ION-EXCHANGE MEMBRANE OF FLUORORESIN HAVING WIDELY RANGING ION-EXCHANGE CAPACITY, AND PROCESS FOR PREPARATION THEREOF

摘要

PROBLEM TO BE SOLVED: To provide an ion-exchange membrane of a fluororesin having a widely ranging ion-exchange capacity, especially an ion-exchange membrane for fuel cells. SOLUTION: The polymer ion-exchange membrane comprises a fluorine-based polymer material having a main body of a long chain-branched polytetrafluoroethylene structure bonded with a polystyrene graft side chain having sulfonic acid groups and also has an ion-exchange capacity of 0.5 to 4 meq/g and a tensile strength at break in the hydrous state of ranging from 1 to 25 MPa. The process for the preparation thereof comprises forming a long chain-branched polytetrafluoroethylene membrane which is irradiated in the range of a radiation dose of 5 to 300 kGy by using a radiation of an electron ray or gamma ray at a specific temperature and under a specific oxygen partial pressure, irradiating again the radiation of an electron ray or gamma ray onto the above membrane, introducing a polystyrene graft side chain by the grafting of styrene onto the irradiated polytetrafluoroethylene membrane in a liquid styrene monomer or in a styrene monomer solution diluted with a solvent, and introducing sulfonic acid groups onto the above polystyrene graft side chain.