Liquid crystalline elastomers based on cyclic cyclosiloxane and mesogenic crosslinking units

Abstract

Cholesteric liquid crystalline elastomers (LCEs) IP–VIP were graft copolymerized by a one-step hydrosilylation reaction with cyclo(pentamethylhydrogeno)siloxane, a cholesteric liquid crystalline (LC) monomer cholesteryl 3-(4-(undec-10-enoyloxy)phenyl)acrylate and crosslinking LC monomer biphenyl-4,4′-diyl bis(4-(allyloxy)benzoate). The effect of crosslinking mesogens on mesomorphic properties of the chiral LCEs was studied by swelling experiments. All the samples IP–VIP showed cholesteric mesophase when they were heated and cooled. 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. In XRD curves, all the samples IP–VIP exhibited diffuse reflections at 2θ ≈ 17° suggesting lack of the smectic-layered packing arrangement, and the intensity of these diffuse diffraction peaks decreases with increase of mesogenic crosslinking units, suggesting that the order between two neighbor LC molecules disturbed by the mesogenic crosslinking agents. 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.