Effect of polypyrrole on the morphology and ionic conductivity of TPU electrolyte containing LiClO₄

The effect of conducting polypyrrole (PPy) on the morphology and ionic conductivity of thermoplastic polyurethane (TPU) doped with LiClO₄ has been described and compared with those of pure TPU system. The TPU-PPy composites were prepared by chemical polymerization of pyrrole inside TPU films. All samples were characterized by their swelling behavior in a liquid electrolyte (LiClO₄/PC), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and AC impedance measurements. Swelling studies indicate an improved chemical stability of the composite compared to TPU. From TGA, the thermal stability of the composite was found to be comparable to pure TPU. A decrease in Tg of the soft segment was observed in the composite from DSC experiments. This may be due to interaction of PPy-NH groups with either carbonyl or ether oxygens of TPU, leading to phase separation of the hard and soft segments. The SEM micrograph of the composite shows the presence of typical cauliflower-like morphology of PPy. The ionic conductivity of the composite was found to be about one order of magnitude higher than pure TPU having the same amount of LiClO₄/PC. The enhancement of conductivity in presence of PPy may be associated with the increased mobility of ClO₄^- ions promoted by coordination of Li⁺ ions with PPy nitrogen atoms.