To solve recyclable problem of aqueous two-phase systems (ATPS), novel recycling ATPS were constructed by two novel pH-response copolymers (P-ADB and P-ADBA) in our lab. In this study, the phase diagram of P-ADB/P-ADBA aqueous two-phase systems was prepared. The effect of pH on the tie lines and binodal curves with 4.87, 5.45, and 6.05 at 25 degrees C were investigated. Two models including Flory-Huggins model and NRTL model were used to correlate the equilibrium data of P-ADB/P-ADBA aqueous two-phase systems. The interaction parameters between two polymers in the two models were determined by fitting experimental data to the objective function. The minimal RMSD of Flory-Huggins model is 0.8777 at pH 6.05 and in NRTL model is 1.0092 at pH 6.05. Flory-Huggins model shows better correlation than NRTL model for P-ADB/P-ADBA aqueous two-phase systems. (C) 2013 Elsevier BAT. All rights reserved.