Novel X-type polyurethane 4 containing 4-(4-nitrophenylazo)-6-nitroresorcinoxy groups as nonlinear optical (NLO) chromophores, which are parts of the polymer main chains, was prepared and characterized. Polyurethane 4 is soluble in common organic solvents such as acetone and N,N-dimethylformamide. It shows thermal stabilities up to 270 degrees C from thermogravimetric analysis with glass transition temperature obtained from differential scanning calorimetry of about 134 degrees C. The second harmonic generation (SHG) coefficient (d(33)) of poled polymer film at 1064 nm fundamental wavelength is 5.37 x 10(-9) esu. Polymer 4 exhibits a thermal stability up to T-g, and no significant SHG decay is observed below 135 degrees C, which is acceptable for NLO device applications. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 760-766