Polymeric gel membranes contain poly(ether-b-amide) (Pebax) and ethylene glycol monophenyl ether (EPH) was prepared via thermally induced phase separation (TIPS) method for the first time. In the membranes, EPH was used as not only diluent to form the gel structure, but also functional liquid to enhance the CO2 permeability and CO2/N-2 selectivity. Comprehensive investigation was carried out to study the phase separation behaviors and membrane performances. Phase diagrams and optical microscope results indicate that the crystallizition of Pebax from a one-phase solution is responsible for the physical network structure of the gel membranes. Meantime, the gel temperature shifted to the lower region with increasing EPH content. Both the pure CO2 permeability and CO2/N-2 ideal selectivity of the membranes were simultaneously increased with the increase of EPH content, which can be ascribed to the multiple synergistic effect of (a) the increased solubility of CO2 by Lewis acid-base interactions between CO2 and ethylene oxide groups in EPH, (b) the barrier effect of EPH on the transport of N-2 and (c) more permeable amorphous phase was formed in polymer matrix. The overall performance of gel membranes with 60 and 80 wt% EPH fall within the attractive region beyond the "Robeson Upper Bound" for CO2/N-2 gas pairs. The successful application of TIPS provides a new route to the structure modulation and performance enhancement of polymer gel membranes in the removal of CO2 from gas streams. (C) 2016 Elsevier B.V. All rights reserved.