A simple and mild route to highly fluorinated model polymers

We have developed a simple and mild method for the fluorination of polybuea diene based on the addition of perfluoroalkyl iodides (RfI) to carbon-carbo n double bonds. Triethylborane (Et3B) was utilized to initiate this free ra dical addition to model polybutadiene (PBD homopolymers and a polystyrene-p olybutadiene block copolymer at room temperature. Optimized reaction condit ions led to consumption of more than 95% of the double bonds and preservati on of narrow molecular weight distribution after the modification. We propo se that the reaction undergoes a cyclization pathway rather than open-chain addition and that five-member ring structures are formed during the additi on of Rd to 1,2-PBD. From H-1 NMR spectroscopy, we estimate that 83% of the double bonds in the 1,2-PBD cyclized with their neighbors. This agrees wel l with a theoretical prediction by Flory for random irreversible cyclizatio n between neighboring polymer repeat units. We also demonstrate the selecti ve fluorination of the 1,2-PBD block in a polystyrene-block-1,2-polybutadie ne (PS-b-1,2-PBD) copolymer. In contrast to the fluorinated homopolymers, s ubsequent hydrogenolysis of this fluorinated PS-b-1,2-PBD copolymer gave a soluble material. The H-1 NMR spectrum and elemental analysis confirmed the complete hydrogenolysis. Preliminary physical characterization was perform ed by differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), contact angle measurements, and small-angle X-ray scattering (SAXS) . The glass transition temperature (T-g) of the fluorinated 1,2-PBD increas es by 75 degreesC, removal of the iodine in the fluorinated PS-b-1,2-PBD co polymer increases the thermal stability by ca. 100 degreesC, and all fluori nated polymers exhibit very low critical surface tensions (14-16 mN/m).