Preparation of novel azo polyurethane urea and the research of its optical properties

The brown azo chromophore molecule 4-(4′-nitrophenyl-diazenyl)phenyl-1,3-diamine (NDPD) was synthesized by diazo coupling reaction with 4-nitroaniline, sodium nitrite, and phenylenediamine. And then the red novel azo polyurethane urea (PUA) was synthesized with isophorone diisocyanate (IPDI), polyether diols (NJ220), and chromophore molecule NDPD. First, the solubility with several kinds of organic solvents, and some mechanical properties of PUA (such as tensile strength and ratio of elongation at break) were measured. Results showed that the PUA has good thermal stability, and its melting point is 114.2 °C. Then the absorption spectrum of PUA was also characterized by UV–vis spectroscopy. Moreover the refractive index n of PUA was obtained by attenuated total reflection (ATR) method at different temperature and wavelength, by which the material's thermo-optic coefficient (dn/dt) was calculated. Results showed that the material has a large thermo-optic coefficient, especially the thermo-optic coefficient could reach −5.25 × 10−4 °C−1 at the wavelength of 650 nm. Finally, the dispersion coefficient was calculated by the Sellmeyer equation. These thermo-optic properties of PUA are important for the application of thermo-optic switch and even all-optical switch.