A series of new side-chain cholesteric elastomers derived from cholesteryl 4-(10-undecylen-1-yloxy)-4'-ethoxybenzoate and phenyl 4,4-bis(10-undecylen-1-yloxybenzoyloxy-p-ethoxybenzoate) was synthesized. The chemical structures of the monomers were confirmed by elemental analyses, Fourier transform infrared, and H-1 NMR and C-13 NMR spectra. The mesomorphic properties of elastomers were investigated with differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X-ray diffraction measurements. The influence of the content of the crosslinking unit on the phase behavior of the elastomers was examined. Monomer M-1 showed a cholesteric phase, and M-2 displayed smectic and nematic phases. The elastomers containing < 15 mol % of the crosslinking units revealed reversible mesomorphic phase transition, wide mesophase temperature ranges, and high thermal stability. (c) 2005 Wiley Periodicals, Inc.