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Poly[lithium-N(4-sulfophenyl) maleimide -co- methoxy oligo-(oxyethylene) methacrylates] [P(LiSMOEn)s] with three different oligoether side chains and different salt concentrations were synthesized. The copolyelectrolytes are essentially random in structure, with blocks of methoxy oligo(oxyethylene) meth-acrylate (MOEnM) recurring sporadically in between the salt units of N(4-sulfophenyl) maleimide. They all show two glass transitions in the temperature range of -100 to 100°C. The first one below -30°C is assigned to the oligo(oxyethylene) side chain (Tg1), while the second one located between 20 and 50°C is attributed to the main chain of the polymer host (Tg2). The maximum ionic conductivity of the copolymer electrolytes, 1.6 × 10-7 S cm-1 at 25°C, occurs at lithium salt concentration [Li+]/[EO] = 2.2 mol%. The ionic conductive behavior of the copolyelectrolytes follows the Vogel-Tammann-Fulcher (VTF) equation. Moreover, a special VTF behavior exists in the copolymers with shorter oligoether side chain and higher salt concentration. Sweep voltammetric results indicate that these copolyelectrolytes have a good electrochemical stability window. [ABSTRACT FROM AUTHOR]