Methyl ester ethoxylates water solubility

CMC). Methyl ester ethoxylates also carry a terminal methoxy group in place of a terminal hydroxyl group. This reduces the hydrogen bonding of the surfactant, which in turn reduces water solubility and the tendency to form aqueous gels. 

Methyl ester ethoxylates, however, are inherently less water soluble than their alcohol ethoxylate counterparts because they contain a terminal me-thoxy group in place of the more hydrophilic hydroxyl group. Consequently, it takes a higher degree of ethoxylation for methyl ester ethoxylates to achieve water solubility. Although it is dilScult to determine the precise ethoxylation level needed to achieve water solubility, studies suggest that methyl ester... 

FIG. 6 Water solubility (inverse cloud point temperature) as a function of EO content (moles) for C12-16 alcohol and methyl ester ethoxylates made with Ca/Al-alkoxide catalyst. (Cloud point temperature = temperature at which 1 % aqueous solution turns cloudy upon slow heating C12-16 alcohol ethoxylate is described in Table 1 distribution of methyl ester = 9% Cj, 8% Cio, 46% C12, 18% C14, 9% Cig, and 10% C18.) (From Ref. 27.)... 

In practice, inverse cloud point temperature is used more as a quality control measure rather than as a solubility requirement. Although methyl ester ethoxylates are less water soluble than their alcohol ethoxylate counterparts, they can achieve comparable formulatability characteristics at somewhat higher ethylene oxide levels. 

The slightly lower surface tension of the methyl ester ethoxylate at and beyond the CMC is thought to be related to the presence of the terminal methoxy group on the ethylene oxide chain. In comparison to a terminal hydroxyl group, a terminal methoxy group is less hydrophilic. The resulting lower water solubility effectively drives more of the surfactant to the air/water interface, resulting in a lower surface tension. 

The impact of unsaturation stems from the increase in rigidity caused by the presence of one or more double bonds to the alkyl chain. Although studies so far show that unsaturation has a relatively low impact on water solubility and viscosity, it has been reported to lower melting points by about 5-10°C [16]. Studies also show (Fig. 20) that unsaturation affects surface properties. Gibbs plots of 14.5-mole ethoxylates produced from hydrogenated and nonhydrogenated Cig is methyl ester show that unsaturation appears to increase surface tension below the CMC. This suggests that unsaturation reduces the hydrophobic character of the methyl ester chain. 

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