Polymer electrolyte (PEO:NH4I) has been complexed with dibenzo-24-crown-8 ether (DB24C8). The conductivity of the complexes has been measured as a function of the crown ether composition. The conductivity of this system is an order of magnitude higher than for the PEO:NH4I system. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) have been done to know about the thermal behaviour of the complexes. The conformational changes have been detected by Fourier transform infrared (FTIR) spectroscopy. Conductivity modification in the complexes has been explained by the chain-like formation in the complexes, increased amorphous phase and the enhanced free volume determined by positron annihilation lifetime spectroscopy (PALS). (C) 2013 Elsevier B.V. All rights reserved.