Synthesis and mesomorphic properties of side-chain cholesteric liquid-crystalline polymers containing menthyl groups

A series of new cholesteric liquid-crystalline polysiloxanes (P-1-P-5) derived from menthyl groups were synthesized. The chemical structures of the monomers and polymers were characterized with Fourier transform infrared, H-1-NMR, C-13-NMR, and elemental analyses. The mesomorphic properties and thermal behavior were investigated with differential scanning calorimetry, polarizing optical microscopy, thermogravimetric analysis, and X-ray diffraction measurements. The influence of the polymer structure on the thermal behavior was discussed. The monomer diosgeninyl 4-allyloxybenzoate exhibited a typical cholesteric oily-streak texture and a focal-conic texture. Polymers P-1-P-5 showed thermotropic liquid-crystalline properties. P-1 displayed a smectic fan-shaped texture, P-2- P-5 showed a cholesteric Grandjean texture, and P-6 and P-7 did not show mesomorphic properties. The experimental results demonstrated that the glass-transition temperature and the clearing temperature decreased, and the mesomorphic properties weakened with an increasing concentration of menthyl units. Moreover, P-1-P-5 exhibited wide mesophase temperature ranges and high thermal stability. (c) 2006 Wiley Periodicals, Inc.