Synthesis of novel Y-type polyurethanes with high thermal stability of dipole alignment and their electro-optic properties

3,4-di-(2'-hydroxyethoxy)benzylidenemalononitrile (3) was prepared and condensed with 2,4-toluenediisocyanate, 1,6-hexamethylenediisocyanate and 3,3'-dimethoxy-4,4'-biphenylenediisocyanate to yield novel Y-type polyurethanes (4-6) containing 3,4-dioxybenzylidenemalononitrile groups as nonlinear optical (NLO) chromophores, which are parts of the polymer backbones. The resulting polyurethanes 4-6 were soluble in common organic solvents such as acetone and DMSO. Polymers 4-6 exhibited a thermal stability up to 260 degrees C from thermogravimetric analysis (TGA) with differential scanning calorimetry (DSC) with T-g values in the range of 96-152 degrees C. The SHG coefficients (d(33)) of poled polymer films were around 6.8 x 10(-9) esu. These poled polymers exhibited a high thermal stability of dipole alignment even at 20 degrees C higher than T-g, and no SHG decay was observed below 175 degrees C due to the partial main chain character of the polymer structure, which is acceptable for NLO device applications.