Cholesteric Liquid-Crystalline Elastomers Prepared from Ionic Bis–Olefinic Crosslinking Units

A series of cyclosiloxane-based cholesteric LCEs were synthesized by using a LC monomer cholest-5-en-3-ol(3β)-4-(2-propenyloxy)benzoate and an ionic divinyl monomer 2,2′-(1,2-ethenediyl)-bis[5-[(4-undecenoyloxy)phenyl]-azo]-benzenesulfonic acid. The polymers were prepared in a one-step reaction with ionic crosslinking contents ranging between mass content 0 and 11.8%. Their chemical structures and liquid-crystalline properties were characterized by FT IR, 1H NMR, DSC, POM and X-ray measurement. The effective crosslink density (Mc) was determined by swelling experiments in mixed buffer/organic solvent mixtures, using Brannon-Peppas models. All the polymers exhibit thermotropic LC properties and reveal cholesteric phase. With increase of ionic crosslinking component in the polymers, the melting behavior disappears and the temperature of clear point decreases. Reflection spectra of cholesteric mesophase of the series of polymers showed that the reflected wavelength becomes broad and shifts to long wavelength with increase of the ionic crosslinking component in the polymer systems.