Water-Soluble Fluorinated Polymer Nanoparticle as 19F MRI Contrast Agent Prepared by Living Random Copolymerization from Dendrimer Initiator

Water-soluble fluorinated polymer nanoparticles (PNPs) with well-defined structure were successfully prepared as a 19F MRI contrast agent by living radical copolymerization of 2,2,3,3-tetrafluoropropyl methacrylate (TFPMA) and tert-butyl methacrylate (tBMA) initiated from a dendritic macroinitiator. The obtained polymers were hydrolyzed and then converted into a sodium salt, yielding water-soluble fluorinated dendritic-star copolymers (PAMAM-g-PTFPMA-co-PMANa). The copolymer showed a sphere-like structure and the diameter increased in the range of 12–25 nm with the increase of the molecular weight. In 19F NMR properties, the T1 and T2 relaxation times were evaluated to be 400 and 70–80 ms, respectively, and were not significantly affected by the molecular weight of the copolymers. 19F MRI in vitro signals can be visualized at the lowest concentration of 0.5 mM (F atom) and detectable even at concentrations lower than 0.2 µM (particle concentration) under this experimental condition, indicating the high sensitivity due to the accumulated fluorine atoms into nanoparticle. Furthermore, in vivo MRI demonstrated the feasibility of the water-soluble fluorinated PNP as a new type of 19F MRI contrast agent.