Perfluoropoly(ethers): Intramolecular disproportionation II

Abstract

It was shown earlier that perfluoropoly(ethers) (PFPEs) have a propensity to undergo the intramolecular disproportionation reaction of the following scheme: (chemical equation presented) The reaction is catalyzed by Lewis acid sites (e.g., Al2O3 or AlCl3) and occurs at sectors where the successive ether oxygens have an odd number of backbone carbons between them. When the number of such backbone carbons is even, the reaction occurs exclusively at chain ends. We examined, in order to further substantiate the parity rule (the even and odd number of carbons between successive ether oxygens), the degradation of two novel PFPE's, perfluoropoly(tetramethylene oxide) and perfluoropoly(dioxolane). Both were found to degrade in accordance with the parity rule. It was also shown earlier that the degradation of Fomblin Z (a linear, random copolymer of -CF2-O- and -CF2-CF2-O- units) in the presence of Al2O3 was preceded by an induction period. We examined the process that occurs during the induction period. The study revealed that, during the induction period, the disproportionation reaction occurs exclusively at sectors where three or more acetal units, -CF2-O-, are linked contiguously, and converts surface aluminum oxide to fluoride in the process. Lastly, an examination of PFPE/AlCl3 mixtures by IR spectroscopy revealed that the disproportionation reaction could commence even at room temperature. It is envisaged that, in magnetic recording files, defect centers of a varying degree of acid strength are incessantly generated on a slider surface, causing PFPE degradation. The process is mitigated if the slider surface is coated with a carbon film, or if a nucleophilic chemical such as X-1P is added to the PFPE lubricant.