Alkyl polyoxyethylene surfactants

Table 6.11 Micellar solubilisation parameters for steroids in r>alkyl polyoxyethylene surfactants C E (where n = alkyl (C) chain length and m = polyoxyethylene (E) chain length) at 25°C°...

Table 5.19 Solubilization of steroids by n-alkyl-polyoxyethylene surfactants [145].

Table 5.21 Micelle/water distribution coefficient, P, , for the solubilization of benzoic acid by n-alkyl-polyoxyethylene surfactants as a function of temperature [163].

It is very often the commercial interest in novel materials which stimulates the growth in their study and eventual exploitation. This is certainly true in the case of thermotropic liquid crystals and their application in electro-optic displays. Indeed, the production of high-strength, high-modulus fibres has seen a wealth of interest in lyotropic main chain polymers. The use of lyotropic side chain polymers has, by comparison, been less well publicized. This is not to say that there are no applications. Alkyl polyoxyethylene surfactants attached to polysiloxane polymers have found uses in many personal care products such as liquid soaps, shampoos, skin creams, and hair mousses. Unfortunately the physical properties of these and other similar materials have been closely guarded secrets and the amount of information available in the literature is low. The limited data which does exist, however, provides us with some interesting structure - behaviour relationships. 

The difficulty with HLB as an index of physicochemical properties is that it is not a unique value, as the data of Zaslavsky et al. (1) on the haemolytic activity of three alkyl mercaptan polyoxyethylene derivatives clearly show in Table 1. Nevertheless data on promotion of the absorption of drugs by series of nonionic surfactants, when plotted as a function of HLB do show patterns of behaviour which can assist in pin-pointing the necessary lipophilicity required for optimal biological activity. It is evident however, that structural specificity plays a part in interactions of nonionic surfactants with biomembranes as shown in Table 1. It is reasonable to assume that membranes with different lipophilicities will"require" surfactants of different HLB to achieve penetration and fluidization one of the difficulties in discerning this optimal value of HLB resides in the problems of analysis of data in the literature. For example, Hirai et al. (8 ) examined the effect of a large series of alkyl polyoxyethylene ethers (C4,C0, Cj2 and C 2 series) on the absorption of insulin through the nasal mucosa of rats. Some results are shown in Table II. 

Citric acid Acidifier Polyoxyethylene alkyl esters Surfactant... 

Occlusion is a condition that could affect drug transport from niosomes and through the stratum corneum. Such an effect was reported for saturated estradiol niosomal formulations composed of polyoxyethylene alkyl ether surfactants and sucrose ester surfactants with cholesterol and dicetyl phosphate, for which occlusion enhanced the drug human stratum corneum transport [43]. 

Eccleston, G.M. Beattie, L. Microstructural changes during storage of systems containing cetostearyl alkohol/ polyoxyethylene alkyl ether surfactants. Drug Dev. Ind. Pharm. 1988, 14, 2499-2518. 

A wide variety of this group of surfactants is commercially available. They include some of the Tritons (alkyl phenol additives, as far as they are non-ionic). Tweens (sorbitan fatty acid ester polyoxyethylene ethers). Spans (sorbitan fatty acid esters) and alkyl polyoxyethylenes (C Ej, where n and x stand for the number of CH2- or CH3-. and CHjO-groups in the hydrophobic and hydrophilic parts of the molecule, respectively). Given our interest in the fundamentals we shall emphasize only the last-mentioned group, and only when n and x are sharply defined emd the two moieties are either linear or branched in a defined way. Unless specified otherwise, there is an OH-group at the end of the E-chain. Notwithstanding the non-ionic nature of these molecules, micelles sometimes appear to cany a (low) charge probably caused by preferential uptake of ionic species. 

Eccleston GM, Beattie L. Microstructural changes during the storage of systems containing cetostearyl alcohol polyoxyethylene alkyl ether surfactants. In Rubinstein MH, ed. Pharmaceutical Technology Drug Stability. Chichester Ellis Horwood, 1989 76-87. 

A combination of SLS and DLS methods was used to investigate the behavior of nonionic micellar solutions in the vicinity of their cloud point. It had been known for many years that at a high temperature the micellar solutions of polyoxyethylene-alkyl ether surfactants (QEOm) separate into two isotropic phases. The solutions become opalescent with the approach of the cloud point, and several different explanations of this phenomenon were proposed. Corti and Degiorgio measured the temperature dependence of D pp and (Ig), and found that they can be described as a result of critical phase separation, connected with intermicellar attraction and long-range fluctuations in the local micellar concentration. Far from the cloud point, the micelles of nonionic surfactants with a large number of ethoxy-groups (m 30) may behave as hard spheres. ... 

