Studies of cation-anion and cation-polymer association in poly(ethylene oxide):: Pb(CF3SO3)2 complexes

Solid polymer electrolytes consisting of poly(ethylene oxide) (PEO) and Pb(CF3SO3) were investigated by vibrational (Raman and infrared) and Pb-207 nuclear magnetic resonance (NMR) spectroscopies. The nu(s)(SO3) symmetric stretch and delta(CF3) deformation vibrational modes both yield information on cation-anion association effects, while the CH2 rocking mode is very sensitive to cation-polyether oxygen interactions. The free ion concentration decreases with increasing temperature, as commonly observed for many other polymer electrolyte systems. In the present case, the largest decrease occurs in the temperature interval between 60 degrees and 70 degrees C, coinciding with melting of the pure PEO phase in the material. However, significant changes in polymer segmental conformation are also observed beginning around 50 degrees C. Both temperature ranges in which the vibrational results exhibit large changes (50-60 degrees and 60-70 degrees C) also show substantial but separate transformations of the Pb-207 NMR chemical shift interaction, which is dominated by cation-oxygen association. Both spectroscopic methods, which are sensitive to dynamic processes occurring on vastly different time scales, are nevertheless consistent in demonstrating the presence of at least two steps in the transition between the low temperature, partially crystalline phase and the high temperature, amorphous phase. (C) 1999 Elsevier Science B.V. All rights reserved.