Synthesis and phase behaviour of new cholesteric monomers and side chain smectic polymers based on cholesterol

Abstract

The synthesis of five new cholesteryl-based monomers (M-1−M-5) and the corresponding smectic comb-like polymers containing cholesteryl groups (P-1−P-5) is presented. The chemical structures were characterised by FT-IR, 1H NMR and elemental analyses. The specific optical rotations were evaluated with a polarimeter. The phase behaviour was investigated by polarising optical microscopy, differential scanning calorimetry, thermogravimetric analysis, and X-ray diffraction. The specific optical rotation values of these monomers and polymers with the same number of phenyl rings and terminal groups were nearly equal; however, they decreased with increasing the aryl numbers in the mesogenic core. The monomers M-1−M-5 showed oily streak and focal conic optical textures, or finger print textures characteristic of the chiral nematic phase. The polymers P-1−P-5 showed the smectic A phase. The melting, clearing, and glass transition temperatures increased, and the mesophase temperature ranges widened with increasing the aryl number in the mesogenic core. However, although the molecular structures of M-4 and M-5 were similar to those of M-3, namely their mesogenic cores contained three phenyl rings, their phase behaviour differed considerably, and T _m and T _i of M-4 and M-5 were less than those of M-3. In addition, M-4 and M-5 showed a clear glass transition similar to the polymer. Furthermore, the ester linkage bond and aryl arrangement in the mesogenic core also affected the phase behaviour.

Keywords:

• liquid crystalline polymers
• phase behaviour
• cholesteric phase
• smectic A phase
• chiral

Acknowledgements

The authors are grateful to National Natural Science Foundation of China (No. 50503005) and Fundamental Research Funds for the Central Universities (No. N090505002) for financial support of this work.