claim 1, wherein the modifying monomer unit has a structure represented by Formula (I-III): ##STR00086## in Formula (I-III), R.sup.1 is a C1 to C6 alkylene group; Y is —C(═O)—, —P(═O)(R.sup.41)—, —P(═S)(R.sup.42)—, —O—, —S—, or a phenylene group; R.sup.33 is a C2 to C6 mono-olefin group substituted by none of halo group and aldehyde group, a C2 to C6 mono-olefin group substituted by a halo group, a C2 to C6 mono-olefin group substituted by an aldehyde group, a C3 to C6 dienyl group substituted by none of halo group and aldehyde group, a C3 to C6 dienyl group substituted by a halo group, a C3 to C6 dienyl group substituted by an aldehyde group, a C4 to C6 trienyl group substituted by none of halo group and aldehyde group, a C4 to C6 trienyl group substituted by a halo group, or a C4 to C6 trienyl group substituted by an aldehyde group; in Formula (I-III), o and p each independently represent 0 or 1; m3 is 1.
5. The modified polyvinyl alcohol-based polymer as claimed in claim 1, wherein the modified polyvinyl alcohol-based polymer has a modification rate of 0.02 percent by mole to 1.26 percent by mole.
6. The modified polyvinyl alcohol-based polymer as claimed in claim 1, wherein the modified polyvinyl alcohol-based polymer comprises a first monomer unit represented by Formula (II), a second monomer unit represented by Formula (III) and a third monomer unit represented by Formula (IV): ##STR00087##
7. The modified polyvinyl alcohol-based polymer as claimed in claim 1, wherein an aqueous solution comprising 0.1 percent by weight of the modified polyvinyl alcohol-based polymer has absorbance at 215 nm wavelength ranging from 0.34 to 0.8 in UV absorption spectroscopy.
8. The modified polyvinyl alcohol-based polymer as claimed in claim 1, wherein an aqueous solution comprising 0.1 percent by weight of the modified polyvinyl alcohol-based polymer has absorbance at 280 nm wavelength ranging from 0.3 to 0.4 in UV absorption spectroscopy.
9. The modified polyvinyl alcohol-based polymer as claimed in claim 1, wherein an aqueous solution comprising 0.1 percent by weight of the modified polyvinyl alcohol-based polymer has absorbance at 320 nm wavelength ranging from 0.06 to 0.09 in UV absorption spectroscopy.
10. The modified polyvinyl alcohol-based polymer as claimed in claim 1, wherein the modified polyvinyl alcohol-based polymer has a yellow index of 10 to 35.
11. The modified polyvinyl alcohol-based polymer as claimed in claim 1, wherein the modified polyvinyl alcohol-based polymer has viscosity of 5.0 cps to 6.55 cps.
12. An application of a modified polyvinyl alcohol-based polymer, comprising mixing a vinyl chloride monomer and the modified polyvinyl alcohol-based polymer as claimed in claim 1 for suspension polymerization.
13. The application of claim 12, wherein, based on the amount of the vinyl chloride monomer, the modified polyvinyl alcohol-based polymer has an amount of 500 ppm to 1200 ppm.
Description
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
(1) Several Examples are used to demonstrate the modified polyvinyl alcohol-based polymer and its application in suspension polymerization, and several Comparative Examples are provided for comparison. A person having ordinary skill in the art can readily understand the advantages and effects of the present disclosure by the following Examples and Comparative Examples. It should be understood that the Examples exemplified in the description are merely used to demonstrate the practice of the present disclosure, not used to limit the scope of the present disclosure. A person having ordinary skill in the art can make modifications or changes according to common knowledge without departing the spirit of the present disclosure to practice or apply the present disclosure.
Modifier
(2) The CAS Nos. and structural formulae of the modifiers which can be chosen for producing the modified polyvinyl alcohol-based polymers are listed in the following Table 1, but are not limited thereto. Based on the chosen modifier, modifying monomer units of the modified polyvinyl alcohol-based polymers are also respectively shown in the following Table 1.
