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In this work, the barrier character of poly(caprolactone) is improved with the addition of a poly(hydroxy amino ether). The analysis by means of thermal, thermomechanical, and morphology characterization reveals that the blends are partially miscible. The characterization of the morphology has revealed that the blends show a droplet matrix morphology. The free volume of the samples has been characterized by positron annihilation lifetime spectroscopy observing a decrease in the free volume as the poly(hydroxyamino ether) (PHAE) content increases. The barrier character to water vapor and carbon dioxide is greatly improved with the addition of PHAE. However, the observed improvement does not arise only from the reduced free volume, playing the interactions between penetrants and polymers a major role. Overall, this work aims to provide a further insight on the factors affecting the improvement of the barrier character of biodegradable polymers, which would allow developing new materials for packaging applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48018.