IONIC-CONDUCTION OF LITHIUM, SODIUM AND MAGNESIUM SALTS WITHIN ORGANIZED SMECTIC LIQUID-CRYSTAL POLYMER ELECTROLYTES

Polymers having the structure [GRAPHICS] where R = -C16H33 Or -C12H25 and n = 5 or 6 (coded C1605 etc.) have been synthesised. Complexes wit h several salts of Li, Na and Mg have been prepared, eg C1605-LiClO4 ( 1:1) where numbers in parenthesis denote the molar proportions of repe ating unit to salt. Using thermal analysis, polarised light microscopy , SAXS and WAXS techniques and energy minimised modelling it is shown that the complexes having 0.5 to 1.0 mol salt per polymer repeating un it form smectic liquid crystal structures above the sidechain melting temperatures leg 43.5 degrees C for C1605-LiClO4 (1:1)). The salt is c omplexed to the two-dimensional helical polyether backbone layers whic h are separated by hydrocarbon layers. Both sheared and unsheared samp les are compared. In contrast to expectation from conventional polymer electrolyte behaviour, the ionic conductivities of the lithium salt c omplexes in the liquid-crystal phases are greatest for systems having the most extensive organisation following the sequence C1605 > C1606 > C1206 and the sheared samples are the more conductive. The lithium sa lt complexes in general have the highest conductivities though Na and Mg complexes are similarly organised and lower conductivities are ascr ibed to lower cation mobilities. (C) 1998 Elsevier Science Ltd. All ri ghts reserved.