Preparation of Novel T-type Polyurethanes with High Thermal Stability of Second Harmonic Generation and Their Nonlinear Optical Properties

摘要

2,5-Di-(2`-hydroxyethoxy)benzylidenemalononitrile (3) was prepared and polymerized with 2,4-toluenediisocyanate and 3,3`-dimethoxy-4,4`-biphenylenediisocyanate to yield novel T-type polyurethanes 4 and 5 containing 2,5-dioxybenzylidenemalononitrile, nonlinear optical (NLO)-chromophores as part of the polymer backbones. Polyurethanes 4 and 5 were soluble in common organic solvents such as acetone and N,Ndimethylformamide and showed a thermal stability up to 250∩ with glass-transition temperatures (Tg) in the range 119-146∩. The second harmonic generation (SHG) coefficients (d33) of poled polymer films at 1064 nm fundamental wavelength were around 5.82 】 10^?9 esu. The dipole alignment exhibited high thermal stability up to T_g, and there was no SHG decay below 140∩ due to the partial main-chain character of the polymer structure, which was acceptable for nonlinear optical device applications.