[en] Methyl 3,4-di-(2'-hydroxyethoxy)benzylidenecyanoacetate was prepared and condensed with terephthaloyl chloride to yield novel Y-type polyester containing 3,4-dioxybenzylidenecyanoacetate groups as NLO-chromophores, which constituted parts of the polymer main chains. The resulting polymer 4 is soluble in common organic solvents such as acetone and N,N-dimethylformamide. Polymer 4 shows thermal stability up to 280 .deg. C in thermogravimetric analysis with glass-transition temperature obtained from differential scanning calorimetry near 105 .deg. C. The second harmonic generation (SHG) coefficient (d₃₃) of poled polymer films at the 1064 nm fundamental wavelength is around 2.42 pm/V. The dipole alignment exhibits high thermal stability up to near T_g, and there is no SHG decay below 100 .deg. C due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications