Carboxylic acid groups have been introduced to the surfaces of poly(vinylidene fluoride) (PVF2), poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP), and poly(chlorotrifluoroethylene) (PCTFE) film by two-step chemical surface modifications. In each case a surface-selective reaction was run to introduce a thin layer (several tens of angstroms) of modified fluoropolymer: PVF2 was dehydrofluorinated with aqueous sodium hydroxide and phase-transfer catalysis, FEP was reduced with sodium naphthalide, and PCTFE was reduced/alkylated with n-butyllithium. The modified layers, susceptible to oxidation, were removed with strong oxidant (potassium chlorate/sulfuric acid) to yield fluoropolymer functionalized with carboxylic acid groups at the sites where virgin and modified polymer were covalently attached. The presence of carboxylic acid groups was indicated by contact angle (wettability) behavior and chemical reaction.
