Process for preparing fluoropolymer

The polymerization initiator-containing solution obtained by mixing a specific perfluorodicarboxylic acid fluoride (A) with CsF in an aprotic polar solvent with stirring to conduct reaction and thereby form a polymerization initiator (B) and then allowing the reaction solution to stand for not less than 72 hours at a temperature of 0 to 30° C. A polymerization initiator-containing solution comprises a specific polymerization initiator (B′) and an aprotic polar solvent. The process for preparing a perfluoropolyether comprises polymerizing hexafluoropropylene oxide in the presence of the polymerization initiator-containing solution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS.

1(

a)-

1(

d) show changes in a

19F-NMR spectrum of a fluorine atom of —CF

2OCs at the end of a polymerization initiator (B) and an integral value of the fluorine atom with time, said polymerization initiator (B) being represented by the following formula (II) and obtained by mixing a perfluorodicarboxylic acid fluoride (A) represented by the following formula (I) with CsF in an aprotic polar solvent with stirring;

FOC—Rf—COF  (I)

wherein Rf is a perfluoroalkylene group having 1 to 4 carbon atoms or a perfluoroalkylene group having 2 to 10 carbon atoms and an ether bond;

CsOCF

2—Rf—CF

2OCs  (II)

wherein Rf is the same as Rf in the formula (I)

FIGS.

1(

a),

1(

b),

1(

c) and

1(

d) show

19F-NMR spectra and integral values of the above fluorine atom measured after a lapse of 24 hours, 48 hours, 96 hours and 30 days, respectively, from disappearance of the starting compound represented by the formula (I).

1. A process for preparing a perfluoropolyether, comprising polymerizing hexafluoropropylene oxide in the presence of a polymerization initiator-containing solution which comprises a polymerization initiator (B′) represented by the following formula (IV) and an aprotic polar solvent;

(FOC)

x—Rf

2—(CF

2OCs)

y  (IV)

wherein Rf

2 is perfluoroalkylene having 1 to 4 carbon atoms or perfluoroalkylene having 2 to 10 carbon atoms and an ether bond, and x and y are numbers satisfying the conditions of x+y=2 and 0.1<y<2.

2. The process for preparing a perfluoropolyether as claimed in claim 1, wherein Rf

2 in the formula (IV) is represented by the following formula (V):

wherein Rf

3 is perfluoroalkylene having 2 to 6 carbon atoms.

3. The process for preparing a perfluoropolyether as claimed in claim 1, wherein the concentration of the polymerization initiator (B′) in the polymerization initiator-containing solution is not less than 4×10

−4 mol/g.

4. The process for preparing a perfluoropolyether as claimed in claim 1, wherein the polymerization initiator (B′) is a compound obtained by allowing a perfluorodicarboxylic acid fluoride (A′) represented by the following formula (VI) to react with CsF in an aprotic polar solvent;

FOC—Rf

4—COF  (VI)

wherein Rf

4 is a perfluoroalkylene group having 1 to 4 carbon atoms or a perfluoroalkylene group having 2 to 10 carbon atoms and an ether bond.

5. The process for preparing a perfluoropolyether as claimed in claim 4, wherein the perfluorodicarboxylic acid fluoride (A′) is represented by the following formula (VII):

wherein Rf

5 is a perfluoroalkylene group having 2 to 4 carbon atoms.

6. The process for preparing a perfluoropolyether as claimed in claim 4, wherein the molar ratio (CsF/perfluorodicarboxylic acid fluoride (A′)) of the CsF to the perfluorodicarboxylic acid fluoride (A′) used is not less than 0.1 and less than 2.

7. The process for preparing a perfluoropolyether as claimed in claim 1, wherein polymerization of the hexafluoropropylene oxide is carried out at a temperature of not higher than −30° C.

8. The process for preparing a perfluoropolyether as claimed in claim 2, wherein the concentration of the polymerization initiator (B′) in the polymerization initiator-containing solution is not less than 4×10

−4 mol/g.

9. The process for preparing a perfluoroether as claimed in claim 7, wherein the concentration of the polymerization initiator (B′) in the polymerization initiator-containing solution is not less than 4×10

−4 mol/g.

10. The process for preparing a perfluoropolyether as claimed in claim 1 wherein, in the polymerization of the hexafluoropropylene oxide, hexafluoropropylene is further used in combination in an amount of 20 to 50% by weight based on the amount of the hexafluoropropylene oxide.

11. The process for preparing a perfluoropolyether as claimed in claim 2, wherein the polymerization initiator (B′) is a compound obtained by allowing a perfluorodicarboxylic acid fluoride (A′) represented by the following formula (VI) to react with CsF in an aprotic polar solvent:

FOC—Rf

4—COF  (VI)

wherein Rf

4 is a perfluoroalkylene group having 1 to 4 carbon atoms or a perfluoroalkylene group having 2 to 10 carbon atoms and an ether bond.

12. The process for preparing a perfluoropolyether as claimed in claim 7, wherein the polymerization initiator (B′) is a compound obtained by allowing a perfluorodicarboxylic acid fluoride (A′) represented by the following formula (VI) to react with CsF in an aprotic polar solvent:

FOC—Rf

4—COF  (VI)

wherein Rf

4 is a perfluoroalkylene group having 1 to 4 carbon atoms or a perfluoroalkylene group having 2 to 10 carbon atoms and an ether bond.

13. The process for preparing a perfluoropolyether as claimed in claim 3, wherein the polymerization initiator (B′) is a compound obtained by allowing a perfluorodicarboxylic acid fluoride (A′) represented by the following formula (VI) to react with CsF in an aprotic polar solvent:

FOC—Rf

4—COF  (VI)

wherein Rf

4 is a perfluoroalkylene group having 1 to 4 carbon atoms or a perfluoroalkylene group having 2 to 10 carbon atoms and an ether bond.

14. The process for preparing a perfluoropolyether as claimed in claim 10, wherein the polymerization initiator (B') is a compound obtained by allowing a perfluorodicarboxylic acid fluoride (A') represented by the following formula (VI) to react with CsF in an aprotic polar solvent;

FOC—Rf

4—COF  (VI)

wherein Rf

4 is perfluoroalkylene group having 1 to 4 carbon atoms or perfluoroalkylene group having 2 to 10 carbon atoms and an ether bond.

15. The process for preparing a perfluoropolyether as claimed in claim 5, wherein the molar ratio (CsF/perfluorodicarboxylic acid fluoride (A′)) of the CsF to the perfluorodicarboxylic acid fluoride (A′) used is not less than 0.1 and less than 2.

16. The process for preparing a perfluoropolyether as claimed in claim 1, wherein the aprotic polar solvent is diglyme, triglyme, tetraglyme or sulfolane.

17. The process for preparing a perfluoropolyether as claimed in claim 1, comprising polymerizing hexafluoropropylene oxide in the presence of a polymerization initiator-containing solution which comprises a polymerization initiator (B′) represented by the following formula (IV) and an aprotic polar solvent;

(FOC)

x—Rf

2—(CF

2OCs)

y  (IV)

wherein Rf

2 is a perfluoroalkylene group having 1 to 4 carbon atoms or a perfluoroalkylene group having 2 to 10 carbon atoms and an ether bond, and x and y are numbers satisfying the conditions of x+y=2 and 0.1<y<1.8.