Liquid-crystalline elastomers containing sulfonic acid groups

A series of ionic liquid-crystalline (LC) elastomers were synthesized by using chemical cross-linking agents containing sulfonic acid groups, which were siloxane-based materials. A ionic divinyl monomer 2,2'-(1,2-ethenediyl)bis[5-[(4-undecenoyloxy)phenyl]azo]benzenesulfonic acid was used as chemical cross-linking agent. Cholest-5-en-3-ol(3beta)-10-undecenoate was synthesized as a liquid-crystalline monomer. The effective cross-link density of the ionic elastomers was determined by swelling experiments in organic/buffer mixtures. Their liquid-crystalline properties were characterized by DSC, POM, and SAXS. A proposed multilayer buildup containing LC segment structure and ionic cross-linking lamellar structure separated by siloxane chains was given. The ion aggregated in domains forces the siloxane chains to fold and form an irregular lamellar structure. The ionic cluster lamellae may be tangled with the rigid mesogenic groups of LC segments to form multiple blocks. Liquid-crystal mesophase region of the polymers become narrow with increasing ionic cross-linking content.