Liquid Crystal-Isotropic Phase Equilibria in Stiff Chain Polymers

Abstract

Most polymers when in solution exist as polymer random coils irrespective of the extent of intramolecular order in the solid state. Certain classes of macromolecules, however, do retain their intramolecular order when molecularly dispersed and behave as stiff chain or rodlike particles. Among these are synthetic polymers such as polyisocyanates1 and polypeptides2 and biological macromolecules such as DNA, tropocollagen3 and tobacco mosaic virus.4 In solution the concentration dependence of stiff and flexible chain polymers can be qualitatively different. In a good solvent flexible chain polymers mix in all proportions with little change in intramolecular or intermolecular order. As the polymer concentration is increased stiff chain polymers may undergo a phase transition from an isotropic to an anisotropic or liquid crystalline solution.4–8 This phenomenon was predicted on the basis of molecular asymmetry alone by Onsager9 and Isihara,10 and later by Flory.11,l2 The Flory lattice model is applicable over the entire composition range and is particularly convenient for comparison with experimental studies.