Fluorination of polyhydrofluoroethylenes. II. Formation of perfluoroalkyl carboxylic acids on the surface region of poly(vinylidene fluoride) film by oxyfluorination, fluorination, and hydrolysis

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Abstract
Oxyfluorination and postfluorination behaviors of poly(vinylidene fluoride) films, as well as hydrolysis of the films treated so far, have been studied by infrared (IR) spectrometry. By exposing the polymer film to a mixture of oxygen and fluorine at about 90°C acyl fluoride groups attendant on the scission of the polymer chains were formed. The oxyfluorinated molecules could be further perfluorinated with fluorine alone at about 90°C, leaving many of the acyl fluoride groups. When the properly oxyfluorinated and postfluorinated film was further treated with a hot 6M sodium hydroxide solution the opaque layer of perfluoroalkyl sodium carboxylate of high molecular weight was formed on the surface of the film, to about 3 μm in thickness, which behaved as a cation exchanger. This new type of cation exchanger of perfluoroalkyl carboxylic acid was significantly more acidic than the usual methacrylic acid exchanger. It was able to adsorb the sodium ions from a neutral sodium chloride solution up to about 70% of the exchange capacity and to keep the ions stable while washing them with water, though it could be regenerated to the hydrogen form with a dilute acetic acid solution. The nature of the new ion exchanger has been examined in some detail by IR spectrometry with Li+, Na+, and Cs+ ions.