FLUOROPOLYMER AND METHOD FOR PRODUCING SAME

Abstract

A method for producing a fluoropolymer, which includes polymerizing a monomer (I) represented by the general formula (I) in an aqueous medium to produce the fluoropolymer of the monomer (I), wherein an oxygen concentration in a reaction system of the polymerization is maintained at 500 ppm by volume or less:

CX.sub.2═CY—CF.sub.2—O—Rf-A   General formula (I):

wherein X and Y are independently H, F, CH.sub.3, or CF.sub.3, and at least one of X and Y is F; Rf is a fluorine-containing alkylene group having 1 to 40 carbon atoms, or a fluorine-containing alkylene group having 2 to 100 carbon atoms and having an ether bond; and A is —COOM, —SO.sub.3M, —OSO.sub.3M, or —C(CF.sub.3).sub.2OM, wherein M is H, a metal atom, NR.sup.7.sub.4, imidazolium optionally having a substituent, pyridinium optionally having a substituent, or phosphonium optionally having a substituent, and R.sup.7 is H or an organic group.

Claims

1. A method for producing a fluoropolymer, comprising polymerizing a monomer (I) represented by the general formula (I) in an aqueous medium to produce the fluoropolymer of the monomer (I), wherein an oxygen concentration in a reaction system of the polymerization is maintained at 500 ppm by volume or less:
CX.sub.2═CY—CF.sub.2—O—Rf-A   General formula (I): wherein X and Y are independently H, F, CH.sub.3, or CF.sub.3, and at least one of X and Y is F; Rf is a fluorine-containing alkylene group having 1 to 40 carbon atoms, or a fluorine-containing alkylene group having 2 to 100 carbon atoms and having an ether bond; and A is —COOM, —SO.sub.3M, —OSO.sub.3M, or —C(CF.sub.3).sub.2OM, wherein M is H, a metal atom, NR.sup.7.sub.4, imidazolium optionally having a substituent, pyridinium optionally having a substituent, or phosphonium optionally having a substituent, and R.sup.7 is H or an organic group.

2. The production method according to claim 1, wherein the monomer (I) is polymerized at a polymerization temperature of 20° C. to 59° C.

3. The production method according to claim 1, wherein the monomer (I) is polymerized in the presence of a polymerization initiator, and the polymerization initiator is a persulfate.

4. The production method according to claim 1, wherein the monomer (I) is polymerized in the presence of a polymerization initiator, and a total amount of the polymerization initiator added for use in the polymerization is 0.00001 to 10% by mass based on the aqueous medium.

5. The production method according to claim 1, wherein an amount of a monomer comprising the monomer (I) present at the beginning of polymerization is 40% by mass or more based on an amount of the aqueous medium present.

6. The production method according to claim 1, wherein a content of a polymerization unit (I) derived from the monomer (I) in the fluoropolymer is 50 mol % or more based on all polymerization units constituting the fluoropolymer.

7. The production method according to claim 1, wherein a content of a polymerization unit (I) derived from the monomer (I) in the fluoropolymer is 99 mol % or more based on all polymerization units constituting the fluoropolymer.

8. The production method according to claim 1, wherein the fluoropolymer has a weight average molecular weight (Mw) of 20.0×10.sup.4 or more.

9. The production method according to claim 1, wherein the fluoropolymer has a weight average molecular weight (Mw) of 40.0×10.sup.4 or more.

10. The production method according to claim 1, wherein the fluoropolymer has a number average molecular weight (Mn) of 8.0×10.sup.4 or more.

11. The production method according to claim 1, wherein an aqueous solution comprising the fluoropolymer is produced.

12. The production method according to claim 1, wherein a composition comprising the aqueous medium and the fluoropolymer is recovered after polymerization is complete, and the composition is treated by at least one means selected from the group consisting of ultrafiltration, microfiltration, dialysis membrane treatment, liquid separation, and reprecipitation.

13. A fluoropolymer of a monomer (I) represented by the general formula (I), wherein a content of a polymerization unit (I) derived from the monomer (I) of 50 mol % or more based on all polymerization units constituting the fluoropolymer, and the fluoropolymer has a weight average molecular weight (Mw) of 40.0×10.sup.4 or more:
CX.sub.2═CY—CF.sub.2—O—Rf-A   General formula (I): wherein X and Y are independently H, F, CH.sub.3, or CF.sub.3, and at least one of X and Y is F; Rf is a fluorine-containing alkylene group having 1 to 40 carbon atoms, or a fluorine-containing alkylene group having 2 to 100 carbon atoms and having an ether bond; and A is —COOM, —SO.sub.3M, —OSO.sub.3M, or —C(CF.sub.3).sub.2OM, wherein M is H, a metal atom, NR.sup.7.sub.4, imidazolium optionally having a substituent, pyridinium optionally having a substituent, or phosphonium optionally having a substituent, and R.sup.7 is H or an organic group.

14. The fluoropolymer according to claim 13, having a number average molecular weight (Mn) of 8.0×10.sup.4 or more.

15. The fluoropolymer according to claim 13, wherein the content of the polymerization unit (I) is 99 mol % or more based on all polymerization units constituting the fluoropolymer.

16. The fluoropolymer according to claim 13, which is substantially free of a dimer and a trimer of the monomer (I).

17. An aqueous solution comprising the fluoropolymer according to claim 13.

18. The aqueous solution according to claim 17, wherein a content of the fluoropolymer is 2% by mass or more based on the aqueous solution.

19. A coating composition comprising the fluoropolymer according to claim 13.

20. A coating composition comprising the aqueous solution according to claim 17.

Description

EXAMPLES

[0256] Next, embodiments of the present disclosure will now be described with reference to Examples, but the present disclosure is not limited only to these Examples.

[0257] The numerical values of the Examples were measured by the following methods.

Oxygen Concentration in Reactor

[0258] Gas discharged from the discharge gas line while nitrogen-bubbling the liquid in the reactor was measured and analyzed using a low-concentration oxygen analyzer (trade name “PS-820-L”, manufactured by Iijima Electronics Corporation) to thus determine the oxygen concentration during reaction.

Concentration of Fluoropolymer in Aqueous Solution (Solid Concentration))

[0259] In a vacuum dryer, about 1 g of an aqueous solution containing a fluoropolymer was dried at 60° C. for 60 minutes, the mass of non-volatile matter was measured, and the ratio of the mass of the non-volatile matter to the mass (1 g) of the aqueous solution was expressed in percentage and taken as the fluoropolymer concentration.

Method for Measuring Weight Average Molecular Weight (Mw) and Number Average Molecular Weight (Mn)

[0260] Mw and Mn of a fluoropolymer were measured by gel permeation chromatography (GPC) using 1260 Infinity II manufactured by Agilent Technologies using columns manufactured by Tosoh Corp. (one TSKgel G3000PW.sub.XL and one TSKgel GMPW.sub.XL connected in series) while allowing a mixed solvent of a Tris buffer and acetonitrile (Tris buffer:acetonitrile=8:2 (v/v)) as a solvent to flow at a flow rate of 0.5 ml/min, and the molecular weights were calculated using monodisperse polyethylene oxide (PEO) and polyethylene glycol (PEG) as standards.

Method for Measuring Content of Dimer and Trimer of Monomer in Fluoropolymer

(1) Extraction from Aqueous Solution

[0261] The solid content of an aqueous solution of a fluoropolymer was measured, and the amount of the aqueous solution corresponding to 0.2 g of the solid content of the fluoropolymer was weighed. Thereafter, water and methanol were added such that the volume ratio of water, including water contained in the aqueous solution, to methanol was 50/50 (% by volume) to obtain a mixed solution containing the fluoropolymer, water, and methanol. Thereafter, the resulting mixed solution was centrifuged at 4,000 rpm for 1 hour, and the supernatant containing the fluoropolymer was recovered as an extract.

[0262] The extract was analyzed using a liquid chromatograph-mass spectrometer (Waters, LC-MS ACQUITY UPLC/TQD) to obtain a chromatogram of the extract.

[0263] The content of a dimer and a trimer of a monomer contained in the extract was obtained by converting the integral values of peaks derived from the dimer and the trimer of the monomer appearing in the chromatogram of the extract into the content of the dimer and the trimer of the monomer using the calibration curve of the analog monomer.

