Macromolecular Engineering of Self-Healing in Transient Metallosupramolecular Polymer Networks

The trade-off between self-healing and mechanical properties of synthetic polymer networks is traditionally addressed by combining supramolecular bonds with fast and slow dynamics in diverse network structures and phase-separated morphologies. However, network topology also plays a crucial role by influencing the local concentration and accessibility of transient bonds, thereby affecting both the mechanical properties and self-healing capacity. To explore this, we introduce a hyperbranched macromolecular additive to a transient metallosupramolecular polymer network constructed by a bifunctional linear precursor. The tris-complexation of phenanthroline ligands located at the end of the linear precursor creates a homogeneous network topology, which is significantly altered when a hyperbranched additive with an extensively larger number of ligands per chain is introduced. Rheological studies reveal that the network connectivity can either increase or decrease, respectively, by the formation of more interchain connections at low precursor concentrations or additional loops at high concentrations. Regardless of these changes, the hyperbranched additive enhances the likelihood of the ligand-exchange reaction, the key element in network dynamics and reformation. This leads to a reduction in flow activation energy, widening of the linear viscoelastic region, and ultimately an increase in self-healing potential. Our findings provide valuable insights for designing transient networks such as vitrimers to achieve a balanced combination of mechanical strength, reversibility, and self-healing.