Yuwei Gu 1 , Eric A. Alt 1 , Heng Wang 2 , Xiaopeng Li 2 , Adam P. Willard 1 , Jeremiah A. Johnson 1 * 1 Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 2 Department of Chemistry, University of South Florida, Tampa 33620 Polymer network topology As a global parameter for polymer networks, network topology dictates a variety of material properties, ranging from static properties to network dynamics. Photoswitching polymer network topology Photoswitching metal-organic cage • Topology switching enables the materials to switch between low-modulus and high-modulus states. • Topology switching is characterized by small angle X-ray scattering (SAXS), wherein d is junction-to- junction distance, r is the radius of the MOC-based junction. Characterization of topology switching • The abundancy of primary loops changes dramatically upon topology switching. • By doping free ligands as “defects”, the storage modulus of the material can be switched by one order of magnitude as the material switches its degree of defect-tolerance upon topology switching. Switching of defect-tolerance Fatigue properties Switching of network dynamics Conditional self-healing properties Conclusion • Introducing a photo-switchable metal- organic cage in polymer gels, for the first time we realized external switching of network topology. • Switching network topology enables the material to switch between two states that have completely different static and dynamic properties. References 1. Gu, Y. et al. Trends Chem. 2019, 1, 318- 334. 2. Gu, Y. et al. Nature 2018, 560, 65-69. 3. Gu, Y et al. Proc. Natl. Acad. Sci. U.S.A. 2017, 114, 4875-4880. 4. Han, M. et al. Angew. Chem. Int. Ed. 2016, 55, 445-449. 5. Zhukhovitskiy, A. V. et al. Nat. Chem. 2016, 8, 33-41.