AdvisorHall, H. K.
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PublisherThe University of Arizona.
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AbstractThis work involves the synthesis of two types of electro-optic monomers and their corresponding polymers. The first type of monomers contain the p-oxy-α-cyanocinnamate structure and were synthesized from ω-hydroxyalkoxy-substituted benzaldehydes and methyl cyanoacetate. These ω-hydroxy-α-cyanoester monomers show a high degree of electron delocalization. Copolyesters were synthesized by copolymerization of these monomers with methyl 12-hydroxydodecanoate by the standard two-stage, high-temperature polyesterification procedure. The copolyesters, incorporating dipolar units all pointing in the same direction, are soluble and solution- and melt-processable. Second harmonic generation (SHG) measurements on chloroform solutions of the copolymers showed enhancements of χ² as large as 20 relative to the dipolar monomers. These are the first known readily soluble main chain polymers that exhibit SHG behavior. The second type of monomers were acrylates containing substituted phenyl esters of benzoic acid as mesogenic (pendant) groups. Specifically, the mesogenic group contained an oxy-aryl-carboxy-aryl-carboxy-alkyl structure separated from the acrylate carbon-carbon double bond by a spacer group, which had a carboxyethyl-carboxyhexyl structure. A synthetic route was established by synthesizing a model monomer containing a 2-methylpropyl group as the alkyl group at the end of the mesogenic group. The model monomer was polymerized free radically and the resulting polymer found to possess a smectic liquid crystalline phase that became isotropic at 103° C. With the synthetic route established, an optically active monomer containing a (S)-2-methyl-1-butyl group as the alkyl group at the end of the mesogenic group was synthesized and polymerized. The optically active polymer was already in a smectic liquid crystalline phase at room temperature (≈25° C) and the phase persisted up to 72.6° C. These results indicate that it is possible to design polymers containing thermotropic liquid crystalline phases by fixing low molecular weight liquid crystalline molecules to a polymer main chain.