Aqueous emulsion polymerization process for producing fluoropolymers
The present invention provides a method of making a fluoropolymer through emulsion polymerization of one or more fluorinated monomers in an aqueous phase in the presence of a fluorinated surfactant. At least part of the fluorinated surfactant is added to the aqueous phase as an aqueous mixture with at least one organic liquid that is not miscible with water and that is selected from halogenated and non-halogenated organic liquids, the mixture having droplets having an average droplet diameter of not more than 1000 nm and the mixture being added to the aqueous phase in such an amount that the total amount of the fluorinated surfactant is not more than 1% by weight based on the weight of the aqueous phase and the total amount of said organic liquid is not more than 1% by weight based on the weight of said aqueous phase. The invention allows for an improvement of the efficiency of an aqueous emulsion polymerization process. In particular, the polymerization time can be reduced and the polymer yield may be improved.
1. Method of making a fluoropolymer through emulsion polymerization of one or more fluorinated monomers in an aqueous phase in the presence of a fluorinated surfactant comprising adding at least part of said fluorinated surfactant to the aqueous phase as an aqueous mixture with at least one organic liquid that is not miscible with water and that is selected from halogenated and non-halogenated organic liquids, said aqueous mixture having droplets having an average droplet diameter of not more than 1000 nm and said aqueous mixture being added to the aqueous phase in such an amount that the total amount of said fluorinated surfactant is not more than 1% by weight based on the weight of the aqueous phase and the total amount of said organic liquid is not more than 1% by weight based on the weight of said aqueous phase, wherein the organic liquid is a perfluorinated or partially fluorinated aliphatic or aromatic organic liquid that contains up to a total of 2 oxygen, sulphur and/or nitrogen atoms per molecule.
2. Method according to claim 1 wherein said organic liquid is capable of participating in the polymerization of said one or more fluorinated monomers such that said organic liquid is built into the structure of said fluoropolymer.
3. Method according to claim 2 , wherein said organic liquid is a halogenated olefinic organic liquid.
4. Method according to claim 1 wherein said organic liquid has a boiling point of at least 100° C.
5. Method according to claim 1 wherein the total combined amount of fluorinated surfactant and organic liquid is less than 1% by weight based on the weight of the aqueous phase.
6. Method according to claim 1 wherein the amount of organic liquid is not more than 0.2% by weight based on the weight of the aqueous phase.
7. Method according to claim 1 wherein said fluorinated surfactant corresponds to the following general formula:
Y—R f -Z-M
wherein Y represents hydrogen, Cl or F; R f represents a linear or branched perfluorinated alkylene having 4 to 10 carbon atoms; Z represents COO − or SO 3 − and M represents a monovalent cation.
8. Method according to claim 6 wherein said fluorinated surfactant is an ammonium or metal salt of perfluoro octanoic acid or perfluoro octane sulphonic acid.
9. Method according to claim 1 wherein said fluorinated monomer comprises a gaseous fluorinated olefinic monomer.
10. Method according to claim 1 wherein said fluorinated monomer comprises tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, vinylidene fluoride and/or perfluoro vinyl ether.
11. Method according to claim 1 wherein said mixture of said fluorinated surfactant with said organic liquid is added to the aqueous phase prior to the start of the polymerization and wherein the mixture is added at such a rate of addition that the mixture is added to the aqueous phase in not more than 10 minutes.
12. Method according to claim 1 wherein said mixture of said fluorinated surfactant with said organic liquid is added to the aqueous phase simultaneously with the addition of an initiator or until 2 minutes after the addition of initiator.
13. Method according to claim 1 wherein at least 10% by weight of said fluorinated surfactant is added as a mixture with said organic liquid to the aqueous phase.
14. Method according to claim 1 wherein all of said fluorinated surfactant is added as a mixture with said organic liquid to the aqueous phase.
15. Method according to claim 1 wherein the amount of said organic liquid in said mixture of said fluorinated surfactant with said organic liquid is between 0.1 and 300% by weight relative to the solids amount of said fluorinated surfactant in said mixture.
16. Method of making a fluoropolymer through emulsion polymerization of one or more fluorinated monomers in an aqueous phase comprising adding to the aqueous phase a fluorinated surfactant having the formula:
Y—R f -Z-M
wherein Y represents hydrogen, Cl or F; R f represents a linear or branched perfluorinated alkylene having 4 to 10 carbon atoms; Z represents COO − or SO 3 − and M represents a monovalent cation;
characterized in that at least part of said fluorinated surfactant is added to the aqueous phase as an aqueous mixture with at least one organic liquid that is not miscible with water and that is a perfluorinated or partially fluorinated aliphatic or aromatic organic liquid that contains up to a total of 12 oxygen, sulphur and/or nitrogen atoms per molecule, said aqueous mixture having droplets having an average droplet diameter of not more than 1000 nm and said mixture being added to the aqueous phase in such an amount that the total amount of said fluorinated surfactant is not more than 1% by weight unused on the weight of the aqueous phase and the total amount of said organic liquid is not more than 1% by weight based on the weight of said aqueous phase.
17. Method according to claim 16 wherein the amount of organic liquid is less than 0.2% by weight based on the weight of the aqueous phase.
18. Method according to claim 16 wherein said organic liquid is not more than 0.01% by weight based on the weight of the aqueous phase.