Synthesis and preliminary characterization of model liquid crystalline ionomers

Model liquid crystalline ionomers have been synthesized that consist of low molecular weight linear chains selectively end-capped at one or both end(s) with an ionic mesogenic group. ω- and α,ω-carboxylato and sulfonato polystyrene chains have been prepared by living anionic polymerization and associated with mesogenic counterions, the structure of which is a rigid azobenzene moiety attached to a quaternary ammonium halide through a flexible spacer. The thermotropic behavior of the liquid crystalline halato(semi)telechelic polymers (LC H(S)TP's) has been studied by differential scanning calorimetry and optical microscopy. Some of them show smectic mesophases in a large temperature range. Actually, the liquid crystalline properties of the LC H(S)TP's depend on the molecular weight and the nature of the ionic end groups. A model, based on a crystal close packing approach, shows that the bulkiness of the sulfonato end groups can prevent the formation of smectic mesophases. The supramolecular organization of the LC H(S)TP's has also been studied by small angle neutron scattering, which agrees with a microphase separation between the polymer chains and the mesogenic counterions.