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Keywords:

  • chiral;
  • liquid crystalline polymers (LCPs);
  • liquid crystal polymer;
  • menthol;
  • phase behavior;
  • synthesis

Abstract

To study structure–mesomorphism relationships of the monomers and polymers based on menthol, four new chiral monomers (M1M4) and the corresponding homopolymers (P1P4) with menthyl group were synthesized. Their chemical structures, formula, phase behavior, and thermal stability were characterized by FTIR, 1H NMR, 13C NMR, elemental analyses, differential scanning calorimetry, polarizing optical microscopy, X-ray diffraction, and thermogravimetric analysis. The selective reflection of light was investigated with ultraviolet/visible spectrometer. The influence of the mesogenic core rigidity, spacer length, and menthyl steric effect on the mesomorphism of M1M4 and P1P4 was examined. By inserting a flexible spacer between the mesogenic core and the terminal menthyl groups, four target monomers and polymers could form the expected mesophase. Moreover, their melting temperature (Tm), glass transition temperature (Tg), clearing temperature (Ti), and mesophase range (ΔT) increased with increasing the mesogenic core rigidity; whereas the Tm and Tg decreased, Ti and ΔT increased with an increase of the spacer length. M1 and M2 showed monotropic and enantiotropic cholesteric phase, respectively, whereas M3 and M4 all revealed chiral smectic C (SmC*), cholesteric and cubic blue phases. In addition, with increasing temperature, the selective reflection of light shifted to the long wavelength region at the SmC* phase range and to the short wavelength region at the cholesteric range, respectively. P1 and P2 only showed a smectic A (SmA) phase, whereas P3 and P4 exhibited the SmC* and SmA phases. All the obtained polymers had very good thermal stability. © 2012 Wiley Periodicals, Inc. J. Polym. Sci. Part A: Polym Chem, 2012