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, 1 H‐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 (ϵ) and its variation with temperature; and the thermal volume expansion coefficient and its variation with temperature of PU were obtained. The dn / dT and ϵ 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 ϵ 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