Degradation of perfluoropoly(ethers) and role of X-1P additives in disk files

Perfluoropoly(ethers) (PFPE's) are the current lubricant of choice for magn etic recording media. It is shown that the degradation of PFPE's in the dis k environment is singularly dominated by the intramolecular disproportionat ion reaction of the following scheme: [GRAPHICS] The reaction is catalyzed by Lewis acid sites (e.g., Al2O3 or AlCl3) and oc curs at sectors where the successive ether oxygens have an odd number of ba ckbone carbons between them. When the number of such backbone carbons is ev en throughout the chain, the reaction occurs exclusively at chain ends. The degradation of PFPE's Fomblin Z, Fomblin Y, Krytox, and Demnum is briefly recounted. A fundamental difference at the molecular level between the two types of degradation (for the odd vs. even number of carbons) leads to prof ound differences in macroscopic manifestations in test tubes as well as in disk files. Examples of such manifestations are shown and discussed. X-1P ( partially fluorinated hexaphenoxy cyclotriphosphazene) is topically advocat ed as an additive to PFPE in disk applications. Its efficacy has been attri buted to its ability to cover the catalytically active slider material (Al2 O3/TiC). A spectroscopic study (NMR, ESR) of X-1P revealed a strong nucleop hilic (Lewis base) nature of the triphosphazene ring. A plausible adsorptio n and reaction mechanism based on the spectroscopic and molecular model stu dies is presented.