TEMPO-polyCAT design, synthesis, and application to alcohol oxidation reactions. To test the viability of the polyCAT concept, we first targeted a TEMPO-catalyzed oxidation reaction that had previously been reported to proceed under homogeneous conditions and within the pores of mesoporous silica using Pd12L24 MOCs. Here, the same TEMPO-conjugated bis-para-pyridine ligand TEMPO-CL was used along with a novel four-arm polyethylene glycol (PEG) star polymer terminated with bis-para-pyridine ligands PEG-PL (Fig. , see Supporting Information section "Materials and Methods" for gel formation conditions). We define the "C:P" ratio as the average number of bis-pyridyl units in each Pd12L24 cage that derive from the catalyst ligand (e.g., TEMPO-CL) and the polymer ligand (e.g., PEG-PL), respectively. Three C:P ratios were screened-9:1, 21:3, and 20:4-to balance a high catalyst loading , see Supporting Information section "EPR Studies" for details). In each case, the catalyst incorporation was quite high, with only 5.3%, 4.5% and 2.6% of the TEMPO-CL not incorporated into the materials prepared from 9:1, 21:3 and 20:4 C:P ratios, respectively (Table ). We note that these gels represent the first materials, to our knowledge, to be crosslinked with acetylene-linked, ~4.6 nm diameter Pd12L24 MOCs. Based on these results, materials prepared using a 20:4 C:P ratio, referred to as "TEMPO-polyCAT," were used for subsequent studies. In addition to limiting catalyst leaching and simultaneously providing a high average catalyst loading, this C:P ratio features an average of 4 polymer strands per MOC junction, thus matching the branch functionality of the PL and providing for a robust "A4 + B4"-like network topology. Cross polarization-magic angle spinning (CP-MAS) H NMR (Fig. ) and smallangle X-ray scattering (SAXS, Fig. ) were used to characterize the structure of TEMPO-polyCAT.