High-molecular-weight polyvinylamine (PVAm)/piperazine glycinate (PG) membranes were successfully synthesized for CO2/N-2 separation from flue gas. PVAm with different molecular weights was synthesized through free radical polymerization by adjusting the monomer concentration and initiator amount. The synthesized PVAm showed both a higher molecular weight and a higher solution viscosity than the commercially available PVAm (Lupamin (R) 9095 from BASF Corporation). The high viscosity of the PVAm solution at a low concentration allowed the preparation of much thinner membranes. It could also help reducing penetration of the polymer solution into the pores of the substrate, further reducing the mass transfer resistance. Consequently, a high CO2 permeance could be obtained from thin membranes with the thickness of 100-200 nm. In the membrane, PVAm acted as the fixed-site carrier for CO2 facilitated transport whereas PG was incorporated into the PVAm polymer matrix and served as the mobile carrier. The PVAm/PG blend solution was coated onto different substrates including polyethersulfone (PES) and polysulfone (PSO substrates. Sodium dodecyl sulfate (SDS) surfactant was incorporated in the coating solution to improve the adhesion between the membrane layer and the substrate in some cases. The resultant PVAm/PG membranes exhibited a high CO2 permeance of about 1100 GPU and a high CO2/N-2 mixed gas selectivity of more than 140 at the typical flue gas temperature of 57 degrees C along with 17% water vapor. (C) 2016 Elsevier B.V. All rights reserved.