Effect of the phase-separated structure on CO₂ separation performance of the poly(amidoamine) dendrimer immobilized in a poly(ethylene glycol) network

The poly(amidoamine) (PAMAM) dendrimer is stably immobilized in a poly(ethylene glycol) (PEG) network upon photo-crosslinking of PEG dimethacrylate (PEGDMA) in the presence of the dendrimer. Structural analysis of the resulting polymeric blend by laser scanning confocal microscopy (LSCM) reveals polymerization-induced phase separation on a micron scale and the formation of a bicontinuous structure of PEG-rich and PAMAM dendrimer-rich phases. The average dendrimer domain size, which is identical to the average spacing of the PEG-rich phase, is determined to be 2.2-2.8 μm depending on the PEG length when the dendrimer content is 50 wt%. When a membrane is fabricated using the polymeric blend, the resulting membrane shows excellent CO₂ separation properties over H₂ especially under higher humidified conditions. The CO₂ separation properties under humidified conditions are associated with the dendrimer domain size in the dry state. A smaller dendrimer domain size gives higher CO₂ permeance and CO ₂/H₂ selectivity under humidified conditions. Absorbed water induces diffusion of the dendrimer into the PEG-rich phase, which gives rise to the enhancement of the solubility of CO₂ in the polymeric blend. As a result, the permeation of CO₂ will be more facilitated by the diffused dendrimer, providing a higher CO₂/H₂ selectivity.