A family of oligomers consisting of poly(oxyethylene) (POE) blocks and secondary amine and phenol functionalities were prepared from the Mannich reaction of alkylphenols, formaldehyde, and POE-diamines. The Mannich oligomers were characterized by amine titration, GPC, 1 H NMR, DSC, and TGA. In aqueous solution, the Mannich amines behaved as nonionic surfactants, exhibiting properties such as inverse temperature solubility behavior (between 24°C and 39°C), phase changes versus concentrations, surface tension reduction, and self-aggregation into particles mostly ranging from 20 to 1400 nm in diameter. The amphipathic balance in the structure, concentration, and pH influenced the self-aggregating size. The 1 H NMR integration further revealed that these aggregates could undergo phase inversions in different solvent environments.