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. 

The second material to come onto the market was the Montecatini Edison fluoropolymer called Fomblin Z33,34 with the structure 

The third material, Demnum,35 was only introduced in 1984 with the structure of (—CF2CF2CF20—) and no new materials had been commercialized since. It was clear that the frill potential of this new area had not yet been fulfilled. 

Work from our research group at the University of Texas on the synthesis of perfluoroethers and perfluoropolyethers by direct fluorination is revolutionizing and, in fact, has revolutionized this field. Our laboratory has been responsible for putting at least 30 new perfluoropolyethers into the literature and in some cases they are now on the commercial chemical market. Exfluor Research Corporation prepared several hundred new perfluoropolyethers expanding upon the work from 

Two of the fluid structures are very interesting. The first structure is a strictly alternating copolymer of ethylene oxide and methylene oxide, 

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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-... 

Many novel small molecule perfluoropolyethers have been made usiag direct fluofination technology. For example, even branched ethers such as perfluoro(pentaerythritol tetramethyl ether) can be prepared ... 

Perfluoropolyethers emerged on the market ia the early 1970s however, for the next 15 years there were only two basic stmctures known. The first perfluoropolyether was the homopolymer of hexafluoropropylene oxide produced by Du Pont having the stmcture... 

Two of the perfluoropolyether fluid stmctures yet to be commercialized are interesting. The first stmcture is a strictly alternating copolymer of ethylene oxide and methylene oxide, which has the longest Hquid range of any molecule containing carbon (40). The second stmcture is the perfluoromethylene oxide polyether which has low temperature Hquid properties down to —120° C ... 

Other perfluoropolyether stmctures that have been synthesized are (24,43)... 

Many perfluoroaUphatic ethers and tertiary amines have been prepared by electrochemical fluorination (1 6), direct fluorination using elemental fluorine (7—9), or, in a few cases, by fluorination using cobalt trifluoride (10). Examples of lower molecular weight materials are shown in Table 1. In addition to these, there are three commercial classes of perfluoropolyethers prepared by anionic polymerization of hexafluoropropene oxide [428-59-1] (11,12), photooxidation of hexafluoropropene [116-15-4] or tetrafluoroethene [116-14-3] (13,14), or by anionic ring-opening polymeriza tion of tetrafluorooxetane [765-63-9] followed by direct fluorination (15). 

Perfluoropolyethers with the linear perfluoropropoxy repeat unit have been commercialized (28). They are prepared by the anionic oligomerization of tetrafluorooxetane followed by direct fluorination to remove the acyl fluoride end group as well as to fluorinate the remaining CH2 groups n can vary widely. 

AH three processes give perfluoropolyethers with a broad distribution of molecular weights. They are typically separated into fractions by vacuum distillation. 

Information on the production levels of the perfluoroethers and perfluorotertiary amines is not disclosed, but the products are available commercially and are marketed, for instance, as part of the Fluorinert Electronic Liquids family by 3M Co. (17). These Hquids have boiling points of 30—215°C with molecular weights of about 300—800. They range in price from 26—88/kg. Perfluoropropene oxide polyethers are marketed by Du Pont with the trade name Krytox (29). The linear perfluoropropene oxide polyethers are marketed by Daikin under the trade name Demnum (28). The perfluoropolyethers derived from photooxidation are marketed by Montefluos under the trade name of Fomblin (30). These three classes of polyethers are priced from about 100—150/kg. 

Reaction of TYZOR TPT with polyperfluoroalkylene ethers containing a carbonyl group produces a complex that is an excellent surface-treating agent, imparting improved surface wettabiUty and anticorrosion properties to metal surfaces (144). These complexes can be used by themselves, or as additives to perfluoropolyethers as vacuum pump oils, lubricant oils, or mold release agents. 

Figure 5 Plot of positive CF3 secondary ion intensity versus ellipsometric thickness from a set of perfluoropolyether standards.

At the present, perfluoropolyether or PFPE, a random copolymer with a linear principal chain structure, has been widely used in HDD as the lubricant. Its chemical structure can be described by A-[(0CF2CF2)p-(0CF2)g]-0-A (p/q s2/3), with the average molecular weight ranging from 2,000 to 4,000 g/mol. Here, the symbol -X denotes the end-bead (eb), corresponding to -CF3 (nonfunctional) in PFPE... 

Sinha, S. K., Kawaguchi, M., Kato, T. et al., "Wear Durability Studies of Ultra-Thin Perfluoropolyether Lubricant on Magnetic Hard Disks, Tribol. Int., Vol. 36,2003, pp. 217-225. 

TyndaU, G. W. and Karis, T. E., Spreading Profiles of Molecu-larly Thin Perfluoropolyether Films, Tribol. Trans., Vol. 42, 1999, pp. 463 70. 

Zhao, X., Bhushan, B., andKajdas, C., Lubrication Studies of Head-Disk Interfaces in a Controlled Environment, Part 2 Degradation Mechanisms of Perfluoropolyether Lubricants," Proc. Inst. Mech. Eng., Part J J. Eng. Tribal., Vol. 214, 2000, pp. 547-559. 

Vurens, G., Zehringer, R., and Saperstein, D., The Decomposition Mechanism of Perfluoropolyether Lubricants During... 

Tyndall, G. W. and Waltman, R. J., Thermodynamics of Confined Perfluoropolyether Film on Amorphous Carbon Surface Determined from the Time-Dependent Evaporation Kinetics," J. Phys. Chem. B, Vol. 104,2000, pp. 7085-7095. 

FIG. 11 Break-free length (distance B-C on inset) as a function of relative humidity for the clean Si(lOO) wafer (Si), the amorphous carbon film (AC), and the bonded perfluoropolyether film (Z-Dol). The inset depicts two dipping experiments on amorphous carbon, at 0% and 97% relative humidity (rH). (From Ref. 50. Copyright 1994 American Institute of Physics.)... 

Monduzzi, M Knacksted, MA Ninham, BW, Microstructure of Perfluoropolyether Water/Oil Microemulsions, Journal of Physical Chemistry 99, 17772, 1995. 

Saunders, A.E., Shah, P.S., Park, E.J., Lim, K.T., Johnston, K.P. and Korgel, B.A. (2004) Solvent density-dependent steric stabilization of perfluoropolyether-coated nanocrystals in supercritical carbon dioxide. Journal of Physical Chemistry B, 108 (41), 15969-15975. 

McLeod, M.C., McHenry, R.S., Beckman, E.J. and Roberts, C.B. (2003) Synthesis and stabilization of silver metallic nanopartides and premetallic intermediates in perfluoropolyether/C02 reverse micelle systems. Journal of Physical Chemistry B, 107 (12), 2693-2700. 

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