THE IMPORTANCE OF ION POLYMER CROSS-LINKS IN POLYMER ELECTROLYTES

Raman-, Brillouin- and photon correlation spectroscopy have been used to study LiCF3SO3 and NaCF3SO3 containing polyethers (PEO and PPO). At focus are factors controlling the ion-polymer interactions, the formation of transient ionic crosslinks and their effect on the local flexibility. Brillouin and photon correlation spectroscopy show that the structural relaxation time is independent of the polymeric chain length for chains longer than n almost-equal-to 20 repeat units. For shorter chains OH bridging slightly stiffens the dynamics whereas for CH3 end-capped chains the local chain flexibility increases dramatically as n decreases. The crossover at approximately 20 monomer indicates the number of monomers involved in the cooperative segmental rearrangements needed for structural relaxations in high M(W) complexes, and thus also for an ionic displacement to occur in these systems. It is found that transient crosslinks are established for n > 4 and they considerably slow down the local dynamics. The density of crosslinks is found to be strongly temperature dependent and this is the reason for departure from T(g) scaled dynamics in the complexes.