Synthesis and characterization of new cholesteric monomers and smectic polymers containing menthyl groups

New cholesteric monomers (M₂−M₅) and the corresponding smectic homopolymers (P₂−P₅) based on menthyl groups were synthesized. The chemical structures were characterized by Fourier transform infrared and ¹H NMR. The specific optical rotations were evaluated with a polarimeter. The structure–property relationships of the new compounds are discussed. The mesomorphism was 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 M₂−M₅ formed the cholesteric or blue phase when a flexible link chain was inserted between the mesogenic core and the terminal menthyl groups by reducing the steric effect. M₁ showed no mesomorphism, while M₂−M₅ revealed enantiotropic cholesteric phase. In addition, M₂ and M₃ also showed a cubic blue phase on cooling. The selective reflection of light for M₂−M₅ shifted to the short reciprocal wavelength region with increasing the temperature or intramolecular spacer length. P₂−P₅ exhibited the smectic A phase. The melting, clearing, and glass transition temperatures increased when increasing the aryl number in the mesogenic core or decreasing the intramolecular spacer length.