To substantiate that our particles are useful as drug release vehicles, we perform degradation experiments and analyze the complex product mixture for remnants of active Lenvatinib. We degrade the prodrug particles by exposure to an aqueous solution of H2O2 (200 mM) over the course of 24 h. H2O2 is chosen as a readily available and representative ROS species (see Figure and). We freeze dry the degraded products after H2O2-induced particle degradation and analyze the residue by LC-MS. We are able to assign the main peak to the prodrug monomer, and a smaller peak to the native Lenvatinib next to other drug fragments of much lower concentration (see Figure and S34 -S36). The release of prodrug monomer alongside the released native Lenvatinib can be explained by the degradation mechanism of the particles, which can occur on each imidazole unit along the polymer backbone species (see Figure ).