PERFLUOROPOLYETHERS - ANALYSIS BY TOF-SIMS

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.