Poly (ethylene-oxide) (PEO)-based membranes have attracted much attention recently for CO 2 separation because CO 2 is highly soluble into PEO and shows high selectivity over other gases such as CH 4 and N 2 . Unfortunately, those membranes are not strong enough mechanically and highly crystalline, which hin- ders their broader applications for separation membranes. In this review discussions are made, as much in detail as possible, on the strategies to improve gas separation performance of PEO-based membranes. Some of techniques such as synthesis of graft copolymers that contain PEO, cross-linking of polymers and blending with long chains polymers contributed significantly to improvement of membrane. Incor- poration of ionic liquids/nanoparticles has also been found effective. However, surface modification of nanoparticles has been done chemically or physically to enhance their compatibility with polymer ma- trix. As a result of all such effort s, an excellent performance, i.e., CO 2 permeability up to 200 Barrer, CO 2 /N 2 selectivity up to 200 and CO 2 /CH 4 selectivity up to 70, could be achieved. Another method is to introduce functional groups into PEO-based polymers which boosted CO 2 permeability up to 200 Barrer with CO 2 /CH 4 selectivity between 40 and 50. The CO 2 permeability of PEO-based membranes increases, without much change in selectivity, when the length of ethylene oxide is increased.
