The interaction of the silver cation of AgClO4 with carbonyl oxygen in poly
(2-ethyl-2-oxazoline) (POZ) was found to be similar to that of AgBF4 by inf
rared and Raman spectroscopic results. The two silver salts are similar in
molecular size and lattice energy. However, the two silver-polymer electrol
ytes showed remarkably different gas transport properties. The POZ:AgClO4 m
embrane showed very low gas permeance compared with the POZ:AgBF4 at the 1:
1 [C=O]:[Ag] mole ratio. The difference in the transport properties has bee
n attributed mostly to the changes in chain mobility upon both the formatio
n of transient cross-links by silver cations and the dangling of the heavy
anions on the main chain. The changes in chain mobility were characterized
by the glass transition temperature and the intersegmental d spacing. The e
xtent of the transient cross-links seems to be strongly associated with the
coordination number of the silver cation; the silver cation in AgClO4 has
a higher coordination number than that in AgBF4. The structure difference f
or the two systems was also confirmed by the difference in the bond length
between the cation and anion calculated from ab initio methods, despite the
very similar lattice energies for two salts. Thus, the gas transport prope
rties were successfully used to monitor the role of the transient cross-lin
k as well as of the neighboring counteranion on the structure and physical
properties of polymer electrolytes.