Phase Behavior in Polymer Blends: The Effect of Microstructure

Abstract

The original mean field theories of the Flory-Huggins and/or equation of statelattice fluid types take no account of microstructure. Issues such as the sequence distribution of the repeat units in a copolymer chain or the presence of a microphase of the micellar type are not addressed. The effect of such microheterogeneities on phase behavior can, however, be taken into account within the spirit of the mean field approach. For example, Flory⁽¹⁾ was able to describe the thermodynamics of solutions of rigid rod polymers very successfully on this basis even though the rods form ordered mesophases in certain temperature/concentration regimes. Later it was shown that sequence distribution effects can also be incorporated and can lead to rather significant deviations from “classical” mean field behavior^(2,3,4) In this paper we first illustrate the application of the modified theory to the case of copolymers containing identical repeat units and statistical distributions of comonomer units but differing only in composition. We then discuss the effects to be expected in such copolymer blends where the compositions are identical but the microstructures differ.