The synthesis of hemiphasmidic monomers 4‐(3,4,5‐triethoxy)benzoyloxy‐4′‐(p‐allyloxy)benzoyloxybiphenyl (M1), 4‐(3,5‐diethoxy)benzoyloxy‐4′‐(p‐allyloxy)‐benzoyloxybiphenyl (M2), and of the corresponding side‐chain liquid‐crystalline polysiloxanes (P1, P2) was carried out. For comparison, rodlike monomer 4‐(p‐ethoxy)‐benzoyloxy‐4′‐(p‐allyloxy)benzoyloxybiphenyl (M3) and its polysiloxanes (P3) were also prepared. The chemical structures of the monomers and polymers obtained were confirmed by FTIR and 1H‐NMR spectra. Their mesomorphic properties and phase behavior were investigated by differential scanning calorimetry, polarizing optical microscopy, and X‐ray diffraction measurements. The relationship between structures and properties was discussed. It was observed that M1 and M3 were enantiotropic nematic phase, M2 was monotropic mesophase, and their poly(methylsiloxanes) (P1–P3) possessed a broad range enantiotropic nematic phases and high thermal stability. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 946–952, 2005