Thermal behavior and ionic conductivity of poly[lithium-N(4-sulfo-phenyl) maleimide -co- methoxy oligo(oxyethylene) methacrylate]

Poly[lithium-N(4-sulfophenyl) maleimide -co- methoxy oligo(oxyethylene) met hacrylates] [P(LiSMOEn)s] with three different oligoether side chains and d ifferent salt concentrations were synthesized. The copolyelectrolytes are e ssentially random in structure, with blocks of methoxy oligo(oxyethylene) m eth-acrylate (MOEnM) recurring sporadically in between the salt units of N( 4-sulfophenyl) maleimide. They all show two glass transitions in the temper ature range of -100 to 100 degrees C. The first one below 30 degrees C is a ssigned to the oligo(oxyethylene) side chain (T-g1), while the second one l ocated between 20 and 50 degrees C is attributed to the main chain of the p olymer host (T-g2) The maximum ionic conductivity of the copolymer electrol ytes, 1.6 x 10(-7) S cm(-1) at 25 degrees C, occurs at lithium salt concent ration [Li+]/[EO] = 2.2 mol%. The ionic conductive behavior of the copolyel ectrolytes follows the Vogel-Tammann-Fulcher (VTF) equation. Moreover, a sp ecial VTF behavior exists in the copolymers with shorter oligoether side ch ain and higher salt concentration. Sweep voltammetric results indicate that these copolyelectrolytes have a good electrochemical stability window.