Chiral Nematic Mesophases of Lyotropic and Thermotropic Cellulose Derivatives

Abstract

Polymer molecules are capable of forming lyotropic and thermotropic liquid crystalline phases. These can be grouped into three general categories; side-chain liquid crystalline polymers, main-chain liquid crystalline polymers, and rigid-rod liquid crystalline polymers. Side-chain liquid crystalline polymers have small mesogenic groups attached to the flexible polymer backbone. Main-chain liquid crystalline polymers contain mesogenic groups within the polymer backbone, joined by flexible segments. It is the mesogenic groups that are responsible for the liquid crystalline behavior of these macromolecules. Rigid-rod liquid crystalline polymers have a rigid or semirigid backbone. The polymer may adopt a helical secondary structure that results in the molecule having a rod-like shape. This is the case for certain polypeptides which possess an α-helical conformation that arises as the result of intramolecular hydrogen bonding and steric effects. Liquid crystalline rigid-rod polymers may also be composed of conformationally rigid monomer units which restrict the flexibility of the chain. These rigid monomers may be para-substituted aromatic groups as in polyamides or polyesters, or the β-linked glucopyranosic units found in cellulose and its derivatives.