A COMPARISON OF IONIC-CONDUCTIVITY BEHAVIOR IN VARIOUS ETHYLENE-OXIDEBASED POLYMER ELECTROLYTES

Glass transition temperatures T-g and ionic conductivities sigma have been measured as a function of salt concentration m for LiCF3SO3 compl exes of three types of ethylene oxide (EO) based materials: (i) low mo lecular weight poly(ethylene oxide)s, viz. tetraglyme, PEG300 and PEG6 00 and end-esterified PEG300, (ii) higher molecular weight amorphous p olymer electrolytes, poly(methoxy polyethylene glycol monomethacrylate ) (PEM), methyl oxyethylene extended poly(propylene oxide) (Me-xPPO), and (iii) some [12] and [13]-crown-4 polymethacrylates (CEP). The vari ation of sigma with temperature T has been fitted to the VTF equation sigma = AT(1/2)exp{-B/(T-T-o)}. It is found (a) that the salt dependen t behaviour of all the amorphous PEO materials is very similar but ver y different from that of the CEPs; (b) that (T-g-T-o) is related to B in an approximately linear manner for all salted systems independent o f polymer type; (c) that for PEO systems, where the formation of ionic cross links is insignificant, T-o is independent of salt concentratio n, but that for the crown ether polymers in which ionic cross links ar e expected, T-o increases with m; and (d) that for the crown ether pol ymers, Aim and B vary weakly with rn and that the A/m and B values for all the ethylene oxide based materials appear to converge to common h igh values at high salt concentrations. This is compatible with the id ea that the solvated cations, incorporated intrahelically, cause the P EO to form crown like configurations. (C) 1998 Published by Elsevier S cience Ltd. All rights reserved.