(122j) Phase-Separation, Gelation, and Dynamics of Associative Polymers

An equilibrium theory for reversible network formation in two-component solutions of associative polymers is presented to account for the phase behavior and 'sticky' dynamics due to hydrogen bonding, metal–ligand, electrostatic, or other pairwise associative interactions. We consider polymers of types A and B with many associating groups per chain and consider only A–B association between the groups. A simple analytical expression for the free energy is derived and is shown to be consistent with the classical Flory–Stockmayer gelation theory. It is shown that association and formation of a reversible network is always accompanied by a tendency for phase separation, even at good solvent conditions, a significant difference from self-associative polymers. Homogeneous networks are most easily stabilized near stoichiometric conditions between A and B associative groups, resulting in a solgelsol transition as the overall composition is altered. Chemical incompatability between the A and B polymers drives a competition between attractively and repulsively-driven phase separation, leading to microphase formation and eutectic behavior. The associative interactions slow molecular relaxations leading to a more general description of the sticky rouse and reptation models.