CATION COMPLEXATION AND CONDUCTIVITY IN CROWN-ETHER BEARING POLYPHOSPHAZENES

An attempt has been made to understand the mechanism of ionic conducti vity in polyphosphazene-salt complexes by the synthesis and study of s ystems with crown ether side groups and salts with different cations. Amorphous phosphazene polymers, bearing either (12-crown-4)-methoxy, ( 15-crown-5)-methoxy, or (18-crown-6)-methoxy pendent groups, either as single-substituent polymers or mixed-substituent species in a 1:3 rat io with 2-(2-methoxyethoxy)ethoxy groups, were synthesized and charact erized. The polymers in which all the side groups are crown ether unit s have glass transition temperatures higher than other oligo(ethyleneo xy) polyphosphazenes. They generate relatively low ionic conductivitie s at ambient temperatures when complexed with lithium triflate or lith ium perchlorate. This suggests that the cation carries a significant p art of the current in ether-type polymers. The ambient temperature ion ic conductivity of the cosubstituent polyphosphazenes, as well as of p oly[bis(2-(2-methoxyethoxy)ethoxy)phosphazene] (MEEP) (3), when comple xed with MClO4 (M = Li, Na, K, Rb, Cs), was measured. The ionic conduc tivity is reduced when a favorable 1:1 or 2:1 crown ether-cation compl ex is formed. The thermal behavior of these polymer-salt complexes was also investigated. The polymers exhibit an increased glass transition temperature when a favorable 2:1 crown ether-cation complex is formed . The relationships between the ionic conductivity and the glass trans ition temperature of the host polymer electrolytes and the stability o f the crown ether-cation complexes formed are discussed.