Dynamic mechanical studies of partially ionized and neutralized Nafion polymers

Abstract

The dynamic mechanical properties of Nafion precursor were determined as a function of the degree of conversion to the sodium ionomer, and those of the acid as a function of the degree of conversion to the cesium salt. A run was also made on the barium neutralized material, as well as on a remolded sample of a partly converted precursor. The precursor shows four dispersions which (in order of decreasing temperature) are identified with the glass transition, motions of the ether side chains, CF2 groups in the backbone, and pendant SO2F groups. Four relaxation regions are also seen in the ionomer, which are identified with the glass transition of the ionic regions and of the matrix, as well as with motions of the ether side chains and the backbone CF2 groups. While the polymers in the acid and the salt forms arc compatible, as seen by the gradual movement of the ionic glass transition peak to higher temperatures with increasing degree of neutralization, the salt and the precursor are not compatible. In the barium salt, the ionic glass transition peak occurs at a temperature close to the melting point of the crystalline regions, and most likely contains a contribution from that process also.