Preparation and electro‐optic properties of novel Y‐type polyimides with highly enhanced thermal stability of second harmonic generation

Abstract

BACKGROUND: In the development of nonlinear optical (NLO) polymers for electro‐optic device applications, stabilization of electrically induced dipole alignment is one of the important criteria. Polyimides for NLO applications have attracted attention because of their high Tg values and high thermal stability. In this work we designed and synthesized a new type of NLO polyimide, in which the pendant NLO chromophores are parts of the polymer backbone. These mid‐type NLO polymers are expected to have the merits of both main‐chain and side‐chain NLO polymers: stabilization of dipole alignment and good solubility. RESULTS: 3,4‐Bis‐(3,4‐dicarboxyphenylcarboxyethoxy)‐4′‐nitrostilbene dianhydride was prepared and reacted with the corresponding aromatic diamine to yield unprecedented Y‐type polyimides containing 3,4‐dioxynitrostilbenyl groups as NLO chromophores, which constituted parts of the polymer backbones. The resulting polyimides are soluble in polar solvents such as dimethylformamide and dimethylsulfoxide. These polymers showed a thermal stability up to 320 °C in thermogravimetric thermograms with Tg values obtained from differential scanning calorimetry thermograms in the range 143–164 °C. The second harmonic generation (SHG) coefficients (d33) of poled polymer films at the 1064 nm−1 fundamental wavelength were around 9.45 × 10−18 C. CONCLUSION: The dipole alignment exhibited exceptionally high thermal stability even at 30 °C higher than Tg. There was no SHG decay below 180–190 °C because of the partial main‐chain character of the polymer structure, which is acceptable for NLO device applications. Copyright © 2007 Society of Chemical Industry

Synthesis and nonlinear optical properties of novel fluorinated polyimides with thiazolylazo chromophores for electrooptic devices

“…High glass transition temperature aromatic polyimides were developed as polymeric backbones for the purpose of restraining the relaxation of the noncentrosymmetric chromophore-alignment induced by an electric field. Various side-chain polyimide-based NLO materials have been synthesized and they exhibit excellent properties, including high temperature alignment stability, good mechanical properties, and low optical loss [3][4][5][6][7][8] . In addition fluorine-containing polyimides (FPIs) have inspired many researchers to utilize the materials for the electrooptic (EO) applications due to the favorable properties such as small optical loss in visible to near-IR regions, high thermal stability, and small moisture sorption.…”