Molecular Design and Structure-Property Investigation of n-Dodecylbenzyloxy Ethoxylates

Nonylphenol ethoxylates (NPEO) exhibit outstanding application performances, especially in stabilizing silicone oil emulsions, but have been globally banned or use-restricted for serious ecological toxicity. A homologous series of nonionic surfactants, n-dodecylbenzyloxy ethoxylates (DBEO), are molecularly designed and synthesized as alternatives to NPEO, where the phenolic group of NPEO was replaced by a benzyloxy group to counteract the harmful characteristics of NPEO, while retaining the benefits. Based on computational studies, we propose a hypothesis that has a conjugation reduction effect (CRE) of DBEO relative to NPEO on the surfactant structure and properties that solves the biodegradation problem while maintaining the outstanding emulsifying capacity of NPEO. A 7-day activated sludge assessment shows that DBEO₈, a representative member of DBEO, is almost 100% biodegradable and that the poor biodegradability of NPEO may be improved by maintaining the vital benzene ring in DBEO molecules, because the oxygen atom of the benzyloxy group is separated from the smaller conjugation system of DBEO. Compared to NPEO₁₀, DBEO₈ has a similar cloud point but exhibits higher benzene solubilization and considerably higher emulsion stabilities for mineral oil, biomass oil, and especially silicone oil; this outcome is ascribed to a probable random coil configuration of PEO caused by the CRE of DBEO. Therefore, molecular design produces DBEO with both excellent biodegradability and outstanding application performances, especially in terms of excellent emulsion stabilities of various oils, as predicted by the CRE hypothesis, thereby serving as an effective alternative to NPEO.