A mesogenic crosslinking agent M-1 was synthesized to minimize the perturbations of nonmesogenic crosslinking agent for liquid-crystalline elastomers. The synthesis of side-chain liquid-crystal line elastomers containing a rigid mesogenic crosslinking agent M-1 and a nematic monomer M-2 was described by a one-step hydrosilylation reaction. The chemical structures of the obtained monomers and network polymers were confirmed by Fourier transform infrared and H-1-NMR spectroscopy. The mesomorphic properties and phase behavior were investigated by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction measurements. The influence of the crosslinking units on the phase behavior was discussed. The liquid-crystal line elastomers containing less than 15 mol % of the crosslinking units showed elasticity, reversible phase transition, and threaded texture. The experimental results demonstrated that isotropic temperature and liquid-crystalline range of polymers P-1-P-7 decreased a little as the concentration of crosslinking agent M-1 increased, and the use of mesomorphic crosslinking agent M-1 promotes the arrangement of liquid-crystalline units from P-1 to P-5. (c) 2005 Wiley Periodicals, Inc.