Synthesis,characterization, and thermo‐optical properties of azobenzene polyurethane containing chiral units

An optically active levoazobenzene polyurethane (PU) was synthesized and was based on the chromophore 4‐(4′‐nitrophenylazo) phenylamine, the chiral reagent L (?)‐tartaric acid, and toluene diisocyanate. The chemical structure and thermal properties were characterized by ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, ¹H‐NMR spectroscopy, and differential scanning calorimetry. The PU had high number‐ and weight‐average molecular weights up to 52 300, a large glass‐transition temperature of 235.7°C, and an optical rotation of ?18.06°, The optical parameters, including the refractive index (n) and thermo‐optic coefficient (dn/dT); the dielectric constant (?) and its variation with temperature; and the thermal volume expansion coefficient and its variation with temperature of PU were obtained. The dn/dT and ? values for the polymer were in the range ?4.1200 to 3.6257 × 10^?4 °C^?1 and 2.00 ± 0.11, respectively. The dn/dT values were one order of magnitude larger than those of inorganic glasses, such as zinc silicate glass (5.5 × 10^?6 °C^?1) and borosilicate glass (4.1 × 10^?6 °C^?1), and were larger than organic materials, such as polystyrene (?1.23 × 10^?4 °C^?1) and poly(methyl methacrylate) (?1.20 × 10^?4 °C^?1). The ? values were lower than that of alicyclic polyimide and semiaromatic polyimide. The obtained PU is expected to be useful for optical switching and optical waveguide areas. The conclusion has a little significance for the development of a new digital optical switch. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010