Self-assembly of discrete cyclic nanostructures mediated by transition metals.

Star polyMOCs with diverse structures, dynamics, and functions by three-component assembly. Kinetic Monte Carlo simulation for quantification of the gel point of polymer networks. Quantifying the impact of molecular defects on polymer network elasticity. Zhong, M., Wang, R., Kawamoto, K., Olsen, B. Nanostructural heterogeneity in polymer networks and gels. From topological gels to slide-ring materials. Network topology and the theory of rubber elasticity. The design of reversible hydrogels to capture extracellular matrix dynamics. Photoinduced plasticity in cross-linked polymers. Mechanochemical strengthening of a synthetic polymer in response to typically destructive shear forces. Photodegradable hydrogels for dynamic tuning of physical and chemical properties. Mimicking biological stress–strain behaviour with synthetic elastomers. DNA sequence-directed shape change of photopatterned hydrogels via high-degree swelling. High-performance vitrimers from commodity thermoplastics through dioxaborolane metathesis. Highly branched and loop-rich gels via formation of metal–organic cages linked by polymers. Optically healable supramolecular polymers. A thermally re-mendable cross-linked polymeric material. Topology-switching materials could prove useful in fields such as soft robotics and photo-actuators and also provide model systems for fundamental polymer physics studies. This photoswitching produces coherent changes in several network properties at once, including branch functionality, junction fluctuations, defect tolerance, shear modulus, stress-relaxation behaviour and self-healing. By using networks of polymer-linked metal–organic cages in which the cages change shape and size on irradiation, we can reversibly switch the network topology with ultraviolet or green light. Here we use cooperative self-assembly as a design principle to prepare a material that can be switched between two topological states. However, many existing systems exhibit only one operational state that is defined by the material’s composition and topology 3, 4, 5, 6 or their responsiveness may be irreversible 7, 9, 10 and limited to a single network property 11, 12 (such as stiffness).

Designing polymer networks from the bottom up with new structural motifs and chemical compositions can be used to impart dynamic features such as malleability or self-healing, or to allow the material to respond to environmental stimuli 3, 4, 5, 6, 7, 8. Polymer networks can have a range of desirable properties such as mechanical strength, wide compositional diversity between different materials, permanent porosity, convenient processability and broad solvent compatibility 1, 2.

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