Ionomer having high oxygen permeability

An ionomer, comprising:

• a repeating unit A;
• a repeating unit B, and
• a repeating unit C,
• the ionomer having an equivalent weight of 250 to 930 and a glass transition temperature of 100° C. to 130° C.,
• the amount of the repeating unit B is 16 to 45 mol %, relative to all the repeating units,
• the repeating unit B being represented by the formula (2):
• wherein Rp represents a monovalent group having a proton exchange group,
• wherein the repeating unit A is at least one repeating unit selected from the group consisting of:
• a repeating unit represented by the formula (3):
• wherein m3 represents an integer of 2 to 6;
• and
• a repeating unit represented by the formula (4):
• wherein Y41 represents F or a C1-C3 perfluoroalkyl group;
• k4 represents 0 or 1;
• n4 represents an integer of 1 to 8;
• when n4 represents an integer of 2 to 8, Y41 in each of respective units —(CF2CFY41—O)n4— may be the same as or different from each other;
• and m4 represents an integer of 1 to 6,
• wherein the repeating unit C that is at least one repeating unit selected from the group consisting of:
• a repeating unit represented by the formula (7):
• wherein Rf71 represents F, Cl, or a C1-C9 linear or branched fluoroalkyl group, and
• a repeating unit represented by the formula (8):
• wherein Y81 represents H or F;
• Y82 represents F or a C1-C9 linear or branched fluoroalkyl group;
• and Y83 represents H, F, Cl, or a C1-C9 linear or branched fluoroalkyl group.