Enhanced conductivity of novel star branched liquid crystalline copolymer based on poly(ethylene oxide) for solid polymer electrolytes

Novel star branched amphiphilic liquid crystalline (LC) copolymers, namely, 4-Arm poly(ethylene oxide)-co-x-[(4-cyano-4′-biphenyl)oxy]alkyl methacrylate (TPEO-MAxLC-Φ) (x = 6, Φ = 20, 30; x = 9, Φ = 10, 19) containing cyanobiphenyl mesogenic pendants (MAxLC) are prepared by atom-transfer radical polymerization (ATRP). The effects of structural variations on the properties, and the relationship between morphology and the ionic conductivity of the copolymer electrolytes are studied. The strong assembly of cyanobiphenyl mesogens induces the copolymers with enantiotropic mesophase, even after doped with LiClO4. And lamellar structures are also achieved by cooperative assembly of hydrophobic mesogen-containing polymethacrylate groups and the hydrophilic TPEO nanoscale aggregation, especially after LC thermal annealing. The ionic conductivity has been improved greatly by incorporation of the cyanobiphenyl mesogens. This is because the mesogens not only favor the ordered morphology to provide the efficient ion transportation pathway, but also suppress TPEO crystallization to offer the movement of TPEO chains. Among all of the electrolyte films, TPEO-MA9LC-19 shows the best ion conductivity of 2.24 × 10−5 S cm−1 at 25 °C and even reaches to 5.39 × 10−5 S cm−1 after annealed at LC states.