Synthesis and properties of novel X-type nonlinear optical polyester containing nitrophenylazonitroresorcinoxy group with highly enhanced SHG thermal stability

• New X-type NLO polyester containing diazonitroresorcinoxy group was prepared.
• The resulting polymer shows a thermal stability up to 280 °C with Tg of 120 °C.
• The SHG coefficient (d33) of the poled polymer film is near 2.13 pm/V.
• The polymer exhibits high SHG thermal stability up to 125 °C.

New X-type polyester (4) containing nitrophenylazonitroresorcinoxy groups as NLO chromophores, which are components of the polymer backbone, was prepared and characterized. Polyester 4 is soluble in common organic solvents such as acetone and N,N-dimethylformamide. It shows a thermal stability up to 280 °C in thermogravimetric analysis with glass-transition temperature (Tg) obtained from differential scanning calorimetry near 120 °C. The second harmonic generation (SHG) coefficient (d33) of poled polymer film at the 1064 nm fundamental wavelength is around 2.13 pm/V. The dipole alignment exhibits a thermal stability even at 5 °C higher than Tg, and there is no SHG decay below 125 °C due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications.