Synthesis and nonlinear optical properties of novel Y-type polyimides with highly enhanced thermal stability of second harmonic generation

2,3-Bis-(3,4-dicarboxyphenylcarboxyethoxy)-40-nitrostilbene dianhydride ( 4) was prepared and reacted with 4,4'-oxydianiline and 4,4'-diaminobenzanilide to yield unprecedented novel polyimides 5-6 containing 2,3-dioxynitrostilbenyl groups as NLO-chromophores, which constituted parts of the polymer backbones. The resulting polyimides 5-6 were soluble in polar solvents such as DMSO and DMF. Polymers 5-6 showed a thermal stability up to 300 degrees C in TGA thermograms with T-g values from DSC thermograms in the range of 135-141 degrees C. The SHG coefficients (d(33)) of poled polymer films were around 6.14 x 10(-9) esu. The dipole alignment of poled polymer films exhibited exceptionally high thermal stability even at 30 degrees C higher than T-g and there was no SHG decay below 170-190 degrees C due to the partial main chain character of polymer structure, which was acceptable for NLO-device applications.