Fluorinated hydrophobic groups

The same procedure has been employed to increase the hydrophobic character of cellulose, by introducing fluorine-containing groups, e.g., 2,2-difluoroethoxy 2,2,2-trifluoroethoxy and octafluoropentoxy. Incorporation of hydrophobic moieties into cellulose is expected to increase the polymer compatibility with other materials, e.g., synthetic polymers. Note that an important part of incompatibility is due to the highly hydrophilic character of cellulose. Decreasing this character is expected to affect Tg of the derivative, as shown by cellulose propionate/octafluoropentoxy acetate (total DS = 3.0, partial DS in each moiety = 1.5), whose Tg is only 53 °C. The products are more stable than their fluorine-free counterparts, and the terminal CF2 - H group affects Tg much less than OH-substituted trifluoroethoxy celMose derivatives [196,197]. 

In 1996, Gratzel, Bonhote and coworkers published the synthesis and properties of ionic liquids with anions containing CF3- and other fluorinated alkyl groups [12]. These are usually highly hydrophobic melts with high stability (even under acidic conditions) against hydrolysis. 

PFCs comprise a large group of compounds characterized by a fully fluorinated hydrophobic linear carbon chain attached to one or more hydrophilic head. PFCs repel both water and oil, and are therefore ideal chemicals for surface treatments. These compounds have been used for many industrial applications including stain repellents (such as Teflon), textile, paints, waxes, polishes, electronics, adhesives, and food packaging [1]. 

In contrast to that, the short fluorinated side groups of poly-XIII did not lead to thermotropic LC phases, but resulted in microphase-separated block copolymers caused by the hydrophobic and oleophobic character of fluorinated polymers. This interpretation was supported by DSC data, which gave the thermal transitions for both blocks. 

Hoffmann-Roder, A., Schweizer, E., Egger, J., et al. (2006) Mapping the fluorophilicity of a hydrophobic pocket synthesis and biological evaluation of tricyclic thrombin inhibitors directing fluorinated alkyl groups into the P pocket. ChemMedChem, 1(11), 1205-1215. 

Surfactants with hydrocarbon-chain hydrophobic groups generally do not lower the surface tension of alkanes, since any orientation of adsorbed surfactant of this type at the air-alkane surface would not reduce the surface free energy. However, fluorinated surfactants can adsorb and orient at the hydrocarbon-air surface to reduce the free energy there. Fluorinated surfactants of the type C6H5CF(CF3) 0[CF2CF(CF3)0]mC3F7 have been observed to reduce the surface tension of m-xylene (28 mN/in) to 10 mN/in (Abe, 1992). 

In fluorosurfactants, the hydrophobic group is a per-fluoroalkyl unit in which all of the hydrogen atoms are replaced by fluorine. Anionic fluorosurfactants can be prepared from all classes of anionics. Their critical micelle (forming) concentration is remarkably low and therefore they depress the surface tension of water to a very low value, even at small concentration levels. Furthermore, they are stable against thermal and chemical influences. Hence, fluorosurfactants can be used in aggressive media and at high temperatures. 

Li Y, Roy A, Badami AS, Hill M, Yang J, Dunn S, McGrath JE (2007) Synthesis and characterization of partially fluorinated hydrophobic-hydrophilic multiblock copolymers containing sulfonate groups for proton exchange membrane. J Power Sources 172 30... 

Fluormated poly(organophosphazenes) have distinctly different properties from their nonfluorinated counterparts. This is due to the stabilizing effect of the fluorinated side groups on the backbone, the hydrophobicity or super-hydrophobicity of films or fibers, and the general biomedical stability and compatibility of polymers with fluorocarbon units in the side group structure. The following examples illustrate some of the main properties. 

Rosen [35] has tabulated values of Tm for a wide variety of anionic, cationic, non-ionic and zwitterionic surfactants and has discussed the effect of surfactant structure on With hydrocarbon surfactants, the length of the hydrophobic group has little effect except when this exceeds 16 carbon atoms when a significant decrease in r jis noted, possibly due to coiling of the chain. Chain branching has only a small effect on T j, as has introduction of fluorine atoms into the hydrophobic chain. With polyoxyethylene non-ionic surfactants of fixed oxy-ethylene chain length the value of appears to be little influenced by the length of the hydrocarbon chain. 

The structure of the hydrophobe of an anionic fluorinated surfactant can be varied more extensively than the structure of the hydrophile. The hydrophobe can be a fully or partially fluorinated alkyl group having a linear or a branched alkyl chain. The hydrophobe can have an aromatic group or contain other elements (O, N, Cl, S, and Si) as well, as shown with the following examples ... 

The fluorinated hydrophobe can be a perfluoroalkyl group or a partially fluorinated alkyl group. Some fluorinated surfactants have hydrophobes containing... 

Surfactants are used most frequently in aqueous systems. Their amphiphilic character arises from the presence of a hydrophilic group and a hydrophobic group in the same molecule. A perfluoroalkyl group of fluorinated surfactants is not only hydrophobic but oleophobic as well. In a hydrocarbon medium, a perfluoroalkyl... 

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