Aqueous polymerization of fluorinated monomer using polymerization agent comprising fluoropolyether acid or salt and short chain fluorosurfactant

1. A process comprising polymerizing at least one fluorinated monomer in an aqueous medium containing initiator and polymerization agent to form an aqueous dispersion of particles of fluoropolymer, said polymerization agent comprising:

fluoropolyether acid or salt thereof having a number average molecular weight of at least about 800 g/mol; and

fluorosurfactant having the formula:

[R 1 —O n -L-A − ] Y +

wherein:

R 1 is CF 3 CF 2 CF 2 —;

n is 1;

L is —CF(CF 3 )—; and

A − is carboxylate; and

Y + is hydrogen or ammonium.

2. A process for polymerizing fluoropolymer comprising:

mixing fluoropolyether acid having a number average molecular weight of at least about 800 g/mol with fluorosurfactant to form an acid mixture, said fluorosurfactant having 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 and phosphonate; and

Y + is hydrogen;

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

dispersing said acid mixture in an aqueous polymerization medium to provide dispersed fluoropolyether acid or salt and surfactant or salt of said surfactant;

polymerizing in said aqueous polymerization medium at least one fluorinated monomer in the presence of initiator and said dispersed fluoropolyether acid or salt and fluorosurfactant or salt of said surfactant to form an aqueous dispersion of particles of fluoropolymer wherein, during said mixing of said fluoropolyether acid and fluorosurfactant, the amount of water is limited so that said acid mixture comprises less than about 50 wt % water.

3. The process of claim 2 further comprising contacting said acid mixture with ammonium hydroxide or alkali metal hydroxide to form salts of said fluoropolyether acid and fluorosurfactant.

4. The process of claim 3 wherein said contacting of said acid mixture with ammonium hydroxide or alkali metal hydroxide is performed by providing said ammonium hydroxide or alkali metal hydroxide in said polymerization medium and mixing said acid mixture into said polymerization medium to disperse said salts of said fluoropolyether acid and fluorosurfactant in said polymerization medium.

5. The process of claim 3 wherein said contacting of said acid mixture with ammonium hydroxide or alkali metal hydroxide is performed using an aqueous ammonium hydroxide or aqueous alkali metal hydroxide to form an aqueous concentrate comprising dispersed salts of said fluoropolyether acid and fluorosurfactant and said dispersing of said salts of said fluoropolyether acid and fluorosurfactant in said polymerization medium is performed by adding said aqueous concentrate to said aqueous polymerization medium.

6. The process of claim 3 wherein said acid mixture is contacted with aqueous ammonium hydroxide.