Preparation and Characterization of Chiral Cyclosiloxane-Based Liquid-Crystalline Elastomers Bearing Menthyl Groups

Chiral side-chain liquid-crystalline elastomers (LCEs) IP similar to IVP containig menthyl groups were synthesized by a one-step hydrosilylation reaction. The chemical structures and LC properties of the monomers and polymers were characterized by use of various experimental techniques. The effect of crosslinking mesogens on mesomorphic properties of the chiral LCEs was studied by swelling experiments. All the samples IP similar to IVP showed cholesteric mesophase when they were heated and cooled, proved by visual observation and X-ray measurements. The glass transition temperature (T-g) of elastomers increased slightly with increase of crosslinking mesogens in the polymer systems, but mesophase-isotropic phase transition temperature (T-i) decreased slightly, suggesting that the temperature range of mesophase became narrow with increase of crosslinking mesogens for all the elastomers. The maximum reflection bands shift slightly to long wavelength and become broad at the same temperature, indicating that the helical structure is partially disrupted because of both the constraint of chemical crosslinking agents and the different mesogenic units.