Yk. Yarovoy et al., Dynamic mechanical spectroscopy and conductivity studies of gel electrolytes based on stereocomplexed poly(methyl methacrylate), SOL ST ION, 118(3-4), 1999, pp. 301-310
Thermally reversible ionically conducting gel electrolytes, comprising blen
ds of atactic and isotactic poly(methyl methacrylate) (PMMA), lithium salt
and an organic solvent, have been prepared and characterized. Due to associ
ation between isotactic PMMA (i-PMMA) and syndiotactic sequences of atactic
PMMA (a-PMMA) strong gels are formed. in solvents which ordinarily do not
form gels with high molecular weight a-PMMA, namely, dimethyl carbonate (DM
C) and diethyl carbonate (DEC). The plot of the dependence of the elastic m
oduli on the fraction of i-PMMA passes through a maximum at similar to 1:1
molar ratio between isotactic and syndiotactic fractions of a-PMMA. However
, the conductivity of the gels is invariant to the ratio of i-PMMA and a-PM
MA. Thus, a gel with a typical polymer content of 15-20 wt%, 1 M lithium sa
lt, and a ratio of i-PMMA to a-PMMA of about 1:3 has an ionic conductivity
in the range of 1 x 10(-3)-4 x 10(-3) S cm(-1) and possesses a dynamic elas
tic modulus one order of magnitude higher than the electrolytes containing
only atactic PMMA. This modulus is obtained at values of the frequency betw
een 0.01 and 100 radians, so that even under static conditions the gels do
not flow and exhibit reversible elasticity to approximately 100% elongation
. Thermal mechanical analysis and calorimetry of these gels show that the p
hysical crosslinks formed by stereocomplexed syndiotactic and isotactic tri
ads melt in the range of 65-85 degrees C depending on the nature of the sol
vent and lithium salt. The fact that these gel electrolytes are thermorever
sible makes them readily processable. After melt casting they form transpar
ent dimensionally stable, self supporting films. (C) 1999 Elsevier Science
B.V. All rights reserved.