Synthesis and Characterization of Benzylidene and Azobenzene Based Photochromic Liquid-Crystalline Polymers

Two series of novel thermotropic main chain liquid crystalline polymers containing photocrosslinkable chalcone and photoisomerizable azobenzene moieties were synthesized from bis[4-(m-hydroxyalkoxy) benzylidene]cycloalkanones [m = 6,8,10] with 4,4'-azobenzene dicarbonylchloride. The chemical structure of the monomers and polymers were confirmed by spectral techniques. The mesophase properties were investigated using hot stage optical polarized microscopy and differential scanning calorimetry. All the polymers exhibited liquid crystalline properties. The thermogravimetric analysis data revealed that the polymers were stable up to 220 degrees C and underwent two-stage decomposition. Photocrosslinking property of the polymers was investigated using UV spectroscopy. The cyclopentanone containing polymers showed faster photocrosslinkability than that of their cyclohexanone counterpart. In addition to the photocrosslinkability of cycloalkanone units, the azo moiety displayed E-Z (trans-cis) isomerization in the polymer backbone.