Synthesis and Nonlinear Optical Properties of Novel Y-type Polyimides with Highly Enhanced Thermal Stability of Second Harmonic Generation

ABSTRACT

2,3-Bis-(3,4-dicarboxyphenylcarboxyethoxy)-4′-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°C in TGA thermograms with T _g values from DSC thermograms in the range of 135–141°C. The SHG coefficients (d ₃₃) of poled polymer films were around 6.14 × 10⁻⁹ esu. The dipole alignment of poled polymer films exhibited exceptionally high thermal stability even at 30°C higher than T _g and there was no SHG decay below 170–190°C due to the partial main chain character of polymer structure, which was acceptable for NLO device applications.

Keywords:

• atomic force microscopy (AFM)
• differential scanning calorimetry (DSC)
• NLO
• polyimides
• relaxation of dipole alignment
• SHG coefficient
• thermogravimetric analysis (TGA)

Acknowledgments

This work was supported by the Inje Research and Scholarship Foundation in 2004 and partly by the Korea Research Foundation Grant (KRF-2004-041-D00214).

Notes

^a Determined from DSC curves measured on a TA 2920 differential scanning calorimeter with a heating rate of 10°C/min under nitrogen atmosphere.

^b Determined from TGA curves measured on a DuPont 951 thermogravimetric analyzer with a heating rate of 10°C/min under nitrogen atmosphere.

^a Polymer film after corona poling.

^b SHG coefficients (d ₃₃) were derived from the analysis of measured Maker-fringes [10].

^c Order parameter Φ = 1 − A₁/A₀, where A₀ and A₁ are the absorbances of the polymer film before and after corona poling, respectively.

^d Film thickness was determined by the optical transmission technique [9].