I. Novel side chain liquid crystalline polymers as nonlinear optical materials. II. Main chain liquid crystalline polymers and polymer model compounds

I. Side chain liquid crystalline polymers offer unique advantages as a new class of organic materials with a potential for nonlinear optical (nlo) response. Three series of side chain liquid crystalline polyesters with the general structure as shown on p. 26 of this dissertation were designed and prepared employing the concept of having the nitroaromatic species serve concomitantly as both the nonlinear optical species and as the only liquid crystalline moiety in the polymer. Differential scanning calorimetry and optical microscopy were used for study of their thermal properties. All of them are enantiotropic liquid crystalline while their corresponding malonate monomers are monotropic liquid crystalline or not liquid crystalline at all.;II. One series of main chain liquid crystalline polyazomethines of the general structure as shown on p. 27 of the dissertation has been synthesized. These materials incorporate three aromatic rings into each rigid mesogenic unit. It was found through examination of optical microscopic and differential scanning calorimetric data that a nematic phase was present in many of these polymers. Indirect evidence supports a smectic phase (or phases) in several of these materials.;Eleven series of small molecule mesogens of general structure as shown on p. 30 of this dissertation were prepared in which a flexible methylene unit has been used as the central linkage. Most of these compounds have liquid crystalline phases. This illustrates that the requirement of rigid central linkage is not a hard and fast rule for liquid crystallinity. Lateral attractions (induced by neighboring polarizable parts of molecules), terminal attractions (induced by polar terminal substituents), spacer chain conformations and the length ratio of rigid aromatic/flexible aliphatic are discussed in the selectivity of mesophases in the halogen terminated small molecule mesogens. Segregation concepts and disordering of the rigid cores were used to explain observations in the alkyl terminated mesogens.