Liquid crystals composed of large, enlongated molecules have significance in materials science. The high degree of orientational order achieved in solutions of these polymers may be passed on to the solid state. This extra order of orientation results in synthetic materials of very high strength and temperature resistance. The research program outlined here focuses on polymers that are elongated due to an internal helical arrangement of their subunits. Two classes of polymers that are helical for very different reasons will be studied: polypeptides held in helical organization by internal hydrogen bonding among the monomers, and polyisocyanates that maintain the helical conformation due to side-chain interactions. We will examine the effects of progressive flexibility, usually brought on by variation of solvent character, in solutions of such macromolecules on phase transitions and liquid crystal formation. Molecular orientational order will be correlated with chain stiffness, as measured by the persistence length of the polymer. The influence of chain rigidity on a liquid crystal elastic modulus will be explored. Solvent variations will be examined on a magnetic filed induced depression of the liquid crystal to isotropic transition temperature. Finally, a unique double, helix-to-coil transition in dilute solution of one of the polypeptides will be further delineated.
