Poly(ethylene glycol)-based networked polymers that had lithium sulfonate salt structures on the network were prepared by heating a mixture of poly(ethylene glycol) diglycidyl ether (PEGGE), poly(ethylene glycol) bis(3-aminopropyl) terminated (PEGBA), and an ionic epoxy monomer, lithium 3-glycidyloxypropanesulfonate (LiGPS). Flexible self-standing networked polymer films showed high thermal stability, low crystallinity, low glass transition temperature, and good mechanical strength. The materials were ion conductive at room temperature even under a dry condition, although the ionic conductivity was rather low (10(-6) to 10 (5) S/m). The ionic conductivity increased with the increase in temperature to above 1 x 10 (4) S/m at 90 degrees C. The film samples became swollen by immersing in propylene carbonate (PC) or PC solution of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The samples swollen in PC showed higher ionic conductivity (ca.1 x 10(-3) S/m at room temperature), and the samples swollen in LiTFSI/PC showed much higher ionic conductivity (nearly 1 S/m at room temperature). (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3113-3118, 2010