Preparation and nonlinear optical properties of novel Y-type polyesters with highly enhanced thermal stability of second harmonic generation

3,4-Di-(2'-hydroxyethoxy)benzylidenemalononitrile (3) was prepared and condensed with terephthaloyl chloride and adipoyl chloride to yield novel Y-type polyesters (4-5) containing 3,4-dioxybenzylidenemalononitrile groups as NLO-chromophores, which constituted parts of the polymer main-chains. The resulting polymers 4-5 are soluble in common organic solvents such as acetone and NN-dimethylformamide. They showed thermal stability up to 300 degrees C in thermogravimetric analysis with glass-transition temperatures obtained from differential scanning calorimetry in the range 89-91 degrees C. The second harmonic generation (SHG) coefficients (d(33)) of poled polymer films at the 1064 nm fundamental wavelength were around 2.47 pm/V. The dipole alignment exhibited high thermal stability even at 10 degrees C higher than T-g, and there is no SHG decay below 100 oC due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications. (C) 2008 Elsevier Ltd. All rights reserved.