A series of side chain liquid crystal polyurethanes (CnCNPs), in which the spacer length was varied from 2 to 12 methylene units, were synthesized by the addition polymerization of alpha-[bis(2-hydroxyethyl)amino]-omega-(4-cyanoazobenzene-4＇-oxy)-alkanes (CnCN-diols) with hexamethylene diisocyanate. The liquid crystalline properties of CnCNPs were characterized by means of differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction. Polyurethanes with spacer length 4 or higher exhibited mesomophic properties. C4CNP and C5CNP exhibited an enantiotropic nematic mesophase, while C6-C12CNPs exhibited enantiotropic bilayer smectic mesophases. CnCNPs have a high tendency to crystallize; crystallization is kinetically controlled. Polyurethane＇s backbone crystallization is closely related to hydrogen bonding. To establish the role of hydrogen bonding in mesophase formation as well as crystallization, Fourier transform infrared spectroscopy studies of CnCNPs were carried out at different temperatures focusing on H-bonds between the N-H and C=O groups of the urethane backbone. With increasing temperature, C=O and N-H stretching bands were evenly shifted to higher wavenumbers, with two exceptions (C4CNP and C5CNP) discussed in detail in the text.