Preparation and thermotropic liquid crystalline properties of semirigid copolyurethanes composed of biphenyl units and partially fluorinated aliphatic chains

New semirigid thermotropic liquid crystalline (LC) copolyurethanes 4 and 5 made up of biphenyl units and partially fluorinated aliphatic chains in the backbones were synthesized by melt polycondensation of a mixture of a dioxydihexanol of biphenyl 1 and two fluorine-containing diols 2a,b taken in definite feed mole ratios with alkylene diphenyl dicarbamates 3a-i having various lengths of aliphatic chains. The assigned structures of copolyurethanes 4 and 5 were identified by FTIR, H-1- and C-13-NMR spectra, and elemental analyses. The thermal and mesogenic properties were evaluated by differential scanning calorimetry (DSC), thermal mechanical analyses (TMA), polarizing microscopy, and temperature-changeable X-ray analyses, whose measurements indicated that the copolymers 4 and 5 form thermotropic nematic phases and have glass transition steps around room temperature. It is suggested that the incorporation of partially fluorinated aliphatic chains into the backbones has no drastic effect on the LC formation in the semirigid copolyurethanes 4 and 5. (C) 1998 John Wiley & Sons, Inc.