Synthesis and characterization of side-chain liquid-crystalline polysiloxanes containing fluorinated units

Several new chiral side-chain LC polysiloxanes (IP–VIIP) bearing fluorinated methyl groups were synthesized with a cholesteric LC monomer and a non-LC monomer containing fluorinated units. The chemical structures and LC properties of the monomers and polymers were characterized by use of various experimental techniques. The effect of copolymer composition on mesomorphic properties of the fluorine-containing polymers was studied as well. The obtained polymers were soluble in many solvents and the specific rotations showed negative values. The temperatures at which 5% weight loss occurred (Td) were greater than 300 °C for all the polymers and the residue weight on heating to 600 °C increased slightly with increase of the monomer containing fluorinated units in the polymer systems. All the polymers displayed two-phase transitions when they were heated and cooled. The IP, IIP, and IIIP exhibited cholesteric textures when they were heated and cooled, while IVP, VP, VIP, and VIIP showed smectic fan-shaped textures. XRD curves of samples of IVP, VP, VIP, and VIIP displayed sharp and strong peaks at low angle, but no sharp peaks were shown at low angle for the samples IP, IIP, and IIIP.