http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
Chemical and morphological investigations of perfluorosulfonate ionomers
High-performance liquid chromatographic procedures were used to study the ion-exchange selectivities of perfluorosulfonate ionomers (PFSI's). HPLC columns were packed with PFSI-coated octadecyl-derivatized silica and were used to elute a variety of large organic cations. Ion-exchange selectivity coefficients for the sample ions were calculated from the HPLC retention data. Structure-reactivity relationships were investigated by correlating the sample ion's molecular structure to its ion-exchange selectivity coefficient. These studies have shown that PFSI's have a remarkable affinity for large, hydrophobic cations. A broad-based series of procedures and instrumental techniques were used to investigate the chemical and morphological characteristics of solution-cast PFSI films and membranes. High equivalent weight PFSI's are insoluble in all solvents at temperatures below ca. 220°C and form pliant and cohesive membranes. In contrast, PFSI films cast from ethanol-water solutions (at room temperature) were found to be soluble in a variety of polar organic solvents at ambient temperature. Furthermore, these solution-cast films were brittle and non-cohesive. Solution-cast PFSI's prepared using high temperatures and suitable solvents were found to have the same desirable physical, mechanical, and chemical characteristics of the as-received polymer. The morphological investigations showed that both the as-received and the high temperature solution-cast PFSI's were partially crystalline. In contrast, the low temperature solution-cast PFSI showed no evidence of crystallinity. A new series of PFSI's, from the Dow Chemical Company, were used to study the effect of equivalent weight on PFSI morphology. All equivalent weights of the Dow PFSI's were found to contain ionic clusters. For equivalent weights greater than ca. 800 g/mole, the Dow PFSI's were found to be semicrystalline and the extent of crystallinity increased with equivalent weight. Dissolution and solution-casting procedures were developed for a wide range of equivalent weights of the Dow PFSI's. The temperatures necessary to completely dissolve these polymers increased with equivalent weight. Furthermore, the evaporation temperatures required to prepare high-quality, insoluble, solution-cast PFSI's increased with equivalent weight.