Salt-containing membranes based on polymethacrylates having poly(ethylene carbonate-co-ethylene oxide) side chains, as well as their blends with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), have been studied. Self-supportive ion conductive membranes were prepared by casting films of methacrylate functional poly(ethylene carbonate-co-ethylene oxide) macromonomers containing lithium bis(trifluorosulfonyl)imide (LiTFSI) salt, followed by irradiation with UV-light to polymerize the methacrylate units in situ. Homogenous electrolyte membranes based on the polymerized macromonomers showed a conductivity of 6.3 x 10(-6) S cm(-1) at 20 degrees C. The preparation of polymer blends, by the addition of PVDF-HFP to the electrolytes, was found to greatly improve the mechanical properties. However, the addition led to an increase of the glass transition temperature (T-g) of the ion conductive phase by similar to 5 degrees C. The conductivity of the blend membranes was thus lower in relation to the corresponding homogeneous polymer electrolytes, and 2.5 x 10(-6) S cm(-1) was recorded for a membrane containing 10 wt % PVDF-HFP at 20 degrees C. Increasing the salt concentration in the blend membranes was found to increase the Tg of the ion conductive component and decrease the propensity for the crystallization of the PVDF-HFP component. (c) 2006 Wiley Periodicals, Inc.