(3) TABLE-US-00001 TABLE 1 CAS Nos. and structural formulae of modifiers, and structural formulae of modifying monomer units. CAS No. of Structural formula of Structural formula of modifier modifier modifying monomer unit 13641-96-8
(4) Besides the modifiers listed in the above Table 1, the skilled artisan also can choose any other ingredient having an isocyanate group and at least one alkenyl group as the modifier, and conduct the modification of polyvinyl alcohol by the method described hereinafter to obtain the modified polyvinyl alcohol-based polymer.
Control: Polyvinyl Alcohol-Based Polymer
(5) Non-modified polyvinyl alcohol-based polymer is used as Control, which has a structure represented by Formula (I′). The non-modified polyvinyl alcohol-based polymer has a polymerization degree of 700, a saponification degree of about 72.36 mol %, viscosity of about 5.99 cps, YI of about 35.95.
(6) ##STR00080##
MODIFIED POLYVINYL ALCOHOL-BASED POLYMER
Examples 1 to 3
(7) For Examples 1 to 3, the polyvinyl alcohol-based polymer (Control) was modified by the following steps a to c, to obtain modified polyvinyl alcohol-based polymers:
(8) a. adding a particular amount of a modifier (as shown in the following Table 2) into 400 parts by weight of methanol (MeOH, as a swelling agent) to obtain a modifying solution;
(9) b. adding the modifying solution into 100 parts by weight of polyvinyl alcohol-based polymer having a polymerization degree of about 700 and a saponification degree of about 72.36 mol % to react at 60° C. for 6 hours, to obtain a modified product;
(10) c. washing the modified product with methanol for multiple times, centrifuging to remove liquid, and drying at 105° C. for 2 hours, to obtain the modified polyvinyl alcohol-based polymer.
Examples 4 to 6 and Comparative Example 1
(11) For Examples 4 to 6 and Comparative Example 1, the polyvinyl alcohol-based polymer (Control) was modified by the following steps a to c, to obtain modified polyvinyl alcohol-based polymers:
(12) a. adding a particular part by weight of modifier (as shown in the following Table 2) into 43 parts by weight of methyl acetate (MeAc, as a swelling agent) to obtain a modifying solution;
(13) b. adding the modifying solution into 100 parts by weight of polyvinyl alcohol-based polymer having a polymerization degree of about 700 and a saponification degree of about 72.36 mol % to react at 60° C. for 6 hours, to obtain a modified product;
(14) c. washing the modified product with methyl acetate for multiple times, centrifuging to remove liquid, and drying at 105° C. for 2 hours, to obtain the modified polyvinyl alcohol-based polymer.
Example 7
(15) For Example 7, the polyvinyl alcohol-based polymer was modified by the following steps a to c, to obtain a modified polyvinyl alcohol-based polymer:
(16) a. adding a particular part by weight of modifier (as shown in the following Table 2) into 43 parts by weight of methyl acetate (as a swelling agent) to obtain a modifying solution;
(17) b. adding the modifying solution into 100 parts by weight of polyvinyl alcohol-based polymer having a polymerization degree of about 700 and a saponification degree of about 73.11 mol % to react at 60° C. for 6 hours, to obtain a modified product;
(18) c. washing the modified product with methyl acetate for multiple times, centrifuging to remove liquid, and drying at 105° C. for 2 hours, to obtain the modified polyvinyl alcohol-based polymer.
Comparative Example 2
(19) For Comparative Example 2, the polyvinyl alcohol-based polymer was modified by the following steps a to c, to obtain modified polyvinyl alcohol-based polymers:
(20) a. adding a particular part by weight of modifier (as shown in the following Table 2) into 43 parts by weight of methyl acetate (as a swelling agent) to obtain a modifying solution;
(21) b. adding the modifying solution into 100 parts by weight of polyvinyl alcohol-based polymer having a polymerization degree of about 700 and a saponification degree of about 86.97 mol % to react at 60° C. for 6 hours, to obtain a modified product;
(22) c. washing the modified product with methyl acetate for multiple times, centrifuging to remove liquid, and drying at 105° C. for 2 hours, to obtain the modified polyvinyl alcohol-based polymer.
