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

2,4-Bis-(3,4-dicarboxyphenylearboxyethoxy)-1-(2,2-dicyanovinyl)benzene dianhydride (4) was prepared and reacted with 4,4'-oxydianiline, 4,4-diaminobenzanilide and 4,4-(hexafluoroisopropylidene)dianiline to yield novel Y-type polyimides 57 containing 2,4-dioxybenzylidenemalononitrile groups as nonlinear optical (NLO) chromophores, which constitute parts of the polymer backbone. The resulting polyimides 5-7 are soluble in polar solvents such as dimethylsulfoxide and N,N-dimethylformamide. Polymers 5-7 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 179-194 degrees C. The second harmonic generation (SHG) coefficients (d(33)) of poled polymer films at the 1064 nm fundamental wavelength were around 5.56 x 10(-9) esu. The dipole alignment exhibited exceptionally high thermal stability even at 20 degrees C higher than the glass-transition temperature there was no SHG decay below 215 degrees C because of the partial main-chain character of polymer structure, which is acceptable for NLO device applications. (C) 2008 Wiley Periodicals, Inc.