Anionic Ring-Opening Polymerization of Hexafluoropropylene Oxide Using Alkali Metal Fluorides as Catalysts: A Mechanistic Study

The anionic ring-opening polymerization of hexafluoropropylene oxide using the conventional alkali metal fluorides/tetraglyme catalytic system in the presence of different fluorinated solvents at various temperatures and under batch conditions is reported. Basically, the sodium fluoride (NaF)/tetraglyme system gave only monoadduct CF₃CF₂CO₂CH₃, while cesium fluoride (CsF)/tetraglyme produced oligomeric product with number-average degree of polymerization (DP_n) less than 5. The higher molar mass polymers were synthesized using the potassium fluoride (KF)/tetraglyme catalytic system and 1,1,1,3,3-pentafluorobutane (C₄F₅H₅) or 1,3-bis(trifluoromethyl)benzene as solvent at 0 °C. Under these conditions, polymers with number-average molar masses ranging between 2500 and 3500 g mol⁻¹ were obtained in high contents (>90%) and almost without any low molar mass (DP_n ≤ 5) contaminants (4−7%). Polymers which chain ends were derived into methyl esters were fully characterized by gas chromatography, ¹⁹F and ¹H NMR, and MALDI-TOF-MS spectroscopy. A kinetic study allowed us to propose a tentative mechanism entailing (i) the livingness of the polymerization of the hexafluoropropylene oxide with KF/tetraglyme catalytic system and (ii) the importance on the control of molar masses of the biphasic gas/liquid environment in the batch autoclave.