Efficiency Boosting of Surfactants with Poly(ethylene oxide)-Poly(alkyl glycidyl ether)s: A New Class of Amphiphilic Polymers

Twenty years ago, it was found that adding small amounts of amphiphilic block copolymers like poly­(ethylene propylene)-co-poly­(ethylene oxide) (PEP-b-PEO) to microemulsion systems strongly increases the efficiency of medium-chain surfactants to solubilize water and oil. Although being predestined to serve as a milestone in microemulsion research, the effect has only scarcely found its way into applications. In this work, we propose new types of efficiency boosters, namely, poly­(ethylene oxide)-poly­(alkyl glycidyl ether carbonate)­s (PEO-b-PAlkGE) and their “carbonated” poly­(ethylene oxide)-poly­(carbonate alkyl glycidyl ether) analogs. Their synthesis via anionic ring-opening polymerization (AROP) from commercially available long-chain alkyl glycidyl ethers (AlkGE) and monomethoxypoly­(ethylene glycol)­s as macroinitiators can be performed at low cost and on a large scale. We demonstrate that these new PEO-b-PAlkGE copolymers with dodecyl and hexadecyl side chains in the nonpolar block strongly increase the efficiency of both pure and technical-grade n-alkyl polyglycol ether surfactants to form microemulsions containing pure n-alkanes or even technical-grade waxes, a result that could be of interest for industrial applications where reduced surfactant needs would have significant economic and ecological implications. For n-decane microemulsions, the boosting effect of PEO-b-PAlkGE and PEP-b-PEO polymers can be scaled on top of each other, when plotting the efficiency semilogarithmically versus the polymeric coverage of the amphiphilic film. Interestingly, a somewhat different scaling behavior was observed for n-octacosane microemulsions at elevated temperatures, suggesting that the polymers show less self-avoidance and rather behave as almost ideal chains. A similar trend was found for the increase of the bending rigidity κ upon polymeric coverage of the amphiphilic film, which was obtained from the analysis of small-angle neutron scattering (SANS) measurements.