DESIGN OF ALKALINE METAL-ION CONDUCTING POLYMER ELECTROLYTES

Polysiloxanes with covalently attached oligo ethylene oxide and di-t-butylphenol (1), naphthol (II), and hexafluoropropanol (III) were synthesized. The crosslinked polymers with a hexamethylene spacer were also prepared. The ion conductivities of the Li, Na, and K salts were measured as a function of temperature. The highest conductivities for K and Na of I at 30-degrees-C were 5.5 X 10(-5) and 5.0 X 10(-5) S/cm, respectively, when the ratio of the ion to ethylene oxide unit was 0.014. On the other hand, Li conductivity was 8.0 x 10(-6) S/cm when the ratio between Li and ethylene oxide unit was 0.019. The maximum conductivities of Li ions of II and III were in the order of 10(-6) and 10(-7) S/cm at 30-degrees-C, respectively. When the polymers were crosslinked by a hexamethylene residue, the ion conductivities decreased while the degree of crosslinking increased. The temperature dependence of the cation conductivities of these systems could be described by the Williams-Landel-Ferry (WLF) and the Vogel-Tammann-Fulcher (VTF) equation. The results demonstrate that ion movement in these polymers is correlated with the polymer segmental motion. The order of ionic conductivity was K+ > Na+ much greater than Li+. This suggests that steric hindrance and pi-electron delocalization of the anions attached to polymer backbone have a large effect on ion-pair separation and their ionic conductivities. Thermogravimetric analysis of the polymers indicated that the degradation temperature for I and II were about 100-degrees-C higher than for poly(siloxane-g-ethylene oxide). This is due to the antioxidant properties of sterically hindered phenols and naphthols. (C) 1993 John Wiley & Sons, Inc.