Synthesis and characterization of fluorine‐containing liquid crystalline polysiloxanes bearing cholesteryl cinnamate mesogens and trifluoromethyl‐substituted mesogens

Abstract

Several novel side-chain liquid crystalline (LC) polysiloxanes bearing cholesteryl cinnamate mesogens and trifluoromethyl-substituted mesogens were synthesized by a one-step hydrosilylation reaction with poly(methylhydrogeno)siloxane, a cholesteric LC monomer cholesteryl 3-(4-allyloxy-phenyl)-acryloate and a fluorocontaining LC monomer 4-[2-(3-trifluoromethyl-phenoxy)acetoxy]-phenyl 4-allyloxy-benzoate. The chemical structures and LC properties of the monomers and polymers were characterized by use of various experimental techniques, such as FTIR, 1 H-NMR, 13 C-NMR, TGA, DSC, POM, and XRD. The temperatures at which 5% weight loss occurred were greater than 300 C for all the polymers, and the residue weight near 600 C increased slightly with increase of the trifluoromethyl-substituted mesogens in the fluorinated polymer systems. The samples containing mainly cholesteryl cinnamate mesogens showed chiral nematic phase when they were heated and cooled, but the samples containing more trifluoromethylsubstituted mesogens exhibited chiral smectic A mesophase. The glass transition temperature of the series of polymers increased slightly with increase of trifluoromethyl-substituted mesogens in the polymer systems, but mesophase-isotropic phase transition temperature did not change greatly. In XRD curves, the intensity of sharp reflections at low angle increased with increase of trifluoromethyl-substituted mesogens in the fluorinated polymers systems, indicating that the smectic order derived from trifluoromethyl-substituted mesogens should be strengthened. These results should be due to the fluorophobic effect between trifluoromethyl-substituted mesogens and the polymer matrix.