Perfluoropolyether surfactant

Although supercritical CO2 is an effective solvent for oils, fats, and similar substances, it is a poor one for nonvolatile hydrophilic (water-loving) substances such as proteins or metallic salts. Adding water as such to the supercritical CO2 is of little help, as the solubility of water in it is limited. Johnson and co-workers216 overcame the latter limitation by forming water-in-C02 emulsions with the aid of an added nontoxic perfluoropolyether surfactant that forms reverse micelles around the water microdroplets, in effect combining the special properties of supercritical CO2 with the solvent power of water. These emulsions can dissolve a variety of biomolecules at near-ambient temperatures, without loss of their biological activity. 

Here again, we might argue that the 5000 MW PFPE-functional material exhibits the best balance between C02-phihcty and anchoring to the polymer parti-de (hydrophilicity). Interestingly, the behavior of the 2500 PFPE surfactant varied as the amount of monomer in the system varies. At an initial concentration of 7% NVF, the behavior of the 2500 MW perfluoropolyether surfactant is as shown in Table 7.1 however when the monomer concentration is increased to 17 wt%, the behavior changes, such that the rate varies as [S] - it is not clear why this behavior occurs. 

The adsorption measurements show that at conditions of monolayer formation 0.5 mMol perfluoropolyether-surfactant can be fixed on 1 g magnetite, and that it is possible to nearly totally eliminate the surfactant from the water carrier. During the adsorption process the modified particles coagulate and can be separated by a simple laboratory magnet. 

Perfluoropolyether surfactants [128-131] have been prepared using perflu-oroalkeneoxide as the hydrophobic group. Monocarboxylic acids were obtained... 

Table 3.13 Physical Properties of Monofunctional Perfluoropolyether Surfactants...

The effect of the chain length of some perfluoropolyether surfactants [40] is shown in Figs. 4.7 and 4.8. 

The relationship between log cmc and HLB values for monocarboxylic and dicarboxylic perfluoropolyether surfactants with a poly(oxyhexafluoropropylene) hydrophobe is also linear [158],... 

For NMR studies of fluorinated surfactants, the most useful nucleus is F, in addition to and H nuclei. Changes ip the F chemical shift at cmc are larger than changes in the proton chemical shifts and, therefore, provide more information on fluorinated surfactants and their micellar structures. F-NMR spectra have been recorded for structural characterization of perfluorononanoic acid [125] and perfluoropolyether surfactants [126]. Micelle formation in solutions of... 

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... 

Oxygen-containing perfluoropolyether derivatives, which are related to the preferred surfactant compatibilizers, could be important. 

Other groups [99, 100] investigated the possibility of carrying out a surfactant-assisted polymerization of VDF in scC02, using diethyl peroxydicarbonate (DEPDC) as a free radical initiator, with the aim of testing several perfluoropolyether compounds synthesized by Solvay Solexis as stabilizers. When ammonium carboxylate derivatives were used, an effective stabilization of the polymer particles was obtained, and the polymer was collected from the reactor with yields of up to 63%. This corresponded to a solid content in the reactor of 220 g I in the form... 

The use of sc C02 instead of toluene as a solvent leads to some rate enhancement in these two systems, although it is clear that this activity is still not practical for most nonpolar, nonvolatile substrates. Significant improvements to the biphasic water/supercritical C02 system were accomplished by forming H20/C02 emulsions using newly developed surfactants (Jacobson et al., 1999). Three different surfactants were used that form water in C02 (w/c) or C02 in water (c/w) emulsions (1) anionic surfactant perfluoropolyether ammonium carboxylate, (2) cationic Lodyne 106A, and (3) nonionic poly(butylene oxide)-h-poly(ethylene oxide). The low interfacial tension, y, between water and C02 (17 mNm-1 at pressures above 70 bar), which is significantly lower than water/alkane systems (30-60 mNm-1),... 

Hexafluoropropylene oxide is an important intermediate in fluoroorganic synthesis. It is useful in the production of surfactants, perfluoropolyether oils, solvents, perfluorinated alkylvinyl ethers, and other materials. 

In a separate 8-mL vial, place 0.2 g of the surfactant ask instructor which one to use) in 6mL of heptane (if AOT sodium bis(2-ethyUiexyl)sulfosuccinate) or water (if fluorinated surfactant ammonium carboxylate perfluoropolyether -[CF30(CF2CF(CF3)0)3CF2C00]-[NH4]+). Shake vigorously until the surfactant is completely dissolved. Add two drops of the filtered aluminate solution to the surfactant solution, and shake vigorously until one phase is obtained i.e., the final solution should not be cloudy). 

In 1993, perfluoropolyether (PFPE) carboxylates, with average molecular weights between 2,500 and 7,500, were reported to be soluble in liquid CO2 (19). However, these high MW polymers were not effective at stabilizing w/c microemulsions. Later, Johnson et al. formed w/c microemulsions with an ammonium carboxylate PFPE (PFPE-COO NH4 surfactant of only 740 MW (30). Success with these surfactants was attributed to the chemical structure itself. PFPE constitutes an extremely C02-philic tail group, accentuated by the presence of pendant fluoromethyl groups, which tend to increase the volume at the interface on the CO2 side and thus favor curvature around the water. 

Similar transformations were used to demonstrate the possibility of using water/ CO2 microemulsions as reaction media, which were stabilized using the anionic perfluoropolyether ammonium carboxylate surfactant [PFPECOO] [NH4] [25]. No additional phase transfer catalysts are necessary under these conditions. For example, the reaction between potassium bromide and benzyl chloride to form benzyl bromide [Eqs. (2)-(4)] resulted in a much better yield in the H2O/CO2 system than in a conventional water-in-oil microemulsion. 

The potential of microemulsions for organometaUic-catalyzed hydrogenations in water/scC02 biphasic systems has been assessed using the rhodium-catalyzed hydrogenation of styrene as a common test reaction [Eq. (7)] [31]. The water-soluble Wilkinson complex [RhCl(TPPTS)3] was applied as catalyst precursor together with anionic perfluoropolyether carboxylates, cationic Lodyne A, or nonionic poly-(butene oxide)-b-poly(ethylene oxide) surfactants. The interfacial tension is small in the presence of the supercritical fluid and small amounts of surfactant (0.1-2.0 wt.%) suffice to form stable microemulsions. The droplet diameter of the microemulsions varied between 0.5 and 15 pm and a surface area of up to 10 m was obtained. 

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