Time-of-flight secondary ion mass spectra were obtained from thin films of perfluorinated poly- and copolyethers up to m/z = 6500. The fragmentation for the perfluoropolyethers under Ar+ bombardment is consistent with the ion stabilities and the structure of their repeating units. The elucidation of the fragmentation patterns for random copolymers Is complicated, because Ions having different structures can correspond to a given peak. The fragmentation patterns are unique and reproducible for each kind of polyether and copolyether, Independent of sample preparation and substrate. Carbonium fragment Ions dominate the positive-ion spectra, and alkoxy Ions dominate the negative-ion spectra; cationized oligomers were detected. Small structural differences In the backbone or terminal groups of otherwise Identical polymers were detected In the spectra as differences in the fragmentation patterns or in the relative peak intensities or shifts in the m/z values of the oligomer peaks. The number-average molecular weights determined from the oligomer distributions of perfluoropofyethers observed In the spectra are in good agreement with those measured by nuclear magnetic resonance and gas chromatography. © 1990, American Chemical Society. All rights reserved.