(23) TABLE-US-00002 TABLE 2 CAS Nos. and amount of modifiers used for Examples 1 to 7 and Comparative Examples 1 and 2, and analysis results of the modified polyvinyl alcohol-based polymers of Examples 1 to 7, Comparative Examples 1 and 2, and the polyvinyl alcohol-based polymer of Control. Modified polyvinyl alcohol- based polymer Modifier Modifi- Saponifi- Amount cation cation CAS (part by rate degree Viscosity No. weight) (mol %) (mol %) (cps) YI Example 1 886577- 5 0.34 72.54 6.04 12.86 76-0 Example 2 13641- 9 1.24 72.10 6.12 22.15 96-8 Example 3 13641- 12 1.26 72.33 6.01 14.00 96-8 Example 4 886577- 0.04 0.04 71.90 5.55 24.78 76-0 Example 5 13641- 0.39 0.21 72.06 5.45 19.97 96-8 Example 6 13641- 0.52 0.29 72.12 5.51 22.11 96-8 Example 7 107023- 1.34 0.14 73.33 6.51 27.09 60-9 Comparative 13641- 11.61 2.03 71.93 not 34.23 Example 1 96-8 soluble Comparative 13641- 0.39 0.17 86.65 5.73 24.70 Example 2 96-8 Control N/A N/A N/A 72.36 5.99 35.95
Testing Example 1: Characteristic Analysis
(24) The methods for analyzing saponification degree, viscosity and yellow index used for the modified polyvinyl alcohol-based polymers of Examples 1 to 7 and Comparative Examples 1 and 2, and the non-modified polyvinyl alcohol of Control are listed below, and the results are described earlier and listed in the above Table 2.
(25) Saponification degree: measured according to the standard method JIS K 6726(1994);
(26) Viscosity: measured according to standard method JIS K 6726(1994); and
(27) YI: measured according to standard method ASTM E313-98.
(28) As shown in the above Table 2, the modified polyvinyl alcohol-based polymers of Examples 1 to 7 have a saponification degree of about 67 mol % to 78 mol %. In addition, the modified polyvinyl alcohol-based polymers of Examples 1 to 7 have viscosity of about 5.0 cps to 6.55 cps, and YI of about 10 to 35.
Testing Example 2: Modification Rate
(29) The modified polyvinyl alcohol-based polymers of Examples 1 to 7 and Comparative Examples 1 and 2 were used as objects to be analyzed in this testing example. Each object to be analyzed was dissolved in hexadeuterodimethyl sulfoxide (DMSO-d6, item number: DLM-10-10, purchased from Cambridge Isotope Laboratories, Inc.) and prepared as a testing sample, and then analyzed at 25° C. by hydrogen-1 NMR spectroscopy (.sup.1H-NMR, Avance II 400 MHz, from Bruker) at 400 MHz and carbon-13 NMR spectroscopy (.sup.13C-NMR, Varian VNMRS-600 NMR Spectrometer, from Varian) at 600 MHz.
(30) In .sup.1H-NMR analysis results of the testing samples, the hydrogen signals corresponding to those on the alkenyl group comprised in X of the modifying monomer unit could be observed at a chemical shift position between 5.8 ppm and 6.5 ppm, and the integral value of the first characteristic peak was obtained accordingly; the hydrogen signal corresponding to that on the methyne group of the main chain connecting with a hydroxyl group could be observed at a chemical shift position between 3.5 ppm and 3.9 ppm, and the integral value of the second characteristic peak was obtained accordingly; the hydrogen signals corresponding to those on the acetoxy group of the side chain could be observed at a chemical shift position between 1.9 ppm and 2.0 ppm, and the integral value of the third characteristic peak was obtained accordingly. The modification rate of each modified polyvinyl alcohol-based polymer in mol % could be obtained by the ratio of integral value of the first characteristic peak to the sum of integral values of the first, second and third characteristic peaks. The results are shown in the above Table 2.
