Synthesis and nonlinear optical properties of novel polyurethanes with high thermal stability of dipole alignment

Abstract

2,3-Di-(2′-hydroxyethoxy)-4′-nitrostilbene ( 2) was prepared and condensed with 2,4-toluenediisocyanate (TDI), 3,3′-dimethoxy-4,4′-biphenylenediisocyanate and 1,6-hexamethylenediisocyanate to yield polyurethanes ( 3– 5) containing the nonlinear optical (NLO)-chromophores 2,3-dioxynitrostilbenyl groups, which constitute parts of the polymer backbones. The resulting polymers ( 3– 5) were soluble in common organic solvents such as acetone and N, N-dimethylformamide (DMF). These polymers showed a thermal stability up to 260 °C in thermogravimetric analysis (TGA) thermograms with glass transition temperature ( T g) values in the range 100–155 °C in differential scanning calorimetry (DSC) thermograms. The second harmonic generation (SHG) coefficients ( d 33) of poled polymer films were around 5.48×10 −10 esu. These poled polymers exhibited a greater thermal stability of dipole alignment even at 20 °C higher than T g due to the partial main chain character of the polymer structure, which is acceptable for NLO device applications.