(177b) PFAS Minimization Via Random Semifluorinated Copolymer Films Prepared By Combining Spin Coating and Ring-Opening Metathesis Polymerization

Perfluoromethyl (-CF₃) and perfluoromethylene (-CF₂-) groups found on fluorinated polymeric materials exhibit the lowest surface energies of any organic functional groups, making materials of this nature highly desired in biomedical, aerospace, semiconductor, and membrane applications. Excessive use of perfluorinated substances (PFAS), however, is generally discouraged, and there is a growing emphasis to find new methods that maintain these characteristically low surface energies while minimizing the overall level of fluorination. We report a method to substantially reduce the amount of PFAS needed to synthesize a low surface energy polymer film through the copolymerization of norbornene (NB) with 5-perfluoro-n-alkylnorbornenes (pNBFns) in a single process that combines spin coating with ring-opening metathesis polymerization (scROMP). scROMP combines polymer film synthesis and deposition into one rapid process, converting monomer into polymer films in under 2 min with < 1/2 mL of solvent and facilitating polymeric materials discovery. Perfluoroalkyl chain lengths n of 4, 6, and 8 were examined with higher n resulting in greater incorporation into the film at a given comonomer ratio. The fluorinated component of the polymer films tended to dominate the surface for all n, with films of higher n exhibiting water contact angles comparable to those of its fluorocarbon homopolymer with even as low as 3% of the fluorinated monomer in the bulk. These films also demonstrate solvent-responsive switching behavior. Changing the contact angle probing liquid from water to hexadecane induced a molecular reorientation of the fluorocarbon groups, burying the -CF₃ and -CF₂- into the film and instead exposing the more omniphilic -CH₂- groups. As a potential application, p(NB-co-NBFn) films were tested as thin film composite membranes for ethanol dehydration, achieving much greater selectivities than that of the pNB membrane even with minimal amounts of fluorocarbon in the membrane. Ultimately, these semifluorinated films function as both low energy surfaces and ethanol dehydrating membranes while possessing minimal amounts of fluorocarbon in the bulk of the film.