Ionic conductivity and morphological study of a thermoplastic polyurethane based electrolyte comprising of mixed soft segments

The morphology and ionic conductivity of three thermoplastic polyurethane (TPU) based polymer electrolytes have been studied by complexing lithium per chlorate (LiClO4) with these TPUs. The TPUs were prepared by using 4,4'-diphenyl methane diisocyanate (MDI) extended with ethylene diamine (EDA) as hard segment and polypropylene glycol (PPG), polytetramethylene glycol (PTMG) and 1:1 mixture of PPG/PTMG as soft segments. The characterization of these polymeric electrolytes doped with different concentrations of LiClO4 were studied by using differential scanning calorimetry (DSC), fourier transform infrared spectroscopy (FT-IR) and AC impedance measurements. Doping was done by two methods: (1) by blending TPU and LiClO4 solutions in dimethyl formamide (DMF), and (2) by immersing dry TPU films in LiClO4 solution in DMF. Ionic conductivity of all the polymeric electrolytes increases with increasing salt concentration for each isotherm and also with increase in amount of plasticizer. The polymeric electrolytes containing both PPG and PTMG as soft segment are found to have almost the same ionic conductivity as that containing only PPG in the soft segment. On the other hand, the dimensional stability of these electrolytes is comparable to that containing PTMG as the soft segment.