Fluorinated copolymer and compositions and articles including the same

A copolymer comprising:

• divalent units represented by formula —[CF2—CF2]—;
• divalent units independently represented by formula:
• wherein a is 0 or 1, b is 2 to 8, c is 0 to 2, e is 3 to 8, and Z is independently a hydrogen, alkyl having up to four carbon atoms, an alkali-metal cation, or a quaternary ammonium cation;
• and
• one or more divalent units independently represented by formula:
• wherein Rf is a linear or branched perfluoroalkyl group having from 2 to 8 carbon atoms and optionally interrupted by one or more —O— groups, z is 0, 1, or 2, each n is independently 1, 2, 3, or 4, and m is 0 or 1;
• wherein when Z is hydrogen, the copolymer has an alpha transition temperature of up to 100° C., wherein the copolymer has an —SO3Z equivalent weight in a range from 300 to 1400, and wherein a variation of the copolymer in which —SO3Z is replaced with —SO2F has a melt flow index of up to 80 grams per ten minutes measured at a temperature of 265° C. and at a support weight of 5 kg.