Polyethylene glycol-functionalized polyoctahedral silsesquioxanes as H + -conducting electrolytes

Proton-conducting electrolytes composed of a mixture of MePEG 7 SO 3 H acid and poly(ethylene) glycol-functionalized polyoctahedral silsesquioxanes (Q 8 M 8 -MePEG n ) are prepared. Eight MePEG n (n = 3, 7, and 12) arms are attached to a (HSiMe 2 O) 8 Si 8 O 12 (Q 8 M 8 H ) core in the molecule. These Q 8 M 8 -MePEG n compounds show nearly the same fractional free volume ( FFV ), but show increased volume fractions of PEG ( V f,PEG ) and viscosities with longer PEG arms. At low MePEG 7 SO 3 H acid concentration (0.26 M), V f,PEG and FFV dominantly affect the ionic conductivity. Q 8 M 8 -MePEG 12 shows the highest conductivity due to the largest V f,PEG at 0.26 M. At a high acid concentration (1.32 M), the differences of V f,PEG are much smaller and viscosity becomes more important. Q 8 M 8 -MePEG 3 reaches the largest conductivity of 1.32 × 10 −4 S cm −1 at 55 °C at 1.32 M because of the lowest viscosity.