Solid polymer electrolyte (SPE) system purely based on poly(vinylidenefluoride-hexafluoropropylene) [P(VdF-HFP)] and magnesium trifluoromethanesulfonate (MgTf) has been synthesized via solution-casting technique with acetone as solvent. Various instruments have been used to examine the structural, morphological, and thermal behaviors of the samples. X-ray diffraction (XRD), horizontal attenuated total reflectance-Fourier transform infrared spectroscopy (HATR-FTIR) and differential scanning calorimetry (DSC) are utilized to study the conversion of crystalline to amorphous nature in the copolymer. The crystallinity of copolymer matrix has been shown to be greatly affected by incorporation of MgTf, even with low concentration and absence of plasticisers. Scanning electron microscopy (SEM), photoluminescence spectroscopy (PL), and AC impedance spectroscopy further corroborate the findings. FTIR spectra suggest complexation has occurred between the constituents in these SPEs. Thermogravimetric analysis (TGA) and DSC thermograms show some improvements in thermal behaviors upon the addition of MgTf. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 2050-2058, 2010