This work focuses on the synthesis and the aqueous solution properties of novel amphiphilic PCL-b-PHPMA diblock copolymers possessing 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) stable radicals covalently conjugated to the hydrophobic poly(epsilon-caprolactone) (PCL) block. A new synthetic approach (a four-step pathway) combining ring-opening polymerization (ROP), carbodiimide chemistry (DCC method), a reversible addition fragmentation chain transfer (RAFT) polymerization technique, and finally chemical oxidation was employed to successfully produce a series of TEMPO-containing PCL-b-PHPMA diblock copolymers for the first time. EPR spectroscopy was applied to verify successful oxidation of the synthesized diblock copolymers and to investigate the dynamics of the polymer chains before and after micellization. The diblock copolymers self-assembled in PBS solution into spherical radical-containing nanoparticles (RNPs), which were characterized by H-1 NMR spectroscopy, dynamic (DLS), static (SLS) light scattering, and cryo-transmission electron microscopy (cryo-TEM). These novel RNPs could find applications, e.g., as drug delivery systems and for the treatment of oxidative stress injuries.