Novel X-type polyurethane 5 containing 4-(2',2'-dicyanovinyl)-5-nitrocatecholic groups as nonlinear optical chromophores, which constitute parts of the polymer backbone, was prepared and characterized. Polyurethane 5 is soluble in common organic solvents such as acetone and N,N-dimethylformamide. It shows thermal stability up to 270 A degrees C from thermogravimetric analysis with a glass-transition temperature obtained from differential scanning calorimetry thermogram of around 113 A degrees C. The second harmonic generation (SHG) coefficient (d (33)) of poled polymer film at 1,064 nm fundamental wavelength is around 5.72 x 10(-9) esu. The dipole alignment exhibits a thermal stability even at 7 A degrees C higher than glass-transition temperature, and there was no SHG decay below 120 A degrees C due to the partial main-chain character of the polymer structure, which is acceptable for nonlinear optical device applications.