Preparation and characterization of side chain cholesteric liquid crystalline polysiloxanes containing two chiral groups

A series of liquid crystalline (LC) polysiloxanes containing diosgeninyl and menthyl groups (from monomers M₁ and M₂, respectively) were synthesized. The chemical structures of the monomers and polymers obtained were confirmed by elemental analysis, Fourier transform infrared spectroscopy, proton NMR and carbon-13 NMR. The LC properties were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X-ray diffraction. Monomer M₁ showed cholesteric oily-streak and spiral textures. Copolymers P₂-P₅ exhibited cholesteric phases. With increasing concentration of M₂ units, the glass transition and clearing temperatures decreased. Experimental results demonstrated that a flexible polymer backbone and a long flexible spacer tended to favour a lower glass transition temperature, higher thermal stability, and wider mesophase temperature range.