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A CO₂-selective molecular gate of poly(amidoamine) dendrimer immobilized in a poly(ethylene glycol) network

Taniguchi, Ikuo, Urai, Hiromi, Kai, Teruhiko, Duan, Shuhong, Kazama, Shingo
Journal of membrane science 2013 v.444 pp. 96-100
X-radiation, amines, artificial membranes, bicarbonates, carbon, carbon dioxide, crosslinking, differential scanning calorimetry, dissociation, heat production, hydrogen, modulus of elasticity, nuclear magnetic resonance spectroscopy, polyethylene glycol, solubility, stable isotopes
A polymeric membrane composed of poly(amidoamine) (PAMAM) dendrimer immobilized in a poly(ethylene glycol) (PEG) network expresses excellent CO₂ separation properties over smaller H₂. The preferential CO₂ permeation can be explained by specific interaction between CO₂ and primary amine of the dendrimer, which enhances CO₂ solubility into the polymeric membrane. CO₂ forms carbamate with the amines or bicarbonate in the presence of water determined by inverse-gate decoupled ¹³C NMR. The resulting carbamate ion pair works to form a quasi-crosslinking, which would suppress H₂ permeation by a CO₂-selective Molecular Gate, while bicarbonate ion can be a major moving species to pass through the polymeric membrane. Attenuated total reflection (ATR) indicates the formation of carbamate. Small-angle X-ray scattering (SAXS) reveals increase in scattering intensity under CO₂ atmosphere due to the formation of scattering particles, which can be a cluster of the dendrimer-CO₂ crosslinks. Tensile testing of the membrane exhibits increase in both Young's modulus and elongation-to-break by CO₂ treatment, suggesting that the crosslinking is reversible and rearrangeable. Differential scanning calorimetry (DSC) also shows an exothermic peak at 120°C, which is associated with dissociation of the crosslinks.