Synthesis and Electro-Optic Properties of Novel T-Type Polyurethane with High Thermal Stability of Second Harmonic Generation

Abstract

2,5-Di-(2′-hydroxyethoxy)benzylidenemalononitrile ( 3 ) was prepared and polyadded with 3,3′-dimethoxy-4,4′-biphenylenediisocyanate to yield novel T-type polyurethane 4 containing 2,5-dioxy benzylidenemalononitrile group as a nonlinear optical (NLO)-chromophore, which constituted parts of the polymer backbones. Polyurethane 4 was soluble in common organic solvents such as acetone and N,N-dimethylformamide. It showed a thermal stability up to 280°C in thermogravimetric analysis thermogram and the glass-transition temperature (T _g ) obtained from differential scanning calorimetry thermogram was around 146°C. The second harmonic generation (SHG) coefficient (d ₃₃) of poled polymer film at 1064 cm⁻¹ fundamental wavelength was around 5.59 × 10⁻⁹ esu. The dipole alignment exhibited high thermal stability up to T _g , and there was no SHG decay below 140°C because of the partial main-chain character of the polymer structure, which was acceptable for nonlinear optical device applications.

Keywords:

• 2,5-Di-(2′-hydroxyethoxy)benzylidenemalononitrile
• differential scanning calorimetry (DSC)
• NLO
• poling
• polyurethanes
• relaxation of dipole alignment
• SHG coefficient
• thermogravimetric analysis (TGA)

Acknowledgments

This work was supported by Korea Research Foundation Grant.

Notes

^a Polymer film.

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

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

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