Head-to-tail mainchain chromophoric polymers have been of interest because of their high chromophore densities [about 30 X 1021 chromophores/cm3 in the case of poly(4-N-ethylene-N-ethylamino)-(alpha) -cyanocinnamate], their proposed tendency to align in an electric field more readily than unconnected chromophores, and the proposed enhancement of the macroscopic hyperpolarizability coefficients. These proposed properties have yet to be proven for the solid state. In fact, results on mainchain nonlinear optical polymers indicate that a much lower degree of alignment resulted than would be expected for unconnected dipoles. It is possible that the head-to-tail configuration of mainchain polymers has too high of an energy barrier to rotation and alignment to allow proper alignment of the dipoles. Therefore, a new class of mainchain polymers, namely head-to-head polymers connected with various flexible spacers (which may allow the dipoles to align) was developed. The synthesis and characterization of these new materials is described. The nonlinear optical properties of several of this new class of mainchain nonlinear optical polymers were compared to the properties of the head-to-tail mainchain polymers.
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