Synthesis and Evaluation of Partly Fluorinated Block Copolymers as MRI Imaging Agents

A series of well-defined diblock copolymers of acrylic acid with partially fluorinated acrylate and methacrylate monomers were synthesized using ATRP as potential F-19 MRI imaging agents. The diblock copolymers could undergo spontaneous self-assembly in mixed and aqueous solvents to form stable micelles with a diameter from approximately 20-45 nm, having a fluorine-rich core that provides a strong signal for MRI examinations. The observed MRI image intensities were related to the NMR longitudinal and transverse relaxation times, and were found to depend on polymer structure and method of micellization. Two distinct T-2 relaxation times were measured; on comparison of expected MRI image intensities with those observed experimentally, it was found that methacrylate polymers show systematically lower signal intensity than acrylate polymers. This is related to the presence of a population of nuclear spins having very short T-2 relaxation times that cannot be detected under high-resolution NMR and MRI conditions.