Polymer electrolytes based on the composite of nitrile rubber (NBR; poly(acrylonitrile-co-1,4-butadiene)) and Li(CF3SO2)(2)N (Li(Tf)(2)N) were prepared and their ionic conductivity was evaluated. NBR with nitrile content of 33% was mixed with 25 wt% Li(Tf)(2)N to show the highest ionic conductivity, while still in the rubbery state. Furthermore, addition of 9.2 wt% imidazolium-type zwitterion enhanced the ionic conductivity of about 8 times (5.6 x 10(-6) S cm(-1) at 50 degrees C) with lithium ion transference number of 0.32. FT-IR investigations suggested that the interaction between NBR and Li+ ion decreased by the addition of zwitterion. DSC measurements on the composites consisting of NBR, Li(Tf)(2)N, and zwitterion strongly suggested micro-phase separation between NBR-rich phase and zwitterion-rich phase. (c) 2007 Elsevier B.V. All rights reserved.