2ND-ORDER NONLINEAR OPTICAL-PROPERTIES AND RELAXATION CHARACTERISTICS OF POLED LINEAR EPOXY POLYMERS WITH TOLANE CHROMOPHORES

A new linear epoxy polymer containing 4-amino-4'-nitrotolane chromophores attached to the chain backbone was synthesized in an attempt to enhance both the poling-induced nonlinear optical susceptibility and its long-term stability. The polymer films poled by corona discharge showed very large nonlinear optical doubling coefficients of d33 congruent-to 89 pm/V and d31 congruent-to 25 pm/V for incident light of 1.06-mu-m wavelength, and a linear electro-optic coefficient r13 congruent-to 8 pm/V at 633 nm wavelength. Poling-induced alignment of the nonlinear optical moieties showed no detectable decay in two weeks at ambient temperature, as studied by the birefringence. Even at 100-degrees-C the relaxation time estimated from the birefringence decay was ca. 450 h, consistent with roughly 16% decrease in d(ij) coefficients in 20 h at this temperature and also the extrapolation from the dielectric alpha relaxation characteristics. The dielectric alpha relaxation temperatures of the poled polymer samples exhibited higher values than that of the unpoled counterpart. This unusual behavior may be due to a significant contribution of Maier-Saupe thermotropic interactions among the tolane moieties that favor parallel alignment.