Amphiphilic graft copolymers consisting of methacrylate backbones carrying approximately 48 wt.% of ethylene oxide [(EO)(9) or (EO)(23)] side chains as ionophilic groups and fluorocarbon or hydrocarbon side chains as ionophobic groups were prepared. Solid polymer electrolytes based on the copolymers and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) were characterized by DSC and the impedance spectroscopy. A maximum ion conductivity of 8 x 10(-5) S cm(-1) at 60 degreesC was found for a polymer electrolyte based on a copolymer having hydrocarbon side chains and (EO)(23) side chains, despite an EO content of only 50 wt.%. No (EO)(n) side chain crystallinity in the electrolytes was detected by calorimetry. The hydrocarbon side chains, on the other hand, were found to form a crystalline phase in the electrolytes. The melting of this phase was not reflected in the shape of the Arrhenius conductivity plot. This indicated that the segmental mobility in the ion conducting phase did not decrease as a result of the presence of the crystalline hydrocarbon phase.