Microphase Formation in Mixtures of Associating Polymers

This paper theoretically explores possible phase diagrams of the associating polymers in which macro- and microphase separation transitions coexist. Our model binary mixture consists of long chains (A) carrying f associative groups and short chains (B) carrying one associative group on their ends. Comb-shaped block copolymers with A as a main chain bearing a different number of side B chains are formed in equilibrium. When A and B unfavorably interact, macro- and microphase separations compete. If the population of the formed block copolymers is sufficiently large, miscibility between A/B chains is so improved that a stable microphase appears in a restricted region on the phase plane near the stoichiometric concentration where the concentration of the mixture agrees with the molecular composition of the fully associated cluster A· Bf. This mocrophase reveals new properties since it is formed by reversible bonds instead of covalent ones. Relation to the recently observed microphase in hydrogen-bonded polymer/surfactant systems is discussed.