New polyurethanes and polyesters for second-order nonlinear optical applications

New polymers for second-order nonlinear optical (NLO) applications were synthesized and characterized. They were distinguished by the presence of chromophore groups, with various molecular hyperpolarizability values, used as pendants on substantially rigid backbones. The polymers were prepared through the reaction of tolylene-2,4-diisocyanate, or a suitable alkyloxyphthaloyl dichloride, with the N,N-diethanol-4-(phenyl) group azo-linked to a nitrofluorenone, nitrostilbene, nitrooxadiazole, or nitrothiadiazole moiety. The polymers exhibited good thermal stability, high glass-transition temperatures, and an absence of crystallinity. The second-order NLO properties of thin, transparent poled films, prepared by spin coating and thermal corona poling, were investigated for some of the polymers. The second harmonic coefficients, ranging between 18 and 25 pm/V, depended more on the alignment of the chromophore groups along the direction of the poling field than on their molecular hyperpolarizability. The temporal stability of the NLO properties of the polymers was also investigated. (C) 2004 Wiley Periodicals, Inc.