Process for producing polymer electrolyte membranes for fuel cells, polymer electrolyte membranes for fuel cells produced by the process, and fuel cell membrane-electrode assemblies using the membranes

Abstract

By performing photograft polymerization of functional monomers such that grafted chains will be introduced from the surface of a polymer base film into its interior without deteriorating its inherent characteristics and also by creating a multiplex crosslinked structure between the grafted chains and the base film under such conditions as to cause preferential radiation-induced crosslinking reaction, there is produced a polymer electrolyte membrane having high enough oxidation resistance and proton conductivity to be suitable for use in fuel cells.

Description

Claims

1. A process for producing a polymer electrolyte membrane for fuel cells comprising the steps of providing a polymer base film, forming on the polymer base film an undercoat which contains a photopolymerization initiator, irradiating the polymer base film with ultraviolet rays as the surface of the undercoat is placed in contact with a liquid mixture of a vinyl monomer capable of retaining sulfonic acid groups and a solvent, so that the vinyl monomer is graft polymerized in a liquid-phase system, then causing the grafted molecular chains themselves, the molecular chains themselves in the base film and the grafted molecular chains and the molecular chains in the base film to crosslink in a multiplex fashion by exposure to radiation, and introducing sulfonic acid groups into aromatic rings in the grafted molecular chains.

2. A process for producing a polymer electrolyte membrane for fuel cells comprising the steps of providing a polymer base film, forming on the polymer base film an undercoat which contains a photopolymerization initiator, irradiating the polymer base film with ultraviolet rays as the surface of the undercoat is placed in contact with a liquid mixture of a vinyl monomer capable of retaining sulfonic acid groups, a polyfunctional vinyl monomer necessary for creating a chemical crosslinked structure and a solvent, so that the vinyl monomers are graft polymerized in a liquid-phase system, then causing the grafted molecular chains themselves, the molecular chains themselves in the base film and the grafted molecular chains and the molecular chains in the base film to crosslink in a multiplex fashion by exposure to radiation, and introducing sulfonic acid groups into aromatic rings in the grafted molecular chains.

3. A process for producing a polymer electrolyte membrane for fuel cells comprising the steps of providing a polymer base film, forming on the polymer base film an undercoat which contains a photopolymerization initiator, irradiating the polymer base film with ultraviolet rays as the surface of the undercoat is placed in contact with the vapor of a liquid mixture of a vinyl monomer capable of retaining sulfonic acid groups and a solvent, so that the vinyl monomer is graft polymerized in a gas-phase system, then causing the grafted molecular chains themselves, the molecular chains themselves in the base film and the grafted molecular chains and the molecular chains in the base film to crosslink in a multiplex fashion by exposure to radiation, and introducing sulfonic acid groups into aromatic rings in the grafted molecular chains.

4. A process for producing a polymer electrolyte membrane for fuel cells comprising the steps of providing a polymer base film, forming on the polymer base film an undercoat which contains a photopolymerization initiator, irradiating the polymer base film with ultraviolet rays as the surface of the undercoat is placed in contact with the vapor of a liquid mixture of a vinyl monomer capable of retaining sulfonic acid groups, a polyfunctional vinyl monomer necessary for creating a chemical crosslinked structure and a solvent, so that the vinyl monomers are graft polymerized in a gas-phase system, then causing the grafted molecular chains themselves, the molecular chains themselves in the base film and the grafted molecular chains and the molecular chains in the base film to crosslink in a multiplex fashion by exposure to radiation, and introducing sulfonic acid groups into aromatic rings in the grafted molecular chains.

5. A polymer electrolyte fuel cell membrane that is produced by the process according to any one of claims 1 to 4, wherein the polymer base film is composed of an olefinic polymer or a fluoropolymer.

6. A polymer electrolyte fuel cell membrane that is produced by the process according to any one of claims 1 to 4, wherein the degree of grafting as the ratio of the weight of the grafted molecular chains to the weight of the base film is 6 to 80% of the vinyl monomer or monomers has been grafted and the membrane has an ion-exchange capacity of 0.3 to 3.0 meq/g.

7. A fuel cell membrane-electrode assembly comprising the polymer electrolyte membrane according to any one of claims 1 to 4 which is joined to an anode and a cathode.