Recycling fluoropolymers to acyl fluorides through shuttle catalysis

The chemical recycling of a small array of fluoropolymers including poly(vinylidene difluoride) is reported. Using a catalytic combination of BF₃·OEt₂ and BF₃·PCy₃, equivalents of HF can be harvested from these fluoropolymers and delivered to acid anhydrides to generate the corresponding acyl fluorides. Catalytic conditions were established and optimised using fluoroethane (HFC-161) as a model substrate and can be applied to a range of acid anhydrides, including acetic anhydride - paving the way for a scalable process. Mechanistic studies suggest that two competitive processes involving both hydrofluorination and fluoroalkylation of the acid anhydride are in operation. Spectroscopic studies in combination with DFT calculations shed light on the roles that BF₃·OEt₂ and BF₃·PCy₃ play in these processes. The methodology was applied to a series of pristine fluoropolymers (PVDF, PVF, ETFE, and HFP-PVDF) along with post-consumer materials including PVDF recovered from a Li-ion battery. Spectroscopic and thermal analyses (powder XRD, XPS, IR spectroscopy, DSC, and TGA) of the recovered fluoropolymer showed that the reaction occurs with decrease in the crystallinity of PVDF, with loss of the α-phase of the pristine material. Defluorination introduces new unsaturated C[double bond, length as m-dash]C and oxygen-containing functional groups into the fluoropolymer and drastically lowers the onset temperature for its thermal decomposition. This approach has the potential not only to recycle the fluorine content of selected fluoropolymers but also create new fluorinated materials with different properties to pristine polymers.