Synthesis and characterization of thermotropic liquid crystalline polyphosphates containing photoreactive moieties

Abstract

New dual mesogens, with α-methylstilbene and p-substituted azobenzene as main chain and side chain, respectively, and containing liquid crystalline polyphosphates, were synthesized. The pendant azobenzene units were unsubstituted or substituted with F, Cl, and Br atoms. All the polymers were synthesized by solution polycondensation using 4,4′-bis(10-hydroxydecyloxy)-α-methylstilbene and 4-substituted phenylazo-4′-phenyloxydecylphosphorodichloridates. A model polymer was synthesized from bis(10-hydroxydecyloxy-4,4′-diphenylpropane) and phenylazo-4′-phenyloxydecylphosphorodichloridate for comparison. The polymers were characterized by FTIR spectroscopy, ¹H and ³¹P NMR, and intrinsic viscosity. Microstructure and mesomorphic properties were determined by hot stage polarizing optical microscopy, differential scanning calorimetry and variable temperature X-ray diffraction. In addition, the polymers were examined for thermal properties by thermogravimetry, electrochemical behaviour by cyclic voltammetry and photo-physical properties by UV spectroscopy. The electrochemical studies reveal that the azobenzene moiety was reduced at 0.95 in the anodic scan. UV irradiation studies indicated that the time taken for completion of photoisomerization depends on the size and dipole moment of the terminal substituents.