Ionic conductivity of a novel smectic polymer electrolyte

Abstract

Polymers having the following general formula have been synthesised ▪ where R is a long chain alkyl substituent such as -C 16H 33. The number of skeletal oxygen atoms n = 5 or 6 (coded C16O5 or C16O6) so that the helix formed by association of neighbouring side groups R, has 18 or 21 skeletal bonds per rotation and so imitates the PEOLi + or PEONa + 2 1 helix. Complexes with LiBF 4 in stoichiometries of 1 mol salt per structural (helical) repeat unit and 0.5 mol per repeat have been prepared. Small-angle- and wide-angle X-ray diffraction, thermal analysis and hot stage polarised light microscopy have been used to show that the complexes form smectic systems in the uncomplexed and complexed forms. In the complexes, cations are enclosed within the helices and the anions lie between planes of helices and the alkyl side chains so that the overall d spacing is 42.9 Å. The -C 16H 33 side chains melt at ca. 40 °C in the complexed material, to give a liquid crystal phase. The liquid crystal-isotropic transition varies slightly according to polymer and stoichiometry and is 89 °C for C16O5:LiBF 4 (1:1). The ionic conductivity-temperature relationship shows well-defined transitions at the phase changes and the complex impedance behaviour also reflects the several states of the system. The conductivity of the (1:1) complex is higher than the (1:0.5) complex and is comparable to P(EO) 6:LiBF 4 in the crystal and istropic phases, but is somewhat lower over the temperature range of the liquid crystal phase.