Preparation of Novel Y-Type Nonlinear Optical Polyimides with High Thermal Stability of Second Harmonic Generation

Abstract

2,4-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 2,4-dioxybenzylidenemalononitrile groups as NLO-chromophores, which constitute parts of the polymer backbone. The resulting polyimides 5-6 are soluble in polar solvents such as dimethylsulfoxide and N,N-dimethylformamide. Polymers 5-6 showed a thermal stability up to 330°C in thermogravimetric analysis thermograms with T g values obtained from differential scanning calorimetry thermograms in the range 179–188°C. The second harmonic generation (SHG) coefficients (d 33) of poled polymer films at the 1064 nm fundamental wavelength were around 6.32 × 10−9 esu. The dipole alignment exhibited exceptionally high thermal stability even at 20°C higher than T g , there was no SHG decay below 200°C because of the partial main chain character of polymer structure, which is acceptable for nonlinear optical device applications.