Solubilizing alkyl chains

Unfortunately, all of the above-described synthetic approaches towards HBC (1) suffer from serious drawbacks, such as harsh reaction conditions, a complicated experimental work-up, and low yields. Furthermore, under aluminum(III) chloride catalysis, dealkylation, migration of the alkyl substituents - or even chlorination of the aromatic system- occurs, which clearly limits the accessibility of functionalized HBC derivatives for further investigations and applications. In order to overcome these problems, the weaker Lewis acid iron(III) chloride in nitromethane was used instead of AICI3, and the reaction conditions were carefully optimized [55, 56]. In this way, access was obtained to a multitude of HBC derivatives 8 and 9 with diverse substitution patterns and symmetries bearing solubilizing alkyl chains and halogen substituents, starting from functionalized hexaphenylbenzenes. The sixfold symmetric hexaphenylbenzenes 10 were synthesized by the Co2(CO)g-catalyzed cyclotrimerization of substituted diphenyl-acetylenes 11 (Scheme 13.4a) [57], whereas the intramolecular Diels-Alder reaction... 

Therefore, it was our idea to proceed from linear to ladder-type polyphenylene structures by bridging neighboring benzene rings via methylene groups. This would not only enforce a planarization of the whole t-system, but also provide extra carbons to attach solubilizing alkyl chains without compromising the conjugation. 

Poly[2,5-dialkoxy-l,4-phenylene) vinylenejs with long solubilizing alkoxy chains dissolve in conventional organic solvents such as chloroform, toluene, or tetrahydrofuran [21, 28, 32-36]. Their emission and absorption spectra are red-shifted relative to PPV itself, and the polymers fluorescence and electroluminescence quantum yields are greater than parent PPV. This benefit may be a consequence of the long alkyl chains isolating the polymer chains from each other. 

The effect of chain length on the pseudo rate constant is shown in Fig. 18. Clearly, the optimum chain length for AOS is 16 carbon atoms. However, at this optimum the rate of oil solubilization for AOS is still below that observed for the reference compound DOBS 103, a sodium alkylbenzenesulfonate with 10-13 carbon atoms in the alkyl chain. Increasing the chain length of IOS subjected to an aging step before hydrolysis with NaOH (IOSa in Fig. 18) leads to a continuously increasing rate of oil solubilization. The highest rate was... 

In summary, directly hydrolyzed IOS has good n-hexadecane solubilizing kinetics. This class of compounds then is attractive for detergent formulations where the kinetics of apolar soil removal is imperative. Also, it is observed that shifting the ionic head group toward the middle of the alkyl chain results in an... 

The effect of surfactant structures and properties on emulsion polymerization have been investigated by numerous authors [82-89]. Efforts were made to study the effects of surfactants with different molecular weights on the rate of polymerization [82], swelling and solubilization effects [83], effects of alkyl chain length of homologous series on the rate of polymerization, particle size... 

The main peculiarity of solutions of reversed micelles is their ability to solubilize a wide class of ionic, polar, apolar, and amphiphilic substances. This is because in these systems a multiplicity of domains coexist apolar bulk solvent, the oriented alkyl chains of the surfactant, and the hydrophilic head group region of the reversed micelles. Ionic and polar substances are hosted in the micellar core, apolar substances are solubilized in the bulk apolar solvent, whereas amphiphilic substances are partitioned between the bulk apolar solvent and the domain comprising the alkyl chains and the surfactant polar heads, i.e., the so-called palisade layer [24],... 

Fullerene derivative 34 substituted with two long alkyl chains (solubilizing groups) and a carboxylic function was used as peripheral subunit for the constructions of the dendrons (Fig. 14). 

What characterizes surfactants is their ability to adsorb onto surfaces and to modify the surface properties. At the gas/liquid interface this leads to a reduction in surface tension. Fig. 4.1 shows the dependence of surface tension on the concentration for different surfactant types [39]. It is obvious from this figure that the nonionic surfactants have a lower surface tension for the same alkyl chain length and concentration than the ionic surfactants. The second effect which can be seen from Fig. 4.1 is the discontinuity of the surface tension-concentration curves with a constant value for the surface tension above this point. The breakpoint of the curves can be correlated to the critical micelle concentration (cmc) above which the formation of micellar aggregates can be observed in the bulk phase. These micelles are characteristic for the ability of surfactants to solubilize hydrophobic substances in aqueous solution. So the concentration of surfactant in the washing liquor has at least to be right above the cmc. 

The choice of the R group leads to materials exhibiting properties which can find applications in diverse fields long alkyl chains help solubilization in organic solvents, whereas triethylene glycols have been used as spacers to attach water-solubilizing moieties, or even electron-donor systems such as ferrocene, which may find applications in photovoltaics, or as bio- and electrochemical sensors [33]. 

The most useful characteristic of the micelle arises from its inner (alkyl chain) part (Figure 3.17). The inner part consists of alkyl groups that are closely packed. It is known that these clusters behave as liquid paraffin (Cn H2n+2). The alkyl chains are thus not fully extended. Hence, one would expect that this inner hydrophobic part of the micelle should exhibit properties that are common to alkanes, such as ability to solubilize all kinds of water-insoluble organic compounds. The solute enters the alkyl core of the micelle and it swells. Equilibrium is reached when the ratio between moles soluteimoles detergent is reached corresponding to the thermodynamic value. 

The far less sensitive response of the chemical shift of the methylene protons to the extent of solubilization suggests that the core of the micelle is mainly composed of alkyl chains and is relatively unaffected by the benzene. 

Liquid crystals are a fascinating topic of study in their own right, but we limit our discussion to a brief description of the ordering in some of the possible structures. In all cases the amphipathic molecules are oriented in such a way as to minimize the contact between water and the alkyl chains. Whether the polar head points outward or not depends on which component dominates the continuous phase the minor component is solubilized inside the micellar structures. 

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