The synthesis of hemiphasmidic monomers 4-[(3,4,5-triethoxy)benzoyloxyl-4'-[(p-allyloxy)benzoyloxylbiphenyl (M-1), 4-[(3,5-diethoxy)benzoyloxyl-4'-[(p-allyloxy)benzoyloxylbiphenyl (M-2), and of the corresponding sidechain liquid-crystalline polysiloxanes (P-1, P-2) was carried out. For comparison, rodlike monomer 4-[(p-ethoxy)benzoyloxy]-4'-[(p-allyloxy)benzoyloxylbiphenyl (M-2) and its polysiloxanes (P-3) were also prepared. The chemical structures of the monomers and polymers obtained were confirmed by FTIR and H-1-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 M-1 and M-3 were enantiotropic nematic phase, M-2 was monotropic mesophase, and their poly(methylsiloxanes) (P-1-P-3) possessed a broad range enantiotropic nematic phases and high thermal stability. (C) 2004 Wiley Periodicals, Inc.