Phase behaviors of comb-like liquid crystalline polysiloxanes containing fluorinated mesogenic units

Several liquid crystalline polysiloxanes (Pa–Pf) bearing fluorinated mesogenic units were synthesized using poly(methylhydrogeno)siloxane, 4′-(4-undec-10-enoyloxy-benzoyloxy)-biphenyl-4-yl 4-fluoro-benzoate and 4′-propionyloxy-biphenyl-4-yl 4-allyloxy-benzoate, and effect of fluorinated mesogenic units on phase behaviors of the fluorinated LC polysiloxanes was studied as well. The samples Pa and Pb showed single nematic mesophase when they were heated and cooled, but Pc, Pd, Pe and Pf exhibited both smectic and nematic phases. The glass transition temperature and smectic A–nematic mesophase transition temperature of polymers increased slightly with increase of fluorinated units in the polymer systems, but mesophase–isotropic phase transition temperature decreased slightly. In XRD curves, the intensity of sharp reflections at low angle increased with increase of fluorinated mesogenic units in the polymersʹ systems, indicating that the longer spacer and the fluorophobic effect of fluorinated mesogenic units could lead to a significant stabilization and even to modifications of smectic mesophases.