Synthesis and structure characterization of liquid crystalline polyacrylates with unconventional fluoroalkylphenyl mesogens

The synthesis, thermal behavior, and bulk microstructure of fluorinated new liquid-crystalline polyacrylates containing spaced fluoroalkylphenyl units in the side chains were studied. While in polyacrylates poly(1) and poly(2) there was a 4-(perfluorooctylethoxy)phenyl benzoate unit, i.e., a two-phenyl mesogenic core, poly(3) contained a 4-perfluorooctylethyl benzoate, i.e., a one-phenyl aromatic core that per se would not be able to promote a thermotropic behavior. X-ray diffraction studies allowed identification of the mesophases (hexatic smectic, disordered smectic, nematic) and study of the evolution of their structures and lattice parameters with temperature. It was found that each polymer presented a rich mesophase polymorphism, including the rather unusual smectic F2- (or I2-) to-nematic transition in poly(3). The electron density profiles along the smectic layer normal were drawn and provided a deeper insight into the packing of the side chains in tilted double layer structures. The strong mesogenic character of the polymers was attributed to the presence of the fluorinated tail on the aromatic core owing to its capability of adopting a rigid-rodlike conformation. A phase separation occurring at the molecular level of the different incompatible aliphatic-aromatic-fluoroaliphatic sections of the polymer repeat unit should efficiently cooperate to the onset of thermotropic mesomorphism.