(2) Calibration Curve of Monomer

[0264] Five concentration levels of a methanol standard solution of a monomer having a known content of 1 ng/mL to 100 ng/mL were prepared, and measurement was made using a liquid chromatograph-mass spectrometer (Waters, LC-MS ACQUITY UPLC/TQD). The relationship between the content of each monomer and the integrated value of a peak corresponding to the content was plotted to prepare a calibration curve (first-order approximation) of each monomer. Next, the calibration curve (first-order approximation) of each monomer was used to prepare calibration curves of the dimer and the trimer of each monomer.

[0265] Measuring instrument configuration and LC-MS measurement conditions are below:

TABLE-US-00001 TABLE 1 LC unit Equipment Acquity UPLC manufactured by Waters Column Acquity UPLC BEH C18 1.7 mm (2.1 × 50 mm) manufactured by Waters Mobile phase A CH.sub.3CN B 20 mM CH.sub.3COONH.sub.4/H.sub.2O 0 .fwdarw. 1.5 min A:B = 10:90 1.5 .fwdarw. 8.5 min A:B = 10:90 .fwdarw. A:B = 90:10 Linear gradient 8.5 .fwdarw. 10 min A:B = 90:10 Flow rate 0.4 mL/mm Column 40° C. temperature Sample injection 5 μL amount MS unit Equipment TQ Detecter Measurement MRM (Multiple Reaction mode Monitoring) Ionization method Electrospray ionization SCAN

[0266] The quantification limit in this measuring instrument configuration is 1 ng/mL.

Example 1

[0267] To a reactor, 7.5 g of perfluoro-(6,6-dihydro-2-trifluoromethyl-3-oxa-5-hexenoic acid) and 17.5 g of water were added, and the liquid in the reactor was stirred for 30 minutes at room temperature while N.sub.2 bubbling. While stirring the mixture at 50° C., ammonium persulfate (APS) was added in an amount corresponding to 0.5 mol % based on the amount of perfluoro-(6,6-dihydro-2-trifluoromethyl-3-oxa-5-hexenoic acid) to initiate the reaction. The reaction was terminated after stirring for 23 hours. The oxygen concentration in the reactor varied between 250 ppm by volume and 350 ppm by volume.

[0268] Water was added to the resulting fluoropolymer-containing aqueous solution to adjust the concentration of the fluoropolymer to 2.0% by mass, and then the aqueous solution was brought into contact with an ultrafiltration membrane (a molecular weight cut-off of 50,000 Da, made of polyacrylonitrile) at 25° C. at a water pressure of 0.1 MPa to carry out ultrafiltration. While suitably adding water, ultrafiltration was continued until a filtrate of water in an amount 7 times greater than the aqueous solution was eventually eluted, and thus an aqueous solution of the fluoropolymer was obtained. The concentration of the aqueous solution carried out by performing ultrafiltration was 2.1% by mass.

[0269] The aqueous solution obtained by carrying out ultrafiltration was analyzed. The resulting fluoropolymer had a weight average molecular weight (Mw) of 40.8×10.sup.4 and a number average molecular weight (Mn) of 10.2×10.sup.4. The content of the dimer and the trimer in the aqueous solution obtained by carrying out ultrafiltration was 0.1% by mass or less based on the fluoropolymer.

Example 2

[0270] To the reactor, 1,650 g of perfluoro-(6,6-dihydro-2-trifluoromethyl-3-oxa-5-hexenoic acid) and 3,850 g of water were added, and the liquid in the reactor was stirred for 30 minutes at room temperature while N.sub.2 bubbling. While stirring the mixture at 52° C., ammonium persulfate (APS) was added in an amount corresponding to 0.5 mol % based on the amount of perfluoro-(6,6-dihydro-2-trifluoromethyl-3-oxa-5-hexenoic acid) to initiate the reaction. The reaction was terminated after stirring for 23 hours. The oxygen concentration in the reactor varied between 11 ppm by volume and 20 ppm by volume.

[0271] Ultrafiltration was carried out on the resulting fluoropolymer-containing aqueous solution in the same manner as Example 1. The concentration of the aqueous solution obtained by carrying out ultrafiltration was 2.1% by mass.

