DENSITIES AND EXPANSION COEFFICIENTS OF NAFION POLYMERS

The densities and expansion coefficients of several Nafions in the acid and salt form were measured. For some samples, effects of variations in the equivalent weight, moisture content, and degree of uniaxial orientation were explored. The densities, which show considerable experimental scatter, seem to be independent of the equivalent weight but to be a strong function of the moisture content. Thin films of the as‐received, unbacked polymer are strongly uniaxially oriented. After annealing, reproducible values of the expansion coefficient can be obtained. Two distinct breaks in the linear expansion curve are seen; in the salts, the upper one correlates with the glass transition of the material, while the lower one is found in the vicinity of the mechanical β‐dispersion of the polymer. The large scatter of the experimental densities is consistent with the hypothesis that the sample is subject either to a microphase separation process which is strongly influenced by the sample history and which affects the density of the material very strongly, or to partial crystallization of the polymer, or both. Copyright © 1979 John Wiley & Sons, Inc.