Synthesis and properties of novel X-type polyurethane containing dicyanovinylnitrocatechol of enhanced SHG thermal stability for electro-optic applications

Abstract

Novel X-type polyurethane 5 containing 4-(2′,2′-dicyanovinyl)-5-nitrocatecholic groups as nonlinear optical chromophores, which constitute parts of the polymer backbone, was prepared and characterized. Polyurethane 5 is soluble in common organic solvents such as acetone and N,N-dimethylformamide. It shows thermal stability up to 270 °C from thermogravimetric analysis with a glass-transition temperature obtained from differential scanning calorimetry thermogram of around 113 °C. The second harmonic generation (SHG) coefficient (d33) of poled polymer film at 1,064 nm fundamental wavelength is around 5.72 × 10−9 esu. The dipole alignment exhibits a thermal stability even at 7 °C higher than glass-transition temperature, and there was no SHG decay below 120 °C due to the partial main-chain character of the polymer structure, which is acceptable for nonlinear optical device applications.