Synthesis and phase behavior of side-chain cholesteric liquid-crystalline elastomers derived from a chiral crosslinking agent

A series of new side-chain cholesteric liquid-crystalline elastomers derived from 4-(10-undecylen-1-yloxy)-4′-(4-ethoxybenzoyloxy)biphenyl and isosorbide di-(10-undecylen-1-ylenate) were synthesized. The chemical structures of the monomers obtained were confirmed by element analyses, FT-IR, 1H NMR and 13C NMR. The mesomorphic properties and thermal stability were investigated by polarizing optical microscopy, differential scanning calorimetry, thermogravimetric analysis, and X-ray diffraction measurements. The influence of the content of the crosslinking unit on the phase behavior of the elastomers was discussed. Monomer M1 showed nematic and different smectic (SA, SC, SB) phase on cooling cycle. Elastomers containing less than 27 mol% of the crosslinking units revealed elasticity, reversible mesomorphic phase transition, wide mesophase temperature ranges, and high thermal stability. Experimental results demonstrated that the glass transition temperature, melting temperatures, clearing temperature and mesophase temperature ranges decreased with increasing the content of the crosslinking unit.