Cation exchange resin, and cation exchange membrane and fuel cell electrolyte membrane using same

A cation exchange resin, comprising:

• a divalent hydrophobic unit shown in any one of the following formulae (1a′), (1b′), (1c′) and (1d′);
• and
• a divalent hydrophilic unit having divalent hydrophilic groups which are repeated via carbon-carbon bond, the divalent hydrophilic groups being composed of one aromatic ring, or being composed of a plurality of aromatic rings which are bonded to each other via a divalent hydrocarbon group, a divalent silicon-containing group, a divalent nitrogen-containing group, a divalent phosphorus-containing group, a divalent oxygen-containing group, a divalent sulfur-containing group, or carbon-carbon bond, at least one of the aromatic rings having a cation exchange group;
• wherein the hydrophobic unit and the hydrophilic unit are bonded to each other via carbon-carbon bond;
• wherein R′ is the same or different and represents a divalent aliphatic hydrocarbon groups having carbon atoms of 1 to 20 or direct bond, a is an integer of 1 to 10.