Statistical thermodynamics of ABA block copolymers. II

A microstructural model for the phase‐separated states of ABA triblock copolymers is proposed. It postulates the simultaneous existence of three phases: pure A, pure B, and a mixed region. Incorporation of the mixed region distinguishes this treatment from all other theories and is responsible for considerable flexibility in the model without increased numbers of parameters. Calculations of free energy changes required to establish specific microstructures permit the prediction of a favored one from among five possibilities: discrete spheres of A (or B), discrete cylinders of A (or B), and lamellae.