Partition of Block Copolymers in Phase-Separating Polymer Solutions

The distribution of the AB diblock copolymer in a phase-separating solution composed of immiscible A and B homopolymers in a common solvent has been investigated theoretically. We have utilized the mixing Gibbs energy density for the interfacial phase based on mean-field lattice theory to this four-component system. Distributions of the AB diblock copolymer in the A and B homopolymer-rich bulk phases and the interfacial region between the separating bulk phases are calculated as a function of the B-block content, degrees of polymerization of the copolymer and A and B homopolymers, as well as interaction parameters among the A and B monomer units and the solvent. The copolymer prefers to distribute more in the interfacial region rather than separating bulk phases at a higher copolymer degree of polymerization and a higher interaction parameter between A and B monomer units. The theory is also compared with Asano et al.'s experimental results [ Langmuir 2015, 31, 7488-7495] for polystyrene-b-poly(ethylene glycol) copolymer added to the phase-separating solution of polystyrene and poly(ethylene glycol) homopolymers dissolved in chloroform.