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.