Hydrophobic groups polyoxypropylenes

Finally, it is worth mentioning that thermodynamically stable vesicles can also be found in the binary systems surfactant/water if the hydrophobic group is sufficiently voluminous. As already mentioned, this has been observed for the double-chain surfactant didode-cyldimethylammoniumbromide DDABr in water [102]. Recently also a L3 phase has been found in the binary system of a polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer and water at high temperatures. This block copolymer has a composition EOsPOsoEOs and hence a very small hydrophilic headgroup. It forms a lamellar phase at room temperature which is transformed into the L3 phase above a certain temperature [103]. The reason for this transition is probably the increased flexibility of the block copolymer film at the high temperature. 

These are polyoxyethylene-polyoxypropylene derivatives with the general formula HO(CH2 CH. O) (CH2.CH(CH3)0), (CH2.CH2.0),H where a = c. The polyoxypropylene hydrophobic groups —(CH2CH(CH3)0) and the polyoxyethylene hydrophilic groups of these compounds may be varied over a wide range to give compounds with the required properties. These compounds are commercially available under the trade name Pluronic, e.g. Pluronic F68 Polyoxypropylene (mol. wt. 1501-1800) 4-140 mol ethylene oxide Pluronic L62 polyoxypropylene (mol. wt. 1501-1800)4-15 mol ethylene oxide and Pluronic L64 polyoxypropylene (mol. wt. 1501-1800) +25 mol ethylene oxide. 

Diblock polyoxyethylene-polyoxypropylene styrenic macromonomers, with the polymerizable group at the end of the hydrophobic part have been prepared and used in styrene emulsion polymerization [34]. Latexes of high stability towards added electrolyte have been obtained. However the HLB was not well-optimized so that a high amount of coagulum was formed (Surfmer XI). 

A number of commercial surfactants are available in which aU or most of the hydrophobic character is derived from the presence of polyoxypropylene (POP) groups. The observed effect of such substitution has been that each propylene oxide group is equivalent to approximately 0.4 methylene carbon. 

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