(31) The examples in which CAS No. 13641-96-8 are used to modify a polyvinyl alcohol-based polymer are exemplified hereinafter, and the modified polyvinyl alcohol-based polymers (such as those of Examples 2, 3, 5 and 6) have a structure represented by Formula (I″). Additionally, in the .sup.1H-NMR analysis results of these modified polyvinyl alcohol-based polymers, the hydrogen signals corresponding to those on the alkenyl group (marked at the position 1 in the following Formula (I″)) comprised in X of the modifying monomer unit could be observed at a chemical shift position between 5.8 ppm and 6.5 ppm, and the integral value of the first characteristic peak was obtained accordingly; the hydrogen signal corresponding to that on the methyne group of the main chain (marked at the position 2 in the following Formula (I″)) connecting with a hydroxyl group could be observed at a chemical shift position between 3.5 ppm and 3.9 ppm, and the integral value of the second characteristic peak was obtained accordingly; the hydrogen signals corresponding to those on the acetoxy group of the side chain (marked at the position 3 in the following Formula (I″)) could be observed at a chemical shift position between 1.9 ppm and 2.0 ppm, and the integral value of the third characteristic peak was obtained accordingly.
(32) ##STR00081##
(33) Additionally, in the .sup.13C-NMR analysis results of each testing sample, carbonyl group signals corresponding to the urethane group (marked at the positions b in the following Formula (I′″)) comprised in the modifying monomer unit could be observed at a chemical shift position between 160 ppm and 170 ppm; and signals corresponding to methyne group (marked at the position a in the following Formula (I″′)) on the main chain could be observed at a chemical shift position between 60 ppm and 80 ppm. It is confirmed that the modified polyvinyl alcohol-based polymers have a modifying monomer unit structure comprising a urethane group.
(34) ##STR00082##
(35) As shown in the above Table 2, the modification rate of Examples 1 to 7 is controlled between 0.02 mol % and 1.5 mol %. On the contrary, the modification rate of Comparative Example 1 is up to 2 mol % or more.
Testing Example 3: Absorbance
(36) The modified polyvinyl alcohol-based polymers of Examples 1 to 7 and Comparative Examples 1 and 2, and the polyvinyl alcohol-based polymer of Control were used as objects to be analyzed in this testing example. Each object to be analyzed was prepared into a 0.1 wt% aqueous solution as a testing sample. Each testing sample was poured into a cuvette with a path length of 1 centimeter, and analyzed with a UV/Vis/NIR spectrometry (V-730, from JASCO), to obtain the absorbance values of each testing sample at wavelengths of 215 nm, 280 nm and 320 nm in UV absorption spectroscopy. The results are shown in the following Table 3.
(37) The absorbance at 215 nm wavelength in UV absorption spectroscopy represents —C(═O) CH═CH— on the main-chain structure in the modified polyvinyl alcohol-based polymer; the absorbance at 280 nm wavelength in UV absorption spectroscopy represents —C(═O)—(CH═CH).sub.2— on the main-chain structure in the modified polyvinyl alcohol-based polymer; and the absorbance at 320 nm wavelength in UV absorption spectroscopy represents —C(═O)—(CH═CH).sub.3— on the main-chain structure in the modified polyvinyl alcohol-based polymer. The higher absorbance at a particular wavelength represents the more corresponding structure in the testing sample.
(38) It should be noted that, the modified polyvinyl alcohol-based polymer of Comparative Example 1 could not be homogenously dissolved in water and prepared into a 0.1 wt % aqueous solution. Thus, it is shown as “-” in the following Table 3.
