Fluorinated copolymer and compositions and articles including the same

The copolymer includes divalent units represented by formula -[CF2-CF2]-, at least one divalent unit represented by formula (I): and at least one divalent unit independently represented by formula (II): A is -N(RFa)2 or a is non-aromatic, 5- to 8-membered, perfluorinated ring comprising one or two nitrogen atoms in the ring and optionally comprising at least one oxygen atom in the ring, each RFa is independently linear or branched perfluoroalkyl having 1 to 8 carbon atoms and optionally interrupted by at least one catenated O or N atom, each Y is independently -H or -F, with the proviso that one Y may be -CF3, h is 0, 1, or 2, each i is independently 2 to 8, and j is 0, 1, or 2. A catalyst ink and polymer electrolyte membrane including the copolymer are also provided.