Nafion - Nomenclature and Molecular Weight

Nomenclature and Molecular Weight

Nafion can be produced as both a powder resin and a copolymer. It has various chemical configurations and thus several chemical names in the IUPAC system. Nafion-H, for example, includes the following systematic names:

• From Chemical Abstracts: ethanesulfonyl fluoride, 2-methyl]-1,2,2,2-tetrafluoroethoxy]-1,1,2,2,-tetrafluoro-, with tetrafluoroethylene
• tetrafluoroethylene-perfluoro-3,6-dioxa-4-methyl-7-octenesulfonic acid copolymer

The molecular weight of Nafion is uncertain due to differences in processing and solution morphology. The structure of a Nafion unit, shown at the top of the page, illustrates the variability of the material; for example, the most basic monomer contains chain variation between the ether groups (the z subscript). Conventional methods of determining molecular weight such as light scattering and gel permeation chromatography are not applicable because Nafion is of course insoluble, although the molecular weight has been estimated at 105-106 Da. Instead, the equivalent weight (EW) and material thickness are used to describe most commercially available membranes. The EW is defined as the weight of Nafion (in molecular mass) per mole of sulfonic acid group. For example, Nafion 117 represents 1100 g EW + 0.007 inch in thickness. In contrast equivalent weight, conventional ion-exchange resins are usually described in terms of their ion exchange capacity (IEC) which is the multiplicative inverse or reciprocal of the equivalent weight. IEC = 1/EW.