Synthesis and characterization of N-substituted polyaniline with mesogen molecules

The N-substituted polyaniline (PANi) was synthesized by incorporation of bromine-terminated mesogens onto the emeraldine form of polyaniline. Firsty three liquid crystalline molecules containing biphenyl units were synthesized. These mesogenic molecules are named as: 6-bromo(4-hexyloxy-biphenyl-4'-oxy) hexane (C-6-C6Br), 5-bromo-(4-hexyloxy-biphenyl-4'-oxy) pentane (C-6-C5Br), 6-bromo-(4-octyloxy-biphenyl-4'-oxy) hexane (C-8-C6Br). Differential scanning calorimetry (DSC) in combination with polarizing optical microscopy (POM) were used to investigate the thermal properties of them. Optical microscopy showed focal conic texture characteristic of the Smectic A phase for (C-6-C5Br) and (C-8-C6Br). For (C-6-C-6-Br) smectic phase was determined. DSC experiments were also found in accord with mesophase formation. For the synthesis of N-substituted polyaniline with these mesogen molecules, the emeraldine base polyaniline was reacted with BuLi to produce the N-anionic polyaniline and then deprotonated polyaniline was reacted with bromine-end mesogen to prepare mesogen-substituted polyaniline through N-substitution reaction. The degree of N-substitution can be controlled by adjusting the molar feed ratio of mesogen to the number of repeat units of PANi. The microstructure and compositions of obtained polymers were characterized by FT-IR, elemental analysis, DSC, and scanning electron microscopy (SEM). The cyclic voltammetry show that the electroactivity of N-substituted polyaniline is strongly dependent on the degree of N-grafting. The solubility of mesogen-substituted polyaniline in common organic solvents such as THF and chloroform was improved by increasing the degree of N-substitution and also the samples are partially soluble in xylene. Liquid crystalline behavior of mesogen-substituted polyanilines was investigated via POM, but no mesophase was observed. Copyright (C) 2008 John Wiley & Sons, Ltd.