Abstract
The synthesis and chemistry associated with the preparation of ionomers consisting of perfluoro-2-(2-fluorosulfonylethoxy) propyl vinyl ether (PSEPVE) is explored. The mechanism of homopolymerization has been extensively studied by kinetic, end group, and molecular weight analysis aided by 19F NMR, MALDI and DSC. It has been found that the polymerization occurs with free radical chemistry, but that multiple pathways of initiation, transfer/propagation and termination are occurring simultaneously. The copolymerization of PSEPVE with chlorotrifluoroethylene (CTFE) is studied extensively with focus on reactivity and structural consequences. Reactivity ratios rPSEPVE = 0.34 and rCTFE = 0.67 under narrow experimental conditions have been determined. As such, these two monomers have been copolymerized yielding random copolymers at intermediate PSEPVE compositions. A qualitative statistical interpretation of the peak areas by NMR indicates a greater tendency toward CTFE block formation at PSEPVE compositions < 0.4. This is further supported by thermal analysis. The solution properties of the amide and sulfonic acid functionalized homo- and copolymers have been explored by NMR, DLS and fluorescence probe studies.
Further modification of the polymeric PSEPVE precursors were conducted by functionalization with sulfonyl chlorides of benzene, terphenyl, and triphenylene. This was accomplished with the intention to confer additional sites of functionalization, notably sulfonation, to the ionomers. The nature of the pendant group has been found to have a substantial impact on solution properties. In particular, water solubility is easily attained in the poly(PSEPVE) benzene sulfonimide, while the incorporation of bulky, rigid aromatic groups in the poly(PSEPVE) triphenylene sulfonimide disulfonic acid product allowed it to retain water insolubility with high charge density (2 meqH+/mol). Perfluoropolysulfonimide gel network polymers are also prepared utilizing similar chemistry. Thermal stabilities upon boiling in aqueous solution are established by monitoring charge density and changes in the 19F NMR spectra of the ionomers.
Fluorinated polymers in the form of polyelectrolyte, copolymer-based ionomers, and chain end functionalized have been proven to yield temperature stable materials of high charge density. The copolymer offers an efficient and selective pathway for the production of ionomers capable of being tailored to targeted charge densities for applications in batteries, fuel cells, sensors and ion exchange membranes.