Thermodynamics and Dynamics of Telechelic Ionic Associating Polymer

Replacing covalent C-C bonds with non-covalent interactions can create more dynamic, easily recyclable polymers. By designing oligomeric building blocks with hydrogen-bonding end groups, supramolecular linear polymers can be constructed, but their low association enthalpy (|ΔH| < 40 kJ/mol) results in short bond lifetimes (t_b) and lower viscosities due to lack of entanglement. In this work, we explore the use of telechelic ionic oligomers with oppositely charged end groups. The large and tunable ionic bond strength (|ΔH| < 200 kJ/mol) results in large binding constants (K_eq) and effective chain lengths N_agg. The enhanced association thermodynamics significantly influence the polymer dynamics. Strong ionic interactions yield longer t_b, and when t_b exceeds the relaxation time of one entanglement strand (t_e), topological confinements from chain entanglement dramatically increases viscosity (h).

We will discuss a 3 kDa polyethylene glycol (PEG) model system, where the hydroxyl-terminated PEG precursor is functionalized into cationic and anionic ionomers (A2 and B2, respectively). Blending A2 and B2 in stoichiometric ratios results in an associating polymer with more than 100-fold increase in viscosity, which is much higher than analogous hydrogen-bonded systems. Using X-ray scattering and small amplitude oscillatory shear rheology, we aim to elucidate the structure–property relationships and design robust, entangled supramolecular polymers that can be assembled and disassembled on demand.