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

The synthesis of new chiral monomers (M-1-M-3) based on menthol and the corresponding polyacrylates (P-1-P-3) is described. The chemical structures, formula and phase behaviour of the obtained monomers and polymers were characterised with FT-IR, H-1-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 M-1-M-3 and P-1-P-3 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. M-1 and P-1 showed no mesophase, while M-2 and M-3 all revealed a SmC* and cholesteric phases. P-2 and P-3 only showed a cholesteric phase.