Tunable Topology and Viscoelasticity of Polymer Networks via Anion-Adaptive Metal-Organic Macrocycles

The mechanical performance of polymer networks is typically engineered over the spatial (e.g., polymer architecture) or temporal hierarchy (e.g., cross-link kinetics), while conventional network systems generally exhibit only one operational state defined by the single network property. Here, for the first time, we utilize the cooperative self-assembly of anion-adaptive metal-organic macrocycles (MOCs) to design polymer networks with tunable topology and viscoelasticity. The self-adaptive topology of MOCs is first demonstrated using a small molecule as the model system. As a result, by incorporating MOCs at the cross-links, the network topology can be tunable via the facile use of different anions due to the spontaneous formation of MOCs with self-adaptive sizes and shapes. In the meantime, the self-adaptive topology at the cross-links also affords the tunable viscoelasticity of the polymer network, which is affected by the network defects and the strength of the metal-ligand coordination, as quantitatively determined by proton multiple-quantum nuclear magnetic resonance (NMR) spectroscopy and rheology, respectively. Furthermore, the application of these polymer networks in drug delivery for cancer treatment has been well demonstrated. We envisage that the incorporation of anion-adaptive MOCs at the junctions of polymer networks can be useful for the facile fabrication of topology- and viscoelasticity-tunable intelligent materials for different types of applications.