Reactions in water are difficult to catalyze due to hydrophobic interactions of reactants and catalysts. Enzymes inspire scientists to create a versatile compartmentalized hydrophobic cavity with a hydrophilic outer sphere in water, capable of mimicking enzymatic catalytic functions. This supramolecular assembly has been achieved by a single chain polymeric nanoparticle (SCPN) functionalized with benzene-1,3,5-tricarboxamide (BTA), which is found to form self-assembling nanoparticles through intermolecular hydrogen bonds in water. Water solubility of the SCPN is achieved by introducing polyethylene glycol (PEG) side chains. While recent work has demonstrated its potential as an efficient catalyst, little is known about its structural and hydration properties. By introducing nitroxide radicals within the hydrophobic element of the polymer, molecular dynamics of the radical and water dynamics near the radical within the SCPN’s cavity can be studied by using electron paramagnetic resonance (EPR) and Overhauser dynamic nuclear polarization (ODNP). Dynamic light scattering revealed that the variation of SCPN’s diameter is negligible upon introducing the nitroxide radicals into the hydrophobic core of SCPN. ODNP analysis demonstrated that water dynamics are 4 to 6 times slower than in free water within the hydrophobic cavity of SCPN with BTA units. From EPR spin label dilution experiments can be concluded that only intramolecular spin label interactions occur and the rotational motion of nitroxide side chains within the SCPN cavity is about 20ns. These findings provide valuable information for future application of SCPN as novel enzyme-inspired synthetic catalysts for reactions in water.