Synthesis and characterization of side‐chain cholesteric liquid‐crystalline polysiloxanes containing different space groups

A series of liquid-crystalline (LC) polysiloxanes were synthesized by two different cholesteric monomers, cholest-5-en-3-ol(3β)-10-undecenoate and cholesteryloxycarbonylmethyl 4-allyloxybenzoate. The chemical structures and LC properties of the monomers and polymers were characterized by various experimental techniques, including Fourier transform infrared spectroscopy, 1H-NMR, elemental analysis, differential scanning calorimetry, and polarized optical microscopy. The specific rotation absolute values increased with increasing rigid spacers between the main chain and the mesogens. All of the polymers exhibited thermotropic LC properties and revealed cholesteric phases with very wide mesophase temperature ranges. With a reduction in the soft-space groups in the series of polymers, the glass-transition temperature and the isotropic temperature increased slightly on heating cycles. Reflection spectra of the cholesteric mesophase of the series of polymers showed that the reflected wavelength shifted to short wavelengths with decreasing soft-space groups in the polymers systems, which suggested that the helical pitch became shorter with increasing rigid-space groups. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009