Enhancing CO₂ Transport Across the PEG/PPG‐Based Crosslinked Rubbery Polymer Membranes with a Sterically Bulky Carbazole‐Based ROMP Comonomer

Abstract

A series of poly(ethylene glycol)‐block‐poly(propylene glycol) (PEG/PPG)‐ and 5,6‐di(9H‐carbazol‐9‐yl)isoindoline‐1,3‐dione (2CZPImide)‐based crosslinked rubbery polymer membranes, denoted as PEG/PPG‐2CZPImide (x:y), are prepared from the norbornene‐functionalized PEG/PPG oligomer (NB‐PEG/PPG‐NB) and 2‐(bicyclo[2.2.1]hept‐5‐en‐2‐ylmethyl)‐5,6‐di(9H‐carbazol‐9‐yl)isoindoline‐1,3‐dione (2CZPImide‐NB) via ring‐opening metathesis polymerization (ROMP). The molar ratio (x:y) of the NB‐PEG/PPG‐NB (x) to 2CZPImide‐NB (y) monomers is varied from 10:1 to 6:1. X‐ray diffraction (XRD), scanning electron microscopy‐energy dispersive X‐ray spectroscopy (SEM‐EDS), and pure gas permeability studies reveal that the comonomer 2CZPImide‐NB successfully increases the d‐spacing among the crystalline PEG/PPG segments, hence enhancing the diffusivity of gases through the membranes. The synthesized membranes exhibit good CO2 separation performance, with CO2 permeabilities ranging from 311.1 to 418.1 Barrer and CO2/N2 and CO2/CH4 selectivities of 39.4–52.0 and 13.4–16.0, respectively, approaching the 2008 Robeson upper bound. Moreover, PEG/PPG‐2CZPImide (6:1), displaying optimal CO2 permeability and CO2/N2 and CO2/CH4 selectivities, shows long‐term stability against physical aging and plasticization resistance up to 20 days and 10 atm, respectively.