Star polymers with a polyhedral oligomeric silsesquioxanes (POSS) core and eight partly fluorinated arms have been synthesized by reversible addition-fragmentation chain transfer polymerization. A macroCTA having eight chain transfer agent (CTA) molecules attached to a POSS core is prepared and used for the synthesis of star polymers by the R-group approach. The arms are composed of statistical copolymers of 2,2,2-trifluoroethyl acrylate and poly(ethylene glycol) methyl ether acrylate. The polymerization kinetics are studied, and yield of star polymer is optimized. Star polymers having different arm lengths are prepared and characterized. The star polymers exhibit a single 19F resonance in 19F nuclear magnetic resonance spectra in aqueous solution, and the T2 relaxation time increases with arm length. The relaxation properties and the fluorine content are consistent with these polymers being effective 19F magnetic resonance imaging (MRI) agents. This work indicates that these POSS-star polymers have potential as theranostic agents for 19F MRI and drug delivery.