Star-shaped polymers having side chain poss groups for solid polymer electrolytes; Synthesis, thermal behavior, dimensional stability, and ionic conductivity

A series of organic/inorganic hybrid star-shaped polymers were synthesized by atom transfer radical polymerization using 3-(3,5,7,9,11,13,15- heptacyclohexyl-pentacyclo[9.5.1.1 ^3,9.1 ^5,15.1 ^7,13]-octasiloxane-1-yl)propyl methacrylate (MA-POSS) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) as monomers and octakis(2-bromo-2-methylpropionoxypropyldimethylsiloxy)octasilsesquioxane as an initiator. Star-shaped polymers with methyl methacrylate (MMA) and PEGMA moieties were also prepared for comparison purposes. Dimensionally stable freestanding film could be obtained from the hybrid star-shaped polymer containing 26 wt % of MA-POSS moieties although its glass transition temperature is very low, -60.9 °C. As a result, the hybrid star-shaped polymer electrolyte containing lithium bis(trifluoromethanesulfonyl)imide showed ionic conductivities (1.75 × 10 ^-5 S/cm at 30 °C), which were two orders of magnitude higher than those of the star-shaped polymer electrolyte with MMA moieties.