Tetrafluoroethylene and perfluorinated allyl ether copolymers

A copolymer comprising

• at least 66% by weight based on the total weight of the copolymer of tetrafluoroethylene units;
• units independently represented by formula
• in a range from 0.2 to 12% by weight, based on the total weight of the copolymer, wherein n is independently from 1 to 6, z is 0, 1, or 2, and Rf is a linear or branched perfluoroalkyl group having from 1 to 8 carbon atoms and optionally interrupted by one or more —O— groups;
• from 5 to 22% by weight based on the total weight of the copolymer of units derived from hexafluoropropylene;
• and
• units represented by formula
• wherein a is 0 or 1, each b is independently from 1 to 4, c is 0 to 4, d is 0 or 1, e is 1 to 6, and X is independently —F, —NH2, —OH, or —OZ, and wherein Z is independently a metallic cation or a quaternary ammonium cation,
• wherein the copolymer has a melt flow index in a range from 1 to 19 grams per 10 minutes;
• and
• wherein the copolymer has up to 200 —SO2X groups per 106 carbon atoms and up to 100 unstable end groups per 106 carbon atoms, wherein X is independently —F, —NH2, —OH, or —OZ, wherein Z is independently a metallic cation or a quaternary ammonium cation, wherein the unstable end groups are selected from —COOM, —CH2OH, —COF, and —CONH2, and wherein M is independently an alkyl group, a hydrogen atom, a metallic cation or a quaternary ammonium cation.