Electron paramagnetic resonance (EPR) spectroscopy was used to gain a deeper understanding of the local nitroxide environment in TEMPO-polyCAT. Compared to TEMPO-CL, the EPR spectrum of TEMPO-polyCAT was significantly broadened as expected for immobilized free radicals (Fig. ). Fitting the spectra revealed clear signs of reduced nitroxide mobility and strong spin-spin exchange interactions, indicative of the nitroxides being crowded within the MOC junctions (see Supporting Information section "EPR Studies" for details). Moreover, the fitting indicated that 94% of the nitroxides existed within a similar chemical environment, which is expected given the symmetry of the MOC junctions. Remarkably, the spectrum for TEMPO-polyCAT was nearly identical to that of a soluble MOC composed of 20:4 TEMPO-CL and a methoxy-functionalized spacer ligand SL (Fig. ). In other words, introduction of polymer linkers to the exterior of the MOCs does not significantly perturb the catalyst environment, which should facilitate predictable and direct translation of these formerly homogeneous catalysts to polyCATs. Additionally, this result provides strong evidence for the existence of wellformed MOC junctions within TEMPO-polyCAT, as the EPR spectrum for an unannealed material with ill-defined metal-organic crosslinks clearly showed a larger distribution of distinct nitroxide environments (see Supporting Information section "EPR Studies" for details). ) to its corresponding aldehyde (2) using TEMPO-polyCAT. e, Comparison of the rate of oxidation of TEMPO-CL free in solution (black) and TEMPO-polyCAT gel (red). f, Cycling of the oxidation using TEMPO-polyCAT. Conversions are calculated based on 1 H NMR integration vs. an internal standard. g, Deswelling, storage, and swelling of the material does not diminish the catalytic activity.