Synthesis of novel T-type nonlinear optical polyester with enhanced thermal stability of second harmonic generation for electro-optic applications

2,5-Di-(2′-hydroxyethoxy)benzylidenemalononitrile (3) was prepared and condensed with terephthaloyl chloride to yield novel T-type polyester (4) containing 2,5-dioxybenzylidenemalononitrile groups as NLO-chromophores, which are parts of the polymer backbones. The resulting polymer 4 was soluble in common organic solvents such as acetone and DMF and showed thermal stability up to 280 °C with Tg of 83 °C. The second harmonic generation (SHG) coefficient (d33) of poled polymer film at the 1,064 nm fundamental wavelength was around 4.46 × 10−9 esu. The dipole alignment exhibited high thermal stability even at 10 °C higher than Tg, and there was no SHG decay below 95 °C due to the partial main-chain character of polymer structure, which was acceptable for NLO device applications.