A novel ionic liquid of trifluoroacetic propylamine, i.e., [CH3CH2CH2NH3+] [CF3COO-] (TFAPA), was synthesized from trifluoroacetic acid and propylamine. The ionic liquid of TFAPA was used to prepare anhydrous, conducting membranes based on polymers of sulfonated poly (ether ether) ketone (SPEEK) or polyvinylidenefluoride (PVDF). The ionic conductivity and mechanical strength of the composite membranes were investigated at elevated temperatures and under anhydrous conditions. Conductivity of 0.030 S/cm was achieved with TFAPA at 180 degrees C, and of 0.019 S/cm with a membrane containing 70% (wt) TFAPA in SPEEK with a sulfortation degree of 86%. at 160 degrees C. Increasing either ionic liquid content or temperature reduced the mechanical strength of the composite membrane. Efforts were made to improve the strength of TFAPA/SPEEK composite membranes by cross-linking the SPEEK, which led to some strength enhancement at 110 degrees C and 130 degrees C. (c) 2008 Elsevier Ltd. All rights reserved.