Polymeric membranes are attractive for CO₂ separation and concentration from different gas streams because of their versatility and energy efficiency; they can compete with, and they may even replace, traditional absorption processes. Here we describe a simple and powerful method for developing nanostructured and CO₂-philic polymer membranes for CO₂ separation. A poly(ethylene oxide)−poly(butylene terephthalate) multiblock copolymer is used as membrane material. Smart additives such as polyethylene glycol dibutyl ether are incorporated as spacers or fillers for producing nanostructured materials. The addition of these specific additives produces CO₂-philic membranes and increases the CO₂ permeability (750 barrer) up to five-fold without the loss of selectivity. The membranes present outstanding performance for CO₂ separation, and the measured CO₂ flux is extremely high (>2 m³ m⁻² h⁻¹ bar⁻¹) with selectivity over H₂ and N₂ of 10 and 40, respectively, making them attractive for CO₂ capture.