Ion-Exchange Membranes from Blends of Sulfonated Polyphosphazene and Kynar FLEX PVDf

摘要

Ion-exchange membranes were prepared by blending sulfonated poly[bis(3-methylphenoxy)]phosphazene (SPOP) with Kynar~(~R) FLEX, a copolymer of vinylidene fluoride and hexafluoropropylene, which was followed by crosslinking with use of ultraviolet or e-beam radiation. It was found that, in general, Kynar FLEX was immiscible on a molecular level with the SPOP. The polymers had, however, acceptable degree of compatibility and no sign of macroscopic phase separation was observed for a relatively wide composition range. The degree of compatibility increased with increasing IEC of the SPOP. Also, when sulfonic groups of the SPOP were converted to the tetrabutylammonium (TBA) form, highly homogeneous, transparent blends were obtained. These, however, could not be crosslinked effectively. The Na-form of SPOP was then used in further studies. A linear correlation was observed between the conductivity and swelling of the blended and crosslinked membranes. A conductivity increase from 0.01 to 0.075 S/cm was accompanied by an increase in swelling from 20 to 80%. Additionally, membranes with the same swelling but prepared from SPOP with higher IEC showed higher conductivity. No significant difference in the swelling versus conductivity dependence was observed between membranes crosslinked with benzophenone and UV light and those crosslinked with electron-beam radiation. Preliminary DMFC tests showed methanol crossover rates to be 3 times lower (6 times lower if thickness corrected) for the blended membranes as compared to Nafion 117.