Synthesis and properties of polyaniline derivatives with liquid crystallinity

Polyanilines with liquid crystalline (LC) substituents, which consist of a flexible methylene spacer and phenylcyclohexyl moiety as a mesogenic core, were synthesized. Polymerizations were performed using ammonium persulfate and perchloric acid as the catalytic system. The polymers were quite soluble in organic solvents such as THF and chloroform. The polymers were characterized by IR, UV-vis, H-1 NMR, and C-13 NMR spectroscopies. The oxidized form of the pristine polyaniline derivative with a liquid crystalline group and neutral form prepared by ammonia treatment were examined with respect to the liquid crystallinity. The polymers with the longer flexible methylene spacer (n = 10) of the oxidized form and neutral form exhibited thermotropic liquid crystallinity. Phase transitions and the corresponding enthalpy changes were evaluated using differential scanning calorimeter measurements. The smectic liquid crystallinity was characterized by fan-shaped texture through polarizing optical microscope observations. The LC domains of polyaniline derivative were growing like strings and aligned parallel to the magnetic field.