Overview

The first fluorinated ionomer was discovered in the early 1960s at the DuPont Experimental Station near Wilmington, Delaware [1]. It was a perfluorinated ionomer that later became known as Nafion . At that time, an exploratory chemistry group within DuPont's Plastics Department headed by Frank Gresham was pursuing a newly discovered synthetic route to prepare perfluorinated vinyl ethers. This route allowed the conversion of almost any perfluorinated acyl fluoride to the corresponding vinyl ether through the addition of hexafluoropropylene epoxide followed by dehalocarbonylation. These perfluoro vinyl ethers were promising monomers for the production of melt-fabricable copolymers of tetrafluoroethylene [2]. Several important monomers, including perfluoro methyl-, ethyl-, and propyl-vinyl ether, became commercially available as result of this work.

One of the vinyl ethers synthesized by this method was based on the reaction product of sulfur trioxide and tetrafluoroethylene. It offered the opportunity to introduce ionic groups into a perfluorinated polymer. Initially, the motivation for this work was simply a curiosity to study polymers with a broad range of compositions, but the presence of ionic groups made this polymer different from anything known before. It was shown that the reactive groups of the precursor polymer allowed vulcanization using curing agents such as magnesium oxide [1]. When combined with perfluoro methyl-vinyl ether as a termonomer, this should yield perfluorinated elastomers with improved properties. Another early expectation was that ionic cross-linking would result in improved mechanical properties, particularly resistance to creep, of fluoropolymers in general. However, none of these early approaches led...