A new series of combined-type, azobenzene-based organophosphorus liquid-crystalline polymers were synthesized, and their photoisomerization properties were studied. The prepared polymers contained azobenzene units as both the main-chain and side-chain mesogens. Various groups were substituted in the terminal of the side-chain azobenzene mesogen, and the effects of the substituents were investigated. All the polymers were prepared at the ambient temperature by solution polycondensation with various 4-substituted phenylazo-4'-phenyloxyhexylphosphorodichloridates and 4,4'-bis(6-hydroxyhexyloxy) azobenzene. The polymers were characterized with gel permeation chromatography, Fourier transform infrared, and H-1, C-13, and P-31 NMR spectroscopy. Thermogravimetric analysis revealed that all the polymers had high char yields. The liquid-crystalline behavior of the polymers was examined with hot-stage optical polarizing microscopy, and all the polymers showed liquid-crystalline properties. The formation of a mesophase was confirmed by differential scanning calorimetry (DSC). The DSC data suggested that mesophase stability was better for electron-withdrawing substituents than for halogens and unsubstituted ones. Ultraviolet irradiation studies indicated that the time taken for the completion of photoisomerization depended on the dipolar moment, size, and donor-acceptor characteristics of the terminal substituents. (C) 2003 Wiley Periodicals, Inc.