Perfluoroalkyl side chains

Kimura used the cholesterol-substituted [15]crown-5 8 in ion sensing membranes. It was found that the addition of the crown ether affects the sensor properties, especially the ion specificity, and it was possible to obtain sensors with extremely high sensitivities [48]. The performance could be further increased by using perfluoroalkyl side chains instead of cholesterol [49]. 

The empirical quantity Yc is defined as the value of Yl (surface tension of the wetted liquid) at the intersection point of the straight line cos 0 against Yl with the horizontal at cos 0. This extrapolation corresponds to complete surface wetting made possible by the liquid. In general, the Yc value depends on the length, composition, branching and terminal groups of perfluoroalkyl side chains, and the crystallinity and tacticity of polymers (Pittman, 1972). 

It has also been reported the mechanism on dewetting by increasing temperature of perfluoroalkyl methacrylate as homo- and copolymer with methyl methacrylate films. The following qualitative model has been proposed (Sheiko et al, 1996). As has already been stated, perfluoroalkyl-substituted polymethacrylates have been shown to form ordered structures based on the crystallisation of the perfluoroalkyl side chains and the incompatibility of the fluorinated and the hydrocarbon segments. 

Perfluoroalkoxy resin (PFA) n. A class of melt-processable fluoroplastics in which perfluoroalkyl side chains are cormected to the fluorocarbon backbone of the polymer through flexible oxygen linkages. 

Fig. 4 Schematic of surface enrichment of grafted perfluoroalkyl side chains in anchored polydimethyl siloxane ultrathin films on gold (see ref, [40])...

By contrast, analogous ultrathin polysiloxane films grafted with perfluropolyethers instead of the perfluoroalkyl side chains exhibit completely different structural behavior [41]. XPS surface enirchment of perfluorinated substituents occurs but only weakly for the perfluro-ether case. Reduced fllm stratification is observed. Additionally, no FTIR evidence for side chain organization is observed. This concurs with NEXAFS work that shows no chain structural anisotropy in these bound polymer films [41],... 

We investigated an interaction of 2-acyl( clohexane-l,3-diones la-c containing a perfluoroalkylated side chain with o-phenylenediamine. A direct reaction of the latter with o-phenylenediamine produees a mixture of acid cleavage products, as reported for their aeyelie analogues [7], As an alternative approach to the synthesis of perfluoroalkylated dibenzo[b,e][l,4]diazepinones, an interaction of enol ethers of 2-perfluoroalkanoylcyclohexane-l,3-diones la- c with o-phenylenediamine is proposed, beeause of an advanced reactivity of enol ethers to nucleophilic reagents versus the initial cyclic P,P -triketones [8],... 

Plots of D versus water volume fraction " show that the concentration dependence of D is in fact described well by the Fujita free volume equation. " This was surprising considering that the underpinning of this equation simply involves available free volume for molecular hopping. The interpretation is that water molecules plasticize the perfluoroalkyl ether side chain domains and this increases D with increasing water content. D for water varied from... 

Photo-stimulated reactions of neopentyl iodide with several carbanionic nucleophiles have been studied in which inhibition experiments with the TEMPO radical trap suggest the reaction occurs via an SrnI mechanism.76 Comparison of 22 nucleophiles in then. Srn 1 reactions with iodobenzene by Fe(II)- and photo-induction has revealed that both are enhanced by high electron-donation ability of the nucleophile. The radical anion Phl is a key intermediate.77 The SET reactions of perfluoroalkyl iodides have been reviewed.78 Flash photolysis of H2O2 was used to generate HO and 0 radicals which were reacted with a, a. z-trifluorotolucnc (TFT) and 4-fluorotoluene (4FT) and the rate constants calculated.79 The diminished reactivity of TFT towards HO or O with respect to toluene or benzene was consistent with radical addition to the aromatic ring, whilst the reactivity of 4FT was of the same order as electron-deficient toluenes, which favour H abstraction from the aliphatic side-chain. 

The electronic effect of perfluoroalkyl substituents on the absorption spectra of arenes is relatively small (e.g., Xmax 3-perfluorooctylthiophe-ne = 229 nm 3-octylthiophene = 235 nm). Thus, the anomalously low absorption maximum of 504 is the effect of twisting around the backbone. It is apparent that the difference in size of the side chains is sufficiently large to cause twisting of the conjugated backbone of 504 due to steric interactions between the perfluoroalkyl substituents and the adjacent repeat unit. 504 exhibits green fluorescence (Xmax = 512 nm) in solution with a maximum blue shifted by 58 nm relative to POT (570 nm). Accordingly, 504 shows a Stokes shift of ca. 1.4 eV (186 nm) compared to only 0.6 eV (126 nm) for POT. 

One of the most attractive and successful attempts in attaining processable aromatic polyimides is the introduction of fluorine atoms in the polymer structure, either as substituents of carbon atoms on the polymer backbone (as mentioned before for perfluoroalkane containing polyimides), or as perfluoromethyl or perfluoroalkyl side substituents. The most popular approach has been the introduction of the hexafluoroisopropylidene group in the main chain as a bulky separator group in the dianhydride monomer or in the diamine one [70]. 

Syntheses of heterocyclic compounds with perfluorinated side chains are mainly performed by substitutional fluorinations of the available fragments or by the introduction of a perfluoroalkyl group in the heterocycle. The development of convenient approaches and direct perfluoro-alkylation methods is a current challenge. 

The chiral ferrocenylmonophosphine ligand 7c, which is analogous to PPFA 3a but contains a perfluoroalkyl group on the aminoethyl side chain, is more enantioselective than PPFA (Scheme 2-48) [67]. The enantioselectivity in the palladium-catalyzed hydrosilylation of cyclopentadiene and 1-vinylcyclohexene is increased to 60% ee and 43% ee, respectively. The polymer-supported PPFA 62 has been used for the hydrosilylation of styrene (15% ee) [68]. 

An interesting mechanism for displacement of fluorine from side chains has been identified317 and is illustrated by 3-trifluoromethylquinoline (Eq. 89). Perfluoroalkyl groups have also been found to behave as leaving groups... 

Nevertheless, there have been many experimental results on the preferred self-assembly used to construct highly ordered perfluoroalkyl layers. For example, an X-ray diffraction analysis study revealed that a C8 perfluoroalkyl moiety as a side chain of polyacrylate was found to be in alignment with the side chains, while a C 2 nonfluoroalkyl moiety was needed for a similar alignment [26]. 

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