The ternary copolymers of poly(ethylene oxide) (PEO), terephthaloyl chloride (TPC), and lithium 2,5-diaminobenzene sulfonate (LDABS) have been synthesized by the separated copolymerization PEG, TPC, and LDABS. Three ternary copolymers, PEO0.12-TPC0.50-LDABS(0.38), PEO0.24-TPC0.50-LDABS(0.26) and PEO0.36-TPC0.51-LDABS(0.13), are thermally stable and mechanically strong ionic conductors. The combination of immobilized anionic groups (SO3-) incorporated into the copolymer to increase the mobile cation concentration and of PEO introduced to enhance ionic conductivity via flexible chain motion. PEO0.24-TPC0.50-LDABS(0.26) was found to be a good polymeric material with good mechanical properties and a high ionic conductivity of 8.37 x 10(-6) S/cm at 25 degrees C.