Oppositely charged polyelectrolytes in solution spontaneously associate into hydrated complexes or coacervates, PECs. The morphology, stability, and properties of PECs depend strongly on their ion content, which moderates the “sticky” reversible interactions between Pol+ and Pol– oppositely charged repeat units. Here, it is shown that the distribution of ions between a PEC and the aqueous solution in which it is immersed is accurately predicted by the Donnan equilibrium. For ideal, stoichiometric mixing of polyelectrolytes, corresponding to an enthalpy of complexation ΔH PEC → 0, the salt, MA, concentration inside the PEC, [MA]PEC, is equal to the solution salt concentration, [MA]s. Isothermal calorimetry measurements along a Hofmeister series show that if mixing is exothermic, [MA]PEC < [MA]s, while for endothermic association of Pol+ and Pol–, [MA]PEC > [MA]s. A set of simple self-consistent expressions illustrate PEC salt response without consideration of net Coulombic or electrostatic forces between charged species. ΔH PEC exactly predicts deviations from ideal Donnan equilibria, which are connected to the equilibria between associated or intrinsic pairs of Pol+Pol– and extrinsic Pol+A– and Pol–M+ pairs, where counterions compensate polyelectrolyte charges. The equilibrium constant K pair for Pol+Pol– pair formation is shown to be proportional to the volume charge density of the hydrated, ion-free complex. K pair may also be used to estimate the critical salt concentration at which polyelectrolytes completely dissociate.

The thiol−Michael adduct is used as a thermoresponsive dynamic cross-linker in polymeric materials. Recently, the thiol−Michael reaction between thiols and conjugated alkenes has been used as a ligation reaction for polymer synthesis and functionalization. Here, the thiol− Michael reaction is demonstrated to be thermally responsive and dynamic. Small molecule model experiments demonstrate the potential for the thiol−Michael adducts to be used in dynamic covalent chemistry. Thiol−acrylate adducts are incorporated into a cross-linker to form a soft polymeric material. These thiol−Michael cross-linked materials display healing after being cut and malleability characteristics at 90 °C. Additionally, the data suggest that there is limited creep and stress relaxation at room temperature with complete recovery of creep once the strain is removed. These thiol−Michael cross-linked polymers show dynamic properties upon thermal stimulus, with long-term stability against mechanical deformation in the absence of this stimulus, opening the way for them to be used in various applications.

The spontaneous association of oppositely charged polyelectrolytes is an example of liquid−liquid phase separation. The resulting hydrated polyelectrolyte complexes or coacervates, both termed "PECs", display a wide range of viscosities. In addition to the usual dependence of viscosity on molecular weight and volume fraction expected for condensed neutral polymers, PECs also contain dense charge pairing between positive, Pol + , and negative, Pol − , repeat units. These "stickers" slow polymer chain dynamics on multiple length scales. Pol + Pol − charge pairs may be broken by the addition of salt to solutions contacting PECs, reducing viscosity ("saloplasticity"). Here, the dynamics of matched pairs of a polycation, poly(methacryloylaminopropyltrimethylammonium chloride), and polyanion, sodium poly(methacrylate), with molecular weights considerably above the entanglement concentration, were measured as a function of temperature and salt concentration. The dynamics of NaCl ions in PECs were also determined and correlated to the segmental relaxation times, which control viscosity. A suite of relaxation times corresponding to ion, monomer, Pol + Pol − pair exchange, entanglement, and reptation was determined or estimated. The zero-shear viscosity, η 0 , was found to be an unusually strong function of molecular weight, with the scaling η 0 ∼ M 5 . A polymer coil size, measured by small-angle neutron scattering, was used in concert with new quantitative expressions to provide a good fit of theory to experiment for this unusual scaling.

A combination of supramolecular and dynamic covalent linkages were used to create creep limited self-healing materials.