[0272] The aqueous solution obtained by carrying out ultrafiltration was analyzed. The resulting fluoropolymer had a weight average molecular weight (Mw) of 46.0×10.sup.4 and a number average molecular weight (Mn) of 12.2×10.sup.4. The content of the dimer and the trimer in the aqueous solution obtained by carrying out ultrafiltration was 0.1% by mass or less based on to the fluoropolymer.

Comparative Example 1

[0273] A fluoropolymer was obtained in the same manner as Example 1 except that the amount of perfluoro-(6,6-dihydro-2-trifluoromethyl-3-oxa-5-hexenoic acid) was changed to 17.5 g, the amount of water was changed to 32.5 g, the temperature was changed to 56° C., and the oxygen concentration in the reactor varied so as to be 9,400 ppm by volume or less.

[0274] Ultrafiltration was carried out on the resulting fluoropolymer-containing aqueous solution in the same manner as Example 1. The concentration of the aqueous solution obtained by carrying out ultrafiltration was 2.0% by mass. The aqueous solution obtained by carrying out ultrafiltration was analyzed. The resulting fluoropolymer had a weight average molecular weight (Mw) of 19.6×10.sup.4 and a number average molecular weight (Mn) of 6.2×10.sup.4. The content of the dimer and the trimer in the aqueous solution obtained by carrying out ultrafiltration was 0.1% by mass or less based on the fluoropolymer.

Comparative Example 2

[0275] A fluoropolymer was obtained in the same manner as Comparative Example 1 except that the temperature was changed to 80° C.

[0276] Ultrafiltration was carried out on the resulting fluoropolymer-containing aqueous solution in the same manner as Example 1. The concentration of the aqueous solution obtained by carrying out ultrafiltration was 2.0% by mass. The aqueous solution obtained by carrying out ultrafiltration was analyzed. The resulting fluoropolymer had a weight average molecular weight (Mw) of 9.6×10.sup.4 and a number average molecular weight (Mn) of 4.3×10.sup.4. The content of the dimer and the trimer in the aqueous solution obtained by carrying out ultrafiltration was 0.1% by mass or less based on the fluoropolymer.

Experimental Example 1 (Preparation of Coating Film)

[0277] In order to form a film having a thickness of 1 μm on a substrate, the concentration of the aqueous solution obtained by carrying out ultrafiltration in Example 1 (the weight average molecular weight (Mw) of the fluoropolymer was 40.8×10.sup.4) was adjusted to thereby prepare a polymer solution having a concentration of the fluoropolymer of 2% by mass. After being stirred with a stirrer for 24 hours, the solution was filtered through a disposable syringe filter having a pore size of 0.2 to give a spin coating solution.

[0278] Using the resulting spin coating solution and a commercially available programmable spin coater, spin coating was performed on a silicon wafer substrate under the following conditions. The spin coating solution was applied on the substrate while rotating the substrate at a rotational speed of 200 rpm for 10 seconds, and then the spin coating solution was applied on the substrate while rotating the substrate at 2,000 rpm for 50 seconds. The film immediately after being formed was dried for 8 hours in a blower-type electric furnace at a temperature of 50° C., and the substrate on which a coating film was formed was removed. The film thickness of the coating film was measured at 5 points with a digital film thickness gauge. The average film thickness of the coating film was 1.03 μm, and it was thus possible to uniformly form a coating film having the intended film thickness.

Comparative Experimental Example 1

[0279] A substrate on which a coating film was formed was prepared in the same manner as Experimental Example 1 except that the aqueous solution obtained by carrying out ultrafiltration in Comparative Example 1 (the weight average molecular weight (Mw) of the fluoropolymer was 19.6×10.sup.4) was used. The average film thickness of the resulting coating film was 10.5 μm, and a film having the intended thickness was not obtained.

Comparative Experimental Example 2

[0280] A substrate on which a coating film was formed was prepared in the same manner as Comparative Experimental Example 1 except that the concentration of the fluoropolymer of the polymer solution was changed to 10% by mass. The resulting coating film had an average thickness of about 1 μm, but had variations in film thickness.

Comparative Experimental Example 3

[0281] A substrate on which a coating film was formed was prepared in the same manner as Comparative Experimental Example 1 except that the rotational speed and the rotational time were changed so that the spin coating solution was applied on the substrate while rotating the substrate at 200 rpm for 60 seconds. The resulting coating film had an average thickness of about 1 μm, but had variations in film thickness.