TOF-SIMS spectra of the following perfluoropolyethers (PFPEs) were ana
lyzed: Demnum-S, Krytox, Fomblin-Z, perfluoropoly(dioxolane), perfluor
opoly(tetramethylene oxide), and perfluoropoly(ethylene oxide). In eac
h case, the PFPE produced an intense negative ion spectrum with simple
patterns persisting into the high-mass region surpassing the mean MW
of the polymer. In contrast, the positive ion spectra are much more co
mplex and compressed toward the low-mass end. Totally unrelated format
ion mechanisms for the positive and negative ions are thus indicated.
It is proposed and substantiated that the negative ion spectra are dom
inated by anions resulting from one-step dissociative electron capture
at ether oxygens, R-O-R' + e(-) --> R-O- + (.)R'. The Demnum molecule
, having locally symmetric ether oxygens, produces two major peaks in
each repetitive fragmentation packet, equal in intensity but displaced
by the mass difference of the two end groups. PFPEs with asymmetric e
ther oxygens produce negative ion spectra resulting from asymmetric cl
eavage. The negative ion pattern of Fomblin-Z can be accurately modele
d with the dissociative electron capture at ether oxygens linking rand
omly distributed methylene and ethylene units. Other less intense peak
s in the negative ion spectra of PFPEs result from multiple electron c
apture events and from polymer chains with anomalous end groups or int
rachain units.