Fluorinated ionomers with reduced amounts of carbonyl end groups

An electrolyte membrane comprising being formed in part from fluoropolymers, wherein each of the fluoropolymers comprises:

• a plurality of pendent groups terminating in —CF2SO3X, wherein X is selected from a group consisting of H+ and a cation;
• and
• at least one —CF2Y end group, wherein Y is selected from a group consisting of a chlorine atom and an —SO3X group.

A method of making a fluoropolymer, the method comprising free-radical polymerizing fluorinated monomers in the presence of a salt, a pseudohalogen, or a combination of the salt and the pseudohalogen, to make the fluoropolymer, wherein the fluoropolymer comprises a plurality of pendent groups terminating in —CF2SO2F and at least one —CF2Y end group, wherein Y is selected from a group consisting of a chlorine atom, a bromine atom, an iodine atom, a nitrile group, and an —SO3X group, wherein X is selected from a group consisting of H+ and a cation.

A method of making a fluoropolymer, the method comprising:

• providing fluorinated monomers, wherein at least one of the fluorinated monomers comprises a sulfonyl fluoride monomer;
• and
• free-radical reacting the fluorinated monomers in the presence of a salt, a pseudohalogen, or a combination of the salt and the pseudohalogen, to make the fluoropolymer, wherein the fluoropolymer has at least about 25% less carbonyl end groups relative to a similar fluoropolymer produced in the absence of the salt or the pseudohalogen.