Synthesis of novel Y-type nonlinear optical polyesters with enhanced thermal stability of dipole alignment

2,4-Di-(2'-hydroxyethoxy)benzylidenemalononitrile (3) was prepared and polymerized with terephthaloyl chloride and adipoyl chloride to yield novel Y-type polyesters 4 and 5 containing dioxybenzylidenemalononitrile groups as NLO-chromophores, which constituted parts of the polymer backbone. The resulting polymers 4 and 5 are soluble in common organic solvents such as acetone and N,N-dimethylformanide. Polymers 4 and 5 showed thermal stability up to 300 degrees C in thermogravimetric analysis with glass-transition temperatures obtained from differential scanning calorimetry in the range 83-94 degrees C. The second harmonic generation (SHG) coefficients (d(33)) of poled polymer films at the 1064 nm fundamental wavelength were around 6.48 x 10(-9) esu. The dipole alignment exhibited high thermal stability even at 10 degrees C higher than T-g and no significant SHG decay was observed below 105 degrees C partially due to the main-chain character of polymer structure, which is acceptable for NLO device applications.