Perfluoropolyethers applications

Film stability is a primary concern for applications. LB films of photopoly-merizable polymeric amphiphiles can be made to crosslink under UV radiation to greatly enhance their thermal stability while retaining the ordered layered structure [178]. Low-molecular-weight perfluoropolyethers are important industrial lubricants for computer disk heads. These small polymers attached to a polar head form continuous films of uniform thickness on LB deposi-... 

The oligomers and polymers described above retain a number of protons that may be undesirable for some demanding applications. The obvious solution is to replace hydrogen with fluorine, and it appears that the only prospect for such transformation is radical fluorination. By the fluorination approach, these F-vinyl ether homopolymers, owing to their unique structures, may provide a new route to novel perfluoropolyethers. 

Perfluoropolyethers emerged on the market in the early 1970s. The first perfluoropolyether was the homopolymer of hexafluoropropylene oxide produced by DuPont, which has the structure [—CF2CF(CF3)0—] and this new lubricant material was called Krytox.31,32 Krytox was and is used in most of the vacuum pumps and diffusion oil pumps for the microelectronics industry because it does not produce any hydrocarbon or fluorocarbon vapor contamination. It also has important applications in the lubrication of computer tapes and in other data processing as well as military and space applications. 

We discovered another synthetic technique that involves the conversion by direct fluorination of hydrocarbon polyesters to perfluoropolyesters followed by treatment with sulfur tetrafluoride to produce new perfluoropolyethers.42 The first paper in this area ofreasearch reported that conversion of poly(2,2-dimethyl-1,3-propylene succinate) and poly( 1,4-butylene adipate) by using the direct fluorination to produce novel branched and linear perfluoropolyethers, respectively. The structures are shown in Figure 14.6. The second paper concerns the application of the direct fluorination technology base directed toward oligomers, diacids, diesters, and surfactants.43... 

Perfluoropolyethers have a wide range of other specialist applications throughout modern technology ranging from the lubrication of computer discs to lubrication of components in chemical plants exposed to corrosive substances. Their broader usage is limited by their costing typically fifty times as much as conventional hydrocarbon lubricants. 

Molecularly thin lubricant film is an important application of nanoscale confined polymeric fluids, and is the focus of this chapter. Ultrathin lubricant films are necessary in high-density data storage to increase the reliability and performance of hard-disk drive (HDD) systems [2-4]. Spinoff and intermittent contact between the slider (or head) and the lubricated disk [ultrathin perfluoropolyether (PFPE) films are applied to the disk s carbon-overcoated surface, as shown in Fig. 1.1] cause loss and reflow of the lubricant film. The relevant HDD technology is summarized briefly in the end-of-chapter Appendix Section A.I, which provides an overview of how certain information technology devices are controlled by nanoscale chemistry. 

Considerable interest still exists in the application of fluorine-containing cyclophosphazenes in lubricant technology. Recent advances in the use of N3P3(OC6H4F-4) (OC6H4CF3-3)6-n (n 2 code name X-IP) as lubricant either by itself or as an additive to perfluoropolyethers (PFPE) have been reviewed. Addition of X-IP to PFPE films reduces the critical dewetting thickness on amorphous nitrogenated carbon compared to that of neat PFPE. The influence of X-IP on the stabilization of the PFPE lubricant for the slider/disk interface in hard disk drives has been studied. Micro-phase separation of X-IP... 

Other types of perfluorinated polymer include ether structures. The monomers of these materials, third-generation fluoropolymers, are trifluoroenol ethers and cyclic difluoroendiol ethers. Perfluoropolyethers (PEA) are readily processable and, because of their transparency, they are often used for chemical apparatus if aggressive reagents are involved. Another application of PFA is as sample vessels for ion analysis (Scheme 4.6). 

Perfluorinated polyethers have also gained importance as actively functional materials. Ionic polymer membranes (e.g. DuPont s Nafion ) based on sulfonic acid-derivatized perfluoropolyethers have been used for nearly 30 years as ion-con-ducting membranes in chloralkali electrolysis cells, replacing the large amounts of toxic mercury used until then in the classic Castner-Kellner cells (Scheme 4.8.). One of the earliest applications of Nafion was as a membrane in the hydrogen-oxygen fuel cells which powered the Apollo spacecraft carrying the first men to the moon. 

Ohsaka, Y. Perfluoropolyether fluids (Demnum) based on oxetanes. In Organofluorine Chemistry. Principles and Commercial Applications Banks, R.E., Ed. Plenum Press New York, 1994 pp 463 67. 

As previously mentioned, another class of fluoropolymers known to be readily soluble in CO2 are perfluoropolyethers (PFPEs) [1]. A unique class of fluoropolymers, PFPE polymers and copolymers have been established as high performance materials, exhibiting low surface energies and low moduli, as well as excellent thermal and chemical stabilities. PFPEs are primarily found in high-performance lubricant applications, e.g., for magnetic data storage media and as heat exchanger fluids. One of the main industrial processes for the production of PFPEs is photooxidation of fluoroolefins [41]. Currently, only TFE and HFP are used commercially in this process. Typically, HFP is photooxidized in bulk because of its very low reactivity, while TFE requires an inert diluent in order to prevent homopolymerization of the olefin. 

The application of the cyclophosphazene N3P3(OC6H4F-4) (OC6H4CF3-3)e (n 2 code name X-IP) as a lubricant is well known. Comparative studies of the tribological properties of X-IP and ionic liquids of al-kylimidazolium tetrafluoroborates have shown a preference for the tetrafluo-roborates as lubricants. The interaction of X-IP with a carbon-coated head at the head-disk interface of hard disk magnetic storage systems in the presence of a perfluoropolyether (PFPE) lubricant, has been diseussed. Attention has been paid to the application of a novel lubricant (A20H) which consists of (234) as the major component and small quantities of (235). The new lubricant displays a lower mobility on carbon surfaces than hydroxyl-... 

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