New chiral liquid crystal monomers and cholesteric polyacrylates: synthesis and characterisation

Abstract

The synthesis of new chiral monomers (M₁ −M₃ ) based on menthol and the corresponding polyacrylates (P₁ −P₃ ) is described. The chemical structures, formula and phase behaviour of the obtained monomers and polymers were characterised with FT-IR, ¹H-NMR, elemental analyses, differential scanning calorimetry (DSC), polarising optical microscopy (POM) and X-ray diffraction (XRD). The effect of the mesogenic core rigidity, spacer length and menthyl steric effect on the phase behaviour of M₁ −M₃ and P₁ −P₃ is discussed. The expected mesophase of the compounds based on menthol can be obtained by inserting a flexible spacer between the mesogenic core and the terminal groups. For the chiral monomers and polyacrylates, their corresponding melting temperature (T _m), glass transition temperature (T _g) and clearing temperature (T _i) increased with an increase of the mesogenic core rigidity; while the T _m, T _g and T _i decreased with increasing the spacer length. M₁ and P₁ showed no mesophase, while M₂ and M₃ all revealed a SmC* and cholesteric phases. P₂ and P₃ only showed a cholesteric phase.

Keywords:

• chiral
• liquid crystal
• polyacrylate
• phase behaviour
• menthol

Acknowledgements

The authors are grateful to Program for Science and Technology Bureau of Shenyang, and Fundamental Research Funds for the Central Universities (N110405006, N100605001 and N110705001) for financial support of this study.