Side-chain cholesteric liquid-crystalline elastomers derived from smectic crosslinking units: Synthesis and phase behavior

New side-chain cholesteric liquid-crystalline elastomers containing cholesteryl 4-allyloxybenzoate as cholesteric mesogenic units and biphenyl 4,4'-bis(10-undecen-1-ylenate) as smectic crosslinking units were synthesized. The chemical structures of the olefinic compounds and polymers obtained were confirmed by element analysis, Fourier transform infrared, proton nuclear magnetic resonance, and carbon-13 nuclear magnetic resonance spectra. The mesogenic properties were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X-ray diffraction measurements. The influence of the concentration of the crosslinking unit on the phase behavior of the elastomers was examined. The elastomers containing less than 17 mol % of the crosslinking units revealed elasticity, reversible mesomorphic phase transition, wider mesophase temperature ranges, and higher thermal stability. The experimental results demonstrated that the glass-transition temperature, isotropization temperature, and mesophase temperature ranges decreased with an increasing concentation of the crosslinking unit. (C) 2004 Wiley Periodicals, Inc.