Chemical Compatibilization, Macro-, and Microphase Separation of Hetero-Associative Polymers

A mean-field equilibrium theory for reversible network formation due to heterotypic pairwise interactions in mixtures of associative polymers is extended via a weak inhomogeneity expansion to account for spatial fluctuations due to chemical incompatibility. We consider solutions and blends of polymers of types A and B with many associating groups per chain, and consider only A–B association between the groups. The structural correlations of the reversibly-bonded polymers are accounted for by considering the Gaussian 4-arm star-like chain conformations between cross-links, which is analogous to an affine-network assumption. Future extensions of this theory could further incorporate strand stretching from swelling or strong segregation. We show that the chemical incompatibility between A and B polymers drives a competition between associative and segregative phase separation. The addition of reversible A–B cross-links between incompatible A and B chains compatibilizes the mixture, minimizing the propensity for macroscopic phase separation into A- and B-rich phases. Under strong binding and segregation conditions, this results in eutectic-like behavior and local microphase segregation. The crossovers from macroscopic to microscopic phase separation occur at isotropic Lifshitz points, resulting in the potential for bicontinuous microemulsions. The reactive blending of such multifunctional polymers presents the opportunity to envision novel properties, processing conditions, and applications accessible by the tunable production of supramolecular complexes, mesophases, and multicomponent polymer networks.