RIGID RODLIKE MAIN-CHAIN POLYMERS WITH CONFORMATIONALLY RESTRICTED NONLINEAR-OPTICAL CHROMOPHORES - SYNTHESIS AND PROPERTIES

The synthesis and characterization of aromatic main chain polyesters with perpendicularly attached nonlinear optical chromophores embedded in long alkoxy side chains are described. The polymers were characterized by differential scanning calorimetry, X-ray diffractometry, and polarized optical microscopy. Nonlinear optical properties of models of the chromophore subunits were investigated separately by electric field induced second harmonic generation (EFISH) and electrooptical absorption measurement (EOAM). Electric poling of the polymers was successfully applied to thin films of the polymer to induce the noncentrosymmetry required for second-order nonlinearity. Characterization of electrooptical properties of the poled polymer films was accomplished by the method of attenuated total reflection. Values for second-order susceptibilities chi(zzz)((2)) ranged from 0.73 to 1.0 pm/V. The long-term stability of the induced polar order of the polymer was investigated by monitoring the intensity of the nonlinear optical response of polymer waveguides as a function of time at a fixed temperature. Excellent stability of the polar order was observed even at 140 degrees C due to the layered structure of the polymer films. The decay of nonlinearity could be fitted by both biexponential and stretched exponential equations.