2,4-Bis-(3,4-dicarboxyphenylcarboxyethoxy)-1-(2,2-dicyanovinyl)benzene dianhydride (4) was prepared and reacted with 1,4-phenylenediamine and 4,4 '-oxydianiline to yield novel Y-type polyimides 5-6 containing 2,4-dioxybenzylidenemalononitrile groups as NLO-chromophores, which constitute parts of the polymer backbone. The resulting polyimides 5-6 are soluble in polar solvents such as dimethylsulfoxide and N,N-dimethylformamide. Polymers 5-6 showed a thermal stability up to 330 degrees C in thermogravimetric analysis thermograms with T-g values obtained from differential scanning calorimetry thermograms in the range 179-188 degrees C. The second harmonic generation (SHG) coefficients (d(33)) of poled polymer films at the 1064nm fundamental wavelength were around 6.32 x 10(-9)esu. The dipole alignment exhibited exceptionally high thermal stability even at 20 degrees C higher than T-g, there was no SHG decay below 200 degrees C because of the partial main chain character of polymer structure, which is acceptable for nonlinear optical device applications.