We have developed a simple and mild method for the fluorination of polybutadiene based on the addition of perfluoroalkyl iodides (RfI) to carbon-carbon double bonds. Triethylborane (Et3B) was utilized to initiate this free radical addition to model polybutadiene (PBD) homopolymers and a polystyrene-polybutadiene block copolymer at room temperature. Optimized reaction conditions led to consumption of more than 95% of the double bonds and preservation of narrow molecular weight distribution after the modification. We propose that the reaction undergoes a cyclization pathway rather than open-chain addition and that five-member ring structures are formed during the addition of RfI to 1,2-PBD. From 1H NMR spectroscopy, we estimate that 83% of the double bonds in the 1,2-PBD cyclized with their neighbors. This agrees well with a theoretical prediction by Flory for random irreversible cyclization between neighboring polymer repeat units. We also demonstrate the selective fluorination of the 1,2-PBD block in a polystyrene-block-1,2-polybutadiene (PS-b-1,2-PBD) copolymer. In contrast to the fluorinated homopolymers, subsequent hydrogenolysis of this fluorinated PS-b-1,2-PBD copolymer gave a soluble material. The 1H NMR spectrum and elemental analysis confirmed the complete hydrogenolysis. Preliminary physical characterization was performed by differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), contact angle measurements, and small-angle X-ray scattering (SAXS). The glass transition temperature (Tg) of the fluorinated 1,2-PBD increases by 75 °C, removal of the iodine in the fluorinated PS-b-1,2-PBD copolymer increases the thermal stability by ca. 100 °C, and all fluorinated polymers exhibit very low critical surface tensions (14-16 mN/m).