A novel cavity-containing porphyrin catalyst based on a previously reported clip architecture, substituted on the Outer race with Urea terminated tails, has been synthesized, and its properties toward the epoxidation or polybutadiene have been studied. It is shown that the presence of the urea tails provides efficient shielding of the manganese porphyrin against destruction and selectively directs the oxidation process to the inside of the catalyst cage, allowing for processive oxidation of a polymer substrate without the need of an additional axial ligand.