Mesomorphic behavior and optical properties of liquid‐crystalline polysiloxanes bearing different chiral groups

A series of side-chain liquid crystalline polysiloxanes bearing different chiral groups were synthesized with a cholesteric liquid crystalline monomer cholesteryl 2-(4-allyloxy-benzoxy)-succinate and a chiral monomer 2-isopropyl-5-methyl-cyclohexyl 4-allyloxy-benzoate. All the chiral polymers showed cholesteric mesophase with very wide mesophase temperature ranges. Along with phase morphology varied from solid state to isotropic state, the sample exhibited varied spectroscopic images, indicating different phase behaviors between mesophase and isotropic state. Optical properties of the polymers were characterized with circular polarization spectra and optical rotation analysis. The specific rotations of the chiral liquid crystalline polymers were all negative values and increased with increase of menthyl component in the polymer systems. As compared with corresponding monomers, the polymers showed significantly lower specific rotations, suggesting that the existence of polysiloxane main chains affect the molecule polarity. The selective light reflection maximum wavelength of the polymers at the same temperature shifted to short wavelength with decrease of cholesteryl component, indicating that the helical pitch becomes shorter due to induction of menthyl groups with high chiral properties. The temperature dependence of selective light reflection maximum wavelength was shifted to a longer wavelength region as the temperature decreased. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

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