Development of absorbents with large absorption capacities is important for improvements in the CO2 capture technology. Polyamines include more than two amine groups in their molecular structures and may exhibit great potential as candidate solvents. In this study, CO2 solubility and speciation in aqueous 3,3'-iminobis(N,N-dimethylpropylamine) (IBDMPA) was experimentally investigated and a chemical equilibrium reaction model was proposed. Solubility measurements were conducted at four different IBDMPA contents (9.37, 18.7, 31.6 and 37.5 mass%) in the temperature range from 40 to 120 degrees C and CO 2 partial pressure in the range of from 2 kPa to 480 kPa. In addition, both proton and carbon nuclear magnetic resonance (NMR) spectroscopic techniques were employed for the quantitative and qualitative analyses of various species in CO2-loaded solutions. Using these experimental results, a chemical equilibrium reaction model was developed for the IBDMPA-H2O-CO2 system based on the electrolyte NRTL model. (C) 2019 Published by Elsevier Ltd.