FTIR and solid state 13C NMR studies on the interaction of lithium cations with polyether poly(urethane urea)

The behaviors of lithium ions in a polyether poly(urethane urea) (PEUU) were investigated by differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, ac impedance and C-13 magic angle spinning (MAS) solid-state NMR measurements. The PEUU used in this study is composed of poly(ethylene glycol) (PEG, mol wt 1000) as the soft segment and 4,4'-methylenebis(cyclohexyl isocyanate) extended with ethylenediamine (EDA) as the hard segment. The results of DSC measurements indicate the formation of transient cross-links between Li+ ions and the ether oxygens on complexation with LiClO4, resulting in an increase in the soft segment T-g. A detailed analysis of -NH stretching regions shows an appreciable shift in the free as well as the hydrogen-bonded -NH stretching bands, suggesting possible interactions of Li+ ions with both hard and soft segments of PEUU. The Arrhenius-like behavior of ionic conductivity with reciprocal temperature implies an activated hopping mechanism for transport of the charge carriers where the charge carriers are decoupled from the segmental motion of the polymer chains. Moreover, significant line broadening, slight upfield chemical shift, and short T-CH, observed in the C-13 NMR spectra for the carbons attached to the ether oxygens as the dopant was added into the polymer, indicate a coordination between the Li cation and the ether oxygens in the soft segments.