THE ROLE OF LITHIUM-SALTS IN THE CONDUCTIVITY AND PHASE MORPHOLOGY OF A THERMOPLASTIC POLYURETHANE

Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), and impedance spectroscopy (IS) were utilized to monitor changes in the morphology of a thermoplastic polyurethane (TPU) as a function of alkali-metal salt concentration. In this study, the alkali-metal salts of LiCF3SO3 and Li(CF3SO2)(2)N were observed to increase the overall bulk conductivity of a phase-segregated polyurethane comprising soft segments of poly(tetramethylene oxide) (PTMO) and hard segments of methylenebis(phenyl isocyanate) (MDI) and 1,4-butanediol (BDO). Significant changes occur in the FTIR spectrum of the TPU above the critical salt concentration (c(c)) of 0.5 mmol/g of TPU, suggesting an interaction of the lithium cation within the hard segment and between the hard and soft phases. A loss in long-range ordering of the hard domain above c(c) has also been observed by DSC. For temperatures around the hard segment T-g (= 110 degrees C) and above, IS revealed an increasing bulk conductivity as the salt concentration was increased. At lower temperatures a maximum in conductivity as a function of salt concentration occurs again at c(c). The results of this study would indicate that the characteristic phase-segregated morphology of the TPU has been altered as a result of the interaction of lithium cations within the polar hard domains and by the promotion of phase intermixing by the coupling of the hard and soft phases.