The goal of this study was to broaden the spectrum of gas permeability and selectivity characteristics of poly(ethylene-co-acrylic acid) (EAA) by combining it with poly(ethylene oxide) (PEO), which has a high selectivity for CO2. To obtain films that differed substantially in their solid state morphologies, EAA was combined with PEO as melt blends and as coextruded films with many alternating, continuous microlayers of EAA and PEO. The solid state structure and thermal behavior were characterized and the permeability to O-2 and CO2 Was measured at 23 degrees C. When the PEO was dispersed as small domains, the particles were too numerous for most of them to contain a heterogeneity that was sufficiently active to nucleate crystallization at the normal T-c. The rubbery, amorphous nature of the PEO domains enhanced the gas permeability of the melt blends. In contrast, the constituent polymers maintained the bulk properties in 5-20 mu m-thick microlayers. The series model accurately described the gas transport properties of microlayered films. Comparison of blends and microlayers revealed that the high CO2 selectivity of PEO was most effectively captured when the PEO phase was continuous, as in the microlayers or in the cocontinuous 50/50 (wt/wt) melt blend. (C) 2008 Wiley Periodicals, Inc.