Perfluoroalkyl chain

Fluorochemicals repel both water and oU because they produce an extremely low energy surface (18—26). The effectiveness of the fluorochemicals depends upon uniform surface coverage and orientation of the molecules on the fiber surface so that the perfluoroalkyl chains are directed away from the surface. The result is a GST as low as 5—10 mN /m (dyne/cm). Fluorochemical finishes are often formulated with nonfluorinated resin-based water-repeUent extenders. These water repeUents not only reduce the cost of the finish but may also improve durabUity (27,28). 

Oxiranes with a single perfluoroalkyl chain are regioselectively opened by nucleophilic reagents at the more accessible carbon [d4] (equation 30). 

The reaction of aliphatic primary amines with alkyl a-hydrogenoperfluorocar-boxylates leads to the corresponding P-alkyl iminoesters as the major or the sole tautomers, depending on the length of the perfluoroalkyl chain [ 103] (equation 89). 

Fig. 15. Tilt angles of the different molecular fragments as a function of temperature for polyphilic compound FsHnOCB aromatic core (circles), alkyl chain (crosses) and perfluoroalkyl chain (diamonds) (Ostrovskii et al. [45])...

As outlined above, immobilization in a fluorinated liquid phase demands the functionahzation of the ligand with perfluoroalkyl chains and, even then, the solubihty is strongly influenced by the nature of the complex. Ionic hquids of the alkylmethyhmidazolium type (Fig. 4) have been recently developed as alternative solvents for organometallic catalysis and have the practical advantage of using directly the commercially available chiral hgands and complexes. 

If nonvolatile liquids are to be used to avoid the problems associated with volatile organic solvents, then it is very desirable that there is some convenient way of recovering the reaction products from the liquid. This approach is used in the biphasic systems described in Chapters 2-5. In the fluorous biphase (Chapter 3), reagents and catalysts are fine-tuned by adding perfluoroalkyl chains, known as ponytails , to ensure that only those chemicals will mix with the fluorous layer. Purification is simply a matter of separating the two phases. Transition metal catalysts with fluorous ligands will remain in the fluorous phase, and the whole catalyst-solvent mixture may be reused for another batch of reactions, as shown schematically in Figure 1.20b. 

Keeping in mind the recovery of the catalyst issue, Pozzi et al. [59] specifically tailored the salen ligand to suit its application in fluorous biphasic (FB) system (Figure 4). Accordingly, authors made modification at 5 and 5 position of Jacobsen catalyst by replacing fert-butyl group with perfluoroalkyl chain 6 or 3,5-bis heptadecafluorooctylphenyl 7, 8 [60]. 

The presence of long perfluoroalkyl chains gives sugars surfactant and emulsifier properties, with interesting applications in the biomedical field. These applications... 

There are several features to note about Figure 4.7. While water will bead on a surface prepared with PTFE or an FA, it will wet a nylon-6,6 surface. For the case of hexadecane, botlr PTFE and FA surfaces will show appreciable contact angles, while a nylon-6,6 surface will be wetted completely (0 = 0). This is the reason that oily soils are relatively difficult to remove from materials made from nylon-6,6. The surface of a material prepared with a FA using perfluoroalkyl chains often has a lower surface tension than PTFE. For comparison, the surface tensions of nylon-6,6, PTFE " and FAs are estimated to be about 46, 24, and 10-20 mN/m, respectively. 

The surface tensions of materials prepared with are some of the lowest attainable with the reagents commonly available, which is why many carpet and textile repellents are based on the chemistry of perfluoroalkyl chains. For example, a nylon-6,6 carpet would be wetted by oily soils, which, according to Eq. (4), would be difficult to remove. The presence of a FA coating on die fiber lowers its surface tension and repels the oil contaminant. In general, a liquid dial has a high surface tension will not wet a solid with low surface tension (e.g., water on PTFE). The converse is also true. A low-surface-tension liquid will wet a high surface tension solid (e.g., hexadecane on nylon-6,6). 

The reactivity of a terminal 1,13-diene with an interstitial deca(difluoromethylene) chain 1 is lower towards expoxidation with hypofluorous acid/acetonitrile complex21 due to the electron-withdrawing effect of the perfluoroalkyl chain attached directly to the C = C bond. The diepoxide 2 is obtained by repeated reaction with a very large excess of the oxidizing agent.21... 

Cr Cub, Cubv d E G HT Iso Isore l LamN LaniSm/col Lamsm/dis LC LT M N/N Rp Rh Rsi SmA Crystalline solid Spheroidic (micellar) cubic phase Bicontinuous cubic phase Layer periodicity Crystalline E phase Glassy state High temperature phase Isotropic liquid Re-entrant isotropic phase Molecular length Laminated nematic phase Correlated laminated smectic phase Non-correlated laminated smectic phase Liquid crystal/Liquid crystalline Low temperature phase Unknown mesophase Nematic phase/Chiral nematic Phase Perfluoroalkyl chain Alkyl chain Carbosilane chain Smectic A phase (nontilted smectic phase)... 

Examples of rod-like molecules with a branched fluorinated chain at one end (compounds 90-93) are collated in Fig. 26 [166]. It is interesting that smectic phases are retained despite the significant size of these chains. This is mainly a result of the intercalation of the aromatic cores and aliphatic spacers of these molecules, which can compensate this steric distortion. These branched chains remove the B and E phases with crystalline layers and replace them by fluid smectic phases, including SmC phases. The comparison in this figure also shows that the bulky and flexible bis(perfluoropropylene oxide) derived chains (compounds 92, 93) can provide LC materials with especially low melting points and broad mesophase ranges due to the higher conformational flexibility of perfluoroethers compared to linear perfluoroalkyl chains [99, 176]. 

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