Hyperbranched poly(ester amine) (HPEA) with terminal secondary amine groups was synthesized by the Michael addition reaction between piperazine and trime-thylolpropanetriacrylate with a molar ratio of 13:6. It was further reacted with a series of aliphatic acid chlorides, including stearoyl chloride, dodecanoyl chloride, and octanoyl chloride, to yield three modified amphiphilic hyperbranched polymers, which were termed HPEA-C18, HPEA-C12, and HPEA-C8, respectively. These polymers were characterized with Fourier transform infrared, H-1 NMR, gel permeation chromatography, and differential scanning calorimetry measurements. Because of the existence of interior tertiary amine groups, the modified amphiphilic polymers were used as host molecules to extract the guest acid dye, methyl orange (MO), from the aqueous layer to the organic layer on the basis of the acid-base interaction. The influences of the pH of the aqueous layer and the length of the alkyl chains in the modified polymers on the phase-transfer performances were investigated. The results indicated that more MO molecules could be extracted at a lower pH because of the formation of more quaternary ammonium ions within the host molecules. As the length of the alkyl chains in the modified polymers increased, both the transfer capability and the intermolecular aggregation at the interface were enhanced. The extracted MO could be reversibly released from the organic layer to the aqueous layer under basic conditions. (c) 2005 Wiley Periodicals, Inc.