Ion-conducting polymers and membranes comprising them
An ion-conducting polymer wherein at least 80% of the repeat units comprise an ion-conducting region and a spacer region is disclosed. The ion-conducting region has an aromatic backbone of one or more aromatic groups, wherein at least one ion-conducting functional group is attached to each aromatic group. The spacer region has an aromatic backbone of at least four aromatic groups, wherein no ion-conducting functional groups are attached to the aromatic backbone. The polymer is suitable for use as a fuel cell membrane, and can be incorporated into membrane electrode assemblies.
1. A polymer consisting of linked units, wherein each of at least 80% of the linked units consists of one ion-conducting region and one spacer region connected thereto, wherein
a) the ion-conducting region consists of one or more aromatic groups, each of the one or more aromatic groups being adjacent to at least one electron-donating group and each of the one or more aromatic groups having attached thereto at least one pendant ion-conducting functional group, wherein if the ion-conducting region includes two or more aromatic groups, then at least two of the aromatic groups are optionally connected by electron-donating groups; and
b) the spacer region consists of at least four aromatic groups, each of the at least four aromatic groups being adjacent to at least one electron-withdrawing group and none of the at least four aromatic groups having attached thereto an ion-conducting functional group, wherein at least two of the at least four aromatic groups are optionally connected by electron-withdrawing groups.
2. A polymer according to claim 1 , wherein at least 95% of the linked units consist of the ion-conducting region and the spacer region.
3. A polymer according to claim 1 , wherein the one or more aromatic groups in the ion-conducting region is/are selected from the group consisting of phenylene, napthylene and anthracenylene groups.
4. A polymer according to claim 1 , wherein each aromatic group in the ion-conducting region is adjacent to an electron-donating group.
5. A polymer according to claim 4 , wherein the electron-donating group is an ether group.
6. A polymer according to claim 1 , wherein the at least one pendant ion-conducting functional group attached to each of the one or more aromatic groups in the ion-conducting region is a sulphonic acid group.
7. A polymer according to claim 1 , wherein the ratio of the number of aromatic groups in the spacer region to the number of aromatic groups in the ion-conducting region is at least 2:1.
8. A polymer according to claim 1 , wherein the at least four aromatic groups in the spacer region are selected from the group consisting of phenylene, napthylene and anthracenylene groups.
9. A polymer according to claim 1 , wherein the at least four aromatic groups in the spacer region are connected by electron withdrawing groups.
10. A polymer according to claim 9 , wherein the electron-withdrawing groups are sulphone or ketone groups.
11. A polymer according to claim 1 , which has an equivalent weight of less than 800 g mol −1 .
12. A polymer according to claim 1 , which has an inherent viscosity of greater than 1.0 dl/g.
13. A polymer solution comprising a polymer according to claim 1 .
14. A polymer electrolyte membrane comprising a polymer according to claim 1 .
15. An electrocatalyst layer on a substrate wherein the electrocatalyst layer comprises a polymer according to claim 1 .
16. A membrane electrode assembly comprising one or both of a polymer electrolyte membrane and an electrocatalyst layer on a substrate, wherein the polymer electrolyte membrane and the electrocatalyst layer comprise a polymer according to claim 1 .