Synthesis and characterization of side-chain cholesteric elastomers derived from an isosorbide crosslinking agent

New liquid crystalline monomer 4-(4-ethoxybenzoyloxy)biphenyl-4′-[(10-undecylen-1-yloxy)-4′-ethoxy]benzoate (M1), chiral crosslinking agent isosorbide di-(10-undecylen-1-yloxybenzoate) (M2), and the corresponding elastomers were prepared. The chemical structures of M1 and M2 were characterized by Fourier transform infrared and 1H-nuclear magnetic resonance. The mesomorphic properties and phase behavior were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X-ray diffraction measurements. M1 exhibited typical threaded texture and droplet texture of nematic phase. The use of chiral crosslinking agent in the polymer networks could induce cholesteric phase. The elastomers containing less than 10 mol% of the chiral crosslinking units showed elasticity, reversible phase transition, wide mesophase temperature ranges, and high thermal stability. For the elastomers P2–P4, the glass transition temperature (Tg) increased; clearing temperature (Ti) and mesophase temperature range (ΔT) decreased with increasing content of the crosslinking unit.