Fluorinated ionomer produced by aqueous polymerization using dispersed particulate of fluorinated ionomer

1. A process for making an aqueous dispersion of fluorinated ionomer particles comprising:

providing dispersed solid particulate of fluorinated ionomer in an aqueous polymerization medium;

polymerizing at least one fluorinated monomer having an ionic group in said aqueous polymerization medium in the presence of said dispersed particulate of fluorinated ionomer and initiator to form the aqueous dispersion of particles of fluorinated ionomer.

2. The process of claim 1 wherein the amount of said dispersed particulate of fluorinated ionomer provided in said aqueous polymerization medium comprises less than 15 wt % of the solids content of said aqueous dispersion of fluorinated ionomer particles produced by said process.

3. The process of claim 1 wherein said particulate of fluorinated ionomer has a weight average particle size of about 2 nm to about 100 nm.

4. The process of claim 1 wherein said fluorinated ionomer of said particulate has an ion exchange ratio of about 3 to about 53.

5. The process of claim 1 wherein at least 90% of the total number of univalent atoms bonded to carbon atoms in said fluorinated ionomer of said particulate are fluorine atoms.

6. The process of claim 1 wherein said fluorinated ionomer of said particulate is perfluorinated.

7. The process of claim 1 wherein said fluorinated ionomer of said particulate comprises a polymer backbone with recurring side chains attached to the polymer backbone with the side chains carrying ionic groups.

8. The process of claim 1 wherein said fluorinated ionomer of said particulate comprises ionic groups having a pKa less than 10.

9. The process of claim 1 wherein said fluorinated ionomer of said particulate comprises ionic groups selected from the group consisting of sulfonate, carboxylate, phosphonate, phosphate and mixtures thereof.

10. The process of claim 1 wherein said fluorinated ionomer of said particulate comprises sulfonate groups.

11. The process of claim 7 wherein said recurring side chains are represented by the formula —(O—CF 2 CFR f ) a —(O—CF 2 ) b —(CFR′ f ) c SO 3 X, wherein R f and R′ f are independently selected from F, Cl or a perfluorinated alkyl group having 1 to 10 carbon atoms, a=0 to 2, b=0 to 1, c=0 to 6, and X is H, Li, Na, K or NH 4 .

12. The process of claim 11 wherein said recurring side chain is represented by the formula —O—CF 2 CF(CF 3 )—O—CF 2 CF 2 —SO 3 X wherein X is H, Li, Na, K or NH 4 .

13. The process of claim 1 wherein said fluorinated ionomer of said particulate in thermoplastic form has a melt flow at 270° C. using a 5 kg weight of about 1 to about 500.

14. The process of claim 1 further comprising providing surfactant in said polymerization medium.

15. The process of claim 1 further comprising providing fluorosurfactant in said polymerization medium.

16. The process of claim 1 further comprising providing fluoroether surfactant in said polymerization medium.

17. The process of claim 15 wherein said fluorosurfactant has the formula:

[R 1 —O n -L-A − ]Y +

wherein:

R 1 is a linear or branched partially or fully fluorinated aliphatic group which may contain ether linkages;

n is 0 or 1;

L is a linear or branched alkylene group which may be nonfluorinated, partially fluorinated or fully fluorinated and which may contain ether linkages;

A − is an anionic group selected from the group consisting of carboxylate, sulfonate, sulfonamide anion, and phosphonate; and

Y + is hydrogen, ammonium or alkali metal cation;

with the proviso that the chain length of R 1 —O n -L- is not greater than 6 atoms.

18. The process of claim 17 wherein n is 1.

19. The process of claim 18 wherein

R 1 is CF 3 CF 2 CF 2 —;

L is —CF(CF 3 )—; and

A − is carboxylate; and

Y + is hydrogen or ammonium.

20. The process of claim 1 wherein said aqueous medium contains less than 300 ppm of perfluoroalkane carboxylic acid or salt fluorosurfactant having 8 or more carbon atoms based on the weight of water in said aqueous polymerization medium.

21. The process of claim 1 wherein said polymerizing produces less than 13 wt % undispersed fluorinated ionomer based on the total weight of fluorinated ionomer produced.

22. The process of claim 1 wherein providing said dispersed fluorinated ionomer particulate in said aqueous polymerization medium is performed by mixing concentrated aqueous liquid dispersion or dispersible powder of said fluorinated ionomer into said aqueous polymerization medium.