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

Abstract

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, 1H 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 ∗ ) , 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 ∗ 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 ∗ 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.