FluorocarbonMinimization Via Semifluorinated CopolymerFilms by Combining Spin Coating and Ring-Opening Metathesis Polymerization

Per- and polyfluoroalkyl substances (PFAS) are ubiquitous in society largely due to their unique surface properties, but significant health concerns associated with these substances underscore the need for PFAS reduction strategies. We report a method to substantially reduce the amount of PFAS, solvent, and time needed to synthesize a low surface energy polymer film through the copolymerization of norbornene (NB) with 5-(perfluoro-<i>n</i>-alkyl)norbornenes (NBF<i>n</i>) in a single process that combines spin coating with ring-opening metathesis polymerization (scROMP). The unique scROMP approach efficiently integrates polymer film synthesis and deposition into one rapid process, converting monomer into polymer films in <2 min with <1 mL of solvent for a 36 cm² film. Perfluoroalkyl chain lengths, <i>n</i>, of 4, 6, and 8 were examined, with the fluorocarbon component tending to dominate the surface for all n, exhibiting water contact angles comparable to those of the fluorocarbon homopolymer even with as little as 2% NBF<i>n</i> in the contacting monomer. As a potential application, these semifluorinated copolymer films were used in ethanol dehydration as low PFAS substitutes for amorphous fluoropolymer membranes. Even 7% fluorocarbon in the polymer (or 2% in the monomer) caused an order-of-magnitude increase in selectivity over a fully hydrocarbon membrane, with additional fluorination up to 63% (50% in monomer), leading to another order-of-magnitude enhancement and properties similar to the pNBF<i>n</i> homopolymer. Additionally, the dense outer fluorocarbon layer provided an ideal setup to estimate the sorption and diffusion components of selectivity for fluorocarbon and hydrocarbon groups within a membrane.