Fluoropolymer Synthesis in Carbon Dioxide-Expanded Liquids: A Practical Approach to Avoid the Use of Perfluorooctanoic Acid

Abstract

Successful polymerization of tetrafluoroethylene (TFE) in CO 2 -expanded liquids to synthesize polytetrafluoroethylene (PTFE) was demonstrated using both hydrocarbon and hydrofluorocarbon solvents. Yields were satisfactory and samples with thermal properties comparable to commercial polymer were produced. The chain transfer reaction that resulted from the use of hydrogen-containing solvents was not as severe as expected. Acetic acid was identified as a particularly promising expandable solvent. Use of this solvent lowers the pressure required for polymerization of TFE, and acetic acid is less environmentally detrimental than halogenated solvents. A wide range of solvent ratios and pressures were found to be suitable for TFE polymerization in CO 2 -expanded acetic acid. Colloidal PTFE samples were obtained in an emulsion-like polymerization run in CO 2 -expanded acetic acid. A commercially-available, conventional hydrocarbon surfactant was used in this research; the process did not require fluorinated surfactants such as perfluoro octanoic acid (PFOA) or other the specially designed surfactants for CO 2 systems.