Alkyl polyoxyethylene

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. 

Hofland et al. investigated the in vitro permeation behavior of estradiol from niosomes (rt-alkyl polyoxyethylenes/cholesterol) through human stratum corneum. In this study examining drug delivery from multilamellar niosomes, small unilamellar niosomes and a micellar solution, all being saturated systems containing 1.5, 1.5, and 0.75 mM estradiol, very low permeation fluxes were detected (64+17, 45 + 15, and 42 + 2 ng/cm2/h, respectively) [40]. 

Alkyl polyglycol ether Alkyl polyoxyethylene glycol HOSTAPUR American Hoechst... 

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. 

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°...

The enhancement of enantioselectivity cannot be an effect of solubility because water-soluble substrates gave enhanced activities but no enantioselectivity increase [54], Acylation of PPM ((2S,4S)-4-diphenylphosphino-2-diphenylphosphinomethyl-pyrrolidine) with the chlorocarbonic ester of alkyl polyoxyethylene ethers (Brij 4)... 

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. 

Nonionic e.g. alkyl polyoxyethylene ether triblock copolymers e.g. Plutonic ) Acidic s°H x-r [16]... 

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.)...

A straight forward method involves a preparation after the Williamson synthesis, which does have some industrial application. In this, the OH end-group of the alkyl polyoxyethylene as starting material is converted by monochloroacetic acid and metallic sodium to form the ester carboxylate and sodium chloride. 

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. 

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

Figure 4.27 Solute thermodynamic activity of alkyl polyoxyethylene ethers in aqueous solutions as a function of molality. CH3CH2 (OCH2CH2)60H-does not form micelles. A CH3(CH2)3(0CH2CH2)60H at 20° C and A at 30° C and (CH3)2CH.CH2-(0CH2CH2)60H at 20° C (CH3CH2)2CH.CH2(0CH2CH2)60H at 20 °C. From Florence [3].

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].

Isolated tissue work should not suffer from such complications. In measuring the effect of a range of alkyl polyoxyethylene ethers on paraquat transfer across rat stomach epithelium, Walters et al. have found [44] no simple correlation between surfactant structure and transport. However, with a group of surfactants such as these with a given polyoxyethylene chain length a certain dependency on alkyl chain length can be seen (Fig. 7.15). 

Tadros [133] predicted an increase in the thickness of adsorbed polyvinyl alcohol layer at the paraffin-water interface with increasing bulk concentration from 3.5 nm at 1 ppm to 67.7 nm at 20 ppm. It is doubtful, however, whether it is possible solely on the evidence of results from application of Equation 8.35, to confirm multilayer formation. Kayes [134] has calculated using this equation, adsorbed layer thicknesses on solid particles for alkyl polyoxyethylene monoethers of 3.2 and 9.2 nm for derivatives with 30 and 60 ethylene oxide residues, respectively, which approximates to monolayer coverage. 

Figure 9.3(a) shows the mode of adsorption of an ionic surfactant at a hydrophilic surface, with its polar head groups close to the surface and non-polar chains pointing out into the aqueous phase. As one proceeds down the diagram, the bulk solution concentration of the surfactant is being increased until bilayers are formed by hydro-phobic associations of the alkyl chains of the surfactant, rendering the surface hydrophilic, (b) shows the possible mode of association of non-ionic alkyl polyoxyethylene ethers at a hydrophilic silica surface at a concentration where bilayers are forming. From Rupprecht [6] with permission. 

Masukawa and Tsujimura (1997) patented a method to determine surfactants in cosmetic products by reversed-phase LC without pre-treatment. Chromatographic conditions involved a binary gradient with methanol and water, ammonium carbonate salt as buffer and LSD detection. Amphoteric surfactants (Cg-Ci6 amidobetaines), an anionic surfactant (Cl2-16 acylmethyltaurine) and two types of nonionic surfactants (Cg i4 diethanolamides and Ci2 14 alkyl polyoxyethylene alcohols) were identified on applying this method. 

Chem. Descrip. Alkyl polyoxyethylene ether Ionic Nature Nonionic... 

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. 

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