Preparation of novel polyimides with high thermal stability of dipole alignment for electro-optic applications

Abstract

3,4-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 3,4-dioxybenzylidenemalononitrile groups as NLO-chromophores, which constitute parts of the polymer backbones. The resulting polyimides 5-6 were soluble in polar solvents such as acetone and N,N-dimethylformamide. Polymers 5-6 showed a thermal stability up to 330 °C in thermogravimetric analysis thermograms with Tg values obtained from differential scanning calorimetry thermograms in the range of 181–190 °C. The second harmonic generation (SHG) coefficients (d33) of poled polymer films at the 1064 nm fundamental wavelength were around 4.73×10-9 esu. The dipole alignment exhibited a thermal stability even at 20 °C higher than the glass-transition temperatures, there was no SHG decay below 200 °C because of the partial main chain character of polymer structure, which was acceptable for nonlinear optical device applications.