Perfluoro-poly(ethers) with hydroxyl end groups: Analysis by TOF-SIMS

Abstract

TOF-SIMS spectra of perfluoro-poly(ethers) (PFPE) with hydroxyl end group(s), Fomblin Z-DOL, Krytox-OH, and Demnum-SA, were analyzed. Previously we have observed that while the positive-ion TOF-SIMS spectra of nonfunctionalized PFPEs are complex and compressed toward the low mass end, the negative-ion spectra show intense simple patterns persisting into a high mass region surpassing the mean molecular weight of the polymer. The rich negative-ion spectra of nonfunctionalized PFPEs are ascribed to anions generated by one-event dissociative capture of low-energy secondary electrons by ether oxygens of the polymer backbone: R-O-R′ + e- →R-O0 + •R′. In stark contrast to nonfunctionalized PFPEs, PFPEs with hydroxyl end group(s) showed, in the positive-ion spectra, a fragmentation pattern persisting into the high mass region and a pattern clearly associated with the parent molecule (molecular weight) distribution. In the negative-ion spectra, the pattern due to anions R-O- encompassing the hydroxyl sector was totally absent. The observed anomalies can be accounted for if one postulates that PFPEs with hydroxyl end group(s) have a strong propensity to ionize at the hydroxyl sector. A possible relevance of such a propensity to the bonding mechanism of Z-DOL (Fomblin Z with hydroxyl end groups) to the carbon overcoat of magnetic recording disks is conjectured.