Poly(amidoamine) (PAMAM) dendrimers display quite high specificity toward CO2, and incorporation of the dendritic molecules in a polymer matrix has been investigated to fabricate CO2 separation membranes. Especially, photopolymerization of poly(ethylene glycol) dimethacrylate (PEGDMA) in the presence of the dendrimers allows forming macroscopically homogeneous membranes. The resulting membranes show excellent CO2 separation from Hj under high humidity, depending on the dendrimer concentration and fabrication. The morphology is studied in detail by various real-space and Fourier-space methods. For example, a laser-scanning confocal microscope observation reveals the formation of a bicontinuous phase structure of the dendrimer-rich and PEG-rich phases upon polymerization-induced phase separation on a couple of microns scale. The macrophase-separated structure is related to the CO2 separation performance. The mechanism of preferential CO 2 separation is elucidated. CO2 partially turns into bicarbonate ions in the membrane under humid conditions, which would be the major migrating species, while the rest of the CO2 forms carbamate with primary amines of the PAMAM dendrimer to form a quasi-crosslinking, which would suppress the H2 permeation by a so-called "CC>2-selective Molecular Gate".
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