Side-chain liquid-crystalline (SCLC) polyurethane elastomers with methoxybiphenyl mesogens pendant on the chain extenders were synthesized by the conventional prepolymer technique and condensation reaction. Two SCLC polyurethanes with mesogens having spacers of six and eight methylene units were prepared. The structures of the mesogenic units and SCLC polyurethanes were confirmed by Fourier transform infrared and 1 H-NMR. The polymer properties were also studied with solubility tests, water-uptake measurements, and inherent-viscosity measurements. The tensile properties indicated that both SCLC polyurethanes were thermoplastic elastomers. Their phasetransition temperatures were studied with differential scanning calorimetry. Wide-angle X-ray diffraction studies revealed the existence of liquid-crystalline phases for both SCLC polyurethanes. Polarizing optical microscopy investigations further confirmed the thermotropic liquid-crystalline behaviors and smectic mesophases of both samples. Thermogravimetric analysis results showed a more rapid degradation in the initial stage and a slower degradation process in the latter stage for both SCLC polymers in comparison with those of the linear starting polyurethane. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 336 -344, 2005