Synthesis, Characterizations, and Thermo-optical Properties of Poly(urethane-imide) Based on Azo-disperse Dye in Its Side Chains.

Anew poly(urethane-imide) (PUI) was prepared by a condensation reaction of a -NCO terminated polyurethane prepolymer and 4,4 -(hexafluoroisopropylidene) diphthalic anhydride (6FDA). This prepolymer was prepared by a reaction of azo chromophore (dispersed red 19) containing two hydroxyl functional groups and isophorone diisocyanate (IPDI). The PUI was characterized by common spectroscopic methods such as UV-vis, FTIR and 1H NMR, and thermal studies using DSC and TGA. The results of DSC and TGA measurements indicated that the PUI exhibits high thermal stability up to its glass-transition temperature (Tg) of 201oC and a weight loss of 5% at heat temperature of 238oC, due to introduction of imide components and formation of strong hydrogen bonds. The weight-average molecular weight (Mw) was 52600 with a polydispersity of 2.14. The measurement of refractive indices (n) was performed using a multi-wavelength light Abbe refractometer with precise temperature control at single wavelength of an attenuated total reflection (ATR) setup. The values of n and thermo-optic coefficient (dn/dT) were used to calculate the dielectric constant (epsilon) and its variation with temperature (d)epsilon)/dT), volume expansion coefficient (beta) and its variation with temperature (d(beta)/dT) according to Lorentz-Lorenz equation. The dn/dT values were from -2.45 * 10^-4 to -5.05 *10^-4 K^-1 at multiwave-lengh light and from -4.1071*10^-4 to -4.3875 *10^-4 K^-1 at different single-wavelength lights. The d(beta)/dT values were from 0.3331 *10^-6 to 1.4668 *10^-6 K^-1 at multiwave-lenght light and from 0.9449 *10^-6 to 1.1094 *10^-6 K^-1 at different single-wavelength lights. The thermooptic coefficient was recorded as 10^-4 K^-1 which was nearly ten-fold that of inorganic materials such as SiO2 (1.1 *10^-5 K^-1) and LiNbO3 (4 * 10^-5 K^-1). The results show that PUI may be useful as low loss optical communication devices and optical switches with low driving power.