(39) TABLE-US-00003 TABLE 3 Absorbance values of 0.1 wt % aqueous solution prepared by Examples 1 to 7, Comparative Examples 1 and 2 and Control at different wavelengths. Absorbance Absorbance Absorbance at 215 nm at 280 nm at 320 nm Example 1 0.608 0.364 0.075 Example 2 0.600 0.321 0.062 Example 3 0.785 0.314 0.071 Example 4 0.348 0.389 0.081 Example 5 0.394 0.380 0.080 Example 6 0.423 0.397 0.086 Example 7 0.551 0.361 0.087 Control 0.323 0.400 0.080 Comparative — — — Example 1 Comparative 0.354 0.383 0.076 Example 2
(40) As shown in the above Table 3, the 0.1 wt % aqueous solutions of the modified polyvinyl alcohol-based polymers of Examples 1 to 7 have absorbance at 215 nm wavelength of 0.34 to 0.8, absorbance at 280 nm wavelength of 0.3 to 0.4, and absorbance at 320 nm wavelength of 0.06 to 0.09.
Application of Modified Polyvinyl Alcohol-Based Polymer
(41) The modified polyvinyl alcohol-based polymer can be used as a dispersant for suspension polymerization, particularly as a dispersant which can be applied to PVC suspension polymerization. Hereinafter, the application of the modified polyvinyl alcohol-based polymer as a dispersant for PVC suspension polymerization is demonstrated.
Examples 1A to 7A, and Comparative Examples 1A and 2A
(42) In Examples 1A to 7A and Comparative Examples 1A and 2A, the modified polyvinyl alcohol-based polymers of Examples 1 to 7 and Comparative Examples 1 and 2 were used respectively as a dispersant, and the polyvinyl chloride-based resins were obtained by the method described below.
(43) First, 2.9 kilograms (kg) of vinyl chloride monomer, 2.9 grams (g) of the dispersant combination (1000 ppm) and 5.3 kg of water were added into a reactor to form a mix solution. In the dispersant combination, based on the amount of the vinyl chloride monomer, the amount of the modified polyvinyl alcohol-based polymer was 800 ppm, the amount of the partially saponified polyvinyl alcohol (polymerization degree: 200; saponification degree: 55 mol %) was 100 ppm, and the amount of hydroxypropyl methylcellulose was 100 ppm.
(44) Then, 2.9 g of di(2-ethylhexyl) peroxydicarbonate (1000 ppm) was added into the mix solution, and heated to 64° C. to conduct suspension polymerization reaction to obtain a polyvinyl chloride slurry.
(45) At last, the pressure of the reactor was lowered to 0.1 MPa, and then the polyvinyl chloride slurry was centrifuged to remove liquid and dried at 60° C. in an oven to obtain PVC resin.
Control A
(46) In Control A, a PVC resin was prepared by the above-mentioned method except the polyvinyl alcohol-based polymer of Control was used to substitute the modified polyvinyl alcohol-based polymers used in the Examples 1A to 7A and Comparative Examples 1A and 2A.
Testing Example 4: Stability of Suspension Polymerization
(47) To evaluate the stabilization effect of each of the modified polyvinyl alcohol-based polymers of Examples and Comparative Examples, and the polyvinyl alcohol-based polymer of Control as a dispersant for suspension polymerization, PVC resins obtained from Examples 1A to 6A, Comparative Examples 1A and 2A, and Control 1A were chosen as samples to be tested in this testing example, and the averaged particle diameter and the proportion of particles with a particle diameter of 60 mesh (inclusive) or more of the PVC resins were measured according to standard method ASTM D1921, so as to evaluate the stabilization effect of the modified polyvinyl alcohol-based polymers as a dispersant. The results are shown in the following Table 4.
(48) Herein, it should be noted that, the modified polyvinyl alcohol-based polymer of Comparative Example 1 could not be homogenously dissolved in water to work as a dispersant, so the Comparative Example 1 could not be used for suspension polymerization and the averaged particle diameter and proportion of particles with a particle diameter of 60 mesh or more of the PVC resin of Comparative Example 1A could not be measured. Thus, it is shown as “-” in the following Table 4.
(49) TABLE-US-00004 TABLE 4 Characteristics of the modified polyvinyl alcohol-based polymers of Examples 1 to 6 and Comparative Examples 1 and 2, and the polyvinyl alcohol- based polymer of Control, and the particle diameter analysis result of the PVC resins obtained in suspension polymerization for which they apply. Modified polyvinyl alcohol- based polymer PVC resin Averaged Proportion of Modification Saponification particle particles of 60 Sample rate degree Sample diameter mesh or more number (mol %) (mol %) number (μm) (%) Example 1 0.34 72.54 Example 1A 121 0.13 Example 2 1.24 72.10 Example 2A 134 0.27 Example 3 1.26 72.33 Example 3A 124 0.89 Example 4 0.04 71.90 Example 4A 126 1.50 Example 5 0.21 72.06 Example 5A 127 0.66 Example 6 0.29 72.12 Example 6A 118 1.93 Comparative 2.03 71.93 Comparative — — Example 1 Example 1A Comparative 0.17 86.65 Comparative 199 3.93 Example 2 Example 2A Control 0 72.36 Control A 169 4.05
(50) The comparison results from the above Table 4 show that, when the dispersant combinations of the same amount are used to regulate the dispersion stability of suspension polymerization reaction, the averaged particle diameter of PVC resins of Examples 1A to 6A is obviously smaller than that of PVC resins of Comparative Example 2A and Control A; and the proportion of particles of 60 mesh or more in PVC resins of Examples 1A to 6A is also obviously less than that of PVC resins of Comparative Example 2A and Control A. Therefore, it is clear that, when the modified polyvinyl alcohol-based polymer has a modifying monomer unit represented by Formula (I), a modification rate of 0.02 mol % to 1.5 mol %, and a saponification degree of 67 mol % to 78 mol %, this modified polyvinyl alcohol-based polymer is suitable to be used as a dispersant for suspension polymerization; and it is particularly advantageous for promoting the dispersion stability of the suspension polymerization reaction of vinyl chloride monomer, to obtain a PVC resin having reduced particle diameter and few coarse particles.
(51) In the particle diameter analysis results of PVC resins of Examples 1A to 6A and Control A, it is found that the dispersion stability of suspension polymerization reaction of vinyl chloride monomer can be specifically promoted by the modified polyvinyl alcohol-based polymers of Examples 1 to 6, compared to the non-modified polyvinyl alcohol-based polymer (Control). Therefore, compared to the PVC resin of Control A, the PVC resins of Examples 1A to 6A have reduced particle diameter and few coarse particles.
(52) Further, in the comparison of Examples 1A to 6A with Comparative Examples 1A and 2A, it is found that Comparative Examples 1 and 2 are modified polyvinyl alcohol-based polymers without approximately controlled modification rate and saponification degree, so they cannot stabilize suspension polymerization reaction as expected. Specifically, the modified polyvinyl alcohol-based polymer of Comparative Example 2 has a saponification degree of more than 78 mol %, so the PVC resin of Comparative Example 2A has a particle diameter not as small as expected, and a number of coarse particles not as few as expected. However, the modified polyvinyl alcohol-based polymer of Comparative Example 1 has a modification rate of more than 1.5 mol %, so the PVC resin of Comparative Example 1A cannot even be subjected to particle diameter analysis.
(53) In summary, the modified polyvinyl alcohol-based polymer of the present disclosure has a modifying monomer unit represented by Formula (I), a saponification degree of 67 mol % to 78 mol % and a modification rate of 0.02 mol % to 1.5 mol %; and the modified polyvinyl alcohol-based polymer is suitable to be used as a dispersant for suspension polymerization, which provides great dispersion stability in suspension polymerization reaction, and makes the produced PVC-based resin have advantages of reduced particle diameter and few coarse particles.