3,4-Di-(2'-hydroxyethoxy)benzylidenemalononitrile (3) was prepared and condensed with 2,4-loluenediisocyanate and 3,3'-dimethoxy-4,4'-biphenylenediisocyanate to yield unprecedented novel Y-type polyurethanes (4-5) containing 3,4-dioxybenzylidenemalononitrile group as a NLO-chromophore, which is a part of the polymer main chain. The resulting polyurethanes 4-5 were soluble in common organic solvents such as acetone and DMF. Polymers 4-5 showed a thermal stability up to 280degreesC in TGA thermograms with T-g values from DSC thermograms in the range of 148-152degreesC. The SHG coefficients (d(33)) of poled polymer films were around 5.96 x 10(-9) esu. These poled polymer films exhibited greater thermal stabilities of dipole alignments even at 20degreesC higher than T-g due to the partial main chain character of the polymer structure, which is acceptable for NLO device applications.