Engineering CO<sub>2</sub>‑Ultraselective Membranes:\nMolecularly Tailored Low-Crystallinity Polyvinylamine-PEGDGE Networks

Facilitated transport membranes (FTMs) with an ultraselective\nlayer\nprepared from amine-rich polyvinylamine (PVAm)/2-(1-piperazinyl)ethylamine\nsalt of sarcosine (PZEA-Sar) (denoted by PM) and an amorphous dendritic\ncross-linked network of PVAm-functionalized poly(ethylene glycol)diglycidyl\nether (PEGDGE) (named PP) were designed for CO<sub>2</sub> separations.\nThe developed membranes expedited CO<sub>2</sub> transport over N<sub>2</sub> through the synergistic effect from the induced CO<sub>2</sub>-philic ethylene oxide groups and highly hydrophilic and polar hydroxyl\ngroups together with the low-crystallinity PP networks, which offer\na high diffusion rate for CO<sub>2</sub>-amine complexes through the\nmembrane and stabilize small molecular mobile carriers via hydrogen\nbonding. The best (PM/PP-10)/polysulfone (PSf) composite membranes\nachieved a superior CO<sub>2</sub>/N<sub>2</sub> selectivity of 230\n(4.6 times higher compared to that of the pristine PVAm/PSf membranes)\npaired with a CO<sub>2</sub> permeance of 100 GPU, exceeding the 2019\nRobeson upper bound. Molecular dynamics (MD) simulations for the PVAm\nand PVAm/PP-10 membranes suggested that the PVAm matrix was swelled\nby the introduced PP-10 network with increased fractional free volume\n(FFV). The engineering of the molecular structure and the manipulation\nof FFV strongly push the limits of selectivity for PVAm-based FTMs,\nwhich may open doors to provide a facile and scalable approach to\ndeveloping CO<sub>2</sub>-ultraselective membranes for carbon capture\nfrom flue gases.