Synthesis and properties of new chiral mesogenic monomers and side-chain smectic homopolymers containing (-)-menthyl groups

The synthesis of new chiral monomers (M-1-M-5) and the corresponding smectic homopolymers (P-1-P-5) containing menthyl groups is described. The chemical structures and purity were characterized by FT-IR, H-1 NMR and elemental analyses. The specific optical rotations were evaluated with a polarimeter. The phase behavior and mesomorphism were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X-ray diffraction. The selective reflection property of light was studied with UV/visible/NIR. The monomers M-2-M-5 formed a chiral smectic C (S-C(center dot)), and cholesteric or blue phase when a flexible linkage chain was inserted between the mesogenic core and the terminal menthyl groups by reducing the steric effect. M-1 showed no mesomorphism, while M-2-M-5 showed enantiotropic S-C(center dot) and cholesteric phases. Moreover, M-5 also exhibited a cubic blue phase on cooling. With increasing temperature, the selective reflection of light shifted to the long wavelength region at the S-C(center dot) phase range, and to the short wavelength region at the cholesteric phase range, respectively. The homopolymers P-1-P-5 all exhibited the batonnet textures of a 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. (C) 2009 Elsevier Ltd. All rights reserved.