Abstract
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 (T g1), while the second one located between 20 and 50°C is attributed to the main chain of the polymer host (T g2). 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.
ACKNOWLEDGEMENT
The authors gratefully thank the National University of Singapore for a research grant for this work.