Hydrophobic regions can be one or two small, well-defined blocks of pendant hydrophobic moieties in an otherwise water-soluble polymer (2-4). An example is a water-soluble sulfonated BAB triblock copolymer where B is hydrophobic f-butylstyrene and A is vinyltoluene (2). However, hydro-phobic regions can also be less well-defined as well as more numerous in a polymer molecule than is the case for a triblock copolymer (5-22). For example, pendant alkyl esters appear to have been randomly incorporated in styrene-maleic anhydride (5) and vinyl benzyl ether-styrene-maleic anhydride (6-ii) copolymers. Also, alkyl polyoxyethylene acrylate monomers can be copolymerized with acrylamide to yield copolymers with pendant hydrophobic chains (12-15). More recently it was found (16-22) that small amounts of water-insoluble monomers that are solubilized by surfactants into aqueous solutions of a hydrophilic monomer produce copolymers with pendant hydrophobic chains, but the size, number, and nature of the hydro-phobic regions has not been determined. 

Commercial polyoxyethylene surfactants contain a wide range of EO sizes, often with a reasonably defined alkyl chain. Bouwstra et al. [116] studied a commercial sample of Cg=C9EOi4 (i.e. a Cig chain with 9-10 cis double bond and a polydisperse EO group). It exhibits phase behavior similar to C12EOg... 

Figure 6 Interfacial tension between oil and water in the presence of a saturated surfactant monolayer versus temperature. The surfactants are alkyl polyoxyethylene glycol ethers C12E5 with hexane, C10E4 with octane, and CsEi with decane. The vertical bars indicate the transition temperatures between the different Winsor systems. (Data from Ref. 50.)...

Commercial polyoxyethylene surfactants contain a wide range of EO sizes, often with a reasonably defined alkyl chain. Bouwstra and co-workers (130) have studied a commercial sample of Cq CqEOh (i.e. a Cig chain with 9-10 cis double bonds and a polydisperse EO group). The latter exhibits phase behaviour similar to C12EO8, with Ii, Hi, Vi and L phases. The Hi phase exits between 35.6 and 74.8 wt% surfactant and up to 84°C. The other phases exist over narrower concentration ranges and to lower temperatures. Similar studies have also been reported by Kunieda and co-workers (131, 132) for a wide range of commercial oleoyl EO derivatives again, the commercial actives behave like pure ones with a shorter EO size. 

As a branch of the surfactant family tree, if the tried-and-true dodecanol is treated with ethylene oxide (OE) and base under rigid anhydrous conditions, the material obtained is an alkyl polyoxyethylene (POE) polyether. 

N-alkylated (e.g., A-methyl and A-ethyl) perfluoroalkanesulfonamides can be converted into nonionic surfactants with a polyoxyethylene head group by reaction of the sulfonamide with excess oxirane in the presence of a base. This synthesis approach is similar to the one outlined in Section 18.2.3.2 for the synthesis of perfluoroalkanesulfonamidoethanols. The reaction of A-methylperfluorobutanesulfonamide with oxirane yields the desired polyoxyethylene surfactants in the presence of potassium hydroxide at 100-120°C (Scheme 18.7). A different approach to similar polyoxyethylene surfactants claims the reaction of perfluoroalkanesulfonamidoethanols with oxirane in the presence of sodium hydroxide as a catalyst (Scheme 18.7). Both approaches can also be extended to other oxirane derivatives, or use perfluoroalkanesulfonamides such as the ones shown in Scheme 18.3 as starting materials. " Polyoxyethylene groups can also be attached to... 

FC-170C is an 80% active, amber colored, nonionic surfactant. It can be described chemically as fluorinated alkyl polyoxyethylene ethanols. 

At all alkyl chain lengths, polyoxyethylene surfactants become insoluble in liquid water at a sufficiently short E chain length. At the Qo chain length, this happens at C10E4, which has a critical temperature of 20.6°C. This compound is poorly soluble in... 

Although in many cases a particular location is preferred, the lifetime of a solubilizate within the micelle is long enough for a rapid interchange between different locations [80]. Mukerjee [81] has discussed the solubilization of benzoic acid derivatives by a series of polyoxyethylene surfactants (the Myrj class of non-ionic surfactants) in terms of an equilibrium distribution between two loci-the polyoxyethylene shell and the hydrocarbon core. The amount of the solubilizate solubilized in the core and polyoxyethylene region was assumed to be proportional to the number of equivalents of the alkyl chain moiety (stearate), Cr, and the number of equivalents of oxyethylene groups, respectively. The... 

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