Conditions have been worked out for determining the absolute water content of Nafion-H by proton NMR. The relative areas of the resonances due to hydroxylic protons can be compared directly with those due to a proton reference substance added in known amount, provided that proper precautions are token to detect the protons of the sample and those of the reference with equal sensitivity. A linear relationship is obtained between the proton content determined by NMR and the water content determined by weight changes. In certain swelling solvents, the chemical shift of the hydroxyl resonance is strongly dependent on the water content, and the chemical shift alone may be used as an indirect measure of the water content. Nafion-H dried in vacuo to constant weight at room temperature is the monohydrate, i.e., RFS03~'H30".

We thank Dr. Grot for providing us with an English language version of this paper. (12) Prolonged heating (10-50 h) was required to reach constant weight, and it seems likely that the reference states chosen by some of the previous workers do not represent equilibrium. Above about 200 °C extensive decomposition occurred.

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