Thermo-responsive branch copolymer was prepared via copolymerization with N- isopropylacrylamide (NIPAm) and the thermo-responsive macromonomer. The main chain and branch chain of thermo-responsive branch copolymer performed two different phase transition temperatures in aqueous solution. After dual-phase-transition

"grape cluster"morphology with large specific surface area could be observed by SEM. There were two break points in light scattering curves

which further explained the dual-phase-transition process in morphology. Two relatively independent endothermic peaks could be observed at 35℃ and 21℃ in DSC curves of the thermo-responsive branch copolymer sample

which described the dual-phase-transition process from the viewpoint of thermodynamics. The order of groups changing induced by temperature was investigated by 2D-IR spectroscopy. The result confirmed that the BA unit

which only existed in the branch chains

changed prior to the NIPAm units. The "grape cluster"morphology effectively increased the specific surface area of thermo- responsive polymer

which might be potentially applied in bioseparation.