Perfluoropolyethers with Acid End Groups: An ESR Study of Decarboxylation

Abstract

An ESR study was performed on photodecarboxylation of perfluoropolyether acids, perfluoropoly(alkene oxide) terminated with carboxylic acid end groups. Three commercially available perfluoropolyethers (Fomblin Z, Krytox, and Demnum) with carboxylic ends were examined. ESR spectra of radicals expected from decarboxylation (e.g., R-O-CF2-CF2•) were readily observed from each sample exposed to 254 nm radiation at 77 K. The observed, ostensible patterns are shown to be intricate manifestations of large anisotropy of α- and β-fluorine hyperfine coupling tensors and the differing orientations of their principal axes. The principal hyperfine coupling tensors of the relevant F nuclei were determined by an iterative simulation process. The structures and conformations of the radicals thus revealed are in good accord with those given by molecular orbital calculations (MNDO). A possible significance of the decarboxylation process in actual material application is discussed. © 1994, American Chemical Society. All rights reserved.