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-phe nyl 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 th ermotropic behavior. X-ray diffraction studies allowed identification of th e mesophases (hexatic smectic, disordered smectic, nematic) and study of th e evolution of their structures and lattice parameters with temperature. It was found that each polymer presented a rich mesophase polymorphism, inclu ding 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 tilte d double layer structures. The strong mesogenic character of the polymers w as attributed to the presence of the fluorinated tail on the aromatic core owing to its capability of adopting a rigid-rodlike conformation. A phase s eparation occurring at the molecular level of the different incompatible al iphatic-aromatic-fluoroaliphatic sections of the polymer repeat unit should efficiently cooperate to the onset of thermotropic mesomorphism.