Phase Behavior and Dynamics of the ABA Triblock Copolymer Poly(ethylene glycol) Distearate Doped with Alkali Metal Salts

The ABA triblock copolymer poly(ethylene glycol) distearate (PEGD), average M n ca. 930, complexed with lithium and sodium perchlorates has been studied by 1 H, 7 Li, 13 C, and 23 Na solid-state nuclear magnetic resonance (NMR), SAXS, DSC, and polarized-light optical microscopy. Unlike other solid polymer electrolytes, highly Li + -doped PEGD samples exhibit sharp 7 Li NMR quadrupolar powder patterns even at temperatures well above the melting point, indicating that this triblock copolymer is microphase separated and the dynamics in the PEG phase are anisotropic. Measurements of the 7 Li central transition line width in highly doped samples show three distinct line narrowings, due to the poly(ethylene glycol) glass transition (∼−20 °C), the stearate melting point of the polymer (∼35 °C), and an order−disorder transition (∼72 °C). 23 Na NMR measurements yield similar results. SAXS, DSC, and optical microscopy with polarized light confirm the presence of a microphase-separated state up to ∼72 °C. 13 C and 1 H NMR show that the segmental mobility in the ordered state is reduced compared to the isotropic melt. The results confirm the previously proposed order−disorder model to explain the dependence of the ionic conductivity on the lithium concentration for Li + -doped PEGD samples.