Engineering CO₂‑Ultraselective Membranes: Molecularly Tailored Low-Crystallinity Polyvinylamine-PEGDGE Networks

Facilitated transport membranes (FTMs) with an ultraselective layer prepared from amine-rich polyvinylamine (PVAm)/2-(1-piperazinyl)ethylamine salt of sarcosine (PZEA-Sar) (denoted by PM) and an amorphous dendritic cross-linked network of PVAm-functionalized poly(ethylene glycol)diglycidyl ether (PEGDGE) (named PP) were designed for CO₂ separations. The developed membranes expedited CO₂ transport over N₂ through the synergistic effect from the induced CO₂-philic ethylene oxide groups and highly hydrophilic and polar hydroxyl groups together with the low-crystallinity PP networks, which offer a high diffusion rate for CO₂-amine complexes through the membrane and stabilize small molecular mobile carriers via hydrogen bonding. The best (PM/PP-10)/polysulfone (PSf) composite membranes achieved a superior CO₂/N₂ selectivity of 230 (4.6 times higher compared to that of the pristine PVAm/PSf membranes) paired with a CO₂ permeance of 100 GPU, exceeding the 2019 Robeson upper bound. Molecular dynamics (MD) simulations for the PVAm and PVAm/PP-10 membranes suggested that the PVAm matrix was swelled by the introduced PP-10 network with increased fractional free volume (FFV). The engineering of the molecular structure and the manipulation of FFV strongly push the limits of selectivity for PVAm-based FTMs, which may open doors to provide a facile and scalable approach to developing CO₂-ultraselective membranes for carbon capture from flue gases.