Synthesis of Crystalline CF₃ -Rich Perfluoropolyethers from Hexafluoropropylene Oxide and...

The synthesis of a CF₃ -rich perfluoropolyether (PFPE) is achieved via the fluoride-catalyzed reaction of hexafluoropropylene oxide (HFPO) with (trifluoromethyl)trimethylsilane (TMSCF₃ , so-called Ruppert-Prakash reagent). Nucleophilic addition of a CF₃ anion to HFPO affords an acyl fluoride via the ring-opening of HFPO, followed by fluoride elimination. Further addition of CF₃ anions to the acyl fluoride gives tertiary perfluoroalkoxide, which attacks HFPO to regenerate an acyl fluoride. Repetition of the sequence via substitution-polymerization affords a new PFPE as a solid, whose structure was confirmed using ¹⁹ F NMR spectroscopy, GC-MS, and MALDI-TOF MS analysis. Thermal and X-ray diffraction analyses revealed a crystalline character. To the best of our knowledge, this is the first example of crystalline PFPE. Based on contact-angle measurements, the critical surface tension of this solid PFPE (13.4 mN m^-1 ) suggests a water- and oil-repellency of this CF₃ -rich PFPE that is higher than that of polytetrafluoroethylene (PTFE; 18.5 mN m^-1 ).