2,3-Di-(2'-hydroxyethoxy)benzylidenemalononitrile (3) was prepared and condensed with 2,4-toluenediisocyanate and 3,3'-dimethoxy-4,4'-biphenylenediisocyanate to yield novel Y-type polyurethanes 4-5 containing 2,3-dioxy benzylidenemalononitrile group as a nonlinear optical (NLO)-chromophore, which constituted parts of the polymer backbones. Polyurethanes 4-5 were soluble in common organic solvents such as acetone and N,N-dimethylformamide. They showed a thermal stability up to 270 degrees C in thermogravimetric analysis thermograms and the glass-transition temperatures (T-g) obtained from differential scanning calorimetry thermograms were around 116-135 degrees C. The second harmonic generation (SHG) coefficients (d(33)) of poled polymer films at 106.4 mm(-1) fundamental wavelength were around 9.07 x 10(-19) C (2.72 x 10(-9) esu). The dipole alignment exhibited high thermal stability up to 10 degrees C higher than T-g, and there was no SHG decay below 145 degrees C due to the partial main-chain character of the polymer structure, which was acceptable for nonlinear optical device applications.