Amphiphilic hyperbranched fluoropolymers as nanoscopic ¹⁹F magnetic resonance imaging agent assemblies

Three hyperbranched fluoropolymers were synthesized and their micelles were constructed as potential ¹⁹F MRI agents. A hyperbranched star-like core was first synthesized via atom transfer radical self-condensing vinyl (co)polymerization (ATR-SCVCP) of 4-chloromethyl styrene (CMS), lauryl acrylate (LA), and 1,1,1-tris(4′- (2″-bromoisobutyryloxy)phenyl)ethane (TBBPE). The polymerization gave a small core with M_n of 5.5 kDa with PDI of 1.6, which served as a macroinitiator. Trifluoroethyl methacrylate (TFEMA) and tert-butyl acrylate (tBA) in different ratios were then "grafted" from the core to give three polymers with M_n of about 120 kDa and PDI values of about 1.6-1.8. After acidolysis of the tert-butyl ester groups, amphiphilic, hyperbranched star-like polymers with M_n of about 100 kDa were obtained. These structures were subjected to micelle formation in aqueous solution to give micelles having TEM-measured diameters ranging from 3-8 nm and DLS-measured hydrodynamic diameters from 20-30 nm. These micelles gave a narrow, single resonance by ¹⁹F NMR spectroscopy, with a half-width of approximately 130 Hz. The T₁/T₂ parameters were about 500 and 50 ms, respectively, and were not significantly affected by the composition and sizes of the micelles. ¹⁹F MRI phantom images of these fluorinated micelles were acquired, which demonstrated that these fluorinated micelles maybe useful as novel ¹⁹F MRI agents for a variety of biomedical studies.